Dry etching characteristics of HfAlO3 thin films in BCl3/Ar plasma using inductively coupled plasma system

In this study, we monitored the HfAlO₃ etch rate and selectivity to SiO₂ as a function of the etch parameters (gas mixing ratio, RF power, DC-bias voltage, and process pressure). A maximum etch rate of 52.6 nm/min was achieved in the 30% BCl₃/(BCl₃ + Ar) plasma. The etch selectivity of HfAlO₃ to SiO₂ reached 1.4. As the RF power and the DC-bias voltage increased, the etch rate of the HfAlO₃ thin film increased. As the process pressure decreased, the etch rate of the HfAlO₃ thin films increased. The chemical state of the etched surfaces was investigated by X-ray Photoelectron Spectroscopy (XPS). According to the results, the etching of HfAlO₃ thin films follows the ion-assisted chemical etching mechanism.     

Plasma etching of high-k and metal gate materials

Etching characteristics of high-k dielectric materials (HfO₂) and metal electrode materials (Pt, TaN) have been studied in high-density chlorine-containing plasmas at pressures around 10 mTorr. The etching of HfO₂ was performed in BCl₃ without rf biasing, giving an etch rate of about 5 nm/min with a high selectivity of >10 over Si and SiO₂. The etching of Pt and TaN was performed in Ar/O₂ with high rf biasing and in Ar/Cl₂ with low rf biasing, respectively, giving a Pt etch rate of about several tens nm/min and a TaN etch rate of about 200 nm/min with a high selectivity of >8 over HfO₂ and SiO₂. The etched profiles were outwardly tapered for Pt, owing to the redeposition of etch or sputter products on feature sidewalls, while the TaN profiles were almost anisotropic, probably owing to the ion-enhanced etching that occurred.     

Surface properties of etched ITO thin films using high density plasma

The etching characteristics of ITO in a BCl₃/Ar plasma, including the etch rate and selectivity of ITO, were investigated. The maximum etch rate of 62.8 nm/min for the ITO thin films was obtained at a BCl₃/Ar gas mixing ratio of 25%/75%. Ion bombardment by physical sputtering was required to obtain such high etch rates, due to the relatively low volatility of the by-products formed during the etching. The chemical reactions on the etched surfaces were investigated using X-ray Photoelectron Spectroscopy (XPS) and the preferential losses on the etched surfaces were investigated using Atomic Force Microscopy (AFM).     

The etching characteristics of Al2O3 thin films in an inductively coupled plasma

In this study, the etching characteristics of ALD deposited Al₂O₃ thin film in a BCl₃/N₂ plasma were investigated. The experiments were performed by comparing the etch rates and the selectivity of Al₂O₃ over SiO₂ as functions of the input plasma parameters, such as the gas mixing ratio, the DC-bias voltage, the RF power, and the process pressure. The maximum etch rate was obtained at 155.8 nm/min under a 15 mTorr process pressure, 700 W of RF power, and a BCl₃ (6 sccm)/N₂ (14 sccm) plasma. The highest etch selectivity was 1.9. We used X-ray photoelectron spectroscopy (XPS) to investigate the chemical reactions on the etched surface. Auger electron spectroscopy (AES) was used for the elemental analysis of the etched surfaces.     

Dry etching process of GaAs in capacitively coupled BCl3-based plasmas

Dry etching of GaAs was investigated in BCl₃, BCl₃/N₂ and BCl₃/Ar discharges with a mechanical pump-based capacitively coupled plasma system. Etched GaAs samples were characterized using scanning electron microscopy and surface profilometry. Optical emission spectroscopy was used to monitor the BCl₃-based plasma during etching. Pure BCl₃ plasma was found to be suitable for GaAs etching at > 100 mTorr while producing a clean and smooth surface and vertical sidewall. Adding N₂ or Ar to the BCl₃ helped increase the etch rates of GaAs. For example, the GaAs etch rate was doubled with 20% N₂ composition in the BCl₃/N₂ plasma compared to the pure BCl₃ discharge at 150 W CCP power and 150 mTorr chamber pressure. The GaAs etch rate was ∼ 0.21 µm/min in the 20 sccm BCl₃ plasma. The BCl₃/Ar plasma also increased etch rates of GaAs with 20% of Ar in the discharge. However, the surface morphology of GaAs was strongly roughened with high percentage (> 30%) of N₂ and Ar in the BCl₃/N₂ and BCl₃/Ar plasma, respectively. Optical emission spectra showed that there was a broad BCl₃-related molecular peak at 450-700 nm wavelength in the pure BCl₃ plasma. When more than 50% N₂ was added to the BCl₃ plasma, an atomic N peak (367.05 nm) and molecular N₂ peaks (550-800 nm) were detected. Etch selectivity of GaAs to photoresist decreased with the increase of % N₂ and Ar in the BCl₃-based plasma.     

The dry etching property of TiO2 thin films using metal-insulator-metal capacitor in inductively coupled plasma system

In this work, we investigated the etching characteristics of TiO₂ thin films and the selectivity of TiO₂ to SiO₂ in a BCl₃/Ar inductively coupled plasma (ICP) system. The maximum etch rate of 84.68 nm/min was obtained for TiO₂ thin films at a gas mixture ratio of BCl₃/Ar (25:75%). In addition, etch rates were measured as a function of etching parameters, such as the RF power, DC-bias voltage and process pressure. Using the X-ray photoelectron spectroscopy analysis the accumulation of chemical reaction on the etched surface was investigated. Based on these data, the ion-assisted physical sputtering was proposed as the main etch mechanism for the BCl₃-containing plasmas.     

The dry etching of a sol-gel deposited ZnO thin film in a high density BCl3/Ar plasma

The etching characteristics of zinc oxide (ZnO) including the etch rate and the selectivity of ZnO in a BCl₃/Ar plasma were investigated. It was found that the ZnO etch rate showed a non-monotonic behavior with an increasing BCl₃ fraction in the BCl₃/Ar plasma, along with the RF power, and gas pressure. At a BCl₃ (80%)/Ar (20%) gas mixture, the maximum ZnO etch rate of 50.3 nm/min and the maximum etch selectivity of 0.75 for ZnO/Si were obtained. Plasma diagnostics done with a quadrupole mass spectrometer delivered the data on the ionic species composition in plasma. Due to the relatively high volatility of the by-products formed during the etching by the BCl₃/Ar plasma, ion bombardment in addition to physical sputtering was required to obtain the high ZnO etch rates. The chemical state of the etched surfaces was investigated with X-ray Photoelectron Spectroscopy (XPS). Inferred from this data, it was suggested that the ZnO etch mechanism was due to ion enhanced chemical etching.     

Improvement in etch selectivity of SiO2 to CVD amorphous carbon mask in dual-frequency capacitively coupled C4F8/CH2F2/O2/Ar plasmas

Highly selective etching of a SiO₂ layer using a chemical vapor deposited (CVD) amorphous carbon (a-C) mask pattern was investigated in a dual-frequency superimposed capacitively coupled plasma etcher. The following process parameters of the C₄F₈/CH₂F₂/O₂/Ar plasmas were varied: the CH₂F₂/(CH₂F₂ + O₂) flow ratio (Q(CH₂F₂)), the high frequency power (P_HF), and the low frequency power (P_LF). It was found a process window exists to obtain infinitely high etch selectivity of the SiO₂ layer to the CVD a-C. The process parameters of Q(CH₂F₂), P_HF, and P_LF played critical roles in determining the process window for oxide/CVD a-C etch selectivity, presumably due to the disproportionate degree of polymerization on the SiO₂ and CVD a-C surfaces.     

Process optimization of CF4/Ar plasma etching of Au using I-optimal design

In this paper, reactive ion etching of Au is performed with CF₄/Ar gases, and process optimization method is suggested using a statistically established process model. The I-optimal design was employed to set up the etching experiment with operating parameters, namely, gas composition, RF power and chamber pressure. Its analysis was performed on individual parameters of the etch rate, selectivity, and profile. In addition, process optimization, including all three responses of interest, is provided simultaneously. We confirmed that a nonvolatile by-product AuF_x was re-deposited on the surface, but controlling the amount of carbon fluoride provided a good etch rate with a satisfactory sidewall profile by reducing by-products. Although RF power is closely related with etch rate, increased power gives poor selectivity due to increased physical etching. Pressure and gas flows strongly interact with each other, affecting sidewall characteristics. Suggested optimization simultaneously considers three responses of interests, which is crucial in process development and optimization for quickly ramping up high volume manufacturing.     

Etch characteristics of indium zinc oxide thin films in a C2F6/Ar plasma

Dry etching of indium zinc oxide (IZO) thin films was performed using inductively coupled plasma reactive ion etching in a C₂F₆/Ar gas. The etch characteristics of IZO films were investigated as a function of gas concentration, coil rf power, dc-bias voltage to substrate, and gas pressure. As the C₂F₆ concentration was increased, the etch rate of the IZO films decreased and the degree of anisotropy in the etch profile also decreased. The etch profile was improved with increasing coil rf power and dc-bias voltage, and decreasing gas pressure. An X-ray photoelectron spectroscopy analysis confirmed the formation of InF₃ and ZnF₂ compounds on the etched surface due to the chemical reaction of IZO films with fluorine radicals. In addition, the film surfaces etched at different conditions were examined by atomic force microscopy. These results demonstrated that the etch mechanism of IZO thin films followed sputter etching with the assistance of chemical reaction.     

The deposition and optical properties of Ge1−xCx thin film and infrared multilayer antireflection coatings

The effects of deposition parameters on the deposition rate, microstructure, and composition of Ge_1−xC_x thin films prepared by plasma enhanced chemical vapor deposition were studied and the films' infrared optical properties were investigated. The results show that the carbon content of these films increases as the precursor gas flow ratio of CH₄:GeH₄ increases, while the infrared refractive index of these films decreases from 4 to 2. The deposition rate increases with the radio-frequency power and reaches a constant value when the power goes above 60 W. Ge_1−xC_x/diamond-like carbon infrared antireflection coatings were prepared, and the transmittance of the coatings in the band of 8 to 14 μm was 88%, which is superior to that of Zinc Sulfide substrate by 14%.     

The effects of gas flow rates on the etch characteristics of silicon nitride with an extreme ultra-violet resist pattern in CH2F2/N2/Ar capacitively coupled plasmas

The effects of CH₂F₂ and N₂ gas flow rates on the etch selectivity of silicon nitride (Si₃N₄) layers to extreme ultra-violet (EUV) resist and the variation of the line edge roughness (LER) of the EUV resist and Si₃N₄ pattern were investigated during etching of a Si₃N₄/EUV resist structure in dual-frequency superimposed CH₂F₂/N₂/Ar capacitive coupled plasmas (DFS-CCP). The flow rates of CH₂F₂ and N₂ gases played a critical role in determining the process window for ultra-high etch selectivity of Si₃N₄/EUV resist due to disproportionate changes in the degree of polymerization on the Si₃N₄ and EUV resist surfaces. Increasing the CH₂F₂ flow rate resulted in a smaller steady state CH_xF_y thickness on the Si₃N₄ and, in turn, enhanced the Si₃N₄ etch rate due to enhanced SiF₄ formation, while a CH_xF_y layer was deposited on the EUV resist surface protecting the resist under certain N₂ flow conditions. The LER values of the etched resist tended to increase at higher CH₂F₂ flow rates compared to the lower CH₂F₂ flow rates that resulted from the increased degree of polymerization.     

Etching characteristics of Al2O3 thin films in inductively coupled BCl3/Ar plasma

The investigation of Al₂O₃ etch characteristics in the BCl₃/Ar inductively coupled plasma was carried out in terms of effects of input process parameters (gas pressure, input power, bias power) on etch rate and etch selectivity over poly-Si and photoresist. It was found that, with the changes in gas pressure and input power, the Al₂O₃ etch rate follows the behavior of ion current density while the process rate is noticeably contributed by the chemical etch pathway. The influence of input power on the etch threshold may be connected with the concurrence of chemical and physical etch pathways in ion-assisted chemical reaction.     

Luminescence properties of Eu ions doped in Y2−xGdxO3 thin films grown by pulsed laser deposition method

Luminescence properties of Y_2−xGd_xO₃:Eu³⁺ (x = 0 to 2.0) thin films are investigated by site-selective laser excitation spectroscopy. The films were grown by pulsed laser deposition method on SiO₂ (100) substrates. Cubic phase Y₂O₃ and Gd₂O₃ and monoclinic phase Gd₂O₃ are identified in the excitation spectrum of the ⁷F₀ → ⁵D₀ transition of Eu³⁺. The emission spectra of the ⁵D₀ → ⁷F_J (J = 1 and 2) transition from individual Eu³⁺ centers were obtained by tuning the laser to resonance with each excitation line. The excitation line at around 580.60 nm corresponds to the line from Eu³⁺ with C₂ site symmetry of cubic phase. New lines at 578.65 and 582.02 nm for the C_S sites of Gd₂O₃ with monoclinic phase are observed by the incorporation of Gd in Y₂O₃ lattice. Energy transfer occurs between Eu³⁺ ions at the C_S sites and from Eu³⁺ ions at the C_S sites to those at the C₂ site in Y_2−xGd_xO₃.     

Chemical bonding of a-Ge1−xCx:H films grown by RF reactive sputtering

Amorphous hydrogenated germanium-carbon (a-Ge_1−xC_x:H) films were deposited by RF reactive sputtering pure Ge (1 1 1) target at different flow rate ratios of CH₄/(CH₄+Ar) in a discharge Ar/CH₄, and their composition and chemical bonding were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). XPS and FTIR results showed the content of germanium in the films decreased with the increase of the flow rate ratio CH₄/(Ar+CH₄), and the Ge-C, Ge-H, C-H bonds were formed in the films. The fraction of Ge-C, Ge-H, and C-H bonds was strongly dependent on the flow rate ratio. Raman results indicated that the films also contain both Ge-Ge and C-C bonding. Based on the change of the chemical bonding of a-Ge_1−xC_x:H films with the flow rate ratio CH₄/(CH₄+Ar), an optimal experimental condition for the application of infrared windows was obtained.     

Chemical vapor deposition of NiSi using Ni(PF3)4 and Si3H8

NiSi_x films were deposited using chemical vapor deposition (CVD) with a Ni(PF₃)₄ and Si₃H₈/H₂ gas system. The step coverage quality of deposited NiSi_x was investigated using a horizontal type of hot-wall low pressure CVD reactor, which maintained a constant temperature throughout the deposition area. The step coverage quality improved as a function of the position of the gas flow direction, where PF₃ gas from decomposition of Ni(PF₃)₄ increased. By injecting PF₃ gas into the Ni(PF₃)₄ and Si₃H₈/H₂ gas system, the step coverage quality markedly improved. This improvement in step coverage quality naturally occurred when PF₃ gas was present, indicating a strong relationship. The Si/Ni deposit ratio at 250 °C is larger than at 180 °C. It caused a decreasing relative deposition rate of Ni to Si. PF₃ molecules appear to be adsorbed on the surface of the deposited film and interfere with faster deposition of active Ni deposition species.     

Simple synthesis of ZrO2/SiOx core/shell nanofibers using ZrSi2 with gallium

ZrO₂/SiO_x core/shell nanofibers with diameter ~ 50 nm were synthesized by the thermal oxidation of ZrSi₂ substrates with gallium. The crystalline ZrO₂ cores were grown with amorphous SiO_x shells. It is proposed that the growth of crystalline ZrO₂ core was guided by the prior supersaturation of Zr species in the molten gallium film, whereas the amorphous SiO_x shell could be attributed to the deposition of SiO vapor on the surface of ZrO₂ core. In addition, the ZrO₂/SiO_x core/shell nanofibers show a wide visible photoluminescence (PL) emission at 480 nm, which should originate from the SiO_x shells.     

Dry etching of TaN thin film using CH4/Ar inductively coupled plasma

In this research, we investigated the TaN etch rate and selectivity with under layer (HfO₂) and mask material (SiO₂) in inductively coupled CH₄/Ar plasma. As the CH₄ content increased from 0% to 80% in CH₄/Ar plasma, the TaN etch rate was increased from 11.9 to 22.8 nm/min. From optical emission spectroscopy (OES), the intensities for CH [431 nm] and H [434 nm] were increased with the increasing CH₄ content from 0% to 100% in CH₄/Ar plasma. The results of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) showed no accumulation of etch by-products from the etched surface of TaN thin film. As a result of OES, AES and XPS analysis, we observed the etch by-products from the surfaces, such as Ta-N-CH and N-CH bonds. Based on the experimental results, the TaN etch was dominated by the chemical etching with the assistance of Ar sputtering in reactive ion etching mechanism.     

HfO2 etching mechanism in inductively-coupled Cl2/Ar plasma

Etching characteristics and the mechanism of HfO₂ thin films in Cl₂/Ar inductively-coupled plasma were investigated. The etch rate of HfO₂ was measured as a function of the Cl₂/Ar mixing ratio in the range of 0 to 100% Ar at a fixed gas pressure (6 mTorr), input power (700 W), and bias power (300 W). We found that an increase in the Ar mixing ratio resulted in a monotonic decrease in the HfO₂ etch rate in the range of 10.3 to 0.7 nm/min while the etch rate of the photoresist increased from 152.1 to 375.0 nm/min for 0 to 100% Ar. To examine the etching mechanism of HfO₂ films, we combined plasma diagnostics using Langmuir probes and quadrupole mass spectrometry with global (zero-dimensional) plasma modeling. We found that the HfO₂ etching process was not controlled by ion-surface interaction kinetics and formally corresponds to the reaction rate-limited etch regime.     

Antireflective characteristics of Ge1−xCx films on sub-wavelength structured ZnS surfaces

Antireflective sub-wavelength structures (SWSs) combined a Ge_1−xC_x coating on Zinc sulfide (ZnS) can enhance the long-wave infrared transmission and durability of ZnS, which have the potent for practical applications. We have investigated the antireflective characteristics of Ge_1−xC_x sub-wavelength periodic hole structures on ZnS through the Fourier modal method (FMM) for application with normally incident, randomly polarized, 10.6 μm wavelength. Then according to the results, we have successfully fabricated the sub-wavelength periodic square hole structures with Ge_0.05C_0.95 films on one side of ZnS. A substantial transmittance improvement for bare ZnS in the 8-12 μm spectral region was obtained.