Relationship of etch reaction and reactive species flux in C4F8/Ar/O-2 plasma for SiO2 selective etching over Si and Si3N4

The relationship between reactive species flux and their modified surfaces was studied in a SiO2 highly selective etching over Si and Si3N4. Sample sp ecimens with large patterns and phi 0.35 mum contact holes were etched usin g C4F8/Ar/O-2 plasma in a dual-frequency (27/0.8 MHz) parallel-plate etchin g system. The amount of CFx reactive species was controlled by adjusting th e C4F8 flow rate ratio while keeping the ion flux (3 X 10(16) cm(-2) s(-1)) and the V-pp of bias radio frequency (1450 V) constant. The highly selecti ve etch process is attained in a certain condition of the radical flux. Qua ntitative analysis using x-ray photoelectron spectroscopy revealed that the etch rate strongly depended on the fluorocarbon (CF) film thickness formed during the etch reaction on SiO2 Si3N4, and Si. In the large-area-etching of Si and Si3N4, the CF film (< 2 nm) formed under conditions with low sele ctivity for SiO2 was thinner than the film (5-6 nm) formed in high-selectiv ity etch conditions. The CF film thickness on SiO2 were less than 1 mn unde r the high-selectivity etch conditions. The thinner CF film thickness on Si O2 is due to the additional oxygen which is an etch product from SiO2, and which can remove CF species from the SiO2 surface. Highly selective etching can be achieved under the proper CFx radical flux condition, in which the CF film is thin on SiO2, and the films on Si and Si3N4 are thicker than the ion projection range. Furthermore, we observed the same trend for etching at the bottoms of the phi 0.35 mum contact holes as with large area etching with result to the CF film thickness change. However, with a small increas e in CF radical flux, the CF film thickness on SiO2 increased abruptly and caused a narrow process window for highly selective etching. (C) 2001 Ameri can Vacuum Society.