Three-dimensional wafer stacking using Cu–Cu bonding for simultaneous formation of electrical, mechanical, and hermetic bonds

CS Tan, L Peng, J Fan, H Li… - IEEE Transactions on …, 2012 - ieeexplore.ieee.org
CS Tan, L Peng, J Fan, H Li, S Gao
IEEE Transactions on Device and Materials Reliability, 2012ieeexplore.ieee.org
Wafer-on-wafer stacking is demonstrated successfully using bumpless Cu-Cu bonding for
the simultaneous formation of electrical connection, mechanical support, and hermetic frame
for 3-D IC application. The ohmic behavior of the Cu-Cu bond is verified. A daisy chain of at
least 44 000 contacts at a 15-μm pitch is connected successfully and sustains thermal
cycling. Postbonding delamination is found to be strongly affected by the wafer curvature
and bond strength. The Cu-Cu hermetic seal ring shows a helium leak rate more than ten …
Wafer-on-wafer stacking is demonstrated successfully using bumpless Cu-Cu bonding for the simultaneous formation of electrical connection, mechanical support, and hermetic frame for 3-D IC application. The ohmic behavior of the Cu-Cu bond is verified. A daisy chain of at least 44 000 contacts at a 15-μm pitch is connected successfully and sustains thermal cycling. Postbonding delamination is found to be strongly affected by the wafer curvature and bond strength. The Cu-Cu hermetic seal ring shows a helium leak rate more than ten times lower than the reject limit (5 × 10 -8 atm · cm/s based on MIL-STD-883E standard) without underfill. This provides a robust IC-to-IC connection density of 4.4 × 10 5 cm -2 , suitable for future wafer-level 3-D integration.
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