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.     

Effect of gas mixing ratio on gas-phase composition and etch rate in an inductively coupled CF4/Ar plasma

In this work, we carried out investigations aimed at understanding the effect of gas mixing ratio on plasma parameters, gas phase composition and etch rate in CF₄/Ar inductively coupled plasma. For this purpose, a combination of experimental methods and modelling was used. Experiments showed that electron temperature and electron density are not very sensitive to variations of Ar content in CF₄/Ar plasma. From a zero-dimensional plasma model, the densities of both neutral and charged particles change monotonically. The analysis of surface kinetics based on an ion-assisted etching mechanism showed the possibility of non-monotonic etch rate behaviour due to a concurrence of chemical and physical etching pathways.     

Etching characteristics and mechanism of Ga-doped ZnO thin films in inductively-coupled HBr/X (X = Ar, He, N2, O2) plasmas

We investigated the etch characteristics and mechanisms of Ga-doped ZnO (Ga-ZnO) thin films in HBr/X (X = Ar, He, N₂, O₂) inductively-coupled plasmas. The etch rates of Ga-ZnO thin films were measured as a function of the additive gas fraction in the range of 0-100% for Ar, He, N₂, and O₂ at a fixed gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (40 sccm). The plasma chemistry was analyzed using a combination of the global (zero-dimensional) plasma model and Langmuir probe diagnostics. By comparing the behavior of the etch rate and fluxes of plasma active species, we found that the Ga-ZnO etch process was not limited by ion-surface interaction kinetics and appeared in the reaction rate-limited etch regime. In the HBr/O₂ plasma, the etch kinetics were probably influenced by oxidation of the etched surface.     

Vacuum-ultraviolet ellipsometry spectra and structural properties of Pb(Zr,Ti)O3 films

Optical properties of PbZr_xTi_1 − xO₃ material have been actively studied in the visible and near band-gap region, but data in the vacuum-ultraviolet spectral region is rather scarce. In this work we focus on well known interband transitions for the perovskite materials, 2p → dγ, located in VUV spectral region. Dielectric functions of chemical solution deposited and sputtered PZT were obtained in the spectral range 1-8.8 eV. Differences between the absorption maxima for chemical solution deposited and sputtered PbZr_xTi_1 − xO₃ samples near Kahn-Leyendecker 2p → dγ interband transition were found and are interpreted by change of interatomic distances. This is confirmed by different lattice constants. In the case of PbZr_xTi_1 − xO₃ film with microcracks, the void fraction was estimated from the effective medium approximation. Direct band-gap energies appear to be nearly the same for all reactive sputtered samples weakly depending of Zr/Ti concentration.     

Inductively coupled Cl2/O2 plasma: experimental investigation and modelling

In this work, we investigated the influence of the Cl₂/O₂ mixing ratio on both the plasma parameters and the volume densities of the neutral and the charged particles in inductively coupled plasma system. The change in the gas mixture composition from pure Cl₂ to O₂ was found to lead to an increase in the electron density and in the electron temperature. Accordingly, the addition of oxygen to chlorine influences electron-impact dissociation kinetics as well as it can cause a stepwise dissociation of Cl₂ molecules through their interaction with oxygen atoms. As a result, in Cl₂-rich plasma, a non-monotonic behaviour of the Cl atom density is possible.     

Surface characteristics of parylene-C films in an inductively coupled O2/CF4 gas plasma

In this article, we report the results obtained from a study carried out on the inductively coupled plasma (ICP) etching of poly-monochloro-para-xylylene (parylene-C) thin films using an O₂/CF₄ gas mixture. The effects of adding CF₄ to the O₂ plasma on the etch rates were investigated. As the CF₄ gas fraction increases up to approximately 16%, the polymer etch rate increases in the range of 277-373 nm/min. In this work, the atomic force microscopy (AFM) analysis indicated that the surface roughness was reduced by the addition of CF₄ to the O₂ plasma. Contact angle measurements showed that the surface energy decreases with increasing CF₄ fraction. At the same time, X-ray photoelectron spectroscopy (XPS) demonstrated the increase in the relative F atomic content on the surface.     

Enhanced ferroelectric properties of epitaxial Pb(Zr,Ti)O3 film with LaAlO3 buffer

PbZr_0.52Ti_0.48O₃ films (PZT) have been grown epitaxially on SrRuO₃/LaAlO₃ (SRO/LAO) substrates using pulse laser deposition. In order to improve the ferroelectric properties of the PZT, one LAO buffer was introduced into the interface of PZT/SRO. The dependence of the electrical properties of the PZT films on the buffer thickness was studied. When a 10-nm-thick buffer was used, the remnant polarization (Pr) of the PZT film reached 58 ± 5 μC/cm², 2 times larger than the sample without any buffer layer. The leakage current was reduced 1-2 orders of magnitude. Besides, the PZT film with 10-nm-thick LAO buffer also exhibited good fatigue endurance after 10⁹ switching cycles. These results could propose one effective way to improve the properties of ferroelectric films deposited on oxide electrodes.     

Ferroelectric properties of Pb(Zr,Ti)O3 films fabricated using a modified sol-gel based process

Ferroelectric PZT(20/80) thick films were fabricated by the screen printing method. And the PZT precursor solution was spin-coated on the PZT thick films to obtain a densification. Electrical properties of the thick films as a function of the firing temperature of the PZT precursor solution were investigated. The thickness of all thick films was approximately 60-62 μm. The porosity increased with increasing the firing temperature of the sol, and the porous microstructure and some large pores were observed above 700 °C due to the PbO evaporation. The relative dielectric constant, remanent polarization and dielectric breakdown strength of the specimen fired at 650 °C were 222, 16.5 μC/cm² and 73 kV/cm, respectively.     

Compositionally graded Pb(Zr,Ti)O3 thin films with different crystallographic orientations

Compositionally graded ferroelectric PbZr_xTi_1−xO₃ (PZT) films were deposited using a sputtering method and crystallized in situ at 500 °C. The films showed purely (100) or (111) crystallographic orientation when grown on Si/SiO₂/TiO₂/Pt substrates, while they exhibited c-axis epitaxial microstructure when prepared on MgO/Pt substrates. Their crystallographic orientation was controlled owing to a thin TiO_x layer sputtered on substrates prior to PZT deposition. Analysis performed by Auger depth profile clearly confirmed the variation of composition in the films. Coercive fields from 80 kV/cm to 200 kV/cm and remnant polarization as large as 45 μC/cm² were obtained. However, no typical offset was observed on hysteresis loops, unlike previous works related to graded PZT films.     

GaN etch rate and surface roughness evolution in Cl2/Ar based inductively coupled plasma etching

Cl₂/Ar based inductively coupled plasma (ICP) etching of GaN is investigated using photoresist mask in a consequential restricted domain of pressure < 1.2 Pa and radio frequency (RF) sample power < 100 W, for selective mesa etching. The etch characteristics and root-mean-square (rms) surface roughness are studied as a function of process parameters viz. process pressure, Cl₂ percentage in total flow rate ratio, and RF sample power at a constant ICP power, to achieve moderate GaN etch rate with anisotropic profiles and smooth surface morphology. The etch rate and resultant surface roughness of etched surface increased with pressure mainly due to dominant reactant limited etch regime. The etch rate and surface roughness show strong dependence on RF sample power with the former increasing and the later decreasing with the applied RF sample power up to 80 W. The process etch yield variation with applied RF sample power is also reported. The studied etch parameters result in highly anisotropic mesa structures with Ga rich etched surface.     

Influencing factors on the pyroelectric properties of Pb(Zr,Ti)O3 thin film for uncooled infrared detector

Zr-rich PZT thin films were synthesized by metallorganic decomposition and their dielectric and pyroelectric properties were investigated with different ratios of zirconium/titanium and poling condition. All the films became effectively (1 1 1) textured and well crystallized at the annealing temperature of 700 °C. With increasing Zr content, coercive field increased and voltage dependent capacitance curve appeared asymmetrical, indicating the presence of antiferroelectric phase, PbZrO₃, in film composition. The pyroelectric coefficient in the practically applicable temperature ranges of 20–60 °C was found to be maximum for the thin film with 0.85 mol of zirconium in PZT. Further increase in zirconium content led to severe deterioration in pyroelectric properties. The values of pyroelectric coefficient and figures of merit were greatly influenced by poling direction and temperature. The result was explained in terms of electric phase and state of polarization in film.     

Etch characteristics of IrMn thin films using an inductively coupled plasma of CH3OH/Ar

An inductively coupled plasma reactive ion etching of IrMn magnetic thin films patterned with Ti hard mask was studied in a CH₃OH/Ar gas mix. As the CH₃OH concentration increased, the etch rates of IrMn thin films and Ti hard mask decreased, while the etch profiles improved with high degree of anisotropy. The effects of coil rf power, dc-bias voltage to substrate and gas pressure on the etch characteristics were investigated. The etch rate increased and the etch profile improved with increasing coil rf power, dc-bias voltage and decreasing gas pressure. X-ray photoelectron spectroscopy revealed that the chemical reaction between IrMn films and CH₃OH gas occurred, leading to the clean and good etch profile with high degree of anisotropy of 90°.     

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.     

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.     

Mechanical properties determined by nanoindentation tests of [Pb(Zr,Ti)O3] and [Pb(Mg1/3Nb2/3)1−xTixO3] sputtered thin films

As the introduction of piezoelectric materials into micro electromechanical systems increases, there is a correlating requirement for understanding the mechanical properties of these films. We have investigated the mechanical properties of unpoled PZT [Pb(Zr,Ti)O₃] and PMNT [Pb(Mg_1/3Nb_2/3)_1−xTi_xO₃] thin films deposited by sputtering. In this study, nano-indentation, a technique which allows determination of the transverse mechanical properties, is used. It is the easiest method for assessing the biaxial elastic modulus and the hardness of thin films. It was confirmed that neither cracks, nor pile-ups, were observed for indentation depths below 20% of the film's thickness.The continuous stiffness method was used and allowed us to demonstrate that the indentation modulus decreases continuously with increasing grain diameter. This can be explained by the orientation changes of the crystallites with increasing grain diameter. The indentation modulus measured under load, or at almost null load (that is when the ferroelectric domains are or are not oriented by the stress) are coherent with those determined by the same method with a hard bulk ceramic. These results tend to show that the compliance C_ij of the hard bulk ceramic can possibly be used with sputtered thin films. The hardness is almost independent of the grain diameter (H_b ≅ 7.5 ± 0.9 GPa) and higher than that for the bulk PZT ceramics considered in this study. PMNT and PZT films have appreciably the same mechanical characteristics. No influence of the film thickness was found on the values of both of these parameters.     

Band bending at free Pb(Zr,Ti)O3 surfaces analyzed by X-ray photoelectron spectroscopy

This paper analyses in detail the core levels evolution of Pb(Zr,Ti)O₃, i.e. Pb 4f, Zr 3d, Ti 2p, O 1s in various conditions: absolutely freshly prepared sample, sample stored under air, and the effects of in vacuum annealing. The aim of the study is to quantify separately the chemical reactivity at the surface and the band bending effects due to the ferroelectric polarization. It is found that freshly prepared samples present mostly inwards (↓) polarization. This phenomenon is mostly revealed by the Ti 2p and O 1s spectra, manifested as a distinct component with 1.8 eV lower binding energy in the O 1s binding energy and by 1.1 eV in the Ti 2p binding energy. Sample aging under air suppresses the inwards polarization, and most signal comes from surfaces not presenting ferroelectric permanent polarization perpendicular to the sample surface. This process conducts also to the formation of Pb(CO₃)₂ on the surface. Annealing to temperatures up to 400 °C stabilizes a surface composed by a main part of surface without polarization perpendicular to the surface, and with some areas presenting outwards (↑) polarization. These areas have, most probably, different terminations, the polarized area being (Ti,Zr)O₂ terminated.     

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.     

Etch characteristics of indium zinc oxide thin films using inductively coupled plasma of a Cl2/Ar gas

Inductively coupled plasma reactive ion etching of indium zinc oxide (IZO) thin films masked with a photoresist was performed using a Cl₂/Ar gas. The etch rate of the IZO thin films increased as Cl₂ gas was added to Ar gas, reaching a maximum at 60% Cl₂ and decreasing thereafter. The degree of anisotropy in the etch profile improved with increasing coil rf power and dc-bias voltage. Changes in pressure had little effect on the etch profile. X-ray photoelectron spectroscopy confirmed the formation of InCl₃ and ZnCl₂ on the etched surface. The surface morphology of the films etched at high Cl₂ concentrations was smoother than that of the films etched at low Cl₂ concentrations. These results suggest that the dry etching of IZO thin films in a Cl₂/Ar gas occurs according to a reactive ion etching mechanism involving ion sputtering and a surface reaction.     

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.     

Growth and characterization of (Pb,La)(Zr,Ti)O3 thin film epilayers on SrTiO3-buffered Si(001)

Ferroelectric Pb_0.92La_0.08Zr_0.4Ti_0.6O₃ (PLZT) thin films were deposited on SrTiO₃-buffered Si(001) substrate by on-axis radio frequency magnetron sputtering. X-ray diffraction analysis revealed epitaxial growth of monocrystalline PLZT films, with an (001) rocking curve full width at half maximum of ∼ 0.3°. φ-scans showed 45° in-plane orientation of the perovskite unit cell relative to that of silicon. The elemental composition of the thin film heterostructure was examined by Auger sputter depth profiling measurements. The recorded profiles suggest that the SrTiO₃ buffer layer serves not only as a template for epitaxial growth, but also as a barrier suppressing Pb-Si interdiffusion between the PLZT layer and the Si substrate. The surface roughness of the PLZT layer was measured at ∼ 4 nm for films with ∼ 500 nm thickness. Wavelength dispersions for the refractive index (n) and the extinction coefficient (k) were obtained from spectroscopic ellipsometry measurements, with n ∼ 2.48 at the main communication wavelength λ = 1550 nm and k < 0.001 for λ > 650 nm. Recorded polarization vs. electric field loops for the PLZT epilayer, with a SrRuO₃ electrode layer interposed between PLZT and SrTiO₃, showed a remnant polarization P_r ≈ 40 µC/cm² and coercive field E_c ≈ 100 kV/cm. These findings suggest that the sputter-deposited PLZT thin films retain the functional properties critical to ferroelectric and electro-optic device applications, also when integrated on a semiconductor substrate.