January, 2004 Jeju Island. Acknowledgements OTFL

Transcription

1 High-Speed Fabrication of Nanostructures using Atomic Force Microscope Lithography Haiwon Lee Department of Chemistry US-Korea NanoForum 02/17, 2005

2 January, 2004 Jeju Island Acknowledgements

3 Contents I. verview Atomic force microscope lithography II. Molecular resists Self-assembled monolayers (SAMs), Spin-cast films III. AFM lithography Anodization process Nanopatterning with organic resists on Si and metal films CNT tip fabrication IV. Application Photo mask fabrication, High-speed lithography system

4 Scaling Trend of Semiconductor Devices Next Generation Lithography Technologies -Proximity X-ray Lithography (PXL): 1X 1.3nm -Extreme Ultra-Violet Lithography (EUVL): 4X 13.5nm -E-beam projection (SCALPEL, PREVAIL) : 4X electrons -Proximity E-beam Lithography (LEEPL) : 1X electrons -Multiple E-beam Lithography: 1X multi electron-beam -Ion Projection Lithography (IPL): 4-5X system -Non-optical lithography SPM, Nanoimprint, Stamping

5 Bare Si substrate 5 % HF Pattern Formation by Anodization Process H H H H H H Si 2 Si substrate Si rganic thin film coated substrate Resist coating Tip (Cathode) reaction 2nH 2 + 2ne - nh 2 + 2nH - Faradaic current - Water column Six protruding H F H H F H Si substrate scan Six Si substrate cantilever Resist Si 2 Si substrate Si cantilever Resist Si 2 Si substrate Resist degradation +Six protruding + Si substrate Si x Sample (Anode) reaction Si + nh 2 Si n + 2nH + + 2ne - Lithographic parameters - Applied voltage & current - Scanning speed - Relative humidity - Resist property - Substrate property - Cantilever tip - Energy level

6 Pulse duration Pattern Formation by Anodization Process - Adsorbed water Faradaic current Si substrate + Anodic oxide V Resonance signal Pulse 0 Tip position Substrate

7 H2NSiCH3H3NH2SiH3CCNHPHHHHSi Zr P Zr P Zr Surface Modification with Self-assembled Monolayers (SAMs)PH H H H H H H 3 C Si CH 3 H 3 C Si CH 3 Hydroxylated silicon wafer 2NH 3 + NH 3 + NH 3 + CH 3 CH 3 H 3 C Si CH 3 H 3 C Si CH 3 + H3 N + H3 N + H3 N

8 Dependence of Surface Functional Groups Temperature : 24 / Humidity : 60 % / Tip : Pt coated silicon tip / Speed : 1 µm/s Contact angle Applied voltage 2V 6V 10V 14V APS 58-59º NH 2 Six Si W : 560 nm W : 530 nm W : 562 nm PTS 65-67º Ph W : 210 nm W : 280 nm W : 230 nm W : 234 nm TS 107º CH 3 W : 124 nm W : 170 nm W :200 nm

9 Dependence of Surface Functional Groups 6 5 NH 2 Ph CH NH 2 Ph CH 3 Height(nm) Width(nm) Voltage(V) Voltage(V)

10 Schematic Diagram of Metal-phosphate SAM H P H H P H ZrCl 2 Zr 2+ o o o p o 2+ Zr 2+ Zr o o o p o Width : 210 nm Width : 54 nm Applied Voltage : 12 V Scan Speed : 30 μm /s Etching Height: 0.8 nm Width: 49 nm Depth : 0.7 nm Width : 56 nm Applied Voltage: 16 V Scan speed: 500 µm/s

11 Preparation of Mixed SAMs Si substrate H2 : NH3 : H22 80, 30 min = 5 : 1 : 1(v/v) Si substrate Negatively charged Si-surface NH 3 + Cl - NH 3 + Cl - CH 3 CH 3 Cl -+ H 3 N Cl -+ H 3 N Cl -+ H 3 N Cl -+ H 3 N NH 3 Cl NH 3 Cl NH 3 Cl NH 3 Cl NH 3 Cl NH 3 Cl NH 3 Cl NH 3 Cl CH 3 CH 3 CH NH 3 Cl CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 + H3 N + H3 N + H3 N + H3 N + H3 N + H3 N + H 3 N + H 3 N H 3 N H 3 N H 3 N H 3 N + + H 3 N H 3 N H3 N H3 N H3 N H3 N H3 N H3 N H3 N H3 N H3 N Si substrate SAM of DAD 2HCl Si substrate Mixed SAMs Si substrate SAM of TDA HCl

12 Line-width / nm Effects of Surface Groups and Substrate Types Applied voltage (p-type) Line-width (p-type) Applied voltage (n-type) Line-width (n-type) Applied voltage / V NH 3 + Cl - NH 3 + Cl - CH 3 CH NH 3 Cl CH 3 Mixed SAM (6:4) Scan speed : 2 mm/s Applied voltage : 12 V Cantilever : Pt-Coated Si Relative humidity : 60 % Line width : 45 nm X TDA HCl + H3 N + H3 N + H 3 N + H 3 N + H3 N + H 3 N DAD 2HCl DAD 2HCl monolayer monolayer Hydrophilic surface, Wide line-width Uniform protruded line TDA HCl monolayer TDA HCl monolayer Hydrophobic surface, Narrow linewidth Rough protruded line Mixed Mixed SAMs SAMs Controlled hydrophilicity Uniform protruded lines Narrow line-width Si substrate

13 PT Poly(3-octylthiophene) Spin-cast Polythiophene Derivatives Films PCBET PBET Poly(3-(2-benzotriazoloethyl)thiophene) PMBET N N N Cl N N N N N N CH 3 S n ( ) ( ) S n ( ) S n S n Applied voltage :10 V, Scan speed : 4 μm /s A A A A μm μm μm μm Line Height: 0.6 nm Line Width: 220 nm Line Height: 0.7 nm Line Width: 50 nm Line height: 0.7nm Line width: 52 nm Line height: 0.8 nm Line width: 50 nm

14 Fabrication on Spin-cast triphenyl-sulfonium triflate Film 10 V 11 V 12 V 13 V 14 V TPS-Tf Tip : NSC15 Humidity : 43 % Temp : 30 Substrate : TPS-Tf/Si Film thickness : 2.0 nm (RMS : 1.5 Å) Tip amplitude : 84.3 nm Line-width (nm) ms 5 ms 10 ms Bias Voltage (V) Line-height (nm) PAG/Si 5 ms Bare Si p(100) 5 ms PAG/Si 1 ms Bare Si p(100) 1 ms Bias Voltage (V)

15 Fabrication on Spin-cast triphenyl-sulfonium triflate Film Mode :Tapping mode Bias Voltage : 10 V Temp : 27 Humidity : 45 % Film Thickness : 2.4 nm Speed: 10 µm/s Line Height : 1.37 nm Line Width : 35.7 nm Speed: 50 µm/s Line Height : 1.19 nm Line Width : 29.2 nm TPS-Tf Speed: 60 µm/s Line Height : 0.75 nm Line Width : 32.9 nm

16 Schematic Diagram of Energy Band Vacuum Level 0 ev Si Tip Fermi Level T = 300 K, N D N A, N D n i N D (Phosphorus) 5.0e17 E F E i = kt ln(n D /n i ) E F = ev Φ metal Si : 4.13 ev W 2 C : 4.55 ev Pt : 5.65 ev Φ organic LUM E F : 5.25 ev Band gap : 3.5 ev W 2 C Tip Work function E F = ev Pt Tip Work function E F = ev HM : 6.99 ev Metal Coated Tip TTF

17 Tip Effect on Threshold Lithographic Voltage Φ b Si - Threshold Voltage Tip 10 V Heavily Doped Si TTF Contact - Φ SC E C E F E V W 2 C - Tip Threshold Voltage 8 V W 2 C TTF Contact > > Φ b - Φ SC E C E F E V Φ SC Pt - Tip Threshold Voltage 5 V Pt TTF Contact - E C E F E V Φ b Si W 2 C Pt Humidity : 40 ~ 45 % Litho. Speed : 10 μm / s Threshold Voltage (V) Fermi Level (ev)

18 Nanostructures on Ta Metal Film Depth : 1.25 nm, Line width : 100 nm C 4 F 8 : 11 sccm Bias power : -120 V Time : 50 sec RF power : 600 W Working pressure : 10 mtorr

19 Aspect Ratio Improvement by Temperature Control Humidity: %, T: Humidity: 30 %, T: Humidity: 30 %, T: Bias voltage : 18 V Bias voltage : 18 V Bias voltage : 18 V Speed : 1 µm/sec Speed : 1 µm/sec Speed : µm/sec Height (nm) Height: 1-2 nm, Width : 50 nm Height profile Distance (µm) µm Height (nm) Distance (µm) µm Height: nm, Width : 78 nm Height profile Height (nm) 300 µm/sec - Height : 2.5 nm,width : 60 nm 400 µm/sec - Height : 1.7 nm, Width : 40 nm Height profile Distance (µm)

20 Fabrication of xide Nanostructure using Pulsed Bias Voltage V Resonance Signal Voltage Pulse 2 µm µm Substrate Pulsed bias is applied at the closest distance between tip and substrate Pulse Duration Time

21 Aspect Ratio Improvement by Applying AC Bias Voltage Fabricated Structures at both AC Bias and DC Bias Applied AC Bias Voltage V ox t ox Lithography Voltage Signal V res t res AC Mode Using AC bias voltage t X =t res =50 ms V ox =10 V, V res =-10 V Pt coated Si Tip Using DC bias voltage AC Bias Voltage Height(nm) 7.6 Width(nm) 48.7 V ox 0 DC Pulsed Bias Voltage Height(nm) 0.84 DC Mode Reducing Space Charge Effect Width(nm) 34.6

22 Lithography Image of Various Duty Ratio 5 4 Height(nm) 3 2 T1 = ms (+15V) T2 = ms (-15V) Duty ratio(%) 120 Voltage = +15V, -15V (AC) Temperature = 23.5 Humidity = 50% Velocity = 10mm/s Duration time: T1+T2= 10ms Width(nm) Duty ratio(%)

23 Real-Time Current Measurement Tip bias voltage Substrate : Ta Humidity : 50 % Temp : 27 Set point : 25 nn Tip Bias : - 10 V Velocity : 0.1 µm/s Non-contact Mode Current (pa) Time vs. current Time (sec)

24 Silicon tip Carbon Nanotube Tip MWCNT-attached tip 500nm Advantage : - Proper structure as a SPM tip - High strength -High resolution Hongjie Dai, APL, 73, 1508 (1998) Disadvantage : - Long fabrication process time - Demand of high junction technology (Increase of contact resistance) Reasonable application in the tapping mode because of high tensile strength and Young s modulus

25 Carbon Nanotube (CNT) Tip Structure of CNT tip CNT Mother tip W- wire Hydrocarbon welding R f 100 kohm TEM photograph of CNT cut electrically in XEM manipulator. Function Generator (2Hz, SAWtooth) Vout = I * R f Schematic for cutting carbon nanotube on CNT tip.

26 Tip Cutting and Length Measurement of CNT MWCNT V Sputtered Nb Threshold voltage: 10V Cutting speed : 0.1~5 nm/s Buckling Amplitude-distance forward forward Amplitude-distance CNT cutting with current discharge method Backward Deflection Backward Deflection 870 nm 270 nm 5.8div = 870nm before cutting 2.7div = 270nm after cutting CNT tip before(left) and after(right) cut with electrical method in AFM.

27 Nanostructure Fabrication Using CNT Tip Bare Si 24 V 10 µm/s Width : 44 nm, Height : 0.7 nm CNT length : 700nm Spin-cast monomer/si 24 V 5 µm/s Width : 44 nm Height : 0.8 nm 17 V 10 µm/s Width : 29 nm Height : 1.3 nm

28 Nanostructure Fabrication on Metal Substrates Using CNT Tip Tantalum CNT length : 350 nm Voltage: 8 V 10 µm/s Titanium Width : 35 nm, Height : 0.4 nm Voltage : 25.5 V Speed : 10 µm/s CNT length : 200 nm Width : 18 nm Height : 0.7 nm Width : 40 nm, Height : 0.6 nm Voltage : 10 V Speed : 10 µm/s Current(nA) Applied Voltage(V) Contact Pt tip CNT tip I-V Curve Pt Tip and CNT Tip

29 Enhancement of Aspect Ratio Using Pulse Generator (Si Substrate) W 2 C tip Pulsed Bias Patterns Height : 1.1 nm Width : 68 nm V Pulsed Voltage DC Bias Patterns Height : 0.5 nm Width : 64 nm 10 V 10 µm/s 0.5 µs 0 CNT tip CNT length : 700nm Pulsed Bias Patterns Height : 0.5 nm Width : 39 nm DC Bias Patterns Substrate Pulse Duration Time Height : 0.3nm Width : 40 nm 10 V 10 µm/s 0.7 µs

30 Depression of Threshold Lithographic Voltage using EFM-CNT tip Si-CNT tip EFM-CNT tip EFM-CNT tip 500 nm 900 nm 500 nm 25V26V 27V 28V 5V 6V 7V 8V 9V 4V 5V 6V 7V 8V Height ( A ) Si-CNT tip : CNT length 500 nm EFM-CNT tip : CNT length 900 nm EFM-CNT tip : CNT length 500 nm EFM-CNT tips Bias Voltage ( V ) (Ta substrate) Current (na) Si-CNT tip Si-CNT (CNT length : 500 nm) EFM-CNT (CNT length : 900 nm) EFM-CNT (CNT lenth : 500 nm) Bias Voltage (V)

31 Fabricated Dots and Line Structures using EFM-CNT Tip (Ta substrate) 17 V 12 V 13 V 14 V 15 V Dot oxide patterns using EFM-CNT tip 700 nm 16 V 15 V Substrate : Ta/Si Velocity : 10 µm/s Humidity : 35 % Temp. : 25 C nm V Line patterns using EFM-CNT tip 13 V 29 nm µm 14 V 15 V

32 Korean National Flag (Teageukgi) Mode : Tapping mode Humidity : 40 % Temp. : 25 Max. Voltage : 9 V Min. Voltage : 0 V Scan Velocity : 10 µm/s Exposure time : 1 ms Substrate : Ti Tip : Pt coating tip (res. Freq. : 302kHz) The smallest Taegeukgi in the world!!

33 Fabrication of EUV Photomask Buffer layer Structure of EUV mask Absorber Capping layer Absorber materials : Cr, Ta, W Mo/Si TEM image of Mo/Si multilayer Silicon Structure of Photo Mask Quarts Damage of ML and limit of pattern size(<30 nm) by electron beam - 40 period stacking

34 Fabrication of New Probe Metal coated tip Top electrode PZT bottom electrode Insulator layer Si Tip bias line( Metal)

35 High-speed AFM Lithography Conventional SPM w/ PZT-tube Scanner High Speed SPM w/ Self-sensing & Self-actuating Probe Lithography System Cantilever and Probe PZT actuator CNT tip Piezoresitive sensor 700 nm Resist and Patterning S N N N H