Vk. Singh et al., STUDY OF SILICON ETCHING IN CF4 O-2 PLASMAS TO ESTABLISH SURFACE REEMISSION AS THE DOMINANT TRANSPORT MECHANISM, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 12(5), 1994, pp. 2952-2962
This article describes an investigation of the etching of polysilicon
in a CF4/O-2 plasma. The ''undercut'' observed in etch profiles is rel
ated to the surface transport of reaction precursors. The possible mec
hanisms for this transport include surface re-emission and surface dif
fusion of the precursors. Simulations of profile evolution, conducted
with both mechanisms, are compared with experimental results. The surf
ace reemission simulations are found to predict experimental profile e
volution accurately, whereas surface diffusion simulations require unp
hysical values for the surface diffusion length. Novel test structures
have been fabricated and etched under the same conditions as used for
trench etching. Surface re-emission simulations accurately predict th
e etch rate deep inside the shadowed cavity of different structures. O
n the other hand, simulations assuming surface diffusion to be dominan
t do not capture even the qualitative trends in test structure etching
. This is strong evidence that surface re-emission is the dominant mec
hanism for transport of etch precursors in CF4/O-2 plasmas.