O2 Etching Research Articles

Optimized inductively coupled plasma etching for poly(methyl-methacrylate-glycidly-methacrylate) optical waveguide

Optical loss is a crucial quality for the application of polymer waveguide devices. The optimized oxygen inductively coupled plasma etching conditions, including antenna power, bias power, chamber pressure, O2 flow rate and etching time for the fabrication of smooth vertical poly(methyl-methacrylate-glycidly-methacrylate) channel waveguide were systematically investigated. Atomic force microscopy and scanning electron microscopy were used to characterize the etch rate, surface roughness and vertical profiles. The increment of etch rate with the antenna power, bias power and O2 flow rate was observed. Bias power and chamber pressure were found to be the main factor affecting the interface roughness. The vertical profiles were proved to be closely related to antenna power, bias power and O2 flow rate. Surface roughness increment was observed when the etching time increased.

In Situ Reduction, Oxygen Etching, and Reduction Using Formic Acid: An Effective Strategy for Controllable Growth of Monodisperse Palladium Nanoparticles on Graphene

AbstractGraphene‐supported, monodisperse palladium nanoparticles (Pd NPs) are fabricated successfully by an effective strategy combining in situ reduction, O2 etching, and reduction using formic acid without the use of surfactants. By utilizing the reductive ability of graphene prepared previously by an in situ, self‐generating template route, Pd2+ ions are first absorbed and partly in situ reduced to give Pd NPs on graphene (denoted as Pd/GN‐SR). The Pd NPs in Pd/GN‐SR exhibit poor monodispersion, large particle size, and low loading on graphene. Some unreduced Pd2+ ions still exist in the solution. Second, formic acid as the secondary reducing reagent is introduced into the same solution after the in situ reduction. Some Pd NPs on graphene are gradually etched to Pd2+ ions by oxygen dissolved in the solution, and therefore become smaller NPs. Meanwhile, with the formic acid further reduction, these Pd2+ ions and unreduced Pd2+ ions are together reduced as small‐sized Pd NPs on graphene (denoted as Pd/GN‐FA). X‐ray powder diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy measurements show that the Pd NPs in Pd/GN‐FA have smaller particle size and higher monodispersion on graphene compared with that in Pd/GN‐SR. Furthermore, the electrooxidation of formic acid on the Pd/GN‐FA catalyst has been investigated by cyclic voltammetry. The Pd/GN‐FA catalyst exhibits enhanced electrocatalytic activity and stability towards formic acid oxidation owing to the small size, the high monodispersion of Pd NPs, and the stabilizing effect of graphene. The results presented herein indicate that the Pd/GN‐FA might be a promising anode electrocatalyst in direct formic acid fuel cells.

Formation of Nanofibers on the Surface of Diamond-Like Carbon Films by RF Oxygen Plasma Etching

Diamond-like carbon (DLC) nanosize fibers were formed by etching DLC films using RF O2 plasma. The DLC films were grown on silicon substrates by an RF plasma chemical vapor deposition (CVD) method, and a small amount of Ni was deposited on the DLC films using a DC magnetron sputtering method before the etching. DLC fibers of 20 nm diameter and 600 nm height were found on the etched surfaces of the DLC films. DLC fibers of similar size that were highly insulating were also obtained by O2 etching without the deposition of Ni. It was found that Al from the RF electrode was sputtered and contaminated the DLC surface during etching, which would have affected the formation of fibers. The anisotropic etching of DLC and the ion-induced growth of carbon fibers are discussed as the formation mechanisms of the DLC fibers. The DLC fibers bent and stuck together during a field-emission scanning electron microscope observation, especially in the slow scanning mode. Such soft fibers can exist vertically and straightly throughout the etching in RF plasma.

Fabrication of graphene nanoribbons via nanowire lithography

AbstractGraphene nanoribbons (GNRs) are the counterpart of nanotubes in graphene nanoelectronics. The search for a cheap, parallel, and deterministic technique for practical implementation of these structures is still open. Nanowire lithography (NWL) consists in using nanowires (NWs) as etch masks to transfer their one‐dimensional morphology to an underlying substrate. Here, we show that oxidized silicon NWs (SiNWs) are a simple and compatible system to implement NWL on graphene. The SiNWs morphology is transferred onto a graphene flake by a low‐power O2 plasma in a deep‐reactive‐ion‐etcher. The process leads to conformal GNRs with diameter comparable to the overlaying NW lateral dimensions. The diameter can be further reduced by multiple O2 etching steps. Field‐effect measurements show the transition to a semiconductor for low diameters.

High index contrast polysiloxane waveguides fabricated by dry etching

The authors demonstrate the production of low loss enhanced index contrast waveguides by reactive ion etching of IPG™ polysiloxane thin films. The use of a silica mask and CHF3∕O2 etch gas led to large etch selectivity between the silica and IPG™ of >20 and etch rates of >100nm∕min. This work indicates that compact optical circuits could be successfully fabricated for telecommunication applications using polysiloxane films.

In-Situ Measurement of the Relative Thermal Contributions of Chemical Reactions and Ions During Plasma Etching

Plasma etch behavior is often explained in terms of "physical" and "chemical" components: both critically related to surface temperatures generated during plasma etching. In an attempt to measure the chemical etch rate component, a specially prepared, 300mm autonomous temperature sensor wafer was used to simultaneously record dynamic surface temperature during plasma etching of photo resist coated and bare silicon surfaces. Data for N2 / H2, Ar / O2, O2 and Cl2 etching chemistries were then compared with measured resist etch rates and RF sensor wafer data. Although insulation of the temperature sensors from the plasma by the 3 micron resist coating prevented calculation of the etch rate chemical component, the capability of this methodology with resist coatings < 500nm was shown. In addition the use of both RF and temperature sensor wafers to quickly identify and correct semiconductor etch process development issues related to isotropic etch non-uniformity was shown.

Graphene Oxidation: Thickness-Dependent Etching and Strong Chemical Doping

Patterned graphene shows substantial potential for applications in future molecular-scale integrated electronics. Environmental effects are a critical issue in a single-layer material where every atom is on the surface. Especially intriguing is the variety of rich chemical interactions shown by molecular oxygen with aromatic molecules. We find that O 2 etching kinetics vary strongly with the number of graphene layers in the sample. Three-layer-thick samples show etching similar to bulk natural graphite. Single-layer graphene reacts faster and shows random etch pits in contrast to natural graphite where nucleation occurs at point defects. In addition, basal plane oxygen species strongly hole dope graphene, with a Fermi level shift of approximately 0.5 eV. These oxygen species desorb partially in an Ar gas flow, or under irradiation by far UV light, and readsorb again in an O 2 atmosphere at room temperature. This strongly doped graphene is very different from "graphene oxide" made by mineral acid attack.

Anisotropic high aspect ratio etch for perfluorcyclobutyl polymers with stress relief technique

The authors have developed an anisotropic, high aspect ratio (18:1) etch for perfluorocyclobutyl (PFCB) polymers with trenches as narrow as 800nm using a CO∕O2 etch chemistry in an inductively coupled plasma reactive ion etcher. Anisotropy is achieved by carbon sidewall passivation. The motivation for this etch development is to use the air trenches as very compact waveguide splitters [S. Kim et al., Opt. Eng. 45, 054602 (2006)]. The authors report a new trench widening mechanism due to tensile stress of the PFCB films and a method of avoiding this widening through the use of additional stress relief trenches on both sides of the desired trench.

Transfer etching of bilayer resists in oxygen-based plasmas

Thin film imaging offers the possibility of extending 248 nm lithography to sub 150 nm resolution. We have been working on a 248 nm bilayer imaging scheme which utilizes a thin Si-containing resist on top of a thick, planarizing underlayer. The image is developed in the top layer and transferred to the underlayer via O2-based plasma etching. This article focuses on three aspects of the critical transfer etch process: etch resistance of the imaging resist, profile control and resist roughening. The imaging resist thickness loss is very fast during the first few seconds of the etch after which the rate diminishes. The relative importance of three phenomena that can explain this nonlinear behavior: oxidation of silicon, deprotection of resist moieties, and plasma etching of resist, are discussed. Fourier transform infrared studies on imaging resist films indicate minimal deprotection-related film thickness losses. X-ray photoelectron spectroscopy analyses of etched films indicate that the extent of surface oxidation increases initially and then becomes constant. Thus, the etching of this category of resists can be described as a combination of the oxidation of the silicon species and sputtering of the oxide-like layer formed. Post-transfer etch profiles using an O2 plasma are shown, and methods to reduce imaging resist faceting and thickness loss either by modifying the imaging layer silicon content or by using passivating plasma chemistries are discussed. The effect of different etching chemistries and processing conditions on imaging layer roughening and striation formation on underlayer sidewalls are explained with the aid of scanning electron microscopy micrographs and atomic force microscopy images of etched feature sidewalls. It is shown that the SO2–O2 etch significantly reduces the sidewall roughness from the postlithograpy values. The ∼3.5 nm rms sidewall roughness observed postetch is comparable to postdeveloped roughness values measured for mature single layer resists. The printing of 125 nm line/space patterns and 150 nm trench features with 10:1 aspect ratios in the underlayer is also demonstrated.

Nanostructured Thin Films of Organic–Organometallic Block Copolymers: One-Step Lithography with Poly(ferrocenylsilanes) by Reactive Ion Etching

The deposition of thin films of inorganic nanoclusters as a route to one-step lithography has been achieved using block copolymers with inherent inorganic (Fe and Si) components. Nanodomains of the organometallic part are resistant to removal during the subsequent O2 etch, which results in well-ordered and separate domains of iron and silicon oxides, as can be seen in the Figure.

Defect analysis of Cl2/HBr/He/O2 etching process by imaging time-of-flight secondary ion mass spectrometry

Defects appeared during Cl2/HBr/He/O2 etching process were investigated by high laterally resolved imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS). The defects with size of one to several microns appeared after the etching process. These defects are electron-beam sensitive during Auger electron spectroscopy and energy dispersive spectrometry analysis. Imaging TOF-SIMS clearly shows that the defect consists of bromine and H2O. Relatively weak oxygen and silicon signals were detected from the defect site. A negative secondary ion mass spectrum from region of interest (ROI) analysis of the defect area shows a very strong Br− signal. A positive secondary ion mass spectrum from ROI analysis has a very strong H2O+ signal from the defect. These results amply demonstrate that imaging TOF-SIMS enables chemical analysis of small defect at outmost surface with high lateral resolution and submonolayer sputtering damage under static SIMS analytical conditions.

Nanostructured Thin Films of Organic-Organometallic Block Copolymers: One-Step Lithography with Poly(ferrocenylsilanes) by Reactive Ion Etching

The deposition of thin films of inorganic nanoclusters as a route to one-step lithography has been achieved using block copolymers with inherent inorganic (Fe and Si) components. Nanodomains of the organometallic part are resistant to removal during the subsequent O2 etch, which results in well-ordered and separate domains of iron and silicon oxides, as can be seen in the Figure.

F2, H2O, and O2 etching rates of diamond and the effects of F2, HF and H2O on the molecular O2 etching of (110) diamond

Oxidation kinetics of natural (110) diamond by oxygen and water were investigated using in situ Fizeau interferometry. Apparent activation energies of 53 and 26 kcal mol−1 were obtained for the etching of (110) type Ia diamond by O2 and H2O respectively. The etch rate was found to follow second-order kinetics with respect to O2 pressure in the pressure range 0.04–10 Torr. For water over the vapour pressure range 0.1–2 Torr, the reaction has a reaction order near unity. The diamond (110) surface was impervious to etching by molecular fluorine at all temperatures up to 1300 °C. Fluorine, hydrogen fluoride and water were found to inhibit the molecular oxygen etching of diamond. Below 900 °C, oxidation is inhibited by the addition of F2 and HF presumably by blocking reactive sites on the diamond surface through formation of CF bonds. Above 900 °C, the fluorine is thought to desorb from the diamond (110) surface, rendering the surface susceptible to further oxidation. Addition of water below 800 °C was found to retard etching by molecular oxygen. This is attributed to the formation of COH bonds, analogous to CF.

Adverse effects on plasma polymerized films due to previous oxygen etching in an ‘‘electrodeless’’ reactor

Amorphous hydrogenated carbon (a-C:H) films prepared by plasma polymerization can contain chemical species due not only to the process gas species, but species from prior processes in the deposition chamber. Our studies showed that standard O2 etching/ cleaning processes done prior to plasma film formation will affect future film deposition rate measurements and carbonyl group formation. Additionally, substrate etching by polymer forming gas species is shown through the 956 cm−1 negative peak in the IR spectrum.

A generalized model of heat effects in surface reactions. II. Application to plasma etching reactions

Part I of this paper presented a generalized model of heat effects operative during surface reactions. The enhancement in reaction rate due to autothermic effects was analyzed as a function of activation energy, bulk temperature, and a parameter termed the characteristic temperature. Application of this model to experimental plasma etching data is presented in part II of this work. Characteristic temperatures calculated from experimental data in numerous plasma etching systems agree closely with the critical characteristic temperature predicted by the heat of the reaction model. Possible reasons for this consistency are given. Further, the autothermic enhancement in the Ta-CF4/O2 etching system is accurately predicted as a function of reactant concentration by a heat of reaction model.

Reactive Ion Etching of TaSix in a CF4-O2 Discharge

ABSTRACTIn the self-alignment technology for GaAs MESFET, the pattern technique for refractory suicide gate is needed. Reactive ion etching (RIE) of TaSix on GaAs has been performed in a mixture of CF4 and O2 Etching properties have been studied as function of oxygen percentage, total pressure and power. The samples were then examined in Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to understand the surface morphology and constitution. It is found that the etch rate of TaSixincreased with increasing oxygen percentage initially, reached a maximum value near 10∼15% O2, then started to decrease with increasing oxygen at applied power 100 watt, pressure 50 mtorr, and total gas flow 40 seem. This etch rate also increases with RF power and total pressure in CF4 + O2 15% gas at gas flow rate 40 sccm. For GaAs etching, the rate is independent of oxygen percentage. This etch rate of GaAs also increases with power, but decreases with total pressure. Meanwhile, the SEM micrograph shows no undercut for sample after RIE at the applied power 140 watt with the pressure of 20 mtorr.

The role of heat transfer during reactive-ion etching of polymer films

A study of the kinetics of O2 and Ar reactive-ion etching (RIE) of organic polymer films and an analysis of substrate heat transfer was carried out. Radiative heat transfer played a significant role in determining the substrate temperature profile during RIE. At the relatively low pressure of 5 mTorr, where anisotropic etch profiles are typically achieved, radiative heat transfer accounted for nearly 85% of the total energy (heat) flux away from the substrate. RIE processing time (substrate temperature) drastically affected the RIE rate of chain-scissioning polymers, which included poly(methyl methacrylate) and poly(α-methylstyrene), while processing time had absolutely no effect on etch rates of cross-linking polymers. To confirm the role of radiative heat transfer during RIE, the underside of a silicon wafer was painted black, which increased the total radiative surface emittance and lowered the steady-state substrate temperature for a given set of RIE conditions. Ultimate etch rates of poly(methyl methacrylate) were measurably lower for films on the black-silicon substrates. Thermal bonding alleviated substrate heating and greatly improved etch rate control.

シリコンウェハー上への無電解めっきの密着性

Electroless nickel plating on silicon wafers were investigated to obtain good adhesion. It was found that complicated micro etch pits ranging from 0.5μm to 1.5μm in depth on the silicon surface produced by etching with potassium hydroxide followed by HF-HNO3-CH3 COOH-H2 O2 etching solution. The micro etch pit formed by this etching sequence showed an interlocking effect with nickel, which permitted mechanical interaction at the nickel-silicon interface.

High resolution trilevel resist

A detailed study of film formation and directional etching for high-resolution trilevel resist was performed. The top layer was CMS and AZ-1350. The intermediate layer was ion beam sputter- deposited SiO2. The bottom layer was AZ-1370. High-temperature baking of the bottom layer prevents crack generation in the SiO2 intermediate layer. Reactive ion etching in O2 gas plamsa with a carbon electrode was used to pattern the bottom layer and gave a residue-free etched surface. A study was made of undercutting during O2 etching with power, temperature, and pressure varied over wide ranges. The results agree with spectroscopic observations of the variation in the ratio of excited neutral species to ionic species in the plasma. Low pressure and low substrate temperature during the bottom layer etching were found to be necessary for a low undercut. The viability of the trilevel resist for submicron patterning was verified.