Abstract:
A nanoimprinting system incorporates a patterned media contact architecture to provide a uniform imprinting pressure across the target imprinting area on a disk substrate. The system leverages the unique disk substrate characteristic of an inner diameter hole by incorporating a membrane suspension, gel-pad buffering, and air cushion loading that exploits the inner diameter hole characteristics of the disk substrate. This design dramatically increases the uniformity of the pressing pressure across the target imprinting area. As a result, a simple and effective improvement of the quality of the patterns imprinted on the recording disk substrate is realized.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates in general to nanoimprinting and, in particular, to an improved system, method, and apparatus for configuring a membrane, pad, and stamper architecture to achieve a uniform base layer and uniform nanoimprinting pressure.  
         [0003]     2. Description of the Related Art  
         [0004]     Nanoimprinting technology has developed into a high profile technology that provides a pathway to the next generation of lithography. The features of nanoimprinting, such as pillars, pits, and tracks, are on the order of about 10 nm in diameter and/or width. The capability of transferring these nano-scaled features from a template, mold, or stamper to a substrate has been vigorously demonstrated. A master is typically used to generate the templates, and the templates are then used for mass imprinting production to avoid damage to the valuable master in any imprinting accident. Moreover, the potentials for nanoimprinting in high throughput and low manufacturing cost could trigger a paradigm shift in today&#39;s optical lithography technology.  
         [0005]     It is important for nanoimprinters to be able to achieve a reasonably uniform pressure along the contact interface so that the pattern built on the template can be uniformly imprinted onto substrates. In other words, an intimate contact simply due to high pressure may be enough to generate a uniform pattern transfer and possibly keep good fidelity of the imprinted features. However, a uniform pressure contact is required to generate not only uniform pattern transfer, but also uniform base layer thickness distribution across the imprinting zone. For example,  FIG. 1  schematically illustrates a typical imprinting configuration that includes a mold/stamper/template  11  having a feature pattern  13  that forms imprinted features  15  in a resist layer  17  with a base layer  18  on a substrate  19 .  
         [0006]     The base layer thickness and uniformity is the parameter that nanoimprinting technology tries to control and perfect. Because the imprinted resist layer is acting as a etch mask for the follow-up reactive ion etch (RIE) step in the nanoimprinting process, the quality of the base layer uniformity is directly linked to the quality of the etched result.  
         [0007]      FIG. 2  depicts the differences in the uniformity of the base layer thickness even with the same fidelity of the imprinted pattern features. The top imprint  21  is sufficient for some applications (i.e., no further processing is required), such as in the compact disc (CD) or DVD stamping business, where good fidelity of the imprinted features is the only requirement and base layer uniformity is unnecessary. See, for example, Japanese Patent JP2004330680.  
         [0008]     However, in nanoimprinting lithography, the uniformity of the base layer becomes critical and the uniformity of bottom imprint  23  is necessary. However, the bottom imprint  23  is only possible with further processing by etching through the imprint to directly transport the pattern to the substrate. Various types of nanoimprinting tooling have been developed and commercialized. Unfortunately, in order to achieve uniform imprinting pressure, either very complicated gimbaling fixtures or much higher imprinting pressure is typically employed.  
         [0009]     Yet another problem is encountered at the edges of the disk substrate (i.e., “edge effects”) due to stress variation along the disk radial direction. As shown in  FIG. 3 , a conventional imprinting contact configuration comprises a substrate vacuum chuck  41  to which is mounted substrate  19 . The stamper  11  is supported by a gel pad  43  and Mylar membrane  45  which extends across an opening in a fixture  47 . Air pressure is applied to the membrane  45  to press the stamper  11  against substrate  19 . As shown in  FIG. 4 , this design produces an approximately 50% variation in contact pressure in the radial direction across the imprinted zone  55  with the gel pad (plot  51 ) or without the gel pad (plot  53 ). Although these solutions are workable, an improved solution would be desirable.  
       SUMMARY OF THE INVENTION  
       [0010]     One embodiment of a system, method, and apparatus for nanoimprinting facilitates its own patterned media contact architecture to provide a uniform imprinting pressure across the entire imprinting area. The present invention employs a significantly simpler but efficient fixture solution compared to prior art designs. As opposed to typical wafer layouts, the present invention leverages the unique disk substrate characteristic of an inner diameter (ID) hole. This solution incorporates a membrane suspension, gel-pad buffering, and air cushion loading while exploiting the ID hole characteristics of the disk substrate to dramatically increase the uniformity of the pressing pressure across the target imprinting area. As a result, a simple and effective improvement of the quality of the patterns imprinted on the recording disk substrate is realized.  
         [0011]     For example, the present invention may comprise an imprinting apparatus comprising a membrane stop ring having an opening; a membrane mounted to the membrane stop ring such that the membrane extends and seals across the opening in the membrane stop ring; a gel pad mounted to the membrane, the gel pad having a disk-like shape including an axial hole; a stamper mounted to the gel pad and having a disk-like shape including an axial hole, and a contact surface with imprint features; and a central block mounted to the membrane and extending through the axial holes of the gel pad and the stamper.  
         [0012]     The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     So that the manner in which the features and advantages of the invention, as well as others which will become apparent are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only an embodiment of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.  
         [0014]      FIG. 1  is a schematic sectional view of a conventional imprinting master and substrate;  
         [0015]      FIG. 2  depicts schematic sectional views comparing imprinted features having poor and good base layer uniformity;  
         [0016]      FIG. 3  is a sectional view of a conventional imprinting contact configuration;  
         [0017]      FIG. 4  is a graphical representation of a contact stress profile generated by the conventional configuration of  FIG. 3 ;  
         [0018]      FIG. 5  is a schematic sectional view of an imprinting system constructed in accordance with the present invention;  
         [0019]      FIG. 6  is a sectional view of an imprinting contact architecture constructed in accordance with the present invention;  
         [0020]      FIG. 7  is a sectional view of an imprinting contact architecture without a center block;  
         [0021]      FIG. 8  is a graphical comparison of contact stress profiles generated by the designs of  FIGS. 6 and 7 ; and  
         [0022]      FIG. 9  is a high level flow diagram depicting one embodiment of a method constructed in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Referring to  FIGS. 5 and 6 , one embodiment of a nanoimprinting system for achieving uniform imprint pressure on a disk substrate is disclosed. The present invention comprises a disk substrate  101  having an outer diameter  103 , an axial hole  105  that defines an inner diameter  107 , and an imprint surface  109  extending in a radial direction. A chuck  110 , such as a vacuum chuck, is used to support the disk substrate  101  opposite the imprint surface  109 .  
         [0024]     The system further comprises a membrane stop ring  111  having an opening  113 . A suspension mechanism or membrane  115 , such as a Mylar membrane (e.g., approximately 30 μm thick), is mounted to the membrane stop ring  111  such that the membrane  115  extends and seals across the opening  113  in the membrane stop ring  111 . A gel pad  117  is mounted to the membrane  115 . The gel pad  117 , which has a thickness of approximately 1 to 2 mm, is employed as a stress buffer and also an interlayer to hold a stamper  125 . The gel pad  117  has an outer diameter  119  and an axial hole  121  that defines an inner diameter  123  such that the gel pad  117  is disk-like or cylindrical in shape and substantially congruent with the disk substrate  101 .  
         [0025]     The stamper  125  is mounted to the gel pad  117 . The stamper  125  has an outer diameter  126 , and an axial hole  129  that defines an inner diameter  131  such that the stamper  125  is disk-like or cylindrical in shape and substantially congruent with the disk substrate  101 . The stamper  125  also has a contact surface  127  with imprint features (see  FIGS. 1 and 2 ) for imprinting a resist layer on the imprint surface  109  of the disk substrate  101 . In one embodiment, the contact surface  127  of the stamper  125  has a radial dimension (see  FIG. 6 ) that is less than a radial dimension of the disk substrate  101  between the inner and outer diameters  103 ,  107  of the disk substrate  101 , such that a radial dimension of the imprint surface  109  of the disk substrate  101  is less than the radial dimension of the disk substrate  101  between the inner and outer diameters  103 ,  107  of the disk substrate  101 . Furthermore, the gel pad  117  may have a radial dimension between its inner and outer diameters  123 ,  119  that is approximately equal to or slightly less than the radial dimension of the contact surface  127  of the stamper  125 .  
         [0026]     The present invention also incorporates a central block  133  that is mounted to the membrane  115  and extends through the axial holes  121 ,  129 ,  105  of the gel pad  117 , the stamper  125 , and the disk substrate  101  into contact with the chuck  110 . In one embodiment, the central block  133  is cylindrical and extends in an axial direction concentric with the axial holes  121 ,  129 ,  105  of the gel pad  117 , the stamper  125 , and the disk substrate  101 , respectively.  
         [0027]     As best shown in  FIG. 6 , the central block  133  has an axial length that is approximately equal to the sum of the axial lengths of the gel pad  117 , the stamper  125 , and the disk substrate  101 . However, because of the flexibility of the membrane  115 , some slight differences (either larger or smaller) will not significantly influence the pressure uniformity. In one embodiment, the central block  133  has an axial dimension that is greater than a combined axial dimension of the stamper  125  and the gel pad  117 . In addition, the central block  133  has a radial dimension that is less than radial dimensions of the inner diameters  123 ,  131 ,  107  of the gel pad  117 , the stamper  125 , and the disk substrate  101 , respectively, such that the central block  133  is free of contact with the gel pad  117 , the stamper  125 , and the disk substrate  101 .  
         [0028]     Referring again to  FIG. 5 , the present invention further comprises one or more directional stages  141  (e.g., x, y, and z directions) and one or more rotational stages  143  for adjusting a position of the chuck  110 . A load cell  145  and leveling mechanism  147  are located between the chuck  110  and the directional and rotational stages  141 ,  143 . A quartz window  149  is located above the apparatus for exposing the disk substrate  101  to UV radiation.  
         [0029]     A sealed first chamber (or upper chamber)  151  is used for pressurizing the stamper  125  via membrane  115  (see arrows in  FIG. 6 ) by introducing air pressure in chamber  151  and thereby imprint on the disk substrate  101 . A separate, sealed second chamber (or lower chamber)  153  contains the disk substrate  101 , and may be evacuated or purged with an inert gas such as argon or nitrogen. The imprinting operation may be controlled by manipulating the pressures in the upper and lower chambers  151 ,  153  independently.  
         [0030]     During the imprinting process, the air inside the upper chamber  151  is first pumped out so that the vacuum suction force holds the membrane  115  together with the stamper  125  and gel pad  117  against the quartz window  149 . This is the standby position of the stamper assembly. After closing the lower chamber  153  by activating the air cylinder  152 , followed by pumping down the chamber  153  to a vacuum state. The upper chamber  151  is then gradually vented to ambient so as to carry on a “vacuum imprinting” or a lower pressure imprinting. These steps form a vacuum environment in the lower chamber  153  and are followed by a low pressure imprinting operation. The pressure range available in the vacuum imprinting scheme can be from 0 to about 10 psi in one embodiment.  
         [0031]     Referring now to  FIG. 7 , an example of an imprinting system that does not utilize a central block is shown for comparison purposes. This example system is identical to that shown in  FIG. 6 , including a disk substrate  201 , a chuck  210 , a stop  211 , membrane  215 , gel pad  217 , and stamper  225 . However, membrane  215  has no central block on which to exert pressure.  
         [0032]     As shown in  FIG. 8 , the absence of the central block in the example of  FIG. 7  has a dramatic effect on the performance (see plot  81 ) of the system. In contrast, the embodiment of the present invention shown in  FIG. 6  (see plot  83 ) yields the unexpected results of significantly reduced edge effects by approximately 50%. The contact stress uniformity can be further improved by either changing the gap size, equating the ID and OD gap sizes, or both. Plots  85  and  83  depict the performance of a system with a central block, both with and without equal ID and OD gap sizes, respectively.  
         [0033]     In addition, the present invention also includes a method of nanoimprinting for achieving uniform imprint pressure. As shown in  FIG. 9 , the method begins as illustrated at step  90 , and comprises providing a stamper and a disk substrate having an outer diameter, an axial hole that defines an inner diameter, and an imprint surface extending in a radial direction (step  91 ); positioning a central block through an axial hole in the stamper (step  93 ); applying resist to the imprint surface of the disk substrate (step  95 ); pressurizing a stamper to imprint the resist layer on the imprint surface of the disk substrate with imprint features such that the central block is also pressurized (step  97 ); curing (e.g., via UV light) the imprint features followed by separation of the stamper and disk substrate (step  98 ), before ending as indicated at step  99 . The imprinted resist layer left on the disk substrate has both imprint feature uniformity and base layer uniformity.  
         [0034]     The method may further comprise providing the central block with an axial dimension that is greater than a combined axial dimension of the stamper and a gel pad, and providing the central block with a radial dimension that is less than radial dimensions of inner diameters of the gel pad, the stamper, and the disk substrate, respectively, such that the central block is free of contact with the gel pad, the stamper, and the disk substrate. In addition, the method may further comprise directionally and rotationally adjusting the disk substrate, adjusting a load and a level of the disk substrate, and exposing the disk substrate to UV radiation.  
         [0035]     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.