Applied Surface Science 257 (2010) 481–486 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Effect of sputtering anisotropic ejection on the optical properties and residual stress of Nb 2 O 5 thin ﬁlms Chuen-Lin Tien ∗ Department of Electrical Engineering, Feng Chia University, 100 Wenhwa Road, Setwen, Taichung, Taiwan, ROC article info Article history: Received 13 April 2010 Received in revised form 6 July 2010 Accepted 6 July 2010 Available online 14 July 2010 Keywords: Thin ﬁlm Niobium pentoxide Ejection angle Residual stress Ion-beam sputtering deposition abstract The effect of sputtering anisotropic ejection on the optical properties and internal stress of niobium pentoxide (Nb 2 O 5 ) ﬁlms prepared by ion-beam sputtering deposition (IBSD) was investigated experi- mentally. Thin ﬁlms were deposited on unheated BK7 glass substrates and silicon wafers at different ejection angles surrounding a metal target. The ejection angles varied from 0 ◦ to 75 ◦ in increments of 15 ◦ for each substrate. It was found that the optical constants of the Nb 2 O 5 ﬁlms were signiﬁcantly inﬂuenced by the sputtering ejection angle. The surface roughness and residual stress in the Nb 2 O 5 thin ﬁlms were also found to vary with the ejection angle. In this work, Nb 2 O 5 ﬁlms had a higher refractive index, lower absorption, lower stress and lower roughness when ﬁlms deposited at an ejection angle of 30 ◦ . © 2010 Elsevier B.V. All rights reserved. 1. Introduction Niobium pentoxide (Nb 2 O 5 ) is very interesting material with many practical applications because of its high refractive index and high transparency to visible light. Nb 2 O 5 is an excellent candidate for optical thin ﬁlm applications. It has been widely used as the high refractive index layers in optical interference ﬁlters [1], optical waveguides [2], gas sensitive materials [3] and electroluminescent devices [4]. There is a variety of techniques that can be utilized to investigate the basic properties of niobium oxide ﬁlms. In this study, ion-beam sputtering deposition (IBSD) was used to prepare Nb 2 O 5 thin ﬁlms. This method was chosen because of its advan- tages of adaptability to low temperature processes, low working pressure, and high impingement energy of the sputtered particles. These features allow niobium oxide ﬁlms to be nearly amorphous, more stable, high density and low absorption. The optical properties of thin oxide ﬁlms are strongly dependent on the deposition conditions. The study is focused on investiga- tion of the inﬂuence of the sputtering ejection angle on the optical and mechanical properties of thin Nb 2 O 5 ﬁlms. The position of a substrate can be described by the ejection angle, which represents the direction of sputtered particles ejected from the target to the substrate. The effect of the substrate position on the properties of thin ﬁlms deposited by sputtering has been investigated in previ- ous studies [5–8]. Takei et al. [5] have reported on the effect of ∗ Tel.: +886 4 24517250x3809; fax: +886 4 24516842. E-mail address: cltien@fcu.edu.tw. the ejection angle on the structure and super conducting prop- erties of Be ﬁlms formed by IBSD. Ishiyama and Taga [6] showed that the electrical properties of ion beam sputtered Ta 2 O 5 ﬁlms depended on the ejection angle of the sputtered particles and the primary ion energy. They discussed the effect of anisotropic ejec- tion during sputtering deposition on the electrical properties. It is well-known that the mechanical properties of ﬁlms are sensitive to the deposition technique employed. The residual stress in ion-beam sputtered ﬁlms plays an important role in optical component appli- cations. Castellano et al. [7] have noted that the stress level varies with the angle of deposition and ﬁlm material. However, there has been very little reported on the ejection angle dependence of opti- cal and stress properties of ion-beam sputtered Nb 2 O 5 thin ﬁlms. A similar phenomenon has been found in sputtering Ta 2 O 5 ﬁlms in a previous study [8]. In this article an extend study on the inﬂu- ence of anisotropic ejection on the optical properties and residual stress of sputtering Nb 2 O 5 thin ﬁlms is investigated. Furthermore, the surface morphology and microstructure of the ﬁlms were char- acterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). 2. Experiments 2.1. Thin ﬁlms preparation Niobium pentoxide (Nb 2 O 5 ) thin ﬁlms were deposited on BK7 glass substrates (1 in. in diameter; 1.5 mm in thickness) and P-type (1 0 0) silicon wafers by using IBSD technique. A schematic repre- sentation of the sputtering coater and the experimental setup is 0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.07.017