20 - Himanshu J. Sant Review Session...

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Himanshu J. Sant Review Session
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Photolithography--Overview * Thin Films Implant Diffusion Etch Test/Sort Polish Photo Patterned wafer Photolithography is at the Center of the Wafer Fabrication Process Courtesy: Mark Madou, UC Irvine Photoresist tone Negative: Prints a pattern that is opposite of the pattern that is on the mask. Positive: Prints a pattern that is the same as the pattern on the mask. Courtesy: Mark Madou, UC Irvine
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Negative Photoresist Negative Lithography Island silicon substrate oxide photoresist Window Areas exposed to light become polymerized and resist the develop chemical. Resulting pattern after the resist is developed. photoresist oxide silicon substrate Ultraviolet Light Exposed area of photoresist Shadow on photoresist Chrome island on glass mask Courtesy: Mark Madou, UC Irvine Positive Photoresist Positive Lithography Areas exposed to light become photosoluble. silicon substrate oxide photoresist Island Window Resulting pattern after the resist is developed. Shadow on photoresist Exposed area of photoresist Chrome island on glass mask photoresist silicon substrate oxide Ultraviolet Light Courtesy: Mark Madou, UC Irvine
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Photoresist Profiles • Vertical – 75-95 0 • Overcut – 45-75 0 • Undercut – 95-110 0 – Negative resist • Permanent – Positive resist (LIFT- OFF) Dose : High Developer: Low Dose : Medium Developer: Moderate Dose : Low Developer: Dominant Courtesy: Mark Madou, UC Irvine Table 1.8, Text for more info. Number and Label 10 Basic Steps of Photolithography HMDS UV Light Source Mask Resist Resist λ λ 4 Exposure Plasma Plasma CF 4 CF 4 O 2 O 2 Plasma Plasma
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Label the 10 Basic Steps of Photolithography HMDS UV Light Source Mask Resist λ λ Plasma Plasma CF 4 CF 4 O 2 O 2 Plasma Plasma Basic Mask Structure • Absorbing Layer – optical, UV wavelengths • photographic emulsion • thin metal films – chrome, white and black, iron oxide, silicon – x-ray wavelengths • “thick,” high Z metals: gold • Blanks • Optical, UV wavelengths: glass • Soda-lime, borosilicate, quartz • X-ray: thin dielectric • Boron nitride
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Light defraction reduces resolution 10-30 µm No defects caused in resist or mask Proximity •Defects in photoresist •Contamination and damage to mask Sub µm resolution Contact Disadvantages Advantages Alignment Exposure Mask aligner Projection exposure Contact exposure Proximity exposure Mask Aligner Technology • Requirements – faithfully reproduce master mask pattern on wafer • High resolution • Low distortion errors – Allow accurate alignment between pattern on wafer and mask (low registration errors) • Overlay error = 1/3 - 1/5 resolution • A mechanical process! – Wafer steppers < 40 nm
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This note was uploaded on 09/02/2010 for the course MEEN 5050 taught by Professor Himanshuj.sant during the Spring '10 term at University of Utah.

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20 - Himanshu J. Sant Review Session...

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