Study On The Electrolyte For Electrochemical Mechanical Polishing Of Copper Used In IC

With development of Ultra Large Scale Integration (ULSI), layers are deeply increased and line width is narrower and narrower. These factors result in RC delay which becomes the vital problem affecting the processing speed of a chip. The common way to solve this problem is to use Low-k material as interlayer dielectric instead of SiO2. In order to reduce permittivity K, We usually increase the porosity of Low-k material. While the more the porosity, the lower the permittivity K value, but mechanical strength of Low-k material will greatly be weakened. The introduction of Low-k material challenges Chemical Mechanical Polishing (CMP), whose pressure is so large that Low-k material can not withstand. A novel method, Electro-Chemical Mechanical Polishing (ECMP), comes out, with low pressure and high efficiency.At first, experiment plan is determined, which includes grinding and polishing as well as measurement of surface roughness and material removal rate. The purity of99.99%copper specimen is used instead of Cu/Si wafer. Copper films are abraded by grinding and CMP before ECMP experiment. After abrading, copper films get better surface quality. Orthogonal experiment is used to determine the process parameters of grinding and CMP.Tafel polarization curve, static etch and electrochemical impedance spectroscopy (EIS) are tested to study inhibition effect of different inhibitors. Comparisons of these results prove PTA is a good inhibitor for Cu-ECMP and Cu-ECMP effect of it is much better than of BTA. Polishing machine is meliorated and tested with lowest polishing roughness (Ra)5.8nm’and material removal rate (MRR)0.045mg/min under0.2V. Finally pH’s influence of electrolyte is studied. With H2SO4and NaOH as pH regulator, polarization curve, EIS and polishing tests of pH=2,4,6,8and10are measured. Polishing tests are done under pH=6with acetic acid and pH=8with ethylenediamine as pH regulator, compared to the earlier tests with H2SO4and NaOH. The best surface roughness with Ra4.9nm and MRR of0.020mg/min under0.8V, pH=6using acetic acid is reached, as well as much bigger material removal rate of0.193mg/min with Ra10.1nm under0.4V, pH=6using acetic acid.