Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material
Reexamination Certificate
1999-04-27
2001-10-23
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
C438S492000, C438S493000, C438S496000, C438S497000, C438S500000, C438S503000, C438S507000, C438S478000, C257S412000, C257S486000
Reexamination Certificate
active
06306739
ABSTRACT:
CROSS-REFERENCES TO RELATED PATENT APPLICATIONS
This patent application is related to Air Force inventions AFB00437 and AFB00473 which are being concurrently filed herewith.
BACKGROUND OF THE INVENTION
One of the major difficulties encountered in forming high quality nitride films is creating conditions in which sufficient nitrogen is incorporated in the film.
The material quality of the nitride can be significantly degraded if the fractional deficiency of nitrogen is as small as one part per hundred thousand. The difficulty arises because molecular gaseous nitrogen, N
2
, is chemically stable: in nitride deposition processes the formation of N
2
is chemically favored over the formation of nitrides. In molecular beam epitaxy (MBE), for example, various schemes have been employed to deliver nitrogen to the substrate in chemically active forms—for example, by exciting gaseous nitrogen via plasma or electron cyclotron resonance sources, or by using ammonia (NH
3
) gas—to increase the likelihood that delivered nitrogen will react with the metal (e.g., with Ga to form GaN), somewhat overcoming the strong propensity of the delivered nitrogen to form N
2
.
There is a large technical literature pertaining to evaporative deposition of films. Long-established methods are summarized in the book by Joseph I. Goldstein et al.,
Scanning Electron Microscopy and X
-
Ray Microanalysis
(New York and London: Plenum Press, 1992), Section 13.6, and in Chapter 9 of the book edited by S. M. Sze,
VLSI Technology
(McGraw-Hill, 1983). MBE has recently been reviewed in an article by K.-Y. Cheng, “Molecular Beam Epitaxy of III-V Compound Semiconductors for Optoelectronic Applications,” Proceedings of the IEEE, Volume 85, No. 11 (November 1997), pp. 1694-1714. Use of MBE methods specifically for deposition of nitride films has recently been reviewed in the article by G. Popovici, H. Morkoç, and S. N. Mohammed, “Deposition and properties of group III nitrides by molecular beam epitaxy,” pp. 19-69 in the book
Group III Nitride Semiconductor Compounds,
edited by Bernard Gil (Oxford University Press, 1998).
BRIEF SUMMARY OF THE INVENTION
This invention relates to the use of ammonium halides (e.g., ammonium chloride, ammonium bromide, or ammonium iodide) to form films of metal nitrides (M-nitrides), specifically in the formation of films and multiple film layers by evaporative deposition methods. It relates to traditional evaporation methods as well as to the family of precisely controllable deposition methods known as molecular beam epitaxy (MBE); the latter includes methods known as solid source MBE (SSMBE), gas source MBE (GSMBE), chemical beam epitaxy (CBE), and metal-organic MBE (MOMBE).
The object of this invention is to deliver nitrogen to the substrate in a new way, which, by increasing the likelihood of nitride formation, promotes growth of superior nitride films in evaporative deposition methods. Such films—in particular, specially designed multiple film layers—may be used to create electronic devices such as metal-semiconductor field effect transistors (MESFETs), metal-insulator field effect transistors (MISFETs), high electron mobility transistors (HEMTs), modulation doped field effect transistors (MODFETs), and heterojunction bipolar transistors (HBTs). They are also employed to form semiconductor light-emitting diodes (LEDs), lasers, and optical detectors, and also optical coatings (e.g., antireflection coatings, reflective coatings, and filters).
This deposition of nitride films under vacuum conditions may include several techniques such as: (1) conventional evaporation methods such as electron beam evaporation and its counterparts in which heat for evaporation is supplied by resistance or RF heating; and (2) MBE and related ultrahigh vacuum methods for depositing films, including methods known as SSMBE, GSMBE, CBE, and MOMBE. In this invention, one or more metal-containing sources and one or more ammonium halides are heated such that they evaporate into a vacuum environment (except that, in MOMBE, beams of metal-containing organometallic source compounds may be created by other means) and made to impinge on a substrate. The materials interact on the substrate to form a film of the desired nitride compound or alloy; the substrate usually will be heated to promote chemical reaction and good film properties such as high crystallinity. Other sources—to provide dopant impurities like silicon or magnesium, for example—would be part of a deposition system envisioned in this invention. Multiple film layers, including quantum wells and superlattices, may be formed using this method, in addition to a single film.
Therefore, one object of the present invention is to provide a process of making metal nitrides by evaporative deposition.
Another object of the present invention is to provide a process of making metal nitride films by evaporative deposition from which new electronic devices may be fabricated.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the pertinent art from the following detailed description of preferred embodiments of the invention and the related drawings.
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Sylwester Porowski, Bulk and Homoepitaxial GaN-growth and Characterisation, Journal of Crystal Growth, 1998, 153-158, 189/190, Elsevier Science B.V., Warsaw, Poland.
Y. Naoi*.K.Kobatake, S. Kurai, K. Nishino, H. Sato, M. Nozaki, S. Sakai, Y. Shintani, Characterization of bulk GaN grown by sublimation technique, Journal of Crystal Growth, 1998, 163-166, 189/190, Elsevier Science B.V., Warshaw, Poland.
R.J. Molanar, P.Maki, R. Aggarwal, Z.L. Liau, E.R. Brown, I. Melngailis W. Gotz, L.T. Romano, N.M. Johnson, Gallium Nitride Thick FIlms Grown by Hydride Vapor Phase Epitaxy, Symposium E “III-Nitride, SiC and Diamond for Electronic Devices”, 1996, vol. 423, Mater. Soc. Symp. Proc., USA.
Glen A. Slack, T.F. McNelly, Growth of HIgh Purity AIN Crystals, Journal of Crystal Growth, 1976, 263-279, 34, North-Holland Publishing Company.
T. Detchprohm, K.Hiramatsu, N. Sawaki, I. Akasaki, The homoepitaxy of GaN by metalorganic vapor phase epitxy using GaN substrates, Journal of Crystal Growth, 1994, 170-174, 137, Elsevier.
Takao Ishii, Yasuo Tazoh, Shinataro Miyazawa, LiGaO2 single crystal as a lattice-matched substrate for hexagonal GaN thin films, Journal of Crystal Growth, 1998, 208-212, 189/190, Elsevier Science B.V.
H.P. Maruska,J.J. Tietjen, The Preparation and Properties of Vapor-Deposited Single Crystal-Line GaN, Applied Physics Letters, Nov. 15, 1969, 327-329, vol. 15 No. 10.
Collier Stanton E.
Lee, Jr. Granvill D.
Smith Matthew
The United States of America as represented by the Secretary of
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