Finite Element Analysis of the Precracked Line Scratch Test
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Finite Element Analysis Of The Precracked Line Scratch Test A.A. Volinsky*, L. Mercado*, V. Sarihan*, and W.W. Gerberich** Motorola, Digital DNATM Labs, Semiconductor Product Sector, AZ ** University of Minnesota, Dept. of Chem. Eng. and Materials Science, Minneapolis, MN. *
ABSTRACT In MEMS packages and silicon devices, the adhesion of interconnects to the substrate is a critical reliability issue. A Precracked Line Scratch Test (PLST) is among one of the available tests to measure the thin line adhesion. In the test, an initial crack is introduced at the interface between the thin line and the substrate. The line is then loaded from the precracked end. The load is recorded continuously while the crack propagates before and after the line buckles. This precracked line scratch test has been applied earlier to tungsten thin lines on silicon wafers [1]. A macroscopic version of the test was also performed to evaluate the analytical model [2]. In the macroscopic tests, polycarbonate lines were bonded to steel substrates with cyanoacrylate. In this paper, finite element analysis is performed for the Precracked Line Scratch Test before line buckling. The energy release rates and phase angles are calculated based on the corresponding load and crack length. The results are then compared to the closed-form solution. Macroscopic experimental model along with the finite element solution has provided a way to derive the interface fracture toughness as a function of the crack length based on the load and crack length history. With the analysis in place, the precracked line scratch test can be used conveniently to study the adhesion of interconnects to passivation layers, MEMS devices and packages on different scales. INTRODUCTION Thin film adhesion is a very important property not only for the microelectronics and magnetic recording industries, but also for emerging technologies such as data transmission through optical switches dependent on microelectromechanical systems (MEMS). Films that adhere well to the substrate are desired. However, spontaneous delamination may occur due to crack growth between thin film and the substrate. This paper considers the Precracked Line Scratch Test (PLST) for quantitatively measuring the practical work of adhesion of thin interconnect lines. The technique is extremely useful since it is applied to the as-deposited, as-processed lines, without changing the interfacial chemistry and film microstructure/properties. Most qualitative adhesion tests empirically infer the adhesive strength by subjecting the specimen to some external load and measuring the critical value at which it fails [3]. While still useful for routine quality control, these tests do not measure the interface fracture toughness Γi, since the strain energy release rate usually can’t be deconvoluted from the work of the external load. There are several qualitative adhesion tests such as the scotch tape or the peel test [4, 5]. These tests are usually easy and fast to perform, but they do not provide accurate values of adhesion. I
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