A four-point bending technique for studying subcritical crack growth in thin films and at interfaces
- PDF / 204,230 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 82 Downloads / 199 Views
MATERIALS RESEARCH
Welcome
Comments
Help
A four-point bending technique for studying subcritical crack growth in thin films and at interfaces Qing Ma Intel Corporation, Santa Clara, California 95052 (Received 8 April 1996; accepted 11 November 1996)
A technique was developed to obtain the subcritical crack growth velocity in a 4-point bending sample by analyzing the load-displacement curve. This was based on the observation that the compliance of a beam increases as the crack grows. Beam theory was used to analyze the general configuration where two cracks propagated in the opposite directions. A simple equation relating the crack velocity to the load and displacement was established, taking advantage of the fact that the compliance was linearly proportional to the crack lengths; thus the absolute crack length was not important. Two methods of obtaining crack velocity as a function of load were demonstrated. First, by analyzing a load-displacement curve, a corresponding velocity curve was obtained. Second, by changing the displacement rate and measuring the corresponding plateau load, a velocity value was calculated for each plateau load. While the former was capable of obtaining the dependence of crack velocity versus load from a single test, the latter was found to be simpler and more consistent. Applications were made to a CVD SiO2 system. In both cases of crack propagation either inside the SiO2 layer or along its interface with a TiN layer, the crack growth velocity changed with the stress intensity at the crack tip exponentially. As a result, a small crack will grow larger under essentially any tensile stresses typically existing in devices, provided that chemical agents facilitating stress corrosion mechanisms are also present.
I. INTRODUCTION
As multilevel interconnect technology enabled ever more complicated integrated circuits and ever more powerful computer chips, it also brought with it a new set of reliability problems, which include interfacial delamination as an important failure mode. Such fracture-related processes often occur over an extended period of time, indicating subcritical crack growth mechanisms in operation. Slow crack growth mechanisms include fatigue due to thermal/electrical cycling and stress corrosion due to moisture and other chemical species. Stress corrosion mechanism is well known in silicate glasses1 and therefore is of particular importance for SiO2 based thin films, which are commonly used as dielectric layers in interconnect structures as illustrated in Fig. 1. This is true even when the crack is insulated from the ambient, because most CVD deposited SiO2 films contain a significant amount of water. It is therefore important to study slow crack growth characteristics for these materials and interfaces. The difficulties of such studies rise from the fact that these materials are available only in the form of thin films, rendering most traditional methodologies used for bulk materials inapplicable and requiring the development of new techniques suitable for thin films a
Data Loading...
