UCSB ME 141B - Photolithography (67 pages)

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Photolithography



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Photolithography

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Lecture Notes


Pages:
67
School:
University of California, Santa Barbara
Course:
Me 141b - MEMS: Processing and Device Characterization
MEMS: Processing and Device Characterization Documents

Unformatted text preview:

ME 141B The MEMS Class Introduction to MEMS and MEMS Design Sumita Pennathur UCSB Outline Class odds and ends Lithography I Photolithography Ebeam lithography Nanoimprint Dip pen Soft Photolithography Photo litho graphy from 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 Patterns are first transferred to an imagable photoresist 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 from subsequent processing Photolithography is a binary pattern transfer there is no gray scale color not depth to the image 10 12 10 3 45 Photolithography Processing Steps 10 12 10 4 45 Photolithography Processing Steps 10 12 10 Clean wafer to remove particles on the surface as well as any traces of organic ionic and metal impurities Dehydration bake to drive off the absorbed water on the surface to promote the adhesion of PR Coating Coat wafer with adhesion promoting form e g HMDS Coat with photoresist Soft bake to drive off excess solvent and to promote adhesion Exposure Post exposure bake optional to supress standing wave effect Develop Clean Dry Hard Bake to harden the PR and improve adhesion to the substrate 5 45 Photoresist Spin Coating Wafer is held on a spinner chuck by vacuum and resis it coated to uniform thickness by spin coating Typically 3000 6000 rpm for 15 30 seconds Resist thickness is set by Primarily resist viscosity Secondarily spinner rotational speed Resist thickness is given by t kp 2 w 1 2 where k spinner constant typically 80 100 p resist solids content in percent w spinner rotational speed in rpm 1000 Most resist thickesses are 1 2 um for commercial processes 10 12 10 6 45 Photoresist Spin Coating 10 12 10 7 45 Spinning Artifacts Striations 30 nm variations in resist thickness due to nonuniform drying of solvent during spin coating 80 100



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