Measurement of Low Carbon Concentration in Polycrystalline Silicon by Second Generation Infrared Absorption Spectroscopy

Measurement of carbon concentration in semiconductor grade polycrystalline silicon by infrared absorption spectroscopy was examined. Synthetic reference removing substitutional carbon (Cs) by electron irradiation was used. Removal ratio dependence on initial [Cs] and electron dose was systematically examined. As a result, production of synthetic reference with [Cs] of about 1013 atoms/cm3 and of block gauge with known [Cs] was successfully accomplished. For estimation of [Cs] in polysilicon after growing float zone crystal, low temperature measurement was examined in addition to the previously established RT measurement. Interfering fractional virtual phonon bands were examined and removed similarly with that at RT. To escape from the contamination during the FZ process, direct measurement of polysilicon was examined. The difference between the two - phonon absorption background spectra at room temperature, low temperature and in polysilicon was clarified. Based on the result, spectrum processing for measurement at low temperature and in polysilicon was established. Measurement procedures for [Cs] down to 1 x 1014 atoms/cm3 was established.