Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
1996-02-16
2001-03-13
Smith, Lynette R. F. (Department: 1641)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C118S715000, C118S728000, C438S800000
Reexamination Certificate
active
06200412
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to chemical vapor deposition (CVD) systems and in particular to arrangements for cleaning high-density-plasma CVD systems.
BACKGROUND OF THE INVENTION
Plasma-assisted chemical vapor deposition systems are used to grow thin films on silicon wafers and other substrates. In the course of growing the film on the wafer or other substrate, the film is also deposited on other locations in the reaction chamber. Periodically, these deposits must be removed to prevent them from building up to the point where particulates are generated. Particulates can, for example, reduce microelectronic device yield, since a die on which a particle has landed during processing must normally be discarded.
It is known to remove film build-up with liquid etchants, vapor etchants and plasma etchants. Of these methods, plasma etching is favored because it provides superior cleaning rates and can be performed without exposing the reaction chamber to the atmosphere. These characteristics are required for high deposition system productivity. If the reaction chamber is being used to deposit a SiO
2
film, for example, NF
3
can be used as a clean gas. The NF
3
plasma creates fluorine radicals which react with the SiO
2
film under the influence of ion bombardment to form SiF
4
and other volatile compounds.
The process gas is injected into the reaction chamber through a process gas injection system, which may include a plurality of tubes. The deposition gas tubes may be directed radially inward from the periphery of the reaction chamber, although other orientations of the tubes are possible. During the deposition process an unwanted film of the deposition material forms on the inner surfaces of the deposition gas tubes. This film must be removed during cleaning.
The conventional practice is to inject the clean gas through the same tubes that were used to introduce the process gas. A problem with this technique is that it has been found to be a very inefficient way of removing the film which forms on the insides of the deposition gas tubes.
Thus there is a clear need for a way of effectively cleaning the deposition gas injection tubes of a plasma-enhanced CVD system.
Fluorine-bearing compounds are frequently used as the clean gas. Following the clean cycle, a fluorine residue remains on the walls and other surfaces of the reaction chamber. The fluorine residue must be removed for safety reasons and to insure that the film adheres to the reaction chamber surfaces in the subsequent deposition cycle. U.S. Pat. No. 5,129,958 describes the use of a reducing gas to remove the fluorine residues, but this process requires the use of elevated reaction chamber temperature, which is difficult for many systems, and therefore takes an undue amount of time.
SUMMARY OF THE INVENTION
A plasma-enhanced chemical vapor deposition system according to this invention includes at least one dedicated clean gas injection orifice or tube. The dedicated orifice or tube is placed at a location where minimal deposition occurs during the operation of the CVD system. In the preferred embodiment, the process gas is injected into the reaction chamber through a plurality of tubes. The dedicated clean gas injection orifice or tube is located between the wafer supporting chuck or platen and the outer wall of the reaction chamber, and at level approximately equal to the level of the wafer supporting chuck or platen when a wafer is being processed in the reaction chamber. This position is chosen to minimize deposition on the clean injector, minimize particle generation from the clean injector, and maintain the ability to effectively clean surfaces near the clean injector. The dedicated clean gas injection orifice or tube is also positioned so that it directs the clean gas to the film-coated surfaces of the reaction chamber before the clean gas reaches the exhaust pump port.
In the preferred embodiment, during deposition processing a hemispherically-shaped coil is used to inductively couple energy to the plasma. The top of the coil is typically connected to a power source while the bottom of the coil (the circumferential turn of the hemisphere) is grounded. In accordance with another aspect of the invention, during cleaning both the top and bottom of the coil are driven by a power source, and the coil as a whole acts to couple energy, mainly capacitively, into the plasma. Also, typically the coil is operated at a significantly higher frequency during the cleaning cycle than during processing. With these modifications, the coil produces a plasma which is particular well suited to cleaning the inside surfaces of the reaction chamber.
The geometry of the coil is such that electrical self-resonances occur at the higher frequencies. It is believed that this property of the coil makes this electrical configuration robust for powering cleaning plasmas of varying compositions and, therefore, varying electrical characteristics.
In accordance with yet another aspect of the invention, a plasma of hydrogen or a hydrogen-oxygen mixture is used to remove fluorine-bearing residues from the surfaces of the reaction chamber following the clean cycle. The use of the plasma makes the fluorine removal possible at low temperatures (25°-100° C.).
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Kilgore Michael D.
Mountsier Thomas W.
Oswalt James C.
Rau Christopher J.
Tobin Jeffrey A.
Novellus Systems Inc.
Ryan V.
Saxon Roberta P.
Skjerven Morrill & MacPherson LLP
Smith Lynette R. F.
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