Characterization of the low-pressure chemical vapor deposition grown rugged polysilicon surface using atomic force microscopy

In this work, rugged polysilicon films are deposited in a state-of-the-art low-pressure chemical vapor deposition reactor to produce the plates of dynamic random access memory charge storage capacitors with higher capacitance per unit area. The films are deposited at temperatures in the vicinity of 575 degrees C. The [311] textured, in situ crystallized films have high surface roughness as compared to the usual rather smooth, [110] textured, as deposited polysilicon. Atomic force microscopy measurement of the roughness of these films posed a challenge since the rugged polysilicon films are made up of a very hard material with a large amplitude of high spatial frequency roughness. A solution was found which involves using probes on which a carbon film has been applied to the standard Si probes. Combining these probes with carefully selected measurement parameters and proper data reduction techniques has produced good results. Using this solution has allowed us to measure the roughness of the rugged polysilicon films as a function of the critically controlled growth temperature and pressure. Substantial differences were found with small changes in temperature, with less difference coming from pressure variations. 570 degrees C and 200 mTorr produced the best results for large batch processing. (C) 1997 American Vacuum Society.