Incidence Angle Dependence of the Silicon Near-Surface Contamination Caused by CF 4 Reactive Ion Beam Etching
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INCIDENCE ANGLE DEPENDENCE OF THE SILICON NEAR-SURFACE CONTAMINATION CAUSED BY CF4 REACTIVE ION BEAM ETCHING C. LEJEUNE, J.P. GRANDCHAMP, J.P. GILLES and E. COLLARD. Institut dElectronique Fondamentale, Universite Paris XI et CNRS (URA 22), Bat. 220,91405 ORSAY Cedex, FRANCE.
ABSTRACT. The incidence angle dependence of silicon near-surface contamination caused by CF4 Reactive Ion Beam Etching was studied using on-line variation of SiF4 partial pressure and Auger Sputter Profiling. Initial and steady state etch rates both vanish at grazing incidence and have a smooth maximum at 20-30 deg. It is shown that whatever is the incidence angle, a CF-blocking overlayer grows involving an etch rate attenuation by a factor which is only slightly dependent on the incidence angle. As the angle increases, with a 500 eV beam, the thickness of the C,F contamination layer decreases monotonically from 1.9 nm down to a constant value of about lnm achieved beyond a critical angle of 45 deg. Then a "CF-reactive mixed layer" is seen over the silicon the etching of which is dominated by surface mechanisms. Conversely with the lower angles, the thickness of the "carbonaceous incorporated layer" becomes larger than that of the mixed layer, and volume mechanisms dominate the silicon removal. 1. INTRODUCTION.
Selective etching of SiO2 over Si is a basic problem in semiconductor technology. Anisotropy and selectivity are both achieved in a plasma environment using either CF4/H2 gas mixtures or CHF3 from either reactive ion etching (RIE) [11 or magnetron ion etching (MIE) [2]. Unfortunately hydrogen atoms and ions have been shown to be responsible for silicon deep damage and contamination [3]. Alternative processes must be investigated. Reactive ion beam etching (RIBE) with halocarbon gases may provide a solution [4]. In all these processes a carbonaceous blocking overlayer has been shown to grow selectively on silicon. It entails the Si etch rate slow down and insures the selectivity. However the mechanisms which govern both the growth and steady state of the overlayer and the removal of the underneath silicon are not yet precisely understood. The aims of this work were to provide further insight into those mechanisms for both further improvement of selective etching processes and future process simulation, whether they are in a plasma or a beam environment .The analysis of the influence of the incidence angle on ion-assisted surface chemistry may be very informative, but it can only be studied from beam experiments. SiO 2 and Si etch yields as a function of angle of incidence in fluorocarbon ion beams at various energy have already been reported [5,6,7]. However their dependence has not been correlated to the associated variation of the thickness and/or structure of the CF contamination overlayer. We report results on the ion incidence angle dependence on both etch yield and nearsurface contamination of Si samples exposed to a 500 eV beam extracted from a CF4 DC excited plasma source. The fundamental role of ion beam composition and energy
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