GB2102027A

GB2102027A - Target for magnetically enhanced sputtering of chromium-iron alloy

Info

Publication number: GB2102027A
Application number: GB08122229A
Authority: GB
Inventors: George Barry Sugden
Original assignee: General Engineering Co Ltd
Current assignee: General Engineering Co Ltd
Priority date: 1981-07-18
Filing date: 1981-07-18
Publication date: 1983-01-26
Also published as: FR2509754A1; DE3219310A1

Abstract

The target comprises a non-magnetic base of either stainless steel or titanium, plated with chromium (between 60% and 80% of its effective area) and studs of titanium (when the base is stainless steel) or stainless steel or iron (when the base is titanium) are welded to the unplated parts. The base may be tubular or planar and, when tubular, the plating may be internal or external. In one particular advantageous form the effective percentage areas of the target contributed by the metals is 76% chromium 19.7% stainless steel and 4.3% titanium. If desired, when the base is stainless steel, the titanium studs can be omitted. Targets of this form have been found to produce in use a chromium finish of the desired quality, clarity and brilliance.

Description

SPECIFICATION Sputtering device target This invention relates to a sputtering device target by means of which it is possible to deposit a metallic film comprising at least chromium and iron on the surface of a workpiece.

The sputtering process permits, for example, a substrate of such as glass or plastics material to be coated with a metal, or metals, for the purpose of producing a decorative, protective, wear resistant or other functional finish.

Sputtering is carried out under vacuum conditions utilising a technique known as 'magnetically enhanced sputtering' and, in contradistinction to other vacuum deposition processes, does not require the melting and subsequent evaporation of the metal to be deposited.

The target comprises the metal to be deposited and may be tubular in form. A typical tubular target may be of the order of 180 mm. in diameter and 2000 mm. in length. An alternative target can be in the form of a flat plate.

Known sputtering processes enable individual met als to be sputtered to produce an alloy coating on the substrate and it is possible to provide, in a suitable vacuum chamber, two or more targets in order that the materials to be deposited on a workpiece to produce the alloy covering can be sputtered simultaneously. Thus it is possible to achieve deposition on a workpiece of an alloy the constituent metals of which cannot easily be deposited on the workpiece by other conventional deposition techniques. In some instances, of course, it may be desired to deposit a conventional alloy on a workpiece in which case initial coating on the tubular carrier of the target can be achieved without difficulty. However, as indicated above, we are concerned here with coating a workpiece with a number of different metals to form an alloy coating, such a coating cannot easily be produced.The initial coating process of the carrier forming the target is therefore extremely costly and good thermal contact of the alloy with the carrier is difficu It to achieve. Additionally there are instances in which it is impossible to produce an alloy target having the required combination of metals in alloy form and thus coating of a single carrier by the alloy required on the workpiece is not possible.

According to one aspect of the present invention there is provided a sputtering device target for use in a sputtering process for depositing a metallic film on the surface of a workpiece comprising a base of non magnetic stainless steel which is plated over a portion of its surface with chromium, the percentage area of the base which is plated together lying between 60% and 80% ofthe base area.

According to another aspect of the present invention there is provided a sputtering device target for use in a sputtering process for depositing a metallic film on the surface of a workpiece comprising a base of non magnetic stainless steel which is plated over a portion of its surface with chromium, and has another portion of its surface covered with discrete regions of titanium, the percentages of the total area of the target provided by the three metals being in the ranges 60 to 75% chromium, 38 to 19% stainless steel and up to 5% titanium.

According to a still further aspect of the present invention there is provided a sputtering device target for use in a sputtering process for depositing a metallic film on the surface of a workpiece comprising a base of titanium which is plated over a portion of its surface with chromium, and support discrete pieces of stainless steel or iron, the percentages of the total area of the target provided by the three metals being in the ranges 60 to 75% chromium, 38 to 19% stainless steel or iron and up to 5% titanium.

A preferred embodiment of the invention may incorporate one or more of the following advantageous features.

(a) The percentages of the total area of the target provided by the three metals are 76% chromium, 19.7% stainless steel and 4.3% titanium.

(b) The percentages of the total area of the target provided by the three metals being in the ranges 60% to 75% chromium, 38 to 19% stainless steel or iron and up to 5% titanium.

(c) The percentage of the total area of the target provided by the three metals are 73% chromium, 25.5% stainless steel and 1.5% titanium.

(d) The percentages ofthe total area of the target provided by the three metals are 69.5% chromium, 28.75% stainless steel and 1.75% titanium.

(e) The percentages of the total area of the target provided by the three metals are 65% chromium, 33% stainless steel and 2.0% titanium.

(f) The percentages of the total area of the target provided by the three metals are 60% chromium, 38% stainless steel and 2% titanium.

(g) A portion of the base stainless steel is plated by stopping off that part of the base which is to remain unplated, immersing the base in an electroplating bath then removing the stopping off material to reveal the unplated stainless steel region beneath.

(h) The discrete regions oftitanium are in the form of studs which are welded to the unplated regions of the base stainless steel.

(i) The discrete pieces of stainless steel or iron are in stud form and are welded to the titanium regions.

(j) The discrete pieces of stainless steel or iron are in stud form and are welded to the chromium plated regions.

(k) The base is a plate (I) The base is a tube.

Fig. 1 shows a side elevational view of a target according to the invention; Fig. 2 shows a side elevational view of part of the target of Figure 1 but to an enlarged scale; Fig. 3 shows an alternative, square plate form, target to the target shown in Figure 1 and Fig. 4 shows a circular plate form target.

Referring to Figures 1 and 2 the target comprises a hollow carrier tube 1 of non magnetic stainless steel on which a helical strip 2 of chromium is deposited.

The stainless steel is of the non magnetic type so as to avoid any unacceptable influence on the magnetic cally enhanced sputtering process during use of the target. Stainless steel having a fairly high chromium content is preferred and in particular those meeting the requirements of British Standards B.S. 1501 Pt. 4 304 and B.S. 1501 pt. 3310S were found to give good results.

The helical chromium strip 2 is advantageously produced on the base tube 1 by electropiating. The desired area of the external surface of the tube 1 is stopped off by winding a constant width of stopping off material around the tube in a helical manner. The stopped off tube 1 is then immersed in an electroplating bath and electroplated with chromium to a depth of, say, 2mm. After removal from the bath, the stopping off material is stripped away to reveal a helix of unplated stainless steel beneath. This helix is designated by the reference numeral 3 in Figures 1 and 2. To complete the target studs 4 6titanium are welded to this stainless steel helix 3.Welding titanium is extremely difficult, but the nature ofthe weld is such that, although what would normally be considered a good mechanical bond is not achieved, a satisfactory thermal bond is. It is the thermal bond, rather than the mechanical bond, which is important to the sputtering process, and providing the requisite amount of titanium on the target in this way has been found to be extremely advantageous in the overall sputtering process.

The target is used in the sputtering process to produce on a substrate workpiece chromium plate of acceptable brilliance and quality. This chromium plate does contain the constituent elements found on the target although not necessarily in the same proportions. This is because the sputtering rates is dependent not only upon the available surface area ofthe metal, but also upon the metal being sputtered itself. Furthermore, as the stainless steel of the base tube 1, is itself a composite containing a relatively large proportion of chromium, the stainless steel can be expected to make a contribution to the chromium on the workpiece as well as provide the iron.

Although in most circumstances a proportion of titanium on the workpiece and therefore on the target is preferred, it may not be essential in all cases. There may also be a relatively small proportion of other metals such as nickel particularly in the stainless steel. The surface area of the main metals of the target lie in the following percentages ranges: Chromium Stainless Steel Titanium 60 to 80% 18 to 40% 0 to 5% Within these overall ranges, the following specific examples are recommended again by percentage of the total available area of the target.

% Chromium % Stainless Steel % Titanium 76 19.7 4.3 75 23.5 1.5 73 25.5 1.5 69.5 28.75 1.75 65 33.0 2.0 60 38.0 2.0 In use the above described target is disposed in a vacuum chamber in the normal way. Magnetic enhancement is achieved by positioning permanent magnets within the tube 1. If these magnets are stationary the magnetic field will vary along the axial length of the tube, and this variation will adversely affect the uniformity of erosion. In order to counteractthis, the magnets may be axially oscillated with the tube in order to vary the magnetic field axially of the tube with respect to time. The workpieces to be coated are normally rotated around the target to ensure that all workpieces are similarly coated.

The target may have a different form to that described above. Instead of a helix the chromium plate may be in the form of spaced rings circumfe rentiallydisposed around the tube 1. In such a case, where the magnets are oscillated, the amplitude of the oscillations should not exceed the width of the adjacent rings. Planar form targets may also beemp- loyed are shown, for example in Figures 3 and 4.

Figure 3 shows a square planar target and figure 4 a circular planar target. In Figure 3 the square stainless non magnetic steel base 31 has chromium plate strips 32, deposited on it and in Figure 4the circular non magnetic stainless steel 41 has chromium plate annuli 42 deposited on it. Titanium studs 34 are welded to the unplated stainless steel strips 33 and titanium studs 44 are welded to the unplated stainless steel annuli 43. Such a planar target is positioned in use in the usual vacuum chamber so as to overlie a plurality of magnets and the workpieces, to be coated are moved across it whilst being rotated if necessary.

As a further variant, chromium may be deposited on the internal surface of a tubulartarget in a similar fashion to the manner in which the external surface is plated. With such a target the workpieces are disposed inside the tube while the magnets are disposed outside.

In all the above embodiments the base material chosen is non magnetic stainless steel. Such steel is readily available in tubular and sheet form and, in the respect at least, the target requirements are relatively easily met. However, titanium is also readily available in tubular and sheet form and, although much more expensive than stainless, its availability makes feasible further embodiments ofthe invention.

In these embodiments the base is made of titanium (whether tubular or of plate form) and is electroplated with chromium as in the previous embodiments. Stainless steel studs or iron are then welded either to the chromium plate orto the titanium. In this case the relatively small dimensions of the studs permits the use therefore of magnetic stainless steel or iron for the distortion of the magnetic field thereby produced in use of the target is also relatively small and can be accommodated. An advantage of the titanium base embodiments is that the target may be used until the chromium plate has virtually disappeared. Since the titanium taken from the base is relatively small the base can then be cleared of any chromium plate remaining and the studs removed. The base can then be replaced and restuded to produce a new target. This can be done over and over again thus making very effective and economic use of this original expensive titanium base.

It will be appreciated that the percentage metal area ranges and values given for the embodiments of Figures 1 and 2 apply equally to these latter described embodiments.

Claims

1. A sputtering device target for use in a sputtering process for depositing a metallic film on the surface of a workpiece comprising a base of non magnetic stainless steel which is plated over a portion of its surface with chromium, the percentage area of the base which is plated lying between 60% and 80% of the base area.

2. A sputtering device target for use in a sputtering process for depositing a metallic film on the surface of a workpiece comprising a base of non magnetic stainless steel which is plated over a portion of its surface with chromium, and has another portion of its surface covered with disctrete regions of titanium, the percentages of the total area of the target provided by the three metals being in the ranges 60 to 75% chromium, 38to 19% stainless steel and up to 5% titanium.

3. A sputtering device target for use in a sputtering process for depositing a metallic film on the surface of a workpiece comprising a base oftitanium which is plated over a portion of its surface with chromium, and support discrete pieces of stainless steel or iron, the percentages ofthe total area of the target provided by the three metals being in the ranges 60% to 75% chromium, 38 to 19% stainless steel or iron and up to 5% of titanium.

4. A sputtering device target as claimed in Claim 2, or 3, in which the percentages of the total area of the target provided by the three metals are 76% chromium, 19.7% stainless steel and 4.3% titanium.

5. A sputtering device target as claimed in Claim 2 or 3 in which the percentages of the total area of the target provided by the three metals are 75% chromium, 23.5% stainless steel and 1.5% titanium.

6. A sputtering device target as claimed in Claim 2, or 3, in which the percentages of the total area of the target provided by the three metals are 73% chromium. 25.5% stainless steel and 1.5% titanium.

7. A sputtering device target as claimed in Claim 2, or 3, in which the percentages ofthe total area of the target provided by the three metals are 69.5% chromium, 28.75% stainless steel and 1.75% titanium.

8. A sputtering device target as claimed in Claim 2, or 3, in which the percentages of the total area of the target provided by the three metals are 65% chromium, 33% stainless steel and 2.0% titanium.

9. A sputtering device target as claimed in Claim 2, or 3, in which the percentages ofthe total area of the target provided by the three metals are 60% chromium, 38% stainless steel and 2% titanium.

10. A sputtering device target as claimed in any of Claims 2 to 8, in which a portion of the base stain less steel is plated by stopping off that port ofthe base which is to remain unplated, immersing the base in a electroplating bath and then removing the stopping off material to reveal the unplated stainless steel regions beneath.

11. A sputtering device target as claimed in any of claim 2 or claim 4 to 10 when appendant to claim 2 in which the discrete region oftitanium are in the form of studs which are welded to the unplated regions of the base stainless steel.

12. A sputtering device target as claimed in any of claims 3 or claim 4 to 10 when appendant to claim 3, in which the discrete pieces of stainless steel or iron are in stud form and are welded to the titanium regions.

13. A sputtering device target as claimed in any of claims 3 or claims 4 to 10 when appendantto claim 3, in which the discrete pieces of stainless steel or iron are in stud form and are welded to the chromium plated regions.

14. A sputtering device target as claimed in any preceding claim in which the base is a plate

15. A sputtering device target as claimed in any of claims 1 to 13, in which the base is a tube.

16. A sputtering device target as clained in any preceding claim, in which the stainless steel is to British Standards BS 1501 Pt. 4304 or B.S. 1501 Pt.

310S.

17. Asputtering device target for use in asputtering process for depositing a metallic film on the surface of a workpiece substantially as hereinbefore described with reference to the accompanying drawings.

18. A workpiece when coated by a sputtering process employing a target as claimed in in any preceding claim.