RAPID THERMAL-DIFFUSION OF ALUMINUM IN SILICON AND ITS INTERACTION WITH PHOSPHORUS

Aluminum diffusion profiles in silicon were produced under rapid therm al processing conditions using a Si-sandwich structure to avoid losses of aluminum by reaction with the quartz reactor. The impact of phosph orus on the diffusion behaviour of aluminum was investigated by predep osition of P into Al-diffused wafers and vice versa. Dopant profiles w ere determined by SIMS (Secondary-Ion-Mass Spectroscopy), electrochemi cal CV- and SRP (Spreading Resistance) analysis. The resulting profile s after Al predeposition at 1293 K exhibit high Al-surface concentrati ons up to the solid solubility limit of about 2 x 10(25) m(-3). It is shown that phosphorus has a great influence on the drive-in behaviour of Al, leading to an accelerated Al diffusion in front of the P profil e (enhanced Al diffusion caused by self-interstitial supersaturation) and an ''up-hill migration'' of Al in the high-concentration regime, w hich can be explained by field-assisted diffusion. A strong retardatio n of aluminum diffusion combined with concentrations well above the so lid-solubility limit was observed during the Al predeposition into P-d iffused wafers.