Radical Etching Research Articles

Sidewall protection by nitrogen and oxygen in poly-Si 1−xGe x anisotropic etching using Cl 2/N 2/O 2 plasma

Sidewall protection by nitrogen and oxygen in poly-Si 1− x Ge x anisotropic etching has been investigated using electron–cyclotron resonance (ECR) chlorine plasma. It was found that the sidewall protection with only N 2 addition is weaker than that of poly-Si. Highly anisotropic etching of poly-Si 0.5Ge 0.5 is achieved by the addition of both N 2 and O 2. In the investigation of X-ray photoelectron spectroscopy (XPS) for poly-Si 0.5Ge 0.5 after the radical dominant etching, it was found that the sidewall protective layer is scarcely formed on Ge surface by not only N 2 addition but also by O 2 addition. From these results, it is suggested that highly anisotropic etching of poly Si 0.5Ge 0.5 is achieved by the etching protection of both N and O on the sidewall against chlorine radical etching.

Identification of MOS Gate Dielectric Breakdown Spot Using High Selectivity Cl Radical Etching Technique

We have developed a simple method for identifying dielectric breakdown spots in gate oxides by using high selectivity Cl radical etching. This method is based on the phenomenon that Cl radicals do not penetrate . They can etch the Si substrate through the breakdown spot which acts as the etching path, namely, the current leakage path. During over‐etching of the poly‐Si gate electrode, a cavelike etched region in the Si substrate appeared under the breakdown spot of the gate oxide. This breakdown spot could be found by focusing the optics on the gate oxide located at a center on the etched region. We confirmed the local structure of the gate oxide which converted to crystallized Si due to intrinsic dielectric breakdown using transmission electron microscopy and energy dispersive x‐ray spectroscopy. Cl radicals can etch the breakdown spot such as part of the crystallized Si in the gate oxide produced by intrinsic dielectric breakdown, and then etch a Si substrate under the breakdown spot.

Characterization of ultraviolet excited Br*-radical etching of InGaAs/InAlAs material system

Dry selective photochemical etching of InGaAs/InAlAs material system, in HBr gas excited by a 172 nm excimer lamp, has been characterized. The etching is thought to be due to the formation of reactive Br*-radicals which are photocreated in the gas phase and then diffused into the solid semiconductor to create volatile products. The etching is temperature sensitive with best etching results at 50–110° C. Atomic force microscope and scanning electron microscope pictures reveal that the surface morphology at this temperature range is smooth and fine. Auger electron spectroscopy and x-ray photoelectron spectroscopy measurements show that at low temperatures the etch products are primarily salts of bromide and are in the liquid phase and thus remain at the surface and a desorption process stops further etching. At slightly elevated temperature range, the creation of oxides and deposition of bromine compounds reduces the etch rate and causes the surface quality to deteriorate. Etching at higher pressure range increases the etch rate of InGaAs but results in surface quality deterioration.

TEPS: Two-dimensional Etching Process Simulator

This paper describes a two-dimensional etching-process simulator, TEPS, which includes a mesh structure generator for uniform/non-uniform grids. In order to simulate an etching profile, the input is first passed through a grid-generator. This grid-generator produces a rectangular two-dimensional mesh structure, which is used for simulating isotropic and anisotropic components of etching (to include ion, radical and wet etching). The numerical model proposed by Yamamoto et al for etching is, used to determine the location after etching. Triangulation of the rectangular elements of the mesh structure is also incorporated. It also reviews the work done in semiconductor process simulations used in Integrated Circuit (IC) fabrication.

Analytic models for plasma-assisted etching of semiconductor trenches

The etching of semiconductor wafers is modeled for etching by radicals (isotropic etching) and etching by both radicals and vertically incident cold ions (anisotropic etching) in a glow-discharge plasma. Explicit analytical expressions for evolving two-dimensional etched surfaces are found by the method of characteristics. These parametric relations are expressed in terms of the position along the initial exposed wafer surface. Exact surface equations are given for the radical etching with two different ansatz for the evolution equation. The superposition of radical etching and etching due to vertically incident, bombarding ions is solved by approximate analytical expressions for the etched surface. Two-dimensional etched surfaces are displayed graphically for various times.

GaAs Surface Cleaning/Etching Using Plasma-Dissociated Cl Radical

Cl radical etching (RE) of GaAs, a previously evaluated dry etching method with very low damage which is suitable for nanometer-scale fabrication, damage removal and surface cleaning, is investigated in comparison with Cl2 etching. At room temperature, etching conditions with a higher chiorine pressure of about 10-3 Torr provide no significant etching rate, whereas etching conditions at a lower chlorine pressure of (4±1)×10-5 Torr provide a moderately slow etching rate (40 Å/min) and precise control of etching depth, both of which are useful for shallow etching of nanometer-scale structures. Effective cleaning of GaAs native oxide and carbon contaminants by the Cl radicals is clearly demonstrated, but this cleaning does not occur when using Cl2 molecules. When the GaAs surface is not covered with such contaminants, both the Cl-RE and the Cl2 etching progress. The roughness of the Cl-radical-etched surface is as low as 50 Å after etching to a depth of 2640 Å. After heat treatment of the Cl-radical-etched sample at 400°C, an atomically ordered and stoichiometric GaAs surface is obtained.

Effects of Hydrogen on Chlorine Radical‐Beam Ion‐Beam Etching of AlxGa1 − xAs with Varying Mole Fraction

We have used and added to radical‐beam ion‐beam etching to explore the possible benefits of H* radicals on surface morphology. Using a novel structure composed of quarter‐wavelength stacks, etch rates of varying Al mole fraction were measured in situ by reflectance interferometry. Although H* radicals neglibly etch , the addition of H* enhances the chlorine (Cl*) etch rate threefold. Contrary to our expectations, the addition of H* to chlorine radical etching also results in a systematic increase in roughness of the surface which is directly correlated to an increase in Al content.

Chemistry of photo-assisted organometallic vapor-phase epitaxy of cadnium telluride

A reaction mechanism is presented for photo-assisted organometallic vapor-phase epitaxy (OMVPE) of cadmium telluride. Dimethylcadmium and dimethyltellurium are photodissociated in the gas into Cd and Te atoms and methyl radicals by 248 nm photons from a continuous-wave laser. The Te atoms and methyl radicals recombine to form Te 2, TeCH 3, and C 2H 6. The Cd atoms and Te species diffuse to the substrate, adsorb, and incorporate into the cadmium telluride film. The film stoichiometry is maintained by Cd sublimation when cadmium is in excess, and by methyl radical etching of Te when tellurium is in excess. This mechanism has been incorporated into a laminar-flow model of the photo-assisted OMVPE reactor. The model predicts that at low laser power and/or high flow rates, the growth rate is controlled by the dimethylcadmium photolysis rate. This yields a linear dependence of the growth rate on the laser power density and the dimethylcadmium pressure. These results are in good agreement with experiments. The model further predicts that elemental tellurium deposits with cadmium telluride over a broad range of operating conditions. Conditions which avoid tellurium deposition are described. In addition, a simple criterion is developed for determining when an excimer laser may be modeled as a continuous light source.

Electrical characterization of very-low energy (0-30 eV) CI-Radical/Ion-beam-etching induced damage using two-dimensional electron gas heterostructures

Damage induced by very low energy (30 eV) Cl reactive ion beam etching (RIBE) and radical etching (RE) has been electrically characterized. GaAs/n-AlGaAs two-dimensional electron gas heterostructures were used as damage sensitive probes. Sheet carrier concentrations and Hall mobilities were measured at 77 K, under dark as well as illuminated conditions. By carefully designing the sample structure, the damaged layer thickness could be estimated by comparing dark and illuminated data. In case of RE, no degradation was detected at depths as shallow as 25 nm from the etched surface. For 30 eV-RIBE, the damage was detected but found to be reasonably small (38% decrease in electron mobility) and shallow (<50 nm). Electrical and optical damage are compared briefly.

Scannint tunnelling microscopy of plasma- and photo-enhanced chemical vapour deposited hydrogenated amorphous silicon

A series of ‘intrinsic’ amorphous silicon (a-Si:H) films produced by photo- and plasma- chemical vapour deposition was studied using scanning tunnelling microscopy (STM). The high resistivity of these films meant that photo-induced enhancement of the carrier concentration in the material was required to enable a stable tunnelling regime to be obtained. This enhancement was achieved using a 3 mW He-Ne laser shone through the back of the sample. Tunnelling I/V spectra showed rectification behaviour typical of metal-insulator-semiconductor tunnelling. In addition, spatially independent photovoltage effects were observed while tunnelling under illumination. A series of I/V data taken as a function of tip/sample separation shows a gradual transition from spectra dominated by weak surface states to a more bulk-like behaviour. The surface roughness of the photo-CVD material (33 A rms) was found to be an order of magnitude greater than that for the plasma-CVD material (6 A rms). This difference may be the result of hydrogen radical etching in the former process.

Methyl radical etching of compound semiconductors with a secondary afterglow reactor

While halogen-based dry etching processes are well established for silicon devices, many compound semiconductors have insufficiently volatile halides for successful conventional dry etch processing. These elements, found in groups II B, III A, IV A, V A, and VI A of the Periodic Table, do form volatile organometallic compounds. A secondary afterglow reactor, in which atomic fluorine produced in a microwave discharge is reacted with methane downstream of the discharge, has been used to etch HgCdTe, CdTe, InP, InSb, and GaAs at temperature-dependent rates between 100 Å and 1000 Å/min. This etching is purely chemical and without ion bombardment, and it shows crystallographic orientation dependence on the etch rate. The activation energies for etching in a methyl/atomic hydrogen ambient range from 2.3 and 7.2 kcal/mol. CdTe(111)B etched faster, smoother, and with a higher activation energy than CdTe(100), which produced a surface with submicron texturing. Specular surfaces were observed with CdTe, InP, InSb, and GaAs, although the HgCdTe etched with significant roughness.

Temperature dependence of H radical etching in the deposition of microcrystalline silicon alloy thin films by HG-sensitized photo-CVD

The etching of a-Si:H by H radicals in Hg-sensitized photo-CVD is studied as a function of deposition temperature, etch temperature and film hydrogen content. For films deposited at the same temperature, etch rates increased as etch temperature decreased from 230°C to 100°C and were temperature independent for temperatures between 100°C and 40°C. Etch rate increased with decreasing deposition temperature, but did not change when hydrogen content was varied by changing pressure and dilution. Under conditions producing high etch rates, microcrystalline films of Si:B:H and SiGe:H were prepared at temperatures as low as 100°C.

The Interaction of Laser Generated Methyl Radicals with Cd, Te, and CdTe Surfaces

ABSTRACTThe mechanism of the interaction of methyl radicals with Cd, Te, and CdTe surfaces has been studied in ultrahigh vacuum by Auger electron spectroscopy and thermal desorption mass spectrometry. Methyl radicals generated by the laser photodissociation of acetone at 193 nm efficiently etch both Te and Te-rich CdTe surfaces. However, there is no evidencefor reaction of methyl radicals with Cd or stoichiometric CdTe. A temperature dependencein the rate of methyl radical etching of Te-rich CdTe is related to a competition between acetone scavanging of radicals on the surface and reaction of radicals to form volatile metalorganics. Acetone itself has a small but finite reaction probability with Te and Te-rich CdTe surfaces.

Halofluorocarbon plasma treatments of polystyrene and poly(methyl methacrylate) surfaces

The effect of halofluorocarbon (CF 4, CF 3Cl, CF 3Br) discharges on polystyrene (PS) and poly(methyl methacrylate) (PMMA) has been studied. It has been shown that, depending on the halogen/halocarbon radical ratio, polymerization or etching can occur. The discharge chemistry has been altered by changing the excitation electrode material, and thus enhancing or depressing the amount of halocarbon radicals in the discharge. In CF 3Br and CF 3Cl plasmas, mass spectroscopy revealed the formation of molecular chlorine and bromine. Ion bombardment has been shown, in both PS and PMMA, to enhance etch rates and to depress the deposition of plasma polymer. While the etch rates of PMMA by CF 4, CF 3Cl and CF 3Br have the same kinetic dependence on bias voltage, the same is not true for PS. In this case the etch rates by CF 3Cl and CF 3Br discharges are preferentially enhanced, due to the different interaction with the species present in the discharge. As to derivatization, the introduction of halogens is more efficient in PS than in PMMA. Interestingly, the introduction of Cl and Br is enhanced much more than that of F, possibly due to the interaction of the PS aromatic ring with molecular chlorine and bromine present in the discharge.

GaAs and AlGaAs crystallographic etching with low-pressure chlorine radicals in an ultrahigh-vacuum system

GaAs and AlGaAs have been crystallographically etched with low-pressure chlorine radicals in an electron-cyclotron resonance (ECR) plasma shower with a new reactive-ion-beam etching (RIBE) system for obtaining damage- and contamination-free etching. The etching begins abruptly at 190 °C and increases gradually above 200 °C. The typical etching rate of a (001) plane is 1 μm/min at a substrate temperature of 300 °C. Mesa-shaped and reverse mesa-shaped grooves with {111}A side wall planes are obtained for 〈1̄10〉- and 〈1̄1̄0〉-oriented line and space masks. For square masks with [110] edge lines, on the other hand, high aspect-ratio columns with {100} vertical side wall planes are obtained. These results show that the etching rate of {111}A is much lower than that of {100}, {110}, or {111}B. AlGaAs is etched similarly to GaAs. Cl2 gas (not plasma excited) performs similar etching. However, the substrate temperature must be about 100 °C higher for the beginning of etching than for the Cl radical etching. These etching technologies are promising for microfabrication of GaAs/AlGaAs optoelectronic devices, replacing conventional wet chemical etching.

Submicrometer-resolution etching of integrated circuit materials with laser-generated atomic fluorine

We have demonstrated submicrometer-resolution lithography by ultraviolet laser-induced radical etching. We previously showed that this method can provide highly specific and efficient etching of various refractory metal/insulator and semiconductor/insulator substrate combinations.

ChemInform Abstract: SURFACE ETCHING BY LASER‐GENERATED FREE RADICALS

AbstractReaktive neutrale Fragmente, die durch Mehrfach‐IR‐Photonendissoziation verschiedener Moleküle (wie CF3Br, CFzClz oder CDF3) mit einem CO2‐Laser erzeugt werden, sind in der Lage, SiO2‐ oder Si3N4‐Oberflächen zu ätzen.

Surface Etching by Laser‐Generated Free Radicals

We have found that reactive neutral fragments, generated by multiple infrared photon dissociation of various molecules with a laser, are capable of etching silicon oxide or nitride surfaces. The laser‐generated radical etching process has a potential for major commercial impact, by eliminating ion‐bombardment damage in the resulting semiconductor device and by permitting more efficient and selective etching to be performed. In addition, this provides an investigative tool for learning the precise identity of the active species, the extent of their interaction with the substrate surface, and the rates of the key steps in the reactions resulting in net removal of silicon.