AlN Films Research Articles

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.

(Invited) The Use of Plasmas for Isotropic Atomic Layer Etching

Atomic layer etching (ALE) is set to be a vital part of the advanced semiconductor manufacturing toolbox, known for its precise control of the film thickness and minimal damage. These benefits are possible due to the sequential self-limiting half-cycles that are employed within an ALE process. Initially, ALE was underestimated due to low etch rates, but it is now experiencing a renaissance due to the requirements imposed by further downscaling.1 The ALE community is mostly divided into two groups: plasma anisotropic and thermal isotropic etching. 2 In this work, the focus is on exploring isotropic plasma ALE, which is a relatively unexplored direction. This approach involves using plasma radicals to modify and/or etch material isotropically, while minimizing the directional ion component of the plasma. Isotropic plasma ALE can offer several benefits over strictly thermal ALE, such as higher etch rates, lower operating temperatures, and the ability to etch more resistant materials.In this talk we will first address some of the different techniques employed for plasma isotropic ALE in the literature. Subsequently, we will discuss our own work, which has focused on two isotropic plasma ALE chemistries. The first involves alternating between plasma fluorination and ligand-exchange half-cycles, this ALE chemistry has been found to be effective for etching Al2O3, HfO2, AlN, and GaN films.3,4 Surface contaminants and roughness were found to be reduced post ALE, an aspect that is particularly important for AlN and GaN films that are used in quantum, power semiconductor and LED applications. The second approach involves using diketone (e.g. acetylacetone, hexafluoroacetylacetone) doses followed by either H2 or O2 plasma exposures for ALE of Al2O3 and ZnO.5 The diketone in this process acts to etch the surface, however due to competitive adsorption of different diketone orientations an etch inhibition layer forms. The plasma step is then utilized to clean the surface, removing the self-limiting inhibitor layer, enabling etching to continue in the next cycle. This ALE chemistry diverges from the typical modification/removal ALE cycle, where a modified layer if often observed on the material post ALE. In comparison the diketone ALE chemistry does not rely on modification of the surface making it an ideal process for surface cleaning. This approach provides improved selectivity over the plasma fluorination process and also enables smoothing.Plasma isotropic ALE is a growing part of the ALE community that can help accelerate the adoption of ALE in academia and industry. The potential benefits of ALE are only just beginning to be explored, and more processes are needed to etch the ever-increasing range of materials utilized in IC manufacturing. Kanarik, K. J., Tan, S. & Gottscho, R. A. Atomic Layer Etching: Rethinking the Art of Etch. J Phys Chem Lett 9, 4814–4821 (2018).George, S. M. Mechanisms of Thermal Atomic Layer Etching. Acc Chem Res 53, 1151–1160 (2020).Chittock, N. J. et al. Isotropic plasma atomic layer etching of Al2O3 using a fluorine containing plasma and Al(CH3)3. Appl Phys Lett 117, 162107 (2020).Wang, H., Hossain, A., Catherall, D. & Minnich, A. J. Isotropic plasma-thermal atomic layer etching of aluminum nitride using SF6 plasma and Al(CH3)3. 1–14 (2022) doi:arXiv.2209.00150.Mameli, A., Verheijen, M. A., Mackus, A. J. M., Kessels, W. M. M. & Roozeboom, F. Isotropic Atomic Layer Etching of ZnO Using Acetylacetone and O2 Plasma. ACS Appl Mater Interfaces 10, 38588–38595 (2018).

Growth mechanism and field emission of B doped AlN films

This paper highlights the effect of boron dopant on the field emission and growth mechanism of AlN films. The films have been grown by reactive RF magnetron sputtering method. For undoped films, columnar AlN structure was obtained. In the case of boron doped AlN films, the structure growth proceeded gradually through four layers of different thicknesses and structures. It was found that boron favors the formation of an amorphous layer within which oxygen and boron based precipitates develops, retarding the growth of columnar morphology. Depth profiling X-ray photoelectron spectroscopy analyses confirm the presence of B-O, B-N, Al-B and Al-O groups.The study on the field emission (FE) properties of undoped and B doped AlN films on Si substrates indicates that the addition of boron allow to improve FE properties with low turn on field of 2.6 V/μm and low threshold filed of 3.07 V/μm. Such good field emission properties can be attributed to the formation of densely nanograined surface and the appearance of boron based groups.

Growth of SiC, AlN, and GaN Films on Silicon Parts of Arbitrary Geometry for Microelectromechanical Applications

Growth of SiC, AlN, and GaN Films on Silicon Parts of Arbitrary Geometry for Microelectromechanical Applications

Effect of flux rate on the growth of AlN films on sapphire by MNVPE

Effect of flux rate on the growth of AlN films on sapphire by MNVPE

Heteroepitaxy of N-polar AlN on C-face 4H-SiC: Structural and optical properties

To date, it has remained challenging to achieve N-polar AlN, which is of great importance for high power, high frequency, and high temperature electronics, acoustic resonators and filters, ultraviolet (UV) optoelectronics, and integrated photonics. Here, we performed a detailed study of the molecular beam epitaxy and characterization of N-polar AlN on C-face 4H-SiC substrates. The N-polar AlN films grown under optimized conditions exhibit an atomically smooth surface and strong excitonic emission in the deep UV with luminescence efficiency exceeding 50% at room temperature. Detailed scanning transmission electron microscopy (STEM) studies suggest that most dislocations are terminated/annihilated within ∼200 nm AlN grown directly on the SiC substrate due to the relatively small (1%) lattice mismatch between AlN and SiC. The strain distribution of AlN is further analyzed by STEM and micro-Raman spectroscopy, and its impact on the temperature-dependent deep UV emission is elucidated.

Microstructure evolution and mechanical behavior of magnetron sputtering AlN–Al nanostructured composite film

In this paper, a series of AlN–Al nanocomposite films are prepared by reactive magnetron sputtering. The effects of N2 flow rate on the microstructure and mechanical properties of the films are studied. The formation and evolution mechanism of the nanocomposite structure are revealed. The results show that with the decrease of N2 flow rate, the microstructure goes through three stages: pure AlN, amorphous Al surrounded nanocrystalline AlN and AlN nanoparticle reinforced Al matrix composite. Benefiting from the good wettability of Al on AlN ceramics, the film deposited at 6 sccm N2 flow rate forms a nanocomposite structure of about 8 nm AlN grains wrapped by 1–2 nm amorphous Al. The hardness of the films increases first and then decreases with the decrease of N2 flow rate, ranging from 4 GPa to 25 GPa. The toughness of the films is analyzed by the ratio of H/E, H3/E2, the normalized plastic depth (δH) and the morphology of large load indentation. The results show that the toughness of the nanocomposite film obtained at 6 sccm N2 flow rate is significantly improved while maintaining the hardness equivalent to that of pure AlN film. The improvement in toughness comes from the microcracks initiated in AlN hindered by the surrounding Al phase.

Full polarization reversal at room temperature in unsubstituted AlN

Room temperature ferroelectricity in unsubstituted AlN films is studied to examine the role of cation substitution into wurtzite materials. AlN and (Al0.7Sc0.3)N films deposited on (111) 0.5 wt. % Nb-doped SrTiO3 have a (0001)-orientation with different in-plane lattice alignments with respect to those of the substrate, depending on the composition and the deposition temperature. The AlN films deposited at 450 °C showed complete ferroelectric switching above 140 °C but local polarization switching at room temperature because a dielectric breakdown occurred before complete switching, while full polarization reversal was observed at all measurement temperatures for (Al0.7Sc0.3)N. Low-temperature deposition, such as at 250 °C, significantly enhanced the dielectric breakdown field and also increased leakage current. As a result, sufficient polarization switching at room temperature was observed in the AlN film deposited at 250 °C. Positive-up/negative-down pulse measurements showed remanent polarization of 150 μC/cm2 and a coercive field of 8.3 MV/cm, in agreement with the theoretical value and temperature dependence observed for the AlN film deposited at 450 °C. The observed coercive field value lies on the line composed of the previously reported data in Sc concentration dependence. This tendency implies that the reduction in the coercive field is primarily attributable to the alteration of crystal lattice anisotropy caused by Sc.