Edge Delamination Testing: A Method for Measuring the Adhesion of Thin-film Coatings in Microelectronic Applications Par
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Edge Delamination Testing: A Method for Measuring the Adhesion of Thin-Film Coatings in Microelectronic Applications Part 1: Numerical Analysis and Preliminary Results EDWARD 0. SHAFFER II, FREDERICK J. MCGARRY AND FRED TRUSELL Massachusetts Institute of Technology Materials Science and Engineering Department, 8-209 77 Massachusetts Ave. Cambridge, MA Abstract We propose a new test to measure the adhesion of thin polymeric coatings used in microelectronic applications. Similar to previous tests [1-3], the edge delamination test (EDT) takes advantage of the thermal residual stress present in the coating to induce delamination. However, in the EDT, we take advantage of lithography to fabricate test geometries that probe a complete range of debond energies. As a result, nearly a hundred adhesion tests can be performed on a single wafer. In this report, we apply finite element analysis to assess the debond energy generated at the coating/substrate interface to determine the feasibility of the test. The analysis also quantifies the effect of various geometries and boundary conditions. We apply the EDT to study the adhesion of Cyclotene TM 3022 polymer to silicon coated with evaporated aluminum. The critical mode I strain energy release rate for the Cyclotene/Aluminum interface with no adhesion promoter is 10.5±0.2 Jim2 . Introduction Polymeric coatings are increasingly being used as interlayer dielectric materials in several electronic applications because of ease of processing, smooth planarization and low dielectric constant. Specifically, thin-film polymeric coatings are used in high density interconnects or multichip modules (MCM) as passivation layers. However, due to large thermal expansion mismatches between the polymer and other constituent materials large residual stresses develop in the electronic parts. Notably, these residual stresses can lead to peeling failures between the various interfaces in the electronic part. The origin of adhesive or cohesive failure is the residual thermal stress that is generated in the film during fabrication of the MCM. These residual stresses can be calculated using numerical methods such as finite element analysis. However, to assess the reliability of a given MCM design, one must have a measurable failure criterion to compare the calculated maximum stresses. Such criteria can be based on the ultimate strength of the constituent materials for cohesive failure, or, critical debond energies between the different materials for adhesive failure. Available in the literature are numerous methods for measuring adhesive strengths.[4] In particular, peel tests [5] and blister tests [6] are predominately used for measuring the adhesion of thin coatings in electronic applications. More recent modifications to blister tests include the island blister test.[7] However, the difficulty with these methods is that load is transferred to the interface through tensile loading of the films. As a result, it is difticult to separate from the measured work that which was used to propagate a debond a
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