Thermo-Elastic Analysis Of Air-Gap Copper Interconnects

The performance of very large-scale integration (VLSI) chips is limited increasingly by interconnects, as critical dimension shrinks. To further reduce the RC delay, air-gap Copper interconnect structure was introduced by IBM, using air gap as dielectric between metal lines, who has the lowest dielectric constant. Current research indicated this interconnect structures could not only greatly reduce the interconnect capacitance, but also improve the leakage current and the time-dependent dielectric breakdown characteristic. Thermo-elastic stress is a very important factor that influences the reliability of Copper interconnects. The high stresses in interconnect structures would bring in adhesion or cohesive failures, and probably lead to electro-migration or stress voiding. Therefore, doing thermo-elastic analysis of Air-gap Cooper interconnects becomes a very pivotal task for the evaluation of reliability, due to its complex processes and unstable structure.This paper presents a thermo-elastic analysis focusing on stresses and deformations induced on Air-gap Copper interconnect structures.First and foremost, a series of Air-gap Cooper interconnect finite element model with different pitches was built based on Hitachi's experimental results. Then made an analysis of stress and deformation of Air-gap Copper interconnects during fabrication according to Hitachi air-gap process flow, and also compared them between models with various pitch and full-filled Copper interconnect model. At last, the defects and potential reliability problem of Air-gap Copper interconnects were predicted from analysis results.Taking the effect of joule heat on Air-gap Copper interconnects into account, the dependence of temperature and stress of Air Copper interconnect structures on current density and thermal boundary condition was simulated. Then compared the differences in thermo-elastic stress of the same Air-gap Copper interconnects under different temperature. And also evaluate the dependence of thermo-elastic stress on the shape of air gap under the same temperature.