|Title of Invention||
"PROCESS FOR MANUFACTURING AN EVAPORATION SOURCE"
|Abstract||The invention relates to a process for manufacturing an evaporation source for physical vapour deposition. The evaporation source comprises the actual sputtering target with an aluminium component and one or more further components as well as a backing plate made from a material having better thermal conductivity than the target. According to the invention the backing plate made of a powdery starting material is pressed, together with the powdery components of the sputtering target, into sandwiched powder fractions and then formed.|
|Full Text||PROCESS FOR MANUFACTURING AN EVAPORATION SOURCE
The invention relates to a process for manufacturing an evaporation source for physical vapour deposition, comprising a target which, in addition to one or more further components, contains an aluminium component and a backing plate, which is connected to the target, made from a material having better thermal conductivity than the target, the target being produced by cold-pressing a mixture of the powdery individual components and subsequently forming it at temperatures below the melting points of the individual components while flowing until a density of at least 98% of the theoretical density is achieved.
Nowadays sputtering targets for physical vapour deposition are used on a large scale for manufacturing various coatings. Their use extends from the production of wear-resistant and corrosion-resistant coatings for a wide range of substrate materials to the production of coated material composites, especially in the semiconductor and electronics industry. This broad spectrum of applications means that a very wide range of coating materials have to be deposited.
It is problematic when different materials have to be deposited at the same time, which would form brittle intermetallic phases during the conventional formation of alloys, so that such alloys can no longer be cold or hot-formed in practice and can only be machined down at considerable expense. Manufacturing sputtering targets from these alloys is therefore very difficult or even impossible.
These problematic materials include, for example, alloys made of aluminium and titanium, which can only be advantageously worked to produce sputtering targets using the above-mentioned process.
This process is described in detail in AT PS 388 752
Sputtering targets are generally fixed by mechanical means to water-cooled copper plates in the sputtering system in order to reduce the surface temperature. In most cases the sputtering target produced completely from the material to be sputtered is located directly on the copper plate.
Since as much material as possible should be atomised with a sputtering target, the overall height of the sputtering targets made should be as large as possible. However, it care should be taken that the thermal resistance of the sputtering targets, which increases as the overall height increases, does not become too large, ensuring that the surface temperature of the sputtering targets can be kept to reliable values.
As the majority of the materials to be atomised can either have relatively good thermal conductivity and/or a relatively high surface temperature without any problems,„conventional sputtering systems are set for sputtering targets with
relatively large overall heights, with the result that using sputtering targets with smaller overall heights in these systems can be very disadvantageous.
In particular, aluminium, which has excellent thermal conductivity, is very frequently used for coating applications using the sputtering technique, so that many sputtering systems, especially with respect to the overall height of the sputtering targets, are set for the good thermal conductivity of aluminium.
It then becomes a problem in these coating machines when aluminium is to be atomised together with materials that have relatively poor thermal conductivity and that, at the same time, must not have surface temperatures that are too high during the sputtering process, in order to prevent, for example, undesired reactions between several components of the sputtering targets. Thus, aluminium is frequently used together with titanium and, if applicable, additional components for coating applications, particularly in protection against wear and tear.
With sputtering targets made of these materials even small quantities of titanium considerably reduce the aluminium's good thermal conductivity. Consequently, with these sputtering targets, if they are manufactured with the overall heights usually provided for sputtering systems, the resulting surface temperatures at high coating rates can be so high that an exothermic reaction occurs, resulting in the destruction of the target.
However, other materials, which are atomised together with aluminium using sputtering targets, can also be critical and cause problems during the coating process. Material combinations of aluminium with Ta, Nd or Y can be used for
electronic applications for example, whereas for optical and magnetic storage media material combinations of aluminium with Ni and Cr are frequently used.
Material combinations of, for example, aluminium with Sn, Zn, Ag, W, Mo, are also frequently used in conjunction with additional Ti portions in applications intended to protect against wear and tear, where one material component acts as a dry-film lubricant.
To ensure that the problems indicated are avoided as much as possible with all these critical material combinations during coating, the deposition rate currently has to be restricted, preventing the surface temperature from rising too high.
One possible way of reducing the surface temperature of such critical sputtering targets even at high coating rates without altering the overall height is by providing the part of the sputtering targets in the area of the contact zone with the water-cooled copper plate with a backing plate made of a good heat-conductive material and then mechanically connecting this backing plate to the copper plate.
Processes for manufacturing such evaporation sources, where the backing plate is connected to the sputtering target by soldering or diffusion bonding are described, for example, in WO 00/22185 or in US 5 397 050.
It is disadvantageous with evaporation sources manufactured in this way that a transition zone of poor thermal conductivity can occur between the target and backing plate, which does not guarantee optimum heat dissipation from the surface of the sputtering targets into the backing plate and then on into the cooled copper plate.
As a temperature on the surface of the sputtering target that is just a few degrees higher, results in disadvantages with respect to the atomisation properties, such transition zones with poor thermal conductivity should be avoided if possible.
The object of this invention is therefore to develop a process for manufacturing an evaporation source for physical vapour deposition, in which the sputtering target containing aluminium components is connected to the backing plate without forming a transition zone of poor thermal conductivity.
According to the invention this object is achieved by pressing the backing plate, which also comprises a powdery starting material, together with the target components, into sandwiched powder fractions and then forming this.
In this way an excellent connection can be produced between the target material and backing plate without the formation of a transition zone with poor thermal conductivity, so that excellent heat dissipation from the surface of the sputtering target into the backing plate and then into the water-cooled copper plate is achieved.
As the sputtering targets are generally bolted or clamped to the water-cooled plate it is a good idea to design the section of the target, which can thus no longer be
atomised anyway, as the backing plate, so that with the same overall height as much material, which can be evaporated effectively, is available compared to sputtering targets without a backing plate.
In order to achieve a particularly good connection of the target material With the backing plate, the target should advantageously consist of at least 15 atom% aluminium.
Sputtering targets where the invention can be realised in a particularly advantageous manner are targets made of 15 atom% aluminium and 85 atom% titanium.
Pure aluminium, which has excellent thermal conductivity, is suitable as a particularly advantageous material for the backing plate of the evaporation source. As aluminium is relatively soft, a good transition zone with low thermal resistance can be achieved thanks to the mechanical connection with the water-cooled copper plate. In addition, the damage to the deposited coating is not too great, if the target material should inadvertently be oversputtered and, as a result, a certain portion of the backing plate is sputtered as well.
However, as well as aluminium, other materials with good thermal conductivity, such as, for example, copper are also suitable for the backing plate.
A proven method for achieving flow of the material during the forming of the pressed forging is the use of the forging process in forging presses.
If the target is constructed from aluminium/titanium, for example 15 atom% aluminium and 85 atom% titanium, carrying out the forging process at a temperature of between 400°C and 450°C has proven worthwhile.
Extrusion is another method of forming the pressed forging while the material is flowing as advantageously as possible.
The advantage of this variant of the manufacturing process according to the invention is that sputtering targets with varying overall heights can be separated from the extrusion billet.
The invention will be explained in more detail below using production examples.
A disc-shaped evaporation source with a 63 mm diameter and a total height of
32 mm, comprising a 20 mm high sputtering target made of 50 atom% aluminium and
50 atom% titanium and a 12 mm high aluminium backing plate, which is firmly fixed
to the sputtering target, was manufactured as follows in accordance with the process
according to the invention.
The aluminium powder and titanium powder for the sputtering target with an average grain size of 30 µm were mixed in an asymmetric moved mixer.
In a two-piece extrusion die of a hydraulic press, which was sufficiently oversized with respect to the final dimensions of the evaporation source, the bottom of the extrusion die was first filled with pure aluminium powder with an average grain size of 30 urn and the powder filling flattened. Then the top of the extrusion die was put in position and filled with the mixed aluminium/titanium powder, the powder mixture was again flattened and the die filling was cold-pressed to form a green compact with 94% of its theoretical density.
The pressed forging underwent secondary compression in a forging press with a half-open forging die with a forging temperature of approximately 200°C in a total of five passes with the individual components flowing or being kneaded.
In addition, the pressed forging was placed in a preheating furnace at a temperature of between 400°C and 450°C prior to the secondary compression and between the individual compression stages. No oxidation protection was required due to the short forming times and low forming temperatures, so that the secondary compression could take place in an unknown condition.
Finally, the evaporation source was mechanically processed to produce the final dimensions.
A metallograph was taken of the transition zone between the material of the sputtering target and the material of the backing plate.
Figure 1 shows this transition zone magnified x 100.
The absolutely homogeneous transition between the material of the sputtering target and the material of the backing plate without the formation of a troublesome intermediate layer with reduced thermal conductivity can be clearly seen.
For comparison purposes a disc-shaped evaporation source with the same dimensions as in Example 1 was produced. In contrast to Example 1 the evaporation source completely comprises a sputtering target made of 50 atom% aluminium and 50 atom% titanium and does not contain an aluminium backing plate. The sputtering target was manufactured with the same production parameters as in Example 1.
For comparison purposes an evaporation source comprising a sputtering target and a backing plate with the same dimensions and same material combinations as in Example 1 was produced. Unlike Example 1 the evaporation source was not manufactured by simultaneous processing of the powdery starting materials. Rather, the backing plate was rough-worked in the same dimensions irrespective of the sputtering target from a copper semifinished product made by melting metallurgy and was then connected using an indium intermediate layer by bonding to the finished sputtering target, which was made by means of powder metallurgy and which was manufactured with the same production parameters as in Example 1.
The evaporation sources corresponding to Examples 1 and 3 were installed one after another in an ARC evaporation plant and atomised under the same coating conditions, which are usually used, with an ARC current intensity of 60 A
corresponding to a flow of 0.7 MW/m2 and the surface temperatures of the individual sputtering targets were thus determined.
The following surface temperatures were produced following an atomisation time of approximately 2 minutes:
The evaporation source manufactured according to the invention in accordance with Example 1 had a surface temperature of 315°C.
The sputtering target manufactured in accordance with Example 2 without a backing plate had a highest surface temperature of 420°C.
The evaporation source manufactured in accordance with Example 3 with a bonded backing plate had a surface temperature of 395°C.
The clearly higher surface temperature compared to Example 1 despite the fact that a backing plate with the same dimensions was used clearly shows the extremely disadvantageous effect of the indium intermediate layer with reduced thermal conductivity required for the bonding.
As even a surface temperature of the sputtering target, which is a few degrees lower, brings with it advantages as regards the atomisation characteristics, the enormous benefit of the evaporation source according to the invention compared with previous evaporation sources according to the prior art is proven.
1. Process for manufacturing an evaporation source for physical vapour deposition, comprising a target which, in addition to one or more additional components, contains an aluminum component and a backing plate, which is connected to the target, characterized in, that the process is carried out by providing the individual components for the target and the components for the backing plate in powder form, shaping sandwiched powder fractions of the mixed individual components for the target and the components for the backing plate, cold pressing of the sandwiched powder fractions and subsequently forming the pressed sandwiched powder fractions at temperatures below the melting points of the individual components of the target while flowing until a density of at least 98% of the theoretical density is achieved under conventional conditions.
2. Process for manufacturing an evaporation source for physical vapour deposition as claimed in claim 1, characterized in that the target comprises at least 15 atom% aluminums.
3. Process for manufacturing an evaporation source for physical vapour deposition as claimed in claim 2, characterized in that the target contains 85 atom % titanium as second component.
4. Process for manufacturing an evaporation source for physical vapour deposition as claimed in one of the claims 1 to 3, characterized in that aluminium is used as the material for the backing plate.
5. Process for manufacturing an evaporation source for physical vapour deposition as claimed in one of the claims 1 to 4, characterized in that the forming is carried out by forging in forge presses.
6. Process for manufacturing an evaporation source for physical vapour deposition as claimed in claim 3, characterized in that the forming is carried out by forging in
forging presses at temperature of between 400 0C to 450 0C.
7. Process for manufacturing an evaporation source for physical vapour deposition as claimed in one of the claims 1 to 4, characterized in that the forming is carried out by extrusion.
8. Process for manufacturing an evaporation source for physical vapour deposition as claimed in claim 3, characterized in that the forming is carried out by extrusion
at a temperature of between 400 0C and 4500 C.
|Indian Patent Application Number||IN/PCT/2002/00101/DEL|
|PG Journal Number||10/2011|
|Date of Filing||25-Jan-2002|
|Name of Patentee||PLANSEE SE|
|Applicant Address||A-6600 REUTTE, AUSTRIA|
|PCT International Classification Number||B22F 3/14|
|PCT International Application Number||PCT/AT2001/00349|
|PCT International Filing date||2001-11-07|