In this paper, we use a variety of analytical techniques to examine the impact of local chemistry, and the mechanical properties, of the encapsulation dielectric films on the post-packaging device rejection rate of integrated circuit devices. A strong dependence of lot rejection rate (LRR) on the effective Young's modulus of the encapsulating dielectric stack is demonstrated; specifically, the device fall out rate increases with increasing Young's modulus. The local concentration of silanol (SiOH) in the encapsulating silicon oxide is found to significantly influence its Youngs modulus values. The increase in LRR with increasing stiffness of the encapsulating layer is attributed to the increase of thermal stress in the metal lines due to their increased constraint. This stems from the strong adhesion of the encapsulating dielectric material to the metal, thus fixing the loci of the surface planes of the metal, which could result in mechanical damage through voiding and delamination.
Citation: Microelectronics Reliability
Pub Type: Journals