Lecture_10-Microlithography

Lecture_10-Microlithography - Lecture 10 Microlithography...

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Microlithography Lecture 10
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IH2655 Spring 2009 Mikael Östling KTH Lithography Introduction Process flow Resists Masks Wafer exposure Projection printers State of the art lithography
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IH2655 Spring 2009 Mikael Östling KTH Introduction (Plummer p 203)
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IH2655 Spring 2009 Mikael Östling KTH
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IH2655 Spring 2009 Mikael Östling KTH Lithography in manufacturing
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IH2655 Spring 2009 Mikael Östling KTH Lithography Process
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IH2655 Spring 2009 Mikael Östling KTH Process flow Before applying photoresist: Surface cleaning and/or dehydration baking Adhesion promoter:HMDS(hexamethyldisilane) Pre-bake: 90-100 ° C at 10-30' Optional post-exposure bake (PEB) for suppressing standing waves in PR Develop: 30-60 s at RT Post-bake: 100-140 ° C at 10-30'
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IH2655 Spring 2009 Mikael Östling KTH Pattern Transfer —— Etching
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IH2655 Spring 2009 Mikael Östling KTH Pattern Transfer —— Lift-off
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IH2655 Spring 2009 Mikael Östling KTH Resist technology Solubility in developer after light exposure is · increased for positive resist · decreased for negative resist Negative resist uncommon today because of limited resolution The resist is composed of: · Resin, usually novolac · Solvent · Photoactive compound (PAC)
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IH2655 Spring 2009 Mikael Östling KTH Large sensitivity for CA DUV resists: 20-40 mJcm -2 compared to 100 mJcm -2 typical for DNQs Post-exposure bake very critical in DUV resist technology (chemical reaction occurs) Sensitivity and contrast for resists Sensitivity: Q 2 Chemical contrast ɣ : Slope of curve, defined as: High Æ high resolution. E.g. DNQ i= 2-3, CA ɣ = 5-10 2 1 10 log 1 Q Q = γ
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IH2655 Spring 2009 Mikael Östling KTH Example positive and negative e-beam resists (PMMA & COP): COP has inferior resolution but higher sensitivity than PMMA
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IH2655 Spring 2009 Mikael Östling KTH Developer is a basic, e.g. NaOH or TMAH (tetramethyl ammonium hydroxide) Problems in resist processing: Tor Ygdevik, EKA -93 Standing waves a problem, in particular when exposing on reflective layers such as metals Suppressed by antireflective coating (ARC) prior to resist spinning
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IH2655 Spring 2009 Mikael Östling KTH Effects of Standing Waves on Patterns
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IH2655 Spring 2009 Mikael Östling KTH 1. Lift-off For avoiding etching of difficult materials Requires cold deposit process! Not suitable for VLSI ( Sze p. 441 ) Special resist processing
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IH2655 Spring 2009 Mikael Östling KTH Under development for VLSI Example tri-layer resist: ( Wolf p. 424 ) Patterning is made in upper layer. This is used as a contact mask for the lower layer. RIE (O 2 ) of polymer in (c) can be replaced by flood exposure 2. Multilayer resist processing
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IH2655 Spring 2009 Mikael Östling KTH Exposed resist can be chemically altered by amine vapors to become non-dissolvable. Flood exposure + development reverses image 3. Image reversal of positive resist
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IH2655 Spring 2009 Mikael Östling KTH Starting material for reticle manufacturing is ~800 Å thick film of chromium covered with resist and anti-reflective coating (ARC) Chromium has very good adhesion and opaque properties Substrate: quartz glass plate Patterned by direct writing using e-beam or laser Usually wet etching of Cr after exposure 4 or 5x magnification is normal for projection litho Pellicle used for dust protection of reticle Mask fabrication
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This note was uploaded on 03/09/2009 for the course EE 300 taught by Professor Y during the Spring '09 term at CUNY City.

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Lecture_10-Microlithography - Lecture 10 Microlithography...

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