Effects of Copper Contamination in Silicon on Thin Oxide Breakdown

Effects of copper contamination on the breakdown and reliability characteristics of thin silicon gate oxides are discussed. Gate oxide integrity is measured for thermal oxides of 45, 75, 120, and 200 A grown on silicon wafers intentionally contaminated with 10 10 -10 15 cm -3 of copper. Copper doping of silicon was performed according to solubility data considerations. The oxide breakdown voltages as a function of copper concentration for the various oxide thicknesses are reported. For 45 A oxide, copper concentration cannot exceed 10 13 cm -3 without severe degradation in oxide quality. The threshold contamination level for 75 A oxides is ten times higher. Premature oxide breakdown is proposed to occur due to copper silicide precipitation, which locally enhances the electrical field. It is concluded that the impact of copper contamination on oxide breakdown is not as severe as that of iron contamination on oxide breakdown. This is due to the difference in segregation properties of the two metals at the Si/SiO 2 interface.