Construction of cross-linked polymer films covalently attached on silicon substrate via a self-assembled monolayer

Abstract

A new synthetic approach was developed to fabricate cross-linked polymer films covalently attached on a silicon substrate via a self-assembled monolayer (SAM) using a low energy proton beam as the initiator. The widely used silane coupling reagent 3-(mercaptopropyl) trimethoxysilane [HS(CH₂)₃Si(OCH₃)₃] was employed as an intermediate SAM to chemically bond the cross-linked polymer film to the silicon substrate. Dotriacontane was selected as a precursor that was spin-coated on the SAM-terminated silicon wafers. The film thickness can be easily controlled by spin-coating precursor solutions of different concentrations. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and contact angle measurements confirmed the formation of SAM on the silicon substrate and the subsequent cross-linkage between the SAM and the upper polymer film formed. The resulting cross-linked polymer films are relatively stable, with all layers covalently attached together so that the whole film could not be removed by rinsing in both organic solvent and even more reactive HF solutions. In particular, the resistance of the cross-linked polymer film towards HF etching can be useful for lithography and device fabrication for polymer based electronics. The capability of using different SAMs to attach various polymer films was also demonstrated.