Now that EUV production is in place, should the yield also be considered?

When the current semiconductor manufacturing process continues to develop below 7nm, the EUV lithography machine has become one of the indispensable tools for IDM and foundries. As TSMC, Samsung, Intel, SK Hynix, and other companies have EUV lithography machines in place, these top semiconductor manufacturers and the sole manufacturer of EUV lithography machines, ASML, have another problem to worry about about about, that is, the mask is dust-proof. membrane.

90% transmission rate

The photomask dust-proof film is a transparent film, which is mainly used to protect expensive photomasks and keep them clean to improve semiconductor production efficiency. Although the lithography machine is generally located in a very strict clean room, many people think that EUV does not need a dust film in the early days of the EUV lithography machine, because there will be no particles, but in actual situations, it is inevitable to avoid impurities in the production process Appear. According to ASML, EUV generates an impurity particle every 10,000 exposures. By using a dust-proof film, the fab can effectively avoid defects caused by contamination.

Although this is an effective solution to wafer defects, it affects the light transmission of the lithography machine. Although the ultraviolet light absorbed by the dustproof film is invisible to the naked eye, it becomes a power loss in the performance of the lithography machine. The transmittance of the current DUV dustproof film has reached more than 99%, but the EUV dustproof film has always been unsatisfactory. Therefore, ASML and related foundries are studying how to produce dustproof films with higher transmittance.

However, because ASML needs to concentrate on the production and development of EUV lithography machines, it is difficult to take into account the production of the dust-proof film, and under their research, the transmittance has been progressing slowly. In 2016, the first EUV dust-proof film launched by ASML only had a transmittance of about 78%. In 2019, after a period of continuous research and development, the average transmittance has only increased by 3.5% to a level of 83%.

Samsung has made it clear that EUV dust-proof film will not be used for less than 90% transmittance. After all, when the current semiconductor is out of stock, the decrease in transmittance affects the output, and the use of the dust-proof film can only affect a small part of the yield. Therefore, neither Samsung nor TSMC currently uses dust-proof films on EUV lithography machines.

In addition to transmittance, EUV dust-proof film has two hurdles, that is, heat dissipation and cost issues, but these two issues are actually the same as transmittance, and both may have to be resolved from the material.

How long is it from official use?

For this reason, on May 31, 2019, ASML reached an agreement with Mitsui Chemicals Co., Ltd., the former will license EUV dust film technology to Mitsui Chemicals, and the latter, who has many years of experience in dust film production, will be responsible for the production. ASML and Canadian company Teledyne is responsible for the development of EUV dust-proof film technology, while Mitsui is engaged in the production of the dust-proof film in Otake City, Japan.

In May of this year, ASML’s sales manager in Korea mentioned that through joint development with Teledyne, they can achieve a transmittance of 90.6% of EUV dust-proof film and a long-lasting power of 400W. Mitsui Chemicals also announced on the 26th of the same month that it officially announced the start of commercial mass production of EUV dust film.

Mitsui Chemicals is not the only producer of EUV dust film. Korean companies FST and S&S Tech are also producing related products. As a major customer of these two manufacturers, Samsung has also invested a lot of money in them. Take FST as an example, using carbon nanotube materials, they have also succeeded in achieving a transmittance of more than 90%, and they have also introduced equipment and tools for automatic installation and detection of dust film. After all, in the production process of using EUV dust-proof film, particle detection on the dust-proof film and cleaning and replacement of the dust-proof film are also very time-consuming and labor-intensive steps.

However, let alone guaranteeing the yield rate of semiconductor production, the EUV dust-proof films of these two are still in the R&D or initial stage, and their own yield rates have not been guaranteed. Although EUV dust-proof films have become their R&D focus, Compared with ASML and Mitsui Chemicals, there is still a gap.

However, Korean media reported that Samsung, the Korean giant, is likely to still use ASML's own photomask and dust-proof film. Because the EUV lithography machine is only manufactured by ASML, if they do not use the dust-proof film recommended by them, it may be difficult to guarantee the follow-up after-sales maintenance work. A machine with more than one billion yuan per unit will be difficult to repair if it is broken.

Carbon Nanotube EUV Dust Film / IMEC

The Belgian Microelectronics Research Center (IMEC) is actually studying EUV dust film. They installed multiple carbon nanotube dust film on the NXE: 3300 EUV lithography machine, and measured a single extreme ultraviolet light transmittance of 97. %, the power it can bear can reach 600W.

Concluding remarks

Although EUV dust-proof film has been put into mass production, industry insiders broke the news that Samsung is likely to start using dust-proof film on EUV lithography machines in 2023. After all, even the transmittance of 90.8% will still have a certain impact on the output. Compared with the transmittance of more than 99% of the DUV lithography machine, there is still a gap. At present, almost all fabs are operating at full load. In terms of output and yield, the latter is obviously not the first choice.