Nondestructive Observation of Defects in Semiconductors with Photoacoustic and Photothermal-Radiation Microscopes

We have developed a new photothermalradiation (PTR) microscope for noncontact and nondestructive evaluation of defects in semiconductors. Thermal radiation from local heating area was detected with a HgCdTe infrared detector which is highly sensitive to the radiation in the wavelength range from 8 to 13 pm. We measured a PTR topograph and a photoluminescence (PL) topograph of a GaAs wafer. We found that the PTR signal increases remarkably at a surface damage on the GaAs wafer where the PL intensity decreases. We also measured PTR topographs of a thermally oxidized Si wafer. It is found that peaks of the PTR topograph correspond to small defects on the oxide films. We found an unexpected result that the PTR signal decreases at a deep scratch in contrast to the increase of the PA signal reported previously. We pointed out that the thermal emissivity of the sample surface is a very important factor for a detailed analysis of the PTR topograph.