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The objective of this program is to identify and develop low cost processing for fabricating large grain size polycrystalline silicon substrates. Metallurgical grade silicon (MG-Si) which is low cost and abundant for industrial usage was chosen as starting material. However, MG-Si cannot be used directly as substrates for solar cell fabrication; the further purification and recrystallization of MG-Si are needed. The conventional method of purifying MG-Si requires the conversion of Si to gaseous chlorosilanes. Chlorosilanes are purified by distallation. The purified chlorosilanes are then converted back to elemental silicon using a chemical vapor deposition process. Purified polysilicon requires recrystallization to become single crystals or large grain polycrystalline form for electronic device or solar cell applications. The techniques being studied under this program use direct methods for the purification of MG-Si. The process uses sequential steps of purification followed by crystal growth. The steps of sequential purification include: (1) leaching of MG-Si charge, 2) phase separation of non-soluble impurities from molten silicon, 3) reactive gas treatment of molten silicon, 4) liquid-liquid extraction (called slagging), and 5) impurity redistribution using ingot pulling. All the purification steps are performed in a consecutive manner using a crystal puller with the exception of step (1).more » The purified ingots will be in a desired ingot dimension and further recrystallization is not necessary. In this quarterly period the study of the purification by (1) reactive gas treatment, and 2) slagging was completed. Selection of reusable crucible has also been made. Progress is reported.« less

osti oai (u.s. department of energy office of scientific and technical information)

Sequential purification and crystal growth for the production of low cost silicon substrates. Quarterly technical progress report No. 2, 1 January 1980-31 March 1980