Thin films of MoN, WN, and perfluorinated silane deposited from dimethylamido precursors as contamination resistant coatings on micro-injection mold inserts Ville Miikkulainen a , Mika Suvanto a , Tapani A. Pakkanen a, ⁎, Samuli Siitonen b , Petri Karvinen b , Markku Kuittinen b , Hannu Kisonen c a Department of Chemistry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland b Department of Physics, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland c Joensuu Science Park (IMTEC) Inc., Karjalankatu 3, FIN-80200, Joensuu, Finland ABSTRACT ARTICLE INFO Article history: Received 14 January 2008 Accepted in revised form 9 May 2008 Available online 17 May 2008 Keywords: Molybdenum nitride Tungsten nitride Atomic layer deposition Micro-injection molding Mold coating To enhance their surface properties, micro-injection mold inserts made of electroplated nickel were coated with thin films of molybdenum nitride and tungsten nitride by atomic layer deposition. Alkylimido– alkylamido complexes were used as precursors together with ammonia. In addition, a perfluorinated hydrophobic coating was deposited by gas-phase method from tridecafluoro-1,1,2,2-tetrahydrooctylmethyl- bis(dimethylamido)silane. Injection molding tests were performed with two plastic materials: poly(4- methyl-1-pentene) copolymer TPX™ and polycarbonate Makrolon® DP1-1265. With both plastics, the nickel insert with thin film of molybdenum nitride was clearly more resistant to contamination than the uncoated insert. Also the perfluorosilane coating provided good resistance to contamination. After the 15,000 shot injection molding test, all of the coatings were still attached to the insert. Friction coefficients were determined between the nitride and silane coatings and the plastic materials. The coatings showing good contamination resistance in injection molding also had a low coefficient of friction. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Plastic parts with micron and submicron features are everyday objects today. Compact discs (CDs) and digital versatile discs (DVDs) are examples of products with features in micron scale [1–3]. One of the growing fields exploiting micro- and nanometer-scale textures in plastics is diffractive optics [4,5]. Micro-injection molding (μ-IM) [6,7] is the most widely used tool for mass production of plastic parts with micron- and submicron-scale textures. With μ-IM, large quantities of plastic parts can be produced fast and cost-effectively. Challenges in the process nevertheless remain. As an example, structures with high aspect ratios are still hard to replicate [8]. In addition, micrometer- scale patterns generate high surface areas, which increase the adhesion between the mold and plastic cast and hinder the ejection of the plastic part [6,7]. The sticking gradually contaminates the mold, and the dimensions of the mold deteriorate. This is a major drawback, since in μ-IM the tolerances for the dimensions of the molded part are strict. The coefficient of friction is an effective measure of the sticking of plastic to the mold [9]. Transition metal nitrides have been widely applied as protective coatings in traditional injection molding. In particular, titanium and chromium nitrides substantially enhance wear resistance and mold release [10–14]. The coatings have been deposited by sputtering or chemical vapor deposition (CVD) methods. However, films deposited by sputtering and CVD suffer from poor adhesion to the substrate, low conformality on patterned substrates, and crack and pinhole forma- tion. These limitations limit, or even prevent, the use of these methods in depositions of protective film on μ-IM mold tools. Poly(tetrafluoroethylene) (PTFE)-based materials have been used to promote anti-adhesion on mold surfaces with submicron features. Electrochemical [15] and plasma polymerization [16], blending with nickel as a solid lubricant [17], and perfluorinated silane [18] and phosphoric acid precursors [19] have been used to deposit PTFE-type films onto mold surfaces. PTFE films suffer, however, from diffusion onto the molded polymer and from heat degradation [16,17,20]. Recently, a novel perfluorinated dialkylamidosilane was introduced as a precursor for hydrophobic coatings on microelectro-mechanical systems (MEMS) [21]. The silane, tridecafluoro-1,1,2,2-tetrahydrooc- tylmethyl-bis(dimethylamido)silane (FOMB(DMA)S), was shown to produce thermally stable hydrophobic films on aluminum oxide without emission of HCl or polymerization of the precursor, which are common disadvantages with the more commonly applied chlorosi- lanes. These results suggest the use of FOMB(DMA)S as a promising way to produce stable hydrophobic films on μ-IM mold surfaces. Atomic layer deposition (ALD) is a CVD-related gas phase deposition method, in which the precursors are fed onto substrates alternately and in cycles [22]. The precursors react in turn with the chemically active groups on the substrate surface, in a saturative, self- limiting manner. Between the precursor pulses the reactor is purged Surface & Coatings Technology 202 (2008) 5103–5109 ⁎ Corresponding author. Tel.: +35813 2513345; fax: +358 13 2513344. E-mail address: Tapani.Pakkanen@joensuu.fi (T.A. Pakkanen). 0257-8972/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2008.05.007 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat