Reactive Ion Etching Process Research Articles

Ultraviolet Laser Damage Dependence on Contamination Concentration in Fused Silica Optics during Reactive Ion Etching Process.

The reactive ion etching (RIE) process of fused silica is often accompanied by surface contamination, which seriously degrades the ultraviolet laser damage performance of the optics. In this study, we find that the contamination behavior on the fused silica surface is very sensitive to the RIE process which can be significantly optimized by changing the plasma generating conditions such as discharge mode, etchant gas and electrode material. Additionally, an optimized RIE process is proposed to thoroughly remove polishing-introduced contamination and efficiently prevent the introduction of other contamination during the etching process. The research demonstrates the feasibility of improving the damage performance of fused silica optics by using the RIE technique.

Laboratory demonstration of a broadband six-level phase mask coronagraph.

The six-level phase mask (SLPM) can be used in a focal plane as an efficient coronagraph [Opt. Express 22, 1884 (2014)]. It has several advantages: high-contrast imaging in broadband with small inner working angle; easy fabrication at low cost by photolithography and reactive ion etching processes; easy implementation with no need of pupil apodization. We present in this paper the first laboratory results demonstrating the high performance of a SLPM with an unobscured pupil. The on-axis attenuation reaches 2 × 10-5 at λ = 800 nm and is better than 10-4 over a 10% spectral bandwidth and better than 10-3 over a 20% bandwidth. Finally, the detection of a planet can be achieved down to 1 λ/D.

Exploitation of semi‐sequential reactive ion etch processes to fabricate in‐plane Si structures

The work reports on the exploitation of semi-sequential deep reactive ion etching (RIE) processes for realisation of deep vertically etched Si structures on Si substrate applicable in fibre-optic sensing systems. These processes employ different mixtures of gases including hexaflourosulphide, hydrogen and oxygen in a RIE system with a programmed passivation and etching sub-cycles. In the so-called semi-sequential processes, the intermediate purging steps are eliminated, which results in remaining little trace of reactant gases from the previous sub-cycle in the RIE machine's chamber, which can participate in the process of current sub-cycle. For the sake of minimum optical losses, which are accomplished by highly smooth vertical sidewalls, several etching processes were applied. In these processes, by controlling the etching parameters such as the flow of gases, plasma power and timing of each subsequence, the process can be controlled for minimum under-etch and surface roughness and maximum verticality of sidewalls. However, time and cost considerations should also be noted in the optimum fabrication process.

A 3-D-Silicon Nanowire FET Biosensor Based on a Novel Hybrid Process

Single-silicon nanowire field-effect transistor (SiNW-FET) devices are powerful tools for the detection and quantification of biochemical molecules. However, traditional SiNW-FET-based biosensors demonstrate low output signals and high fluctuation noises, which results from the tiny scale of a single channel and electrical property deterioration caused by the dry etching process. To improve the performance of the SiNW-FET biosensors, here we developed a 3-D-SiNW-FET by using a hybrid process of deep reactive ion etching and isotropic wet etching with HF, HNO3 and HAc (HNA) mixed solution. The 3-D-SiNW-FET that included $5\times7$ nanowire channels with a wire diameter of approximately 300 nm was successfully fabricated with the novel hybrid process. Compared with the performance of single-and 2-D-SiNW-FETs, the 3-D-SiNW-FET showed a fairly good ability to stabilize and enhance the source-drain current by parallelizing the signals of the multiple channels. With the fabricated 3-D-SiNW-FET, immunoglobulin G was detected at a concentration as low as 5 fM. [2017-0102]

Fabrication of Si3N4/SiO2 tiered resonant nanopillars with nickel caps arrays: application for optochemical sensing

A controlled, 3D selective inductively coupled plasma reactive ion etching process (ICP-RIE) was employed to fabricate high aspect ratio tiered resonant nanopillars (TR-NPs) made of two Bragg reflectors consisting of a stack of Si3N4/SiO2 alternate layers, a resonant SiO2 central cavity, and nickel caps. The 3D etching process led to a vertical full etching, and also to a horizontal highly selective etching that preserves SiO2 layers while the Si3N4 layers are slowly etched. Resulting TR-NPs periodic arrays were tested as optical sensors and highlighted a 28% increment in bulk sensitivity (379 nm RIU−1) comparing with conventional Si3N4/SiO2 resonant NPs without metal caps (296 nm RIU−1) considering the resonance feature located in the 580-630 nm wavelength range.

Design optimization and antireflection of silicon nanowire arrays fabricated by Au-assisted chemical etching

In this work, we have synthesized a highly periodic silicon nanowire (SiNW) arrays with the spacing from 300 nm to 1000 nm by combining nanosphere lithography (NSL) and metal-assisted chemical etching (MACE). It has been demonstrated that it is effective to produce large-area, well-separated and controlled SiNW arrays. We also present a simple method to solve the problem of distorting spherical shape by angled-deposition method according to shadowing effect during NSL process. So we do not need to reduce the diameter of polystyrene (PS) spheres heavily and avoid making spherical shape distorted and rough. The large-area Au meshes can be further optimized using angled-deposition method and have a small nanohole diameter and relatively large nanohole spacings. And the center-center distance of PSs used as mask merely keeps invariable with 820 nm and 1300 nm pitch after reactive ion etching (RIE) process. The method help improve the distortion of spherical shape heavily during NSL process so that we can obtain SiNW arrays with controlled diameter, length and density using the non-close-packed PSs as the mask. Furthermore, the SiNW arrays obtained by MACE can improve antireflection properties of silicon substrate. The high surface area of SiNW arrays makes the reflectance below 10% or less over a wavelength range of 300–1000 nm. The antireflection structure (ARS) is great of importance in application of nanoscale optical devices.

Drug loaded biodegradable polymer microneedles fabricated by hot embossing

This study demonstrates a fast low temperature method for fabrication of drug loaded polymer microneedles (MNs). First, arrays of tapered pillar MNs with a length of 275 ± 3 μm (mean ± SD) and a diameter of 84 ± 1 μm were fabricated in Si with a three-step deep reactive ion etching (DRIE) process. The Si MNs were used as a template for fabrication of polydimethylsiloxane (PDMS) stamps. The stamps were applied for replication of the MNs in spin coated poly‑ε‑caprolactone (PCL) films by hot embossing at 60 °C and a pressure of 1.4 MPa for 3 min. The resulting PCL MNs perfectly resembled the Si MNs and had a length of 270 ± 5 μm and a diameter of 84 ± 3 μm. The MNs had sufficient mechanical strength to penetrate the surface of a 10 w/w% gelatine gel without deformation. Finally, PCL MNs containing 20 w/w% of furosemide were fabricated and drug release by diffusion was demonstrated.

Advanced Fabrication of Single-Crystal Diamond Membranes for Quantum Technologies.

Many promising applications of single crystal diamond and its color centers as sensor platform and in photonics require free-standing membranes with a thickness ranging from several micrometers to the few 100 nm range. In this work, we present an approach to conveniently fabricate such thin membranes with up to about one millimeter in size. We use commercially available diamond plates (thickness 50 m) in an inductively coupled reactive ion etching process which is based on argon, oxygen and SF. We thus avoid using toxic, corrosive feed gases and add an alternative to previously presented recipes involving chlorine-based etching steps. Our membranes are smooth (RMS roughness <1 nm) and show moderate thickness variation (central part: <1 m over ≈200 × 200 m). Due to an improved etch mask geometry, our membranes stay reliably attached to the diamond plate in our chlorine-based as well as SF-based processes. Our results thus open the route towards higher reliability in diamond device fabrication and up-scaling.

Preparation of composite micro/nano structure on the silicon surface by reactive ion etching: Enhanced anti-reflective and hydrophobic properties

A silicon substrate with micro-pyramid structure (black silicon) is prepared by wet chemical etching and then subjected to reactive ion etching (RIE) in the mixed gas condition of SF6, CHF3 and He. We systematically study the impacts of flow rates of SF6, CHF3 and He, the etching pressure and the etching time on the surface morphology and reflectivity through various characterizations. Meanwhile, we explore and obtain the optimal combination of parameters for the preparation of composite structure that match the RIE process based on the basis of micro-pyramid silicon substrate. The composite sample prepared under the optimum parameters exhibits excellent anti-reflective performance, hydrophobic, self-cleaning and anti-corrosive properties. Based on the above characteristics, the composite micro/nano structure can be applied to solar cells, photodetectors, LEDs, outdoor devices and other important fields.

Improvement of Deep Reactive Ion Etching Process For Motional Resistance Reduction of Capacitively Transduced Vibrating Resonators

Motional resistance is one of the most important performance metrics for high qualitfy factor, low power, and complementary metaloxide semiconductor (CMOS)-compatible capacitively transduced vibrating micromechanical resonators. The motional resistance is primarily set by the electrode-to-resonator air gap that can be formed by deep reactive ion etching (DRIE) process. Although the state-of-the-art DRIE technologies can achieve a narrow capacitive air gap down to 1 m or less, the effective gap tends to be larger than designed values due to the sidewall roughness known as scalloping. Systematic modifications of all key process parameters are presented in this article for lowering the sidewall roughness to result in an up to 2x reduction of the effective capacitive transducer gap, which could lead to an up to 16x decrease of the effective motional resistance.

Improvement in current density of nano- and micro-structured Si solar cells by cost-effective elastomeric stamp process

Effective incident light should be controlled for improving the current density of solar cells by employing nano- and micro-structures on silicon surface. The elastomeric stamp process, which is more cost effective and simpler than conventional photolithography, was proposed for the fabrication of nano- and micro-structures. Polydimethylsiloxane (PDMS) was poured on a mother pattern with a diameter of 6 μm and a spacing of 2 μm; then, curing was performed to create a PDMS mold. The regular micropattern was stamped on a low-viscosity resin-coated silicon surface, followed by the simple reactive ion etching process. Nano-structures were formed using the Ag-based electroless etching process. As etching time was increased to 6 min, reflectance decreased to 4.53% and current density improved from 22.35 to 34.72 mA/cm2.

Enhanced blue responses in nanostructured Si solar cells by shallow doping

Optimally designed Si nanostructures are very effective for light trapping in crystalline silicon (c-Si) solar cells. However, when the lateral feature size of Si nanostructures is comparable to the junction depth of the emitter, dopant diffusion in the lateral direction leads to excessive doping in the nanostructured emitter whereby poor blue responses arise in the external quantum efficiency (EQE). The primary goal of this study is to find the correlation of emitter junction depth and carrier collection efficiency in nanostructured c-Si solar cells in order to enhance the blue responses. We prepared Si nanostructures of nanocone shape by colloidal lithography, with silica beads of 520 nm in diameter, followed by a reactive ion etching process. c-Si solar cells with a standard cell architecture of an Al back surface field were fabricated varying the emitter junction depth. We varied the emitter junction depth by adjusting the doping level from heavy doping to moderate doping to light doping and achieved greatly enhanced blue responses in EQE from 47%–92% at a wavelength of 400 nm. The junction depth analysis by secondary ion mass-spectroscopy profiling and the scanning electron microscopy measurements provided us with the design guide of the doping level depending on the nanostructure feature size for high efficiency nanostructured c-Si solar cells. Optical simulations showed us that Si nanostructures can serve as an optical resonator to amplify the incident light field, which needs to be considered in the design of nanostructured c-Si solar cells.

Enhanced efficiency of crystalline Si solar cells based on kerfless-thin wafers with nanohole arrays

Several techniques have been proposed for kerfless wafering of thin Si wafers, which is one of the most essential techniques for reducing Si material loss in conventional wafering methods to lower cell cost. Proton induced exfoliation is one of promising kerfless techniques due to the simplicity of the process of implantation and cleaving. However, for application to high efficiency solar cells, it is necessary to cope with some problems such as implantation damage removal and texturing of (111) oriented wafers. This study analyzes the end-of-range defects at both kerfless and donor wafers and ion cutting sites. Thermal treatment and isotropic etching processes allow nearly complete removal of implantation damages in the cleaved-thin wafers. Combining laser interference lithography and a reactive ion etch process, a facile nanoscale texturing process for the kerfless thin wafers of a (111) crystal orientation has been developed. We demonstrate that the introduction of nanohole array textures with an optimal design and complete damage removal lead to an improved efficiency of 15.2% based on the kerfless wafer of a 48 μm thickness using the standard architecture of the Al back surface field.

Sub-10 nm electron and helium ion beam lithography using a recently developed alumina resist

Electron Beam Lithography (EBL) at sub-10nm resolution is mainly limited by resist contrast and proximity effects. In this work, we investigate the use of a recently developed alumina-based resist as a negative-tone resist for EBL at 100keV and focused helium ion beam lithography (FHIBL). The resist is synthesized using a sol-gel method and turns into a near completely inorganic alumina system when exposed to the electron/ion beam. We first investigate the effect on the resist contrast curve on i) development temperature; ii) stability of the resist after exposure and before post-baking and development; and iii) aging of the resist solution. We demonstrate the patterning of isolated features as small as 6.5nm using an EBL and 5nm using FHIBL and a resolution down to 10nm for FHIB exposed films. Finally, we demonstrate the pattern transfer of 10nm lines with an aspect ratio of 10 in silicon, using an optimized reactive ion etching process.

INVITED] Sensing properties of micro-cavity in-line Mach-Zehnder interferometer enhanced by reactive ion etching

In this work, we discuss an application of reactive ion etching (RIE) for enhancing the sensing properties of a micro-cavity in-line Mach-Zehnder interferometer (µIMZI). The µIMZI was fabricated using femtosecond laser micromachining in a standard single-mode fiber as a circular hole with a diameter of 54 µm. Next, the structures underwent two kinds of RIE using as reactive gases: sulfur hexafluoride (SF6) and oxygen (O2) mixtures (SF6/O2) or O2 itself. When RIE with SF6/O2 was applied, it allowed for an efficient and well-controlled etching of the fabricated structure at nanometers level observed as an increase in spectral depths of the minima in the µIMZI transmission spectrum. A similar RIE process with O2 alone was ineffective. The well-defined minima obtained with the SF6/O2 RIE significantly improved the resolution of measurements made with the µIMZI. The effect was demonstrated for high-resolution refractive index (RI) measurements of liquids in the cavity. The result of the RIE process was to clean the micro-cavity bottom, increase its depth, and smooth its sidewalls. As an additional effect, the wettability of the micro-cavity surface was improved, making the RI measurements faster and more repeatable. Moreover, we demonstrated that RIE with SF6/O2 results in more stable wettability improvement than when O2 is applied as a reactive gas.

Modified inductively coupled plasma reactive ion etch process for high aspect ratio etching of fused silica, borosilicate and aluminosilicate glass substrates

We report on the etching of glass substrates of various compositions in a modified inductively coupled plasma – reactive ion etch (ICP-RIE) tool using SF6 as the plasma source gas and NF3 and H2O gases introduced downstream near the surface of the wafer through a diffuser gas inlet. Using this modified system, we have been able to achieve etch rates as high as 1.06 μm/min, 1.04 μm/min, and 0.45 μm/min with surface smoothness of ∼2 Å, ∼67 Å, ∼4 Å for fused silica, borosilicate glass, and aluminosilicate glass respectively after 5 min etches. We examine the role of ion flux and fluorine radicals and molecules on the etch rate and the etch smoothness. We analyze the results obtained on 41 etches through multivariate statistical analysis and use the Pearson coefficient and P-value to determine the importance of these parameters for each of the glass substrate compositions. Overall for all three glass compositions, etch rate is critically influenced by ion flux. Fluorine based radicals and molecular fragments influence both the etch rate and surface smoothness of fused silica whereas they primarily influence the surface smoothness for borosilicate glass. The large fraction of impurity atoms of Ca and Al in aluminosilicate glass form non-volatile fluorides in the etched areas and therefore the etch rate and surface smoothness of aluminosilicate glass is primarily influenced ion flux and very little by the fluorine chemistry. We also examine the role of the layout of the metal mask layer on how it influences the charging of glass substrates during etching and therefore the etch rate.

Local sensor based on nanowire field effect transistor from inhomogeneously doped silicon on insulator

We present the original method for fabricating a sensitive field/charge sensor based on field effect transistor (FET) with a nanowire channel that uses CMOS-compatible processes only. A FET with a kink-like silicon nanowire channel was fabricated from the inhomogeneously doped silicon on insulator wafer very close (∼100 nm) to the extremely sharp corner of a silicon chip forming local probe. The single e-beam lithographic process with a shadow deposition technique, followed by separate two reactive ion etching processes, was used to define the narrow semiconductor nanowire channel. The sensors charge sensitivity was evaluated to be in the range of 0.1–0.2 e/Hz from the analysis of their transport and noise characteristics. The proposed method provides a good opportunity for the relatively simple manufacture of a local field sensor for measuring the electrical field distribution, potential profiles, and charge dynamics for a wide range of mesoscopic objects. Diagnostic systems and devices based on such sensors can be used in various fields of physics, chemistry, material science, biology, electronics, medicine, etc.

RIE dynamics for extreme wafer thinning applications

Over the past few years, extreme wafer thinning has acquired more interest due to its importance in 3D stacked system architecture. This technique facilitates multi-wafer stacking for via last advanced packaging. From a cost and wafer integrity point of view, it has been demonstrated that the best process flow combines grinding with fast Si removal using Reactive Ion Etching (RIE). For this integration scheme, final thickness, and global flatness are key for subsequent steps. The wafer thinning performances are driven by several steps and can lead to lot, wafer to wafer and within wafer variations especially at the extreme edge. The first part of this study is to demonstrate stable wafer thinning with good control of the remaining Si (up to 5μm) during the RIE process. This uses an innovative in-situ endpoint system (Near Infra-Red reflectometry) where the Si thickness is monitored whilst etching. The second part will focus on adjustment of the etch profile to compensate for incoming non-uniformity. This has been investigated from three different perspectives: Hardware modification where the ceramic ring surrounding the wafer is modified, process modification to change the etch front through changing the gas flow and plasma shape and changing the edge trim to introduce additional loading at the edge.

Across Substrate Lateral Dimensional Repeatability Using a Highly-Anisotropic Deep Etch Process on Fused Silica Material Layers

This letter reports the research performed on the measurement of the repeatability of the resultant lateral dimensions across fused silica substrates that were etched using an inductively-coupled plasma reactive-ion etch process. We have developed and previously reported a highly-anisotropic plasma etch process with the demonstrated etch depths of over 100 microns deep into fused silica substrates and aspect ratios greater than 10 to 1. The across substrate repeatability of the lateral dimensions of the etched features is an extremely important parameter for any plasma etch process. The measured etched feature lateral dimensional repeatability for an average etch depth of 100 microns was found to be approximately 2.41% across each wafer over a total of 120 measurements taken. The capability to etch highly-anisotropic deep features with repeatable dimensional control into fused silica has important implications for a number of important MEMS applications. [2017-0088]

Nano crystalline diamond MicroWave Chemical Vapor Deposition growth on three dimension structured silicon substrates at low temperature

Nano crystalline diamond (NCD) films grown at a temperature below 400 °C can open new applications on temperature sensitive substrates such as polymers or low-melting point alloys. One requirement for the applicative use of NCD is the ability of depositing on a structured substrate having high aspect ratio. This work presents a study on the three dimensional (3D) conformity of NCD deposition at low temperature (350 °C) and low pressure (30 Pa). Silicon wafers have been structured using a mask-less photolithography and (hardmask-less) Deep Reactive Ion Etching (DRIE) process and seeded with nano-diamond particles. The NCD films were grown on these 3D patterned Si substrates with various trench geometries to provide means of determining the limiting geometries of this technique. By measuring the step coverage with changing trench width, a threshold for conformal NCD growth can be determined. The NCD films at the bottom of the 100 μm deep trenches were continuous down to an aspect ratio of 1:7.