Production of low cost silicon wafers by continuous casting method-development of drip-controlled method

The continuous casting method (CCM) has been designed to obtain low cost silicon wafers. This method has the objective of wafer cost reduction production effect through the installation of a pre-heating zone and a crystal growth and cooling zone separately on both sides of a silicon melting and injecting zone. We have developed the drip-controlled method (DCM) as a casting method for CCM. In DCM, the injection of molten silicon and the crystal growth are carried out simultaneously and the heat of molten silicon is utilized actively as a heat source to control the crystal growth. DCM is the most effective casting method for continuous casting. Batch-type ingots with a size of 320 mm square, height 260-300 mm, were produced by DCM. An oxygen content of 5-15 ppma and a carbon content of less than 5 ppma were obtained throughout the ingots. The cell efficiency yield of more than 13.5% was 80% against the growth direction, with a wafer size of 100 mm/spl times/100 mm using our standard cell process. A maximum value was found of 14.3% measured in JQA. The solar cell efficiency, the carrier lifetime and the diffusion length measured in this study showed DCM had an advantage for obtaining one-directional growth and columnar structure.