抄録
Further integration in semiconductor devices requires less-damaged wafers and damage-free fabrication processes, and sensitive and nondestructive evaluation for low-level damages is in high demand.
A new measurement method for photothermal displacement has been developed and successfully applied to evaluation of lattice damages in semiconductor. When a semiconductor surface is illuminated by a focused and intensity-modulated laser pump beam, an absorbed laser power causes a small photothermal displacement of several tens of picometers on the surface depending upon thermal properties of the surface layer. The thermal properties, especially thermal conductivity, are drastically influenced by the concentration of lattice damages. A highly sensitive laser heterodyne-interferometric probe with a resolution of 0.1 picometers detects small displacement and quantifies lattice damages in the surface layer.
This paper describes the principle of this method focusing upon how to obtain high sensitivity to photothermal displacement, in other words, to lattice damages. Demonstrations of photothermal displacements observed with polished wafers, low-dose ion implanted wafers and ECR etched wafers, and discussions on the limit of this photothermal displacement are also presented.
