NF3 Plasma Research Articles

Mechanism study of H2-plasma assisted Si3N4 layered etch

The cyclic two-step process, comprised of energetic H2 plasma followed by HF wet clean or in situ NF3 plasma, demonstrates Si3N4 layer-by-layer removal capability exceeding 10 nm per cycle, surpassing typical atomic layer etch methods by an order of magnitude. In this paper, we investigated the surface reaction mechanisms via first principle density functional theory simulations and surface analysis. The results unveiled that energetic H2 plasma, in the first step, selectively removes nitrogen (N) in preference to silicon (Si), generating ammonia (NHx) and transforming Si3N4 into SiON upon exposure to air, which becomes removable by HF wet clean in the second step. For the second step employing in situ NF3 plasma, it further leverages H-passivated surfaces to enhance NF3 dissociation and provide alternative reaction pathways to yield volatile byproducts such as SiHF3 and SiFx, thereby significantly improving nitride removal efficiency.

Enhanced electrochemical performance of N, F co-doped and etched needle coke-based lithium-ion battery anode materials by NF3 plasma treatment

NF3 plasma treatments were used to improve the electrochemical properties of needle coke-based lithium-ion battery (LIB) anode materials. The effects of the NF3 plasma treatments on the chemical, structural, and morphological properties of the needle cokes were evaluated with various analyses, and simultaneous heteroatom doping coupled with surface etching was identified. With these effects, N and F functional groups and micropores were generated on the surfaces of the needle cokes. The NF3 plasma-modified needle cokes were analyzed with LIB performance tests, and considerable enhancements were observed in the discharge capacities, rate capabilities and cycling stabilities. The resulting nitrogen functional groups and micropores improved the lithium storage capacities and rates by providing lithium-ion adsorption sites. The fluorine functional groups enhanced the cycling stability by forming LiF-based SEI layers. These effects of the NF3 plasma treatment on the electrochemical properties were proven with analytical techniques, and mechanisms for the overall process were suggested based on the results. The NF3 plasma-treated needle cokes are promising materials for fast charging LIB anodes with high stabilities and competitive discharge capacities.

Surface analysis of yttrium oxyfluoride deposited via air plasma spraying for Erosion resistance against NF3 plasma

Surface analysis of yttrium oxyfluoride deposited via air plasma spraying for Erosion resistance against NF3 plasma

As-Grown Crystalline InGaZnO by Spray Pyrolysis on a Flexible Substrate for a Thin-Film Transistor with Excellent Stability.

The development of low-cost, high-mobility oxide thin-film transistors (TFTs) with excellent stability is of increasing interest. The coplanar oxide TFTs can be used for high-speed, large-area, and high-resolution displays. Here, we report highly oriented, as-grown crystalline InGaZnO (c-IGZO) with very low oxygen vacancy defects using spray pyrolysis at the substrate temperature of 425 °C. The c-IGZO exhibits a highly oriented, c-axis aligned crystal perpendicular to the substrate with a high mass density of 6.73 g cm-3 without any disordered incubation layer. Its resistivity can be decreased to 0.42 mΩ cm by NF3 plasma doping, which is essential to achieving high-performance coplanar TFT. We have demonstrated the application of this material to high-performance flexible TFTs. The self-aligned, coplanar c-IGZO TFTs on the polyimide substrate exhibit an average field-effect mobility of 39.60 cm2 V-1 s-1, threshold voltage of -1.00 V, subthreshold swing of 0.21 V dec-1, and on/off current ratio over 108. The ring oscillator and gate driver made of the c-IGZO TFTs exhibit a propagation delay of 8.77 ns/stage and rising/falling times of 648/564 ns, respectively. Therefore, the as-grown c-IGZO by spray pyrolysis has the potential to be utilized as a new oxide semiconductor for the production of low-cost, flexible TFT electronics.

Simulation of silicon etching in NF3 plasma reactor

Simulation of silicon etching in NF3 plasma reactor

High‐performance, coplanar amorphous InGaZnO thin‐film transistors by spray pyrolysis on polyimide substrate for low‐cost manufacturing of foldable active‐matrix organic light emitting diode display

AbstractWe report a method for low‐cost deposition of bubble‐free, high‐quality amorphous InGaZnO (a‐IGZO) on polyimide (PI) substrate for foldable active‐matrix organic light emitting diode (AMOLED) display by spray pyrolysis. The coplanar thin‐film transistor (TFT) with spray‐pyrolyzed (SP) a‐IGZO on PI substrate exhibits threshold voltage (VTH) of −0.8 V, saturation mobility of 40.95 cm2 V−1 s−1, and subthreshold swing of 0.18 V per decade with on/off drain current ratio of ~108. The high mobility TFT could be achieved using high substrate temperature (350°C) and low contact resistance by NF3 plasma on the SP a‐IGZO. The TFT shows a ΔVTH of −0.4 V when it is bent on a cylinder of 1‐mm radius. The TFT shows the ΔVTH of +0.05 V for positive bias temperature stress at +20 V at 60°C for 1 h. The ring oscillator made of a‐IGZO TFTs exhibits an oscillation frequency of 2.38 MHz at VDD of 10 V with a propagation delay of 9.13 ns per stage. Therefore, the a‐IGZO TFT by spray pyrolysis could be used for low‐cost, high‐performance, and flexible display TFT backplane.

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.

Spectroscopic Analysis of NF3 Plasmas with Oxygen Additive for PECVD Chamber Cleaning

As semiconductors’ device fabrication is highly integrated, the number of the deposition processes is continuously increasing, and the chamber cleaning process becomes essential for deposition equipment to maintain a normal chamber condition. Although the use of NF3 gas for the chamber cleaning is common, it causes several environmental and safety issues. However, not much research has been performed on NF3 plasma at high pressures, such as in cleaning processes. To understand fluorine in NF3, herein, oxygen was added to N2 and NF3 plasma and then compared. Plasma emission spectra were compared using an OES data, and their analyses were performed via a line-ratio method employing the collisional-radiative model. As a result confirmed that the changes in electron temperature, electron density, and chemical species in the plasma could be explained. Additionally, the characteristics of NF3 plasmas with respect to fluorine were confirmed by comparing the oxygenated N2 plasma and the NF3 plasma.

Stability and plasma etching behavior of yttrium-based coatings by air plasma spray process

In recent days, many studies have focused on fluorine-saturated yttrium-based coatings for better material performance in semiconductor processing chambers. In this investigation, yttrium oxide (Y2O3) and yttrium oxyfluoride (YOF) powders were synthesized using a simple solid-state wet chemical process. Then, the Y2O3 and YOF powder feedstocks were coated on an aluminum (Al) substrate using the atmospheric plasma spraying (APS) technique at different plasma powers of 25.6, and 25.2, 33.2 kW, respectively. Microstructure, macroscopic property, and chemical stability of dense Y2O3 and YOF-coated samples were analyzed. The Vickers hardness values of Y2O3 and YOF coated samples were 369.2 ± 32, and 267.1 ± 25, 241.9 ± 31 at plasma powers of 25.6, and 25.2, 33.2 kW, respectively. Y2O3 sample was showed higher hardness value due to less porosity. The etching behavior of the Y2O3 and YOF coatings was analyzed using PECVD- NF3 plasma. X-ray photoelectron spectrum analysis (XPS) has confirmed the fluorination on the etched surfaces. The relative intensity ratios of the YF to YO peaks on the Y2O3 and YOF coatings after exposure to NF3 plasma were 1.30 and 1.48, respectively. This indicated that the YOF coating showed a strong fluorination layer and superior resistance for fluorine-plasma exposure compared to Y2O3, which is more appropriate for use as a protective material for the inner wall reactors. Therefore, YOF coated samples have good stability with high erosion resistance, which is highly suggested for applications in the semiconductor industry.

Spray Pyrolyzed Amorphous InGaZnO for High Performance, Self‐Aligned Coplanar Thin‐Film Transistor Backplanes

AbstractHigh‐performance, spray‐pyrolyzed amorphous indium‐gallium‐zinc oxide (a‐IGZO) thin‐film transistor (TFT) with self‐aligned (SA) coplanar structure is demonstrated. The spray‐pyrolyzed a‐IGZO film exhibits bubbles‐free smooth surface roughness (0.81 nm) and low oxygen‐related defects (22.5%). The fluorine‐doped a‐IGZO film shows a low resistivity of 1.18 × 10−3 Ω‐cm by NF3 plasma treatment. This is sufficient to obtain ohmic contact with the source/drain electrodes and doped IGZO in the offset region of the SA coplanar TFT. The spray‐pyrolyzed a‐IGZO TFT exhibits the field‐effect mobility (µFE) of 18.17 cm2 V−1 s−1, the threshold voltage (VTH) of −1.52 V, the subthreshold swing (SS) of 0.266 V dec−1, and a high on/off current ratio (Ion/Ioff) over 108 with a very low gate leakage current (<10−13 A). The hysteresis‐free and highly stable performances are achieved due to the excellent a‐IGZO channel and SiO2 gate insulator interface. A twenty‐three‐stage ring oscillator is demonstrated with SA coplanar TFTs, exhibiting a high oscillation frequency of 2.66 MHz and a low propagation delay of 8.17 ns/stage. Therefore, the spray‐pyrolyzed a‐IGZO film can be a promising metal oxide semiconductor for high‐performance TFTs backplane in large areas and high‐resolution display applications.

A study of the NF3 plasma etching reaction with cobalt oxide films grown on an inorganic compounds

In this study, an NF3 plasma etching reaction with a cobalt oxide (Co3O4) films grown on the surface of inorganic compounds using granite was investigated. Experimental results showed that the etching rate can be up to 1.604 μm/min at 380 °C under 150 W of RF power. EDS and XPS analysis showed that main reaction product is CoF2, which is generated by fluorination in NF3 plasma. The etching rate of cobalt oxide films grown on inorganic compounds in this study was affected by surface roughness and etch selectivity. This study demonstrates that the plasma surface decontamination can effectively and efficiently remove contaminated nuclides such as cobalt attached to aggregate in concrete generated when decommissioning of nuclear power plants.

Atomic layer etching of Al2O3 with NF3 plasma fluorination and trimethylaluminum ligand exchange

In this study, a cyclic isotropic plasma atomic layer etching (ALE) process was developed for aluminum oxide that involves fluorination with NF3 plasma and ligand exchange with trimethylaluminum (TMA). The isotropic plasma ALE consists of two steps: fluorination and removal. During the fluorination step, the Al2O3 surface was fluorinated to AlOFx with NF3 plasma at 100 °C. The formation of the AlOFx layer was confirmed by x-ray photoelectron spectroscopy analysis, and the atomic fraction of fluorine on the surface was saturated at 25% after 50 s of plasma fluorination. The depths of the fluorinated layers were in the range of 0.79–1.14 nm at different plasma powers. In the removal step, the fluorinated layer was removed by a ligand exchange reaction with TMA at an elevated temperature range of 250–480 °C. The etch per cycle (EPC) was 0.20–0.30 nm/cycle and saturated after 30 s in the temperature range of 290–330 °C. No etching was observed below 250 °C, and the EPC increased in the temperature range of 250–300 °C during the removal step with the ligand exchange reaction and reached the maximum at 300 °C. Then, the EPC was significantly reduced at high temperatures, possibly due to TMA decomposition. The fluorine atomic fraction on the surface was reduced to 14% after the removal. In conclusion, Al2O3 was successfully etched at the atomic scale by the cyclic plasma ALE process. The average surface roughness of Al2O3 was reduced from 8.6 to 5.3 Å after 20 cycles of etching.

Lithiophilic NiF2 coating inducing LiF-rich solid electrolyte interphase by a novel NF3 plasma treatment for highly stable Li metal anode

A three-dimensional lithiophilic skeleton is an effective strategy that is widely studied due to its large specific surface area and the lithiophilicity for suppressing the growth of dendrites on Li metal anodes. However, there are few studies on the lithiophilicity of the metal fluoride. In this study, we employ a novel NF3 plasma fluoridized strategy to fabricate a NiF2 coating on Ni foams for the first time. Due to the lithiophilic NiF2 layer, the Li+ flux tends to deposit preferentially on the sites of NiF2 and homogeneously distributes around the surface of the Ni foam, leading to a smooth and dense Li deposition. Moreover, the LiF-rich solid electrolyte interphase layer generated from the reaction between Li and NiF2 significantly improves the interfacial stability. The fluoridized Ni foam exhibits a highly stable cycling performance of over 2000 cycles at 2 mA cm−2 and over 1600 h at 1 mA cm−2. In addition, the fluoridized Ni foam@Li || LiFePO4 full cell delivers a capacity retention of 93% after 250 cycles at 1C. This work provides a safe and simple plasma strategy to construct a lithiophilic metal fluoride coating for strengthening the solid electrolyte interphase and suppressing the growth of Li dendrites.

High Voltage Amorphous InGaZnO TFT With F Doped Drain Offset Structure

We report high voltage amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) using a drain offset structure. The a-IGZO TFT with drain offset length (Loff) = 2.5 μm exhibits a maximum operating voltage (VDS, Max) over 90 V, which increases with Loff. The drastic current drop from output characteristics appears for VDS>VDS, Max with a positive threshold voltage shift and increased subthreshold swing from transfer characteristics. We obtain maximum lattice temperatures of ~130 °C for both the conventional and drain offset TFTs due to Joule heating (JH) within the a-IGZO layer by TCAD simulation. It indicates that the rise in temperature by JH is almost independent of Loff. The JH is uniformly distributed over the entire Loff in drain offset TFT compared with a drastic increase near the drain side in conventional TFT. NF3 plasma treatment enhances conductivity at offset region, resulting in large VDS, Max.

Combined effects of NH3 and NF3 post plasma treatment on the performance of spray coated ZnO thin film transistors

We investigate the effects of NH3 and NF3 post plasma-treatment on the performance of spray-coated ZnO thin film transistors (TFTs). Both NH3 and NF3 plasma treatment are varied from 10 to 40 s. The properties of plasma treated ZnO were studied by Hall Effect measurements, UV–visible spectroscopy, photoluminescence, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. NF3 plasma treatment causes n-type doping and generates carriers by F incorporation. While, NH3 plasma can cause not only n-type doping by Hydrogen incorporation but also creates acceptor-like states by the formation of Vo–H complex and inducing Nitrogen in ZnO. Owing to the N incorporation, the threshold voltage can be controlled by NH3 plasma treatment. The appropriate NH3 and NF3 plasma treatments for 10 s each greatly enhance theperformance of ZnO TFTs, exhibiting the saturation mobility and subthreshold swing of 20.65 cm2 V−1 s−1 and 0.18 V dec–1, respectively. Therefore, it is concluded that NH3 and NF3 plasma-treatment can be a useful technique to enhance the device performance and to improve the stability of solution-processed metal-oxide TFTs.

Silicon Oxide Etching Process of NF3 and F3NO Plasmas with a Residual Gas Analyzer.

The use of NF3 is significantly increasing every year. However, NF3 is a greenhouse gas with a very high global warming potential. Therefore, the development of a material to replace NF3 is required. F3NO is considered a potential replacement to NF3. In this study, the characteristics and cleaning performance of the F3NO plasma to replace the greenhouse gas NF3 were examined. Etching of SiO2 thin films was performed, the DC offset of the plasma of both gases (i.e., NF3 and F3NO) was analyzed, and a residual gas analysis was performed. Based on the analysis results, the characteristics of the F3NO plasma were studied, and the SiO2 etch rates of the NF3 and F3NO plasmas were compared. The results show that the etch rates of the two gases have a difference of 95% on average, and therefore, the cleaning performance of the F3NO plasma was demonstrated, and the potential benefit of replacing NF3 with F3NO was confirmed.

Formation of F-Doped Offset Region for Spray Pyrolyzed Self-Aligned Coplanar Amorphous Zinc–Tin–Oxide Thin-Film Transistor by NF₃ Plasma Treatment

We report the high performance of self-aligned (SA), amorphous zinc–tin–oxide (a-ZTO) coplanar thin-film transistor (TFT) by spray pyrolysis. The a-ZTO thin film deposited by spray at 350 °C has a low surface roughness (0.39 nm) and no bubble. The resistivity of a-ZTO could be decreased to $2\times 10^{-3} \Omega $ cm by NF3 plasma exposure and it was used for the offset regions of SA coplanar TFT. The coplanar a-ZTO TFT exhibits the field-effect mobility ( $\mu _{{\mathrm {FE}}}$ ) of 5.13 cm $^{2}\text{V}^{-1}\text{s}^{-1}$ , turn-on voltage ( ${V}_{ \mathrm{\scriptscriptstyle ON}}$ ) of ~0 V, the subthreshold swing of 139 mV/decade, and high On/Off-current ratio over $\sim 10^{7}$ . The SA coplanar a-ZTO TFT exhibited high stability with a threshold voltage shift ( $\Delta {V}_{{\mathrm {TH}}}$ ) of 0 V under the gate bias stress of ${V}_{{\mathrm {GS}}} = +20$ V for 1 h.

Performance Improvement for Spray-Coated ZnO TFT by F Doping With Spray-Coated Zr–Al–O Gate Insulator

We report the fluorine (F) doping effect on zinc oxide (ZnO) thin-film transistor (TFT) fabricated by spray pyrolysis on spray-coated zirconia alumina oxide (ZAO) gate insulator. F doping was performed by NF3 plasma treatment on ZnO thin film. The ZnO film shows ${C}$ -axis-aligned hexagonal structure, which remains unchanged by F doping. The photoluminescence (PL) spectra and X-ray photoelectron spectroscopy (XPS) show a reduction in oxygen-related defects by F doping. Valance band edge XPS spectra show the shift of Fermi energy level from 2.46 to 3.12 eV which reveals that the more carriers are generated in the conduction band and defect states are reduced. The F-doped ZnO (F:ZnO) TFT exhibits the saturation mobility of 31.59 cm2V−1s−1, the subthreshold swing of 238mV/dec, ON/ OFF current ratio of ~108, and zero hysteresis voltage. The F:ZnO TFT also shows significant improvement of threshold voltage shift ( $\Delta \text{V}_{TH}$ ) under negative/positive gate bias stress compared to pristine ZnO. The enhancement of mobility and stability is attributed to the substitution of oxygen (O) and passivation of oxygen vacancies ( ${V}_{o}$ ) by F in ZnO. Therefore, it is expected that F doping is an effective method to improve the performance and stability of solution-processed oxide TFTs.

Role of sulfur in catalyzing fluorine atom fast etching of silicon with smooth surface morphology

Chemical reaction probabilities, defined as the number of silicon atoms removed per incident fluorine atom, have been investigated in mixtures of NF3 and SF6 plasmas in an inductively-coupled plasma reactor. Fluorine atom densities were measured by optical emission actinometry, and isotropic etching rates were measured by the degree of undercutting of SiO2-masked silicon by cross-sectional scanning electron microscopy. In addition, atomic force microscopy was used to examine surface morphology of etched Si surfaces. The F atom reaction probabilities derived from isotropic etching rates indicate an ∼30-fold higher reaction probability in SF6 plasmas compared with values in NF3 plasmas. Surfaces etched in SF6 plasmas were much smoother than those etched in NF3 plasmas. The addition of only 10% SF6 to an NF3 plasma produced a much higher reaction probability (∼5-fold) than in a pure NF3 plasma. This surprising enhancement of reaction probabilities for F with Si in SF6 plasmas is further investigated, based on the mechanism of adsorbed sulfur acting as a catalyst to greatly enhance the etching rate of Si. Dilute sulfur solutions in isopropyl alcohol were allowed to evaporate on the masked Si samples, depositing sulfur in relatively high concentrations near mask edges in ∼2 μm diameter periodic “strings of beads.” The sulfur-dosed sample etched several times faster at the center of each bead than a sample not exposed to sulfur that was placed side by side. The catalytic effect of sulfur is ascribed to an enhanced F sticking coefficient and/or decreased desorption rate on a surface covered with sulfur.

Anisotropic atomic layer etching of W using fluorine radicals/oxygen ion beam

AbstractAtomic layer etching (ALE) has advantages such as precise thickness control, high etch selectivity, and no‐increase in surface roughness which can be applied to sub 10 nm semiconductor device fabrication. In this study, anisotropic ALE of tungsten (W), which is used as an interconnect layer and gate material of semiconductor devices, was investigated by sequentially exposing to F radicals by NF3 plasma to form a WFy layer and following exposure to an oxygen ion beam to remove the WFy layer by forming volatile WOxFy at room temperature. A wide ALE window of F radical adsorption time of ( ≥ 10 s/cycle) and Ox+ ion desorption time of (10 ≤ t ≤ 50 s/cycle at + 44–51 eV of Ox+ ion energy) could be identified, and at the ALE conditions, a precise etch rate of ~2.6 Å/cycle was obtained while increasing the W etch depth linearly with increasing the number of etch cycles. At the optimized W ALE conditions, the W surface roughness after the W ALE was similar to the as‐received W and the etch selectivity over SiO2 was close to infinite. However, after the W ALE, ~ 10% F diffused into W was observed on the etched W surface, and which could be removed by a following process.