ESOL, a South Korean semiconductor EUV (Extreme Ultraviolet) solution provider, is working on an equipment that can measure the completeness of a next-generation EUV mask that has never been made before. Its plan is to commercialize such equipment with its own patented technologies.
According to the industry on June 14, ESOL is working fast to develop an equipment that can accurately measure the performance of a next-generation EUV mask “phase-shifting mask (PSM)”.
The “photolithography” process that prints a pattern on a wafer using light is absolutely necessary in semiconductor manufacturing. Also, “mask” is absolutely necessary during the photolithography process. In order for light to carry the image of a circuit and reach a wafer, it goes through a mask that is patterned with the image of a circuit.
Structure of a mask that is used in the EUV photolithography process is different from others as “reflective” mask is needed in order to offset EUV beam’s property of being absorbed into every matter. Reflective mask is divided into an area that creates the image of a circuit by reflecting light and an absorber that creates a dark space by absorbing light.
Some people within the industry believe that it is not possible to accurately project the image of a circuit for microfabrication processes under 5nm with current EUV masks. Interference from reflected light becomes more serious as the width between circuits becomes narrower making it more difficult to accurately project the image of a circuit.
PSM was designed in order to resolve the issue. It is made by a material that causes a phase difference in light that creates an image of a nearby circuit. While current masks either completely absorb or deflect an EUV beam, PSM creates phase differences of light that reaches the PSM so that even tiny circuits have a clear contrast range.
There is still a long way before PSM can be commercialized. Multinational corporations such as Intel and ASML recognize the importance of PSM. In South Korea, a research team led by Professor An Jin-ho of Hanyang University is devoting its research on PSM.

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<ESOL’s demo equipment that can measure the performance of a phase-shifting mask. (Picture: ESOL)>

However, it is heard that it is virtually impossible to develop a material that can be sustained while causing phase difference. Also, because there is yet to be any equipment that can measure the phase difference created by a PSM, it has not been possible to quantify the performance of a PSM but just check its potential.
ESOL will look to be the first company in the world to develop an PSM inspection equipment in order to accelerate development of PSM. It has secured a patented technology for measuring the performance of a PSM by applying a principle from the “double slit” experiment that Thomas Young performed in order to demonstrate light waves. ESOL’s technology measures a phase value by reflecting diffracted light that passes through metal with rectangular holes onto a PSM.
“After measuring the phase value of a PSM with out prototype equipment, there was only a margin of error of 0.2°.” said Vice-President Lee Dong-geun of ESOL. “It was the world’s first case of quantifying a phase value that remained as only a theory-based estimation.”
ESOL announced its research result at an EUV lithography society where great EUV scholars around the world attend and received positive comments.
“We are attempting to create an equipment that has not been commercialized and it will push forward commercialization of PSM.” said President Kim Byung-guk.
In addition to equipment for measuring the completeness of PSM, ESOL developed and commercialized various EUV-related equipment such as an equipment that reviews any defect of EUV mask called SREM and an equipment that measures the completeness of an EUV photoresist called EMiLE.
Staff Reporter Kang, Hyeryung |