Joong S. Jeon

Electrochemistry of Chemical Vapor Deposited Tungsten Films with Relevance to Chemical Mechanical Polishing

The electrochemical behavior of chemically vapor deposited tungsten films in solutions of interest to tungsten chemical mechanical polishing has been investigated using dc potentiodynamic polarization, linear polarization, and Tafel methods. It was found that in the absence of an oxidizer, the tungsten surface was passivated most effectively at acidic pH values. At pH 2 or 4, a WO{sub 2}/WO{sub 3} duplex oxide layer of less than 50 A thickness was detected over the tungsten layer by X-ray photoelectron spectroscopy. The oxide layer formed at pH 2 was much thicker, and had better passivity compared to the oxide formed at pH 4. Addition of H{sub 2}O{sub 2} at pH 2 or 4 resulted in a dramatic increase in tungsten dissolution.

Electrochemical Measurements during the Chemical Mechanical Polishing of Tungsten Thin Films

A polishing tool and a potentiostat were used to simultaneously polish and measure the direct current (dc) open-circuit potential and anodic polarization behavior of chemical vapor deposited tungsten films in the presence of various oxidants. Of the different oxidants tested at pH 1.5 or pH 4.4, (NH 4 ) 6 Mo 7 O 24 formed the most protective passive layer on tungsten. Even in the presence of the most aggressive oxidant, Fe(NO 3 ) 3 , the dissolution rates of chemical vapor deposited tungsten were approximately 3 nm/min during abrasion, which is a very small fraction of typical removal rates reported for chemical mechanical polishing of tungsten. This indicates that electrochemical oxidation followed by abrasive removal of the oxidation product and dissolution may not be the primary mechanism for tungsten removal. Atomic force microscopy scans of polis ed tungsten films indicate that corrosion assisted fracture may be an important removal mechanism for tungsten during chemical mechanical polishing.

Electrical properties of thin SiON/Ta2O5 gate dielectric stacks

The electrical characteristics of metal–oxide–semiconductor capacitors with SiON/Ta2O5 gate dielectric stacks with thin Ta2O5 layers (6–10 nm) are investigated. From the field and temperature dependence of the current of the gate stacks, it is shown that the main conduction mechanism at low bias is tunneling through the stack and that Poole–Frenkel conduction in the Ta2O5 layer becomes important at larger bias and temperature. From the analysis of the data in the high voltage and temperature range, taking into account the field distribution in both layers, the refractive index n of Ta2O5 and the energy level φB of traps involved in Poole–Frenkel conduction are found to be 2.3 and 0.85 eV, respectively. It is also shown that the gate current density of the stack is reduced by one to three orders of magnitude as compared to SiO2 layers with equivalent electrical thickness (2.5–3 nm). The temperature acceleration effect on the time-dependent dielectric breakdown is shown to be much reduced in the SiON/Ta2O5 ...

Quantitative Analysis of Adsorbed Serum Albumin on Segmented Polyurethane Using FT-IR/ATR Spectroscopy

FT-IR attenuated total reflection (ATR) spectroscopy was applied to quantitatively determine the extent of bovine serum albumin adsorbed onto a biomedical-grade poly(ether)urethane film deposited on a ZnSe internal reflection element (IRE). The method of adsorption density determination was based on the optical principles for a stratified medium consisting of three layers. The spectral peak area due to bulk solution was less than 1% of total peak area. The measured adsorption density of albumin in a flowing system was 3.9 μg/cm2 at a solution concentration of 4.5 g/100 mL.

A Comparative Electrochemical Study of Copper Deposition onto Silicon from Dilute and Buffered Hydrofluoric Acids

An electrochemical direct current polarization method was used to investigate characteristics of copper deposition onto silicon from dilute and buffered hydrofluoric acid solutions. The corrosion current density and corrosion potential of silicon were not very sensitive to the Cu 2+ concentration, up to 1000 parts per billion, in buffered hydrofluoric acid. However, the extent of copper deposition, as measured by total reflection X-ray fluorescence, increased as the Cu 2+ concentration in solution increased. In dilute hydrofluoric acid, Cu 3+ addition had a significant and systematic effect on the corrosion potential and corrosion current density of silicon. However, in both types of solution, the cathodic current calculated from the measured copper deposition was found to be only a small fraction of the corrosion current (less than 1%). This indicates that the primary cathodic reaction is not copper ion reduction but hydrogen ion reduction. Illumination affected the electrochemical behavior of both p- and n-type silicon in Cu 2+ spiked dilute hydrofluoric acid, but only that of p-type silicon in buffered hydrofluoric acid.

Effect of Temperature on the Interaction of Silicon with Nonionic Surfactants in Alkaline Solutions

The interaction of silicon wafers with alkaline solutions of octylphenol polyethylene oxide nonionic surfactants of different ethylene oxide chain length has been characterized at 25, 50, and 75°C. Wettability of silicon wafers was improved significantly at higher temperatures. Surfactants with long ethylene oxide chains exhibited less adsorption than surfactants with short ethylene oxide chains, and increase in solution temperature resulted in increased adsorption. Generally, the addition of surfactants to alkaline solution decreased the surface roughness of silicon ; however, the degree of reduction of surface roughness was influenced by the length of ethylene oxide chain and conditioning temperature.

Electrochemical Impedance Spectroscopy of Copper Deposition on Silicon from Dilute Hydrofluoric Acid Solutions

Electrochemical impedance spectroscopy was used to probe the mechanism of copper deposition on silicon from dilute hydrofluoric acid solutions. Reaction parameters such as polarization resistance and space-charge capacitance were evaluated using an equivalent circuit model. The electrochemical impedance technique was found to be sensitive to parts per billion levels of Cu 2+ ion in dilute hydrofluoric acid solutions. An inductive loop appeared in Nyquist plots only when Cu 2+ ions were present in hydrofluoric acid solutions. Both the polarization resistance and inductance decreased significantly as the solution Cu 2+ concentration increased. Addition of a nonionic surfactant to hydrofluoric acid solutions significantly altered impedance characteristics of the silicon/solution interface. Total reflection X-ray fluorescence results showed that illumination enhanced deposition of copper on silicon nearly an order of magnitude.

Electrochemical Investigation of Copper Contamination on Silicon Wafers from HF Solutions

Copper contamination of silicon wafers from 50 :1 HF solutions containing 0 to 100 ppb Cu was studied using dc electrochemical techniques. As the level of copper concentration in HF solutions increased, the corrosion current density and corrosion potential of silicon as well as the amount of copper deposition were increased. Upon addition of a nonionic surfactant, the corrosion potential, corrosion current density, and the extent of copper deposition were decreased. However, the levels of deposited copper and surface roughness were dependent on surfactant concentration. When H 2 O 2 was added to copper-spiked HF solutions, the open-circuit potential of silicon recovered to a value that is characteristic for silicon immersed in a mixture of H 2 O 2 and HF indicating the removal of deposited copper on silicon.

Behavior of Polyethylene Oxide Based Nonionic Surfactants in Silicon Processing Using Alkaline Solutions

The adsorption of polyethylene oxide (PEO) based nonionic surfactants onto hydrophobic silicon from an alkaline solution was investigated using an in situ attenuated total reflection Fourier transform infrared spectroscopy technique. The adsorption/desorption profiles of surfactants were affected by the type and length of the hydrophobic group and the lengths of hydrophilic PEO chains. Complete wetting of hydrophobic silicon was measured at surfactant concentrations in the range of 50 to 200 ppm. Surfactant adsorption was controlled by hydrophobic attractions between the hydrophobic moiety of surfactant and the silicon surface. The addition of surfactant to alkaline solutions dramatically reduced the etch rate of silicon and resulted in a smoother silicon surface. Oxidizing treatments followed by buffered oxide etching (BOE) were effective in the complete removal of adsorbed surfactant.

Quantitative analysis of albumin adsorption onto uncoated and poly(ether)urethane-coated ZnSe surfaces using the attenuated total reflection FTIR technique

An attenuated total reflection (ATR) Fourier transform infrared radiation (FTIR) technique has been explored for the in situ quantitative analysis of bovine serum albumin (BSA) adsorption from aqueous solutions onto a segmented poly(ether)urethane film deposited on a ZnSe internal reflection element (IRE) and onto a bare ZnSe IRE surface. The IR spectral area of the amide II band was used for the quantitative analysis of adsorption. BSA adsorption reached equilibrium within 30 min and changed linearly with solution concentration in the range 0.5–6 wt.% and was found to be dependent on the solution pH and substrate type. At the physiological concentration, BSA adsorption densities of 2.4 mg cm−2 and 3.9 μg cm−2 were obtained for ZnSe and polyurethane respectively. The adsorption density was higher at pH 7 than that at pH 3 or 11, and both α-helix and β-sheet structures were present in the adsorbed layer. BSA adsorbed onto these solids appears to adopt an extended conformation and the long axis of the molecule appears to lie in the plane of the interface. Adsorption density was higher on the more hydrophobic polyurethane surface than on the relatively less hydrophobic ZnSe crystal surface.