The absorption of extreme ultraviolet (EUV) light by the mask-protecting pellicle could be the most critical problem preventing widespread EUV adoption because EUV source power is still too limited to facilitate its use in mass production. We found that transmission loss due to the EUV pellicle could be compensated through the use of proper optical proximity correction (OPC) applied to the mask-pellicle system. Patterning results of optical proximity correction corrected masks with different transmission pellicles are shown for various one-dimensional and two-dimensional patterns. From the results, it is clearly shown that we do not need to increase the dose to avoid the throughput loss, even when using a pellicle with 80% one-pass transmission. The OPC process described in this paper can speed EUV adoption by allowing the use of much thicker films with higher absorption.
The absorption of extreme-ultraviolet (EUV) pellicle could be the most critical problem because the EUV source power is still not good enough for achieving mass production. We found that the transmission loss due to the EUV pellicle could be compensated through proper optical proximity correction (OPC) of a pellicled mask. Patterning results of OPCed masks with different transmission pellicles are shown for various 1D and 2D patterns. From the results, it is clearly shown that we do not need to increase the dose to avoid the throughput loss even if a pellicle which has 80 % one-pass transmission is used. Therefore, the EUV pellicle manufacturing would be much easier because we can use much thicker film with higher absorption.
The extreme-ultraviolet lithography (EUVL) has been regarded as the best candidate to achieve high resolution patterning below 1x nm node. From the Rayleigh criterion, a numerical aperture (NA) should be increased to make the high resolution pattern. A new absorber structure which has sufficient image contrast and small height is needed for realization of high NA optics. In this study, 28 nm-thick ruthenium oxide (RuO2) is suggested for the absorber material. We could obtain higher image contrast and better H-V bias by using the RuO2 absorber compared to the other materials such as TaN and TaBN.
We report the effect of the mesh support for the EUV pellicle on the wafer pattern image. The intensity distribution passing through the meshed pellicle was simulated with a partially coherent EUV beam showing that its non-uniformity and the CD uniformity are increased with the mesh width. In order to reduce a non-uniformity of the intensity distribution and CD uniformity, the mesh width should be narrower and the height becomes smaller as well. Thus, the image deformation on the wafer due to the mesh can be avoided by optimizing the mesh structure and thus the pellicle with the mesh support can be used for the EUV lithography.
Extreme ultraviolet lithography is about to be realized in mass production even though there are many obstacles to be
overcome. Several years ago, the EUV pellicle was suggested by some people, but the idea of using the EUV pellicle
was abandoned by most people because there were big problems that were believed to be almost impossible to
overcome. The EUV pellicle should be made of an inorganic material instead of a common organic pellicle and should
be very thin due to EUV transmission. In addition to that the support of the very thin pellicle film should be used. The
structure of the support of the pellicle thin film should not make any noticeable intensity difference on the top of the
patterned mask side. However, the experimental result of the Intel showed the interference images with their suggested
support structure. In the Intel's report, the structure of the support was honeycomb or regular mesh type with a ~ 10 μm
line width and a ~100 μm pitch size. We study the intensity distributions on the top of mask for various combinations
around the above the mentioned scales and the support structures. The usable structure of the support will be reported
based on our simulation results, which would open the possibility of the EUV pellicle in mass production.