Thermodynamic Stability of Low-k Amorphous SiOCH Dielectric Films

Jiewei Chen, Sean W. King, Elayaraja Muthuswamy, Anastasia Koryttseva, Di Wu, Alexandra Navrotsky, R. Riedel

Research output: Contribution to journalArticlepeer-review

20 Scopus citations

Abstract

Si–O–C-based amorphous or nanostructured materials are now relatively common and of interest for numerous electronic, optical, thermal, mechanical, nuclear, and biomedical applications. Using plasma-enhanced chemical vapor deposition (PECVD), hydrogen atoms are incorporated into the system to form SiOCH dielectric films with very low dielectric constants (k). While these low-k dielectrics exhibit chemical stability as deposited, they tend to lose hydrogen and carbon (as labile organic groups) and convert to SiO2 during thermal annealing and other fabrication processes. Therefore, knowledge of their thermodynamic properties is essential for understanding the conditions under which they can be stable. High-temperature oxidative drop solution calorimetry measurement in molten sodium molybdate solvent at 800°C showed that these materials possess negative formation enthalpies from their crystalline constituents (SiC, SiO2, C, Si) and H2. The formation enthalpies at room temperature become less exothermic with increasing carbon content and more exothermic with increasing hydrogen content. Fourier transform infrared spectroscopy (FTIR) spectroscopy examined the structure from a microscopic perspective. Different from polymer-derived ceramics with similar composition, these low-k dielectrics are mainly comprised of Si–O(C)–Si networks, and the primary configuration of carbon is methyl groups. The thermodynamic data, together with the structural analysis suggest that the conversion of sp2 carbon in the matrix to surface organic functional groups by incorporating hydrogen increases thermodynamic stability. However, the energetic stabilization by hydrogen incorporation is not enough to offset the large entropy gain upon hydrogen release, so hydrogen loss during processing at higher temperatures must be managed by kinetic rather than thermodynamic strategies.

Original languageEnglish (US)
Pages (from-to)2752-2759
Number of pages8
JournalJournal of the American Ceramic Society
Volume99
Issue number8
DOIs
StatePublished - Aug 1 2016
Externally publishedYes

Keywords

  • amorphous low-k SiOCH films
  • formation enthalpy
  • thermodynamic stability

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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