GB2039962A

GB2039962A - Sputtering system

Info

Publication number: GB2039962A
Application number: GB7936617A
Authority: GB
Original assignee: BOC Ltd
Current assignee: BOC Ltd
Priority date: 1978-12-29
Filing date: 1979-10-22
Publication date: 1980-08-20
Also published as: GB2039962B

Abstract

An electrode assembly for a sputtering system includes a cathode 8 adapted to present a target surface of relatively large surface area and an anode 18 of smaller area positioned close to but spaced from and centrally of the cathode so as to define with the cathode a substantially annular cathode. <IMAGE>

Description

SPECIFICATION Sputtering system This invention relates to an electrode system, particularly for sputtering apparatus, which is apparatus for removing atoms from a cathode by bombarding it with positive ions obtained from a gaseous discharge, usually while subjected to an applied magnetic field. The atoms ejected from the cathode are caused to deposit themselves on the adjacent surface of a substrate where they build up to form coherent films of chosen thickness. In the passage between the cathodic target and the anode, the electrons may be caused to follow extended spiral paths by applied magnetic fields so as to encourage collisions with gas molecules, and consequent ionisation, therefore producing increased discharge densities even at lower than normal operating pressures for sputtering.The practice of modifying the electron paths, by applying magnetic or electric fields, is used for creating conditions for cool sputter deposition.

In sputtering apparatus it is known to use a so-called 'DC diode', including an annular cathode.

This leads to the use of complex electrical insulation, mechanical construction, and thermal conduction arrangements.

The present invention aims at providing an electrode assembly of simpler construction for a sputtering system.

According to the present invention, there is provided an electrode assembly for a sputtering system, comprising a cathode adapted to present a target surface of a predetermined surface area and an anode of relatively smaller surface area facing, adjacent to and centrally of the target surface for masking a central area of the target surface.

Preferably, the cathode target surface area is circular and the anode surface area is circular, the cathode and anode defining together an annular cathode target surface area.

The present invention will now be described by way of example with reference to the accompanying diagrammatic drawing, in which: Figure lisa diagrammatic sectional view of the respective parts of one form of electrode assembly of the present invention, and Figure 2 is a diagrammatic plan view of the electrode assembly shown in Figure 1.

The electrode assembly includes a base 2 for the electrodes, having a front surface 4 facing towards a space 6 in which a gaseous discharge is arranged to take place when the sputtering apparatus is energised. Positive ions from the discharge are intended to fall on the front, target, face 20 of a disc-shaped cathode 8 supported from base 2 by means of a hollow electric insulator 10 through which passes a conductor 12 by means of which the cathode 8 is connected to the negative pole of a source 14 of high tension direct current, of which the other pole is connected to the base 2, which is usually earthed.

Mounted on front face 4 is a support 16 for a smaller disc-shaped anode 18 positioned centrally of the target face 20 of cathode 8, and sufficiently far from it to be electrically insulated from it and in the 'cathode fall', usually referred to as 'Crookes dark space'. The anode 18 is of similar shape to, but significantly smaller than, the front face of cathode 8, so as to leave an outer annulus of the target face 20 exposed to space 6. The electrode assembly thus presents to space 6 a central portion functioning as an anode at zero or positive voltage, and an outer annular cathode at a suitable negative voltage.Thus the electrode assembly functions as if it were an annular electrode assembly, with the central anode being effective to suppress electrons being emitted from the centre of the target face 20, thus resulting in the substrate being coated having fewer electrons impinging on it, and therefore remaining cooler.

In a sputtering system intended to be used as a sputter coater it is usual to mount magnets adjacent to the electrodes so as to cause the secondary electrons ejected from the cathode to follow spiral paths and fall on bodies other than the substrate being coated. These magnets have been omitted from the accompanying drawing for clarity, but there would be no difficulty in fitting such magnets in appropriate positions in a simplified electrode assembly of the present invention.

The front surface 4 is provided with a metal ring 22 functioning as an earthed shield to prevent electrons from falling on, and sputtering taking place from the side surface of the cathode 8. In an alternative form of the present invention, the earthed shield 22 could be extended significantly above the target face 20, and the anode 18 be secured to a thin rod extending through aligned holes in the shield 22, to provide a simpler support for the anode. The rod could be clamped by a screw to the shield to prevent it from rotating or being displaced longitudinally.

When it is desired to sputter a substrate with gold or some other precious metal, the use of a circular cathode, as opposed to an annular one, lends itself particularly well to this purpose. All that one needs to do is to cut out a circle of appropriate size from a sheet of the metal in question, and position it on the cathode so that it is at the same potential as the cathode and one face thereof becomes the new target face.

Although the present invention has been described and illustrated with reference to a circular cathode and anode, it is applicable to electrodes of any shape. Indeed, the anode need not have the same shape as has the cathode, but it must be smaller and positioned substantially centrally thereby masking a central area of the target surface.

1. An electrode assembly for a sputtering system comprising a cathode adapted to present a target surface of a predetermined surface area and an anode of relatively smaller surface area facing, adjacent to and centrally of the target surface for masking a central area of the target surface.

2. An electrode assembly as claimed in claim 1, in which the cathode target surface area is circular and the anode surface area is circular, the cathode and anode defining together an annular cathode

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Sputtering system This invention relates to an electrode system, particularly for sputtering apparatus, which is apparatus for removing atoms from a cathode by bombarding it with positive ions obtained from a gaseous discharge, usually while subjected to an applied magnetic field. The atoms ejected from the cathode are caused to deposit themselves on the adjacent surface of a substrate where they build up to form coherent films of chosen thickness. In the passage between the cathodic target and the anode, the electrons may be caused to follow extended spiral paths by applied magnetic fields so as to encourage collisions with gas molecules, and consequent ionisation, therefore producing increased discharge densities even at lower than normal operating pressures for sputtering.The practice of modifying the electron paths, by applying magnetic or electric fields, is used for creating conditions for cool sputter deposition. In sputtering apparatus it is known to use a so-called 'DC diode', including an annular cathode. This leads to the use of complex electrical insulation, mechanical construction, and thermal conduction arrangements. The present invention aims at providing an electrode assembly of simpler construction for a sputtering system. According to the present invention, there is provided an electrode assembly for a sputtering system, comprising a cathode adapted to present a target surface of a predetermined surface area and an anode of relatively smaller surface area facing, adjacent to and centrally of the target surface for masking a central area of the target surface. Preferably, the cathode target surface area is circular and the anode surface area is circular, the cathode and anode defining together an annular cathode target surface area. The present invention will now be described by way of example with reference to the accompanying diagrammatic drawing, in which: Figure lisa diagrammatic sectional view of the respective parts of one form of electrode assembly of the present invention, and Figure 2 is a diagrammatic plan view of the electrode assembly shown in Figure 1. The electrode assembly includes a base 2 for the electrodes, having a front surface 4 facing towards a space 6 in which a gaseous discharge is arranged to take place when the sputtering apparatus is energised. Positive ions from the discharge are intended to fall on the front, target, face 20 of a disc-shaped cathode 8 supported from base 2 by means of a hollow electric insulator 10 through which passes a conductor 12 by means of which the cathode 8 is connected to the negative pole of a source 14 of high tension direct current, of which the other pole is connected to the base 2, which is usually earthed. Mounted on front face 4 is a support 16 for a smaller disc-shaped anode 18 positioned centrally of the target face 20 of cathode 8, and sufficiently far from it to be electrically insulated from it and in the 'cathode fall', usually referred to as 'Crookes dark space'. The anode 18 is of similar shape to, but significantly smaller than, the front face of cathode 8, so as to leave an outer annulus of the target face 20 exposed to space 6. The electrode assembly thus presents to space 6 a central portion functioning as an anode at zero or positive voltage, and an outer annular cathode at a suitable negative voltage.Thus the electrode assembly functions as if it were an annular electrode assembly, with the central anode being effective to suppress electrons being emitted from the centre of the target face 20, thus resulting in the substrate being coated having fewer electrons impinging on it, and therefore remaining cooler. In a sputtering system intended to be used as a sputter coater it is usual to mount magnets adjacent to the electrodes so as to cause the secondary electrons ejected from the cathode to follow spiral paths and fall on bodies other than the substrate being coated. These magnets have been omitted from the accompanying drawing for clarity, but there would be no difficulty in fitting such magnets in appropriate positions in a simplified electrode assembly of the present invention. The front surface 4 is provided with a metal ring 22 functioning as an earthed shield to prevent electrons from falling on, and sputtering taking place from the side surface of the cathode 8. In an alternative form of the present invention, the earthed shield 22 could be extended significantly above the target face 20, and the anode 18 be secured to a thin rod extending through aligned holes in the shield 22, to provide a simpler support for the anode. The rod could be clamped by a screw to the shield to prevent it from rotating or being displaced longitudinally. When it is desired to sputter a substrate with gold or some other precious metal, the use of a circular cathode, as opposed to an annular one, lends itself particularly well to this purpose. All that one needs to do is to cut out a circle of appropriate size from a sheet of the metal in question, and position it on the cathode so that it is at the same potential as the cathode and one face thereof becomes the new target face. Although the present invention has been described and illustrated with reference to a circular cathode and anode, it is applicable to electrodes of any shape. Indeed, the anode need not have the same shape as has the cathode, but it must be smaller and positioned substantially centrally thereby masking a central area of the target surface. CLAIMS

2. An electrode assembly as claimed in claim 1, in which the cathode target surface area is circular and the anode surface area is circular, the cathode and anode defining together an annular cathode target surface area.

3. An electrode assembly as claimed in claim 2, in which the cathode is supported from a base by an electric insulator and a support mounted on the base carries the anode.

4. An electrode assembly as claimed in claim 3, in which a metal ring surrounds the cathode and functions as an earth shield.

5. An electrode assembly as claimed in claim 1 or 2, in which the cathode is supported from a base by an electric insulator and is surrounded by a metal ring which functions as an earth shield and extends beyond the target surface area of the cathode, and a rod extending diametrically across the metal ring, which rod supports the anode.

6. An electrode assembly for a sputtering system, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the Figures of the accompanying drawing.