Development of separation inspection technique for micro-cracks and particles using non-contact stress-induced light scattering method

Abstract

Fine-polishing techniques, such as chemical mechanical polishing treatments, are important techniques in glass substrate manufacturing. However, these techniques may cause microcracks under the surface of glass substrates because they use mechanical friction. We propose a Non-contact thermal Stress-Induced LightScattering Method (N-SILSM) using a heating device for inspecting surfaces to detect polishing-induced microcracks. The N-SILSM can detect microcracks in a product under a fine-polished surface. It is a technique for exposing microcracks by exploiting the change in light-scattering from microcrack tips due to temperature variation-induced stress. Additionally, optical properties change due to temperature variations. However, at manufacturing sites, it is ideal that inspection systems be able to distinguish between microcracks and tiny particles. In this report, we carry out the selective detection of microcracks and tiny particles using a N-SILSM with temperature variation. Experimental results showed that the amount of change in the lightscattering intensity alters the cubic function regardless of the size of the microcracks, and also confirmed that tiny particles show very little change in light-scattering intensity. In addition, the possibility of microcrack size estimation was suggested from the magnitude of the change in light-scattering intensity. From the above results, it has been shown that microcracks and tiny particles can be identified and measured by a N-SILSM utilizing temperature change, and that microcrack size estimation can be based on the change in light-scattering intensity. Thus, it has been suggested that N-SILSM is a useful inspection technique for distinguishing between microcracks and tiny particles.