GB2281448A - Electric motor assembly in a sealed vessel - Google Patents

Abstract

An apparatus for rotating an object within a sealed vessel whilst the object is heated and cooled. The apparatus comprises a hollow rotor 13 mounted within a hollow stator, the stator being supported within and by the vessel. An object may be mounted on the rotor, and heating and/or cooling means are supported adjacent the object. Vacuum tight feedthroughs 22, 24 are mounted in the vessel wall, and services 3 pass through the feedthrough to the heating and cooling means 26, 25. The stator may be energised by electrical lines which pass through the wall of the vessel via one of the vacuum tight feedthroughs 22. Thus energisation of the stator enables the motion of the rotor to be controlled. <IMAGE>

Description

APPARATUS FOR ROTATING AN OBJECT WITHIN A SEALED VESSEL The present invention relates to an apparatus for rotating an object within a sealed vessel. Such apparatus is required in a number of applications, one of which is in the processing of semiconductor substrates within a vacuum chamber. Other applications are the processing of hazardous materials, which processing requires rotating machinery located within a sealed enclosure.

It is often necessary when processing for example semiconductor substrates within a vacuum vessel to be able to heat and/or cool the substrate. It is also necessary to either intermittently or continuously rotate the substrate during processing. It is obviously essential to be able to rotate a component inside the vessel whilst maintaining the vacuum integrity of the vessel, which in the case of semiconductor processing equipment is evacuated to an ultra-high vacuum. Contamination of the space within the vessel must be minimised, and thus contaminants must not be released into the vessel by the rotation apparatus.

Several methods for achieving rotation of an object within a vacuum vessel are known. For example U.S. Patent Specification No.

3435128 describes an apparatus in which a shaft or tube penetrates the vacuum vessel wall, the opening in the vacuum vessel being sealed by a compressible material. Another arrangement suitable for passing services through a vacuum vessel wall is described by SL Barker and SJ Pearce in the Journal of Physics 1977, Volume 10, pages 1231 to 1232.

Although these arrangements allow some degree of rotation they are not suitable for continuous rotation, especially in ultra high vacuum applications. An improved version of the seal is described in the Journal of Vacuum Science and Technology, 1982, Volume 21, page 1031 by A. Parras et al. This is a UHV compatible device but is most suitable for manual use only. It relies upon a series of seals with the spaces between adjacent seals differentially pumped.

A further known method for sealing a shaft subject to rotation is described in U.S. Patent Specification 3612549. This uses fine magnetic particles suspended in a suitable fluid and constrained by magnetic fields. Such seals are available from Ferrofluidic Corporation of The United States and their agents. European Patent Specification 0108206 describes an example and use of such a magnetic fluid seal for sealing electrodes or rotating shafts extending through a vessel wall.

A PTFE grommet shaft seal is described in Vacuum, 1978, Volume 26, pages 349 to 350 by O. Auciello et al. This is used to seal a rotating shaft which carries refrigerant to a specimen holder.

None of the seals previously described are particularly useful in applications which require prolonged rotation in UHV or hostile environment applications.

Mechanisms which do not incorporate a rotating shaft extending through the vessel wall are ideally suited to UHV applications particularly from the point of view of long term reliability. Such mechanisms are known. In one known arrangement, a bent shaft is mounted in bearings inside the vacuum vessel and is caused to rotate by continuously oscillating the bellows externally. This "wobbles" the bent shaft to transmit the necessary rotary motion as described in Nuclear Instruments and Methods, 1975, volume 126, pages 241 to 245 by W.C. Turnkenberg et al. In another known arrangement, rotary motion is transmitted between inner and outer rotating members via a flexible membrane as described in The Journal of Physics, 1973, volume 6, pages 701 to 702 by A.A. Parry and R.G. Linford. Unfortunately mechanisms relying upon bellows or other flexible sealing members are not able to withstand long term continuous rotation.

Magnetically coupled rotary motion drives are described in U.S.

Patent Specification Nos. 3157808 and 3268750. In these arrangements permanent magnets are mounted within and outside the vacuum vessel, rotation of the outer permanent magnets causing the inner permanent magnets to rotate as a result of magnetic coupling. Another approach is described in the Review of Scientific Instruments, 1981, volume 52, 20, pages 301 - 302 by T. Engle. In such an arrangement a motor stator is mounted outside the vacuum vessel with the armature inside the enclosure. This method imparts motion to the rotor within the assembly in the same way as in a conventional motor.

A mechanism which is claimed to be superior to those referred to above is described in British Patent Specification GB2213316.

Rotation of an inner tubular rotor is effected by mounting ring magnets on bearings both inside and outside the vessel, and by rotating the outer magnets. This causes the inner magnets to rotate with the rotor tube on which the inner magnets are mounted. As the rotor is tubular, services such as electrical and coolant fluid supplies can be fed through the tubular rotor. This is particularly advantageous in semiconductor processing apparatus. Unfortunately the described device does have disadvantages, notably a relatively low magnetic coupling force and high magnetic hysteresis which can cause the rotor to oscillate when the movement of the outer magnet is stopped. Finally, as the two sets of magnets are separated by the vessel wall which must be tubular there is a major constraint on the position in which the object mounted on the rotor can be presented to processing equipment.

It is an object of the present invention to provide an apparatus which obviates or mitigates the problems outlined above.

According to the present invention, there is provided an apparatus for rotating an object within a sealed vessel, whilst heating and/or cooling the object, comprising a hollow rotor mounted within a hollow stator, the stator being supported within and by the vessel, means for mounting the object on the rotor, heating and/or cooling means supported adjacent the object mounting means, at least one vacuum tight feedthrough mounted in the vessel wall, services which pass through the said at least one vacuum tight feedthrough to the heating and/or cooling means, and means for energising the stator which pass through the wall of the vessel via the said at least one vacuum tight feedthrough, energisation of the stator causing the rotor to turn within the vessel.

With an arrangement as defined in the preceding paragraph, the stator and rotor can be very closely magnetically coupled and accordingly high torque can be applied to the rotor. This makes it a relatively simple matter to impart whatever motion is required to the rotor, whether continuous or intermittent. Furthermore the rotor may be held by magnetic forces in any one of a number of predetermined positions. Essentially the rotor and stator form components of a conventional motor assembly. It is a relatively simple matter to provide energy to the stator through a fixed feedthrough in the vessel wall. There is no particular problem associated with mounting a stator within even a UHV vessel as the emission of contaminants from the stator can be minimal. There are no gear trains required within the vessel. Furthermore, the rotor and stator assembly may be mounted at any one of a wide variety of appropriate positions within the vessel. This makes the possible application of the apparatus far more flexible than in an apparatus which relies upon magnetic coupling through the vessel wall and therefore predetermines the relative position of the rotor and the vessel.

The rotor and stator assembly could be permanently mounted in one position relative to the vessel or mounted so as to be movable between predetermined alternative positions within the vessel.

The rotor may be in the form of a plurality of separate hollow coaxial tubular rotors each of which is independently drivable. This would of course again increase the flexibility of the apparatus.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a section through a first embodiment of the invention; and Fig. 2 is a section through a second embodiment of the invention.

Fig. 1 illustrates an apparatus which includes a rotatable support head 1 for supporting a substrate 2. Services 3, for example power cables, sensor cables and coolant lines, extend to the space inside the support head 1. A source 4 of deposition material is located beneath the support head 1.

A vacuum enclosure is formed by an upper housing 5 and a lower vessel 6 joined together by flanges 7. A vacuum pump 8 maintains a vacuum within the enclosure and a pressure sensing element 9 enables the pressure within the enclosure to be monitored.

Deposition material is produced from the source 4 and a shutter 10 allows or prevents the passage of deposition material from the source 4 to the substrate 2. A means of operating the shutter (not shown) is provided. The apparatus as illustrated is intended for use with particulate beam sources, but could be used with a source for the supply of gaseous or liquid substances.

The substrate 2 has a front face 11 and a rear face 12, and is mounted on the support head which in turn is mounted on a hollow tubular rotor 13. The rotor 13 is mounted on inner bearings 14 and 15, supported on a fixed hollow tube 16. An inner armature 17 is fixed to an upper portion 18 of the rotor 13. The components 1, 13 and 18 could be formed as illustrated as an integral structure, or as an assembly of separate components. For example the upper portion 18 of the tube may be separable from the lower portion.

The armature 17 is fixed to the tube 18 by a clip 19. A stator 20 is held by a clip 21 inside the housing 5 and is energised via cables that pass through a vacuum tight electrical feedthrough 22.

When the stator 20 is energised, the armature 17 becomes magnetically coupled to the stator. The armature 17 may be magnetically held stationary, or rotated in steps, or rotated continuously, about an axis 23, dependent upon the electrical energy supplied to tne stator 20.

A services feedthrough 24 allows various services to be fed through a flange into the vacuum enclosure. The services 3 include coolant tubes through which a cooling medium may pass to a cooling panel 25, electrical leads connected to a heat source 26, and thermocouple wire pairs connected to a thermocouple 27. The services 3 pass through the stationary tube 16 which is fixed to the housing 5. The stationary tube 16 forms a structure which supports the heat source 26, cooling panel 25, heat shields 28, thermocouple 27, and associated service umbilicals.

Although not shown in Fig. 1, the rotatable head 1 may hold a plurality of substrates or other objects, and the source form may be offset to the main rotation axis 23. In operation, the substrate is rotated as described, while material from the deposition source 4 is deposited on the front substrate face 11. The rear face 12 is heated by the heat source 26, and the hollow tube 16 is offered protection from the heat source 26 by the radiation shields 28 and the cooling panel 26. The arrangement of a heater 26 and services allows the operation of the equipment without interfering with the transfer of material from the deposition source 4 to the substrate surface 11.

In the apparatus of Fig. 1, the opening defined by flanges 7 when the housing 5 and vessel 6 are separated has to be sufficiently large to allow the lower end of the apparatus mounted on housing 5 to be inserted into the casing 6. This is not the case as illustrated in Fig. 1, where for the purposes of showing greater detail the support head 1 is shown to a larger scale than is in fact possible since the support head must be insertable into the casing 6. Thus, for a given size of support head the rotating assembly must be relatively large and cumbersome.

Referring now to Fig. 2, this illustrates an alternative way in which a rotating support can be mounted within a vacuum vessel. In the assembly of Fig. 2, an electrical motor 29 is mounted on a structure 30 that in turn is mounted on a wall of the chamber 31. The motor is rotatable about axis 32 and at its axial end facing a source 33 supports a substrate (not shown). The chamber is closed by a simple flange 34 supporting vacuum tight feedthroughs 35 and 36 for appropriate services. A pump 37 and pressure sensor 38 complete the assembly.

The motor comprises a coaxial arrangement similar to the assembly of Fig. 1, that is it comprises a hollow rotor through which services are fed to heating and cooling means mounted on a stationary tube. The rotor is mounted on the stationary tube and supports the substrate facing the source 33.

Thus, in the arrangement of Fig. 2, the substrate rotating device is independently mounted in the chamber on the chamber wall, which is a far more flexible arrangement than that shown in Fig. 1.

Therefore the arrangement of Fig. 2 is simpler, contains less component parts, and is less prone to the introduction of contamination to the process substrate. Furthermore the arrangement has a greater flexibility in mounting substrates than is the case with the arrangement of Fig. 1 or any previously known device.

Claims (4)

1. An apparatus for rotating an object within a sealed vessel, whilst heating and/or cooling the object, comprising a hollow rotor mounted within a hollow stator, the stator being supported within and by the vessel, means for mounting the object on the rotor, heating and/or cooling means supported adjacent the object mounting means, at least one vacuum tight feedthrough mounted in the vessel wall, services which pass through the said at least one vacuum tight feedthrough to the heating and/or cooling means, and means for energising the stator which pass through the wall of the vessel via the said at least one vacuum tight feedthrough, energisation of the stator causing the rotor to turn within the vessel.

2. An apparatus according to claim 1, wherein the stator and rotor assembly is movable relative to the vessel.

3. An apparatus according to claim 1 or 2, wherein a plurality of hollow coaxial tubular rotors are provided which are independently drivable.

4. An apparatus substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.