Abstract:
A spin processing apparatus can prevent contamination of workpieces by wear particles, and can operate at high efficiency while lowering the noise level associated with the operation of the apparatus. The spin processing apparatus includes a chamber, a spin holder disposed inside the chamber for holding workpieces, and driver device for rotating the spin holder. A supporting device is provided for rotatably supporting the spin holder in a non-contact manner through a magnetically-operated mechanism.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for providing processing such as dewatering and drying of workpieces such as washed semiconductor wafers, for example, while spinning the workpieces in a chamber defining a clean environment. 
     2. Description of the Related Art 
     In manufacturing processes for making semiconductor devices and liquid crystal displays, sometimes there is a need to quickly dry disk-shaped workpieces or wafers which have been subjected to rigorous washing steps. Some of such apparatuses are based on drying the wafer by spinning off the liquid by centrifugal force in a chamber of so-called spin drying apparatus. There are two types of spin drying apparatuses: a vertical type with a vertical spinning axis with the advantage of a small installation space, and a horizontal type with a horizontal spinning axis with the advantage of convenient vertical loading of wafers. 
     Both type of spin drying apparatuses share a common structural feature that a workpiece is held in a rotating wafer holder, having a rotation shaft extending along the rotational axis of the holder inside a chamber. In a widely used design for supporting the wafer holder, the rotation shaft is rotatably supported through a contact-type bearing and is united to a drive shaft of a drive device by mechanical coupling. 
     However, such contact-type bearing mechanisms for the rotation shaft are vulnerable to wear and generation of wear debris, presenting a problem of contamination of the wafers which had been subjected to careful cleaning. Another problem is that the service life of the bearing device is shortened by frictional wear, resulting in a lower operation efficiency due to frequent requirements for maintenance. The working environment is also degrade by noise generated by the operation of high-speed spin dryer. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a spin processing apparatus that can prevent contamination of workpieces by wear particles, and can operate at high efficiency while lowering the noise level associated with the operation of the apparatus. 
     Such object has been achieved in a spin processing apparatus for processing workpieces while rotating the same comprising: a chamber; a spin holder disposed inside the chamber for holding workpieces therein; a driver device for rotating the spin holder; a supporting device for rotatably supporting the spin holder in a non-contact manner through a magnetically-operated mechanism. 
     Accordingly, by rotatably supporting the spin holder in a non-contacting manner by using a magnetically-operated mechanism, generation of wear debris can be prevented. Lowering of service life due to wear of the rotation sections and associated noise generation can also be prevented. 
     The magnetically-operated mechanism may be comprised by radial magnetic bearing means for rotatably supporting a rotation shaft extending along a rotational axis of the spin holder, and axial magnetic bearing means. 
     The rotation shaft may be operatively joined to the driver device by way of magnetic coupling means in a non-contact manner. By using such a configuration and providing a in-between partition member, the interior space of the chamber can be separated from the drive-side devices so that cleanliness inside the chamber is improved. Also, residual vibrational movement of the spin holder can be prevented by the use of an anti-vibration positioning device. 
     The chamber may be provided with fluid handling means for introducing or discharging a gaseous or liquid medium. Accordingly, by introducing or discharging a gaseous or liquid medium while spin processing the workpieces, processes of cleaning and drying can be facilitated to increase the operational efficiency of the apparatus. 
     The apparatus may be provides with pressure control means for controlling a chamber pressure over a range of pressures from atmospheric pressure to a high vacuum. Accordingly, by controlling the interior pressure of the chamber, high vacuum or pressure variation can be utilized to perform various processes. 
     The magnetically-operated mechanism may be provided with gas flow means for eliminating particles residing in the mechanism by flowing a purge gas through the mechanism. According, further protection is provided to eliminate contamination of workpieces. 
     As explained above, the present spin processing apparatus utilizes magnetic bearings for rotating members to provide support in a non-contact manner, it is able to prevent generation of particles produced by wear of support members so that contamination arising from the apparatus can be prevented even for those workpieces requiring a high degree of cleanliness. Furthermore, loss of service life due to wear and the necessity for frequent inspections are reduced to provide high production efficiency, and the working environment is improved by reducing sources of noise generation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall cross sectional view of a first embodiment of the apparatus; 
     FIG. 2 is a cut-away cross sectional view of an axial bearing unit; 
     FIGS. 3A,  3 B are schematic cross sectional views of an anti-vibration positioning device; 
     FIG. 4 is a block diagram of the anti-vibration positioning circuit; 
     FIG. 5 is an overall cross sectional view of a second embodiment of the apparatus; and 
     FIG. 6 is an overall cross sectional view of a third embodiment of the apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, preferred embodiments will be presented with reference to the drawings. FIGS. 1 and 2 show a first embodiment of the spin drying apparatus of the present invention for spin drying of workpieces W such as semiconductor wafers. The apparatus is comprised by: a chamber  10  having a roughly cylindrical space R; a spin holder  12 , for holding workpieces W, having a frame structure and rotatably held inside the chamber  10 ; and drive motor  40  for rotating the spin holder  12 . Spin holder  12  includes two side plates  12   a , rods  12   b , connecting the two side plates  12   a,  and two rotation shafts  14   a,    14   b  aligned on rotational axis and extending away from the plates  12   a . In the bottom region of the chamber  10 , a discharge opening  10   a  is provided to discharge liquid extracted from the workpieces W and the working atmosphere inside the chamber  10 . 
     Within the chamber  10 , a first support block  26  is provided on the open-side of the apparatus, having an intake path  26   a  of a Y-shaped cross-sectional profile to communicate the interior space R with the exterior environment via an unshown air filter, while a second support block  30  is provided on the drive-side (or sealed side) of the apparatus. The intake path  26   a  may be communicated to an exterior gas source for providing clean and inactive gas. A radial magnetic bearing  16   a  is provided between the rotation shaft  14   a  and the first support block  26 , and radial magnetic bearing  16   b , an axial magnetic bearing  18  and a magnetic coupler  50  are provided between the rotation shaft  14   b  and the second support block  30 . All the components described above constitute the support mechanism for rotatably supporting the spin holder  12 . 
     In more detail, a sleeve member  20  is attached so as to surround and rotate with the open-side rotation shaft  14   a , and a rotor-side magnetic member  22   a  is attached to the outer periphery of the sleeve member  20 , and a stator-side magnetic member  24   a  is attached to the inner surface of block  26  opposite to the rotor-side magnetic member  22   a . In this embodiment, these magnetic material members  22   a ,  24   a  are all made of permanent magnet, and comprise a passive-type radial magnetic bearing unit which does not perform any control functions. 
     On the sealed-side rotation shaft  14   b , a cylindrical rotation member  28  having a small-diameter section  28   a , an expansion section  28   b  and a large-diameter section  28   c  is attached so as to rotate as a unit with the shaft  14   b . Another passive type radial magnetic bearing  16   b  similar to the open-side radial bearing  16   a  is provide between the small-diameter section  28   a  and the second support block  30 . In detail, a rotor-side magnetic member  22   b  is provided on the outer surface at a proximal end of the cylindrical rotation member  28  and a stator-side magnetic member  24   b  is provided on the inner surface of block  30  opposing a rotational magnetic member  22   b . These radial magnetic bearings  16   a ,  16   b  are designed so that the opposing magnets become slightly displaced to each other at the operational position of the apparatus so that the spin holder  12  will be biased towards the sealed-side of the apparatus. 
     As shown if FIGS. 1 and 2, a target disk  36  comprised by a hollow magnetic disk is provided in the expansion section  28   b  of the cylindrical rotation member  28 , and a corresponding electromagnet  34  with a coil  32  to oppose the target disk  36  is attached inside the second support block  30 . Axial magnetic bearing  18  is thus actively controllable for controlling the displacement of the spin holder  12  by balancing the force of attraction generated by the electromagnet  34  with the axial force produced by the biased displacement of radial magnetic bearings  16   a ,  16   b.    
     Magnetic coupler  50  is provided for detachably coupling drive shaft  42  of the drive motor  40  and the rotation shaft  14   b  on the drive-side. Magnetic coupler  50  is comprised by a driver magnetic member  54  and follower magnetic member  56 , in such a way that the driver magnetic member  54  is disposed on the outer surface of a sleeve  52  which is attached to the distal end of the drive shaft  42  to rotate with the drive shaft  42 , and that the follower magnetic member  56  is disposed on the inner surface opposite to the driver magnetic member  54  in the large diameter section  28   c . Electromagnetic coupling between the two magnetic members  54 ,  56  allows the follower magnetic member  56  to follow the rotation of the drive motor  40  through the driver magnetic member  54  so as to rotate the cylindrical rotation member  28  and the spin holder  12  as a unit. 
     On the inside wall of the chamber at the driver-side, a cup-shaped partition member  58  is provided to protrude between the sleeve  52  and the large-diameter section  28   c  of the cylindrical rotation member  28 . The partition member  58  hermetically separates the interior space of the chamber from the drive motor-side space. A touchdown bearing  59  is provided at a tip end of the partition member  58  to prevent excessive wobble of the rotation shaft  14   b  during an emergency. A tube portion of the partition member  58  is designed so that neither the material of construction nor its size would interfere with the electromagnetic coupling action between the driver magnetic member  54  and the follower magnetic member  56 . 
     The apparatus is provided with a damper device  60  and an anti-vibration positioning device  62  for quickly responding to residual vibrational movement generated by stopping of the spin holder  12 . Damper device  60  is comprised by and electromagnet  66  with a coil  64  which surrounds the outer peripheral surface of the target disk  36 . The anti-vibration positioning device  62  is comprised by and electromagnet  70  having a coil  68  opposing the sealed-side surface of the target disk  36 . A rail  74  extending in the tangential direction is provided on the second support block  30 , on which a guide  72  attached to proximal end of the electromagnet  70  is slidably mounted for supporting the anti-vibration positioning device  62 . The device  62  is provided with a sensor for detecting operating parameters (displacement, speed) so that electric current outputted by a control circuitry (both not shown) is amplified and supplied to the coil  68  of the device  62 . 
     FIGS. 3A,  3 B are partial enlarged views of the anti-vibration positioning device  62 , and FIG. 4 is a block diagram of the control circuitry. Terms used in these drawings are as follows: S is a transfer function of the system; Ip is moment of inertia of the spin section; θ is angular rotation of spin holder  12 ; K 1  is magnetic coupling stiffness of magnetic coupler  50 ; T 1  is magnetic coupling torque of magnetic coupler  50 ; K 2  is coupling stiffness of anti-vibration positioning device  62 ; T 2  is coupling torque of the device  62 ; C 2  is attenuation stiffness factor of the device  62 ; and M 2  is mass of a movable portion of the device  62 . 
     The operation of the spin drying apparatus will be described in the following. Workpieces W are held in place in and aligned manner in the spin holder  12 , then the drive motor  40  is activated to rotate the spin holder  12  while simultaneously exhausting the chamber atmosphere through the discharge opening  10   a  using and exhaust device (not shown), so that clean air is introduced through the inlet opening of the intake path  26  to quickly dry the workpieces W. Since the spin holder  12  is firmly but non-contactingly supported by radial magnetic bearings  16   a ,  16   b  and the axial magnetic bearing  18 , a stable and smooth rotation motion is generated even at high speeds. 
     When the drying process is completed, and the drive motor  40  is to be stopped, the damper device  60  and the anti-vibration positioning device  62  are activated, so that the damper device  60  works to quickly stop the rotation and position the spin holder  12 , and the device  62  works to dissipate the magnetic energy produced by the axial movement of target disk  36  and preventing vibrational movement of the spin holder  12 . These measures contribute to high operational efficiency and stable operation of the spin drying apparatus. 
     Since the chamber  10  is hermetically sealed from the drive motor  40  with the partition member  58 , even when the chamber  10  is operating under a vacuum, there is no contamination of the interior space of the chamber  10  with substances such as oil used in the drive motor  40 . Further, a purge gas inlet  10   b  is provided to introduce a purge gas (nitrogen gas) into the cylindrical space R so that a positive pressure is maintained in the chamber-side space of the partition member  58  for further preventing the flow of substances from the motor-side of the apparatus. Control wires are led through a cable path  76  provided in the chamber  10  and the second support block  30 . 
     In this embodiment, radial bearings  16   a ,  16   b  are passive-type magnetic bearings without using electromagnets so that the spin holder  12  is supported stably at the axial ends thereof while making the apparatus compact and the control devices simple. The apparatus is made further compact by the use of the axial bearing  18  with the electromagnet  34  to bias the radial bearings  16   a ,  16   b  arranged in an offset position. 
     In the above embodiment, passive-type radial magnetic bearings are used, but it is obvious that active-type radial magnetic bearings can be used. In such a case, although the assembly becomes more complex because of additional controls and sensors needed, a higher degree of control can be achieved. 
     Also, as indicated in FIG. 3B, pole  71  of the electromagnet  70  for the anti-vibration positioning device  62  is located in a specific circumferential location of the target disk  36  so that the device  62  is activated at a specified position of the spin holder  12 . Another possible configuration is to arrange a plurality of protrusions or radially extending channels spaced apart at regular intervals in the circumferential direction of the target disk  36  so that the device  62  may be activated at any position of the spin holder  12 . This arrangement eliminates a disadvantage of imbalance introduced by locating the pole  71  at one specific location. 
     FIG. 5 shows a second embodiment in which the drive-side magnetic bearings are housed in bearing casing  11  disposed on the outside of the chamber  10 . The second support block  30  constituting the fixed side of the drive side bearing structure encloses the casing  11  adjacent to the chamber  10 , and cylindrical section  30   b  of the second support  30  protrudes through the drive-side wall of the chamber  10 . 
     The structure of the magnetic bearings  16   a ,  16   b ,  18 , and anti-vibration positioning device  62  are basically the same as those shown in FIG. 1, and their explanations are omitted. In this embodiment, drive-side bearings can be serviced readily by simply removing the bearing casing  11  from the chamber  10 . Also, although not shown in the drawing, both air intake and discharge paths are provided in the cylindrical walls of the chamber  10 , and therefore, the first support block  26  is not provided with an intake path. 
     FIG. 6 shows a third embodiment, which is an overhung type where the spin holder  12  is supported only at one end thereof. Support and rotation mechanisms are integrated into a bearing/drive unit  80  having magnetic bearings and a drive motor. The unit  80  is disposed outside the chamber  10 , and the spin holder  12  is connected directly to the drive shaft  82  of the unit  80 . 
     The bearing/drive unit  80  is comprised by: a motor section  84  for rotating the drive shaft  82 ; radial magnetic bearings  86   a ,  86   b  disposed on both lateral ends of the motor section  84 ; and an axial magnetic bearing  88  disposed on the end of the drive shaft  82  opposite to the chamber  10 . The drive shaft  82  can be rotated at high speeds under active control of five axes. 
     In this embodiment, all sliding sections, including touchdown bearing, are eliminated from the interior space of the chamber  10  so that high cleanliness can be maintained at all times. However, because the spin holder  12  is supported at one end only, a long span length of the bearing sections is necessary to prevent shifting of the center of rotation of the spin holder  12 , and because of the increased length of support, a higher power motor is necessary.