Low-damage etching of poly-Si and SiO₂ via a low-energy electron beam in inductively coupled CF₄ plasma

Abstract

Electron-assisted etching of poly-Si and SiO2 is performed via a grid system in inductively coupled CF4 plasma. The feasibility of electron-assisted etching is discussed with a focus on the low-surface damage of the etching. The etch rate increases with electron beam energy, which indicates that the electrons assist the surface etching process. To verify this, etching of poly-Si and SiO2 is performed in several plasma conditions, which leads to differences in etch rate that depend on the presence or absence of radicals and electron beams. Poly-Si and SiO2 are not etched without radicals of CF4 plasma, but they are etched when such radicals are present. When the electron beam and radicals exist simultaneously, the etch rate increases more dramatically than in the case of a CF4 plasma without an electron beam, demonstrating that the electron beam assists the etching process. Optical emission spectroscopy is employed to verify the F radical does not affect the etch rate increase. The surface roughness is measured after electron-assisted etching and compared with the surface roughness after ion-assisted etching.