An optically non-destructive, non-contact, and vibration-insensitive edge quality assessment system for semiconductor and harddisk drive industries

This paper proposes an edge quality assessment system for a sub-millimeter thick wafer bar suitable for semiconductor and harddisk drive industries. Our key approach is based on Fourier optics analysis in a retro-reflective optical architecture featuring nondestructive and non-contact measurement. In our proposed design, a collimated optical beam is incident on a sub-millimeter thick wafer bar from its side. In this way, part of the optical beam is reflected back and is then Fourier transformed on a two-dimensional image sensor. By investigating the far-field diffraction pattern, important parameters of the wafer bar such as thickness, surface parallelism, edge parallelism, and surface defect can simultaneously be analyzed. To our knowledge, this is the first time that these important parameters are analyzed by only one system. Other key features include low cost and vibration insensitivity. Our field test study using a 635-nm wavelength laser and a 15-cm plano-convex lens for specified 246-μm thick rectangular wafer bars are discussed.