Reflow Phenomenon Analysis of Large Scale Integrated Cu Interconnections in Via Holes by Viscoelastic Deformation Simulation

Abstract

The reflow phenomenon of Cu interconnections deposited over via holes was analyzed by viscoelastic deformation simulation using a finite-element method to clarify the embedding mechanism of Cu interconnections into via holes in a novel dual-damascene fabrication technology, which combined sputter deposition and high-pressure annealing. Cu is considered to be a viscoelastic body, and the stress distribution and deformation behavior of Cu interconnections were calculated. As a result, the deformation behavior of the Cu interconnections exhibited close agreement between the calculated and the observed values. From our series of results, we inferred that Cu interconnections are embedded into via holes by the creep deformation mechanism defined in this study during the high-pressure annealing process.

A Study of Difference in Reflow Characteristics Between Electroplated and Sputtered Cu in a Dual-Damascene Fabrication Process for Silicon Semiconductor Devices

“…The use of the sputtered Cu films may not be practical considering the maximum tolerable temperature for low-k dielectrics. The filling performance of sputtered Cu films can be improved by increasing the pressure applied during high-pressure high-temperature treatment, 24 but an upper limit to the pressure is 200 MPa because of the restrictions in the high-pressure annealing system. 13 Therefore, the following means seems to be effective in order to improve the reflow characteristics of the sputtered Cu films to realize the novel dualdamascene fabrication technology: (1) increasing the vacancy concentration in Cu films, and (2) decreasing the temperature at which defect components, i.e., vacancies or dislocations, begin to be restored.…”

“…22,23 It has been shown that Cu films deposited in vias or trenches are embedded in them through the mechanism of creep deformation during the highpressure annealing process. 24 In this case, the dominant plastic deformation mechanism is apparently core diffusion creep or Coble creep. 25 Therefore, the difference in filling performance between electroplated and sputtered Cu films may be strongly influenced by defects, such as vacancies, grain boundaries, stacking faults, etc., which control core diffusion creep and Coble creep.…”