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Integrated Circuits Lab


									Materials Engineering 25          San Jose State University                          LabNotes

                                       Integrated Circuits Lab

1.0 Learning Objectives
After successfully completing this laboratory workshop, including the assigned reading, the lab
bluesheets, the lab quizzes, and any required reports, the student will be able to:
 List the major steps used in photolithography.
 Describe the role photolithography plays in the manufacturing of integrated circuits.

2.0 Resources
Callister, Materials Science and Engineering: An Introduction, Chapter 19.14
Intel Museum’s Site on How Chips are Made & How a Transistor Works:
Lucent Technologies: The Invention of the Transistor:
Infrastructure’s Semiconductor Manufacturing Tutorial:
The Virtual Cleanroom Tour:
PBS’s Tutorial on the Transistor:
Case Technologies Links to Over 50 Semiconductor Tutorials:
IEEE key Events in the History of Computing:
Texas Instrument’s Microelectronics Page:
American Microsemiconductor Transistor Tutorials:
Florida State’s Interactive Tutorials on Electricity, Magnetism, and Transistors:

3.0 Materials Applications
Integrated circuits are formed by depositing, patterning, and etching layers of semiconductors,
insulators, and metals. A complex pattern of these layers is created to build and connect millions
of electrical components (transistors, resistors, diodes, capacitors…) on a single chip.

4.0 Background on Photolithography
The patterning of the layers is done with photolithography. Positive photoresist reacts with
ultraviolet light (UV) to become soluble in basic solutions. First, a thin layer of photoresist is
applied by spinning a wafer with a solution of photoresist. Then the thin layer is baked to remove

Integrated Circuits                                                                              LN 10-1
Materials Engineering 25           San Jose State University                        LabNotes

the solvents, and to make the film less sticky. Baking also improves the resolution of the printed
image. The photoresist is exposed using a mask with a dark pattern; the dark pattern shadows
the UV. In the developer, the part of the film that is not shadowed is dissolved away, leaving only
the shadowed part. As a result, a pattern is printed on the wafer. Such a printed photoresist
pattern would be used for further steps in a real integrated circuit fabrication process.

5.0 Experiment

5.1 Safety
Students new to the IC Labs must work with a lab instructor present in the room at all times. The
lab instructor will teach safety as part of this exercise.

5.2 Equipment and materials
       Tweezers
       MTI OmniChuck photoresist spinner, metal wafer cassette
       oven, timer or wrist watch
       BLAK-RAY B-100A UV lamp, overlay mask, wood wafer plate, glass cover plate
       develop station: ventilated grey sink, beakers, plastic squirt bottles, manual blow gun
       Olympus microscope
       silicon wafer, vial of photoresist, developer solution, deionized rinse water

5.3 Procedures
1. Obtain a silicon wafer and a vial of photoresist. Look at the wafer for obvious contamination.
   Do not use a dirty wafer; move any dirty wafers to the used wafer box.
2. Place the wafer into a metal cassette, using tweezers. Load the cassette onto the spinner.
   Do not touch the wafer with your bare hands. Pour the vial of resist onto the wafer. After
   spinning on the resist, use a metal cassette for storing the wafer before baking. During spin,
   read the spin speed dial for actual spin speed.
3. Bake the wafer at 90 C for 30 minutes. Expose wafers which were baked by prior students.
   After bake, store your wafers in the wafer storage location, for use by the next students,
4. Expose the photoresist using the overlay foil as a mask. Place the wafer on a wood wafer
   plate, photoresist side up. Cover the wafer with the mask. Align the mask as required. Cover
   the mask with the glass cover plate. Expose the wafer for the recommended time using the
   UV lamp. Be sure to align the wood plate with the lines drawn on the table.
5. Develop the photoresist. Rinse and blow dry the wafer. Developer can burn your eyes.

Develop techniques:

Integrated Circuits                                                                            LN 10-2
Materials Engineering 25         San Jose State University                       LabNotes

Continuously move the wafer in the develop solution. Remove the wafer briefly every five
seconds or so to look at it. Observe the red photoresist being removed. Partially developed
photoresist looks "rainbowed", or multicolored. Watch for this, and note the time which it takes to
clear away the rainbow. The unexposed photoresist will remain; it has an olive-green color; it will
have the same pattern as the mask. After the rainbow clears, continue developing to double the
time. In other words, the correct develop time is double the time which it takes to remove the
rainbowed photoesist.

6.0 Assignment
Submit a report (one page maximum) to your lab instructor. Include in your report:
1. How this lab relates to the semiconductor industry
2. The procedures (in your own words).
3. If anything went wrong, explain the problem.
4. Answer the following questions in your report: What do you think happens if a wafer is left
   sitting in one of the other rooms (with white light) for about an hour after the bake? What
   variables exist in this experiment that need to be controlled to have a repeatable lithography

Integrated Circuits                                                                         LN 10-3

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