Multiple Layer Sputter Deposition and Laser Annealing of Silicon Films
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MULTIPLE LAYER SPUTTER DEPOSITION AND LASER ANNEALING OF SILICON FILMS.
W. W. ANDERSON, H. F. MAC MILLAN, J. Lockheed Missiles and Space Company,
S. KATZEFF AND M. LOPEZ Inc., Sunnyvale, CA 94086
ABSTRACT The formation of single crystal multiple layers on silicon substrates with thicknesses in excess of I pm has been demonstrated to be a viable process. Film build-up is via repetitions of the steps (1) pre-deposition chemical cleaning of wafer, (2) magnetron sputter deposition of 0.3 pm thick amorphous Si, (3) interfacial mixing via 190 keV implantation of Si, and (4) film epitaxial crystallization via pulsed laser annealing. Doping has been demonstrated by both (1) P ion implantation and (2) P incorporation from PH3 included in the sputter gas ambient.
INTRODUCTION Epitaxial crystallization by pulsed laser annealing of a-Si films deposited by evaporation [1,2] and CVD [3] is well established. In fact, multilayer film crystallization by in situ laser annealing has been demonstrated [3]. Inhibition of laser crystallization of sputter deposited films has been encountered and ascribed either to entrapped Ar [4] or H [5,6]. In this paper we discuss the formation of single crystal multiple layers on oriented silicon substrates with total thickness in excess of I pm. Film buildup was by repetitious steps of sputter depositing a-Si followed by irradiation with a Q switched Nd: Glass laser. By appropriate sample treatment, we have obtained epitaxial crystallization of sputter deposited a-Si and avoided the necessity of in situ annealing for multilayer formation.
EPI LAYER PREPARATION Substrates were oriented p-type B doped wafers 3 inches in diameter. Nominal resistivity was 8Q-cm. Organic and particulate surface contaminants were removed by a 10 minute immersion in a H2SO :Cr O3 solution 0 at 95 C followed by a 10 minute rinse in flowing deionlzeý wa~er (15 MQ). The nascent silicon oxide was removed by a two-minute immersion in 10:1 H 2O:HF followed by another 10 minute deionized water rinse. The substrates were then blown dry with dry, filtered N2 and loaded into the deposition chamber. A planar magnetron sputtering system was used for deposition of Si films. The most significant feature of magnetron sputtering is the large sputtering rate that can be achieved. Even at high power levels, plasma confinement results in reduced film heating and damage because of reduced electron and ion bombardment of the deposited film. High deposition rates reduce the undesired incorporation of ambient gas species. Undoped Si targets are sufficiently conductive that dc sputtering can be utilized. In this work, films were deposited at an Ar pressure of 3 mtorr, substrate temperature of 300%C and deposition rates of 2.5 to 3.0 nm/sec for 100 sec. Most doping was done by ion implantation of P following film deposition. However, P doping during deposition by adding PH3 to the Mat.
Res. Soc.
symp. Proc. Vol.
23 (1984) (Elsevier
Science Publishing Co.,
Inc.
242
sputter ambient was deygnstsated (PH 3 partial pressure of 9.0 x 10 sul
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