Research on Effects of Slurry Additives in Cu CMP for ULSI Manufacturing

In this paper, in order to analyze the oxidation, dissolution and corrosive inhibition effects of additives in the slurry for copper Chemical-mechanical polishing(CMP), the slurry(pH5) with the peroxide as an oxidant, the citric acid as a complexing agent and the benzotriazole(BTA) as an inhibitor is studied. The static etching rate and polishing rate of the Cu-H2O2-Citric acid-BTA slurry are measured. The electrochemical behavior involved in the dissolution and corrosive inhibition of copper in the solutions containing additives is investigated by the electrochemical impedance spectroscopy (EIS) studies. The surface roughness is measured using ZYGO 3-D surface profiler. It is observed that when the slurry is with only 5wt% peroxide existing, copper is stable and slight etching rate on the copper is produced, and the etching rate is only 8.7nm/min. When 0.6wt% citric acid presents after adding 5wt% hydrogen peroxide, the etching rate will increase by 5.3 times, with a blue complexing product emerging. When the inhibitor BTA is added, the corrosion will be effectively restrained. From the EIS results, the impedance of copper in 5wt% peroxide solution which is in passivation can be greatly decreased by adding the citric acid as a complexing reagent. And the impedance of copper in the solution containing peroxide and citric acid can be increased by the addition of BTA. The surface roughness of the wafer polished with the slurry of 5wt% peroxide+0.6wt% citric acid+0.12wt% BTA slurry is Ra 4.7 Å.

Removal of TaN/Ta Barrier with Variable Selectivity to Copper and TEOS

Highly selective 2nd step copper slurries developed by Rodel have efficient barrier (TaN) polishing rates at extremely low down force (1000 Å/min at one psi, and 2000 Å/min at 3 psi). Removal rates of dielectrics (TEOS or low k CDO) can be independently adjusted from zero to nearly any designed value and copper removal rates can be independently controlled from 20 to 500 Å /min, while maintaining the high barrier removal rates. In addition, zero loss of low-k dielectric capping layers has been demonstrated, and zero loss of high metal density (90%) domain of pattern wafers with 30 seconds overpolishing has been demonstrated. Experiments also show that the high selectivity is a true CMP effect and not due to static etching.