Patent Application
20190145418
The present disclosure relates to turbomolecular pumps. More specifically, the present disclosure is directed to various embodiments of turbomolecular pumps that may be dynamically rebalanced during operation to counter the effects of, for example, condensation of process material on the rotors or stators during a vacuum deposition process.
Physical vapor deposition (PVD) is directed to a variety of vacuum deposition methods which can be used to produce thin films and coatings. Such processes typically require the use of hostile gases at low pressures within a vacuum chamber. These processes include, for example, plasma deposition, plasma etching, low pressure chemical vapor deposition and ion implantation.
Historically, many PVD processes utilized oil diffusion high vacuum pumps. However, many industries have moved away from the use of oil diffusion pumps as part of PVD process equipment due to contamination. That is, the operating principle of oil diffusion pumps dictates that the working oil of the pump be directly exposed to the chamber that is evacuated. Oil molecules thus migrate into the process chamber, intermingle with the gases and contaminate the process. For many PVD applications where contamination is a concern (e.g., semi-conductor manufacturing), turbomolecular pumps have become the industry standard, as such pumps typically do not contaminate the local vacuum environment.
Turbomolecular pumps are basically high-speed turbines that operate on kinetic gas principles. That is, turbomolecular pumps work on the principle that gas molecules can be given momentum in a desired direction by repeated collision with a moving solid surface. In a turbomolecular pump, rapidly spinning rotor blades ‘hit’ gas molecules from the inlet of the pump towards the exhaust in order to create or maintain a vacuum. Most turbomolecular pumps employ multiple stages, each consisting of a set or stack of rotating rotor blades/vanes and stationary stator blades/vanes. Typically, the rotor of a turbomolecular pump rotates on sealed and/or magnetic levitation bearings, which results in little or no contamination. In any arrangement, gas molecules captured by the upper stages of the pump are pushed into the lower stages and successively compressed. As the gas molecules enter through the inlet, the rotor, which has a number of angled vanes, hits the molecules. Thus the mechanical energy of the vanes is transferred to the gas molecules. With this newly acquired momentum, the gas molecules enter into the gas transfer areas in the stator vanes. This leads them to the next stage where they again collide with a rotating rotor vane surface, and this process is continued, finally leading the molecules outwards through the exhaust.
To achieve low vacuum levels, turbomolecular pumps run at high rotational speeds. In order to obtain extremely low pressures down to, for example, 1 micropascal, rotation rates of 20,000 to 90,000 revolutions per minute are often necessary. Such high rotation rates stress the rotor bearings of the pump requiring periodic maintenance and/or replacement of the bearings. Bearing can be further stressed in PVD processes where a deposition process generates metal or chemical vapors that can deposit/condense on the turbo pump rotor blades. Such deposition/condensation can create an unbalanced condition for the turbo pump rotor. Such an unbalanced condition can significantly shorten the life of the bearings thereby requiring early bearing replacement and/or rebalancing of the rotor.
A turbomolecular pump is provided having a number of novel features that may be utilized alone or in various combinations. In one arrangement, a stator stack and rotor stack have corresponding conical, curved or frustum shapes that allow for adjusting the clearance between the stator vanes and rotor vanes of the pump to provide adjustable compression ratios and/or to adjust clearances. In another arrangement, the actuator or drive mechanism of the pump is formed from coils attached to the blades of upper stage of a rotor stack which are controlled to interact with a plurality of stationary magnets attached to the housing of the pump to rotate the stator stack. In another arrangement, a control system of the pump utilizes the coils of the rotor drive to dynamically balance the pump during operation.
In one aspect, a turbomolecular pump is provided that allows for adjusting clearances between stator vanes and rotor vanes. Such adjustment may be done prior to pump operation and/or dynamically during pump operation. The pump includes a rotor stack having a plurality of sets of rotor vanes, which extend radially outward from a hub, which rotates about a stationary shaft (e.g., rotor shaft). The rotor stack rotates within a stator stack having a plurality of sets of stator vanes that extend radially inward from an outer stator housing (e.g., toward the hub of the rotor stack). The rotor stack and stator stack are disposed within a pump housing. The rotor stack and stator stack have generally matching curved profiles in cross-section. In one arrangement, the curved profiles are conical profiles. However, the term conical as utilized herein is intended to include variations from a cone. That is, the profiles may be frustum shaped or otherwise curved. In any arrangement, a profile of the rotor stack, as defined by the tips of the different sets of rotor blades, defines a first conical profile. A profile of the stator stack, as defined by root surfaces between different sets of stator blades, defines a second conical profile. One or more adjustable connectors attach the stator stack to the pump housing. Adjustment of the connectors allows for adjusting a vertical position of the stator stack relative to a vertical axis of the pump, where the vertical axis is defined by a central axis of the rotor shaft. In contrast, the position of the rotor stack may remain fixed. This adjustment allows adjusting the axial position of the second conical surface of the stator stack relative to the axial position of the first conical surface defined by the rotor stack. Such adjustment, in combination with the conical profiles of the stator stack and rotor stack, provides adjustment in two dimensions between the stator vanes and the rotor vanes. More specifically, a distance between the tips of the rotor vanes and the root surfaces of the stator housing may be increased or decreased in conjunction with adjusting the distance between the top and or bottom edges of the stator and rotor vanes. This allows for adjusting the compression of the pump and/or adjusting clearance of the vanes to account for condensation buildup.
In another aspect, a turbomolecular pump is provided that utilizes coils attached to rotor vanes as a drive motor for the pump. Stated otherwise, the pump utilizes a rotor drive system. The pump includes a rotor stack having a plurality of sets of rotor vanes, which extend radially outward from a hub, which rotates about a stationary shaft. The rotor stack rotates within a stator stack having a plurality of sets of stator vanes that extend radially inward from an outer stator housing (e.g., toward the hub of the rotor stack). The rotor stack and stator stack are disposed within a pump housing. One set of the blades of the rotor stack includes a plurality of electrical coils attached thereto. These coils interact with a plurality of magnets fixedly attached the pump housing. A control system provides drive signals to each of the plurality of coils such that they are attracted and/or repelled by the magnets to impart rotation to the rotor stack.
In another aspect, a turbomolecular pump having a rotor drive system may be dynamically balanced during operation. The pump includes a rotor stack disposed within a stator stack, which are both disposed within a housing. The rotor stack rotates about a stationary shaft associated with the housing. At least one bearing rotatably couples the rotor stack to the rotor shaft. Each bearing further includes one or more optical strain sensors that generate output signals indicative of strains on or in the bearing. The outputs are provided to a control system that is configured to provide a plurality of individual drive signals to a plurality of coils attached to at least a first set of rotor blades of the rotor stack. More particularly, the control system utilizes the outputs from the optical sensors to determine an imbalance in the rotor stack. Upon determining an imbalance in the rotor stack, individual drive signals are provided to each of the individual coils. The individual drive signals may be adjusted to counteract the imbalance. In one arrangement, the outputs of the optical sensors are provided to the control system via optical filaments. Use of optical sensors and filaments allows utilizing the pump in electrically noisy environments. In a further arrangement, the drive signals are provided to each individual coil utilizing optical signals, which again allow for use in electrically noisy environments. In one arrangement, optical drive signals are provided to optical actuators which are disposed proximate to insulated gate bipolar transistors (IGBTs). The IGBTs are connected to the rotor stack and are further electrically connected to one of the coils. The IGBTs are also in electrical contact with an electrically powered bearing of the pump. Upon receiving an optical drive signal, each IGBT opens for a duration and magnitude associated with the drive signal to provide individual drive signals to the individual coils. In further arrangement, the pump utilizes one or more position sensors to identify the location of each coil in order to provide individual drive signals to those coils.
In any aspect, the pump may be configured to allow for the replacement of bearings without removing the pump from, for example, a vacuum chamber. The pump may also be constructed of materials that allow for extended use in high temperature environments.
Reference will now be made to the accompanying drawings, which at least assist in illustrating the various pertinent features of the presented inventions. The following description is presented for purposes of illustration and description and is not intended to limit the inventions to the forms disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the presented inventions. The embodiments described herein are further intended to explain the best modes known of practicing the inventions and to enable others skilled in the art to utilize the inventions in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the presented inventions.
As shown in
As noted above, one unique feature of the pump 10 is the ability to adjust the stator stack 20 relative to the rotor stack 30 to adjust the clearance between the stator vanes and the rotor vanes. The conical or frustum shape allows the stator vanes to effectively move in two directions relative to the rotor vanes to adjust the clearances there between. Adjusting the clearance between the stator vanes and the rotor vanes allows for adjusting the compression of the pump 10 as well as adjusting clearance to account for build up or condensation of PVD materials on the rotor vanes.
As shown in
As shown
As noted above, a unique feature of the presently disclosed pump is that the rotor stack 20 forms a portion of the actuator mechanism for the pump 10. Previously, turbo pumps have utilized a separate electric motor to rotate the rotor stack of the pump. In the present pump 10, the actuator for the pump is formed from coils attached to the upper set of rotor vanes which are controlled to interact with a plurality of stationary magnets attached to the housing of the pump. In this feature, the rotor stack in addition to providing compression and movement of gas molecules also forms an electromagnetic stator of a drive motor for the pump.
As best shown in
The coils 34 are selectively actuated to impart rotation to the rotor stack 30. More specifically, plurality of coils 34 attached to the plurality of rotor vanes 32A interact with a corresponding plurality of permanent magnets 40, which are fixedly attached to the housing 12. See
In order to control the rotation of the rotor stack, a control system of the pump 10 must know the angular orientation of the rotor blades 32A and their supported coils 34. In the present embodiment, a plurality of optical sensors 42 are disposed radially around the outer periphery of the first row/set of rotor blades 32A. In the illustrated embodiment, each of these optical sensors 42 is disposed within a recess in a casing of the stator stack 20. Further, in the present embodiment, each optical sensor 42 is connected to the control system of the pump via a fiber optic filament 44. In operation, the optical sensors 42 output information that is utilized by the control system to determine the orientation of an adjacent stator vane 32 such the control system may controllably operate the coils 34 to control the rotation of the stator stack 20.
The present embodiment utilizes fiber optic filaments 44 to connect the optical sensors to the control system. Other embodiments may utilize non-optical sensors to provide such sensing and may utilize different connections. However, the utilization of fiber optic sensors and fiber optic filaments provides a benefit for the presented pump. Particularly, the pump 10 is often utilized in PVD processes where ionized matter and/or plasma fields exist. Such ionized matter in plasma fields often result in considerable electronic noise. Additional electronic noise is generated by the high speed operation of the pump itself. Along these lines, the use of optical sensors and optical signal transmission significantly reduces or eliminates potential interference that may arise from electronic noise.
As noted above, another feature of the pump is the ability to dynamically balance the pump during operation. During a PVD process, which generates chemical vapors or metals, turbo pump vanes can be subject to condensation of any process materials which can create an unbalanced condition for the turbo pump rotor. To minimize the vapor deposition on the vanes, turbo pumps are often externally heated. However, heating of turbo pumps is time-limited in extreme conditions (e.g., high temperatures). Such high temperature operation can result in premature bearing failure. The presented turbo pump 10 provides a mechanism for dynamically balancing the rotor during operation to offset imbalances that may occur due to condensation of process materials on the rotor vanes. More specifically, the use of the stator vane drive, described above, allows applying the non-uniform drive forces to the rotor stack, which can counteract imbalances that occur during operation.
As previously noted, the rotor stack 30 is rotatably coupled to the rotor shaft 26 by upper and lower bearing assemblies 28A, 28B. Each of these bearing assemblies 28A, 28B further incorporates an optical strain sensor 50A, 50B, respectively. These optical strains sensors 50A, 50B (hereafter 50 unless specifically referenced) are annular elements that surround their respective bearing assembly and which are connected to the control system by their respective optical filament sets 46A or 46B.
To counteract the effects of an imbalance in the rotor stack 30, the processor 64 generates individual drive signals (e.g., drive pulses) for each of the coils 34 attached to each of the rotor blades 32A. That is, in the illustrated embodiment, the processor 64 generates thirty-six individual drive signals for each of the coils 341-36 attached to each of the thirty-six individual stator vanes 32A1-36, respectively.
A system for applying individual signals to individual coils 34 of the rotating rotor stack and powering each of the individual coils 34 is further illustrated in
In order to provide individual drive signals to individual coils, individual filaments 681 and 19 (only two shown) of the filament bundle 68 enter the pump 10 alongside the stationary rotor shaft 26. These filaments 68 each terminate at a fiber optic actuator 54, which is disposed adjacent to an optically actuated insulated-gate bipolar transistor (IGBT) 90. The IGBT is in electrical connection with the electrified seal 80. Upon a filament (e.g., filament 6819) providing an optical signal (e.g., drive signal) to the optical actuator 54, the optical actuator 54 outputs a light pulse corresponding to the drive signal to the optical IGBT 90. The IGBT 90 opens for a duration and magnitude corresponding to the drive signal provided by the processor via the filament 6819. That is, the IGBT passes electrical power to the coil 3419 via the electrical connector 38. The power is provided to the coil 3419 with a corresponding duration and magnitude to the drive signal provided for that coil. The energized coil interacts with an adjacent permanent magnet 40 as described above to rotate the rotor stack.
As may be appreciated, each individual coil 34 is connected to an individual IGBT 90 via an individual connector 38. Along these lines, the IBGTs are connected to the hub 36 of the rotor stack and rotate with the rotor stack. In this regard, the drive signals provided to the IGBTs by the optical actuators 50 must be provided when the optical IGBT is aligned with the optical actuator 50. This information is known by the processor via the optical position sensors 42. Again, due to the processing speeds of modern computers, delivery of the drive signals to individual coils is possible even at high rotational speeds.
Though a number of features have been discussed, the pump 10 includes a number of additional features that are novel alone and/or in various combination with the features discussed above. For example, the pump is configured to facilitate field maintenance. As best show in in
The foregoing description has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the inventions and/or aspects of the inventions to the forms disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the presented inventions. The embodiments described hereinabove are further intended to explain best modes known of practicing the inventions and to enable others skilled in the art to utilize the inventions in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the presented inventions. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.
