WO2002068714A1

WO2002068714A1 - Electrostatic chuck

Info

Publication number: WO2002068714A1
Application number: PCT/GB2002/000223
Authority: WO
Inventors: David Andrew Tossell; Matthew Peter Martin
Original assignee: Trikon Holdings Limited
Priority date: 2001-02-22
Filing date: 2002-01-18
Publication date: 2002-09-06
Also published as: GB0104341D0

Abstract

This invention relates to an electrostatic chuck 10 which comprises a top ceramic layer 11, an intermediate ceramic layer 12 and a pattern 13, the top layer 11 and intermediate layer 12 being bonded by a layer of adhesive 14 in which an electrode 15 is also located. The electrode is significantly smaller than the wafer location, with the result that the portion 11 is effectively oversized protecting the electrode from etching around the edge of the wafer. The arrangement also reduces backside etching of the wafer, good edge cooling of the wafer and improved uniformity and processing.

Description

ELECTROSTATIC CHUCK

This invention relates to electrostatic chucks. US-A-5507874 describes an electrostatic chuck in which the electrode may be smaller than the wafer and in which the encapsulating dielectric falls away from the edge of the wafer. When the wafer is being etched this introduces the likelihood of backside etching of the part of the wafer that is exposed at its periphery and also the dielectric may be relatively easily etched through to the electrode.

From one aspect the present invention consists in an electrostatic chuck forming a wafer location including an F electrode having a diameter less than that of the location, the electrode being encased in a dielectric body having a flat upper surface for receiving the wafer characterised in that the chuck further includes a sacrificial ring of dielectric material surrounding the body to extend, the flat upper surface beyond the wafer location. The provision of the sacrificial ring, which may be integral with the body, means that before either the backside of the wafer or the . electrode can be attacked by the etching process, a substantial portion of the ring itself has to be eaten away. It is particularly preferred that the ring is separable from the body to allow replacement of the ring, without the need to replace the body or the electrode. In that case it is preferred that the boundary, at the upper face, between the ring and the body lies within the wafer location. In this way, in use, the boundary will be shielded by the wafer and not act as a point of weakness at which preferential etching might occur. Particularly conveniently the ring and body are stepped for mutual engagement. This means that the thickness of dielectric on the ring which needs to extend into the wafer location can be reduced, hence reducing the cost of the replacement ring. It also allows positive location of the ring.

Although the invention has been defined above it is to be understood that it includes any .inventive combination of the feature set out above or in the following description. The invention may be performed in various ways and specific embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic vertical section through one edge of an electrostatic chuck; and Figure 2 is a corresponding view through an alternative embodiment.

In Figure 1 an electrostatic chuck is generally indicated at 10 and comprises a top ceramic layer 11, an intermediate ceramic layer 12 and a platen 13, the top layer 11 and intermediate layer 12 being bonded by a layer of adhesive 14 in which an electrode 15 is also located. A wafer 16 is shown lying on the flat upper surface of the ceramic layer 11 and is located in a wafer location 17, which is bounded, at the edge shown in Figure 1, by the vertical dotted line 18. It will be noted that the electrode 15 has a radius of 2mm less than that of the wafer location 17. As wafers are processed the hatched area slowly becomes etched away, but because the electrode 15 is well spaced from this area, no damage is done to the electrode 15 and the life of the chuck can be extended. The oversizing of the layer 11, in combination with the reduced electrode 15 therefore protects the electrode 15 and reduces the likelihood of backside etching of the wafers 16. It also provides good wafer edge cooling and more uniform RF and DC electric fields upon the wafer. This improved uniformity of temperature and electrical fields provides for a more uniform process across the wafer. This directly improves process results upon a wafer and indirectly it widens the "process window" improving equipment functionality and process reliability. Even with this improved configuration shown in Figure

1, the chuck will eventually fail, when high powered etching is occurring and .Figure 2 shows a way to significantly increase the life of the chuck again. In this arrangement, the top electrode 11 stops ^' short of the edge of the wafer location 17 and is stepped downwardly. The edges of the adhesive layer 14 and the intermediate ceramic layer 12 align almost exactly with the edge of the location 17. A dielectric ceramic ring 19 is then located around the main chuck portion 20 (which comprises layers 11, 12, 14 and the electrode 15) . The ring 19 has an inward flange 21 that sits on the step formed by the ceramic layer 11. It will be readily understood that in this case, when the ring 19 becomes etched sufficiently to expose the main body 20, it can readily be replaced preventing any damage to the main body 20. The stepped arrangement ensures that the boundary 22 between the ring 19 and the ceramic layer 11 lies within the wafer location 17 and is hence shielded, during etching, by the wafer 16. It will be appreciated that other engagement configurations between the ring 19 and the ceramic layer 11 could be formed and it will be particularly noted that the ceramic ring 19 forms a continuous flat surface with the ceramic layer 11 and indeed forms part of the wafer location 17.

Claims

1. An electrostatic chuck forming a wafer location of known diameter including an RF electrode having a diameter less than that of the location the electrode being encased in a dielectric body having a flat upper surface for receiving the wafer characterised in that the chuck further includes a sacrificial ring of dielectric material surrounding the body to extend the flat upper surface beyond the wafer location.

2. A chuck as claimed in Claim 1 wherein the ring is integral with the body.

3. A chuck as claimed in Claim 1 wherein in the ring is separable from the body to allow replacement .

4. A chuck as claimed in Claim 3 wherein the boundary, at the upper face, between the ring and the body lies within the wafer location.

5. A chuck as claimed in Claim 3 or Claim 4 wherein in the ring and body are stepped for mutual engagement.