Sidewall-angle effect on the bottom etch profile in SiO2 etching using a CF4 plasma

The dependence of the bottom etch profile on the sidewall angle in the CF4 plasma etching of an SiO2 film was investigated using a Faraday cage, which allowed ions to impinge on the sidewall at specified angles. The bottom et ch profile obtained at -500 V was not affected by the sidewall when the ang le between the sidewall and the bottom surface was 45 degrees but showed mi crotrenching when the angle was greater than 60 degrees. The microtrench de pth increased until the angle reached 80 degrees, beyond which the local et ch rate was drastically reduced to allow the corner rounding of the bottom profile. As the sidewall angle increases, the etch rate of the bottom surfa ce near the corner is controlled by two opposing factors. The decreasing nu mber of incident ions on the sidewall surface and the increasing shadowing of the bottom surface from ions and neutrals by the sidewall contribute to the reduced etch rate, whereas the increasing kinetic energy and the narrow er ion-angular distribution of the ions reflected from the sidewall contrib ute to the enhancement of the etch rate. In addition to these factors, the enhanced roughness of the sidewall surface due to the fluorocarbon film dep osition plays;the critical role of suppressing the microtrench formation. M icrotrenching was not observed when the sidewall surface was covered with r ough fluorocarbon film but was observed when the surface was smooth due to the energy transferred by ions higher than the threshold energy for the flu orocarbon film sputtering. (C) 2001 American Vacuum Society.