Photolithography Overviewmyplace.frontier.com/~stevebrainerd1/PHOTOLITHOGRAPHY/Week 1... · w/overview 38 Photolithography Overview Photoresist CDs Dose Vs Spacewidth Contact CD Vs

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 OverviewMoore’s 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 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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Photolithography OverviewPhotoresist removal: Strip Post etch

Photolithography Overviewmyplace.frontier.com/~stevebrainerd1/PHOTOLITHOGRAPHY/Week 1... · w/overview 38 Photolithography Overview Photoresist CDs Dose Vs Spacewidth Contact CD Vs

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