Positioning system of a metrological AFM: design considerations

Transcription

1 Positioning system of a metrological AFM: design considerations AFM workshop LNE, Trappes Jan Piot K.U.Leuven Division PMA

2 Overview Introduction General layout metrological AFM Layout of the positioning system Fine positioning unit Sample holder Coarse approach mechanism Conclusions 2

3 Introduction Project goal Calibration device for traceable measurements Designed for FPS Economy, SMEs, Self-employed and Energy Specifications: 1 nm accuracy stroke of 100 µm x 100 µm x 100 µm calibration nanogrids direct measurements

4 General design considerations

5 General design considerations

6 Overview Introduction General layout metrological AFM Layout of the positioning system Fine positioning unit Sample holder Coarse approach mechanism Conclusions 6

7 Layout of the positioning system

8 Layout of the positioning system Invar sample holder I No strict requirements on coarse positioning table (between mirrors) Compact low mass coarse XY-table Abbe point maintained II III Alignment maintained Compensation of alignment errors after approach

9 Layout of the positioning system Ordering components Rotations coarse XY High mass on nanostage Rotations coarse XY Thermal stability

10 Overview Introduction General layout metrological AFM Layout of the positioning system Fine positioning unit Sample holder Coarse approach mechanism Conclusions 10

11 Fine positioning unit: nanostage Compromises Error source Uncertainty [nm] Serial versus parallel? Bandwidth Parasitic rotation Material? CTE Thermal conductivity Costs Mass Kinematic design X, Y Z Machine frame Abbe error Cosine error Mirror tilt error Mirror orthogonality Thermal drift Interferometers Refractive index change Laser wavelength accuracy Laser wavelength stability Mirror flatness Polarisation error Thermal drift Optical system resolution AFM-probe AFM resolution Positioning stage Stage resolution Result

12 Fine positioning unit: nanostage Material choice and kinematic mount sample coarse positioning table sample coarse positioning table mirror support mirror support Fine positioning stage mirror mirror support mirror support Fine positioning stage mirror positioning frame with integrated coarse approach mechanism base frame positioning frame with integrated coarse approach mechanism base frame More mass on kinematic mount Lower resonance frequency

13 Fine positioning unit: nanostage Specifications Parasitic rotations: 3 µrad Resolution: 0.2 nm Aluminium Low profile Stiffness: 1 N/µm

14 Overview Introduction General layout metrological AFM Layout of the positioning system Fine positioning unit Sample holder Coarse approach mechanism Conclusions 14

15 Sample holder design sample coarse positioning table mirror support mirror support Fine positioning stage mirror coarse positioning table sample positioning frame with integrated coarse approach mechanism mirror mount base frame interferometer target mirrors kinematic connection to nanostage

16 Sample holder design Properties Invar (part metrology loop) Coarse XY no influence on alignment coarse positioning table mirror mount sample Mass : 0.65 kg Compromise: stage resonance versus component stiffness kinematic connection to nanostage interferometer target mirrors

17 Sample holder design Compromise: nanostage resonance versus component stiffness m sample 1750 holder Hz k stage High mass for design tolerances Low mass for high resonance 1750 Hz Place mass where it needs to be using simulations Spectral density [db g/hz 1/2 ] X-axis Y-axis Z-axis Frequency [Hz]

18 Sample holder design Thermal design scanhead interferometer sample holder nanostage positioning frame

19 Overview Introduction General layout metrological AFM Layout of the positioning system Fine positioning unit Sample holder Coarse approach mechanism Conclusions 19

20 Sample approach mechanism Functions Approach sample to probe tip Align sample to frame Requirements Mechanical stability Thermal stability Safe approach Sufficient alignment possibilities

21 Sample approach mechanism sample coarse positioning table mirror support mirror support Fine positioning stage mirror positioning frame with integrated coarse approach mechanism base frame

22 Sample approach mechanism Specifications Mechanical Thermal Alignment Robustness Material automated approach 1.3 µm resolution 1 mm stroke no heat production during scan fast thermal settling time alignment accuracy of 45 arcseconds in X- and Y-directions alignment accuracy of 25 arcseconds in X- and Y-directions rotation range of 0.4 degrees safe approach aluminium (rigid connection to base)

23 Sample approach mechanism Considerations Kinematic design (stiffness!) Alignment possibilities (stiffness!) Careful design of rods

24 Prototype

25 Conclusions Positioning system: ordering components Fine positioning unit Parasitic rotations Material choice Sample holder Component stiffness Nanostage resonance frequency Sample approach mechanism Resonance frequency Kinematic mounting, stroke