Photolithography stevebrainerd1/PHOTOLITHOGRAPHY/Week 1...  w/overview 38 Photolithography Overview

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  • 9/29/03 Brainerd/photoclass/ECE580/Overview/overview

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    Photolithography Overviewhttp://www.intel.com/research/silicon/mooreslaw.htm

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    Photolithography OverviewMoores law only holds due to photolithography

    advancements in reducing linewidths

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    Photolithography OverviewAll processing to create electric components and circuits rely on

    photolithography

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    Photolithography OverviewTypical MOS transistor NMOS = n-type carrier across

    gate

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    Photolithography OverviewTransistor fabrication

    N-MOS P-MOS

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    Photolithography OverviewInterconnect

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    Photolithography Overview Chapter 1 sections 1-7 :

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    Photolithography Overview

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    Photolithography Overview Basic process flow

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    Photolithography Overview

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    Photolithography Overview Wafer clean: removal of Organics and metalics

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    Photolithography OverviewHMDS Hexamethyldisilazane

    Prime: Replaces surface adsorbed H2O and gives off Ammonia. This material produces a bond with the wafer surface creating a polar surface ( electrostatic).

    No surface wetting by Photoresist occurs on an un-treated SiO2 surface with these bonded hydroxyl groups. Basically the Photoresist is hydrophobic and will not adhere to a hydrophilic surface. The HMDS is a hydroxyl getter and creates a hydrophobic surface, which the Photoresist had good adhesion.

    BOTTOMLINE: Priming adjusts the surface energy of the wafer so that it is comparable to the surface energy of the Photoresist.

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    Photolithography OverviewPhotoresist

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    Photolithography OverviewSpin Coat

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    Photolithography OverviewSpin Coat: RPMs: Spread or cast, Ramp,and terminal

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    Photolithography OverviewSpin Coat

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    Photolithography OverviewSpin Coat

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    Photolithography OverviewSoftbake

    Removes solvent from film and stablizingcoating: typical:

    90C to 120C I-line DNQ 100C to 130C: DUV CAR

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    Photolithography OverviewAlignment

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    Photolithography OverviewPhotoresist Exposure

    DNQ photoresist

    actinic radiation

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    Photolithography OverviewDUV: Photoresist Exposure wavelengths below 200nm

    All use excimer lasers Note 248nm = KrF laser

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    Photolithography OverviewPhotoresist Exposure

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    Photolithography OverviewExposure and feature type

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    Photolithography OverviewPositive and Negative Tone Photoresists

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    Photolithography OverviewContact/Proximity/Projection printing

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    Photolithography OverviewProjection printing: Typical stepper

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    Photolithography OverviewProjection printing: Numerical Aperture

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    Photolithography OverviewProjection printing: High NA lenshttp://www.research.ibm.com/journal/rd/411/singh.html

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    Photolithography OverviewProjection printing: Resolution

    http://www.research.ibm.com/journal/rd/411/singh.html

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    Photolithography OverviewProjection printing: Depth of Focushttp://www.research.ibm.com/journal/rd/411/singh.html

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    Photolithography OverviewProjection printing: Depth of Focushttp://www.research.ibm.com/journal/rd/411/singh.html

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    Photolithography OverviewOptical lithography Performance: Resolution

    NA and wavelength coherent systems

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    Photolithography OverviewPhotoresist Standing waves:

    reflection/interference

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    Photolithography OverviewPhotoresist Post Exposure Bake

    Purposes: key idea DNQ/Novolak positive tone: diffusion bake : Diffusion of

    PAC to improve CD contact by removing standing waves. PAG/Novolak negative tone: (acid hardened resist: AHR)

    Diffusion of H+ ion to react with polymer causing polymer to become insoluble.( PAG: Triazine)

    DUV PAG/Blocking group/PHS: Diffusion of H+ ion to react with blocking group causing PHS to become soluble

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    Photolithography OverviewPhotoresist exposure and dissolution

    Key ideas: DNQ and Novolak Resin I-line 365nm system 1. DNQ or Photo Active Compound PAC is an Inhibitor: It inhibits

    Development rate when present! There is very little dissolution in an OH solution.

    2. Photolytic conversion of DNQ to ICA in by exposure to Near UV radiation ( Hg lamp) increases development rate

    PAG and Poly Hydroxystyrene PHS DUV CAR 248nm system 1. PAG Photo-Acid-Generator creates an Acid (H+) upon exposure to

    248nm radiation. There is very little dissolution in an OH solution. 2. The addition of thermal energy using a PEB bake causes the H+ to

    diffuse and react with the blocking group, causing the exposed area to become soluble.

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    Photolithography OverviewPhotoresist Development Threshold dose

    Develop exposed photoresist in TMAH (2.38%) basic solution

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    Photolithography OverviewPhotoresist CDs Dose Vs linewidth

    Polysilicon Linewidth DUV photoresist0 Focus offset.

    y = -0.0267x + 1.0649R2 = 0.9727

    0.58

    0.6

    0.62

    0.64

    0.66

    0.68

    0.7

    13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 18.5 19Exposure Dose

    Phot

    ores

    ist l

    inew

    idth

    CD

    um

    ACENALLALRAULAURZCENZLLZLRZULZURLinear (AUL)

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    Photolithography OverviewPhotoresist CDs Dose Vs Spacewidth

    Contact CD Vs Exposure Dose Mj/cm2 IX405 i-line Photoresist Nominal 0.80u

    y = 0.0013x + 0.5853R2 = 0.927

    0.65

    0.70

    0.75

    0.80

    0.85

    0.90

    0.95

    100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250

    ASML 5500/100C Exposure dose mj/cm2

    Con

    tact

    Pho

    tore

    sist

    C

    D m

    icro

    ns

    201CEN DILinear (201CEN DI)

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    Photolithography OverviewI-line Positive tone Photoresist 365nm

    http://www.jsrusa.com/resists.htm

    Line dense

    isolated line

    isolated space

    contact

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    Photolithography OverviewI-line negative tone Photoresist 365nm

    http://www.jsrusa.com/resists.htm

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    Photolithography OverviewDUV Photoresist KrF 248nm

    http://www.jsrusa.com/krfr11je.htm

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    Photolithography OverviewDUV Photoresist OH contamination issue

    http://www.iemw.tuwien.ac.at/publication/workshop0600/Hudek.html

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    Photolithography OverviewPhotoresist Post-develop bake Hardbake

    Improve adhesion of photoresist for subsequent wet processing:

    Wet etches: BHF, Acetic acid, H2O2 Plateup: Au or Cu Increasing hardbake temperature will cause

    photoresist patterns to flow.

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    Photolithography OverviewPhotoresist Etch

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    Photolithography OverviewPhotoresist Etch: RIE

    http://www.iemw.tuwien.ac.at/publication/workshop0600/Hudek.html

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