Chi-Cheng Hung

Bis-(3-sodiumsulfopropyl disulfide) Decomposition with Cathodic Current Flowing in a Copper-Electroplating Bath

The composition of the plating electrolyte is important in a copper (Cu) electroplating process. The consumption rate of bis(3-sodiumsulfopropyl disulfide) (SPS) has a strong correlation with the electroplating current density. The decomposition of SPS is relative to the electroplating charge and to the age of the Cu anode. The cathodic current density improves SPS breakdown, and it increases the generation of by-products resulting from SPS decomposition. The aged bath is examined using potentiodynamic polarization and electrochemical impedance spectroscopy. The aged bath helps increase cupric ion reduction because the concentration of cupric ions increases with time after Cu electroplating. The SPS species reacted with cuprous ions to produce the Cu-accelerator complex, which increased the depolarization effect.

Galvanic Corrosion Between TaN x Barriers and Copper Seed

In semiconductor metallization processes, the galvanic corrosion of metals should be controlled to improve the process integrity. Refractory metals such as tantalum and tantalum nitride (TaN x ) are widely used as a barrier metal to prevent the copper (Cu) metal from diffusing into the dielectric layers. In this study, the galvanic effect between the Cu seed and the TaN x film, which is deposited with different nitrogen (N 2 ) gas flow rates was investigated using chemical mechanical polishing slurries. It was found that the galvanic corrosion of the TaN x films decreased whereas the galvanic corrosion of the Cu seed increased as the N 2 gas flow rate increased. The whole Cu corrosion rate was higher than that of the TaN x films because the intrinsic corrosion of the Cu seed dominated the overall Cu corrosion rate in the acidic slurry, but for the TaN x films the galvanic corrosion dominated. This study also proposed a model to reveal the galvanic effect between the Cu seed and various TaN x films.

Effect of bis-(3-sodiumsulfopropyl disulfide) byproducts on copper defects after chemical mechanical polishing

In the semiconductor metallization process, the superior gap-fill capability of copper (Cu) electroplating is mainly due to external additives, such as bis-(3-sodiumsulfopropyl disulfide) (SPS), which is used as an accelerator. This study demonstrates that the byproducts of SPS induced Cu defects after a chemical-mechanical-polishing (CMP) process. In conventional cyclic-voltammetric-stripping analysis, the byproducts generated from organic additives are very difficult to quantify. In this study, the authors used mass-spectrum analysis to quantify SPS byproducts and found that the SPS byproduct, 1,3-propanedisulfonic acid, correlated with the formation of Cu defects because it influenced the properties of electroplated Cu films and the chemical corrosion rate, then induced defects after the CMP process.

Investigation of Galvanic Corrosion Between TaN x Barriers and Copper Seed by Electrochemical Impedance Spectroscopy

In this article, electrochemical impedance spectroscopy is used to characterize the mechanism of galvanic corrosion between copper Cu seeds and tantalum nitride TaNx barriers deposited with different N2 flow rates. By way of software simulating with EIS data, an equivalent circuit is built up to explain the corrosion behavior of the TaNx films’ relation to the Cu seeds in an acidic chemical-mechanical-polishing slurry. The equivalent circuit can respond to changes in resistance and capacitance elements of the Cu‐TaNx electrochemical system. It is found that the charge-transfer resistance of the TaNx galvanic corrosion increases with the N2 flow rate, whereas the resistance of a tantalum-oxide layer is opposite because increasing the N content of the TaNx films inhibits corrosion and oxidation of the Ta metals. The result is consistent with our previous investigation that the galvanic corrosion of the TaNx films to the Cu seeds is retarded by the N element C. C. Hung, Y. S. Wang, W. H. Lee, S. C. Chang, and

Competitive Adsorption Between Bis(3-sodiumsulfopropyl disulfide) and Polyalkylene Glycols on Copper Electroplating

In semiconductor copper (Cu) metallization, external organic additives including bis(3-sodiumsulfopropyl disulfide) (SPS) and polyalkylene glycols (PAG) are necessary and widely used to improve the gap-fill capability of Cu electroplating for high-aspect-ratio features. In this study, the interaction of SPS and PAG (SPS-PAG) in the electrolytes was investigated. The results not only show the antisuppression effects of SPS in the presence of PAG, but also indicate the competitive adsorption between SPS and PAG. The proposed mechanism is that when SPS-PAG are added to a plating bath, the Cu-electroplating rate is influenced by competing adsorptions of SPS-PAG and SPS, which disperses PAG species far away from the Cu surface to enhance electroplating rates. The elements (charge-transfer resistance, adsorption-layer resistance, and inductance) of the equivalent circuit simulated using the electrochemistry-impedance spectroscopy data also demonstrate the behavior of SPS-PAG competing reactions.

Role of surface tension in copper electroplating

This study demonstrates that the surface tension of plating solutions should be optimized to achieve a compromise between the gap-filling capability of copper electroplating and the formation of copper-void defects. The plating solution with lower surface tension has better gap filling but generates more air bubbles during copper electroplating. For a low-surface-tension electrolyte, the improvement in the gap-filling capability is caused by the enhancement in the ability of fluids to wet high-aspect-ratio features, whereas the increase in the formation of copper-void defects results from more air bubbles generated during the electroplating process. This study provides a model to describe the role of surface tension in copper electroplating.

Investigation of Copper Scratches and Void Defects after Chemical Mechanical Polishing

In semiconductor metallization processes, copper metal is widely used for interconnection lines due to its low resistivity. However, various defects, such as scratches and voids, are usually formed after chemical mechanical polishing (CMP), which influences manufacturing yield because the copper metal is soft and easily corroded. In this study, our results indicate that defect formation is related to the properties of electroplated copper films. By increasing the plating current densities, the number of void defects increases while the number of scratch defects decreases after CMP. It is suggested that the increase in void defects with plating current densities is due to the increase in film tensile stress, while the decrease in scratch defects results from an increase in film hardness.

Investigation of the suppression effect of polyethylene glycol on copper electroplating by electrochemical impedance spectroscopy

Polyethylene glycol (PEG) is an additive that is commonly used as a suppressor in the semiconductor copper (Cu)-electroplating process. In this study, electrochemical impedance spectroscopy (EIS) was used to analyze the electrochemical behavior of PEG in the Cu-electroplating process. Polarization analysis, cyclic-voltammetry stripping, and cell voltage versus plating time were examined to clarify the suppression behavior of PEG. The equivalent circuit simulated from the EIS data shows that PEG inhibited the Cu-electroplating rate by increasing the charge-transfer resistance as well as the resistance of the adsorption layer. The presence of a large inductance demonstrated the strong adsorption of cuprous-PEG-chloride complexes on the Cu surface during the Cu-electroplating process. Increasing the PEG concentration appears to increase the resistances of charge transfer, the adsorption layer, and the inductance of the electroplating system.

Investigation of Static Corrosion Between W Metals and TiN x Barriers in a W Chemical-Mechanical-Polishing Slurry

In order to control the polishing qualities of tungsten (W) and titanium nitride (TiN,) films in W chemical-mechanical-polishing (WCMP) processes, the electrochemical behavior between the W and the TiN x films deposited at various N 2 flow rates was examined in this study. Metrologies, including X-ray diffractrometry, Auger electron spectrometry, and scanning electron microscopy, were used to verify the physical properties of the TiN x films, while electrochemical analyses, including electrochemical impedance spectroscopy, potential dynamic curves, and potential difference measurements, were used to characterize the mechanism of galvanic corrosion between the W and the TiN x films deposited at various N 2 flow rates. The results show that the N content of the TiN x films influences not only the physical properties of the TiN x films but also the chemical activity in the WCMP slurries. The equivalent circuit, including the charge-transfer resistance and the titanium-oxide resistance associated with tantalum-oxide capacitance, was built to characterize the mechanism of the galvanic corrosion between the W and the TiN x metals.

Magnetic Effect during Copper Electroplating Using Electrochemical Impedance Spectroscopy

In this paper, the effect of the intensity of the magnetic field on copper electroplating was investigated. Our results indicate that the variation of the magnetic field on the surface of the cathode electrode affected the electroplating rate of the electroplated copper film. By increasing the intensity of the magnetic field, the copper-electroplating rate increases. However, the magnetic field did not affect the grain sizes or shapes of the copper electroplated films. Electrochemical impedance spectroscopy (EIS) was used to analyze the electrochemical effect of the magnetic field during the copper electroplating process. Cyclic-voltammetry stripping, and cell voltage versus plating time were examined to clarify the acceleration behavior of the magnetic field. The proposed equivalent circuit shows that the magnetic field enhanced the copper-electroplating rate by decreasing the charge-transfer resistance as well as the resistance of the diffusion layer.