Lithography Explored

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					Lithography Explored

    Leslie Chapman
     June 27, 2007
TEKS Objectives
 • (A) plan and implement investigative
   procedures including asking questions,
   formulating testable hypotheses, and
   selecting equipment and technology.

 • (B) identify uses of electromagnetic waves in
   various technological applications, such as
   fiber optics, optical scanners, microwaves,
   and microfabrication.

 • (C) communicate valid conclusions.
Language (SIOP) Objectives
 Students will:
 • Discuss their plan in groups.
 • Write their plan and have it reviewed by
   instructor prior to starting experiment.
 • State and justify their conclusions.
THE ASSIGNMENT

 •   Design a CD label for your favorite
     music artist using the UV
     Lithography technique.
Lithography Process

                  Post
                           Prepare
                Exposure
                           Substrate
                  Bake




                                         Apply
      Develop
                                       Photoresist




                Expose     Softbake
Background Information
  • Process
     through which
     very small 3-D
     features can be                              UV Light

     produced.                                    Mask
                                                  (transparency
  • Involves a                                    with design)

     series of steps                                  Positive
                                                      Photoresist
     that creates                                     (S-1813)
     successive                    Substrate (CD)

     layers of
Substrate – process
     materials. photoresist is exposed to radiation
           The
starts here. Silicon is
 Photoresist –
           using
the preferred a the mask which contains a pattern
Lithography Process
 • Create a mask.
 • Start with a
   substrate
 • Cover surface
   with
   photoresist.
 • Soft bake
 • Expose the
   wafer to energy
 • Develop the
   wafer
   Types of Lithography
     X-ray
       UV
    Photo
Changing light source = type of lithography


                                          X-ray
                                           UV Light
                                          Photo
Industrial Uses of Lithography
 • Electronics and             • Automobile
   Telecommunications
   – Television, radio and
                                 – Cars (microchips
     printers                      trigger inflation of air
   – Calculators and watches       bag)
   – Video cameras and           – Traffic light (signals)
     computers
     (microprocessor)          • Pharmaceutical
   – Cell phones and
     waveguides                  – Lab on a chip
 • Aviation and                  – Portable blood
   Aerospace                       analyzers (microchip-
   – Airplanes, meterology         based sensing
     equipment and                 devices)
     Spaceships
Applications of Lithography
• Complex MEMS Ratchet • A truly amazing MEMS
  Mechanism              device. It is a sophisticated
                             MEMS Thermal Actuator
Incredible MEMS Clutch mechanism. This is actually a complex device
that required a working clutch mechanism. Gears are 50 microns across.
An early micromotor built in the SUMMiT technology.
For size comparison a microscopic dust mite is
shown on top.
                                        Applications of X-ray Lithography



                                                            Micro gears




                          Micro motor core




                                                       Switching mechanism




                                                                             Examples [9]
[9] http://www.ca/sandia.gov/liga/tech.html
THE ASSIGNMENT
•   Work in pairs to Design a CD label for your
    favorite music artist using the UV
    Lithography technique.
•   Each pair will design two CD labels
    –   One CD will be the control.
    –   The other CD will be varied (photoresist or exposure
        time).
•   State and justify the impact your variation had
    on the final product.
•   Constraints
    –   Design must be drawn in black ink only.
    –   Design must be able to fit on a CD.
• Create a design
• Transfer the design to transparency
  paper (inkjet or copy machine)
• Keep the transparency clean
1. Prepare Substrate
 •         Clean with
           isopropanol
 •         Bake at 115°C
           for 60 seconds
             Post
                      Prepare
           Exposure
                      Substrate
             Bake




                                    Apply
 Develop
                                  Photoresist




           Expose     Softbake
2. Apply Positive Photoresist
                      • Photoresist is spin
                        coated on to CD
                      • Students will dip CD
                        in S-1813 to get even
                        spread.
                      • Effective for λ 340 –
                        450 nm
                                        Post
                                                 Prepare
                                      Exposure
                                                 Substrate
                                        Bake




                                                              Apply
                            Develop
                                                            Photoresist




                                      Expose     Softbake
3. Softbake
 • 115°C for 60
   seconds
 • Complete when
   photoresist is
   hard to the touch.          Post
                                        Prepare
                             Exposure

 • Temp. range:
                                        Substrate
                               Bake



   5 – 550°C (41 -      Develop
                                               Apply

   1022°F)
                                             Photoresist




                             Expose     Softbake
4. Expose
                                                • Long wave UV mini
                                                  lamp (Intensity = 230
                                                  μW/cm2)
                                                • Exposure time: 25
                                                  seconds

             Post
                      Prepare
           Exposure
                      Substrate
             Bake




                                    Apply
 Develop
                                  Photoresist




           Expose     Softbake
5. Develop
                                     •            Immerse wafer in solution
                                                  for 40 – 60 seconds.
                                                  Agitation is
                                                  recommended.
                                     •            Quickly remove the wafer
                                                  from the developer bath
                                                  and rinse with deionized
                                                  water bath for 30 seconds
                                                  (using the wafer holder).
                                     •            Place the wafer on a
                                                  clean room wipe.
                         Post
                       Exposure
                                     •
                                  Prepare
                                                  Dry the wafer holder.
                                  Substrate
                         Bake




                                                Apply
             Develop
                                              Photoresist




                       Expose     Softbake
6. Post Exposure Bake
 • Bake at 115°C
   for 60 seconds
 •   Set a hotplate to
     the required
     temperature.
 •   Place the wafer on
     the hotplate, start
     timing.
 •   When the time is
     up, remove the
     wafer.
Reminders
 • Aprons, gloves and safety goggles
   required at all times.
 • UV goggles required during exposure.
 • The more photoresist present, the
   longer the bake time.
Teacher Expectations
 •   Thorough Planning
 •   Mask Design
 •   Implementation
 •   Conclusions explained
Points (for Instructor) to Consider

 • Give time limit on mask design. Students may
   design on computer or by hand. Intricacy of
   design may impact exposure quality.
 • Thickness of photoresist impacts bake time
 • Exposure time could impact image seen on
   substrate
 • Substrate surface must be very clean
 • Students must wear UV goggles when
   operating UV lamp
Time Frame
 Three class periods (50 minutes each)
   1. Day One – Background Info, Mask
      Design, Substrate Preparation,
   2. Day Two – Wafer Preparation, Apply
      photoresist, Softbake
   3. Day Three – Expose, Develop, State
      Conclusions
THANK YOU
 •   Dr. Kim
 •   Mr. Creary
 •   Dr. Conkey
 •   Dr. Srinivasa
 •   Mr. Derry
 •   Colleagues in the program