THE EFFECTS OF PREHEATINGS ON AXIAL OXYGEN PRECIPITATION UNIFORMITY IN CZOCHRALSKI SILICON-CRYSTALS

The puller thermal history effect on axial oxygen precipitation depends on the subsequent heat treatment. Two approaches can improve the axial oxygen precipitation uniformity after a two-step heat treatment (800-degrees-C/2 h + 1050-degrees-C/16 h). A high temperature rapid thermal process (RTP) preheating, 1200-degrees-C for 2 min in argon ambient can influence the thermal history effect by reducing the oxygen precipitation at the seed-end of the crystal in comparison to the tang-end. Low temperature preheat treatments, such as thermal donor annihilation heat treatment and polysilicon CVD processes, can increase the oxygen precipitation of the tang-end wafers much more than that of the seed-end and, therefore, also increase the uniformity of the precipitation.