AVS 46th International Symposium
    Nanometer-scale Science and Technology Division Friday Sessions
       Session MS+PS-FrM

Paper MS+PS-FrM6
Effect of W Reaction Byproducts on W/poly-Si Stack Gate Etching Process

Friday, October 29, 1999, 10:00 am, Room 611

Session: Diagnostics and Processes in Etching
Presenter: H. Morioka, Fujitsu Limited, Japan
Authors: H. Morioka, Fujitsu Limited, Japan
M. Nakaishi, Fujitsu Limited, Japan
N. Abe, Fujitsu Limited, Japan
Correspondent: Click to Email
W/(barrier layer)/poly Si stack is one of the most promising candidate for gate electrode structure of memory-embedded logic LSIs and DRAMs in the next generation because of low sheet resistance and compatibility with self-aligned contact (SAC) process, etc. Generally, the chemistry of W/poly Si stack gate etching is halogen-base, and most of W etching chemistry have higher etch rate of poly-Si than that of W itself. Although oxygen addition can increase the selectivity to poly Si above 1 by inhibiting Si etching, some troubles are still observed during poly Si etching step, such as non-uniform enhancement of etch rate, undercut profile, and serious RIE-lag. These facts make it difficult to achieve W/poly Si stack gate etching against very thin gate oxide. So, we examined the effect of W reaction byproducts on etching characteristics of other layers. Our experiments were performed on a high-density plasma (HDP) etcher whose plasma source could be operated in continuous mode or pulse modulated mode. We also compared fluorine-base chemistry with chlorine-base one to investigate the difference of etching byproducts. In this experiment, we found that W etching byproducts from a sample wafer and chamber wall enhanced the etch rate of poly-Si and SiO@sub 2@ especially for chlorine-base chemistry, and pulse modulation of plasma could reduce this enhancement. These facts suggest that W etching byproducts were decomposed into fragments in the plasma, these species were deposited on the sample surface and varied the etching characteristics. It is probable that pulse modulation reduced the dissociation of W reaction byproducts because of low electron temperature during afterglow.