Search for Vacancies in Laser Annealed Silicon

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H. J. STEIN AND P. S. PEERCY Sandia National Laboratories,

P. O. Box 5800,

Albuquerque,

New Mexico

ABSTRACT In an effort to enhance vacancy trapping and detection in laser-annealed Si, float zone Si was implanted with oxygen to achieve concentrations between one and two orders of magnitude greater than the equilibrium saturation limit. Oxygen, which is known to be an effective trap for vacancies, was found to incorporate efficiently into Si regrown with Q-switched laser annealing Interstitial oxygen, oxygen-vacancy defects and divacancies were observed after implantation. The laser-regrown layers, however, were free of detectable vacancy-associated defects. INTRODUCTION Previous studies have shown that laser annealing can produce Si layers which are free from extended defects detectable by TEM [1]. Small defects, however, such as vacancies, vacancy impurity complexes, isolated interstitials and divacancies, could remain in the layers and would not be resolved in the TEM measurements. Electrically active states associated with small defects have been reported by Kimerling and Benton [21 for laser-annealed layers which exhibited perfect microstructures. They found an energy level for one electrically detectable defect to be different in oxygen-containing from that in oxygen-free Si. In addition, a recent x-ray diffractometry study by Servidori, et al., [3] showed residual disorder not detectable by TEM in ion implanted and laser annealed Si. The disorder was ascribed to carbon and oxygen impurities associated with vacancy-type defects. Infrared absorption has been used extensively for measurements of interstitial oxygen, oi, and of irradiation-produced oxygen-vacancy, O-V, and divacancy, V-V, defects in Si [4]. Infrared absorption, however, would not be sufficiently sensitive to observe O-V defects in thin layers with oxygen at the saturation concentration [5] of molten Si. On the other hand, if trapping of implanted oxygen at the resolidification interface occurs for 0 in Si, then vacancy trapping by > 5 percent of the implanted oxygen should be observable by infrared absorption methods. Oxygen also enhances vacancy trapping by other vacancies to form V-V defects [6]. We have used infrared absorption to search for vacancy trapping in oxygen implanted and laser-annealed Si, and to obtain information on 0 retention above the equilibrium saturation concentration in laser-melted Si.

*This work performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract number DE-AC04-76DP00789.

Mat.

Res.

Soc.

Symp. Proc.

Vol.

13 (1983) OElsevier Science Publishing Co.,

Inc.

230 EXPERIMENTAL DETAILS Silicon samples 6 x 6 x -0.6 mm were prepared from (111) and (100) float zone Si. A syton polish followed by a chemical etch polish was found to yield surfaces that were best suited for the experiments. The crystalline defects after implantation were more clearly resolved when the surfaces were etched, particularly for the lower energy implants, and the etch gave a slightly uneven surface