photolithred

photolithred - Overview of the Photolithography Process...

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ENGR 494C and 594C: Microsystems Principles Photolithography 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. • 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 for subsequent processing. • Photolithography is a binary pattern transfer: there is no gray-scale, color, nor depth to the image. Key Historical Events in Photolithography • 1826- Joseph Nicephore Niepce, in Chalon, France, takes the first photograph using bitumen of Judea on a pewter plate, developed using oil of lavender and mineral spiri ts. • 1843- William Henry Fox Talbot, in England, develops dichromated gelatin, patented in Britain in 1852. • 1935- Louis Minsk of Eastman Kodak developed the first synthetic photopolymer, poly(vinyl cinnamate), the basis of the first negative photoresists. • 1940- Otto Suess of Kalle Div. of Hoechst AG, developed the first diazoquinone-based positive photoresist. • 1954- Louis Plambeck, Jr., of Du Pont, develops the Dycryl polymeric letterpress plate. Overview of the Photolithography Process • Surface Preparation • Coating (Spin Casting) • Pre-Bake (Soft Bake) • Alignment • Exposure • Development • Post-Bake (Hard Bake) • Processing Using the Photoresist as a Masking Film • Stripping • Post Processing Cleaning (Ashing) Wafer Cleaning - 1 • Typical contaminants that must be removed prior to photoresist coating: • dust from scribing or cleaving (minimized by laser scribing) • atmospheric dust (minimized by good clean room practice) • abrasive particles (from lapping or CMP) • lint from wipers (minimized by using lint-free wipers) • photoresist residue from previous photolithography (minimized by performing oxygen plasma ashing) • bacteria (minimized by good DI water system) • films from other sources: – solvent residue –H 2 O residue – photoresist or developer residue –o i l – silicone Wafer Cleaning - 2 • Standard degrease: – 2-5 min. soak in acetone with ultrasonic agitation – 2-5 min. soak in methanol with ultrasonic agitation – 2-5 min. soak in DI H 2 O with ultrasonic agitation – 30 sec. rinse under free flowing DI H 2 O – spin rinse dry for wafers; N 2 blow off dry for tools and chucks • For particularly troublesome grease, oil, or wax stains: – Start with 2-5 min. soak in 1,1,1-trichloroethane (TCA) or trichloroethylene (TCE) with ultrasonic agitation prior to acetone • Hazards: – TCE is carcinogenic; 1,1,1-TCA is less so – acetone is flammable – methanol is toxic by skin adsorption
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R. B. Darling / EE-527 Wafer Cleaning - 3 • RCA clean: use for new silicon wafers out of the box – 1. APW: NH 4 OH (1) + H 2 O 2 (3) + H 2 O (15) @ 70 ° C for 15 min.
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photolithred - Overview of the Photolithography Process...

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