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 Moores 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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3 - Photolithography Himanshu J. Sant Fundamentals of...

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