Reactive Sputter Etching Research Articles

Enhanced field emission properties of thin-multiwalled carbon nanotubes: Role of SiOx coating

We report the fabrication, characterization, and field emission properties of (silicon oxide) SiOx coated thin-multiwalled carbon nanotubes (t-MWNTs). The coated t-MWNTs show improved field emission behavior. Initially, raw t-MWNTs (diameter ∼5–8nm) were functionalized by acid treatment. Using spin on glass as a Si precursor, SiOx was coated on the nanotubes by routine chemical methods. The coated samples were characterized by high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) techniques. The HRTEM results show that the local thickness of the coating varies from ∼1to2nm. The FTIR investigations show the formation of nanophases, such as Si–C, Si–O–C, and intercalated Si–O, at the coating/nanotube interface. The TGA reveals that the coating prevents the high-temperature oxidation and degradation of the nanotubes. The field emission characteristics of the coated, functionalized, and raw nanotubes show that the turn-on fields and current density are improved for the coated nanotubes. This improvement was attributed to the lowering of the work function and dielectric constant of the C∕SiOx interface layer and the localization of the density of states close to the Fermi energy for the coated nanotubes. The analysis of the emission stability spectra shows that the coated nanotubes have a more favorable lifetime. The observed enhancement was attributed to the protection of the nanotubes from the reactive sputter etching during the field emission process. The details of the analysis are presented.

New surface improvement techniques for engineering plastics

AbstractSputter etching process and reactive sputter etching process in radio frequency(RF)glow discharge for surface improvement technique of engineering plastics, especially P T F E (polytetrafluoroethylene) were studied. In the case of sputter etching in Ar gas. characteristic cone like structures were developed on the P T F E surface, resulting in improvement of adhesive property. In reactive sputter etching in H2O gas, the P T F E surface changed chemically and showed wettability.

Radio-frequency reactive sputter etching in magnetron fields

The etch rates of materials in rf discharges can be enhanced at low target voltages and low discharge pressures by the application of magnetic fields. In a previous article magnetic enhancement in diode and hollow cathode systems was experimentally studied using an axial magnetic field, applied perpendicular to the target. The field in the present article is applied parallel to the target surface, in a magnetron configuration. Experimental results are given here for etch rate, uniformity, and power input. Etch rates of SiO2 were studied as a function of CF4 pressure, magnetron field, and mechanical discharge confinement. Various electrode shapes were used to confine the discharge and hence increase discharge ionization. Etch rate uniformity at low pressure was measured as a function of electrode confinement and magnetic field, and is discussed in terms of both the motion of glow electrons and the measured sheath (or dark space) heights. Etch rates increase with increasing gas pressure, electrode confinement, or magnetron field. At 2 Pa CF4 pressure and 975 Vpp at 13.56 MHz in a diode machine, etch rates increased by a factor of 10 using either electrode confinement or a 208 G magnetron field. Both methods improve electron trapping, thereby increasing ionization and etch rates. With applied voltage and gas pressure held constant, magnetron fields increase etch rate by a factor of 9 for a diode, 5 for an unconfined hollow cathode, and 1.7 for a target confined hollow cathode. Magnetron fields result in very poor etch rate uniformity, which can however be improved by adding electrode confinement to improve electron trapping. Etch power efficiency varied by only 33% over the magnetic field range studied here, indicating little magnetic field-induced depletion of chemically reactive species even in our most intense discharges. However, compared to the diode, power efficiency was up to two times greater in the electrode-confined hollow cathodes due to their more efficient utilization of these chemically reactive species.

Reactive sputter etching in axial magnetic fields

Magnetic fields are often applied to radio-frequency discharges in order to obtain high rate operation at low target voltages and low discharge pressures. It is known that discharge ionization is improved due to retention of electrons by magnetic fields. Here, a detailed comparison of axial magnetic enhancement and hollow cathode enhancement is made. Also included is the performance of a diode system. Our comparison criteria are (i) etch rate and (ii) surface power efficiency, for a given applied target voltage and gas pressure. High power efficiency is related to low substrate heating, which is important in high-rate semiconductor wafer processing. The axial configuration used here is one of three types of magnetic enhancement in common use (the others being magnetron and multipolar). It has the advantage of simple experimental design due to the uniform magnetic field across the target surface. Most of the results given here describe SiO2 etching in CF4 gas; however, some results for Si etching in SF6 are also given. Diode uniformity and reproducibility is poor in axial magnetic fields. This is not the case with the hollow cathodes, and we ascribe this difference to the difference in energy of typical electrons that are approaching target sheaths in the two cases. The rate enhancement available from axial magnetic fields in simple diode and target confined hollow cathode geometries is a factor of 2–3, for a given target voltage and at 1 Pa pressure of CF4. An even larger improvement of 16 times is obtained in the unconfined hollow cathode at low pressures. However, power efficiency is not improved by magnetic fields in any of the systems. These results can be understood in terms of the relative loss rates of electrons and neutrals from the discharge. Electron retention increases ionization, which raises both etch rates and input power. Neutral retention can increase rates, with little effect on input power. Thus, axial magnetic fields seem to be most appropriate where rate is not limited by the availability of active neutral species, and where electron energies approaching the target sheath are high.

Reactive sputter etching of magnetic materials in an HCl plasma

In an rf low-pressure HCl plasma NiZn and MnZn ferrite etch up to five times as fast as in an otherwise comparable Ar sputter etch process. Selectivity towards Al2O3 as an etch mask is of order 10. No redeposited material and very little trenching are seen. The etched slopes have a steepness up to 70°, resulting from redeposition and enhanced etching on the sidewalls. This is shown by experiments and by computer simulations.

Reactive sputter sectioning: A tool for polymer film analysis

Reactive sputter etching has been used to create thinned ‘‘sections’’ of polymer films for use in microstructural analysis. This paper emphasizes the features of the sputter etching process which must be controlled to permit efficient sectioning without the introduction of artifacts, such as microstructural changes induced by heating and surface texture which might obscure subsequent analysis. Sample mounting techniques which allow oxygen sputter etching rates of 20 μm/h without heating of the film above 50 °C and simple electrode surface design rules which allow etching for long periods with very low levels of surface texturing are described. The minimum oxygen flow rates which must be supplied to prevent a depletion of the oxygen reactant and a concomitant reduction in the etch rate are noted. The utility of the technique is demonstrated with results from a study of the microstructure of a cast polypropylene film as a function of depth through the film.

Si photo etching in Cl 2 Gas using a high power Hg lamp

A new surface treatment equipment, using photo etching, was developed. The deep UV source involved two mercury lamps, which were microwave excited. The deep UV light was directed onto a sample in the process chamber through a 5 inch quartz window. The Si substrate etching rate increased linearly with Cl 2 pressure. The maximum Si etching rate and uniformity across the 4 inch Si(100) substrate were 1300 Å/min and ≈16%, respectively. Photo etching, using Cl 2 gas, was applied for damage recovery of SiO 2 reactive sputter etching (RSE). Auger analysis showed impurity contamination, such as carbon and fluorine atoms, after SiO 2 etching on the Si substrate employing CF 4 mixed with H 2 gas. Such contamination could be removed and a clean Si surface appeared after the photo etching.

A comparison of different methods for removal of damage caused by reactive sputter etching of silicon

The influence of etch time and power density on damage introduced in silicon by reactive sputter etching has been investigated. The induced damage was characterized by Schottky barrier height measurements, backscattering–channeling technique, and transmission electron microscopy. The study also comprises three methods for removal of the damage. It was found that the surface could be fully restored by means of thermal oxidation or plasma oxidation followed by a HF dip. These results were verified both by electrical measurements and by backscattering–channeling technique. The rapid thermal annealing treatment seems to fully restore the surface etched at a power density of 0.5 W/cm2 or lower. For higher power densities, the surface is not fully restored, but a considerable improvement is found.

Annealing and oxidation effects after CF 4/H 2 dry etching for damage recovery

When a Si substrate, just after SiO 2 etching, is exposed to an additional etch using CF 4 + H 2 reactive sputter etching, carbon and fluorine atoms penetrate into the Si substrate to a depth of ≈ 100–150 Å. The effects of an annealing and oxidation atmosphere for this damage recovery and impurity redistribution in the Si substrate are investigated using IMA and Secco etching. Annealing in N 2 gas is only effective for removing fluorine atoms. After dry O 2 oxidation, though the carbon atoms are removed, the fluorine atoms are still confined in the oxidized layer. Under wet oxidation, carbon and fluorine atoms are removed as soon as the damaged layer is oxidized. Moreover, after 300 Å wet oxidation, no impurity atoms or defects are observed. Wet oxidation may serve as a pretreatment for Si selective epitaxial growth on a dry etched Si substrate.

Summary Abstract: Removal of reactive sputter etching induced damage in silicon

Summary Abstract: Removal of reactive sputter etching induced damage in silicon

Summary Abstract: Diagnostics of low‐pressure oxygen radio‐frequency plasmas and the mechanism for polymer etching: A comparison of reactive sputter etching and magnetron sputter etching

Summary Abstract: Diagnostics of low‐pressure oxygen radio‐frequency plasmas and the mechanism for polymer etching: A comparison of reactive sputter etching and magnetron sputter etching

Surface Damage on GaAs Induced by Reactive Ion Etching and Sputter Etching

surface damage induced by reactive ion etching (RIE) using various gases is compared with sputter etching using inert gases. Anisotropic etching of with minimal surface damage can be obtained with most of the RIE conditions used. Sputter etching using inert gases introduces substantial damage on the surface, and the degree of damage is inversely proportional to the ion mass. In addition, we have found that the damage induced by Ar sputter etching can be greatly reduced by the introduction of reactive gases during etching. Recovery of the diode characteristics is observed after removing 500Å of the etched surface using wet chemical solution or by removing 200Å of the etched surface using RIE in at 30V.

Diagnostics of Low-Pressure Oxygen RF Plasmas and the Mechanism for Polymer Etching: A Comparison of Reactive Sputter Etching and Magnetron Sputter Etching

We have compared low-pressure oxygen RF plasmas and the etching of photoresist in a reactive sputter etch reactor and in a magnetron etch reactor using Langmuir probe, optical emission actinometry, and mass spectrometry measurements. The Langmuir probe data allow the determination of the plasma ion density and electron temperature, and thus the ion flux onto the substrate. The optical data yield information on the presence of O atoms and O2+ ions. Stable reactant and product species are monitored with a mass spectrometer. The main difference between the two reactors is that in magnetron sputter etching (MSE), the ion flux to the substrate is about an order of magnitude higher, under comparable plasma conditions, than in reactive sputter etching (RSE). This accounts for the higher etch rate in MSE. However, the etch yield per ion is higher in RSE because of the higher ion energy. Etch rates correlate neither with the ion flux to the substrate nor with the density of O atoms in the plasma, but change in parallel with the consumption of reactant gas. We conclude that in etching a polymer in a low-pressure oxygen plasma, the main neutral reactant species are O2 molecules, and an important role of the ions is to remove reaction products from the substrate surface.

The Role of F Atoms in the Reactive Sputter Etching of Silicon Dioxide: Langmuir Probe and Optical Actinometry Measurements

ABSTRACTReactive sputter etching of SiO2 in a low-pressure CF4 -O2 plasma has been investigated using a Langmuir probe to determine ion fluxes to the substrate and optical actinometry to monitor the concentration of F atoms, [F]. Etch yields Y, i.e. the number of substrate atoms removed per impinging ion, are obtained vs O2 composition and vs pressure. At constant pressure Y decreases slightly, but [F] increases considerably, with increasing O2 content. On the other hand, at constant O2 composition both Y and [F] increase strongly with increasing pressure. These results suggest that at low [F], relative to the ion flux to the substrate, the dominant etch mechanism is direct reactive ion etching, with the ions themselves as the main reactants, whereas at high [F] the overall etching is ion-enhanced, with F atoms as the main neutral reactants.

Angle‐Resolved X‐Ray Photoelectron Spectroscopy Study for Reactive‐Sputter‐Etched GaAs Surface

The chemical state and oxide layer structure of the surface after reactive sputter etching (RSE) with gas were investigated by angle resolved x‐ray photoelectron spectroscopy (XPS). From the XPS results taken at a low take‐off angle, an As‐depleted layer exists in the top surface. The surface oxide is found to be composed of two layers consisting of a first layer and a mixed second layer. The thickness of the top layer increases with increasing bias voltage from 0 to 7Å, while the mixed layer thickness is rather likely to be reduced. The total oxide layer thickness of the surface grows gradually thicker with increasing bias voltage over the 0.2–0.8 kV region and is nearly equal to that of the native oxide before etching unless the mirror gloss of the surface is destroyed by RSE.

Fabrication of coils with high aspect ratios for thin-film magnetic heads

A new method of fabricating densely wound thin-film coils with high aspect ratios has been developed for thin-film magnetic heads. The processing steps are (1) thick polyimide resin spin coated on a substrate is patterned by reactive sputter etching using a finely patterned Mo mask; (2) conducting material of almost the same thickness as the polyimide resin is evaporated on to the patterned layer; (3) the Mo mask and conducting material formed on the Mo mask are selectively removed by electrochemical etching; and (4) polyimide resin is spin coated to smooth the surface of the coil layer. The Mo mask and polyimide resin can be patterned with an accuracy of better than 0.1 μm by selecting the appropriate etching conditions. A thick coil with 4 μm linewidth, 2 μm height, and 2 μm space between conductors can be produced and embedded in polyimide resin. The surface roughness of the resin over the coil is less than 0.2 μm.

In situ low damage techniques for cleaning silicon surfaces prior to metal deposition

Abstract The reproducible fabrication of ohmic contacts and Schottky barriers requires that silicon surfaces be cleaned thoroughly without introducing any crystallographic damage. In situ techniques for accomplishing this are reviewed. It is concluded that reactive sputter etching under conditions of high gas pressure and low bombarding potential is necessary to accomplish this.

Mechanism of Dry Etching of Silicon Dioxide: A Case of Direct Reactive Ion Etching

Reactive sputter etching of with plasmas has been investigated in a parallel‐plate reactor by combining etch‐rate measurements with concurrent determination of ion densities (using a Langmuir probe) and the composition of neutral plasma species (using a mass spectrometer), and by examining etched profiles in the SEM. The importance of geometrical variables, such as plate separation and plate area, and the electrical parameters appropriate for characterizing the discharge are discussed. Etch rates are found to follow the ion density and to be fairly independent of the plasma chemistry under most experimental conditions. Moreover, a comparison of reactive sputter etching and reactive ion beam etching of with and shows that etch yields per incoming ion are essentially independent of the flux of neutral radicals to the substrate. This strongly suggests as the dominant etch mechanism for direct reactive ion etching, where ions themselves are the main reactants in the etch reaction. Measured etch yields are consistent with this picture. However, the plasma chemistry has a decisive influence on the etch rate of Si, and thus on the etch selectivity of with respect to Si, and also on the exact shape of profiles etched into .

A throttle valve for automatic pressure control in sputtering and reactive sputter etching : H. W. Lehmann, B. J. Curtis and R. Fehlmann. Vacuum34, 679 (1984)

A throttle valve for automatic pressure control in sputtering and reactive sputter etching : H. W. Lehmann, B. J. Curtis and R. Fehlmann. Vacuum34, 679 (1984)

Fabrication and resist exposure characteristics of 50 keV nanometer e-beam lithography system

A 50 keV nanometer e‐beam lithography system was fabricated using a Zr–W thermal field emitter. The system has a beam current ranging from 6×10−12 to 1×10−9 A, a minimum beam spot of 2.4 nm and a scanning field of 240×180 μm2. It was found that the total emission and the specimen current was stable with a fluctuation less than 0.5% for more than 3 h. To investigate nanometer pattern delineation characteristics, the effect of various exposure parameters on a delineated line width were measured and a line pattern with a width less than 20 nm was fabricated. A 40 nm wide one dimensional MOS structure was also fabricated using Ni liftoff and reactive sputter etching techniques.