PMMA layers (novolak layers) feature an extremely smooth surface. A surface roughness of less than 2nm was measured on resists which were thus optimized. This characteristic can be used for the smoothing of glass surfaces, for instance.
Allresist offers the protective coating SX AR-PC 5000/40 for HF and KOH etchings already for a few years. Layers of 5 μm are able to withstand a 48 % hydrofluoric acidic solution for several hours. Also 40 % KOH solutions for silicon etchings do not attack the layer.
The new, highly insulating protective coating SX AR-PC 5060 F-Protect represents a good alternative to the well-known resist Cytop®.
Sensitive substrates can be protected against damage during handling with resist SX AR-PC 5000/3.1, which is especially important in the case of double-sided procedures.
Since problems may occur when PMMA protective coatings are applied, new ideas emerged how to optimise the coating properties of these resists. So far, protective coatings tend to show under certain circumstances the so-called “cotton candy effect” during spin coating, which means that fine PMMA threads are formed.
The protective coatings AR-PC 503 and AR-PC 504 have been successfully used for many years in aggressive KOH etching procedures. These resists are traditionally produced with the solvent chlorobenzene.
Protective coatings are in most cases composed of novolacs or PMMA polymers. Both polymers ensure a sufficiently high protective effect against mechanical damages as well as sufficiently high resistance against acidic solutions.
Protective coatings AR-PC 503 and 504 are able to withstand the presence of 40%, 85°C warm KOH for several hours. The polymer PMMA is not attacked under these conditions. These resists can consequently be used to protect front and back surface of wafers during deep silicon etching.