Research On The Optimization And Mechanism Of Copper Electrochemical Mechanical Planarization

Global Planarization is a key process in the fabrication of Integrated Circuits (IC) wafers, because it can provide more interconnect layers and guarantee high speed data transmission. With the application of Cu/low k interconnect, the conventional Chemical Mechanical Planarization (CMP) technology can no longer meet the need to fabricate next generation IC, because during CMP process, the large downforce may cause problems suche as damage to low k material and dishing effect. The novel Electrochemical Mechanical Planarization (ECMP) technology combines electrochemical and mechanical effects, remove copper with high rate under small downforce. Because the Material Removal Rate (MRR) during ECMP process is directly controlled by applied voltage, not by downforce, ECMP can achieve high MRR and do no damage to the low k material. ECMP has great application prospect.In this study, ECMP experiments are conducted on a remolded pin-on-disk friction and wear tester, with a three-electrode system; a method to optimize the experimental parameters is proposed. First, the elctro-chemical properties of copper is studied using Linear Sweep Voltammetry(LSV) and Chronoamperometry in various electrolytes including H₃PO₄, KOH, KH₂PO₄, K₂HPO₄ and K₃PO₄ with different concentrations of BTA. Based on anodic current, MRR and inhibit efficiency, experiment conditions such as electrolyte and a range of voltage can be optimized. Under such conditions, subsequent ECMP experiments are carried out. According to the results of ECMP experiments, the condition of 0.5V in 30%H3PO4+0.01M BTA is optimized. The influences of voltage, load and rotation rate on MRR is also studied.In the standard contact mode of Atomic Force Microscopy (AFM), the surface morphologies of copper after ECMP are studied, and the influence of voltage on post ECMP copper surface is analyzed. To further investigate the properties of Cu-BTA film, static elctro-chemical treatment in a polytetrafluoroethylene electro-chemical cell is applied to a better defined copper surface which is achieved through polishing with micro diamond grinds. The morphologies of copper surface after elctro-chemical treatemtn are examined by AFM. The formation and exsistence condition of Cu-BTA film are studied. The electrochemical mechanism during ECMP process is explained in a molecular scale.