advancing the standard - genisys-gmbh.com

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Advancing the Standard

Which PEC ?

BEAMeeting March 2021


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• 2D PEC• PEC vs Shape-PEC

• PEC vs Corner-PEC

• 3D PEC• Single Layer Resist

• Surface PEC

• Topo PEC

• Multilayer Resist • Edge PEC vs

• T-gate PEC

Agenda



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• Correction is divided into Long-range, Mid-range and Short-range.

• Long-range correction is always a dose correction• Based on fast FFT-based convolution

• Short-range implemented as i) dose modulation or ii) shape modulation • Uses direct convolutions - fast when few features are involved

Proximity Effect Correction



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• Surface PEC

• Topo PEC


• T-gate PEC

Agenda



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Dose PEC

• Optimal for most scenarios

• Fine dose control

• Higher Contrast and more stable forcomplex shapes

• Drawback for Line ends• In case, blur >> feature size

Resulting LES is hard to correct

Short- and Mid-Range Dose- vs Shape-PEC

Shape PEC

• Allows ODUS (Over Dose Under Size)

• Under size is limited by smallest

feature size.

• Limited by BSS• Shift Step Size = n x BSS

• Lower contrast (without ODUS), lessstable for complex curved shapes(without ODUS)

• Advantage: LES can be corrected



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• The enhancement of image contrast by ODUS

• The dependence of image contrast on pattern density

Methods Contrast Comparison

Simulation of 100 nm lines, 100keV exposure on 200nm PMMA 950K on GaAs

Dose PEC Shape PEC ODUS

ILS = 4.36 ILS = 4.14 ILS = 6.56

ILS = 2.13ILS = 1.43 ILS = 1.43

isoline

dense line



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Single layer resist lift-off process by achieving negative resist profile

Shape PEC-ODUS ApplicationsContrast enhancement for negative resist mr-EBL 6000 (microresist tech.)- 1:1 line spaces, 75nm

PEC

Shape-PEC

Dose PEC

ODUS(overdose = 2)

75 nm lines not printing well, remaining resist in gaps

Courtesy : Columbia UnivCourtesy : Weizmann Inst. Of Science

3.17

4.67



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• Dose PEC is limited by contrast

• Shape-PEC with ODUS improves the contrast and the process window

Interesting Border Case

PEC

OD=2

Courtesy : University of British Coulmbia



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• BUT: Shape PEC not practical on (large area) photonic devices• Performance issues

• Solution: From ODUS correction, extract Bias Value from small area • Apply Bias to Pattern, and Dose PEC the entire pattern

Interesting Border Case - ODUS

OD=2



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• Surface PEC

• Topo PEC


• T-gate PEC

Agenda



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PEC vs Corner-PEC

PEC

Corner-PEC

25 nm HSQPre-baked at 170oC for 2 min, I= 500 pA, Dose 19000 uC/cm2

Developed in Salty developer

Hexagons Triangles

Courtesy : Cornell University



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Corner PEC- breaking down a shape in bulk, edges and corners and 2-D energy diagram of the triangle using corner PEC.

2-D energy diagram of a triangle using PEC

E-Beam simulation comparision



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• Dose PEC is method of choice (effective and stable) for most application• Fine dose control

• Relatively faster automated approach

• ODUS offers advanced solution for some application, but needs special attention on complex layouts• Enabling to push image contrast (litho quality) beyond Dose PEC

• Higher edge quality, steeper resist profile

• More stable process (larger process window)

• For large pattern volume the computation can be expensive

• Corner PEC is good to sharpen the corners• But: It’s a manual process – with lots of trial and error

Recommendation for 2D PEC



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• Surface PEC

• Topo PEC


• T-gate PEC

Agenda



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Some 3D samplesof E-BEAM

Courtesy: PSI, Switzerland

3D structures by hybrid nanomanufacturing processes

Symmetric/Asymmetric Circle

Multi-level,Sloped & BinaryMulti-level/Sloped

Convex/Concave Mixed/Hybrid



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3D Surface PEC

• Possibility to use 3D PSF

• To use Lateral development correction using the resist model derived from contrast curve



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3D-Topo PEC

• 3D Topo-PEC allows using region dependent PSF, for PEC corrections that consider underlying features

• The Topo-PEC module has been extended to allow careful control of the dose at topography edges

SiO₂Au

Si

PMMA

SiNx Membrane

Si Si

SiNxPMMA

No AuAuSi/SiNx

SiNx



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• Surface PEC

• Topo PEC


• T-gate PEC

Agenda



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Multi Layer Resist Process

• Exposure may consist of multiple (e.g. two) „target“ layers• PEC needs to adjust to two targets• D2C of resist 1 at one exposure layer• D2C of resist 2 at other exposure layer

Resist 1-PMMA

Resist 2-MMA

Resist 2-MMA

Resist 1-PMMA

Wafer

Wafer

-4000

-3000

-2000

-1000

0

Res

ist

2

Exposure Dose (µC/cm2)

PMMA –MAA 8.5%+12%0 100 200 300

-4000

-3000

-2000

-1000

0

0 200 400 600

Res

ist

1

Exposure Dose(µC/cm2)

PMMA-950k 5% 300RPM

Resist 2

Wafer

Wafer

Resist 1



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• The top layer is defining the feature dimension

• The bottom layer is defining the undercut• Optimized lift-off process

• May also generate a „resist bridge“ (Dolan Bridge)

3D Edge PEC for Undercut-Control

Resist 1-PMMA

Resist 2-MMA

Wafer

WaferBEAMeeting March 2021


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• Common task in Quantum technology is generating Josephson Junction

• This is done using multi-layer process• generating a „resist bridge“ (Dolan Bridge)

• Forming the Josephson junction by shadow evaporation under an angle

Dolan Bridge

N Foroozani et al 2019 Quantum Sci. Technol. 4 025012In this work the Dolan bridge is generated using optical (stepper) lithography

After resist development

Yu-Lin Wu et al 2013 Chinese Phys. B 22 060309



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3D Edge PEC for Bridges

• The top is building a metal bridge after metalization

• The bottom layer creates the foots for interconnection

Courtesy : Weizmann Inst. Of Science

Resist 1-PMMAResist 2-MMA

Wafer

Wafer



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T-Gate is often oversized

Oversize > 30nm

• T-gate done using Edge PEC end up oversized

• Design 84 nm results in >> 100nm

• Lower base dose gives residues

• Gate already too large when cleared!




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Root Cause of Oversize

Oversize > 30nm due to lateral development




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• Development front moves not only down, but also to the side

• The development to the side is dependent on background energy and blur

• The lateral development bias needs to be considered

Dedicated T-Gate - PEC

Lateral Bias



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3D T-Gate PEC:

This mode is optimized for double-layer T-Gate process. It considers the full resist contrast curves of both resists, models and corrects lateral development bias, and enables contrast enhancement by ODUS of gate.

T-Gate PEC with gate & wing layer

Courtesy : Fudan University



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The correct edge placement is assured in a complementary step by simulating the lateral development. For this purpose the T-Gate mode now requires contrast curves in order to enable the simulation.

T-Gate PEC with resist development

-4000

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

0 200 400 600

Th

ickn

ess A

Exposure Dose MicC/cm2

PMMA 950K-5% 3000RPM

-7000

-6000

-5000

-4000

-3000

-2000

-1000

0

0 50 100 150 200 250 300

Th

ickn

ess A

Exposure Dose micC/cm2

PMMA-MAA 8.5% + 12%Wing Gate



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• Edge PEC can take multiple resist layer whereas T-gate takes only two layers resist for correction

• T-gate PEC specially for T-gate correction• Inherent Lateral development correction– resist model from contrast curve

• Correction clubbed with ODUS

3D Edge PEC vs T-gate PEC



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• 2D PEC• Dose PEC is method of choice (effective and stable) for most

application

• ODUS offers advanced solution for some application, but needs special attention on complex layouts

• Corner PEC is good to sharpen the corners


• Surface PEC – used for grey tone lithography

• Topo PEC – PEC corrections that consider underlying features, uses region dependent PSF

• Multilayer Resist • Edge PEC – low sensitive resist defines the critical feature dimensions

• T-gate PEC – Inherent lateral development correction and allows use of ODUS

Summary



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30BEAMeeting March 2021

advancing the standard - genisys-gmbh.com

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