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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: http://www.intel.com/intel/intelis/museum/INDEX.HTM Lucent Technologies: The Invention of the Transistor: http://www.lucent.com/minds/transistor/ Infrastructure’s Semiconductor Manufacturing Tutorial: http://www.infras.com/Tutorial/sld001.htm The Virtual Cleanroom Tour: http://www.e-try.com/semiproc.htm PBS’s Tutorial on the Transistor: http://www.pbs.org/transistor/ Case Technologies Links to Over 50 Semiconductor Tutorials: http://www.casetechnology.com/links.html#Tutorials IEEE key Events in the History of Computing: http://22.214.171.124/~history/50th/30.minute.show.html Texas Instrument’s Microelectronics Page: http://www.ti.com/research/docs/michome.htm American Microsemiconductor Transistor Tutorials: http://www.americanmicrosemi.com/tutorials.htm Florida State’s Interactive Tutorials on Electricity, Magnetism, and Transistors: http://micro.magnet.fsu.edu/electromag/java/index.html 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 process? Integrated Circuits LN 10-3
"Integrated Circuits Lab"