Application of Monte Carlo Simulation to Nanoelectronics

I-11: A New Understanding of Electromigration Induced Void Nucleation, Growth, and Movement in Cu Interconnects

1: S. G. Mhaisalkar,
1 and 3: A. Guask,
2: A. Krishnamoorthy, and
1,2: A. V. Vairagar
  1. School of Materials Science & Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798
  2. Semiconductor Process Technologies – Advanced Interconnect, Institute of Microelectronics, 11 Science Park Road, Singapore 117685
  3. Cherkasy National University,Cherkasy 18017, Ukraine *email: subodh@ntu.edu.sg, Ph. +65-6790-5793 Fax: +65-6790-9081

Abstract
In sub-micron damascene Cu interconnects, the dominant role of interfacial diffusion at the Cu/dielectric cap interface is widely accepted. Thus the role of the interfacial structure, composition, adhesion, is expected to play a significant role in determining the electromigration lifetime of the advanced interconnects. However, the inter-relationship of all these factors, materials, processes, and the dual damascene architecture on the void nucleation, growth, and eventual failure is still far from understood. In this study the effect of reducing, inert, and reactive gas treatments so as to induce compositional changes at the interface as well as different cap layers including silicon carbides, nitrides and their variants were studied. Upper and lower level test structures were subjected to different treatments after CMP and the electromigration performance was assessed on the package level. In untreated samples, the asymmetry of the test structures leads to higher MTFs for the upper layer test structures; however it was determined that upon surface treatments, the MTFs of lower layer test structures showed a 2x improvement and could achieve lifetimes comparable to the upper layer test structures. The role of the interfacial composition and microstructure on this improvement was studied through TEM and XPS and the role of interfacial adhesion was studied using four point adhesion tests and nano scratch tests. In order to completely characterize the effect of the interface on electromigration and to determine the nature of void nucleation, growth, and void migration; in-situ SEM electromigration experiments were carried out and the observed results indicate that the void formation is controlled through heterogeneous nucleation at the interface.