Chiang Mai Journal of Science

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Polysilicon is the main raw material in making silicon wafers in which integrated circuits are made of. The polysilicon production chains start off with high purity sand which is decomposed into metallurgical-grade silicon (MGS). The reaction of MGS with hydrogen chloride (HCl) will form trichlorosilane (SiHCl3) which then goes through several purification steps in order to obtain pure SiHCl3. The subsequent reaction of SiHCl3 and H2 in a chemical vapour deposition (CVD) reactor will deposit very pure polysilicon onto a thin monosilicon seed rod. The polysilicon samples were sent for testing at an independent laboratory and
analyzed using XRF spectroscopy to determine the main impurities of P, B, O and C. Several other impurities were also measured which includes Fe, Cr, Ni, Cu, Zn, and Sb. Based on the measurement of the impurity concentrations, the purity of the polysilicon is at 99.9995% which is below the requirement for an electronic-grade polysilicon which is 99.999999999%. Resistivity measurement shows a high concentration of P content which indicates that it is an n-type polysilicon.

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