Patent Publication Number: US-2012034105-A1

Title: Linear peristaltic pump

Description:
BACKGROUND 
     In semiconductor manufacturing environments, photoresist is deposited onto semiconductor wafers by a process known as spin coating. In spin coating, a deposition mechanism deposits a predetermined amount of photoresist onto the center of a wafer; a spin mechanism then spins the wafer. The spinning motion of the wafer provides an essentially uniform layer of photoresist having a precisely specified thickness. The photoresist itself, along with having an essentially uniform thickness, will also be free of contaminants. 
     Photoresist in such an environment needs to be delivered to an outlet in a tightly controlled manner with an almost zero tolerance for contaminants. That is, photoresist is moved from a storage container to a deposition area at a constant volumetric flow rate. Further, the medium through which the photoresist moves is not to introduce particulates. 
     In order to accomplish these demanding objectives, a conventional pump system designed to deliver photoresist from storage container to deposition mechanism employs a series of filters and valves. 
     SUMMARY 
     Unfortunately, such a conventional pump system as that described above suffers from deficiencies. For example, diaphragm and syringe type pump systems tend to have multiple check valves which make it difficult to control photoresist contaminant levels and add substantially to cost. Conventional rotary type, multiple element-element peristaltic pump systems, while simple, will pulsate the flow, which is undesirable. 
     In contrast to the above-described conventional pump system, an improved technique for delivering a fluid to an outlet from a storage container takes the form of a linear peristaltic pump which enables the use of two elements: a single bearing and a valve. The single bearing provides enough pressure to a flexible tube in which the fluid moves to close the tube off at a single location. The valve controls the fluid flow out of the flexible tube at the egress point in conjunction with the bearing and is attached to the flexible tube at a single location. In this manner, when the bearing is engaged with the flexible tube, the bearing divides the flexible tube into two subvolumes, one of which contains fluid to be moved toward the egress point at the far end of the flexible tube and the other creating suction for intake of fluid immediately behind the bearing. A bearing controller moves the bearing along the surface of the flexible tube when so engaged; in doing so, the bearing moves the fluid. When the fluid has been moved from the flexible tube, the bearing controller lifts the bearing from the flexible tube, the valve closes and the bearing controller then moves the bearing back to a starting position, and back toward the flexible tube, where the above-described process repeats itself. 
     One embodiment of the improved technique is a peristaltic pump device configured to move a fluid from a storage container along an interior of a flexible tube. The peristaltic pump device includes a single roller constructed and arranged to apply pressure to an outer surface of the flexible tube when fluid from the storage container is in the interior of the flexible tube. The peristaltic pump device also includes a roller controller constructed and arranged to constrain the single roller to movements (i) along the outer surface of the flexible tube, (ii) toward the outer surface of the flexible tube to provide a compression of a volume of the interior of the flexible tube, the compression sufficient to divide the volume of the interior of the flexible tube into two distinct subvolumes and (iii) away from the outer surface of the flexible tube to relieve the compression. The peristaltic pump device further includes a valve attached to the flexible tube at a single location, the valve constructed and arranged to, in conjunction with the single roller, control flow of the fluid through the interior of the flexible tube. 
     A further embodiment of the improved technique is a method of moving a fluid from a storage container along an interior of a flexible tube. The method includes drawing the fluid from the storage container to a near end of the flexible tube. The method also includes moving a single roller to an outer surface of the flexible tube, the moving ceasing when the single roller divides the interior of the flexible tube into two subvolumes in which fluid in each subvolume does not flow into the other subvolume. The method further includes moving the single roller along the outer surface of the flexible tube while maintaining a pressure sufficient for the interior of the flexible tube to remain divided into the two subvolumes. The method further includes operating a valve constructed and arranged to control flow of the fluid through the interior of the flexible tube to a far end of the flexible tube, the valve attached to the flexible tube at a single location. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of various embodiments of the invention. 
         FIG. 1  is a drawing of a peristaltic pump device which operates according to the improved technique. 
         FIG. 2  is a schematic drawing of a photoresist delivery system which utilizes the peristaltic pump device illustrated in  FIG. 1 . 
         FIG. 3  is a flow chart which illustrates the method carried out by the improved technique. 
     
    
    
     DETAILED DESCRIPTION 
     An improved technique for delivering a fluid to an outlet from a storage container takes the form of a linear peristaltic pump which enables the use of two elements: a single bearing and a valve. The single bearing provides enough pressure to a flexible tube in which the fluid moves to close the tube off at a single location. The valve controls the fluid flow out of the flexible tube at the egress point in conjunction with the bearing and is attached to the flexible tube at a single location. In this manner, when the bearing is engaged with the flexible tube, the bearing divides the flexible tube into two subvolumes, one of which contains fluid to be moved toward the egress point at the far end of the flexible tube and the other creating suction for intake of fluid immediately behind the bearing. A bearing controller moves the bearing along the surface of the flexible tube when so engaged; in doing so, the bearing moves the fluid. When the fluid has been moved from the flexible tube, the bearing controller lifts the bearing from the flexible tube, the valve closes and the bearing controller then moves the bearing back to a starting position, and back toward the flexible tube, where the above-described process repeats itself. 
       FIG. 1  shows a peristaltic pump device  10  which is suitable for use by the improved technique. The peristaltic pump device  10  includes a flexible tube  14 , a bearing  16 , a motor  18 , and a linkage system  20 . Bearing  16  is controlled by motor  18  via linkage system  20 . At one end of the flexible tube is a valve  30 . At a far end of flexible tube  14  is a filter  28 . 
     Flexible tube  14  connects, at one end, to a storage tank or source containing fluid to be moved through flexible tube  14 . Flexible tube  14 , if used to move photoresist, is typically about 1 foot long, with a ⅜ inch inner diameter (ID) and ⅝ inch outer diameter (OD). In such an application, flexible tube  14  is made of GORE 500, although other materials are possible. 
     Bearing  16  is configured to move along flexible tube  14 , providing a degree of compression. Bearing  16  is a cylindrically shaped bearing having a borehole and smooth surface. The borehole in this case has a ¼ inch bore diameter and a ¾ inch outer diameter. A bearing as described here is manufactured by AST Bearings LLC, Montville, N.J. 
     Motor  18  is configured to control the motion of bearing  16 . Motor  18  is a servo motor rated at 16,000 counts per revolution, while providing about 60 oz-in of continuous torque with which to maintain a compression on flexible tube  14  using bearing  16 . A motor as described here is manufactured by Teknic, Inc. of Pittsford, N.Y. 
     Linkage system  20  connects the motion of motor  18  to that of bearing  16  and defines the compression that bearing  16  is able to apply to flexible tube  14 . Linkage system  20  includes a pulley system  22 , a ballscrew  24 , and a linkage bearing  26 . Motor  18  drives pulley system  22 , which is connected to ballscrew  24 , along which linkage bearing  26  moves. 
     Pulley system  22 , which includes a timing belt  21  and a pair of hubs  23 , links the output of motor  18  to other moving parts of the pump device  10 . Timing belt  21  is a ¼-inch wide polyurethane, double-sided belt with a Kevlar tension member. Timing belt  21  further has a 0.08 inch pitch and  150  grooves. Hubs  23  are made from aluminum alloy, have a ¼ inch borehole, and are designed to fit ¼ inch timing belts. An outer hub surface also has a 0.08 inch pitch and has 36 grooves. A timing belt and pulley hub such as that described here is manufactured by SDP/SI, Inc., New Hyde Park, NY. 
     Ball screw  24  is connected to timing belt  21  and is configured to receive output from motor  18  through timing belt  21 . Ball screw  24  is configured to convert a rotational motion [induced from timing belt  21 ] into a linear motion and includes a 0.5 m long shaft along which the linear motion occurs. A ball shaft such as that described here is manufactured by THK Co., LTD, Schaumberg, Ill. 
     Ball screw  24  also includes linkage bearing  26 , which moves along ball screw  24  in the linear motion. Linkage bearing  26  is connected to bearing  16  and guides the movement of bearing  16  along flexible tube  14 . 
     Linkage bearing  26  is further configured to move bearing  16  along a direction normal to ball screw  24 . This motion ensures that bearing  16  can be moved toward and away from flexible tube  14  in order to provide an appropriate amount of pressure for compression and for relief. 
     Filter  28  is configured to remove contaminants from the fluid before it is sent to an outlet. Preferably, filter  28  is positioned closer to the near end of flexible tube than is valve  30 . Filter  28  is rated to 0.2 microns. Filters such as those described here are manufactured by Parker Hannifin, Cleveland, Ohio. 
     Valve  30  is configured to control, in conjunction with bearing  16 , a flow rate of the fluid through flexible tube  14 . Valve  30  is a pneumatic actuated, 2-way valve rated for high pressures (up to 100 PSIG) ; at room temperatures, this translates into a flow rate of almost 18 liters/minute. Valves such as those described here are manufactured by Saint Gobain Performance Plastics—USA, Garden Grove, Calif. 
     During operation, bearing  16  is moved away from an outer surface of flexible tube  14 . At the end of flexible tube  14  connected to a storage tank containing fluid to be. moved by peristaltic pump  10  (the near end of flexible tube  14 ), fluid is taken into flexible tube  14 . Linkage system  20  guides bearing  16  to a start position along flexible tube  14  close to the near end. At this point, valve  30  opens. Bearing  16  then moves against the outer surface of the near end of flexible tube  14  in such a way that opposite interior surfaces of flexible tube  14  touch and there are two subvolumes within flexible tube  14 . Bearing  16  then moves at a predetermined rate along the outer surface of flexible tube  14  from the near end to a far end of flexible tube  14 . In this movement along the outer surface, the roller in effect squeezes, without touching, the fluid through the interior of flexible tube  14  toward the far end. Controlling fluid flow at one end of flexible tube  14  is valve  30 , which can be activated pneumatically to start or stop flow of the fluid in or out of flexible tube  14  at either end. Flow rate can be limited, however, by filter  28 , which removes any contaminants in the fluid before the fluid is sent to an outlet. 
     When bearing  16  reaches an end point along flexible tube  14 , linkage system  20  lifts bearing  16  away from flexible tube  14 . At this point, valve  30  closes and the operation described above repeats. 
     Advantageously, peristaltic pump  10  is able to deliver a larger, non-pulsating fluid flow because there is only a single valve controlling fluid flow. Because valve  30  is a pneumatically actuated valve, valve  30  is able to withstand higher pressures and can deliver the smooth flows expected in a high throughput semiconductor manufacturing environment. Further, because there are few moving parts in peristaltic pump  10 , peristaltic pump  10  is less expensive, has fewer opportunities for the introduction of contaminants into the fluid and is easier to maintain. 
     Details of operation of peristaltic pump  10  within a semiconductor manufacturing environment are discussed below with respect to  FIG. 2 . 
       FIG. 2  shows a semiconductor manufacturing environment which utilizes peristaltic pump  10 . Specifically, illustrated in  FIG. 2  is a spin coat system  40  which is constructed and arranged to deliver a predetermined amount of photoresist to wafer  48  within a fixed time interval. Spin coat system  40  includes peristaltic pump  10 , photoresist container  42  and photoresist delivery device  44 . 
     Photoresist container  42  usually holds one gallon of photoresist and is placed in a position accessible to peristaltic pump  10 . Flexible tube  14  of peristaltic pump  10  is connected to an opening in container  42  through which photoresist is acquired (e.g., by capillary action). 
     Photoresist delivery device  44  transfers photoresist from the output of peristaltic pump  10  to wafer  48 . Photoresist delivery device  44  includes a nozzle  46  out of which photoresist is introduced onto the surface of wafer  48 . 
     Flow rate and flow volumes delivered to an outlet connected to spin coat system  40  are determined by needs of the spin coat system  40 , for example, the volume of photoresist needed to coat a  12  inch wafer over a  5  second period. Because motor  18  is a high resolution servo motor and the valve is pneumatically activated, the flow rate and volume is precisely controlled. Because of the fact that it is a peristaltic pump moving the fluid along the interior of flexible tube  14 , contaminants within the fluid are limited, allowing a greater flow rate through filter  28  and permitting a greater throughput in coating wafers with photoresist. 
     When dispensing photoresist, it is desireable to ensure that there is no “final drop” in the outlet. Accordingly, before the fluid reaches the outlet, one sucks back a column of fluid within flexible tube  14 . Such a suck back is accomplished by moving bearing  16  along the outer surface of flexible tube  14  toward the near end for a short distance and then closing valve  30  and lifting bearing  16  away from flexible tube  14  to return it to the start position as described above. 
     While various embodiments of the invention have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
     For example, valve  30  can be positioned at the near end of flexible tube  30 . 
     Further, valve  30  can be a suckback valve having suckback capability. That is, instead of reversing flow, valve  30  sucks back fluid on its far side. 
     Furthermore, peristaltic pump  10  can be utilized in environments other than the semiconductor processing environments discussed above. For example, peristaltic pump  10  can be configured for use in intravenous fluid delivery devices.