AlN Deposition Research Articles

High-Q film bulk acoustic resonator with high quality AlN film based on transfer method

Thin film bulk acoustic resonator (FBAR) with high quality factor (Q) is preferred for many communication applications. AlN film deposited in conventional FBAR fabrication process is poor, resulting in unsatisfactory device performance. This study demonstrated the comparison of two Si-substrate FBARs, adopting the same AlN deposition process by physical vapor deposition (PVD) method, however using different device fabrication method. Instead of depositing AlN film on Mo/SiO2/Si substrate in existing fabrication process, we deposited AlN directly on Si substrate by PVD to get better crystal quality piezoelectric layer of the FBAR. The full width at half maximum (FWHM) of rocking curve and surface roughness of AlN directly deposited on Si substrate are 1.4° and 1.96 nm, while those of AlN deposited on Mo/SiO2/Si substrate are 8.5° and 5.54 nm, respectively, indicating AlN deposited directly on Si substrate has a better crystal quality than that on Mo/SiO2/Si substrate. The dielectric loss of FBAR using AlN developed on Si substrate decreases from 0.4 Ω to 0.11 Ω leading to the increase of Q m from 470 to 830. By preserving the high quality AlN deposited on Si substate with film transfer method, the FBAR device enjoys an increasing of Q-values as high as 76%.

Highly textured AlN film synthesized on a graphene-like undercoating

Piezoelectric properties of polycrystalline AlN films are strongly dependent on the texture of the material. For a number of applications, such as microelectromechanical systems (MEMS) and acoustic resonators, it is important to have a well-defined (002) orientation of the crystallites. Using an original method of selective deposition of graphene-like films (GLFs) followed by a simple, safe and efficient chemical vapor deposition (CVD) of AlN, we clearly demonstrate that the GLF sublayer does enhance the texture quality of AlN columnar structures. The improved crystal orientation along the (002) direction for AlN film grown on GLFs is locally visualized using a scanning electron microscope (SEM) and quantitatively reinforced using Raman spectroscopy.

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.

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).

Study on c-axis orientation of AlN thin film on the influence Al buffer layer and Ar/N2 gas flow ratio in reactive magnetron sputtering

AlN is a piezoelectric material suitable for high temperature dynamic pressure sensing applications. Its piezoelectric coefficient purely depends on its crystal structure and growth direction. Highly c-axis (002) orientation exhibits high piezoelectric coefficient. Deposition of highly (002) oriented AlN thin film poses a challenge since such a growth depends on multiple process parameters and substrate material. In this work, AlN thin film was deposited using reactive radio frequency (RF) magnetron sputtering to correlate the gas flow rate and crystal orientation. AlN deposition was carried out on Si (100) substrate with and without 220 nm Al buffer layer under different Ar/N2 gas flow ratio. The samples were analyzed through X-ray diffraction technique. Results indicated that for the optimized value of 1:1 Ar/N2, (002) AlN intensity at its maximum for both AlN/Si and AlN/Al/Si samples. It is also observed that the use of 220 nm Al buffer layer on Si substrate enhanced the (002) intensity compared to AlN/Si.

Characterization and Reliability Analysis of Enhancement-Mode PEALD AlN/LPCVD SiNx GaN MISFET with In Situ H2/N2 Plasma Pretreatment

An effective in situ H2/N2 pretreatment technique for enhancement-mode GaN MISFET with a PEALD AlN/LPCVD SiNx Dual Gate Dielectric is presented. This technique features in situ H2 (15%)/N2 (85%) plasma pretreatment prior to AlN deposition. By using in situ H2 (15%)/N2 (85%) plasma pretreatment and a PEALD AlN protection layer, combined with an LPCVD SiNx gate dielectric, the quality of the AlN/GaN interface can be further improved due to the reduced interface trap densities between the AlN/GaN interface. The interface protection technique enables the successful integration of a high-quality PEALD AlN/LPCVD SiNx gate dielectric in an E-mode GaN MISFET with high performance, high stability, and high reliability. The fabricated enhancement-mode GaN MISFET exhibits a high gate swing and high channel effective mobility of 187.5 cm2/Vs, a threshold voltage of 2.9 V defined at 1 µA/mm, an on/off current ratio of 108, and a breakdown voltage of 1760 V defined at ID = 10 μm/mm. Our experiments showed a significant reduction in dynamic ON resistance and the suppression of current collapse when using the enhancement-mode GaN MISFET with PEALD AlN/LPCVD SiNx under high drain bias switching conditions, especially when the VDS is greater than the 60 V drain bias switch operating state.

Enhanced structural and optical properties of semipolar (112¯2) AlGaN film with insertion of AlN/AlGaN superlattice

The high-quality semipolar (112¯2) AlGaN films with high Al contents were successfully deposited on (101¯0) m-plane sapphire substrates with the insertion of AlN/AlGaN superlattice (SL) by metal-organic chemical vapor deposition technology. The dependence of structural and optical properties of the (112¯2) AlGaN film on the deposition parameters for the inserted AlN/AlGaN SL was investigated extensively premised on the characterization results of the optical microscope, atomic force microscopy, relative optical transmittance spectroscopy, high-resolution x-ray diffraction, and photoluminescence spectroscopy. It was discovered that the insertion of the AlN/AlGaN SL grown under an optimized stabilization time of 10 s between the deposition of AlN and AlGaN sublayers could be used to make significant enhancements in surface morphological characteristics, crystal quality, and optical properties of the (112¯2) AlGaN film. The mechanism for the defects reduction in the (112¯2) AlGaN film was revealed to be owing to the increase in bending and annihilating probability of the threading dislocations, basal-plane stacking faults, and other structural defects promoted by introducing sufficiently high desorbed Ga atom-induced vacancy concentration in the optimized thermal treatment process.

Over 200 cm2 V−1 s−1 of electron inversion channel mobility for AlSiO/GaN MOSFET with nitrided interface

By controlling a metal-oxide-semiconductor interface of an AlSiO/GaN system, the electron inversion channel mobility was significantly improved to 229 cm2 V−1 s−1 in a field-effect transistor. A 3 nm thick AlN interlayer formed by atomic layer deposition effectively suppressed the oxidation of the GaN surface and reduced the border traps, resulting in high channel mobility. An additional nitrogen radical treatment before AlN deposition further improved the subthreshold slope and the channel mobility, which was consistent with the lower charged defects extracted from the mobility analysis in the low effective normal field region.

Physics-separating artificial neural networks for predicting sputtering and thin film deposition of AlN in Ar/N2 discharges on experimental timescales

Understanding and modeling plasma–surface interactions frame a multi-scale as well as multi-physics problem. Scale-bridging machine learning surface surrogate models have been demonstrated to perceive the fundamental atomic fidelity for the physical vapor deposition of pure metals. However, the immense computational cost of the data-generating simulations render a practical application with predictions on relevant timescales impracticable. This issue is resolved in this work for the sputter deposition of AlN in Ar/N2 discharges by developing a scheme that populates the parameter spaces effectively. Hybrid reactive molecular dynamics/time-stamped force-bias Monte Carlo simulations of randomized plasma-surface interactions/diffusion processes are used to setup a physics-separating artificial neural network. The application of this generic machine learning model to a specific experimental reference case study enables the systematic analysis of the particle flux emission as well as underlying system state (e.g. composition, density, point defect structure) evolution within process times of up to 45 min.

Surface chemical mechanisms of trimethyl aluminum in atomic layer deposition of AlN

Two different pathways for decomposition of adsorbed trimethyl aluminum in the ALD of AlN have been investigated by computation chemistry. The two pathways give different saturation coverage and thus growth per cycle.

Low-Temperature Atomic Layer Deposition of AlN Using Trimethyl Aluminum and Plasma Excited Ar Diluted Ammonia

Low-Temperature Atomic Layer Deposition of AlN Using Trimethyl Aluminum and Plasma Excited Ar Diluted Ammonia

Structure and Electrochemical Behavior of AlN, AlTiN, and AlTiSiN Physical Vapor Deposition Coatings in 3% NaCl Solution

Structure and Electrochemical Behavior of AlN, AlTiN, and AlTiSiN Physical Vapor Deposition Coatings in 3% NaCl Solution

Effect of reactive gas condition on nonpolar AlN film growth on MnS/Si (100) by reactive DC sputtering

The effects of reactive gas flow conditions on nonpolar AlN film growth on MnS/Si (100) substrates using reactive DC magnetron sputtering were investigated. During AlN deposition at a substrate temperature of 750 °C, the MnS surface can be unintentionally nitrided, resulting in a decrease in the crystallinity of the AlN. Low-temperature growth of the AlN layer at 300 °C prevents this nitridation and results in the crystallization of nonpolar AlN. A N2 flow equal to 30% of the Ar sputtering gas flow was found to improve the crystallinity of the nonpolar AlN and to reduce nitrogen defects, which play an important role in interfacial reactions. Nitrogen defects promote the formation of alloys such as AlMn and MnSi that degrade the interface and can significantly decompose the MnS. A higher proportion of N2 improves the nonpolar AlN crystallinity, reduces the concentration of defects and suppresses reactions at the AlN/MnS interface.

Negative-ion bombardment increases during low-pressure sputtering deposition and their effects on the crystallinities and piezoelectric properties of scandium aluminum nitride films

Scandium aluminum nitride (ScAlN) films are being actively researched to explore their potential for use in bulk acoustic wave and surface acoustic wave resonators because of their good piezoelectric properties. Sputtering is commonly used in ScAlN film deposition. Unfortunately, it has been reported that film quality metrics such as the crystallinity and piezoelectric properties can deteriorate before the Sc concentration reaches 43% without an isostructural phase transition. One reason for this is bombardment with negative ions generated from carbon and oxygen impurities in the Sc ingots. Because the number of negative ions increases during low-pressure sputtering deposition, their effect on film quality may be considerable. In this study, we investigated negative-ion bombardment of the substrate during sputtering deposition and its effects on ScAlN crystallinity and piezoelectric properties. Negative-ion energy distribution measurements indicated that many more negative ions collide with the substrate during ScAlN film deposition than during AlN deposition. In addition, decreasing the sputtering pressure further increased the number of negative ions and their energies. It is well known that film quality improves at low pressures because increasing the mean free path reduces thermalization and scattering of sputtered particles. Although, AlN crystallinity and piezoelectric properties improved at low pressures, the properties of ScAlN films deteriorated dramatically. Therefore, the results indicated that ion bombardment increase at low pressure adversely effects ScAlN crystal growth, deteriorating crystallinity and piezoelectric properties. ScAlN films may be improved further by suppressing negative-ion bombardment of the substrate.

(Invited) Deposition of Crystalline AlN on Si and SiC Using Atomic Layer Annealing and Pulsed ALD/CVD

The low-temperature (< 400 oC) deposition of polycrystalline AlN films on silicon and silicon carbide is demonstrated by atomic layer annealing (ALA) using tris(dimethylamido) aluminum (TDMAA) and anhydrous N2H4 with an argon plasma treatment utilizing a DC or RF bias to tune the ion energy. ALA is a variant of ALD in which after the N2H4 and TDMAA are dose, a pulse of low energy rare ions ions is employed to induce crystalinity. Using TDMAA and N2H4 + Ar+ or Kr+ high-quality AlN films are deposited with large grain size and low oxygen/carbon contamination which can be used as a templating layer for further high speed AlN film growth via sputtering. The deposition of high quality AlN films deposited by ALA are successfully used as templates for sputtered AlN resulting in a >2x improvement in average grain size when compared to an analogous amorphous template layer. TEM imaging shows a crystalline interface between the AlN and Si(111) which is ideal for heat transfer. For SiC, DC bias is not effective due to the large bandgap so ALA must be performed with RF bias to accelerate the ions. Alternative high temperature (580oC thermal ALD with a CVD component using N2H4 and TDMAA can be employed to grow extremely large grain on SiC which can act as a template or rapid growth of highly crystalline AlN by sputtering.

Atomic Layer Deposition of AlN on Graphene

Graphene is a material with great promise for several applications within electronics. However, using graphene in any such application requires its integration in a stack of thin layers of materials. The ideal structure of graphene has a fully saturated surface without any binding sites for chemisorption of growth species, making film growth on graphene highly challenging. Herein, an attempt to deposit very thin layers of AlN using an atomic layer deposition approach is reported. It is demonstrated using X‐ray photoelectron spectroscopy that Al–N are formed in the films deposited on graphene and shown by scanning electron microscopy and atomic force microscopy that the films have an island morphology. These results may be considered promising toward the development of a growth protocol for AlN on graphene and possibly also for 2D AlN fabrication.

Adsorption configuration of AlN on sapphire surface using first-principles calculations

First-principles calculations of Al atom, N atom, and AlN molecule adsorption on sapphire surface have been carried out to explain the atomic-scale insight into the initial adsorption processes of AlN deposition on sapphire substrate. The results reveal that Al atom, N atom, and AlN molecule all form chemical bonds with substrate atoms when adsorbed on sapphire surface. Moreover, the bonding between AlN molecules and sapphire substrate are more complex than that of Al atom and N atom. Meanwhile, AlN with N atom closer to sapphire substrate has the largest charge transfer when adsorbed, which is consistent with its most complex bonding with substrate atoms. Furthermore, the bonds are formed deviating from the sapphire hexagon at an angle of about 30° or 60° when AlN molecule adsorbed. As a result, the lattice constant after the bonding of AlN shrinks and is closer to that of AlN, which directly reduces the crystal mismatch between AlN and sapphire. Thus, it is easier to obtain a template with a lattice closer to AlN. The results obtained provide theoretical guidance for obtaining better templates for growing AlN thin films on sapphire substrate.

GaN-on-silicon transistors with reduced current collapse and improved blocking voltage by means of local substrate removal

We report on the demonstration of low trapping effects above 1200 V of GaN-on-silicon transistors using a local substrate removal (LSR) followed by a thick backside ultra-wide-bandgap AlN deposition. Substrate ramp measurements show reduced hysteresis up to 3000 V. It has been found that the LSR approach not only enables the extension operation voltage capabilities of GaN-on-silicon HEMTs with low on-resistance but also allow for the reduction of trapping effects directly affecting their dynamic behavior. This work points out that a large part of the electron trapping under high bias occurs at the AlN nucleation layer and Si substrate interface.

Kinetic analysis of face-centered-cubic Ti1−xAlxN film deposition by chemical vapor deposition

Metastable Al-rich face-centered-cubic (fcc) TiAlN polycrystals have attracted attention as coating materials. However, the mechanism of chemical vapor deposition (CVD) of TiAlN has yet to be clarified. In this study, we performed a kinetic analysis of fcc-TiAlN deposition by investigating its dependence on deposition temperature and the partial pressures of metal sources. We deposited metastable fcc-Ti0.25Al0.75N polycrystals of a single phase that oriented in the deposition direction from TiCl4/AlCl3/NH3. The activation energy of TiAlN formation around 800 °C was less than 10 kJ/mol. TiAlN was deposited by a first-order reaction with different partial pressures of metal sources. TiAlN was formed by the combined deposition of TiN and AlN. The overall reaction rate constants for TiN and AlN and the mass transfer coefficients of the precursors TiCl4 and AlCl3 had similar values. Therefore, the deposition of fcc-TiAlN under the investigated experimental conditions was limited by precursor diffusion in the reactor.