Thermodynamic Calculations as the Basis for CVD Production of Silicide Coatings

Abstract

The exponential increase in computing power realized over the past three decades has required devices of ever-decreasing dimensions. With these reductions in feature size, each generation of circuit technology creates a new set of materials-science challenges, as exemplified by the use of silicide-based diffusion barriers.The use of transition-metal silicides in the semiconductor industry began in the early 1980s with (in retrospect) fairly thick films, simple compositions, and minimal microstructural requirements. The implementation of thin-film binary silicides in integrated circuit (IC) applications required the development of appropriate modeling techniques to select the deposited metal, its gaseous precursor, and the Silicon precursor. These vectors were used to define experimental conditions to yield desired films. Chemical-vapor-deposition (CVD) experiments were simulated and CVD phase diagrams were used to describe the changing film properties with different thermodynamic conditions.In the early 1990s, research began to focus on CVD of ternary Systems (Ta-Si-N, Ti-Si-N). Modeling these complex Systems required optimization of the thermodynamic data and careful evaluation of the ternary phase diagrams.Current-generation materials are deposited in extremely thin layers (ULSI, or ultralarge-scale integration), composed of multiple elements from a variety of gas sources, an d have tailored micro-structures. As described in this article, early thermodynamic modeis helped develop deposition techniques for early-generation silicides. As the technological requirements increased, the modeling method s evolved in parallel, yielding continued insight into the relevant processes. Current work on CVD modeling couples thermodynamic calculations with heat and mass transfer. Incorporating both kinetic and thermodynamic effects, these methods provide a more realistic description of the CVD reactor.