Study On The Test Bench And Electrolyte Of Copper Interconnection Layer ECMP

With the development of Ultra Large Scale Integrated Circuit (ULSI), the feature size of chip is decreasing, so the RC delay becomes the vital problem which will affect the processing speed of the chip. To decrease the RC delay, Cu is used as the metal material of interconnection to decrease the resistivity instead of Al, and Low-k material is used as interlayer dielectric to decrease barrier capacitance instead of SiO2. However, the introduction of Low-k material challenges for Chemical Mechanical Polishing (CMP), because the pressure of CMP is so large that Low-k material can't withstand. In this paper, an electrolyte with high-k abrasive is proposed, a copper Electro-Chemical Mechanical Polishing (ECMP) comprehensive simulated test bed is established, and the Cu-ECMP process is researched.A Cu-ECMP comprehensive simulated test bench is designed firstly, which has three kinds of motion form, such as the rotation of work piece, the rotation of polishing head, and linear motion of polishing head, and has the function of electrochemical testing. For satisfying the requirement of low pressure(<2.5psi), handle, micrometer, connecting rod, pull rod, ball bushing, compression spring and other parts are connected to impose the polishing pressure, and the polishing pressure can be exactly adjusted from 1psi to 2.5psi.Secondly, the electrolyte of Cu-ECMP is researched in-depth. Both testing Tafel polarization curve and static etch experiment are used, glycine is chosen to be the complexing agent in the electrolyte, because its corrosion potential is lowest and static etch rate is highest among of citric acid, glycine and acetic acid; TSA is chosen as the inhibitor in the electrolyte, because its static etch rate is highest, and inhibitory effect is best among of TSA, BTA, and ADS. By Cu-ECMP experiment, rutile TiO2 with high dielectric constant is chosen as the abrasive among of rutile TiO2, anatase TiO2, and SiO2. The single-factor polishing experiment is used to optimum seek the content of electrolyte, the result is that 100ml electrolyte contains 0.05M glycine,0.01M TSA, and 1g rutile TiO2.Finally, the process parameters in Cu-ECMP are studied by orthogonal experiment, a group of optimized parameters is obtained:the speed of polishing head is 200r/min, the speed of work piece is 200r/min, the polishing pressure is 1.5psi, and the polishing time is 30min. In Cu-ECMP, the material removal rate of the copper is 0.06mg/min, the surface roughness Ra of the copper reaches 8.9nm by optimization of electrolyte and process parameters.