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Production Proven, High Precision Temporary Bond/De-bond Process
Keywords: Temporary Bonding, Carrier Glass, Total Thickness Variation
Wafer thinning represents a critical step in 2.5D and 3D-IC integration. Achieving low total thickness variation (TTV) of a bonded stack is essential since it directly impacts the TTV of the thinned device wafer. It is essential to understand and utilize appropriate processes and materials that provide precision bonded stacks prior to thinning operations in order to achieve high process yields. The 3M™ Wafer Support System (WSS) combines proprietary 3M temporary bonding technologies with equipment designed to provide a cost effective solution for high volume manufacturing of ultra-thin wafers for 3D- IC integration. The 3M WSS utilizes a Light to Heat Conversion (LTHC) coating along with UV curable adhesives that are designed for temporary bonding of semiconductor wafers to temporary glass carriers. Bonding can accommodate features as large as 100 um and enable thinning down to 20 um thickness. After thinning, a laser is used to de-bond the glass carrier allowing low force and chemical free process. Since it is light based, the 3M WSS process utilizes glass carriers that are transparent at the operating wavelength. Semiconductor glass carriers developed from Corning’s fusion forming process have a number of attributes that make them highly desirable for use in temporary bonding applications. This process delivers glass at target thickness (no grind/polish required) with a pristine surface, extremely tight tolerance on thickness and TTV and low warp/bow over large volumes of material. Additionally, carriers with TTV < 1 um over an entire 300 mm diameter with no grind or polishing has been demonstrated. Furthermore, given that this glass is formed in sheets as large as three meters in size, there is tremendous flexibility in the size of the carriers as well as ability to scale to high volume manufacturing in a cost effective way. This work will provide recent developments that leverage attributes of 3M WSS and Corning’s semiconductor glass carriers to minimize TTV of bonded stacks. Data showing direct measurement of the TTV of each layer of the bonded stack under different process conditions will be presented. The ability to deliver bonded stacks with TTV < 5 um and precision thinned silicon wafers in a high throughput environment will also be demonstrated.
Blake Dronen, Technical Manager
3M Company
Maplewood, MN

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