MEASUREMENT OF WAFER SURFACE USING SHADOW MOIRE TECHNIQUE WITH TALBOTEFFECT

In this paper, a modified shadow moire technique is applied to measure surface topology of wafers. When a wafer is sliced, either by an inne r-diameter (ID) saw or wiresaw, the surface needs to be measured to en sure the consistency of quality. Two important characteristics of the wafer surface measurements are the warpage and total thickness variati on ( TTV). Currently, the most commonly used method of wafer measureme nt employs a pair of capacitive measuring probes which sample points o n the surface of a rotating wafer to obtain the contours of surface. M any sampling points on the surface are needed for mor e accurate measu rements; however, this will require more time for the inspection of wa fers during production. An innovative alternative for full-field, whol e-wafer measurement is developed using a laser light source and the mo dified shadow moire technique. This methodology enables one to examine the whole wafer surface quickly and simultaneously. In this study, a 40 lines/mm (1000 lines/inch) reference grating is employed as the sta ndard to create a shadow moire pattern. In addition, the Talbot effect is utilized to adjust the gap, or the so-called Talbot distance, betw een the grating and the wafer surface such that a fringe pattern of go od quality can be obtained. By using the phase shifting technique, the resolution (or sensitivity) can be enhanced by two order of magnitude . The results show that not only the full view of the whole wafer surf ace can be obtained, but enhanced surface resolution and accuracy can also be realized. In addition, warpage due to excessive residual stres ses can be observed distinctly with fringe patterns because of the glo bal and interconnected moire fringes. This process is faster especiall y when dealing with wafers with diameter larger than 200 mm (8 ''). Ex perimental results of both 200 mm single crystalline and 100 x 90 mm p olycrystalline wafers are presented. The system can also be fully auto mated to become an on-line inspection tool.