Standard wafer processing uses the CTE (coefficient of thermal expansion) matched carrier such as blank wafer or glass as support structure holding down with vacuum chuck in performing the different processing steps including temperature as high as 250-350ºC. Matched CTE at around 7 ppm/ºC minimize the need to consider the interfacial stress due to the temporary bonding adhesives that are typically having vastly different CTE from 60 ppm/ºC and up.
AIT developed a temporary bonding adhesive that are extremely flexible and yet has strong shear bond strength during backgrinding and wafer processing. While these novel temporary bonding adhesives can be used with the traditional wafer processing using glass or wafer carrier described in separate section, with the use of disposal carrier, the wafer per hour throughput can be multiplied.
With the temporary bonding adhesive pre-applied onto the thin disposable carrier, the melt-lamination onto the active side of the device wafer is simplified. Besides traditional wafer temporary bonding equipment for vacuum assisted heated plate pressure lamination, AIT also developed a process for direct lamination using precision pre-heated calendaring roll lamination equipment for even faster throughput.
The biggest advantage with the use of the patent pending disposal carrier approach is in the de-bonding and separation of device wafer from the carrier. The following is an illustration of the difference in process of de-bonding:
The key of success is the molecularly engineered highly conforming and stretchable flexible temporary bonding adhesive having high shear bonding and high temperature stability.
- Pre-applied onto a disposable carrier removed several processing steps in deposition and forming tight total thickness variation of less than 5µm.
- The ability for the temporary bonding adhesive to peel-release from the device wafer without the use of heat-sliding and focused laser ablation that are relatively equipment and time intensive.
- In addition, the molecular structure having ability to peel-release clean without residual on device increases the number of wafer throughput per hour several fold.
- This disposable carrier with the adhesive layer is cost effective enough to be tossed.
The following table details the properties of the three format of the AIT patent-pending temporary bonding adhesive on disposable carrier solutions.
- GD-PRCL-350-WS uses a disposable carrier that is closely matched to that of the device wafer such as silicon.
- GD-UVR-350-SS uses a disposable carrier that is not as closely matched to that of the device wafer.
- GD-UVR-350-FG uses a proprietary high temperature carrier that is translucent to transparent.