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					NanoImprint Lithography

                                Ali Ghassemi alig@unm.edu
                                May5th, 2009
                                ECE 487
                                University of New Mexico
                                Instructor: Robert S. Blewer




           Ali Ghassemi alig@unm.edu University
                      of New Mexico                            1
                                Topics
   What is NanoImprint Lithography?
   General Purpose
   NIL vs. photo Lithography?
   History
   Process
   Stamps (Mold)
   Types of NanoImprint Lithography
   Advantages & Disadvantages
   Applications
   Summery and Conclusion

                       Ali Ghassemi alig@unm.edu University
                                  of New Mexico               2
    What Is NanoImprint Lithography?
   Nanoimprint lithography (NIL) is an
    inexpensive way of manufacturing
    miniature devises
        Similar outcome as photo lithography
         but takes a different approach
        Uses a polymer or monomer resist spun
         onto a wafer
        A mold pressed into the polymer
        Is cured with Heat or UV depending
         on the process
        Mold is Lifted and pattern is etched
        Imprint lithography is more of a
         physical process than a chemical
         process



                                Ali Ghassemi alig@unm.edu University
                                           of New Mexico               3
Basic NIL Process




  Ali Ghassemi alig@unm.edu University
             of New Mexico               4
      NIL vs. Photo Lithography?
   Smaller Feature sizes making photo
    lithography extremely challenging
    and expensive
        Extreme Ultraviolet Lithography
             Extraordinary challenging chip
              designs
             Complex multi-patterning
              processes
             Increase in cycle time and cost
             Lower devise yield
   NanoImprint Lithography could be
    the Future
             Low cost of ownership
             High resolution extendibility
             Process Simplicity
             High Throughput
                           Ali Ghassemi alig@unm.edu University
                                      of New Mexico               5
                                      History
   Nanoimprint lithography was
    developed by Professor Stephen Y.
    Chou and his students at Princeton
    University
        NIL was first demonstrated in 1995
         when Dr. Chou and his group made
         vias and trenches with a minimum
         size of 25nm, and 100nm Depth
        Also created sub 25nm quantum dots




                               Ali Ghassemi alig@unm.edu University
                                          of New Mexico               6
                                              Process
   NIL process has 3 important parameters that need to be considered
        Substrate
              Size and shape
                    Size from a few millimeters to 8 inch wafers
                    Most common shapes are round and square
              Materials
                    Most common substrate materials are semiconductor (especially silicon), Silicon dioxide (glass
                     and quartz), and polymer
        Patterning materials
              Polymethylmethacrylate (PMMA) most common imprint material (type of polymer)
              Lift-Off Resist (LOR)
              mr-L 6000 – multi-purpose material used in T-NIL, P-NIL, and EBL
              mr-l 9000 – methacrylate polymer base
        Imprint parameters
              Temperature
                    Depends on pattern material and stamp/substrate material
              Pressure
                    Viscosity of pattern material determines the choice of imprint pressure
                    High density or large structures need higher pressure
              Hold time
                    Viscosity of pattern material and density and size of the structures determine the duration
              Release temperature
                    Tg temperature is the main parameter for choosing release temperature
                    It is important to be bellow Tg, otherwise polymer will deform after separation
                                     Ali Ghassemi alig@unm.edu University
                                                of New Mexico                                                         7
                                      Stamps (Mold)
   The most important part of a working imprint process
        Substrate material, patterning method, and anti-sticking layer are three key components in
         stamp manufacturing process.
              Most common substrate material: Silicon, Silicon Dioxide, Polymers, Quartz, Nickel, and Diamond
                     Silicon based stamps are the most common types used today
              Different patterning methods:
                     Electron beam lithography (EBL)
                     Ultra violet lithography (UVL)
                     Laser lithography
                     Atomic f orce microscope lithography (AFM)
                     X-ray Lithography
              As imprint feature sizes reduce, pattern density rises, polymer sticking will become a problem. To
               avoid this stamp/polymer interaction forces have to be reduced using the following methods:
                     Depositing a monolayer of molecules on stamp surf ace
                            Self -assembled monolayer (SAM) used f or Si-based stamps
                     Depositing a polymer layer on stamp surf ace
                     Include anti-sticking molecules in imprint material




                                        Ali Ghassemi alig@unm.edu University
                                                   of New Mexico                                                    8
      Types of NanoImprint Lithography
   Thermoplastic Nanoimprint lithography (T-
    NIL)
      Earliest form of NIL, and the most well
       documented in research papers
      Also called Hot Embossing
             Thermoplastic Polymer is spun on to the
              wafer surface
             Then a mold with nanostructures on its
              surface is brought to contact with sample
              and pressed under certain pressure
             Then polymer is heated up beyond the glass
              transition temperature, and the pattern of
              the mold is pressed onto the softened
              polymer film
             The whole stack is cooled and the mold is
              separated from the sample
             A pattern transfer process, Reactive Ion
              Etch (RIE), is used to transfer the pattern
              onto the substrate



                                      Ali Ghassemi alig@unm.edu University
                                                 of New Mexico               9
    Types of NanoImprint Lithography
    Photo Nanoimprint lithography
    (P-NIL)
    Most used in industrial research
    Also called Cold Embossing
          Liquid curable photo resist (low
           viscosity monomer) is applied to the
           substrate
          A Transparent mold is pressed into
           the liquid
          The mold is exposed to UV light
           curing the resist and solidifying it
          The mold is removed and a RIE is
           used to transfer the pattern to the
           substrate
          Possibility to reach industry
           throughput requirement of about 50
           wafers/hour


                                Ali Ghassemi alig@unm.edu University
                                           of New Mexico               10
     Types of NanoImprint Lithography
   Direct Patterning
        Not as important as P-NIL and T-NIL
             Patterned without polymer in a one step imprint process
             Laser Assisted Direct Imprinting (LADI) uses a laser to radiate on the
              substrate which is in contact with mold
                   Quartz mold is used to do the imprint due to transparent properties
             Laser radiates onto the silicon, the near-surface is heated and melts
             Cooling and solidification of the molten layer, transforms patterns of the
              mold to the silicon




                                 Ali Ghassemi alig@unm.edu University
                                            of New Mexico                                  11
           Advantages & Disadvantages
   Sub 5nm patterning resolution                    Overlay Structure Accuracy
                                                     Thermal expansion effects
   Low cost of ownership
                                                     Edges of the sample does not replicate well
   High throughput                                   (Typically Small substrates)
   Process simplicity                               Mold removal step (Yield killing step)
   Multiple metal layers in one step




                              Ali Ghassemi alig@unm.edu University
                                         of New Mexico                                              12
                                         Applications
   NIL has the potential to replace
    traditional photolithography in IC’s
              Photo Lithography tools are the most
               expensive tools in a factory
   NIL can be used to created very dense
    memory chips
              Discrete Track Recording (DTR) technique
   NIL can be used to create very small nano
    structures
              Replication of 3D objects such as MEMs
               components
   Smart Sensors for Microelectronics
              Sensors for light, temperature, molecules,
               even DNA or Genetic diseases.




                                        Ali Ghassemi alig@unm.edu University
                                                   of New Mexico               13
                                 Conclusion
   NanoImprint lithography could be the future of pattern transfer in IC’s
   Unlike Complex EUV lithography processes, NIL is a very simplistic way of
    transferring patterns onto wafers
   Patterning multiple metal layers in one step can reduce the amount of steps needed to
    created an IC thus increasing throughput
   High resolution, sub 5nm feature sizes
   Simplicity and minimal steps means lower cost of ownership
   Many promising applications for NIL in the future




                              Ali Ghassemi alig@unm.edu University
                                         of New Mexico                                  14
Question?




Ali Ghassemi alig@unm.edu University
           of New Mexico               15
                               Sources
   General                                      Photos
       www.nrc-
                                                       www.nrc-
        cnrc.gc.ca/.../0508nanoimprint_e.ht
        ml
                                                        nrc.gc.ca/.../0508nanoimprint_e.
                                                        html
       http://www.molecularimprints.com
       http://www.flipchips.com                       http://sst.pennnet.com/display_a
       http://www.patrickcarlberg.dk/Down
                                                        rticle/249599/28/ARTCL/none/no
        load%20area/Dissertation%20no%2                 ne/1/Nanoimprint-lithography:-
        0articles.pdf                                   the-semiconductor-industry-
       http://faculty.stut.edu.tw/~chchuang            and-beyond/
        /paper/pdf%20files/national-11.pdf             www.zyvexlabs.com
       A From (Solid State Electronic                 www.zyvex.com/MicroGraph
        Laboratory, Department of
        Electrical Engineering and                     www.set-sas.fr/en/multipage.xml
        Computer Science, University of
        Michigan, 3411 EECS, 1301 Beal,
        Ann Arbor, MI 481092122, USA)

                          Ali Ghassemi alig@unm.edu University
                                     of New Mexico                                16

				
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