Why is a lithography machine so difficult to build, and what are the differences between different lithography technologies

The lithography machine is known as the crown jewel of the semiconductor industry, and it is also the most complex and critical process step in semiconductor manufacturing. Its main function is to transfer the chip circuit diagram on the reticle to the silicon wafer. The process level of lithography directly determines the process level and performance level of the chip.

The lithography machine is known as the crown jewel of the semiconductor industry, and it is also the most complex and critical process step in semiconductor manufacturing. Its main function is to transfer the chip circuit diagram on the reticle to the silicon wafer. The process level of lithography directly determines the process level and performance level of the chip.

According to the different exposure methods, lithography can be divided into three lithography techniques: contact lithography, proximity lithography and projection lithography.

contact lithography

In contact lithography, the silicon wafer coated with photoresist is in direct contact with the mask. Due to the close contact between the photoresist and the mask, a relatively high resolution can be obtained. The main problem of contact exposure is that it is easy to damage the mask and photoresist. When the reticle contacts and aligns with the silicon wafer, a small amount of dust on the silicon wafer may cause damage on the reticle, so that this defect will appear on all silicon wafers exposed with this reticle in the future. Therefore, it is difficult to obtain defect-free VLSI chips by using contact lithography, so contact lithography technology is generally only suitable for small and medium-scale integrated circuits.

proximity lithography

Proximity exposure is similar to contact exposure, except that there is a small gap between the silicon wafer and the mask during exposure. This gap is generally between 10 and 25 microns, which can greatly reduce the damage to the mask. . The resolution of proximity exposure is low, generally between 2 and 4 microns, so proximity lithography machines can only be assembled in integrated circuit production lines with large feature sizes. The main advantage of contact or proximity lithography machines is higher production efficiency.

projection lithography

Projection exposure is an exposure method that uses a lens or mirror to project the pattern on the mask onto the substrate. In this exposure method, the damage to the mask can be completely avoided due to the long distance between the mask and the silicon wafer. In order to improve the resolution, in projection exposure, only a small part of the silicon wafer is exposed each time, and then the whole wafer is exposed by scanning and step-and-repeat method. In modern integrated circuit technology, the most used lithography system is the step-by-step projection lithography machine. Using a step-by-step projection lithography machine, combined with techniques such as phase-shift masks, patterns with a minimum line width of 0.10 microns have been obtained.

Lithography technology is not difficult to say, but the development and manufacture of lithography machines is difficult. What is the reason why lithography machines are so difficult to manufacture, and why are so many countries and manufacturers stuck?

In fact, the technical principle of the lithography machine uses laser light irradiation to project the chip circuit diagram on the photomask onto the silicon substrate coated with photoresist, and finally the chip circuit diagram is formed on the silicon substrate. The two most important components seem to be the light source and the lens. At present, the laser source is mainly produced in the United States, while the lens is provided by Germany and Japan.

These two important components are basically available to everyone. What really shines is the assembly technology. A lithography machine needs to use more than 30,000 components, and these 30,000 components need to be assembled into a lithography machine. The assembly process required is very high, and ordinary enterprises and technicians cannot meet the requirements. More importantly, this process requires continuous testing, running-in, and cooperation with chip manufacturers. ASML’s major shareholders are leading semiconductor manufacturers such as TSMC, Intel, and Samsung. It is difficult for other manufacturers to enter the game at this time. too big.

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