Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Patent
1986-12-23
1989-03-07
Moore, David K.
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
313156, 313161, 31323131, 313552, 315 34, 31511121, 315176, 315344, H05H 146
Patent
active
048109355
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention concerns the generation of plasmas. More particularly, it concerns the generation of high density plasmas at low pressures. The invention is especially useful for the generation of large volume plasmas in insulating cavities for use in dry etching applications and in the modification of surface properties of materials, but it is not limited to these applications.
BACKGROUND ART
The use of plasmas for etching and other purposes is well known. A convenient reference paper on plasma etching is the paper by Paul J. Marcoux entitled "Dry etching--an overview", published in Hewlett Packard Journal, Aug. 1982, pages 19 to 23.
The equipment that is used to produce a plasma consists of: (within which the plasma is generated); discharge tube); provide a source of the ions and electrons which form the plasma); source of power to establish the plasma); and network into the plasma.
Normally, the plasma tube is a metal cylinder of circular cross-section. However, cylinders of pyrex and quartz glass have been used by the present inventor (see the publications referred to below, in this paragraph). Among the antennas used to couple the rf power into the plasma, the most effective is a double loop antenna, which fits tightly against the sides of the discharge tube (see, for example, the experimental equipment described in the papers by (a) R. W. Boswell, in Physics Letters, Volume 33A, December 1970, pages 457 and 458, (b) R. W. Boswell et al in Physics Letters, Volume 91A, September 1982, pages 163 to 166, and (c) R. W. Boswell in Plasma Physics and Controlled Fusion, Volume 26, pages 1147 to 1162, 1984).
DISCLOSURE OF THE PRESENT INVENTION
It has been recognised for some time that more efficient production of silicon chips (and other semiconductor devices) for computers could be achieved if the area of the silicon wafer (or the wafer of the other semiconductor material) that is etched to form the chips could be increased. Efficient production of high density plasmas of larger volume (that is, in a discharge tube of greater internal diameter) has been theoretically possible, but has not been achieved in practice prior to the development of the present invention. Furthermore, the production of a larger volume plasma would be of little benefit unless this plasma is substantially uniform and has a reasonably high density of the non-charged atomic species (usually fluorine) which are used to perform the etching.
It is an object of the present invention to provide the means for producing a plasma which has a significantly larger volume than has been produced previously, and which has a substantially uniform volume of non-charged atomic species.
This objective is achieved by establishing the plasma in a cavity which is connected to an adjoining auxiliary region, at the same internal pressure as the cavity, into which the plasma extends. In a preferred form of the present invention, the plasma is established at a much lower pressure than has been used previously, and under resonance conditions (discovered by the present inventor) which result in the production of a high volume of atomic gas species.
With regard to the basic form of the present invention, the present inventor has found that if a plasma is generated in a plasma tube that is connected to an auxiliary region at the same low pressure as the plasma tube, then the plasma extends into that auxiliary region. The auxiliary region may have a volume that is substantially larger than the volume of the plasma. A sample to be etched can be supported in the plasma tube or (preferably) in the auxiliary region, where it will be contacted by the plasma.
With regard to the low pressure operation of the plasma the present inventor has found, in the course of the application of his previous scientific work (see the aforementioned scientific papers) to the field of dry etching of semiconductor materials, that if a gas (such as sulphur hexafluoride) which contains reactive species is used for dry etching of silicon, there is a substantial increase
REFERENCES:
patent: 3437864 (1969-04-01), Kofoid et al.
patent: 4438368 (1984-03-01), Abe et al.
patent: 4574179 (1986-03-01), Masuzawa et al.
patent: 4631438 (1986-12-01), Jacquot
patent: 4645977 (1987-02-01), Kurokawa et al.
Moore David K.
Powell Mark R.
The Australian National University
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