GB2311651A

GB2311651A - Clamping device

Info

Publication number: GB2311651A
Application number: GB9606428A
Authority: GB
Inventors: Peter Michael Corser Martineau
Original assignee: Surface Technology Systems Ltd
Current assignee: Surface Technology Systems Ltd
Priority date: 1996-03-27
Filing date: 1996-03-27
Publication date: 1997-10-01
Also published as: GB9606428D0; DE19713034A1; FR2747236A1; JPH104134A

Description

2311651 clamping Device This invention relates to a clamping device for

use with workpieces, such as semi-conductor wafers or wafer carriers.

It has long been know that it is desirable to clamp semi-conductor wafers or wafer carriers to their support electrodes, commonly against an 0-ring, so that backside pressure can be applied to achieve constant thermal conditions over the whole of the part of the wafer in which devices are being formed. Vacuum and electrostatic clamping systems has been proposed, but these are complex and introduce their own problems, such as the inability to clamp insulating substrates. Accordingly, the most common way to clamp a wafer to its support electrode is to engage the periphery of the upper face of the wafer against inwardly projecting clamping fingers (or a continuous clamping ring) which derive their clamping force from the degree to which they or the wafer are deflected. There are two known ways of engaging the wafer and these clamping fingers. In the first the clamping fingers are mounted in a fixed ring and the wafer is brought up on its electrode to engage against the fingers. This movement is necessary in order to allow sufficient space between the ring and the support electrode for the wafer loading mechanism to load wafers onto the support electrode. The second arrangement, which is the equivalent, is to lower the clamping ring down towards the electrode. Similar considerations apply to other 2 workpieces such as thin films, discrete or integrated devices etc.

In many methods of treatment there is a further electrode and/or a plasma region spaced from the support electrode and the characteristics of the treatment are altered depending on the spacing between the electrodes or the support electrode and the plasma region. The above described clamping arrangements significantly restricts the degree to which this electrode region spacing can be adjusted.

From one aspect the invention consists of a clamp device for clamping a workpiece to a moveable electrode support, comprising clamping means for engaging the wafer and free standing support means for supporting the clamping means apart from an electrode support loading position, the clamping means having sufficient mass to clamp a wafer to the electrode support when the support means are moved from their standing position by the moving electrode support and workpiece.

It will be appreciated that a soon as the wafer moves above the rest position of the clamping means, the free standing support means is lifted upwardly and its weight pushes downwardly on the wafer through the clamping means.

With the clamping device thus suspended, the electrode support can be moved into any desired spacing from another electrode or a plasma region. After processing, the electrode support can be lowered until the free standing support means re-engages in its rest position and the wafer 3 is then no longer clamped. The electrode support is then lowered slightly further to leave sufficient space for the wafer to be unloaded and the next wafer to be loaded.

In a preferred embodiment the clamping means comprises an outer frame and a number of inwardly extending projection or a continuous ring for engaging the periphery of the wafer. The projections or ring may conveniently be flexible. The frame may be in the f orm a ring, in which case the projection may extend radially inwards or the ring may be concentric.

The support means may include weights and these weights may be removable or adjustable so that the clamping force can be adjusted. The supports means may include a plurality of legs and in that case the weights may form feet for the legs and/or extend between the legs.

Although the invention has been described above it is to be understood it includes any inventive combination of the features set out above or in the following description.

A specific embodiment will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a treatment chamber; Figure 2 is an exploded view of a part of a clamping arrangement; Figure 3 is a partial side view of the support electrode and the clamping device; and Figure 4 is a scrap view showing the clamping device engaging a wafer.

4 Turning to Figure 1, a semi-conductor wafer treatment apparatus has a chamber 10, an upper electrode 11, a support electrode 12 and gate 14 through which a wafer transfer mechanism (not shown) can load wafers 13 onto electrode 12. 5 A clamp device is generally indicated at 15.

The clamp device 15 includes an annular frame 16, which carries inwardly extending radial projection 17, and support legs 18 having weights 19 at their lower end. The legs 18 stand on the base 20 of the chamber, although it will be understood they could stand on any suitable ledge or shelf.

The support electrode 12 is mounted on a lifting mechanism 21 so that it can be moved vertically towards and away from the electrode 11.

In use, the wafer transfer mechanism enters through gate 14 and loads a wafer 13 onto the support electrode 12, which is in its solid line position. The support electrode 12 is then elevated and in due course the tips 22 of the projection 17 engage the outer periphery of the upper face 23 of the wafer 13. Further upward movement of the electrode 12 causes these projections to be lifted and, with them, the legs 18 and weights 19 are lifted from the base 20. As soon as the clamp device 15 leaves its rest position its full weight bears down on the wafer 13 clamping it against an 0ring or electrode 12. The electrode 12, and hence wafer 13, can then be elevated towards the electrode 11 until any desired spacing is achieved. Guide means may be provided to guide the movement of the legs 18 and f or weights 19 to maintain the orientation of the clamp device 15.

It will be seen that the clamping device 15 is not only extremely simple and easy to manufacture it requires no moving parts other than those already provided for repositioning the electrode 12. Further, as is indicated in Figure 3, a range of dif f erent weights may be provided so that different clamping forces can be achieved and as can be seen in Figure 4, a clamping ring extension 16a may be provided to allow for different wafer diameters. It is believed that it is generally desirable to have projection 17 which are def lectable to a degree, so as to cushion the engagement between the wafer and the clamping device 15. The clamping ring extension 16a is one way of achieving a standard deflection with different size diameters of wafer. However, provided that care is used in engaging the wafer with the clamping device 15, there is no mechanical reason why the projections could not be rigid. Indeed, if both the projections and the workpiece are rigid special care may be required to achieve suitable deceleration of the moving part prior to contact.

As has been mentioned already the apparatus may be used with any suitable workpiece and the tips of the projections may be replaced by a continuous or substantially continuous ring.

6 claims 1. A clamp device for clamping a workpiece to a movable electrode, comprising clamping means for engaging the workpiece and f ree-standing support means f or supporting the clamping means apart from an electrode clamping loading position, the clamping means having sufficient mass to clamp a wafer to the electrode support when the support means are moved from their standing position by the moving electrode support and workpiece.

2. A device as claimed in claim 1, wherein the clamping means comprises an outer f rame and a number of inwardly extending projections or a ring for engaging the periphery of the wafer.

Claims

3. A device as claimed in Claim 2, wherein the projections or ring are

flexible.

4. A device as claimed in claim 1 or claim 2 wherein the frame is a ring and the projections extend radially.

5. A device as claimed in any one of the preceding claims, wherein the support means include weights.

6. A device as claimed in claim 5, wherein the weights are removable or adjustable.

7. A device as claimed in any one of the preceding claims, wherein the support means includes a plurality of legs.

8. A device as claimed in claim 7 as dependent on claim or claim 6, wherein the weights form feet for the legs and/or extend between the legs.

7 9. A device as substantially hereinbef ore described with reference to the accompanying drawings.

10. Apparatus for treating wafer including a treatment chamber having a plasma region and a workpiece support electrodes, the electrode being actually located spaced from the region, means for moving the support electrode towards the region and a clamp device as claimed in any one of the preceding claims dimensioned to free stand on a part of the chamber or an extension thereof when the electrode is in loading position and to be lifted therefrom by the workpiece electrode when the electrode is moved towards the region.

11. Apparatus substantially as hereinbef ore described with reference to the accompanying drawings.