A study on the adhesion enhancement of polyetherimide to Si wafer using an Al-chelate treatment during multichip module fabrication

Al-chelate coupling agent was successfully applied to improve the adhesion strength of a thermoplastic polyetherimide resin, Ultem 1000® to a silicon wafer during the fabrication of multichip module (MCM) substrates. The origin of the enhanced adhesion strength achieved by applying Al chelate was also investigated using a surface characterization experiment and a theoretical approach. The peel strength of as-laminated Ultem film on an untreated Si wafer was the same as that on a coupler-treated one right after lamination. However, the Ultem layer laminated on an untreated Si wafer lost its adhesion strength to zero within 24 h of 85°C/85% relative humidity (RH) aging. In contrast, the Ultem film laminated on the coupler-treated Si wafer maintained its adhesion strength even after 30 days of 85°C/85% RH treatment. Atomic force microscopy (AFM), surface energy calculation using contact angle measurement, and high-resolution X-ray photoelectron spectroscopy (XPS) analysis were conducted to characterize the surface conditions of a bare Si wafer and a coupler-treated Si wafer. It was revealed by the AFM experiment that the surface roughening caused by Al-chelate treatment was negligible, meaning that the enhanced adhesion stability during 85°C/85% RH aging is mainly attributed to the surface characteristic change of Si substrate. Based on the results of XPS analysis and contact angle measurement, a model of surface bonding structure of an Al-chelate treated Si wafer was suggested and compared with that of a bare Si wafer. Finally, peel strength variation of Si wafers with and without the coupling agent as a function of 85°C/85% RH aging times can be explained by the zero point of charge consideration. Stable lamination based MCMs and micro-via build-up processes can also be obtained using these results.