GOI Impact of Cu, Ni and Al Atoms on the Wafer Surface Prior to RTP and Furnace Oxidations

Abstract

AbstractThe effects of Al, Cu, and Ni on Gate Oxide Integrity (GOI) are evaluated in a critical process sequence relevant for current CMOS technology. The test process is designed to evaluate the GOI effect of these metals after multiple oxide growth and strip steps. This work compares oxide growth in a furnace and Rapid Thermal Processing (RTP). Wearout and E ramp measurements show that Ni contamination is detrimental for GOI only after multiple oxidations. Atomic Force Measurement (AFM) showed that precipitates (presumably NiSi2) form at the interface during the first oxidation. These precipitates are oxidized during the next oxidation and lead to oxide surface roughness and local Fowler Nordheim (FN) current enhancements. RTP results in a higher density of these defects as compared to furnace oxidation. Cu is fast-diffusing into the substrate and leads to defects only during the n+-poly process. Therefore, no influence of the oxide process variations on the Cu defect formation was found. In addition, no difference for furnace or RTP processes was observed. Cu precipitates that form at the poly/oxide interface lead to very pronounced FN current enhancements. As Al is built in the oxide structure, no electrode roughness occurs that leads to FN current enhancement. RTP grown oxides are less affected by Al contamination. Al can be removed by stripping the oxide, whereas Ni and Cu cannot.