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Karl Suss MA-6 Mask Aligner

Table of Contents:
I: Introduction
II: Machine Specifications
III: Operating Instructions
IV: Troubleshooting
V: DO's and DON'Ts
VI: Check-off requirements

Additional Resources:
Karl Suss Operating Instructions

I. Introduction

Mask aligners are used in photolithographic processes to transfer a pattern from a mask to a photoresist coating on the substrate. The photoresist-coated substrate is exposed 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 optimized for your resist.

II. Machine Specifications

Capabilities

Mask Sizes: 4", 5", 7"
Wafer Sizes: 2", 3", 4", 6"

Exposure Setpoints

The MA-6 uses a 350W mercury lamp that exposes across the spectrum 230nm to 400nm. It has two intensity settings (CI-1 and CI-2) whereby the controller maintains a constant intensity during exposure.

CI-1: initially calibrated for 5mW/cm2 at 365nm
CI-2: initially calibrated for 20mW/cm2 at 405nm

Meters are available to measure the intensity at set wavelengths for calculating exposure times.

** UV Filter for the 365nm wavelength available upon request **

Checking the UV Intensity

There are two UV-meter available:

OAI meter for 365nm
Karl-Suss meter for 405nm

To measure the intensity:

1. Turn-off <CHANGE-MASK> and confirm it by pressing <ENTER>.

2. Place the probe in the middle of chuck, facing upward. For added protection against UV exposure you may insert in the mask holder as a shield.

3. Turn on the meter.

4. Press <LAMP-TEST>

5. Read the number on the meter.

6. Press <LAMP-TEST>

7. Turn off the meter and put the probe back in the case.

Fixed Parameters (Do not adjust)

WEC Pressure: 0.2 bar
Vacuum Seal: 0.2 bar
PreVac Time: 4 sec
FullVac Time: 4 sec
Purge Time: 4 sec
WEC Type

Variable Parameters

Alignment Gap
Vacuum Chamber
Exposure Time
Exposure Type

Flood Exposure: Use when no mask is needed.
Soft Contact: The substrate is held against the mask, but remains secured to the chuck by the chuck vacuum.
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: 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: The space between the wafer and mask is evacuated, bringing the wafer in very tight contact with the mask.
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.

III. Operating Instructions

Loading a mask

The message display should read "-Change Mask - Press ENTER to toggle mask vacuum. Vacuum: Off". If it does not, press <CHANGE MASK> to enter the change mask mode.
If the mask holder is not the correct size for your mask, then unscrew the vacuum line from the holder, get the proper mask holder from the drawer next to the machine, and attach the vacuum line to it.
Place your mask onto the mask holder with the metal side facing up. Use the three screws on the surface of the holder to properly position your mask.
Press <ENTER> on the machine to toggle the mask vacuum on.
On the mask holder, push down on the metal piece on the clamp until it clicks to engage the safety clamp.
Pick up the mask holder, invert it so that the mask is now on the bottom, and gently slide it into the machine. Make sure that the mask holder is properly centered left and right, and that it is fully pushed into the machine.
Press <CHANGE MASK> on the machine to engage the mask holder vacuum. The message display should now read "Ready for Load".

Selecting a contact mode and adjusting the exposure settings

To change the contact mode, press <SELECT PROGRAM>. Use the up and down arrow keys to change between the different contact modes on the message display. When you have found the one you want to use, hit <SELECT PROGRAM> again to select it.
To change the exposure time and alignment gap, press <EDIT PARAMETERS>. Use the left and right arrow keys to toggle between the various parameters on the message display. Use the up and down arrow keys to change the value of the current parameter. When finished with all changes, press <EDIT PARAMETERS> again to enter them into the machine.
IMPORTANT: Only the EXPOSURE TIME, ALIGNMENT GAP, and EXPOSURE TYPE parameters should be adjusted. No user should change any of the other settings without permission from cleanroom staff.

Note: You can also adjust the exposure type in <EDIT PARAMETERS> menu, without entering to <SELECT PROGRAM> menu.

Loading a wafer

Press <LOAD>. The message display should now read "Pull slide and load wafer onto chuck".
By using X and Y knobs, bring the chuck to the center position.
Pull the slide out of the machine. If the wafer chuck is not the correct size, then replace it at this time with the right chuck from the drawer next to the machine. Simply pick up the chuck to remove it from the slide and insert the new one. Make sure the white alignment mark on the chuck is facing the positioning pin on the slide. For the vacuum exposure types use the rubber-edged chucks.
Place your wafer onto the chuck. Use the three screws on the surface of the chuck to position your wafer with the major flat along the bottom two screws.
Press <ENTER> to engage the wafer vacuum. The message display should now read "Move slide into machine. Confirm with ENTER".
Gently push the slide into the machine and press <ENTER>. The machine will now move your wafer into the alignment gap you specified and bring the microscope down for alignment. The message display should now read "Align Substrates".

Aligning substrates

Turn the monitor on.
Toggle the split field to " left " and activate <FAST>.
Using the arrow keys, find a mask alignment mark near the left side of the mask.
Now press <SET REFERENCE>.
Toggle the splitfield to the middle position (both left and right).
Search for the closest mask alignment mark in the right splitfield (try to locate one on the right-most side of the mask). If you have trouble locating the alignment mark in the right splitfield, press <SCAN> and begin your search again in a new direction.
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.
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).
Move to the highest microscope magnification and press <ALIGNMENT CHECK>. Your wafer is now placed into your previously chosen contact mode with your mask, so that you may preview your exact alignment before exposure.
IMPORTANT: Do not adjust the X, Y, & q knobs on the alignment stage while in alignment check. Doing so will cause damage to your wafer, mask, and the MA-6.
If you are not happy with the alignment, then press <ALIGNMENT CHECK> again to take your wafer out of contact and make the appropriate adjustments.
Once you have a satisfactory alignment, press <EXPOSURE> to expose your wafer. Make sure to leave the machine in alignment check mode when you do this.

Unloading a wafer

If you have just exposed your wafer, then the machine will automatically go into the unloading mode. If you wish to unload your wafer without exposing it, then press <UNLOAD>.
The message display should now read either "Pull slide and unload exposed wafer" or "Pull slide and unload wafer", depending upon whether you had exposed your wafer or not.
Either way, fully pull the slide out and unload your wafer from the chuck. If you do not pull it completely out, then the machine will not turn off the vacuum on the wafer.
The message display should now read "Ready for Load". You may now load a new wafer into the machine, or unload your mask from it.

Unloading a mask

Press <CHANGE MASK> to disengage the vacuum on the mask holder and move the microscope out of the way. The message display should now read "-Change Mask - Press ENTER to toggle mask vacuum. Vacuum: On".
Gently pull the mask holder out of the machine, invert it, and place it on the platform next to the machine.
Press <ENTER> to toggle the mask vacuum off.
Unlock the safety clamp by pulling back on the bottom piece.
You may now pick up your mask from the holder.

Backside alignment instructions

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

IV. Troubleshooting

Q:When I get to the MA-6 and want to load my mask, the message display does not read "-Change Mask - Press ENTER to toggle mask vacuum. Vacuum: Off".

A: The message display probably reads "Ready for Load". If it does, then simply press to go into change mask mode. If it does not, then ask Cleanroom Staff for assistance.

Q:After I have loaded my wafer and the microscope has moved down into position for alignment, I can't see any features on the monitor.

A: If the button is lit, then the BSA microscopes are currently being used. Press to turn them off. Also, make sure that the Illumination switch on the panel is set to TSA. If you still can not see anything then ask Cleanroom Staff for assistance.

Q:I have loaded my wafer but the microscope did not move down.

A: Again, the machine is probably in BSA mode (the button is lit). Unload your wafer first, press , and switch the Illumination to TSA. If this is not the case then ask Cleanroom Staff for assistance.

Q:When loading my mask, I pressed to engage the mask vacuum, but the message display says "Loss of Mask Vacuum".

A: First of all make sure that you have logged in to the machine. If that was not the reason, check to make sure the safety clamp is not engaged at this time. If it is, then the mask will not sit perfectly flat, preventing a vacuum from forming. Also check to make sure that the vacuum line is properly inserted into the mask holder. If neither of these is the case, then see Cleanroom Staff for assistance.

V. DO's and DON'Ts

DO

Leave the machine in alignment check when pressing <EXPOSE>.
Check the lamp intensity using an intensity meter and the <LAMP TEST> button.
Engage the mechanical safety clamp on the mask holder when loading a mask.
Look away from the UV light when exposing a wafer.
Turn the monitor off when finished with the machine (if no one is waiting to use it next).
Cure the photoresist on your wafer ("soft bake") before placing it in the MA-6 to prevent the photoresist from sticking to your mask.

DO NOT

Turn off the system.
Change the WEC Type in the parameters menu.
Press <EDIT PROGRAM> when changing the exposure type, exposure time, or alignment gap.
Change parameters after loading your wafer.
Adjust the WEC Pressure or Vacuum Seal.
Adjust the wafer position when in alignment check mode.
Attempt to do maintenance on the machine.
Exceed number 15.00 (written in black) on X and Y knobs.
Put your wafer over the marking screws on the chuck.

VI. Check-off requirements

The trainee must demonstrate the following procedures to become checked-off on the MA-6 Mask Aligner.

Measure the UV intensity.
Change the mask holder.
Change the chuck.
Load a mask.
Change the exposure type, exposure time, and alignment gap as specified by the trainer.
Load a wafer.
Display knowledge of focusing and adjusting the microscope, moving the wafer to align it to the mask, proper use of the alignment check feature, and exposing the wafer. (Note: The trainee will NOT have to obtain a proper alignment for the check-off. They will only have to demonstrate the procedure for obtaining one.)
Unload the wafer.
Unload the mask.
Answer any questions posed by the trainer.

Important: For the check-off session please bring a (dummy) wafer covered with photoresist, and also a mask.