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|An Overview of Thin-Wafer Handling for 3D IC Integration|
|Keywords: Thin-wafer handling, 3D IC integration, Adhesive|
|One of the key reasons why 3D IC integration is so attractive to semiconductor industry today is because it uses thin chips/interposers with TSVs (through-silicon vias), for examples, 50μm or less for memory chips and 200μm or less for active and passive interposers. Making the chip thin is not a big problem because most back-grinding machine can grind wafers to as thin as 5μm. However, handling thin TSV wafers through all the fabrication and packaging assembly processes is difficult. Usually, the TSV chip/interposer wafer is temporarily bonded with an adhesive on a support (carrier) wafer before back-grinding to expose the Cu TSVs (Cu revealing) and make the wafer thin. Then it goes through the fabrication processes, such as metallization, passivation, underbump metallurgy, and solder bumping. After all these are done, removing the thin wafer from the support wafer (debonding) poses another big challenge. In this study, the state-of-the-art of: (a) adhesive materials such as the LC-series and light-to-heat-convention (LTHC) layer provided by 3M, HT-10.10 and ZoneBOND by Brewer Science, TZNR-A series and WSP series by TOK, XP-BCB by DOW, WL-40XX and WL-30XX by Dow Corning, HD-3007 and HD-7010 by Du Pont, and TMAT by Thin Materials; (b) supporting wafers such as glass and silicon; (c) equipments such as TWM12000 for bonding and TWR12000 for debonding provided by TOK, 850TB for temporary bonding and 850DB for debonding by EVG, XBS300 for both temporary bonding and debonding provided by SUSS, and WSS by 3M; and (d) processes such as mechanical peel-off, solvent release, a combination of mechanical peel-off and solvent release, thermal-sliding, and laser irradiation will be presented and examined. Thin-wafer handling issues and their potential solutions for the chip/interposer wafer, supporting wafer, temporary bonding, thinning, backside processed, debonding, and assembly will also be presented. Finally, a guideline for selecting adhesive materials is given.|
|John H. Lau,
Chutung, Hsinchu,, Taiwan