Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-12-21
2001-12-25
Bueker, Richard (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S708000, C118S715000, C118S730000, C118S724000
Reexamination Certificate
active
06332928
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates, in general, to apparatus for producing flow modulation epitaxy, and more particularly relates to a high throughput organometallic vapor phase epitaxy (OMVPE) apparatus for deposition of material on substrates. In a preferred embodiment, the invention is directed to a cold wall reactor, which is convertible to a hot wall reactor, for epitaxial deposition of compound semiconductor materials.
Reactors for use in chemical vapor deposition, for example for epitaxial processing of semiconductor materials, or wafers, are generally well known. Two types of reactor are available for epitaxial processing, one being referred to as a cold wall reactor and the other being referred to as a hot wall reactor. Both types are well known, and the particular reactor used depends upon the type of reaction to be performed. For example, silicon processing is normally done in a hot wall reactor device.
In a chemical vapor deposition reactor, the chemicals used in the process have a tendency to decompose on the cell wall as well as on the substrate as they flow through the cell. Layers of decomposed reactants build on the cell wall, and eventually these layers begin to flake off, producing particulate contaminates in the cell which damage the wafer being processed. In addition, certain compounds produce a chemical memory effect; i.e., impurities accumulate on the cell wall, and then are released during a later run, contaminating that later run. To prevent such contamination, the cells must be periodically cleaned. Usually, however, this can only be done by disassembling the device, which not only is time-consuming, but causes the entire cell to become contaminated by the atmosphere. Thus, there is a need for a mechanism for cleaning reactor cells without the need to disassemble them and without risking contamination.
Furthermore, in many chemical vapor deposition reactors a cooling mechanism is provided to reduce the temperature of the hot reactive gases after they have passed over the wafer to be treated and prior to their removal from the reactor by external vacuum equipment. In such devices, however, as the cooled gases flow out of the chamber, the chemicals carried by the gases condense or precipitate onto the vacuum equipment, requiring time consuming and expensive maintenance to avoid serious damage to the equipment. When phosphide compounds are used in reactors of this type, for example in the formation of red lasers, such compounds present an additional problem, for yellow, red or white phosphorous compounds are pyrophoric and spontaneously catch fire if exposed to the atmosphere. If such products precipitate onto the reactor walls or reach the vacuum equipment, opening the reactor to clean it can result in a fire.
Finally, difficulties have been encountered in the gas distribution systems used with various cell geometries, for it is difficult to obtain a proper seal for the reactor chamber, thereby limiting the structural arrangement of the reactor and the consequent flow paths. As a result, many reactor arrangements cause the gases to be directed onto flat surfaces. The gases rebound from such surfaces, resulting in a highly undesirable recirculation of the reactive gases within the chamber. Thus, a simplified reactor geometry having improved fluid dynamics for the gas flowing into the chamber that will avoid recirculation problems is highly desirable.
SUMMARY OF THE INVENTION
The present invention resolves the problems of prior reactor devices as discussed above. Accordingly, the invention provides, among other things, a vertical barrel, concentric cylinder design for a cold wall reactor cell which can be converted to a hot wall cell for cleaning the interior of the reactor.
In accordance with the invention, the reactor includes inner and outer concentric cylinders which preferably are quartz tubes, which cooperate to define an annular reactor cell. A susceptor is mounted in the annular reactor cell, adjacent the exterior surface of the inner cylinder, and includes an outwardly sloping, or conical, outer surface which receives wafers to be treated. The susceptor is supported in the cell by a rotation fixture which includes a support cylinder, which may be another quartz tube, having an upper edge which engages the bottom of the susceptor and having a lower edge supported on a support bearing carried by a lower end cap for the reactor cell. The rotation fixture also includes a gear wheel mounted on the exterior of the support cylinder and driven by a corresponding drive gear mounted on the shaft of a drive motor.
A lift fixture includes a top end cap supporting a lift cylinder, which preferably is a quartz tube surrounding the inner reactor cell cylinder. The lift cylinder has a lower shoulder which engages the susceptor and an upper shoulder which engages the end cap. When the lift fixture is moved upwardly, the susceptor is pulled through the top end of the outer reactor cylinder to provide access to wafers on the susceptor and to allow them to be inspected, adjusted and/or replaced. The lift cylinder is rotatable with respect to the top closure so the susceptor may be rotated when lifted for access to all the wafers on the susceptor.
The outer reactor cell cylinder surrounds and encloses the inner reactor cylinder, the susceptor, and the upper lift cylinder, and is secured at its upper end to the top end cap and at its lower end to a bottom end cap. Both end caps preferably are stainless steel, with appropriate seals between the cylinder and the stainless steel end caps being provided. The inner reactor cell cylinder is closed at its top end, and extends downwardly through, and is sealed to, the lower end cap so that the interior of this tube is exposed to atmosphere while the annular region between the cylinders is sealed from ambient atmosphere. An induction heating coil, quartz lamps, or other suitable heat source extends into the inner reactor cylinder to heat the susceptor and thus the wafers which the susceptor supports. The sealed annular region between the inner and reactor cylinders functions as a closed reaction cell.
Hot reaction gases are introduced into the reaction cell at its top end, one or more outlet pumping ports with included filter assemblies are located below the outer reactor cell cylinder, preferably in the lower end cap, for drawing the gases downwardly over the outer surface of the susceptor and the wafers mounted thereon for delivering unused reaction gases to an external vacuum source. Between the susceptor and the outlet port, and surrounding the rotation fixture, is an annular cooler which serves to cool the process gases prior to their exiting the cell. This condenses the majority of unused reactants into their solid phases for trapping by the filters in the outlet ports to prevent the exhaust gas plumbing and valves from being coated with film during reactor operation. Additional cooling is provided by a split clamshell cooling jacket which surrounds the reactor cell cylinder.
The upper and lower end caps preferably are surrounded by conventional dry box enclosures which contain an inert gas and which thereby enable the upper and lower caps to be opened for access to the susceptor and access to and cleaning of the outlet port filters without contaminating the interior of the cell and without the risk of fire or smoke from pyrophoric deposits.
The heat source used with the present invention preferably is a heating coil which is excited by a radio frequency (RF) generator, with the RF power being coupled to the graphite susceptor which forms an inductive load for the coil. The susceptor is thereby heated directly, while the surrounding outer reactor cylinder is heated indirectly, by radiation from the hot graphite, by conduction through the gas present in the cell, or through the supporting rotation fixture, rather than inductively. The reaction chamber is said to be a cold wall cell because of this method of heating. An alternative radiant heating method for cold wall operation is the use of an arra
Butterfield Barry P.
Shealy J. Richard
Bueker Richard
Cornell Research Foundation Inc.
Jones Tullar & Cooper P.C.
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