A New Ion Beam Deposition Technique for Low Temperature Silicon Epitaxy
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S. Mohajerzadeh*, C.R. Selvakumar*, D.E. Brodie", M.D. Robertson" and J.M. Corbett" *Department of Electrical and Computer Engineering, **Department of Physics, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1
Abstract We report the results of an investigation to grow thin Si films on Si substrates at low substrate temperatures using ionized SiH 4 gas generated with a Kaufman type ion gun. This investigation shows island-growth at higher substrate temperatures (500-700'C) in the form of square-based pyramids. By lowering the substrate temperature to 300*C, we were able to achieve a planar growth. The growth rate can be enhanced by introducing elemental Si from a thermal evaporation source. Scanning electron microscopy, transmission electron microscopy and electron diffraction analysis were used to study the crystalline quality of the samples prepared at different temperatures.
Introduction Ion beam deposition techniques are of great interest to many researchers in view of their potential capabilities for the growth of thin film semiconductors[1-3]. The kinetic energy of the ions can enhance the likelihood of epitaxial growth at lower substrate temperatures. Most of the reports based on the use of energetic ions to grow Si thin films have concentrated on sputtering techniques[2]. The use of a Si+ beam for direct deposition onto a Si substrate is another alternative for Si homoepitaxy at low substrate temperatures[3]. The plasma enhanced chemical vapor deposition, although mostly a chemical reaction technique, uses energetic reactive ions to enhance the growth rate of the films. In this paper, we report the preliminary results of the use of a new ion beam deposition technique to grow thin Si films on Si substrates. Silicon films were grown at different substrate temperatures and their atomic structures studied using electron microscopy.
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Mat. Res. Soc. Symp. Proc. Vol. 388 01995 Materials Research Society
Experimental Set-up The equipment used for this study is illustrated in Figure 1. A cylindrical vacuum chamber pumped by a diffusion pump and backed by a rotary mechanical pump was used. A base pressure of l X10-7 Torr (1.3 x 10'
Pa) is typically attained. A commer-
cially available IonTek Kaufiman type ion source was used to ionize the gas and to direct the ion beam towards the substrate. During the film growth the substrate is grounded to reduce any chance of charge pilage on the substrate surface. The ion gun bombards the surface
Substrate
of the substrate at an angle of 20' with respect to the normal of its surface. The ion beam energy and current can be adjusted between 30-1000 eV and 0-30 mA,
Ar
Ion
respectively. Ultra high purity argon and silane (Sill4 ) gasses are used as sources for the ion beam. For the gun to operate, a chamber pressure of about 1 x10
4
Torr (1.3 x 102 Pa) is
Figure
1: Schematic diagram of
the deposition chamber.
required. For this study, 1
- cm n-type Si substrates were used. Each Si substrate
was cleaned for 15 mins. in a standard RCA solution. Before
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