The Effect of Temperature on Nickel Deposited as an Underlayer Between Copper Filler and Silicon Wafer

Abstract

Through silicon via (TSV) has garnered a lot of interest in the semiconductor industry due to its ability to provide the shortest interconnect path. The coefficient of thermal expansion (CTE) mismatch between the copper (Cu) interconnection filler and the silicon (Si) wafer result in reliability issues of the TSV system. This research proposed the introduction of an underlayer between the Cu filler and Si wafer in order to reduce the CTE mismatch in the TSV. The chosen underlayer is nickel (Ni) as it has a CTE value placed in between Cu and Si at 13 ppm/°C (Cu = 17 ppm/°C, Si = 2.8 ppm/°C). The Ni layer was deposited using the electroless deposition process at different temperature of plating bath (75 °C, 85 °C, and 95 °C) and deposition time (20, 40, and 60 minutes). The analysis of the microstructure of the Ni layer deposited on the Si wafer was characterized. The adhesion test was conducted using the ATM D3359 (Measuring Adhesion by Tape Test) Standard for coating adhesion test and the 4-Point Probe Test for the resistivity measurement. It was found that the optimum Ni plating temperature was at 85 °C based on its adhesion and high stability of plating bath. The resistivity test showed that the increased of Nickel underlayer thickness deposited between copper and Si wafer has slightly increased the resistivity.