Properties of Silicon Oxynitride and Aluminum Oxynitride Coatings Deposited Using Ion Assisted Deposition
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PROPERTIES OF SILICON OXYNITRIDE AND ALUMINUM OXYNITRIDE COATINGS DEPOSITED USING ION ASSISTED DEPOSITION G.A. Al-Jumaily*, T.A. Mooney*, W.A. Spurgeon**, and H.M. Dauplaise** *Barr Associates, 2 Lyberty Way, Westford, MA 01886 **Army Materials Technology Laboratory, Watertown, MA 02172
ABSTRACT Optical thin films of nitrides, oxynitrides and oxides of aluminum and silicon were deposited using ion assisted deposition. Coatings were deposited by thermal evaporation of AIN and e-beam evaporation of Si with simultaneous bombardment with 300 eV ions of nitrogen, a mixture of nitrogen and oxygen or oxygen. The chemical composition and the index of refraction of the coating was varied by varying the gas mixture in the ion beam. Optical properties of and environmental stability of coatings were examined. Results indicated that coatings are stable even under severe conditions of humidity and temperature. Introduction Silicon nitride and oxynitride coatings are becoming increasingly important for optical and microelectronic applications. Optically, silicon nitride has relatively high index of refraction in the visible region of the spectrum. The coatings are hard with exceptional environmental durability. The material has a wide transmission band that extends from the UV to the near IR. Silicon nitride has been deposited by chemical vapor deposition (CVD), rf sputtering, ion implantation, thermal evaporation and ion assisted deposition (IAD).[1,2] The deposition, characterization, and applications of silicon nitride has been reviewed by Morosanu [3]. Deposition of coatings using CVD involves raising the substrate temperature to values as high as 7000 C. Thermal evaporation of thin films has the advantage that coatings can be deposited at lower temperatures. However, silicon nitride coatings deposited using conventional thermal evaporation have numerous structural defects which make this method unsuitable for microelectronic applications [3]. Martin et al. [4] used rf sputtering to deposited optical filters using a combination of Si02 and Si 3N4 . The filters were found to be stable at extreme conditions of temperature and humidity. Netterfield et al. [1] used IAD to deposit silicon nitride and silicon dioxide coatings by evaporation of silicon (Si) with simultaneous bombardment with low energy nitrogen and oxygen ions respectively. Aluminum nitride (AIN) and oxynitride have similar properties to silicon nitride and oxynitride. Thermal evaporation of AlN causes the material to dissociate and the resulting films are highly absorbing. Coatings of AlN are deposited by reactive evaporation in 1 x 10-3 Torr of nitrogen backfill in the presence of a glow discharge. Thin films of AlN have also been deposited by reactive sputtering in a planar dc magnetron system [5]. In this paper we examine the optical properties of silicon oxynitrides and aluminum oxynitrides deposited using IAD. Deposition Arrangement Coatings were deposited in a 60 cm box coater. Figure 1 is a schematic illustration of the deposition arrangement. 7 The vacuum
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