SPUTTER DEPOSITION

Abstract: A film is deposited on a substrate (25) from a plurality of sputter sources (21) to (23) arranged so that their major axes of emission intersect at a common point (26). The substrate (25) can be moved across the intersecting beams of the sources so that a film larger than the area of the intersecting beams is formed, and the sources (21) to (23) can be individually controlled so that a film of different layers can be formed when the substrate (25) is stationary and the film is made up of regions of different composition when the substrate is moved. Energetic neutral particles can also be directed at the substrate.

Description: SPUTTER DEPOSITION This invention relates to a film deposited on a substrate by sputtering. Such films may be used in semi-conductor, optical, X-ray and microwave devices. It is important that the thickness of such films is strictly controlled and the film is free from contamination. when the film is formed by deposition from more than one source, a method which involves positioning a substrate opposite sources with an inter- mediate period of transit between the two s urces, lends itself to the possibility of contamination during the intermediate period. The contamination may be by stray gas molecules and the gas content of the resulting film has then to be reduced by subsequent sintering for example. Optical and X-ray films made in this way may have crystal structures and interfaces which make them particularly susceptible to water vapour. The present invention avoids the disadvantage of the intermediate period described above by providing a plurality of sputter sources arranged such that their respective major axes intersect at a common point. The term "major axis" is defined as the direction of maximum output from- the source. The substrate on which the film is to be deposited is located at or near this common point. Deposition from the sources can be simultaneous or in turn but, unless desired, there is no need for an*intermediate period between depositing from different sources. Previously, sputter sources have been very bulky, so that if they had been arranged with respective major axes intersecting at a common point, the angle between the axes would have had to be so great that deposition on the substrate would have been adversely affected by tha, razing angle of incidence. If the common point were made so far from the sources to reduce this angle to a manageable value, then the distance of the common point from the sources would be so large in relation to the mean free path or sputtered particles in the atmosphere of the apparatus that deposition would again be adversely affected. Previous sputter sources also generated strong stray magnetic fields, so that their minimum separation would have worked against the require- ment for a small angle between their major axes. The present availability of sources with rare earth magnets avoids these problems by providing sources which are compact and do not have stray magnetic fields. When a dielectric material is to be sputtered, it is necessary to energise the source with rf energy, since the dielectric will simply absorb a direct voltage. Sputter sources are sometimes used in conjunction with a beam of energetic particles to assist the deposition process, but when the particles are charged, they inter- act with the rf energy of the sources. We have found that a beam of neutral energetic particles is also good for such purposes, and such a beam has the advantage that there is no interaction with the rf energy. Examples of the invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a diagrammatic side elevation of a pair of sputter sources and a substrate; Figure 2 is a plan view; and Figure 3 is a perspective view of another embodiment. In Figure 1, two,sputter sources 11 and 12 are arranged relative to a substrate 13 so that their major axes 14- and 15 intersect at point 16 on the substrate. The sources are of about 5 cm diameter and the point 16 is .about 10 cm from the sources. The angle between the axes 14- and 15 is therefore about 4-5 so that the angle of incidence of sputtered particles on the substrate is about 22-^°. The mean free path for typical sputtered particles in a low pressure atmosphere of argon is about 10 cm, and it is preferable that the point 16 is spaced from the sources by less than the mean free path for effective deposition. At point 16, deposition from the sources 11 and 12 will be equal, assuming the sources are of equal output distribution. To the left of point 16 the matter deposited from source 11 increases in relation to the matter deposited from source 12 and vice-versa. Over a small region on either side of point 16, deposition ■ from the two sources is substantially equal. The substrate 13 is shielded from deposition from the sources outside this region by a slotted shield 17, so that any unbalanced deposition is avoided. The substrate 13 is moved at constant speed within its plane across the slot while both sources are energised, so that a film is deposited equally from both sources. It has been found that the distribution in the direction at right angles to the plane of Figure 1 is of uni orm thickness over a wider dimension than the width of the slot, so that, as seen in Figure 2, the slot can be elongate without loss of uniformity of film thickness. A carriage for moving the substrate 13 is indicated diagrammatically at lδ. This arrangement can be used to deposit alloys or inter-metallic ilms, using different sources to deposit different components of the alloy, the strengths of the sources being adjusted in accordance with the concentra¬ tions of the components. Alloys can be made in this way from components whose lattice structure do not allow them to melt together in the conventional way. Cermets can be formed since the sources are not limited to the sputtering of metal. Films containing successive strips of different components can be deposited by controlling the energisation of the sources as the substrate is moved past the slot. In this way the change in composition is achieved without any inter- mediate period in which contamination can occur. The composition can be smoothly changed by smoothly changing the energisation of the sources. hen the sources are identical, the present arrangement can be used to deposit a uniform film over a wider area than is possible with a single source, as shown in Figure 3 * In this arrangement, the substrate 25 is arranged a short distance in front of the point 26 of intersection of the major axes of the sources i In this figure there are three sources 21 to 23 arranged on a part-spherical surface 24-, but any plural number of sources can be used and they may be arranged in groups, each of which has a plurality of sources with major axes intersecting at a point, but the point may be different for different groups. With the substrate a little separated from the point or points of intersection of the major axes, the maximum contribution to deposition from each source will occur at different points on the substrate. As one moves across the substrate from one such point towards another, the contribution from one source will fall, whereas the contribution from another source will rise. The arrangement of the sources is chosen so that the total deposition remains as nearly uniform as possible across a wide area of the substrate. If a film is required larger than this area, then the area is prov¬ ided with a shutter as in the embodiment of Figure 1 and the substrate is moved at constant speed across the space behind it. The deposition of such films can be improved by bombarding the receiving surface with ions prior to deposition, or with energetic neutral particles at some stage in the film formation process. The impingement of energetic atoms or molecules on the growing film enhances the effects of both pre-sputter bombardment and the multi-source to produce films of hitherto unrealised properties. Moreover the beneficial effects of bomb¬ arding the receiving surface prior to deposition may be enhanced by commencing the deposition while continuing the bombardment. There is shown in the figure the optional addition of a saddle field source 31 of neutral particles located behind the surface 24: and directing a fast atom beam __\2 through a hole ^3 in the surface 24- to impinge upon the receiving surface 25. Extra such saddle field sources may be used when different effects are required.

Claims: CLAIMS: - 1. A method of depositing a film on a substrate 13 comprising arranging a plurality of sputter sources 1 , 12 such that their major axes of emission 14-, 1 inter- sect at a common point 16 on or adjacent the substrate - 13. 2. A method as claimed in claim 1 wherein the dis¬ tance of the substrate 13 from each source 11, 12 is less than the mean free path for sputtered particles. 3- A method as claimed in claim 1 or claim 2 com¬ prising moving the substrate behind a slot 17 which defines an area of deposition of sputter particles on the substrate 13. 4-. A method as claimed in any one of claims 1 to 3 comprising directing a beam 32 of energetic neutral particles onto the substrate. 5. A method as claimed in any one of claims 1 to 4- wherein the sources 11, 12 are of different materials and the sources 11 , 12 are individually controlled. 6. Sputter deposition apparatus comprising a plural¬ ity of sputter sources 11, 12 arranged with their major axes of emission 14-, 15 intersecting at a common point 16 and means 18 to support a substrate 13 at or adjacent the common point 16 to receive particles from the sources 11, 12. 7. Apparatus as claimed in claim 6 comprising means 17 defining a window to define an area over which part¬ icles can pass to the substrate 3 and the supporting means 18 is arranged to move the substrate 13 behind the window 17 to present successive areas on the substrate to the window. 8._ Apparatus as claimed in claim 6 or claim 7 com¬ prising a source 31 of energetic neutral particles for directing a beam 32 onto the substrate 13• 9. Apparatus as claimed in any one of claims 6 to 8 wherein said sources 11, 12 comprise rare earth magnets.

Inventors: EVANS DAVID ROGER, EVANS, DAVID, ROGER
Applicants: ION TECH LTD, ION TECH LIMITED
Application year: 1984
Main classification: C23C14
IPC codes: C23C14, H01J37