Defect Reduction Progress in Step and Flash Imprint Lithography

Transcription

1 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

2 Introduction The purpose of this work is to understand and minimize the impact of template defects on the total defectivity of imprint lithography. Outline Review historical progress of imprint defectivity Describe dominant sources of imprint defects Review results of defect inspection of imprinted wafers using KT 2132 automated defect inspection tool. Describe template pattern, fabrication, and inspection for low imprint defectivity Describe the Program Defect Test Structures for sensitivity analysis of defect inspection Summarize

3 Progress in S-FIL Defect Reduction at MII Defect Density by Date(KLA-2132) Defect Density cm Non-commercial imprint masks Commercial imprint masks Improved adhesion layer Improved wafer cleanliness and imprint mask dicing process 02/ / / / / / / / / /2007 Date Defect density of imprint lithography has decreased by roughly an order of magnitude per year Total defect density dominated by templates and the cleanliness of materials wafers, and templates

4 S-FIL Defectivity 1. Template Fab. Defects Template 4. Bubbles 2. Material Contaminants Planarization layer Substrate 3. Front Side Particles 5. Back Side Particles Template Planarization layer Substrate Planarization layer Substrate 6. Improper Release Template Planarization layer Substrate 7. Post-Imprint Fall-On Particles

5 Imprint Defectivity Imprio 250 Imprinted wafer 89 fields Inspected al fields Inspected area per field ~1 cm 2 Pareto at right shows total defect densities for random and repeating defects Template was not inspected during Fabrication Defect sizes > 200 nm (KT 2132) Template has 3 defects defect density = 3.1 cm -2 Total wafer defect density = 3.4 cm -2 Imprint defectivity = 0.2 cm Template Ion Contm. Defect Density by Type Fall on Particle Plug Random 0.04 Prior Particle 0.04

6 Multiple Wafer Run Defectivity: I250-3 Imprinted wafers with MII I250 tool 89 fields per wafer Internally coated wafers - older generation tools Manually cleaned templates Template defect density = 3.1 cm -2 Inspected 21 fields per wafer Defect Density cm Wafer Defect Density Total Defect Density with Template Defects Removed Pilot Total Defect Density Repeating Defect Density Imprint # Wafer # 0.2 % fields had particles causing feature contamination

7 Particles that Increase Repeating Defectivity Monomer filled feature w/o direct connection to wafer Particle Ni ion - TOFSIMS Monomer filled feature with good support 5 um Template Li ion - TOFSIMS Wafer Monomer 5 um 5 um Particle locally holds template away from wafer 5 um

8 Particles that Do Not Increase Repeating Defectivity Imprint um Particle that did not cause template feature contamination, no change in repeating defect density Particle that caused limited repeating defect in 4 fields

9 Detailed Template Fabrication and Inspection Pattern Lithography and Etch 1000Å Mesa Lithography and Etch Dice Clean NTAR7 Resist Cr Quartz/SiO mm 15mm Litho PEB DEV Cr Etch Resist Strip Quartz Etch Coat Litho DEV Cr Strip BOE Resist (Mesa) Strip n Cr Strip Resist Strip/Clean Clean Inspection Inspection 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

10 Template Pattern for Defect Inspection Features: Metal-1 and Contact arrays For Inspection by KLA-2132 Minimum CD is: 350 nm for M1 400 nm for contacts For e-beam Inspection Minimum CD is: 70 nm for M1 120 nm for contacts Program Defects area Layout optimized for efficient inspection of template and imprinted wafers with automated defect inspection tools Inspection area: ~1 cm 2 100nm SRAM M1 Template Pattern Area 70 nm SRAM M1 13 mm 70, 80, 90nm SRAM M1 350nm M1 400nm Ct. 120nm DRAM Contact

11 Template Defect Inspections (counts) Defect Total Template Defectivity Through Fabrication After Cr and quartz etch After Mesa etch After Cr strip Templates fabricated by commercial mask vendor Inspection were performed with a KLA-5XX tool by vendor 90 nm pixel Reflected light mode Maximum sensitivity Post Cr strip inspection in plate form. Template #

12 KLA 5xx Inspection Captured Defects Template #4 Post Cr Strip Inspection 7 total defects Defects were contamination SEM investigation of subsequent imprints showed that defects were removed by imprinting or cleaning

13 Imprint Defectivity Template #4 Prototype Imprint Tool 1.2 Defect Density by Type Imprinted wafers 68 fields per wafer Inspected area 1 cm 2 per field Pareto at right shows total defect densities for random and repeating defects Defect sizes > 200 nm (KT 2132) Total wafer defect density = 1.7 cm -2 Defect density of: M1 area = 1.67 cm -2 Contact area = 0.061cm -2 Plug Repeating RLT Depression Ion Contm. random Swelling

14 Programmed Defect Pattern Layout Template Pattern Area Program Defect Area Program defect area has 8 sub-die columns Only 3 sub-die contain program defects Each sub-die is an array with 47 columns of 100 nm SRAM M1 features 6 types of programmed defects were used Columnar Array of 100nm SRAM features Program Defects in these sub-die

15 Programmed Defect Types and Sizes Normal Cell A: 1-Dimensional extension F: 1-Dimensional mouse bite B: 2-Dimensional extension E: 2-Dimensional mouse bite C: Line-end shortening D: Shrinking contact A. 1-Dimensional extensions Width = 100nm, Height increasing from 10 to 150nm in 5nm increments B. 2-Dimensional extensions Width = Height increasing from 10 to 150nm in 5nm increments C. Line-end shortening decreasing in 5nm increments to 145nm end reduction D. Shrinking contacts decreasing in 2nm increments reducing 172nm contact size by 58nm E. 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.

16 Reflected Mode Detection Limits: Chrome After pedestal etch - Binary chrome / quartz surface 100% Post BOE Chrome Inspection (Plates 1 & 2) Reflected Die to Die inspection Sensitivity: 100/100 Pobability of Detection (24 samples/point) 80% 60% 40% 20% 0% Defect Size in data (nm) Shrinking Contact 1D MouseBite 2D Extension Line End Shortening 1D Extension 2D MouseBite

17 Reflected Mode Detection on Quartz Final surface ready to imprint (etched quartz) Quartz Inspection Reflected Mode (Plates 1 & 2) 100% Reflected Mode Die to Die inspection Sensitivity: 100/100 Pobability of Detection (24 samples/point) 80% 60% 40% 20% 0% Defect Size in data (nm) Shrinking Contact 1D Extension 2D Extension Line End Shortening 1D MouseBite 2D MouseBite

18 Quartz Detection Limits Relative to Actual Size Quartz Inspection Reflected Mode (Plates 1 & 2) Shrinking Contact 0.018um % Pobability of Detection (24 samples/point) 4 Images taken of imprinted features 80% 2D Mouse Bite 0.059um 60% 40% 20% 0% Measured Defect Size (nm) Shrinking Contact Line End Shortening Line shortening =0.028um 1D Ext = 0.028um 1D Extension 1D MouseBite 2D Extension 2D MouseBite 2D Ext = 0.036um 1D Mouse Bite 0.043um

19 Program Defect Inspection Results Minimum defect size at 90% capture rate Defect Type Reflected mode Cr (data size nm) Reflected mode quartz (data size nm) Reflected mode quartz (actual defect size nm) Shrinking contact D mouse bite D mouse bite D Extension Line End Shortening D extension Quartz inspection results are similar to chrome binary inspection Detection capability well below 90nm pixel size

20 Summary Imprint defectivity continuing to decrease, 10 to <2 cm -2 Many fields with 0 imprint specific defects (KT-2132 inspection) Zero defect templates can be produced (KT-5XX inspection) Defect sizes of 21nm to 78nm are detectable, depending on the type of defect Template repair and eliminating dicing will further reduce template defectivity Defect levels of less 1cm-2 are achievable

21 Acknowledgments The authors would like to thank DNP and IMO for providing templates for this study The authors also thank Mark Melliar-Smith for his support of this project This work was funded in part by NIST-ATP