Ultra-Thin Wafer Processing utilizing Temporary Bonding

摘要

The microelectronics industry is spreading to non-traditional markets aimed at consumer transactions. Newly developed and upcoming applications including RF-ID Tags, Chip Cards or Wearable Electronics require ever thinner and more flexible electronic circuits. These applications require increasingly thinner substrates and push manufacturing processes into the thin and ultra-thin regimes. Although thin silicon wafers (e.g. < 100μm) become flexible, the material is also becoming mechanically unstable. The same is true of compound semiconductor materials however, these materials are also rather brittle. The changes in mechanical performance present challenges to high yield and automated volume manufacturing. A reliable support and handling technique is required to ensure safe processing through the manufacturing steps of these ultra-thin substrates. The most established way in the semiconductor industry for such a technique is the temporary bonding of those materials to rigid carrier. The supported device material is then back thinned and has the mechanical strength of the carrier material. After final processing, like e.g. further lithography, deposition, etc, the thin device wafer is now getting de-bonded onto a dicing tape. The paper discusses various methods of mounting (temporary bonding) the device wafer on a rigid carrier. Due to the use of various intermediate substances, like thermal or UV release dry adhesive film, waxes or resists, several different methods are used to apply the intermediate materials on the wafer. A newly developed method for fully automated punching and lamination of dry-adhesive films is introduced. The tape is laminated onto a carrier wafer and the device wafer is bonded onto this stack enabling a "pyramid"-like structure. With this technology thin-wafer applications are achieving high yield manufacturing in combination with low cost-of-ownership. This facilitates the transition from pilot-line production into high volume. After back thinning and further process steps, the thin and fragile device wafer (usually below 100μm) has to be de-bonded again from the rigid carrier. These details will also be presented. Modular equipment solutions for R&D activities as well as for pilot line and cassette-to-cassette operation for high volume production will be discussed.