Chapter 9.1
(ksba6)
1.0
Title
Karl Suss BA6 Bond Aligner
2.0
Purpose
The Karl Suss MA/BA6 can be used in two modes: mask
align (MA6) for lithography and
bond align (BA6) for wafer-to-wafer alignment followed by clamping or prebonding.
This chapter describes the bond alignment capability of the
tool (BA6). For mask align mode
refer to the Chapter 4.17. The Karl Suss BA6 is a bottom side
wafer-wafer bond aligner with alignment accuracies down to 1 micron
or better. Only trained and approved users may use this bond aligner. The
system includes a number of unique features including:
► Bottom side
alignment using bottom viewing optics,
CCD imaging with frame
grabber and TV monitor. This allows registration of features on the backside
of one wafer to the topside of the
other wafer (BACKSIDE ALIGNMENT MARKS OR THROUGH-WAFER ETCH WINDOWS ARE
NEEDED FOR ALIGNMENT).
► Automatic
computer control with
LCD status and
user prompting and keypad
entry. Up to 100 programs may be
stored with 7 on line at any one time. Each
program may be edited for key
parameters pertinent to the bond mode.
► Anodic bonding
(transparent glass substrates to
silicon) and silicon fusion
bonding programs are available with options for slide/fixture load/unload.
With the current machine
configuration LOADING IS
ALWAYS BY SLIDE. Unloading is by
slide only for
silicon fusion pre-bonding. Unload by fixture when
performing clamping following by anodic bond in the SB6 The seven programs on-line
are summarized as follows:
Available
Programs:
1.
Anodic bonding/Prox: Load slide - Unload fixture. The only
parameters that needs to be entered is alignment gap and WEC type. Proximity
WEC is usually selected.
2.
Silicon fusion: Load slide - Unload slide. Used for
Si-Si pre-bonding, typically before the wafers are annealed in the furnace for
fusion bonding. Since the wafers are actually pressed against each other, in
addition to alignment gap, the pre-vacuum, vacuum and purge times have to be
entered. This is similar to vacuum contact program in MA6 mode.
Programs NOT used:
Silicon fusion: Load fixture -
Unload fixture
Not used.
Silicon fusion: Load slide -
unload fixture
The only parameter that needs to be entered is alignment gap.
Silicon fusion: Load fixture -
Unload slide
Not used.
Anodic
bonding/Prox: Load fixture - Unload fixture
Not
used.
Anodic
bonding/Prox: Load fixture - Unload slide
Not
used.
Laser pre-bond option is necessary which is not available with the current
system.
►
Wafer sizes can be either 4 inch or 6 inch. Change
over from 4 to 6 inch and vice versa may be made in a
minute or two. For other substrate sizes special chucks can
be ordered.
►
Fast or slow scanning of
mask/substrate with a
memory toggle to quickly
view between 2 locations
(as when checking alignment key and some other known critical pattern). Aids
alignment using one objective.
3.0 BA6
Setup
Before starting, verify that the machine is in
the correct idle state:
►
System power is ON and the
machine is in
the **MA6** mode.
►
TV monitor is off.
►
Lamp power is on with supply readout at 900 in
constant intensity mode 1.
►
Mask and wafer trays are on
stage with dummy
mask no wafer is on the chuck.
►
Pressure = 5-6 bar; Nitrogen = 1-2 bar.
►
When you enable machine look
out for any
problem reports.
Start-up Procedure
(1)
While machine is in MA6 mode, remove mask holder by pressing "CHANGE MASK" button.
Place mask on the table to the left of stage.
(2)
Turn machine off by
turning the green knob
on the display panel.
(3)
Turn machine back to ON. Hold knob in ON position for a couple of seconds until "KARL SUSS
precision instruments" is displayed. If
this is not
done the breakers
at the back of the machine might
trip and need to be reset.
(4)
Press LOAD when prompted. Machine
will go through starting up routine.
(5)
Select **BA6** machine configuration using Y arrows to toggle
between BA6/MA6 modes. Press ENTER.
(6)
Machine will ask user to push lamp housing all the way to the
back. Push it back manually (very carefully and slowly) until a clicking sound
is heard and the lamp house locks in place.
(7)
Press F1 to bring up microscope
UP/DOWN menu. Press enter to move microscope up.
(8)
Remove the mask adapter frame by unscrewing the
nuts, which hold the
frame onto the stage. The frame is quite heavy and
very expensive piece
of equipment. EXERT CAUTION
WHEN HANDLING IT. Place the frame on the shelf below the machine making
sure it is stable and secured in place.
(9)
Select the appropriate bond
adapter frame from the slots on the shelf below the machine. The frames are
bulky (silver color) and easy to identify. The smaller (4")
frame is used
for silicon fusion pre-bonding
only. Anodic bonding of both 4 and 6" wafers use the 6" frame.
(10)
Place the frame onto the stage. Make sure it
secured properly onto the stage. Also make sure the clamps are in the up
position. If they are not you
can do it manually.
(11)
Select the proper upper
chuck for your
application from the chucks stored in the storage cabinet behind
and to the left of the machine. For
silicon fusion *pre-bonding*
i.e. load slide - unload slide you would use the Si fusion upper chuck. For
other applications you would
use the 4" transport fixture, which is usually found sitting on the
transport arm of the SB6 bonder.
Place chuck carefully taking care not to damage the clamps and/or
spacers. IMPORTANT: THE FLAT ON THE
CHUCK WITH THE NOTCH SHOULD BE TOWARDS YOU.
(12)
Replace bottom chuck with the proper chuck for your application. For silicon fusion
pre-bond you would use the 4" vacuum bond chuck with rubber seal. For
other applications using the
transport fixture use the 4" bond chuck. Store away the MA6 vacuum
chuck you just replaced.
4.0 Viewing, Loading, Saving and
Editing a Program
The BA6 allows 7 different program recipes (described earlier) to
be in online memory at one time. Any
one of these programs can be immediately chosen by simply pushing "Select Program" pad until the appropriate program appears in the
display. Up to 100 programs (numbered 0-99) may be stored in archived memory.
These programs must be loaded before they can be executed.
To see what programs are stored:
(1)
Press "Edit Program". Pad flashes.
(2)
Hit Y (up/down arrow) keys. Each program #, bonding mode &
alignment gap is displayed as
you scroll through each program. You can scroll up or down through the
list by pressing the Y-up or
Y-down key.
(3)
To exit looking at programs, press flashing "Edit Program" key.
To load an already stored program:
(1)
Push "Edit Program". Pad flashes.
(2)
Press X-lateral key to scroll between: 1 "Save Prgm to"; 2
"Load Prgm from"; 3 "Delete Prgm #"; 4 "Exit
Prgm editor without change". Scroll to 2, Load Prgm from.
(3)
Press Y key until desired program number appears in
LCD display.
(4)
Press flashing "Edit Program" key to load stored program into online memory.
Example: To
load program 9
(1) Press "Edit
Program".
(2) Press X-lateral
key once to scroll to "Load Prgm from".
(3) Press Y-up/down
key 9 times to scroll to recipe 9.
(4)
Press "Edit Program" again to load recipe and exit
edit mode.
To change a
stored program:
(1)
Load desired program as described previously.
(2)
Press "Edit Parameter" key, light flashes.
(3)
Press X-lateral key to
scroll through parameters.
For soft or hard contact modes parameters are: Expose
Time, Alignment Gap and Wedge Error Compensation (WEC) Mode.
Note: For vacuum mode there are
additional parameters.
Select parameter or
parameters to be changed. Saving a program also saves the objective
position.
(4)
Press Y-up/down key to change parameter to desired value.
(5)
Press "Edit
Parameter" key again.
Change appears on display
and light stops flashing. Now
you still need to save this program if you want to use it again
in the future.
To save it as another program:
(1)
Press "Edit Program" key. Light flashes.
(2)
"Save Prgm to" is displayed.
(3)
Press Y-up/down key to select program # to save to.
Note: You
can save a
program on top of another program, but first make sure that program is
not needed. If you wish to
save to a particular program # AND that recipe is empty simply
press "Edit Program".
(4)
Press "Edit Program" key again to execute save.
To Delete program (to free up 1 of
99 slots for a new program):
(1) Press "Edit
Program" key. Light flashes.
(2) Press X-lateral
key twice to scroll to option 3,
"Delete Prgm #"
(3) Press Y-up/down
key until program you
wish to delete appears.
(4) Press flashing
"Edit Program" key again.
Flashing stops and program is
deleted.
To Exit the "Edit Program" mode without making a change:
After entering
the "Edit Program" mode by pressing "Edit Program" key:
(1) Press X-lateral
key until option 4, "Exit Prgm Editor..." is displayed.
(2) Press "Edit
Program" key again. Light stops flashing
and edit mode is exited.
To make a change without loading a new program:
Example: To change alignment gap for the
next substrate only:
(1) Press "Edit
Parameter" key. "Alignment gap" is displayed as the 1st parameter to change.
(2) Press Y-up/down
key to increase/decrease gap.
(3)
Press flashing "Edit Parameter" key again. New align.
Gap should be displayed.
5.0 Wafer
Loading
There are 2 bottom wafer bond chucks, both 4
inch, one for fusion
pre-bonding (this one
has an inflatable rubber seal ring) and the other for all other bonding
applications. The vacuum grooves
on the chuck must be completely covered by your substrate. Make sure you have
the right chuck installed
for your application. If a
different wafer chuck is desired, push straight up on chuck and remove. Place
desired chuck into circular
opening and align white line on chuck to pin on tray.
Always handle wafer chuck by the rim,
do NOT touch chuck directly.
CAUTION: These chucks
are made by precision machining
and should be handled with care. Do not drop, scratch or otherwise
damage them. Store unused chuck in proper location.
(1)
Adjust wafer rotation knob to 0 (so that rotation finger is
centered) and set X & Y
micrometers for the stage to 10.
(2)
Push "Load" key. The
display will ask
you to insert proper
bonding frame. Since
you have already done so press "Enter".
(3)
The display will then ask to
insert the proper
bottom chuck. Since you should already have installed the proper chuck
press "Enter".
(4)
Place your substrate with the side to be bonded down making sure
all vacuum grooves are covered. The wafer should sit between the 4 positioning
pins with steel balls with the flat
towards you.
(5)
Press "Enter" and slowly push tray all the way into
the machine.
(6)
Push "Enter". The wafer
is positioned onto
the upper chuck by vacuum and control lever of the proximity
flags is activated.
(7)
For silicon fusion bonding programs you should now use the
BSA microscope to find the alignment marks on your wafer.
Once you have found the marks and
adjusted focus the image should be grabbed. BSA set-up and
operation is described in later sections. For anodic bonding applications, the program assumes that you have a transparent bottom
wafer and does not give the frame grabbing
option at this stage.
In this case you would load the
second wafer and then use BSA to grab image.
(8)
Pull out slide and load 2nd wafer with the side to
be bonded up.
(9)
Press "Enter"
and slowly push tray all the way into
the machine.
(10)
Press "Enter". The
second wafer is
brought into its uppermost position and WEC is performed. After WEC the proximity
flags are retracted and wafer is brought to its align position.
6.0 BSA Microscope Set-up and Wafer Alignment
The bottom microscope (BSA) is used to align the backside
of the bottom wafer to the front side of the top in silicon fusion
bonding mode. It accomplishes this by using a CCD camera, which screen
grabs, or stores an image of the wafer PRIOR to putting your second wafer
in. The microscope is then locked into place while your second wafer is loaded. The second wafer must have backside
alignment marks or etched windows. The
second wafer is then
viewed through the quartz chuck by the bottom microscope and alignment
is done by moving the WAFER ONLY.
Both the mask's stored
image and the
real time wafer image is viewed on the TV monitor.
(1)
Verify machine idle mode and start up machine as
previously described.
(2)
Select desired bonding program and parameter settings as described above.
Note: This
step is very important and
should be done before loading your wafers.
(3)
Load first wafer as previously described.
(4)
Press "BSA/IR" illumination switch (image can be
seen on monitor).
Note: Top
microscope is never used in BA6 mode.
(5)
Activate bottom microscope movement controls by pressing "BSA Microscope" pad (Key illuminates). The X-Y keys and
"Fast" keys may now be used to move bottom microscope for scanning
the wafer.
(6)
There are 3 keypads "Left, Both and Right" which
determine mode of movement; "Left" -for left
objective movement, "Both" - for both objective movement
etc. Select desired mode
first before using X-Y arrow
keys to move bottom microscope.
(7)
Find the alignment marks on the wafer.
(8)
Press "Top/Bottom"
key to activate wafer focus
(Key should illuminate) if it is not already on.
(9)
Set the 3-position
field switch to
desired value (Left = left objective,
center = split field, right = right objective). Split field mode
is the recommended mode.
(10)
Adjust "Upper Substrate" left and right focus
knobs to get a sharp image on
monitor.
(11)
Adjust left and right illumination knobs to adjust lighting.
(12)
Bottom microscope
position may be
read out on
LCD, Xl = left objective x position, Xr = right objective x position, Yl
= left objective Y position
etc. Rotation is accomplished by moving one
objective relative to the other.
(13)
Once you have moved to and focused your alignment marks press
"Grab image" to capture image.
Note: This
must be done every time you load a new wafer.
The mask and microscope are now locked
down and may not be moved. To cancel "Grab Image" and restart, press
"Grab Image" again, make your adjustment and press "Grab
Image" a third time.
(14)
Load second wafer as described in the previous section.
(15)
Once the second wafer is loaded "Top/Bottom" key
should be in bottom mode (Light
NOT lit). If light is on, press key.
Note: If
you are using the anodic bonding program
then you will grab image now and not in the previous steps. At this
stage you would:
(1)
Select "Top/Bottom" key so that is lit i.e.
top substrate is selected.
(2)
Move BSA microscope objectives
and find alignment marks on your top (Si) wafer (looking through the glass
wafer) as described above. Grab
image of Si wafer alignment marks. Upon completion of
this step, the objectives of the BSA microscope are automatically focused
to the plane of the glass wafer.
(16)
Rotate "Lower substrate" focus and illumination knobs. (Use
both left and right knobs if you are in split field or either knob for
the appropriate single objective.)
(17)
All movement now is done by moving the wafer, using wafer X,
Y and R knobs. If too much
resistance is felt during wafer movement, or alignment gap needs to be changed for any
reason, unload and change program parameter and load again. Align
appropriate alignment marks on the
bottom wafer to alignment
marks on captured top wafer
image. Verify appropriate program
and alignment gap
are selected, if not you will have to unload, correct program and load
again.
(18)
For silicon fusion pre-bonding applications you will now press
"Pre-bond". The wafers will be pressed together with full
vacuum and the lowered down as a stack
to the slide. For
anodic bonding or fusion bonding involving unload by
fixture jump to step (20).
(19)
Pull substrate slide out and unload wafer stack and press
"Enter".
(20)
For anodic bonding or fusion bonding with unload by fixture,
press "Perform Clamping". The 2 wafers will be
securely clamped in the transport fixture.
(21)
Unload fixture and confirm with enter.
7.0 Machine Shutdown
When you are finished bonding all of your substrates:
(1)
Remove your last substrate by sliding wafer tray straight out and removing wafer stack. If unloading
fixture, confirm with enter.
(2)
Push tray all the way into the BA6.
(3)
Press flashing "Enter"
(4)
Turn the machine off.
(5)
Remove the bond adapter frame and
put it back in its place below the machine.
(6)
Put the mask adapter frame back on the stage.