Influence of sputtering parameters on structures and residual stress of AlN films deposited by DC reactive magnetron sputtering at room temperature H.Y. Liu, G.S. Tang, F. Zeng n , F. Pan n Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China article info Article history: Received 13 June 2012 Received in revised form 6 September 2012 Accepted 4 October 2012 Communicated by D.W. Shaw Available online 16 October 2012 Keywords: A1. X-ray diffraction B1. Nitrides B2. Acousto-optic materials B2. Piezoelectric materials B2. Semiconducting aluminum compounds abstract A series of AlN films were deposited on (100) silicon substrate at room temperature with varying deposition conditions, i.e., nitrogen concentration in sputtering gases (N 2 /(N 2 þAr)), sputtering pressure, sputtering power, etc. The evolution of c-axis preferential orientation and residual stresses of the synthesized films were investigated as a function of deposition parameters. It is demonstrated that highly c-axis oriented AlN thin films, with full width at half maximum value of the rocking curve of 3.11, can be obtained on Si (100) at room temperature with a nitrogen concentration of 40%, a sputtering pressure of 0.4 Pa and sputtering power of 145 W. The degree of c-axis orientation increases with decrease in nitrogen concentrations and sputtering pressure. The stresses of films gradually increase to high compressive state as the nitrogen concentration increases and decrease to slightly compressive state with increasing sputtering power. A transition from tensile to compressive is observed with varying sputtering pressure. A nearly unstressed AlN film, with compact structure and surface roughness of ca. 0.929 nm, was synthesized under the optimized deposition condition, which is suitable for surface acoustic wave and bulk acoustic wave applications. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Aluminum nitride (AlN), one of the most interesting III–V compound semiconductor with a hexagonal close-packed wurt- zite structure, has drawn great attention over the past decade due to the fact that AlN exhibits a variety of outstanding physical properties, viz., a direct band gap (6.2 eV), high melting point (3273 K), high thermal conductivity (285 W/mK) and very high dielectric constant (8.5) [1,2]. Besides, due to its excellent acoustic properties with high acoustic velocity (6000 m/s), high tempera- ture stability and compatibility with conventional silicon manu- facturing technologies, aluminum nitride is also a promising candidate as a piezoelectric material for application in electro- acoustic devices such as surface acoustic wave (SAW), bulk acoustic wave (BAW) and microelectromechanical system (MEMS) [3–5]. As for applications in micro- and nano-electronics as a piezo- electric material, AlN films are expected to have a microstructure with smooth surface and highly preferential orientation, hence, a large variety of deposition methods, such as vapor phase epitaxy [6,7], molecular beam epitaxy [8,9], chemical vapor deposition [2,10], ion beam nitridation [11], pulsed laser deposition [12,13] and reactive sputtering, etc. [14–17], have been extensively used to fabricate device-grade AlN films. Even though there are special advantages in the fabrication of lattice-matched nitrides of group III semiconductors for techniques such as metallorganic chemical vapor deposition, molecular beam epitaxy and chemical vapor deposition, high process temperatures often result in degradation of the substrate and AlN layers due to substantial thermal damage. Therefore, exploring low temperature processes is neces- sary. Among the aforementioned sputtering techniques, reactive sputtering method is a good candidate for fabricating highly c-axis orientated AlN films and is extensively used due to its various advantages, viz., (a) an easy process with significant degree of freedom to manipulate the growth parameters, (b) the ability for large-scale production with relatively low cost and low substrate temperature, (c) the ease in handling and operation, etc. Since traces of non-(002) planes paralleling to substrate appearing in AlN film can result in the degradation of piezo- electric response [3], and intrinsic stress in the films can have a major impact on the performance and reliability of the devices, many of the sputtering parameters, such as gas composition, sputtering pressure, substrate temperature, gas flow rate as well as sputtering power, are manipulated in order to obtain a highly c-axis oriented AlN film with tiny stress. In this article, we report on the successful use of DC reactive magnetron sputtering technique for the fabrication of highly (002)-oriented AlN films on Si (100) at room temperature. The process conditions such as sputtering pressure, sputtering power, nitrogen concentration, Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2012.10.008 n Corresponding authors. E-mail addresses: zengfei@mail.tsinghua.edu.cn (F. Zeng), panf@mail.tsinghua.edu.cn (F. Pan). Journal of Crystal Growth 363 (2013) 80–85