Course work: Stages of production of microprocessors. Processor Manufacturing - From Sand to Computer Modern Processor Technologies

LECTURE PLAN

1. Seven generations of processors

2. Production technology

3. Technological stages of microprocessor production

1. Seven generations of processors

The first generation (8086 and 8088 processors and 8087 math coprocessor) laid the architectural foundation - a set of "unequal" 16-bit registers, a segment addressing system within 1 MB with a wide variety of modes, an instruction system, an interrupt system, and a number of other attributes. The processors used "small" pipelining: while some nodes were executing the current command, the prefetch block fetched the next one from memory.

The third generation (80286 and 80287 coprocessor) added the so-called "protected mode" to the family, which allows using virtual memory up to 1 GB in size for each task, using addressable physical memory within 16 MB. Protected mode has become the basis for building multitasking operating systems, in which the privilege system strictly regulates the relationship of tasks with memory, the operating system, and with each other. It should be noted that the performance of the 80286 processors has increased not only due to the increase in clock frequency, but also due to significant improvements in the pipeline.

The third generation (80386/80387 with "suffixes" DX and SX, which determine the width of the external bus) was marked by the transition to a 32-bit architecture. In addition to expanding the range of values represented (16 bits represent integers in the range from 0 to 65535 or from –32768 to +32767, and 32 bits - more than four billion), the capacity of the addressable memory has increased. The Microsoft Windows operating system began to be widely used with these processors.

The fourth generation (80486 also DX and SX) did not add major changes to the architecture, however, a number of measures were taken to improve performance. In these processors, the execution pipeline was significantly complicated. Manufacturers abandoned the external coprocessor - it began to be placed on the same crystal with the central one.

The fifth generation (Pentium processor from Intel and K5 from AMD) gave a superscalar architecture. To quickly supply pipelines with instructions and data from memory, the data bus of these processors is made 64-bit. Later this generation had an extension ММХ (Matrics Math Extensions instruction set) - a set of commands for extending matrix mathematical operations (originally Multimedia Extension instruction set)). Traditional 32-bit processors can add two 8-bit numbers, placing each number in the lower-order bits of 32-bit registers. In this case, the 24 most significant bits of the registers are not used, and therefore, it turns out that with one addition operation ADD, simply the addition of two 8-bit numbers is carried out. MMX commands operate with 64 bits at once, where eight 8-bit numbers can be stored, and it is possible to add them with other 8-bit numbers in one ADD operation. MMX registers can also be used to simultaneously add four 16-bit words or two 32-bit long words. This principle is called SIMD (Single Instruction / Multiple Data). The new commands were mainly intended to speed up the execution of multimedia programs, but use them with multimedia technology. A new type of arithmetic has appeared in MMX - with saturation: if the result of an operation does not fit in the bit grid, then overflow (or "anti-overflow") does not occur, but the maximum (or minimum) possible value of the number is set.

The sixth generation of processors originated with the Pentium Pro and continued in the Pentium III, Celeron and Xeon processors (from AMD, the K6, K6-2, K6-2 +, K6-III processors can serve as an example). The basis here is dynamic execution, the execution of commands is not in the order prescribed program code, but in how it will be more convenient for the processor. It should be noted here that there are similarities between the fifth and sixth generation processors, namely the addition of the fifth generation expansion was supplemented by the MMX expansion, the sixth generation received extensions that increase the MMX capabilities. AMD has this extension 3dNnoy !, and Intel has SSE (Streaming SIMD Extensions).

The seventh generation began with AMD's Athlon processor. The processor had the characteristics conditioning the development superscalarity and super pipelines... Later, Intel also released its seventh-generation Pentium 4 processor.

2. Production technology

Currently, we can observe an interesting trend in the market: on the one hand, manufacturing companies are trying to quickly introduce new technical processes and technologies into their products, on the other hand, there is an artificial limitation of the growth of processor frequencies. This is due to the fact that the feeling of incomplete readiness of the market for the next change of processor families affects, and the manufacturing firms have not yet received enough profit from the sales of the CPUs being produced now. It should be noted here that for companies, the price of the finished product is fundamental in comparison with other interests. but great importance a decrease in the rate of development of microprocessors is associated with an understanding of the need to introduce new technologies that will increase productivity with a minimum amount of technological costs

Manufacturers had to solve a number of problems when switching to new technical processes. The 90nm technology norm has proven to be a significant technology hurdle for many chip makers. This is confirmed by TSMC, this company is engaged in the production of chips for many major manufacturers of the market, namely AMD, nVidia, ATI, VIA. For a long time, she was unable to debug the production of chips using 0.09 micron technology, which led to a low yield of usable crystals. This led AMD to postpone the release of its SOI (Silicon-on-Insulator) processors for a long time. This is due to the fact that it was on this dimension of the elements that disadvantages that were not previously perceptible appeared, such as leakage currents, a large scatter of parameters and an exponential increase in heat release. One alternative solution is the use of SOI silicon-on-insulator technology, which AMD recently introduced in its 64-bit processors. However, it cost her a lot of effort and overcoming a considerable number of technological barriers. But it should be noted that this technology has many advantages that can compensate for its shortcomings. The essence of this technology is quite logical - the transistor is separated from the silicon substrate by another thin insulator layer. The positive qualities include. The absence of uncontrolled movement of electrons under the channel of the transistor, affecting its electrical characteristics - time. After the supply of the unlocking current to the gate, the time of channel ionization to the operating state, until the moment when the operating current flows through it, decreases, this entails an improvement in the second key parameter of the transistor performance, the time of its on / off. It is also possible, at the same speed, to simply lower the unlocking current - three. Or find some kind of solution between the possibility of increasing the speed of work and the possibility of reducing the voltage. While maintaining the same unlocking current, the increase in transistor performance can be up to 30%, if you leave the frequency the same, making an emphasis on energy saving, in this case the performance can be up to 50%. As a result, the characteristics of the channel become more predictable, and the transistor itself becomes more resistant to sporadic errors, an example of which are cosmic particles entering the channel substrate and unexpectedly ionizing it. Getting into the substrate located under the insulator layer, they do not affect the operation of the transistor in any way. The only drawback of SOI is that it is necessary to decrease the depth of the emitter / collector region, which in turn results in an increase in its resistance as the thickness decreases.

Another reason that contributed to the slowdown in the growth rate of frequencies is the low activity of manufacturers in the market. For example, each AMD company worked on the widespread introduction of 64-bit processors, Intel during this period improved a new technical process, debugging for an increased yield of usable crystals.

The introduction of new technologies into technical processes is obvious, but it becomes more difficult for technologists each time. The first Pentium processors (1993) were produced using the 0.8 micron process technology, then 0.6 microns each. In 1995, for the first time for the 6th generation processors, the 0.35 micron process technology was used. In 1997, it changed to 0.25 microns, and in 1999 - to 0.18 microns. Modern processors are made according to the 0.13 and 0.09 micron technologies introduced in 2004.

It is necessary to describe the very structure of the transistor, namely, a thin layer of silicon dioxide, an insulator located between the gate and the channel, and performing the function of a barrier for electrons, preventing leakage of the gate current. Accordingly, the thicker this layer, the better it performs its insulating functions, but it is an integral part of the channel, and it is no less obvious that if manufacturers are going to reduce the channel length (transistor size), then its thickness must be reduced at a very fast pace. Over the past several decades, the thickness of this layer has averaged about 1/45 of the entire length of the channel. But this process has its end - as the same Intel claimed, if you continue to use SiO2, as it has been over the past 30 years, the minimum layer thickness will be 2.3. nm, otherwise the leak will become simply unrealistic. Until recently, nothing has been done to reduce the subchannel leakage, at present the situation is beginning to change, since the operating current, along with the gate response time, is one of the two main parameters characterizing the speed of the transistor, and the leakage in the off state is directly reflected on it ( on maintaining the required efficiency of the transistor). It is necessary, accordingly, to increase the operating current, with all the ensuing consequences.

The main stages of production

Manufacturing a microprocessor is a complex process that includes more than 300 stages. Microprocessors are formed on the surface of thin circular silicon wafers - substrates, as a result of a certain sequence of different processing processes using chemicals, gases and ultraviolet radiation.

The substrates are usually 200 millimeters in diameter. However, Intel has already switched to 450mm wafers. Switching to larger diameter plates will reduce the cost of manufacturing microcircuits, increase energy efficiency and reduce emissions of harmful gases into the atmosphere. The surface area of 450mm wafers is more than double that of 300mm wafers. As a result, twice as many finished products can be produced from a single 450mm substrate.

The wafers are made from silicon, which is refined, melted and grown into long cylindrical crystals. The crystals are then cut into thin wafers and polished until their surfaces are mirror-smooth and free from defects. Then, sequentially, cyclically repeating thermal oxidation, photolithography, impurity diffusion, epitaxy are performed.

In the process of manufacturing microcircuits, the thinnest layers of materials are applied to the blank plates in the form of carefully calculated patterns. One plate fits up to several hundred microprocessors. The entire process of manufacturing processors can be divided into several stages: growing silicon dioxide and creating conductive regions, testing and manufacturing.

Growing silicon dioxide and creating conductive regions

The microprocessor manufacturing process begins with "growing" an insulating layer of silicon dioxide on the surface of a polished plate. This stage is carried out in an electric oven at a very high temperature. The thickness of the oxide layer depends on the temperature and time that the plate spends in the oven.

This is followed by photolithography - a process during which a schematic drawing is formed on the surface of the plate. First, a temporary layer of a photosensitive material is applied to the plate - a photoresist, onto which an image of transparent areas of the template, or photomask, is projected using ultraviolet radiation. Masks are made during processor design and are used to generate circuit patterns in each layer of the processor. Under the influence of radiation, the illuminated areas of the photolayer become soluble, and they are removed with the help of a solvent (hydrofluoric acid), revealing the silicon dioxide underneath.

The exposed silica is removed by a process called etching. Then the remaining photolayer is removed, as a result, a pattern of silicon dioxide remains on the semiconductor wafer. As a result of a number of additional operations of photolithography and etching, polycrystalline silicon with the properties of a conductor is also applied to the wafer. During the next operation, called "doping", the exposed areas of the silicon wafer are bombarded with ions of various chemical elements, which form negative and positive charges in silicon, which change the electrical conductivity of these areas.

The imposition of new layers with subsequent etching of the circuit is carried out several times, while for interlayer connections in the layers "windows" are left, which are filled with metal, forming electrical connections between the layers. Intel used copper conductors in its 0.13 micron manufacturing process. Intel used aluminum in its 0.18 micron manufacturing process and previous generation processes. Both copper and aluminum are good conductors of electricity. When using the 0.18-micron technical process, 6 layers were used, when introducing the 90 nm technical process in 2004, 7 layers of silicon were used.

Each layer of the processor has its own pattern, together all these layers form a three-dimensional electronic circuit. The application of the layers is repeated 20 - 25 times over several weeks.

Testing

In order to withstand the stresses to which the substrates are subjected during the deposition of layers, silicon wafers must initially be sufficiently thick. Therefore, before cutting the plate into separate microprocessors, its thickness is reduced by 33% using special processes and contaminants are removed from the back side. After that, a layer of a special material is applied to the reverse side of the "processed" plate, which improves the subsequent fastening of the crystal to the case. This layer provides electrical contact between the back surface of the integrated circuit and the package after assembly.

After that, the plate is tested to check the quality of all processing operations. To determine the correctness of the processor, their individual components are checked. If a malfunction is detected, the data obtained is analyzed to identify the stage at which the error occurred.

Electrical probes are then connected to each processor and supplied with power. The processors are tested by the computer, it determines whether the characteristics of the manufactured processors meet the specified parameters.

Manufacturing of the case

After testing, the wafers are sent to the assembly plant, where they are cut into small rectangles, each containing an integrated circuit, using a special precision saw. Non-working crystals are discarded.

Then each crystal is placed in an individual case. The case protects the crystal from external influences and provides its electrical connection to the board on which it will be installed. Tiny balls of solder, located at specific points on the crystal, are soldered to the electrical leads of the package. At this stage, electrical signals can flow from the board to the chip and vice versa.

After installing the crystal in the case, the processor is retested to determine its performance. Defective processors are discarded, and serviceable processors are subjected to stress tests: the effects of various temperature and humidity conditions, as well as electrostatic discharges. After each stress test, the processor is tested to determine its functional state. Then the processors are sorted according to their behavior at different clock frequencies and supply voltages.

3. Technological stages of microprocessor production

How chips are made

Chip production involves the imposition of thin layers with a complex "pattern" on silicon substrates. First, an insulating layer is created that works like an electrical shutter. The substrates are cut into a single crystal-cylinder with thin "pancakes", so that later they can be easily cut into separate processor crystals. Electrical probes are used to test each crystal on the substrate. Finally, the substrate is cut into individual cores, the non-working cores are immediately discarded. Depending on the characteristics, the core becomes one or another processor and is wrapped in a package that makes it easier to install the processor on motherboard... All functional blocks go through intensive stress tests.

It all starts with substrates

The first step in manufacturing processors is done in a clean room. It should be noted that this is a very capital intensive production. More than $ 2-3 billion can be spent on the construction of a modern plant with all the equipment. Only after full adjustment and testing of the equipment can the plant produce processors in series.

In general, the chip manufacturing process consists of a series of substrate processing steps. This includes the creation of the substrates themselves, which will subsequently be cut into individual crystals.

Substrate production

The first stage is growing a single crystal. For this, a seed crystal is embedded in a bath of molten silicon, which is located just above the melting point of polycrystalline silicon. It is important that the crystals grow slowly for about a day to ensure that the atoms are in the correct arrangement. Polycrystalline or amorphous silicon is composed of many different crystals that will lead to unwanted surface structures with poor electrical properties.

Once the silicon is melted, it can be doped with other substances that change its electrical properties. The whole process takes place in a sealed room with a special air composition so that silicon does not oxidize.

The single crystal is cut into "pancakes" using a circular high-precision diamond saw that does not create large irregularities on the surface of the substrates. In this case, the surface of the substrates is still not perfectly flat, so additional operations are required. The appearance of single crystals can be seen in Figure 1.

Rice. 1. Appearance of a single crystal

First, using rotating steel plates and an alumina abrasive, a thick layer is removed from the substrates (a process called lapping). As a result, irregularities ranging in size from 0.05 mm to approximately 0.002 mm (2000 nm) are eliminated. Then round off the edges of each backing, as sharp edges can peel off layers. Further, the etching process is used, when with the help of various chemicals (hydrofluoric acid, acetic acid, nitric acid) the surface is smoothed by about 50 microns more. Physically, the surface does not deteriorate, since the whole process is completely chemical. It allows you to remove the remaining errors in the crystal structure, as a result of which the surface will be close to ideal.

The last step is polishing, which smooths the surface to roughness, maximum 3 nm. Polishing is carried out using a mixture of sodium hydroxide and granular silica.

Currently, microprocessor substrates are 300 mm or 450 mm in diameter, which allows chip manufacturers to obtain multiple processors from each of them. In general, the larger the substrate diameter, the more chips of the same size can be produced. A 300mm substrate, for example, provides more than twice the number of processors than a 200mm.

Doping and diffusion

Doping is performed both with the finished substrate and during photolithography processes. This makes it possible to change the electrical properties of certain regions and layers, and not the entire structure of the crystal.

The dopant can be added by diffusion. The dopant atoms fill the free space inside the crystal lattice, between the silicon structures. In some cases, an existing structure can also be alloyed. Diffusion is carried out using gases (nitrogen and argon) or using solids or other sources of dopant.

Create a mask

To create sections of an integrated circuit, a photolithography process is used. In this case, it is not necessary to irradiate the entire surface of the substrate; in such cases, it is important to use the so-called masks, which transmit high-intensity radiation only to certain areas. Masks can be compared to black and white negative. Integrated circuits have many layers (20 or more), and each layer requires its own mask.

A thin chrome film structure is applied to the surface of a quartz glass plate to create a pattern. At the same time, expensive instruments using an electron flow or laser prescribe the necessary IC data, as a result of which a chrome template is obtained on the surface of the quartz substrate. It should be noted that any change in the integrated circuit leads to the need to produce new masks, so the whole process of making edits is very expensive.

Photoligraphy makes it possible to form a structure on a silicon substrate. The process is repeated several times until many layers are created. The layers can include different materials, here also the connection with microscopic wires is provided. Before starting the photolithography process, the substrate is cleaned and heated to remove sticky particles and water. At the next stage, the substrate is coated with silicon dioxide using a special device. Next, a bonding agent is applied to the substrate, which ensures that the photoresist material to be applied in the next step remains on the substrate. The photoresist material is applied to the middle of the substrate, which then begins to rotate at a high speed so that the layer is evenly distributed over the entire surface of the substrate. Then the substrate is heated again. The photolithography process is shown in Figure 2.

Rice. 2. The photolithography process

Then, through the mask, the cover is irradiated with a quantum laser, hard ultraviolet radiation, X-rays, beams of electrons or ions - all of these sources of light or energy can be used. Electron beams are mainly used to create masks, X-rays and ion beams for research purposes, and industrial production today is dominated by hard UV radiation and gas lasers.

Hard UV radiation with a wavelength of 13.5 nm irradiates the photoresist material while passing through the mask. Projection and focusing times are very important for the desired results. Poor focusing will leave extra particles of photoresist material as some of the holes in the mask will not be properly irradiated. A similar situation will turn out if the projection time is too short. Then the structure of the photoresist material will be too wide, the areas under the holes will be underexposed. However, excessive projection time creates too large areas under the holes and too narrow a photoresist material structure. This is the complexity of the regulation of the production process. Incorrect adjustment will lead to serious deviations in the connecting conductors. A special stepping projection device moves the substrate in the desired position. After that, you can project a line or one section, in most cases corresponding to one processor crystal. Additional micro-installations can make additional changes. For example, debug existing technology and optimize the technical process. Micro-installations usually work on areas of less than 1 sq. mm, while conventional installations cover larger areas.

There are wet and dry etching processes that treat areas of silica. Wet processes use chemical compounds and dry processes use gas. A separate process is the removal of the residues of the photoresist material. Manufacturers often combine wet and dry removal so that the photoresist material is completely removed. This is important because the photoresist material is organic and, if not removed, can lead to defects on the substrate.

After etching and cleaning, you can proceed to inspect the substrate, which usually happens at each important stage, or transfer the substrate to a new photolithography cycle. Checking the substrates is shown in Figure 3.

Rice. 3. Inspection of substrates

Testing of finished substrates is performed on probe control installations that work with the entire substrate. Probe contacts are superimposed on the contacts of each crystal, which allows electrical tests to be carried out. By using software all functions of each core are tested. The Substrate Cutting process is shown in Figure 4.

Rice. 4. The process of cutting the substrate

By cutting the support, individual cores are obtained. If defective crystals (containing errors) are detected, they are separated from the good ones. Previously, damaged crystals were physically marked, now there is no need for this, all information is stored in a single database.

Further, the functional core must be placed in a processor package, for which an adhesive material is used. After that, you need to make wire connections connecting the legs of the package and the crystal itself (Figure 5). For this, gold, aluminum or copper connections are used.

Rice. 5. Wired substrate connection

Most modern processors use plastic packaging with heat distribution... In particular, the core is packed in ceramic or plastic packaging, which helps to prevent mechanical damage. Modern processors are equipped with a heat spreader, devices that provide heat dissipation and chip protection (Figure 6).

Rice. 6. Processor packaging

The last step is testing the processor, which is done at elevated temperatures, in accordance with the processor's specifications. The processor is automatically installed in the test socket, after which all the necessary functions are analyzed.

How microcircuits are made

To understand what is the main difference between these two technologies, it is necessary to take a short excursion into the very technology of production of modern processors or integrated circuits.

As is known from the school physics course, in modern electronics, the main components of integrated circuits are p-type and n-type semiconductors (depending on the type of conductivity). A semiconductor is a substance that surpasses dielectrics in conductivity, but is inferior to metals. Silicon (Si) can serve as the basis of both types of semiconductors, which in its pure form (the so-called intrinsic semiconductor) does not conduct electric current well, but the addition (introduction) of a certain impurity into silicon makes it possible to radically change its conducting properties. There are two types of impurities: donor and acceptor. A donor impurity leads to the formation of n-type semiconductors with an electronic type of conductivity, and an acceptor impurity leads to the formation of p-type semiconductors with a hole type of conductivity. Contacts of p- and n-semiconductors make it possible to form transistors - the main structural elements of modern microcircuits. These transistors, called CMOS transistors, can be in two basic states: open, when they conduct electricity, and locked, when they do not conduct electricity. Since CMOS transistors are the main elements of modern microcircuits, let's talk about them in more detail.

How a CMOS transistor works

The simplest n-type CMOS transistor has three electrodes: source, gate, and drain. The transistor itself is made in a p-type semiconductor with hole conductivity, and n-type semiconductors with electronic conductivity are formed in the drain and source regions. Naturally, due to the diffusion of holes from the p-region to the n-region and the reverse diffusion of electrons from the n-region to the p-region, depleted layers (layers in which there are no major charge carriers) are formed at the boundaries of the transitions of the p- and n-regions. In the normal state, that is, when no voltage is applied to the gate, the transistor is in a "locked" state, that is, it is not able to conduct current from the source to the drain. The situation does not change, even if we apply a voltage between the drain and the source (in this case, we do not take into account the leakage currents caused by the movement under the influence of the generated electric fields of minority charge carriers, that is, holes for the n-region and electrons for the p-region).

However, if a positive potential is applied to the gate (Fig. 1), then the situation will change radically. Under the influence of the electric field of the gate, holes are pushed deep into the p-semiconductor, and electrons, on the contrary, are drawn into the region under the gate, forming an electron-enriched channel between the source and drain. When a positive voltage is applied to the gate, these electrons begin to move from source to drain. In this case, the transistor conducts current - they say that the transistor "opens". If the voltage is removed from the gate, electrons stop being drawn into the region between the source and drain, the conducting channel is destroyed, and the transistor stops passing current, that is, it is "locked". Thus, by changing the voltage at the gate, you can open or turn off the transistor, in the same way as you can turn on or off a conventional toggle switch, controlling the passage of current through the circuit. This is why transistors are sometimes called electronic switches. However, unlike conventional mechanical switches, CMOS transistors are virtually inertialess and capable of going from open to locked state trillions of times per second! It is this characteristic, that is, the ability of instantaneous switching, that ultimately determines the speed of the processor, which consists of tens of millions of such simplest transistors.

So, a modern integrated circuit consists of tens of millions of the simplest CMOS transistors. Let us dwell in more detail on the process of manufacturing microcircuits, the first stage of which is the production of silicon substrates.

Step 1. Growing blanks

The creation of such substrates begins with the growth of a cylindrical silicon single crystal. These single crystal billets are then cut into wafers approximately 1/40 "thick and 200 mm (8") or 300 mm (12 ") in diameter. These are the silicon substrates used for the production of microcircuits.

When forming wafers from silicon single crystals, the fact that for ideal crystal structures the physical properties largely depend on the chosen direction (anisotropy property) is taken into account. For example, the resistance of a silicon substrate will be different in the longitudinal and transverse directions. Similarly, depending on the orientation of the crystal lattice, a silicon crystal will react differently to any external influences associated with its further processing (for example, etching, sputtering, etc.). Therefore, the plate must be cut from the single crystal in such a way that the orientation of the crystal lattice relative to the surface is strictly maintained in a certain direction.

As already noted, the diameter of the silicon single crystal preform is either 200 or 300 mm. Moreover, the diameter of 300 mm is a relatively new technology, which we will discuss below. It is clear that a plate of this diameter can accommodate far more than one microcircuit, even if we are talking about an Intel Pentium 4 processor. Indeed, several dozen microcircuits (processors) are formed on one such plate-substrate, but for simplicity we will consider only the processes occurring on a small area of one future microprocessor.

Step 2. Applying a protective dielectric film (SiO2)

After the formation of the silicon substrate, the stage of creating the most complex semiconductor structure begins.

To do this, it is necessary to introduce the so-called donor and acceptor impurities into silicon. However, the question arises - how to implement the introduction of impurities according to a precisely given pattern-pattern? To make this possible, those areas where it is not required to introduce impurities are protected with a special silicon dioxide film, leaving only those areas exposed that are subjected to further processing (Fig. 2). The process of forming such a protective film of the desired pattern consists of several stages.

At the first stage, the entire silicon wafer is completely covered with a thin film of silicon dioxide (SiO2), which is a very good insulator and acts as a protective film during further processing of the silicon crystal. The wafers are placed in a chamber, where oxygen diffuses into the surface layers of the wafer at high temperature (from 900 to 1100 ° C) and pressure, leading to the oxidation of silicon and to the formation of a surface film of silicon dioxide. In order for the silicon dioxide film to have a precisely specified thickness and be free from defects, it is necessary to strictly maintain a constant temperature at all points of the wafer during the oxidation process. If not the entire wafer is to be covered with a silicon dioxide film, then a Si3N4 mask is first applied to the silicon substrate to prevent unwanted oxidation.

Step 3. Applying the photoresist

After the silicon substrate is covered with a protective film of silicon dioxide, it is necessary to remove this film from those places that will be subjected to further processing. Removal of the film is carried out by etching, and to protect the remaining areas from etching, a layer of a so-called photoresist is applied to the surface of the wafer. The term "photoresists" refers to formulations that are light-sensitive and resistant to aggressive factors. The applied compositions should have, on the one hand, certain photographic properties (under the influence of ultraviolet light, they become soluble and washed out during the etching process), and on the other hand, resistive, allowing them to withstand etching in acids and alkalis, heating, etc. The main purpose of photoresists is to create a protective relief of the desired configuration.

The process of applying a photoresist and its further irradiation with ultraviolet light according to a given pattern is called photolithography and includes the following basic operations: the formation of a photoresist layer (processing of the substrate, application, drying), the formation of a protective relief (exposure, development, drying) and transfer of the image to the substrate (etching, sputtering etc.).

Before applying the photoresist layer (Fig. 3) to the substrate, the latter is pretreated, as a result of which its adhesion to the photoresist layer is improved. The centrifugation method is used to apply a uniform layer of photoresist. The substrate is placed on a rotating disk (centrifuge), and under the influence of centrifugal forces, the photoresist is distributed over the surface of the substrate in an almost uniform layer. (Speaking of a practically uniform layer, one should take into account the fact that, under the action of centrifugal forces, the thickness of the resulting film increases from the center to the edges; however, this method of applying a photoresist makes it possible to withstand fluctuations in the layer thickness within ± 10%.)

Step 4. Lithography

After the application and drying of the photoresist layer, the stage of formation of the necessary protective relief begins. The relief is formed as a result of the fact that under the action of ultraviolet radiation falling on certain areas of the photoresist layer, the latter changes the properties of solubility, for example, the illuminated areas stop dissolving in the solvent, which remove areas of the layer that were not exposed to lighting, or vice versa - the illuminated areas dissolve. By the method of forming the relief, photoresists are divided into negative and positive. Negative photoresists under the influence of ultraviolet radiation form protective areas of the relief. On the other hand, positive photoresists, when exposed to ultraviolet radiation, acquire flow properties and are washed out by the solvent. Accordingly, the protective layer is formed in those areas that are not exposed to ultraviolet radiation.

To illuminate the desired areas of the photoresist layer, a special mask template is used. Most often, optical glass plates with opaque elements obtained by photographic or otherwise are used for this purpose. In fact, such a template contains a drawing of one of the layers of the future microcircuit (there can be several hundred such layers in total). Since this template is a reference, it must be executed with great precision. In addition, taking into account the fact that a lot of photographic plates will be made from one photomask, it must be durable and resistant to damage. Hence, it is clear that a photomask is a very expensive thing: depending on the complexity of the microcircuit, it can cost tens of thousands of dollars.

Ultraviolet radiation, passing through such a template (Fig. 4), illuminates only the necessary areas of the surface of the photoresist layer. After irradiation, the photoresist undergoes development, as a result of which unnecessary portions of the layer are removed. This opens the corresponding part of the silicon dioxide layer.

Despite the seeming simplicity of the photolithographic process, it is this stage in the production of microcircuits that is the most difficult. The fact is that, in accordance with Moore's prediction, the number of transistors on one microcircuit increases exponentially (doubles every two years). Such an increase in the number of transistors is possible only due to a decrease in their size, but it is precisely the decrease that "rests" on the lithography process. In order to make the transistors smaller, it is necessary to reduce the geometric dimensions of the lines applied to the photoresist layer. But there is a limit to everything - it is not so easy to focus a laser beam on a point. The fact is that, in accordance with the laws of wave optics, the minimum spot size into which a laser beam is focused (in fact, it is not just a spot, but a diffraction pattern) is determined, among other factors, by the length of the light wave. The development of lithographic technology since its invention in the early 70s has been in the direction of shrinking the wavelength of light. This is what made it possible to reduce the size of the elements of the integrated circuit. Since the mid-1980s, photolithography has begun to use ultraviolet radiation produced by a laser. The idea is simple: the wavelength of ultraviolet radiation is shorter than the wavelength of light in the visible range, therefore, it is possible to obtain thinner lines on the surface of the photoresist. Until recently, lithography used deep ultraviolet radiation (Deep Ultra Violet, DUV) with a wavelength of 248 nm. However, when photolithography crossed the 200 nm boundary, serious problems arose that for the first time called into question the possibility of further use of this technology. For example, at wavelengths less than 200 microns, too much light is absorbed by the light-sensitive layer, so the process of transferring the circuit template to the processor becomes more complicated and slower. Challenges like these are prompting researchers and manufacturers to seek alternatives to traditional lithographic technology.

A new lithographic technology called EUV lithography (Extreme UltraViolet) is based on the use of ultraviolet radiation with a wavelength of 13 nm.

The transition from DUV to EUV lithography provides more than a 10-fold decrease in the wavelength and a transition to a range where it is comparable to the size of only a few tens of atoms.

The currently used lithographic technology allows the deposition of a template with a minimum conductor width of 100 nm, while EUV lithography makes it possible to print lines of much smaller width - up to 30 nm. Controlling ultrashort radiation is not as easy as it sounds. Since EUV radiation is well absorbed by glass, the new technology involves the use of a series of four special convex mirrors that reduce and focus the image obtained after applying the mask (Fig. 5,,). Each such mirror contains 80 separate metal layers approximately 12 atoms thick.

Step 5. Etching

After exposure of the photoresist layer, the etching stage begins in order to remove the silicon dioxide film (Fig. 8).

The pickling process is often associated with acid baths. This acid etching method is well known to radio amateurs who made printed circuit boards on their own. To do this, a pattern of the tracks of the future board is applied to the foil textolite with varnish, which acts as a protective layer, and then the plate is lowered into a bath with nitric acid. Unnecessary areas of the foil are etched away, exposing a clean textolite. This method has a number of disadvantages, the main one being the inability to accurately control the layer removal process, since too many factors affect the etching process: acid concentration, temperature, convection, etc. In addition, the acid interacts with the material in all directions and gradually penetrates under the edge of the photoresist mask, that is, destroys the layers covered with the photoresist from the side. Therefore, in the manufacture of processors, a dry etching method is used, also called plasma. This method allows you to accurately control the etching process, and the destruction of the etched layer occurs strictly in the vertical direction.

Dry etching uses ionized gas (plasma) to remove silicon dioxide from the wafer surface and react with the silicon dioxide surface to form volatile byproducts.

After the etching procedure, that is, when the required areas of pure silicon are exposed, the rest of the photolayer is removed. Thus, a silicon dioxide pattern remains on the silicon substrate.

Step 6. Diffusion (ion implantation)

Recall that the previous process of forming the required pattern on a silicon substrate was required in order to create semiconductor structures in the right places by introducing a donor or acceptor impurity. The process of impurity introduction is carried out by means of diffusion (Fig. 9) - uniform introduction of impurity atoms into the silicon crystal lattice. Antimony, arsenic or phosphorus are usually used to obtain an n-type semiconductor. To obtain a p-type semiconductor, boron, gallium or aluminum is used as an impurity.

For the diffusion process of the dopant, ion implantation is used. The implantation process consists in the fact that the ions of the desired impurity are "fired" from the high-voltage accelerator and, having sufficient energy, penetrate into the surface layers of silicon.

So, at the end of the stage of ion implantation, the required layer of the semiconductor structure has been created. However, microprocessors can have several such layers. To create the next layer, an additional thin layer of silicon dioxide is grown in the resulting diagram. After that, a layer of polycrystalline silicon and another layer of photoresist are applied. Ultraviolet radiation is passed through the second mask and highlights the corresponding pattern on the photo layer. Then again the stages of dissolution of the photo layer, etching and ion implantation follow.

Step 7. Spraying and deposition

The imposition of new layers is carried out several times, while for interlayer connections in the layers "windows" are left, which are filled with metal atoms; as a result, metal stripes are created on the crystal - conductive regions. Thus, in modern processors, connections are established between layers that form a complex three-dimensional scheme. The process of growing and processing all layers takes several weeks, and the production cycle itself consists of more than 300 stages. As a result, hundreds of identical processors are formed on a silicon wafer.

To withstand the stresses that the wafers are subjected to during the layer deposition process, silicon substrates are initially made thick enough. Therefore, before cutting the wafer into individual processors, its thickness is reduced by 33% and contamination from the back side is removed. Then a layer of a special material is applied to the back side of the substrate, which improves the attachment of the crystal to the case of the future processor.

Step 8. Final stage

At the end of the formation cycle, all processors are thoroughly tested. Then, concrete, already tested crystals are cut out of the substrate plate using a special device (Fig. 10).

Each microprocessor is embedded in a protective case, which also provides electrical connection of the microprocessor chip to external devices. The type of enclosure depends on the type and intended use of the microprocessor.

After being sealed into the housing, each microprocessor is re-tested. Defective processors are rejected, and serviceable ones are subjected to stress tests. The processors are then sorted based on their behavior at different clock speeds and supply voltages.

Advanced technologies

The technological process of manufacturing microcircuits (in particular, processors) is considered by us in a very simplified way. But even this superficial presentation allows us to understand the technological difficulties that one has to face when reducing the size of transistors.

However, before considering new promising technologies, let us answer the question posed at the very beginning of the article: what is the design standard of the technological process and how, in fact, the design standard of 130 nm differs from the standard of 180 nm? 130 nm or 180 nm is the characteristic minimum distance between two adjacent elements in one layer of the microcircuit, that is, a kind of grid step to which the elements of the microcircuit are bound. At the same time, it is quite obvious that the smaller this characteristic size, the more transistors can be placed on the same area of the microcircuit.

Currently, Intel processors use a 0.13-micron manufacturing process. This technology is used to manufacture the Intel Pentium 4 processor with the Northwood core, the Intel Pentium III processor with the Tualatin core, and the Intel Celeron processor. In the case of using such a technological process, the effective channel width of the transistor is 60 nm, and the thickness of the gate oxide layer does not exceed 1.5 nm. All in all, the Intel Pentium 4 processor houses 55 million transistors.

Along with an increase in the density of transistors in the processor crystal, the 0.13-micron technology, which replaced the 0.18-micron technology, has other innovations. First, it uses copper connections between the individual transistors (in 0.18 micron technology, the connections were aluminum). Secondly, the 0.13 micron technology provides lower power consumption. For mobile technology, for example, this means that the power consumption of microprocessors is reduced and the battery life is longer.

Well, the last innovation that was implemented in the transition to the 0.13-micron technological process is the use of silicon wafers (wafer) with a diameter of 300 mm. Recall that before that, most processors and microcircuits were manufactured on the basis of 200 mm wafers.

Increasing the diameter of the plates allows you to reduce the cost of each processor and increase the yield of products of the proper quality. Indeed, the area of a plate with a diameter of 300 mm is 2.25 times larger than the area of a plate with a diameter of 200 mm, respectively, and the number of processors obtained from one plate with a diameter of 300 mm is more than twice as large.

In 2003, it is expected to introduce a new technological process with an even lower design standard, namely the 90-nanometer one. The new manufacturing process, which Intel will use to manufacture most of its products, including processors, chipsets and communications equipment, was developed at Intel's 300mm wafer D1C pilot plant in Hillsboro, Oregon.

On October 23, 2002, Intel announced the opening of a new $ 2 billion facility in Rio Rancho, New Mexico. The new plant, called the F11X, will use state-of-the-art technology to manufacture processors on 300mm wafers using a 0.13 micron design rate process. In 2003 the plant will be transferred to a technological process with a design standard of 90 nm.

In addition, Intel has already announced the resumption of construction at Fab 24 in Lakeslip, Ireland, to manufacture semiconductor components on 300mm silicon wafers with a 90nm design rule. The new enterprise with a total area of over 1 million sq. M. ft. with ultra clean rooms with an area of 160 thousand square meters. ft. is expected to be operational in the first half of 2004 and will employ over a thousand employees. The cost of the facility is about $ 2 billion.

The 90nm process uses a variety of advanced technologies. It is also the world's smallest commercially available CMOS transistors with a gate length of 50 nm (Fig. 11), which provides increased performance while reducing power consumption, and the thinnest gate oxide layer ever made of transistors - just 1.2 nm (Fig. 12), or less than 5 atomic layers, and the industry's first implementation of high-performance strained silicon technology.

Of the listed characteristics, perhaps only the notion of "strained silicon" needs commentary (Fig. 13). In such silicon, the distance between atoms is greater than in a conventional semiconductor. This, in turn, provides a freer flow of current, similar to how traffic moves more freely and faster on a road with wider traffic lanes.

As a result of all the innovations, the performance of transistors is improved by 10-20%, with an increase in production costs by only 2%.

In addition, the 90nm process uses seven layers per chip (Figure 14), one more layer than the 130nm process, and copper connections.

All of these features, combined with 300mm silicon wafers, provide Intel with gains in performance, production, and cost. Consumers also benefit as Intel's new technology process continues to grow the industry in line with Moore's Law, while improving processor performance over and over again.

The production of microcircuits is a very difficult business, and the closed nature of this market is dictated primarily by the peculiarities of the photolithography technology that is dominant today. Microscopic electronic circuits are projected onto a silicon wafer through photomasks, each of which can cost up to $ 200,000. Meanwhile, at least 50 such masks are required to make one chip. Add to this the cost of trial and error when developing new models, and you realize that only very large companies can produce processors in very large quantities.

But what about scientific laboratories and high-tech startups that need non-standard schemes? How to be a military man, for whom buying processors from a "potential enemy" is not comme il faut, to put it mildly?

We visited the Russian production site of the Dutch company Mapper, thanks to which the manufacture of microcircuits can cease to be the lot of celestials and turn into an occupation for mere mortals. Well, or almost simple. Here, on the territory of Technopolis "Moscow", with the financial support of the corporation "Rusnano", a key component of the Mapper technology is produced - an electro-optical system.

Before diving into the nuances of Mapper maskless lithography, however, it's worth remembering the basics of conventional photolithography.

Hulking light

On a modern processor Intel Core The i7 can house about 2 billion transistors (depending on the model), each of which is 14 nm in size. In pursuit of computing power, manufacturers annually reduce the size of transistors and increase their number. The likely technological limit in this race can be considered 5 nm: at such distances, quantum effects begin to manifest themselves, due to which electrons in neighboring cells can behave unpredictably.

To apply microscopic semiconductor structures to a silicon wafer, a process similar to working with a photo enlarger is used. Unless his goal is the opposite - to make the image as small as possible. Plate (or protective film) are covered with a photoresist - a polymer photosensitive material that changes its properties when exposed to light. The desired chip pattern is exposed to the photoresist through a mask and a collecting lens. The printed plates are typically four times smaller than the masks.

Substances such as silicon or germanium each have four electrons at the outer energy level. They form beautiful crystals that look like metal. But, unlike metal, they do not conduct electric current: all their electrons are involved in powerful covalent bonds and cannot move. However, everything changes if you add to them a little donor impurity from a substance with five electrons at the outer level (phosphorus or arsenic). Four electrons bond with silicon, and one remains free. Donor-doped silicon (n-type) is a good conductor. If we add to silicon an acceptor impurity from a substance with three electrons at the external level (boron, indium), "holes", a virtual analogue of a positive charge, are formed in a similar way. In this case, we are talking about a p-type semiconductor. By connecting p- and n-type conductors, we get a diode - a semiconductor device that passes current in only one direction. Combination p-n-p or n-p-n gives us a transistor - current flows through it only if a certain voltage is applied to the center conductor.

The diffraction of light makes its own adjustments to this process: the beam, passing through the holes of the mask, is slightly refracted, and instead of one point, a series of concentric circles is exposed, like from a stone thrown into a whirlpool. Fortunately, diffraction is inversely related to wavelength, which is what engineers are using when using ultraviolet light with a wavelength of 195 nm. Why not even less? It's just that the shorter wave will not be refracted by the collecting lens, the rays will pass through without focusing. It is also impossible to increase the collecting ability of the lens - spherical aberration will not allow: each ray will pass the optical axis at its point, breaking focus.

The maximum contour width that can be displayed using photolithography is 70 nm. Higher-resolution chips are printed in several steps: they apply 70-nanometer outlines, etch the circuit, and then expose the next part through a new mask.

Now in development is the technology of photolithography in deep ultraviolet, using light with an extreme wavelength of about 13.5 nm. The technology involves the use of vacuum and multilayer mirrors with reflection based on interlayer interference. The mask will also not be translucent, but a reflective element. Mirrors are devoid of the phenomenon of refraction, so they can work with light of any wavelength. But for now, this is only a concept that may be applied in the future.

How processors are made today

A perfectly polished round silicon wafer with a diameter of 30 cm is coated with a thin layer of photoresist. Centrifugal force helps to distribute the photoresist evenly.

The future circuit is exposed to the photoresist through a mask. This process is repeated many times because many chips are made from one wafer.

The part of the photoresist that has been exposed to ultraviolet radiation becomes soluble and can be easily removed with chemicals.

Areas of the silicon wafer not protected by the photoresist are chemically etched. Depressions are formed in their place.

A layer of photoresist is again applied to the plate. This time, exposure is used to expose those areas that will undergo ion bombardment.

Under the influence of an electric field, impurity ions are accelerated to speeds of more than 300,000 km / h and penetrate into silicon, giving it the properties of a semiconductor.

After removing the remnants of the photoresist, ready-made transistors remain on the plate. A dielectric layer is applied on top, in which holes for contacts are etched using the same technology.

The plate is placed in a copper sulfate solution and a conductive layer is applied to it by electrolysis. Then the entire layer is removed by grinding, and the contacts remain in the holes.

The contacts are connected by a multi-storey network of metal "wires". The number of "floors" can be up to 20, and the general layout of the conductors is called the processor architecture.

Only now is the plate being sawn into many individual chips. Each "crystal" is tested and only then installed on a board with contacts and covered with a silver radiator cap.

13,000 TVs

An alternative to photolithography is electrolytography, when it is exposed not with light, but with electrons, and not with a photo, but with an electroresist. The electron beam is easily focused to a point of minimum size, down to 1 nm. The technology resembles the cathode-ray tube of a television: a focused stream of electrons is deflected by control coils, drawing an image on a silicon wafer.

Until recently, this technology could not compete with the traditional method due to its low speed. In order for an electroresist to react to radiation, it must accept a certain number of electrons per unit area, so one beam can expose at best 1 cm2 / h. This is acceptable for single orders from laboratories, but not applicable in industry.

Unfortunately, it is impossible to solve the problem by increasing the energy of the beam: charges of the same name are repelled, therefore, as the current increases, the electron beam becomes wider. But you can increase the number of rays by exposing several zones at the same time. And if several - this is 13,000, as in the Mapper technology, then, according to calculations, it is possible to print already ten full-value chips per hour.

Of course, it would be impossible to combine 13,000 cathode ray tubes in one device. In the case of the Mapper, radiation from a source is directed to a collimator lens, which forms a wide, parallel electron beam. An aperture matrix stands in its way, which turns it into 13,000 individual beams. The beams pass through a blanker array - a 13,000-hole silicon wafer. A deflection electrode is located near each of them. If a current is applied to it, the electrons "miss" their hole, and one of the 13,000 rays is turned off.

After passing through the blankers, the beams are directed to an array of deflectors, each of which can deflect its beam a couple of microns to the right or left relative to the movement of the plate (so the Mapper still resembles 13,000 CRTs). Finally, each beam is additionally focused by its own microlens, after which it is directed to the electroresist. To date, Mapper technology has been tested at the French Research Institute for Microelectronics CEA-Leti and at TSMC, which produces microprocessors for leading market players (including the Apple iPhone 6S). Key components of the system, including silicon electronic lenses, are manufactured at the Moscow plant.

Mapper technology promises new perspectives not only for research laboratories and small-scale (including military) production, but also for large players. Nowadays, to test prototypes of new processors, you have to make exactly the same photomasks as for mass production. The possibility of relatively rapid prototyping of circuits promises not only to reduce development costs, but also to accelerate progress in this area. Which ultimately plays into the hands of the mass consumer of electronics, that is, all of us.

CPU this is the heart of anyone modern computer... Any microprocessor is essentially a large-scale integrated circuit on which transistors are located. By passing electric current, transistors allow you to create binary logic (on - off) calculations. Modern processors are based on 45 nm technology. 45nm (nanometer) is the size of one transistor located on the processor plate. Until recently, 90 nm technology was mainly used.

The plates are made of silicon, which is the 2nd largest deposit in the earth's crust.

Silicon is obtained by chemical treatment, purifying it from impurities. After that, they begin to melt it, forming a silicon cylinder with a diameter of 300 millimeters. This cylinder is then cut into plates with a diamond thread. Each plate is about 1 mm thick. In order for the plate to have an ideal surface, after cutting with a thread, it is ground with a special grinder.

After that, the surface of the silicon wafer is perfectly flat. By the way, many manufacturing companies have already announced the possibility of working with 450 mm plates. The larger the surface, the more transistors to place, and the higher the processor performance.

CPU consists of a silicon wafer, on the surface of which there are up to nine levels of transistors, separated by oxide layers, for insulation.

Processor technology development

Gordon Moore, one of the founders of Intel, one of the leaders in the production of processors in the world, in 1965, based on his observations, discovered the law according to which new models of processors and microcircuits appeared at regular intervals. The growth in the number of transistors in processors is growing by about 2 times in 2 years. For 40 years, Gordon Moore's Law has been working without distortion. Mastering future technologies is just around the corner - there are already working prototypes based on 32nm and 22nm processor technology. Until mid-2004, processor power depended primarily on the processor frequency, but since 2005, the processor frequency has practically ceased to grow. There is a new technology for multi-core processor. That is, several processor cores are created with an equal clock frequency, and during operation, the power of the cores is summed up. This increases the overall processor power.

Below you can watch a video about processor manufacturing.

How chips are made

Chip production involves the imposition of thin layers with a complex "pattern" on silicon substrates. First, an insulating layer is created that works like an electrical shutter. As for the production of substrates, they must be cut into thin "pancakes" from a solid single crystal-cylinder, so that later they can be easily cut into separate processor crystals. Electrical probes are used to test each crystal on the substrate. Finally, the substrate is cut into individual cores, the non-working cores are immediately sifted out. Depending on the characteristics, the core becomes one or another processor and is wrapped in a package that makes it easier to install the processor on the motherboard. All functional blocks go through intensive stress tests.

It all starts with substrates

The first step in manufacturing processors is done in a clean room. By the way, it is important to note that such a technological production is an accumulation of huge capital on square meter... Construction of a modern plant with all the equipment can easily cost $ 2–3 billion, and test runs of new technologies take several months. Only then can the plant mass-produce processors.

In general, the chip manufacturing process consists of several substrate processing steps. This includes the creation of the substrates themselves, which will eventually be cut into separate crystals Figurnov, V.E. IBM PC for the user.-M., 2004. - P.204.

Substrate production

The first stage is growing a single crystal. For this, a seed crystal is embedded in a bath of molten silicon, which is located just above the melting point of polycrystalline silicon. It is important that the crystals grow slowly (about a day) to ensure that the atoms are in the correct arrangement. Polycrystalline or amorphous silicon is composed of many different crystals that will lead to unwanted surface structures with poor electrical properties.

The single crystal is cut into "pancakes" using a very precise diamond circular saw, which does not create large irregularities on the surface of the substrates. Of course, in this case, the surface of the substrates is still not perfectly flat, so additional operations are required. Single crystals are shown in Figure 1.

Figure 1. External view of a single crystal.

First, using rotating steel plates and an abrasive material (such as aluminum oxide), a thick layer is removed from the substrates (a process called lapping). As a result, irregularities ranging in size from 0.05 mm to approximately 0.002 mm (2000 nm) are eliminated. Then round off the edges of each backing, as sharp edges can peel off layers. Further, the etching process is used, when with the help of various chemicals (hydrofluoric acid, acetic acid, nitric acid) the surface is smoothed by about 50 microns more. Physically, the surface does not deteriorate, since the whole process is completely chemical. It allows you to remove the remaining errors in the crystal structure, as a result of which the surface will be close to ideal.

The last step is polishing, which smoothes the surface to unevenness, maximum 3 nm. Polishing is carried out using a mixture of sodium hydroxide and granular silica.

Today, microprocessor substrates are either 200mm or 300mm in diameter, allowing chip manufacturers to get multiple processors from each. The next step will be 450mm substrates, but they shouldn't be expected until 2013. In general, the larger the substrate diameter, the more chips of the same size can be produced. A 300mm substrate, for example, provides more than twice the number of processors than a 200mm.

Doping and diffusion

The doping that is performed during the growth of the single crystal has already been mentioned. But doping is done both with the finished substrate and later during photolithography processes. This allows you to change the electrical properties of certain areas and layers, and not the entire structure of the crystal.

The dopant can be added via diffusion. The dopant atoms fill the free space inside the crystal lattice, between the silicon structures. In some cases, an existing structure can also be alloyed. Diffusion is carried out with the help of gases (nitrogen and argon) or with the help of solids or other sources of dopant Hasegawa, H. - The world of computers in questions and answers.-M., 2004 - P.89 ..

Create a mask

To create the regions of an integrated circuit, a photolithography process is used. Since it is not necessary to irradiate the entire surface of the substrate in this case, it is important to use so-called masks, which transmit high-intensity radiation only to certain areas. Masks can be compared to black and white negative. Integrated circuits have many layers (20 or more), and each layer requires its own mask.

A thin chrome film structure is applied to the surface of a quartz glass plate to create a pattern. At the same time, expensive instruments using an electron flow or laser prescribe the necessary IC data, as a result of which a chrome template is obtained on the surface of the quartz substrate. It is important to understand that each modification of the integrated circuit leads to the need to produce new masks, so the whole process of making edits is very costly.

Photolithography

A structure is formed on a silicon substrate using photolithography. The process is repeated several times until many layers are created (more than 20). Layers can consist of different materials, moreover, you also need to think over the connections with microscopic wires. All layers can be doped Wood, A. Microprocessors in questions and answers. - M., 2005.-P.87.

Before the photolithography process begins, the substrate is cleaned and heated to remove sticky particles and water. Then the substrate is coated with silicon dioxide using a special device. Next, a bonding agent is applied to the substrate, which ensures that the photoresist material to be applied in the next step remains on the substrate. The photoresist material is applied to the middle of the substrate, which then begins to rotate at a high speed so that the layer is evenly distributed over the entire surface of the substrate. Then the substrate is heated again. The principle of photolithography is shown in Figure 2.

Figure 2. The principle of photolithography

Hard UV radiation with a wavelength of 13.5 nm irradiates the photoresist material while passing through the mask. Projection time and focus are very important to obtain the desired result. Poor focusing will leave extra particles of photoresist material as some of the holes in the mask will not be properly irradiated. The same will happen if the projection time is too short. Then the structure of the photoresist material will be too wide, the areas under the holes will be underexposed. On the other hand, excessive projection time creates too large areas under the holes and too narrow a photoresist material structure. As a rule, it is very time consuming and difficult to regulate and optimize the process. Unsuccessful adjustment will lead to serious deviations in the connecting conductors Mayorov, S.I. Information business: commercial distribution and marketing. - M., 2007. -P.147 .. A special step projection device moves the substrate to the desired position. Then a line or one section can be projected, most often corresponding to one processor die. Additional micro-installations can make other changes. They can debug the existing technology and optimize the technical process Kukin, V.N. Informatics: organization and management. -M., 2005.-P.78 .. Microinstallations usually work on areas less than 1 sq. M. mm, while conventional installations cover larger areas.

After etching and cleaning, you can proceed to inspect the substrate, which usually happens at each important stage, or transfer the substrate to a new photolithography cycle. The substrate test is shown in Figure 3.

Figure 3. Substrate test

Finished substrates are tested in so-called probe installations. They work with the entire substrate. Probe contacts are superimposed on the contacts of each crystal, which allows electrical tests to be carried out. All functions of each core are tested using software. The cutting of the substrate is shown in Figure 4.

Figure 4. Cutting the backing

By cutting, individual cores can be obtained from the substrate. On this moment Probe control units have already identified which crystals contain errors, so after cutting, they can be separated from the good ones. Previously, damaged crystals were physically marked, now there is no need for this, all information is stored in a single database Semenenko, V.A., Stupin. Yu.V. Handbook on electronic computing technology. - M., 2006. - P.45 ..

The functional core must then be bonded to the processor packaging using an adhesive material. After that, you need to make wire connections connecting the contacts or legs of the package and the crystal itself (Figure 5). Gold, aluminum or copper connections can be used.

Most modern processors use plastic wrap with a heat spreader. Typically, the core is wrapped in ceramic or plastic wrap to prevent damage. Modern processors are equipped with a so-called heat spreader, which provides additional protection for the crystal (Figure 6).

Figure 5. Wired Substrate Connection

The last stage involves testing the processor, what happens at elevated temperatures, in accordance with the processor's specifications. The processor is automatically installed in the test socket, after which all the necessary functions are analyzed.

Figure 6. Processor packaging