POCl3 and Boron Gettering of LSI Silicon Devices: Similarities and Differences

Abstract

The effectiveness of and boron gettering in reducing emitter‐collector shorts (pipes) in LSI devices was studied. In our work, we used a lower diffusion temperature (800°C) than used in previous work (900°– 1150°C). To compensate for the lower temperature, the phosphosilicate glass was retained during the heat‐treatments following the diffusion. A factor of two reduction in pipe density was achieved with gettering. Boron gettering was less effective. These results have been interpreted to show that the reduction in pipe density is dependent on the solubility of leakage‐causing metallic impurities (copper) in the gettering layer. Copper solubility depends not only on the dopant surface concentration but also on the entire dopant profile in the gettering layer. Heavily dislocated samples, that are difficult to cure with gettering, can be gettered to some extent using phosphorus gettering. Dislocation loops, punched out by oxide precipitates that are generated in Czochralski wafers during extensive annealing also getter metallic impurities (intrinsic gettering, with a precipitate‐free surface layer and peak concentration of precipitation induced defects at 250 μm below the surface). This contribution to gettering is especially important at low concentrations of the extrinsic gettering specie.