Effect of Initial High Temperature Annealing and Gettering Processes on the Refresh Time of High Density Dynamic Random Access Memory Devices

Abstract

The effect of initial high temperature annealing and gettering processes on the refresh time of high density dynamic random access memory devices was studied. The results show that under the present device processing conditions, both intrinsic and extrinsic gettering via a polysilicon back side layer are comparably effective. In comparison to an initial annealing at 1200°C in a mixed ambient, annealing in a hydrogen gas ambient shows strong improvement in the refresh time of memory devices fabricated near the edge of the wafer. Nevertheless, a dependence of the refresh time on the radial position on the hydrogen annealed wafer implies that hydrogen annealing may not completely eliminate crystal originated defects in the silicon substrate. The most effective annealing temperature was found to be 1300°C where the radial dependence of the refresh time is virtually eliminated. Based upon the present analysis, it is concluded that an improvement in the refresh time of memory devices can be accomplished when the crystal originated defects which include D‐defects and oxide polyhedral precipitates are eliminated from the device active region prior to the device manufacturing process.