High speed focused ion (and electron) beam nanofabrication

Transcription

1 High speed focused ion (and electron) beam nanofabrication John Melngailis, Department of Electrical and Computer Engineering and Institute for Research in Electronics and Applied Physics University of MarylandCollege Park, MD Tel e mail: melng@umd.edu

2 Producing a Patterned dose of Ions (or Electrons) on the Surface Low fabrication rate vs. inflexible fabrication

3 Schematic of projection maskless patterning system (IMS) (or electron) IMS Vienna, Austria (25 years working on ion projection)

4 Projection Mask Less Lithography / Patterning PML2 PMLP Electron Source programmable Aperture Plate System Ion Source 200x 5 kev Reduction Electron Beam Optics Wafer Stage 50 kev 22nm hp node Projection Mask-Less Lithography < 4µm < 4 µm 200x < 20 nm IMS Vienna, Austria Stage 200x Reduction Ion Beam Optics 5-50 kev < 20nm Direct Projection Mask-Less Patterning

5 Why do this? maskless lithography (exposure of resist) eliminate high cost of mask* low volume chip making resistless nanofabrication non planar geometries in situ processing * Or make the mask cheaper (IMS NuFlare)

6 Schematic of projection maskless patterning system (IMS) any ion! Key IMS Vienna, Austria (25 years working on ion projection)

7 Programmable aperture plate concept I.L. Berry, A.A.Mondelli, J.Nichols, J.Melngailis, J.Vac.Soc.Technol. B15, 2382 (1997)

8 APS programmable Aperture Plate Systemare Redundancy Redundancy Redundancy Redundancy Redundancy Layer Substrate Layer Layer Substrate Substrate Layer Substrate Layer Layer Substrate Substrate High Redundancy

9 First functional CMOS-APS (Dec 9, 2008) Si Base Plate 43,008 programmable apertures (within 5.76mm x 6.73mm field) Blanking Plate with integrated CMOS electronics Aperture Plate with 43, µm x 3.75µm openings (beneath) Fraunhoffer Institut Siliziumtechnologie

10 Projection maskless patterning system (IMS) IMS Nanofabrication Vienna, Austria

11 15 kev electron exposure of 50nm thick HSQ resist with 200x reduction 22nm hp 32nm hp 45nm hp 16nm hp

12 10keV Hydrogen ion beam exposure of 20nm HSQ resist 25 µc/cm 2 16 nm hp 32 nm hp 32 nm hp 16 nm hp Center of 25µm x 25µm exposure field Corner of 25µm x 25µm exposure field

13 1st PMLP results with programmable APS (4k beams) 10keV Argon ion beam greytone, 5 µc/cm² Pattern Design GDSII Exposure in 20nm non-car Data Preparation* 33nm * Data Preparation was done with Layout Beamer Software from GenISys

14 Shapes milled with multibeam system at IMS Si GaAs E.Platzgummer,, H. Loeschner,, G. Gross

15 Milling rate 1.9min/10 3 μm 3 22 hr./10 3 μm 3 with 20pA FIB

16 CHARPAN Tool: Blur vs. 10 & 20 kev H + and Ar + Beam Current Blur [FWHM] = σ Blur [nm] Total Blur 10 kev Ar + 20 kev Ar kev H + 20 kev H Current through optical column [na] From H. Loeschner IMS Nanofabrication, Vienna

17 Main limitation to maximum beam current: Stochastic blur introduced at the beam crossover with a waist diameter D A.Weidenhauser, R.Spehr, H.Rose, Optik, 69, 126 (1984)

18 Beam current 1 μa* (200keV) Ion Atomic mass Exposure rate Exposure rate for dose of 3x10 13 /cm 2 (resist exposure and implantation) Exposure rate for dose of /cm 2 (grow, or remove film e.g. Si 0.1μm thick, Y = 5 atoms/ion) H+ 1 5 sec/ cm min./mm a) Ar a) Kr na** (50keV) H min/mm 2 (29.6 min /10 5 μm 3) 14 a) Ar (1.9min/10 3 μm 3) 9.8 a) Kr (2.7min/10 3 μm 3) * I.L. Berry, A.A.Mondelli, J.Nichols, J.Melngailis, J.Vac.Soc.Technol. B15, 2382 (1997) ** E. Platzgumer, H.Loeschner, G.Gross, SPIE Photomask, BACUS (Monterey, CA, Sept. 2007) &, J. Vac. Sci. Technol. B26, 2059 (2008) a) Scaled using WSR formula.

19 Resistless Fabrication: Electrons vs. Ions electrons: min. beam diam. <1nm current ~10pA to μa direct material alteration beam induced chemistry, with precursor gas deposition etching ions: min. beam diam. ~5 10nm current ~ 5pA 10nA milling beam induced chemistry with precursor gas deposition etching implantation

20 Why use electron rather than ion beam induced deposition? no implantation of substrate, no lattice damage or sputtering easy and accurate placement (SEM)

21 Contacts to carbon nanotubes by electron beam induced deposition of gold T. Brintlinger, M. Fuhrer, J. Melngailis, UMd I. Utke, T. Bret, P. Hoffmann. EPFL P. Doppelt, CNRS, Paris J.Vac. Sci. Technol. B23, 3174 (2005)

22 Precursor gases used with electron beams for UMd Projects: - C 9 H 17 Pt- (methylcyclopentadienyl)trimethyl platinum (high concentration of carbon in high resistivity deposit) - AuClPF 3 - very unstable, - but low resistivity deposit, - successfully made good contacts to carbon nanotubes (at EPFL) -Pt(PF 3 ) 4 -new tetrakis (trifluoro phosphene) platinum John D. Barry, Matthew Ervin, Jay Molstad, Alma Wickenden, Todd Brintlinger, Patrik Hoffmann and John Melngailis, J.Vac Sci. Technol. B24 (2006)

23 A Pt line 80 nm wide deposited from Pt(PF 3 ) 4 across four gold fingers Lowest Resistivity μΩcm The beam current was 65pA. The center-to-center spacing of the four gold fingers is 13μm. The length of the line across the four fingers is 42μm. This structure is used to measure the resistance and resistivity of the deposit.

24 Platinum pillar The pillar is grown in 10 min. using a stationary beam with a current of 2.8nA.

25 Ion beam implantation (maskless, resistless) vary dose from device to device on the same chip vary dose within a device, e.g. doping gradient

26 RFID Tag read only memory Laser Cut Links Laser Cut Links (also EM Microelectronic)

27 I DSat / I DSat0 Ids/Ids Normalized I DSat vs. Dose, Ids NMOS vs Dose B 50 kev As 170 kev Ar 60 kev Ga 130 kev E E+11 1.E+12 1.E+13 1.E+14 Dose (ion/cm^2) Source-drain current vs. ion dose at V T + 2v For NMOS and PMOS I DSat Ids/Ids0 / I DSat I DSat vs. Dose, PMOS Normalized Ids vs Dose B 50 kev As 170 kev Ar 60 kev Ga 130 kev E E+11 1.E+12 1.E+13 1.E+14 Dose (ion/cm^2) )

28 Wafers-per-hour calculation assuming single Ga beam 0.8X0.8mm chip. 120 Transistor channels/chip 200mm wafer Transistor channels 1μm x 2μm Implanted area, alignment not critical 6μm

29 Wafers per hour calculation, (contd.) 3 x 10 4 chips/200mm wafer 3.6 x 10 6 transistors/wafer, 3μm 2 ea. area to implant 100pA ion current in beam ( ~ 6 x 10 8 ions/sec.) dose needed = ions/cm 2 or 3 x 10 4 ions/transistor or 50μsec/ transistor or 180 sec.(3 min) beam-on time per wafer assume write-on-the-fly, double beam-on time to 6min. stage speed 8cm/sec.

30 Examples of devices made using FIB implantation BJT s with gradients in base (Motorola) MOSFETs with gradients in channel (Hitachi, Cambridgu U. MIT) CCD s with gradient in channels (MIT) Flash A/D converters (Hughes) Tunable Gunn diodes (MIT)

31 Tunable Gunn diode with gradient of doping in GaAs H. J. Lezec, et. al. IEEE Trans. El. Dev. Letters, Vol. 9, 476 (1988)

32 Opportunities and challenges identify new applications understand and develop processes (e.g. features produced wider than beam diameter) develop ion sources, various species develop aperture plate

33 Summary new electronic or ion multibeam systems writing speeds 1000x or more faster than single focus beam systems resist exposure (dose /cm 2 to /cm 2 ) and implantation (e.g.rfid tags and other devices) doable on wafer scale material addition and the removal is key to in situ processing over more limited areas (electrons or ions)