Extreme ultra-violet (EUV) lithography technology is being developed for the patterning of sub-22nm node. Line edge
roughness (LER) is the one of the important issues together with the resist performance like resolution and sensitivity.
There are some novel resists for EUV lithography that can be used for obtaining the target resolution and sensitivity,
while the line edge roughness do not reached the target values in most resist yet. In order to reduce the LER, the
molecular resist has been widely studied due to their small size compared to the conventional polymer resist. There is
another approach to reduce the LER by reducing the acid diffusion length, but it is not easy to reduce down the acid
diffusion length. We tried a new approach to reduce down the LER by changing the shape or structure of the molecular
resist. A new molecular resist shape that shows the anisotropic structure is tried to see the LER and whether this
anisotropic resist can be used for LER reduction. It turns out that the LER is minimum when the molecular chain
alignment is along the depth, while LER is maximum when the molecular chain is randomly distributed.
Extreme ultra-violet lithography (EUVL) has been prepared for next generation lithography for several years.
We could get sub-22 nm line and space (L/S) pattern using EUVL, but there are still some problems such as
roughness, sensitivity, and resolution. According to 2007 ITRS roadmap, line edge roughness (LER) has to be
below 1.9 nm to get a 22 nm node, but it is too difficult to control line width roughness (LWR) because line
width is determined by not only the post exposure bake (PEB) time, temperature and acid diffusion length, but
also the component and size of the resist. A new method is suggested to reduce the roughness. The surface
roughness can be smoothed by applying the resist reflow process (RRP) for the developed resist. We made resist
profile which has surface roughness by applying exposure, PEB and development process for line and space
pattern. The surface roughness is calculated by changing parameters such as the protected ratio of resin. The
PEB time is also varied. We compared difference between 1:1 L/S and 1:3 L/S pattern for 22 nm. Developed
resist baked above the glass transition temperature will flow and the surface will be smoothed. As a result, LER
and LWR will be much smaller after RRP. The result shows that the decreasing ratio of LER due to RRP is
larger when initial LER is large. We believe that current ~ 5 nm LWR can be smoothed to ~ 1 nm by using RRP
The purpose of extreme ultraviolet (EUV) lithography is to make pattern size of sub-22 nm. However, there are
still some challenges to be overcome for EUV photoresist such as reducing the line edge roughness (LER) and
line width roughness. The roughness of conventional polymer resists is large because of large polymer size.
Thus many new molecular resists are studied and being developed in order to reduce roughness. To reduce LER
we analyzed the size and structure of each ingredient of the suggested molecular resists. The varied parameters
are the amount of photo acid generator, quencher and the size of the monomer. The protecting ratio of resin and
protected number of a molecule are also varied. Monte-Carlo simulation is used for ingredient dispersion and
acid diffusion direction to see the effect to LER. Solid-EUV is used to get the aerial image and photo generated
acid for 22 nm node and ChemOffice is used to analyze molecular structure and volume.