Etch‐Induced Physical Damage and Contamination during Highly Selective Oxide Etching Using  C 4 F 8 /  H 2 Helicon Wave Plasmas

Abstract

Physical damage and residue remaining on the silicon wafer during the oxide overetching using helicon wave plasmas, and the effects of various cleaning and annealing methods on the removal of the remaining damage and residue, were investigated. The remaining residue was composed of carbon, fluorine, and oxygen, and the addition of 30% H 2 to the C 4 F 8 plasma changed the C/F ratio, the carbon bonding states, and the thickness of the residue on the etched silicon surface. Hydrogen was also present in the residue. The fluorine component in the residue was easily removed by O 2 plasma cleaning, while the carbon component still remained, regardless of gas chemistry. Most of the residues on the etched surfaces could be removed by oxygen-plasma cleaning followed by thermal annealing over 450ЊC. Physical defects were observed on the silicon wafers overetched by both C 4 F 8 plasma and 70% C 4 F 8 /30% H 2 plasma. Compared to the silicon wafer overetched by C 4 F 8 plasma, the observed defects were located deeper after the overetching by 70% C 4 F 8 /30% H 2 plasma. Annealing at 1000ЊC for 30 min was required to completely remove these defects for C 4 F 8 plasma overetched silicon, and higher temperatures were required for 70% C 4 F 8 /30% H 2 plasma overetched silicon. The residue appears to reduce the formation of Co silicides more compared to the physical defects remaining on the silicon surface.