Nondestructive characterization of residual strain in large-diameter semiconductor crystal ingot using three-dimensional infrared photoelastic CT method

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The purpose of this work is to develop a new technique by which there e-dimensional distribution of residual strain in large-diameter semiconductor crystal ingots such as silicon and GaAs can be characterized nondestructively as standard ingot form and then for it to be intended for practical use. To do so, we have developed a three-dimensional infrared photoelastic CT equipment, in which a linearly-polarized light beam is introduced both along to the z-axis into a cylindrical semiconductor crystal ingot and the polarization of the transmitted light beam is analyzed, and then pratically characterized the residual strain in LEC-grown GaAs single crystal ingots, FZ-grown dislocation-free Si single crystal ingots, and CZ-grown Si single crystal ingots.It was difficult for us to make the infrared photoelastic measurement in as-grown LEC-GaAs ingots, because there were many concave or convex ditches on their cylindrical surface. However, we have designed a new technique by which we can make … More the photoelastic measurement in cylindrically-grinded ingots under the condition of rough surfaces, not polished mirror surfaces. With this new technique, we become able to characterize pseudo-three-dimensional distribution of residual strain in LEC-GaAs single crystal ingots. On the other hand, it was possible for us to make the infrared photoelstic measurement in dislocation-free FZ-Si single crystal ingots. It was found that the birefringence induced due to optical anisotropy was dominated over that photoelastically induced by residual strain, since the residual strain was extremely small in the FZ-Si ingots. Although the optical anisotropy was also dominated in CZ-grown Si ingots, we have demonstrated that the residual-strain-induced birefringence can be measu.Red by introducing the probing infrared light beam along the [100] crystallographic directions. According to our work, the infrared photoelastic technique developed here is very useful in investigating dislocations in large-diameter Si single crystals. Less