Ion/Neutral Beam Assisted Etching of Semiconductors
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ION/NEUTRAL BEAM ASSISTED ETCHING OF SEMICONDUCTORS: Chemical Modifications of the Adsorbed Phase Glenn. C. Tyrrell, Duncan Marshall and Richard B. Jackman Electronic and Electrical Engineering, University College London, Torrington Place, London, WCIE 7JE, UK
ABSTRACT This paper addresses the fundamental aspects of etching semiconductors with inert gas beams in the presence of a suitable precursor gas. In particular, the changes that an energetic bombarding ion/neutral species cause to the surface and sub-surface region of a solid are considered, both in terms of the introduction of damage to the semiconductor and chemical processes that are provoked in the adsorbed states present.
The implications for practical
etching reactions are then discussed. 1. Introduction
The collision of low energy (250 eV), then bond breaking can occur creating a free host species. Subsequent collisions into the surface can be described by a 'collisional cascade' approach [6141. It is believed that the subsequent backscattering of cascade species can give rise to 13 secondary cascades and to sputtering. This process is rapid (10- s), but is followed by a thermalised relaxation process or 'thermal spike' [15,161 which drives interstitials, vacancies and any free carriers created by cascade processes further into the semiconductor, thus enhancing damage mechanisms. In a CAIBE experiment, the impact of an inert gas ion with an adsorbate covered surface can give rise to a number of other energy exchange processes. These include electronic / vibrational excitation of the outer atoms and collisional cascades in, and sputtering of, the near surface species 161. To utilise these effects for low damage semiconductor etching first requires a precise knowledge of the adsorbed phases formed between the precursor gas used and the semiconductor concerned and the changes provoked in, and beneath, this phase by the
Mat. Res. Soc. Symp. Proc. Vol. 223. @1991Materials Research Society
Downloaded from https://www.cambridge.org/core. Macquarie University, on 30 May 2020 at 04:28:22, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-223-61
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impinging beam. The use of surface sensitive spectroscopies to study this region is thus essential. This paper considers the way in which particle bombardment affects surfaces at a macroscopic level. The presence of an adsorbed phase during bombardment is the addressed and the implications for a CAIBE process considered. 2. The introduction of a chemically active component; adsorption processes To achieve etching with a chemical origin, a chemically active component is required in addition to the inert gas beam. In a CAIBE experiment, this species is introduced with a thermal distribution of energies towards the surface which is undergoing concurrent, higher energy, bombardment from the inert beam. For simplicity, we will consider the reaction of halogens with silicon [17,18]. The reactions of halogens on InP and GaAs have also been stu
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