Microelectromechanical Systems

Microelectromechanical Systems - EE 515/415 MEMS Wk 2:...

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Unformatted text preview: EE 515/415 MEMS Wk 2: Applications & Photolithography David T. Shaw EE Fall 2009 Traditional Applications (1992) video play play play play play video Inertial Devices: MEMS Inertial Measurement Units (IMU’s) MEMS lock arming system MEMS Gyroscopes MEMS JET / ROCKET ENGINE RF MEMS Telecomms MEMS for Ordnance R &D Status MEMS RFID Ultimate Sensitivity (1zg = 10-21 g) X. L. Feng et al, Nature, May 2008 Nanomechanical Tunneling of Single Electrons G. A. Steele et al, Science, August, 2009 Microfluidic Systems Video 1 Video 2 Microfluidic MEMS Video 3 Video 4 a 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) MEMS technology builds from the basic silicon ICs manufacturing process flow Significant distinctions between MEMS and ICs are noted in bold italics. Source: Electronics Technology Office, DARPA Photolithography (Chapt 1) • A process of transferring geometric shapes from the mask to the surface of silicon wafer. • Steps include wafer cleaning, barrier layer formation, photresist application, soft baking, mask alignment, exposure and development, and hard baking. Positive and Negative Resist Underlying material is removed upon irradiation Underlying material remains upon irradiation Reference to Text Fig. 1.2 Resist 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. Surface Preparation (HMDS vapor prime) • Dehydration bake in enclosed chamber with exhaust • Clean and dry wafer surface (hydrophobic) • Hexamethyldisilazane (HMDS) • Temp ~ 200 - 250 ° C • Time ~ 60 sec. HMDS Wafer Cleaning 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 • bacteria (minimized by good DI water system) • films from other sources: – solvent residue – H 2 O residue – photoresist or developer residue – oil Wafer Priming Adhesion promoters are used to assist resist coating. • Resist adhesion factors: • moisture content on surface • wetting characteristics of resist • type of primer • delay in exposure and prebake • resist chemistry • surface smoothness • stress from coating process • surface contamination • Ideally want no H 2 O on wafer surface Photoresist Application • Wafer held onto vacuum chuck • Dispense ~5ml of photoresist • Slow spin ~ 500 rpm • Ramp up to ~ 3000 - 5000 rpm • Quality measures: – time – speed – thickness – uniformity – particles & defects vacuum chuck spindle to vacuum pump photoresist dispenser •...
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This note was uploaded on 02/19/2011 for the course EE 515 taught by Professor Dr.shaw during the Fall '10 term at SUNY Buffalo.

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Microelectromechanical Systems - EE 515/415 MEMS Wk 2:...

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