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					                         Materials & Processing for Si Compatibility


                                              Charles T. Sullivan
                                      ctsulli@sandia.gov, 505/844-9254
                        Center for Compound Semiconductor Science and Technology
                         Microsystem Science, Technology and Components Center

                                                      Shawn Lin and Jim Fleming




                                      Introductory overview
                                      Photonic Bandgap Materials




Optical Interconnects for High Performance Computing Workshop
Oak Ridge 11/8-9/99
                                                                                  Sandia National Laboratories
Possible Options for On-Chip Waveguide Interconnects

       • Hard dielectric waveguides
          – low-loss optical fiber compatibility
              » low index contrast N ~ 0.005
              »  = 0.1 dB/cm to < 0.01 dB/cm
              » e.g., LPCVD-based buried BPSG/TEOS
          – higher-index for higher-density routing
              » high index contrast N > 0.1
              »  < 0.1 dB/cm ?
              » e.g., LPCVD-based SiON/TEOS
       • Polymeric waveguides
          – low-temperature post-processing
              » low index contrast N ~ 0.05-0.005
              »  ~ 0.1 dB/cm to 0.5 dB/cm, depending on 
              » e.g., fluorinated acrylates or polyimides




                                                             Sandia National Laboratories
                  Possible Applications of PBG Materials
              Potential Applications

1) Passive devices
                                        The Photonic Bandgap is present
                                           at any angle of incidence
- Infrared Mirrors
                                                                             Bandstop is Largely
                                                                            Independent of Angle
- Thermal Emissivity Modification
                                                            1000
- Prisms                                                                        <100>
      - Optical Communications                                                          




                                        Transmittance (%)
- Cavities                                                                                           <011>
   - Spectroscopy                                           100
      - Military and Optical
        Communications
                                                                                                    (a)  = 0°
                                                                       a
- Waveguides                                                           b                            (b)  = 30°
    - 90° bends possible                                     10        c
      in three dimensions                                              d                            (c)  = 40°
                                                                       e
2) Active devices                                                                                   (d)  = 50°

                                                                                                    (e)  = 60°
- Ultra-Fast Switches                                         1
- Si Infrared LED’s                                                0       12
                                                                           10    14 16   18                       20
- Si Infrared Lasers
                                                                       Wavelength (m)
                                                                           Wavelength
                                                                                      (µm)
3) Integrated devices
- Photonic circuits

                                                                                            Sandia National Laboratories
       Simulated Electric Field Patterns for
          90-degree Waveguide Bend

2D Square Lattice                3D Square Lattice




                                               Sandia National Laboratories
90-degree Waveguide Bend at Millimeter-Wave Frequencies

                          1.2

                          1.0
Transmission Efficiency




                                     theory


                          0.8
                                     experiment

                          0.6

                          0.4

                          0.2

                           0
                                75         80     85     90     95  100   105        110
                                                    Frequency (GHz)         Sandia National Laboratories
                                                                 The Microfabrication Challenge



                                 1.2        Communications
Minimum Feature Size (microns)




                                 1.0                                                                                The minimum feature size
                                            Optical




                                                                                                                    for a lattice with bandgap


                                                                                         Military Applications
                                 0.8
                                                                                                                          of 1.5 micron is
                                 0.6       Highly Complex
                                                                                                                           0.18 microns!
                                                                    More straight-
                                 0.4                                forw ard, but
                                                                    limited by s tress

                                 0.2

                                  0
                                       0     2               4     6        8       10   12                      14 16
                                                 Wavelength of Mid-gap, (microns)

                                                                                                                                 Sandia National Laboratories
       3D Silicon Photonic Crystal at Mid-IR Frequencies

                                 Technology   - precise stacking;
Top
                                              - smooth planarization;
View                             Challenges   - large area uniformity.




Side
View

            poly-Si




          Si substrate

           4-layer crystal                           Sandia National Laboratories
Mold Process Flow
    Mold Process Flow
       1)   Deposit oxide with thickness
            equal to that of the layer.
       2)   Pattern and etch mold.


       3)   Fill mold with polysilicon. Poly
            thickness equal to that of the layer
            thickness.
            (Only works for designs where W ~T)


       4)   Deposit thin SiN, CMP stopping layer.




       5)   Pattern the second level.




       6)   Fill gaps between patterned
            poly with oxide.




       7)   Chemical mechanically polish,
            stopping on SiN.


                                                    Sandia National Laboratories
   The Simple Cubic Structure
Fabricated Using the Mold Process



                                 120




             Transmittance (%)
                                           Simple Cubic
                                 100

                                 80

                                 60

                                 40

                                 20
                                                                      10L
                                  0
                                       4     6   8   10      12        14       16
                                             Wavelength ( m)
                                                          Sandia National Laboratories
                              Fillet Flow Process
Fillet Process Flow
       1)   Deposit SiN (first layer only), poly
            with layer thickness (2200Å) and
            SiN hard mask (500Å). Deposit 5000Å
            oxide sacrifical layer.                  6)   Etch SiN in hot phosphoric acid.




       2)   Pattern oxide with lines and spaces,
            6500Å lines, 6500Å space. Etch oxide
            in HF, remove ~900Å isotropically.       7)   Use fillet as a mask for poly etch.




       3)   Deposit 1800Å polysilicon fillet layer

                                                     8)   Fill spaces between lines with oxide.



       4)   Form fillet using anisotropic RIE.

                                                     9)   CMP, stopping on the SiN.



       5     Remove sacrifical oxide in HF.



                                                                    Sandia National Laboratories
1.5µm Bandgap Fillet Structure

                         Measured Results
                               bandgap

                  100               3L

                                         4L

                  20



                   1.3   1.4     1.5     1.6    1.7 1.8
                               Wavelength (m)




                                           Sandia National Laboratories
Novel Structures Under Investigation




                                       Sandia National Laboratories
             Singlemode 3D Defect Cavity

  Modal Volume: 0.83
                                  Defect Volume: 0.23

                                                          7
                                                                    6
                                                          5
                         6.4m
                         (0.6)                           3 4

                                                          2
                                                          1

Higher-Q                               9.2m (0.8 )
 Results

                                                Sandia National Laboratories

				
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posted:5/9/2013
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