AVS 69 Session PS-TuP: Plasma Science and Technology Poster Session

Addressing challenges in semiconductor industry often faced by advanced packaging, sensors, and MEMS by promoting cost-effective solutions has been the ultimate challenge throughout the years. This study explores the use of Plasma Dicing technologies such as plasma singulator systems (MDS-100 & MDS-300 SINGULATOR®) to facilitate and promote an increase in die count per wafer establishing a higher production volume with performance. Plasma dicing offers several advantages, including an improved die surface area per wafer promoting an increase in yield per wafer to be processed. The ability to navigate the incorporation of smooth sidewalls, and achievement of street sizes ≤10μm promotes new advantages in the semiconductor industry. Plasma dicing not only removes material in dicing streets by Bosch process implementation but also prevents any physical impact on each die while performed using polymer deposition to facilitate the protection of sidewalls during etching. To enable several applications in the semiconductor industry, including increased device performance, absorption, and electrical conductivity throughout devices, polymer removal and post-etch cleaning are required which has been mainly performed by wet-etching procedures. Wet clean polymer removal has been tested for our standard Plasma-Therm wafer by using both 3M™ Novec™ 7100 Engineered Fluid and EKC265™ separately and analyzed using Energy Dispersive X-Ray Spectroscopy (EDX) to investigate the removal of residues of Carbon and Fluoropolymer. Although successful removal of polymer from the sidewalls was achieved, the amount of liquid required may increase the cost but also the residual waste, preventing proper process control, causing direct damage to the samples due to chemical nature, and handling issues. To address these limitations, we propose the introduction and implementation of dry plasma cleaning solutions that can perform the removal of polymers and photoresist materials without any device damage. At Plasma-Therm, LLC photoresist can be removed by a dry-etching step performed after completion of the Bosch process in a singulator system but also it can be accomplished by using a High-Density Radical Flux (HDRF™) process tool, which not only enables polymer removal but also is designed to perform photoresist strip allowing smoothing of sidewalls for several applications without causing device damage. This tool not only allows us to move from wet-etching by eliminating contamination of samples by particles or residues but also provides a more efficient and effective alternative to wet-etching processes for the removal of polymer and photoresist.

As plasma medicine is more and more developed and studied for treatment of pathologies such as skin cancer (Terefinkoet al. 2021)or tumorous intestinal cells (Hadefi et al. 2022, Bastin et al. 2020)as well as for decontamination (Deng et al. 2007), the question of the effect of plasma on medical devices rises.

In this work, we are interested in endoscopes and the way plasma could damage them. Indeed, endoscopes working channelscould be used to carry plasma inside a body to a desired target, but the effect of the plasma on the endoscope itself must be investigated. As the surfaces of the channels of endoscopes are coated with PTFE, mainly for its lubricating properties, we studied the plasma-induced degradation of a PTFE tube in a setup that mimics the characteristics of an endoscope device already described in previous work (Bastin et al. 2019). XPS wasused to study the chemical and roughness modifications of the PTFE surface andFTIR was used to study the species ejected to the gas phase.

Given the preliminary nature of current exploratory studies in this field, we employed diverse parameters for our investigation.Different plasma compositions were used: He, He-O₂(3%O₂), He-H₂O, Ar, Ar-O₂(3%O₂), Ar-H₂O, and air withflow rates of 1,5 L/min. The AC electrical power varied from 10 W to 70 W.

Depending on the plasma treatment applied, variable amounts of gaseous fluorinated compounds like COF₂and HF have been detected.They result from the degradation of the PTFE polymeric chains by energetic species created in the plasma. In a pure helium plasma, these species are mainly metastable helium and high energy electrons, capable of breaking C-C and C-F bonds, hence creating carbon and fluorine radicals on the surface. Those radicals will then react with surrounding gas species.

The addition of oxygen containing molecules in the gas mixture (H₂O, O₂) creates higher amount of COF₂than without.The amounts observed of those three species is a direct measurement of the ability of the discharge to degrade the PTFE. The COF₂is believed to originate directly from the PTFE degradation by atomic oxygen (O^–) (Vandecasteel et al.), whereas the HF should be formed by hydrolysis of COF₂. With pure gases (He and Ar) plasma, some water and air impurities could still introduce oxygen atoms, hydroxyl groups and nitrogen containing groups.

We observed a drastic increase of the concentrations of fluorine species with the Ar-H₂O plasma compared to the He-H₂O plasma.

The XPS analyses show a defluorination of the PTFE surfacethat depends on the plasma composition and power, and in agreement with the production of COF₂and HF detected by gas phase IR.

Acknowledgements:

This work is funded by the ARC project “COSMIC” and by the Michel Cremer foundation

As the memory device sizes reach scaling limit, the device structures are changing from 2D to 3D device structure. For 3D device structures, it has been known that improving high aspect ratio (HAR) etching process is one of the most important processes in device manufacturing as it determines the density of the devices. To improve the etch properties such as selectivity and etched profiles, various etch techniques have been widely studied including changing process schemes and equipment. But still, changing etch gas is known to be one of the essential solutions in improving plasma etching results. Recently, it has been reported that the etch profiles of HAR etching can be improved by using WF₆ as an additive material, but no detailed results and etch mechanism on the effect of metal-halide containing additive gas have not been reported. Therefore, in this study, the effects of metal-halide containing additives including WF₆ on etching characteristics were investigated. It was found that HAR etch properties can be controlled and improved by using various additive gases containing carbon or fluorine. Therefore, the effect of various additive materials on dielectric etch properties will be reported for next generation HAR etching.

Indium gallium zinc oxide (IGZO) is used in next-generation semiconductors and displays and requires anisotropic etch profile, fast etch rate, and high mask selectivity.In particular, as IGZO is used for gates in semiconductors and displays, the CD (critical dimension) is getting smaller and smaller, so highly anisotropic etching is crucial. Additionally, it is important to completely clean the etch residue in the chamber after IGZO is etched.In this study, IGZO was etched, and chamber cleaning was performed using various HFC-type gases (C_xH_yF_z) in an ICP etcher. The results showed that mixing H and F-based gases was more effective in increasing the etch rate and etch selectivity of IGZO than using them alone. In fact, it is difficult to etch IGZO because zinc is easily etched by halogen gases, but it is found that the gases combined with C, H, and F make it easier to etch zinc. C₃H_xF_y (x+y=8) gas was found to be better than CH_xF_y (x+y=4) gas, as it lowers the binding energy. In addition, by using a H₂/Ar plasma, the etch by-products formed on the chamber sidewall by the etching using HFC-type gases (C_xH_yF_z) could be effectivly removed.

Metallic nanoparticles (NPs) offer a wide range of applications in electronics, energy, biology, catalysis, and the production of carbon nanomaterials like carbon nanotubes (CNTs). Synthesis of NPs from the vapor phase using plasma methods such as spark discharge generation is promising for industrial scalability. The behavior of nucleating systems in reactive environments, especially reactive plasma environments, is understudied. Moreover, charge-induced dipole interactions between ions and neutrals are thought to play a key role in the nucleation, coalescence, and aggregation of NPs in dusty plasmas [1]. Because the lengthscales and timescales associated with vapor-phase NP formation are too small to effectively probe experimentally, a promising alternative is molecular dynamics (MD) simulation. MD can give strong insight into the nanoparticle formation process with its atomic resolution. In this work, we use MD simulations with a reactive forcefield to study iron vapor nucleation in the presence of ions, radicals, and molecular species relevant to the production of CNTs (i.e., H, H₂, C, CH, CH₂, CH₃, CH₄, C₂, C₂H, C₂H₂, and ions). The effects of atomic-scale phenomena on metal vapor nucleation and nanoparticle behavior in a plasma environment will be discussed.

[1] Girshick, Steven L. "Particle nucleation and growth in dusty plasmas: On the importance of charged-neutral interactions." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 38.1 (2020): 011001.

The recent COVID pandemic raised the necessity to develop strategies to limit the contamination of human populations by viruses. Amongst the routes explored, the development of antiviral and antimicrobial surfaces is an elegant approach as it could represent a long term, passive (no need of chemicals or human action) and sustainable solutions. Although the antimicrobial action of copper surfaces is well known and documented (even in history books), it represents an expensive solution, and the potential toxicity of copper ions for cells can not be neglected. Titanium oxide, in its anatase phase, is known to possess strong oxidative properties, and is used as coating for “self cleaning” or “easy to clean” surfaces. It possesses strong antimicrobial properties. However, the main drawback is that anatase is only active when irradiated with UV light, which prevents the use of such surfaces in interiors. To circumvent this, nitrogen doped TiO2 coatings were developed using an atmospheric pressure dielectric barrier discharge, and exposed to a variety of coronaviruses, including the SarsCOV2.

Coatings were deposited by PACVD from TTIP in an Ar/O2/NH3 discharge (variable O2 and NH3 concentrations) at various substrate temperatures [1], using a new type of heating device [2,3]. They were characterized by XPS, Tauc plot (for the bandgap), and by SEM. Selected coatings were then put in contact with solutions containing coronaviruses and exposed to white light. Negative and positive controls were realized on fully inactive surfaces (plastic), or fully active surfaces (copper), respectively. It is shown that some surfaces exhibit an antiviral activity.

References :

[1] A. Chauvin et al, Surf.Coat.Technol, submitted

[2] A. Remy et al, Thin Solid Films (2019), 137437

[3] A. Remy, F. Reniers, EP3768048A1

Acknowledgements :

This work is funded by the special research program of the FNRS-Belgium “PER-Virusurf”, and by the ULB special COVID fund

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* Work funded by the Lam Research Foundation.

The wet etchingwhich has been mainly used for the isotropic etching presents challeges in nano-patterns due to the inability to etch the bottom of the pattern or pattern leaning by surface tension. Therefore, the development of a dry etching process for next-generation semiconductor devices is necessary. Currently, the most widely used isotropic dry etching processes of SiO₂ are the HF/NH₃ vapor process and the NF₃/NH₃ plasma process. The conversion of SiO₂ to an ammonium salt such as (NH₄)₂SiF₆ occurs in these processes, and the desorption of the reacted compounds is achieved through a heating process. However, the formation of ammonium salts during NH₃-based processes can produce solid powders that may contaminate the substrate and become particle sources in the chamber. Therefore, in this study, gas combinations without NH₃ were used for the cylic dry etching of SiO₂ over Si₃N₄. HF was formed using an NF₃/H₂ remote plasma, and methanol vapors were injected outside the plasma discharge region to eliminate F radicals produced by NF₃ dissociation andinduce spontaneous etching of Si-based materials. Under the optimized conditions, the etching depth per cycle of SiO₂ was about ~13 nm/cycle, and the selectivity with Si₃N₄ was over 50 and the selectivity with Si was over 20. Surface composition and bonding statewere analyzed to confirm surface damage and to investigate the etching mechanism.

In the semiconductor industry, perfluorocarbon and hydrofluorocarbon gases are widely used as etching gases. However, some currently commercialized gases have a negative impact on the global environment due to their high GWP (global warming potential) values. Therefore, it is essential to replace those with gases with a low GWP and similar characteristics. In this study, evaluation was conducted to replace existing perfluorocarbon and hydrofluorocarbon gases with high GWP, such as CF₄ and CHF₃, with C₂F₄O and C₂H₂F₂, which have a relatively high boiling point for easy recovery in a liquid state at room temperature and a low GWP, respectively. In the experiment, SiON (silicon oxynitride) film was etched using C₂F₄O/C₂H₂F₂ plasmas in a CCP (capacitively coupled plasma) equipment and the etch rates of PR (photoresist) and SiON films, and PR/SiON selectivity were measured. The etch profiles were observed by SEM (scanning electron microscopy) and XPS (X-ray photoelectron spectroscopy) was used to analyze the surface characteristics of the sample after etching. The results showed that the plasma etching characteristics with mixed gases of C₂F₄O/C₂H₂F₂ showed a higher PR/SiON selectivity and anisotropic SiON etching profile compared to those with conventional mixed gases of CF₄/CHF₃. Therefore, selective and anisotropic etching of SiON film masked with PR could be achieved with low global warming gas combination of C₂F₄O/C₂H₂F₂. Details of experiments and analysis data will be reported in the presentation.

Do Seong Pyun¹, Ji Yeon Lee¹,Dae Whan Kim¹, Yun Jong Jang², Doo San Kim², Hae In Kwon², Hong Seong Gil², Gyoung Chan Kim², Ju Young Kim² and Geun Young Yeom^2,3

¹Department of Semiconductor Display Engineering, Sungkyunkwan University, Suwon 16419, Korea

²School of Advanced Materials Science andEngineering, Sungkyunkwan Universtiy, Suwon, Gyeonggido 16419, Republic of Korea.

³SKKU Advanced Institute of Nano Technology (SAINT), Sungkyunkwan Universtiy, Suwon, Gyeonggido 16419, Republic of Korea.

To improve the integrity and performance and to reduce the power consumption of semiconductor, the line width between patterns of interconnects has been shrunk continuously. In order to solve this challange, Cu is currently used as an interconnect material with a barrier material in a damascene structure because it has low resistivity. However, Cu also shows a rapid increase of resistivity in a critical dimension (CD) of less than 10 nm due to long mean free path in addition to a limitation in scaling down due to the requirement of a barrier material. Therefore, the importance of new materials such as Mo, Ru, Co, etc. to substitute Cu has been increased to solve this problem. In this experiment, atomic layer etching (ALE) of Mo has been carried out by using O₂/Cl₂ gases as adsorption process and Ar⁺ ion beam for desorption process. By using ICP-type ion beam for desorption step, fine control of the ion energy was possible during the ALE. In the adsorption step, by using O₂/Cl₂ plasmas, the Mo surface was modified into MoCl_x and MoO_xCl_y. In the desorption step, the modified Mo surface such as MoCl_x and MoO_xCl_y was removed using an Ar⁺ ion beam. After the ALE process, physical and chemical analysis of the Mo surface was performed using X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), etc.

Recent developments in power supply technology have made a greater variety of custom waveforms achievable at a scale relevant to semiconductor processing. These custom waveforms provide additional degrees of freedom that can be used to control the ion energy distributions. Dual-frequency capacitively coupled plasmas (CCPs) are often used with a sinusoidal high frequency to generate the plasma and a low-frequency custom waveform to accelerate the ions. Many etching processes use electronegative gases, introducing negative ions which have much lower mobility than electrons and altering the plasma dynamics and sheath behavior.

In this work, we explore the impact of oxygen and the resulting negative ions on the plasma dynamics and the control of the ion energy distribution for dual-frequency CCPs. The focus is on regimes of interest for atomic layer etching (ALE), where the desired ion energy is relatively low (< 100 eV), but must be more precisely controlled. EDIPIC, a particle-in-cell Monte Carlo Collision (PIC-MCC) model, is used to model the plasma in a one-dimensional simulation. A high-frequency (60 MHz) sinusoidal voltage is applied to the upper electrode, and the tailored voltage waveform is applied to the lower electrode at 400 kHz. In this case, the tailored waveform is a triangular positive pulse, with a negative voltage applied in the interpulse period.

The changing plasma dynamics with the varying Ar/O₂ mixtures will be discussed, as well as the impact of the amplitude of the custom waveform. Variations in the waveform, such as the duration of the positive pulse and the magnitude of the negative voltage, may also be explored. The impact on the ion angular and energy distribution, as well as the electric field dynamics in the sheath during the pulse and the role of secondary electron emission, are discussed. In particular, narrow ion energy distributions with a tunable energy are desirable for ALE, with a minimum flux of high energy ions, as these may cause etching that is not self-limiting and destroy the atomic precision.

As microelectronics technologies become more advanced, high aspect ratio (HAR) etching has become more challenging in recent years. In this work, plasma simulations are used to better understand industrial capacitively coupled plasmas (CCPs) with the goal of controlling ion energies and ion-radical flux ratios using tailored voltage waveforms. The use of a dual-frequency CCP enables high-quality HAR etching by controlling the ion energy and angular distributions. A regime in which ion flux and energy can be more independently controlled is accessed by applying two different frequencies of applied voltage, and tailoring the voltage waveforms can control ion energy and angular distributions. To achieve narrow ion energy and angular distributions, high voltages and low pressures are typically applied. As a result, fluid and hybrid models become inaccurate, and a kinetic approach is required. We investigate the dynamics of low-pressure (7 mTorr) dual-frequency argon plasmas in a 5 cm gap between electrodes using EDIPIC, a Monte Carlo collision-based particle-in-cell (PIC/MCC) simulation. In this work, we introduce the electrical asymmetry effect by tailoring voltage waveforms at the lower electrode (i.e., the wafer). The triangular pulsed tailored voltage waveform of low frequency (400 kHz) is applied to the lower electrode and sinusoidal high frequency (60 MHz) on the upper electrode. The effects of changing the peak-to-peak voltage of the driving voltage waveforms on the ion average energy, ion velocity, and secondary electron yields at the surface of the electrode are discussed. We found that increasing the amplitude of the low-frequency waveforms (100-1000 V) resulted in a tens of eV increase in the average ion energy in bulk regions and a significant increase in ion energy reaching the electrode surface (100-500 eV). Conversely, increasing the peak-to-peak voltage of high-frequency waveforms led to an increased density of bulk plasma but did not significantly change the average ion energy. Furthermore, inclusion of secondary electron emissions (SEE), using energy-dependent SEE yields, resulted in increased electron collisions with the electrodes due to the low-energy electrons emitted from the electrodes. Additionally, during the positive pulse from the low-frequency voltage waveform, electrons only collided with the low-frequency electrode with a slight decrease in ion collisions, which springs back as the positive cycle relaxes.

Electron beam (e-beam) generated plasmas can produce desirable species for material processing applications by leveraging control of electron energy, while simultaneously maintaining a low electron temperature.¹ In particular, e-beam generated plasmas can be used to produce low energy ions in the periphery of the primary electron beam.² This production is enabled by the presence of metastable species in the discharge periphery. In this work, we measured the absolute density of argon (1s₅) metastable density in an e-beam generated ExB secondary electron emission plasma source by laser induced fluorescence. We used a Langmuir probe to obtain the electron temperature and density. The measured electron density and Ar(1s₅) densities were on the order of 10¹⁶ m^-3, while the electron temperature was less than 1eV. The electron density and the Ar(1s₅) density reduced, while the electron temperature remained constant as a function of distance from the center of the discharge. A one-dimensional continuity equation model showed that there is continuous production of argon metastables even outside the core plasma region. Two distinct regions were identified in the spatial profile of Ar(1s₅) level inside and outside the core plasma region. These results suggest that there is an additional source of production of Ar(1s₅) in the core of the plasma in addition to the direct excitation by electrons from the ground state of argon.

Acknowledgement: This work was supported by the U.S. Department of Energy through contract DE-AC02-09CH11466.

Producing high-aspect-ratio (HAR) features with plasma etching is becoming increasingly important as the market demands solid-state non-volatile memory storage. In order to minimize bowing and twisting defects in HAR features, precision control of the ion energy distribution (IED) is required. Eagle Harbor Technologies (EHT), Inc. has previously developed a Rapid Capacitor Charger power system that can charge capacitance to high voltage in tens of nanoseconds and operate at 400 kHz. In this work, EHT is investigating ion energy control with these high-voltage custom waveforms. The experimental test chamber includes a 60 MHz capacitively coupled plasma source and a pedestal that can be biased using the Rapid Capacitor Charger waveforms. EHT will present the chamber modifications, retarding field energy analyzer details, and IED measurements. Based on these measurements, the next steps will be discussed.

In the manufacturing processes of 3D NAND, the high aspect ratio contact (HARC) etching process, which is one of the most critical steps, has encountered a significant challenge. HARC, typically performed at room temperature, has become increasingly difficult to achieve the desired high aspect ratio while maintaining high productivity. This challenge is expected to become harder when considering devices with highly stacked alternating layers of silicon-containing materials, such as SiO₂ and SiN. Therefore, cryogenic HARC technology has emerged as a promising solution to overcome this challenge, as it offers advantages in terms of productivity and better etch profile. Consequently, we conducted cryogenic aspect ratio etching of SiO₂ at CF₄/H₂/Ar plasma in a cryogenic reactive ion etch system. Overall, our results revealed that cryogenic aspect ratio etching of SiO₂ showed a higher etch rate and a higher aspect ratio under the experimental conditions. With these conditions, we conducted the cryogenic aspect ratio contact etching of SiO₂ for the comparison with the etching of SiO₂ at RT as well.

Low temperature plasma has been widely used in semiconductor manufacturing process. The characteristics of low temperature plasma that are important in semiconductor manufacturing include electron density, electron temperature and electron energy distribution. Specifically, electron density is important to understand plasma physics and plasma process. The electron density is commonly measured using a Langmuir probe. The probe inserts a tip into plasma and voltage is applied to the probe. Charged particles in plasma move to the probe and current generated by the movement is measured to determine plasma density. However, the measured signals interfere with radio frequency and plasma perturbation by the probe distorts the plasma characteristics.

In this study, plasma density was measured using microwave reflectometer without plasma perturbation. The microwave signal radiated by Wi-Fi antenna is reflected by the plasma and collected through the antenna. The electron density measured by analyzing a phenomenon arising from the correlation between the microwave and plasma angular frequencies. The plasma angular frequency is derived using the reflection or transmission phenomenon of microwaves, which depends on the refractive index of the plasma. The refractive index of a plasma N is related to the microwave angular frequency ω and the plasma angular frequency wave ω_p, i.e. N = (1 − ω_p/ω)^1/2. The plasma angular frequency depends only on the plasma density as ω_p=(n_ee²/ε₀m_e)^1/2. When the microwave frequency is equal to plasma frequency, the refractive index of the plasma becomes zero and the reflection becomes maximum. The S₁₁ parameter is calculated by measuring the intensity of the reflected signals on the frequency sweep. The reflectivity was analyzed by measuring the difference between the S₁₁ parameter before and after plasma discharge.

Deposition of patterned coatings to generate hybrid surface properties often require a multi-step process, such as the use of masks or lithography [1]. We proposed recently a simple scalable method for the deposition of patterned coatings (morphological and chemical contrasts) [2]. As a case study, the deposition of propargyl methacrylate (PMA) based-coatings was realized, as, due to its structure (one double and one triple bond), this molecule allows very fast deposition, and can lead to hydrophobic coatings, without the need of fluorinated atoms. Moreover, we showed that, depending on the deposition conditions, one could obtain hybrid hydrophilic/hydrophobic patterns. In a recent paper, we showed that pulsing the power (in the ms range) leads to more localized filaments, to a global change in the plasma behaviour and to a change in the coating chemistry [3].

In this poster, we investigate the interplay between the interelectrode gap and the precursor gas flow on the overall plasma discharge and on the resulting (localized) coating. The plasma discharge is characterized by a high speed camera, and mass spectrometry, whereas the coating is characterized using micro-XPS and infrared spectroscopy in IRRAS mode. We show that increasing the gap necessitates an overall higher power to sustain the plasma, resulting in a higher voltage (according to Paschen Law) that leads to a global higher electron energy in the filaments. Such higher power injected into the discharge induces surface discharges between the immobilized filaments. In parallel, increasing the precursor gas flow leads to a higher luminosity in the inter-filament space. The coating thickness and chemistry is similarly influenced by the gap and the precursor flow. Increasing the gap and precursor flow lead to an increase in the coating diameter under the filaments but the thickness of the spots decreases when increasing too much gap. A better preservation of the chemical functionalities of the precursor inside the coating deposits is obtained for higher gas flows and low gaps, which is correlated with the mass spectroscopy analysis of the plasma phase. Results are interpreted in terms of the evolution of the Yasuda parameter.

References :

[1]. A. Demaude, C. Poleunis, E. Goormaghtigh, P. Viville, R. Lazzaroni, A. Delcorte, M. Gordon, and F. Reniers, Langmuir, 2019, 35, 9677−9683.

[2] A. Demaude, K. Baert, D. Petitjean, J. Zveny, E. Goormaghtigh, T. Hauffman, M. Gordon, and F. Reniers, Advanced Science. 2022, 2200237.

[3] A. Demaude, M. Brabant, D. Petitjean, M. Gordon, F. Reniers, Plasma Chemistry and Plasma Processing, 2023. https://doi.org/10.1007/s11090-023-10355-6

Optical emission spectroscopy (OES) is a widely used technique for noninvasive plasma measurement. However, the deposition of polymers on the viewport can lead to a reduction in light intensity, even under the same experimental conditions (e.g., pressure, power). It can be useful to measure the thickness of the deposition layer to compensate for the reduction in light intensity.

We applied three different voltages to an electrical probe to obtain deposition layer impedance. In an equivalent circuit model, the plasma sheath can be regarded as a parallel circuit of sheath resistance and sheath capacitance, representing displacement current and conduction current, respectively. The deposition layer can be considered as a dielectric film. By solving three equations derived from three voltages of different frequencies, we calculated the capacitance of the dielectric and determined its thickness.

However, two problems arose. First, due to the voltages applied to the probe, the floating potential shifted, distorting the plasma sheath resistance. Second, a significantly high impedance ratio between the plasma sheath and deposition layer made it challenging to obtain the thickness of the deposition layer. Therefore, we modulated the amplitude of the applied voltages to minimize distortion and decreased the frequencies to increase the dielectric impedance. Consequently, the error in the measured deposition layer thickness could be greatly reduced.

Nitrogen-trifluoride (NF₃) is mainly used as a reactive gas in cleaning and etching process in the semiconductor and display fabrication. However, NF₃ is a greenhouse gas with a high potential for global warming. As regulations related to the green index are getting stronger worldwide, the need for gas to replace NF₃ is increasing.

In this study, an experiment was conducted on F₃NO gas as a gas to replace NF₃. The plasma etching process was similarly diagnosed by RGA and OES, and the etch rate was calculated by measuring the refection. The etch rate of silicon oxide during F₃NO/Ar plasma etching is approximately 94% of that for NF3/Ar plasma etching. The RGA and OES measurements confrmed that more O⁺, NO⁺, and O₂⁺ ions were generated in the F₃NO plasma than in the NF₃ plasma.

Pulsed capacitive RF plasma is demanded for the semiconductor etching because it mitigates plasma-induced damage. Repeating pulse-on and pulse-off time lowers ion energy and electron temperature compared to a continuous wave plasma, resulting in less wafer damage. This study performed a pulse-driven two-dimensional (2D) particle-in-cell (PIC) simulation parallelized with a graphics processing unit (GPU) to investigate the plasma dynamics for the time duration of ms. We investigated the effects of a 2D electrode structure empowered low-frequency (LF) pulsed voltage added to a high-frequency (HF) sinusoidal wave on the plasma potential, electron density, and electron temperature by varying frequency and pressure conditions. Plasmas diffuse for a sufficiently long afterglow period in the LF pulse and re-ignited from a lower electron density when the pulse is on again. The electron heating mechanisms are reported for the ramp-up and ramp-down phases at different frequencies.

The crossing frequency method of the cutoff probe, which is composed of radiating and detecting tips, has been recently developed for electron density measurement. However, this method faces challenge in accurately deducing electron density due to cavity resonances, which is caused by the standing wave resonance between the chamber wall and the cutoff probe. In this research, we propose an arrival time difference-based elimination method. As the cavity resonance occurs later in time compared to the directly transmitted between two tips, cavity resonance can be eliminated by adjusting the signal detection time. On the contrary with a conventional frequency sweeping system, we established a ns-pulse radiation and detection system, which can convert signals in time domain to that in frequency domain, so-called S₂₁ by using Fast Fourier transform. As a result, by adjusting the detection time, the cavity resonance peaks in S₂₁ spectrum were eliminated. By using this method, the crossing frequency can be clearly determined under wide range of chamber pressure and plasma density environments. This research not only addresses the challenges associated with high-pressure plasma measurements but also presents a reliable technique for obtaining precise electron density insides a cavity structure such as a vacuum chamber.

In conventional a global model, ion losses have been considered as the average of sheath voltages, without accounting for the ion energy distribution, making it inaccurate. In this research, we propose a global model with Monte Carlo Collision (GM/MCC) method for Ar capacitively coupled plasma (CCP). The input parameters in the GM/MCC are voltage and current waveforms of the powered electrode. Referenced on a 13.56 MHz Ar CCP source, we compared the electron density calculated through the GM/MCC with that measured by the cutoff probe and as a result, the discrepancy ranges from 30% to 70%. Hence, the GM/MCC is a simple-and-accurate model to analyze a conventional CCP source. Besides, the GM/MCC can be employed as a plasma monitoring sensor accompanied with voltage/current probe of the powered electrode in a CCP source.

Multipactor [1] is a nonlinear discharge phenomenon occurring in RF and microwave components and systems in which a high frequency RF field creates an electron avalanche sustained through secondary electron emission [2] from metallic or dielectric surfaces. It can be detrimental to RF devices creating problems [1,3] such as the breakdown of dielectric windows, erosion of metallic structures, melting of internal components, etc. In addition, multipactor can often detune RF systems, cause multi-tone coupling and signal distortion, limit the transmission or delivery of RF power [1,3].

This work presents a study of two-surface multipactor discharge in a parallel plate geometry induced by a non-sinusoidal Gaussian-type RF field waveform [4,5]. We employ 3D electromagnetic Particle in Cell (PIC) simulations using Computer Simulation Technology (CST) Particle Studio [6,7], and Monte Carlo (MC) simulations [6,7] to examine the effects of RF amplitude and the half peak width of the Gaussian-type electric field on multipactor susceptibility and time dependent physics [4-7].

The threshold peak RF voltage and the threshold time-averaged RF power per unit area for multipactor development increase with a Gaussian-type electric field compared to those with a sinusoidal electric field. The threshold peak RF voltage and RF power for multipactor increase as the full width at half maximum and/or half minimum (FWHM) of the Gaussian profile decreases. Expansion of multipactor susceptibility bands is observed compared to the sinusoidal RF operation. A high initial seed current density is found to shrink the multipactor susceptibility bands in the presence of space charge. The effect of space charge on multipactor susceptibility decreases as the FWHM of the Gaussian profile decreases.

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3. A. Iqbal, D.-Q. Wen, J. Verboncoeur, and P. Zhang, “Recent Advances in Multipactor Physics and Mitigation,” High Voltage, 2023 (in the press), https://doi.org/10.1049/hve2.12335.
4. D.-Q. Wen, A. Iqbal, P. Zhang, and J. P. Verboncoeur, Physics of Plasmas 26, 093503 (2019).
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This work was supported by the Air Force of Scientific Research (AFOSR) MURI Grant Nos. FA9550-18-1-0062 and FA9550-21-1-0367.

Low pressure capacitively coupled plasmas (CCPs) are widely used in plasma processing, such as etching, sputtering, cleaning. In recent work, we presented the important role of realistic electron-induced secondary electron emission (SEE), metastable atom and photon-induced secondary electrons from electrodes on the plasma density in low pressure capacitive argon discharges at 13.56MHz. Including the surface processes, the plasma density from the kinetic particle-in-cell (PIC) simulations shows good agreement with experimental measurements [Schulenberg et al Plasma Sources Sci. Technol. 30 (2021) 105003] at low pressure (1-10 Pa). In this work, we investigated the high voltage-driven capacitive discharges at low pressure via the validated PIC model and studied the reversed electric field pointing from the electrode towards the bulk plasma. The reversed field is induced by the strong secondary electron emission during the phase of sheath collapse. Especially, we explored the transition behavior of the formation of field reversal as a function of driving voltage amplitude and found the field reversal starts to be formed at around 750 V for CCP with an electrode spacing of 4 cm at 10 mTorr argon and 13.56 MHz. Accordingly, the electron energy distribution function incident on the electrode shows peaks from around 3 eV to 10 eV while spanning the driving voltage from 150V to 2000 V, showing potentially favorable effects in plasma processing where directional electrons are preferred to solely thermal diffusion electrons. The field reversals found at macroscale will also be examined for microplasmas considering a similarity law.

This work was supported by the Air Force Office of Scientific Research (AFOSR) MURI Grant FA9550-21-1-0367 and NSF-DOE Partnership Grant for DE-SC0022078. the Icelandic Research Fund Grant Nos.163086 and 217999, and a gift from the Applied Materials Corporation, AKT Display Division.

An Extreme-Ultraviolet (EUV) source has been developed at Illinois to expose candidate EUV resist materials and to study the plasma responsible for making EUV light. The EUV source consists of two EUV Multilayer Mirrors (MLM), 0ne collecting the light and another focusing the light on a x-y-z translation stage to approximately a 1 mm square area.The x-y translation allows for different samples to be exposed.The adjustment allows for best focus.The light is produced by striking a swappable tin-containing target with 7ns long pulses from a 100Hz, 350 mJ Nd:YAG laser at 1064 nm.To calibrate the EUV produced, measurements were made at the collector mirror position with a broad-spectrum photodiode detector limited to EUV by using a 150nm Zr based transmission filters.Photodiode readings are confirmed through the use of EUV-sensitive photoresist coated wafers. Experiments have been performed using pure Sn targets and Sn-containing ceramics (typically 5 a%), based on Spectraflux 100B (Lithium Metaborate/Lithium Tetraborate 80/20) as a primary component. Optical Emission Spectroscopy is used as an additional method for observing the LPP, with ongoing efforts regarding mitigation and removal of the debris produced. Laser power/focus, operating pressure, and target composition are investigated to optimize the system with the twin objectives of both maximizing EUV dosage and minimizing debris production. The setup is capable of exposing samples for research purposes in the field of novel EUV photoresist and examining methods for improving line-edge-roughness and dosage required for full development.