Motivation by dffhrtcv3

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									                                   Motivation

•   IC business requires a sub 100 nm Next Generation Lithography tool.
     –   (100 nm for 16GDRAM)
•   Any of the following 4 major candidates are not prevailing.
     –   EUV(Extreme UV)
     –   SCALPEL(SCattering with Angular Limitation in Projection Electron beam Lithography)
     –   X-ray with Synchrotron
     –   IPL(Ion Projection Lithography)
•   Generally, it is assumed that due to the large lateral straggling of ions in the
    membrane mask, it is not possible to get high resolution with ion beam -
    which is not necessarily so.
•   As a first step towards Ion beam lithography (IBL) using membrane mask,
    it is necessary to demonstrate the good spatial resolution
    Advantage and Disadvantage of IBL
             Advantage
•   Good sensitivity for 0.1 um pattern
                                                           Comparison of limiting resolutions
     – X-ray : 375 mJ/cm2
     – e-beam : 100 uC/cm2                           1.0

                                                                                             X-RAY
     – IBL : 4.5 uC/cm2 (720mJ)
                                                     0.9

                                                     0.8

•   Good intrinsic resolution                        0.7
                                                                    ION
                                                                                                     OPTICS

     – 10 nm : limitation not from the




                                          contrast
                                                     0.6

                                                     0.5
       wavelength but from PR                                                        E-BEAM
                                                     0.4

                                                     0.3
                                                               multilayer resist
                                                     0.2
                                                               single layer resist

            Disadvantage                             0.1

                                                     0.0

•   vacuum treatment                                    0.01                           0.1                    1

                                                                           Line Width [m]
•   1:1 membrane mask
•   lateral straggling
•   non familiar method - no extensive
    study
 Current Status of Ion Beam Lithography

                   IPL
• IMS (Ionen Mikrofabikations System) and
  Vienna University since 1986
• ALG consortium in USA
• Siemens, ASM lithography, Leica and IMS-
  Stuttgart formulated $36M 3-year research
  program in 2000
• 0.1 um pre-production type stepper in 1999




 IBL with membrane mask
 • No dominant study after the proximity IBL
   by Hughes Research Laboratory
                            Experiment

                     2m LPCVD Si3N4 membrane                     Proton beam
Mask Preparation     on Si Wafer
                     Backside etch-off by KOH


                     220 - 500 keV           Au wire
Proton Irradiation          13   2
                     4 X 10 /cm                        Si wafer   2m Si3N4
                                                                  Membrane

                                                                  PMMA
  Development        Developer
                     60% diethyleneglykol-monobutylether
                     20% morpholine
                     15% aqua regia
                      5% etanolamine

                     40oC 4 min. in ultrasonic bath
  KIGAM Implantation System
                                                                                          chamber
                                                                 X-Y
                                                               Scanner
RF source
                                                              scan freq
                                                              = 64x517
                          1.7 MV tandem Van de Graaff




                                                        analyzing
               injector                                  magnet



SNICS source
                                                                               electron
                                                               collimator      supplier
                                      precollimator
                                                                                                    target
                                                                                                    holder




                                                                                                        cooling
                                                          beam                                           water
                                                                            electron
                                                        previewer
                                                                            suppressor
   Simulation of Dose distribution at PR

                                         450 - 500 keV           slit width = 1 or 10 m
• Purpose : To see and                   Protons
  understand the dose
  distribution at pattern edges
  which is directly responsible
  for the edge definition in the
  development process
• Simulation tool : TRIM           membrane :
                                                  slit center
  (SRIM2000)                       2m Si3N4
                                                                          PMMA
• Simulation Geometry :
  simple infinite slit
                                                                event distribution of
                                                                passing-thru protons
                                                                at 2000A or
                                                                infinite thick
                                                                PMMA
             Factors affecting the line definition

                       Mask Quality
                                                                            e-beam writing
•       mask production by e-beam writer
•       problem : approx. 1 m thick PMMA should be                                     PMMA 1m
        used - Resolution worsening                                                      Au 100A

•       distortion during irradiation                                                   2 m Si3N4

                                                                  develop               Si wafer


                    Ion Beam quality
    •   Parellelity and homogeniety
    •   dose measurement                                  electroplating and etch off

                     Development
•       precise temperature control - find the
        temperature at which until the midde irradiated         backside etch
        point is developed
•       not controllable by develop time because of the
        statistical character of melting process
                     Change of molecular weight by proton irradiation


•                        Molecular weight of PMMA changes drastically by proton irradiation which
                         enables the very well defined structure reproduction

                                                                                     Molecular weight distribution resulting from irradiation
                                                                                                              800
                     8
                               pristine




                                                                               molecular weight [arb. unit]
                               7x1012 ions/cm2
                               5x1013 ions/cm2                                                                600
                     6         3x1014 ions/cm2
    Relative yield




                                                                                                              400
                     4

                                                                                                                        Syncrotron Radiation
                                                                                                                                                         Proton Beam
                                                                                                              200
                     2



                                                                                                                0
                     0
                                                                                                                    0        200        400     600     800      1000
                         102         103            104            105   106
                                           Molecular weight [Da]                                                                           depth [m]
                                                                  Result of simulation - 1m slit

                                                                                                                                                              Change of position distribution of protons
                                           Position distribution of protons entering resist surface                                                           passing through a 200nm PMMA resist
                                           through a 1m width slit membrane mask                                                                             after 1m width slit membrane mask
                                           Membrane : 2m Si3N4                                                                                               membrane : 2m Si3N4
                                           PR : 200nm PMMA                                                                                                    Proton Energy : 450 keV


                               12000                                                                                                        7000


                                                                                                                                            6000       Gaussian fit
                               10000                                              14 to 86 % width                                                     to the differentiated edge                50% dose position = 505 nm




                                                                                                             Number of Events [arbitrary]
Number of Events [arbitrary]




                                                                                                                                                                                                 14 to 86 % width = 220 nm
                                                                                                                                            5000
                               8000                                                  440 nm
                                            350 keV                                                                                         4000
                               6000
                                                                                     260 nm
                                            400 keV                                                                                         3000
                               4000                                                                                                                           after PR

                                                                                     190 nm                                                 2000
                                            450 keV
                               2000                                                                                                                                                             50 % dose position = 507 nm
                                                                                                                                            1000                                                14 to 86 % width = 195 nm
                                            500 keV                                   160 nm                                                                 before PR
                                  0                                                                                                           0



                                   -2000      -1500   -1000   -500      0      500     1000    1500   2000                                     -2000      -1500     -1000       -500    0      500      1000     1500     2000

                                                          Distance from Slit Center [nm]                                                                                  Distance from Slit Center [nm]
                                                         Result of simulation - 1m slit

                                    Change of the 50% dose position and 14 - 86 % dose width         Small conclusion
                                    of protons through 200 nm PMMA resist.
                                    membrane mask : 2m Si3N4
                                                                                               •   Theoretically, the edge
                               70
                                                                                                   definition can be controlled
                               60
                                                                                                   within 20 nm if the
Change of 50 % Dose Position
or 14 - 86 % Dose Width [nm]




                               50
                                                                                                   development process can be
                               40                        14 - 86 % dose width
                                                                                                   performed very precisely
                               30


                               20


                               10
                                                                                               •   Even taking into account the 14
                                                    50% dose position
                               0
                                                                                                   - 86 % dose width, edge
                                                                                                   definition can be controlled at
                                              350          400           450         500
                                                                                                   least within 50nm with rather
                                                       Initial Proton Energy [keV]
                                                                                                   rough develop condition
                                            Comparison of Simulation and Experiment
                                                                       - for the case of large mask to PR distance


                                                                                                             Depth profile of PMMA after
                                       Position distribution of protons along the penetration depth          development
                                       in a thick resist through a 10m width slit membrane mask
                                       when the mask to PR distance is large (35m)                          Proton Energy : 500keV
                                       Proton Energy : 500keV
                                       Membrane : 2m Si3N4
                                                                                                             Membrane : m Si3N4
                                       PR : PMMA                                                             shadow width : 100m
                                       Proton Range in PMMA : 3.8m
                                                                                                             Mask to PR distance : 35m
                               8000




                               6000
Number of Events [arbitrary]




                               4000

                                            m

                               2000         m
                                             m
                                             m
                                             1m
                                 0
                                            surface



                                      -20        -15   -10        -5       0       5          10   15   20

                                                             Distance from Slit Center [m]
                         Extreme Cases

Depth profile of PMMA after development
Proton Energy : 500keV
Membrane : m Si3N4
shadow width : 100m


                                          Mask to PR distance = 0




                                           Mask to PR distance = 530m
                       AFM results




Edge configuration              Edge configuration
500keV proton                   800 keV proton
Au wire mask w/o membrane       Au wire mask with
                                10 m mylar membrane
                  SEM observations

                                     400keV with membrane
                                     mask to sample : contact
                                     tilt angle 50o




                                     450keV with membrane
                                     mask to sample : 5m
                                     tilt angle 50o

500keV w/o membrane
tilt angle 50o
                             Conclusion

• Simulation results show the good possibility of employing IBL using
  membrane mask as the NGL tool.
• Well below 100nm pattern definition can be obtained if develop
  condition can be found at which only until the middle dose position at
  the pattern edge is developed.
• There are still, however, many basic works to be performed before real
  launch. They are :
    1. The relationship between proton dose, develop condition (Temperature,
       time) and pattern edge (the position until which PR is developed)
    2. Mask quality (e-beam writing)

    3. Understanding the deviation of simulation result and the real measurement
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