Residual Strain in the AlN Layers Deposited by Reactive-Gas Pulsed Sputtering Deposition
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Transactions on Electrical and Electronic Materials https://doi.org/10.1007/s42341-020-00204-0
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Residual Strain in the AlN Layers Deposited by Reactive‑Gas Pulsed Sputtering Deposition Jun‑Seck Choi1 · Dong‑Wan Ko1 · Sung‑Min Cho2 · Sang‑Tae Lee3 · Ji‑Ho Chang1,2 Received: 17 June 2019 / Revised: 23 May 2020 / Accepted: 30 May 2020 © The Korean Institute of Electrical and Electronic Material Engineers 2020
Abstract High-quality AlN films were sputtered onto c-Al2O3 substrates by reactive-gas pulsed sputtering deposition. The plasma power was varied from 300 to 800 W, and AlN films were sputtered at room temperature. AlN layer with a Full-Width at Half-Maximum (FWHM) at 1120 arcsec X-ray diffraction was achieved at the plasma power of 600 W. However, the AlN films revealed considerable residual compressive strain. The cause of the residual strain was discussed from the various points of view including surface color, Al-content in the film, residual strain and XRD FWHM, as well as the metallic cluster density. All results can be explained in terms of increase of Al-clustering especially at high sputtering power condition. Keywords AlN · PSD · Plasma power · Crystal quality · Residual strain
1 Introduction Aluminum nitride (AlN), an III–V family compound, has the structure of hexagonal wurtzite. The lattice constant is reported as a-axis = 3.111 Å and c-axis = 4.979 Å. [1]. As it features a wide bandgap (6.2 eV), high electrical resistivity (109–1011 Ω m), high resistance to breakdown voltage, high acoustic propagation speed, and low transmission loss, AlN has been studied for various applications such as ultraviolet light devices [2], surface acoustic wave devices [3, 4], and MEMS [5, 6]. AlN films have been prepared so far by various methods including chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), and reactive magnetron sputtering (RMS) [7–14]. However, those conventional growth methods have been restricted by narrow growth window, so the crystal quality was still unsatisfactory. Hence, it is note worth that pulsed sputter deposition (PSD) is useful for the growth of high-quality thin films * Ji‑Ho Chang [email protected] 1
Major of Electronic Materials Engineering, KMOU, Busan 49112, Korea
2
Department of Convergence Study on the Ocean Science and Technology, KMOU, Busan 49112, Korea
3
Department of Offshore Plant Management, KMOU, Busan 49112, Korea
at low growth temperatures [15]. Also, there has already been a report on the successful growth of high-quality AlN thin films on SiC substrates at room temperature [15]. However, to the best of our knowledge, the PSD of AlN films onto Al2O3 substrates has not been demonstrated yet. In this experiment, high-quality AlN films were prepared by PSD. Also, the influence of sputtering parameters on the quality of AlN thin films was discussed by focusing on the cause of the residual strain in the films.
2 Experiments AlN films were deposited using high-vacuum equipment with a load-lock ch
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