Diagnostics of Gas-Phase Epitaxy Processes
Investigation of the Kinetics and Disintegration of Hydride Molecules in Epitaxy Processes with Gas Sources by Submillimeter Spectroscopy Method
Tech Area / Field
- CHE-THE/Physical and Theoretical Chemistry/Chemistry
- INF-ELE/Microelectronics and Optoelectronics/Information and Communications
8 Project completed
Senior Project Manager
VNIIEF, Russia, N. Novgorod reg., Sarov
- Nizhegorodsky State Technical University, Russia, N. Novgorod reg., N. Novgorod\nInstitute of Physics of Microstructures, Russia, N. Novgorod reg., N. Novgorod
- MOTOROLA, USA, AZ, Mesa
Project summaryThe objective of this project is to research into a possibility of using a submillimeter spectrometer in low-pressure gas-phase epitaxy set-ups to ensure the best conditions of heterostructures growth, and also to develop a technique that would allow, using this spectrometer, to determine directly in the process of epitaxial growth the ways and rates of pyrolysis of hydride molecules, concentrations of their disintegration by-products both in the volume and on the heated growth surface, and the characteristics of growing layers.
The project pursues solution of a fundamental problem of applying the methods of chemical vacuum epitaxy to growth of perfect-structure strained heterocompositions of Si and Ge, including those with layers of Si-Ge-C solid solution that feature nanometer thickness and interface abruptness.
Growth of heterostructures based on Si-Ge-C solid solutions using high-purity hydrides has been of intense research interest lately due to the application opportunities for these materials in electronic engineering. The layers quality is largely dependent on purity of the original components and a growth method used. Contamination of working gases with dopiness may occur in containers themselves as well as in gas supply lines. Development of techniques enabling measurements of minimal portions of well-approved molecules of arsine, phosphine and other alloying gases directly in a growth process when the working gas comes in contact with heated parts of the set-up, without having to install auxiliary apparatus into the growth chamber, may prove quite promising but it first needs to be evaluated experimentally.
Along with the conventional mass-spectrometry methods which allow analysis of gas composition within a vacuum chamber a considerable interest is shown for the submillimeter spectroscopy technique as applied to analysis of a growth process. This method provides more informative data on the properties of gas molecules and their radicals not only in the reactor volume but also directly on a growth surface. Therefore, developing and upgrading of both direct and indirect methods to determine various parameters of gas mixtures on a test surface and establishing of primary experimental dependencies is viewed as the first step towards solution of the above problem.
Hydrides GeH4, SiH4, CH4 used for growth of layers are beyond the reach of submillimeters methods. Yet, it is possible to measure their radicals: GeHj, SiHj (j=1,2,3) (resonance frequencies of rotational spectra of molecules, molecule concentrations both in the reactor volume and on a growing layer surface). Of particular interest might be the molecules of GeH3 (SiH3) which bear a structural similarity to an ammonia molecule – the classical object of submillimeter spectroscopy. Knowledge of the chemosorption process features, the pyrolysis kinetics of hydride molecules and patterns of their disintegration, the concentrations of disintegration by-products on surface depending on gas pressure, temperature of the pyrolysis process, possible surface interactions and presence or absence of additional atomic and molecular flows is crucial in study of mechanisms underlying formation of complexes, in particular, hydrogen-containing clusters, and incorporation of atoms and molecules of matter into a growing epitaxial layer.
Development of adequate physical-chemical and mathematical models reflecting real processes of pyrolysis and complex-formation of hydride molecules on an epitaxial surface is possible only provided there is ample experimental information on the disintegration rates of inpidual molecules and their activation energies, which in its turn can be obtained either directly from a technological experiment for layer growth, or by, for example, spectroscopic methods. We will seek solution to the problem with an extensive method combining simultaneous studies:
– of the spectral characteristics in the submillimeter wavelength range of hydride molecules (Si,Ge)nHx and their complexes (Sin-Gem)Hx both in the volume of a high-vacuum technological set-up and on a growing layer surface;
– of the experimental dependencies of an epitaxial layer growth rate on different technological parameters (density of auxiliary catalytic flows of Si and Ge atoms, growth temperature, partial pressures of gases, state of a growth surface, etc.);
– of the characteristics of the pyrolysis rates of hydride molecules for various patterns of their disintegration by the methods of mathematical simulation.
Along with the fundamental research, the project seeks solution of the following applied problems:
1. Development of a novel method to control gas composition in a growth chamber:
– control of a molecule content in the reactor, detectable with this method to an accuracy yet unattained by other techniques: arsine, phosphine, diborane, carbon dioxide which provide background alloying of a growing layer;
– control of a water, oxygen, etc. content responsible for the appearance of deep centers in a films and, as a result, formation of the effective centers of recombination of nonequilibrium charge carriers;
– evaluation of concentrations of the disintegration products of hydrides used in an epitaxy process.
2. Development of a method for determining a degree of a growth surface coverage with the hydride disintegration products and of a method for independent control of a growing film composition throughout a growth process (both for key elements: Si, Ge, C and for impurity: As, P, etc.) and of a concentration of hydrogen atoms in the layer.
3. Determination of the rates and patterns of hydride disintegration on a growing layer surface with a view to predicting nonstationary processes on the growth surface and independent monitoring throughout a growth process of the composition- and the alloying profiles of a growing layer.
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