Replicating characteristics by SR lithography

Process optimization and pattern replication on various substrates by synchrotron radiation lithography was carried out to evaluate the problems for 0.15 micrometers level resists patters for 1-Gbit dynamic random access memory. It was found that the exposure latitude was rather restricted by the resist residue remaining between lines (scum) and the pattern collapse than the normally used +/- 10-percent critical dimensions. A simple Fresnel diffraction calculation including the phase-shifting effect and mask contrast showed that the occurrence of the scum was mainly determined by the optical images of x-rays, and could not be significantly improved by the resist process condition. We used the mask/wafer proximity gap of 20 micrometers to get a good optical image and 5000-angstrom resist thickness to suppress the pattern collapse. On the other hand, the replicating characteristics on the light element substrates were similar to that on the Si substrate, especially good on the SiN substrate, but the residues caused by secondary electrons ont he metal substrates and the catalytic reaction on the Pt substrate were observed. It was shown that protection layers could suppress those residues and serve a good pattern profile.