193-nm excimer laser-assisted etching of polysilicon was studied in the presence of CI2. Maximum etch rates of 1.25 Å/pulse were obtained for pressures of about 400 torr and fluences exceeding 400 mJ/(cm2-pulse). The etch rate increased with both fluence (100-550 mJ/(cm2-pulse)) and pressure (50-800 torr). An adsorptive etch mechanism similar to NF3 etching has been proposed, where Cl2 molecules diffuse to the surface, adsorb, and then react after absorbing laser radiation. This is consistent with photon and molecular flux considerations and the availability of reaction sites. Thermal effects where Cl2 molecules decompose to Cl atoms on “hot” polysilicon surfaces may assist this process, and appear to dominate under conditions of lower pressure (<400 torr) and higher fluence. Etching caused by the gas phase formation of Cl atoms is minimal due to the low Cl2 absorption cross section at 193 nm.
Simple projection etching results showed that micron lines can be etched in polysilicon by use of this chemistry.