Using the OAI Model 200 Tabletop Mask Aligner

Warning: Whenever the shutter is open you may be exposed to UV radiation. Therefore always wear UV blocking eye protection and, if your hands are directly under the lamp, UV blocking gloves (nitrile, e.g.).

Startup

Check the vacuum and compressed gas status. If necessary, turn on the vacuum pump and open the vacuum valve on top of the pump. If necessary, open the top on the nitrogen tank. The pressure reading on the regulator should be about 60 psig. Turn on the toggle switch labeled “Timer”.

Note: `X' = right to left, `Y' = toward and away from you, `Z' = vertical direction and `Theta' is rotation in the `XY' plane.

Turning on and warming up the lamp

1. Plug in the blower that exhausts ozone from the lamp. The blower is housed in the hood with the spincoater.

2. Check to be sure that the settings on the front panel of the constant intensity controller/lamp power supply (the black box to the left of the aligner) are as follows:

Current-Voltage selector “VOLTS”

Intensity-Power selector “WATTS”

Channel “A”

Mode “C/I” (this means constant intensity mode)

Five knobs across bottom “Don't mess with `em, they are preset”

Once you have verified these settings, you can turn on the power switch.

3. To “ignite” the lamp, depress the “Start” switch momentarily, releasing when the lamp ignites (you can tell when this happens because the voltage drops and the power supply makes a high pitched sound).

4. The lamp needs to warm up for at least five minutes. At the end of this time, verify that the Lamp Power is at 275 Watts. If it is not, inform your instructor.

5. Switch the intensity-power selector to “mW/cm²”. It should read near zero. Now that the lamp is warm, perform an intensity reading with the OAI UV Powermeter. To do this, place the meter on the mask in the alignment module (see below if you haven't loaded a mask yet), set the exposure for about 10 seconds (set on the front panel-left side of the aligner), and slide the alignment module into position under the lamp housing. Note the intensity reading on the meter. The intensity has been set at 15 mW/cm² and your reading should be close to that value.

Loading the mask

1. Inspect the mask. Make sure it is clean and oriented such that the emulsion side is down and the top of the mask is away from you. If the mask has writing on it, you should be able to read the text normally.

2. Loosen the 6 thumbscrews on top of the mask frame (the mask frame is the black plate on top of the sliding alignment module) that hold down the mask holding clamps.

3. Slide the mask underneath the two holding clamps. Slide the mask away from you until is rests flush against two fixed pins. Keeping contact with these pins, slide the mask to the left to contact a third pin. When the mask is in contact with all three pins, tighten the 6 thumbscrews just finger tight.

4. The large circular insert in the mask frame rotates in the frame and is held in place by two thumbscrews. If necessary, loosen the thumbscrews and rotate the insert until the mask pattern is squared up with the front of the alignment module.

5. Push in the “Mask Vacuum” knob to fix the mask on the mask frame.

Loading the substrate

Note: You need to get the microscope out of the way and move the alignment module clear of the exposure module in order to raise the mask frame

1. Move the microscope to the back of the aligner by pressing in on the button on the main supporting arm (that slides on a rail in the base of the aligner) and pushing the whole stage back.

2. Press the button on the black handle on the front of the alignment module and slide the alignment module all the way to the right-hand stop.

3. Switch the “Mask Frame” toggle to “Open”. The mask frame will rise to about a 40† angle.

4. Place your chip on the cross in the middle of the vacuum chuck. The chip must cover the entire cross, otherwise it will not be held down properly when vacuum is applied. Take care to align your chip parallel to the front edge of the aligner and be sure that the any previous patterning is oriented properly (i.e. the chip should be oriented the same way as it was for any previous patterning steps).

5. When the substrate is properly positioned, switch on the “Sub. Vac.” toggle.

6. Switch the “Mask Frame” toggle to “Closed”. The mask frame should lower and be held in place by vacuum.

Alignment

1. Move the microscope back over the mask by pressing in on the button on the main supporting arm and sliding the stage toward you. Finer positioning of the microscope can be accomplished by use the two buttons on the back of the positioning handle just to the right of the microscope. Pressing the top button permits `Y' positioning and the bottom button permits `X' positioning.

2. Turn on the fiber optic illuminator to about 40-50% power and focus the microscope on the mask structure (see below for instructions on proper adjustment of the microscope).

3. Next you will raise the substrate toward the sample. Be sure that the “Ball Vac.” toggle is in the “Unlock” position. On the front panel there is a D.C. ammeter and black knob that are collectively referred to as the “Chuck `Z' Adjust”. The current controlled here feeds an electronic clutch that engages a belt on the `Z' adjust knob (the big black one on the front of the alignment module). We want the smallest current that allows us to raise the substrate up into contact with the mask. Turn the black knob clockwise until the reading on the ammeter is about 15-20. Slowly turn the knob on the front of the alignment module to raise the substrate into contact with the mask. When contact is made, you should feel a significant resistance while turning the black knob and the belt will stop moving. Contacting the mask should level the chuck. Switch the “Ball Vac.” toggle to the “Lock” position.

Note: You can watch the whole raising process in the microscope. You will want to use low magnification for set-up and for locating any alignment features because the low magnification provides the greatest depth of field and field of view.

5. Lower the substrate a little and align the features. It will be easier if the microscope is properly adjusted for your eyes.

6. When you are satisfied with the alignment, raise the substrate into contact with the mask. Apply vacuum by switching the “Contact Vac.” toggle to “On”. You are now ready to expose your substrate.

Exposure

1. Check or set the desired exposure time (in seconds) on the left of the front panel of the aligner.

2. Press the button on the handle of the alignment module and slide it under the lamp housing. After about one second, the shutter will automatically open, expose your sample and close.

3. Slide the alignment module back to the alignment position.

Removing your substrate

1. Toggle the “Contact Vac.” switch to the “Off” position. Shut off the contact vacuum by turning the “Contact Vac. Adjust” valve fully clockwise. Switch on the “Nitrogen purge” toggle and open the “Nitrogen purge flow valve” to vent the contact vacuum.

2. Be sure to lower the substrate out of contact with the mask so that the next user will not smack their sample with the mask when they close the mask frame.

2. Once the contact vacuum has been vented, open the mask frame and release the substrate vacuum. You can now remove the substrate.

Shutting down the system (If someone is going to use the aligner in the next hour, don't shut it down)

1. Turn off the power on the front panel of the intensity controller.

2. After allowing the lamp to cool for a few minutes, turn of the exhaust blower in the fume hood.

3. Close the vacuum valve and turn off the vacuum pump.

4. Turn off the compressed gas supplies (both 60 psig line and 30 psig line).

5. Turn off the “Timer” toggle.

Proper focusing procedure for the microscope...taken from its Instruction Manual.

“The whole point of stereoscopic microscopes is that, when properly adjusted, the observer sees the object image in three-dimensions and can perceive heights and depths on the specimen. This is a great advantage in material examination and quality control techniques.

To achieve these desirable height/depth effects the image coming from the binocular eyepieces must be “fused” into a single image by the observer – this requires some practice and careful setting of the binocular body.

The procedure is as follows:

The operator should move the eyepiece tubes in and out (laterally) to find the place where the distance between eyepiece centers matches the distance between the pupils of his own eyes. This is the “interpupillary distance” and will vary somewhat from operator to operator. When these distances are equal (or “match”), one central image is seen by the operator.

Finally it is necessary to adjust the microscope so that focus remains sharp through the whole range of magnification (zoom) and so that the image is seen sharply focussed in both the right and left hand eyepieces.

a. Set the microscope magnification to the highest power by turning the zoom control ring counter-clockwise.

b. Focus sharply on the specimen.

c. Set the microscope to the lowest magnification by turning the zoom control ring clockwise. Do not touch the focus.

d. Looking with the right eye through the right-hand eyepiece, turn the eyepiece's diopter adjustment ring until the image is precisely in focus.

e. Do the same with the left eye and left-hand eyepiece.

f. The fused microscope image should now be uniformly sharp throughout the zoom range without refocusing.”