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Xiaogan Liang, Keith J. Morton, Robert H. Austin, and Stephen Y. Chou Nano Lett., 2007, 7 (12), 3774-3780 1.

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Presentation on theme: "Xiaogan Liang, Keith J. Morton, Robert H. Austin, and Stephen Y. Chou Nano Lett., 2007, 7 (12), 3774-3780 1."— Presentation transcript:

1 Xiaogan Liang, Keith J. Morton, Robert H. Austin, and Stephen Y. Chou Nano Lett., 2007, 7 (12),

2 What we need… From microfluidics to nanofluidics… From random nanopores to nanochannels… “Single Sub-20 nm Wide, Centimeter-Long Nanofluidic Channel…” Single channel Sub-20 nm width Centimeter length 2

3 Limitations of writing tools Electron/ion beam lithography or scanning probe Writing field restricted to ~100 um Stitching multiple fields too inaccurate for sub-20 nm structures Fixed-beam/-probe tools with a moving stage cannot maintain sub-20 nm over centimeter distances. Writing tool noise/Line edge roughness (LER) Average size of 5-50 nm Clogs channel before width is reduced to 20 nm 3

4 Fabrication – Mold Fabrication SiO2 mask layer on SOI wafer Patterned by photolithography Preferentially etch direction Remove mask layer Conformal LPCVD of uniform SiN Etch SiN, selective Si etch Pattern additional device 4

5 Fabrication – Direct Imprinting Release agent treatment Imprint channel in functional material Optionally use RIE to transfer channel to substrate 5

6 Key advantages Atomic smoothness of sidewall over several centimeters Overcomes LER from photolithography Channel width tightly controlled by LPCVD thickness Limited by thin film deposition not lithography resolution Channel uniformity and continuity ensured by conformal deposition Roughness doesn’t clog channel 6

7 Results SiO2 LER (3σ): 100’s nm In contrast, anisotropically etched Si nearly atomically smooth and vertical. 7

8 Results SiO2 LER (3σ): 100’s nm In contrast, anisotropically etched Si nearly atomically smooth and vertical. 8

9 Results Kink shift induced by misalignment with {111} crystallographic axis. 9

10 Results Mold LER (3σ): 1.6 nm Imprint LER (3σ): 3 nm RIE etched SiO2 LER (3σ): 6 nm 10

11 References Xiaogan Liang, Keith J. Morton, Robert H. Austin, and Stephen Y. Chou, Nano Lett., 2007, 7 (12),

12 Jong-Sun Yi 1 Stephen Y. Chou & Qiangfei Xia, Nature Nanotechnology, 3, (2008) 2 Ying Wang, Xiaogan Liang, Yixing Liang and Stephen Y. Chou, Nano Lett., 2008, 8 (7), pp 1986–

13 Improving Fabrication Overcome limitations, including defects, line-edge roughness, and minimum size for feature linewidth. Extrinsic defects (e.g., deviations from intended design) Intrinsic limitations: caused by the fundamentally statistical nature of a fabrication method (e.g., noise in photon, electron, or ion generation, scattering, variations in chemical reaction) Demonstrate a new method to remove defects, improve and even reshape nanostructures after fabrication: self-perfection by liquefaction (SPEL) 13

14 Not completely new… Lasers have been previously used for similar applications. e.g., surface planarization, edge roughness smoothing of optical disks (below), etc. Nature 421, (27 February 2003) 14

15 SPEL Three forms demonstrated: open-SPEL, capped-SPEL, guided-SPEL Selective melting of nanostructures for short periods under different boundary conditions 15

16 Improvements Line-edge roughness (LER) Figures of merit: standard deviation (σ) and correlation length (ξ) Smoothing to below the red-zone limit (3 nm) Reshaping of structure 16

17 Results – open-SPEL Substantial reduction of LER Drawback: Grating lines suffer from rounded sidewalls and top-surface Near-perfect circular dots 17

18 Results – capped-SPEL Similar improvement of LER Produces flat top-surface and vertical sidewalls May be possible to keep corners sharp 18

19 Results – guided-SPEL Molten structures rise against surface tension until they reach the plate. Higher aspect ratios due to conservation of material volume Not clearly understood, as the high surface tension of Si and Cr should require strong pulling forces. 19

20 Limitations and Future work Cannot be applied when defect dimensions are comparable with dimensions of the structure. Cannot fix defects where the total materials are insufficient. Ends of lines become rounded Effect on complex structures? Multiple laser pulses to further improve LER Exploiting different surface properties Applicable to metals, semiconductors, and polymers Scale to large-area wafers 20

21 Sub-10 nm trench, line, and hole a. nanoimprinted 200 nm period polymer grating b. after P-SPEL c. cross-section shows possible partial-joining at base of adjacent lines 21

22 Sub-10 nm trench, line, and hole After removing residual polymer between lines (O2 RIE) with Cr mask a) CF4/H2-RIE to transfer pattern into Si or b) Cr deposition to create lines 22

23 References “Improved nanofabrication through guided transient liquefaction”, Stephen Y. Chou & Qiangfei Xia, Nature Nanotechnology 3, (2008) “Sub-10-nm Wide Trench, Line, and Hole Fabrication Using Pressed Self-Perfection”, Ying Wang, Xiaogan Liang, Yixing Liang and Stephen Y. Chou, Nano Lett., 2008, 8 (7), pp 1986–


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