Impact of microbump induced stress in thinned 3D-LSIs after wafer bonding

Micro-Raman spectroscopic technique has been employed to study the induced stress/strain by the metal microbumps in 3D-LSI Si die/wafer after wafer thinning and bonding, and the impact of bump spacing, bump size, bonding temperature and bonding force in the stress distribution in such a microbump bonded LSIs has been investigated. It is inferred that (i) the Si present at the interface (between CuSn and LSI die/wafer) is under compressive stress, and it decreases exponentially in the cross-sectional direction both in the die and the wafer; (ii) in the lateral direction, the compressive stress produced by the adjacent microbumps overlapped to each other at the region of bump-spacing; (iii) qualitatively, the residual mechanical stress/strain increases with the bonding temperature and the size of the microbump, i.e. it is large for the higher bonding temperature (as high as >;300 MPa @300°C) than for the non-bonded microbump (a maximum of only +125 MPa @ 280°C); (iv) the metal microbump exerted a large compressive stress up to the depth of >;10 μm in the bonded 3D-LSI die/wafer.