The Study On The Reliability And Failure Mechanism Of Copper Interconnection In VDSM

An amount of research is carried on the major reliability problems of copper (Cu) interconnect system based on the theory study, emulation and experiment in this paper. We are devoted to resolve the reliability issues of the copper interconnect system, when the dimension of interconnect line become shrinking gradually.The deeply study is carried out on the phenomenon of Cu interconnect electromigration (EM) failure through the comparison with the technology and the reliability issues of aluminum interconnect system. The mechanism of EM of Cu interconnect is analyzed in detail. A physical model of the mass transport of Cu interconnect is found based on the vacancy exchange mechanism. The numerical result of this model is accord with the data showed in literature and the experimental data. An amount of EM accelerated failure tests are operated on the samples in order to study the EM character of Cu interconnect on the condition of different stress and different lines width. A phenomenon is found through the experiment and the model that the voids grow and agglomerate along the interface of Cu and cap dielectric and concentrate at cathode end of the line. The work shows, the EM failure mechanism of Cu interconnect is changed when the dimension beyond the 90nm/65nm. The interface diffusion has become an important failure mechanism. Because of the high aspect ratio, via will endure high stress, which lead it is easy to fail with EM. Three different structures of via are proposed. The emulations and failure tests are implemented with on the structures. The EM characters of the structures are evaluated through the result of the experiments and emulations. The via structures with better EM character are proposed, which are instructive to the design of the Cu interconnect system. It is helpful to improve the reliability of Cu interconnect system.A continuity equation on Cu+ diffusion and the analytical resolution of the time-dependent dielectric breakdown (TDDB) lifetime is obtained based on the research of TDDB failure mechanism. Subsequently, the TDDB lifetime evaluated model is found. The comparison between the model and literature shows that the simulation result is accord with the experiment data excellently(deviation<10%) at high electric field(beyond 6MV/cm)and small line space (100nm) on the condition of different temperature, current density and line spaces. The electrical characters of interconnect lines with different line space and width are simulated with the ISE. The TDDB failure tests are operated on interconnect samples. The results of simulation and experiment show that the electric field between interconnect lines get stronger with the reduction of the line spaces. In addition, a new effect named fine line effect is found. In this phenomenon, the electric field on the lines will become stronger with the reduction of the line width, when the line width is close to the line space. The results about TDDB of this paper show that the line space will be an important factor, which shortens the line's TDDB lifetime because of the stronger electric field between the lines or the fine line effect, when it is less than 200nm. It will induce serious TDDB failure and the reliability of Cu interconnect system if the reduction of line space is neglected. Finally, a serious measurements are propose to improve the TDDB failure of Cu interconnect system.