Inspection of processes during silicon wafer sawing using low coherence interferometry in the near infrared wavelength region

Abstract

Multi-wire sawing of silicon wafers is a tribological process. Slurry consisting of small silicon carbide particles embedded in polyethyleneglycol carries out the abrasive material removal process. During this process small silicon chips are removed from the bulk material. Low coherence interferometry (LCI) is widely used for high accuracy surface topography measurements of materials. This paper presents an application of LCI where the surface of a material (silicon) is inspected from the inside. Light in the near infrared (NIR) wavelength region is used. High spatial resolution is necessary to be able to observe the processes on the micro scale. Therefore a modified solid immersion approach is suggested. That makes it possible to reach a spatial resolution in the range of the illumination wavelength. The topography changes produced by the chippings are in the range of some micrometers. To be able to estimate the volumes of the Si chippings interferometric phase measurements are applied.