Metrology by pupil imaging

Mike Adel, March 2014

Outline

The pupil Animal kingdom Optics

Pupil imaging Optical architecture The Fourier domain

Overlay metrology by pupil imaging What is overlay? Target architecture Quantification

Evolution has generated diversity in pupil structure.

The pupil means many things

Exposure vs Depth of field

What happens when we put the image sensor in the pupil?

6 confidential

Field imaging architecture

IlluminationFieldStop

Fiber from source

Image Sensor

Objective

Target

BS

Mirror

pupil

7 confidential

Pupil imaging architecture

IFS

Fiber from source

CFS

Pupil image Sensor

Objective

Target

BS

Apodizer (spatial filter)

Mirror

Apodizer (spatial filter)

What is overlay metrology and why is it important?

Very Tight (Ångstrom level) Position Control

Scan

ner w

avel

engt

h [n

m]

9

Overlay metrology is enabled by quantification of symmetry breaking.

Field imaging Pupil imaging

Pupil image

-F0 F0

Rotational Symmetry Translational Symmetry

It’s all about diffraction

θd

dSinθ = mλ

For zero offset, first orders are symmetric.

I+

I_I0

Ax1 = I_- I+

X1X2 Y2Y1

With 4 cells, overlay can be measured in x & y

𝑂𝑉𝐿𝑥≃𝐹 0𝐴𝑥 1−𝐴𝑥 2

𝐴𝑥 1+ 𝐴𝑥 2

X1X2 Y2Y1

Summary

The pupil has many meanings and uses in optics.

The pupil is also a location in the optical path which enables the image to be viewed in the Fourier domain.

Overlay metrology is enabled by pupil imaging of overlaid periodic structures.

Translational offsets between periodic structures are required in order to quantify symmetry breaking in the pupil image.

-F0 F0I+I_I0

Thank YouAcknowledgements: Thanks to Mark Ghinovker for DFTs…

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0 50 100 150 200 250 300 350 400 450 500 550 600

Wavelength (nm)

Rela

tive

Inte

nsity

EUV

Shorter wavelength = higher resolutionEvolution of lithography light sources

Tungsten filamentlight source & power

supply ~$500Circa 1965

I-Line

H-Line

G-Line

Mercurylamp & power supply ~$5kCirca 1985

UPExcimer Laser & beamline ~$500kCirca 2005

ArFKrF

13.5

EUV light source~ 5m$?Circa 2015?

What happens in

the meantime?