Interfacial adhesion of polymeric adhesive film on different surfaces in the fabrication of polymer photonic devices M. A. Uddin Æ W. F. Ho Æ Hau Ping Chan Received: 29 July 2006 / Accepted: 16 January 2007 / Published online: 13 February 2007 Ó Springer Science+Business Media, LLC 2007 Abstract One main critical issue in the fabrication of polymer optical devices is the adhesion strength of polymeric layer to the substrate. High adhesion strength is desirable and critical in order to avoid peeling out of polymeric layer from the substrate due to stress generated during fabrication, handling and lifetime. Therefore, the aim of this study is to investi- gate the interfacial adhesion of polymeric adhesive film on different possible substrate surfaces such as pure silicon wafer, silica on silicon wafer, and thin metal layer (Chromium–Cr) on silicon wafer under different processing conditions. Surface morphology of the substrates before deposition was characterized by atomic force microscope (AFM). Adhesive shear but- ton was made on those substrates by using photoli- thography process and the interfacial adhesion was measured by using a Dage D2400 shear tester. The effect of exposing in high temperature and typical damp heat condition on the interfacial adhesion was also studied. We found that the best adhesion perfor- mance was obtained for the case using Cr thin in all processing conditions, especially under heat treatment and damp heat test. From this study, we suggest that a thin layer of metal film on silicon wafer can be use to improve the adhesion and the reliability of the polymer photonic devices. The oxidized silica on silicon wafer is an alternative choice at the expense of reducing adhesion performance. Moreover, using silica layer has the advantage over Cr layer that one fabrication step can be reduced since the silica layer itself can effec- tively act as the lower cladding of the devices. 1 Introduction As for the choice of the materials for the photonic de- vices, polymer waveguide technology is attractive for photonic integrated circuits (PICs) due to numerous advantages. These advantages include easy deposition on diverse substrates like semi-conductors and ferrites, broad selection of available patterning procedures such as photobleaching and laser writing, and low cost to satisfy a significant industry need [1]. The key require- ment of polymer optical waveguide fabrication includes simple and straightforward thin film deposition process. And spin coating technique is the simplest and most commonly used method to form thin films onto wafer [2]. The critical issues of spin-coated adhesive in this application are film thickness and adhesion strength. Many studies have been directed to predict the final film thickness, but no attempt has been paid to compare the interfacial adhesion of adhesive film among those substrates for different process conditions. High adhe- sion strength is desirable and critical in order to avoid peeling out of polymeric layer from the substrate due to stress generated during fabrication, handling and lifetime [3]. For example, Fig. 1a shows the typical SEM picture of the interfacial failure (large delamina- tion) of a channel waveguide. Figure 1b also shows the typical failure of spin coated thin polymer film where it is peeling out from the silicon substrate. Therefore, it is very clear that the adhesion issue determines the M. A. Uddin  W. F. Ho  H. P. Chan (&) Optoelectronics Research Center & Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Kowloon, Hong Kong e-mail: eehpchan@cityu.edu.hk 123 J Mater Sci: Mater Electron (2007) 18:655–663 DOI 10.1007/s10854-007-9118-7