Demonstration of sub-4 nm nanoimprint lithography using a template fabricated by helium ion beam lithography

Demonstration of sub-4 nm nanoimprint lithography using a template fabricated by helium ion beam lithography Wen-Di Li*, Wei Wu** and R. Stanley Williams Hewlett-Packard Labs *Current address: University of Hong Kong **Current address: University of Southern California 1 Copyright Copyright 2010 Hewlett-Packard 2010 Development Development Company, Company, L.P. L.P.

Single-digit Nanometer Era 2022 10 9.5 2 *ITRS roadmap 2011 update

End of the Roadmap? 1 nm Manipulating molecules Lithography in common sense 3

Nanoimprint Lithography --- Proven Technology with Molecular Resolution Master Mold Resist Substrate 1. Imprint Polymer SiO 2 Mold Imprinted Polymer Chou et al, APL 1995 & Science,1996 2. Cure Polymer and Separate Mold 2 nm single line 3. Pattern Transfer to Substrate (RIE) 4 Hua et al, Nano Lett., 2004 Austin et al, Nanotech. 2005

NIL Using Electron Beam Lithography Fabricated Templates Nanoimprinted resist Transferred metallic structure Smallest half-pitch EBL pattern in HSQ: 4.5 nm Yang et al, J. Vac. Sci. Techno. 2009 5 Wu et al, Nano Lett., 2008; Morecroft et al, J. Vac. Sci. Techno., 2009

Latest Helium Ion Microscope Rearranged tungsten atoms for bright helium ion source Typical trimer image on HP HIM B.W. Ward et al, J. Vac. Sci. Technol. B, 2006 0.24 nm record imaging resolution was demonstrated using HIM 20 nm 6 From Carl Zeiss

Helium Ion Beam Lithography: Next Generation Scanning Beam Lithography V. Sidorkin et al, J. Vac. Sci. Technol. B, 2009 D. Winston et al, J. Vac. Sci. Technol. B, 2009 7

Combination of HIBL and NIL to Reach Single-digit Design at Low Cost and High Throughput 1. Fabricate NIL template using a scanning helium ion beam Expecting superior resolution compared with EBL based fabrication Can HIBL exceed the patterning resolution of EBL? 2. NIL to transfer high-resolution patterns Molecular resolution; low cost; and high throughput New challenges in sub-10 nm NIL using HIBL patterned template? 3. Device fabrication at sub-10 nm 8

Equipments and Procedures Raith ELPHY Multibeam Pattern Generator: 16 bits DAC 50 ns minimum dwell time Writing field: 10 um for 0.2 nm step Single pixel lines for nested L s Carl Zeiss Orion PLUS Helium Ion Microscope: 35 kv Working Voltage 5 um aperture for smallest features Current: 0.5~1pA Working distance: ~7.5 mm Gun temperature at writing: ~72K stable Resist preparation: Diluted HSQ solution for ~12 nm thick film on silicon substrate at about 3000 RPM Air dry, no baking Resist development: 1% NaCl and 4% NaOH in de-ionized water, 4 min Pattern characterization: FEI XL 30 SEM operated at 20kV (typically) 9

HIBL for Sub-4 nm Patterning on HSQ Resist 5 nm half pitch 4 nm half pitch 3.5 nm half pitch 10 nm full pitch 8 nm full pitch 7 nm full pitch HSQ thickness: 12 nm Imaged under SEM at 20kV 10

Low Proximity Effect of HIBL Patterning 16-nm pitch gratings (8 nm linewidth) over 5 um by 5 um area (1 um by 1 um shown here), edge and center look almost same 11

Wide Dose Window of HIBL Patterning 24-nm pitch nested L s can be clearly patterned and resolved between 120 and 320 pc/cm 120 pc/cm 320 pc/cm 12

Nanoimprint Using HIBL Template Template after HIBL and development HSQ Silicon Short exposure to O 2 plasma and coating of mold release agent Mold release agent UV nanoimprint using HIBL template 4 nm titanium UV-curable NIL resist Fused silica 13

Imprinted Resist with 4-nm Half-pitch Lines 12 nm half pitch 5 nm half pitch 4 nm half pitch Sample coated with 2 nm platinum and imaged under XL30 SEM at 20kV 14

Mechanical Stiffness of Sub-10 nm NIL Template Lines distorted by the mechanical press, resist flow, etc. during the imprinting process Template after 1 st NIL 4.5 nm half-pitch Template after 1 st NIL 5.5 nm half-pitch 4 nm 12 nm 15

Towards Sub-10 nm NIL Templates With High Mechanical Strength Possible approaches: 1/ Develop an EBL/HIBL resist with higher mechanical strength; 2/ Etch into the substrate using the patterned resist as a mask; 3/ Direct milling of a thin layer of hard material. He + beam Si 3 N 4 carrying membrane Hard material 16

Helium Ion Direct Milling of Gold SEM from top SiN side 10 nm line, 30 nm pitch He+ beam 20 nm Si3N4 30 nm Au Gold was deposited by e-beam evaporation Gold is smooth on the Si3N4 side and rough on the bottom side 10 nm line, 30 nm pitch 17 SEM from Gold side

5 nm Half Pitch Lines Patterned in 10 nm Thick Chromium He + beam 8 nm half pitch 20 nm Si 3 N 4 membrane 10 nm chromium 5 nm half pitch 18

Continuous Carrying Membrane after Helium Ion Milling 2500 nc/cm He + beam 20 nm Si 3 N 4 membrane 10 nm chromium Continuous carrying membrane is important to avoid distortion of the pattern 100 nc/cm 19

Summary We demonstrated single-digit nanometer patterning solution combining helium ion beam lithography and nanoimprint lithography 4 nm half-pitch lines patterned by HIBL on HSQ resist 4 nm half-pitch lines transferred by UV-curable NIL using HIBL patterned template We observed the deformation of sub-10 nm template patterns after imprinting process, and demonstrated a direct milling approach to potentially improve the mechanical strength of sub-10 nm NIL template patterns 5 nm half-pitch lines milled in 10 nm thick chromium film on the back side of 20 nm thick Si 3 N 4 membrane 20