By market researchers, the market potential for ultra-thin wafers, GaN wafer with backside metallization is estimated to be above 40% of the wafer market by the year 2010.
Wafer handling
To handle delicate thin wafers the bonding of the device wafer is done with a rigid carrier substrate before the back-thinning process. With the use of an adhesive bonding layer, the originally thick device wafer is bonded with its active surface to a carrier wafer. After performing backside processing along with the thinning process and eventually further process steps (lithography, etching, etc.), the thin device wafer, supported by the rigid GaN substrate needs to be released from the carrier wafer along with enabling dicing and packaging processes in the final stages.
By using different approaches the adhesives used for temporary bonding allow the release of the device wafer: after exposure to UV light UV release adhesives then above a release temperature thermal release adhesives have to be heated, and for debonding of the device wafer from the carrier solvent release adhesives have to be dissolved in a chemical solvent.
The temporarily bonded stack that consists of the device wafer, intermediate layer, and carrier wafer is then further processed with the use of several different techniques (e.g. lithography, etching, etc.). So before the selection of the intermediate layers for the targeted application different aspects need to be taken into account. While selecting the adhesive method that is used between the carrier and GaN wafer China, few parameters that need to be considered are the chemical resistance, ease of processing, temperature capability, and thickness variations.
Temporary bonding and debonding with waxes For the spin-coated wax, the highest level of uniformity is necessary.
For a wax layer, the bonding strength is large enough to cope with harsh mechanical processes such asgrinding and polishing. For the release of the device wafer from the carrier, two methods can be used: The wax can either be dissolved in a solvent or softened and released by heating.
Due to the increasing popularity of dry-film adhesive tapes, mainly for thermal-release bonding, it is attributed mainly to the ease of the application and the enhanced thermal release temperature.
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