Etching Of Films Research Articles

Machine learning-based run-to-run control of a spatial thermal atomic layer etching reactor

In response to the next technological revolution, atomic layer processes have emerged to produce high-performing, thin-film semiconductor materials. To overcome the long purging times required for conventional atomic layer processes, spatial atomic layer processes have been recognized for their ability to reduce processing times; however, they lack characterization and control. This research aims to construct two novel run-to-run (R2R) control systems using a machine learning model with an artificial neural network (ANN) and an exponentially weighted moving average (EWMA) method for the spatial thermal atomic layer etching (SALE) of aluminum oxide thin films. The two R2R controllers are used in conjunction with a multiscale computational fluid dynamics model of a SALE process with various disturbances to test their effectiveness. Closed-loop simulation results demonstrate that the ANN-based R2R control system reduces etching per cycle variability, maintains the process output within a small region around the setpoint, and outperforms the traditional EWMA-based R2R control system in efficiency.

Enabling High Aspect Ratio 3D NAND Scaling through Deposition and Etch Co-Optimization (DECO)

Over the past decade, the demands for 3D NAND flash memory devices have been increased tremendously due to ever growing digital economics in consumer electronics, data centers, IOT, healthcare and automotive industries. The growth is further accelerated during the recent Covid period. The industry was able to keep up the scaling roadmap by stacking more memory cell in vertical direction to realize higher bit density at reducing cost per Gig-bit.Unlike devices scaling via feature size reduction, 3D NAND flash vertical stack scaling puts challenges mostly on film deposition and etch. Among many steps, high aspect ratio (HAR) ONON channel hole formation modules remained the most critical steps. Forming billions of perfect channel holes from top to bottom without distortion and twisting is the grand challenge. Besides individual etch and deposition module optimization, deposition and etch Co-optimization (DECO) could provide new opportunities. In this paper, we will present a summary of the recent progress in the approaches and the benefits of DECO as potential pathways to overcome the HAR ONON patterning. We will discuss the ONON Tier Optimization for profile control to reduce the top bowing and enlarge the bottom CD. We will introduce a sacrificial liner approach to prevent top CD enlargement at deeper etch depth. We will also discuss new mask materials for better etch selectivity and profile control to enable the scaling roadmap.

(Invited) Surface Modification to Control Wetting and Adhesion of Aqueous Solutions

rf plasmas and electrochemical treatments have been used extensively for thin film deposition and etching in the fabrication of microelectronic and photonic devices. These methods can be applied to non-traditional substrates (e.g., paper and stainless steel) to alter surface and bulk properties to create (i) paper-based analytical devices with application to microfluidic devices, and (ii) antibacterial structures on stainless steel. Two examples will be described. First, the effects of plasma-based oxygen etching of cellulose surfaces followed by plasma-enhanced fluorocarbon film deposition will be described and shown to control wetting and adhesion of water droplets. These process steps can also be used to form fully enclosed hydrophilic channels in bulk paper and thereby allow microfluidic device fabrication on inexpensive and renewable substrates. Electrochemical etching of stainless steel creates micro- and nano-structures on stainless steel surfaces that repel water and bacteria. These surfaces have potential applications in orthopedic implants and consumer metal products prone to bacterial contamination.

(Invited) Plasma-Based Thin Film Technology in Fabrication of Nano- to Giga-Sized Electronics

This talk is presented to honor Professor Noel Buckley who has made many important contributions in compound semiconductors, copper thin film deposition, batteries, and other topics critical to the manufacture of modern optoelectronics. He is also a good friend, colleague, and collaborator for 3 decades.Plasma technology has been broadly used in the mass production of modern electronics varying from nano-sized devices in ICs to giga-dimension flat panel displays. It is especially critical to the preparation of thin films with well-controlled properties, geometry, and reliability. In this talk, the speaker shall discuss the recent development of plasma thin film deposition, etching, and reaction in his laboratory for the manufacture of electronic and optoelectronic products. Room-temperature plasma-based copper etch processes for sub 0.5 μm geometry patterns ICs and large-area direct-view TFT LCDsSputter deposited sub 1 nm EOT high-k gate dielectrics, nanocrystals embedded high-k dielectric nonvolatile memories, and solid-state incandescent light emitting devices (SSI-LEDs)Plasma oxidation of copper as a self-aligned passivation film

Effect of treatment time and radio frequency power on roughness and wettability of oxygen plasma-etched Cadmium Telluride thin films

The thermal evaporated Cadmium Telluride (CdTe) on Indium tin oxide substrates was etched using Oxygen plasma at various treatment times and radio frequency (RF) power. The roughness and wettability parameters were calculated using atomic force microscopy and contact angle (CA) analysis. The morphology evolution increases the interface width w and the lateral correlation length ξ with etching time and RF power. The local roughness exponent near-0.5 shows the self-affine of the surface during the etching process. The obtained experimental exponents in the present work introduce the universality class of the scaling exponents. The surface hydrophilicity of films was studied using the measurement of the two droplets CA on the film surface and the surface energy. The physical and chemical structure of the surface affected by oxygen plasma causes the surface to become more rough and hydroxyl group formation. Infra-Red spectra of the untreated and etched films using Fourier transform infrared spectroscopy confirmed the presence of the CdTe bond and a hydroxyl group. The wettability behavior of the etched films demonstrated the transition from the Cassie-Baxter state to the Wenzel state. Results show surface energy of the etched films increases, and theirs become hydrophilic.

Effect of the addition of O2 on copper etching using high density plasma of acetylacetonate/Ar

In the present study, the high density plasma etching of copper thin films masked with SiO2 was conducted using an acetylacetone/O2/Ar gas mixture. As the concentration of acetylacetone increased, the etch rates for the copper film decreased but the etch selectivity increased. The addition of O2 gas to the acetylacetone/Ar mixture greatly improved the etch profile without the redeposition on the sidewalls of the copper film. This was attributed to the formation of copper compounds containing oxygen with the assistance of a polymeric protection layer. Good etch profile for the copper film was obtained using an acetylacetone/O2/Ar gas mixture with a 4:1 vol ratio of acetylacetone to O2. The proposed acetylacetone/O2/Ar gas mixture thus represents a potential candidate gas for the dry etching of copper films.

A statistical method to optimize the chemical etching process of zinc oxide thin films.

Zinc oxide (ZnO) is an attractive material for microscale and nanoscale devices. Its desirable semiconductor, piezoelectric and optical properties make it useful in applications ranging from microphones to missile warning systems to biometric sensors. This work introduces a demonstration of blending statistics and chemical etching of thin films to identify the dominant factors and interaction between factors, and develop statistically enhanced models on etch rate and selectivity of c-axis-oriented nanocrystalline ZnO thin films. Over other mineral acids, ammonium chloride (NH4Cl) solutions have commonly been used to wet etch microscale ZnO devices because of their controllable etch rate and near-linear behaviour. Etchant concentration and temperature were found to have a significant effect on etch rate. Moreover, this is the first demonstration that has identified multi-factor interactions between temperature and concentration, and between temperature and agitation. A linear model was developed relating etch rate and its variance against these significant factors and multi-factor interactions. An average selectivity of 73 : 1 was measured with none of the experimental factors having a significant effect on the selectivity. This statistical study captures the significant variance observed by other researchers. Furthermore, it enables statistically enhanced microfabrication processes for other materials.

Spectroscopic Analysis of CF4/O2 Plasma Mixed with N2 for Si3N4 Dry Etching

Silicon nitride (Si3N4) etching using CF4/O2 mixed with N2 has become very popular in 3D NAND flash structures. However, studies on Si3N4 dry etching based on optical emission spectroscopy (OES) are lacking; in particular, no study has reported the use of OES for analyzing N2-mixed CF4/O2 plasma. Thus, this study demonstrates an OES-based approach for analyzing a mixed-gas plasma for etching Si3N4 thin films. The state of each single gas plasma of CF4, O2, and N2 as well as that of mixed plasmas of heterogeneous gases CF4/O2, CF4/N2, and O2/N2 was investigated to analyze the mixed-gas plasma. Furthermore, the amount of N2 in the CF4/O2 plasma varied from 0 to 8 sccm. The relationship between the OES analysis results and the Si3N4 etch rate was subsequently established using Si3N4 film etching, and the explanation was verified through a chemical reaction modeling and surface reaction. Therefore, our study confirmed the alteration in chemical species and quantity that occurred when N2 was added to CF4/O2 plasma and the effect of the alteration on Si3N4 etch.

Fabrication of Three-Dimensionally Deformable Metal Structures Using Precision Electroforming.

It is difficult to fabricate three-dimensional structures using semiconductor-process technology, because it is based on two-dimensional layered structure fabrication and the etching of thin films. In this study, we fabricated metal structures that can be dynamically deformed from two-dimensional to three-dimensional shapes by combining patterning using photolithography with electroforming technology. First, a resist structure was formed on a Cu substrate. Then, using a Ni sulfamate electroforming bath, a Ni structure was formed by electroforming the fabricated resist structure. Finally, the resist structure was removed to release the Ni structure fabricated on the substrate, and electroforming was used to Au-plate the entire surface. Scanning-electron microscopy revealed that the structure presented a high aspect ratio (thickness/resist width = 3.5), and metal structures could be fabricated without defects across the entire surface, including a high aspect ratio. The metallic structures had an average film thickness of 12.9 µm with σ = 0.49 µm, hardness of 600 HV, and slit width of 7.9 µm with σ = 0.25 µm. This microfabrication enables the fabrication of metal structures that deform dynamically in response to hydrodynamic forces in liquid and can be applied to fields such as environmental science, agriculture, and medicine.

Study of the Surface Texture of Magnetron Sputtered Transparent Conducting ZnO:Al films by Atomic Force Microscopy

Abstract: Transparent conducting ZnO: Al films with proper surface texture have been developed on glass substrate at 3500C by rf-magnetron sputtering under Ar and Ar+O2 gas ambients. ZnO:Al films exhibit low resistivity (~ 8.9x10-4 Ω-cm), and high optical transmittance (T~ 85% to 90%) in visible region. Study of surface texture ZnO:Al films by dry (hydrogen plasma) etching and wet chemical etching in diluted 0.5% HCl acid solution have been reported in this paper. Due to hydrogen plasma etching surface topography as well as morphology of ZnO:Al films is modified into suitable texture for light scattering. But surface texture is deteriorated drastically for wet chemical etched films. Electrical properties have been improved slightly and optical transmittance remains undeviated due to H-plasma etching but significant changes in electrical and optical properties have been observed in wet chemical etching. Keywords: ZnO:Al films, Surface Texture, Wet Chemical etching, Atomic Force Micrograph, Thin film solar cell

Multiscale computational fluid dynamics modeling of spatial thermal atomic layer etching

Spatial atomic layer deposition and etching processes have emerged to reduce the overall process time while maintaining the conformity of thin films by functioning continuously. This research constructs an multiscale computational fluid dynamics (CFD) model with a dynamic mesh that combines a microscopic kinetic Monte Carlo algorithm of the film etching with a CFD simulation of the gas phase for the spatial thermal atomic layer etching of Al2O3. Using this model, we evaluate the effect that design and operation variables including the gap distance, purge and precursor gas flow rates, substrate velocity, and vacuum pressure have on the substrate film etching per cycle and uniformity. Numerical results suggest that small gap distances with sufficiently high N2 flow are desired to accomplish effective precursor separation for reactor configuration and the process operation requires low substrate velocities and low vacuum pressures to achieve optimal film quality and conformance.

High Energy Density and Temperature Stability in PVDF/PMMA via In Situ Polymerization Blending.

Dielectrics with improved energy density have long-standing demand for miniature and lightweight energy storage capacitors for electrical and electronic systems. Recently, polyvinylidene fluoride (PVDF)-based ferroelectric polymers have shown attractive energy storage performance, such as high dielectric permittivity and high breakdown strength, and are regarded as one of the most promising candidates. However, the non-negligible energy loss and inferior temperature stability of PVDF-based polymers deteriorated the energy storage performance or even the thermal runaway, which could be ascribed to vulnerable amorphous regions at elevated temperatures. Herein, a new strategy was proposed to achieve high energy density and high temperature stability simultaneously of PVDF/PMMA blends by in situ polymerization. The rigidity of the amorphous region was ideally strengthened by in situ polymerization of methyl methacrylate (MMA) monomers in a PVDF matrix to obtain PVDF/PMMA blends. The atomic force microscopic study of the microstructure of etched films showed the ultra-homogenous distribution of PMMA with high glass transition temperature in the PVDF matrix. Consequently, the temperature variation was remarkably decreased, while the high polarization response was maintained. Accordingly, the high energy density of ∼8 J/cm3 with ∼80% efficiency was achieved between 30 and 90 °C in PVDF/PMMA films with 39–62% PMMA content, outperforming most of the dielectric polymers. Our work could provide a general solution to substantially optimize the temperature stability of dielectric polymers for energy storage applications and other associated functions.

Energy Distribution Functions of Ions Generated by a Circular-type Anode Layer Ion Source

An anode layer ion source, or an ALIS, is classified as a gridless ion source that produces a high-energy ion beam for either surface etching or thin film deposition. In the present work, the energy distribution functions of the ions generated in a circular ALIS were measured using a retarding field energy analyzer (RFA). Consequently, the average density and energy of the ions arriving at the ground surface were determined for the given range of process parameters. The IEDFs show two different groups of ions, namely, a narrow low energy group and a broad high energy group. The low-energy ions are probably generated in the background plasma and accelerated via the cathode sheath adjacent to the RFA. High-energy ions, on the other hand, are possibly generated in the discharge channel and gain an energy of up to 0.7eVanode through the anode sheath. The variations in average ion energies and densities as a function of process conditions could be due to the potential profile between the source and the ground surface.

In situ studies on atomic layer etching of aluminum oxide using sequential reactions with trimethylaluminum and hydrogen fluoride

Controlled thin film etching is essential for future semiconductor devices, especially with complex high aspect ratio structures. Therefore, self-limiting atomic layer etching processes are of great interest to the semiconductor industry. In this work, a process for atomic layer etching of aluminum oxide (Al2O3) films using sequential and self-limiting thermal reactions with trimethylaluminum and hydrogen fluoride as reactants was demonstrated. The Al2O3 films were grown by atomic layer deposition using trimethylaluminum and water. The cycle-by-cycle etching was monitored throughout the entire atomic layer etching process time using in situ and in real-time spectroscopic ellipsometry. The studies revealed that the sequential surface reactions were self-limiting versus reactant exposure. Spectroscopic ellipsometry analysis also confirmed the linear removal of Al2O3. Various process pressures ranging from 50 to 200 Pa were employed for Al2O3 etching. The Al2O3 etch rates increased with process pressures: Al2O3 etch rates of 0.92, 1.14, 1.22, and 1.31 Å/cycle were obtained at 300 °C for process pressures of 50, 100, 150, and 200 Pa, respectively. The Al2O3 etch rates increased with the temperature from 0.55 Å/cycle at 250 °C to 1.38 Å/cycle at 350 °C. Furthermore, this paper examined the temperature dependence of the rivalry between the removal (Al2O3 etching) and growth (AlF3 deposition) processes using the reactants trimethylaluminum and hydrogen fluoride. The authors determined that 225 °C is the transition temperature between AlF3 atomic layer deposition and Al2O3 atomic layer etching. The high sensitivity of in vacuo x-ray photoelectron spectroscopy allowed the investigation of the interface reactions for a single etching pulse as well as the initial etch mechanism. The x-ray photoelectron spectroscopy measurements indicated that the fluorinated layer is not completely removed after each trimethylaluminum exposure. The Al2O3 atomic layer etching process mechanism may also be applicable to etch other materials such as HfO2.

Reactive ion etching of tantalum in silicon tetrachloride

A precise patterning of metal structures plays an essential role in the development of feasible metal-based devices. By examining the etching conditions under which a layer of material is properly etched, the etching process can be further optimised and hence controlled. This work reports on the reactive ion etching (RIE) of micrometric films of tantalum (Ta) using silicon tetrachloride (SiCl4)/Argon (Ar) plasmas. The etching characteristics have been studied with respect to SiCl4/Ar ratio, plasma power and chamber pressure. It has been found that increasing the flow rate of SiCl4 or plasma power leads to an increase in the etching rate. Moreover, the observations suggest that it is ineffective to increase the flow rate of Ar to more than 30 sccm and the plasma pressure to more than 100 mTorr. The work implemented here represents an important step for the development of tantalum-based structures that can be used in a wide range of devices.

Experimental investigation of the electron sheath resonance (ESR) effect in parallel plate radio-frequency capacitively coupled plasmas

Abstract We have conducted a systematic experimental investigation on the electron heating mechanism named as electron sheath resonance (ESR) effect, with a parallel plate discharge configuration under various experimental conditions. In all conditions, a clear plasma density peak was observed at the magnetic field for ESR, providing a direct evidence for the effect. Further analysis suggests that the more significant ESR effect should appear at higher frequency, lower pressure discharges with larger electrodes. The results form a basis for further studies of the ESR effect, which is also meaningful to practical applications such as etching and thin film deposition processes.

Scanning-free digital holography for decoupling the refractive index and thickness via a constrained equation of higher degree.

Digital holography is one of the most popular quantitative phase imaging techniques, but the refractive index and the thickness are always coupled in the phase. To solve the decoupling problem, multiple scanning methods such as tomography and total reflection are usually used, which is time-consuming. To increase the imaging speed and reduce the system cost, it is urgent to seek the decoupling method of scanning-free digital holography. In this paper, we find that the decoupling method of scanning-free digital holography can be transformed into a problem of solving constrained higher order equations. By introducing the Fresnel reflection formula, a six-degree equation about refractive index is constructed and the corresponding algorithm for solving the equation is given. By using the algorithm, the refractive index and thickness can be decoupled successfully. A series of results show that the proposed method is effective and has high anti-noise performance. This method provides a mathematical possibility for scanning-free digital holography to decouple the refractive index and complex pixel stepped thickness distributions. Therefore, it may provide a theoretical basis for the subsequent development of a real scanning-free digital holography system, which may have potential applications in the measurement of optical devices produced by the modern film deposition process and etching process.

Multiscale computational fluid dynamics modeling of thermal atomic layer etching: Application to chamber configuration design

Atomic layer etching (ALE) is a promising method that can overcome the challenges that are encountered during the assembly of nanoscale devces. Experiments may be conducted to investigate chamber configuration designs and optimal operating conditions; however, they can be costly and time consuming. Therefore, this work develops a multiscale computational fluid dynamics (CFD) modeling framework to simulate thermal ALE of aluminum oxide thin films. First, a CFD reactor model for four different reactor designs (typical, multi-inlet, showerhead, and inclined plate) is constructed through Ansys software. Next, the macroscopic CFD model is combined with a previously developed microscopic model of the etching process, which is based on a kinetic Monte Carlo algorithm to describe the features of the atomistic etching processes occurring on the film. The multiscale CFD model is used to determine the best reactor configuration for achieving film etching uniformity while minimizing process operating time resulting in a reduction of reagent consumption.

Formation of Functional Silicon Nitride Layers by Selective Plasmochemical Etching

At present, with the development of nanotechnology, plasma-chemical etching remains practically the only tool for transferring an integrated circuit pattern in a masking layer to a substrate material due to the fact that the pattern transfer accuracy is comparable to the size of etching gas ions. Requirements for plasma technology: permissible defects, selectivity (material selectivity), line width control, etching uniformity are becoming more stringent and, as a consequence, more difficult to implement. To increase the rate and selectivity of plasma-chemical etching of silicon nitride films during plasma processing of a gas mixture consisting of both a fluorine-containing gas and oxygen, sulfur hexafluoride with a concentration of 70–91 vol.% was used as a fluorine-containing gas with an oxygen concentration of 9–30 vol.%.

Electric signals measured during plasma thin-film etching and their connection to the electron concentration and the properties of the treated surface

The electric characteristics of a discharge are usually changed when a thin film is deposited on or etched from a discharge electrode or a substrate. The electric characteristics include the plasma potential, discharge voltage and discharge current, including higher harmonic frequencies of these quantities. This fact can be used for the monitoring of various plasma processes, but the mechanism by which the thin film influences the electric characteristics of the discharge has not been fully clarified. Our study of diamond-like carbon (DLC) film etching verified that variations of electric discharge parameters are caused by variations of electron concentration, which is caused by a difference in the electron emission yield between the DLC film and its substrate.