MEASUREMENT OF CARBON CONCENTRATION IN POLYCRYSTALLINE SILICON USING FTIR

The carbon concentration in polycrystalline silicon produced via the Siemens process, the hydrogen reduction of trichlorosilane, was evaluated using FTIR. Samples measured included: as grown polycrystalline silicon, high-temperature annealed polycrystalline silicon, and float zone refined single-crystalline silicon. It was found that infrared measurements made on high-temperature annealed polycrystalline silicon samples display similar carbon concentrations as those obtained on float zone refined single-crystalline silicon samples. Little, if any, evidence exists for the occurrence of significant amounts of interstitial carbon in low carbon concentration polycrystalline silicon material. High-temperature annealing of polycrystalline silicon results in improved spectrum quality, and therefore, reduces the detection limit and improves the accuracy of the carbon measurement in polycrystalline silicon. A liquid helium sample Dewar was successfully used for cryogenic temperature measurement resulting in further improvement in sensitivity.