[Original] How CPU is made

xiaoxiao2021-03-06  1

Note This is an article on the "microcomputer" introducing the CPU manufacturing (rather than design). As the core component of the computer, the CPU (Central Processor Unit, Central Processor) has always been very mysterious in the heart of the user: in the minds of most users, it is just a noun abbreviation, they even don't even have it. Come out; in the eyes of some hardware masters, the CPU is mostly more than ten square meters, with a lot of pieces of a block, and the core part of the CPU is even less than one square centimeter. They know that this less than one square centimeter is made of how much micron process, knows it integrates hundreds of millions of transistors, but freshly understands the manufacturing process of the CPU. Today, let us learn more about how the CPU is practicing. Most of the basic materials know that modern CPUs are made of silicon materials. Silicon is a non-gold element. From the perspective of chemistry, since it is at the junction of the metal element region and the non-metallic element region in the element cycle, the nature of the semiconductor is suitable for manufacturing a variety of small transistors. It is currently most suitable for the manufacture of materials for modern large-scale integrated circuits. In a sense, the main ingredients of the sand on the beach are also silicon (silica), and the silicon materials used in the production of CPUs are actually extracted from the sand. Of course, some other materials should be used during the manufacturing process of the CPU. This is why we won't see Intel or AMD just pull the ton of sand to their manufacturer. At the same time, manufacturing CPUs have extremely high purity requirements for silicon materials, although derived from inexpensive sand, but because of the complexity of the material purification process, we can still compare one hundred grams of high-purity silicon and one ton of sand prices. Another basic material for manufacturing CPUs is metal. The metal is used to make a circuit in which the CPU connects each element. Aluminum is one of the common metal materials because it is cheap and the performance is not bad. Today's mainstream CPU uses copper to replace aluminum because aluminum has too much electric mobility, which has not been able to meet the needs of current rapidly developed CPU manufacturing processes. The electromigration means that the individual atoms of the metal (eg, high voltage) are moved from the original place under certain conditions. Obviously, if the atoms are constantly being moved from the metal microcircuit of the connecting element, the circuit will become a thousand holes until the circuit is broken. This is why the overclockman tries to substantially improve the voltage of Northwood Pentium 4, this tragic CPU often in the "Sudden Northwood Death Syndrome, SNDS". . SNDS enables Intel to apply copper interconnect technology to the production process of the CPU. Copper interconnect technology can significantly reduce electromigration, and can also be smaller than the circuit manufactured by aluminum process, which is also a problem that cannot be ignored in the nanometer manufacturing process. Not only this, the resistance of copper is much smaller than the aluminum. The advantages make the copper interconnect process quickly replace the position of aluminum and become the mainstream of CPU manufacturing. In addition to silicon and a certain metal material, there are many complex chemical materials that also participate in the manufacturing work of the CPU. After preparing to work to solve the problem of manufacturing CPU, we have begun to enter the preparation. Some raw materials will be processed in the process of preparation, in order to make the electrical properties to achieve the requirements of the manufacturing CPU. One is silicon. First, it will be purified by chemical methods, pure to almost no impurities. At the same time, it has to be converted into a silicon crystal, from essentially and the sand of the sand. In this process, raw material silicon will be melted and put into a huge quartz furnace.

At this time, a seed crystal is placed in the furnace so that the silicon transistor is grown around the seed crystal until a close perfect single crystal silicon is formed. If you do the copper bronze crystalline experiments very well in high school, or how the single crystal rock sugar is manufactured, I believe this process is not difficult to understand. At the same time, you need to understand that many solid matter have crystal structures such as salt. This is also the case in the CPU manufacturing process. Careful and slowly mixed with silica, silicon transistors surrounded by seed crystals to the same direction. In the end, a piece of silicon is produced. The current silicon ingot is mostly 200 mm, while the CPU manufacturer is preparing to make 300 mm diameter silicon ingots. Making greater silicon ingots in the premise of ensuring that the quality is unchanged, but the investment of CPU vendors solves this technical problem. It takes approximately $ 3.5 billion in manufacturing mills that produce 300 mm diameter silicon ingots, and Intel will make more complex CPUs produced by their silicon materials. The construction of a similar manufacturing plant that produces 200mm diameter silicon ingots is as 1.5 billion US dollars. As the first person to eat crabs, Intel will clearly need to pay a bigger price. It is more difficult to build such a manufacturing plant, but it can be seen from the following, this investment is worth it. There are still many manufacturing methods of silicon ingots, only one of them described above, called CZ manufacturing method. The silicon ingot is created and is integrated into a perfect cylinder (Fig. 1), which will be cut into a sheet, referred to as a wafer. Wafer is really used for the manufacture of CPUs. In general, the wafer cuts thinner, the more the CPU finished product of the same amount of silicon material can be manufactured. Next, the wafer will be polished and is checked whether there is a deformation or other problem. Here, the quality check directly determines the final goodness of the CPU, which is extremely important. The wafer that is not problematic will be incorporated in the appropriate other material to produce various transistors above. The incorporated material is deposited in a slit between the silicon atom. Currently used transistor manufacturing technology is called CMOS (Complementary Metal Oxide Semiconductors, complementary metal oxide semiconductor) technology, I believe you often see this word. Simply explained that CMOS's CMOS refers to the relationship between two different MOS circuit "N" circuits and "P" circuits: they are complementary. In the electronics, "N" and "P" are negative and posTIVE abbreviations, which are used to represent polarity. It can be understood in a simple understanding of the "P" type transistor on the "N" type substrate, and "n" wells can be installed on the "P" substrate to manufacture "N" type transistors. In most cases, the manufacturer is incorporated into the wafer into the wafer to produce a "P" substrate because it is capable of manufacturing a more excellent performance on the "P" substrate, and can effectively save space "N" type Transistors; in this process, the manufacturing plant will try to avoid "P" type transistors. Next, this wafer will be sent to a high-temperature furnace, of course we can't let it melt this this time. By closely monitoring the temperature, pressure and heating time in the furnace, the surface of the wafer will be oxidized into a layer of a particular thickness of silica (SiO2) as part of the transistor door circuit. If you have learned a logic circuit, you will definitely know the concept of doorship. Through the gate circuit, enter a certain level will result in a certain output level, and the output level is different depending on the gate circuit. The level of the level is indicated by the image of 0 and 1, which is why the computer uses binary. In Intel uses a CPU manufactured by 90 nano-processes, this door circuit is only two atoms. The final step of preparing work is to apply a layer of photosensitive resist film on the wafer, which has photosensitive, and the photosensitive portion can be cleaned by a particular chemical, and is separated from partially partially no exposure.

Completion of the door circuit This is the most complex part of the CPU manufacturing process, which is the photolithography technology. It can be said that photolithography technology pushes the application of light to the limit. The CPU manufacturer will expose the specific area of ​​the photosensitive resist film covered on the wafer and changes their chemical properties. In order to avoid unwanted areas that do not need to be exposed, it is necessary to make a mask to mask these areas. I want you to recognize this concept in the software, like Photoshop, which is also small here. Here, even if the wavelength is very short and uses a large lens, it means that the best focus is carried out, the edge of the mask is still affected, and it can be simply imagined that the edge is blurred. Note that the scale we discussed now, each mask is complex to an imaginable, if you want to describe it, at least 10GB of data, and create a CPU, at least 20 such masks. For any mask, try to imagine the map of Beijing, including its suburbs; then zoom it into a squares of small paper. Finally, don't forget to connect each map, of course, I am not as simple as using a line. When the mask is completed, they will be covered on the wafer, and the short wavelength light will take photos of the photoresist film through the holes of these quartz masks to expose. Next, the light is stopped and the mask is removed, and the exposed photosensitive resist film is cleaned off using a particular chemical solution, and a layer of silicon is attached to the resist film below. When the remaining photosensitive resist film is also removed, the wafer left the undulating silica mountain range, of course, you can't see them. Next, another layer of silica is added, and a layer of polysilicon is added, and then a layer of photosensitive resist film is further covered. Polysilicon is another portion of the gate circuit mentioned above, and before, this is made of metal (ie, M: Metal in CMOS). The photosensitive resist film is again capped to determine the masks of these polysilicon leaves, and accept light baptism. Then, the exposed silicon will be bombarded by atoms to create n well or p well, combined with the substrate manufactured above, and the door circuit is completed. Repeating may you think that a CPU has been almost manufactured in a complicated step. In fact, at this time, the CPU has less than one-fifth. The next step is as complex as above, that is, adding silica layers again, etching again, adding it again ... repeating, forming a 3D structure (Figure 2), this is the core of the ultimate CPU . The metal is filled with metal as a conductor every few layers. Intel's Pentium 4 processor has 7 layers, while AMD's Athlon 64 has reached 9 floors. The number of layers is determined in the design of the CPU, and the current amount of current. Test, test and test After several weeks of the CPU core from the original wafer to one layer of silicon, metal and other materials, it is time to see the monster that manufactured. This step will test the electrical performance of the wafer to check whether there is any error, and which step appears in these errors (if possible). Next, each CPU core on the wafer will be subsequent (not cut) test (Figure 3). Through the wafer will be cut into several separate CPU cores, the invalid core found in the above test will be placed one side. Next, the core will be packaged and installed on the substrate. Then, most mainstream CPUs will install an integrated heat-dissipation reverse deform (IHS) on the core. Each CPU will be fully tested to verify all of its functions.

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