Abstract:
A method of aligning die and stamping substrate for nano-imprint lithography is described. The method includes aligning the die by linearly displacing the die along a first axis using a first flexure member and pressing the die along a second axis substantially perpendicular to the first axis while maintaining coupling of the die with the first flexure member.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a divisional of Ser. No. 10/807,702 filed Mar. 23, 2004 now U.S. Pat. No. 7,229,266. 
    
    
     TECHNICAL FIELD 
     Embodiments of this invention relate to the field of manufacturing and, more specifically, to a die press used in manufacturing. 
     BACKGROUND 
     A disk drive system includes one or more magnetic recording disks and control mechanisms for storing data within approximately circular tracks on the disk. A disk is composed of a substrate and one or more layers deposited on the substrate (e.g., aluminum). A trend in the design of disk drive systems is to increase the recording density of the magnetic recording disk used in the system. One method for increasing recording density is to pattern the surface of the disk with discrete tracks, referred to as discrete track recording (DTR). A DTR pattern may be formed by nano-imprint lithography (NIL) techniques, in which a pre-embossed forming tool (a.k.a., stamper, embosser, etc.), having an inverse pattern to be imprinted, is pressed into an embossable film (i.e., polymer) disposed above a disk substrate to form an initial pattern of compressed areas. This initial pattern ultimately forms a pattern of raised and recessed areas. After stamping the embossable film, an etching process may be used to transfer the pattern through the embossable film by removing the residual film in the compressed areas. After the imprint lithography process, another etching process may be used to form the pattern in a layer (e.g., substrate, nickel-phosphorous, soft magnetic layer, etc.) residing underneath the embossable film. 
     One prior DTR structure contains a pattern of concentric raised areas and recessed areas under a magnetic recording layer. The raised areas (also known as hills, lands, elevations, etc.) are used for storing data and the recessed areas (also known as troughs, valleys, grooves, etc.) provide inter-track isolation to reduce noise. The raised areas may have a width less than the width of the recording head such that portions of the head extend over the recessed areas during operation. The recessed areas have a depth relative to fly height of a recording head and raised areas. The recessed areas are sufficiently distanced from the head to inhibit storage of data by the head in the magnetic layer directly below the recessed areas. The raised areas are sufficiently close to the head to enable the writing of data in the magnetic layer directly on the raised areas. Therefore, when data are written to the recoding medium, the raised areas correspond to the data tracks. The recessed areas isolate the raised areas (e.g., the data tracks) from one another, resulting in data tracks that are defined both physically and magnetically. 
     A press may be used to imprint embossable films residing on one or both sides of a disk substrate. The press utilizes a die for each side of the disk to be imprinted. The die is coupled to a stamper that is pressed into the film to form the imprinted pattern in the film. A DTR disk may not be viable if the imprinting surface of the stamper is not concentrically aligned with the center of a disk substrate. This requirement may be particularly important when data tracks are generated on both sides of the disk because the data tracks on each side need to be in co-axial alignment with each other. As such, the imprinting of an embossable film above a disk substrate requires an alignment step, in which a centerline of the disk is aligned with a centerline of the imprinting surface, before the embossable film is actually imprinted. 
     Conventional presses utilize 2 and 4 post precision die sets to attain alignment of the top and bottom dies used to imprint films on each side of a disk. A 4-post die set is illustrated in  FIG. 1 . One problem with such post die sets is that the posts contain bushings or ball bearing sleeves (guides) that wear out or seals that leak lubricant over repeated use. Another problem with such die sets is that the multiple posts hinder access to the die space. Furthermore, current specialized press alignment methods typically require the use of an air bearing supported die that is adjusted to correct for alignment offset. In addition, such presses must be stopped, the die must then be unclamped, supporting air pressure applied, positional adjustments made, supporting air pressure removed, and the die be re-clamped in order to secure the alignment. As a result, the use of such presses results in high maintenance costs due to frequent mechanical wear and breakdown of components, inconsistent accuracy and reliability, and slower manufacturing cycle times. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which: 
         FIG. 1  illustrates a conventional 4-post die set. 
         FIG. 2  is a frontal perspective view illustrating one embodiment of a press. 
         FIG. 3  is a cross section view illustrating one embodiment of rod and receiver. 
         FIG. 4  illustrates a side perspective view of one embodiment of the press shown in  FIG. 2 . 
         FIG. 5  illustrates one embodiment of the press in a closed, or down, position. 
         FIG. 6  illustrates one embodiment of the press in an open, or up, position. 
         FIG. 7  illustrates one embodiment of the press having a shroud. 
         FIG. 8  illustrates one embodiment of a single flexure position adjustment mechanism. 
         FIG. 9  illustrates an alternative embodiment of a press having the single flexure position adjustment of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth such as examples of specific materials or components in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that these specific details need not be employed to practice the invention. In other instances, well known components or methods have not been described in detail in order to avoid unnecessarily obscuring the present invention. 
     The terms “above,” “below,” and “between” as used herein refer to a relative position of one layer or component with respect to other layers or components. As such, a first layer or component disposed above or below another layer or component may be directly in contact with the first layer or component or may have one or more intervening layers or components. 
     It should be noted that the apparatus and methods discussed herein may be used for pressing various types of workpieces. In one embodiment, the apparatus and methods discussed herein may be used for the imprinting of embossable films for the production of magnetic recording disks. The magnetic recording disk may be, for example, a DTR longitudinal magnetic recording disk having, for example, a nickel-phosphorous (NiP) plated substrate as a base structure. Alternatively, the magnetic recording disk may be a DTR perpendicular magnetic recording disk having a soft magnetic film disposed above a substrate for the base structure. In an alternative embodiment, the apparatus and methods discussed herein may be used for the imprinting of embossable materials for the production of other types of digital recording disks, for examples, optical recording disks such as a compact disc (CD) and a digital-versatile-disk (DVD). In yet other embodiments, the apparatus and methods discussed herein may be used in other applications, for examples, the production of semiconductor wafers, display panels (e.g., liquid crystal display panels), etc. 
     By way of example only, embodiments of a press may be described with respect to imprinting of a film above a disk substrate. However, it will be appreciated by one of skill in the art that embodiments of an imprinting system may be easily adapted for substrates that vary in shape and size (e.g., square, rectangular), for the production of different types of substrates discussed above. Embodiments of an imprinting system described herein may be used for imprinting embossable films with nano-imprint lithography techniques. Alternatively, other scale imprint lithography techniques may be used, such as micro-imprint lithography. 
       FIG. 2  is a front perspective view illustrating one embodiment a press system. Press  100  may include upper die  110 , lower die  120 , a thrust mechanism and an alignment mechanism. In one embodiment, the alignment mechanism may include two flexure rods  160  and  170  and corresponding driving mechanisms to adjust the position (position adjustment mechanisms) of upper die  110  to, for example, to align the upper die  110  with lower die  120  as discussed below in relation to  FIG. 4 . Rods  160  and  170  are made of a material and have dimensions (e.g., diameter and length) that allow for the rods to flex when upper die is raised from the illustrated closed position to an open position, as discussed below in relation to  FIGS. 5 and 6 . In one embodiment, rods  160  and  170  may have lengths in approximately the range of 20-36 inches and diameters in approximately the range of 0.25 to 0.75 inches. Such dimensions are only exemplary and rods  160  and  170  may have other dimensions. 
     In one embodiment, press  100  may include hand cranks  163  and  173  may be used to adjust the Z axis position of rods  160  and  170  for planar alignment of the non-flexed rods when press  100  is in the closed position. Alternatively, other mechanisms may be used to for planar alignment of the rods, for example, motors. 
     In the illustrated embodiment of  FIG. 2 , rods  160  and  170  are coupled to upper die  110  at locations that are approximately 90 degrees to each other (e.g., corresponding to a X &amp; Y axis). The rod  160 ,  170  are fixed in the upper die  110  at a first end of the rods. The rod ends may be permanently coupled (e.g., welded) or detachably coupled (e.g., screwed, bolted, etc.) to the upper die at their first ends. Dies  110  and  120  have each been illustrated in the figures with a particular embodiment of press  100  in which the dies have a stepped form. Alternatively, dies  110  and  120  need not have a stepped form. 
     The other ends of rods  160  and  170  are coupled to the position adjustment mechanisms. In one particular embodiment, rods  160  and  170  are coupled to spindles  161  and  171 , respectively, by threaded engagement. These ends of the rods may be threaded with a fine pitch thread  320  and reside inside a corresponding fine-pitch female thread  330  receiver  340 , as illustrated in  FIG. 3 . The female threaded receiver  340  is affixed to a rotatable spindle (e.g., rotatable spindles  161  and  171 ). The rotations of spindles  161  and  171  are controlled by corresponding motors  162  and  172 , respectively. Alternatively, a common motor may be coupled to both of spindles  161  and  171 . Motors  161  and  171  may be, for example, servo or stepper motors. Alternatively, other types of motors known in the art may be used. In this manner, rods  160  and  170  may be moved linearly along the Y axis and X axis, respectively, to align upper die  110  with a desired reference, as discussed below. 
     In one embodiment, motors  162  and  172  may drive spindles  161  and  171 , respectively, via a worm reduction gear. In this embodiment, through this compound motion control means, a very fine degree of rod (and thereby upper die  110 ) motion may be attained. For example, using an 80 pitch thread, a 90:1 worm reduction and a 200 step stepper motor, the total linear displacement of e.g., one step of a stepper motor for one of the rods  160 ,  170  is approximately 0.0000007″ or 0.00000176 mm. Alternatively, other pitch threads, worm reduction ratios, and motor steps may be used. It should be noted that system backlash may be far greater than such a displacement. Backlash  310  is the clearance between the male threads  320  of a rod (e.g., rod  160 ) and the female threads  330  of a receiver  340 , as illustrated in  FIG. 3 . However, using a closed-loop control system, the servo control will drive the upper die  110  until all backlash  310  is removed and the upper die  110  translates the required amount of position correction for proper alignment. In one embodiment, a clamp  350  (as illustrated in  FIG. 3 ) may be used to secure the receiver  340  in order to reduce or eliminate backlash  310  in the system. 
     In alternative embodiments, other mechanisms may be used to engage and move rods  160  and  170 . In one embodiment, for example, a rack and pinion assembly may be used with a rack disposed on the rod that engages a pinion driven by a motor. In another embodiment, the rods may have a pin that engages a CAM surface on a track. In yet another embodiment, for another example, a rod may be coupled to a hydraulic cylinder that drives the rod. Alternatively, the positioning rods may be directly driven by linear servomotors, which have no intervening gears or threads and resultant backlash. 
       FIG. 4  illustrates a side perspective view of one embodiment of the press shown in  FIG. 2 . In one embodiment, the position of the upper die  110  (and the corresponding amount of alignment required) may be determined by a sensor  116  fixedly mounted to, for example, lower die  120  and/or table  191 . A sensing element of sensor  116  is directed toward a target  117  coupled to the movable upper die  110 . When a workpiece (not shown) is pressed (e.g., imprinted) by upper die  110  and/or lower die  120  and a resulting feature on the workpiece (e.g., imprinted pattern on an embossable layer of a substrate) determined to be offset by some amount (e.g., imprinted track offset from a center of the substrate and/or imprinted tracks on each side of the substrate are not co-axially aligned with each other), that amount of offset may be adjustment by a servo control system (e.g., a computer or operator controlling motors  162 ,  172  to move rods  160 ,  170 ). The sensor  116  may be used to confirm when the proper amount of motion of upper die  110  (through motion of rod  160  and/or rod  170 ) has been achieved to align the workpiece with the upper die  110 . Such an inspection may be done on a real-time or sampling basis. 
     The alignment mechanism described above provides a way to change an upper die position in real-time, without the use of, for example, air bearing supported lower die-sets of previously described conventional presses or without the need to stop the press during production. It should also be noted that the alignment mechanism described above is not limited to only alignment of an upper die but may also be used to align a lower die with, for example, a precision guided ram on the upper die. Alignment of a die may be performed, for example, while a workpiece is inserted and removed from between dies  110  and  120 . A workpiece transport device (not shown) may be disposed next to or affixed to table  191  to transport a workpiece to and from dies  110 ,  120  such as a vacuum chuck coupled to a robotic arm that extends over table  191 . Alternatively, other types of workpiece transport devices may be used. 
     Referring back to  FIG. 2 , the application of a force to upper die  110  along the Z-axis is generated by a sealed bladder  190  that may be disposed, for example, below table  191 . Upon application of gas (e.g., air) pressure to the bladder  190 , the bladder expands against a thrust plate  192 . Thrust plate  192  presses a toggle link  193  that pushes bell crank  194 . Bell crank  194 , in turn, pushes against thrusting rod  210  and, in turn, pushes thrusting pad  220  down onto upper die  110 . A high pressing force may be attained by such a configuration. In one embodiment, thrusting rod  210  may be pivotably coupled to thrusting pad  220  using a pin inserted through a collar portion  220  of thrusting pad  220  and a receiving pin portion  212  of thrusting rod  210 , as illustrated in  FIG. 5 . 
       FIG. 5  illustrates the press  100  position where upper die  110  is pressed down on lower die  120  in a closed position. The dashed lines for rods  160  and  170  conceptually illustrate the position of the rods prior to the application of force to upper die  110  by thrust pad  220 . When the press is open, the rods are flexed from their initial position (shown by the solid lines) a distance  175  to their flexed position (shown by the dashed lines). When the thrusting force is applied to upper die  110 , upper die  110  moves down to a closed position and, thereby, flexure rods  170  and  160  return to their non-flexed position. It should be noted that the amount of flex  175  of rods  160  and  170 , in particular, is not to scale and has been exaggerated in order to illustrate the operation of press  100 . 
     Referring again to  FIG. 2 , when the pressure in bladder  190  is released, the bladder contracts and pulls on toggle link  193 . Toggle link  193 , in turn, pulls up thrusting rod  210  and, thereby, thrusting pad  220 . As thrusting pad  220  raises, it in turn lifts upper die  110 , as illustrated in  FIG. 6 . 
       FIG. 6  illustrates one embodiment of the press in an open position. In this embodiment, the thrust rod  210  is pivotally coupled to the thrust pad  220  as discussed above. In the open position, upper die  110  is raised off of lower die  120  a distance  630  to allow for insertion and removal of a workpiece. Thrust pad  220 , while still being connected to upper die  110  via a floating linkage  229 , has its surface raised off of upper die  110  a distance  640 . In one embodiment, the thrust pad  220  contains a gas inlet  610 . The gas inlet  610  is configured to direct gas (e.g., air) between a gas bearing surface of the thrust pad  220  and the upper die  110 . In one embodiment, a pressurized gas (e.g., 100 psi) may be introduced through inlet  610  into the interface between the surface  221  of thrust pad  220  and the surface of  111  of upper die  110 . If surface  221  of the thrust pad  220  is, for example, 10 square inches, then 1000 lbs of force can be generated on upper die  110  along the Z axis without imparting any substantial motion to upper die  110  along the X and Y axes during pressing. Depending on the force generated at the gas bearing interface, such lack of motion of upper die  110  along the X and Y axes may be due to a lack of mechanical contact between the thrust pad  220  and the upper die that could otherwise cause motion of the upper die. Alternatively, if substantially higher forces are used that results in contact between thrust pad  220  and upper die  110 , such contact is limited to a time when the dies are closed in contact, and thrust pad  220  has no substantial translation along the X and Y axes that may generate a corresponding translation to upper die  110  upon contact. The pressures, dimensions, and forces provided above are only exemplary to illustrate the operation of the press and may have other values. In one embodiment, thrust pad  220  may include a vacuum ring  620  to remove any particulates at the gas bearing interface and/or to reduce disturbance of laminar flow  650 . 
       FIG. 7  illustrates one embodiment of the press having a shroud. In this embodiment, press  100  may include a shroud  705  which has a labyrinth seal  710 ,  720  to contain any particulates generated from the interface of thrust pad  220  and the upper die  110 . The enshrouded press  100  frame may be evacuated such that particulates are drawn away from dies  110 ,  120  and into the base  790  where the particulates may be further removed by means known in the art. 
     Press  100  enables easier access to the die space than exists with multiple post die sets. Such easier access is further facilitated by the location of many of the press mechanisms behind dies  110 ,  120 . In addition, no lubrication between the flexure rod(s) and the dies is required because there are no moving parts between them, only the flexure action of the rod(s). Press  100  may also be produced at very low manufacturing cost because no ultra-precisions parts may be required. Moreover, in one embodiment, press  100  may not contain any seals that could leak in the press during operation. 
       FIG. 8  illustrates one embodiment of a single flexure position adjustment mechanism. In this embodiment, a single flexure member  870  may be used to adjust the position of a die (e.g., upper die  110 ) and provide for alignment of the die along both the X and Y axes. In this particular embodiment, the single flexure member  870  has the approximate prismatic shape of a blade. Alternatively, a flexure member having other shapes may be used, for example, rod shaped. Flex member  870  is constructed from a material and has dimensions (e.g., thickness and length) that allows for the member to flex  175  when die  110  is raised from a closed position to an open position, as discussed above, yet the width of the flex member is such that X-Y planer motion is substantially eliminated. In an exemplary embodiment, flexure member  870  may have a length in approximately the range of 20-36 inches and a thickness in approximately the range of 0.03 to 0.5 inches and a width in approximately the range of 0.12 to 5 inches. Such dimensions are only exemplary and flexure member  870  may have other dimensions. 
     Flexure member  870  is coupled to a die (e.g., die  110 ) at one of its ends. Flexure member  870  is coupled to a position adjustment mechanism  875  at its other end. In one embodiment, position adjustment mechanism  875  includes an x-axis slide  881  that is coupled to a motor  891  and a y-axis slide  882  coupled to motor  892 . Motors  891  and  892  may be, for example, closed loop servo motors. Alternatively, other types of motors, as discussed previously, may be used. In an alternative embodiment, a common motor may be coupled to both of x-axis slide  881  and y-axis slide  882 . 
       FIG. 9  illustrates one embodiment of press  100  with the single flexure position adjustment mechanism of  FIG. 8 . The operation of the components of press  100  of  FIG. 9  is similar to that previously discussed above. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. For example, although certain figures and methods herein are discussed with respect to single-sided imprinting, they may be used for double-sided imprinting as well. The specification and figures are, accordingly, to be regarded in an illustrative rather than a restrictive sense.