Striation defects are a thickness pattern of coating material on the wafer that has an apparent form similar to a sinusoid. The ridges and valleys are lined up parallel to the major fluid flow direction of coating solution during the spin-coating process. Since they formed a very regularly spaced pattern then we were able to diffract light from them and use the peak intensity to determine the average striation spacing in chosen locations on the wafer. This figure shows the experimental setup:

 

Typical images generated from diffraction off of the striation patterns are shown below.  (a) Shows the diffracted image as viewed through a 1mm slit (to reduce the light intensity).  These slit-images were fed in to our image acquisition software package for precise intensity and diffraction angle (y) measurements.  (b) Shows the diffracted image as it appears when shined on to the surface of a thin ruler – placed directly on the image screen.  These diffracted images allow for a simpler although (seemingly) less precise determination of the diffraction angle (y) values:

We determined that the laser measurement was of comparable accuracy as direct measurement from image files. This work has been submitted for publication and is currently under review.