Effect of film chemistry on refractive index of plasma-enhanced chemical vapor deposited silicon oxynitride films: A cor
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S.D. Woltera) Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708
C.A. Bower RTI International, Center for Materials & Electronic Technologies, Research Triangle Park, North Carolina 27709
B.R. Stoner RTI International, Center for Materials & Electronic Technologies, Research Triangle Park, North Carolina 27709; and Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708
J.T. Glass Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708 (Received 14 January 2008; accepted 14 February 2008)
Thick SiOxNy films were deposited by radiofrequency (rf) plasma chemical vapor deposition using silane (SiH4) and nitrous oxide (N2O) source gases. The influence of deposition conditions of gas flow ratio, rf plasma mixed-frequency ratio (100 kHz, 13.56 MHz), and rf power on the refractive index were examined. It was observed that the refractive index of the SiOxNy films increased with N and Si concentration as measured via x-ray photoelectron spectroscopy. Interestingly, a variation of refractive index with N2O:SiH4 flow ratio for the two drive frequencies was observed, suggesting that oxynitride bonding plays an important role in determining the optical properties. The two drive frequencies also led to differences in hydrogen concentration that were found to be correlated with refractive index. Hydrogen concentration has been linked to significant optical absorption losses above index values of ∼1.6, which we identified as a saturation level in our films.
I. INTRODUCTION
Silicon oxynitride has gained popularity for its application in active and passive optical devices owing to the developing field of photonics and the need for suitable dielectric materials. The interest is centered on the tunability of the refractive index (in theory, 1.46 for silicon dioxide to 2.0 for silicon nitride) that can be achieved by varying the ratio of the constituent atoms. In the past, researchers have grown this material with a mixture of silane, nitrous oxide, and ammonia precursors,1,2 although recent studies3–8 have shown that it can also be
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0176 J. Mater. Res., Vol. 23, No. 5, May 2008
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produced using mixtures of silane and nitrous oxide alone. While researchers have successfully deposited oxynitride films with desired properties such as low optical absorption loss and high growth rate, to date these films are limited to the lower end of the refractive index range (up to 1.50). To exploit their true potential, films of higher refractive index values with lower optical absorption loss are required. A vast amount of literature is available on the material chemistry and deposition of silicon oxynitride, motivated by the desire to seek an alternative to silicon dioxide, primarily for microelectronic applications.9–16 Most of this research has been targeted for gate d
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