Aerosol jet fog (ajFOG) deposition of aluminum oxide phosphate thin films from an aqueous fog
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Ryan H. Mansergh and Yu Huang Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA
Matthew G. Kast Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1253, USA
Douglas A. Keszler Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA
John F. Conley Jr.a) School of Electrical Engineering and Computer Science, Oregon State University, Corvallis, Oregon 97331-5501, USA (Received 29 June 2016; accepted 30 August 2016)
A new lab-based aerosol jet fog (ajFOG) deposition system with an atomizer consisting of two opposing jets located within the deposition chamber is introduced and its capabilities are examined. The unique opposing configuration of the atomizer enables the formation of a highly uniform fog even from low volatility precursors. Aluminum oxide phosphate (AlPO) thin films were deposited onto Si wafers at room temperature and sub-atmospheric pressure by using an aqueous precursor. Films were characterized by spectroscopic ellipsometry, x-ray diffraction and reflectivity, scanning electron microscopy, and metal/oxide/semiconductor (MOS) capacitor electrical measurements. Film thickness uniformity, density, surface roughness, and charge transport mechanisms were found to be comparable to spin-coated thin films deposited using the same precursor, demonstrating the effectiveness of this aerosol technique. A process model was developed to predict film thickness as a function of precursor concentration, exposure time, fog settling time, and number of exposures.
I. INTRODUCTION
In this work, we introduce a new lab-based aerosol jet fog (ajFOG) deposition system by producing and validating high-quality aluminum oxide phosphate films. We show that uniform films are readily deposited from a homogeneous fog at room temperature and pressure. The semiconductor, glass, and solar industries have historically relied on vacuum deposition to produce uniform thin films on various flat and textured substrates.1 As these industries explore and introduce new technologies, opportunities arise to consider new costeffective, environment friendly, and less energy intensive deposition techniques, especially to address scaling issues. Solution-based spin coating, for example, satisfies most needs and produces high quality organic and inorganic thin films,2 but physical limitations restrict its use to modest substrate sizes.3,4 Lately, researchers have Contributing Editor: Gary L. Messing a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.341
been addressing spin coating constraints by investigating aerosol techniques such as spray coating,5 spray pyrolysis,6 mist chemical vapor deposition (MCVD),7 and liquid source misted chemical deposition (LSMCD).8 These techniques aim to initially produce homogeneous aerosols of volatile molecules, liquids, or solutions9,10 that then deposit to form uniform films, potentially over large areas. Among aerosol methods, LSMCD so far produces the most uniform and smoo
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