Wet Etching Behavior Research Articles

Deuterium Isotopic Effect on Nanometer-Sized Narrow Spaces Formed by Silicon Walls

Introduction Inspired by Okuyama et al. [1], fundamental studies on the wet-etching behavior of SiO2 films in single-nanometer scale gaps between silicon walls play an extremely significant role in optimizing the manufacturing of advanced semiconductors with complex 3D nanostructures. A well-known explanation for SiO2 etching behavior in narrow spaces is the change in the reactant concentration. Various attempts have been made to supply reactants to narrow spaces [2-4]. However, the wet-etching phenomenon in narrow spaces remains unclear, and further elucidation of the underlying mechanism is required. In this study, the etching behavior of SiO2 films confined between two silicon walls was investigated using a reactant consumption model. We attempted to suppress the reactions on the wall surface using the deuterium isotope effect, which is often used to control reactions [5]. Experimental Methods and Discussion First, we investigated the differences between hydrogen fluoride and deuterium fluoride in reactions on silicon surfaces. Silicon prisms machined from silicon wafers were prepared. The proportion of Si–H bonds on the prism was measured by infrared spectroscopy in multiple internal reflection geometry (MIR-IRAS) after immersing the silicon prisms in a mixture of dilute hydrogen fluoride, D2O, and deionized water for 2 min. The Si–H bond ratio on the prism surface increased with the increase in the proportion of hydrogen in the mixture, observed as the upward concave profile shown in Fig. 1. This suggests that deuterium fluoride reacts more slowly with the silicon surface than hydrogen fluoride, i.e., dilute deuterium fluoride reduces the reactant consumption on the silicon surface compared to dilute hydrogen fluoride. In dilute deuterium fluoride, the hydrogen fluoride is diluted with sufficient D2O such that hydrogen becomes negligible.Second, to examine the influence of the reactant consumption by the silicon walls, we measured the etching rates of SiO2 films with different film thicknesses sandwiched between two silicon layers. We performed etching tests on coupon samples in beakers with dilute hydrogen fluoride or dilute deuterium fluoride (w/o additive) at room temperature. The etching amounts of the confined SiO2 film and blanket SiO2 film as a control were measured by cross-sectional scanning electron microscopy (X-SEM), transmission electron microscopy with a focused ion beam (FIB-TEM), and spectroscopic film measurements. The etching rate was calculated by dividing the etched amount by the etching time. The etching rate in the narrow space was normalized to the reference etching rate. It was found that the etching rate in dilute deuterium fluoride is higher than that in hydrogen fluoride without deuterium fluoride (Fig 2(a)). Moreover, we performed an etching test on coupons with dilute hydrogen fluoride or dilute deuterium fluoride with an acidic additive (w/acid) and discovered that the etching rate in the narrow space was increased upon acid addition. Summary In this study, we verified the effect of deuterium fluoride on the etching behavior in nanometer-sized narrow spaces. We discovered that deuterium fluoride increased the etching rate in narrow spaces compared with hydrogen fluoride. We attribute these advantages of deuterium fluoride in the SiO2 etching rate in the narrow space to the consumption control of the reactant. At the PRiME 2024 conference, we would like to discuss our study and the effects of additives on the etching effectiveness of deuterium fluoride.REFERENCE:[1] A. Okuyama, S. Saito, Y. Hagimoto, K. Nishi, A. Suzuki, T. Toshima and H. Iwamoto, Solid State Phenomena, 2019 (2015) 115-118.[2] D. Ueda, Y. Hanawa H. Kitagawa, N. Fujiwara, M. Otsuji, H. Takahashi and K. Fukami, Solid State Phenomena, 314 (2021) 155-160.[3] S. Kumari, Shan. Hu and P. D’elia, Solid State Phenomena, 346 (2023) 149-154.[4] G. Vereecke, H. Debruyn, Q. D. Keyser, R. Vos, A. Dutta and F. Holsteys, Solid State Phenomena, 282 (2018) 182-189.[5] Kenneth B. Wiberg, Chemical Reviews, 55 (4) (1955) 713-743. Figure 1

Deuterium Isotopic Effect on Nanometer-Sized Narrow Spaces Formed by Silicon Walls

Unveiling a solid–liquid reaction in a nanoconfined region is required to control the wet processes of advanced semiconductors whose sizes can reach several nanometers. In this study, using deuterium isotope effects, we investigated the influence of reactant consumption by confining walls on the etching rate of nanoconfined spaces. By analyzing the states of the silicon surface and the etching rate of SiO2 film confined by the silicon walls in hydrofluoric acid diluted with H2O or D2O, we observed that deuterium can suppress the reaction on the wall surface and that deuterium fluoride increases the etching rate in nanoconfined regions. Therefore, we conclude that the wet-etching behavior can be determined by the reactant consumption on the confining walls.

Photochemical wet etching of (0 0 1) plane ß-phase Ga2O3, and its anisotropic etching behavior

The photochemical (PC) wet etching behavior of (001) plane β-phase Ga2O3(β-Ga2O3)single crystal was investigated using potassium hydroxide etchant solution under ultraviolet illumination in the temperature range of 80–95 °C. The etch rate was 1.65 nm/min at 80 °C, and increased up to 4.88 nm/min at 95 °C. The etch rate of the (001) plane β-Ga2O3shows strong temperature dependence with the activation energy of 0.798 eV. The PC wet etching characteristics of the (001) plane β-Ga2O3was compared with those of (2¯01) and (010) plane β-Ga2O3. The etch rates increased in order of the (010), (2¯01), and (001) plane, which is accordance with the increasing surface energy trend. The oval line-shaped grooves aligned along [010] direction were observed on the etched (001) plane β-Ga2O3 crystal surface after 30 min. PC wet etching at 80 °C.

Surface Morphology Evolution during Chemical Mechanical Polishing Based on Microscale Material Removal Modeling for Monocrystalline Silicon.

Chemical–mechanical polishing (CMP) is widely adopted as a key bridge between fine rotation grinding and ion beam figuring in super-smooth monocrystalline silicon mirror manufacturing. However, controlling mid- to short-spatial-period errors during CMP is a challenge owing to the complex chemical–mechanical material removal process during surface morphology formation. In this study, the nature of chemical and mechanical material removal during CMP is theoretically studied based on a three-system elastic–plastic model and wet chemical etching behavior. The effect of the applied load, material properties, abrasive size distribution, and chemical reaction rate on the polishing surface morphology is evaluated. A microscale material removal model is established to numerically predict the silicon surface morphology and to explain the surface roughness evolution and the source of nanoscale intrinsic polishing scratches. The simulated surface morphology is consistent with the experimental results obtained by using the same polishing parameters tested by employing profilometry and atomic force microscopy. The PSD curve for both simulated surface and experimental results by profilometry and atomic force microscopy follows linear relation with double-logarithmic coordinates. This model can be used to adjust the polishing parameters for surface quality optimization, which facilitates CMP manufacturing.

Wet Etching Behavior of Amorphous CuZr Thin Film in Hydrogen Peroxide Solution for Stretchable Display

Stretchable displays, a key benchmark for the next generation of display technologies, will be bendable, foldable, flexible and use a stretchable copper film. Amorphous CuZr has been selected for the copper metallization of the stretchable display due to its excellent elongation properties compared to conventional metals. However, little is known about the etching mechanism for amorphous CuZr and copper in a hydrogen peroxide solution containing fluorine ions. In this paper, the wet etching behavior of amorphous Cu50Zr50 thin films in a hydrogen peroxide-based copper wet etchant is studied using an electrochemical potentio-dynamic technique and surface analysis. An anodic Tafel slope of approximately 30 mV/decade is obtained. A new dissolution mechanism in the presence of 0.1 M fluoride ions in hydrogen peroxide solution is suggested. It should be noted that the wet etching rate of amorphous CuZr is strongly dependent on the existence of fluoride ions in the wet etchant.

Fabrication of crystal plane oriented trenches in gallium nitride using SF6 + Ar dry etching and wet etching post-treatment

During the last few years and with the commercialization of the gallium nitride based high electron mobility transistor, research effort on gallium nitride has been strongly increasing. Besides activities regarding lateral devices like the gallium nitride high electron mobility transistor, progress in the growth of native gallium nitride substrates encourages the development of vertical devices. In particular, for power electronics above 600 V, vertical architecture shows superior performance compared to lateral devices. This makes the vertical approach interesting for the use in traction inverters in the rising market of e-mobility. A key aspect in the fabrication of most vertical devices is the formation and optimization of trenches in the semiconductor. In this work, the fabrication of 1.5–2μm deep, crystal plane oriented trenches in gallium nitride with lateral dimension as small as 1μm is demonstrated. The trenches were produced by means of plasma etching based on sulfur hexafluoride and argon as well as a subsequent wet etching step in tetramethylammonium hydroxide and potassium hydroxide. By accurately aligning the trenches along the [1¯010]- and [12¯10]-directions, the authors were able to evaluate the wet etching behavior of the respective crystal planes and achieved smooth vertical sidewalls.

Fabrication of silicon electrodes used for micro electrochemical machining

In micro electrochemical machining (ECM), stray corrosion always causes undesired material dissolution and deteriorates the machining localization. Adopting sidewall insulating films on the electrode is proven to be an effective approach for reducing stray corrosion. Sidewall films with characteristics of good insulation, thin thickness, and excellent durability are required. In previous work, we proposed a heavily-doped silicon electrode, on which silicon-based films were prepared and acted as the insulating films. To fabricate silicon electrodes, this research investigates wet etching behavior of heavily doped Si (100) and then presents a fabrication process. Firstly, shapes of micro electrodes are designed on photomasks of lithography. Aiming at patterned profiles, effects of etchants on etch rate, dimension accuracy and surface integrity are investigated. Experimental results indicate that tetramethylammonium hydroxide (TMAH) leads to smoother electrode surfaces and fewer defects compared with potassium hydroxide. Then, insulation and durability performances of silicon-based films are investigated. 500 nm SiO2 and 300 nm Si3N4 composite film achieves more durable insulation and excellent compactness. Consequently, silicon electrodes with the dimension of 86 × 54 μm are fabricated on the Si (100) wafer with 25 wt% TMAH etchant, on which SiO2 and Si3N4 film is deposited by low-pressure chemical vapor deposition. In ECM experiments, stray corrosion of the non-machined surface is significantly reduced, and the sidewall taper of the machined structure is reduced to 5.5°. The validity and durability of silicon electrodes for micro ECM processes are verified.

Morphological and crystallographic evolution of patterned silicon substrate etched in TMAH solutions

Wet etching of Si substrate enables fabrication of sophisticated Si microstructures for a number of applications. However, the detailed anisotropic etching behavior of Si in the alkaline TMAH solutions is still not well understood. In this study, insights into the wet etching behavior of (100) patterned silicon substrate (PSiS) with circular aperture SiO2 mask in TMAH solutions of varying concentrations (1–25 wt%) are obtained through systematically studying the morphological and crystallographic evolutions of PSiS. Etching in 1 wt% TMAH revealed the widest spectrum of morphological evolutions including the rounded apertures, inverted octahedral frustums, octahedral pyramids, and pyramids. In contrast, etching in 5–25 wt% TMAH revealed features of inverted octahedral frustums, pyramidal frustums, and pyramids. A series of crystallographic planes formed due to anisotropic crystallographic etching were indexed as—C1 {3¯40}, C2 {1¯10}, C3 {1¯11¯}, C4 {2¯11¯}, and C5 {1 14 0}, and the etching rates of which were determined to explain the morphological evolution and anisotropic etching mechanism. This work contributes to the controllable fabrication of sophisticated Si microstructures for Si-based optoelectronic devices with potentially enhanced performance.

Oxidation and wet-etching behavior of MoAlTi thin films deposited by sputtering from a rotatable MoAlTi compound target

Within the current work, MoAlTi thin films have been developed and deposited by d.c. magnetron sputtering from a cold gas sprayed MoAlTi cylindrical rotatable target, to act as a novel molybdenum-based thin film system with improved oxidation and good wet-etching behavior. Chemical composition, microstructure, oxidation behavior, wet-etching properties, and electrical resistivity of the films are compared to those of a pure Mo reference film. Deviations in the chemical composition of the films with respect to the target are attributed to differences in gas phase scattering of the individual sputtered species. The films deposited are characterized by the formation of an Mo-based body-centered cubic solid solution, resulting in an increased electrical resistivity compared to the pure Mo film. While alloying Mo films with Al and Ti decreases the wet-etching rate in a phosphoric acid-based etching solution, the oxidation behavior could be significantly improved and the metallic-reflecting surface was maintained after annealing for 1 h at 330 °C in air.

Etching behavior of ZnO:Ga thin films

Abstract Gallium doped zinc oxide (ZnO:Ga) thin films were deposited on glass substrates by means of r.f. magnetron sputtering at room temperature, non-reactively. Both the wet chemical etching behavior and the influence of etching time variations on ZnO:Ga films were investigated. 0.1 % HCl was used as an etchant and the etching time varied in small increments. The thickness of the etched films was determined using scanning electron microscopy (SEM). The etching depth of the ZnO:Ga thin films increased from 13 to 58 % and the resistivity was 10−3 Ω × cm at different etching times. X-ray diffraction (XRD) results revealed that etching did not influence the crystal structure in a clear way. The (002) peak intensity to thickness ratio reached its maximum at 15 s while full width at half maximum (FWHM) was determined as the minimum. Morphological investigations were conducted using both high resolution scanning electron microscopy (HRSEM) and atomic force microscopy (AFM). The surface of the etched films became rougher and the root mean square (RMS) values increased according to etching time; at 15 s etching the RMS value was calculated to be 8.48 nm. The optical transmittance was measured using an ultraviolet–visible (UV–VIS) spectrophotometer and decreased from 86.60 to 82.50 % while haze increased from 0.85 to 16.68 %.

Oxidation and wet etching behavior of sputtered Mo-Ti-Al films

Exposure of Mo thin films above 300 °C in ambient atmosphere results in surface oxidation, leading to the formation of colored oxide films deteriorating their performance in thin film transistor liquid crystal displays. In this study, the influence of the alloying elements Ti and Al on microstructure, electrical properties, oxidation and wet etching behavior of Mo thin films was investigated. Mo1−x−yTixAly films (with x ≈ 0.08 and 0 ≤ y ≤ 0.24) were deposited by direct current magnetron sputtering and annealed in ambient air at 330 °C for 1 h. The oxidation resistance of Mo-Ti-Al films was enhanced with increasing Al content. A minimum Al content of y = 0.16 was necessary to form a thin protective Al2O3 surface layer and to prevent the formation of colored molybdenum oxides. The wet etching rate of the Mo-Ti-Al films in a commonly used mixture of phosphoric-, acetic-, and nitric acid decreased with increasing Al content, but was still acceptable for thin film transistor liquid crystal displays applications.

Impact of Electrostatic Effects on Wet Etching Phenomenon in Nanoscale Region

The microminiaturization of semiconductor devices has made it necessary to control the wet etching process on the nanometer order. It is therefore extremely important to understand wet etching reactions in the nanoscale region of solid-liquid interfaces, in order to assist in optimizing process conditions to satisfy the severe demand for semiconductor devices. Simulations performed to analyze the behavior of liquid molecules in the nanoscale region have been reported [1], but there have been few reports of detailed experimental results. We here report detailed experimental results on the wet etching behavior of SiO2 film in the nanoscale region between Si materials.

Wet Etching Behavior of Poly-Si in TMAH Solution

Since Tetramethylammonium Hydroxide (TMAH) became widely used as a silicon etchant, e.g. the dummy gate removal for gate-last approach (RMG) [1, or Si fin formation on FinFET [, some careful preparations and optimizations have required implementation. These adaptations have involved not only chemical-related issues, but also hardware-related in order to satisfy the necessary process performance.

Effect of nitric acid on wet etching behavior of Cu/Mo for TFT application

Recently, copper metallization has been widely developed in TFT-LCD industry, because of its lowest electrical resistivity compared to other metal candidates such as aluminum and molybdenum. In addition, the copper metallization becomes more significant issue in a high frequency driving TFT-LCD with large sized panel. Since the copper has a low adhesion force against the glass substrate, the copper is inevitably used with an aid of an adhesive metal layer such as Ti, Ta and Mo. When the dissimilar metals like the copper and molybdenum are exposed together in a wet etchant, a typical galvanic reaction occurs and this results in an undercutting of copper line or partial stains on the metal surface after drying. Especially, it is well-known that the suitable taper angle of Cu/Mo is difficult to obtain. Such failures often lead to a bad performance of thin film transistor and the display quality. Wet galvanic corrosion behavior of DC magnetron sputtered the double layers of Mo alloys and copper on the glass substrate has been examined. Compared with Cu/Mo–Ti system, the pure Mo/Cu system shows recessed galvanic corrosion behavior.

Fabrication of Transparent Semiconducting Indium Zinc Tin Oxide Thin Films and Its Wet Chemical Etching Characteristics in Hydrochloric Acid

We have fabricated the transparent semiconducting indium zinc tin oxide (IZTO) thin films on polymeric substrates at room temperature by RF-magnetron sputtering method, and investigated their wet chemical etching behavior in HCl solution. The study has revealed that the control of O2 flow rate during deposition attribute to the variation of resistivity for IZTO films, resulting in the conductor–semiconductor conductivity transition. The increasing etchant molarity and temperature of etching solution lead to the increase in etching rate of IZTO films according to the chemical dissolution reaction. As a result, the IZTO active channel is defined successfully, suggesting sufficient possibility for the application to flexible transparent thin film transistors.

Chemical Reactions During Wet-Etching Process of LSMO/PZT/LSMO-Structured Device Fabrication

Wet-etching behavior of Lanthanum Strontium Manganate (LSMO) electrode and ferroelectric Pb 0.52 Zr 0.48 TiO 3 (PZT) for large area thin film using LSMO/PZT/LSMO micro-sensing device was investigated using various etching solutions. The results show that PZT and LSMO thin films can be protected by the Pt hard etching mask. The etching mechanism of PZT film was attributed to the double replacement reaction etching model. The difference of etching rates of PZT and LSMO may cause damage of upper electrodes resulting in device failure. A careful design of the mask pattern of PZT and a well control of etching time are suggested to prevent the problem.

The influence of plasma power on the temperature-dependant conductivity and on the wet chemical etch rate of sputter-deposited alumina thin films

Aluminum oxide (Al 2O 3) thin films are synthesized by reactive d.c. magnetron sputter deposition on silicon substrates. The impact of varying plasma power P p (i.e. 400 to 1000 W) and of thin film temperatures T up to 540 °C on the electrical performance are evaluated, as these dielectric layers with a thickness of 450 nm are targeted as potential candidates for high temperature sensor applications. From 150 °C to 500 °C, the current–voltage measurements show a leakage current behavior according to the Poole–Frenkel electron emission with an activation energy of 1.16 eV. At T > 500 °C, the conductivity increases above average, in respect to the extrapolated Poole–Frenkel behavior at T < 500 °C, most probably due to the migration of charged ions, such as Ar +, incorporated into the film during deposition. Basically, samples synthesized at higher plasma levels show an enhanced electrical insulation behavior. This result is supported by measurements applying optical ellipsometry as well as by the determination of the wet chemical etching behavior in phosphoric-based acid at different bath temperatures. At higher plasma power, the refractive index shows a slight tendency to increase, staying, however, below the value of single-crystalline Al 2O 3. In contrast, the etch rate decreases by a factor of 1.5 at samples deposited at 1000 W when lowering the temperature of the etchant from 90 °C to 60 °C. These results indicate an enhanced film density at higher P p values as the microstructure of the Al 2O 3 films is X-ray amorphous independent of plasma power and post-deposition annealing temperatures up to 650 °C.

A study on the wet etching behavior of AZO (ZnO:Al) transparent conducting film

This paper studies the wet etching behavior of AZO (ZnO:Al) transparent conducting film with tetramethylammonium hydroxide (TMAH). The optimum optoelectronic film is prepared first using designated RF power, film thickness and controlled annealing heat treatment parameters. The AZO film is then etched using TMAH etchant and AZ4620 photoresist with controlled etchant concentration and temperature to examine the etching process effect on the AZO film optoelectronic properties. The experimental results show TMAH:H 2O = 2.38:97.62 under 45 °C at the average etch rate of 22 nm/min as the preferred parameters. The activation energy drops as the TMAH concentration rises, while the etch rate increases along with the increase in TMAH concentration and temperature. After lithography, etching and photoresist removal, the conductivity of AZO film dramatically drops from 2.4 × 10 −3 Ω cm to 3.0 × 10 −3 Ω cm, while its transmittance decreases from 89% to 83%. This is due to the poor chemical stability of AZO film against AZ4620 photoresist, leading to an increase in surface roughness. In the photoresist postbaking process, carbon atoms diffused within the AZO film produce poor crystallinity. The slight decreases in zinc and aluminum in the thin film causes a carrier concentration change, which affect the AZO film optoelectronic properties.

Surface textured MF-sputtered ZnO films for microcrystalline silicon-based thin-film solar cells

Highly conductive and transparent aluminum-doped zinc oxide (ZnO:Al) films were prepared by reactive mid-frequency (MF) magnetron sputtering at high growth rates. By varying the deposition pressure, pronounced differences with respect to film structure and wet chemical etching behavior were obtained. Optimized films develop good light-scattering properties upon etching leading to high efficiencies when applied to amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon-based thin-film solar cells and modules. Initial efficiencies of 7.5% for a μc-Si:H single junction and 9.7% for an a-Si:H/μc-Si:H tandem module were achieved on an aperture area of 64 cm2.

Surface morphology and removal rates for dry- and wet-etched novel resonator materials: Part II. La 3Ga 5.5Nb 0.5O 14

The wet and dry etching behavior of La 3Ga 5.5Nb 0.5O 14 is reported. The ultimate application for this material is as crystal resonators whose operating frequency is inversely proportional to sample thickness. Reaction-limited wet etching in HCl or HF at ≥25°C, or HNO 3 at ≥60°C produced removal rates up to 9500 Å·min −1 (HCl at 65°C), with surface root-mean-square (RMS) roughnesses about a factor of two higher than on an unetched control sample. Dry etching in Cl 2-based plasmas produced removal rates up to 950 Å·min −1, with surfaces RMS values also about a factor of two higher than on control samples. Significant surface roughening occurred during dry etching when higher ion fluxes were used.