Chemical Effects of substrate Temperature and Feed Gas Composition on Ion Beam Deposited AlN and AlN:H
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L. HUANG, X. D. WANG, K. W. HIPPS, U. MAZUR, J. T. DICKINSON, AND R. HEFFRON Materials Science Program, Washington State University, Pullman, WA 99164-4620, USA
ABSTRACT
Direct ion beam sputter deposition of AIN is studied using both pure nitrogen and a 75% N2 /25% H 2 mixture as the feed gas for the ion gun. The chemical characteristics of these films are probed using infrared spectroscopy and chemical etching. The presence of Al-N 2 species is associated with reactive and highly defective films. The presence of NHx species increases by several orders of magnitude the rate at which AIN film are etched by base. However, stoichiometric and low defect AIN films prepared by depositing AlN:H onto substrates heated to 200 'C have reactivities similar to the best AIN films produced in the absence of hydrogen.
INTRODUCTION Aluminum nitride has a large band gap, 1 a high density, large thermal conductivity, a small thermal expansion coefficient, and a very large volume resistivity. 2 Aluminum nitride is a hard material. 3 Thin films of freshly prepared AMN and AIN:H are even harder, with the hydrogenated film being about as hard as alumina. 4 AIN is chemically stable to attack by atmospheric gasses at temperatures less than 700 C. 5-8 Most of the work on AIN film growth to date has resulted in films that are crystalline and preferentially oriented relative to the substrate surface, although changes in deposition conditions can change which axis is preferred. 9 -12 While oriented crystalline films are needed for piezoelectric devices, they are not always the most desirable form for thin film applications. Aita has suggested that nanocrystalline AMN films might serve as excellent corrosion inhibitors. 13 Hasegawa has suggested that an amorphous form of AIN might have superior properties for electronic applications, since a mismatch between the substrate and AMN lattice constants would not result in high levels of strain. 14 Mazur and coworkers found that single ion-beam sputter deposited (IBSD) AIN films were oriented microcrystalline, extremely inert chemically, but adhered poorly to substrates such as glass or mica - where extended stress relief patterns could be observed. 9,15,16,17 The addition of as little as 5% hydrogen to the ion beam feed gas eliminated these stress failures and atomically smooth coatings resulted on virtually any substrate at room temperature. It has been shown that these AIN:H and AIN:H 18 19 derived films are nanocrystalline. , Impurities can play a significant role in degrading the long term performance of these amorphous films. For example, the AMN:H films produced by ion beam deposition onto room temperature substrates are extremely susceptible to attack by water vapor in air. After 10 days, they blister due to conversion of AMN to aluminum oxyhydroxide, which is easily monitored by 367 Mat. Res. Soc. Symp. Proc. Vol. 388 01995 Materials Research Society
infrared In this paperfilms. we correlate presence of specific defects in AIN films with the spectroscopy.9 chemical reactivity of these
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