Thermodynamics of germanium chemical vapor deposition via germane and digermane

Abstract

Chemical vapor deposition is notoriously a challenging chemical process. Growth rates are stated either under mass-transfer control or under kinetic control at lower temperature. But a few drastic assumptions enable a radical simplification of the reaction mechanism. And both growth regimes are unified with Sedgwick’s simplified thermodynamic model. Linear functions of temperature akin to Gibbs free energy of reaction are mined out of germanium deposition experiments. Two growth mechanisms are identified, one with ΔHro = 83.4 kcal/mol (Ge–H bond) and a second one with ΔHro = 104.2 kcal/mol (H – H bond). The contribution of higher order germane is also discerned in germane thermal decomposition. The square root coupling of growth rates to input flows is neatly demonstrated with thermodynamics. Finally, chemical vapor deposition growth rate vs. precursor partial pressure plot fingerprints a hydrogen Langmuir adsorption isotherm. The adsorption isotherm reveals a thermodynamic contribution beneath a mass-transfer control.