e-beam lithography.ppt

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1 E-beam lithography

2 Lithography! (Alois Senefelder) 1798

3 Novel nanolithography techniques E-beam FIB SPM Direct writing Low throughput Imprinting

5 Method Feature Size ( mm) UV Photolithography UV 1 Laser DWW 1-2 Electron Beam ( ) Ion Beam X-Ray Lithography X <0.1

6 mask and maskless techniques M.A.Schimdt MIT opencourse 3.155J/6.152J (direct writing)

7 M.A.Schimdt MIT opencourse 3.155J/6.152J

9 1200~4800rpm 30~60sec 0.5mm~2.5mm (1999)

10 e-beam laser-beam / / Toppan photomask Inc.

11 (etch)(lift-off) (1999)

12 From NanonScience lab, AS

13 SEM Y Y X X

type using tungsten single crystal emitters the

14 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.

15 Types of electron emitter (1994)

16 Electron extraction brightness current Bias voltage Brightness: Tungsten filament: LaB 6 : field emission=1:10:1000 (1994)

17 Beam aperture Limiting Aperture ( micro micro). Len1 Beam Limiting Aperture (Current density), Beam

18 Astigmatism( ):, (Stigmator). Stigmator Stigmator :,.

19 blanking deflectors & blanking aperture Blenking deflector Beam, Blanking Aperture. : 1. Beam. 2. On/Off, Beam Blanking Aperture.

20 SE detector CDEM Faraday cup MCP

21 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

22 E-beam lithography

23 X signal Y signal Beam blanker Topcon SEM +NPGS

24 (PMMA) (1999)

25 lift-off PMMA copolymer T-gate figures from MicroChem

26 PMMA : Step1-500 rpm / 10 Step rpm / 30 : 10 (PMMA)

27 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

28 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;

29 NPGS software Writing parameters Alignment AL) Pattern writing PG) Run file CAD file

30 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)

31 Line spacing Center-to-center E-beam E-beam

32 Dosage line dose (nc/cm) area dose (uc/cm 2 ) point dose (fc)

33 Develop MIBK(Methyl isobutyl ketone)/ipa(sopropyl alcohol) 30s~60s Rinse: IPA PMMA Acetone

34 Images from Raith

35 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

36 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

37 Sample gallery E-beam+ Topcon SEM +NPGS E-beam+

38 Alignment key Alignment key photo : E-beam

39 Photo+lift-off : E-beam& (CF 4 plasma) 75nm SiN photo + : 500mm Si (KOH) E-beam + :

40 ion-beam (back-scattering) IC IC (dual beams)

41 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

42 Beam collumn Ion energy : 5-50 kev Beam current : tens of nanoamps

43 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 In Damage layer thickness, A

44 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

45 1. (Precisional Cutting) 2. (Enhanced Etching Iodine/Selective Etching XeF2) 25:1(typical) 40:1(Si)

46 FIB assisted CVD (Selective Deposition) (Metal and TEOS Deposition) Pt) (W) IC

47 Sample gallery

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