Defect Reduction Progress in Step and Flash Imprint Lithography

Kosta Selinidis, John G. Maltabes, Ian McMackin , Joseph Perez, Douglas J. Resnick, and S. V. Sreenivasan

BACUS 2007

BACUS 2007 6730-14

Introduction

Outline4 Review historical progress of imprint defectivity

4 Describe dominant sources of imprint defects

4 Review results of defect inspection of imprinted wafers using KT 2132 automated defect inspection tool.

4 Describe template pattern, fabrication, and inspection for low imprint defectivity

4 Describe the Program Defect Test Structures for sensitivity analysis of defect inspection

4 Summarize

The purpose of this work is to understand and minimize the impact of template defects on the total defectivity of imprint lithography.

BACUS 2007 6730-14

10

100

1000

10000

02/2

004

06/2

004

10/2

004

02/2

005

06/2

005

10/2

005

02/2

006

06/2

006

10/2

006

02/2

007

Date

Defect Density by Date(KLA-2132)

4 Defect density of imprint lithography has decreased by roughly an order of magnitude per year

4 Total defect density dominated by templates and the cleanliness of materials wafers, and templates

Improved adhesion layer

Non-commercial imprint masks

Commercial imprint masks

Improved wafer cleanliness and imprint mask dicing process

Def

ect D

ensi

ty c

m-2

Progress in S-FIL Defect Reduction at MII

BACUS 2007 6730-14

S-FIL Defectivity

5. Back Side Particles

1. Template Fab. Defects Planarization layer

Substrate

Template

Template

Substrate

Substrate

Substrate

Template

Planarization layer

Planarization layer

Planarization layer

3. Front Side Particles

6. ImproperRelease

2. Material Contaminants

7. Post-Imprint Fall-On Particles

4. Bubbles

BACUS 2007 6730-14

Imprint Defectivity Imprio 250

3.14 Imprinted wafer

– 89 fields– Inspected al fields– Inspected area per field ~1 cm2

4 Pareto at right shows total defect densities for random and repeating defects

4 Template was not inspected during Fabrication

4 Defect sizes > 200 nm (KT 2132)4 Template has 3 defects g defect density = 3.1 cm-2

4 Total wafer defect density = 3.4 cm-2

4 Imprint defectivity = 0.2 cm-2

Random

Template

Defect Density by Type

0.08 0.07 0.06

Ion Contm.

Fall on Particle

0.04

Prior Particle

Plug

0.04

BACUS 2007 6730-14

Multiple Wafer Run Defectivity: I250-3

4 Imprinted wafers with MII I250 tool

– 89 fields per wafer – Internally coated wafers

- older generation tools

– Manually cleaned templates

4 Template defect density = 3.1 cm-2

4 Inspected 21 fields per wafer

0.2 % fields had particles causing feature contamination

Wafer #5Pilot 1 10

Wafer Defect Density

0

1

2

3

4

5

6

7

0100 200 300 400 500 600 700 800 900 100

0 Imprint #

Def

ect

Den

sity

cm

-2

Total Defect Density

Repeating Defect Density

Wafer #5Pilot 1 10

Wafer Defect Density

0

1

2

3

4

5

6

7

0100 200 300 400 500 600 700 800 900 1000 Imprint #

Def

ect

Den

sity

cm

-2

Total Defect Density withTemplate Defects Removed

BACUS 2007 6730-14

Particles that Increase Repeating Defectivity

5 um

5 um5 um

5 um

Li ion - TOFSIMS

Ni ion - TOFSIMS

Template

Monomer

Wafer

Monomer filled feature w/o direct connection to wafer Particle

Monomer filled feature with good support

Particle locally holds template away from wafer

BACUS 2007 6730-14

Particles that Do Not Increase Repeating Defectivity

Particle that did not cause template feature contamination, no change in repeating defect density

5 um

Imprint 1Imprint 1Imprint 2Imprint 3Imprint 4

Particle that caused limited repeating defect in 4 fields

BACUS 2007 6730-14

Detailed Template Fabrication and Inspection

Inspections performed on 6025 plates with multiple imprint mask patterns.

After high resolution patterning and inspection the plate is diced to form 4 templates

Insp

ection

BOE(Mesa)

CrStrip

NTAR7

6.35mm 15µm

PEBDEV

CrEtch

ResistStrip

QuartzEtch

CoatLitho

DEV ResistStrip

Litho

1000Å

BOE(Mesa)

CrStrip

NTAR7

6.35mm 15µm

PEBDEV

CrEtch

ResistStrip

QuartzEtch

CoatLitho

DEV ResistStrip

Litho

1000Å

Pattern Lithography and Etch

Clean

CrStripStrip/CleanCr

StripStrip/CleanResist

Strip/CleanResist

Strip/CleanCleanClean

Resist

Cr

Quartz/SiO2

Resist

Cr

Quartz/SiO2

Resist

Cr

Quartz/SiO2

Insp

ection

Insp

ection

Mesa Lithography and Etch

Dice

BACUS 2007 6730-14

Template Pattern for Defect Inspection

350nm M1

400nm Ct.

100nm SRAM

M1

70, 80, 90nmSRAM M1

120nm DRAMContact

Template Pattern Area

13 mm

Inspection area: ~1 cm270 nm SRAM M1

4 Features: Metal-1 and Contact arrays

4 For Inspection by KLA-2132 Minimum CD is:

– 350 nm for M1– 400 nm for contacts

4 For e-Beam Inspection Minimum CD is:

– 70 nm for M1– 120 nm for contacts

4 Program Defects area4 Layout optimized for

efficient inspection of template and imprinted wafers with automated defect inspection tools

BACUS 2007 6730-14

Template Defect Inspections

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8

Template #

Def

ect T

ota

l

After Cr and quartz etch

After Mesa etch

After Cr strip

4 Templatesfabricated by commercial mask vendor

4 Inspection were performed with a KLA-5XX tool by vendor

– 90 nm pixel– Reflected light

mode– Maximum

sensitivity

4 Post Cr strip inspection in plate form.

(co

un

ts)

Template Defectivity Through Fabrication

BACUS 2007 6730-14

KLA 5xx Inspection Captured Defects

Template #4 Post Cr Strip Inspection

47 total defects– Defects were contamination– SEM investigation of subsequent imprints showed

that defects were removed by imprinting or cleaning

BACUS 2007 6730-14

Imprint Defectivity Template #4

1.2

0.4

4 Prototype Imprint Tool4 Imprinted wafers

– 68 fields per wafer– Inspected area 1 cm2 per field

4 Pareto at right shows total defect densities for random and repeating defects

4 Defect sizes > 200 nm (KT 2132)

4 Total wafer defect density = 1.7 cm-2

4 Defect density of:– M1 area = 1.67 cm-2

– Contact area = 0.061cm-2

random

Plug Swelling

Defect Density by Type

0.090.03

Ion Contm.

RLT Depression

Repeating

BACUS 2007 6730-14

Programmed Defect Pattern Layout

4 Program defect area has 8 sub-die columns4 Only 3 sub-die contain program defects4 Each sub-die is an array with 47 columns of

100 nm SRAM M1 features4 6 types of programmed defects were used

Template Pattern Area

Program Defects in these sub-die

Columnar Array of

100nm SRAM features

Program Defect Area

BACUS 2007 6730-14

Programmed Defect Types and Sizes

A. 1-Dimensional extensions Width = 100nm, Height increasing from 10 to 150nm in 5nm incrementsB. 2-Dimensional extensions Width = Height increasing from 10 to 150nm in 5nm incrementsC. Line-end shortening decreasing in 5nm increments to 145nm end reductionD. Shrinking contacts decreasing in 2nm increments reducing 172nm contact size by 58nmE. 2-Dimensional mouse bites Width = Height increasing from 4 to 116nm in 4nm increments.F. 1-Dimensional mouse bites Width = 100nm, Height increasing from 4 to 116nm in 4nm increments.

Normal CellA: 1-Dimensional extension

C: Line-end shortening

E: 2-Dimensional mouse bite

D: Shrinking contact

B: 2-Dimensional extension

F: 1-Dimensional mouse bite

BACUS 2007 6730-14

Reflected Mode Detection Limits: Chrome

4 After pedestal etch -Binary chrome / quartz surface

4 Reflected Die to Die inspection

4 Sensitivity: 100/100

Post BOE Chrome Inspection (Plates 1 & 2)

0%

20%

40%

60%

80%

100%

0 20 40 60 80 100 120 140 160

Defect Size in data (nm)

Po

bab

ility

of

Det

ecti

on

(2

4 sa

mp

les/

po

int)

Shrinking Contact 1D MouseBite 2D ExtensionLine End Shortening 1D Extension 2D MouseBite

BACUS 2007 6730-14

Reflected Mode Detection on Quartz

4 Final surface – ready to imprint (etched quartz)

4 Reflected Mode Die to Die inspection

4 Sensitivity: 100/100

Quartz Inspection Reflected Mode (Plates 1 & 2)

0%

20%

40%

60%

80%

100%

0 20 40 60 80 100 120 140 160

Defect Size in data (nm)

Po

bab

ility

of

Det

ecti

on

(2

4 sa

mp

les/

po

int)

Shrinking Contact 1D Extension 2D ExtensionLine End Shortening 1D MouseBite 2D MouseBite

BACUS 2007 6730-14

Quartz Detection Limits Relative to Actual Size

Quartz Inspection Reflected Mode (Plates 1 & 2)

0%

20%

40%

60%

80%

100%

0 20 40 60 80 100 120 140 160

Measured Defect Size (nm)

Po

bab

ility

of D

etec

tio

n

(24

sam

ple

s/p

oin

t)

Shrinking Contact 1D Extension 2D ExtensionLine End Shortening 1D MouseBite 2D MouseBite

1D Ext = 0.028um2D Ext = 0.036um

Line shortening=0.028um

Shrinking Contact 0.018um

170

1D Mouse Bite0.043um

2D Mouse Bite0.059um

152

4 Images taken of imprinted features

BACUS 2007 6730-14

Program Defect Inspection Results

4Minimum defect size at 90% capture rate

4Quartz inspection results are similar to chrome binary inspection

4Detection capability well below 90nm pixel size

75

40

45

96

84

20

Reflected mode quartz

(data size nm)

50

39

37

78

69

21

Reflected mode quartz

(actual defect size nm)

752D extension

60Line End Shortening

601D Extension

802D mouse bite

501D mouse bite

18Shrinking contact

Reflected mode Cr

(data size nm)

Defect Type

BACUS 2007 6730-14

Summary

4 Imprint defectivity continuing to decrease, 10 to <2 cm-2

– Many fields with 0 imprint specific defects (KT-2132 inspection)

4 Zero defect templates can be produced (KT-5XX inspection)

4 Defect sizes of 21nm to 78nm are detectable, depending on the type of defect

4 Template repair and eliminating dicing will further reduce template defectivity

Defect levels of less 1cm-2 are achievable

BACUS 2007 6730-14

Acknowledgments

4The authors would like to thank DNP and IMO for providing templates for this study

4The authors also thank Mark Melliar-Smith for his support of this project

This work was funded in part by NIST-ATP