Kazumasa Kawase

Development of a Method for Resist Removal by Ozone with Acetic Acid Vapor

A method of removing the photoresist using ozone gas with acetic acid vapor has been developed. Glass substrates (size 100 X 100 mm 2 ) coated with I-line resist were treated under the conditions of substrate temperature, (T S ) 27-50°C; acetic acid vapor, 2-18 vol %; ozone, 0-9.3 vol % (0-200 g/m 3 ); total gas flow rate, 2 L/min; and gas pressure, 100 kPa. A previous ozone treatment with oversaturated water vapor or sprayed water overcame the limitation of ozone diffusion into the resist by the control of the water film on the resist. In this study, pure acetic acid vapor has been first applied for the resist removal by ozone in order to improve the oxidation rate of the resist, because acetic acid is an inactive solvent in the ozonization, and the solubility of ozone is much higher than water. It was observed that the resist removal rate increased with acetic acid and ozone concentration, and reached at 6 μm/min at Ts = 50°C, which was about six times greater than that of the previous ozone treatment. Metal corrosion of molybdenum and aluminum electrodes was found negligible during the ozone treatment with acetic acid vapor. The mechanism of resist removal without the metal corrosion by ozone with acetic acid vapor is also discussed, based on the solubility of ozone in acetic acid and the corrosion current in ozonized solutions.

XPS study of H-terminated silicon surface under inert gas and UHV annealing

We have investigated the changes of chemical bonding states of an H-terminated silicon surface under inert gas (Ar,N 2 ) and ultrahigh vacuum (UHV) annealing using X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). SiC is formed (corresponding to ∼0.1 monolayer) under inert gas and UHV annealing at around 500°C, which is coincident with the temperature of the dangling bonds formation at the silicon surface by hydrogen desorption, whereas SiC is not formed under O 2 annealing. From the precise analysis using a combination of XPS and TDS, the SiC formation is related to the reaction between the silicon surface and the organic contamination that is unavoidably adsorbed during air exposure. We also studied the electrical properties of metal oxide semiconductor capacitors with a chemical vapor deposited silicon oxide gate insulator formed on Ar- and O 2 -annealed silicon surfaces. Ar preannealing increases the leakage current by approximately 10 - 4 times compared with O 2 annealing.

Densification of chemical vapor deposition silicon dioxide film using oxygen radical oxidation

Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) were treated with oxygen radical oxidation using Ar/O2 plasma excited by microwave. The mass density depth profiles, carrier trap densities, and current-voltage characteristics of the radical-oxidized CVD-SiO2 films were investigated. The mass density depth profiles were estimated with x ray reflectivity measurement using synchrotron radiation of SPring-8. The carrier trap densities were estimated with x ray photoelectron spectroscopy time-dependent measurement. The mass densities of the radical-oxidized CVD-SiO2 films were increased near the SiO2 surface. The densities of the carrier trap centers in these films were decreased. The leakage currents of the metal-oxide-semiconductor capacitors fabricated by using these films were reduced. It is probable that the insulation properties of the CVD-SiO2 film are improved by the increase in the mass density and the decrease in the carrier trap density caused by the restoration of the Si-O net...

Angle resolved X-ray photoelectron spectroscopic study of ultrathin oxynitrides

Abstract We studied nitrogen distribution, concentration and chemical state in NO- and N2O-exposed silicon oxide films, to understand the relationship between nitridation and suppression of stress-induced leakage current (SILC) resulting from Fowler–Nordheim (F–N) stress. We applied angle resolved X-ray photoelectron spectroscopy (ARXPS) and electron energy loss spectroscopy (EELS) to obtain information at less than 2-nm thick film-substrate interface layers. Si3N4-like layer is formed only at the film-substrate interface in NO oxynitride. Nitrogen atoms in N2O oxynitride are broadly distributed in the oxynitride film near the interface because the interface moves deeper from the surface during N2O nitridation due to both oxidation and nitridation proceed simultaneously. SILC of both NO and N2O oxynitride decrease exceedingly. It is clear that both NO and N2O nitridation is effective in suppressing SILC in spite of the quite difference in the distribution, concentration and chemical state of nitrogen atoms.

Densification of Chemical Vapor Deposition Silicon Dioxide Film Using Ozone Treatment

Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) have been treated with ozone (O3) or oxygen (O2) gas ambient at 450 °C. Density depth profiles of the SiO2 films were investigated using X-ray reflectivity analysis with synchrotron radiation. The density depth profile of the base CVD-SiO2 film without the O3 or O2 treatment is low (~2.03 g/cm3) and constant. That of the CVD-SiO2 film with the O3 treatment is not constant. The O3-treated CVD-SiO2 film is composed of a middle-density top layer (~2.13 g/cm3), a low-density center layer (~2.03 g/cm3), and a high-density bottom layer (~2.24 g/cm3). The density depth profile of the CVD-SiO2 film treated with O2 gas agrees with that of the base CVD-SiO2 film. The temperature or presence of O2 molecules during the O3 treatment at 450 °C does not affect the densification of the base CVD-SiO2 film. Therefore, the active species that densify the base CVD-SiO2 film during the O3 treatment are oxygen (O) radicals generated by the thermal decomposition of O3 molecules. The middle-density top layer near the SiO2 surface is formed by the reconstruction of a Si–O network with the oxidation of oxygen vacancies in the base CVD-SiO2 film with O radicals. The high-density bottom layer near the SiO2/Si interface is formed by the oxidation of the silicon substrate with O radicals that diffuse through the low-density base CVD-SiO2 film. The penetration length of O radicals in the base CVD-SiO2 film is very large because the thickness of the high-density bottom layer does not depend on the thickness of the base CVD-SiO2 film up to 16.8 nm at least. Therefore, this densification method for the CVD-SiO2 film with O3 treatment can be applied to the formation of either thin or thick SiO2 films.

Control of nitrogen depth profile near silicon oxynitride/Si(100) interface formed by radical nitridation

Depth profiles of composition and chemical structures in radical nitrided silicon oxynitride films formed with Ar/N2, Xe/N2, or Ar/NH3 plasma excited by microwave have been investigated by X-ray photoelectron spectroscopy combined with step etching in HF solution. The relationship between the intensities of emission from N2+ radical in these plasmas and the concentration of nitrogen atoms forming Si3≡N configuration near the silicon oxynitride film/Si substrate interface nitrided using these plasmas was studied. The emission intensities from N2+ radical generated in Xe/N2 or Ar/NH3 plasma are a quarter or one-sixth of that from N2+ radical generated in Ar/N2 plasma respectively. However, the emission from NH radical is also detected in Ar/NH3 plasma. Although the nitrogen concentration of Xe/N2 plasma is smaller than that of Ar/N2 plasma at the film/substrate interface, that of Ar/NH3 plasma is larger than that of Ar/N2 plasma at the interface. It is important for the reduction of the nitrogen concentration near the film/substrate interface to use Xe/N2 plasma in which both of the generation efficiencies of N2+ and NH radicals are low.

Control of Nitrogen Depth Profile and Chemical Bonding State in Silicon Oxynitride Films Formed by Radical Nitridation

Chemical bonding states and depth profiles of nitrogen in radical nitrided silicon oxide film formed in Ar/N2 plasma excited by microwave has been investigated using X-ray photoelectron spectroscopy with HF step etching. The main chemical bonding state of nitrogen atom is Si3≡N configuration, and the other unknown bonding state (termed Nhigh) is observed, whose peak energy shift is about +4.8 eV. The nitrogen atoms forming Si3≡N configuration accumulate only at the film surface and those forming Nhigh configuration are distributed deeper in the films. The Nhigh bond is very weak because it is desorbed completely at low temperature (300–500°C). Although the nitrogen atoms forming Nhigh configuration are removed by post O2-annealing, those forming Si3≡N configuration migrate toward the film/substrate interface and they increase negative bias temperature instability. In the case of ultra thin film, nitriding species forming Nhigh bond reach the film/substrate interface and form Si3≡N bond at the interface. Suppression of the generation of nitriding species forming Nhigh bond in the plasma is very important. It is clear that Nhigh bond is reduced using Ar/NH3 plasma.

Mass densification and defect restoration in chemical vapor deposition silicon dioxide film using Ar plasma excited by microwave

Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) have been treated with Ar plasma excited by microwave. The changes of the mass densities, carrier trap densities, and thicknesses of the CVD-SiO2 films with the Ar plasma treatments were investigated. The mass density depth profiles were estimated with X-Ray Reflectivity (XRR) analysis using synchrotron radiation. The densities of carrier trap centers due to defects of Si-O bond network were estimated with X-ray Photoelectron Spectroscopy (XPS) time-dependent measurement. The changes of the thicknesses due to the oxidation of Si substrates were estimated with the XRR and XPS. The mass densities of the CVD-SiO2 films are increased by the Ar plasma treatments. The carrier trap densities of the films are decreased by the treatments. The thicknesses of the films are not changed by the treatments. It has been clarified that the mass densification and defect restoration in the CVD-SiO2 films are caused by the Ar plasma treatments without the oxidation of the Si substrates.Silicon dioxide (SiO2) films formed by chemical vapor deposition (CVD) have been treated with Ar plasma excited by microwave. The changes of the mass densities, carrier trap densities, and thicknesses of the CVD-SiO2 films with the Ar plasma treatments were investigated. The mass density depth profiles were estimated with X-Ray Reflectivity (XRR) analysis using synchrotron radiation. The densities of carrier trap centers due to defects of Si-O bond network were estimated with X-ray Photoelectron Spectroscopy (XPS) time-dependent measurement. The changes of the thicknesses due to the oxidation of Si substrates were estimated with the XRR and XPS. The mass densities of the CVD-SiO2 films are increased by the Ar plasma treatments. The carrier trap densities of the films are decreased by the treatments. The thicknesses of the films are not changed by the treatments. It has been clarified that the mass densification and defect restoration in the CVD-SiO2 films are caused by the Ar plasma treatments without the...

Integration Process Development for Improved Compatibility with Organic Non-Porous Ultralow-k Dielectric Fluorocarbon on Advanced Cu Interconnects

Integration of an organic non-porous ultralow-k dielectric, fluorocarbon (k= 2.2), into advanced Cu interconnects was demonstrated. The challenges of process-induced damage, such as delamination and variances of both the structure and electrical properties of the fluorocarbon during fabrication, were investigated on Cu/fluorocarbon damascene interconnects. A titanium-based barrier layer, instead of a tantalum-based barrier layer, was used to avoid delamination between Cu and fluorocarbon in Cu/fluorocarbon interconnects. A moisture-hermetic dielectric protective layer was also effective to avoid damage induced by wet chemical cleaning. On the other hand, a post-etching nitrogen plasma treatment to form a stable protective layer on the surface of the fluorocarbon was proposed for the practical minimization of damage introduction to fluorocarbon in the following damascene process, such as post-etching cleaning.

X-ray photoelectron spectroscopy study of the origin of the improved device performance by a thin Al layer insertion between AlGaN and schottky gate on the AlGaN/GaN high-electron-mobility transistor

An insertion of a thin Al layer between the AlGaN surface and the gate metal is effective in improving not only gate leakage current but also current collapse in AlGaN/GaN high-electron-mobility transistors. In order to investigate the origin of the reduced trap density, which is considered as the reason for the improvements of transistor characteristics, the chemical properties around the gate metal was examined using X-ray photoelectron spectroscopy. As a result we found the formation of the AlOx layer at the interface between the AlGaN and the gate metal by thin Al layer insertion, which is speculated to affect the reduction of trap density and the improvement of transistor characteristics.