GB2209769A

GB2209769A - Sputter coating

Info

Publication number: GB2209769A
Application number: GB8821920A
Authority: GB
Inventors: Anthony Cyril Evans
Original assignee: Ion Tech Ltd
Current assignee: Ion Tech Ltd
Priority date: 1987-09-16
Filing date: 1988-09-19
Publication date: 1989-05-24
Also published as: GB8821920D0

Abstract

A sputter system as illustrated in Fig. 2 has an anode which in operation includes the surface to be coated by sputtering a cathode which in operation includes the target which is the source of coating material, an electric field generating means between anode and cathode and magnetic field generating means which with the electric field contain electrons in the target area for increasing ionising collisions, the magnetic field generating means including magnetic material which extends towards the anode beyond the surface supporting the target on its side remote from the anode and preferably by more than the height of the original target body (which will be destroyed by the sputtering operation). In one embodiment the magnetic material forms north and south pole pieces, a pair of pole pieces of opposite polarity extending closer to each other in the region closer to the anode than in the region remote from the anode. This modification concentrates the magnetic lines of force to the region on the side of the target facing the anode, rather than within the target body. <IMAGE>

Description

SPUTTER COATING A well known method of coating thin films of material on a substrate 'rakes use of the process of sputtering. Sputtering occurs when a potential of a few hundred volts is applied between two plates in a gas chamber at a pressure of about 0.2m bar. The gas at this pressure is ionised under the action of the field (generally an inert gas is used, such as argon). The positive gas ions bombard the cathode as a result of which material is transferred from the cathode (the target) to the anode (the substrate). With diode sputtering the pressure is relatively high and the deposition rate is low (lnm/sec).

If a magnetic field is applied parallel to the cathode surface, the combined magnetic and electric fields confine the electrons to the vicinity of the cathode, increasing their path length by typically 100 times the length of electron path in the simple diode system.

The number of ionising collisions per electron with the gas is therefore greatly increased, increasing the plasma density and hence the deposition rate. Also the operating pressure is decreased by two or three orders of magnitude to the range 10 4 to 5 x 10 bar.

A practical example of a device that uses this type of plasma enhancement is the so-called planar magnetron. One form of this device uses a series of permanent magnets arranged behind the target to produce the required magnetic field. An electrostatic field generates the plasma. In this design, the target is a simple flat disc (Figure 1). Because the poles of the magnetic assembly are behind the target, a target material that has an appreciable magnetic susceptibility will tend to shield the space above the target frcm the influence of the magnets with a consequent reduction of the enhancement effect.

In the extreme case of highly magnetic materials such as iron the field is ccmpletely diverted through the target as a result of which the magnetron operates as a diode without electron confinement and hence at high pressure with slow deposition.

In the known planar magnetron described, the field produced by the magnets comprise lines of flux which extend through the target and return therethrough, the magnetic material being restricted to the area below the target. According to the invention, set out in Claim 1, the magnets are so arranged that the flux penetrates the target only to such a limited extent as to maintain a magnetic field above the target sufficient to contain the electrons and to arrange this magentic material extends above the bottom surface, and preferably the whole, of the target. The flux then skims the top surface region with little extent through the depth of the target.

The target may be in the shape of disc, rectangle or other shape with a central aperture. Preferably pole pieces are located in this aperture and around the edges and extend through the plane of the target.

The target and pole pieces are held at the same potential and are preferably of the same material, or the pole pieces may be capped with the target material.

In one example of the invention as shown in Figure 2, an earthed substrate 11 and an earthed cap-shape non-magnetic shield 12 are provided, as in Figure 1. Within the shield 12 two pole pieces 13 and 14 are provided, the piece 13 comprising an annular ring magnetized with equidistantly spaced magnets 23 around it, the outer boundary of the pole piece 13 lying closely adjacent the inside edge of the cup shield 12. The other pole piece 14 has a pole of opposite sign to 13 at its centre magnetised by magent 24 and is located centrally within the shield 12. At the upper portion of the outside edge of the pole piece 14 is formed recess 23 to support an aluminium spacing ring 16. This ring may be formed in more than one piece in order to be assembled within the recess or the ring may be positioned with the detachable pole piece removed. The target is placed round ring 16.The ring 16, target 21 and magnets 23 and 24 are supported on a cooled copper plate 22.

The pole piece 13, the ring 16 and target 21 are all annular, concentric with the pole piece 14.

Sputtering takes place primarily between the substrate 11 and the target 21 since the pole piece 14 provides a shield over the aluminium spacing ring 16. Because the pole pieces 13 and 14 are at a high negative potential (e.g. -1000 volts) as well as the target 21, some sputtering takes place between the substrate 11 and the pole pieces 13 and 14 which are therefore preferably made of the same material as the target 21 or capped with the target material to avoid contamination of the sputtered film. The pole pieces 13 and 14 extend above the surface of the target ring 21 and establish a suitable magnetic field above the ring 21 so that when the plasma is formed above the target ring by the voltage between the rings and the substrate most of the ions bombard the target.

The electrons are constrained by the magnetic field to remain close to the target and constrained from drifting out of the plasma by the negative electrostatic field on the inner and outer pole pieces. This electrostatic field provides the constraint which would have been provided by the greater vertical component of the magnetic flux in the device of Figure 1.

Claims

CLAIMS :

1. A sputter system comprising an anode, means for supporting a target of material to be sputtered, electric field generating means and magnetic field generating means for generating a magnetic field with which the electric fields will contain electrons over the target position, the magnetic field generating means including magnetic material which extends towards the anode beyond the surface supporting the target on its side remote from the anode.

2. A system as claimed in Claim 1 wherein the magnetic material extends closer to the anode than the intended position of the target.

3. A system as claimed in Claim 2 wherein the magnetic material forms north and south pole pieces, a pair of pole pieces of opposite polarity extending closer to each other in the region closer to the anode than in the region remote from the anode.

4. A sputter system substantially as hereinbefore described with reference to and as illustrated in Fig. 2 of the accompanying drawings.