Rotary motion transmitter and heat treatment method for sealed chamber

A rotary motion transmitter with an electromagnetic feedthrough device for transmitting rotary motion from the outside to a vacuum chamber (10) designed for treating a specimen in a vacuum environment. The device comprises an evacuated and sealed rotor (14) which contains permanent magnets and, in turn, is hermetically sealed within a capsule (16). The interior of the capsule (16) communicates with the interior of the chamber (10). A removable stator winding unit (22) having electromagnetic windings which interact with the rotor (14) to transmit rotational motion to the rotor is fitted onto the capsule (16). The rotor (14) is rigidly connected to an output shaft (12) which extends into the sealed chamber (10) for supporting and positioning an object to be treated in vacuum. Thus the device combines in itself a rotary feedthrough for transmitting motion to the vacuum chamber (10) and an electric drive motor for positioning an object inside the chamber. This simplifies the construction, reduces its weight, makes it less expensive, protects it from contaminated exterior environments, etc. The transmitter also provides a method for baking the interior of the chamber to evaporate moisture components which are then removed by pumping. For this purpose, the removable stator winding unit (22) is removed and replaced by a cooling jacket (44). This allows baking without dismantling the rotor (14), since its permanent magnets are protected from thermal deterioration by cooling with the surrounding jacket (44).

BACKGROUND 
1. Field of Invention 
The present invention relates to a motion transmitting device, particularly 
to an electromagnetic device for transmitting rotary motion to a sealed 
chamber, particularly, a vacuum chamber. The invention also relates to a 
method of heat treatment, particularly baking the interior of a sealed 
vacuum chamber. 
2. Description of Prior Art 
It is often desirable or necessary to rotate objects within a sealed 
chamber which has a pressure differential with the outside. For instance, 
when a test specimen, such as a semiconductor wafer, is mounted on a shaft 
in a chamber, it is often necessary to change the position of the 
specimen. For this purpose, rotary motion feedthrough mechanisms have been 
known and used in the past. Specifically, such a mechanism comprises a 
shaft which extends from inside the sealed chamber to the outside via a 
rotary feedthrough connection so that the shaft can be rotated from 
outside of the chamber. The feedthrough connection is an airtight device 
which retains the pressure differential between the chamber and the 
outside. Such an arrangement is especially useful where it would be 
impractical to open the chamber merely to rotate the object. 
In those cases where it is necessary to reposition a specimen in a sealed 
vacuum chamber via a stepper motor under program control, the 
above-mentioned feedthrough mechanism is used as an intermediate sealed 
mechanical drive device for transmitting motion from the external stepper 
motor to a specimen holder located inside the chamber. The provision of 
the feedthrough mechanism increases the weight of the system as a whole, 
and makes it more expensive to manufacture. One such feedthrough mechanism 
is described in page 96, the Catalog of Huntington Mechanical 
Laboratories, Inc., 1990, p. 96, Mountain View, Calif. 
As is known in the art, after assembling and prior to use, a vacuum chamber 
is normally subjected to a heat treatment procedure known as baking. 
Baking consists of heating the interior of the chamber to a temperature of 
up to 450.degree. C., e.g., by infrared lamps located inside the chamber, 
while the chamber is maintained under vacuum. Baking is necessary for 
cleaning the interior of the chamber from absorbed gases and other 
impurities, and especially for evaporating and removing moisture which can 
adhere to the inner walls of the chamber and which cannot be easily 
removed by vacuum. Upon completion of baking, the infrared lamps are 
removed from the chamber, and the chamber is evacuated and sealed. 
In case the vacuum chamber is equipped with a motor-driven feedthrough 
device, baking requires that the electric motor be removed, since, when 
the temperature exceeds the Curie point, the magnets in the motor may lose 
their magnetism. Therefore additional time is required for removing the 
electric motor. (As the feedthrough mechanism itself is sealed by a 
bellows, it remains hermetically sealed after removal of the motor.) Upon 
completion of baking, additional time is required for reinstalling the 
motor in place. 
Another essential drawback of feedthrough devices with bellows-type seals 
is a possibility of occasional rupture or failure of the bellows, e.g., 
due to fatigue. In case the chamber contains a poisonous material, such as 
gaseous cyanide used in a technological process inside the chamber, the 
failure of the bellows will allow the gas to leak to the outside, 
presenting a serious health problem for personnel. 
OBJECTS AND ADVANTAGES 
It is accordingly an object of the present invention to eliminate the above 
disadvantages of conventional devices for transmitting rotary motions to a 
sealed chamber. Other objects are to provide rotary motion transmitter 
which combines in itself functions of a stepper motor and a feedthrough 
mechanism, which is light in weight, simple in construction, inexpensive 
to manufacture, allows baking without complete dismantling of the motor, 
and allows cooling of the electric motor rotor during the baking 
procedure. A further object is to provide a new and efficient method of 
baking the interior of a vacuum chamber for removing components without 
dismantling the entire drive motor of a feedthrough device for such a 
chamber. A still further object is to provide a method of baking which can 
be carried out quickly and reliably. Another object is to prevent the 
interior of the chamber from leakage to the surrounding environment in 
case of unexpected failure of the isolation system. 
Yet further objects and advantages will become apparent after consideration 
of the ensuing description and the accompanying drawings.

FIG. 1 
Detailed Description of Rotary Motion Transmitter 
As shown in FIG. 1, which is a cross-sectional side view, the rotary motion 
transmitter comprises a sealed vacuum chamber 10 which is used for 
treating in vacuum a specimen (not shown) which may be supported by a 
specimen holder (not shown) attached to the end of a shaft 12 located 
inside vacuum chamber 10. 
Shaft 12, which is an output shaft of the transmitter of the invention, can 
be connected to or made integrally with a rotor 14 which is sealed in a 
cup-shaped capsule 16 made of a magnetic material, e.g., stainless steel, 
which has low magnetic permeability. Capsule 16 is airtight and is welded 
to a mounting flange 17 by a hermetic welding seam 18 formed on the inner 
side of capsule 16. Flange 17, in turn, is connected to a flange 19 of 
chamber 10 through a sealing device 20, such as a knife-edge seal commonly 
used in ultra-high vacuum applications. 
Rotor 14 has a conventional construction with permanent magnets which are 
not shown as the structure of the rotor is beyond the scope of the present 
invention. The magnets magnetically interact with a rotating magnetic 
field generated by a stator winding unit 22 which embraces encapsulated 
rotor 14. In order to prevent contaminants from rotor 14 from reaching the 
interior of chamber 10, the space inside rotor 14 itself is evacuated 
through a tube 26 which is then hermetically closed by means of a special 
pinch tool (not shown). Thus, rotor 14 is sealed from vacuum chamber 10, 
while the latter is sealed from the outside by capsule 16. 
Rotor 14 is rotatingly supported by front bearings 28 which are located in 
flange 17 and by rear bearings 30 which are installed in a rear wall 32 of 
capsule 16. 
A small gap 34 of about 50 microns is formed between the outer surface of 
rotor 14 and the inner surface of capsule 16 to ensure free rotation of 
rotor 14 while keeping it as close as possible to stator winding unit 22. 
Stator winding unit 22 is removable and slidingly fitted onto the outer 
surface of capsule 16. Accurate positioning of stator winding unit 22 is 
ensured by locating pins 36 and 38 which are press-fitted into flange 17 
and are insertable into respective openings on the facing end of stator 
winding unit 22. Stator winding unit 22 is attached to flange 19 by 
mounting bolts (not shown). 
Stator winding unit 22 may have a conventional construction of the type 
used in a conventional brushless stepper motor. The magnetic field 
generated by windings 22 interacts in a conventional manner with permanent 
magnets of rotor 14 to cause its rotation. The magnetic field passes 
through capsule 16 with low, e.g., 30-40%, loss. 
Thus the stator and rotor of the transmitter in fact form a brushless 
electric motor. The rotor is sealed in a capsule 16 whose interior 
communicates with vacuum chamber 10. The stator is removable and has 
conventional windings arranged outside the capsule. 
A space 42 is sealed by capsule 16 and communicates with the interior of 
chamber 10. 
FIG. 2 
Rotary Motion Transmitter with Windings Removed 
Prior to baking, the mounting bolts (not shown) are disconnected, and 
stator winding unit 22 is removed from capsule 16 (FIG. 2). In order to 
protect the permanent magnets of rotor 14 from deterioration because of 
high temperature developed during baking (up to 450.degree. C.), stator 
windings 22 are replaced by a cooling jacket 44. Rotor 14 remains in place 
and the vacuum in gap 34, space 42, and chamber 10 is not violated since 
hermeticity of the system is ensured by hermetically sealed capsule 16. 
Cooling may be carried out by the circulation of water or any other coolant 
which is admitted into jacket 44 through an inlet port 46 and is 
discharged through an outlet port 48. Cooling jacket 44 may have the same 
outer configuration as the stator. The same locating pins 36 and 38 and 
bolts 40 can be used for the alignment and attachment of cooling jacket 44 
to flange 17. 
In one specific embodiment stator winding unit 22 had a diameter of 85 mm 
and an overall length of 100 mm. The transmitter allowed angular 
positioning of a specimen with an accuracy of 0.9.degree.. It had a total 
weight of 3.0 kg, while a prior-art transmitter consisting of a rotary 
feedthrough with an electric drive weighed about 5 kg. 
Dismantling of stator winding unit 22 prior to baking and replacement 
thereof by cooling jacket 44 for baking took only a few minutes. 
Assembling Operation 
After rotor 14 is manufactured and prior to assembling it into hermetically 
sealed capsule 16, the interior of rotor 14 is evacuated through tube 26, 
and tube 26 is then sealed by pinching with a special pinching tool (not 
shown). Sealed rotor 14 is installed into cup-shaped capsule 16 so that it 
is rotatingly supported by bearings 30 with small gap 34 between the outer 
surface of rotor 14 and the inner surface of capsule 16. Capsule 16 is 
then welded to flange 17 by ultra-high vacuum weld seam 18. Bearings 28 
are installed into flange 17 for rotatingly supporting the front end of 
rotor 14, i.e., output shaft 12. 
Cooling jacket 44 is then placed onto capsule 16 so that pins 38 and 40 are 
inserted into the openings on the front end of cooling jacket 44, and the 
jacket is then fixed by bolts 40 to flange 17. The latter, in turn is 
attached through sealing device 20 to mounting flange 19 of vacuum chamber 
10. 
Heaters such as infrared lamps 21 (FIG. 2) are preliminarily installed into 
chamber 10. Chamber 10 is connected to a source of vacuum and while the 
interior of chamber 10 is maintained under vacuum, it is heated by 
infrared lamps 21 to a temperature of baking (up to 450.degree. C.) which 
is sufficient for evaporating moisture contained inside the chamber. 
Vapors and other impurities are pumped out from chamber 10 by vacuum. 
When baking is completed, heat lamps 21 may remain in chamber 10, removable 
cooling jacket 44 is disconnected from flange 17 and is replaced by 
removable stator winding unit 22 which is guided onto capsule 16 so that 
pins 38 and 40 are inserted into the openings on the front end of the 
stator, and the stator is then fixed by the bolts to flange 17. 
A specimen (not shown) is then inserted into chamber 10 via an access port 
or interlock (not shown) on the other end of chamber 10 and is attached to 
the end of shaft 12. 
The transmitter is now ready for operation. 
Operation of the Apparatus 
Stator winding unit 22 is energized so as to induce a magnetic field in 
rotor 14. This rotates rotor 14 through a predetermined angle in 
accordance with the principle of operation of a conventional stepper 
motor. As a result, the specimen is placed in the required position, and 
is then treated in this position in accordance with a predetermined 
program which controls rotation of rotor 14 and operation of specimen 
treating instruments (not shown). 
Summary, Ramifications, and Scope 
Thus it has been shown that the rotary motion transmitter of the invention 
can transmit rotary motions from outside to within a sealed chamber. The 
transmitter combines in itself the functions of a stepper motor and a 
feedthrough mechanism. It is light in weight, simple in construction, 
inexpensive to manufacture, allows baking without complete dismantling of 
the motor, and allows cooling of the electric motor rotor during the 
baking procedure. 
It also has been shown that the design of the transmitter provides a quick, 
inexpensive, efficient, and reliable method of baking the interior of a 
sealed vacuum chamber without dismantling the entire electromagnetic drive 
motor and without danger of deteriorating the rotor of the drive motor 
under the effect of the high temperature developed in baking. 
Although the transmitter has been shown and described in the form of a 
specific embodiment, its parts, materials, and configurations are given 
only as examples, and many other modifications of transmitters for 
transmitting rotary motions to a sealed chamber are possible. For 
examples, the sealed chamber may be pressurized or contain a hazardous 
substance. Capsule 16 can be made of a material other than stainless 
steel, provided this material has low magnetic permeability. Means other 
than bolts 40 can be used for locking removable stator unit 22 in place. 
The interior of cooling jacket 44 can be cooled by a cooling coil rather 
than by circulating liquid or gaseous coolant. The interior of the vacuum 
chamber can be heated by heaters other than infrared lamps. The specimen 
can be subjected to different treatments, such as ion implantation, etc. 
If necessary, a specimen can be treated mechanically or machined by tools 
attached to shaft 12 which may hold a drill. When such a drill is rotated, 
the specimen can be fed toward the drill for drilling a hole, etc. Many 
other applications are possible. Therefore, the scope of the invention 
should be determined, not by examples given, but by the appended claims 
and their legal equivalents.