AVS 49th International Symposium
    Plasma Science Wednesday Sessions
       Session PS+MM-WeA

Paper PS+MM-WeA9
Mechanisms Involved in the Silicon Cryogenic Etching Process

Wednesday, November 6, 2002, 4:40 pm, Room C-105

Session: Feature Profile Evolution /Plasma Processing for MEMS
Presenter: M. Boufnichel, GREMI / ST Microelectronics, France
Authors: M. Boufnichel, GREMI / ST Microelectronics, France
P. Lefaucheux, GREMI, France
R. Dussart, GREMI, France
P. Ranson, GREMI-Universite d'Orleans-CNRS, France
Correspondent: Click to Email
In this study, we investigated the etching and passivation mechanisms involved in the deep cryogenic etching of silicon trenches. More precisely, we studied the dependence of sticking coefficient of oxygen and fluorine as regards to wafer temperature. We showed that fluorine radicals sticking coefficient does not strongly depend on wafer temperature at the contrary to oxygen radicals. XPS measurements allowed us to obtain further informations concerning the nature and behaviour of the passivation layer deposited on trench sides during the cryogenic silicon etching with a SF6/O2 mixture. XPS measurements pointed at the fact that the passivation layer formed during the cryogenic etching of silicon is not mainly composed of SiO2 species. Furthermore, a new method has been employed to determine the effective angular dispersion of ions (EIAD) involved in the etching of silicon and its impact on trench etching evolution. A comparison of the performances of RF and LF bias generators has also been performed so as to highlight the impact of bias-frequency on profile characteristics. A complete study of the etching mechanisms would not have been possible without parallel measurements of physical plasma parameters using Langmuir probe and actinometry with Optical Emission Spectroscopy (OES). The parallel between the etching experiments and diagnostics measurements shows for example that local bowing seems to depend on ion local surface bombardment and passivating mechanisms. Finally, we are able to etch deep anisotropic trenches (100 microns deep and 2 microns in aperture) at a high etch rate, high selectivity (SiO2 mask) and high anisotropy. We performed to reduce or eliminate defects such as local bowing, undercut and notching for different application: etching of HARTs (High Aspect Ratio Trenches), LARTs (Low Aspect Ratio Trenches), vias, SOI (Silicon On Insulator) layers.