GB2053763A

GB2053763A - Soldering a non-solderable sputtering target to a metallic support

Info

Publication number: GB2053763A
Application number: GB8018405A
Authority: GB
Original assignee: DEMETRON
Current assignee: DEMETRON
Priority date: 1979-06-08
Filing date: 1980-06-05
Publication date: 1981-02-11
Also published as: DE2923174A1; FR2458599A1

Abstract

Sputtering targets with non- solderable target materials in dimensions of larger than, e.g. 20 cm (diameter) are difficult to produce by conventional methods because relatively large apparatus is required for metallising the surface of the target before soldering. The invention avoids this difficulty by initially arranging an adhesive layer (3), a metal foil (4) and a layer of soft solder (5) between the target (1) and the metallic support plate (2). <IMAGE>

Description

SPECIFICATION Sputtering target This invention relates to a sputtering target, particularly in large dimensions, comprising an actual non-solderable target and a metallic support.

In sputtering (cathode sputtering), particles are dislodged from the sputtering target by bombardment with high-energy ions and are deposited on a substrate to be coated where they form firmly adhering layers of the target material.

During the ion bombardment process, heat is generated on the surface of the target and has to be dissipated through suitable cooling measures because the target would otherwise become too hot and would decompose or melt. In general, the heat generated is dissipated through the rear of the target, i.e. through a metalic target support plate thoroughly cooled from outside. The actual target has to be connected to this support plate in such a way that the connection is both mechanically strong and effectively conducts heat. In addition, an electrically conductive connection between the rear of the target and the support plate is required in many cases.In addition, mechanical tensions between the target and the support plate, such as can arise for example through different heating or cooling of the target and support, have to be strictly avoided to ensure that the target is not destroyed, above all when it is made of readily breakable materials.

The target is normally applied to the metallic support by soldering with soft or hard solders and bonding. In the case of soldering, particularly if the target material itself is not solderable, metallic intermediate layers are generally applied to the target, for example by sputtering, vapour deposition or electroplating, in order to obtain a solderable target. In the case of bonding, solvent-free adhesives, for example epoxide resins, are normally used, substances of high conductivity, such as for example powders, beads, wires or nets of metals or graphite, generally being embedded in them in order to improve thermal conductivity and to obtain electrical conductivity.

However, these bonds are attended by the disadvantage that, after they have hardened, the adhesives show no more plastic deformability, with the result that mechanical tensions are built up in the adhesive layer if the target and support have different coefficients of thermal expansion and are heated or cooled to different extents, as is normally the case. This method fails in particular when the target and support have relatively large dimensions, for example of from 20 to 200 cm, because the mechanical tensions become too great and result in breakage of the actual target or the layer of adhesive.

If for example a 200 cm target of a combination of quartz and copper is exposed to a temperature difference of around 1 50 C, a difference in expansion of the order of 0.45 cm is obtained.

In addition, targets applied by bonding are difficult to replace because the target can only be removed from the support with considerable effort and adhering residues of adhesive complicate further use.

Accordingly, the standard method of joining the target to the support is soldering, particularly softsoldering, because providing a suitable solder having a low expansion limit and minimal solidification is selected, as is the case for example with indium, lead, tin or their alloys, the mechanical tensions remain minimal, bond strength is adequate and good electrical and thermal conductivity are guaranteed. Soft solders have the advantage over hard solders that they have lower solidification points, with the result that the different coefficients of thermal expansion of the target and support material lead to lower mechanical tensions on cooling from the soldering temperature.

Another advantage of the soft-soldered joint lies in the fact that the residues of used, i.e. sputtered-out, target can easily be removed by heating to the melting temperature of the solder and a new target can be applied to the same support plate. However, the soldered joints are attended by the disadvantage that, where non-solderable, particularly non-softsolderable, target materials are used, a solderable metal layer first has to be applied to the target, normally by vapour deposition or sputtering.

However, this involves difficulties, particularly in the case of relatively large dimensions, for example with target diameters of larger than 20 cm or even larger than 100 cm, because such large vapour deposition or sputtering installations are generally not avaiiable.

According, an object of the present invention is to provide a sputtering target, particularly in large dimensions, comprising an actual non-softsolderable-target and a metallic support which has a layer of soft solder between the target and the support, but in which the surface of the target does not have to be metalised and nevertheless can be soldered without significant mechanical tensions being built up between the target and the support in the event of heating or cooling to different extents.

According to the invention an adhesive layer, a metal foil and a layer of soft solder are initially arranged between the target and the support.

A thin, readily solderable metal foil is bonded to the target using a solvent-free adhesive which, to improve thermal conductivity and to obtain electrical conductivity, advantageously contains powders, beads, wires or nets of metals or graphite. The thickness of this metal foil is generally from 10 to 1 0001lm and preferably from 20 to 200 Rm. A preferred thickness for the foil is 50 Fm, suitable materials for the foil being any metals and alloys which can be effectively wetted with solder, but preferably silver, copper, nickel and their alloys, above all iron-nicket and iron-nickel-cobalt alloys, with which the coefficient of expansion of the metal foil may generally be adapted with advantage to that of the target material.

The thickness of the metal foil is so minimal that it is able to follow the thermal expansion of the target material without significant tensions being built up in the layer of adhesive (due to the elasticity modulus and the coefficients of thermal expansion of the foil and target) which could result in breakage of the target.

The target with the metal foil bonded to it may be soldered onto the support plate in known manner using a low-melting soft solder, the working temperature of the soft solder having to be adapted to the short-term thermal stability of the adhesive. Soft solders based on indium, tin and lead have proved to be suitable for this purpose.

The accompanying drawing diagrammatically illustrates one example of an embodiment of a sputtering target according to the invention. It consists of a target (1), for example of quartz, carbon, silicon or silicon nitride, to which a metal foil (4) is applied using a layer (3) of adhesive, for example of an epoxide resin. This metal foil (4) is soldered onto the support plate (2) by a layer (5) of soft solder, for example an indium solder. A support plate (2) consists for example of copper or steel and is cooled from outside, preferably with water.

Claims

1. A sputtering target, particularly in large dimensions, comprising an actual non-solderable target and a metallic support, an adhesive layer, a metal foil and a layer (5) of solft solder being initially arranged between the target and the support.

2. A sputtering target as claimed in Claim 1, wherein the adhesive layer contains powders, beads, wires or nets of metals or graphite.

3. A sputtering target as claimed in Claim 1 or 2, wherein the metal foil has a thickness of from 20 to 200calm.

4. A sputtering target as claimed in any of Claims 1 to 3, wherein the metal foil consists of copper, silver, nickel, iron or their alloys.

5. A sputtering target as claimed in any of Claims 1 to 4, wherein the coefficients of thermal expansion of the metal foil and target are adapted through the choice of the foil material.

6. A sputtering target as claimed in any of Claims 1 to 5, wherein the layer of solder consists of indium, lead, tin ortheiralloys.

7. A sputtering target substantially as described with particular reference to the accompanying drawings.