Conventional Reactive Ion Etching Research Articles

Improvement of Laser Damage Resistance of Fused Silica Using Oxygen-Aided Reactive Ion Etching

Reactive ion etching (RIE) with fluorocarbon plasma is a facile method to tracelessly remove the subsurface damage layer of fused silica but has the drawback of unsatisfactory improvement in laser damage resistance due to the induction of secondary defects. This work proposes to incorporate O2 into the CHF3/Ar feedstock of RIE to suppress the formation of secondary defects during the etching process. Experimental results confirm that both the chemical structural defects, such as oxygen-deficient center (ODC) and non-bridging oxygen hole center (NBOHC) defects, and the impurity element defects, such as fluorine, are significantly reduced with this method. Laser-induced damage resistance is consequently greatly improved, with the 0% probability damage threshold increasing by 121% compared to the originally polished sample and by 41% compared to the sample treated with conventional RIE.

Pseudo-Wet Plasma Mechanism Enabling High-Throughput Dry Etching of SiO2 by Cryogenic-Assisted Surface Reactions.

Manufacturing semiconductor devices requires advanced patterning technologies, including reactive ion etching (RIE) based on the synergistic interactions between ions and etch gas. However, these interactions weaken as devices continuously scale down to sub-nanoscale, primarily attributed to the diminished transport of radicals and ions into the small features. This leads to a significant decrease in etch rate (ER). Here, a novel synergistic interaction involving ions, surface-adsorbed chemistries, and materials at cryogenic temperatures is found to exhibit a significant increase in the ER of SiO2 using CF4/H2 plasmas. The ER increases twofold when plasma with H2/(CF4 + H2) = 33% is used and the substrate temperature is lowered from 20 to -60°C. The adsorption of HF and H2O on the SiO2 surface at cryogenic temperatures is confirmed using in situ Fourier transform infrared spectroscopy. The synergistic interactions of the surface-adsorbed HF/H2O as etching catalysts and plasma species result in the ER enhancement. Therefore, a mechanism called "pseudo-wet plasma etching" is proposed to explain the cryogenic etching process. This synergy demonstrates that the enhanced etch process is determined by the surface interactions between ions, surface-adsorbed chemistry, and the material being etched, rather than interactions between ion and gas phase, as observed in the conventional RIE.

Surface damage formation during atomic layer etching of silicon with chlorine adsorption

As semiconductor device structures continue to approach the nanometer size range, new challenges in the fabrication of such devices have arisen. For example, the need for high-aspect-ratio, highly selective, controllable, and isotropic or anisotropic etching at the nanometer scale are some of them. Recently, atomic layer etching (ALE) has attracted much attention as an alternative to the conventional reactive ion etching (RIE) to address these issues. In comparison with RIE, ALE offers highly uniform etching over a large area with a precise etched depth and little damage to the underlying material surface. However, the extent of the surface damage formation in ALE processes has not been extensively reported yet. In this study, molecular dynamics simulation is used to examine the surface damages and reaction mechanisms during plasma-assisted (PA-) ALE of silicon (Si) with chlorine (Cl) radical adsorption and low-energy Ar+ ion irradiation for desorption. Several ALE cycles have been simulated and reproducible etched depths per cycle have been obtained. Based on the depth profiles, a damaged surface layer with a thickness of about 1.5 nm is found to be caused by the ALE process even at a very low ion incident energy of 20 eV in the simulation. The thickness of a damaged-layer on the etched surface slightly increases with the ion incident energy for the energy range examined in this study (20–60 eV), and Cl atoms deposited on the surface in the ALE adsorption step are transported deeper in the damaged-layer by the ion bombardment. Our simulation results indicate that a certain damage formation cannot be avoided on the “as-etched” surface of a PA-ALE process and, if the damaged-layer inadvertently affects the device performance, further action to mitigate the damage needs to be taken.

(Invited) Area-Selective Spatial ALD of SiO2 Interleaved with Etch-Back Supercycles: Quantification of Area Selectivity By Low Energy Ion Scattering

Area-selective ALD interleaved with etch-back steps in a supercycle fashion has recently been reported as very effective in achieving high selectivity. Such supercycles can result in lower defectivity on the non-growth area and thicker layers on the growth area, as compared to solely area-selective ALD.1, 2 Here, we use low energy ion scattering (LEIS) to probe the selectivity of the first supercycle, consisting of plasma-enhanced selective spatial-ALD of SiO2 and conventional CF4-based reactive ion etching (RIE). Given its extreme sensitivity to the top monolayer(s) of a thin film, LEIS can reliably quantify the selectivity/defectivity on the non-growth areas in terms of surface coverage and derived thickness.A three-step approach was used for the area-selective spatial ALD of SiO2,3 which consisted of inhibitor, silicon precursor (BDEAS), and O2 plasma exposures. The process selectivity as a function of the number of cycles was probed using LEIS to monitor the SiO2 surface coverage on the non-growth area. After 20 spatial ALD cycles, no silicon was detected on the non-growth area (detection limit 2 % SiO2 surface coverage), implying excellent process selectivity. Increasing the number of ALD cycles resulted in a gradual loss of selectivity. Interestingly after 110 ALD cycles, the SiO2 coverage was 86%, indicating a not yet closed layer. At the same time, a SiO2 thickness of 11 nm was measured on the growth area, using spectroscopic ellipsometry. As the last step of the super-cycle, a 3 seconds RIE was sufficient to bring the SiO2 coverage back to zero on the non-growth area, while an 8 nm thick SiO2 layer was left on the growth area.The data presented in this work demonstrate the effectiveness of combining area-selective spatial ALD + etch-back corrections to achieve extreme SiO2 selectivity while retaining high deposition rates. Finally, we have extended the plasma-enhanced area-selective spatial ALD of SiO2 to other oxides and metals non-growth areas. REFERENCES 1. R. Vallat et al., JVSTA, 35, 01B104 (2017).2. S. K. Song et al., Chem. Mater. 31 4793-4804 (2019).3. A. Mameli et al., ACS Nano, 11, 9303-9311 (2017). Figure 1

A Self-Assembled Graphene Ribbon Device on SiC

Graphene ribbons, which may be fabricated by a wide variety of experimental techniques such as chemical processing, unzipping or etching of carbon nanotubes, molecular precursors, ion implantation, and so on, can find promising applications in interconnects, terahertz sensors, and plasmonic devices. Here we report measurements on self-assembled graphene ribbons that are prepared by a controlled high-temperature sublimation technique. The epitaxial graphene ribbons on SiC can be readily and efficiently located by confocal laser scanning microscopy for device fabrication using a removable metal protection layer to avoid contamination of the graphene and hexagonal boron nitride to serve as a top-gate dielectric spacer. These self-assembled graphene ribbons have smooth edges, and the observation of a magnetoresistance side peak in such a structure is consistent with diffusive boundary scattering in the quasi-ballistic regime. In contrast, graphene ribbons defined by electron-beam lithography and subsequent conventional reactive ion etching on the same SiC wafer only show pronounced negative magnetoresistance due to strong disorder in the edge structures (chemical dopants, the resolution of electron-beam lithography, etc.). Our experimental approaches are applicable to wafer-scale, graphene-based integrated circuits.

Atomic layer etching of AlGaN using Cl2 and Ar gas chemistry and UV damage evaluation

The atomic layer etching (ALE) characteristics of AlGaN using Cl2 plasma in the modification step and Ar plasma in the removal step were investigated in comparison with conventional reactive ion etching (RIE). Although surface roughening and GaN composition changes were observed in the RIE process, the ALE process did not result in such changes. However, the etching damage of the AlGaN layer evaluated using cathodoluminescence in AlGaN/GaN stacked films in the case of ALE was 30% higher than that in RIE. This was attributed to the longer process time of ALE compared to RIE. The GaN layer underneath the AlGaN layer was also damaged. This could be mainly caused by UV photons during the modification step using Cl2 plasma. The authors introduced a modification step using Cl2 gas instead of Cl2 plasma; thus, the etching damage was successfully reduced while maintaining good surface characteristics.

GaN LEDs fabricated using SF 6 plasma RIE

In this work, the authors report a cost-effective fabrication method for making gallium nitride (GaN) light emitting diode (LED) arrays using SF6 plasma in a conventional reactive-ion etching (RIE) system. The etch rates for GaN were investigated with different radio-frequency power and carrier substrates. The surface roughness due to the etching was also determined for the various recipes used. The optical intensity and the temperature change during operation of the fabricated LED's were investigated. The effect of post-fabrication annealing on enhancement in the electrical and optical properties of the LED's was investigated.

Enhanced Performance of Ge Photodiodes via Monolithic Antireflection Texturing and α-Ge Self-Passivation by Inverse Metal-Assisted Chemical Etching.

Surface antireflection micro and nanostructures, normally formed by conventional reactive ion etching, offer advantages in photovoltaic and optoelectronic applications, including wider spectral wavelength ranges and acceptance angles. One challenge in incorporating these structures into devices is that optimal optical properties do not always translate into electrical performance due to surface damage, which significantly increases surface recombination. Here, we present a simple approach for fabricating antireflection structures, with self-passivated amorphous Ge (α-Ge) surfaces, on single crystalline Ge (c-Ge) surface using the inverse metal-assisted chemical etching technology (I-MacEtch). Vertical Schottky Ge photodiodes fabricated with surface structures involving arrays of pyramids or periodic nano-indentations show clear improvements not only in responsivity, due to enhanced optical absorption, but also in dark current. The dark current reduction is attributed to the Schottky barrier height increase and self-passivation effect of the i-MacEtch induced α-Ge layer formed on top of the c-Ge surface. The results demonstrated in this work show that MacEtch can be a viable technology for advanced light trapping and surface engineering in Ge and other semiconductor based optoelectronic devices.

Large-Scale and Defect-Free Silicon Metamaterials with Magnetic Response.

All-dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. Here, we experimentally demonstrate a silicon based large-scale magnetic metamaterial, which is fabricated with standard photolithography and conventional reactive ion etching process. The periodically arrayed silicon sub-wavelength structures possess electric and magnetic responses with low loss in mid-infrared wavelength range. We investigate the electric and magnetic resonances dependencies on the structural parameters and demonstrate the possibility of obtaining strong dielectric-based magnetic resonance through a broad band range. The optical responses are quite uniform over a large area about 2 × 2 cm2. The scalability of this design and compatibility fabrication method with highly developed semiconductor devices process could lead to new avenues of manipulating light for low-loss, large-area and real integrated photonic applications.

Development of a two-dimensional scanning micro-mirror utilizing magnetic polymer composite

In this study, we propose a magnetically driven micro-mirror, constructed using negative photoresist SU-8 containing magnetic particles, as a magnetic actuator and torsion bar structure. Because the magnetic polymer composite uses thick negative photoresist SU-8 as the main material, the micro-mirror is simply fabricated in just a few steps by conventional photolithography and deep reactive ion etching. A fabricated prototype of the micro-mirror, which is magnetically driven by using an external magnetic field, is shown to deflect with two-dimensional optical deflection angles of 6.5 and 12.5°. Moreover, Lissajous scanning motion of the fabricated mirror is achieved.

Fabrication of three-dimensional GaAs antireflective structures by metal-assisted chemical etching

Antireflective GaAs subwavelength structures (SWSs) were fabricated by Au-assisted chemical etching. Thermally agglomerated Au nanoparticles caused catalytic reactions with the GaAs substrates in KMnO4 and HF etchant. Various features of the Au nanoparticles agglomerated after heat treatment of Au thin films. The reflectance of GaAs strongly depended on the three-dimensional features of the GaAs SWSs, which were controlled by Au agglomeration and chemical etching. GaAs SWSs dramatically reduced the total reflectance to 4.5% in a wavelength rage of 200–850nm up to the incident angle of 50°. Solar-weighted total reflectance values quantitatively confirmed the highly efficient antireflective coating fabricated by metal assisted chemical etching on GaAs SWSs. To our knowledge, this is the first report that fabricates GaAs SWSs using metal-assisted chemical etching with thermally agglomerated metal catalyst. This technique is a viable alternative to conventional reactive ion etching and nano-lithography for fabricating antireflective SWSs for III–V solar cells.

Precise control of defects in graphene using oxygen plasma

The authors report on a facile method for introducing defects in graphene in a controlled manner. Samples were mounted face down between supports, and exposed to oxygen plasma in a reactive ion etching (RIE) system. Defect density and the rate of defect formation in graphene were analyzed according to the oxygen flow rates and power conditions, using Raman spectroscopy. The mechanism of defect formation was systematically investigated via both experiment and density functional theory (DFT) calculation. Based on our DFT results, sp3 oxygen in the epoxide form would most likely be induced in pristine graphene after exposure to the oxygen plasma. Defect engineering through the fine tuning of the graphene disorder using a conventional RIE system has great potential for use in various graphene-based applications.

Micro-mixer device with deep channels in silicon using modified RIE process: fabrication, packaging and characterization

In the present work, silicon based micromixer microfluidic devices have been fabricated in silicon substrates of 2-inch diameter. These devices are of 2-input and 1-output port configuration bearing channel depth in the range 80---280 µm. Conventional reactive ion etching (RIE) process used in integrated circuit fabrication was modified to get reasonably high silicon etch rate (~1.2 µm/min). It was anticipated that devices with channel depth in excess of 150 µm would become weak and susceptible to breakage. For such devices, a bonded pair of silicon having a 0.5 µm SiO2 at the bonded interface was used as the starting substrate. The processed silicon wafer bearing channels was anodically bonded to a Corning® 7740 glass plate of identical size for fluid confinement. Through-holes for input/output ports were made either in Si substrate or in glass plate before carrying out anodic bonding. Micro-channels were characterized using stylus and optical profiler. Surface roughness of the channel was observed to increase with increasing channel depth. The devices were packaged in a polycarbonate housing and pressure drop versus flow rate measurements were carried out. Reynolds number and friction factor were calculated for devices with 82 µm deep channels. It was observed that up to 25 sccm of gas and 10 ml/min of liquid, the flow was laminar in nature. It is envisaged that using bonded silicon wafer pair and combination of RIE and wet etching, it is possible to get an etch stop at the SiO2 layer of the bonded silicon interface with much smaller value of surface roughness rendering smooth channel surface.

Monocrystalline-like silicon solar cells fabricated by wet and dry texturing processes for improving light-trapping effect

Surface texturing techniques of crystalline silicon (Si) wafers are an effective and permanent method for increases in the conversion efficiency of solar cells by reducing reflection losses and improving light trapping effects compared to antireflection coatings such as hydrogenated silicon nitride (SiNx:H) thin films. In this study, monocrystalline-like Si surfaces were textured by acidic solutions followed by reactive ion etching (RIE). Also, we investigated the optical and electrical properties of Si surfaces prepared by different texturing processes. By using the acidic and RIE texturing processes for monocrystalline-like Si surfaces, we achieved open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and conversion efficiency as high as 633 mV, 36.7 mA/cm2, 77.5% and 18%, respectively, in a solar cell with an active surface area of 156 × 156 mm2 (243 cm2). Compared to the conventional acidic texturing, the acidic and RIE texturing of front Si surfaces improved the solar cell conversion efficiency of 0.9%. Therefore, the results indicate that large-area monocrystalline-like Si solar cells with high efficiency can be fabricated by standard wet chemical and additional RIE texturing processes.

Modulating particle adhesion with micro-patterned surfaces.

We report the first experimental study on the modulation of adhesion force distribution by surface micro-patterns and its impact on particle attachment. The effect of substratum topography on particle adhesion was evaluated using well-defined microscopic surface patterns consisting of orthogonal arrays of cuboid pillars or pits with different sizes and spacing fabricated by the conventional photolithography and reactive ion etching (RIE). Adhesion of carboxyl modified poly(styrene-co-acrylic-acid) particles of 6 μm in diameter under favorable deposition conditions was found to be markedly lower on all the micro-patterned surfaces compared with that on the smooth control surface, and particle adhesion depended on the characteristic dimensions of the surface micro-structures relative to the particle size. Particle adhesion was minimal when the pillar cross-sectional dimension was below a critical value close to the diameter of the particle while the spacing between pillars was less important. Meanwhile, particles adhered displayed unique distribution on the micro-patterned surfaces. The majority of particles preferentially adhered on or close to the edge of the pillars (in the valley). Atomic force microscopy measurements using a colloidal probe revealed that the surface features strongly modulated the spatial and probability distribution of adhesion forces on the micro-patterned surfaces. Micro-sized pillars changed the adhesion force probability distribution from monomodal to bimodal, with significantly reduced maximum adhesion force. This was hypothesized to be responsible for the reduced total particle adhesion.

Angled etching of (001) rutile Nb–TiO2 substrate using SF6-based capacitively coupled plasma reactive ion etching

We demonstrated the plasma etching of a (001) rutile Nb–TiO2 substrate using SF6 plasma. A vertical etching profile and a smooth etched surface were obtained. In addition, the angled etching of a (001) rutile Nb–TiO2 substrate was achieved in a conventional SF6 reactive ion etching system for the first time. The etching angle was determined by the angle of the groove of the holder. We believe that our simple dry etching technique is suitable for the formation of a three-dimensional photonic crystal with complete photonic bandgap (CPBG) and optical waveguides.

An integrated Mach–Zehnder interferometric biosensor with a silicon oxynitride waveguide by plasma-enhanced chemical vapor deposition

We report the design and fabrication of an integrated Mach–Zehnder interferometric (MZI) biochip based on silicon oxynitride layers deposited with a plasma-enhanced chemical vapor deposition (PECVD) process. A rib waveguide for an integrated MZI sensor has been designed to have a high surface sensitivity and a single-mode behavior by using an effective index method. The integrated MZI chip operating at 637 nm is fabricated via conventional photolithography and reactive ion etching. As a biosensor application, the real-time and label-free detection of the covalent immobilization and hybridization of DNA strands is performed and verified with this device.

Singular Sheet Etching of Graphene with Oxygen Plasma

This paper reports a simple and controllable post-synthesis method for engineering the number of graphene layers based on oxygen plasma etching. Singular sheet etching (SSE) of graphene was achieved with the optimum process duration of 38 seconds. As a demonstration of this SSE process, monolayer graphene films were produced from bilayer graphenes. Experimental investigations verified that the oxygen plasma etching removes a single layer graphene sheet in an anisotropic fashion rather than anisotropic mode. In addition, etching via the oxygen plasma at the ground electrodes introduced fewer defects to the bottom graphene layer compared with the conventional oxygen reactive ion etching using the powered electrodes. Such defects can further be reduced with an effective annealing treatment in an argon environment at 900–1000°C. These results demonstrate that our developed SSE method has enabled a microelectronics manufacturing compatible way for single sheet precision subtraction of graphene layers and a potential technique for producing large size graphenes with high yield from multilayer graphite materials.

Singular Sheet Etching of Graphene with Oxygen Plasma

Abstract This paper reports a simple and controllable post-synthesis method for engineering the number of graphene layers based on oxygen plasma etching. Singular sheet etching (SSE) of graphene was achieved with the optimum process duration of 38 seconds. As a demonstration of this SSE process, monolayer graphene films were produced from bilayer graphenes. Experimental investigations verified that the oxygen plasma etching removes a single layer graphene sheet in an anisotropic fashion rather than anisotropic mode. In addition, etching via the oxygen plasma at the ground electrodes introduced fewer defects to the bottom graphene layer compared with the conventional oxygen reactive ion etching using the powered electrodes. Such defects can further be reduced with an effective annealing treatment in an argon environment at 900–1000°C. These results demonstrate that our developed SSE method has enabled a microelectronics manufacturing compatible way for single sheet precision subtraction of graphene layers and a potential technique for producing large size graphenes with high yield from multilayer graphite materials.

A New Concept for Spatially-Divided Reactive Ion Etching with ALD-Based Passivation

Conventional Deep Reactive Ion Etching (DRIE) is a plasma etch process with alternating half-cycles of 1) Si-etching with SF6 to form gaseous SiFx etch products, and 2) passivation with C4F8 polymerizing as a protecting fluorocarbon deposit on the sidewalls and bottom of the etched features. We report on a novel alternative and disruptive technology concept of Spatially-divided Deep Reactive Ion Etching, where the process is converted from the time-divided into the spatially divided regime. The spatial division can be accomplished by ~20 to 100 μm high inert gas-bearing ‘curtains’ that confine the reactive gases to individual (often linear) injection slots constructed in a gas injector head. By horizontally moving the substrate back and forth under the head one can realize the alternate exposures to compose the overall cycle.Next improvement in the spatially-divided approach is the replacement of the CVD-based C4F8 passivation steps by ALD-based oxide (e.g. SiO2) deposition cycles. The method can have industrial potential in cost-effective creation of advanced 3D TSV interconnects and MEMS, but also in advanced patterning of, e.g., nanoscale FinFET devices with reduced line edge roughness, thus approaching Atomic Layer Etching accuracy.