BACKGROUND OF THE INVENTION
This invention relates to the deposition of thin layers from reactive gases, and, more particularly, to a system for delivering such gases to a deposition reactor.
In chemical vapor deposition (CVD), one or more reactive gases is contacted to a substrate that has been energized, as by heating. With the proper selection of the reactive gas or gases, the substrate type and temperature, gas partial and total pressures, and other operating parameters, the reactive gases deposit a selected material as a gradually thickening layer onto the surface of the substrate. The deposition continues until the desired thickness is reached.
The reactive gases used in the reactive deposition are provided from either gaseous or liquid sources. Liquid sources have become increasingly popular, as the reactive gases are often safer to handle and less toxic when provided in their liquid forms. Prior to the reactive deposition, the liquid source is heated to produce a vapor of the reactive gas, which is conducted to the substrate and reacted.
Several heretofore unsolved problems have been encountered in delivery systems that utilize liquid sources of the reactive gases. Flow variations in individual gases are sometimes observed, leading to variations in composition of the deposited layer. Deposits can build up in the interior of the delivery system. Contaminants can enter the system during operating transitions such as the changing of sources. Although acceptable deposited structures can often be made in spite of these problems, it would be preferred to improve deposition and delivery system operation through their solution.
There is therefore a need for an improved reactive gas delivery system for use with liquid sources. The present invention fulfills this need, and further provides related inventions.
SUMMARY OF THE INVENTION
The present invention provides a gas delivery system operating from at least one liquid source, for use in reactive gas deposition procedures such as chemical vapor deposition. The gas delivery system minimizes the introduction of contamination during changeovers and at other times. Flow variations are also largely avoided by preventing the deposition of unreacted vapor in the gas delivery system. The absence of contamination and the avoidance of the deposition of unreacted vapor prevents the buildup of contamination deposits within the gas delivery system. The gas delivery system of the invention is compatible with the use of high-precision controllers such as mass flow controllers, permitting careful control of the composition of the deposited layers.
In accordance with the invention, a liquid deposition source delivery system comprises means for supplying a flow of a vapor having a boiling point greater than ambient temperature and means for controlling the flow of the vapor. The means for controlling has an upstream side in communication with the means for supplying and a downstream side. The apparatus also includes means for distributing a flow of the vapor, which is in communication with the downstream side of the means for controlling the flow of the vapor. There is a means for heating at least a portion of the
means for supplying, the means for controlling the flow of the vapor, and at least a portion of the means for distributing.
In another embodiment, a liquid deposition source delivery system comprises a reactant source of a liquid chemical reactant, and a first heater positioned adjacent to the reactant source. A vapor collection system is in communication with the reactant source to collect vapor evolved from the reactant source. A flow controller has an upstream side in communication with the vapor collection system and a downstream side. The apparatus includes a vapor distribution system in communication with the downstream side of the flow controller. A second heater is positioned adjacent to the flow controller, at least a portion of the vapor collection system, and at least a portion of the vapor distribution system.
The second heater, also called the means for heating, prevents reactive gas previously vaporized from the reactant source from depositing in the flow controller, the vapor collection system, and the vapor distribution system. These components are heated to a temperature above the boiling point of the reactive gas flowing in that portion of the system. The reactive gas therefore cannot deposit prior to reaching a reactor.
To minimize contamination, there is preferably provided a two-part purge system. The purge system includes a first gas purge system in communication with the vapor collection system and the upstream side of the flow controller and/or a second gas purge system in communication with the vapor distribution system and the downstream side of the flow controller. In the preferred approach, both the first and second purge systems are provided, to prevent contaminants from entering the gas delivery system during transient conditions such as source changeovers, and to clean contaminants from the delivery system if they do reach it.
The present invention provides an advance in the art of gas delivery systems, particularly those for use in reactive deposition procedures such as chemical vapor deposition. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a reactive gas deposition system; and
FIG. 2 is a more detailed schematic diagram of the gas delivery portion of the deposition system of FIG. 1.
DETAILED DESCRIPTION OF THE
FIG. 1 illustrates a reactive gas deposition system 20 in which the present invention is used. FIG. 2 illustrates a portion of the deposition system 20, the gas delivery system 22 of the invention, in more detail. These systems 20 and 22 are illustrated with various combinations of gas flow sources and deliveries utilized in a preferred embodiment. The present invention is not limited to these particular combinations.
The reactive gas deposition system 20 includes a reactor 24, typically in the form of a quartz tube, that is heated by a furnace 26 around the reactor 24. A substrate 28, upon which the reactive gas deposition product is to be deposited, is supported within the reactor by a fixture 30.