Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Reexamination Certificate
1999-02-02
2001-05-29
Meeks, Timothy (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
C427S255391, C427S255394, C118S719000, C118S724000
Reexamination Certificate
active
06238739
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the formation of Ti
1-x
Al
x
N type compounds on substrates.
BACKGROUND OF THE INVENTION
The advantages of such coatings are well-known. It is known since a long time that it is particularly useful to deposit TiN layers on parts that have to be surface hardened, for example for coating tools, to increase their resistance to wear. However, it has been noted that TiN layers are liable to deterioration with time due to oxidation. However, the introduction of aluminum in the TiN array provides a good resistance to oxidation because, during use, a thin Al
2
O
3
layer is formed and protects the hard coating, which largely increases the lifetime of the tool. This result is not obtained by a mixed deposit of TiN and AlN.
Thus, many searches have been made for implementing Ti
1-x
Al
x
N coatings. The known methods are mainly physical deposits such as reactive sputtering, possibly magnetron enhanced, and arc reactive coatings. These methods are not easy to implement, in particular due to the problem of making the sources. Additionally, sputtering type methods or projection type methods are not well adapted to the coating of parts having complex shapes.
Therefore, one has tried to find a deposition method of the CVD type. However, while it is known to make CVD deposition of TiN layers or AlN layers from titanium chloride and aluminum chloride in the presence of ammonia and/or nitrogen, it has always been considered that the simultaneous use of titanium chloride and aluminum chloride will provide mixed depositions of AlN and TiN and not to the deposition of an homogeneous layer of Ti
1-x
Al
x
N type phase.
Additionally, attempts to make CVD coatings from organo-metallic compounds of titanium and aluminum have been unsuccessful up to now.
One will more particularly consider the article of Sang-Hyeob Lee, Ho-Joon Ryoo and Jung-Joog Lee of the Seoul University, J. Vac. Sci. Technol., A 12(4), July-August 1994. In the introductory part of this article, the authors summarize the various known processes for forming Ti
1-x
Al
x
N coatings such as above-mentioned and indicate the difficulties that exist due to the fact that TiN has a NaCl type structure while AlN crystallizes in an hexagonal structure of the wurtzite type. However, the authors tried to find a new CVD method and claimed to obtain Ti
1-x
Al
x
N coatings by a plasma enhanced CVD method, using TiCl
4
, AlCl
3
, NH
3
, H
2
and argon (forming the plasma) in an RF plasma or 15-200 watts. It would be emphasized that a plasma enhanced CVD deposition is not a simple operation and is not adapted to coat parts having complex shapes.
An object of the invention is to provide a method of CVD depositing Ti
1-x
Al
x
N layers from simple precursors, and without a plasma enhancement.
SUMMARY OF THE INVENTION
To attain this object, the applicant observed that, if a suitable temperature range is selected, it is possible to use simple precursors comprising titanium chloride, aluminum chloride and ammonia, i.e. the same precursors as those suggested in the above-mentioned article but, that in this temperature range, it is not useful to operate in a plasma.
More particularly, the invention provides a method of forming a coating of Ti
1-x
Al
x
N on a part, comprising the steps of heating a CVD chamber at a temperature of between 250 and 500° C.; arranging in this chamber the part to be coated, at a temperature of 550 to 650° C.; and injecting in the chamber a mixture of aluminum and titanium chlorides, NH
3
and H
2
, the molar quantity of NH
3
being higher than the molar quantity of the chlorides and the molar quantity of hydrogen being higher than five times the molar quantity of the chlorides.
According to an embodiment of the invention, the pressure is in a range of 10
2
to 10
5
Pa.
According to an embodiment of the invention, the aluminum and titanium chlorides are TiCl
4
and AlCl
3
.
According to an embodiment of the invention, the chlorides are obtained by injecting chlorine in an intermediate chamber adjacent to said chamber, and containing an aluminum-titanium alloy at a temperature of 650-750° C., the chlorine rate being selected so that no chlorine not combined with titanium and aluminum exists at the output of this intermediate chamber.
The invention also provides an apparatus of formation of a coating of Ti
1-x
Al
x
N in a CVD enclosure, wherein the enclosure comprises a reaction chamber in which is arranged the part to be coated, at a temperature of 550-650° C.; an auxiliary chamber receiving chlorine and containing an aluminum-titanium alloy at a temperature of 650-750° C.; and a mixture chamber at a temperature of 250-550° C. receiving ammonia, hydrogen and possibly a carrier gas such as argon and the outflow from the auxiliary chamber.
REFERENCES:
patent: 4842710 (1989-06-01), Freller et al.
patent: 5071693 (1991-12-01), Sue et al.
patent: 5252360 (1993-10-01), Huttl et al.
patent: 5272014 (1993-12-01), Leyendecker et al.
Hakansson, G. et al., “Microstructure and Physical Properties of Polycrystalline Metastable TiO.5AIO.5N Alloys Grown by DC Magnetron Sputter Deposition.” Thin Solid Films, 153 (1987) 55-65.*
Lee, Sang-Hyeob et al., “(Ti1-xAlx)N coatings by plasma-enhanced chemical vapor deposition”. J. Vac. Sci. Technol., A 12(4), Jul./Aug. 1994, pp. 1602-1607.
Bernard Claude
Blanquet Elisabeth
Dutron Anne-Marie
Madar Roland
Rouault Alain
Centre National de la Recherche Scientifique
Chen Bret
Duane Morris & Heckscher
Meeks Timothy
Plevy Arthur L.
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