It’s common knowledge among those working feverishly to bring 3D TSVs to market that one of the areas still being ironed out in the back-end-of-line processes is thin wafer handling. Research institutes along with materials and equipment suppliers (IMEC, Léti, Sematech, SUSS MicroTec, EV Group, 3M, Brewer Science, T-MAT, Dupont all come to mind) have come up with an assortment of viable and cost effective methods for temporary bonding and debonding of a support carrier wafer. The sticking point (no pun intended) appears to lie in the debonding process, especially when working with 300mm wafers.
At IMAPS International, I heard about an alternative solution in development at Institute for Microelectronics (IME) in Singapore, in a project lead by Xiaowu Zhang, Ph.D. Working with Brewer Science’ Waferbond material and and EV Group bonder to form the temporary bond, the team experimented with the debond process by using a perforated support wafer. After backside processing, thinning to 50µm, the wafers are soaked in Waferbond remover solution at 90°C. The “release holes” in the support wafer measured 1mm in diameter and were set at a pitch of 3mm, however this didn’t allow enough of the chemical solution through to dissolve the adhesive, so breakage of the processed device wafer was still occurring. But according to Zhang’s paper, when the pitch of the holes was reduced to 2mm, along with an increased number of wafer edge perforations, the chemical solution penetrated the bonding adhesive more uniformly, allowing for successful debond of the wafers.
This caught my eye, because it’s different from the Thermoslide process developed by Brewer Science and EVG, which relies on heating the support wafer to soften the adhesive before sliding them apart. However since I merely follow these technologies and report on this stuff, I’d like to hear opinions on this from the engineers who have been working on solutions to the debond process. What do you think? Comments are encouraged!