Removal Of Carbon Contamination Research Articles

Carbonate formation during post-deposition ambient exposure of high-k dielectrics

When thick films of group-III (La, Y)- and group-IV (Hf, Zr)-based high-k dielectrics are exposed to ambient for several months, Fourier transform infrared spectroscopy shows formation of carbonate species in the film bulk, likely due to reaction with atmospheric CO2. Group-III-based films show signs of carbonate feature growth within 10 min of air exposure, especially in films processed at relatively low temperatures (<600 °C). Carbonate formation is verified also for group-IV-based films, but at a significantly reduced concentration. Post-exposure annealing can reduce the carbonate observed in the IR spectra. However, post-exposure annealing likely does not remove carbon contamination, and it results in interface silicon oxide growth. The observed reactions of high-k films with the ambient may impose significant constraints on the post-deposition handling of high-k films.

Comparison of two surface preparations used in the homoepitaxial growth of silicon films by plasma enhanced chemical vapor deposition

The effect of surface preparation on the growth of epitaxial Si films by plasma enhanced chemical vapor deposition was investigated. The surface preparations considered were an ex situ ozone scrub and an in situ Ar/H2-plasma clean. Both methods were found to be effective at removing carbon contamination from the substrate surface which is critical for epitaxial growth. The thin-film quality was determined by Rutherford backscatter spectrometry, high-resolution x-ray diffraction, and transmission electron microscopy. To gain insight into mechanisms controlling the in situ cleaning process, hydrogen was replaced by deuterium in the plasma clean prior to film growth. The film/substrate interface was then analyzed by secondary ion mass spectrometry. Surprisingly, the plasma clean had little influence on the interfacial hydrogen concentration established by the previous hydrofluoric acid dip. It was found that hydrogen remains bound to C and O contaminants at the interface caused by the initial growth surface, and that neither an ex situ process containing an ozone scrub nor an in situ process containing a hydrogen-plasma clean could completely remove them.

Competing interaction of different thiol species on gold surfaces

Self-assembled monolayers (SAMs) of thiol molecules show very interesting properties. We have investigated the possibilities of creating mixed thiol films, consisting of two structurally and chemically very different thiol species. We used the aliphatic hexadecanethiol and the aromatic 2-mercapto-benzothiazol (MBT). The interaction of both species after successive adsorption on gold was investigated using XPS. We found, that hexadecanethiol displaces the MBT from gold surfaces, similar to the removal of carbon contamination by the alkanethiol. In contrast, MBT cannot replace the adsorbed alkanethiol layer. Therefore, the creation of mixed films has to start with a partial coverage of hexadecanethiol, followed by the MBT, which now can assemble to the uncovered surface without disturbing the alkanethiol.

Effect of Ultraviolet Irradiation on Silicon Oxide Films Prepared by Radio Frequency Plasma‐Enhanced Chemical Vapor Deposition

Silicon oxide films have been prepared by radio frequency plasma‐enhanced chemical vapor deposition using only an organosilicon compound as a source gas without mixing oxygen. Five types of organosilicon compounds, namely, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, and tetramethylsilane were used. Ultraviolet light was vertically irradiated on a substrate during deposition to enhance carbon contamination removal from the deposited films and improve chemical composition (increase the O/Si ratio). Films prepared with ultraviolet irradiation were high‐quality with lower carbon contamination. Furthermore, the O/Si ratios of the films increased in the presence of the ultraviolet irradiation; however no effects due to ultraviolet irradiation were observed when the films were prepared with tetramethylsilane, as it does not contain any oxygen atoms. It is clear that oxygen atoms in the organosilicon compounds were enhanced by the carbon contamination removal from the films and the increase of the O/Si ratio when ultraviolet light was irradiated vertically on the substrate. However, the chemical bonding states changed very little when ultraviolet light was irradiated horizontally on the substrate. We applied this technique to plasma systems not using oxygen gas and succeeded in decreasing carbon contamination and increasing the O/Si ratios in the deposited films. The microhardness of the deposited films increased remarkably with increasing numbers of methoxy groups and with vertical ultraviolet irradiation.

プラズマを利用したフッ素ゴムとアルミニウムとの接着

The adhesion strength of fluorine-containing rubber (a copolymer of CF2=CH2 and CF2=CF-CF3) to plasma treated aluminum was studied using X-ray photoelectron spectroscopy data and the water contact angle. Plasma treatments were as follows. (a) argon plasma treatment of aluminum at elevated temperatures in the presence of polytetrafluoroethylene (PTFE), sputtering PTFE onto the metal surface and (b) argon plasma treatments in the absence or in the presence of PTFE of plasma polymerized film (PPF) of cyclohexane previously formed on the aluminum surface. Adhesion was conducted by inserting rubber between two treated aluminum samples and adding compressive stress at high temperature. Adhesive strength was measured using Instron test equipment. Adhesive strength using treatment (a) was much greater than without treatment and slowly increased with increasing temperature, being due to the removal of carbon contaminants and the introduction of CF2 groups on the surface. Adhesive strength using treatment (b) increased several times compared to that without plasma treatments. The PPF surface after treatment (b) exhibited a hydrophihc nature, thought to play a significant role in adhesion.

Reduced-Pressure UV Photo-Oxidation of Organic Contaminants on Si Surfaces

ABSTRACTA reduced-pressure ultraviolet (UV) photo-oxidation process is described for the removal of organic contamination from Si surfaces with concomitant growth of an ultra-thin oxide passivation layer. As in situ photo-generation of ozone (O3) from dioxygen (O2) is impractical at millitorr pressures, a 2% O3/O2 mixture from an ozone generator is fed to the surface conditioning chamber. UV/O3 surface conditioning employing simultaneous 254/185 nm UV irradiation results in essentially complete removal of carbon contamination in 180 s at 100 mTorr and 100–200°C. Kinetics studies employing cyclohexane-contaminated Si(100) surfaces suggest that carbon removal occurs via two consecutive first-order processes: initial fast photo-oxidation of adsorbed cyclohexane to readily desorbed products and slower photo-oxidation of adsorbed carbonyl intermediates to CO2 and H2O. The activation energies for both processes are 2–3 kcal/mol, consistent with the involvement of photo-generated atomic oxygen species. Self-limiting growth of an ultra-thin oxide passivation layer occurs concomitantly with carbon removal. At saturation, the oxide layer is only 3–4 Å thick, and the growth kinetics are described by a first-order Langmuirian adsorption model.

Combined photochemical processes for silicon technology: substrate cleaning, silicon dioxide deposition and annealing

A combination of low-pressure mercury lamp radiation-assisted processes for removal of carbon contaminants from the silicon substrate, SiO 2 chemical vapor deposition (CVD) from an Si 2H 6/O 2 mixture, and annealing of the deposited layers has been employed to fabricate dielectric-semiconductor structures with sufficiently good properties at low temperature (250°C) using gas-phase techniques only.

Photoemission study of synchrotron radiation induced reactions of TEOS adsorbed on silicon surface

We have investigated the synchrotron radiation (SR) induced chemical reactions of tetraethoxysilane Si(OC 2H 5) 4 (TEOS) adsorbed on Si, using photoemission spectroscopy. TEOS adsorbs on the Si surface with its molecular structure intact, at least below room temperature. SR in the vacuum ultraviolet region decomposes the TEOS molecules adsorbed on Si to form a silicon oxide like film, but some carbon remains in the film. Results of irradiation experiments on condensed layers of TEOS and water adsorbed on Si at 85 K indicate that the addition of water enhances the removal of carbon contamination in the oxide film.

In situ optical element cleaning with photon activated oxygen

Abstract The severe flux losses seen in synchrotron radiation beamlines due to carbon contamination of optical surfaces has stimulated a search for decontamination techniques to restore these surface to their pristine efficiencies. In situ techniques are preferred for their potential for minimizing labor and beamline downtime costs. Glow discharge activated O2, with or without additions of H2O, has been the most successful procedure to date and is capable of cleaning the surfaces without degrading their optical properties provided the system is properly designed and operated. The method is scarcely ideal, however, since real possibilities for contamination from the discharges exist, considerable instrument modification may be required to allow plasma access to the optics, and total cycle times are 1–3 days, which may be a significant operating cost on new, ultrahigh intensity beamlines. In this work we demonstrate the existence of a new in situ decontamination technique, presenting initial work showing that synchrotron radiation itself can sufficiently activate dry oxygen to successfully remove carbon contamination films. This technique offers particular promise in two areas. First, used in situ, the cleaning action takes place in exactly the same places where contamination occurs, since both processes are activated by the same radiation, and no instrument modifications are required. Second, it suggests that if the optical elements were continuously exposed to oxygen at an appropriate partial pressure, carbon contamination could be suppressed completely. We are now planning experiments to understand the physics, chemistry and kinetics of this new decontamination technique.

Surface Cleaning Prior to Formation of Si/SiO2 Interfaces by Remote Plasma-Enhanced Chemical Vapor Deposition (RPECVD)

ABSTRACTEx situ UV/O2 cleaning prior to SiO2 deposition by RPECVD results in an SiO2/Si interface with mid-gap Dit values 2-5 times higher than interfaces formed by in situ exposure of HF-etched wafers to plasma-generated atomic O. In situ exposures to plasma-generated atomic H and atomic O are each effective at removing carbon contamination acquired by the UV/O2 cleaned wafers during transfer and introduction to the RPECVD chamber. However, in situ exposure of the photochemical oxide layer to atomic O results in higher mid-gap Dit values, and in situ exposure to atomic H results in creation of dangling bond defects (Pb centers).

In situ dc oxygen-discharge cleaning system for optical elements

I n situ dc oxygen-discharge cleaning arrangements have been developed at the Photon Factory for the removal of carbon contamination from optical surfaces. A high cleaning rate could be achieved by producing an oxygen plasma close to the optical elements with special care taken to avoid any harmful effects from the discharge; contaminant carbon was completely removed within a few hours, at most. This short exposure time and the use of dry oxygen gas resulted in a restoration of the original ultrahigh vacuum without a bakeout. Results with a Seya-Namioka beamline for gas-phase experiments showed a flux enhancement amounting to a factor of 50, and results with a grasshopper beamline showed a nearly complete recovery of the light intensity, even at the carbon K edge.

Reduction of GaAs metal–semiconductor field effect transistor sidegating by ultraviolet/ozone cleanup prior to molecular-beam epitaxial growth

This work demonstrates that UV-ozone cleaning of substrates prior to molecular-beam epitaxial growth, which has been shown by other workers to remove carbon contamination, is effective in suppressing sidegating problems otherwise encountered in GaAs metal–semiconductor field effect transistors fabricated on the epitaxial layers.

In situ reactive cleaning of X-ray optics by glow discharge

We have developed a method of in situ reactive glow discharge cleaning of X-ray optical surfaces which is capable of complete removal of carbon contamination [E.D. Johnson et al., Rev. Sci. Instr. 58 (1987) 1042]. Our work is the first to successfully clean an entire optical system in situ and characterize its performance at short wavelengths (as low as 10 Å). The apparatus required is quite simple and can easily be fitted to most existing UHV (ultrahigh vacuum) mirror boxes or monochromators. The advantages of this technique over previously available methods include dramatic improvements in instrument performance and reductions in down time since the whole process typically takes a few days. This paper will briefly describe our results and detail the experimental considerations for application of the technique on different monochromator geometries. Possible improvements and extensions of the technique are also discussed.

In situ reactive glow discharge cleaning of x-ray optical surfaces

We report the first implementation of an in situ glow discharge cleaning procedure for the removal of carbon contamination from x-ray optical surfaces. In situ cleaning obviates the need for the time-consuming and costly process of element removal, cleaning or repolishing, remounting, and realignment usually necessary to restore x-ray optics to their original condition. The apparatus required is quite simple and can easily be fitted to most existing UHV (ultrahigh vacuum) mirror boxes or monochromators. Results with several monochromators at the Brookhaven National Labs National Synchrotron Light Source (NSLS) show that better than original performance can be obtained at the carbon K edge, since the elements are not exposed to atmosphere after in situ cleaning and do not accumulate the adventitious carbon layer associated with more traditional methods. Possible improvements and extensions of the technique are also described.

Carbon abundance measurements in oceanic basalts: the need for a consensus

Large systematic discrepancies currently exist among the carbon data reported for oceanic basalts by different laboratories. These discrepancies are likely attributable both to non-uniform criteria for the removal of carbon contamination from the samples, and to systematic errors in analytical procedures. In order to solve these problems, investigators must agree upon effective criteria for the removal of carbon contamination, and they must create an accurately calibrated set of basaltic glass carbon standards.

Stoichiometric and oxygen deficient MoO 3(010) surfaces

The (010) surface of single crystal MoO 3 has been prepared and examined using LEED, XPS, UPS, and ELS. Three methods yield the stoichiometric surface: scraping in UHV and annealing, ion etching followed by reoxidation (770 K, 10 2 Pa O 2), or oxygen treatment to remove carbon contamination. LEED shows the surface periodicity is the same as that of the bulk (010). The MoO 3 valence band is 7 eV wide with density of states maxima at 1.5, 3.6, and 5.6 eV below the top of the valence band. Heating MoO 3 in vacuum reduces the surface region. XPS indicates the O/Mo atomic ratio decreases to 2.85 ± 0.12 on heating to 600 K. Ar ion bombardment disorders the surface and reduces the surface O/Mo atomic ratio to 1.6. Annealing of reduced surfaces at > 770 K incompletely reoxidizes them by diffusion of oxygen from the bulk. UPS of reduced and annealed MoO 3 exhibits two new emission features in the bandgap at 0.9 and 2.0 eV above the top of the valence band. These features originate from Mo derived states of a defect involving two or more Mo atoms, such as crystallographic shear planes. Because of the insulating nature of MoO 3, surface charging and electron beam induced damage were substantial hindrances to electron spectroscopic examination.

UV–Ozone Cleaning of GaAs for MBE

A simple method of removing carbon contamination from GaAs substrates using exposure to ozone and ultraviolet light is described.