Effect of Thermal Degradation on the Adhesion of Polyimide/Silicon Interface
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EFFECT OF THERMAL DEGRADATION ON THE ADHESION OF POLYIMIDE/SILICON INTERFACE Y Z. CHU AND C. J. DURNING Department of Chemical Engineering and Materials Science, Columbia University, New York, NY 10027 ABSTRACT The object of this work is to identify the most important structure features in the bonding of polyimide/silicon during the curing and degradation. An essential tool for this work is a quantitative adhesion measurement which can relate the macroscopic adhesion strength to the microscopic interfacial structures. We apply the blister test for this purpose. In particular, the test is applied to examine the effect of thermal history on the adhesion of PMDA-ODA polyimide on silicon surface. Our studies show that the test is accurate and sensitive. The adhesion data reveal that increases in adhesion strength coincide with the formation of certain thermal degradation products as revealed in the earlier thermal degradation studies. This suggests a mechanism for increases in adhesion strength with curing temperature, based on chemical and physical modification of the interface. INTRODUCTION Polyimides have become the most important class of organic materials in modern microelectronics applications[1]. They are usually employed as thin films. The interfacial mechanical strength of polyimide to a variety of substrates is critical. A comprehensive understanding of the relationship between the physical and chemical structure of the interfaces and their mechanical strength is of great concern. A variety of state-of-the-art techniques have been used to study the interface structures of polyimide/substrate junctions. X-ray photoelectron spectroscopy (XPS) [2-7] and ultraviolet photoelectron spectroscopy (UPS) [3-8] have been used to provide information on the nature of chemical stuctures at the interface. These microscopic properties must be correlated with macroscopic mechanical properties which represent fundamental and/or technological figures of merit for judging the quality of the interfacial bonding. This correlation, which is necessary for understanding the mechanisms of adhesion, needs sensitive and accurate methods for measuring the adhesion strength, i.e., the adhesion energy of the interface. So far, such correlations have not yet been established mainly because of a lack of reliable adhesion data. The object of this work is to identify the most important structure features in the adhesion of PMDA-ODA polyimide to silicon during curing and degradation. We apply the blister test for this purpose. Our prevoius studies [9-11] proved that the reproducibility and sensitivity of the test is exceptionally good. In what follows we describe the application of the test to examine the effect of thermal history on the adhesion of PMDA-ODA polyimide on silicon surface.
Mat. Res. Soc. Symp. Proc. Vol. 282. 01993 Materials Research Society
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EXPERIMENTAL Material The polyimide investigated was pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide, formed from a polyamic acid solution (PI-2540, Du Pont). The resulting
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