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3 - Photolithography Himanshu J Sant Fundamentals of...

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Unformatted text preview: Photolithography Himanshu J. Sant Fundamentals of Microfabrication Source: R.B. Darling, B. K. Gale, M. Madou and F. Solzbacher Fundamentals of Microfabrication Learning Objectives • To understand important elements related to photolithography • To review details on photoresists and resist tones • To review lithography steps • To highlight important features and limitations • To detail photomask patterning • To review post-processing and other lithography techniques Fundamentals of Microfabrication Why Lithography? Really small features • Keep up with Moore’s law Fundamentals of Microfabrication Photolithography • Photo-litho-graphy: latin : light-stone-writing • Photolithography is an optical means for transferring patterns onto a substrate • It is essentially the same process that is used in lithographic printing Fundamentals of Microfabrication Goals of Photolithography • Faithful transfer of CAD drawing for mask pattern to the silicon wafer – From wafer to wafer – From device to device • High resolution or minimum possible feature size – Critical dimension – Linewidth • High throughput Fundamentals of Microfabrication Lithography Information Flow 1. Design (CAD) file – Mask writing tool and process 2. Mask (photomask) – Optical lithography tool 3. Exposure systems 4. Photosensitive film (photoresist) application 5. Alignment of mask and wafer (substrate) 6. Exposure of the photoresist 7. Development of patterns 8. Post processing • Etching (after postbake) • Lift-off 9. Physical structure on wafer Optics Photochemistry Mechanical Fundamentals of Microfabrication Photolithography -- Photomask •Controlled light exposure using a mask •Wavelength of light? •Mask: Chrome on glass •Imagable resist layer Fundamentals of Microfabrication 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 Fundamentals of Microfabrication How does it work? • Patterns are first transferred to an imagable photoresist (resist)layer. • Photoresist is a liquid film that can be spread out onto a substrate, exposed with a desired pattern, and developed into a selectively placed layer for subsequent processing. • Photolithography is a binary pattern transfer: there is no gray-scale, color, nor depth to the image. Fundamentals of Microfabrication Photolithography-- a closer look Fundamentals of Microfabrication 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 Fundamentals of Microfabrication Negative Photoresist Negative Lithography Island silicon substrate oxide photoresist Window Areas exposed to light become polymerized and resist the develop chemical....
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  • Spring '10
  • HimanshuJ.Sant
  • Ultraviolet, Semiconductor device fabrication, Electron beam lithography, Microfabrication, Photoresist

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3 - Photolithography Himanshu J Sant Fundamentals of...

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