Nanoholes for leak metrology

Transcription

1 Vacuum Metrology for Industry Nanoholes for leak metrology Università Degli Studi di Genova, Italy

2 OUTLINE INTRODUCTION FABRICATION OF NANOHOLES GEOMETRICAL CHARACTERIZATION LEAK DEVICES RESULTS: PTB INRIM IMT Institute of Metals and Technology

3 Nanoholes Why? The behavior of many types of leak artefacts is not predictable using only their geometry For leak artefacts working in the molecular flow regime, the conductance and the flow rates can be easily predicted from their geometry Molecular flow Kn 1 Kn = λ d Mean free path Representative physical length scale λ d d is the diameter of a circular tube

4 p=1000 mbar λ ~ 200 nm

5 Why nanoholes? The behavior of many types of leak artefacts is not predictable using only their geometry For leak artefacts working in the molecular flow regime the conductance and the flow rates can be easily predicted from their geometry Molecular flow Kn 1 Mean free path Kn = λ d λ Representative physical length scale λ d d 200 nm

6 Nanotechnology: Tools and techniques The nanoholes are manufactured by: Focused Ion Beam (FIB) milling silicon nitride membrane Resolution: 7 nm The nanoholes shape are characterized by: Scanning Electron Microscopy (SEM) Resolution: 1 nm Scanning Transmission electron Microscopy (STEM) Resolution: nm Focused Ion Beam CrossBeam 1540XB by Zeiss Ultra High Resolution Field Emission SE M(UHR-FE-SEM) Atomic Force Microscopy (AFM). Resolution: Z = 0.1 nm; X-Y = tip dependent resolution Atomic Force Microscope Dimension 3100 by Digital Instruments - Veeco

7 FABRICATION: FIB FIB SEM 5 mm Si 3 N 4 membrane 200 nm 100 nm 5 nm Si chip

8 FIB SEM FIB PARAMETERS Ion Energy Current Dwell Time 30 kev Ga (I) ion energy 200 nm membrane thickness 200 pa current 50 pa current Dwell time 2s Dwell time 1s Dwell time 2s Dwell time 1s NO HOLE 30 kev Ga (I) ion energy 100 nm membrane thickness 100 pa current 50 pa current Dwell time 2s Dwell time 1s Dwell time 2s Dwell time 1s Hole diameter 200 nm Hole diameter <100 nm

9 Geometrical Characterization Scanning Transmission Electron Microscopy (STEM) Scanning Electron Microscopy (SEM) Atomic Force Microscopy (AFM) Focused Ion Beam (FIB)

10 SEM & STEM analysis a c OPEN AREA (nm 2 ) RADIUS (nm) b

11 AFM analysis AFM 3100 Dimension VEECO

12 WHAT ABOUT THE INNER PART?

13 a? 1? b 2 c? 3

14 FIB Cross-section Electron Beam (SEM) 54 Ion Beam (FIB) Electron Beam (SEM) Ion Beam (FIB) Si 3 N 4 Membrane Drilling the hole with a single spot of the FIB Milling an area of the membrane with FIB close to the orifice in order to get a SEM image of the vertical walls of the hole SEM image of the cross section

15 Platinum deposition

16 Pt SiN 50 nm 150 nm Simulation of flow through the nano-hole by means of DSMC method. A modified version of the dsmcfoam solver of the OpenFOAM computational package.

17 Leak Devices

18 Nanoholes Calibration: Examples Against Vacuum He Ar N 2

19 R= 92 nm

20 R= 92 nm

21 Array with 48 nanoholes Nominal dimension: Average diameter D = 249 nm Length T= 100 nm Nanoholes array Mean thermal speed K. Jousten, Handbook of Vacuum Technology, Wiley-VCH (2008) Helium Calculated conductance L/s

22 Helium Measured Conductance L/s

23 Array of nano-holes calibrated against atmosphere

24 Array of nano-holes calibrated against atmosphere He N 2 Ar R134

25

26 Array of 6 nanoholes calibrated against vacuum (IMT) D=156 nm D=179 nm Institute of Metals and Technology D=201 nm Length 100 nm D=165 nm D=198 nm D=191 nm Estimated total conductance = 4,0 E-8 L/s

27 Helium throughput and conductance Measured conductance = 4.5E-8 L/s

28 Outgassing Reference Device based on nanoholes technology A small device realized in cooperation UNGE-INRIM-IMT has been used as outgassing reference Layout Under patenting Some details about nanohole: The nanohole, obtained in a thin Si 3 N 4 membrane, was realized at Genova University by FIB. The nominal dimension of the nanohole are: Diameter = 213 nm Length = 100 nm

29 Conductance (L s -1 g 1/2 mol -1/2 ) 1,75E-08 1,70E-08 1,65E-08 1,60E-08 1,55E-08 1,50E-08 1,45E-08 1,40E-08 1,35E % He Ar 1,30E Upstream Pressure (mbar)

30 Acknowledgements This work is funded by EMRP (European Metrology Research Programme). The EMRP is jointly funded by the EMRP participating countries within EURAMET and European Union.