Autostoichiometric vapor deposition: Part I. Theory
- PDF / 565,875 Bytes
- 6 Pages / 576 x 792 pts Page_size
- 95 Downloads / 231 Views
The possibility of an autostoichiometric vapor deposition is explored. Heterometal-organic complexes such as double alkoxides are potential candidate precursors for such deposition. Two reaction schemes, the hydrolysis-assisted pyrolysis and the hydrolysis-polycondensation of double alkoxides, are identified to be autostoichiometric reactions. A simple low-pressure apparatus is suggested for autostoichiometric vapor deposition. Mass-flow analysis allows for the identification of a nonstoichiometry factor K which can be used as a quantitative measure of the precursor's autostoichiometric capability.
I. INTRODUCTION Multicomponent oxide thin films have in recent years received wide interest for their attractive electrical and optical properties. Potential application of such materials as active media for optical signal processing has prompted intensive investigations among materials scientists and engineers. Two fabrication techniques stand out as the most extensively studied for multicomponent oxides: Sol-gel processing of ferroelectric oxides1 and metal-organic chemical vapor deposition (MOCVD).2 From the chemistry standpoint, deposition of multicomponent oxides involves the delivery of metal elements of various forms in stoichiometric ratios to the substrate surface. Sol-gel processing achieves stoichiometry with a thin liquid solution film on substrates that contain soluble metal-organic compounds in prescribed proportions. Subsequent heating to cause crystallization generally does not disturb the film stoichiometry due to the relatively low temperatures required to effect crystallization of high melting point oxides. In other words, the stoichiometry is normally prescribed in sol-gel processing. The main difficulty associated with sol-gel is its discontinuous deposition of films. A single dip or spin coating generally results in films of a few thousand angstroms thick. Multiple coating and firing cycles are necessary to obtain films with thicknesses in the micron range. MOCVD provides a means of continuous deposition of oxides on the molecular level, thus rendering convenient control over film thicknesses and microstructure. However, when the oxide system contains more than one metal element, the stoichiometry can no longer be prescribed as is done in sol-gel processing. MOCVD of a multicomponent oxide involves the use of separate metal-organic compounds for each component. In ordinary operations, the precursor compounds are independently transported into the vapor phase by evaporation or other means. Whether a given vapor phase 2536
J. Mater. Res., Vol. 10, No. 10, Oct 1995
http://journals.cambridge.org
Downloaded: 14 Mar 2015
composition results in the desired film stoichiometry is determined only after a compositional analysis of the deposited film is performed. The information is then used as feedback to adjust individual precursor flow rates. Many cycles of operation are necessary before an acceptable approximation can be reached. In addition, carefully obtained operational parameters are not universal
Data Loading...
