The Novel Way to Inspection Technique for SiC Substrate by Applying Stress Effects

Abstract

Silicon carbide (SiC) has attracted much attention as an important material for high temperature, high power and high frequency devices, because it has advantages compared to silicon (Si) devices. However, SiC substrates are made the same way with Si substrates in production manufacturing. In production site, fine polishing techniques, such as a chemical mechanical polishing treatment (CMP), are some of the most important base techniques used for the semiconductor manufacturing. Mechanical interaction in the form of friction occurs between the abrasive and the substrate surface during polishing, which may cause formation of latent flaws on the silicon carbide (SiC) substrate surface. Fine polishing-induced latent flaws may become obvious during a subsequent cleaning process if SiC substrates are corroded away by chemical interaction with the cleaning liquid. Latent flaws thus reduce product yield. Recently, many nondestructive inspection systems that use light scattering from foreign matter particles for their detection have been made commercially available for use in production sites. These systems use laser incident light and a photo-detector (e.g. a photomultiplier tube) for detecting light scattering from foreign particles with high sensitivity. Inspection systems based on Rayleigh scattering and Mie scattering can detect particles smaller than the laser wavelength. However, these systems detect all light scattering as foreign matter particles on the surface. Therefore, these system cannot discriminate between latent flaws and particles. In addition, these inspection techniques cannot detect defects under the surface of substrates. We propose a novel inspection technique for fine polishing-induced latent flaws by combining the light scattering method with stress effects, referred to as the stress-induced light scattering method (SILSM, Y. Sakata, et al, Review of Scientific Instruments, Vol. 85, No. 8, p. 083303-1 (2014)). In this method, samples are deformed by an actuator and stress effects are induced around the tips of latent flaws. Due to the photo elastic effect, the refractive index of the material around the tip of a latent flaw is changed. This changed refractive index is in turn detected by a cooled CCD camera as variations in the light scattering intensity. In this report, latent flaws under the surface of SiC substrate are detected non-destructively by applying SILSM, and the utility of SILSM will be evaluated as a novel inspection technique for the substrate. In addition, the results detected by SILSM is compared with the results of conventional laser raman spectrometry and photo-luminescence results, respectively. And latent flaws under SiC substrate surface is evaluated from various directions. This research was partially supported by AIST-AMRI budget for Exploratory Research and we gratefully acknowledged this budget with deepest appreciation.