ULTRA-SHALLOW P(-JUNCTION FORMATION IN SILICON BY EXCIMER-LASER DOPING - A HEAT AND MASS-TRANSFER PERSPECTIVE())

Heat and mass transfer at the nanosecond time scale and the nanometer length scale in pulsed laser fabrication of ultra-shallow p(+)-junctio ns is studied in this work. A new technique is developed to fabricate the ultra-shallow p(+)-junctions with pulsed laser doping of crystalli ne silicon with a solid spin-on-glass (SOG) dopant, through the nanose cond pulsed laser heating, melting, and boron mass diffusion in the 10 0 nm thin silicon layer close to the surface. High boron concentration of 10(20) atoms cc(-1) and the 'box-like' junction profile are achiev ed. The key mechanism determining the 'box-like' junction shape is fou nd to be the melt-solid interface limited diffusion. The ultra-shallow p(+)-junctions with the depth from 30 to 400 nn are successfully made by the excimer laser. The optimal laser fluence condition for SOG dop ing is found about 0.6-0.8 J cm(-2) by studying the ultra-Shallow p(+) -junction boron profiles measured by the secondary ion mass spectrosco py (SIMS) vs the laser fluence and the pulse number. The one-dimension al numerical analysis agrees reasonably with the experiment, within th e available physical picture. Possible mechanisms such as boron diffus ivity dependence on the dopant concentration in the molten silicon are proposed. Copyright (C) 1996 Elsevier Science Ltd.