Electromigration Study of Cu Dual-damascene Interconnects with a CVD MSQ Low k Dielectric
- PDF / 690,283 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 104 Downloads / 249 Views
E1.9.1
Electromigration Study of Cu Dual-damascene Interconnects with a CVD MSQ Low k Dielectric Xia Lu, Ki-Don Lee, Sean Yoon, Hideki Matsuhashi1, Michael Lu2, Kai Zhang2, and Paul S. Ho Microelectronics Research Center, The University of Texas at Austin, Austin, TX 78712 1 PDF Solutions, Inc., San Jose, CA 95110 2 LSI Logic Corporation, Santa Clara, CA 95054 ABSTRACT Electromigration reliability in Cu dual-damascene interconnects with a CVD MSQ low k dielectric was investigated. Statistical studies were carried out using the critical length (LC) test structures containing multi-link line/via elements with varying line lengths. EM lifetime characteristics, critical current density-length product (jL)c, and failure mechanisms were discussed and compared with Cu/oxide structures. Our results suggested that the diffusion at the cap layer interface was the dominant mechanism for EM mass transport. The confinement effect, in terms of an effective modulus B, can be used to account for the shorter EM lifetime and smaller critical current density-length product (jL)c observed for Cu/CVD MSQ low k interconnects. Failure analysis by FIB confirmed the presence of multiple failure modes including voiding at the via bottom, Cu extrusion and delamination at Cu / cap layer interface.
INTRODUCTION Electromigration (EM) is a major reliability concern for on-chip interconnects [1, 2]. It arises from the mass transport of diffusing metal atoms under the influence of an electric current. Under EM, a back stress is generated due to mass accumulation at the anode end of an interconnect line. This leads to a stress gradient driving mass transport opposite to the EM flux, reducing the net mass transport by a back-stress flow. This EM-induced stress evolution, as well as the driving force of the electric current, governs the EM reliability of the interconnect structures. Korhonen et al. [3] proposed a model on stress evolution due to electromigration in Al/SiO2 interconnects. The implementation of low k interlevel dielectrics (ILD) significantly alters the EM-induced stress buildup in interconnects. Low k materials are often polymer-based, and are mechanically much softer, expand more and conduct less heat compared with traditional SiO2based materials. The weaker thermomechanical properties have caused significant concerns on EM reliability of Cu/low k interconnects and generated considerable interests recently. A recent analysis by Hau-Riege et al. [4] on stress evolution in the Cu dual-damascene structures showed that the mechanical properties of low k dielectrics have less of an adverse effect on interconnect reliability than we expected. That is due to the reinforcement of low k dielectrics by the surrounding barrier and cap layers. The goal of this paper is to investigate how the thermomechanical confinement impacts the EM lifetime characteristics and the critical current density-length product (jL)c in a Cu/CVD MSQ low k interconnect.
Downloaded from https://www.cambridge.org/core. La Trobe University, on 20 Jun 2020 at 12:45:14,
Data Loading...
