Multiple-Scan E-Beam Method Applied to a Range of Semiconducting Materials
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and Materials Processing
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MULTIPLE-SCAN E-BEAM METHOD APPLIED TO A RANGE OF SEMICONDUCTING MATERIALS N.J. SHAH, R.A. McMAHON, J.G.S. WILLIAMS AND H. AHMED Engineering Department, Cambridge University, Trumpington Street, Cambridge CB2 IPZ, England
ABSTRACT This paper describes the conditions for activating ion implants in a range of semiconductor materials in the solid state. This includes phosphorus and arsenic implants into silicon, boron and phosphorus implants into SOS, gallium into germanium and silicon into gallium arsenide. For each material the restoration of electrical activity correlates with structural data from RBS analysis. Negligible implant diffusion occurs for the typical annealing treatments which result in full activation of dopants.
INTRODUCTION There are many advantages in replacing prolonged high temperature furnace annealing for the activation of implanted ions in semiconductors. In silicon, the electrical activation of implants without diffusion derives the full benefit of the precise ion distribution available through implantation, and is essential for the further reduction of device dimensions. Rapid annealing of compound semiconductors, particularly gallium arsenide, allows doping by implantation without the problems of decomposition associated with furnace annealing. This paper describes the principle of the multiple-scan electron beam annealing method and its application to the solid state processing of a number of semiconducting materials. Electron beam parameters are presented for the activation of boron, phosphorus and arsenic implants in silicon and in silicon on sapphire, gallium in germanium and silicon in gallium arsenide. The results of annealing by the multiple scan technique are shown, and are related to the anneal conditions. Alternatives to furnace heating exist in either the liquid state or the solid state [Ti. Examples of the former are pulsed electron beam and pulsed laser beam annealing. Annealing in the multiple-scan method occurs in the solid state. Alternatively solid-state annealing can also be carried out with C-W scanned lasers, C-W scanned electron beams, microwave heating and resistive strip heating. THE MULTIPLE-SCAN METHOD In the multiple-scan electron beam annealing method [F1, a focussed electron beam is moved rapidly in randomly overlapped raster scans over the specimen. The scanning is sufficiently fast (minimum scan speeds of 1 kHz and 4 Hz; typically 50 kHz and 400 Hz) to make the scanned beam equivalent to a uniform power flux incident on the specimen surface. The power density, defined as the incident power per unit area, equals the beam power (beam current times beam voltage) divided by the total scanned area. This applies for a wide range of scanning speeds, beam diameters and combinations of beam voltage and current. The scanned area is generally made greater than the area of the specimen being irradiated, in order to ensure uniform heating of the specimen. The specimen
202 is mounted in thermal isolation during annealing, so that the heat is
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