GB2208657A

GB2208657A - Thin film alloying

Info

Publication number: GB2208657A
Application number: GB8818979A
Authority: GB
Inventors: Anthony Cyril Evans
Original assignee: Ion Tech Ltd
Current assignee: Ion Tech Ltd
Priority date: 1987-08-10
Filing date: 1988-08-10
Publication date: 1989-04-12
Also published as: GB8818979D0; GB8718916D0

Abstract

A method of depositing material on a substrate from a plurality of sources each having a deposition axis comprises arranging the sources S1, S2, S3, with their deposition axes A1, A2, A3 parallel and spaced around a circle C1 of radius R whose plane is normal to the parallel axes, causing relative rotation of the substrate and said sources about a rotation axis parallel to said axes at a radius equal to the radius of said circle, and controlling the speed of rotation and outputs of said sources so that less than a monolayer is deposited on the substrate as it makes one pass relative to one source. The source may be a sputtering target, a magnetron, an electron beam heated hearth, a filament source, or an electrically heated boat. In particular there are a plurality of substrates, each being mounted about the same axis at the same radius for movement relative to said sources. As illustrated in the Fig. the outputs of each source spaced out from the deposition axis 6 deposit material uniformly over circles C4, C5, C6, on disc D. The circles C4, C5, and C6 have their centres lying on circle C2 of radius R on disc D coaxial with C1. As the disc D rotates, the substrates pass through the circles and receive deposits of material from the sources. The rates of deposition and rotation are governed so that more than one revolution of the disc is required to build up a complete monolayer on a substrate. This ensures an even formation of an alloy from the sources. <IMAGE>

Description

THIN FILM ALLOYING APPARATUS This invention relates to a method of producing thin films comprised of mixtures of materials or alloys.

A requirement exists for thin films of uniform thickness and in the case of an alloy of uniform composition.

Methods of achieving uniform thickness of films deposited in vacuums already exist and are well known.

The distribution of deposited material on a plane surface normal to the axis of symnetry of a source of material such as a sputtering target, an electron beam heated hearth, a filament source, or electrically heated boat etc. is symmetrical about that axis.

If for co-deposition two or more sources are directed to the same area of a substrate the axes of symmetry of at least all but one source must be inclined to the normal of the substrate. This results in the distribution of material at the substrate surface being skewed. It is not possible to superpose these skewed distributions to give uniform composition over extended areas.

Tb overcome this problem, the invention provides a method of depositing material on a substrate from a plurality of sources each having a deposition axis comprising arranging the sources with their deposition axes parallel and spaced around a circle whose plane is normal to the parallel axes, causing relative rotation of the substrate and said sources about a rotation axis parallel to said axes at a radius equal to the radius of said circle, and controlling the speed of rotation and outputs of said sources so that less than a monolayer is deposited on the substrate as it makes one pass relative to one source.

For example, if the deposition rate from a source is lOOOAmin, the source covers a 900 segment and the substrate rotates at lOOOrpm, then the average deposition thickness would be 0.255 . Taking the thickness of a monolayer to be 3A, it follows that 8.5t of the substrate was coated. (X = 1 Angstrom unit = 10 m).

If two further sources with different materials covered two other 900 segments at the same rate, a complete revolution would provide a coverage of 25.5% of three materials uniformly distributed. In this example, four revolutions would cover the substrate with just over one monolayer of an alloy composed of three equal constituents. By varying the relative rates of deposition from the sources at constant rotational speed, the composition of the alloy can be varied. The number of constituents depends of course on the number of sources, which is only limited by the space available on the circumference of the pitch circle.

The same technique may be used with magnetrons of different geometries, e.g. cylindrical magnetrons. In any geometry the speed of rotation of the substrate relative to the target must be such that only a fraction of the substrate is coated in any one pass, the allowable fraction being preferably less than half for a two constituent film and in general inversely proportional to the number of constituents, i.e. targets. The substrate circle or source circle or both may rotate about the rotation axis.

Mbre than one substrate may be provided, the substrates being mounted about the same axis at the same radius for movement relative to said sources.

The accompanying sketch shows an example of the invention in diagram form. The sources Sl, Sg and S3 are arranged with their deposition axes At, Az, A3 parallel and arranged on a circle Ct of radius R whose plane is normal to the axes As, Ai, Aa. The outputs of each source spread out from the deposition axis to deposit material uniformly over circles C4, C, Cb on disc D. The circles C C and C, have their centres lying on circle CZ of radius R on disc D coaxial with C . As the disc D rotates, the substrates pass through the circles and receive deposits of material from the sources. Shutters may be provided to limit the deposition areas from the circles on the disc to have exit and entry boundaries parallel to the leading and trailing edges of the substrates to ensure that the deposition is uniform over the substrates. The rates of deposition and rotation are governed so that more than one revolution of the disc is required to build up a complete monolayer on a substrate. This ensures an even formation of an alloy from the sources.

The separation of the sources S1, S2 and S3 form the disc D is such that the circles C1, C5 and C6 at least circumscribe the sub- strates.

Claims

CLAIMS:

1. A method of depositing material on a substrate fram a plurality of sources each having a deposition axis comprising arranging the sources with their deposition axes parallel and spaced around a circle whose plane is normal to the parallel axes, causing relative rotation of the substrate and said sources about a rotation axis parallel to said axes at a radius equal to the radius of said circle, and controlling the speed of rotation and outputs of said sources so that less than a monolayer is deposited on the substrate as it makes one pass relative to one source.

2. A method as claimed in claim 1 comprising providing a plurality of said substrates, each being mounted about the same axis at the same radius for movement relative to said sources.

3. A method as claimed in claim 1 or in claim 2, comprising adjusting the fraction of the monolayer which is deposited in one pass relative to one source to be inversely proportional to the number of sources.

4. A method of depositing material substantially as herein described with reference to the accompanying drawings.

5. An alloy prepared by the method as claimed in any one of claims 1 to 4.