Dependence Of Etch Rate Research Articles

Modeling of surface evolution in plasma etching for SiC microgroove fabrication

Monocrystalline silicon carbide (SiC) has attracted attention for applications in devices operating in harsh environments due to its excellent physicochemical properties. However, it is difficult to obtain extremely small-feature sizes with undamaged surfaces due to its extremely high hardness. Herein, a novel method to fabricate SiC microgrooves is proposed that combines molding with inductively coupled plasma (ICP) etching process. First, a Ni–P microgroove master mold was fabricated by ultraprecision cutting and replicated on a polydimethylsiloxane (PDMS) surface, which was then used as the microgroove mold for hot embossing. Then, the patterned mask fabricated by hot embossing was transferred to the SiC substrate by ICP etching. To obtain customized microgrooves, an interface-evolution model based on angular dependence theory was established. A numerical method based on a string algorithm approach is developed for interface-evolution simulations. During ICP etching, the characteristic size d of homogeneous materials and the sidewall angle in heterogeneous materials varied with the sidewall angle of the SU-8 mask due to the angular dependence of etch rate. Finally, seven sets of microgrooves were machined on SU-8 to study the interface-evolution process. Variations in the characteristic size Δd and sidewall angle θ for each unit in homogeneous material, as well as the variations in sidewall angle before and after etching in heterogeneous materials are described. The high accuracy of the proposed interface-evolution model was experimentally validated.

Selective Wet and Dry Etching of NiO over β-Ga2O3

Patterning of NiO/Ga2O3 heterojunctions requires the development of selective wet and dry etch processes. Solutions of 1:4 HNO3 :H2O exhibited measurable etch rates for NiO above 40 °C and activation energy for wet etching of 172.9 kJ.mol-1 (41.3 kCal.mol-1, 1.8 eV/atom), which is firmly in the reaction-limited regime. The selectivity over β-Ga2O3 was infinite for temperatures up to 55°C. The strong negative enthalpy for producing the etch product Ga(OH)4 suggests that HNO3-based wet etching of NiO occurs via the formation and dissolution of hydroxides. For dry etching, Cl2/Ar Inductively Coupled Plasmas produced etch rates for NiO up to 800Å.min-1, with maximum selectivities of < 1 over β-Ga2O3. The ion energy threshold for initiation of the etching of NiO was ~55 eV and the etch mechanism was ion-driven, as determined by the linear dependence of etch rate on the square root of ion energy incident on the surface.

A two-step wet etching process of PZT thin film with ultra-low undercut for MEMS applications

Wet etching methods of lead zirconate titanate (PZT) film suffer from high residual risk and severe undercut erosion. In this study, a two-step etching approach replace with the traditional concept of multi-acid mixing etchant, which increases the precision of PZT film and fixes the residual issues that were difficult to avoid in the conventional scheme. The two-step etching of the PZT film's mechanism is investigated using XRD and TEM. The impact of the etchant's composition ratio on the etching effect is demonstrated, and the ideal process range and debugging direction can be accurately identified. The undercut ratio (0.62) of the etching method proposed in this study is substantially lower than that in prior studies. In addition, the etching rate and selectivity between photoresists are 60 nm/s and 1.14, respectively. The sidewall forms an inclined plane of around 30 degrees due to the crystal orientation dependent etch rates. The results of the polarization hysteresis loop demonstrate that there is no significant performance loss before and after the wet etching process. A two-step wet etching process of PZT thin film with ultra-low undercut ratio (0.62) is developed. The baseline recipe with a high etch rate, and the selectivity with photoresist is 1.14, and the sidewalls etch into an inclined plane of about 30 degrees. • A new two-step wet etching recipe for PZT film, which use different etchant to etch different phases in PZT film, obtains ultra-low undercut ratio (0.62) and does not generate residual risk, has been developed. • Experimental results have demonstrated that ultra-low undercut, high etch rate, no residual and high selectivity can be simultaneously achieved without using any special processing condition. • Etch results with different acid concentrations in different etchant, processing phenomenon analysis with XRD and TEM, and Interpretation of the etching process and comparison of ferroelectric parameters for the results before and after etching, which can be proven suitability for various etching purposes.

Threshold Ion Energies and Cleaning of Etch Residues During Inductively Coupled Etching of NiO/Ga2O3 in BCl3

BCl3 is an attractive plasma etchant for oxides because it is a Lewis acid used to scavenge native oxides on many semiconductors due to the strong B–O bonding. We investigated BCl3-based dry etching of the NiO/Ga2O3 heterojunction system. BCl3/Ar Inductively Coupled Plasmas produced maximum etch rates for NiO up to 300 Å.min−1 and 800 Å.min−1 for β-Ga2O3 under moderate plasma power conditions suitable for low damage pattern transfer. The selectivity for NiO: Ga2O3 was <1 under all conditions. The ion energy threshold for initiation of etching of NiO was between 35–60 eV, depending on the condition and the etch mechanism was ion-driven, as determined by the linear dependence of etch rate on the square root of ion energy incident on the surface. By sharp contrast, the etching of Ga2O3 had a stronger chemical component, without a well-defined ion energy threshold. The as-etched NiO and Ga2O3 surfaces show chlorine residues, which can be removed on both materials by the standard 1NH4OH: 10H2O or 1HCl: 10H2O rinses used for native oxide removal. According to the location of the Cl 2p3/2 peak, the Cl is ionically bonded.

SiO2 etching and surface evolution using combined exposure to CF4/O2 remote plasma and electron beam

Electron-based surface activation of surfaces functionalized by remote plasma appears like a flexible and novel approach to atomic scale etching and deposition. Relative to plasma-based dry etching that uses ion bombardment of a substrate to achieve controlled material removal, electron beam-induced etching (EBIE) is expected to reduce surface damage, including atom displacement, surface roughness, and undesired material removal. One of the issues with EBIE is the limited number of chemical precursors that can be used to functionalize material surfaces. In this work, we demonstrate a new configuration that was designed to leverage flexible surface functionalization using a remote plasma source, and, by combining with electron beam bombardment to remove the chemically reacted surface layer through plasma-assisted electron beam-induced etching, achieve highly controlled etching. This article describes the experimental configuration used for this demonstration that consists of a remote plasma source and an electron flood gun for enabling electron beam-induced etching of SiO2 with Ar/CF4/O2 precursors. We evaluated the parametric dependence of SiO2 etching rate on processing parameters of the flood gun, including electron energy and emission current, and of the remote plasma source, including radiofrequency source power and flow rate of CF4/O2, respectively. Additionally, two prototypical processing cases were demonstrated by temporally combining or separating remote plasma treatment and electron beam irradiation. The results validate the performance of this approach for etching applications, including photomask repair and atomic layer etching of SiO2. Surface characterization results that provide mechanistic insights into these processes are also presented and discussed.

Selective Wet and Dry Etching of NiO over β-Ga2O3

Patterning of NiO/Ga2O3 heterojunctions requires development of selective wet and dry etch processes. Solutions of 1:4 HNO3:H2O exhibited measurable etch rates for NiO above 40 °C and activation energy for wet etching of 172.9 kJ.mol−1 (41.3 kCal.mol−1, 1.8 eV atom−1), which is firmly in the reaction-limited regime. The selectivity over β-Ga2O3 was infinite for temperatures up to 55 °C. The strong negative enthalpy for producing the etch product Ga(OH)4 suggests HNO3-based wet etching of NiO occurs via formation and dissolution of hydroxides. For dry etching, Cl2/Ar Inductively Coupled Plasmas produced etch rates for NiO up to 800 Å.min−1, with maximum selectivities of <1 over β-Ga2O3. The ion energy threshold for initiation of etching of NiO was ∼55 eV and the etch mechanism was ion-driven, as determined the linear dependence of etch rate on the square root of ion energy incident on the surface.

Evolution of lithography-to-etch bias in multi-patterning processes

Quantitatively accurate, physics-based, computational modeling of etching and lithography processes is essential for modern semiconductor manufacturing. This paper presents lithography and etch models for a trilayer process in a back end of the line manufacturing vehicle. These models are calibrated and verified against top-down scanning electron microscope (SEM) and cross-sectional SEM measurements. Calibration errors are within 2 nm, while the maximum verification error is less than 3 nm. A fluorocarbon plasma etch of the spin-on-glass (SOG) layer accounts for most of the etch bias present in the process. The tapered profile in the SOG etch step is generated due to the polymerization process by fluorocarbon radicals generated in the plasma. The model predicts a strong correlation between the etch bias in the SOG etch step and the neutral-to-ion flux ratio in the plasma. The second etch step of the flow, which etches the spin-on-carbon (SOC) layer using an H2/N2 plasma, results in a negative etch bias (increase in CDs) for all measured features. The ratio of hydrogen to nitrogen radical fluxes effectively controls the etch bias in this step, with the model predicting an increase in the etch bias from negative to positive values as the H-to-N ratio decreases. The model also indicates an aspect ratio dependent etch rate in the SOG and SOC etch steps, as seen in the etch front evolution in a three-dimensional test feature. The third and final step of the process, SiO2-etch, generates an insignificant etch bias in all the test structures. Finally, the accuracy of the etch simulations is shown to be dependent on the accuracy of the incoming photoresist shapes. Models that consider only the top-down SEM measurement as input and do not account for an accurate photoresist profile, suffered significant errors in the post-etch CD predictions.

Simultaneous Micro- and Nanoscale Silicon Fabrication by Metal-Assisted Chemical Etch

Abstract Simultaneous micro- and nanoscale etching of silicon on a wafer-scale is nowadays performed using plasma etching techniques. These plasma techniques, however, suffer from low throughput due to aspect-ratio dependent etch (ARDE) rate, etch lag from changes in feature size, loading effects from increased etch area, and undesirable surface characteristics such as sidewall taper and scalloping, which are particularly problematic at the nanoscale and can affect the etch uniformity. Additionally, the hardware required for plasma etching can be very expensive. A potential alternative, which addresses the above issues with plasma etching is metal assisted chemical etch (MacEtch). To date, however, an integrated micro- and nanoscale MacEtch process, which has uniform and clean (i.e., without nanowire-like defects in microscale areas) etch front has not been presented in the literature. In this work, we present for the first time a feasible process flow for simultaneous micro-and nanoscale silicon etching without nanowire-like defects, which we call integrated micro- and nanoscale MacEtch (IMN-MacEtch). Successful etching of silicon features ranging from 100 nm to 100 μm was achieved with etch rates of about 1.8 μm/min in a single step to achieve features with an aspect ratio (AR) ∼18:1. We thus conclude that the process represents a feasible alternative to current dry etch methods for patterning feature sizes spanning three orders of magnitude.

Understanding of Etching Mechanism of Si3N4 Film in H3PO4 Solution For The Fabrication of 3D NAND Devices

Silicon nitride (Si3N4) has been widely used as an insulating or etch stop layer in the semiconductor devices [1]. For example, in a 3D V-NAND flash memory manufacturing process, Si3N4 is alternately stacked with silicon oxide (SiO2) to form a NAND structure. Here, it is necessary to selectively etch Si3N4 avoiding etching of SiO2 in the repeated Si3N4/SiO2 multi-stack layers. In general, phosphoric acid (H3PO4) is used to selectively etch Si3N4 against SiO2 [2]. However, since the concentration of H3PO4 solution changes with the evaporation of H2O, it is not easy to determine the concentration dependence of Si3N4 etching rate in H3PO4 solution. In order to properly control the shape of the 3D V-NAND structure, it is necessary to extensively understand the effect of H3PO4 concentration on the Si3N4 etching. The study of Si3N4 etching has been mainly focused on the effect of additives in H3PO4 on the behavior of Si3N4 etching to solve the issue such as oxide regrowth so far [3, 4]. Fundamental study of the Si3N4 etching reaction mechanism in H3PO4 is lacking. In this study, the Si3N4 etching mechanism in H3PO4 solution is elucidated systematically.For the investigation of Si3N4 etching reaction mechanism, LPCVD Si3N4 blanket wafer and Si3N4/SiO2 multi-stack layered trench wafer were used. Etching experiments of of Si3N4 were conducted in 10-95 wt% H3PO4 solutions at 160 °C. Spectroscopic ellipsometry and field emission scanning electron microscopy were used to measure the etching rate of Si3N4 after etching process.First, the changes in etching rate of Si3N4 in the various concentrations of H3PO4 solution were investigated. As shown in Fig. 1, according to our kinetic calculation and experiments, etching rate of Si3N4 increased as the H3PO4 concentration increased until the concentration of H3PO4 reaches a certain concentration that produced the highest etching rate. However, etching rate of Si3N4 decreased with the concentration of H3PO4 beyond the critical H3PO4 concentration. According to the results, there may be two concentrations of H3PO4 solution which produce an identical etching rate of Si3N4. It is also suggested that not only H3PO4 but also H2O plays an important role in the Si3N4 etching kinetics.To investigate the role of H2O and H3PO4 in the etching reaction of Si3N4, kinetic isotope effect (KIE) of Si3N4 etching reaction in H3PO4 solution was used. KIE provides information about which reactant determines the rate-limiting step. In this study, each reactant of Si3N4 etching reaction, H2O or H3PO4, was substituted with D2O and D3PO4, respectively. Then, etching of Si3N4 was conducted in four different solutions. As shown in Fig. 2, when H3PO4 was replaced by D3PO4, the Si3N4 etching rate was not significantly changed. However, when H2O was replaced by D2O, the Si3N4 etching rate decreased by 30 %. Therefore, it is thought that rate-limiting step of the Si3N4 etching reaction is determined by an elementary reaction related to H2O rather than H3PO4.Based on the above results, Si3N4 etching reaction mechanism was suggested. First, the Si3N4 surface termination (-NH2) is substituted with H2PO4 -, which is a weak nucleophile, by an SN1-like reaction. When H2PO4 - binds to Si, the backbone of Si3N4 is weakened because the electronegativity of O (3.44) is greater than N (3.04). Next, the Si-N of the weakened backbone of Si3N4 is substituted with Si-OH by an SN2-like reaction of H2O. This SN2-like reaction is considered as a rate-limiting step. It is believed that understanding of etching mechanism of Si3N4 in H3PO4 solution will improve selective etching process of Si3N4 for the integration of 3D V-NAND.

Various evolution trends of sample thickness in fluorocarbon film deposition on SiO2

Recently, fluorocarbon (FC) film deposition on a SiO2 surface has become one of the most important processes in semiconductor manufacturing because the formation of a passivation layer on SiO2 during the deposition process plays a crucial role in atomic layer etching and high aspect ratio contact (HARC) etching, areas that are attracting intense interest in the semiconductor industry. In this work, various trends of sample thickness change, namely, decreasing, increasing, and anomalously increasing trends with time, were observed during FC film deposition on a SiO2 surface. The total thickness including both SiO2 and FC film was found to change during the deposition process in various ways depending on the plasma conditions. This can be successfully explained by considering the mechanism of SiO2 etching with FC plasma, taking into account the dependence of the SiO2 etch rate on FC film thickness. This result is expected to be utilized in semiconductor processes such as HARC etching where a precise control of film thickness is needed.

Statistical insights into the reaction of fluorine atoms with silicon

The dependences of silicon etching rate on the concentration of F atoms are investigated theoretically. The nonlinear regression analysis of the experimental data indicates that the reaction of F atoms with silicon is 2nd overall order reaction. The relationship between overall reaction order and kinetic reaction order is established using the etching rate equation. It is found that kinetic reaction order monotonically decreases with the increase in concentration of F atoms due to the increased surface coverage. Surface passivation by the reaction products is not observed under the investigated experimental conditions.

Laser nanoablation of a diamond surface in air and vacuum

The nanoablation (cold laser-induced etching) of a diamond surface has been experimentally investigated at different ambient air pressures ranging from atmospheric to high vacuum (10-7 Torr). The exposure of a diamond monocrystal sample was performed by using the second harmonic (λ=400 nm) of a Ti-sapphire laser (τ=120 fs). The pressure dependence of the surface etching rate was obtained and corroborates a model that regards nanoablation as a result of multiphoton photochemical oxidation of the diamond. The features of the diamond oxidation at various environmental pressures are discussed as well as the effect of a surface water layer on the etching rate of the diamond.

BCl3-Based Dry Etching of Exfoliated (100) ß-Ga2O3 Flakes

We report on BCl3-based dry etching characteristics of (100) β-Ga2O3 flakes using inductively coupled plasma etching technique, which were prepared by mechanical exfoliation from Ga2O3 single crystal. The etch rate of (100) Ga2O3 flake increased with increasing bias rf powers up to 52 nm min−1 using 25 sccm BCl3/15 sccm N2 gas chemistry. We also examined the etch rate dependence of Ga2O3 on crystal orientation. The (100) Ga2O3 flake has the lowest etch rate when compared with (010) and Ga2O3 surfaces. The lowest etch rate of (100) Ga2O3 surface results from less Ga-O bond breaking efficiency and low dangling bond density on the surface. It is notable that Ga2O3 surface is etched at higher rate than (010) and (100) Ga2O3 surfaces. The surface morphologies of etched (100) Ga2O3 surface exhibited little change, and rms roughness values remained less than 1.5 nm over a broad range of etch conditions.

Bottom-up Patterning of Semiconductor Nanostructures for Large-Area Electronics

We demonstrate a versatile and programmable route to mask, with nanoscale precision, the surface of semiconductor nanostructures in an entirely bottom-up fashion. This capability promises to dramatically increase the manufacturing rate of high performance (i.e., > GHz, < 1 V) semiconductor devices for large-area, flexible electronics. Our approach – Selective CoAxial Lithography via Etching of Surfaces (SCALES) – involves three main steps: (1) Bottom-up synthesis of single crystalline semiconductor nanowires with an axially-encoded composition profile, (2) blanket surface-initiated polymerization of a masking material, and (3) selective removal of the masking material only from regions whose underlying surface is susceptible to an etchant. We show, among other examples, the selective patterning of dopant-modulated Si nanowires with a polymethylmethacrylate (PMMA) mask by leveraging the dependence of KOH etch rate on doping level. We will describe the role of polymerization parameters and post-polymerization etching on the patterning process with a suite of spectroscopy and microscopy techniques. Nanoscale masks produced via the SCALES process can subsequently direct the deposition of the oxides and metals needed to construct complete, fully-functional devices.

Nanoscale details of liquid drops on 1D patterned surfaces revealed by etching

This paper reports the wetting properties and spatially dependent etch rate variation on the interaction of a dilute potassium hydroxide (KOH):water droplet with a nanopatterned one-dimensional, 500-nm period, grooved photoresist surface. The KOH liquid drop showed a hydrophilic contact angle both along and perpendicular to the grooves and a more significant elongation distortion as compared to a deionized water drop. From the etching of the photoresist lines by the KOH solution, monitored by SEM after the drop was removed, the droplet was in a Cassie–Baxter state with the liquid excluded from the grooves and was pinned at the edge of the grating lines. The etch rate varied with the evaporation rate of the droplet and showed a dependence on the local contact angle with faster etching for smaller contact angles.

Understanding the mechanism of Beraha-I type color etching: Determination of the orientation dependent etch rate, layer refractive index and a method for quantifying the angle between surface normal and the 〈100〉, 〈111〉 directions for individual grains

A grey cast iron specimen was investigated by Beraha-I type color etching for the purpose of developing a functional model for the etching kinetics and subsequently a method which would enable the estimation of ferrite grain orientations with respect to specific directions, solely based on optical microscopy. For this, the etching process was observed real-time in a microfluidic cell and a custom image processing software was developed to interpret the color information. Scanning electron microscopy with electron backscatter diffraction (SEM-EBSD) and atomic force microscopy (AFM) were used to determine the grain orientation and the relative thickness of the developed interference layer respectively, which were used for further calculations. It was shown that in the initial phase the etching process experiences a delay, which can be connected to breaking an oxide barrier above the ferrite grains. This delay was found to be influenced by the idle time between sample preparation and the start of etching. However, it was proven that a characteristic cycle etch rate can be defined between the first interference minimum and maximum, which shows correlation with both the 〈100〉 and 〈111〉 directions and which is also independent from the delay during the initiation phase. The exact value and orientation dependence of this cycle etch rate was experimentally determined along with the refractive index of the developed film. Our method was demonstrated to be applicable for the estimation of the angle between the surface normal and the 〈100〉, 〈111〉 directions for individual ferrite grains in the cast iron specimen, with an average absolute error of 3°, by using optical microscopy only. The method is implemented and was made available in the form of a Matlab program.

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.

Polymer Optical Fiber Modification By Etching Using Hansen Solubility Parameters—A Case Study of TOPAS, Zeonex, and PMMA

Solvents can be used in the fabrication process of Polymer Optical Fiber (POF) sensors, as tapering or etching agents. We present a general approach—the use of Hansen solubility parameters—for identifying usable solvents for etching and present the first results on etching of TOPAS and Zeonex POFs. We also present alternatives to acetone in the form of trichloroethylene and THF, as etching solvents for PMMA, as well as results on the etching rate dependence on fiber orientation and annealing.

Optical Nanofabrication of Concave Microlens Arrays

AbstractFor the simple and versatile fabrication of nanosmooth finished microlens arrays on hard materials, an approach combining femtosecond laser modification with subsequent ion beam etching is demonstrated. This method is based on the dependence of the plasma etching rate on the laser fluence used to modify the surface. The fabricated microlenses exhibit a low surface roughness of approximately 2.5 nm, due to the high precision of the plasma etching and benefit from the smooth interface between the laser‐modified and pristine subsurface regions. Microlenses with focal lengths ranging from 60 to 100 µm are realized by controlling the laser fluence, exposure dose, and etching time. Uniform square and hexagonal microlens arrays are fabricated on both hard and ultrahard materials and glasses (fused silica, GaAs, SiC, diamond) by the same process and deliver high‐quality focusing and imaging.

Comparison of linear transformations for deriving kinetic constants during silicon etching in Cl2 environment

The chemical etching of n-type polycrystalline silicon films in Cl2 environment at three different temperatures is investigated. The experimental dependences of silicon etching rate on pressure of Cl2 molecules are described using the Michaelis–Menten equation. The experimental data are presented using Lineweaver–Burk, Hanes-Woolf, and Eadie–Hofstee plots. The linear transformations are used to derive reaction rate constants, desorption rate constants, and Michaelis constants. True values of the kinetic constants are determined using Michaelis–Menten saturation curves. The linear transformations are compared using mean absolute percentage errors (MAPEs) of the kinetic constants. It is found that the Hanes–Woolf plot provides the most accurate values of the kinetic constants.