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 pla tes of dynamic random access memory charge storage capacitors with hig her capacitance per unit area. The films are deposited at temperatures in the vicinity of 575 degrees C. The [311] textured, in situ crystal lized films have high surface roughness as compared to the usual rathe r smooth, [110] textured, as deposited polysilicon. Atomic force micro scopy measurement of the roughness of these films posed a challenge si nce the rugged polysilicon films are made up of a very hard material w ith 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 careful ly selected measurement parameters and proper data reduction technique s has produced good results. Using this solution has allowed us to mea sure the roughness of the rugged polysilicon films as a function of th e critically controlled growth temperature and pressure. Substantial d ifferences were found with small changes in temperature, with less dif ference coming from pressure variations. 570 degrees C and 200 mTorr p roduced the best results for large batch processing. (C) 1997 American Vacuum Society.