Development of 3D Thin WLCSP Using Vertical Via Last TSV Technology with Various Temporary Bonding Materials and Low Temperature PECVD Process

3D WLCSP using via last TSV (through silicon via) technology is an ideal packaging technology to meet small-form-factor, high I/O density, high-speed and most important, lower cost. For thin 3D WLCSP with TSVs, a number of critical processes need to be developed such as oxide etch, via cleaning and wafer de-bonding. In the present paper, processes for 8 inch, thin WLCSP with TSV diameter of 40μm and final Si thickness of 100μm were developed. Two kinds of package schemes were fabricated. One is bump last, in which the pads are on the front side of the wafer and Cu pillar bumps on the backside. Another is bump first, in which Cu pillars are plated on front side of the wafer and pads on backside. In both the packages, Cu pillars are of 50μm height and 50μm diameter. Cu/Ni/Au RDL with ~5μm thickness is fabricated on the backside of the chips. In this paper, the measurement method for the oxide thickness at the bottom of the TSVs and the cleaning of the by-product polymers on the sidewall of the vias using special chemical solutions were reported. For the bump last scheme, all the processes are developed and ready for production. Using HT1010, the PECVD process can be performed at a low temperature of 140°C with a single-frequency. After de-bond, a yield of 99.66% was achieved according to the AOI measurement of the Cu pillar bumps. For bump first scheme, several adhesive materials were tested and cannot meet the process requirements. It was revealed that high temperature temporary adhesive should be used since the thicker adhesive will cause a temperature increasing during PECVD process and lead to failure of the temporary bonding interface. Material for the laser de-bond method was verified, and wafer de-bonding was successful demonstrated.