CANON PLA-501F: Double Side Mask Aligner

Standard Operationg Procedure Rev. 02, 04/14

Canon PLA-501F double-side 100mm mask aligner
Authors:
Rev.00: Andras G. Pattantyus-Abraham, Ali Izadi-Najafabadi
Rev.01, 02: Mario Beaudoin

Superuser(s)
Mario Beaudoin
Alina Kulpa

Purpose:
To offer an SOP that will serve as a checklist to qualified users of the AMPEL cleanroom double-side, 100 mm mask aligner. The current revision only covers single sided alignment. Experienced users are referred to the Neutronix manual for backside alignment (see references).

References:
Canon: PLA-501F Operator Manual.
Neutronix: instructions for IR backside illumination.

Introduction
The mask aligner allows exposure in three different printing modes:

  • Contact mode
    • Hard: vacuum is used to press the wafer and photomask together
    • Soft: a moderate vacuum is used to press the wafer and photomask together
  • Proximity (non-contact) mode
    • The wafer and the photomask are separated by a gap set by the PRINT GAP.

The hard contact mode provides the best resolution, while the other modes could be used for more sensitive samples. If you are planning to use contact mode, make sure photoresist has been baked prior to exposure, in order to avoid damaging your mask! The mask aligner is designed to work with 4” wafers. Wafer pieces may be used as well but are not ideal. The aligner calibrates the spacing between the substrate and the mask plate before every exposure. The calibrator plate has three contact points distributed around its perimeter, and one contact point at the centre. The use of wafer pieces positioned only at the centre of the chuck is possible, but the centre contact point on the calibrator tends to mark the photoresist.

Normal (single-sided) operation is described here. For double-sided operation with the IR illumination system, refer to the Neutronix instruction sheets.

Safety Considerations
Only users qualified by a superuser may operate the mask aligner. UV-blocking goggles (UVEX labelled goggles, available near the mask aligner and in the gowning area) should be worn at all times when the Hg lamp is operational.

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Figure 1. Canon Mask Aligner PLA-501F figure to be uploaded

Mask Aligner Operation

  1. System gases and vacuum
    1. Toggle UP the 3 switches on the black box on the left hand side of the aligner.
  2. Hg lamp (USHIO 250W, Super High Pressure Mercury Lamp)
    1. Turn on the POWER switch.
    2. Press the START button, until there is a current reading.
    3. DO NOT HOLD LONGER THAN 6 SECONDS
    4. If ignition has not occurred, wait for 3 seconds before trying again.
    5. Let the lamp warm up for 10 min
    6. If needed, Use the CURRENT ADJ knob to bring the current into the desired operation range, as indicated by the black area on the current scale.
    7. Note the Hg lamp hours in the mask aligner log book.

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  3. Main power
    1. Turn on POWER to the mask aligner, using the switch on the main panel.
    2. If you will be using the microscope, turn on the fiber optic illuminator.
  4. Utilities
    1. Turn on utilities by opening the three brass valves on the black manifold on the LHS of the aligner
    2. With the pressure gauges on the left side, check that the following values are obtained:
      1. Nitrogen: 1 kg/cm2 or more
      2. Air: 2.5 kg/cm2 or more
      3. Vacuum: 45 – 76 cm Hg
    3. The valves must be shut off at the end of the session.
  5. Check UV Calibration
    1. If the UV intensity was last measured more than 1 month ago, it must be measured again.
    2. Place the sensor of the Karl Süss UV meter on the centre of the wafer chuck.
    3. Make sure the autohand is out of the way.
    4. Make sure the saddle is locked in place.
    5. Press STOP on the front panel and UNIFORMITY on the main panel. This will expose the sensor to the Hg lamp illumination until UNIFORMITY is pressed again.
    6. Note the measured intensity in the log book.
    7. Adjust the exposure time in your recipe accordingly.

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  6. Load photomask
    1. Release the saddle with the lever at the back left and swing it out of the way
    2. Place mask with metal side down on photomask plate. Align the mask with the three guide pins. Press MASK LOAD to hold the mask in place with the vacuum ring.
    3. Make sure on the main panel under alignment, the MANUAL button is selected.

     

  7. Load wafer
    1. Press START – the autohand goes in
    2. Place wafer on bulls-eye.
    3. Press START – autohand comes out to pick up the wafer. Substrate is calibrated and then brought up to the ALIGN GAP value. This gap may be altered on the front panel. Typically, 60μm is a safe value for alignment.nnContact between the substrate and the photomask may be observed by the appearance of interference fringes when the alignment gap is reduced.
  8. Align wafer
    1. Perform a rough alignment by eye with the saddle still swung out of the way by rotating the photomask and shifting the wafer using the wafer XY control (alignment grip, push white button for coarse motion).
    2. Swing the saddle back in place.
    3. Align wafer with photomask using left and right hand objectives. Reduce the ALIGN GAP if necessary to bring the wafer and photomask into focus. The wafer will shift slightly (and possibly randomly) when it is brought up to contact the photomask, so trial and error may be necessary for aligning small features (< 5μm).
    4. Press the flashing ALIGN button – this brings the wafer into the selected printing mode (contact/non-contact).
    5. Check the alignment again.

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  9. Exposure
    1. Set the desired exposure time (light integral, on the main panel below the monitor) in seconds.
    2. Press EXPOSE.
    3. The wafer will be taken out automatically by the wafer handler. Note that the autohand can mishandle the wafer if the chuck has been moved to an extreme position during alignment. If this happens, the wafer must be fished out with a tweezer. Try to avoid this situation! Once the EXPOSE button has been pressed, a set of steps are automatically followed, with the final step being unloading of the wafer. If the wafer is at an extreme position the autohand will not be able to unload the wafer. You will have to stop the sequence by pressing STOP and RESET.
  10. Shutdown
    1. Swing the saddle out of the way.
    2. Press MASK LOAD and remove mask.
    3. Return the saddle to its central position.
    4. Turn off Hg lamp.
    5. Wait 5min with gases ON to ensure Hg lamp cools down.
    6. Turn off power on the main panel.
    7. Turn off all valves for the utilities.

Using the microscope:

  • The microscope is focused using the upper knob on the right side of the saddle (Fig. 4)
  • The position of the two objectives above the wafer can be independently adjusted using the two knobs at each side of the saddle.
  • The left objective can be focused independently using the upper knob on the left side of the saddle (Fig. 5).
  • The field of view is translated using the lever on the left side of the saddle (Fig. 5). The black button must be depressed to release the lever.
  • Use the shutter above the eyepieces to switch between the CRT and the eyepieces.
  • Note that the left image on the CRT corresponds to the right objective.

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