Glancing angle deposition of thin films

Details Glancing angle deposition of thin films Glancing angle deposition of thin films

1997-07-30

2001-03-27

Dixon, Merrick (Department: 1774)

Adhesive bonding and miscellaneous chemical manufacture

Surface bonding means and/or assembly means therefor

C427S255700, C427S255120, C427S255290, C156S314000

Reexamination Certificate

active

06206065

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.
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.
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.
The inventors have proposed improvements to the methods of Azzam and Hamaguchi, as described in “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.
In these references, the relationship of porosity to column angle is fixed, and there has been no way to vary porosity while maintaining the column angle fixed. The present invention seeks to overcome this limitation in the earlier references.
SUMMARY OF THE INVENTION
There is thus proposed, according to an aspect of the invention, a method of growing vapor deposited thin films, the method comprising the steps of:
A) initially exposing a surface of a substrate to a vapor flux under a given set of growth conditions at an oblique incident angle while rotating the direction of arrival of the vapor flux at the substrate at a rotation speed about a normal to the substrate to grow a first portion of a thin film formed of a plurality of columns growing in a first growth direction;
B) subsequently, and while exposing the surface to vapor flux, altering the set of growth conditions, namely the rotation speed of the direction of arrival of the vapor flux at of the substrate, to cause a second portion of each of the plurality of columns to grow in a growth direction offset from the first growth direction; and
C) repeating steps A and B to create a first thin film formed of columns on the substrate.
During step A, the substrate may be rotated an integral number of times, or, to create a helical pattern, rotated nearly an integral a number of times and paused between periods of rotation at sequentially offset positions.
An optical filter may thus be made with plural thin film layers, wherein each thin film layer is formed by repeating steps A and B.
Preferably, the rotation speed of the direction of arrival of the vapor flux at the substrate during step A is sufficiently high that the direction of arrival of the vapor flux at the substrate rotates at least once within the time required for the thin film to grow a distance, measured normal to the substrate, substantially equal to the adatom diffusion length of the material being deposited.
According to a further aspect of the invention, there is provided a microstructure comprising a first thin film of plural columns extending from a surface of a substrate, wherein the columns are formed under a given set of conditions by vapor deposition on the surface of the substrate from vapor flux incident at an angle &thgr;
f
to a normal to the surface of the substrate, where 0°<&thgr;
f
<90°, the vapor being deposited at least in part while the direction of arrival of the vapor flux at the substrate is rotating, and the columns exhibit the property that 0°<&thgr;
c
<&thgr;
n
where &thgr;
c
is the angle between the columns and a normal to the surface of the substrate and &thgr;
n
is the angle at which the columns would grow under the given set of conditions without rotation of the direction of arrival of the vapor flux at the substrate.
Preferably, the columns are formed at least in part while the direction of arrival of the vapor flux at the substrate is rotating at a rotation speed that is sufficiently high that the direction of arrival of the vapor flux at the substrate rotates at least once within the time required for the thin film to grow a distance, measured normal to the substrate, substantially equal to the adatom diffusion length of the material being deposited.
A second thin film may be formed on top of the first thin film with a different porosity, which may be created by deposition of the second thin film with a different incident angle of vapor flux than the incident angle &thgr;
f
for the first thin film. The plural thin films may form a continuous stack of thin film layers, one of the plural thin film layers being placed against the top of the first thin film, with each thin film layer having a different porosity from adjacent thin film layers. The thin film may have an refractive index that varies with distance from the substrate.
There is also provided a method of growing vapor deposited thin films, the method comprising the steps of:
exposing a surface of a substrate to a vapor flux at an oblique incident angle while rotating the direction of arrival of the vapor flux at the substrate at a rotation speed about a normal to the substrate to grow a thin film formed of a plurality of columns growing in a first growth direction; and
the rotation speed being sufficiently high that the the direction of arrival of the vapor flux at substrate rotates at least once within the time required for the thin film to grow a distance, measured normal to the substrate, substantially equal to the adatom diffusion length of the material being deposited.
According to a further aspect of the invention, there is provided the step of, while rotating the direction of arrival of the vapor flux at the substrate, varying the oblique incident angle of the vapor flux to vary the density and hence refractive index of the thin film.
According to a further aspect of the invention, the oblique incident angle of vapor flux is varied to produce alternating bands of high and low density material deposited on the substrate.
According to a further aspect of the invention, there is provided a method of filtering electromagnetic radiation, wherein the electromagnetic radiation includes radiation having a frequency &lgr; and the electromagnetic radiation is propagating along a light path, the method comprising the steps of:
placing an optical filter in the light path, wherein the optical filter comprises plural helical columns extending from a substrate, the helical columns each having a pitch p sufficiently smaller than &lgr; (for example, p<&lgr;/4, or p<&lgr;/10) that propagation of light is unaffected by the helical structure of the columns.
These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.


REFERENCES:
patent: 3699298 (1972-10-01), B

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