photolithography 光刻 part i: optics

Xing Sheng, EE@Tsinghua

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Xing Sheng盛兴

Department of Electronic EngineeringTsinghua University

xingsheng@tsinghua.edu.cn

Photolithography 光刻Part I: Optics

Principles of Micro- and Nanofabrication for Electronic and Photonic Devices

Xing Sheng, EE@Tsinghua

Integrate Circuits

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Moore's law

transistor number transistor size

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Transistor Size

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< 100 nm1 cm

1947 2000s

~ 2 mm

1961

revolution evolution

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CMOS Process

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'Lithography is the cornerstone of modern IC technology'---- Silicon VLSI, Plummer et al.,

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Lithography

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litho- 石头-graph 图案

石版画

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Photography

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曝光

显影

打印

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Photolithography（光刻）

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Xing Sheng, EE@Tsinghua

Photolithography（光刻）

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光刻胶

掩膜

光源

Video

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Exposure (曝光)

接触式 接近式 投影式

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Exposure (曝光)

stepper (步进投影)

mass chip production in industry

Video

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Photomasks (掩膜)

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write by laser or electron beam

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Photomasks (掩膜)

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Photomasks (掩膜)

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Layout design CAD tools

see examples

Transparency film flexible mask

Chrome mask glass substrate

chrome coating

Example

transparency film chrome mask

design layout

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Resolution

ideal case actual case

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Resolution

diffraction: light is a wave!

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Resolution

the smaller, the harder

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Resolution

contact and proximity mode

gR ~

R resolution wavelengthg gap size

smaller , g ---> smaller R

UV, DUV, EUV, x-ray, ...g minimum: resist film thickness

Xing Sheng, EE@Tsinghua

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Resolution

projection mode

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Resolution

modulation transfer function (MTF)

minmax

minmax

II

IIMTF

ideal MTF = 1poor MTF ~ 0

MTF = ?

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Resolution

diffraction pattern (Airy's disk)

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Resolution

Rayleigh Criterion:the first diffraction minimum of one source

coincides with the maximum of another

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Resolution

smaller , larger NA ---> smaller resolution

UV, DUV, EUV, x-ray, ...n refractive index (air: 1, oil: 1.4~1.7)sin maximum = 1.0

resolution

sin6.0~n

R

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Spatial Coherence

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Resolution Improvement

sin6.0~n

R decrease increase increase n???

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Large Aperture

FAST (天眼，贵州)

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Immersion Lithography

n = 1.0n > 1.0

If high index fluid n = 1.7,resolution is reduced by ~40%

B. J. Lin (林本坚)2018 未来科学大奖

B. J. Lin, Microelec. Eng. 6, 31 (1987)

sin6.0~n

R

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Phase Shift Mask

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Double Patterning

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Double Patterning

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Multiple Patterning

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Optical Proximity Correction (OPC)

mask resist

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Resolution Improvement

sin6.0~n

R

For deep-UV, = 193 nm

17 nm+ immersion (n = 1.7)

+ quad pattern

34 nm+ immersion (n = 1.7)

+ double pattern

......

68 nm+ immersion (n = 1.7)

116 nmnormal R

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Manufacturing Gets Complicated

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multiple patterning steps

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Depth of Focus (DOF)

depth of focus(DOF)

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Depth of Focus (DOF)on focusoff focus

trade-off between resolution and DOF

off focuslarge NA (光圈)

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Light Sources

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Mercury (Hg) arc lamp g-line 436 nm, h-line 405 nm, i-line 365 nm

sin6.0~n

R

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Light Sources

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Mercury (Hg) arc lamp g-line 436 nm, h-line 405 nm, i-line 365 nm

yellow light in cleanroom

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Light Sources

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Deep UV (DUV) excimer lasers: KrF (248 nm), ArF (193 nm)

Extreme UV (EUV) Tin (Sn) plasma lasers, 13.5 nm

X-ray 0.01 ~ 10 nm

Electron beam (E-beam)

...

sin6.0~n

R

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Optics for EUV

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at EUV ( = 13.5 nm):glass is not transparentmetal is not reflectiveeven air is absorptive

quartz glass metals

air

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Optics for EUV

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reflective masks

multilayer mirrors(Mo/Si)

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Optics

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UV (365 nm) EUV (13.5 nm)

optical loss > 95%

everything in the vacuum!

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Equipment

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UV (365 nm)resolution ~ 2 mprice ~ 200,000 RMB

EUV (13.5 nm)resolution ~ 10 nmprice ~ 100,000,000 $$$

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X-ray Lithography

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wavelength 0.01~10 nm

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Electron Beam (Ebeam) Lithography

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similar to a scanning electron microscope (SEM)

wavelength

V

23.1)nm(

wave-particle duality

momentum

h

Example:for V = 30 kV, = 0.007 nm

Xing Sheng, EE@Tsinghua

The resolution is limited by secondary electrons higher V -> lower resolution

resolution ~ 10 nm

No mask for electron, only direct writing! slow process

Only for research purposes now

Electron Beam (Ebeam) Lithography

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proximity effect

Video

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NanoPhotonics

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Optical Cloak

50J. Valentine, et al., Nature Mater. 8, 568 (2008)

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Metalens

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40 m 300 nm

M. Khorasaninejad, et al., Science 352, 1190 (2016)

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Top Down vs. Bottom Up

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Bottom Up Approaches

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nanowire growth block copolymer assembly

quantum dot anodized alumina

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Nano Structures in Nature

54E. Armstrong and C. O'Dwyer, J. Mater. Chem. C 3, 6109 (2015)