The Texture and Electrical Properties of Zr and ZrN x Thin Films Deposited by Dc Sputtering
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THE TEXTURE AND ELECTRICAL PROPERTIES OF Zr AND ZrNx THIN FILMS DEPOSITED BY DC SPUTTERING CHUAN-PU LIU; HENG-GHIEH YANG Department of Materials Science and Engineering, National Cheng-Kung University, Tainan, Taiwan 701 ABSTRACT Zr and ZrNx thin films are grown on Si(001) by DC magnetron sputtering. The detailed microstructure evolution and its corresponding electrical properties are systematically studied with various processing parameters including applied power, N2/Ar ratio, substrate bias and substrate temperature by 4-point probe, EPMA and XRD. It is found that while the negative substrate bias can decrease the resistivity of both Zr and ZrNx thin films, the texture microstructure of each thin film in the series is changed differently. As increasing N2/Ar ratio, the resistivity decreases in the beginning and then increases rapidly, which results from the variations of compositions and phases, while this minimum resistivity point shifts to a higher N2/Ar ratio for the films sputtered under higher applied power. The substrate temperature not only decreases the ZrNx film resistivity, but also increases the (002) preferred orientations most efficiently. The cause of each phenomenon is briefly discussed. Finally, two samples showing different degrees of (002) to (111) textures are annealed to investigate the diffusion barrier properties from a sandwich structure of Cu/ZrNx/Si(001). Results from 4-point probe reveal that the film with higher degree of (111) textures has a superior thermal stability. INTRODUCTION Due to their superior mechanical properties, Zr and ZrNx thin films have long been largely applied in hard coatings [1]. In addition, ZrNx possesses not only the lowest electrical resistivity of 13.6 mW-cm in bulk among all the transition-metal nitrides but also the better thermal stability (DH= -87.3 kcal/mole) than TiN (DH= -80.4 kcal/mole) [2,3]. Thereby, ZrN has also been suggested to be a good candidate for diffusion barriers in IC technology [4,5]. However, the physical properties of thin films are often anisotropic and controlled by their detailed microstructures, including crystallinity and preferred orientations. For example, the electrical resistivity of ZrNx is lower in (002) than that in (111). The growth mechanism for anisotropic textures has been studied on TiN [6] and ZrN [7] by sputtering. In this paper, we investigate the dependence of the textures of Zr and ZrNx on various processing parameters during thin film growth by DC magnetron sputtering. Subsequently, we discuss the influence of the textures of ZrNx films on the thermal stability upon annealing. EXPERIMENTAL DETAILS A DC magnetron sputter is employed to deposit Zr or ZrNx thin films on n-type Si(001) substrates while ZrNx films are produced by reactive sputtering with N2. The Zr target (99.95% purity) is pre-sputtered for 5 minutes after base pressure of 3´10-6 torr is reached. During this experiment, working pressure is fixed at 8´10-3 torr for Zr and 6´10-3 torr for ZrNx, while total gas flow is maintained at 40 sccm and 50 sccm,
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