Processing clear wafers
The "wafer present" sensors on the automatic svgcoat and svgdev tracks have been upgraded and should be able to detect the presence of transparent substrates. So, clear wafers can be processed, for the most part, identically to silicon wafers.
One common problem with photolithography on clear wafers, however, is that during exposure, there will be eflection of the UV light off the backside of the wafer. The result is double-exposure of the resist, in which the lines appear to have a halo (the thickness of the halo depends on the thickness of the substrate.) For gross geometries, this is likely not a problem. For fine geometries there are two solutions:
1. Use of an antireflective coating. This may be a thin film (a thin layer of TiN is typically used in industry). There are many commercial spin coatings available as well.
2. Use of dyed photoresist. SNF stocks a dyed resist version of AZ3612. Contact Mahnaz Mansourpour for more information.
Stanford Nanofabrication Facility
Last Modified 08/29/2003