Reactive Ion Etching Of Silicon Research Articles

Individually Addressable, Submicrometer Band Electrode Arrays. 1. Fabrication from Multilayered Materials

Useful analytical application of submicrometer band electrodes depends strongly upon developing reproducible, convenient fabrication and characterization procedures. We report fabrication of arrays of individually addressable submicrometer band electrodes that are 2 mm long and functional down to 37.0 nm in width, using multilayered materials and conventional microfabrication techniques. Fabrication involves thermal vapor deposition of a chromium adhesion layer and a gold layer on glass, followed by plasma-enhanced chemical vapor deposition of a silicon nitride layer, photolithography, and reactive ion etching. The topography of each layer was studied using contact-mode atomic force microscopy. Surfaces show larger features as the thickness of gold increases. Silicon nitride topography shows a relatively smoother surface, indicating that it may serve as a planarizing layer for subsequent gold layers. Cyclic voltammetry at 0.10 V/s of individual band electrodes in a solution of Ru(NH3)63+ shows a typical sigmoidal response, as would be expected when the diffusion layer exceeds the smallest dimension of the electrodes. At faster scan rates, peak-shaped voltammograms are observed, as expected. Good reproducibility of electrochemical behavior was obtained for electrodes in the same array.

A lateral symmetrically bistable buckled beam

We have micromachined a lateral symmetrically bistable buckled beam for snap-in holding structures by oxidizing released beams micromachined on thick silicon-on-insulator wafers. The wafers were prepared by bonding and chemical mechanical polishing, and the structures were fabricated by deep silicon reactive ion etching using the black silicon method, subsequently released and thermally oxidized. The bistability was monitored in situ in a scanning electron microscope using a micromanipulator. Guidelines for designing beams of an expected performance are given and arguments for considering beams that are not `fairly slender' have been found.

Suspended optical waveguide with in-plane degree of freedom for microelectromechanical applications

A suspended optical waveguide displacement sensor (SOWDS) based on single crystal silicon beams with an inherent in-plane degree of freedom is presented. The SOWDS technology is based on the single crystal silicon reactive ion etching and metallisation (SCREAM) process, and opens new methods of monolithically integrating optical manipulation with SCREAM based sensors and actuators.

Surface modelling of reactive ion etching of silicon–germanium alloys in a SF6 plasma

Abstract Reactive ion etching (RIE) of amorphous Si x Ge 1− x alloys (0≤ x ≤100%) in a low-pressure SF 6 plasma has been investigated by means of quasi in situ X-ray photoelectron spectroscopy. The reactive layer on the etched alloys mainly consists of SiF, GeF, SiS and GeS 2 species. The sulfur and fluorine coverages on both Ge and Si atoms depend on the SiGe alloy stoichiometry in agreement with the nonlinear evolution of the alloy etch rates. A simple etching model where the etch rate is assumed to be proportional to the fluorine coverages has been developed for the description of the Si x Ge 1− x etching mechanism.

Low temperature reactive ion etching of silicon with SF6/O2 plasmas

An investigation of low temperature reactive ion etching of silicon to produce ultrasmall structures is presented. Etching was performed between 10–100 mTorr with SF6/O2 plasmas. The silicon samples were cooled using liquid nitrogen, allowing the temperature to be controlled over the range of +25 to −120 °C. With a flow rate of 1 sccm of SF6 and sample temperatures below −85 °C the etch produces nearly anisotropic etching in agreement with predictions of the reactive spot model. At higher flow rates etching produced facetted features indicating higher chemical reactivity of the plasma with the silicon. With the addition of O2 to the plasma the facetting became even more pronounced.

Vertical mirrors fabricated by deep reactive ion etching for fiber-optic switching applications

We report on vertical mirrors fabricated by deep reactive ion etching of silicon. The mirror height is 75 /spl mu/m, covering the fiber core of a single-mode fiber when the latter is placed into a groove of equal depth and etched simultaneously with the mirror. To obtain a uniform etch depth, etching is stopped on a buried oxide layer. Using the buried oxide as a sacrificial layer allows to fabricate mirrors with suspension and actuation structures as well as fiber-alignment grooves in one and the same processing step. A minimal mirror thickness of 2.3 /spl mu/m was achieved, resulting in an aspect ratio higher than 30. The verticality was better than 89.3/spl deg/. In the upper part of the mirror a surface roughness below 40 nm rms was obtained. At a wavelength of 1300 nm the reflectivity of the aluminum-coated mirrors was measured to be higher than 76%. Using a reactive ion etched mirror we have fabricated an optical fiber switch with electrostatic actuation. The coupling loss in the bar state of two packaged prototypes was between 0.6 and 1.7 dB and between 1.4 and 3.4 dB in the cross state. The switching time is below 0.2 ms.

Electroluminescent device based on silicon nanopillars

Silicon nanopillars were fabricated by using deep UV lithography, highly anisotropic silicon reactive ion etching based on fluorine chemistry, and high-temperature thermal oxidation for further thinning. Pillars with a diameter below 10 nm and a height in the 0.4–0.6 μm range were obtained while lying on a very smooth bottom silicon surface. An isolating transparent polymer was then used to fill in the etched area containing the pillars and, therefore, planarize and isolate the pillars. Oxygen plasma was used in order to remove the resistance from the top of the pillars. They were then contacted by a thin contact layer (gold or indium tin oxide), evaporated on the top of them. An Ohmic contact was also formed on the back side of the wafer. The obtained device showed rectifying behavior and forward voltages exceeding 10–12 V electroluminescence was observed, visible with the naked eye.

A survey on the reactive ion etching of silicon in microtechnology

This article is a brief review of dry etching as applied to pattern transfer, primarily in silicon technology. It focuses on concepts and topics for etching materials of interest in micromechanics. The basis of plasma-assisted etching, the main dry etching technique, is explained and plasma system configurations are described such as reactive ion etching (RIE). An important feature of RIE is its ability to achieve etch directionality. The mechanism behind this directionality and various plasma chemistries to fulfil this task will be explained. Multi-step plasma chemistries are found to be useful to etch, release and passivate micromechanical structures in one run successfully. Plasma etching is extremely sensitive to many variables, making etch results inconsistent and irreproducible. Therefore, important plasma parameters, mask materials and their influences will be treated. Moreover, RIE has its own specific problems, and solutions will be formulated. The result of an RIE process depends in a non-linear way on a great number of parameters. Therefore, a careful data acquisition is necessary. Also, plasma monitoring is needed for the determination of the etch end point for a given process. This review is ended with some promising current trends in plasma etching.

Experimental study and computer simulation of aspect ratio dependent effects observed in silicon reactive ion etching

The aspect ratio dependent etching of deep trenches in silicon is investigated as a function of polymer deposition rate which, in turn, depends on the C2Cl3F3 content in a SF6C2Cl3F3 gas mixture. The experimental results are compared to computer simulations. A model which takes into account simultaneous ion-enhanced etching and polymer deposition is developed to explain the observed two-dimensional effects such as feature size dependent profile evolution, RIE lag, and inverse RIE lag. Computer program includes different transport mechanisms of ions, reactive neutrals, polymer precursors and some parameters, namely, the angular distributions of species, sticking coefficients, and re-emission functions. The influence of these parameters on aspect ratio dependent etching is considered.

Molecular-dynamics simulations of direct reactive ion etching of silicon by fluorine and chlorine

We report results from molecular-dynamics simulations of F+ and Cl+ impact of silicon surfaces, at normal incidence and over a range of energies (10, 25, and 50 eV). The halogen content of the silicon layer increases with halogen fluence, and the simulations are continued until an apparent, quasisteady state in halogen coverage has occurred. Although in some cases the quantitative results differ, F+ and Cl+ are qualitatively similar in steady-state halogen coverage, depth of penetration, etch mechanisms, and etch yield dependence on ion energy. In both cases, a mixed halogenated silicon layer forms, with a substantial degree of surface roughness (∼1–2 nm for 25 or 50 eV ions). At 10 eV for both F+ and Cl+, the apparent steady-state coverage is about 2 equivalent monolayers and the depth of F+ (Cl+) penetration is about 15 Å. For 25 and 50 eV ions, the corresponding coverage (approximately independent of ion energy and type) is about 3 monolayers. The corresponding depth of penetration is about 35 Å. The silicon etch yield is a function of ion composition and energy: These values ranged from 0.25 at 10 eV to 0.45 at 50 eV for F+ and from 0.06 at 10 eV to 0.14 at 50 eV for Cl+. Simulations revealed that the dominant Si etch mechanism and the silicon etch product stoichiometry changed with ion energy. In addition to physical and chemical sputtering, an additional etch mechanism has been observed in the simulations. We term this mechanism direct abstractive etching (DAE). In DAE, an incoming F+ reacts with a surface SiFx, creating a volatile SiFx+1 that leaves the surface with nonthermal energies, similar to physically sputtered products. At 10 eV F+, DAE accounts for ∼80% of the etched species, but at higher energies this mechanism is less likely. DAE is observed for Cl+ impact as well. Comparison of simulation predictions to available experimental results shows at least qualitative agreement, suggesting the approximations made in the simulations are reasonable.

Anisotropic Reactive Ion Etching of Silicon Using SF 6 / O 2 / CHF 3 Gas Mixtures

Reactive ion etching of silicon in an RF parallel plate system, using , plasmas has been studied. Etching behavior was found to be a function of loading, the cathode material, and the mask material. Good results with respect to reproducibility and uniformity have been obtained by using silicon as the cathode material and silicon dioxide as the masking material for mask designs where most of the surface is etched. Etch rate, selectivity, anisotropy, and self‐bias voltage have been examined as a function of flow, flow, flow, pressure, and the RF power, using response surface methodology, in order to optimize anisotropic etching conditions. The effects of the variables on the measured responses are discussed. The anisotropic etch mechanism is based on ion‐enhanced inhibitor etching. provides the reactive neutral etching species, supplies the inhibitor film forming species, and and generate ion species that suppress the formation of the inhibitor film at horizontal surfaces. Anisotropic etching of high aspect ratio structures with smooth etch surfaces has been achieved. The technique is applied to the fabrication of three‐dimensional micromechanical structures.

Small free energy barrier and postdesorption collisions: The keys towards the understanding of reactive ion etching of silicon.

Reactive ion etching of Si with C${\mathrm{l}}_{2}$ as the reactive gas has been examined with molecular dynamics simulations. The volatility of ${\mathrm{SiCl}}_{x}$ molecules is determined by Gibbs free energy calculations as a function of temperature. The high entropy of activation of the desorbing molecules results in an unexpected low desorption barrier under etching conditions. Etching simulations show that many sputtered molecules undergo one or more collisions with protrusions on the corrugated surface. This results in a redistribution of the kinetic energy and a consistent interpretation of experimental results.

Highly anisotropic room-temperature sub-half-micron Si reactive ion etching using fluorine only containing gases

Silicon reactive ion etching using a mixture of SF 6 and CHF 3 at room temperature was investigated. The etching characteristics as a function of gas composition, rf power, pressure and masking material as well as electrode material were studied. Highly anisotropic, vertical and with smooth surface silicon pillars, lines and trenches with aspect ratios as high as 25:1 with dimensions down to 50 nm were obtained

Process-induced particle formation in the sputtering and reactive ion etching of silicon and silicon dioxide

Particle formation has been studied in Ar sputtering plasmas and CCl2F2-Ar reactive ion etching plasmas from Si and SiO2 substrates by laser light scattering, scanning and transmission electron microscopy and optical emission plasma diagnostics. Particles nucleate and grow continuously, and are swept out into the exhaust under a wide variety of plasma conditions. Within a more limited range of values for pressure and flow rate, particles grow large enough in the plasma so as to form a particle cloud suspended above the substrate. Stability and position of the cloud depend on the process conditions. When particles become visible by light scattering, at a diameter of about 200 nm, they are essentially spherical and monodisperse in size, but the size distribution becomes much wider as the average particle size increases with increasing discharge time. In sputtering, particles smaller than about 100 nm are quite porous, have a somewhat more irregular shape and exhibit a spherulitic (spherically columnar) mode of growth. Optical emission spectroscopy of the plasma and compositional analysis of the particles indicate that in all cases, Si atoms are responsible for particle nucleation and growth. These observations are discussed in terms of possible mechanisms for generation and transport of plasma species in the discharge, particle nucleation and growth, particle transport and particle cloud formation.

Analysis and removal of impurities and defects in reactive ion etched silicon using a novel depth-profiling technique

The analysis and removal of residual damage induced by reactive ion etching of silicon were studied with a new ultrashallow depth-profiling technique of silicon. In this technique, which is known to give a depth resolution of better than 0.5 nm [Lau et al., Appl. Phys. Lett. 63, 78 (1993)], a few atomic layers of silicon were oxidized by an ultraviolet/ozone exposure at room temperature and subsequently removed by an HF wet etch. In the present study, the compositional changes during depth profiling and the amount of silicon removed per oxidation/etch cycle were estimated by x-ray photoelectron spectroscopy. In addition, Rutherford backscattering spectroscopy was used to confirm the compositional changes and to measure defect depth distributions. Further, surface-charge spectroscopy was applied to determine the minimum oxidation/etching required to completely remove Fermi-level pinning associated with the residual damage. The results showed that these profiling and analysis techniques, when applied in a coherent manner, can provide an accurate picture of the residual damage induced by reactive ion etching. More importantly, the study also showed that the oxidation/etching technique can be applied as a well-controlled process for removing the residual damage.

Monte Carlo simulation and measurement of silicon reactive ion etching profiles

A two-dimensional plasma etching model based on the simbad Monte Carlo thin-film growth simulation program has been modified to include ion-enhanced etch processes. The modified program has been applied to a study of sidewall passivation in the etching of silicon in a CF4/O2 plasma. Experimentally measured mask undercut in the etching of 0.8-μm-wide lines was reduced from 150 Å/min to virtually zero with an increase in oxygen from 8% to 45% of total gas flow. The corresponding decrease in etch rate was from about 750 to 325 Å/min. Simulations account for this change based on competition between oxidation and flourine etching of the silicon surface. Reactive gases follow collisionless trajectories at the simulation scale and have a high probability of diffuse re-emission following contact with the surface. This simulation method extends current profile simulation capabilities for a well-known etching chemistry.

Temperature dependent electron-beam-induced-current investigation of electronic damages in silicon due to reactive ion etching

The damage introduced by reactive ion etching in silicon was investigated by the planar-electron-beam-induced-current (PEBIC) method. A reduction of the EBIC signal in the etched areas is detected and studied of temperature dependency in the range of 5 K<T<300 K. The EBIC contrast between etched and unetched areas increases with decreasing temperature. Our results are interpreted by a reduction of the net acceptor dopant impurity near the etched surface.

Experimental study of anisotropy mechanisms during reactive ion etching of silicon in a SF6/C2Cl3F3 plasma

Abstract The experimental results of the investigations of the mechanisms of anisotropy of silicon RIE, using a SF6/C2Cl3F3 plasma, are presented and discussed.

Influence of reactant transport on fluorine reactive ion etching of deep trenches in silicon

The reactive ion etching of silicon by fluorine in high-aspect ratio features was modeled to assess the relative importance of reactant transport on etching rate at the bottom of rectangular trenches. The flux of ions to the feature bottom was found by summing two components: ions arriving directly from the plasma and ions reflected from the sidewalls before reaching the bottom. The transport of neutral reactants within the feature was modeled with diffuse scattering and reaction rates following the kinetics reported by Gray et al. [J. Vac. Sci. Technol. B 11, 1243 (1993)] at all surfaces. The etching rate was found to depend most strongly upon the ion flux under typical process conditions, because of relatively low fluorine reaction probability and low reactant depletion within the feature. Reactant transport limitations are expected to be more important under conditions of low fluorine to ion flux ratio, high-substrate temperature, and high-ion energy.

Mass and energy analysis of gaseous species in NF3 plasma during silicon reactive ion etching

Neutral molecules and positive ions, extracted directly from the reaction zone during reactive ion etching of silicon in NF3 plasma, have been identified by quadrupole mass spectrometry. The main etching end products are SiF4 molecules and SiF+3 ions. Reactive species that contribute to the etching are atomic F radicals and F+2 molecular ions. Most of the positive ions in the plasma hold NF+2 ions and this facilitates etching of negatively biased Si by bombardment. Likewise, the kinetic energy of ions that impinge on an electrically grounded surface can be measured by using a cylindrical mirror analyzer. Within a certain range of plasma parameters there are no obvious differences in kinetic energies among the observed ions in the plasma. Under a constant NF3 pressure of 6.7 Pa, the characteristic mean ion energy of 4 eV at an rf power of 10 W increases to 20 eV by increasing the rf power to 90 W.