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RAPID THERMAL ANNEALING OF Si-IMPLANTED GaAs D.H. ROSENBLATT,* W.R. HITCHENS,* S. SHATAS,** A. GAT,** AND D.A. BETTS*** *Watkins-Johnson Co., Palo Alto, CA 94304; **AG Associates, Palo Alto, CA 94303; ***Charles Evans and Associates, San Mateo, CA 94402 ABSTRACT Heatpulse rapid thermal annealing was used to activate Si implants of 3.5 2x 1012 cm- 2 at 100 keV and 1.0 x 1013 and 1.0 x 1014 cm- at 200 keV into semi-insulating GaAs. The effects of Si 3 N4 encapsulation, anneal temperature and time, and substrate Cr-doping level were investigated. The annealed samples were characterized with C-V, Van der Pauw, differential Hall, and SIMS measurements. Conventional furnace anneals were carried out for comparison, and in all cases, Heatpulse anneals produced sharper carrier concentration profiles. 84% electrical activation was ob2 0 tained for the 200 keV, 1.0 x 1013 cm- implant after a 950 C, 5 sec. Heatpulse anneal. Capped Heatpulse anneals produced less Cr depletion from the implanted region than furnace anneals. INTRODUCTION Rapid thermal processing techniques have recently been investigated as alternatives to conventional furnace annealing of ion-implanted GaAs [1-31. Preliminary results obtained show that this method results in high activation efficiency with reduced dopant redistribution from the initial implanted profile, which are desirable characteristics for the fabrication of GaAs MESFET devices. EXPERIMENTAL The Heatpulse process technique for annealing ion-implanted GaAs is illustrated in Fig. 1. The GaAs sample is placed on a 100 mm Si support wafer positioned inside a rectangular quartz tube in the annealing chamber. High-intensity visible light, produced by arrays of tungsten-halogen lamps, rapidly heats the sample to temperatures as high as 11006C. The lamp intensity is controlled by a microcomputer using the thermocouple output as a feedback signal. In a typical anneal cycle, the sample is heated at 75 - 100 0 C/sec. until the desired peak temperature is reached, and held at that temperature for 5 sec. Semi-insulating GaAs (100) samples were prepared from nominally undoped LEC, 3 3 lightly Cr-doped LEC (ca. I x 1016 cm- ), and heavily Cr-doped HB (ca. 1 x 1017 cm- ) substrates. The samples were chemically etched and then implanted at room temperature with 2 8 Si+ or 2 9 Si+ in a non-channeling orientation. The dose/energy combinations used were 3.5 x 1012 cm- 2 at 100 keV and 1.0 x 1013 and 1.0 x 1014 cm-2at 200 keV. Heatpulse annealed samples were either capped with Si 3 N4 and annealed face down on the Si support wafer or annealed capless using the proximity technique (face-to-face with another GaAs wafer) in the absence of an As overpressure. The Si 3 N4 caps were plasma deposited from a SiH 4 /NH 3 /Ar mixture at 200 0 C. Typical caps were 1000A thick with an index of refraction of 1.92. Heatpulse annealing was performed in a 90% Ar/10% H2 ambient, over a temperature range of 850 - 1075 0 C, and for I - 20 second anneal times. Caps were used in most cases to reduce surface As loss during Heatpulse