Measured Etch Rate Research Articles

Computational approach for plasma process optimization combined with deep learning model

As semiconductor device structures become more complex and sophisticated, the formation of finer and deeper patterns is required. To achieve a higher yield for mass production as the number of process steps increases and process variables become more diverse, process optimization requires extensive engineering effort to meet the target process requirements, such as uniformity. In this study, we propose an efficient process design framework that can efficiently search for optimal process conditions by combining deep learning (DL) with plasma simulations. To establish the DL model, a dataset was created using a two-dimensional (2D) hybrid plasma equipment model code for an argon inductively coupled plasma system under a given process window. The DL model was implemented and trained using the dataset to learn the functional relationship between the process conditions and their consequential plasma states, which was characterized by 2D field data. The performance of the DL model was confirmed by comparison of the output with the ground truth, validating its high consistency. Moreover, the DL results provide a reasonable interpretation of the fundamental features of plasmas and show a good correlation with the experimental observations in terms of the measured etch rate characteristics. Using the designed DL, an extensive exploration of process variables was conducted to find the optimal processing condition using the multi-objective particle swarm optimization algorithm for the given objective functions of high etch rate and its uniform distribution. The obtained optimal candidates were evaluated and compared to other process conditions experimentally, demonstrating a fairly enhanced etch rate and uniformity at the same time. The proposed computational framework substantially reduced trial-and-error repetitions in tailoring process conditions from a practical perspective. Moreover, it will serve as an effective tool to narrow the processing window, particularly in the early stages of development for advanced equipment and processes.

Re-deposition of ITER-grade Be on plasma gun facility QSPA-Be: Characterization & plasma cleaning

Studies of contaminants obtained by spraying ITER-grade Be on a quasi-stationary plasma gun facility QSPA-Be are presented. Contaminating films, consisting mainly of Be and O in approximately equal proportions, were deposited on substrates of quartz, sapphire, single crystalline silicon (SC-Si) and NaCl crystal. Characterization of the deposits was performed using SEM, XPS, EBS, AFM, SE, TEM&SAED and micro-interferometry showing polycrystalline BeO films similar as found in JET-ILW. Films on SC-Si and NaCl were used to characterize their composition and morphology. The cleaning rates in the 81.36 MHz RF discharges in He or D2 at 2 Pa were measured on the SC-Si target. The measured etching rate of the deposited films was several times higher than the rate calculated from the theoretical value of beryllium oxide sputtering yield. Test cleaning of these contaminants was carried out in a capacitively coupled RF discharge (CCRF) from the surface of sapphire and quartz plates, which were considered as a mock-ups of the protective window of the first mirror unit (FMU) designed for ITER divertor Thomson scattering diagnostic system (DTS).

Atmospheric Pressure Dry Etching of Polysilicon Layers for Highly Reverse Bias‐Stable TOPCon Solar Cells

Single‐sided etching (SSE) of a‐Si/poly‐Si is typically considered a challenge for realizing a cost‐efficient TOPCon production sequence, as there is a certain degree of unwanted wrap‐around for poly‐Si deposition technologies such as low pressure chemical vapor deposition, plasma‐enhanced chemical vapor deposition, and atmospheric pressure chemical vapor deposition. To date, alkaline or acidic wet‐chemical solutions in either inline or batch configurations are used for this purpose. Herein, an alternative SSE process is proposed using an inline dry etching tool, which applies molecular fluorine as the etching gas under atmospheric pressure conditions. The developed etching process performs complete etching of both as‐deposited amorphous silicon and annealed polycrystalline silicon layers, either intrinsic or doped, and with measured etch rates of >3 μm min−1 at 10% F2 concentration allows etching of a typical layer thickness of 200 nm in just a few seconds. The etching process is also configured to perform excellent edge isolation while maintaining a low wrap‐around etching (d rear < 500 μm) at the opposing‐side. The etching process is successfully transferred to the industrial TOPCon solar cell architecture, yielding high parallel resistances (S shunt,avg. > 1500 kΩ cm2), low reverse current density (J rev,avg < 0.8 mA cm−2) measured at a bias voltage of −12 V, and independently certified conversion efficiencies of up to 23.3%.

Thermal Isotropic Atomic Layer Etching of Metallic Molybdenum

In high aspect ratio structures such as 3D NAND stacks, high-k oxides or certain metals need to be removed from sidewalls and even non-line-of-site locations where access via reactive ion etching would be challenging or impossible. To achieve etching in these locations, thermal processes need to be applied that lack any intrinsic directionality and are therefore isotropic. Thermal Atomic Layer Etching is one option to facilitate this kind of process. Therefore, it has gathered significant attention recently and is now being explored in academia and industry.In this work, we demonstrate isotropic Atomic Layer Etching on metallic molybdenum using a three-step process that involves oxygenation of the metal surface, a conversion reaction using boron-trichloride followed by a hydrogen-fluoride clean step. We measured the etch rate per cycle to be around 10 Å with low temperature dependence in the range between 150°C and 250°C.Furthermore, we examined the effectiveness of various oxygenation methods on the surface of metallic molybdenum films. These methods included thermal oxygenation as a function of temperature, oxygenation by a remote plasma and in-situ plasma fluorination. We established that an oxygenation level of more than 70% as measured with XPS is needed in order for the ALE process to work. Levels in this range could be achieved via in-situ plasma oxygenation as well as with a remote plasma. Thermal oxygenation, on the other hand, required substrate temperatures in access of 400°C to oxygenate at the 70% level.In this study we also show an example of molybdenum ALE in an application that involved the removal of this metal from a 50:1 aspect ratio 3D NAND structure. We measured etch rates on vertical and horizontal surfaces as well as the depth dependence in removal rate of molybdenum.

A quantitative description of fission-track etching in apatite

Abstract We measured the apatite etch rate νR in 5.5 M HNO3 at 21 °C as a function of orientation. Results for Durango apatite evidence that νR varies by a factor >5 with angle to the c-axis. Our measurements also provided track etch rates νT and surface etch rates νS. However, these cannot be combined for calculating track etching or counting efficiencies. By inserting the measured etch rates in a recent model, we calculate the geometries and dimensions of surface tracks in different apatite faces. The proposed model must be recalibrated for different etching protocols and adapted for other minerals. We submit that the new model justifies reviewing track counting efficiencies based on the existing (νB-νT) etch model. We anticipate that this will have an effect on practical aspects of fission track dating. Single-track step-etch data show that the confined track lengths increase with etch time at a decreasing average rate νL that differs from the track etch rate νT and the apatite etch rate νR. Both νT and νL exhibit large track-to-track differences that produce irreducible length variation related to the latent-track structure resulting from formation and annealing. Step etching and track width measurements are effective for reducing or eliminating procedure-related artifacts from track length data, and so for accessing more fundamental track properties.

Etching Kinetics and Surface Conditions for KNbxOy Thin Films with Fluorine- and Chlorine-Based Plasma Chemistries

The investigation of etching kinetics and surface conditions for KNbxOy thin films in CF4 + Ar and Cl2 + Ar inductively coupled plasmas was carried out. The variable processing parameters were Ar content in a feed gas (0–75% Ar), gas pressure (4–10 mTorr) and input power (400–700 W) at constant bias power of 100 W. The combination of plasma diagnostics by Langmuir probes and plasma modeling provided the data on internal plasma parameters, gas-phase chemistry and steady-state densities of plasma active species. The compositional changes of the etched surfaces were investigated using X-ray photoelectron spectroscopy (XPS). It was found that the fluorine-based etching chemistry provides the much lower halogen atom flux together with the much higher KNbxOy etching rate under the condition of quite close ion momentum fluxes in both gas systems. The correlations between measured etching rates and model-predicted fluxes of active species suggested the neutral-flux-limited etching regime with the much lower effective reaction probability between KNbxOy and Cl atoms. The last effect may be related to lower volatility of NbClx compared with NbFx (that is confirmed by XPS data) as well as to the higher energy threshold for KNbxOy + Cl reaction.

Gas-phase chemistry and etching mechanism of SiNx thin films in C4F8 + Ar inductively coupled plasma

In this study, we investigated the etching characteristics of non-stoichiometric SiNx thin films in C4F8 + Ar inductively coupled rf (13.56 MHz) plasma. The SiNx etching rates together with SiNx/Si and SiNx/SiO2 etching selectivities were measured as functions of the gas pressure (4–10 mTorr, or 0.53–1.33 Pa), input power (700–1000 W), bias power (100–400 W), and C4F8/Ar mixing ratio (0%–75% Ar). Data on internal plasma parameters and plasma chemistry as well as steady-state plasma composition were obtained by both Langmuir probe diagnostics and zero-dimensional plasma modeling. The etching mechanism of SiNx was analyzed through the relationship between the measured etching rates and model-predicted fluxes of active species (F atoms, CFx radicals, and positive ions). It was confirmed that within the given range of input process conditions, the SiNx etching process 1) appears in the steady-state etching regime, 2) exhibits the features of ion-assisted chemical reactions in the neutral-flux-limited mode, and 3) is influenced by the thickness of the fluorocarbon polymer film. It was shown that the influence of input process parameters on the effective probability of SiNx + F chemical reaction may be adequately characterized by the fluorocarbon radicals/fluorine atoms and fluorocarbon radicals/ion energy flux ratios.

High-precision in-situ size measurements of single microparticles in an RF plasma

An in-situ method to measure the radii of single microparticles in plasmas with high precision is presented. The particles are trapped in the plasma sheath and illuminated with laser light. Using out-of-focus imaging and polarizing optics, the angle- and polarization-resolved scattering intensities are measured and compared to Lorenz-Mie theory. A two-stage fit procedure is introduced to obtain the complex refractive index in addition to the particle radius. Complementary long-distance microscopy measurements are performed to compare with fit results. The method is applied to particles of different materials used in complex plasma research to measure etch rates due to plasma inherent processes.

Etching Mechanisms and Surface Conditions for SiOxNy Thin Films in CF4 + CHF3 + O2 Inductively Coupled Plasma

In this work, we investigated the etching characteristics of SiOxNy thin films in CF4 + CHF3 + O2 inductively coupled radiofrequency (13.56 MHz) plasma. SiOxNy etching rates were measured as functions of the CF4/CHF3 mixing ratio at constant O2 fraction, gas pressure (10 mTorr), input power (500 W) and bias power (100 W). The conditions of the etched surfaces were examined by X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements. Data on internal plasma parameters and steady-state plasma composition were obtained by Langmuir probe diagnostics and zero-dimensional plasma modeling. It was found that the substitution of CF4 for CHF3 suppresses the SiOxNy etching rate as well as results in increasing both amount of residual fluorocarbon polymer and SiOxNy/Si etching selectivity. The SiOxNy etching mechanism was analyzed by considering the relationships between measured etching rates and model-predicted fluxes of active species (F atoms, CFx radicals and positive ions). It was proposed that the SiOxNy etching process: (1) exhibits features of ion-assisted chemical reactions in the neutral-flux-limited mode, and (2) involves the contributions of by HF molecules. The effective probability of the SiOxNy + F reaction is correlated with the amount of deposited fluorocarbon polymer while the hydrophobic nature of the plasma-treated SiOxNy surface confirms the presence of a continuous fluorocarbon polymer film.

Design, fabrication and characterization of glass phase steps for application in phase shifting interferometry

In this paper, we report on the design and fabrication of a low-cost phase shifter for application in phase shifting interferometry. Phase shifting interferometry is a powerful method for surface characterization. It uses interference data recorded during a series of predetermined phase shifts to recover the induced phase by the object surface. These controlled phase shifts are typically performed by putting a piezo-electric ceramic behind one of interferometer mirrors. Applying the controlled voltage to this ceramic provides the desired phase shifts. The piezo-electric positioners are very expensive. Phase shifting interferometry has different algorithms. One of the most effective algorithms is the four step phase shifting interferometry. In this algorithm, four interferograms are taken; then the unknown phase term due to surface is extracted by combining these interferograms. Here, we have proposed a low-cost alternative for piezo-electric positioners. Firstly, using the Fresnel diffraction from the phase step, we have measured etch rate of glass by HF acid. Then, a phase step with a quarter wavelength phase shift has been fabricated on a glass plate. The step height has been measured using Fresnel diffraction (phase step diffractometer) and interferometry. Then a stepwise structure has been fabricated on glass, providing phase shifts needed in the four step phase shifting interferometry.

PLASMA PARAMETERS, DENSITIES OF ACTIVE SPECIES AND ETCHING KINETICS IN C4F8+Ar GAS MIXTURE

In this work, we performed the combined (experimental and model-based) study of gas-phase plasma characteristics and etching kinetics for both Si and SiO2 in the C4F8 + Ar gas mixture. The experiments were carried out at constant total gas pressure (p = 6 mTorr), input power (W = 900 W) and bias power (Wdc = 200 W) while the C4F8/Ar mixing ratio was varied in the range of 0–75% Ar. The data on internal plasma parameters, plasma chemistry as well as the steady-state plasma composition were obtained by both Langmuir probe diagnostics and 0-dimensional plasma modeling. The etching mechanisms were investigated through the analysis of relationships between the measured etching rates and the model-predicted fluxes of active species (F atoms, polymerizing CFx radicals and positive ions). It was found that, under the given set of experimental conditions, the Si and SiO2 etching process 1) appears in the steady-state etching regime; 2) exhibits the features of the ion-assisted chemical reactions in the neutral-flux-limited mode; and 3) is influenced by the fluorocarbon polymer film thickness. It was shown that the influence of input process parameters on the effective probability of chemical reaction between Si, SiO2 and fluorine atoms may be adequately characterized by the fluorocarbon radicals/fluorine atoms and fluorocarbon radicals/ion energy flux ratios.

Application of Fresnel diffraction to fabrication and characterization of glass phase steps.

In this paper we used Fresnel diffraction in order to study the effects of hydrofluoric acid concentration and temperature on glass etching rate. The technique is very simple and accurate, and nanoscale change of the glass thickness can be detected and measured during etching. Using measured etching rates we have fabricated several glass phase steps. The fabricated phase steps were characterized by Fresnel diffractometry and optical interferometry. Using this method one can fabricate and characterize low-cost phase shifters of appropriate accuracy in less than 1h.

Hybrid process of fabricating high-quality micro wine-glass fused silica resonators

A new hybrid method, which combines improved glass-blown technology with wet etching, is reported to fabricate micro wine-glass resonators with high-quality fused silica. The optimum placement is compared to achieve the resonators with good shell shape. The typical shell diameter is about 4mm and its thickness covers from dozens to hundreds of micrometers. The etching rates in corrosion solutions with different ratios and at different thicknesses of hemispherical shells are studied. We also conclude how to precisely control the thickness. The corrosion solutions with different ratios of HF solution to NH4F solution make the spherical shells rougher in different degrees. The best roughness is 0.581 nm in the 1: 8 ratio corrosion solution while the original roughness is 0.537 nm. This fact shows that the resonator remains atomically smooth surface. Based on the glassblowing spherical fused silica structure, the thickness of the resonator is effectively controlled by buffered oxide etch (BOE) technology according to the measured etching rate. The measured resonant frequency of the hemispherical shell at ambient pressure and room temperature is 1.75 kHz of rocking mode which is close to the simulated frequency. Using such a low-cost hybrid approach, we can fabricate high-quality microscale resonators in batch.

Etching of polymers, proteins and bacterial spores by atmospheric pressure DBD plasma in air

Many studies proved that non-equilibrium discharges generated at atmospheric pressure are highly effective for the bio-decontamination of surfaces of various materials. One of the key processes that leads to a desired result is plasma etching and thus the evaluation of etching rates of organic materials is of high importance. However, the comparison of reported results is rather difficult if impossible as different authors use diverse sources of atmospheric plasma that are operated at significantly different operational parameters. Therefore, we report here on the systematic study of the etching of nine different common polymers that mimic the different structures of more complicated biological systems, bovine serum albumin (BSA) selected as the model protein and spores of Bacillus subtilis taken as a representative of highly resistant micro-organisms. The treatment of these materials was performed by means of atmospheric pressure dielectric barrier discharge (DBD) sustained in open air at constant conditions. All tested polymers, BSA and spores, were readily etched by DBD plasma. However, the measured etching rates were found to be dependent on the chemical structure of treated materials, namely on the presence of oxygen in the structure of polymers.

Modeling and experimental investigation of the plasma uniformity in CF4/O2 capacitively coupled plasmas, operating in single frequency and dual frequency regime

A two-dimensional hybrid Monte Carlo–fluid model, incorporating a full-wave solution of Maxwell's equations, is employed to describe the behavior of high frequency (HF) and very high frequency capacitively coupled plasmas (CCPs), operating both at single frequency (SF) and dual frequency (DF) in a CF4/O2 gas mixture. First, the authors investigate the plasma composition, and the simulations reveal that besides CF4 and O2, also COF2, CF3, and CO2 are important neutral species, and CF3+ and F− are the most important positive and negative ions. Second, by comparing the results of the model with and without taking into account the electromagnetic effects for a SF CCP, it is clear that the electromagnetic effects are important, both at 27 and 60 MHz, because they affect the absolute values of the calculation results and also (to some extent) the spatial profiles, which accordingly affects the uniformity in plasma processing. In order to improve the plasma radial uniformity, which is important for the etch process, a low frequency (LF) source is added to the discharge. Therefore, in the major part of the paper, the plasma uniformity is investigated for both SF and DF CCPs, operating at a HF of 27 and 60 MHz and a LF of 2 MHz. For this purpose, the authors measure the etch rates as a function of position on the wafer in a wide range of LF powers, and the authors compare them with the calculated fluxes toward the wafer of the plasma species playing a role in the etch process, to explain the trends in the measured etch rate profiles. It is found that at a HF of 60 MHz, the uniformity of the etch rate is effectively improved by adding a LF power of 2 MHz and 300 W, while its absolute value increases by about 50%, thus a high etch rate with a uniform distribution is observed under this condition.

Numerical investigation of HBr/He transformer coupled plasmas used for silicon etching

A two-dimensional hybrid Monte Carlo—fluid model is applied to study HBr/He inductively coupled plasmas used for etching of Si. Complete sets of gas-phase and surface reactions are presented and the effects of the gas mixing ratio on the plasma characteristics and on the etch rates are discussed. A comparison with experimentally measured etch rates is made to validate the modelling results. The etch rate in the HBr plasma is found to be quite low under the investigated conditions compared to typical etch rates of Si with F- or Cl-containing gases. This allows for a higher control and fine-tuning of the etch rate when creating ultra-small features. Our calculations predict a higher electron temperature at higher He fraction, because the electrons do not lose their energy so efficiently in vibrational and rotational excitations. As a consequence, electron impact ionization and dissociation become more important, yielding higher densities of ions, electrons and H atoms. This results in more pronounced sputtering of the surface. Nevertheless, the overall etch rate decreases upon increasing He fraction, suggesting that chemical etching is still the determining factor for the overall etch rate.

Interactions between arrayed hollow cathodes

An array of novel hollow cathode plasma sources of 4 mm diameter and driven by up to 500 W of 13.56 MHz rf power was constructed. It was investigated using spatially resolved Langmuir probe measurements in the plasma expansion region. Initial results suggest the plasma observed downstream is the combination of a diffusion from the exit orifice of the 30 mm long cylindrical source region and a uniform plasma created in the expansion region. By measuring the ion density of the plasma plumes produced by two or more active hollow cathode sources, their mutual interaction has been inferred with the aim of determining whether a much larger array of sources could be envisioned. The effectiveness of the plasma in dissociating reactive species was tested using SF6 and measuring etch rates on unbiased silicon wafers. The results have been modelled and show that it is possible to produce a uniform spread of ±5%.

Selective InAs/GaSb strained layer superlattice etch stop layers for GaSb substrate removal

This paper reports the use of an InAs/GaSb strained layer superlattice (SLS) as an etch stop layer for GaSb substrate removal with a BCl3/SF6 etch chemistry. Optimum chamber conditions were determined by measuring etch rates and selectivities for two types of superlattices. It was found that selectivity of GaSb over a superlattice is maximized if the reactive ion etching (RIE) chamber pressure is maximized and BCl3 is 80 % of the gas mixture. Selectivities of up to about 475 were measured. Greater selectivity was achieved with superlattices composed of thicker InAs layers.

Optically monitoring and controlling nanoscale topography during semiconductor etching

We present epi-diffraction phase microscopy (epi-DPM) as a non-destructive optical method for monitoring semiconductor fabrication processes in real time and with nanometer level sensitivity. The method uses a compact Mach–Zehnder interferometer to recover quantitative amplitude and phase maps of the field reflected by the sample. The low temporal noise of 0.6 nm per pixel at 8.93 frames per second enabled us to collect a three-dimensional movie showing the dynamics of wet etching and thereby accurately quantify non-uniformities in the etch rate both across the sample and over time. By displaying a gray-scale digital image on the sample with a computer projector, we performed photochemical etching to define arrays of microlenses while simultaneously monitoring their etch profiles with epi-DPM. Semiconductor etching can now be monitored in real time at nanoscale resolution using a non-destructive optical imaging technique that combines a conventional microscope with a compact Mach–Zehnder interferometer. Developed by Chris Edwards, Amir Arbabi, Gabriel Popescu, and Lynford Goddard at the University of Illinois at Urbana-Champaign in the United States, epi-diffraction phase microscopy makes it possible to collect three-dimensional videos of semiconductor fabrication processes using a CCD camera. The approach is able to measure etch rates at each location across the sample with a resolution of 0.085 nm s−1 per pixel. Such an in situ monitoring capability could be useful for improving the manufacturing quality of a wide variety of semiconductor devices.

Reliability assessment of the complete 3D etch rate distribution of Si in anisotropic etchants based on vertically micromachined wagon wheel samples

As a sequel to part I (Gosálvez et al J. Micromech. Microeng. 12 125007), the present paper is part II of a series of two papers dedicated to the presentation of a novel, large-throughput, experimental procedure to determine the complete three-dimensional orientation dependence of the etch rate of silicon by using vertically micromachined wagon wheel samples. While the first part provides the experimental details and compares the results to realistic simulations, the present paper focuses on characterizing the reliability of the obtained etch rates. For this purpose, the shape of the etched structures is analyzed and corresponding formulas are derived, enabling the estimation of an upper bound to the measured etch rates. It is shown that the measured etch rates remain below this limit, strongly indicating that the observed wedge retraction values are consistent with the assumed geometrical shape of the wedges. An exception to this rule are the etch rates of {1 1 0} obtained from ⟨1 1 0⟩-oriented wafers, which are systematically larger. This deviation is explained by a kinetic acceleration process due to the small size of the step-flow structures that are formed on the affected wagon wheel spokes. The comparison to previous experiments indicates that the proposed method provides similar or even more accurate etch rates for some of the etchants with a more affordable and less labor-intensive approach.