Grinding induced subsurface cracks in silicon wafers

Silicon wafers are used for production of most microchips. Various processe s are needed to transfer a silicon crystal ingot into wafers. To ensure hig h surface quality, the damage layer generated by each of the machining proc esses (such as lapping and grinding) has to be removed by its subsequent pr ocesses. Therefore it is essential to assess the subsurface damage for each machining process. This paper presents the observation of subsurface crack s in silicon wafers machined by surface grinding process. Based on cross-se ctional microscopy methods, several crack configurations are identified. Sa mples taken from different locations on the wafers are examined to investig ate the effects of sample location on crack depth. The effects of grinding parameters such as feedrate and wheel rotational speed on the depth of subs urface crack have been studied by a set of factorial design experiments. Fu rthermore, the relation between the depth of subsurface crack and the wheel grit size is experimentally determined. (C) 1999 Elsevier Science Ltd. All rights reserved.