SiO 2 Etching Mechanisms Under Low-Temperature PF 5 /C 4 F 6 Plasma Conditions

In this study, the etching characteristics of SiO 2 films are investigated using an inductively coupled plasma system with a gas composed of PF 5 and C 4 F 6 . The substrate temperature is maintained low, at −30 °C, during the process. To elucidate the etching mechanism, the fundamental plasma characteristics of the PF 5 /C 4 F 6 mixture are analyzed using optical emission spectroscopy, and complementary measurements are performed with a quadrupole mass spectrometer. The analysis reveals that PF 5 not only supplies fluorine radicals but also generates high-mass PF x ions, which deliver a significant amount of physical energy to the substrate. In contrast, C 4 F 6 provides reactive species such as fluorine and CF 3 , which contribute to chemical etching; however, excessive C 4 F 6 injection, above 15 sccm, leads to the formation of CF x polymer layers on the surface, thereby limiting the etch rate. Under optimized passivation conditions, increasing the bias power enhances the physical bombardment effect, resulting in a higher etch rate without significantly promoting sidewall etching. Consequently, high-aspect-ratio profiles are achieved. At PF 5 = 15 sccm and C 4 F 6 = 10 sccm, bias power = 150 W, and pattern spacing = 60 nm, the post-etch spacing is maintained below 65 nm and a maximum aspect ratio of 22 is obtained.