Brewer Science is developing a material that meets your description: a
spin applied material, cured at under 250 degrees Celsius, able to withstand
8 or more hours of 85 degree Celsius KOH (35%).  This material is removed
with standard photoresist removal process.

"D. Zhou"  wrote:Dear all,

Does anyone know where I can get some high melting-point wax which can be
used to protect the device side of the chip when doing KOH etch at 80
degrees to remove the substrate ? Many thanks.