Introduction: |
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:
- Regulator & gauges. Set these to the pressure indicated
on the dial for the size wafer you are Using.
- ON/OFF switch for aligner and vacuum to mask holder
- Wafer/Contact/Separation/Parallelism Indicators
The "Operational Control" Panel has soft-touch buttons, and
houses:
- Microscope "Directional" buttons
- Wafer Stage (Shuttle) "Command" buttons
- Contact mode buttons
- Vacuum to chuck to secure wafer to chuck alignment.
- N2 Purge to use with negative photoresist.
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Safety: |
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.
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Procedure: |
- 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.
- 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.
- Turn power on by pressing red POWER switch; red button
will light up.
- 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.
- Press ALIGN.
- Zero wafer chuck by moving x, y and theta micrometers in
the "wafer shuttle".
- Set exposure time by
- pressing the "set exposure time" button
- 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.
- close this function by pressing the "set
exposure time" button.
- 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.
- Remove mask-holder from shuttle...
- Turn knurled knobs counter-clockwise to loosen the
plate.
- 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.
- Open mask-holder clips to accommodate mask below the clips.
Mask should sit below the clips.
- 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.
- 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.
- Secure mask-holder/mask by finger tightening knurled knobs
until the knob "snags" to a stop.
- 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).
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Slide TRANSPORT SLIDE in until it locks. Vacuum to chuck
will automatically activate as TRANSPORT SLIDE is brought
under the mask.
- Make sure SEPARATION LEVER is at zero.
- 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.
- 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.
- Align mask pattern to wafer...
- 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.
- 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.
- 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.
- 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.
- Do final alignment and contact the wafer to the
mask. Re-focus
microscope to confirm final alignment accuracy.
- Press LOAD to bring WAFER SHUTTLE under UV lamp.
- 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.
- 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.
- 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.
- Turn machine off...
- Remove mask and return mask-holder to its position
on the WAFER
SHUTTLE. Do not secure mask-holder to frame.
- Return TRANSPORT SLIDE under the mask-holder.
- Press LOAD to leave the shuttle in the load position
(shuttle underneath
the UV optics).
- Turn off machine power, microscope lights, and detector
and
camera/monitor (if used).
- "Disengage" in CORAL.
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