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Chip as the most sophisticated industrial products of human civilization at present, its production process is extremely sensitive to impurity pollution, especially the advanced process of nanometer level, a few ions mixed into the substrate can affect the doping and change the electrical characteristics of the chip; a few molecules dancing in the air can interfere with the lamination and reduce the production yield of the chip; a few grains of dust falling on the surface are enough to short circuit the open circuit and destroy the physical structure of the chip, therefore Therefore, the production of chips must be carried out in an absolutely clean and stable environment, which is the production room of chips, the Clean Room.
In major chip factories, different levels of clean rooms occupy most of the locations, where the density of airborne dust particles and even gas molecules have to be controlled at extremely low ranges. Temperature, humidity, pressure, micro-vibration and other indicators must also be precisely regulated, otherwise the chip production will be difficult. Of course, not only the semiconductor industry, clean room and clean engineering technology, in photovoltaic, medical aerospace, biotechnology and food processing industries, have a wide range of applications. But this, the chip production clean room, its clean class, construction difficulties and construction costs are the highest. So high-end, is not a clean workshop? Even if the lithography is stuck, what can be the difficulty of building a workshop behind closed doors? Believe me, after listening to this issue, what is called clean, you will have a new understanding.
Cleanliness level：
First of all, to give you a science, clean level, the international common clean room standard is ISO 14644-1, according to the diameter and density of particles, the degree of cleanliness in a closed space, divided into 1-9 levels, the smaller the number, the higher the level, each higher level, clean 10 times, including ISO 4-8 levels, corresponding to the domestic commonly known as 10 to 100,000 levels. We occasionally hear in the news, 100-class laboratory, thousand operating theater, referring to their cleanliness level, if your city’s air quality is excellent, then congratulations, every breath of air you breathe today, barely reaching the passing line of ISO pad 9.
And compared to the pandemonium in the city, the hospital operating room is much cleaner inside. Here the density of impurities in the air, hundreds to thousands of times lower than the outside world, corresponding to ISO level 5-7; however, the requirements of obstetrics and gynecology, will be a little lower, level 8 can meet the human production. However, the production of chips, generally can not be lower than ISO level 3, the key processes often have to be carried out in the ISO2 or even level 1 environment. In the ISO2 level, PM0.5 (particle size ≥ 0.5μm) of particulate matter, such as a grain of bacteria, can not exceed 4 per cubic meter; PM0.1 (particle size ≥ 0.1μm) of particulate matter, such as viruses, per cubic meter, can not exceed 100, and to the highest IOS1 level, bacteria such a behemoth, simply not allowed to enter, as for the small particles of 0.1 microns, per cubic meters up to 10 grains, by volume, equivalent to the Dongting Lake, sprinkle 10 grains of salt, so compared with human maternity ward, the chip maternity ward to clean a million times, we carbon-based organisms, at most worry about PM2.5, while the silicon-based chip is really a little PM0.1 are not afforded.
Air circulation：
So here’s the question: how does a high quality clean room in a fab stay clean? First, we need an extremely powerful HVAC system, set of heating and ventilation air conditioning (HVAC for short), in the semiconductor clean room, the dilution or removal of impurities particles, is the use of a large number of fan filtration unit, through the uninterrupted filtration and airflow circulation to achieve the way; fan filtration unit is the soul of the net room, in essence, is an air conditioner plus filter composition of the air purifier.
Semiconductor clean room needs filters, divided into two kinds, ISO5 below the low level of clean room, with high efficiency filters, its filtering efficiency of PM0.3 particles up to 99.97%, and ISO4 above the high level of clean room, must be used ultra-high efficiency filters, their filtration efficiency of 0.1 micron particles, more than 99.999%; in addition to filters, but also have to add blowers, so that the clean room Here, according to the airflow circulation mode, and can be divided into one-way flow and non-one-way flow clean room, non-one-way flow, also known as turbulent flow clean room, the top layer is arranged with a small number of extension filter unit, the wall on both sides of the return port, after the filter to supplement the clean air, through the uneven diffusion of airflow, to dilute the concentration of indoor particles, this way and my fish tank, a This way is just like my fish tank, a water injection port, a water discharge port.
The air in the clean room is the same, but this mainly relies on diffusion dilution, low cleaning efficiency, so only for ISO5 level below the clean room, such as in the chip assembly, testing and packaging area, and to achieve ISO1-4 level, you must use the one-way flow also known as laminar flow clean room. The characteristics of this airflow mode, that is, the wind blowing, has been blowing, overhead with a large number of fan filter units, covering most or even all of the ceiling, people in it look up, full of wind vents, look down, the ground is all pit, these vents, so that the wind blowing downward, can be vertical into the return layer downstairs, and then through the back space back to the top, this one-way airflow cycle, equivalent to the entire clean room, has been Put under the faucet rinse, just not with water, but parallel and uniform airflow, as long as you come to work in the chip factory, you can experience the real wind to wash the dust. Produce a little impurity, will be immediately blown away by the airflow, filtered and cleared.
Therefore, the general chip factory, there are at least four floors, process equipment and personnel, in the middle of the tool man layer, the head is installed fan filter unit pressurized layer (Pressurized Plenum), downstairs is a variety of ducts return air layer (Return Air Floor), the bottom layer is what kind of power facilities and gas storage equipment. In addition to the air circulation system, the chip clean room also needs to maintain a constant pressure difference to prevent the spread of impurities leakage and cross-contamination, taking into account the cost of construction, semiconductor plants are usually composed of different levels of clean room with: for example, the process area is ISO3, the test area is ISO6, the corridor aisle is ISO9, the concentration of impurities before each other, a difference of 1000 times, and the osmotic pressure of the solution Similar to the osmotic pressure of the solution, the suspended particles in the space will automatically diffuse to the area with the lowest concentration, but you can not completely isolate each area, after all, people need to walk, materials need to flow, many manufacturing processes of the chip, but also need wafers frequently to and from the process and test area. This means that as soon as the door is opened, the impurity particles in the low-level area, will flood into the high-level area to cause pollution.
In order to inhibit the tendency of such particles to migrate and spread, the chip factory needs to pressurize the clean room so that it maintains a pressure difference of about 10 Pa with the adjacent area. In addition, once the seal of the clean room has a problem, the air only goes out, which can prevent the outside dirt from coming in, and the example of reverse operation is the virus laboratory and isolation ward. They are clean rooms here to avoid the dirty things inside going out, and the negative pressure is added, which can greatly inhibit the pathogen outflow in case of leakage. In addition to maintaining a constant pressure difference, the adjacent areas in the chip factory with different degrees of cleanliness are separated by two doors, the middle of which is an air lock room (Air Lock), allowing personnel and materials to further buffer and inhibit the migration of impurities when opening the doors to and from the factory. If there is a particle mixed into the critical production process, and the diameter is greater than 50% of the characteristic size, it will directly lead to the chip scrap, if more than 20%, it is also a time bomb, affecting the reliability of future use of the chip.
But for chip production, there are many other types of pollutants, the most difficult is the airborne Molecular Contamination, including volatile acid and alkali substances, condensable substances, etc. The diameter of these molecular-level pollutants, to be much smaller than the suspended particles, whether it is a high-efficiency filter, or ultra-high efficiency filters, are It is difficult to stop them. If the chip factory site is not carefully selected, built in a low-quality air city, then even if the equipment plant is exactly the same, chip production yields, but also because the environment is different and affected. For example, in photolithography, because the photomask, the graphics projected on the wafer, so the photomask must be transparent and clear, but if the air, ammonia and sulfur dioxide molecular concentration, more than a drop, it is easy in the photomask or wafer surface, condensing a mist of varying sizes, the industry is called fog defects (Haze), photomask once tainted, then the more cattle lithography, but also can not carve a good chip to.
How to control these molecular pollutants in the air, is a great headache for the fab, if you do not want to bear the additional burden of expensive chemical filters, then the plant is best built in a place of high air quality. In addition to air, metal ions in the solvent, will also affect the doping concentration of the semiconductor, changing the electrical characteristics of the device, so the chip manufacturing, all the gases and solvents used, must also be high-purity, such as cleaning wafers with water, not drops of pure distilled water, but more pure deionized water. The industry called 18 megohm water, referring to its resistivity, up to 18 megohms, usually we say that water is conductive, it is because the water is not pure enough, which dissolved in a variety of impurities ions and other conductive substances, and chip factory with water, basically an insulator, in short, in the eyes of the chip, everything can be a source of pollution, including water, air, building materials, paint, equipment, chemical solvents, trace of the previous process residues, etc., the most important source of pollution, or the human in the clean room itself.
The average normal person loses 60 hairs per day and produces 50 milligrams of dander per hour, and from the time you open the video, to now in 10 minutes, there are more than 200,000 dead skin cells out of your body and become the food of bacteria and dust mites, in addition to our secretion of sweat grease, spittle star, all the staff in the clean room, become a mobile source of pollution. For example, the operator Ming, accidentally in the wafer cleaning tank drops a bead of sweat, which although only 4 times 10 of -7 times mol nano ions, but enough to make 1000 wafers scrapped, a wafer can cut out 50 graphics cards.
Micro environment is in a large clean room, and then a cleaner mini clean room, the critical step of the process equipment set in it, so that the operator only through the reserved gloves to control, this clean room set wa, can meet the process requirements based on reducing pollution, while saving construction costs, after all, the cost of building a senior clean room is too high, and in the critical area (Critical Area) using mini In addition, the high degree of automation in the chip factory, wafer transfer between different process processes, the use of overhead rail transport (OHT), replacing the use of trolleys to transport wafers staff, these are you in the Fab promotional video, often seen , running around on the overhead rail box, this box is called the front open type Wafer transport boxes (FOUP), they are the bus of chips, and micro-environment as full of nitrogen, clean level is also the same, to ensure that the wafer in the transfer and in and out of the process equipment, always in a protected environment.
Of course, even if the high degree of automation chip factory, or the need for someone to operate and maintain, join you are process, equipment, or measurement engineers, to work in the factory is a common thing, but to be honest, it is really hard, just with a mask, gloves, wearing airtight dust-free clothes, it has been very hard, inside in order to prevent static electricity, humidity is also adjusted very high, the space is closed, people are more likely to be bored. Plus indoor airflow to keep clean, overhead all the fans, the noise is quite large, noise-canceling headphones can not top the kind of summary is that the chip factory girls less, maintain production in three shifts, the work environment is not friendly, wet and stuffy and very noisy, in exchange for you to run not run?
In addition, like other large factory workers, the boss is not in the time, you can occasionally touch the fish scratching water, chip factory, not to mention scratching water, drinking water are not allowed, snacks to look at the phone, must go to a specific area, want to come to the root wazi refreshing, you must change the factory, and smoking within half an hour, are not allowed to return, otherwise the second-hand smoke particles in the breath, it is easy to chip smoked to death, of course, for engineers. Poor environment less girls, in fact, are not a problem, the current chip manufacturing industry is a major reason for the lack of people, or because the money is less. In my previous explanatory video below, you can often see the process to do equipment brothers in the group to warm up, we have the same education, but in most domestic enterprises, manufacturing process post salary, is to design and verification post much lower than.
I believe that in the people watching my video, there are many want to join the motherland’s chip business, if you are a chip engineer, you are willing to enter the factory to do the process, or on the machine to do the design? I think most people have feelings in their hearts, but the body is still very honest, after all, engineers are also people, also have to support their families, earn money to buy a house, but I want to say that the wind and water turn, the rise and fall of an industry, it is really difficult to predict the ups and downs, to electrical and electronic engineering, for example, when I first entered the undergraduate, microelectronics or no one in the country to choose the cold direction, most people want to go to the strong electric, graduated well into the power grid or career, wait until the time of graduate school, strong electricity has entered the cold, artificial intelligence machine vision direction of the course, in the Department of Electronics students, much favored, because to the Internet to engage in the big factory money flying fast, and to my work, because of the well-known reasons, the chip industry is more and more attention, the first intuitive feeling is that the IC design verification and other positions of fresh graduates wages are climbing rapidly, and even the old and new The first intuitive feeling is that the IC design verification and other positions of fresh graduates’ wages are climbing rapidly, and even the old and new employees’ salaries are upside down, maybe in two years, the wind will blow to the process and equipment and other underlying manufacturing direction, and then later, the spring of the basic disciplines of biochemical and environmental materials, may not be far away.
Ok, I’ve gone a bit far, I’ll talk to you about the functions, treatment and contempt chain of each position in the semiconductor industry chain when I have the chance. Back to the cleanroom engineering technology we are talking about today, although it mainly serves the semiconductor industry, but in fact, behind the scenes involves many other professions, such as chemical, structural, fluid mechanics, civil engineering, water supply and drainage, etc.. As a large engineering country, China’s clean room technology progress is still very fast, the head of enterprises (units) such as electronic engineering design institute, (electronic information industry) eleven institutions, CEC four companies, Yaxiang integrated, etc., in recent years have been actively involved in the construction of the major domestic chip plants, but the domestic market is still mainly focused on the lower end of the clean room, can build ISO4 class above the high-end clean room of very few companies, and this is precisely At present, as the core equipment in the chip clean room, the fan filter unit, basically from the United States, Germany and Japan manufacturers, and the core equipment in the core, is the ultra-high efficiency filter (ULPA Filter), more precisely, is the 0.1 micron ultra-fine glass fiber filter paper inside, the filter is a service life, every few years must be replaced. Therefore, it is not only a necessary equipment for plant construction, but also a consumable to maintain production.
At present, the ultra-high efficiency filter, mainly from American Air Fliter and Japan inorganic (Nippon Muki) and other American and Japanese suppliers, there is no domestic alternative for the time being, of course, in addition to equipment, our clean room engineering technology, because of the late start, in technical experience and customer recognition, and other countries there are gaps, but in comparison, the technical barriers to clean room and However, in comparison, the technical barriers of clean room are not too high, as long as we keep our feet on the ground and make efforts to accumulate, these shortcomings will definitely be made up. Well so far, we have finished talking about the former life of the chip and the clean room, now the preconditions for chip production have been unlocked, the next issue, I will formally explain the front-end manufacturing steps of the wafer, interested in semiconductors and chips, remember to pay attention, let us start from lithography, see you soon.
