AlN Films Research Articles

Achieving a High Thermally Conductive One Micron AlN Deposition by High Power Impulse Magnetron Sputtering plus Kick.

High-power impulse magnetron sputtering (HiPIMS) plus kick is a physical vapor deposition method that employs bipolar microsecond-scale voltage pulsing to precisely control the ion energy during sputter deposition. HiPIMS plus kick for AlN deposition is difficult since nitride deposition is challenged by low surface diffusion and high susceptibility to ion damage. In this current study, a systematic examination of the process parameters of HiPIMS plus kick was conducted. Under optimized main negative pulsing conditions, this study documented that a 25 V positive kick biasing for AlN deposition is ideal for optimizing a high quality film, as shown by X-ray diffraction and transmission electron microscopy as well as optimal thermal conductivity while increasing high speed deposition (25 nm/min) and obtaining ultrasmooth surfaces (rms roughness = 0.5 nm). HiPIMS plus kick was employed to deposit a single-texture 1 μm AlN film with a 7.4° rocking curve, indicating well oriented grains, which correlated with high thermal conductivity (121 W/m·K). The data are consistent with the optimal kick voltage enabling enhanced surface diffusion due to ion-substrate collisions without damaging the AlN grains.

Deposition and structural investigation of uniform AlN(100) films at wafer scale through RF magnetron sputtering

a-axis-oriented AlN(100) films are identified as promising candidates for surface acoustic wave devices owing to their high transversal-acoustic velocity. Achieving uniform films across a wafer scale is crucial for enhancing device performance and minimizing manufacturing costs. In this study, we employ radio-frequency magnetron sputtering to deposit AlN(100) films on 2-in Si(100) wafers. We further examine the influence of various process parameters on the nonuniformity of film thickness and structural properties, including crystallite size, microstrain, and dislocation density. The optimization of parameters leads to the selection of a gas flow ratio of N2:Ar = 4:7, a sputtering power of 160 W, and a substrate temperature of 350 °C. Under these optimized conditions, the AlN films not only demonstrate a preferred (100) orientation and remarkable crystallinity, as indicated by a full width at half maximum of the X-ray diffraction peak of just 0.03°, but also achieve an optimal film thickness nonuniformity of 1.66 %. Our results offer valuable insights for the wafer-scale fabrication of AlN(100) films, potentially enhancing industrial production yields and reducing costs.

Controlled exfoliation of wafer-scale single-crystalline AlN film on MOCVD-grown layered h-BN

In this work, we present a stress-free AlN film with improved crystal quality assisted by h-BN and demonstrate the mechanical exfoliation of wafer-scale single-crystal AlN freestanding membrane and reveal the controllable exfoliation mechanism of AlN. Uniform and continuous wafer-scale h-BN is directly grown on c-plane sapphire using a flow modulation epitaxy mode by metal-organic chemical vapor deposition. The nucleation and evolution processes of quasi-van der Waals epitaxy (QvdWE) of AlN on h-BN are revealed. It is found that O2-plasma-treated h-BN can effectively promote the nucleation islands of AlN and contribute to the release of biaxial stress and the reduction of dislocation density in the epilayers. Eventually, the QvdWE growth of a stress-free AlN film (0.08 GPa) is achieved, and wafer-scale mechanical exfoliation of the AlN membrane has been realized. This work provides an effective strategy for the quality improvement of III-nitride films and paves the way for the vertical structure and flexible deep-ultraviolet optoelectronic devices.

193 nm immersion photodetector with an ultra-high EQE of 83.7%

With the development of chip to high-density integration, the requirement of lithography precision is higher and higher. In this process, controlling the power of the lithography exposure light source is very important to improve the quality of the chip. However, most detectors are unable to conduct light detection in liquid environments, especially in the aspects of real-time detection and calibration of light power in immersion deep ultraviolet lithography. In this paper, the AlN film epitaxial on n-SiC substrate by MOCVD is used as the photoelectrode, based on which an immersion detector with a quick response to 193 nm vacuum ultraviolet (VUV) light is fabricated. Impressively, under 0 V bias, the detector achieves a high responsiveness (130 mA/W) and an EQE up to 83.7% under an excitation with lower light power (45 nW), illustrating its ability to perform highly efficient detection of light signals and underwater imaging in weak-light environment. In addition, the detector also has the shortest detection wavelength when compared with the immersion photodetectors reported so far. At the same time, the simulated immersion lithography monitoring experiment shows that the detector has good real-time monitoring ability. In a word, this work provides a novel method for detecting underwater light power and can work as reference for realizing the real-time monitoring of immersive lithography light sources in future applications.

Effects of gamma-ray irradiation on material and electrical properties of AlN gate dielectric on 4H-SiC

This article investigates the radiation effects on as-deposited and annealed AlN films on 4H-SiC substrates under gamma-rays. The AlN films are prepared using plasma-enhanced-atomic-layer-deposition on an n-type 4H-SiC substrate. The AlN/4H-SiC MIS structure is subjected to gamma-ray irradiation with total doses of 0, 300, and 600 krad(Si). Physical, chemical, and electrical methods were employed to study the variations in surface morphology, charge transport, and interfacial trapping characteristics induced by irradiation. After 300 krad(Si) irradiation, the as-deposited and annealed samples exhibit their highest root mean square values of 0.917 nm and 1.190 nm, respectively, which is attributed to N vacancy defects induced by irradiation. Under irradiation, the flatband voltage (V fb) of the as-deposited sample shifts from 2.24 to 0.78 V, while the annealed sample shifts from 1.18 to 2.16 V. X-ray photoelectron spectrum analysis reveals the decomposition of O-related defects in the as-deposited AlN and the formation of Al(NO x ) y compounds in the annealed sample. Furthermore, the space-charge-limits-conduction (SCLC) in the as-deposited sample is enhanced after radiation, while the barrier height of the annealed sample decreases from 1.12 to 0.84 eV, accompanied by the occurrence of the SCLC. The physical mechanism of the degradation of electrical performance in irradiated devices is the introduction of defects like N vacancies and O-related defects like Al(NO x ) y . These findings provide valuable insights for SiC power devices in space applications.

Epitaxial AlN film with improved quality on Si (111) substrates realized by boron pretreatment via MOCVD

This study investigated the growth of AlN epitaxial films on 2-in. Si(111) via metal-organic chemical vapor deposition. By introducing triethylboron (TEB) during trimethylaluminum pretreatment, a nearly crack free AlN epilayer with a thickness of 500 nm was acquired. The x-ray diffraction rocking curves of AlN (002) and (102) exhibited full width at half maximum values of 0.22° and 0.36°, respectively. Atomic force microscopy image analysis showed that after the introduction of TEB, larger grains appeared on the surface of Si(111) substrate, promoting the 3D growth pattern of the subsequent AlN buffer layer. Laytec reflection curves depicted the morphological transition from 3D to 2D growth mode during AlN deposition. At the same time, the curvature value was significantly reduced by 20 km−1, and the Raman spectrum peak of E2(high) shifted from 648.7 to 652.5 cm−1, indicating that the surface tensile stress was greatly reduced, effectively suppressing the crack problem of AlN on Si(111).

The elasticity and piezoelectricity of AlN containing charged vacancies

Wurtzite aluminum nitride (w-AlN) piezoelectric film plays a key role in modern MEMS actuators and sensors. Density functional theory can be used to predict the elastic and piezoelectric properties of AlN containing various charged vacancies, thereby obtaining methods for improving the piezoelectric properties. The theoretical investigations suggested that the Young’s modulus of defectants are smaller than that of intrinsic AlN, indicating that charged vacancies can effectively improve the elastic properties of AlN. A high piezoelectric coefficient d 33 values were obtained in V Al 3 − , V N 1 + and V N 3 + that may be a cause of the non-symmetrical charges assignation. This work suggests that the elasticity and piezoelectricity of AlN films can be effectively enhancing using the introduction of charged vacancies.

High performance of Ag/AlN/Si Schottky diode: Study of the DC sputtering power effect on its electrical properties

The DC sputtering power (DCSP) effect on the chemical composition, structural and electrical properties of Ag/AlN/Si Schottky diode was studied. The AlN films grown on Si substrate were examined by X-ray diffraction (XRD), Fourier Transformed Infra-Red (FTIR), and Raman spectroscopy. The analyzes by XRD, FTIR and Raman show stability at the level of the structure and the qualitative chemical composition of the AlN layer for DCSP of 200 W and 400 W. However, the quantity of chemical compounds on the surface of AlN is affected by this variation. From Current-Voltage (I-V) measurements, the ideality factor (n), barrier height (φb), and series resistance (Rs) were extracted by adopting Cheung functions. Diodes with an AlN interlayer elaborated at 400 W have good rectifying behavior with n, Rs and φb of 3.11, 1930 Ω, and 0.93 eV, respectively. The enhancement of the Ag/AlN/Si diode performance was attributed to the reduction of undesirable impurities in the Ag/AlN interface as well as the morphological improvement of the AlN layer. Capacitance-Voltage (C-V) measurements showed that carrier donor concentrations are strongly affected by DC sputtering power. The elaborate structures may provide new materials with electrical properties having a wide range of applications in electronics and photovoltaic field.

Design of a multi-physics coupling MEMS pressure sensor

The pressure measurement of explosion shock wave puts forward high requirements on the temperature resistance and response speed of the sensor. In this paper, a multi-physics coupling pressure sensor is designed to meet requirements. The sensor mainly consists of a Fabry-Perot cavity optical fiber sensing unit, a piezoelectric pressure sensing unit and a thermometric resistance temperature measurement module. Firstly, the structure of the sensor is designed. The top and bottom surfaces of the Fabry-Perot cavity are composed of a silicon diaphragm and a quartz glass. The piezoelectric pressure sensing unit is an AlN film including its electrodes. Pt thermometric resistance is developed to realize real-time temperature monitoring. Secondly, the fabrication process of the sensor is discussed, especially three key technologies. An Al film is sputtered to increase the reflectivity of the quartz glass. The SU-8 photoresist is applied to accurately control the thickness of Fabry-Perot cavity. Etching is adopted to work out the graphics of the AlN piezoelectric film. At last, a complete fabrication process of the sensor is described. The fabrication of multilayer films begins with a double-sided polishing silicon wafer, while Fabry-Perot cavity was from a double-sided polishing quartz glass. Then two parts of the sensor are combined to ensure the multi-physics coupling sensor to achieve complete function.

Single-Crystalline Bulk Acoustic Wave Resonators Fabricated With AlN Film Grown by a Combination of PLD and MOCVD Methods

Single-Crystalline Bulk Acoustic Wave Resonators Fabricated With AlN Film Grown by a Combination of PLD and MOCVD Methods

Relationship between Annealing and V/III Ratios during MNVPE of AlN Films

Relationship between Annealing and V/III Ratios during MNVPE of AlN Films

High‐Quality Nonpolar a‐Plane AlGaN Film Grown on Si‐Doped AlN Template by Metal Organic Chemical Vapor Deposition

High crystalline quality and flat a‐plane aluminum gallium nitride (AlGaN) films are obtained on Si‐doped AlN templates with a moderate silane (SiH4) flow rate by metal‐organic chemical vapor deposition (MOCVD). The effects of the SiH4 flow rate on the surface morphology, crystalline quality, stress state, and optical property of a‐plane AlN templates and AlGaN films are comprehensively investigated. As the SiH4 flow rate increases from 0 to 7.0 nmol min−1, the full width at half maximum of X‐ray rocking curve values along [0001]/[1–100] directions for the AlGaN films are monotonically reduced to 1124/1143 arcsec. Meanwhile, the surface root mean square roughness value is decreased to 0.88 nm. These achievements are attributed to the suppression of the anisotropy degrees and in‐plane stress of AlN templates. In addition, an excess SiH4 flow rate leads to deteriorated surface morphologies and increased basal plane stacking fault (BPSF) densities for both AlN and AlGaN films. This work suggests that doping AlN layers with an appropriate SiH4 flow rate is a promising route to obtain high‐quality a‐plane AlGaN films for efficient nonpolar deep ultraviolet (DUV) devices.

Structural and Optical Properties of Aluminium Nitride Thin Films Fabricated Using Pulsed Laser Deposition and DC Magnetron Sputtering on Various Substrates

Abstract Aluminium nitride thin films were fabricated using pulsed laser deposition and DC magnetron sputtering. Different technological parameters and the effects of different substrates on the optical and structural parameters of AlN samples were studied. An X-ray diffraction study was performed for the layer deposited on the Si3N4 substrate. A high-energy electron diffraction study was also carried out for the layer deposited on a KCl substrate. Transmission spectra of layers on quartz, sapphire, and glass substrates were obtained. An evaluation of the optical band gap of the obtained layers was carried out (Eg form 3.81 to 5.81 eV) and the refractive index was calculated (2.58). The relative density of the film (N1TN-AlN sample) is 1.26 and was calculated using the Lorentz-Lorentz relationship. Layers of aluminium nitride show an amorphous character with a polycrystalline region. It was shown that the properties of AlN films strongly depend on the method, growth conditions, and substrate used.

A high-performance infrared photoacoustic sensor with improved low-frequency response microphone

Infrared photoacoustic gas sensors with the advantages of good selectivity, low interference, fast response speed, good stability, high accuracy, good explosion-proof performance, high signal-to-noise ratio, and long service life, have developed rapidly in recent years. In order to solve the problem of poor low-frequency response performance of the MEMS piezoelectric thin film microphone sensor prepared with AlN and Mo thin films in infrared photoacoustic gas sensors, this article analyzes its principle and tests an improved solution. The internal stress distribution was changed through hot tempering experiments, significantly improving its structure. The article qualitatively and quantitatively analyzes the inherent mechanism of this phenomenon. The experimental results confirm that the improved scheme improves its response performance under low-frequency signals, with good stability and repeatability.

Improving the structural performance of low-temperature sputtered AlN on silicon substrate

Preparing high-quality AlN films at low temperatures is always highly demanded in plenty of application-fields, despite the high temperature is always necessary to enable the AlN crystallization. Therefore, improving the structural properties at low temperature is still challenging in the field. In the present work, a metal organic chemical vapor deposition (MOCVD) grown AlN nucleation layer is employed to improve the crystallinity and morphology of sputtered AlN on 6-inch Si (111) substrate at temperatures even as low as 100 °C where it is not principally possible to achieve crystallization of sputtered AlN. When compared with the as-sputtered AlN prepared even at 650 °C, it is found that the full width at half maximum of AlN (002) x-ray rocking curves is intensively decreased to 0.96° from 1.61°, and such a reduction indicates that the screw dislocation density is decreased from 7.31 × 1010 down to 2.14 × 1010 cm−2. In addition to the crystallinity, the morphology is also obviously improved that the root-mean-square roughness is reduced from 4.99 nm down to 0.83 nm in a scanned area of 3 × 3 μm2 through introducing AlN nucleation. Therefore, such a combination highlights the contribution of AlN nucleation grown by MOCVD in improving the structural properties of low-temperature sputtered AlN layer which is compatible with the manufacturing of Si integrated circuits.

Demonstration of controllable Si doping in N-polar AlN using plasma-assisted molecular beam epitaxy

In this study, we present the demonstration of controllable Si doping in N-polar AlN films grown on single-crystal AlN substrates by plasma-assisted molecular beam epitaxy. Through optimization of growth conditions, we obtained high-quality N-polar AlN films at 950 °C. However, our studies revealed that Si incorporation dramatically decreases at such high growth temperature. To enable higher Si incorporation, a hybrid low-temperature and high-temperature growth condition was developed by using Ga as a surfactant at low-temperature growth. By lowering the growth temperature of AlN to 750 °C, we were able to incorporate Si with concentrations as high as 2×1020 cm−3 and demonstrated an electron concentration as high as 1.25×1019 cm−3 at room temperature. The secondary ion mass spectrometry analysis revealed that, <0.2% Ga is incorporated in the AlN films grown with Ga as a surfactant at low temperature.

Structure and Electrical Conductivity of Thin AlN Films on Si

Structure and Electrical Conductivity of Thin AlN Films on Si

Metalorganic Chemical Vapor Deposition of AlN on High Degree Roughness Vertical Surfaces for MEMS Fabrication

AbstractAluminum nitride (AlN) grown on vertical surfaces can be utilized for the fabrication of advanced piezoelectric microelectromechanical systems (MEMS). The in‐plane motion of the parts of a MEMS element is possible when AlN is deposited on the vertical surfaces of the moving structure. For the best device performance, AlN must have high crystal quality, uniform coverage of the vertical sidewalls, and c‐axis crystalline orientation perpendicular to the plane of a vertical surface. The impact of the surface roughness (Rq) of the vertical sidewalls formed in Si using wet and dry etching methods on the crystal quality, crystallographic orientation, and uniformity of the metalorganic chemical vapor deposited (MOCVD) AlN thin films is studied in this paper. In both cases, AlN films demonstrated full sidewall coverage and grew crystalline in the c‐axis direction. AlN films grown on vertical Si surfaces achieved using anisotropic wet etching are highly crystalline and oriented in [0001] direction, while the films grown on vertical surfaces achieved using dry etching displayed a lower level of alignment with the Si sidewalls.

The AlN lattice-polarity inversion in a high-temperature-annealed c-oriented AlN/sapphire originated from the diffusion of Al and O atoms from sapphire.

AlN films are widely used owing to their superior characteristics, including an ultra-wide bandgap, high breakdown field, and radiation resistance. High-temperature annealing (HTA) makes it easy to obtain high-quality AlN films, with the advantages of a simple process, good repeatability, and low cost. However, it is always found that there is a lattice-polarity inversion from a N-polarity near the sapphire to an Al-polarity in the HTA c-oriented AlN/sapphire. Currently, the formation mechanism is still unclear, which hinders its further wide applications. Therefore, the formation mechanism of the polarity inversion and its impacts on the quality and stress profile of the upper AlN in the HTA c-oriented AlN/sapphire were investigated. The results imply that the inversion originated from the diffusion of the Al and O atoms from the sapphire. Due to the presence of abundant Al vacancies (VAl) in the upper AlN, Al atoms in the sapphire diffuse into the upper AlN during the annealing to fill the VAl, resulting in the O-terminated sapphire, leading to the N-polar AlN. Meanwhile, O atoms in the sapphire also diffuse into the upper AlN during the annealing, forming an AlxOyNz layer and causing the inversion from N- to Al-polarity. The inversion has insignificant impacts on the quality and stress distribution of the upper AlN. Besides, this study predicts the presence of a two-dimensional electron gas at the inversion interface. However, the measured electron concentration is much lower than that predicted, which may be due to the defect compensation, low polarization level, and strong impurity scattering.

Structure and Cathodoluminescence Properties in Tb3+ and Eu3+ Doped AlN Films

For the first time, Tb3+ and Eu3+ co‐doped AlN films were prepared using ion implantation, and the crystal structure and cathodoluminescence (CL) properties of films were investigated. Raman scattering and X‐Ray diffraction (XRD) show that high‐dose Tb3+ implantation leads to an increase in internal compressive stress. The non‐radiative resonant energy transfer was suggested between the Tb3+ and defects in the AlN host. The energy transfer mechanism between Tb3+ and Eu3+ in AlN films is discussed. Adjusting the dose ratio of Eu3+ with respect to Tb3+ allows for effective control of chromaticity coordinates and color temperatures.