Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-10-15
2001-10-09
Pianalto, Bernard (Department: 1762)
Stock material or miscellaneous articles
Composite
Of inorganic material
C427S131000, C427S248100, C428S189000, C428S195100, C428S698000, C428S700000, C428S701000, C428S702000, C428S704000
Reexamination Certificate
active
06299991
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method for depositing a ferromagnetic compound, such as chromium dioxide (CrO
2
), in thin film form in a selective fashion over a substrate, such that the growth occurs only above specific regions of the substrate that have been appropriately modified.
More specifically, the invention relates to a method for depositing such a ferromagnetic compound in a selective growth process for a plurality of applications including magnetic memory and storage-based devices, as well as other devices.
2. Description of the Related Art
Conventional systems utilize chromium dioxide (CrO
2
) as an important ferromagnetic material which is used, for example, as a particulate magnetic recording media. Chromium dioxide has the rutile crystal structure which is tetragonal with lattice parameters of a=4.423 Å and c=2.917 Å. The chromium ions are in the Cr
+4
state with the electronic configuration [Ar]3d
2
with a magnetic moment of 2 &mgr;
B
per ion.
Because of its half-metallic nature, where the majority spin electrons have a metallic character and the minority spin electrons have a semiconducting character (e.g., see K. Schwarz, J. Phys. F 16, 211 (1986)), chromium dioxide also is ideally suited for use in magnetic tunnel junction (MTJ) devices. Suitable applications for CrO
2
include, as a media for magnetic storage, and as a component in magnetic tunnel junction devices.
Recently, there have been attempts to deposit CrO
2
in the form of thin films (though not in a selective area fashion), as described, for example, in R. C. DeVries, “Epitaxial Growth of CrO
2
”, Mat. Res. Bull.
1, 83 (1966); S. Ishibashi, T. Namikawa, and M. Satou, “Epitaxial Growth of CrO
2
in Air”,
Japan J. Appl. Phys.
17, 249 (1978); S. Ishibashi, T. Namikawa, and M. Satou, “Epitaxial Growth of Ferromagnetic CrO
2
Films in Air”,
Mat. Res. Bull.
14, 51 (1979); and K. P. Kamper, W. Schmitt, G. Guntherodt, R. J. Gambino, and R. Ruff, “CrO
2
-A New Half-Metallic Ferromagnet?”,
Phys. Rev. Lett.
59, 2788 (1987).
However, these studies have been confined to the uniform deposition of CrO
2
that covered the entire substrate (e.g., a substantially continuous deposition). Further, selective area growth of CrO
2
has not been attempted on predetermined locations (e.g., those that could be patterned) on the substrate surface with arbitrary size dimensions. Thus, control in the deposition of such films has been limited, and thus the applications of such films have been limited.
Selective area growth, which consists of depositing a material over a substrate in such a fashion that material is deposited only on specific regions of substrate that have been appropriately modified, is an established technique in the field of compound semiconductors and metal deposition.
In the area of semiconductor deposition, selective growth has been used for the production of higher quality thin film optoelectronic devices for making better light emitters, and in the case of metals, selective growth has been used for different applications such as plugs for hole filling in Si technology. The particular technical details for selective area growth of various systems are quite diverse due to the different chemistries involved.
Thus, as noted above, selective area growth has not been used for applications in ferromagnetic thin films or in forming any substrates used in magnetic memory applications, for example.
The conventional method of patterning blanket thin films using photolithography and etching is difficult in the case of CrO
2
since it is not readily etched in a reactive plasma or with wet chemicals. Hence, selective area growth would be a preferred approach since it requires no subsequent patterning steps.
SUMMARY OF THE INVENTION
In view of the foregoing and other problems of the conventional structures and methods, it is an object of the present invention to provide a structure and method for allowing selective area deposition of a ferromagnetic material such as CrO
2
.
In a first aspect of the invention, a method of forming a magnetic device, includes selective area deposition of a ferromagnetic material on a substrate, part of the substrate surface being covered with material with a crystalline structure that shares one or more symmetry relations with the crystal structure of the ferromagnetic material.
These symmetry relations do not have to be the characteristic symmetry element that defines membership into the particular crystal system. As an example, a substrate is considered that is hexagonal, so that its characteristic symmetry element is a 6-fold rotation axis. Further considered is a ferromagnetic thin film that is tetragonal so that its characteristic symmetry element is a single 4-fold rotation axis. In this case, the symmetry element that these two structures share is that of 2-fold rotation symmetry about these axes since it is obvious that both the 6-fold axis (of the hexagonal structure) and the 4-fold axis (of the tetragonal structure) possess 2-fold symmetry.
Generally, the technique utilizes the idea of deposition of CrO
2
on a surface by the reaction CrO
3
=CrO
2
+1/2O
2
.
The present inventors have found that, at an appropriate substrate temperature, the above reaction will proceed only on certain surfaces, but the reaction will not occur on other surfaces. This discovery by the present inventors is the basis for a selective area growth process. If a substrate surface is patterned in the form of features consisting of two materials, A and B such that CrO
2
grows on A but not on B, then the spatial growth of CrO
2
can be controlled selectively by appropriately pre-patterning the substrate surface with features of A and B. The relationship between the surface symmetry of the two constituents is important. Thus, surfaces on which growth can occur will be from a crystalline system that is trigonal, monoclinic, or a system with a symmetry higher than monoclinic such as orthorhombic, tetragonal, or cubic; or a system with a symmetry higher than trigonal such as hexagonal—as long as one can define a symmetry relationship between CrO
2
and the substrate. Substrates on which growth will not occur will be amorphous such as SiO
2
.
Thus, with the unique and unobvious features of the present invention, selective area growth can be used for applications of ferromagnetic thin films including magnetic memory applications.
REFERENCES:
Kamper, et al., “CrO2-A New Half-Metallic Ferromagnet?”, vol. 59, No. 24, Physical Review Letters, Dec. 14, 1987, pp. 2788-2791.
Tsaur, et al., “Low-dislocation-density GaAs epilayers grown on Ge-coated Si substrates by means of lateral epitaxial overgrowth”, Appl. Phys. Lett. 41(4), Aug. 15, 1982, pp. 347-349.
Ishibashi, et. al., “Epitaxial Growth of CrO2 on Sapphire in Air”, Japan. J. Appl. Phys. vol. 17 (1978), No. 1, pp. 249-250, (No month avail.).
Karlheinz Schwarz, “CrO2 predicted as a half-metallic ferromagnet”, J. Phys. F: Met. Phys. 16(1986) pp. L211-L215, (No month avail.).
R. C. DeVries, “Epitaxial Growth of CrO2”, Mat. Res. Bull. vol. 1, pp. 83-93, 1966. Pergamon Press, Inc. (No month avail.).
Ishibashi, et. al., “Epitaxial Growth of Ferromagnetic CrO2 Films in Air”, Mat. Res. Bull. vol. 14, pp. 51-57, 1979. Pergamon Press, Inc. (No month avail.).
Bojarczuk, Jr. Nestor A.
Duncombe Peter R.
Guha Supratik
Gupta Arunava
Karasinski Joseph M.
International Business Machines - Corporation
McGinn & Gibb PLLC
Pianalto Bernard
Underweiser Marian
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