WO1985004232A1

WO1985004232A1 - Valve

Info

Publication number: WO1985004232A1
Application number: PCT/GB1985/000099
Authority: WO
Inventors: David Roger Evans
Original assignee: Meotron Limited
Priority date: 1984-03-13
Filing date: 1985-03-12
Publication date: 1985-09-26
Also published as: GB8406491D0

Abstract

A valve plate (13) moves from a retracted position in which it is completely clear of a valve aperture (11) laterally of the aperture axis to an intermediate position in which it is aligned with but spaced from the valve aperture and then axially to a closed position in which it closes the valve aperture. The two movements are caused in mutually exclusive time periods. The conductance of the aperture (11) past the valve plate (13) is linearly related to the movement of a drive input.

Description

VALVE

This invention relates to valves for use in apparatus in which a shut-off and a flow impedance function are required.

One application of this invention is to the manufacture and processing of silicon wafers for chip manufacture which takes place at very low pressure and requires an extremely clean environment. It is necessary in the wafer processing apparatus to be able both to shut off the processing chamber from the vacuum pumps and to vary the flow impedance between the pumps and the chamber, because pumps which are suitable for working at the very low pressures, which are experienced, can become swamped if there is insufficient control. Another common requirement is that in certain circumstances there must be no impedance to flow through the valve aperture.

To date these requirements have only been approached by providing separate shut off valve and impedance altering devices. The result is that excessive space is taken and two completely separate drive systems have to be provided. In addition the shut-off valves have either closed by sliding over the seal around the valve aperture, causing scuffing of the seal and contamination of the environment, or they have been linearly closed by means of linear devices such as rams or simple harmonic motion devices such as cranks. In either case there is no proper control of the closing force and again damage to the seal can occur.

According to the invention there is provided a combined shut-off and impedance varying valve as set out in claim 1 of the claims of this specification.

Examples of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a side elevation, partly broken away, of a valve chamber,

Figure 2 is a plan, also partly broken away, of the chamber of Figure 1 , Figure 3 is a plan and Figure 4 a side elevation of a linkage used in the apparatus of Figure 1,

Figure 5 shows a modification of the apparatus of Figures 1 to _J and

Figure 6 shows another possible modification of the apparatus.

The valve body shown in Figure 1 comprises a first aperture 11 intended to connect to a vacuum chamber in which semiconductor wafers are processed and a second valve aperture 12 intended to be connected to a vacuum pump. A valve plate 13 is shown in its fully retracted position, from which it moves upwards, laterally of the apertures 11 and 12 and then axially of the apertures to the left to close the aperture 11, engaging a valve seat around the rim of the aperture 11.

A pair of guide rails 15 support a T-shaped carriage 16 (best seen in Figure 2) for the lateral movement. Two wheels 17 are mounted on the cross-piece 16a of the carriage 16 and run on one rail 15 and a single wheel 17 on the stem lόb of the carriage runs on the other rail 15- The valve plate 13 is mounted on the stem lόb by a linkage lS to be described.

A drive shaft 21 rotates a cam 22 about a shaft 23 by means of bevel gears 24« The cam 22 drives cam followers 25 and 26 located diametrically opposite each other with respect to the shaft 23• The cam 22 has a semi-circular portion subtending lδ0° at the shaft 23 and since cam followers are diametrically opposite, it follows that only one cam follower will be moved laterally at any one time as the cam 22 rotates. Cam follower 25 rotates a torsion shaft 27 by means of bevel gears 28 to operate the linkage IS as will be later described. Cam follower 26 is fixedly connected to an arm 31 of a linkage 29 which comprises two arms 31 and 32 mounted on shafts 33 and 34 and connected by an arm 35. An arm 36 is fixed on shaft 34 parallel to but spaced from the arm 32 and an arm 37 connects the end of the arm 36 to the stem lόb of the carriage 16 so that as the follower 26 rotates clockwise on shaft 33 the carriage 16 moves from the retracted position shown in Figure 2 to a position in which the plate 13 is axially aligned with the aperture 11. Only the arms 36 and 37 of the linkage lie inside the vacuum chamber 10. The cam 22, the cam followers 25 and 26 and the remainder of the linkage 29 lie outside the chamber 10, connected to the arm 5 36 by the shaft 37 by the shaft 34 which passes through a rotating vacuum seal 38. Similarly the bevel gears 28 lie outside the chamber 10, the torsion shaft 27 passing into the chamber through another rotating vacuum seal 39- This arrangement reduces lubrication problems which are encountered in vacuum environments.

Figures 3 and 4 show the linkage IS connecting the torsion shaft 23 to the valve plate 13> A first arm 41 is connected ^• to rotate with the torsion shaft 27 and a second arm 42 is mounted for rotation about a fixed point 43. The two arms 41 5 and 4 are connected by an arm 44_. but do not remain parallel since the lengths of the arms 41 and 4 are unequal. During a 60 degree rotation of arm 41_. the arm 42 only rotates through 55 degrees. An arm 45 is pivoted to the arm 42 at a point separate from the pivot point of the arm 44 and the 0 arms 42 and 45 together form a toggle mechanism 46. The plate 13 is mounted by a resilient disc 47 on a sub-carriage 8 slidably supported on the stem of the carriage 16. At the limit of lateral movement of the follower 25_. the toggle mechanism links 42 and 45 are in a straight line, so that downward pressure on the valve plate 13 does not cause the linkage lδ to reverse.

The linkage 18 is constructed and arranged so that as the arm 41 rotates about the shaft 27 from 60° to 120° to the longitudinal direction of the rails 15 , the line joining the point 43 to the pivot with arm 44 on the arm 42 moves from 56° to 111° to that longitudinal direction, while the line joining the point 43 to the pivot with arm 45 at the same time moves from 35° to 90°.The effective lengths of the arms are:

Arm: 41 44 45

Length (mm): 30 70 29-5. The length of the arm 42 from the point 43 to the pivot with arm 44 is 33πιm and to the pivot with arm 45 is 29«5mπι and the separation of the torsion shaft axis from the point 43 at right angles to the longitudinal direction of the rails 15 is 12.5πmι.

In operation, as the cam 22 rotates from the position shown in Figure 2, the cam follower 25 remains stationary and the follower 26 moves laterally to move the plate 13 into alignment with the aperture 11. When the cam has rotated through 90 degrees, the lateral movement of the cam follower 26 stops and the follower 25 starts to move laterally to raise the plate 13 towards the valve seat at aperture 11 as the cam 22 rotates further. The design of the cam 22 and of the linkage lδ is such that there is a linear relationship between rotation of the drive shaft 23 and the conductance of the passageway through the aperture 11 as restricted by the plate 13- It will be seen that the plate 13 approaches the seat transversely of the aperture axis, so that no scuffing of the valve plate 13 can occur. The introduction of an impedance in the pumping line to limit gas throughput or control process pressures necessarily leads to a reduction in effective pump speed. Whilst this is necessary and desirable for the sputter gas, usually argon, it applies equally to other gases which are desorbed from chamber walls, sealing rings, etc.. The result is that an undue fraction of the total chamber pressure may consist of these background gases. Many processes are adversely affected by the presence of such desorbed gases which are typically those gases easily condensed such as water vapour and carbon dioxide.

Figure 5 shows a modification of the apparatus so far described to combat this problem. The valve plate 13 is shown in its fully retracted position. A separate cryogenic device 51 including cooled baffles 52 is mounted on a similar but separate transport system so that the device 51 can be brought up to the illustrated position opposite the aperture 11 to absorb the gases from inside the vacuum chamber 10 while it is being pumped. After the undesired gases have been absorbed by the device 51 _> the device 51 is withdrawn and the aperture closed by the plate 13- The device 51 can then be regenerated by increasing its temperature while the vacuum pump operates through the aperture 12. Any number of additional devices can be mounted in the chamber 10, arranged radially of the axis of the aperture 11 and each provided with its own transport system as described with reference to Figures 1 to , .

The valve described above may be used in sputtering or dry etching of semiconductor wafers, for example. The linkages described may be modified as required. The advantage of the presently described valve is that the change in conductance is linearly related to the movement of the input shaft. Figure 6 shows a further modification of the apparatus so far described in which a hollow conduit in the form of a metallic cylinder όl is mounted around the valve plate 13 with an internal bore slightly larger than the diameter of the apertures 11 and 12. When a metal such as copper or silver is used, the cylinder 6l presents a highly conducting path for electromagnetic waves of high frequency or for plasma, since the electromagnetic penetration into the body of the valve is minimised. The cylinder 6l is mounted on the carriage 16 to extend with minimum clearance between its ends and the valve body, but with a limited diameter which keeps it clear of the rails 15 and the torsion rod 27 so that it can be moved with the plate 13 laterally of the apertures 11 and 12. When the valve plate 13 is withdrawn laterally, the cylinder is also withdrawn. When in the position shown in Figure 6, the cylinder 61 defines tlie internal geometry of the valve such that the path of gas molecules through the space formed by the inlet and outlet apertures, the cylinder 61 and the valve plate 13 may be more accurately predicted and the geometry optimised for varying the conductance.

A similar cylinder could be mounted around the cryogenic device 51 i*¹ Figure 5 to optimise cryogenic trapping. Except when another piece of apparatus such as the cryogenic device 51 of Figure 5 i desired to be moved into alignment with the apertures 11 and 12, it would be possible to mount a further hollow cylinder on the carriage 16 carrying the plate 13 so that it is aligned with the apertures 11 and 12 when the first cylinder 6l enclosing the valve plate 13 is fully withdrawn. The further cylinder will define the geometry of the valve between the apertures when the valve is fully open.

Claims

l._. A combined shut-off and impedance varying valve comprising a valve seat (11) defining a valve aperture, a valve plate (13) movable axially and laterally of the valve seat to close the aperture and characterised by a drive mechanism (21-48) for driving said valve plate with said axial and lateral movements in mutually exclusive time periods.

2. A valve as claimed in claim 1 wherein the drive mechanism comprises a single cam (22) and, for each of said axial and lateral movements, a separate cam follower (25_.26) engaging said cam and a drive connection (27,28,39-48; 29j31-38) between the cam follower and the plate.

3- A valve as claimed in claim 2 wherein the axial movement- drive connection comprises a toggle mechanism (42,45) •

4- A valve as claimed in any one of the preceding claims comprising guide means (15,16) for supporting the valve plate (13) during said lateral movement, said drive mechanism (21-48) being independent of the guide means.

5. A valve as claimed in any one of claims 1 to 4 comprising a val-vre body (10) in a wall of which the valve seat (ll) is formed and within which the valve plate 13 moves and a hollow conduit (6l) surrounding the valve plate (13) and extending close to the valve body (10), the hollow conduit (6l) being movable laterally with the valve plate (13) "to the position in which the valve plate (13) is aligned with the valve seat (ll) so as to conduct gases from the valve aperture through the body when the valve plate is withdrawn therefrom. _ ^*. _

6. A valve as claimed In claim 5 comprising a further hollow conduit mounted for movement with the first-mentioned conduit (6l) and located to conduct gases from the valve seat (11) through the valve body (10) when the valve plate (13) is withdrawn laterally from the valve seat (11).

7. A valve as claimed in claim 5 °^r claim 6 wherein the or each hollow conduit (6l) is a cylinder.

8. A valve as claimed in any one of claims 1 to 5 comprising a cryogenic device (51) movable laterally in and out of alignment with the valve seat (ll) to condense gases drawn through the valve aperture when the valve plate (13) is withdrawn from the valve seat (11).

9. A valve as claimed in claim S comprising separate drive mechanisms (21-48) for the valve plate (13) and the cryogenic device (51).

10. A combined shut-off and impedance varying valve substantially as herein described with reference to and as illustrated in Figures 1 to 4 alone or as modified by Figure 5 or Figure 6 of the accompanying drawings.