Quality Of Aluminum Nitride Films Research Articles

Improving quality of AlN films on GaAs substrate via in-situ plasma pre-treatment in plasma enhanced atomic layer deposition

Using plasma-enhanced atomic layer deposition (PEALD), we achieved the low-temperature growth of aluminum nitride (AlN) films on GaAs substrate. The effect of in-situ plasma pre-treatment on AlN films growth has been thoroughly investigated in detail. After in-situ plasma pre-treatment, the surface roughness closely matched that of the substrate, the interfaces between AlN films and GaAs substrate were extremely sharp, and the film density increased from 3.05 g/cm3 to 3.15 g/cm3. Additionally, the oxygen content in the AlN films decreased from 35.5 % to 18.8 %. This indicates that in-situ plasma pre-treatment is an effective method for reducing impurity content and improving film quality.

Effect of H Plasma Treatment of the Nucleation Layer on AlN Epitaxy in Microwave Plasma Chemical Vapor Deposition

The crystallinity of nucleation layers has significant influence on the crystallinity of aluminum nitride (AlN) epilayers. In this work, the etching effect of hydrogen (H) plasma was used to improve the nucleation-layer crystallinity. AlN nucleation layers were first cooled in a H-plasma atmosphere; then, AlN films were deposited on the processed nucleation layers, and the whole epitaxial process was carried out in high-temperature microwave plasma chemical vapor deposition (MPCVD) without the participation of ammonia. X-ray rocking curves (XRCs) showed that the cooling process obviously improved the crystal quality of AlN films, which was attributed to the preferential etching effect of H plasma on low-crystallinity nucleation islands. When a H2 flow rate of 135 sccm was used to process the nucleation layer, the AlN film with the narrowest (002) XRC full width at half-maximum (FWHM) of 86 arcsec was obtained. Possible growth mechanisms were suggested for the observations.

Improving the crystal quality of AlN films by nanosecond laser annealing

Aluminum nitride (AlN) thin film of thickness 300 nm grown on sapphire substrate was annealed by a nanosecond laser at a wavelength of 532 nm. The laser energy values were 2 J, 3 J, 4 J, and 4.5 J, respectively. In order to increase the absorption of laser energy by the sample, 50 nm thick tungsten films were deposited on the left half of the sample. Surface morphology and Raman spectrum of AlN films were characterized before and after annealing using scanning electron microscope (SEM) and Raman spectrometer, respectively. The SEM micrographs have shown that the surface of AlN film had a large number of voids before annealing. After annealing, the size of the voids becomes smaller and their number decreases with the increase of laser energy density. The full width at half maximum (FWHM) of AlN film was roughly 6-10 cm−1 before annealing and 4-8 cm−1 after annealing. The results showed that the surface morphology and FWHM of the AlN films were improved after laser annealing compared with those before annealing. Finally, COMSOL Multiphysics simulated the temperature field change of AlN film after laser irradiation and the evolution of its surface.

Resolving Impurities in Atomic Layer Deposited Aluminum Nitride through Low Cost, High Efficiency Precursor Design.

A heteroleptic amidoalane precursor is presented as a more suitably designed candidate to replace trimethylaluminum (TMA) for atomic layer deposition of aluminum nitride (AlN). The lack of C-Al bonds and the strongly reducing hydride ligands in [AlH2(NMe2)]3 (1) were specifically chosen to limit impurities in target aluminum nitride (AlN) films. Compound 1 is made in a high yield, scalable synthesis involving lithium aluminum hydride and dimethylammonium chloride. It has a vapor pressure of 1 Torr at 40 °C and evaporates with negligible residual mass in thermogravimetric experiments. Ammonia (NH3) plasma and 1 in an atomic layer deposition (ALD) process produced crystalline AlN films above 200 °C with an Al:N ratio of 1.04. Carbon and oxygen impurities in resultant AlN films were reduced to <1% and <2%, respectively. By using a precursor with a rational and advantageous design, we can improve the material quality of AlN films compared to those deposited using the industrial standard trimethylaluminum and could reduce material cost by up to 2 orders of magnitude.

Growth of Semi-Polar (101¯3) AlN Film on M-Plane Sapphire with High-Temperature Nitridation by HVPE.

Aluminum nitride (AlN) films were grown on the m-plane sapphire by high-temperature hydride vapor phase epitaxy (HVPE). The effect of high-temperature nitridation on the quality of AlN film was studied. The high-temperature nitridation is favorable for the formation of semi-polar single (103) orientation AlN film, the quality of which shows strong dependence on the nitridation temperature. The full width at half maximum of X-ray diffraction for (103) AlN film was only 0.343° at the optimum nitridation temperature of 1300 °C. It is found that the nano-holes were formed on the surface of substrates by the decomposition of sapphire in the process of high-temperature nitridation, which is closely related to the quality improvement of AlN. At the critical nitridation temperature of 1300 °C, the average size of the nano-holes is about 70 nm, which is in favor of promoting the rapid coalescence of AlN micro-grains in the early stages. However, the size of nano-holes will be enlarged with the further increase of nitridation temperature, which begins to play a negative role in the coalescence of AlN grains. As a result, the grain size will be increased and extended to the epilayer, leading to the deterioration of the AlN film.

Smoothing the surface roughness of aluminum nitride films obtained by magnetron sputtering

When producing aluminum nitride films used in radio electronic devices on bulk (BAW) and surface acoustic waves (SAW), such as resonators, filters, sensors, by magnetron sputtering, a problem arises due to the large surface roughness of the films, as a result of which acoustic waves scatter on irregularities and, as a result, deterioration of the resonance characteristics of the devices. In this paper, we study the possibility of improving the surface quality of aluminum nitride films by smoothing the surface roughness upon irradiation with a beam of cluster argon ions. It is shown that the effect of low-energy (10 V/atom) argon cluster ions leads to surface modification, removal of residual chemical contaminants in the near-surface layer, and additional smoothing of the film surface at an ultra-small thickness of the etched layer (<100 nm).

Research of surface morphology of aluminum nitride films obtained by magnetron sputtering method

In this paper, we studied the surface morphology of aluminum nitride films obtained by magnetron sputtering intended for use in electronic devices. The main problem with this method of film formation is the large surface roughness of the film; therefore, the task to be solved is to improve the surface quality of aluminum nitride films by smoothing the surface roughness.

Mechanical, Corrosion and Biological Properties of Room-Temperature Sputtered Aluminum Nitride Films with Dissimilar Nanostructure.

Aluminum Nitride (AlN) has been long time being regarded as highly interesting material for developing sensing applications (including biosensors and implantable sensors). AlN, due to its appealing electronic properties, is envisaged lately to serve as a multi-functional biosensing platform. Although generally exploited for its intrinsic piezoelectricity, its surface morphology and mechanical performance (elastic modulus, hardness, wear, scratch and tensile resistance to delamination, adherence to the substrate), corrosion resistance and cytocompatibility are also essential features for high performance sustainable biosensor devices. However, information about AlN suitability for such applications is rather scarce or at best scattered and incomplete. Here, we aim to deliver a comprehensive evaluation of the morpho-structural, compositional, mechanical, electrochemical and biological properties of reactive radio-frequency magnetron sputtered AlN nanostructured thin films with various degrees of c-axis texturing, deposited at a low temperature (~50 °C) on Si (100) substrates. The inter-conditionality elicited between the base pressure level attained in the reactor chamber and crystalline quality of AlN films is highlighted. The potential suitability of nanostructured AlN (in form of thin films) for the realization of various type of sensors (with emphasis on bio-sensors) is thoroughly probed, thus unveiling its advantages and limitations, as well as suggesting paths to safely exploit the remarkable prospects of this type of materials.

Effect of working pressure and annealing temperature on single-phase AlN films

Single-phase aluminum nitride (AlN) films were synthesized on Si substrates by RF sputtering at different working pressures and different annealing temperatures. Effect of two factors on crystal quality, surface roughness and molecular structure was investigated. As the working pressure rose, the crystal quality of AlN films first increased and then decreased, reaching the best quality at the pressure of 0.7 Pa in the range of 0.3–2.5 Pa. When the annealing temperature was 100 °C, root-mean-square surface roughness was greatly reduced from 1.510 nm to 0.554 nm. In addition annealing technology could evidently enhance Al–N covalent bond density. In short, this work provides an effective approach to fabricate high-quality AlN (1 0 0) films for future applications of AlN-based devices.

Effect of sputtering pressure on crystalline quality and residual stress of AlN films deposited at 823 K on nitrided sapphire substrates by pulsed DC reactive sputtering

Aluminum nitride (AlN) is a promising material for use in applications such as deep-ultraviolet light-emitting diodes (UV-LEDs) and surface acoustic wave (SAW) devices. In the present study, the effect of sputtering pressure on the surface morphology, crystalline quality, and residual stress of AlN films deposited at 823 K on nitrided a-plane sapphire substrates, which have high-crystalline-quality c-plane AlN thin layers, by pulsed DC reactive sputtering was investigated. The c-axis-oriented AlN films were homoepitaxially grown on nitrided sapphire substrates at sputtering pressures of 0.4–1.5 Pa. Surface damage of the AlN sputtered films increased with increasing sputtering pressure because of arcing (abnormal electrical discharge) during sputtering. The sputtering pressure affected the crystalline quality and residual stress of AlN sputtered films because of a change in the number and energy of Ar+ ions and Al sputtered atoms. The crystalline quality of AlN films was improved by deposition with lower sputtering pressure.

Effect of sputtering power on surface characteristics and crystal quality of AlN films deposited by pulsed DC reactive sputtering

Aluminum nitride (AlN) is a promising material for use as a substrate for AlGaN‐based ultraviolet LEDs and piezoelectric devices. Among the sputtering methods, pulsed DC sputtering provides a superior growth rate and dense AlN films because of the promotion of two‐dimensional growth. In this study, the effect of sputtering power on surface characteristics, crystal quality, and residual stress of AlN films deposited by pulsed DC reactive sputtering on a nitrided sapphire substrate was investigated. The homoepitaxial growth of AlN films on this substrate gives high crystal quality compared with the use of other substrates such as sapphire or Si for heteroepitaxial growth. Surface damage on the AlN films increased with an increase in sputtering power, leading to a rough surface. At all sputtering powers, c‐axis oriented AlN films were obtained in this study. From the difference in lattice constant compared with the AlN bulk, the inplane compressive stress of the AlN sputtered films was confirmed as residual stress. Residual stress in the AlN films was mostly caused by a peening effect rather than a thermal expansion coefficient difference.

Underlayer Influence on AlN Deposition by Reactive Magnetron Sputtering

Sputter deposited aluminum nitride (AlN) thin film is the preferred piezoelectric material for microelectromechanical systems (MEMS) devices, such as film bulk acoustic resonator (FBAR) resonators and accelerometers. Silicon dioxide (SiO2) is usually used as a sacrificial layer which will be etched with BOE eventually to release the membrane. In the article, thermal oxide, as well as several types of SiO2 with different properties made by plasma enhanced chemical vapor deposition (PECVD) were selected as the underlying film. The influence of the surface morphology of silicon dioxide underlayer on the crystallinity of reactively sputtered c-axis oriented AlN thin films was investigated. The results show that the quality of AlN films is affected by the surface roughness of the underlying SiO2 film. The full width at half maximum (FWHM) of the x-ray rocking curve for 1μm AlN film ranged from 7.8¢ª to 1.5¢ª depending on the properties of PECVD SiO2 films. The rougher surface of underlayer worsen the crystallinity of AlN films, while adding chemical mechanical planarization (CMP) step was found to improve FWHM to 1.2¢ª. This paper discusses possible mechanisms for the influence of underlayer surface morphology on the properties of sputter deposited AlN films.

Microstructure of epitaxial AlN layers on sapphire substrates deposited by physical vapor deposition

ABSTRACTAsymmetric (10L) XRD peaks have been employed as a measure of epitaxial quality for aluminum nitride (AlN) nucleation layers (NL) deposited on sapphire substrate. Epitaxial AlN films have been deposited on 2-6” sapphire substrate by reactive sputtering. FWHM of AlN (103) and (105) were found to be an excellent indicator of quality of AlN films for GaN growth. AlN films produced nucleation layers with highly reproducible microstructure and GaN film growth. NLs had in-plane and out-of-plane texture as evident by the pole-figure results and selected area diffraction pattern. Based on electron microscopy results, AlN film thickness for complete atomic ordering was estimated to be 6-7 nm and most of the edge dislocations were seen in the first 20 nm of the film. Excellent thickness and texture uniformity were seen on planar and patterned sapphire substrates. A compressive stress of 2.9±0.2 GPa was seen in our BKM films. The maximum screw and edge dislocation densities of films were found to be ∼3 x 108 cm−2 and ∼9 x 109 cm−2 respectively. The root mean square roughnesses of A-polar films were found to be &lt; 0.3 nm.

直流反应磁控溅射在氮化的蓝宝石衬底上制备AlN薄膜

Aluminum nitride ( AlN ) films were prepared successfully on sapphire and nitrided sapphire substrates by reactive DC magnetron sputtering. The effect of nitridation of sapphire substrate on the growth of AlN films was studied. The films were characterized by X-ray diffraction ( XRD ) , atomic force microscopy ( AFM ) and optical ab- sorption spectrum. XRD patterns of AlN films exhibited a strong preferential c -axis orientation , and nitridation of sap- phire substrate could improve the crystal quality of AlN films and also decrease the residual stress of films. But AFM results revealed that the grain size distribution of films deposited on nitrided sapphire substrates was not more homoge- nous than that of films deposited on sapphire substrates , and optical absorption results also showed nitridation of sap- phire substrate nearly had no effect on the optical behavior of AlN films.

Effects of pulse parameters on the pulsed-DC reactive sputtering of AlN thin films

A series of studies on the pulsed-DC reactive sputtering of highly (002)-textured aluminum nitride (AlN) thin films was conducted with systematically adjusted pulse parameters including reverse voltage, pulse frequency, and pulse duration. The film quality was evaluated by the full width at half maximum (FWHM) of the (002) rocking curve as well as the (002) peak intensity. In the asymmetric bipolar mode, the FWHM increases while the peak intensity decreases with reverse voltage, implying a detrimental effect of reverse voltage on the quality of AlN film. Whereas in the unipolar mode, the film quality improves with pulse frequency as evidenced by the decreasing FWHM and increasing peak intensity. It is also found that there is a critical pulse duration of about 500 μs, beyond which the FWHM starts to increase while the peak intensity starts to decrease due to target poisoning. Typical measurements on thus-optimized AlN film show a roughness of 1.7 nm and a (002) FWHM of less than 1.9°.

Influence of the texture on Raman and X-ray diffraction characteristics of polycrystalline AlN films

The phonon modes of various polycrystalline aluminum nitride (AlN) films deposited by RF reactive sputtering with different textures have been studied. The comparison between Raman spectra and X-ray diffraction (XRD) patterns was performed to find out the influence of the texture on the phonon mode in polycrystalline AlN films. The E 2 (high) mode and the A 1 (TO) mode were observed in Raman scattering along the growth c axis. The orientation and the crystal quality of AlN film have a great impact on the phonon vibration. The deterioration of (002) orientation and the appearance of other orientations on the XRD pattern lead to enhancement of A 1 (TO) mode in the film. The broadening of the Raman peaks can be associated with degeneration in crystal quality. Furthermore, by combining the energy shift of E 2 (high) mode with the measured residual stress, the Raman-stress factor of the polycrystalline AlN films is found to be − 4.1 ± 0.3 × 10 − 9 cm − 1 /Pa for E 2 (high) phonon.

PENNING DISCHARGE PLASMA SOURCE AND ITS APPLICATION TO SYNTHESIS OF NANOSTRUCTURED AlN FILMS

Penning discharge (PD) sputtering deposition technique is developed and first used in synthesis of nanostructured aluminum nitride (AlN) films. The advantage of the present PD is that discharge current is linearly dependent on power supply voltage. Maximal discharge current up to 180 mA is obtained for power supply voltage of 5 kV with a ballast resistor of 25 kΩ. In contrast, the discharge voltage is only 290 V. Installation of smaller value of the ballast resistor will yield larger discharge current, whereas discharge voltage remains nearly unchanged, which is an important factor employed to the synthesis of high quality of AlN films. The preferred orientations of nanoscale AlN particles distributions on the surface of the substrates are observed. The increase of the power voltage (discharge current) for sputtering deposition yields different patterns of the nanoscale particles, but sizes of the particles are unchanged. Typical A 1– TO and A1– LO bands in Raman spectra of the films are identified, respectively.

Effect of AlN Film Thickness and Top Electrode Materials on Characteristics of Thin-Film Bulk Acoustic-Wave Resonator Devices

Highly c-axis-oriented aluminum nitride (AlN) thin films were deposited on Mo electrodes by reactive RF magnetron sputtering and their thickness effects on thin-film bulk acoustic-wave resonator (FBAR) characteristics are presented. The results obtained in this study show that thick AlN films have a strong c-axis orientation and tend to promote a small rocking curve full-width at half-maximum (FWHM), but a high grain size and a high surface roughness, hence degrading the characteristics of FBARs. The characteristics of FBARs depend not only the thickness and quality of AlN films, but also the thickness of the top electrode and the type of material used. Specifically, an increase in either AlN film or top electrode thickness increases parallel resonant quality factor (QP), but reduces effective electromechanical coupling coefficient (keff2). However, the resonance provides a maximum keff2 when AlN film thickness approaches the fundamental one-half-wavelength. The effects of the type of top-electrode material and AlN film thickness on the keff2 and quality factor of the fabricated FBARs are also discussed.