MTL Fabrication

Ksaligner-2 - Standard Operating Procedure

CORAL Name: ksaligner2
Model Number: MA-4
Location: TRL
What it does: mask alignment

The Karl Suss aligner is a precision mask alignment and expose system, incorporating conventional as well as IR (back-to-front) alignment capabilities. The optical system employs a splitfield revolving microscope with 3.5x, 10x, and 25x objectives, and 10x binocular eyepieces. Three viewing modes (splitfield, full left-hand image, and full right-hand image) are possible. The are four directional buttons for movement of the microscope, and a FAST button for rapid movement. The IR alignment system utilizes a high intensity chromatic light source that produces large infrared output. It includes two fiber optic illuminators for backside illumination, an IR detector, and a viewing TV camera.

The exposure system uses a 350 W high pressure mercury lamp and has an exposure controller with 3 channels (constant power, CP, or constant intensity, CI, 1 or 2); the wavelength is 320 nm. Exposure is initiated with the exposure button on the "Operational Control" panel. Currently we use only CI 1, set to recieve 6mW/cm2.

Wafer stage movement is controlled by x, y and theta aligning verniers. A variety of chucks and mask holders are available to accommodate various wafer and mask sizes. There are four wafer to mask contact modes (std. soft, std. hard, soft vac. and full vacuum.

There are two control panels. The "Front Panel Control" houses:

  1. Regulator & gauges. Set these to the pressure indicated on the dial for the size wafer you are Using.
  2. ON/OFF switch for aligner and vacuum to mask holder
  3. Wafer/Contact/Separation/Parallelism Indicators

The "Operational Control" Panel has soft-touch buttons, and houses:

  1. Microscope "Directional" buttons
  2. Wafer Stage (Shuttle) "Command" buttons
  3. Contact mode buttons
  4. Vacuum to chuck to secure wafer to chuck alignment.
  5. N2 Purge to use with negative photoresist.

The system employs a high-pressure mercury lamp. This lamp is to be changed only by an MTL staff member. The aligner must be operated with all its protection shields in place. If a catastrophic failure of the lamp should occur, avoid touching glass debris or inhaling mercury vapor fumes. Notify a staff member at once.

The UV light produced by the lamp can cause erythema of the skin (similar to sunburn), conjunctivitis and possible retinal burn that could result in blindness. Though the operator is protected from direct exposure to UV light it is recommended that the operator does not look at the mask/wafer assembly at the time of the exposure; indirect UV light may also harm the eye retina.

The IR light used for back to front alignment may also cause retinal burns. The microscope filters the large infrared output to protect the operator when looking through the eye pieces.

Broken wafers also represent a potential eye hazard. Wear safety goggles/glasses when Using the aligner and when removing wafer pieces from the equipment.


  1. Check Equipment Reservations in CORAL to insure that you reserved the correct machine in the correct facility for the correct date. Another user may have reservations; it is your responsibility to honor them, if this is the case.

  2. Use the "Engage" command in CORAL for the equipment that you are about to use; use this command BEFORE you start the operation. Insure that the correct facility is set (TRL) and that your lot name is entered correctly. Enter the quantity of wafers that you are processing in the comments field.

    NOTE: Contamination control is of extreme importance in TRL. You must know what contamination level your wafers classify into, and use labware and equipment of the same classification. Broadly, the lab and this piece of equipment are classified into "GOLD" (red-tagged) and "CMOS" contamination categories. This machine can process both GOLD and CMOS wafers, but you must choose either the GOLD or CMOS chucks and mask-plates. These items have finely machined surfaces which are both fragile and expensive, and care must be taken to ensure nothing except your wafer or mask ever touches one of these processing surfaces. You will need to use appropriately classified support equipment such as the GOLD or CMOS developing areas, beakers, and tweezers.

  3. Turn power on by pressing red POWER switch; red button will light up.

  4. Press load switch, as directed by LCD. Shuttle will move under microscope.

    Note: Shuttle movement will last 30-40 sec. Don't push shuttle any time or try to remove mask holder and/or chuck slider before movement is completed.

  5. Press ALIGN.

  6. Zero wafer chuck by moving x, y and theta micrometers in the "wafer shuttle".
  7. Set exposure time by

    1. pressing the "set exposure time" button
    2. Using the microscope up/down keypad arrows, in conjunction w/ holding down the "fast" button to set the desired exposure time. OCG 825-20 should take about 35-45 sec, AZ 4620P may take 10min.
    3. close this function by pressing the "set exposure time" button.

  8. Choose your contact mode: soft or hard for less or more contact pressure, and press vacuum if the better resolution provided by this mode is required.

  9. Remove mask-holder from shuttle...

    1. Turn knurled knobs counter-clockwise to loosen the plate.
    2. Slowly remove mask-holder, thus allowing the microscope to move up, out of the way.

    Note: You will damage the microscope Objectives if you remove the mask-holder too quickly.

  10. Open mask-holder clips to accommodate mask below the clips. Mask should sit below the clips.

  11. Place mask so that the non-Chrome side of the mask (shiny glass side) contacts the metal mask holder and rests against the stop pins. Release clips slowly.

  12. Toggle vacuum ON to the mask-holder and return mask-holder assembly to the shuttle. Be sure to test this vacuum by attempting to move the mask, which will now be securely locked in place.

  13. Secure mask-holder/mask by finger tightening knurled knobs until the knob "snags" to a stop.

  14. Align the microscope to the mask (Using split-level microscope)...

    Note: First level aligning does not require aligning microscope to the mask (see wafer loading).
    1. Turn microscope power supply ON. Switch is located on the back of the power supply. Light can be directed 100% to objectives, 50% to objectives/50% to TV camera, or 100% to camera, by rotating the arrow indicator knob located on the right hand side of the microscope head.
      Note: The TV camera is always used when in IR mode, but can also be used for front-side alignment.
    2. Focus the microscope to the mask pattern by rotating coarse and semi-fine focus knobs, located on the back on both sides of the
      microscope. Note: The Fine focus/objective separator knobs, located on the front face of microscope, serve the dual purpose of separating the objectives from 30-90 mm as well as for fine focUsing to achieve the same focus depth for the two objectives.
    3. Align the microscope objectives to the aligning marks on the mask. Turn objective lock-knobs counter-clockwise to unlock the objectives. Locate aligning marks on the mask and proceed to find the best objectives separation on the x coordinate with y = 0, by combining microscope DIRECTIONAL BUTTONS and OBJECTIVE SEPARATION movements.
    4. Lock objectives and do final FINE focUsing by Using OBJECTIVE SEPARATION/FINE FOCUS knobs. Note: The fine focUsing knob has a total rotation of only 1/8 of a turn.

  15. Slide TRANSPORT SLIDE chuck assembly from underneath the mask.

    Caution: The TRANSPORT SLIDE moves freely on ball bearings and a harsh movement could damage the slide and send the wafer flying off chuck if wafer vacuum is off.

  16. Place the wafer on the chuck with the wafer resting against the pins. Use caution near the inflatable red rubber gasket around the chuck; puncturing it will damage the seal in the Vacuum Chamber contact mode.

  17. Slide TRANSPORT SLIDE in until it locks. Vacuum to chuck will automatically activate as TRANSPORT SLIDE is brought under the mask.

  18. Make sure SEPARATION LEVER is at zero.

  19. Use the CONTACT LEVER located on the left hand side of WAFER SHUTTLE and steadily turn lever clockwise approximately 90 degrees (1/4 turn), until you hear a "click". The light on the CHUCK DOWN button will appear on the front of the touch pad. CONTACT and WAFER MASK PARALLEL buttons will light up on FRONT PANEL CONTROLS. CAUTION: Never use CONTACT LEVER to bring the wafer chuck down; always use the CHUCK DOWN button.

  20. Separate wafer from the mask by pulling SEPARATION LEVER toward the front of WAFER SHUTTLE. Separation can be adjusted from 0 to 90 um. CONTACT button will go off and SEPARATION button will light up on FRONT PANEL CONTROLS.

  21. Align mask pattern to wafer...

    1. Initially set the 3.5x objectives on microscope turret. These objectives give a depth of focus of 60 um. If your features on the mask are above 10 um and the aligning marks are comfortably large (more than 5 um) you may not have to use larger objectives.
    2. Look through microscope objectives to find your previous aligning mark on the wafer by combining x-y-theta movements for the chuck and x-y directional movements for microscope.
    3. Once aligning has been approximated, contact the wafer to the mask by Using SEPARATION LEVER and inspect the alignment. Note: CONTACT button will light up on FRONT PANEL CONTROLS.
    4. If the wafer is misaligned, separate wafer to a level where both mask and wafer images are sharp on the field of view and proceed to do the final aligning.

      CAUTION: Damage to mask and wafer may occur if x-y-theta on the WAFER SHUTTLE are moved while wafer is contacted to the mask.

    5. Do final alignment and contact the wafer to the mask. Re-focus
      microscope to confirm final alignment accuracy.

  22. Press LOAD to bring WAFER SHUTTLE under UV lamp.

  23. Press EXPOSE to expose wafer. Warning: Do not look at UV light while wafer is being exposed. Note: Check the CP1 channel on the EXPOSURE CONTROLLER to make sure 6mW/cm2 is being delivered to the photoresist on the wafer.

  24. After exposure wafer/chuck will drop to the original position on the TRANSPORT SLIDE. Press ALIGN to bring WAFER SHUTTLE to its original location.

    Note: Do not rush to remove wafer from TRANSPORT SLIDE as lock pin remains on for 30 sec. after the ALIGN button has been depressed.

  25. Carefully pull TRANSPORT SLIDE out and remove wafer. Repeat above operations to expose other wafers.

    Note: Always develop/inspect the first exposed wafer to make sure exposure is correct and the pattern is reproduced faithfully.

  26. Turn machine off...

    1. Remove mask and return mask-holder to its position on the WAFER
      SHUTTLE. Do not secure mask-holder to frame.
    2. Return TRANSPORT SLIDE under the mask-holder.
    3. Press LOAD to leave the shuttle in the load position (shuttle underneath
      the UV optics).
    4. Turn off machine power, microscope lights, and detector and
      camera/monitor (if used).

  27. "Disengage" in CORAL.
Author: Kurt Broderick, 2/00