Thin Wafer Handling Challenges and Emerging Solutions

Temporary bonding attaches substrates to a carrier so that after thinning to the desired thickness further backside fabrications steps can be conducted with "normal" process flows in standard semiconductor equipment. The selection of a suitable temporary adhesive is key to the success of thin wafer handling. The major requirements of temporary adhesives are related to its process flow, thermal stability, chemical resistance, and mechanical strength. The ideal thermal stability should allow high temperature processing up to 400C for dielectric deposition in high aspect ratio vias, polymer curing, solder reflow, metal sintering, permanent bonding or other high temperature processing. The adhesive must be resistant to the chemicals commonly used after wafer thinning. Mechanical strength is required to hold the thin wafer rigidly during processing, especially during permanent bonding applications otherwise the thinned wafer will flex and prevent bonding. The challenge arises in finding a simultaneous solution to these problems while allowing for the gentle release of the thinned substrate to its final, permanent substrate or package without yield loss or stress. This paper will highlight some of the more recent solutions for thin wafer handling that have emerged through technology innovation.