CZ-Si結晶成長における石英の溶解および酸素の偏析(<小特集>シリコン結晶成長における酸素輸送と欠陥制御)

抄録

Oxygen in the Czochralski (CZ) silicon crystal is incorporated during the crystal growth in which a silica crucible is used for containing the silicon melt and some silica dissolves into the silicon melt. As the first process of the oxygen transportation in CZ-Si crystal growth, the silica dissolution process, including the dissolution rate and formation of the interfacial phase (brownish ring) have been investigated. It is found that the dissolution rate can be con-trolled by changing the sample assembly. The dissolution rate is much faster in the region near triple junction of Si melt, silica glass and Ar atmosphere, which is the fundamental concept for the proposal of the sessile drop method. An approximate intrinsic silica dissolution rate has been obtained with the sessile drop method. The inter-facial phase of so-called "brownish rings" has been investigated using an in situ observation method. A formation mechanism of the brownish rings has been proposed based on the observation results. As another oxygen transportation process, oxygen equilibrium segregation coefficient has been investigated as follows. Single silicon crystals have been grown successfully under the equilibrium condition of a SiO_2-Si-SiO system in a closed silica ampoule with a vertical directional freezing method. The oxygen concentration in the grown single crystals was obtained using Fourier transform infrared spectroscopy (FT-IR) and secondary ion mass spectroscopy (SIMS) techniques as 1.7±0.1 (×10^<18> atoms/cm^3). The equilibrium segregation coefficient of oxygen was obtained by comparing the oxygen concentration in the silicon crystal to the oxygen solubility in the silicon melt. Then, the equilibrium oxygen segregation coefficient was determined to be 0.8±0.1.