Fast Etch Rate Research Articles

Metal Ions’ Dynamic Effect on Metal-Assisted Catalyzed Etching of Silicon in Acid Solution

Metal-assisted catalyzed etching (MACE) technology is convenient and efficient for fabricating large-area silicon nanowires at room temperature. However, the mechanism requires further exploration, particularly the dynamic effect of various ions in the acid-etching solution. This paper investigated the MACE of silicon wafers predeposited with metal nanofilms in an HF-M(NO3)x-H2O etching solution (where M(NO3)x is the nitrate of the fourth-period elements of the periodic table). The oxidizing ability of Fe3+ and NO3− was demonstrated, and the dynamic influence of metal ions on the etching process was discussed. The results show that the MACE of silicon can be realized in various HF-M(NO3)x-H2O etching solutions, such as KNO3, Al(NO3)3, Cr(NO3)3, Mn(NO3)2, Ni(NO3)2, Co(NO3)2, HNO3, and Ca(NO3)2. It is confirmed that the concentration and type of cations in the etching solution affect the etching rate and morphology of silicon. Fe3+ and NO3− act as oxidants in catalytic etching. The fastest etching rate is about 5~6 μm/h in Ni(NO3)2, Co(NO3)2, and Ca(NO3)2 etching solutions. However, a high concentration of K+ hinders silicon etching. This study expands the application of MACE etching solution systems.

Reactive ion etching of indium gallium zinc oxide (IGZO) and chamber cleaning using low global warming potential gas

Indium gallium zinc oxide (IGZO) is attracting increasing attention as a promising semiconducting material for use in next-generation semiconductors and display devices; for the application of IGZO to next-generation devices, it is necessary to have dry etch characteristics such as highly anisotropic etch profile, fast etch rate, and high mask selectivity. In the present study, IGZO was etched with various hydrofluorocarbon (HFC)-type gases (CxHyFz) in an inductively coupled plasma (ICP) etcher and, the etch characteristics and the possibility of removing the residue forming on the chamber wall by in-situ chamber cleaning was investigated. This study also investigated the use of low global warming potential (GWP) gas in IGZO etching, in response to the fact that HFC-type gases tend to show high GWP. The results showed that, when HFC-type gases were used in the etching of IGZO, the ratio of H/F in HFC affected the IGZO etch rate and etch selectivity. Among the HFC gases used in the experiment, such as CHxFy (x + y = 4) and C3HxFy (x + y = 8), IGZO was etched faster with the gas with higher H/F ratio, which was attributed to the easier removal of zinc in IGZO during the etching, along with the removal of In through the formation of more volatile In(CHx)y; this is attributed to the fact that, among IGZO components, zinc was the most difficult material to etch with the HFC gases. Among the HFC-type gases investigated, C3H6F2 (HFC-272ca), which is a low GWP (GWP100yr = 139) gas, showed the highest etch rate of ∼ 55 nm/min, the lowest dimensional loss (less than 7 nm for photoresist masked IGZO), and the most anisotropic etch profile with the lowest surface roughness. During the etching with HFC gases, compounds such as GaHx/Ga(CHx)y, COx, In(CHx)y, and Zn(CHxFy)z were expected to have been produced as byproducts, and these were removed through Ar+ ion sputtering from the IGZO surface, but some of the these compounds were accumulated on the chamber wall along with dissociated HFCs that were formed during the etching. However, it was possible to completely remove these etch byproducts that had been formed on the chamber wall by using a H2/Ar plasma.

Efficiency of high energy fluorocarbon molecule bombardment for fast etch rate and its limitation: A molecular dynamics study

The RF power of the High Aspect Ratio (HAR) patterning equipment used for 3D NAND memory etching processes rapidly increased recently. However, despite implementing higher ion energy, its effect on increasing the etch rate is not satisfactory. This letter studies the energy transfer efficiency between bombarding fluorocarbon (FC) molecules and the SiO2 substrate, and discusses the limitation of securing the etch rate by high-energy FC molecules.

Evaluation of etching performance of single etching gases for high-κ films

The continuous advancement of CMOS technology has put forward higher requirements for dielectric etching processes. However, conventional mixed etching gases fail to elucidate the contribution of each gas. The role of single etching gas in the etching process remains elusive. In this work, we investigated the etching characteristics of high-κ thin films using a variety of single fluorine-based or chlorine-based gases. We further analyzed the underlying reasons for the observed differences in etching behaviors with different gases. Our findings demonstrate that BCl3 is the optimal single etching gas for HfO2 and Al2O3 films with a fast and stable etching rate, while the films etched by Cl2, BCl3, CF4, CHF3, and C4F8 exhibited varying degrees of etching residuals. The outstanding etching performance of BCl3 is attributed to the interaction between physical bombardment and chemical reactions. Furthermore, we propose a set of evaluation methods for etching residues and mechanisms. These results provide valuable insights into the etching process and facilitate the selection of appropriate etching gases for high-κ films in advanced semiconductor process nodes.

Surface properties of Al-doped ZnO thin film before and after CF4/Ar plasma etching

Al-doped ZnO (AZO) is considered as an alternative to transparent conductive oxide materials. Patterning and achieving a stable surface are important challenges in the development and optimization of dry etching processes, which must be overcome for the application of AZO in various devices. Therefore, in this study, the etch rate and surface properties of an AZO thin film after plasma etching using the adaptive coupled plasma system were investigated. The fastest etch rate was achieved with a CF4/Ar ratio of 50:50 sccm. Regardless of the ratio of CF4 to Ar, the transmittance of the film in the visible region exceeded 80%. X-ray photoelectron spectroscopy analysis of the AZO thin film confirmed that metal-F bonding persists on the surface after plasma etching. It was also shown that F eliminates O vacancies. Consequently, the work function and bandgap energy increased as the ratio of CF4 increased. This study not only provides information on the effect of plasma on AZO thin film, but identifies the cause of changes in the device characteristics during device fabrication.

Deep Etching of Silicon Based on Metal-Assisted Chemical Etching.

A deep etching method for silicon “micro”structures was successfully developed. This wet etching process is based on metal-assisted chemical etching (MACE), which was previously mainly utilized to etch the features that have lateral dimensions of “nanometers.” In this novel MACE, the critical improvement was to promote the “out-of-plane” mass transfer at the metal/Si interface with an ultrathin metal film. This enabled us to etch micrometer-wide holes, which was previously challenging due to the mass transport limitation. In addition, it was found that when ethanol was used as a solvent instead of water, the formation of porous defects was suppressed. Under the optimized etch conditions, deep (>200 μm) and vertical (>88°) holes could be carved out at a fast etch rate (>0.4 μm/min). This novel deep MACE will find utility in applications such as microelectromechanical systems (MEMS) devices or biosensors.

Atomic Layer Etching of Silicon Oxide with CF3I and O2 Plasma

Perfluorinated compounds (PFCs) such as CF4, C2F6, C3F8, and C4F8 have been widely used in plasma dry etching and in-situ deposition chamber cleaning processes.[1] More recently, the PFCs have been used in atomic layer etching (ALE), which is considered the promising etching technique that can control the etched thickness in atomic scale levels.[2] However, PFCs generally have a high global warming potential (GWP), which is a significant figure of merit concerned with global warming. CF3I has been studied as a dry etching gas to replace PFCs because of its ultra-low GWP (GWP100=0.3). However, most of the results have been required at high plasma power over 1000 W, which made it difficult to commercialize.[3] Therefore, the feasibility of applying CF3I to ALE processed at low plasma power (400 W or less) is an important factor to replace PFCs. In this study, ALE of SiO2 was performed with CF3I as an etchant gas. In the ALE process, one cycle involved two steps: surface modification and removal steps. In the first step, surface modification, CF3I plasma was treated on the SiO2 surface to deposit fluorocarbon polymer. In the second step, removal step, O2 plasma was used to remove the deposited polymer. When fluorocarbon polymer was removed by O2 plasma, SiO2 film was etched by the byproduct of volatile SiFx generated in the interlayer between fluorocarbon polymer and SiO2. The surface change in the respective modification and removal step was confirmed by X-ray photoelectron spectroscopy (XPS), and the etched thickness of SiO2 film during ALE process was measured by using ellipsometry and transmission electron microscopy (TEM). As a result of SiO2 ALE using CF3I, etched thickness per cycle (EPC) saturation with both CF3I plasma treatment time and O2 plasma treatment time shows that etching was proceeding to atomic scale. When the plasma power is 300 W, the EPC is 0.93 nm/cycle. It means the fast etch rate enough to replace other PFCs at a low power condition.[2] References [1] C. J. Mogab, et. al., J. Appl. Phys. 49, 3796 (1978).[2] D. Metzler, et. al., J. Vac. Sci. Technol. A 32, 020603 (2014).[3] A. Misra, et. al., D. Rufin, Mat. Let. 34 415 (1998).

Effects of Post-Etch Microstructures on the Optical Transmittance of Silica Ridge Waveguides.

Silica waveguides are often etched by reactive ion etch (RIE) processes. These processes can leave residual topography that can increase optical loss. We investigated the relation between optical loss and various RIE etch. A wet etch step meant to remove microstructures was also considered and compared. Ridge waveguides were fabricated in plasma enhanced chemical vapor deposited films by three different RIE processes, each with a different gas composition, pressure setting, and applied power setting. Half of each set of waveguides were also subjected to a hydrofluoric acid (HF) solution. The waveguides were tested for optical transmission via the cutback method. The transmission vs waveguide length measurements were plotted to fit an exponential curve and the optical loss and measurement uncertainty for each waveguide set was calculated. Clear distinctions in optical loss were found between the different RIE processes. The HF treatment also has an effect, significantly reducing optical loss for two processes and increasing it for the third. Of the tested RIE processes, one can be suggested for silica waveguides. It results in the lowest optical loss and coincidently has the fastest etch rate.

Selective Wet Etching of Silicon Germanium in Composite Vertical Nanowires.

Silicon germanium (SixGe1-x or SiGe) is an important semiconductor material for the fabrication of nanowire-based gate-all-around transistors in the next-generation logic and memory devices. During the fabrication process, SiGe can be used either as a sacrificial layer to form suspended horizontal Si nanowires or, because of its higher carrier mobility, as a possible channel material that replaces Si in both horizontal and vertical nanowires. In both cases, there is a pressing need to understand and develop nanoscale etching processes that enable controlled and selective removal of SiGe with respect to Si. Here, we developed and tested solution-based selective etching processes for SiGe in composite (SiNx/Si0.75Ge0.25/Si) vertical nanowires. The etching solutions were formed by mixing acetic acid (CH3COOH), hydrogen peroxide (H2O2), and hydrofluoric acid (HF). Here, CH3COOH and H2O2react to form highly oxidizing peracetic acid (PAA orCH3 CO3H). The hydrofluoric acid serves both as a catalyst for PAA formation and as an etchant for oxidized SiGe. Our study shows that an increase in anyofthe two oxidizer(H2O2 and PAA)concentrations increases the etch rate, and the fastest etch rate of SiGe is associated with the highest PAA concentration. Moreover, using in situ liquid-phase TEM imaging, we tested the stability of nanowires during wet etching and identified the SiGe/Si interfaceto be the weakest plane; we found that once the diameter of the 160-nm-tall Si0.75Ge0.25 nanowire reaches ∼15 nm during the etching, the nanowire breaks at or very close to this interface. Our study provides important insight into the details of the nanoscale wet etching of SiGe and some of the associated failure modes that are becoming extremely relevant for the fabrication processes as the size of the transistors shrink with every new device generation.

Anisotropic etching of β-Ga2O3 using hot phosphoric acid

We report a systematic investigation on the anisotropic etching behavior of β-Ga2O3. A wagon wheel pattern was designed and fabricated on (010)-oriented β-Ga2O3 substrates. The wet etching in hot phosphoric acid was found to be effective in reducing the sidewall roughness caused by plasma dry etching. The angular dependence of the sidewall etch rate and inclination angles after wet etching was evaluated. The fins aligned along the [001] direction showed nearly vertical sidewalls after wet etching and a fast sidewall etch rate, making it feasible for the fabrication of ultrascaled vertical channel devices. The fins aligned in the angular range between the [203] and [201] directions showed slanted sidewalls with high tilt angles, which could be useful in reducing the peak electric field near the corners of high power devices. The observed anisotropic etching in this work offers a low-cost, low damage, and controllable fabrication method for ultrascaled and advanced device structures.

In-plane silicon microneedles with open capillary microfluidic networks by deep reactive ion etching and sacrificial layer based sharpening

The deep reactive ion etching (DRIE) of in-plane silicon microneedles with open capillary microfluidic network is presented. The in-plane needle design allows easy fabrication of long needles for accessing abundant dermal fluids and improves the correlation with blood biomarkers. However, the anisotropic DRIE yields wedge-shaped (not sharp) needle tip. We developed a sharpening process using the sacrificial layers (remaining unetched silicon layer below the needle shaft) to facilitate the buildup of the concentration gradient of the etching species during the wet etching sharpening process, resulting in the relatively fast etching rate at shaft top than the bottom. As a result, the wedge-shaped structure is sharpened to conical structure, tapering smoothly from the base to the apex. Such sharp microneedles have been demonstrated to be sufficiently robust to penetrate porcine skins, with needles being intact after repetitive penetrations. The fabricated silicon devices are treated with oxygen plasma for making the surface hydrophilic, such that the capillary fluid is introduced within the open microfluidic network.

Fabrication of ZnO/Si lamb wave acoustic devices

Surface acoustic wave devices have widespread applications in various fields including in communication and wireless sensing devices. However some shortcomings like lower sensitivity and the corrosion of IDT’s limit their application as sensing devices. Lamb wave SAW devices have proved to be promising for sensing applications. In the present work effort has been made to find out the optimum etching temperature in order to get the sufficiently fast etch rate and smooth surface for the fabrication of SiO2/Si membrane for Lamb wave acoustic (LWA) devices. Piezoelectric ZnO thin film deposited using rf sputtering technique has been integrated with the SiO2/Si membrane. The bulk etching of Silicon has been carried out from back side of each LWA device using wet etching. The devices are packaged and frequency response is studied using a network analyzer. The antisymmetric and symmetric modes of the Lamb wave devices have been identified.

Novel Fast Etch Rate BARC for ArF Immersion Lithography

Novel Fast Etch Rate BARC for ArF Immersion Lithography

A comparative study of wet etching and contacts on [formula omitted] and (010) oriented β-Ga2O3

We report on the effect of β-Ga2O3 crystal orientation on wet etching and Ohmic contact formation. The photochemical etching rate in KOH solutions of (2¯01) oriented, n-type bulk single crystals grown by the edge-defined film-fed growth method is ∼3–4 times higher than for the (010) planes. The activation energy for etching was 0.498 eV and 0.424 eV for (2¯01) and (010) orientations, respectively, suggesting the etching is reaction-limited with the same rate-limiting step. Ti (200 Å)/Au (1500 Å) metallization deposited on the two different orientations and annealed at 450 °C showed Ohmic current-voltage (I-V) behavior for (2¯01) but rectifying characteristics for (010). For (010) Ga2O3, there exists 2 types of surfaces having Ga and O atomic densities of 0.58 and 0.87 × 1015 cm−2, respectively. By contrast, for (2¯01) Ga2O3 surfaces, there exist 2 types of surface, with each type terminated with only Ga or O. If the surface is terminated with O, the dangling bond densities of O are 1.78 and 2.68 × 1015 cm−2, respectively. We found that (2¯01)–oriented Ga2O3 is etched at higher rates and is easier to form Ohmic contacts than (010) Ga2O3. The higher density of oxygen dangling bonds on the (2¯01) plane correlates with the faster etch rates and pronounced Ohmic behavior from deposited metals.

Deep plasma etching of Parylene C patterns for biomedical applications

We report on the plasma etching of thick (∼23μm) Parylene C structures. Parylene C is a transparent polymer that benefits from high biocompatibility, flexibility and chemical inertness, and has gained increased attention over the years in the biomedical field. In the manufacturing process, highly defined structuration steps of Parylene C are essential, but techniques based on laser, scalpel and wet etching have shown to be unsuitable for properly cut structures. Plasma etching remains nowadays the most widespread option, though fast etching rate, lack of residues and high aspect ratios are still hard to achieve. To overcome these issues, the selection of both mask material and plasma conditions is crucial. Here, three masks - metal, positive and negative photoresists - are tested as stencils, and several plasma parameters are briefly studied in order to obtain the highest etching rate while maintaining good coverage. We showed that increasing the RF power up to a considerable 2800W while maintaining a moderate physical contribution (bias power, pressure, temperature), is optimal in the achievement of fast PaC etching without inducing thermal stress. Besides, the addition of a short fluorinated plasma in the midst of the process is shown to alleviate residues. For the first time, negative photoresist Intervia Bump Plating (BPN) coating followed by ICP11Inductively coupled plasma. -RIE22Reactive ion etching. are used in order to pattern Parylene C-based structures, with a clean cut, vertical profile and fast etching rate (∼0.87±0.06μm/min) and a selectivity of 0.5. This solution was carried out to release unitary Parylene-based neural probes from a silicon wafer. Finally, cytotoxicity assays on these neural implants were performed to make sure that no trace of mask or stripper residues jeopardizes device biocompatibility.

Inductively-coupled-plasma reactive ion etching of single-crystal β-Ga2O3

Dry etching behavior of unintentionally-doped β-Ga2O3 has been studied in a BCl3/Ar chemistry using inductively-coupled-plasma reactive ion etching (ICP-RIE). The effects of various etch parameters like ICP and RIE powers, BCl3/Ar gas ratio and chamber pressure on etch rate are studied systematically. Higher ICP, RIE powers and lower pressure conditions are found to enhance the etch rate. A synergic etching mechanism between chemical and physical components is proposed and used to obtain fast Ga2O3 etch rates more than 160 nm/min, nearly-vertical sidewalls and smooth etched surfaces. The findings of this work will enable Ga2O3 vertical devices for power electronics.

Chemical tapering of polymer optical fiber

Polymer optical fibers (POFs) have significant advantages over numerous sensing applications. The key element in developing sensor is by removing the cladding of the fiber. The use of organic solvent is one of the methods to create tapered POF in order to expose the core region. In this study, the etching chemicals involved is acetone, methyl isobutyl ketone (MIBK), and acetone-methanol mixture. The POF is immersed in 100%, 80%, and 50% of acetone and MIBK dilution. In addition, the mixture of acetone and methanol is also used for POF etching by the ratio 2:1 of the volume. Acetone has shown to be the most reactive solvent towards POF due to its fastest etching rate compared to MIBK and acetone-methanol mixture. The POF is immersed and lifted from the solution for a specific time, depending on the power loss properties for the purpose of producing unclad POF. In comparison to silica fiber optic, the advantages of POF in terms of its simple technique and easy handling enable it to produce unclad POF without damaging the core region. The surface roughness of the POF is investigated under the microscope after being immersed into different solvent. This method of chemical tapering of POF can be used as the fundamental technique for sensor development. Next, the unclad fiber is immersed into ethanol solutions in order to determine the reaction of unclad POF towards its surrounding. The findings show that this particular sensor is sensitive towards concentration changes ranging between 10 wt% to 50 wt%.

Highly anisotropic etching of Ta thin films using high density plasmas of halogen based gases

Inductively coupled plasma reactive ion etching of Ta thin films masked with photoresist was performed using C2F6/Ar, HBr/Ar and Cl2/Ar gases. The etch characteristics such as etch rate, etch selectivity and etch profile were investigated in different gas concentrations of each gas. The Cl2 chemistry showed high degree of anisotropy in etch profile as well as fastest etch rate and highest etch selectivity of Ta films among these gases. Optical emission spectroscopy revealed that the increase in chlorine radicals with increasing Cl2 concentration was responsible for the increase in the Ta etch rate. The etch rate of Ta films increased with increasing ICP rf power and dc-bias voltage, and decreasing process pressure. Good etch profiles were obtained at high rf power and dc-bias voltage, and low process pressure. X-ray photoelectron spectroscopy confirmed the existence of a chemical reaction of Ta with chlorine radicals by forming tantalum chlorides. These results suggested that Ta etching in Cl2/Ar follows the typical reactive ion etching mechanism. It was concluded that a high degree of anisotropy and high etch rate of Ta films were achieved using Cl2/Ar gas.

Silicon etching using only Oxygen at high temperature: An alternative approach to Si micro-machining on 150 mm Si wafers

Using a combination of low-pressure oxygen and high temperatures, isotropic and anisotropic silicon (Si) etch rates can be controlled up to ten micron per minute. By varying the process conditions, we show that the vertical-to-lateral etch rate ratio can be controlled from 1:1 isotropic etch to 1.8:1 anisotropic. This simple Si etching technique combines the main respective advantages of both wet and dry Si etching techniques such as fast Si etch rate, stiction-free, and high etch rate uniformity across a wafer. In addition, this alternative O2-based Si etching technique has additional advantages not commonly associated with dry etchants such as avoiding the use of halogens and has no toxic by-products, which improves safety and simplifies waste disposal. Furthermore, this process also exhibits very high selectivity (>1000:1) with conventional hard masks such as silicon carbide, silicon dioxide and silicon nitride, enabling deep Si etching. In these initial studies, etch rates as high as 9.2 μm/min could be achieved at 1150 °C. Empirical estimation for the calculation of the etch rate as a function of the feature size and oxygen flow rate are presented and used as proof of concepts.

Optical properties of high aspect ratio plasma etched silicon nanowires: fabrication-induced variability dramatically reduces reflectance

In this work we investigate both experimentally and theoretically the optical properties of aligned, perpendicular to the substrate, high aspect ratio (AR), plasma etched Si nanowires (SiNWs) with controlled variability. We focus on the role of imperfections in fabrication, which manifest themselves as dimensional variability of SiNW, lattice defects or positional randomization. SiNW arrays are fabricated by e-beam lithography (perfectly ordered array) or colloidal particle self-assembly (quasi-ordered array) followed by cryogenic Si plasma etching, which offers fast etch rate (up to 3 μm min−1) combined with clean, smooth, and controllable sidewall profile, but induces some dimensional variability on the diameters of the SiNWs. Sub-200 nm diameter SiNWs having AR as high as 37:1 are demonstrated. The total reflectance of SiNWs is below 2% in a wide range of the optical spectrum. We experimentally demonstrate improved light absorption when moving from a perfectly ordered (after e-beam lithography) to a defective and quasi-ordered (after colloidal self-assembly) SiNW array. In addition our measured reflectivity (for both ordered and quasi-ordered SiNWs) is much lower compared to the one predicted theoretically for a perfect SiNWs array, using full-electrodynamic calculations with the layer-multiple-scattering method. To explain such low reflectivity, we model the influence of disorder using the average T-matrix approximation and show that even small dimensional variability (10–20%) leads to dramatic reduction of the reflectance (matching the experimental results) and increased light trapping inside the SiNW justifying their possible application in photovoltaic devices.