The application of Developing Low-warpage Bonding Pair by Finite Element Analysis

Facing with the significant reduction on mechanical strength of ultra-thin wafer, temporary bonding and de-bonding (TBDB) process was developed to ensure that wafers could successfully and safely complete the subsequent processes. Unfortunately, the mismatch in coefficients of thermal expansion (CTE) between the carrier wafer and device wafer (Si) would produce significant mechanical stress as the bonding pair experienced a huge temperature variation. To resolve this, a series of finite element analysis (FEA) simulations and experiments were carried out in this paper. Hypermesh and Abaqus were employed to construct the model of bonding pair. Firstly, a cooling load (130~25℃) was applied, the bonding pair behaved like a symmetrically bowl-shape (low in the middle and high at the edges) and the warpage was 6.39 mm. Then a series of single factor studies (SFS) of each parameter (E, CTE and ν) for TBM-1 were carried out. The results showed that only E has a great impact on warpage, especially when it was lower than 1 MPa, the warpage ranged from 3.83 mm to 6.39 mm. While SFS were performed on CTE (300~420 ppm/k) and ν (0.17~0.47), the warpage variation was negligible. Therefore, we redesigned and synthesized another low modulus material (TBM-2). And the warpage of the bonding pair made with TBM-2 was lower than that made with TBM-1, and it has been proven under different high temperature processes. In addition, a series FEA were conducted on the influence of glass wafer, TBM, silicon wafer’s thickness on warpage, and it has been proven that as the thickness of glass wafer, TBM and silicon wafer increased, the warpage value of bonding pairs reduced gradually.