Analysis of film residual stress on a of 4-point bend test for thin film adhesion
- PDF / 149,564 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 266 Views
O4.18.1
Analysis of film residual stress on a of 4-point bend test for thin film adhesion Sassan Roham, Timothy Hight Dept. of Mechanical Engineering Santa Clara University, Santa Clara, CA. ABSTRACT The four-point bend (4PB) test has emerged as a method of choice in semiconductor industry for obtaining bimaterial interface adhesion data. When measuring the interface adhesion using 4PB test, it is essential to obtain a crack through the interface of interest. The deposited films, however, posses intrinsic and extrinsic stresses which affect the ratio between energy release rates for interface cracking and crack penetration. Crack penetration and deflection at a bimaterial interface and the role of residual stress has been broadly studied before. However, the results are based on asymptotic analysis regarding interface between two semi-infinite half spaces, where the results do not directly account for boundary conditions and finite size effects of an actual test specimen. In this paper, we look at the role these residual stresses play on the competition between deflection and penetration energy release rates of a bimaterial interface and the extent of which the previous assumption of two semi-infinite media can be accepted. INTRODUCTION In current IC devices, interfacial adhesion of a bimaterial interface is a key reliability issue of the system. During manufacturing, operation or deposition, intrinsic and extrinsic stresses imposed on multiplayer films can cause degradation, delamination and ultimately failure of the device. Many tests have been developed that measure the adhesion energy of a bimaterial interface. Several articles have reviewed these test methods and detailed discussions are presented regarding mechanics of thin films, interface adhesion and advantages and disadvantages of each test. The most recent article is by Volinsky et al., [1], where they review adhesion tests based on their classifications and discuss some theoretical models. Bagchi & Evans, [2], also review several of these test methods, stating their respective advantages and disadvantages. In this paper, we first discuss the theoretical framework for calculating the stress intensity factors for this test configuration. This is followed by a discussion on the role of residual stress on interface crack penetration and crack deflection at a bimaterial interface. Finally, we present the results from the literature and put our work in a suitable viewpoint with concluding remarks. BACKGROUND A typical 4PB specimen is shown in Figure 1a. In a 4PB test configuration a vertical pre-crack is notched on the top substrate. During initial loading of the specimen, the notch breaks placing the vertical crack past the top substrate. A desired crack configuration is when the vertical crack deflects along the interface of the film stack. Figure 1b) shows a typical 4PB film stack, which is the subject of the study here. The interface critical energy release rate, Gc, is the energy per unit increase in crack area required to fracture the interface thereby
Data Loading...
