Reactive Ion Etching System Research Articles

Fast ultra-deep silicon cavities: Toward isotropically etched spherical silicon molds using an ICP-DRIE

This paper investigates the parameter optimization of isotropic bulk silicon microscale etching using an inductively coupled plasma-deep reactive ion etching (ICP-DRIE) system. Etch profile characteristics, depending on the process and feature size, have been studied. The authors report detailed observations of the results for various etching parameters, including pressure from 30 to 70 mTorr, sulfur hexafluoride flow rate from 100 to 500 sccm, platen power from 20 to 150 W, and ICP power from 2000 to 2500 W. The goal here is to present anisotropic and isotropic etch processes for a wide range of applications in microfluidics, microelectromechanical-systems, and micro-optoelectronic mechanical system fabrication. A deep anisotropic etch through a 1.4 mm thick silicon wafer with smoothly etched surfaces has been achieved. Isotropic plasma etching is obtained, including a relation between the etching depth, the undercut, and the normalized radius of curvature of the profile. The authors have demonstrated an isotropic plasma potential that is much higher than those that can be produced by isotropic wet etching of silicon for the generation of more complex forms such as the manufacturing microlens molds. In particular, the authors have presented the possibility of creating aspheric shapes with a desirable negative conic constant (k<0) and a potential high numerical aperture. The choice of using photoresist masks provides better flexibility and economical processing. The presented results can be valuable for a wide range of applications, thus allowing a massive production using only a single commercial ICP-DRIE tool, which is of low cost and is compatible with an industrial perspective.

Plasma etched c-Si wafer with proper pyramid-like nanostructures for photovoltaic applications

Dry and maskless texturing process of mono-crystalline silicon wafers using CF4/O2 plasma in a reactive ion etching (RIE) system has been developed with the aim of obtaining optimized surface texture characterized by low optical reflection loss for photovoltaic applications. In this study c-Si has been successfully subjected to plasma etching at unusual process conditions, specifically high value of substrate temperature (15 °C) coupled with high value of process pressure (40 Pa). Different c-Si surface textures are produced at different etch durations.Specifically, pyramid-like morphology appears at very short etch time and crater-like nanostructures form at longer etch time, whereas the former gives the lowest average reflectance (<5%). Furthermore, we clearly observe a slowing down of the etching rate starting from 5 min and in correspondence with the appearance of the sponge-like structure coupled with pores formation. Geometric parameters of morphological features, such as RMS and average inclination angle of the surface features, have been correlated with some specific texture functions such as angular distribution of scattered light Ps(θ) obtained by Angular Resolved Scattering (ARS) technique. Shape and slope of the texture features strongly determine the amount of forward scattered light and, as a consequence, the amount of reflectance decrease. Surface texture obtained after only 3 min of etch and characterized both by well distributed small normal pyramids and by high average inclination angle, proves to be more effective in giving reflection reduction respect to other surface textures characterized by inhomogeneously distributed large cavities. Finally, we can well suppose that this small pyramid-like texture on Si-substrates can be used for the preparation of highly efficient heterojunction-based solar cells (Si-HJT).

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.

Fabrication of Miniaturized Capacitive Pressure Sensor Using Thin Film Metallic Glass

In this paper, we proposed the process of the diaphragm for miniaturizing MEMS capacitive pressure sensor and controlling its sensitivity. We fabricated micro diaphragm using a Ru 65 Zr 30 Al 5 (at.%) thin film metallic glass (TFMG). The as-sputtered TFMG on Si substrate were annealed at 315-440°C for 5 minutes in vacuum. After annealing, micro diaphragms were fabricated by an etching Si substrate using a reactive ion etching system. Although the diaphragm without annealing had dome structure, the diaphragm annealed above 340°C formed a flat structure. The deflection of the diaphragm against applied pressure depended on the annealing temperature and decreased at higher temperatures. The pressure sensor was modeled using this diaphragms. The pressure measurement range and sensitivity were 250 Pa and 6.4×10-3 pF/Pa, respectively, for annealed at 340°C, and 1800 Pa, and 8.1 × 10-4 pF/Pa, respectively for annealed at 440°C.

Design, Fabrication, and Characterization of Scandium Aluminum Nitride-Based Piezoelectric Micromachined Ultrasonic Transducers

This paper presents the design, fabrication, and characterization of piezoelectric micromachined ultrasound transducers (PMUTs) based on scandium aluminum nitride (ScxAl1–xN) thin films (x = 15%). ScAlN thin film was prepared with a dual magnetron system and patterned by a reactive ion etching system utilizing chlorine-based chemistry with an etching rate of 160 nm/min. The film was characterized by X-ray diffraction, which indicated a crystalline structure expansion compared with pure AlN and a well-aligned ScAlN film. ScAlN PMUTs were fabricated by a two-mask process based on cavity SOI wafers. ScAlN PMUTs with 50- and 40- $\mu \text{m}$ diameter had a large dynamic displacement sensitivity measured in air of 25 nm/V at 17 MHz and 10 nm/V at 25 MHz, twice that of AlN PMUTs with the same dimensions. The peak displacement as a function of electrode coverage was characterized, with maximum displacement achieved with an electrode radius equal to 70% of the PMUT radius. Electrical impedance measurements indicated that the ScAlN PMUTs had 36% greater electromechanical coupling coefficient ( $\text{k}_{\mathrm {t}}^{2})$ compared with AlN PMUTs. The output pressure of a $7\times7$ ScAlN PMUT array was 0.7 kPa/V at ~1.7 mm away from the array, which is approximately three times greater that of an $8\times8$ AlN PMUT array with the same element geometry and fill factor measured at the same distance. Acoustic spreading loss and PMUT insertion loss from mechanical transmit to receive were characterized with a 15 $\times $ 15 ScAlN PMUT array via hydrophone and laser Doppler vibrometer. [17509-2017]

Atomic layer etching of gallium nitride (0001)

In this work, atomic layer etching (ALE) of thin film Ga-polar GaN(0001) is reported in detail using sequential surface modification by Cl2 adsorption and removal of the modified surface layer by low energy Ar plasma exposure in a standard reactive ion etching system. The feasibility and reproducibility of the process are demonstrated by patterning GaN(0001) films by the ALE process using photoresist as an etch mask. The demonstrated ALE is deemed to be useful for the fabrication of nanoscale structures and high electron mobility transistors and expected to be adoptable for ALE of other materials.

Single-step inductively coupled plasma etching of sputtered Nb2O5/SiO2 multilayer stacks using chromium etch mask

This paper presents the dry etching characteristics of Nb2O5/SiO2 multilayer stacks deposited using ion beam sputtering. Dry etching is achieved by using a combination of CHF3 and Ar gases in an inductively coupled plasma (ICP)-reactive ion etching system. The effect of the etching parameters such as the gas ratio (CHF3/Ar), radio-frequency power, ICP power, chamber pressure, and temperature is investigated. An etching recipe is optimized to achieve a high etch rate, good selectivity, and optimum etch profile. The optimized etching recipe provides a single step etch solution for both dielectric materials. Furthermore, the deposition and structuring process of a chromium based etch mask is investigated.

Design and fabrication of surface trimmed silicon-on-insulator waveguide with adiabatic spot-size converters.

Theoretical and experimental studies reveal that a predefined single-mode rib waveguide fabricated in silicon-on-insulator (SOI) substrate with a device layer thickness of 2μm can be adiabatically trimmed down to submicron waveguide dimensions (<1 μm), resulting in regional modification of waveguide properties. The fabrication process involves physical trimming/removal of a waveguide surface by plasma etchants that is spatially filtered by a shadow mask with a rectangular aperture inside a reactive ion etching system. The exact position of a shadow mask above a sample surface has been optimized (∼500 μm) to obtain the desired adiabatic spot-size converters of length up to 1mm at both ends of the trimmed waveguides. For experimental demonstration, three different sets of 15-mm-long single-mode waveguides fabricated in 2-μm SOI were adiabatically trimmed in the middle for three different lengths of 3, 5, and 7mm, respectively. Excess propagation loss and group index of a trimmed submicron waveguide section were extracted by analyzing the wavelength-dependent Fabry-Perot transmission characteristics of the device with polished input/output end facets. The insertion loss of a typical spot-size converter designed for the guidance of TE-like polarization has been recorded to be ∼0.25 dB for a wide range of wavelengths (1500 nm≤λ≤1600 nm). As predicted by numerical simulation, no polarization rotation has been observed in all the trimmed submicron waveguides. The proposed surface trimming technique can be potentially used to tune the waveguide cross-section/geometry for phase error correction and/or to avail stronger light-matter interactions at a desired location of an integrated optical circuit.

Development of Desk Top Thermally Assisted Reactive Ion Etching Systems

Development of Desk Top Thermally Assisted Reactive Ion Etching Systems

Microstructure Formation on Polytetrafluoroethylene (PTFE) and Perfluoroalkoxy (PFA) Bulk Plates by a Magnetron Enhanced Reactive Ion Etching System

Microstructure Formation on Polytetrafluoroethylene (PTFE) and Perfluoroalkoxy (PFA) Bulk Plates by a Magnetron Enhanced Reactive Ion Etching System

Integrated Optical Rectangular-Edge Filter Devices in SOI

An integrated optical design of a rectangular-edge filter device in 250-nm silicon-on-insulator platform is proposed and demonstrated experimentally. The device is designed with a multimode waveguide (supporting at least two modes) with asymmetric side-wall grating, which is adiabatically interfaced with input/output single-mode waveguides. The input/output access waveguides are terminated with grating couplers for optical characterizations. Design parameters are optimized for a sharp-edge or nearly rectangular-edge filter response in optical C-band (1530 nm $\leq \lambda _{\text{edge}} \leq $ 1565 nm). The submicron features and the entire footprint of the devices were defined with a single-step e-beam lithography process by using negative-tone resist and subsequent dry etching of $\sim$ 100 nm by using an inductively coupled reactive ion etching system. All the fabricated devices exhibit a rectangular-edge filter response at $\lambda _{\text{edge}} \sim $ 1560 nm with an edge-extinction of $>$ 40 dB at the rate of 118 dB/nm. The rectangular-edge is followed by a broad pass-band of $\sim $ 40 nm till the first-order Bragg reflected wavelength of $\lambda _B^{00} \sim $ 1600 nm in the transmission characteristics obtained for 1520 nm $\leq \lambda \leq$ 1620 nm. Tunability of a rectangular-edge filter is verified with cladding refractive index change and the observed refractive index sensitivity of the edge is $\sim$ 18 nm/RIU. The limit of detection for 1-dB transmitted power extinction at $\lambda _{\text{edge}}$ of a typical fabricated device is estimated to be 5.3 $\times\, \text{10}^{-4}$ RIU.

Experimental realization of Talbot array illumination for a 2-dimensional phase grating

We present the result of a multiple phase level Talbot array illuminator (TAI) based on two dimensional phase grating. The grating was fabricated on glass by a Deep Reactive Ion Etching (DRIE) system with optimized gas combination recipe. The opening ratio of the grating is ∼0.71 with a phase step of 11π. The experimental study on Talbot array illuminations (TAI's) of this fabricated device in near-field region was carried out using a He-Ne laser. The TAI's were observed at the positions 2.81 mm, 8.59 mm, 14.28 mm, and 20.57 mm along the light propagation direction. The computer simulations of wave field distribution in near field region at different fractional Talbot distances have been generated. These simulated results are in reasonably good agreement with our experimental observed results. Our analysis on Talbot array illumination (TAI's) shows that the multiple harmonic phase modulations are transformed into intensity modulations at 1/8, 3/8, 5/8, and 7/8 fractional Talbot position. We have observed three different grating images, viz., attenuated, phase contrast, and diffraction contrast images. We also show the presence of a considerable amount of phase change at the edge of each phase sublevel that enhances the contrast of differential phase contrast imaging. Therefore, the phase contrast signal can be detected at a fractional position using single phase grating without the need of phase stepping.

Surface micromachining of polydimethylsiloxane for microfluidics applications.

Polydimethylsiloxane (PDMS) elastomer has emerged as one of the most frequently applied materials in microfluidics. However, precise and large-scale surface micromachining of PDMS remains challenging, limiting applications of PDMS for microfluidic structures with high-resolution features. Herein, surface patterning of PDMS was achieved using a simple yet effective method combining direct photolithography followed by reactive-ion etching (RIE). This method incorporated a unique step of using oxygen plasma to activate PDMS surfaces to a hydrophilic state, thereby enabling improved adhesion of photoresist on top of PDMS surfaces for subsequent photolithography. RIE was applied to transfer patterns from photoresist to underlying PDMS thin films. Systematic experiments were conducted in the present work to characterize PDMS etch rate and etch selectivity of PDMS to photoresist as a function of various RIE parameters, including pressure, RF power, and gas flow rate and composition. We further compared two common RIE systems with and without bias power and employed inductively coupled plasma and capacitively coupled plasma sources, respectively, in terms of their PDMS etching performances. The RIE-based PDMS surface micromachining technique is compatible with conventional Si-based surface and bulk micromachining techniques, thus opening promising opportunities for generating hybrid microfluidic devices with novel functionalities.

Structural Control of Hybrid Colloidal Particle Surface by Plasma-etching Treatment

A reactive-ion etching system was used to control the surface of gold–polystyrene hybrid colloidal particles with an eccentric structure, and a function of the etched particles was demonstrated as ...

Fabrication of High Aspect Ratio SiO2and Tempax Glass Pillar Structures and Its Application for Optical Modulator Device

This paper presents the fabrication of deep SiO2 and Tempax glass pillar structures by using reactive ion etching system, which intends to realize optical modulator mounted on an image sensor. The optical modulator consists of high aspect ratio SiO2 or Tempax glass pillars that can modulate the transmitted light intensity by moving a liquid in and out of the spaces between pillars based on the reversible electrowetting of liquid on top of micro-pillars surfaces. SiO2 pillars having smooth surfaces, vertical shapes, and high aspect ratio of 12 with a depth of 12 $\mu \text{m}$ , diameter of 1 $\mu \text{m}$ , and the pitch of the two pillars of $2~\mu \text{m}$ has been achieved. In addition, Tempax glass pillar structures are also successfully fabricated under investigation of gas mixtures of SF6 and O2. Finally, a 7.2 mm $\times \,\, 9.6$ mm optical window area integrated with an image sensor for an optical modulator has been demonstrated where high transmission modulation together with a large contrast has been observed of approximately 65% and 0.86 for cases with and without matching oil penetration, respectively. [2016-0036]

Effects on micropyramid and nanoneedle structures for superhydrophobicity on Si surface

This study proposes a method for increasing hydrophobicity using a reactive ion etching (RIE) system. The aim was to study and optimize a surface with hierarchical structures. The effects of micropyramid and nanoneedle structures were investigated for improving superhydrophobicity on the Si surface. To investigate the effects of nanoneedle structures for hydrophobicity, RIE parameters such as the gas ratio, gas pressure, and process time were changed. To compare the contact angles with varying parameters, polytetrafluoroethylene (PTFE) was coated to eliminate oxidation effects on the Si surface. The optimized process conditions for the superhydrophobic surface were saw damage removal for 40 min and RIE for 20 min with O2/SF6 = 33%/67%. In the optimized process, the contact angles for the micropyramid, PTFE coating on the micropyramid, micropyramid and nanoneedle, and PTFE coating on the micropyramid and nanoneedle samples were 102.8°, 132.5°, 142.8°, and 171.7°, respectively.

0.76% absolute efficiency increase for screen-printed multicrystalline silicon solar cells with nanostructures by reactive ion etching

In this study, the reactive ion etching in combination with alkaline etching was employed to texture the surface of a 156×156mm2 multi-crystalline silicon wafers to reduce their solar reflectivity and improve conversion efficiency. Reactive gases comprising chlorine (Cl2), sulfur hexafluoride (SF6) and oxygen (O2), were activated in the radio-frequency (rf) plasma to fabricate pyramids in an reactive ion etching (RIE) system. The multi-crystalline Si substrates were etched in various compositions of gases to form the nanostructures of various shapes. Besides the nanoscale features, the high density of nanostructures formed on the multi-crystalline Si surface was also required to significantly reduce the reflectivity. A low reflectivity surface was successfully fabricated with the average reflectivity significantly reduced down to <2% for the wavelength range of 300–850nm. The short wavelength spectral response (blue response) improvement is observed in RIE textured solar cells compared to the standard textured cells. The RIE textured surfaces in combination with optimized emitter resistance result in a remarkable enhancement of short circuit current density. Compared with the acidic textured solar cells, the absolute conversion efficiency of the alkaline+RIE textured cells was improved by 0.76% in average.

NV-center diamond cantilevers: Extending the range of available fabrication methods

We present an alternative fabrication process for single crystal diamond cantilevers that consist of a platform carrying a nanopillar containing nitrogen vacancy centers close to its surface. These cantilevers are suitable for vector magnetometry by fitting them to the scanning unit of an atomic force microscope. Our methods extend existing technology to lower electron voltages (30kV) and standard reactive ion etching. Special procedures are presented to overcome both restrictions due to charging of the diamond during electron beam lithography and limitations of the etch depth due to the low plasma density in reactive ion etching systems. The presence of nitrogen vacancy centers in the fabricated nanostructures is confirmed by photoluminescence measurements.

Improvement of conversion efficiency of multi-crystalline silicon solar cells using reactive ion etching with surface pre-etching

In this study, a large-area (156×156mm2) sub-wavelength antireflection structure has been fabricated on multi-crystalline Si substrates to reduce their surface reflectivity. A reactive ion etching (RIE) system was used to fabricate nanostructures on the multi-crystalline silicon surface. Reactive gases, comprised of chlorine (Cl2), sulfur hexafluoride (SF6) and oxygen (O2), were activated to fabricate nanoscale pyramids by radio frequency plasma. The pre-etching of poly-Si substrates using acidic and alkaline solutions was studied for creating the microstructures, which may affect the subsequent formation of nano-structures by RIE. Both the solar reflectance and the effective carrier lifetimes of multi-crystalline Si surface are measured to understand the effects of two pre-etching solutions. The pre-etching of silicon wafers using the acidic solution before RIE was found to improve the solar cell efficiency better than that using the alkaline solution. The absolute efficiency of solar cells with acidic pre-etching and RIE texturing can be improved by 0.64% over the traditional conventional cells.

Control of 3D IC process steps by optical metrologies

This paper evaluates various optical metrology techniques for in-line control of the uniformity of 3D stacked structures. Advanced packaging technologies are rapidly evolving and 3D architectures require very well controlled process steps. Optical metrology techniques are now used for TSV but also for interconnect processing. In engineering mode, at the process implementation step, these techniques must be evaluated and then used to get uniform and repeatable processes. Among the 3D TSV Via middle process flow, the temporary bonding, wafer thinning and TSV reveal are key 3D process steps to get a uniform backside copper nail signature. High aspect ratio TSV are etched in Front End of the line and deep reactive ion etching systems generates radial non uniformities signatures. The wafer backside processing challenge consists in compensating this issue among the entire wafer surface. In this paper, all these process steps were characterized in order to quantify their specific intra-wafer dispersion signature .of the related key parameters. Cross correlation between the various intra-wafer process step signatures was then analyzed to verify the data set consistency and several process parameters analyzed to get a simple model. This model was then used to get a very uniform copper nail signature. For small diameter TSV and corresponding copper nails, a comparison has been done between full field OCT and confocal chromatic techniques.