EFFECTS OF ETCH PRODUCTS AND SURFACE OXIDATION ON PROFILE EVOLUTION DURING ELECTRON-CYCLOTRON-RESONANCE PLASMA-ETCHING OF POLY-SI

Evolution of etched profiles has been numerically investigated during electron cyclotron resonance (ECR) Cl-2/O-2 plasma etching of polycrys talline Si. The calculations included the processes of chemically enha nced ion etching and passivation layer formation, which are important in such low-pressure, high-density plasma etching environments. The si dewall passivation was modeled by taking account of the redeposition o f etch products on sidewalls of etched features. In addition, the effe ct of surface oxidation was also included in the model. Etched profile s were then simulated to examine effects of the neutral-to-ion flux ra tio onto the substrate, sticking coefficient of etch products, and add itional incident fluxes of etch products and oxygen atoms. Numerical r esults indicated that in typical ECR plasma etching environments, wher e the gas pressure is P-0 less than or equal to 1 mTorr and the ion cu rrent density is J(i) similar to 10 mA/cm(2) onto the substrate, the c hlorinated surface coverage a is microscopically nonuniform on sidewal ls and bottom surfaces of etched features: alpha less than or equal to 0.3 at the bottom and alpha approximate to 1 on the sidewalls. This m icroscopic nonuniformity in coverage was found to lead to inversely ta pered etched profiles without any sidewall passivation. These profiles changed to vertical and further tapered, when simultaneous redepositi on of etch products were taken into account with their sticking coeffi cients S-p greater than or equal to 0.1. Furthermore, it was shown tha t in the presence of oxidation, the sidewall surfaces are easily oxidi zed, and the lateral etching is effectively reduced during overetch. ( C) 1996 American Vacuum Society.