BORON INCORPORATION IN EPITAXIAL SILICON USING SI2H6 AND B2H6 IN AN ULTRAHIGH-VACUUM RAPID THERMAL CHEMICAL-VAPOR-DEPOSITION REACTOR

Boron incorporation in Si during Si epitaxy was studied in an ultrahig h-vacuum rapid thermal chemical vapor deposition (UHV-RTCVD) reactor. The films were deposited using Si2H6 and B2H6 diluted in H-2 as the re active gases over a doping range from 1 X 10(16) to 1 X 10(19) cm(-3). The experiments were carried out in a temperature range of 650-800 de grees C and a total pressure of 80 mTorr. The experimental results rev ealed a minimal effect of B2H6 on the Si growth rate. Boron concentrat ion in Si was found to be proportional to the B2H6 flow rate and indep endent of the deposition temperature. This was found to be true even t hough the growth rate changed by a factor of five in the temperature r ange investigated. This is suggestive of a thermodynamic equilibrium b etween B in the gas phase and B on the growing Si surface. The results are consistent with the claim that B2H6 dissociates as BH3 in the gas phase which chemisorbs on the growing Si surface. In this paper, we d emonstrate that by UHV-RTCVD, retrograde doping profiles with sharp do ping transitions and doped multilayers with a precise control over fil m thickness can be obtained. This is attributed to the cold-walled nat ure of the growth environment which eliminates the chamber memory effe ct typically observed in hot-wall reactors.