Radical etching with an aperture plate: correlating F atom density and highly selective etching of poly-Si and Si 3 N 4 over SiO 2 in CF 4 /O 2 /He plasma

Abstract To achieve high-precision and low-damage etching processes in semiconductor manufacturing, this study employs a capacitively coupled plasma etching system incorporating a grounded aluminium aperture plate to realize efficient radical-dominant etching process. Etch rates of poly-silicon (poly-Si), silicon nitride (Si 3 N 4 ), and SiO 2 were evaluated using CF 4 /O 2 /He as the discharge gas. A systematic investigation was conducted on the effects of radio-frequency power, working pressure, and gas flow rates on the etch selectivity and surface roughness, comparing radical etching with reactive ion etching (RIE). Optical emission actinometry was employed to in-situ quantify the relative density of fluorine (F) atoms, and to elucidate their correlation with etch selectivity. Results demonstrate that the aperture-plate configuration achieved an ion-filtration efficiency of up to 99.9999%, effectively suppressing ion-induced surface damage. Under the optimized radical-etching conditions (200 W discharge power, 40 Pa gas pressure, and 150/30/20 ml min −1 CF 4 /O 2 /He flow rates), the relative density of F reached 3.11 × 10 13 molecule cm −3 , enabling high etch selectivity of 66 for poly-Si/SiO 2 and 26 for Si 3 N 4 /SiO 2 . Moreover, the surface roughness of the samples for radical etching was significantly superior to that obtained in RIE mode. These results confirm that tailoring plasma composition through an aperture-plate configuration is an effective strategy for achieving highly selective and low-damage etching, providing significant potential for the advancing etching process.