CW Laser Annealing of Low Dose Implants in GaAs
- PDF / 1,117,644 Bytes
- 6 Pages / 414 x 635.4 pts Page_size
- 81 Downloads / 227 Views
275
CW LASER ANNEALING OF LOW DOSE IMPLANTS IN GaAs
YVES I. NISSIM AND JAMES F. GIBBONS Stanford Electronics Laboratories, Stanford, California, 94305
ABSTRACT (ý 1013 annealing low dose implants The possibility of 2 cm- ) in GaAs using a cw scanning laser has been investigated. We have observed that above the threshold of laser-induced damage, a gallium oxide (£-Ga 2 0 3 ) can be grown at laser scan speeds of 0.5 mm/sec. The heat transferred to the substrate during the growth of the oxide is utilized to anneal low dose Si implanted layers. As suggested by sheet electrical measurements, close to complete activation of the implanted species is obtained.
INTRODUCTION A considerable interest has developed during the last four years in the use of lasers and electron beams for processing of Si and GaAs. GaAs, being a much more brittle and unstable material than Si, has enjoyed only moderate success with both pulsed and cw irradiations. Annealing with a pulsed beam has resulted resulted in good activation and recrystallization for high and medium implanted doses [1], although with anomalously low mobilities. Cw laser irradiation has been reported [2) for medium dose implants. Significant activation and high mobilities have been obtained. However, in both techniques, the annealing of low doses (typically used for active channels in GaAs MESFETs) has been largely unsuccessful. One of the major difficulties associated with transient processing of GaAs is that it decomposes (due to As evaporation) at relatively low temperatures. For cw irradiation, these factors limit the amount of incident power one can use to scan a substrate. Deterioration of the surface (slip lines, thermal etching) have been observed at a maximum induced temperature of about 800 0 C using a conventional focusing lens. In this paper we describe a technique to induce higher temperatures in the GaAs by growing a surface oxide during the laser scanning. The thermal stress created by high incident laser power is released in the oxide formation. The approach described in reference [2] using an elliptical beam is employed 2 to anneal low dose (1013 cm- ) implants in GaAs. Results below the laser damage threshold are first described, leading to relatively poor annealing. As the incident power is increased, a gallium oxide (£-Ga 2 0 3 ) is formed at scanning speeds of - 0.5 mm/sec. An analysis of the laser parameters that optimize the growth of this oxide over a large area is presented. Auger spectroscopy and x-ray analysis are used to study the composition and identify the oxide. The formation of "-Ga 2 0 3 will provide enough heat to the substrate to anneal deep implanted layers. PRELIMINARY RESULTS Cr-doped GaAs substrates oriented along the direction were used in this 2 experiment. Silicon (SiH+) ions at a dose of 1013 cmand an energy of 120 keV 12 12 2 cm-2 cmat 120 keV) and S (5x10 Co-implants of Si (5x10 were implanted. at 140 keV) were also performed in an effort to encourage Si incorporation onto Ga sites. The annealing was carried out using the cw
Data Loading...
