Vacuum Chemical Epitaxy: High Throughput GaAs Epitaxy Without Arsine
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VACUUM CHEMICAL EPITAXY: HIGH THROUGHPUT GaAs EPITAXY WITHOUT ARSINE L. M. Fraas*, G. R. Girard*, and V. S. Sundaram*, Boeing High Technology Center*, P.O. Box 24969, Seattle, WA. 98124-6269, and Chris Master** and Rick Stall** Emcore, Inc.**, 35 Elizabeth Avenue, Somerset, NJ 08873 Introduction: Metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) are well established methods for growing epitaxial GaAs and AlGaAs films. However, MOCVD equipment uses the highly toxic gas, arsine, and MBE equipment is very costly and coats only one wafer at a time. We have developed a vacuum chemical epitaxy (VCE) reactor which avoids the use of arsine and allows multiple wafers to be coated in a production environment. Our vacuum chemical epitaxy reactor closely resembles a molecular beam epitaxy system in that wafers are loaded into a stainless steel vacuum chamber though a load chamber. Also as in MBE, arsenic vapors are supplied as reactant by heating solid arsenic sources thereby avoiding the use of arsine. However, in our VCE reactor, a large number of wafers (fourteen 2" or six 3") are coated at one time in a vacuum system by the substitution of group III alkyl sources for the elemental metal sources traditionally used in MBE. Higher wafer throughput results because in VCE, the metal-alkyl sources for Ga, Al, and dopants can be mixed at room temperature and distributed uniformly though a large area injector to multiple substrates as a homogeneous array of mixed element molecular beams. The VCE reactor that we have built and that we shall describe here uniformly deposits films on 7" diameter substrate platters. Each platter contains seven 2" or three 3" diameter wafers. The load chamber contains up to nine platters. The vacuum chamber is equipped with two VCE growth zones and two arsenic ovens, one per growth zone. Finally, each oven has a 1 kg arsenic capacity. The VCE Growth Zone: Figure 1 shows schematically a top view and a cross section of a VCE growth zone. In this figure, a platter is shown in the top view with seven 2" diameter wafers. The wafers are mounted face down (side view) above the metal-alkyl injector. An array of holes in the metal-alkyl injector (top view) creates an array of mixed metal-alkyl molecular beams. The positions and diameters of the metal-alkyl injector holes are varied via a computer model in order to provide a uniform metal-alkyl molecular flux at the wafer platter. The Ga, Al, and dopant adatoms at the wafer surfaces are provided through metal-alkyl molecular beams. These metal adatoms are reacted with arsenic vapor. A constant, low but finite (approximately 10E-4 torr), arsenic vapor pressure is maintained at the substrate platter by a hot wall arsenic confinement chamber (side view) with an arsenic injector ring at its perimeter (side and top views). Holes in the base of the hot wall arsenic confinement chamber are aligned with the holes in the metal-alkyl injector assembly. The arsenic vapor pressure is in fact high enough to react with all the metal adatoms but
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