The LEICA MZ75 optical microscope is used to check the height of the wafer/substrate prior to it being loaded into the ebeam tool. It is also used to measure the exact position where one wants to write.
The table of the LEICA MZ75 optical microscope is a replica of the actual ebeam tool stage and uses the same locking/unlocking mechanism to secure the holders. There are 6 sapphire pins, 3 at the bottom, 3 on the front side that control the exact placement of the holder on the stage (and optical microscope table). These pins match exactly position of the pins of every substrate holder. Any damage done to any of these pins – dirt, scratch – will result in an incorrect placement of the holder, and may lead to holders slipping (and massive drift) during writing of the job. PLEASE, take a great care not to damage or dirty any of these pins!!!
Loading and locking the holder
To load the holder, slide it first carefully onto the alignment microscope. The holder is unlocked – the locking mechanism screw groove is vertical, and the holder can wiggle a bit. Use the tool provided to turn the locking screw 90 degrees clockwise. DO NOT TURN THE LOCK MORE THEN 90 DEGREES AND DO NOT TURN IT IN THE WRONG DIRECTION. THIS CAN SERIOUSLY DAMAGE THE HOLDER. When properly locked, the locking screw groove is perfectly horizontal and the holder is securely locked on the stage/table – it does not move or wiggle.
Checking wafer height and measuring coordinates
Now that the holder is securely locked on the stage, turn on both the microscope and the laser interferometer power supplies – they are on the table on the left side of the microscope. Move your wafer under the microscope and read the height value on the height-meter. If you do not see any value, press the “start” black button and the reading will appear. The value needs to be between plus and minus 50 micrometer. If it is, check that it is true anywhere on the wafer/chip where you want to write. If it isn’t, you may need to remove the holder, remove the wafer, clean the backside of the wafer, clean the holder carefully, re-mount everything and try again. The ebeam tool will refuse to write on any substrate that does not have the surface in the above height range. In case of the piece part holder, you can manually adjust the height using the three very small height calibration screws.
To measure the position where you want to write your pattern, move to the Faraday cup of the holder. It is easier to find it at low magnification, but before you start measuring, zoom all the way in and center the Faraday cup in the crosshair. Press the “Zero X” and “Zero Y” red buttons on the position meter. This will reset the origin for the table measurement system and effectively make the Faraday cup a reference point. From now on do not touch neither magnification, nor focus. Move to the exact location where you want the center of your design to be. Write down the exact coordinates and also record the holder number.
Move the table from under the objective lens, carefully unlock the locking screw by turning it 90 degrees counterclockwise, remove the holder from the microscope and place it into the holder window. Switch off both the microscope and the height interferometer.