H2 Plasma Research Articles

(Best Paper Award) Aluminum Josephson Junction Formation on 200mm Wafers Using Different Oxidation Techniques

For superconducting quantum circuits with a large number of Qubits, reproducible components are crucial for reducing entanglement decoherence. Particularly for reliable industrial manufacturing on full-scale 200 mm' wafers, a very high uniformity level is required to ensure sufficient coherence times. In the present work the special focus was put on manufacturing Al/AlOx/Al Josephson junctions (JJ), which are the most important component of many quantum circuit. Fully Al-based CMOS-compatible JJ’s were produced using a double dry etch process. After patterning the first Al metallization several oxidation processes have been investigated.Static oxidation has been performed by first removing the native AlOx in a multi-chamber system with Ar milling. The final tunneling oxide was controlled by applying a specific pressure in the chamber under a pure O2 atmosphere. Afterwards, without breaking the vacuum, the second Al metallization has been deposited by sputtering. Oxide thicknesses between 1 and 2.5 nm were achieved. A full mapping of the process homogeneity will be given.On the other hand, a dynamic recipe controlled plasma oxidation process was performed, where the native AlOx was first removed by a H2 plasma followed by a defined reoxidation with an oxygen plasma. The resulting oxides had thicknesses up to 10 nm. The second Al metallization was again deposited by sputtering.Both oxidation processes were carefully studied to understand the initial oxidation process of the aluminum surface. Special attention was devoted to the non-destructive removal of the native AlOx with respect to the Al interface. Because the oxide thicknesses varied between 1 and 10 nm, the transition between direct and Fowler-Nordheim tunneling could be investigated. The process-stability on full scale 200 mm wafers and on chip size could be determined via test structures as well as the resistance variation of the Josephson junctions. Furthermore, the electrical properties of the different oxides could be measured and analyzed on wafer level. These studies provide insight into the structure and composition of the aluminum oxides and the applicability for Qubits.

Plasma treatment for chemical SiOx enables excellent passivation of p-type polysilicon passivating contact featuring the lowest J of ∼6 fA/cm2

We study the preparation of high-quality p-type tunnel oxide passivated contact (p-TOPCon) using plasma-enhanced chemical vapor deposition (PECVD) technology in this work. We propose to use different plasmas to treat the ultrathin SiOx to improve the passivation quality of p-TOPCon. Experimentally, we use the nitric acid oxidation (NAOS) SiOx as the precursor and use pure N2, pure H2, and N2O/H2 plasmas to treat the SiOx precursor layer. Three observations are found. 1) Pure H2 plasma treatment can improve the SiOx quality by increasing the Si4+ content, but the passivation quality is not improved because of the etching effect of H2 plasma and the reduction of SiOx thickness. 2) The pure N2O plasma can improve the passivation quality but increases the contact resistivity (ρc) because of the increase of the SiOx thickness. 3) The N2O/H2 plasma treatment improves the passivation quality more effectively than pure N2O plasma, and meanwhile, it also keeps the contact resistivity at an acceptable value for high-efficiency solar cells. We assume that the atomic H provides the energy to etch the weak and dangling bonds and make SiOx thinner, while the atomic O that makes SiOx thickness unchanged balances the etching effect of atomic H. With the optimized N2O/H2 plasma treatment, the passivation quality of p-TOPCon is improved, featuring the best implied open-circuit voltage (iVoc) of ∼732 mV and the lowest single-sided saturation current density (J0,s) of ∼6 fA/cm2 on the lifetime sample with the n-type silicon substrate and the AlOx/SiNx capping layer. These results demonstrate that the plasma treatment is a promising way to boost the passivation quality of PECVD p-TOPCon structures. Finally, as an example, we use numerical simulation to predict the performances of the solar cells integrating the p-TOPCon structure on the rear side of n-c-Si and demonstrate a 24.8% efficiency with the p-TOPCon whose SiOx is improved by the optimized plasma treatment.

Toolbox of Advanced Atomic Layer Deposition Processes for Tailoring Large-Area MoS2 Thin Films at 150 °C.

Two-dimensional MoS2 is a promising material for applications, including electronics and electrocatalysis. However, scalable methods capable of depositing MoS2 at low temperatures are scarce. Herein, we present a toolbox of advanced plasma-enhanced atomic layer deposition (ALD) processes, producing wafer-scale polycrystalline MoS2 films of accurately controlled thickness. Our ALD processes are based on two individually controlled plasma exposures, one optimized for deposition and the other for modification. In this way, film properties can be tailored toward different applications at a very low deposition temperature of 150 °C. For the modification step, either H2 or Ar plasma can be used to combat excess sulfur incorporation and crystallize the films. Using H2 plasma, a higher degree of crystallinity compared with other reported low-temperature processes is achieved. Applying H2 plasma steps periodically instead of every ALD cycle allows for control of the morphology and enables deposition of smooth, polycrystalline MoS2 films. Using an Ar plasma instead, more disordered MoS2 films are deposited, which show promise for the electrochemical hydrogen evolution reaction. For electronics, our processes enable control of the carrier density from 6 × 1016 to 2 × 1021 cm-3 with Hall mobilities up to 0.3 cm2 V-1 s-1. The process toolbox forms a basis for rational design of low-temperature transition metal dichalcogenide deposition processes compatible with a range of substrates and applications.

In Situ Monitoring of Etching Characteristic and Surface Reactions in Atomic Layer Etching of SiN Using Cyclic CF4/H2 and H2 Plasmas.

Cyclic atomic layer etching (ALE) of SiN with high selectivity to SiO2, utilizing a hydrofluorocarbon deposition followed by exposure to hydrogen plasma, is presented. The surface reaction mechanism and etching behavior were investigated with in situ attenuated total reflectance Fourier transformation infrared spectroscopy (ATR-FTIR) and spectroscopic ellipsometry. In the deposition step, the hydrofluorocarbon film was deposited on top of the SiN films using the CF4/H2 plasmas with varying H2 contents (33 to 85%). Subsequently, the surface-modified SiN film was exposed to a hydrogen plasma for etching. The self-limiting SiN etching was observed, where the etch depth solely depended on the F concentration of the deposited hydrofluorocarbon layer once its thickness exceeded a critical value. A high selectivity of approximately 8.6 for SiN over SiO2 was achieved. The in situ ATR-FTIR spectra revealed that during the deposition step, besides the formation of the C-H peak associated with hydrofluorocarbon deposition, the appearance of the N-H4 absorbance band indicated the formation of an ammonium fluorosilicate layer on top of SiN. In the subsequent H2 plasma etching step, both the surface modification layer and the pre-deposited hydrofluorocarbon layer were removed. The removal of the surface-modified layer and hydrofluorocarbon layer was associated with the etch rate during H2 plasma exposure. These findings indicate the importance of the formation and removal of the surface modification layer for achieving ALE of SiN. The dissociation of the hydrofluorocarbon layer by the H2 plasma released reactants that interacted with SiN, leading to the formation of a new surface modification layer. The etching process significantly slowed down once the hydrofluorocarbon deposition and surface modification layer were completely removed.

Phosphorus deactivation by hydrogen on hot carrier stressed high-voltage N-channel field effect transistor CMOS device demonstrated by scanning capacitance microscopy imaging

Junction profiles of hot electron stressed high-voltage N-channel field effect transistor (NFET) devices were measured by scanning capacitance microscopy. Deactivation of phosphorous was observed on the drain side. To directly establish a link between phosphorus deactivation and hydrogen, junction profiles were measured on an unstressed NFET (N-type metal-oxide-semiconductor) device with and without H2 plasma treatment and with subsequent 400 °C annealing in helium. Phosphorus deactivation was observed in the device after H2 plasma treatment, while subsequent 400 °C annealing led to dissociation of the P–H (or H–Si–P) bond and recovery of the device junctions.

Studying the efficacy of hydrogen plasma treatment for enabling the etching of thermally annealed ruthenium in chemical solutions

Ruthenium (Ru) is a noble metal and is known to be resistant to many common chemicals and mixtures. We report in this study a controlled etching/recessing of Ru via wet processing and a combination of dry and wet process using metal-free chemical mixtures. The wet etching study was performed using both as-deposited and annealed atomic layer deposited ruthenium (Ru) films. The etching rate of Ru film in periodic acid mixtures was found to decrease substantially after being annealed at elevated temperatures (300 and 420 °C). X-ray photoelectron spectroscopy results indicated that this behavior could be explained by the formation of a thin surface ruthenium oxide layer induced by the thermal anneal. A short treatment in H2-based atmosphere at elevated temperature or in H2 plasma rendered the annealed Ru film etchable, explained by the reduction of RuOx film at the surface. The increase in surface roughness after wet etching was most likely caused by the gradual formation of oxidized Ru at the surface. Similarly, non-uniform etching of Ru was also observed for damascene Ru structure with the critical dimension ranging from ∼12 to 35 nm. An alternative approach using O2-based plasma achieved a good control of the etching (recessing) depth but also generated a thin layer of “residues” close to the interface between Ru and the liner (TiN). The results from this study have demonstrated that a short H2 plasma treatment prior to the wet process using the same chemical mixtures was able to etch the modified Ru surface layer together with the interfacial residues selectively to bulk Ru.

Aluminum Josephson Junction Formation on 200mm Wafers Using Different Oxidation Techniques

This work focuses on the manufacturing of Al/AlOx/Al Josephson junctions (JJs), which are essential components of many quantum circuits. Two processes were studied to understand the oxidation of the aluminum surface. Static oxidation was performed by removing native AlOx in a cluster system with Ar-ion beam milling and controlling the final tunneling oxide by applying a specific O2 pressure in the chamber. Controlled plasma oxidation was performed by removing native AlOx with a H2 plasma followed by a defined reoxidation with an oxygen plasma. The resulting oxides had thicknesses up to 10 nm and their electrical properties were analyzed on wafer level, providing insight into the structure and composition of the aluminum oxides and their applicability for Qubits. This work is crucial for reliable industrial manufacturing on full-scale 200 mm wafers with a very high uniformity level.

Self-Formation of a Ru/ZnO Multifunctional Bilayer for the Next-Generation Interconnect Technology via Area-Selective Atomic Layer Deposition.

This study suggests a Ru/ZnO bilayer grown using area-selective atomic layer deposition (AS-ALD) as a multifunctional layer for advanced Cu metallization. As a diffusion barrier and glue layer, ZnO is selectively grown on SiO2 , excluding Cu, where Ru, as a liner and seed layer, is grown on both surfaces. Dodecanethiol (DDT) is used as an inhibitor for the AS-ALD of ZnO using diethylzinc and H2 O at 120 °C. H2 plasma treatment removes the DDT adsorbed on Cu, forming inhibitor-free surfaces. The ALD-Ru film is then successfully deposited at 220 °C using tricarbonyl(trimethylenemethane)ruthenium and O2 . The Cu/bilayer/Si structural and electrical properties are investigated to determine the diffusion barrier performance of the bilayer film. Copper silicide is not formed without the conductivity degradation of the Cu/bilayer/Si structure, even after annealing at 700 °C. The effect of ZnO on the Ru/SiO2 structure interfacial adhesion energy is investigated using a double-cantilever-beam test and is found to increase with ZnO between Ru and SiO2 . Consequently, the Ru/ZnO bilayer can be a multifunctional layer for advanced Cu interconnects. Additionally, the formation of a bottomless barrier by eliminating ZnO on the via bottom, or Cu, is expected to decrease the via resistance for the ever-shrinking Cu lines.

Force-Based Characterization of the Wetting Properties of LDPE Surfaces Treated with CF4 and H2 Plasmas.

Low-density polyethylene (LDPE) films are widely used in packaging, insulation and many other commodity applications due to their excellent mechanical and chemical properties. However, the water-wetting and water-repellant properties of these films are insufficient for certain applications. In this study, bare LDPE and textured LDPE (T-LDPE) films were subjected to low-pressure plasmas, such as carbon tetrafluoride (CF4) and hydrogen (H2), to see the effect of plasma treatment on the wetting properties of LDPE films. In addition, the surface of the LDPE film was textured to improve the hydrophobicity through the lotus effect. The LDPE and T-LDPE films had contact angle (θ) values of 98.6° ± 0.6 and 143.6° ± 1.0, respectively. After CF4 plasma treatments, the θ values of the surfaces increased for both surfaces, albeit within the standard deviation for the T-LDPE film. On the other hand, the contact angle values after H2 plasma treatment decreased for both surfaces. The surface energy measurements supported the changes in the contact angle values: exposure to H2 plasma decreased the contact angle, while exposure to CF4 plasma increased the contact angle. Kinetic friction force measurements of water drops on LDPE and T-LDPE films showed a decrease in friction after the CF4 plasma treatment, consistent with the contact angle and surface energy measurements. Notably, the kinetic friction force measurements proved to be more sensitive compared to the contact angle measurements in differentiating the wetting properties of the T-LDPE versus 3× CF4-plasma-treated LDPE films. Based on Atomic Force Microscopy (AFM) images of the flat LDPE samples, the 3× CF4 plasma treatment did not significantly change the surface morphology or roughness. However, in the case of the T-LDPE samples, Scanning Electron Microscopy (SEM) images showed noticeable morphological changes, which were more significant at sharp edges of the surface structures.

Fabrication of sub-5 nm uniform zirconium oxide films on corrugated copper substrates by a scalable polymer brush assisted deposition method

We demonstrate a polymer brush assisted approach for the fabrication of continuous zirconium oxide (ZrO2) films over large areas with high uniformity (pin-hole free) on copper (Cu) substrates. This approach involves the use of a thiol-terminated polymethyl methacrylate brush (PMMA-SH) as the template layer for the selective infiltration of zirconium oxynitrate (ZrN2O7). The preparation of a highly uniform covalently grafted polymer monolayer on the Cu substrate is the critical factor in fabricating a metal oxide film of uniform thickness across the surface. Infiltration is reliant on the chemical interactions between the polymer functional group and the metal precursor. A following reductive H2 plasma treatment process results in ZrO2 film formation whilst the surface Cu2O passive oxide layer was reduced to a Cu/Cu2O interface. Fundamental analysis of the infiltration process and the resulting ZrO2 film was determined by XPS, and GA-FTIR. Results derived from these techniques confirm the inclusion of the ZrN2O7 into the polymer films. Cross-sectional transmission electron microscopy and energy dispersive X-ray mapping analysis corroborate the formation of ZrO2 layer at Cu substrate. We believe that this quick and facile methodology to prepare ZrO2 films is potentially scalable to other high-κ dielectric materials of high interest in microelectronic applications.

Low-pressure-RF plasma modification of UiO-66 and its application in methylene blue adsorption

Defect engineering of metal-organic frameworks has attracted increasing attention in recent years for potential applications in gas storage and catalysis. In this study, defective UiO-66 is obtained by Ar and H2 plasma treatments. Compared with the pristine UiO-66, a new aperture with a size of ∼4 nm appears for a sample with the plasma modification, indicating the formation of mesopores within UiO-66 framework. Characterization results demonstrate that the pore volume, surface area and the number of Lewis and Brönsted acid sites can be easily tuned by varying the discharge parameters. The adsorption performance of UiO-66 is evaluated for the adsorption of methyl blue. In comparison to the pristine UiO-66 and the sample with H2 plasma treatment, the Ar plasma modified sample shows excellent adsorption activity due to the suitable pore size and volume. Equilibrium adsorption capacity as high as 40.6 mg·g−1 is achieved for the UiO-66 (Ar) sample.

Improved Silicon Surface Passivation by ALD Al2O3/SiO2 Multilayers with In‐Situ Plasma Treatments

AbstractAl2O3 is one of the most effective dielectric surface passivation layers for silicon solar cells, but recent studies indicate that there is still room for improvement. Instead of a single layer, multilayers of only a few nanometers thickness offer the possibility to tailor material properties on a nanometer scale. In this study, the effect of various plasma treatments performed at different stages during the ALD deposition of Al2O3/SiO2 multilayers on the silicon surface passivation quality is evaluated. Significant improvements in surface passivation quality for some plasma treatments are observed, particularly for single Al2O3/SiO2 bilayers treated with a H2 plasma after SiO2 deposition. This treatment resulted in a surface recombination parameter J0 as low as 0.35 fA cm−2 on (100) surfaces of 10 Ω cm n‐type silicon, more than a factor of 5 lower than that of Al2O3 single layers without plasma treatment. Capacitance‐voltage measurements indicate that the improved surface passivation of the plasma‐treated samples results from an enhanced chemical interface passivation rather than an improved field effect. In addition, a superior temperature stability of the surface passivation quality is found for various plasma‐treated multilayers.

Plasma-assisted fluidized-bed atomic layer deposition of Pd-Cu nanoparticles on porous powder for CO2 hydrogenation

A novel plasma-assisted fluidized-bed atomic layer deposition process to synthesize Pd-Cu bimetallic nanoparticles is reported, using palladium hexafluoroacetylacetonate, copper(I)-N, N′-di-iso-propylacetamidinate and H2 plasma. The process allows us to uniformly deposit Pd-Cu nanoparticles in porous powder, which is a mixture of γ-Al2O3 (30 wt%), amorphous aluminum silicate (50 wt%) and molecular sieve (20 wt%) (ASM). With metal loadings of 13.1 and 2.5 mg g−1 for Pd and Cu, respectively, the afforded 13.1Pd-2.5Cu catalyst shows excellent catalytic performance for the hydrogenation of CO2 in a dielectric barrier discharge reactor with no intentional heating. Under the condition of discharge input power of 24.6 W, H2-to-CO2 ratio of 4 in feed gas, and gas hourly space velocity of 7595 h−1, the conversion of CO2 can reach as high as 38.0%, with the CH4 and CH3OH product selectivities of 6.7% and 12.8%, respectively. Density functional theory calculations are further employed to understand the associated CH3OH formation mechanism.

Chlorine Induced In-Situ Growth of TiO2 Nanoparticles on PVC Nano Fibers

PVC-TiO2-DBD nanocomposites were synthesized via combined approaches of electrospinning, H2 plasma treatment and hydrothermal reaction. The spinning solution composition and the amount of PVC were investigated and optimized in order to obtain membranes with uniform structure and high chemical activity. It was found that TiO2 NPs were distributed homogeneously on the surface of the PVC fibers. Chemical bonds such as Ti-Cl and C-O-Ti bonds were formed to tightly immobilize the TiO2 NPs on the PVC surface. The effect of H2 plasma treatment on the surface of the PVC membranes was studied. Meanwhile, using ABS and PS as substrates, the influence of various groups, including chlorine bonds, C=C double bonds, cyano and phenyl groups on the possible promotion mechanism of different chemical bonds for the TiO2 deposition was also studied. Possible mechanisms for the enhancement of the deposition of TiO2 were given.

Room-Temperature Magnetism in 2D MnGa4 -H Induced by Hydrogen Insertion.

2D room-temperature magnetic materials are of great importance in future spintronic devices while only very few are reported. Herein, a plasma-enhanced chemical vapor deposition approach is exploited to construct the 2D room-temperature magnetic MnGa4 -H single crystal with a thickness down to 2.2nm. The employment of H2 plasma makes hydrogen atoms can be easily inserted into the MnGa4 lattice to modulate the atomic distance and charge state, thereby ferrimagnetism can be achieved without destroying the structural configuration. The as-obtained 2D MnGa4 -H crystal is high-quality, air-stable, and thermo-stable, demonstrating robust and stable room-temperature magnetism with a high Curie temperature above 620K. This work enriches the 2D room-temperature magnetic family and opens up the possibility for the development of spintronic devices based on 2D magnetic alloys.

TALIF at H− ion sources for the determination of the density and EDF of atomic hydrogen

The production of H− ions in negative ion sources relevant for particle accelerator facilities and neutral beam injection systems is based predominantly on the surface conversion of H atoms at a low work function surface covered with caesium (the plasma grid (PG)). Therefore, the H atom density n H and energy distribution function (EDF) close to the PG determine the amount of surface produced H− ions. As a direct method for the density and EDF determination, two-photon absorption laser induced fluorescence (TALIF) on H atoms was implemented at the ion source of the teststand BATMAN Upgrade (BUG) being the first time that this was accomplished at an H− ion source. Several challenges had to be overcome concerning the application of the diagnostic at the complex facility and the evaluation of the fluorescence signals against a bright H background. The observed line profiles suggest a Maxwellian EDF with an H atom temperature of K. The presence of highly energetic H atoms (measured by optical emission spectroscopy, (OES)) could not be resolved by the TALIF system due to the insufficient signal-to-noise ratio. Atomic densities were measured for H2 and D2 plasmas for varying ion source parameters at BUG resulting in values between m−3 and m−3 for hydrogen. For the operation with deuterium, higher atomic densities are observed for similar ion source parameters which agree well with the previous results obtained with OES.

Surface activated bonding of ALD Al2O3 films

Room temperature direct bonding of plasma enhanced ALD Al2O3 films was achieved by using surface activated bonding. ALD Al2O3 films were amorphous with C and O impurities contained. The high deposition power and H2 plasma post-treatment increased the crystallinity and hydrophilicity of ALD Al2O3 films, respectively. However, both methods increased the surface roughness of films slightly. The bond strength of ALD Al2O3 films was not changed obviously by raising the deposition power, but it experienced a slight decrease after H2 plasma post-treatment. The water in the debonding atmosphere influenced the bond strength of standard ALD Al2O3 films greatly, which was 0.54 J m−2 in humid air and 1.00 J m−2 in anhydrous N2. The bond strength in vacuum was just a little larger than that in anhydrous N2 suggesting that the trapped water at the bonding interface was less.

A study of hydrogen plasma-induced charging effect in EUV lithography systems

In the extreme ultraviolet lithography system, EUV-induced hydrogen plasma charging effect is observed by in situ embedded micro-detector array. The 4k-pixel on-wafer array can detect and store the distributions of H2 plasma in each in-pixel floating gate for non-destructive off-line read. The local uniformity of H2 plasma intensity extracted by the threshold voltages on an array and its distributions across a wafer by the average bit cell current of MDAs provide insights into the detailed conditions inside advanced EUV lithography chambers.

H2 Plasma and PMA Effects on PEALD-Al2O3 Films with Different O2 Plasma Exposure Times for CIS Passivation Layers

In this study, the electrical properties of Al2O3 film were analyzed and optimized to improve the properties of the passivation layer of CMOS image sensors (CISs). During Al2O3 deposition processing, the O2 plasma exposure time was adjusted, and H2 plasma treatment as well as post-metallization annealing (PMA) were performed as posttreatments. The flat-band voltage (Vfb) was significantly shifted (ΔVfb = 2.54 V) in the case of the Al2O3 film with a shorter O2 plasma exposure time; however, with a longer O2 plasma exposure time, Vfb was slightly shifted (ΔVfb = 0.61 V) owing to the reduction in the carbon impurity content. Additionally, the as-deposited Al2O3 sample with a shorter O2 plasma exposure time had a larger number of interface traps (interface trap density, Dit = 8.98 × 1013 eV-1·cm-2). However, Dit was reduced to 1.12 × 1012 eV-1·cm-2 by increasing the O2 plasma exposure time and further reduced after PMA. Consequently, we fabricated an Al2O3 film suitable for application as a CIS passivation layer with a reduced number of interface traps. However, the Al2O3 film with increased O2 plasma exposure time deteriorated owing to plasma damage after H2 plasma treatment, which is a method of reducing carbon impurity content. This deterioration was validated using the C-V hump and breakdown characteristics.

Applications and mechanisms of anisotropic two-step Si3N4 etching with hydrogen plasma conditioning

The ability to precisely form Si3N4 spacers is critical to the success of dynamic random-access memory and NAND (NOT AND) flash memory technology development. In this study, we investigated the mechanisms and process windows of an innovative two-step nitride (Si3N4) etch consisting of H2 plasma processing in an inductively coupled plasma chamber followed by either buffered oxide etch (BOE, a mix of NH4F and HF solution) wet clean or in situ NF3 plasma etch. We obtained layer–by-layer removal with each layer’s removal capable of more than 10 nm. We revealed that H can penetrate more than 20 nm deep into the nitride film to transform pristine Si3N4 into SiON after air exposure, which can be subsequently removed by BOE wet clean. The H2 and BOE steps do not need to run back-to-back; the modified SiON layer is stable enough to sustain elevated temperature processing and can be removed by BOE later down-the-line integration. We also demonstrated that using NF3 plasma can have highly selective etch of nitride over oxide due to the incubation time difference between these two types of films. It takes much longer time to initiate the chemical reaction for oxide compared with nitride. Critically, the role of H2 is not the key for high selectivity; instead, it provides an etch directionality and shortens the incubation time for both nitride and oxide.