Traceable cantilever stiffness calibration method using a MEMS nano-force transducer

Transcription

1 Traceable cantilever stiffness calibration method using a MEMS nano-force transducer Sai Gao 1, Uwe Brand 1, Wolfgang Engl 2, Thomas Sulzbach 2 1 PTB, 5.11 Hardness and tactile probing methods 2 Nanoworld Services GmbH, Erlangen

2 Overview 1. EMRP Project MechProNO" 2. Stiffness calibration of AFM-Cantilevers using MEMS 3. Improvement of the Thermal Tune Method 4. New Silicon Reference Springs with stop limit Seite 2

3 1 EMRP-Project MechProNO Nano-object Nanoindentation CR-FM Ag NWs 88 ± ZnO NWs Ag: Silver, ZnO: tin oxide, NW: nanowire, MWCNT: multiwall carbon nanotube 1 Measured Elastic Modulus E (GPa) Electro-mech. Beam Tensile tech. resonance tech. bending Three point bending ± 5 MWCNTs 21 ± ± G. Stan et al. Scanning Probe Microscopy in Nanoscience and Nanotechnology, Springer, 2010 Seite 3

4 Available materials and objects 1. n-pillars from Si (h = 80/225 nm), Resist (h = 155/323 nm) 2. n-cantilever and n-bridges from Si, SiO 2, Si-Nitrid (t50nm) 3. Spherical Nano-Particle: SiO 2 (80, 100, 282 nm) Gold (57/48 nm) on SiO 2 and Si<100> Silver (50/46 nm) SiO 2 and Si<100> TiOx (< 150 nm: 28 nm) SiO 2 and Si<100> 4. Rods: Gold (21/20x77) on SiO 2 and Si<100> 5. Wires Silver (60 nm x 10 µm) height: 77 nm 440 nm height: 77 nm 440 nm FIB Seite 4

5 Kraft [µn] BAM: Force Measurement inside FIB with Kleindiek FMT-400 at Si lamella Silicium Lamelle L= 9,97µm k=12,86 N/m FMT-400 sensor Tip force constant (calculation): 2 to 4 N/m Maximum tip force: 80 μn ,0 0,2 0,4 0,6 0,8 1,0 Weg [µm] E Si = 429 GPa % 5 Seite 5

6 deflection, nm Relative Deflection, nm PTB: Stiffness Measurement with AFM Cantilever: Si 3 N 4 L = 5 µm, b = 1 µm, h = 50 nm 10 Measurement result L = 4.28 µm ± 5 % 0 1 L = nn 0.6 nn 1.2 nn 2.4 nn 4.8 nn 9.6 nn 9.6 nn E = 488 GPa + 57 % F Scan direction AFM : Icon. ScanAsyst mode, 0.2 Hz scan F = 0.3 nn, 0.6 nn, 1.2, 2.4, 4.8, 9.6 nn (U 30 %) x, nm z = Analytical result 0.3 nn 0.6 nn 1.2 nn 2.4 nn 4.8 nn 9.6 nn 4 F L3 E b h Cantilever length, µm E = 310 GPa 50 nm 79 nm Seite 6

7 deformation, nm Relative Deflection, nm Profile, nm PTB: Stiffness Measurement with AFM Cantilever: Si 3 N 4 L = 5 µm, b = 5 µm, h = 50 nm L = 5 Measurement result L = 4.7 µm 200 ± 5 % 0.6 nn 1.2 nn 2.4 nn nn 9.6 nn nn 38.4 nn E = 1276 GPa x nm F Scan direction AFM : Icon. ScanAsyst mode, 0.2 Hz scan F = 0.3 nn, 0.6 nn, 1.2, 2.4, 4.8, 9.6 nn (U 30 %) x, nm z = Analytical result 4 F L3 E b h 3 E = 310 GPa 0.6 nn 1.2 nn 2.4 nn 4.8 nn 9.6 nn 19.2 nn 38.4 nn Cantilever length, µm 82 nm Seite 7

8 FEM Simulation results Si 3 N 4 E = 310 GPa, n = 0.27 L = 5 µm Beam_thickness = 0.05 µm Substrate_L = 10, Substrate_W = 10 Substrate_T = 2 Beam_Width b = 0.1 / 1 / 5 µm width b = 0.1 µm k 0.1 = N/m % K b =0.1 = /K b = 1 = / K b = 5 = width b = 5 µm k 5 = N/m %

9 Auslenkung, nm Displacement [nm] Z-stage 2 PTB: New Stiffness Calibration Method using MEMS actuators PSD Displacement resolution: 0.2 nm z Laser DI 5000 AFM head Force resolution: 2.6 nn Size: 2 mm x 5 mm x y Cantilever MEMS 140 Nano-force actuator 120 jump-out k 2 DI 5000 X-Y Stage 100 Positioning system jump-in PTB Calibration k 1 k 1 cantilever k MEMS k Force Kraft, [nn] k ( 1) Prototype of an electrostatic MEMS actuator Typical measurement curve Seite 9

10 New Stiffness Calibration Method using MEMS actuators U(k C ) 7 % MEMS k C = 2.53(8) N/m 8 % Cantilever Seite 10

11 Measurement uncertainty of the new method Uncertainty contributions 1. k MEMS : 4 % 2. statistics: 3 % 3. Stiffness setup: k Instr 200 kn/m < 0.1 % 4. measured slopes k1 and k2: < 0.2 % 5. drift effects: 5 % U(k C ) 7 % Boundary conditions: 1. k MEMS = 13/3 N/m available For U = 7 %: 0.1 < k MEMS /k C < 10 0,3 N/m < k C < 130 N/m can be measured 2. Future new MEMS: 0.5/1/5/30/100 N/m S. Gao, Z. Zhang, Y. Wu, K. Herrmann: Towards quantitative determination of the spring constant of a scanning force microscope cantilever with a microelectromechanical nano-force actuator. Meas. Sci. Techn. 21 (2010) Seite 11

12 Smallest probing forces possible Typical deflections: 3 µm (k = 40 N/m) F max = 120 µn (tip damage) 1,5 µm (k = 0,1 N/m) F max = 150 nn Smallest deflection possible: 30 nm (k = 0,1 N/m) F max = 3 nn 30 nm (k = 40 N/m) F max = 1200 nn (tip damage?) d plast F max 3 π Y r tip F max π H r tip d plast (Si) 3 nm tip fracture? (it seems so) Seite 12

13 Force in µn Calibration of MEMS stiffness in the PTB Deflection in µm Two balances: U(k) = 4 % Mettler SAG245: Sartorius SE2: 0,1 µn < F < 4 N 1 nn < F < 20 mn Seite 13

14 3 Improvement of the Thermal Tune Method by Reference Cantilevers Idea NanoWorld: Apply Thermal Noise method + use calibrated reference cantilevers for calibration NanoWorld: U(k C ) itn = 10 % Comparison measurements with PTB (Case study 1) showed that the mean deviation of NanoWorld values was %. Seite 14

15 Comparison Measurement NanoWorld - PTB 2,63 Seite 15

16 4 Draw backs of Cantilever on reference cantilever method Richard S. Gates and Mark G. Reitsma: Precise atomic force microscope cantilever spring constant calibration using a reference cantilever array. REVIEW OF SCIENTIFIC INSTRUMENTS 78, Seite 16

17 Improvement: New Silicon reference springs: Meander springs Advantage: very small change of stiffness versus probing location (L) Probing area 0,75 mm x 1 mm Length: 20 mm Width: 2 mm Height: 0.5 mm material: Silicon all values are in mm Seite 17

18 FORCE [µn] Residual2 [µn] Metrological properties of meander springs First meander springs Dk = -0.1 % Dk/Dx = -1 %/300 µm Dk = - 1 % FORCE Residual2 k = 15 N/m down up Deflection [µm] Nonlinearity: -2 ± Seite 18

19 Force F in in µn Further improvement: stop limit Idea: reference spring with two additional calilbration points for force (12 µn) and deflection (3 µm) Bending point F Bend k 1 z Bend Deflection z in µm Seite 19

20 Realization: two MEMS springs Material: single crystal silicon Spring 1 Therm. DL/L: K -1 E: 169 GPa H: 12 GPa Spring 2 Area of contact Seite 20

21 Stiffness in dependence of loading position Seite 21

22 Nonlinearity of the measured force-deflection curves Nonlinearity < 0.2 % Dk(Load-Unloading) 0.1 % Seite 22

23 Temperature dependence of parameters: 0.1 % Test series T in C k in N/m F_Bend in µn h_bend in µm no. of measur. Duration in h Loading position 1 22,10 4,038(6) ± 0,16 12,727(20) ± 0,26 3,156(5) ± 0, centre 2 22,70 4,042(4) ± 0,16 12,729(16) ± 0,26 3,152(3) ± 0, centre Seite 23

24 5 Summary New PTB calibration method for the bending stiffness of AFM cantilevers using MEMS with U(k) 7 % Improved Thermal Tune method successfully tested: U(k) 10 % New meander reference springs reduce achievable F uncertainty Prototype of a MEMS reference spring with stop limit successfully tested: two further calibration points for deflection (3 µm) and force (12 µn) Seite 24

25 Acknowledgement Production of MEMS: Susann Hahn, Karla Hiller (TU Chemnitz) FIB-processing of the MEMS: Nicole Wollschläger, Werner Österle (BAM, Berlin) Production of the meander springs: Erwin Peiner (TU Braunschweig), Thomas Frank (CiS Erfurt) MEMS calibration: Radovan Popadic Mikro-Nano Assembly: Helmut Wolff AFM: Min Xu, Frank Pohlenz REM: Helmut Wolff, Thomas Ahbe Elektronics: Dierk Holger Neddermeyer, Joachim Pilarczyk Thank you very much! Physikalisch-Technische Bundesanstalt Braunschweig und Berlin Bundesallee Braunschweig U. Brand Working group 5.11 Telefon: uwe.brand@ptb.de Stand: 03/2015