When you use your mobile phone to browse Weibo, Douyin, or play large-scale games on your computer, or chase popular dramas, people all lament the magic of artificial intelligence, big data, and cloud computing. Proud of the times. However, many people may not know how much the chip plays in it. In our daily life, there are shadows of chips everywhere. Chips are not only installed in computers, but also in our mobile phones, televisions, air conditioners, and water heaters. Even remote controls that are common in life cannot be separated from chips.
How the chip is made
Now that chips play such an important role in all aspects of people’s lives, how are they made?
The main raw material of the chip-silicon, can evolve into a chip (as shown in Figure 1) after a series of delicate and complex processing processes such as wafer manufacturing, previous processes, and packaging processes. As the core of chip manufacturing, each layer of the previous process needs to use a photolithography machine for pattern transfer engraving exposure in order to form the original pattern. Among them, the first layer needs to align the pattern of the mask with the shape of the substrate for exposure, and each subsequent mask needs to be aligned with the previously completed patterns or structures on the substrate for over-engraving exposure. In addition, the mask required for each layer is also manufactured by a photoetching machine, so the photoetching machine is the mother machine of chip manufacturing. It can also be said that the lithography machine is the manufacturing mother machine of the information age, which has a great influence on chip manufacturing.
The chip front-end process requires not only a lithography machine, but also a homogenizer, baking equipment, cleaning equipment, thin film equipment (PVD, CVD, EVD, PECVD, MOCVD, etc.), etching equipment (reactive ion etching, gas etching, etc.) , Liquid corrosion, etc.), ion implantation equipment and other process equipment and process testing equipment (testing equipment for film thickness, morphology, defects, line width, overprinting accuracy, etc.). Among them, the most technically difficult, most costly and most critical equipment is the lithography machine.
Draw football field on hair
As the saying goes: “Workers must first sharpen their tools if they want to do well.” Good tools play a key role in the manufacturing process. The development of manufacturing tools has also gone through a long period of time (as shown in Figure 2). In the pre-industrial era, people used human hands as tools to manufacture various production and living utensils by hand; into the industrial age, machine tools replaced human hands to complete the processing of various precision components; with the advancement of technology, mankind entered the information age. Devices with macrostructures manufactured by machine tools can no longer meet people’s demand for high information capacity. Lithography machines with micron and nanometer manufacturing capabilities have become the king of manufacturing in the new era.
As the name implies, the so-called lithography machine uses light as the medium to depict micro-nano in square inches to achieve various micron or even nano-level pattern processing. At present, the thinnest line that can be processed by the most advanced photolithography machine has reached 13 nanometers. The diameter of our human hair is about 50 to 70 microns, and the line of only 1/5000 of the diameter of the hair can be drawn by photolithography.
Wei Xueying, a famous essayist at the end of the Ming Dynasty, wrote a famous essay called “He Zhou Ji”. The article begins by saying: “Ming Qiqiao people call Wang Shuyuan, who can use wood in diameter to form palaces, utensils, figures, birds and beasts, woods and stones, regardless of the situation and pictograms, but each has a modality.” The author went on to say, Wang Shuyuan I once gave myself a small boat carved with peach pits, which was carved with the pattern of Su Shi taking a boat tour of Chibi. This small peach-core boat is carved with 5 people, 8 windows, a boat canopy made of rue bamboo leaves, a boat oar, a stove, a teapot, a hand roll, a rosary, and a total of 34 words such as couplets, titles and seal scripts. However, calculating its length, it turned out to be less than an inch. Finally, the author can’t help but sigh that his skill is really superb.
In real life, there is indeed a miniature small boat similar to the one mentioned in “He Zhou Ji”. It was carved in the Qing Dynasty and is now housed in the National Palace Museum in Taipei. This small boat carved with olive pits is based on Su Dongpo’s “Hou Chibi Fu”: In the small cabin, Su Dongpo and two guests sit leisurely in the cabin, and the table in front of them is messy. Outside the cabin, there are also carved boys, boatmen and helmsman. Although the characters are small, their detailed and vivid expressions are different.
The ancients hand-carved a flat boat on walnuts and olive pits, which is exquisite; today’s people can use the tool made in the information age—the lithography machine to carve patterns on a strand of hair, even Able to portray a football field (Figure 4).
Permeate daily life
For ordinary people, what they use in real life are things that can be seen and touched; is the “high-precision” equipment such as lithography machines too high and too small, and too far away from people Up? actually not.
In fact, the lithography machine has now penetrated into all aspects of our lives (Figure 5): The reason why the computers and TV screens we use can show colorful graphics is due to the processing of the lithography machine on the panel. Pixel graphics; the reason why household LED lights and other products can emit light is due to the positive and negative structure processed by photolithography; the CPU in the computer can achieve various fast calculations, relying on its internal Various micro-nano structures processed by photolithography machines; the reason why household cars can sense the speed, temperature, tire pressure and other conditions in the car in real time is also the use of various sensors processed by photolithography machines. In the information age, lithography machines can not only complete the traditional chip manufacturing such as computer CPUs and FPGAs (field programmable gate arrays), but also flat-panel displays, LEDs, sensors and other “generalized chips” with certain functions and a certain degree of integration. The main processing method.
It can be said that as the king of manufacturing in the information age, all kinds of “chips” processed by lithography machines are ubiquitous and omnipotent.
Contact, projection, and direct writing of the “three masters”
Of course, in the face of the complex and diverse needs of the market, it is naturally impossible for the lithography machine to “conquer the world” with one move. According to different application scenarios, the current mainstream lithography machines can be divided into three types: proximity, projection, and direct-write lithography machines. Each type of lithography machine has different working principles and different characteristics, so it is suitable for different processing scenarios (Figure 6).
Proximity contact lithography machine
In the working process, the close contact lithography machine has a micro-nano patterned mold (mask) in contact with the surface of the structure to be processed, and under the irradiation of ultraviolet light, the pattern on the mask is transferred to the surface of the pattern to be processed. Its working principle is similar to our “hand shadow” game (Figure 7): use existing graphics to block the spread of light, thereby forming a pattern of light and dark, combined with the photosensitive characteristics of the surface to be processed, record us The required graphics.
This method is characterized by relatively simple equipment structure, high processing efficiency, low cost, easy to achieve large chip area exposure, convenient use, long focal depth, and strong process adaptability; however, there are also low resolution and exposure graphics quality. The shortcomings such as poor, poor process consistency, etc., can only realize the 1:1 copy of the pattern, and cannot further reduce the copied pattern. The thinnest line it can process is only on the order of micrometers.
Although the proximity contact lithography machine has its shortcomings, as a copy-type lithography method that is currently widely used in device manufacturing, it has relatively low requirements for lithography resolution, large chip area, thick glue, and non-standard substrates. , Integrated circuits (IC) and various devices other than flat panel displays are basically based on this kind of photolithography method.
Proximity contact lithography includes three types: manual, semi-automatic and fully automatic. Manual mode means that the loading and unloading, alignment, and exposure are all manually operated; semi-automatic mode refers to the automatic operation mode for all alignment and exposure except for the loading and unloading; fully automatic mode refers to pre-alignment, loading and unloading, and Alignment and exposure all adopt automatic operation.
Projection lithography machine
The working principle of the projection lithography machine is similar to that of a camera (Figure 8). During the working process, the mask (external image) is imaged onto the substrate (the surface of the photosensitive medium) through the projection objective (lens).
Because the projection lithography machine adopts the projection type working method, the mask and the substrate are no longer in contact with each other, which greatly avoids damage to the mask or the substrate; moreover, the use of the projection lens to change the reduction magnification can be processed The structure is finer than the reticle pattern. In addition, the projection lithography machine has the exposure capability of scanning imaging, and the work efficiency is extremely high. Due to its outstanding performance advantages, projection lithography machines have been the mainstream lithography equipment in the field of lithography machines since their inception. At present, high-end chips such as GPUs, FPGAs, and LEDs are all processed by projection lithography machines.
Although the working principle is similar, the complexity of the projection lithography machine is far greater than that of the camera, and it contains dozens of key subsystems (Figure 9). In the working process, the various subsystems cooperate closely to ensure that the lithography machine can still achieve high resolution (13 nanometer line width) and high-quality graphics processing capabilities under high-speed working conditions.
Today, the most advanced projection lithography machine is priced at nearly 1 billion yuan per unit, and the price is so high that it is staggering. The high price reflects the value and technical content of the equipment. Therefore, the projection lithography machine is considered to be the jewel in the crown of the semiconductor manufacturing industry. It is extremely difficult to develop and is a manifestation of the highest level of human technology. At present, only a few companies in the world, such as ASML, Nikon and Canon, have the ability to mass-produce high-end projection lithography machines.
Direct Write Lithography Machine
It can be seen from the introduction of the previous two lithography machines that both lithography machines adopt the “copy” mode of operation, that is, both “copy” the pattern on the mask to the surface to be processed, but the pattern on the mask Where did it come from? This requires the direct write lithography machine that we will introduce next.
The working principle of the direct write lithography machine is similar to our writing (Figure 10). In the working process, the equipment uses a variety of means to focus the beam (or electron beam, ion beam) into a smaller point similar to our pen tip; then, it drives the pen tip or the substrate to achieve relative movement between the two, thereby Finish any graphics processing we want.
The direct-write lithography machine can complete the processing of any pattern, and the processing accuracy is extremely high, and the thinnest line processed can reach the nanometer level. However, in the process of pattern processing, the direct-write lithography machine is processed by dots. The work efficiency is extremely low and it is difficult to realize large-area direct writing. It is not suitable for the preparation of large-scale structures. Therefore, it is mainly used as a mask at present. The processing method of the template.
After understanding the basic knowledge of lithography machine, some people may ask: Is it possible to manufacture chips with a lithography machine?
Because through the previous introduction, we can easily find that from an ordinary substrate to the final chip we use, there are hundreds of process links in the middle, any error in any link will affect the final chip quality. Lithography is only one of the most critical links. Just like our painting: Although drawing is very important, a good work also requires good paper, paint, cutting, mounting and other materials and processes.
Smaller, bigger and more three-dimensional
For a long time, lithography machines have been pursuing higher information capacity, and high resolution, large area, and three-dimensionality are the main directions for their future development.
In terms of high resolution, we continuously reduce the wavelength of the light source used and enhance the minimum line imaging capability of the projection objective to achieve the goal of continuously reducing the minimum line width that can be processed; however, this means that the lithography machine The manufacturing difficulty and manufacturing cost will increase sharply, and it has gradually approached its physical limit.
In order to further improve the resolution, various new lithography methods have emerged, including surface plasma lithography, nanoimprinting, multiphoton lithography, etc. These lithography methods are likely to become the next generation of mainstream lithography technology.
With the improvement of lithography resolution, the processing line width is getting thinner and thinner, and the current electronic chip process is becoming more and more precise, from 14 nanometers to 7 nanometers, and then to 5 nanometers, and now 3 nanometer technology is being developed; but electronic chips After all, there is a limit, and 1 nanometer will become the “limit” of electronic chips. When it is less than 1 nanometer, the gap size of the internal structure of the chip is almost close to the distance of atoms, the physical form of silicon itself will become very unstable, and the current will easily break down the thin oxygen layer, causing a short circuit between the electrodes or the metal film of the transistor. The needle was blown by the current, resulting in an open circuit on both poles.
Once the limit size is reached, the development of traditional electronic chips will also stagnate, because this problem is that there is no way to use existing technical means to improve, only to find new alternative methods.
In the future, photonic chips are most likely to “success” electronic chips. The chips in today’s smart phones are basically electronic chips. Photonic chips use silicon and silicon substrates to replace electrons with photons as the transmission medium. Photon particles are smaller, move faster, consume less energy, and have stronger anti-interference. The photonic chip perfectly integrates the speed and bandwidth of light, and the product performance will be improved by more than 10 times, but the energy consumption is only traditional electronics. 1% of the chip.
According to reports, my country has now manufactured the first orbital angular momentum waveguide photonic chip, and has complete intellectual property rights for this technology.
In terms of large areas, large-area lithography machines are mainly used in the display industry. In order to enable us to use flat-screen TVs with a larger screen area, the processing area of the lithography machine is getting larger and larger. The processing area of the lithography machine on the 10th generation line of LCD panels has reached 2880 mm × 3130 mm, but the minimum processing line width is only It is about 3 microns. With the development of the display industry, the emergence of display technologies requiring smaller processing line widths such as AMOLED and high-definition displays. This type of equipment is no longer only pursuing the goal of large, and how to reduce the minimum processing line width on a large basis will become An important direction for the development of this type of lithography equipment.
In terms of three dimensions, we process each layer of graphics as a plane. As the thinnest line width of processing gradually reaches the physical limit, the potential in the horizontal plane has been exhausted, and it will be possible to develop vertically in the future, that is, to replace the two-dimensional graphics with a three-dimensional structure to further increase the information capacity.