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

Abstract

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.

Polarity inversion of AlN film grown on nitrided a-plane sapphire substrate with pulsed DC reactive sputtering

“…14 In this study, increasing the P O 2 meant an increased number of O atoms and decreased number of Ar atoms in the mixture gas. When an AlN film was sputtered at higher P O 2 , there were fewer Ar atoms in the chamber because the total pressure was kept constant.…”

“…The XRC-FWHM values of (0002) and (1012) The residual stresses along the a-and c-axes (σ a and σ c , respectively) of the AlN films sputtered on the nitrided a-plane sapphire at room temperature (RT) were calculated using a comparison with the AlN bulk values following the same equations in our previous study. 14 The dislocation was observed with a transmission electron microscope (TEM; Hitachi HighTechnologies, H-9000NAR) using an acceleration voltage of 300 kV and a magnification accuracy of ±5%.…”

“…The residual stress of the sputtered films on a substrate was considered to be mainly affected by a peening effect. 14 The peening effect is a bombardment of atoms or ions with a certain amount of kinetic energy on the growing surface during sputtering. The peening effect causes a compressive stress in the in-plane direction on the growing surface of the AlN film owing to the constraint of the underlying film.…”

Effects of Growth Conditions on AlN Layer Grown by Ga-Al Liquid Phase Epitaxy

“…In our group, we had developed a method for fabricating high-quality AlN thin lms by nitriding sapphire under controlled conditions 18,19) . Using the nitrided sapphire substrate as a template, DC-pulsed sputter deposition 20,21) and RF reactive sputtering techniques 22,23) have been investigated. Recently, authors have developed the Ga-Al liquid phase epitaxy (LPE) technique on the nitrided sapphire substrate, and have successfully grown 1.2-μm-thick AlN layer at 1573 K under normal pressure of N 2 gas for 5 h 24,25) .…”

Non‐Polar a‐Plane AlN Growth on Nitrided r‐Plane Sapphire by Ga–Al Liquid‐Phase Epitaxy

“…Our group has developed several techniques to fabricate AlN layers on sapphire substrates . In particular, we fabricated high‐quality single crystalline c ‐plane AlN thin films by thermal nitridation on c ‐ and a ‐plane sapphire substrates.…”