Study of structure development of Titanium Nitride on inclined substrates K. Kishor Kumar ⁎, P.M. Raole, P.A. Rayjada, N.L. Chauhan, S. Mukherjee FCIPT, Institute for Plasma Research, A-10/B, GIDC Electronics Estate, Sector-25, Gandhinagar, Pin 382 044, Gujarat, India abstract article info Available online 5 May 2011 Keywords: Titanium Nitride Off-normal deposition Microstructure Crystallite size Microstrain For magnetron sputter deposited coatings, the structure development during growth mostly depends on the mobility of the adatom over the substrate. The mobility is significantly affected by the orientation of the substrate with respect to the direction of the incident flux of sputtered atoms. The structural properties like crystallite size, crystallographic structure, column orientation, etc., are therefore influenced. This is relevant as the real work pieces over which the overlay functional coatings has to be applied are three dimensional in nature with the surfaces being off-normal to the incident flux. In the present investigation, the effect of incident angle on the various aspects of the structure development of Titanium Nitride coatings, having wide tribological applications, deposited on Si substrates by reactive magnetron sputter deposition was studied. A planar magnetron, with cathode diameter 75 mm and mounted with pure Ti target was used and TiN was deposited in a mixture of argon and nitrogen gas. The deposition was done for different durations. The deposited coatings were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results indicate the formation of well defined columnar microstructure in the coatings. The column inclination is compared with the well known ‘Tangent rule’. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Magnetron sputter deposited coatings generally consist of elon- gated columns of a few tens of nanometers in width, which grow from the substrate to the film surface. The Thornton Structure Zone model gives the conditions for the formation of such columns [1]. In case of real substrates which require surface modification, the three dimensional nature can cause off-normal incidence of sputter flux and this will subsequently affect the columnar growth and orientation of the columns with respect to the substrate normal. The columnar microstructure characteristic of sputter deposited coatings could be clearly distinguished in cross sectional scanning electron micrographs [2]. Coatings grown on off-normal substrates by magnetron sputter deposition techniques show columnar microstructure with the columns tilted towards the depositing flux [3]. It has been observed that the direction of the tilted columns is not exactly parallel to the depositing flux [4]. This has been observed in the case of coatings deposited by other techniques also, as in the case of pulsed cathodic arc deposition [5], where the flux to the substrate consists of small particles formed from the coalescence of the evaporated atoms. The column tilt angle (β) is observed to be lower than the angle of the incident flux (α), both angle measured with respect to the substrate normal and empirically related by the so called Tangent rule [6], tan α = 2 tan β: ð1Þ However, this relation is not considered to be universally correct [7] and deviations have been observed at higher angles (α N 60°), whereas the rule has been verified for lower angles (0° b α b 60°) [8]. The tilt in column direction can cause anisotropies in the macroscopic properties and is hence important in tribological and functional coatings, which are deposited on three dimensional substrates, where normal incidence cannot be ensured over the entire substrate area. In the present study, the effect of off-normal deposition on certain structural properties of magnetron sputter deposited Titanium Nitride (TiN) coatings having wide tribological applications is studied. The column tilt and coating thickness were measured for TiN coatings deposited by magnetron sputter deposition method on Si (100) wafers. In order to emulate the three dimensional nature of the real substrates, the plane substrates were oriented at different angles. The coatings were deposited for constant bias conditions of the magnetron, for various durations and the effect of coating thickness was studied. 2. Deposition and characterization of coatings 2.1. Deposition setup The deposition setup consisted of a cylindrical SS 304 chamber mounted with a planar magnetron having target diameter 75 mm. A base pressure of 2 × 10 -5 mbar was attained in the chamber. The magnetron was operated in the DC mode. For depositing TiN, pure Ti target was used with Argon as the sputtering gas and N 2 as the reactive gas. Both were introduced using Gas Flow Controllers with Surface & Coatings Technology 205 (2011) S187–S191 ⁎ Corresponding author. Tel.: + 91 79 23269009; fax: + 91 79 23269001. E-mail address: kishor@ipr.res.in (K.K. Kumar). 0257-8972/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2011.04.093 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat