Techniques for Improving SIMS Depth Resolution: C[sub 60]+] Primary Ions and Backside Depth Profile Analysis

Abstract

We are evaluating methods to improve depth resolution for SIMS analyses of semiconductors. Two methods that show promise are: (1) backside depth profile analysis and (2) the use of cluster primary ion beams. Backside analysis improves depth resolution by eliminating sample‐induced artifacts caused by sputtering through processing layers on the front side of the wafer. Mechanical backside sample preparation however, also introduces artifacts. The most troublesome artifact is inclined (non‐planar) polishing. Using a combination of both secondary ion image depth profiling and image analysis techniques, the effects of inclined polishing are minimized. A Buckminsterfullerene C60+ primary ion source has been interfaced to a magnetic sector SIMS instrument for the purpose of depth profile analysis. Application of this source to NIST SRM 2135a (nickel/ chromium multilayer depth profile standard) demonstrated that all layers of this standard were completely resolved. Initial applications of C60+ to silicon have produced some unexpected results that are not completely understood at this time. Research is underway to evaluate the application of C60+ primary ions to silicon semiconductors and other materials of interest.