E-beam lithography
Lithography! (Alois Senefelder) 1798
Novel nanolithography techniques E-beam FIB SPM Direct writing Low throughput Imprinting
Method Feature Size ( mm) UV Photolithography UV 1 Laser DWW 1-2 Electron Beam 0.25-0.1 ( ) Ion Beam 0.05-0.1 X-Ray Lithography X <0.1
mask and maskless techniques M.A.Schimdt MIT opencourse 3.155J/6.152J (direct writing)
M.A.Schimdt MIT opencourse 3.155J/6.152J
http://britneyspears.ac/physics/fabrication/photolithography.htm
1200~4800rpm 30~60sec 0.5mm~2.5mm 21 4 451(1999)
e-beam laser-beam / / Toppan photomask Inc.
(etch)(lift-off) 21 4 451(1999)
From NanonScience lab, AS
SEM Y Y X X
Types of electron emitter Thermionic emitters: tungsten tip or LaB 6 tip field emission guns (FEG) cold-cathode type using tungsten single crystal emitters the thermally-assisted Schottky type, using emitters of zirconium oxide.
Types of electron emitter (1994)
Electron extraction brightness current Bias voltage Brightness: Tungsten filament: LaB 6 : field emission=1:10:1000 (1994)
Beam aperture Limiting Aperture ( micro micro). Len1 Beam Limiting Aperture (Current density), Beam
Astigmatism( ):, (Stigmator). Stigmator Stigmator :,.
blanking deflectors & blanking aperture Blenking deflector Beam, Blanking Aperture. : 1. Beam. 2. On/Off, Beam Blanking Aperture.
SE detector CDEM Faraday cup MCP
SE: depth 100A, energy<50ev BSE: energy=e-beam energy Auger electron: 50eV~2keV EELS: electron energy loss spectroscopy X-ray AES BSE SE Diffraction electron TEM EELS
E-beam lithography
X signal Y signal Beam blanker Topcon SEM +NPGS
(PMMA) 21 4 451(1999)
lift-off PMMA copolymer T-gate figures from MicroChem
PMMA : Step1-500 rpm / 10 Step2-3000 rpm / 30 : 10 (PMMA)
Nano-pattern generation system (NPGS) Developed by J C Nabity in 1990s Virtually any SEM, STEM, or FIB can be used with NPGS Patterns are created using DesignCAD
NPGS Hardware Required Connections (bold arrows): Analog XY Inputs; +/-3v to +/-10v range typical Picoammeter; read the beam current hitting the sample is required for lithography. Typical Connections (thin arrows): Image Signal; within +/-10v; used for NPGS Alignment feature. Blanker; within +/-5v, <200 ma;
NPGS software Writing parameters Alignment AL) Pattern writing PG) Run file CAD file
Writing parameters <Alignment> 1. Origin Offset(x,y):[0,0] 2. Magnification: Alignment [1000] 3. Center-to-Center Distance(nm): [500] 4. Line Spacing(nm): [500] 5. Configuration Parameter:[1] 6. Measured Beam Current(pA): 7. Dwell:Alignment [20] <Patten> 1. Origin Offset(x,y):[0,0] 2. Magnification: [1000] 3. Center-to-Center Distance(nm): [5] 4. Line Spacing(nm): [5] 5. Configuration Parameter:[1] 6. Measured Beam Current(pA): 7. Dwell:( Area Line)
Line spacing Center-to-center E-beam E-beam
Dosage line dose (nc/cm) area dose (uc/cm 2 ) point dose (fc)
Develop MIBK(Methyl isobutyl ketone)/ipa(sopropyl alcohol) 30s~60s Rinse: IPA PMMA Acetone
Images from Raith
Example- Standard E-beam lithography and shadow evaporation of Al on Si substrate. 28 o 150nm e beam Suspended mask PMMA 4% Ge PMMA 6% developping & dry etching Metal deposition Metal deposition I-shape island Al 2 O 3 tunnel barrier
Why aluminum? The native oxide layer of aluminum serves as a high quality tunneling barrier AlO x Al Al Oxidation parameter: Oxygen pressure 10~50mtorr time : 1min~5min Al/AlO x /Al junction specific capacitance: 45fF/ m 2 Typical Al/AlO x /Al junction capacitance: 0.5~1fF
Sample gallery E-beam+ Topcon SEM +NPGS E-beam+
Alignment key Alignment key photo : E-beam
Photo+lift-off : E-beam& (CF 4 plasma) 75nm SiN photo + : 500mm Si (KOH) E-beam + :
ion-beam (back-scattering) IC IC (dual beams)
liquid metal ion source (LIMS) Most widespread are instruments using gallium(ga) ion sources easy to build a Ga liquid metal ion source (LMIS) Electrode Ga W wire tip
Beam collumn Ion energy : 5-50 kev Beam current : tens of nanoamps
Ion Damage destructive to the specimen sputter atoms from the surface be implanted into the top few nanometers of the surface Ion Energy,keV Ga Damage layer thickness, A 5 78 57 10 126 88 20 199 133 30 262 171 40 307 195 50 364 240 In Damage layer thickness, A
Dual beam system TEM 5 to 30kV (5kV steps) 4nm at 30kV 20nA 2mm 0.5 to 15kV 5nm at 1kV SEM column main chamber Carbon, Tungsten TEOS Nikon
1. (Precisional Cutting) 2. (Enhanced Etching Iodine/Selective Etching XeF2) 25:1(typical) 40:1(Si) http://tech.digitimes.com.tw/
FIB assisted CVD (Selective Deposition) (Metal and TEOS Deposition) Pt) (W) IC 50 100 http://tech.digitimes.com.tw/
Sample gallery