Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Reexamination Certificate
1998-07-15
2001-04-17
Bueker, Richard (Department: 1763)
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
C118S712000, C118S715000, C118S725000, C118S730000, C427S255500
Reexamination Certificate
active
06217937
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.
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 array of quartz lamps located inside the rotation fixture in place of the heating coil.
To turn the cold wall cell into a hot wall cell for a “self cleaning” operation, the cooling jacket is removed and a split clamshell furnace is provided around the outside of the outer reactor cylinder. During cell cleaning, the wall of the outer cylinder is heated and a corrosive gas such as HCl or a corrosive plasma is injected into the reactor cell to etch deposits off the cell wall and the susceptor. Heating the wall also produces a heating mismatch which will cause deposits to crack and flake off the wall. Using this approach, the cell can be cleaned periodically so that the deposits do not build up and contaminate the cell with particulate matter or with previously used reactants, and this allows cleaning to be done without disassembly or exposure to the atmosphere, thereby preventing atmospheric contamination of the cell.
The present invention is also directed to a reactor gas injection structure which is usable with a variety of reactor cells, but which is particularly adapted to use with the reactor of the present invention to allow the cell to operate in a variety of different modes. Injection ports are located at the top of the cell, adjacent the top end cap, and permit injection of reactant gases through selected ports located symmetrically around the exterior of the reaction cell. Selected gases or gas mixtures can be injected through single selected ports, or through several ports for dispersal around the entire cell. The injection ports preferably are located symmetrically around the cell, with four ports defining four growth zones, for example, and additional ports being provided to permit a uniform distribution of gases in the reactor. The localization of a reactant gas in each zone is provided by establishing a vertical laminar flow in the reaction cell
Bueker Richard
Cornell Research Foundation Inc.
Jones Tullar & Cooper PC
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