NANYTE BEAM Manual
NANYTE BEAM Manual BM-001-A3 / V1.1a Page 29 of 33
Galvo scanner position calibration
The galvo controls the position of the laser beam spot, with respect to the camera coordinates.
Calibration is required because optical aberrations such as pincushion can severely distort the
galvo coordinates by few microns. A second order fitting with 10 coefficients is used to map the
galvo coordinates to the camera coordinates.
To start the galvo calibration, insert a clean polished silicon substrate onto the sample stage and
position BEAM ENGINE on the silicon substrate. Click calibrate galvos and this will automatically
dim the illumination LED, allowing the camera to easily identify the laser beam spot. The laser
spot is scanned across the entire field of view. Simultaneously, the input galvo position (blue) and
the detected spot position (black) is updated on a pop-up window.
Once all 81 data points are collected, the second order fitting is performed and the galvo rescans
the field of view. This time, the detected spot positions are in green and should be much closer
to the input galvo position. On the main window, the error after calibration is also printed. Usually
this is less than 200 nm.
Stepper calibration
Similarly, the stepper stage is mapped to the camera coordinates. However, an affine
transformation is used instead, which accounts for rotation, stretch and shear. To perform the
stepper calibration, first a ‘dirty’ silicon substrate of at least 1 cm by 1 cm is required. The ‘dirty’
sample can be obtained by making fingerprints on a pristine silicon wafer.
Next, insert the dirty silicon substrate onto the sample stage and position the BEAM ENGINE close
to the center of the silicon substrate. Press ‘F’ or click on focus to ensure proper focus is available.
Then click the calibrate stepper button. This will move the stage in both x- and y- directions. The
software performs image registration to obtain the sub-pixel displacement of the camera image.
With about 100 samples of x- and y- image displacements vs stage displacements, it is possible
to calculate the transformation matrix between the stage and the camera. An example calibration
matrix is shown below. While only 4 decimals are shown, these values require more precision.
As bonus, the stepper repeatability test button is also available. Running this test will displace the
stage by a random x- and y- value and then moving back to the starting point. The image
registration will determine the amount of shift between the before and after image. Thus, a
repeatability value can be generated. Usually this is less than 0.3 um.
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