L15-Photolithography

L15-Photolithography - Photolithography Source: Dr. R. B....

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Photolithography Source: Dr. R. B. Darling (UW) lecture notes on photolithography
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Why Lithography? Simple layers of thin films do not make a device. To create a device such as a transistor, layers of thin films have to be patterned, etched and coated. Lithography combines these processes and can create millions of devices in batch. A MOSFET Device The MOSFET as patterned on a wafer
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What is Lithography? Lithography is the transfer of geometric shapes on a mask to a smooth surface. The process itself goes back to 1796 when it was a printing method using ink, metal plates and paper. In modern semiconductor manufacturing, photolithography uses optical radiation to image the mask on a silicon wafer using photoresist layers. Other methods are electron beam, scanning probe, X-ray and XUV lithography.
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Steps Used in Photolithography Surface cleaning Barrier layer formation (Oxidation) Spin coating with photoresist Soft baking Mask alignment Exposure Development Hard baking Post process cleaning
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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 oil silicone
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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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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. 2. DI H 2 O rinse for 5 min. 3. 10:1 BOE for 1 min. 4. DI H 2 O rinse for 5 min. 5. HPW: HCl (1) + H 2 O 2 (3) + H 2 O (15) @ 70°C for 15 min. 6. DI H 2 O rinse for 5 min. 7. Spin & rinse dry
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Wafer Priming Adhesion promoters are used to assist resist coating. Resist adhesion factors:
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This document was uploaded on 02/29/2012.

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L15-Photolithography - Photolithography Source: Dr. R. B....

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