Synthesis and optical properties of amorphous Si3N 4- xPx dielectrics and complementary insights from ab initio structural simulations

J. B. Tice, V. R. D'Costa, Gordon Grzybowski, Andrew Chizmeshya, J. Tolle, Jose Menendez, John Kouvetakis

Research output: Contribution to journalArticle

1 Scopus citations

Abstract

Applications that require tuning of the properties of amorphous Si 3N4 currently make use of nonstoichiometric silicon oxynitrides or silicon nitrides. In this study compositional tuning is employed to produce a new family of amorphous dielectrics with near stoichiometric Si3N4-xPx (x ∼0-1) compositions and adjustable optical response. Air stable and thermally robust materials are deposited at 650-700 °C on Si wafers with a growth rates as high as 0.2 μm/min via CVD reactions of P(SiH3)3 with NH 3. An alternative route involving P(SiH3) 3/N(SiH3)3 mixtures with ammonia was also explored and found to yield comparable materials. Precise control of the reactant fluxes produces alloys in which the PSi3 molecular core of the precursor is likely incorporated intact into the covalent nitride network, leading to an assemblage of corner-shared SiN4 and SiN3P tetrahedra containing residual N-H bonds. The optical properties of the resultant materials have been studied by spectroscopic ellipsometry, which indicated that the incorporation of P systematically decreases the band gap while increasing the refractive index. Density-functional theory simulations were used to reconcile the molecular geometry of the precursors with local bonding in the solids and predict that the incorporated PSi3 cores adopt a planar geometry for low P contents (up to x = 0.5) and become slightly puckered as P increases to x = 1. This implies that the more rigid Si 3N units initially induce a planarization in their softer Si 3P counterparts, leading to hexagonal-type ground-state structures with slightly lower symmetry than that of the β-Si3N4 prototype. The simulations of the band-structure for Si3N 3.5P0.5 and Si3N3P confirm the decreasing trend observed in the optical band gap as the P content is increased.

Original languageEnglish (US)
Pages (from-to)5296-5305
Number of pages10
JournalChemistry of Materials
Volume22
Issue number18
DOIs
StatePublished - Sep 28 2010

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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