Karl Suss MA-6 Mask Aligner

Trainers

A mask aligner is used to expose a photoresist-coated substrate to ultra-violet light through a photo mask, which casts a shadow on the surface to define the photoresist mask.

Different photoresists are sensitive to light at different wavelengths. It is important to select an aligner with an output wavelength optimised for your resist.

Features

• optimized for 435 nm exposure wavelength
• supports substrates up to 6" in diameter
• supports five different exposure methods

Operating Instructions

Programs

Soft Contact

In this mode, the substrate is held against the mask, but remains secured to the chuck by the chuck vacuum.

Hard Contact

In hard contact, the wafer is held against the mask, the vacuum that holds the wafer to the chuck is released, and nitrogen is used to apply pressure to the bottom of the wafer.

Low Vacuum Contact

In this mode the space between the wafer and mask is partially evacuated. Nitrogen is bled in to prevent complete evacuation. This causes less wear to the wafer and mask than vacuum contact.

Vacuum Contact

In vacuum contact the space between the wafer and mask is evacuated, bringing the wafer in very tight contact with the mask.

Proximity

In proximity mode the wafer is not placed into contact with the mask. The space between the wafer and mask can be set using the exposure gap parameter.

Selecting a program

1. If the program name and program parameters are already correct, proceed to [Loading the wafer].
2. Press <SELECT PROGRAM> repeatedly until you arrive at an appropriate program for your application. (See info about programs above.)
   Soft Contact
   Hard Contact
   Lo Vacuum Contact
   Vacuum Contact
   Proximity
3. Press <EDIT PARAMETERS> and use the arrow keys to choose suitable gap and exposure time settings.
4. For all programs except Proximity, there is a parameter called WEC. This parameter determines whether the proximity flags are used during the stage leveling procedure just before alignment. You should always choose Contact, not Proximity, in order to avoid an "Overcurrent" error.
5. For the Proximity program and any other program which uses Proximity as a WEC choice (rather than using WEC Contact), you must set the stage micrometers before loading your sample to ensure that the stage is centered. The positions are:
   X: 10mm, Y: 10mm, Theta: Center
6. When the parameters are correct, press <EDIT PARAMETERS> once more.

Loading the wafer

1. Press <LOAD>.
2. The display message will now read " Pull slide and load wafer onto chuck. Confirm with ENTER " .
3. If the exposure chuck is not the correct size, replace it with the appropriate exposure chuck. Ensure that the white alignment mark on the exposure chuck is facing toward the positioning pin on the exposure chuck slide.
4. Place the wafer on the exposure chuck so that the major flat rests on the two bottom-most set screws and that the minor flat rests against the set screw on the left side.
5. Press <ENTER>. This applies the wafer vacuum seal. The display message now reads, " Move slide into machine. Confirm with ENTER. "
6. Move the slide all the way into the slot until it clicks.
7. Press <ENTER>.
8. The display message will display, " Performing WEC, please wait... " , as it performs the Wedge Error Correction. In addition, if the microscope was in the up position, it will now lower into the down position.
9. The display message will now read, " Align substrates " .

Aligning substrates

1. Turn the monitor on.
2. Toggle the split field to " left " and activate <FAST>.
3. Using the arrow keys, find a mask alignment mark near the left side of the mask.
4. Now press <SET REFERENCE>.
5. Toggle the splitfield to the middle position (both left and right).
6. Search for the closest mask alignment mark in the right splitfield (try to locate one on the right-most side of the mask).
7. If you have trouble locating the alignment mark in the right splitfield, press <SCAN> and begin your search again in a new direction.
8. Now, once you have found a mask alignment mark in the right splitfield, the left alignment mark may not appear in the left splitfield. If this is the case, you may have to adjust the top-most knobs on the left and right of the alignment stage in order to bring both left and right mask alignment marks into their respective splitfields.
9. Once you have an alignment mark in each of the splitfields, use the X, Y, & q knobs at the alignment stage to align the alignment marks on the wafer with the mask alignment marks which are already in view. (Note : You may have to first use the arrow keys to find a nearby alignment mark on the wafer. At any time, just press <SCAN> to return to your mask alignment marks)
10. With the fine tuning of the alignment marks complete, using the arrow keys, move over to the circuit layout region and use the Y adjustment knob at the alignment stage to bring the layout of the mask and wafer inline vertically. (Note: If you make a mistake, press <SCAN> and return to step 9)
11. Once the alignment is complete, press the <EXPOSE> button. (Important: Look away from the mask aligner during the exposure process!) The exposure process is comprised of the following steps: the microscope will move up, the lamp will slide out over the mask, go through the exposure process, the lamp will slide back in, and then the microscope will come back down.
12. The display message will now read, " Pull slide and unload exposed wafer Confirm with ENTER " .
13. Pull the slide all the way out until it clicks.
14. Unload the wafer.
15. Press <ENTER>.
16. The display message will now read, " Ready for LOAD " .
17. Now push the slide all the way in until it clicks.
18. If you would like to expose additional wafers, return to the [Selecting a Program] section. If you are finished, proceed to the [Ending the mask alignment process] section.

Ending the mask alignment process

1. Press <CHANGE MASK>. The microscope will now move to the up position.
2. The display message will now read, " -Change Mask - Press ENTER to toggle mask vacuum Vacuum: On " . (Important: Do not toggle mask vacuum at this point!)
3. Pull the mask frame out of the alignment stage slot, rotate counter-clockwise 180 degrees, and gently place on the mask frame holder.
4. Press <ENTER> to toggle the mask vacuum to off.
5. The display message will now read, " -Change Mask - Press ENTER to toggle mask vacuum Vacuum: Off " .
6. Remove the mask.
7. If using a special mask frame, disconnect the mask frame vacuum by pushing in on the red coupler and pulling out on the brass tube end-connector and return it to its proper place. If using the mask frame provided with the mask aligner, the mask frame need not be disconnected.
8. Switch off the monitor.

Instructions for BSA on MA-6

1. Load Mask as you normally would
2. Press the BSA button to activate the BS scopes, and move the illumination switch from TSA to BSA
3. Move the BS scopes to positions such that they can see through the windows on the wafer plate (easiest to do this by sight)
4. Position the scopes so that they view separate alignment marks adjusting focus on the knobs for the top layer (Top/Bottom button is illuminated)
5. Grab image
6. Switch the focus to bottom layer
7. Load and align the wafer to the image and expose