Patterned Wafer Defect Density Analysis of Step and Flash Imprint Lithography

I. McMackin, W. Martin, J. Perez, K. Selinidis, J. Maltabes, F. Xu, D. Resnick, SV Sreenivasan

EIPBN 2007

Introduction

Outline4 Describe template pattern, fabrication, and inspection

4 Review historical progress of imprint defectivity

4 Define the major types and sources of imprint defects

4 Review results of defect inspection of wafers imprinted on a prototype imprint lithography tool and on an MII I250 using KT 2132 automated defect inspection tool.

4 Describe dominate sources of imprint defects4 Results of high resolution imprint inspection using KT eS32

4 Summary

The purpose of this work is to understand the causes of defects specific to imprint lithography.

Template Pattern for Defect Inspection

350nm M1

400nm Ct.

100nm SRAM

M1

70, 80, 90nmSRAM M1

120nm DRAMContact

4 Features: Metal-1 and Contact arrays

4 For Inspection by KT-2132 Minimum CD is:

– 400 nm for M1– 350 nm for contacts

4 For e-Beam inspection minimum CD is:

– 70 nm for M1– 120 nm for contacts

4 Layout was optimized for ease of inspection on mask and wafer defect inspection tools

Template Active Area

13 mm

Inspection area: ~1 cm2

70 nm SRAM M1

Detailed Template Fabrication and Inspection

Inspections performed on plates with multiple template patterns.

Pattern Lithography and Etch Mesa Litho and Etch Dice

Insp

ection

Insp

ection

Insp

ection

Resist

Cr

Quartz/SiO2

BOE(Mesa)

CrStrip

CrStrip

ResistStrip/Clean

Clean

NTAR7

6.35mm 15µm

PEBDEV

CrEtch

ResistStrip

QuartzEtch

CoatLitho

DEV ResistStrip

Litho Coat

1000Å

Dice

Resist

Cr

Quartz/SiO2

Resist

Cr

Quartz/SiO2

BOE(Mesa)

CrStrip

CrStrip

ResistStrip/Clean

Clean

NTAR7

6.35mm 15µm

PEBDEV

CrEtch

ResistStrip

QuartzEtch

CoatLitho

DEV ResistStrip

Litho Coat

1000Å

Dice

Pattern Lithography and Etch

Mesa Lithography and Etch

Dice Clean

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 Templates fabricated by commercial mask vendor

4 Inspections were performed with a KT-576 tool by mask vendor

– 90 nm pixel– Reflected light

mode– Maximum

sensitivity

4 Inspection after Cr strip and Mesa Etch was of templates in plate form.

(co

un

ts)

Template Defectivity Through Fabrication

0 defects

KT 576 Inspection Captured Defects

Template #4 Post Cr Strip Inspection

47 total defects captured– All were contamination defects– None persisted in imprints

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(KT-2132)

4 Now we show how to proceed to < 5 cm-2

Improved adhesion layer

Non-commercial templates

Commercial templates

Improved wafer cleanliness and template dicing process

Def

ect D

ensi

ty c

m-2

Progress in S-FIL Defect Reduction at MII

S-FIL Defectivity

5. Back Side Particles

1. Template FabDefects

Planarization layerSubstrate

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

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

Multiple Wafer Run Defectivity: Template 4

4 Prototype Imprint Tool

4 Internally coated wafers - older generation tools

4 2% of fields of this run had hot spots, they did not contribute to repeating defectivity

4 Defectivity increases with contamination by imprinting on particles

– 11 particles caused feature plugging

4 Not all particles cause feature contamination Wafer #0 7 15 22 29

Wafer Defect Density - Template 4

0

5

10

15

20

25

0 500 1000 1500 2000 Imprint #

Def

ects

/cm

2

Total

Repeating

Particles that Increase Repeating Defectivity

5 um

5 um5 um

5 um

Li ion - TOFSIMS

Ni ion - TOFSIMS

These large particles cause plugging of feature but did not damage the template

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

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

Imprint Defectivity Imprio 250

3.14 Template was not inspected

during Fabrication4 Template has 3 defects g defect density = 3.1 cm-2

4 Imprinted wafers– 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 Defect sizes > 200 nm (KT 2132)

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

Multiple Wafer Run Defectivity: I250-3

4 I250 tool with improved ECU and template handling.

– Internally coated wafers - older generation tools

– Manually cleaned templates

4 3 Template defects4 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

High Resolution Wafer Inspection

4 Defect detection was performed on a KT eS32 electron-beam wafer inspection tool and KT-2132

4 Imprints were made with a prior version of Defect template– Minimum CD is 350 nm for Metal-1 and 400 nm for contacts

4 2 fields on a wafer were inspected, the 1st and the last, 77th .– M1 and contact areas were inspected– Total inspected area on the wafer ~ 2 cm2

– ~ 1 hour inspection time per field

4 Inspection sensitivity: 50% capture rate for a 40 nm defect

4 Additional defects found by eS32 inspection– 2 new template defects– Particles

4 No new imprint related defectivity was found

Comparison of KT-eS32 and KT-2132 inspections

1

3.1

11.7

30

Density cm-2

KT-eS32

0Edge roughness

1

1

0

Density cm-2

KT-2132

Plug

Template

Particle

Type

Repeating Template Defects Found only by eS32

4 Edge-roughness defects:– Predominately random and

occurring in sizes of 10 to 175 nm. – Found only on the bottom edge of

horizontal lines g False defects

4 Particles defects found by e-Beam did not contribute to repeating defectivity

4 Three template pattern defects were found g repeating imprint defects

4 One contaminated contact was detected g repeating plug

eS32 Defect Inspection Summary

4The total defect density of the two fields measured by the eS32 without particles is 4 cm-2.

1Plug

3.1Template

11.7Particle

Density cm-2Type

Imprint Defect Density measured by eS32

No new imprint specific defects were found by high resolution inspection

Summary

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

– Many fields with 0 imprint specific defects (KT-2132 inspection)– High resolution e-beam inspection did not show any increase in imprint

related defectivity.

4 Out of 7 classes of defects in the S-FIL process flow only Front-Side particles are responsible for defect levels > approx. 0.1 cm-2

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

4 Further imprint defect reduction focus on Front-Side particles– Clean wafer coating and template handling– material purity improvement

Defect levels of less 1cm-2 are achievable

Acknowledgments

4NIST-ATP4KLA-Tencor – Mark McCord4Molecular Imprints – Brian Fletcher