Valley Design took the initiative many years ago by introducing glass and ceramic wafers made to SEMI specifications. The usual glass for this purpose is soda lime or borosilicate. When temperature is involved, borosilicate withstands higher temperatures. Valley Design offers a full line of different glasses and even quartz or ceramic material for this application. Thickness can range from 0.005 inches to several millimeters.
Edges are ground and beveled, and an indexing notch is optional.