In the field of semiconductor wafer processing, increasing demands for large-scale integration, high density silicon packages has resulted in making semiconductor dies very thin. For example, for some applications, silicon (Si) wafers are backside grinded and polished down to a thickness of 50 μm or thinner. Although single crystal Si has very high mechanical strength, Si wafers and/or chips can become fragile as they are thinned. Defects can also be introduced by processing steps such as through-silicon via (TSV) processing, polishing, and dicing, which further reduces the mechanical strength of a thinned wafer or chip. Therefore, handling thinned Si wafers presents a significant challenge to most automation equipment.
In order to facilitate the processing of a device wafer, a mechanical handler wafer (or carrier wafer) is usually attached to the device wafer to enhance the mechanical integrity of the device wafer during processing. When processing of the device wafer is complete, the handler wafer needs to be released from the device wafer. The most common approach to handling a device wafer is to laminate the handler wafer with the device wafer using specially developed adhesives. Depending on factors such as the processing steps, the product requirements, and the type of the adhesive, various techniques have been used or proposed to debond or separate a thinned device wafer from a mechanical handler wafer, including thermal release, chemical dissolving, and laser ablation techniques.
A typical laser-assisted debonding process uses a polymeric adhesive (which is capable of sufficient absorption of energy in the UV (ultra violet) spectrum) to bond a device wafer to a UV transparent glass handler wafer. A laser ablation process is performed to ablate the polymeric adhesive and achieve debonding between the glass handler wafer and the device wafer. The use of a glass handler in the UV laser ablation process has several drawback including poor thermal conductivity, incompatibility with certain semiconductor processing equipment, as well as high cost. Although the use of Si wafer handlers can potentially overcome these drawbacks, silicon is not transparent to UV spectrum and therefore is not compatible with previously developed UV laser release technology.
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