We have already developed several candidates of future resists using not only monomer but also the molecular
glass resists as high performance resist materials and discussed them on the former talk. Those novel adamantane based
molecular glass resists were made sure of sufficiently high Tg and the highly etch resistance. However some of them
were not satisfied as resist materials due to their higher or lower solubility. Then we have designed and synthesized new
adamantane based molecular glass resists containing acetal and ester moieties for the lower dose sensitivity and the
excellent transparency at 193 nm. Further more, the protecting groups were modified in order to control the solubility
into both a conventional solvents for the spin on the wafers and a developer.
Novel adamantane-based molecular glass resists were modified their polarity of the hydroxyl group of cholic
acid moiety in order to improve their film thickness loss by subtrahend and / or by capping the hydroxyl group. These
treatments affected their adhesion to a wafer greatly. The capping technique using with any units can introduce various
functional groups and applied versatile improvements.
GR-14 that were capped their hydroxyl group with acetyl unit was imaged sub 100 nm line and space by the EB
exposure. Although, the excess subtraction of hydroxyl group has reduced its film property like GR-11 that made from
lithocholic acid. We made sure that the imperfect resist for its improvement of the film thickness loss such as GR-17,
GR-18 and GR-19 was affected by BARCs as the under layer.
The adamantane-based molecular glass resist were studied its functional capability for lithography process in this work. GR-5 represented adamantane-based molecular glass resist were described as compared with the conventional polymer for 193 nm lithography. Low molecular weight which is one of the features of the molecular glass resist are expected to reduce the line width roughness (LWR) and the line edge roughness (LER). We evaluated the surface roughness (Ra; arithmetic mean departures of roughness profile from the mean line) by using the atomic force microscopy (AFM) instead. GR-5 has actually lower Ra value of 0.345 nm after the exposure and the development process. As the result of the confirmation of the GR-5's performance between the refractive index (n) and transparency (T), although n value stood on over 1.8, T value was less than 30% at 193 nm wave length. It is not likely to solve the higher refractive index and the higher transparency simultaneously. Further the scope of the adamantane-based molecular glass resist to apply for the EUV lithograph was found.
There are some practical candidates for next generation lithography (NGL). However, many subjects are left behind and
there is still no effective technique. One of those subjects is reduction of line edge roughness (LER)/line width
roughness (LWR). As compared with 2-methyl-2-adamantyl methacrylate which is mostly used in 193nm lithography as
acid cleavable monomer, it became clear that our new monomers were effective in reduction of LER/LWR by
measuring surface roughness (Ra) with the analysis of atomic force microscopy (AFM). We found out that the
monomers which have acetal as acid cleavable unit has high exposure sensitivity and effective in the reduction of Ra.
Moreover, we tried to synthesize high refractive index polymer by introducing a sulfur atom that is another subject of
NGL. By synthesizing some monomers, it became clear that the bond type of sulfur atom affects a refractive index
greatly. It was also checked that a refractive index and transparency have a relation of a trade-off.
The adamantyl acrylate monomers are mostly used in 193 nm lithography due to their high transparency and excellent
contrast after the development. We have designed and synthesized various monomers based on adamantane moieties
from 65nm node forward the 32 nm node. So, we think that it's our duty to challenge from the design of a monomer to
those subjects for NGL.
As the feature dimensions decreases there are several issues must be addressed to implement the corresponding technology in high volume production. Line width roughness (LWR) and line edge roughness (LER) are the most important technological issue arises as the feature dimension decreases. In order to improve both of LWR and LER, we have developed novel low molecular weight glass resists as high performance resist materials. These molecular glass resists are adamantane derivatives and are highly transparent at 193 nm. We have prepared series of new molecular glass resists based on adamantane core carrying acetal and ester protecting groups. Particularly, adamantane core derivatives of tripod structure were investigated in detail. Several compositions of them showed glass transition temperatures (Tg) above 120 oC. Lithographic evaluation confirmed their high sensitivity at 254 nm and e-beam exposure. It also resolved feature size as small as 200 nm line/space when it evaluated using e-beam lithography. These new molecular glass resists also have high plasma-etch resistance.