CHARACTERISTICS OF PHOTOACOUSTIC DISPLACEMENT FOR SILICON DAMAGED BY ION-IMPLANTATION

A decrease in the thermal conductivity and the optical absorption leng th of a silicon wafer damaged by ion implantation causes an increase i n the amplitude of photoacoustic displacement (PAD) on the sample surf ace. The behaviors of the PAD were investigated by thermoelastic analy sis. The theoretical results indicate that the amplitude of PAD is app roximately proportional to the square of the thickness of the damaged layer and is characterized by the ratio of the optical-absorption coef ficient to the thermal conductivity of the damaged layer. Experimental results, which were quantitatively measured by a highly sensitive PAD interferometer, can be explained well by the theoretical predictions. The thermal conductivity of the damaged layer by implantation above c ritical amorphization dose can be estimated to be 1-3 W/mK by comparis on of the experimental data with the theoretical results. (C) 1995 Ame rican Institute of Physics.