Electrolytic Analysis of Oxide Leakage in Simox Material

Abstract

The effect of particles on beam blocking has been suggested by several researchers, with simulated particles of >0.5pm diameter causing a nonstoichiometric buried oxide layer formation [2-41. Using the CuSO4 electrolytic plating technique to examine the presence of surface to substrate leakage paths, we have found a direct effect of particle presence on the occurrence of buried oxide pinholes. Actual plate maps as correlated with total particle counts for three single implant wafers of standard buried oxide (3800A) thickness are shown in Figure 1. Examination of the material by this method reveals buried oxide pinholes which vary in shape, but do not vary in number with time for low plate density material as will be shown. SEM analysis shows that the buried oxide pinhole structures are consistent in size with electrical leakage data reported by others. The material cross-sections that will be presented show Type I as well as possible mechanisms for Type I1 defects which yield leakage currents as low as 1nA [6]. Figure 2 shows the SPC tracking for particles (>lp) as measured by the Tencor 4000 surfscan and associated Cu plate densities per lot. The.Cu plate density measurements are shown to directly track with total particle measurements. Figures 3a (early 1992 SIMOX plate density) and 3b (mid 1992 SIMOX plate density) show the buried oxide plate density as a function of BOX thickness. Numbers are greatly reduced in both Cu plate density as well as dependency on thickness from earlier SIMOX material[5]. A slight dependence on buried oxide thickness is observed for early 1992 Cu plate density wafers. However, when the Cu plate density is reduced to below 0.1 /cm2, no dependence of the electrolytic leakage density on buried oxide thickness is observed. Further information on the correlation to buried oxide capacitor leakage measurements will be shown and discussed. The support of the SO1 Manufacturing Technology Program, U.S. Air Force WRDC, Wright-Patterson AFB, OH, is gratefully acknowledged.