Effect Of Rapid Thermal Annealing On Void Defects And Denuded Zone In Large-Diameter CZ-Si

The influence of rapid thermal annealing (RTA) on flow pattern defects (FPDs) in Czochralski silicon wafers was investigated in this paper. Ar, N₂, N₂/O₂(9%), N2/O₂(14%) and O₂ were used as the atmosphere of RTA, respectively. The density of FPDs depends greatly on the annealing atmosphere. The density of FPDs was the highest after annealing in N₂, and then was that in Ar. It was the lowest after annealing in O₂. In the case of N₂/O₂ mixed atmosphere, the FPDs density decreased with the increase of O₂ in the N₂/O₂ mixed atmosphere. In addition, the densities of FPDs after RTA decreased obviously on the surface and in the region of 20μm depth from the surface as well. The mechanism of the effect of annealing atmosphere on the void disappearance was discussed. The annihilation of voids was controlled by both concentration of interstitial oxygen and density of point defects.The impurities that were doped in silicon influence the density of void defects greatly. Big doping impurities increase void defects density, but small doping impurities reduce them. After RTA in Ar atmosphere at high temperature, the FPDs density decreased more in Sb-doped wafer than that in lightly B-doped wafer. In addition, the FPDs density in lightly B-doped wafer after RTA was lower in O₂ than that in Ar, but the opposite result was got in the heavily Sb-doped wafer.The relationship of FPDs and magic denuded zone (MDZ) in CZ silicon wafers was discussed after pre-RTA in different atmosphere. After pre-RTA at high temperature, the wafers were annealed at 800℃(4 hours)+ 1000℃(16 hours) to form MDZ. After annealing in Ar or N2/O₂(9%) mixed atmosphere, low FPDs density, high oxygen precipitation density and wide denuded zone occurred in wafer. In the case of N₂/O₂ mixed atmosphere, with the increase of O₂ in N₂/O₂ mixed atmosphere, the FPDs density and the oxygen precipitation density decreased. So the FPDs density and oxygen precipitation density can be controlled through adjusting the proportion of N₂ and O₂ in N₂/O₂ mixed atmosphere.