Ming-Shih Tsai

Effect of Surface Passivation Removal on Planarization Efficiency in Cu Abrasive-Free Polishing

Selective removal of surface passivation on protruded Cu film is a critical factor of Cu planarization. For a stress-free Cu abrasive-free polishing (Cu AFP) process, due to the lack of mechanical abrasion by abrasives, apolishing pad is used instead of abrasives to remove surface passivation during Cu planarization. Thus, the planarization efficiency in Cu AFP relates to the efficiency of surface passivation removed by a pad. Comparing Cu oxides with a non-native Cu-BTA (Cu-Benzotriazole) monolayer used as surface passivation, this study found that an oxide-free Cu surface should be required in Cu AFP. When Cu oxides function as surface passivation in Cu AFP, they are removed with greater difficulty by a pad resulting in low planarization efficiency. Contrary to Cu oxides, high planarization efficiency can be obtained with non-native Cu-BTA as surface passivation in Cu AFP.

The removal selectivity of titanium and aluminum in chemical mechanical planarization

The removal selectivity control of aluminum and titanium metal barrier during aluminum chemical mechanical polishing in the Damascene process is known to be critical for surface planarity without metal dishing and dielectric erosion. Unfortunately, the electrochemical behaviors of aluminum and titanium are dissimilar, as one may expect. In this study, in situ electrochemical impedance spectroscopy was carried out to investigate the influences of H 2 O 2 concentration, slurry pH, and metal oxide formation through the passivation on aluminum and titanium. As H 2 O 2 concentration increases, the measured impedance of aluminum and titanium decreases, or the oxidation rates of these two metals are enhanced upon increasing the oxidizer concentration. As the slurry pH increases, the removal rate of polished titanium increases, but it decreases for polished aluminum. The removal rate of titanium was limited to its oxidation rate and aluminum was limited to its oxide dissolution rate.

Study on Pressure–Independent Cu Removal in Cu Abrasive–Free Polishing

Pattern effect, a critical issue in metal planarization, results from different pattern designs bringing a variation of effective local pressure. In order to optimize the pattern effect in Cu planarization, Cu removal should be pressure independent. Recently, it was found that Cu abrasive-free polishing (AFP) technology could benefit pressure-independent Cu removal for Cu planarization by controlling the down force. In this study, by using 5-methyl-lH-benzotriazole as a corrosion inhibitor, pressure-independent Cu removal with AFP slurries can be achieved below a 3 psi down force. Thus, the pattern effect in Cu planarization can be optimized with AFP slurries by low down force.

Electrochemical behavior of copper chemical mechanical polishing in KIO3 slurry

The electrochemical behavior of polishing copper with colloidal silica abrasive slurry formulated with KIO3 oxidizer has been investigated. For planarization of the surface morphology, the control of the surface passivation of Cu is critical during polishing. KIO3 is not only an oxidizer but also a passivator for copper in an acidic slurry by forming a CuI layer on the surface. With alkaline slurry, Cu2O is the primary corrosion product on the Cu surface. The copper corrosion rate and removal rate can be decreased dramatically with increasing slurry pH. The low corrosion resistance or high corrosion susceptibility of Cu as determined by electrochemical measurements is the basis for the high removal rates. The copper removal rate is reduced from 4600 to 650 A/min when the slurry pH is increased from 2 to 5; and the copper removal rate levels off at pH 7 with a steady-state removal rate of 200 A/min.

CMP of polyimide for low-k dielectric application in ULSI

Polyimide CMP is investigated for its feasibility in IMD planarization applications. The polish rates of polyimide are found to be heavily dependent upon the degree of imidization and hydroxyl activity in silica-based alkaline slurry. TMAH, tetra-methyl-ammonium hydroxide, added into the slurry enhances the removal rate of polyimide due to the improved wettability on the hydrophobic polyimide surface. Surface planarity is degraded during CMP, but can be significantly improved by a curing after CMP. By means of bias-temperature-stress analysis, it is found that mobile ions, like K/sup +/ and Na/sup +/, do not diffuse into the bulk of the polished film. Dielectric constant and leakage current density of polyimide being polished do not deteriorate, indicating polyimide directly capped with an oxide layer is promising for use as IMDs.