Nondestructive measurement of striation defect spacing using laser diffraction

A simple method is presented for measuring the characteristic spacing between striation defects that sometimes develop when coatings are deposited by the spin-coating process. Striation defects, because of their substantial regularity of thickness variation, are able to diffract laser light. By measuring the diffraction angle, it is possible to determine a characteristic spacing that corresponds to the most dominant spatial frequency for the striation defects that have formed. This diffraction technique is compared with other methods for determining the average striation spacing. This noncontact characterization technique may also be applicable to other regularly or quasi-regularly spaced defect structures that appear in coatings or other materials. The limits and accuracy of this technique are discussed in detail.