Shadow sculpted thin films

Details Shadow sculpted thin films Shadow sculpted thin films

1998-11-12

2001-06-19

Williams, Hezron (Department: 2856)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including sheet or component perpendicular to plane of web...

C427S256000, C427S248100, C427S255500, C333S141000, C333S145000, C333S146000

Reexamination Certificate

active

06248422

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the deposition of shadow sculpted thin films on substrates.
CLAIM TO COPYRIGHT
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
REFERENCE TO MICROFICHE APPENDIX
A microfiche appendix containing software for implementing aspects of the method of the invention disclosed herein forms part of this patent document. The microfiche is on one sheet, and has 27 frames and can be found in parent application Ser. No. 08/681,434 filed Jul. 23, 1996, now U.S. Pat. No. 5,866,204.
BACKGROUND OF THE INVENTION
In the art of growing thin films, it is known to expose a substrate to an oblique incident vapor flux in conditions of limited adatom diffusion and thus grow a columnar microstructure on the substrate.
The optical properties of the resulting microstructure are dependent in part on the material used, the porosity of the microstructure and the orientation of the columns of the thin film.
Hamaguchi et al, U.S. Pat. No. 4,874,664, describe lateral shifting or rotation of the position of the substrate in relation to the vapor flux to create uniform film growth and film layers that have columns with different orientations in the different layers. In Hamaguchi et al, the entire substrate is rotated in between periods of exposure of the substrate to vapor flux, or the substrate is laterally shifted during exposure to vapor flux.
The angle of the incident vapor flux in the prior art tends to be in the range from near 0° to 70° where the angle is measured between the vapor arrival line and the substrate normal, which may be referred to as the polar angle. Where the polar angle is zero, the deposited film is a uniform layer, and does not generate the columnar microstructure. For stationary substrates, results have been published for polar angles reaching close to 90°. The angle of growth of the columns is related in a way poorly understood to the angle of incidence of the vapor flux, but is always observed to be smaller, as measured from the substrate normal, than the angle of incidence.
A paper of Azzam, “Chiral thin solid films”, Appl. Phys. Lett. 61 (26) Dec. 28, 1992, has proposed rotation of the substrate while it is exposed to the oblique incident vapor flux to generate a helical microstructure having helicoidal bianisotropic properties. The proposed rotation of the substrate is about an axis perpendicular to the surface of the substrate, which is referred to in this patent document as rotation about the azimuth, or variation of the azimuthal angle. No particular polar angle is specified, though a figure shows an angle of less than 60°. The inventors have attempted to grow microfilm structures by rotation of the substrate in the presence of a vapor flux incident at a polar angle of about 60° and 70°. However, the resulting structure does not show well defined structures.
The paper of Assam is a theoretical paper and fails to provide directions on how to carry out the method in practice. In addition, the patent of Hamaguchi et al provides only one particular microstructure, with limited variation of the columnar growth.
SUMMARY OF THE INVENTION
This invention seeks to overcome some of the limitations of the prior art and provide a film forming system method and apparatus that allows for the growth of complex microstructures with predetermined patterns of growth. In addition, porosity and optical properties of the shadow sculpted thin film are enhanced by expanding the range of incidence angles of the vapor flux.
According to an aspect of the invention, there is provided an apparatus for growing thin films on a substrate having a surface, the apparatus comprising a vacuum chamber; a vapor source; a first motor disposed in the vacuum chamber above the vapor source, and having a first rotational axis, the first motor having a shaft and means for mounting a substrate on the shaft such that the first rotational axis is normal to the surface of the substrate; a driver for the first motor; a deposition rate monitor having output signals indicative of thin film growth on a substrate exposed to vapor flux from the vapor source; and a controller responsive to the output signals for instructing the drivers to cause the first motor to rotate according to a desired pattern. According to a second aspect of the apparatus of the invention, there is also provided a second motor disposed in the vacuum chamber above the vapor source, and having a second rotational axis at about 90° to the first rotational axis. The first motor is mounted on the shaft of the second motor such that the second rotational axis is parallel to the surface of the substrate. A driver, which may be the same driver as for the first motor, is also provided for the second motor. The controller is also responsive to the output signals to cause the second motor to rotate according to a second desired pattern.
In a further aspect of the invention, a thin film microstructure is provided wherein vapor deposited material extends in distinct helical columns from a substrate. The columns may be capped, and may be supplied with electrodes to form a delay line or a variable wavelength optical filter.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.


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“Helical Microstructures Grown by Laser Assisted Chemical Vapour Deposition” by Mats Boman, Helena Westberg, Stefan Johansson and J. Schweitz, Feb. 1992, IEEE, pp. 162-167.*
Codeposition of continuous composition rugate filters, William J. Gunning et al., Applied Optics, vol. 28, No. 14, Jul. 15, 1989, pp. 2945-2948.
Engineered sculptured nematic thin films, R. Messier et al., J. Vac. Sci. Technol. A 15(4), Jul./Aug. 1997, pp. 2148-2152.
Tailoring growth and local composition by oblique-incidence deposition: a review and new experimental data, Herma van Kranenburg and Cock Lodder, Materials Science and Engineering R11, No. 7, Jan. 15, 1994, p. 295-354.
Optical rotation in helical sculptured thin films, K. Robbie, M.J. Brett, and A. Lakhtakia, Department of Electrical Engineering and Microelectronic Centre, University of Alberta, Edmonton, unpublished, submitted to Nature. No Date.
Chiral thin solid films: Method of deposition and applicationss R.M.A. Azzam, Appl. Phys. Lett. 61(26), Dec. 28, 1992, p. 3118-3120.
Sculptured Thin Films (STFs) for Optical, Chemical and Biological Applications, A. Lakhtakia, R. Messier, M.J. Brett and K. Robbie, Innovations in Materials Research, vol. 1, No. 2, p. 167-176, Jul., 1996.
First thin film realization of a helicoidal bianisotropic medium, Kevin Robbie and Michael J. Brett, Akhlesh Lakhtakia, J. Vac. Sci. Technol. A 18(6), Nov./Dec. 1995, p. 2991-2993. The subject matter of this paper was also disclosed at a meeting at Pennsylvania State University, U.S.A., in Aug., 1995.
Fabrication of thin films with highly porous microstructures, K. Robbie, L.J. Friedrich, and S.K. Dew, T. Smy, M.J. Brett, J. Vac. Sci. Technol. A 13(3), May/Jun. 1995, p. 1032-1035. The subject matter of

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