How to calibrate the stages

It is not necessary to do a precise alignment of the coordinate systems of laser and stages, because the coordinate system of the laser can be rotated in the software. However, to achieve maximum precision, it might be useful to have a precise alignment: In the laser software one can only adjust the angle in degrees with an accuracy of two digits past the comma. This translates to a residual error of around 0.1 mrad. Across 150mm this leads to an error of 13µm which is below the accuracy of the laser scanner of 25µm.
To do the alignment, the Y-stage is mounted in the laser cabinet, the screws shouldn't be fixed. In the upper right corner, one screw is attached so that the stage can be rotated around that point (see Fig.1). In the lower left, a linear stage is placed (Fig.2). With this setup, the angle can be adjusted precisely. A manual linear stage is carefully placed on top of the Y-stage and a Wafer is fixed on top of it. Now, a straight line is laser-cut into the wafer and the angle error can be measured with the laser microscope. After a few iterations, the angle error can be corrected with a precision that is limited by the resolution of the laser scanner.

Figure 1	Figure 2

The MICOS HPS170 stages are mounted orthogornally. The alignment is achieved by pins. This however is not precise enough for our applications. To manually adjust the angle, remove one pin and loosen the screws of the stages. To reach the screws, you have to drive the stage to its middle position. Mount the PRS-110 rotation stage so that you can still reach one screw. Place the foil mask with the black cross on top of the rotation stage. You can fix it in place with 4 M6 screws. Use a washer! Now align the x-coordinate in parallel with the foil mask by using the alignment program with a correction angle of 0°. Now you can adjust the y-axis by carefully knocking on it and measuring the angle. Repeat until the two axes are at an angle of 90°.