Hi all, I am using SF6+He to etch silicon. I thought He will be helpful to get a smother surface. I fixed all the other parameters like pressure, power, etching time... and only change the flow rate of SF6 and He. The strange thing is that the etching speed of SF6:He=10:20 was larger than that of SF6:He=20:20. (They were etched in same machine and at same day, one after the other) And also I found that if I fix the gas flow of SF6 and only change the persentage of He, the etching rate will increase with increasing the persentage of He. All these seem to indicate that He can not only cool the photoresist, but also will help the etching. Does anyone else has similar experience. And I am not sure what kind effect of He to side wall, will it make the process more isotropic or more anisotropic? Thanks a lot! Peng Yao DOEs lab Electrical Engineering Dept. Univeristy of delaware Newark D.E 19716