True influence of wafer-backside copper contamination during the back-end process on device characteristics

Abstract

The influence of backside Cu contamination during the back-end process on the electrical characteristics of MOSFETs was revealed. The influence is well explained in terms of Cu diffusion behavior at 400/spl deg/C, which strongly depends on SiO/sub 2/ thickness at front and back sides of wafers. Cu atoms brought into the Si wafer can not diffuse into the thick front-side SiO/sub 2/ film, but Cu atoms exist inside Si near the SiO/sub 2//Si interface after annealing. Accordingly, backside Cu contamination during the back-end process does not affect Time Zero Dielectric Breakdown (TZDB), Dit, or Vfb, but it decreases Time Dependent Dielectric Breakdown (TDDB) lifetime and drastically enhances short-channel effect due to impurity compensation.