The exposure device for the next-generation lithography technology for semiconductors, i.e. extreme ultraviolet lithography (EUV lithography or EUVL) technology, appears to use large quantities of hydrogen, reports The Gas Review.

For the EUVL exposure device, a flow of large quantities of hydrogen is used as the atmosphere gas around the tin droplets when a CO2 or YAG (Yttrium, Aluminium and Garnet) laser is irradiated to dissolved tin (Sn) droplets to generate ultrafine EUV light.

It is estimated that over 100,000m3 of hydrogen will be consumed each month. It is also possible that hydrogen radicals will be used to clean the EUVL exposure device.

LPP method will use large quantities of hydrogen

The EUVL exposure device is indispensable for fine processing of 10-nanometer or less. It produces EUV light that exceeds the light generated by KrF and Ar excimer lasers.

The LPP (Laser Produced Plasma) method is used, which is different from that used up until now in terms of luminescence method. With the EUVL exposure device, tin is melted and tin droplets are formed and then irradiated with a CO2 laser. The EUV light that is generated is then focused. It appears that it is not a particularly new technology and practical application of EUVL is proceeding as we enter into the 10-nanometer age.

During this process, a large quantity of a reducing gas is made to flow as the atmosphere gas to prevent the tin from oxidizing. The most likely reducing gas is hydrogen.

But if large quantities of tin and hydrogen are used, stannane (SnH4) will be produced as the result of the reaction between them. It does not easily dissolve in water and it is combustible (it spontaneously ignites when it comes into contact with the air). A new exhaust gas treatment method is therefore required.

Furthermore, it is possible that hydrogen will be used to clean the EUVL exposure device. According to one document, gas containing hydrogen is placed into contact with molybdenum or a molybdenum alloy that has been heated to between 1,000 and 1,600 degrees Celsius in order to use the resulting hydrogen radicals. Contaminants must be removed and prevented, but the hydrogen radicals will remove catalysts and resigns that remain in the device.

TSMC introduces EUVL on a full scale

So far, the only company that has introduced EUVL on a full scale is Taiwan Semiconductor Manufacturing (TSMC), who is the world’s largest foundry. The company are leading in actual application of 11 to 14 nanometer ultramicro fabrication. As a foundry, TSMC is known for possessing a wide range of semiconductor manufacturing processes, and one of them is EUVL.

The Gas Review reports that rumours say South Korean Samsung Electronics, US Intel, US Micron Technology and other companies will introduce EUVL in manufacturing processes for DRAM devices and microprocessors.

Unfortunately, the chances of Japan introducing EUVL at this point are slim. It is mainly DRAM that requires ultramicro fabrication. Micron Technology is studying introducing EUVL into its Singapore plant, but it does not appear that there are plans to introduce it into its Higashihiroshima plant.

On the other hand, it is thought that EUVL is not necessary for 3D-NAND flash memory devices. Kioxia is using a liquid immersion ArF excimer laser for them. For the time being, Japan cannot expect any new demand for hydrogen.

Who will profit from supplying hydrogen?

However, several gas producers in Japan have received inquiries from Taiwan, South Korea and elsewhere concerning hydrogen supply methods and purification equipment. Hydrogen is not used directly in the process, so that the required purity is not all that high, but supplying 100,000m3 of hydrogen per month would not be easy with compressed hydrogen. Onsite supply that uses hydrocarbon gas reforming or water electrolysis is more realistic, but even then there are problems.

For hydrocarbon gas reforming, methane, propane, methanol, or something similar would be used as the raw material, but electronics manufacturers are very reluctant about increasing emissions of carbon dioxide. On the other hand, water electrolysis requires large amounts of electricity. To make matters worse, semiconductor manufacturing plants are already major consumers of extreme amounts of electricity. The use of EUVL alone will mean an increase in the per unit consumption of electricity. One source told The Gas Review that Linde LienHwa will provide onsite supply of hydrogen to TSMC.

Even for 3D-NAND flash memory devices, the number of dry etchers is being increased to handle processing a larger number of layers, and in South Korea, the Korea Electric Power is telling Samsung Electronics and SK Hynix that they will not be able to continue providing electricity for semiconductor manufacturing equipment in the same way as in the past. To handle this situation, it is said that both companies are studying the construction of their power plants.