Tilt Measurement

This workflow is intended to measure the substrate’s local height using the system like an AFM in contact mode. Its main application is to derive the X and Y tilts of the substrate. From this set of measures, one can compensate the offset they induce which can become significant far enough from the approach point.

Deviations of the substrate from the horizontal plane induce a local height Z(X,Y)_substrate different from the Z(0,0)_substrate = 0 height set at the approach point. If this deviation becomes larger than a voxel height, the tip would approach a position below the substrate level, resulting in collision with high deflection and risks of breaking or clogging the tip.

When this deviation Z(X,Y)_substrate is too negative, the voxel position becomes too far from the sample to grow. Either the print times out or the voxel grows from a neighboring voxel, creating detrimental free standing parts.

1. Tilt measurement in a nutshell

This correction is especially advised when printing structures with a large footprint (>100um along X or Y) to avoid such detrimental effects.

Tilt measurement uses the absolute coordinates from the XYZ axes. In any camera’s view, the measurement is centered around the absolute coordinate of the target point, modulo the relevant alignment offsets (top/bottom camera calibration, 3D printing calibration and probe alignment).

Points will be measured from top left to bottom right and a file {YYYY-MM-DD-HH-MM-SS}_substratemap.csv with the absolute coordinates measured at each contact point will be created in the %USERPROFILE%\Documents\Exaddon\Substrate Maps subfolder.

2. Parameters

First the positioning parameters are entered:

• Width and height of the area to scan
• Number N of measurement positions along X and Y
• Number R of approaches at each position
• The average distance between points is displayed

This gives R*N² measurements performed on the surface.

The detections parameters are :

• The deflection setpoint (in mV) to trigger the detection of the surface.
• The approach speed of the tip on the sample. A higher value gives a lower scanning time but higher deflections at each contact.
• The retraction distance applied after each contact. Make sure this is always higher than any feature on the scanned area.

Once completed, use the Voxel Cloud Generator to analyze and compensate for the tilts in the subsequent printed structures.

3. Absolute alignment of a structure

Another use of the tilt measurement workflow is to image small, specific areas of a substrate and use the resulting topological image to align a structure more precisely than the pinpoint positioning feature, limited by the optical resolution from the top camera (few microns). With this approach, the imaging resolution is limited by the XY pitch of the measurement grid and the aperture diameter of the tip (~100 nm).

Prerequisites

The following steps must be validated to use the tilt measurement as a topological analysis tool:

• The whole system is accurately calibrated
• The laser is aligned and maximized
• The probe alignment workflow is NOT completed, or the offset is set to (0, 0)
• No pressure is applied as approaching the substrate could lead to the deposition of material and the clogging of the tip
• The 3D printing calibration is completed

Scanning pre-existent structures

1. From the top view, center the screen on top of the area to scan.
2. Enter the Tilt Measurement workflow. Set a retract height of at least 5µm larger than the maximum scanned structure’s height to avoid any side collisions during traveling. Optimize the number of points, approach speed and setpoint before clicking OK.
3. The stages moves to the corresponding and scans around the target point as defined in the workflow. The stages go back to their original position at the end of the scan.
4. Use the voxel cloud generator or the MATLAB workspace to plot the surface and read the absolute coordinates of the scanned area.

Absolute positioning

1. Image the area where the structure needs to be printed

2. Use topographical analysis to determine the start position

3. Create a print file with the new start position

4. Print the new file without any changes
   

Note

Make sure to not change any parameters of the calibrated system. Otherwise, the positioning might be off and tilt measurement has to be performed again.