Infrared measurements of interstitial oxygen in heavily doped silicon.

Infrared spectroscopy is widely used to measure the concentration of interstitial oxygen impurities in silicon. The technique is applied to crystals with resistivity greater than about 0.1 ohm-cm; at lower resistivities free carrier absorption makes the measurements unreliable. We have investigated infrared measurements of low resistivity silicon using a new procedure and we show that measurements are possible well below 0.1 ohm- cm, with the limit appearing to be about 0.02 ohm-cm for n- type silicon and 0.05 ohm-cm for p- type. We compare our data with oxygen concentrations determined by secondary ion mass spectroscopy on the same samples. The two techniques are in good agreement, demonstrating the reliability of the infrared procedure at low resistivities.