Research On Reliability Problems Of Copper/low K Interconnects

The main purpose of this article is to study the reliability of copper/low-k interconnects, especially on Electromigration and Stress-migration failure. The test method and failure mechanism of Electromigration were studied, and effective methods to improve the electromigration reliability were discussed. Finite Element Analysis was used to study residual stress in Cu interconnects, different structures including various via diameter, line width, residual length, and dielectric material were investigated to analyze structural effects on residual stress. Stress-induced voiding test of Cu interconnects had been done to observe the voiding location. Stress-induced voiding failure in Cu interconnects with different via diameter was studied. The voiding mechanism and the effect of via size on stress migration had been studied.The results indicated that the Cu/dielectric interface was the fastest diffusion path, improving the interface characteristic can effectively depress Electromigration failure. Residual stress reached the maximum value inside the via, and stress gradient achieved the peak value in lower metal line under the corner of the via. Residual stress decreased as the via diameter or the dielectric constant of ILD decreasing, and increased as the line width or the residual length decreasing. Stress gradient decreased as the via diameter, the dielectric constant of ILD or the residual length decreasing, and increased as the line width increasing. The vacancies diffused in the direction of the stress gradient and nucleate at the peak value of the stress gradient. The voiding rate was co-determined by the stress and the stress gradient.