General-Purpose Self-Focussing Scanner
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
This article describes a general purpose scanner which provides a capability for simultaneous focus and inspection read-out at the same point on a surface under inspection. The self-focussing feature of the scanner, here disclosed, obtains from the use of an image position change involving the vertical motion of the surface under inspection. Most substrates submitted for visual quality inspection are only approximately flat and level, thereby causing problems in maintenance of focus during scan for quality defects. Other material surfaces having specular reflective properties, such as microlithographic masks and silicon wafers, also pose significant illumination problems to a general purpose scanner used to inspect both diffuse and specular surfaces. These problems are overcome by the system shown in Fig.