AVS 69 Session TF-ThP: Thin Film Poster Session

Background

Along with the miniaturization of semiconductor devices, equipment using plasma processes such as dry etcher is required to have high plasma durability and low particle generation. Yttrium oxide (Y₂O₃) is used as a passivation film on the surface of the parts which are equipped in the chamber. In recent years, Y₂O₃ films with high heat resistance are required to etch low-volatility or difficult-to-etch materials and developed for new plasma processes. In this study, we focused on the difference of thermal expansion between quartz substrate and Y₂O₃ film, then report that Y₂O₃ film with high heat resistance of 500°C was obtained introducing intermediate layer Y₂O₃-SiO₂

Experiment

In this study, Y₂O₃ and Y₂O₃-SiO₂ films were deposited on quartz substrate using the ion-assisted deposition method (IAD). The Y₂O₃-SiO₂ film which is the intermediate layer was formed by two-source co-evaporation of Y₂O₃ and SiO₂. Plasma resistance was evaluated by measuring the etched depth of the film using a profilometer after etching with CF₄ plasma. For heat resistance, the presence or absence of cracks was evaluated using an optical microscope after annealing in atmospheric environment. In addition, crystallinity and morphology were confirmed by X-ray diffraction measurement (XRD) and scanning electron microscopy (SEM), respectively.

Results and Discussion

On the basis of the XRD analysis results, the obtained Y₂O₃ film crystal structure was a cubic crystal with the (222) orientation as the main peak. In addition, a uniform surface morphology without voids and pores was obtained from surface and cross-sectional SEM observation. The etching rate was 0.009 μm/hr, which was 1/100 of quartz. Moreover, in the heat resistance test results, there were no cracks at 400 °C, and cracks occurred at 500 °C. In the quartz/Y₂O₃-SiO₂/Y₂O₃ stacked film intended to improve heat resistance, there were no cracks at 500 °C, but cracks occurred at 600 °C. Thus, by introducing the intermediate layer, Y2O3 stacked film having heat resistance at 500 °C was obtained. The reason for the improvement on heat resistance is presumed that the thermal expansion coefficient of Y₂O₃-SiO₂ has an intermediate value between quartz (0.5 ppm/°C) and Y₂O₃ (7 ppm/°C), which reduces thermal strain and stress. The detailed mechanism is under analysis.

In recent years, transparent conductive films have been used for touch panels, liquid crystal displays, solar cell electrodes, and other applications. Currently, indium tin oxide (ITO) or other oxide semiconductors are the mainstream materials that combine transparency and electrical conductivity. On the other hand, indium (In) is a rare metal with limited the production area, which limits its stable supply and causes significant price fluctuations. In this study, we focused on zinc oxide (ZnO) with sufficient resources and improved the transparency and electrical conductivity of ZnO by doping titanium (Ti).

The sample substrate was a slid glass with 15 x 10 mm in a size that ultrasonically cleaned with ethanol for 10 minutes. The oxide thin films were deposited by reactive sputtering using the multi-process coating system (BC5146, ULVAC Corp.). The deposition conditions were Zn sputtering input power of 20 W with an Ar gas flow rate of 20 sccm and an O₂ gas flow rate of 5 sccm to obtain a film thickness of 50 nm. At the same time, Ti was doped from 0 to 40 % with calculating from the Ti sputtering rate. For example, in the case of 10 % in the Ti doping, the sputtering rate of Zn is 0.085 nm/s (RF input power 20 W) and that of Ti is 0.0094 nm/s (DC input power 53 W).

For optical properties, transmittance was measured using a UV-visible spectrophotometer (UV-2550, Shimadzu Corp.). For electrical characteristics, the electrical conductivity was calculated from the resistance value of the deposited sample using a four-point probe (RG-5, NPS Corp.) with a pin spacing of 1.0 mm. Crystal structure analysis was performed by X-ray diffraction (SmartLab, Rigaku Co., Ltd.) at an X-ray incidence angle of 0.4 degrees.

The optimum condition for the transmittance and electrical conductivity was obtained at ZnO doped with Ti of 30 %. The transmittance and electrical conductivity of the film were 95.2 % and 739 S/m, respectively.

When synthesizing copolymer thin films, accurate measurements of the polymer composition are essential to understanding and optimizing material properties. Determining the composition of thin films synthesized from the solution phase (e.g. spin coating, or spin casting) is straight forward, since researchers generally know the composition of the polymer before fabricating the film. In polymer vapor deposition of copolymers, the characterization of composition relies instead on techniques like Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). While helpful in some applications, chain re-orientation at the polymer-air interface and adventitious carbon often bias XPS data – making it an unreliable tool for standalone film compositional measurement. FTIR transmission spectra are more commonly used to determine composition by comparing peak areas associated with known chemical functionality. This technique uses the Beer-Lambert law to relate composition to absorption and pathlength (film thickness). To obtain composition from this method, it is necessary to measure film thickness (generally using ellipsometry) and assume that all films being analyzed have equal density. For certain chemistries, copolymerization changes the polymer packing, causing density to vary significantly with composition. When uncorrected, the assumption of constant density leads to large errors and non-physical compositions. In the process of collecting film thickness from spectroscopic ellipsometry, the refractive index of the film is also measured. Because the density and refractive index are related through the Lorentz-Lorenz equation, film density is easily estimated. By applying a density correction, we demonstrate significant improvements to the measurement of composition from FTIR at essentially zero cost. Density correction improves the accuracy of compositional analysis using data that is already collected in many labs, making it a simple and cost effective improvement to existing methods.

The reactions of trisilylamine (TSA) precursor on silicon nitride (SiN) thin film in atomic layer deposition (ALD) process was investigated by density functional theory (DFT). A N-rich, H-terminated surface model was used to simulate the surface after NH₃ plasma treatment. Two reaction mechanisms were proposed depending on the abundance of excess hydrogens on the surface: (1) TSA reactions with primary amine (-NH₂) and (2) TSA reactions with hydrogenated primary amine (-NH₃). The source of excess hydrogen originates from the H radical from the NH₃ plasma which can survive on the SiN surface by being captured by the surface amine groups. Results show that in the first mechanism, the rate-determining step for TSA chemisorption is the TSA-adduct formation step which requires overcoming an energy barrier of 0.67eV predicted by climbing-image nudged elastic band (CI-NEB) method (i.e., TSA(g) + -NH₂ → -NH-SiH₃ + (SiH₃)₂NH(g)). In the second mechanism, the rate-determining step is the hydrogen transfer step with a much lower energy barrier of 0.34eV (i.e., TSA(g) + -NH₃ → •SiH₃(g) + (SiH₃)₂NH(g) + -NH₂).

The cathode material Li_xCoO₂ (LCO) and related intercalation oxides are widely used in lithium-ion batteries and are now being investigated for applications in catalysis and neuromorphic computing[1][2][3], leading to great interest in their surface properties and mechanisms. The ability of LCO to change its composition from stoichiometric LiCoO₂ to Li_xCoO₂ is the key feature for most technological applications. This process changes its atomic and electronic structures. Oriented islands and epitaxial thin films of Li_xCoO₂ grown on SrTiO₃ (STO) have been studied at the Nanospectroscopy beamline of the Elettra storage ring using photoemission electron microscopy (PEEM) and low energy electron microscopy (LEEM)[4].

Different surface morphologies have been studied during Li deintercalation, including the phase coexistence regime. Stoichiometric LCO islands and films were delithiated in situ under UHV conditions by preferential Ne⁺ sputtering followed by thermal treatment. Surface crystallinity and morphology were maintained throughout the experiments. The effects of delithiation on island size, distribution and the surrounding substrate and wetting layer were characterized. A shift in the valence band position towards the Fermi energy marks the IMT and is accompanied by a change in the surface conduction, observed as changes in the charge shift of the PEEM spectra. This has allowed us to relate the Li content to the metallization and therefore emergence and propagation of the IMT.

The spatial resolution of PEEM provides further and more detailed information on phase formation and evolution, as well as nucleation points and domain sizes. We were able to isolate the contribution of the different phases formed in the 0.5<x<1 region.

[1] N. Nitta, F. Wu, J. T. Lee, and G. Yushin, Materials Today, 18 (5), (2015).

[2] Z. Lu, H. Wang, D. Kong, K. Yan, P. C. Hsu, G. Zheng, H. Yao, Z. Liang, X. Sun, and Y. Cui, Nature Communications 5:1 5, 1 (2014).

[3] E. J. Fuller, F. el Gabaly, F. Léonard, S. Agarwal, S. J. Plimpton, R. B. Jacobs-Gedrim, C. D. James, M. J. Marinella, and A. A. Talin, Advanced Materials 29, 1604310 (2017).

[4] A. Locatelli, L. Aballe, T. O. Mentes, M. Kiskinova, and E. Bauer, Surface and Interface Analysis, 38, 1554–1557 (2016).

There have been very few studies of antiperovskite structure Mn₃GaN in general although it was seen in molecular beam epitaxial growth as a second-phase precipitate when growing MnGaN [1]. And so, we grow thin films of Mn₃GaN on MgO (001) substrates using rf N–Plasma MBE. In this abstract, we will discuss the growth recipe and surface study of Mn₃GaN. To take advantage of noncollinear antiferromagnetic thin films in spintronics applications, it is important to study their spin structures using local probes like spin polarized scanning tunnelling microscopy. Initially we start with room temperature scanning tunneling microscopy of MBE–grown Mn₃GaN surfaces and later will progress toward variable low temperature spin–polarized scanning tunnelling microscopy. In our work, Mn₃GaN is deposited at 250 ± 10°C with a Mn: Ga: N flux ratio of 3:1:1. We keep the Ga:N ratio fixed using an RF plasma nitrogen source. The sample surface is continuously monitored throughout the growth using reflection high energy electron diffraction. During growth, the RHEED pattern was observed to be highly streaky, indicating an atomically smooth surface. In addition, we observed half-order fractional streaks (2x pattern) in the [100] direction. The calculated in–plane lattice constant based on RHEED is 3.89 ± 0.06 Å. This value is very close to the theoretical lattice constant a of Mn₃GaN (3.898 Å) [3] and with the in–plane experimental value for sample growth by sputtering (3.896 Å); and in that work, the authors also observed a 2x pattern [2]. We also measure the out–of–plane lattice constant using X–ray diffraction. For the major 002 peak, the value calculated is 3.84 ± 0.06 Å which also agrees well with the theoretical value (3.898 Å) [3] and with the experimental reported c value (3.881 Å) [2]. Rutherford backscattering confirms a stoichiometry of 3:1:1.

This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE–FG02–06ER46317.

References:

[1] KH. Kim, KJ. Lee, HS. Kang, FC. Yu, JA. Kim, DJ. Kim, KH. Baik, SH. Yoo, CG. Kim, YS. Kim, “Molecular beam epitaxial growth of GaN and GaMnN using a single precursor,” Physica Status Solidi (b) 241(7), 1458 (2004).

[2] T. Hajiri, K. Matsuura, K. Sonoda, E. Tanaka, K. Ueda, & H. Asano. “Spin–Orbit-Torque Switching of Noncollinear Antiferromagnetic Antiperovskite Manganese Nitride Mn₃GaN,” Physical Review Applied, 16(2), 024003(2021).

[3] E. F. Bertaut, D. Fruchart, J. P. Bouchaud, and R. Fruchart. Diffraction Neutronique de Mn₃GaN. Solid State Commun. 6, 251–256 (1968).

The periodic Mo/Si bilayers were deposited on Si substrate by RF magnetron sputtering with cooling system.The effects of substrate temperature on the surface roughness and interface of Mo/Si bilayers were investigated by atomic force microscopy (AFM), and high resolution transmission electron microscopy (HRTEM), The AFM measurements showed the Mo/Si bilayers to have a uniform morphology with a very low surface roughness value under 0.2 nm. It was found that the Mo-on-Si and Si-on-Mo interfaces of Mo/Si bilayers were clearly observed by HRTEM in sputtering without using cooling system. The thickness of Mo-on-Si interface was almost 0.45 nm in the Mo/Si bilayers. However, the thickness of the Si-on-Mo interface was increased with increasing layers of Mo/Si bilayers. It was increased from 0.9 to 1.36 nm. After using cooling system in sputtering, the temperature was 15 ℃, the Mo-on-Si and Si-on-Mo interfaces were all under 0.1 nm.The improved interface of Mo/Si bilayer was attributed the interdiffusion of Mo/Si bilayer was been improved in sputtering by cooling system.

This research aims to present the potential and advantages of implementing optical emission spectroscopy (OES) as a non-invasive technique to investigate and optimize the plasma-assisted atomic layer deposition (ALD) process for AlN thin films. OES enables the identification of species present in the plasma and analysis of the light emitted, rendering it as a crucial tool for evaluating the reactant species delivered to the surface and for gaining unique insights into the surface reaction products and possible mechanisms of the deposition process. The incorporation of time-resolved OES measurements allows for the determination of optimal precursor dosing and plasma exposure times necessary for saturating half-reactions, thereby enhancing the efficiency of the ALD process. Additionally, the versatility of time-resolved OES as a process monitoring tool for plasma-assisted ALD processes on production equipment provides the capability for real-time detection of process faults and monitoring of reactor wall conditions.

AlN thin films were deposited by employing trimethylaluminum (TMA) in combination with various nitrogen plasmas (N2/H2/Ar). The growth experiments were carried out in a hollow-cathode plasma-ALD reactor at 200 °C and 100 W RF plasma power. The light emission during the plasma half-cycle is coupled into a multimode fiber through one of the optical access ports via a collimating lens which feeds a compact spectrometer unit spanning from 300 to 1000 nm with a wavelength resolution of ~2 nm. The spectral data obtained from the AlN deposition procedure was assessed by examining the emission spectrum within the initial few milliseconds of a plasma half-cycle that followed a TMA dose, and contrasting it with the emission spectrum observed towards the end of the same half-cycle, when the plasma had become adequately saturated. The differences in the emission spectra are due to the reactions initiated by plasma species with precursor fragments adsorbed at the surface. At the end of the plasma step, when the surface reactions have saturated, the emission spectrum recorded during the ALD cycle resembles that of a steady-state plasma. The results indicate that time-resolved OES measurements can help determine optimal precursor dosing and plasma exposure times to enhance the efficiency of the ALD process. Future work involves a more detailed investigation of surface ligand-exchange reactions, plasma-surface interactions, and formed reaction byproducts in real-time to gain a deeper insight into the ALD process.

Titanium dioxide (TiO₂) thin film has been deposited on glass and silica substrates by using Sol-Gel spin coating method. The effect of annealing temperature on the structure, surface morphology, optical and electrical properties of these films are characterized by Raman, XRD, FT/IR, UVvis and four-point-probes measurements. XRD confirms the anatase phase of TiO₂. Maximum crystal sizes are found to be ~31 nm on silica and ~23 nm on glass substrates at 500^oC respectively. Electrical resistivity decreased with increasing annealing temperature having the higher value on glass substrates observed.

Lanthanide oxide films have many applications in optics, catalysis, and semiconductor devices. Er₂O₃ films have useful properties that arise from its high dielectric constant, a large band gap energy, high refractive index, and thermodynamic stability at high temperatures. These properties have led to the investigation of Er₂O₃ films for possible inclusion in CMOS devices, antireflective and protective coatings on solar cells, and passivation layers for III-V semiconductors. Er₂O₃ films have been grown by many techniques, including PVD, CVD, and ALD. ALD is an important technique, since it gives Angstrom-level thickness control and can afford 100% conformal coverage in high aspect ratio features. ALD precursors reported to date for Er₂O₃ films have problems that include low reactivity toward water as a co-reactant, oxidation of substrates when ozone is used as the co-reactant, and variable thermal stabilities. Recently, we described a series of volatile and thermally stable lanthanide(III) complexes that contain enaminolate ligands.¹ We report here detailed synthetic studies of the Er(L¹)₃ precursor complex, its ALD precursor properties, and its use in the ALD of Er₂O₃ films using water as the co-reactant. Depending upon the reaction conditions during precursor synthesis the compounds Er(L¹)₃, Er(L¹)₃(L¹H), or K[Er(L¹)₄] can be isolated. The reaction conditions can be selected to provide high yields of Er(L¹)₃. The volatility and thermal stability characteristics of Er(L¹)₃ are favorable for use as precursors for Er₂O₃ and other rare-earth oxides. An ALD window in the growth of Er₂O₃ films using Er(L¹)₃ with water as the co-reactant was observed from 150 to 250 °C, with a growth rate of 0.25 Å/cycle. The films were characterized by electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. Advantages of Er(L¹)₃ include its simple synthesis, good volatility and high thermal stability, and high reactivity with water to afford Er₂O₃ films. This class of new ALD precursors has the potential to enable more widespread use of the favorable properties of rare-earth oxide compounds and can be expanded to multi-component complex oxides containing rare earths.

Titanium nitride deposition-sputtered sensors have been shown to function as sensitive pH sensors. The electrical conductivity and inertness of TiN advocates for this functionality. Literature has shown results only for DC-sputtered TiN pH sensors, however. This research identifies and analyzes the differences between DC-sputtered TiN sensors and those fabricated with HiPIMS and HiPIMS with Kick. The methods differ in their power source. Note that DC-sputtering involves a DC power signal. HiPIMS stands for High Power Impulse Magnetron Sputtering and uses a square wave power signal. HiPIMS with Kick also requires a square wave, but involves a short pulse before relaxing to the equilibrium voltage. For all sputtering methods, the power input to the titanium target averages at 250W. Additionally, the initial chamber pressures are all 10^-6 torr. Some settings differ to achieve consistent deposition rates between the techniques, such as the working pressure (3-5 mtorr). To create the sensors, TiN is deposited onto a ceramic screen-printed electrode (with gold metallic ink). There are four leads: active, counter, reference, and signal. The active and signal leads connect to the active electrode. The counter and reference leads connect to their own respective electrodes. TiN is deposited onto the active electrode. The reference electrode is composed of Ag/AgCl. In aqueous environments, a potential difference forms between the active and reference electrodes. This voltage is used to determine the pH of the solution. To compare the sensors, measured properties include sensitivity, hysteresis, response time, and drift. To measure sensitivity, the Nernst equation is employed to determine the linear relationship between voltage and pH. The slope of this graph directly relates with sensitivity, with steeper slopes denoting higher sensitivity (and vice versa). To measure hysteresis, the sensor measures a sequence of pH buffer solutions in time-contained steps (i.e. a pH sequence 4, 7, 10, 7, 4 limited to 240 seconds each). The voltage difference that exists between a first-stage measurement and a second-stage measurement of the same solution denotes hysteresis. For measuring response time and drift, the sensor is placed into a solution for a duration of time. Response time is the duration that exists between the initial exposure to the solution and the point when the output is first within 0.1 pH of the true value. Drift is longitudinal. Measured over the course of hours, drift is the output decay rate from the sensor's initial steady state. The Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) are used characterize the TiN depositions. The SEM characterizes the topographic features of the depositions. The AFM characterizes the film thickness.

Weak interactions, non-uniformity and powdery assemblies limited the wide application of metal organic frameworks (MOFs) in devices^{[1, 2]}. We report a new strategy for area-selective assembly of MOF particles to prepare a thin film with the assistance of atomic layer deposition (ALD)^[3-5].The mechanism of this strategy is utilizing ALD pretreatment to induce the growth ofhydroxy double salt (HDS) nanosheets on substrates, and the HDS nanosheets are then chemicallyconverted into a MOF structure^[6]. Self-assembled hierarchically porous MOF films such as ZIF-67 (Co), ZIF-8 (Zn), Ni-MOF (Ni), PCN-333 (Fe), MIL-53 (Fe), etc. were formed on both flat and complex three-dimensional (3D) substrates at a combination of gas and liquid fabrication approaches, and can be precisely patterned by photolithography^[7-10]. We demonstrate that the MOF film obtained possesses excellent electrochemical activity and can be applied in biosensor for ultra-high sensitivity and a low limit of detectiontowards glucose, lactic acid and dopamine^[5-7]. This strategy is promising to prepare MOF film-based on-chip devices with advanced functions.

References:

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[2] Adv. Mater. 2018, 30, 1802011

[3] Zhe Zhao, et al. Adv. Funct. Mater. 2019, 29, 1906365.

[4] Zhe Zhao, et al.J. Mater. Res. 2020, 35, 701.

[5] Zhe Zhao, et al. Chem. Eng. J. 2021, 417, 129285.

[6] Zhe Zhao, et al. J. Mater. Chem. A 2020, 8, 26119.

[7] Zhe Zhao, et al. Nano Today 2022,42, 101347.

[8] Zhe Zhao, et al. J. Materiomics 2020, 6, 209.

[9] Zhe Zhao, et al. Chin. Sci. Bull. 2021,doi: 10.1360/TB-2021-0093.

[10] Zhe Zhao, et al. Electrochem. Energ. Rev., 2022, 5, 31.