Coating processes – Measuring – testing – or indicating – Thickness or uniformity of thickness determined
Patent
1987-04-07
1988-09-13
Pianalto, Bernard D.
Coating processes
Measuring, testing, or indicating
Thickness or uniformity of thickness determined
427 38, B05D 306
Patent
active
047708956
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of controlling uniformity of growing alloy film.
Low energy gap semiconducting material for use in infrared opto-electronic devices may be prepared in the form of thin uniform layers supported by suitable substrates. The substrate is selected because of its high degree of crystalline perfection and its suitability for epitaxial growth of the required film.
A variety of film growth methods are used for epitaxial growth, dependent somewhat on the materials involved. The alloy semiconducting compounds formed by materials such as cadmium, mercury and tellurium may be grown epitaxially on crystalline substrates in an ultra high vacuum by monitoring the growth with reflected high energy electron diffraction (RHEED).
Despite this sophisticated control the material composition and properties vary unacceptably over the area of the prepared layer and this lack of uniformity impedes the development of many opto-electronic devices.
It is the object of the present invention to provide a method of control and a method of production of the alloy film which will maintain the highest possible uniformity of the film.
The objects of the invention are achieved by use of a low energy ion beam or a series of ion beams impinging on the surface of the growing film, control of the ion beam or beams being by the utilization of information obtained by a uniformity probe or probes, based on ellipsometry and/or 2 photon reflectivity measurements, to both direct and/or control the beam or beams.
As an example of how the invention can be carried into effect, the accompanying drawing which forms part of this specification shows in diagramatic form how the ion beam or beams are controlled. At least one ion beam is scanned across the growing film. Control of the energy and intensity of all beams is determined by information obtained from the scanning reflectivity probe or probes and a computer may be used to evaluate algorithms and carry out the necessary adjustments in a closed loop manner.
The invention comprises at least one low energy molecular beam directed onto a substrate on which a film is to be grown, and is characterised by a uniformity measurement probe comprising a light source directed to the substrate on which the film is to be grown, and a detector to receive a signal from the light source reflected by the growing film, a corrector gun adapted to direct a corrector beam, onto the growing film, means to correlate at least the detector and the corrector beam to incrementally scan areas of the growing film, and computer means to control the said corrector beam from the signal received by the said detector.
The method consists in controlling the uniformity of a growing alloy film formed by directing at least one molecular beam onto a surface to grow a film on the surface while directing at least one uniformity measurement probe onto the growing film and incrementally scanning the surface with a detector forming part of the uniformity probe to produce a correction signal, and controlling the uniformity of the film being deposited by directing onto the area being scanned a corrector beam from a computer under control of the corrector signal.
The probe is conveniently an ellipsometry probe, but a 2 photon reflectivity probe can be used or both can be used simultaneously.
In order to enable the invention to be fully understood, a preferred arrangement will be described with reference to the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic drawing showing three different molecular beam sources directed to a substrate on which a film is being grown and showing two uniformity probes, namely an ellipsometry probe and detector and a 2 photon reflectivity probe, including also a RHEED electron gun and fluorescent screen which however are not necessarily essential to the invention,
FIG. 2 is a schematic view showing basic ellipsometric data as used in the formula included later herein,
FIG. 3 is a diagram showing the relationship of the ellipsometry measurement bea
REFERENCES:
patent: 4159919 (1979-07-01), McFee et al.
patent: 4525376 (1985-06-01), Edgerton
Pianalto Bernard D.
The Commonwealth of Australia
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