Semiconductor layers are often grown on substrates to make solid state transducers, such as light-emitting diodes (“LEDs”), by epitaxially growing materials on sapphire or other types of substrates. Lasers, chemical etchants, or grinders are generally used to remove sapphire substrates from the epitaxial layers. Lasers can deliver photon energy through the sapphire substrates to heat and decompose (e.g., melt) epitaxial material at the epitaxial/substrate interfaces to separate the epitaxial layers from the substrates. Unfortunately, rapid heating and cooling of the epitaxial material associated with laser lift off processes can damage one or more of the epitaxial layers. The damage can include cracking (e.g., crack initiation, crack growth, etc.) and often results in crack propagation across the entire wafer assembly.
Conventional chemical etching lift off processes often involve exposing the edge of a wafer assembly to a chemical etchant such that the chemical etchant travels toward the center of the wafer assembly through voids formed by a reaction between an epitaxial layer and a growth wafer. To lift the entire epitaxial layer from the wafer, the chemical etchant must reach the center of the wafer assembly, which often leads to relatively long etch times. For example, the chemical etchant must travel four inches radially inward along the epitaxial/wafer interface to reach the center of an eight inch diameter wafer assembly. Additionally, it is difficult to consistently deliver the chemical etchant through the voids along the entire epitaxial/wafer interface. Grinding processes are often used to mechanically remove substrates from the epitaxial layers as an alternative to chemical etching. Unfortunately, mechanical grinding can damage the epitaxial layer and produce relatively large scratches which are removed by a subsequent polishing process.