Transflection, a new illumination technique for in line crack detection in crystalline silicon wafers

Abstract

Crack detection is mandatory for high yield production of crystalline silicon solar cells. Instrumentation for in-line crack detection is a part of today's standard production lines. However the commercial equipment available today has some serious weaknesses allowing some parts with cracks to pass the inspection. In this paper some of these weaknesses are described and a new illumination technique is presented to eliminate these weaknesses. The illumination technique introduced is known form other fields of optical metrology under the name of transflection or interactance. With transflection an area of wafer surface is illuminated, the light is coupled into the wafer and interacts with any defect in the light path and is emitted from the wafer surface at a different position. A crack will obstruct light and so create a clear signature in the emitted intensity. The technique suppresses the grain pattern from multi crystalline silicon wafers and also allows detection of cracks independent of crack orientation.

Transflection, a new illumination technique for in line crack detection in crystalline silicon wafers