Effect of Pulse Duration on the Annealing of Ion Implanted Silicon with a XeCl Excimer Laser and Solar Cells
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EFFECT OF PULSE DURATION ON THE ANNEALING OF ION IMPLANTED SILICON WITH A XeCl EXCIMER LASER AND SOLAR CELLS*
R. T. YOUNG Helionetics, Inc., San Diego, CA 92123, and Oak Ridge National Laboratory, Oak Ridge, TN 37830 J. NARAYAN AND W. H. CHRISTIE+ Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 G. A. van der LEEDEN, D. E. ROTHE, AND R. L. SANDSTROM Helionetics, Inc., San Diego, CA 92123
ABSTRACT The advantages of pulsed excimer lasers for semiconductor processing are reviewed. Studies of XeCl excimer laser annealing with pulses of 25 and 70 nsec duration and energy 2 densities in the range from 0.5-3.0 J/cm are discussed. The annealing characteristics are described in terms of the results of melt depth, dopant profile spreading, and electrical properties (sheet resistivity, diode characteristics) measurements. Solar cells with efficiencies as high as 16.7% AMI have been fabricated using glow discharge implantation and XeCl laser annealing.
INTRODUCTION The advantages of using pulsed excimer lasers for semiconductor processing have been demonstrated recently. [1-3] It has been shown that, regardless of the large differences in the optical properties of Si at the wavelengths of UV excimer lasers (e.g., 308 nm for XeCl lasers) and ruby (694 nm) or frequency doubled Nd:YAG (530 nm) lasers, [4] the quality of annealing, assessed in terms of damage removal in the implanted layer, dopant profile behavior, and junction properties, is very similar. However, because of the good optical quality of the beam and perhaps because of the trapezoidal (rather than Gaussian) temporal shape of the excimer laser pulses, excellent annealing can be obtained without the use of beam homogenizers and substrate heating [3]. This provides important simplifications for application of laser annealing to semiconductor processing. Furthermore, other features of excimer lasers, such as good energy conversion efficiency, excellent pulse-to-pulse reproducibility, square or rectangular shapes of the laser beam, and high average power [5] may make laser techniques commercially viable for large volume material processing. Advances in excimer laser technology indicate that, in addition to the capability for scaling up both the energy per pulse and the pulse repetition rate, the pulse duration time Tk can be easily adjusted over a range from 10 to several hundred nsec. Variation of TZ over this range with solid state lasers is very difficult, if not impossible. Melting model calculations [61 show that, * Research sponsored
jointly by the Solar Energy Research Institute under
contract BS-0-9078-1 and by Helionetics, Inc. Operated by Union Carbide Corporation under contract W-7405-eng-26 with the U.S. Department of Energy. +Analytical Chemistry Division *Present address: Guest scientist, Solid State Division, Oak Ridge National Laboratory, Mat. Res.
Oak Ridge,
Soc. Syrup. Proc.
Vol.
TN 37830 13 (1983)
Published by Elsevier Science Publishing Co.,
Inc.
402 for the same energy density EZ, the depth of melting increases w
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