Gas separation: processes – Deflecting
Reexamination Certificate
1999-06-18
2001-07-10
Simmons, David A. (Department: 1724)
Gas separation: processes
Deflecting
C095S288000, C055S434100, C055S434200, C055S465000, C055SDIG001
Reexamination Certificate
active
06258153
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to the field of process engineering, and concerns a device for the deposition of substances from a gas phase.
In the production of semiconductor components, CVD processes (CVD=chemical vapor deposition) are commonly used for applying layer structures to semiconductor substrates. In these CVD processes, a plurality of reaction partners are introduced into a reaction chamber of a reactor using a carrier gas. The reaction partners, also referred to as initial products or precursor compounds, may be fed to the reaction chamber via one or more feed lines. In addition, other gases, e.g. oxidizing agents (O
2
) or inert gases (N
2
, Ar) are usually introduced into the reaction chamber in order to dilute the reaction partners. The reaction partners and oxidizing agents introduced react with one another to form the desired layer. This takes place on the surface of a semiconductor substrate placed in the reaction chamber. By varying the initial concentration of the reaction partners, the stoichiometric ratio of the individual constituents of the layers which are formed can be adjusted. In the deposition of metal oxide ceramics, e.g. SrBi
2
Ta
2
O
9
(SBT) or (Ba,Sr)TiO
3
(BST), which are employed for memory applications in the semiconductor industry, the reaction partners or initial products predominantly consist of metal complexes which are in gas form at elevated temperatures. In order to prevent the unused initial products from reaching downstream pumps or the surroundings, downstream cold traps for collecting unused initial products are used in the reaction chamber. These are intended to remove the initial products as fully as possible from the gas flowing through the cold traps.
A deposition system of the foregoing type is described, for example, in U.S. Pat. No. 4,647,338 to Jan Visser. In the process disclosed there for the production of a semiconductor component, a CVD system consisting of a reaction chamber and a downstream cold trap are used. A disadvantage, however, is that in that system deposition of unused initial products can actually take place even before, i.e., upstream of, the cold trap, which may cause clogging of feed lines and the like.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a device for depositing substances, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which avoids the premature deposition of the substances.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for depositing substances, such as a cold trap, comprising:
a housing having a deposition chamber with an inner wall maintained at a given deposition temperature for depositing substances thereon;
a feed having a delivery end extending to the deposition chamber for introducing the substances to be deposited into the deposition chamber, the feed being maintained at a transport temperature above the given deposition temperature, wherein a deposition of the substances is substantially prevented at the transport temperature;
the deposition chamber being formed with an outlet opening; and
a thermal insulation between the feed and the inner wall for preventing the delivery end of the feed from being cooled to the given deposition temperature.
In other words, the objects of the invention are satisfied with the device in which at least one inner wall of the deposition chamber is provided with a predetermined deposition temperature for the deposition of the substances on this inner wall and in which the feed, maintained at a transport temperature above the deposition temperature so that the substances are not deposited, is thermally insulated from the inner wall. This prevents the feed from being cooled toward its delivery end down to the deposition temperature.
The substances to be deposited are, for example, initial products for a CVD process which are dispersed in a carrier gas. These are transported into the deposition chamber via the feed using the carrier-gas flow. In order to prevent premature deposition of the substances, the feed has an elevated transport temperature. The transport temperature is customarily significantly above the deposition temperature of the inner wall. In order to prevent or reduce a temperature gradient along the feed as far as its delivery end, thermal insulation is arranged between the feed and the inner wall. The effect achieved by this is that the delivery end has a temperature above the deposition temperature, so that premature deposition of the substances there is effectively prevented. The temperature gradient between the cool inner wall and the hot feed falls, according to the invention, primarily through the thermal insulation. It is therefore not until after entering the deposition chamber that the incoming substances come into contact with the cool walls (inner wall) and are not fully deposited until then.
Preferably, the thermal insulation even prevents cooling of the delivery end to below the transport temperature, i.e. the feed is at the transport temperature as far as its delivery end.
In the simplest embodiment, the feed is formed by a tube that extends all the way to the deposition chamber. The tube may be designed in one or more parts. Expediently, there is also an inlet bore in the thermal insulation for introducing the substances, the inlet bore being in this case part of the feed. Preferably, the feed is enclosed by a heater, which may also extend as far as the delivery end.
In accordance with an added feature of the invention, the deposition chamber has a connector on its outside, into which the feed protrudes with its delivery end as far as the deposition chamber and is thermally insulated from the connector.
Owing to the connector holding the feed on the outside of the deposition chamber, the temperature gradient is partially fed through this connector. At its opposite end from the deposition chamber, the connector may also enter into direct contact with the feed. At that point of contact, the connector is therefore at the transport temperature. Conversely, at its end next to the deposition chamber, it is at a significantly lower temperature, which is between the transport temperature and the deposition temperature. So that the temperature gradient along the connector is not imparted to the feed, thermal insulation is preferably arranged between the latter and the connector.
The inner wall of the deposition chamber, which is at the deposition temperature, may be formed either by the inside of the deposition chamber or by separate surfaces arranged inside the deposition chamber. It has proved advantageous for the delivery end to protrude to a certain extent into the deposition chamber. If, in spite of the thermal insulation, substances are already deposited at the delivery end, then they can drain off from there without wetting the inner wall. Because of the high transport temperature, the substances condense there as a liquid. As a result, possible solidification of the substances in the immediate vicinity of the delivery end, and therefore clogging of the feed, are advantageously avoided.
In accordance with another feature of the invention, a heater is provided around the connector or between the connector and the feed.
For reliable temperature control of the feed, a heater is provided either between it and the connector or around the connector on its outside. If the heater is provided between the feed and the connector, it serves as thermal insulation at the same time.
A further advantageous embodiment is wherein the feed is fed downward to the deposition chamber.
Owing to the feed directed at a slant to the deposition chamber, it is easier for substances which may already have been deposited to flow away inside the feed. Since a deposition process is always subject to a temperature-dependent distribution between the substance which has already been deposited and that which is still in gas form, even when there i
Greenberg Laurence A.
Hopkins Robert A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Simmons David A.
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