Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
2000-09-06
2003-07-15
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S094000, C117S093000, C117S101000, C117S105000, C117S200000, C118S715000
Reexamination Certificate
active
06592664
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of epitaxial deposition of atoms or molecules from a reactive gas on a deposition surface of a substrate. The present invention relates to a corresponding device which includes a heating device for supplying energy into the substrate, thereby heating at least the deposition surface, and a reactive gas supply device for conducting the reactive gas onto the heated surface of the substrate.
BACKGROUND INFORMATION
Methods for deposition, in particular for epitaxial deposition, of atoms from a reactive gas on a deposition surface of a substrate are conventional. In particular, such methods for deposition of silicon or silicon carbide from the gaseous phase on a substrate have been used. For this purpose, a suitable reactive gas is conducted onto a heated deposition surface of a substrate arranged, for example, in a vacuum chamber. In such deposition methods, also referred to as Chemical Vapor Deposition (CVD), the minimum temperature of the deposition surface of the substrate in systems normally used in industry for silicon deposition is approximately 1000° C. and for silicon carbide deposition approximately 1600° C. Such high temperatures on the deposition surface of the substrate are necessary in order to thermally activate the atoms of the reactive gas to be adsorbed from the gaseous phase after the reactive gas impinges on the deposition surface. Atoms activated in this manner are characterized by increased mobility, a sufficient mobility enabling them to conform to the lattice position of a host substrate. In this manner a desired monocrystalline layer growth is achieved on the deposition surface of the substrate.
The relatively high operating temperatures used in such deposition methods have the disadvantage that only substrates made of highly thermostable materials can be used for deposition. Furthermore, particularly in the case of silicon carbide deposition, the deposition systems cannot be made of a neutral quartz material that is advantageous for the deposition process, since this material has insufficient resistance to such high operating temperatures. The use of highly refractory graphite as a construction material for deposition systems of this type is not optimum, since graphite contaminates the interior of the deposition systems that yields an unacceptable deposition result in deposition processes subject to problems.
SUMMARY
The method according to the present invention includes the following steps:
A first amount of energy is supplied by heating at least the deposition surface. The first amount of energy is less than the energy amount necessary for the epitaxial deposition of atoms or molecules of the reactive gas on the deposition surface.
An ionized inert gas is conducted, at least from time to time, onto the deposition surface in order to supply, at least from time to time, a second amount of energy through the effect of ions of the ionized inert gas on the deposition surface. The first energy amount and the second energy amount add up, at least from time to time, to a total amount of energy that is sufficient for the epitaxial deposition of atoms or molecules of the reactive gas onto the deposition surface.
As a result, due to the supply of the second amount of energy and the effects of the inert gas ions on the deposition surface, the supply of thermal energy necessary for epitaxial layer deposition can be advantageously lower than in conventional deposition methods in which a supply of thermal energy is provided exclusively to achieve the necessary deposition temperature on the deposition surface of the substrate. This is due to the fact that, because of the effect of the ions of the ionized inert gas on the substrate surface, an additional activation energy favoring epitaxial deposition is provided for the atoms of the reactive gas to be adsorbed from the gaseous phase. This activation energy is added to the first thermally supplied energy amount to form a total amount of energy. The mobility of the reactive gas atoms to be deposited on the deposition surface is increased by the total amount of energy resulting from the sum of energy amounts supplied onto the deposition surface independently of one another, so that the atoms can conform to the lattice locations serving as hosts, so that epitaxy, i.e., monocrystalline layer growth, is obtained. Thus, the total amount of energy supplied to the deposition surface is sufficient to guarantee epitaxial deposition of the reactive gas atoms on the deposition surface of the substrate as activation energy, and the temperature to be achieved by heating the deposition surface of the substrate is advantageously lower as compared to that of conventional deposition methods. This allows thermally unstable substrates such as porous silicon or porous silicon carbide substrates to be used for layer deposition, while using quartz deposition systems, which have sufficiently high stability at the deposition temperatures. The deposition temperatures obtained after heating the deposition surface of the substrate are now relatively low and do not negatively affect the deposition process through contamination, which would occur, for example, if refractory graphite were used as the construction material.
According to an advantageous embodiment, the first energy amount and the second energy amount are supplied to the deposition surface at different times. Due to the separation in time of the supply of the two energy amounts, a controlled and accurate energy supply to the deposition surface is achieved in a simple and reliable manner to provide sufficient activation energy for deposition of the reactive gas atoms on the deposition surface. Advantageously, thermal energy (first energy amount) is initially supplied to the deposition surface. When the desired temperature is reached on the deposition surface, the ionized inert gas is conducted onto it, thereby supplying the second energy amount.
The ionized inert gas is advantageously conducted separately from the reactive gas in the direction of the deposition surface. By conducting the ionized inert gas in the direction of the deposition surface separately from the reactive gas the ionized inert gas is prevented from mixing with the reactive gas for a sufficiently long period of time, so that undesirable gas phase reactions occur between the two gases before they impinge on the deposition surface. The separate supply of the two gases in the direction of the deposition surface also enables both the reactive gas and the ionized inert gas to be conducted, as uniformly distributed as possible, onto the entire deposition surface in a controlled and optimum manner.
The ionized inert gas, for example, is conducted onto the deposition surface at the same time as the reactive gas. By conducting both gases onto the deposition surface simultaneously, the resulting total time of the deposition process is advantageously reduced.
According to an another embodiment, the ionized inert gas and the reactive gas are conducted onto the deposition surface at separate times, with either first the ionized inert gas and then the reactive gas or first the reactive gas and then the ionized inert gas being conducted onto the deposition surface in each deposition cycle. This provides a particularly compact design of the system used for deposition, since only one common gas supply device must be provided for both the inert gas or ionized inert gas and the reactive gas, and an ionizing unit can be provided in this supply device, which is in operation when inert gas is being supplied, to generate ionized inert gas, and is switched into a non-operational state when reactive gas is being supplied. Furthermore, by supplying ionized inert gas and (non-ionized) reactive gas at different times, the occurrence of undesirable gas phase reactions between the two gases or within the reactive gas is prevented in a simple and reliable manner.
The ionized inert gas and the reactive gas are conducted, for example, onto the deposition surface at different times in an
Frey Wilhelm
Heyers Klaus
Laermer Franz
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