Oil-free Compressed Air in Semiconductor

in the semiconductor industry, there is a saying that almost all practitioners agree: air is the blood of the production line. The blood must be pure, oil-free, and dry. Even if a little oil or water vapor is mixed in, the whole batch of chips may be scrapped. Therefore, oil-free compressed air is not an option in semiconductor manufacturing, but a necessary option.

Semiconductor why air so "cleanliness"

the lines on a semiconductor chip are as thin as nanometers, tens of thousands of times thinner than a hair. At this scale, a particle of dust that is invisible to the naked eye or a drop of oil mist that is invisible to the naked eye can short-circuit or fail the entire circuit.

When the oil touches the surface of the chip, it will form an invisible film, resulting in abnormal electrical signals. When moisture touches the sensitive material in the chip, it will cause a chemical reaction, which will cause the chip performance to decline or even break down directly.

Therefore, the requirements of the semiconductor industry for compressed air can be summarized in three words: absolutely oil-free, extremely dry, and very clean. In the industry, the highest standard is usually called zero-grade oil-free, which means that the oil content in the air must be zero.

Oil-free compressed air throughout every step

from the front-end silicon wafer manufacturing to the final packaging test, almost every link is inseparable from oil-free compressed air.

Pull crystal and slice link

the starting point of the semiconductor is a single crystal silicon rod, which should be pulled out, cut into thin slices, polished and polished. In these steps, compressed air is used to purge tiny particles from the surface of the silicon wafer and to drive cutting and grinding equipment. As long as there is a little oil in the air, the surface of the silicon wafer will leave an oil film, and all subsequent processes will be dried in vain.

lithography link

photolithography is the core step in the manufacture of chips, which is equivalent to "printing" circuit patterns on silicon wafers. This process of air cleanliness requirements are the highest in all links. Compressed air is used to purge the photoresist surface and drive precision pneumatic components. Many valves and cylinders in the lithography machine are controlled by oil-free compressed air. If the air pressure fluctuates slightly, the pattern will shift and the whole wafer will be wasted.

Etching and film deposition links

etching is to remove unnecessary materials, and thin film deposition is to lay down the necessary materials layer by layer. Both of these steps require compressed air to maintain a stable pressure in the chamber, while oil-free air is used to purge the residue. If there is oil in the air, the deposited film will be mixed with impurities, and the uniformity and thickness of the film will be problematic.

ion implantation link

ion implantation is a key step in "doping" silicon wafers and requires extremely precise pneumatic control. Compressed air-driven valves must respond quickly and act accurately, and the premise of all this is that there can be no oil mist in the air, otherwise the valve will be stuck, the response will be slow, and the injection accuracy will be gone.

Cleaning and purging links

in the process of chip manufacturing, the silicon wafer should be cleaned repeatedly, and the surface should be dried with oil-free compressed air after each step of cleaning. If the air used for purging contains oil, the oil will remain on the surface of the silicon wafer, and the following process will be completely contaminated.

Packaging and testing

after the chip is ready, it should be packaged and tested. When packaging, compressed air is used to drive the placement machine and wire bonding machine, and when testing, compressed air is used to pressurize the chip to detect whether there is any leakage. These links also require air without oil and water, otherwise the packaging quality and test results are not reliable.

Nitrogen production link

nitrogen is widely used as a protective gas in semiconductor production. Nitrogen is used to prevent the material from being oxidized during sintering, and nitrogen is used to isolate the air during encapsulation. The nitrogen is separated from the compressed air, and the air quality provided by the air compressor directly determines the purity of the nitrogen. The air is not clean, nitrogen is not clean.

water lubricated air compressor is more and more suitable for semiconductor industry

although the traditional oil-injected screw air compressor is low in cost, it has an inherent trouble: oil. Part of the oil in the compression chamber will inevitably become oil mist and mix into the air. No matter how many filters are added, it is difficult to be 100% clean. Moreover, oil mist will accumulate on the heat exchange tube of the cold dryer, and the heat dissipation will become worse over time. The cold dryer will have to work harder, the electricity bill will go up, and the maintenance will be frequent.

Although the dry oil-free screw machine has no oil problem, because there is no liquid in the cavity to fill the gap, the gas leakage is more serious, the efficiency is low, and the dry grinding between the rotors is fast, and the maintenance cost is not low.

The water lubricated air compressor just makes up the short board of these two schemes.

It uses clean water instead of oil to do the three things of lubrication, sealing and cooling. Because the water does not evaporate, does not produce oil mist, out of the air from the source is oil-free, cleanliness is very high. The specific heat capacity of water is large, and the ability to take away heat is stronger than that of oil. The temperature is controlled more smoothly during the compression process. The gas will not waste energy due to the high temperature, so the efficiency is higher than that of dry oil-free models.

In the semiconductor industry, after the water-lubricated air compressor is equipped with a cold dryer, the entire gas path will be much cleaner than the traditional solution. There will be no sludge on the heat exchange tube of the cold dryer, and the heat dissipation efficiency is always on-line, without frequent cleaning, and the operation is more stable. Photolithography, etching, thin film deposition, which require extremely high air quality, can be more reliably guaranteed.

Moreover, the water lubricated air compressor does not have such consumables as oil filter element and oil and gas separation core, and the later maintenance cost is much lower than that of the oil injection machine. The discharged gas and water are separated by a separation device, and the water is recycled back for subsequent use. No waste oil is generated, and the environmental protection pressure is also small.

For semiconductor factories, choosing a water-lubricated air compressor has another hidden advantage: the whole gas path is fresher, the nitrogen generator, cold dryer and filter at the back end do not have to work so hard, the service life is longer, the frequency of changing consumables is lower, and the long-term cost is more cost-effective.

One word summary

In the semiconductor industry, oil-free compressed air is not an auxiliary equipment, but a core infrastructure as important as lithography and etching machines. From pulling to packaging, every step is inseparable from it. Water-lubricated air compressors are becoming more and more mainstream gas supply options in the semiconductor industry because they eliminate oil pollution from the source, have high efficiency, low maintenance, and have good effects with post-processing equipment. The air is clean, the chip can be clean, the product can be qualified.