Two-step method for the deposition of AlN by radio frequency sputtering

Abstract

This paper presents a detailed study of the influence of deposition conditions on structural and morphological properties of AlN thin films synthesized on c-sapphire substrates by radio frequency (RF) reactive sputtering. After the optimization of deposition parameters such as RF power and substrate temperature, the substrate bias has been identified as a critical variable to improve the structural properties of the AlN layers. The use of negative bias leads to a decrease of the full-width at half-maximum (FWHM) of the rocking curve of the AlN(0002) x-ray reflection and an increase of the grain size. However, 2θ/ω x-ray scans of layers grown under negative bias reveal lattice disorder at the AlN/sapphire interface, which is attributed to the highly accelerated positive ions (Al + , N + , N 2 + ) arriving to the substrate at the initial stages of the deposition process. In order to prevent this interface degradation, we propose a twostep deposition method which consists of starting the growth with an unbiased AlN buffer layer, at least 30 nm thick, followed by AlN deposition under negative bias. This procedure results in high-quality AlN layers with FWHM of the rocking curve of the (0002) reflection of 1.63°, grain size of~40 nm and root-mean-square surface roughness of 0.4 nm.

Morphology and arrangement of InN nanocolumns deposited by radio-frequency sputtering: Effect of the buffer layer

“…As summarized in Table 1, the full-width at half-maximum (FWHM) values of the InN(0002) rocking curve decreases from 2.4°, when using the low-growth-rate InN buffer layer, to 1.5°and 1.2°, in the case of us-AlN and bs-AlN buffer layers, respectively. The upgrade of the crystalline quality of negatively-biased AlN layers has been previously reported, being attributed to an increase of the kinetic energy of the species reaching the growing surface [22,25]. Thereby, the enhanced structural properties of the bs-AlN-based buffer layer, compared to us-AlN, results in a better crystal quality of the subsequent InN film.…”

“…The columnar growth type present in the layers is then attributed to the used slightly N-rich growth conditions, as it is confirmed by the larger InN deposition rate obtained for columnar-mode growth compared to the almost compact InN sample (S3) (see Table 1). This columnar deposition could be hindered by the increase of the nucleation points density when using a biased AlN buffer which induces initial lattice disorder at the interface AlN-sapphire [22] enabling, in turn, the grain coalescence. This behavior has been also observed in InN layers grown on GaN-templates, in which a change in the nucleation layer could lead to a structural change in InN with its morphology evolving from columnar to compact [26].…”

“…This bias value was previously optimized for the deposition of RF sputtered AlN films [22]; -S4: a double AlN buffer layer consisting of 30 nm of us-AlN followed by 30 nm of bs-AlN. This growth sequence was formerly reported to provide the best crystalline quality of RF sputtered AlN [22].…”

“…It has also been reported that biasing the substrate can lead to an improvement of the structural quality of RF-sputtered AlN through an increase in the kinetic energy of the impinging ions [22]. In this work, we investigate the influence of biasing the AlN-on-sapphire buffer layer on the nanostructure of the InN films deposited on top by RF reactive sputtering.…”

InN-Based Optical Waveguides Developed by RF Sputtering for All-Optical Applications at 1.55 <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>

“…The synthesis of the buffer was carried out following a previously optimized two-step deposition method [11]. The InN layer deposition was performed at 40 W of RF power, 450 ºC of substrate temperature, 3.5 mTorr of sputtering pressure and pure nitrogen (6N) atmosphere.…”