Microsystems Technology Laboratories

These machines use high-pressure Mercury bulbs, which may only be changed by MTL staff. All protecting shields must be in place before operation. If a catastrophic failure of the lamp should occur, avoid touching glass debris or inhaling mercury vapor fumes. Notify staff at once.

The UV light produced by these bulbs can cause eye damage, especially cataracts, after long term, indirect exposure, so you should never look at the light. Always wear protective plastic safety glasses to provide additional UV protection.

1. Verify the toggle switches on the manometer box are on, and the dials show pressure, vacuum, and the power supply is on and "running", by pushing the DS display button. It should switch from light received at the chuck, zero except during exposure, to wattage going through the bulb, normally 200 W for the left machine, and 275 W for the right machine.
2. Choose the appropriate contact mode, soft for fragile wafers, or when ultimate resolution is not critical, or hard, for more contact force and resolution.
3. Set the correct time for exposure. We have been getting good results with about 2-4 seconds exposure per micron of resist thickness, but this is very resist specific, and need be characterized for your application.
4. Zero the wafer chuck by moving the x, y, and theta micrometers, to center the chuck within its range of travel. This, along with centering your wafer on the chuck, will help prevent out of plane wafer/mask errors, (incorrect wedge error compensation) which destroy resolution.
5. Turn the machine power on, then load the mask onto the maskholder, chrome side facing away from the maskholder. The non-Cr side will appear shiny, like a mirror, and will be in contact with the maskholder. Turn mask vacuum on, and load the mask/maskholder into the aligner, and tighten the two knurled knobs to secure in place.
6. Use the optic to align the microscope to an alignment feature on your mask, pressing the red buttons on the microscope-positioning arm to free it for movement over the mask.
7. Slide the wafer shuttle out, and install an appropriate chuck; choose one with vacuum holes arrayed to not extend outside the perimeter of your wafer sample, so vacuum to the wafer is not compromised. There is a chuck alignment slot, keyed to a pin on the shuttle, which must insert for proper operation.
8. Load your wafer onto the wafer shuttle, press the wafer vacuum button on the slide if you wish to prevent the wafer from sliding on the chuck, then move the transport slide into the aligner until it stops. Rotate the CONTACT LEVER on the left, in a smooth arc of about 150 degrees, to bring the wafer into contact with the mask. You will hear a click when in contact, and the CONTACT light will go on. Inspect the wafer-mask contact from the side: if the mask and wafer are not in contact, rotate the stage height dial until they come into contact; conversely, if the contact is made near the beginning of the contact lever travel range, move the stage height lower. Note some chucks are of different height, and wafers may be unusually thick, as well, requiring stage height adjustments.
9. After contact is made, slide the separation lever just behind and under the contact lever to your desired separation between wafer and mask, adjustable from 0 to 150u, approximately. This will cause the SEPARATION light to come on. If you look in the microscope while moving the slide, you will see a shadow appear on the wafer from the mask. When in separation, move your wafer underneath the mask alignment features, hopefully on each side of the mask to eliminate any theta error, until your wafer alignment features correspond exactly to your mask alignment features. Wafer stage movement is controlled by x, y and theta aligning verniers (micrometers). You may wish to make slight corrections to focus and reduce your separation distance to facilitate fine alignment, and when done, slide the lever back into contact position. The shadows on the wafer should now disappear, and the SEPARATION light will go out.
   
   CAUTION: Damage to mask and wafer may occur if x-y-theta on the WAFER SHUTTLE is moved while wafer is contacted to the mask.
   
   
10. Press the expose button. Note: Check the CP1 channel on the EXPOSURE CONTROLLER to make sure 4.5 mW/cm2 is being delivered to the photoresist on the wafer. Warning: Do not look at UV light while wafer is being exposed.
11. After exposure, lower the contact lever, move the transport slide out sideways, and remove wafer. Note: Always develop/inspect the first exposed wafer to make sure exposure level is correct (exposed areas are open and thin resist lines are not overexposed, gone) before continuing with your next wafer.
12. Repeat above operations to expose other wafers.
13. Remove mask; put dummy mask back into mask holder. Turn machine power, microscope bulb, off.
    
    NEVER ALLOW ANYTHING TO TOUCH THE SURFACE OF A WAFER CHUCK OR A MASK HOLDER! THESE ARE FRAGILE AND EXPENSIVE.