Chapter 4.03
1.0
Title
ASML DUV Stepper Model 5500/90
2.0
Purpose
The ASML 5500/90 model is a fully automated step and repeat
camera (stepper), capable of resolving sub-micron features sizes, as small as
0.35 µm in a production environment (vendor specification). The stepper can be
pushed beyond this limit with a good focus and exposure set up catered for a
specific layer. This tool utilizes a Cymer 5600 model laser for its 248 nm
wavelength Excimer laser light source (KrF). Therefore, it is a deep UV (DUV)
stepper.
3.0
Scope
This document outlines necessary information for the operation of ASML
5500/90 DUV stepper located in the GL4. Standard processing, as well as
Mix&Match mode applications, are outlined in this manual.
4.0
Applicable
Documents
4.1 SVG 8800 coat and developer tracks, Chapter 4.01
of the lab manual
4.2
ASML mask generation, Chapter 3.1 –
Appendix C of the lab manual
4.3
ASML mask specification in GCA pattern
generator, Chapter
3.3 – Appendix II of the lab manual
4.4
ASML (vendor) manuals are available in the
Microlab office - Hard copy
4.5 Cymer laser manual posted at
https://microlab.berkeley.edu/staff/e-manual/emanuals.html
4.6 Cymer laser initialization procedure posted
at https://microlab.berkeley.edu/staff (accessible by staff, only)
5.0
Definitions &
Process Terminology
5.1
ASML Reticle: 6” × 6” quartz
plate (mask) at specific thickness (0.25 or 0.15 or 0.12 inches).
5.2
Flash Field: Exposed area
(field) at each exposure step (same for all layers in a particular job).
5.3
Stepper Job: A job or recipe
that defines the flash field size, and stepping pattern for stepper.
5.4
DUV Resist: A photosensitive
material sensitive to DUV light (λ = 248 nm or 193 nm or 157 nm). The
Cymer laser used in our 5500/90 ASML stepper generates light at 248 nm
wavelength.
5.5
E0 (E-zero or clear
energy): The minimum exposure energy needed to clear the resist pattern.
5.6
SMIF Pod: Environmentally
enclosed box used to load and unload reticles onto the stepper.
5.7
Asyst Loader Unit (ALU): This is
a reticle loading station that can automatically load the reticles into a SMIF
pods.
5.8
Advanced Reticle Management System (ARMS): Provides a means
of automatically identifying, loading/retrieving reticles from the SMIF pod, as
well as placing them onto the ASML reticle table.
5.9
Reticle Table: A delicate table
part of the stepper, where a selected reticle is loaded, aligned, and clamped
down, before wafer alignment/exposure steps can take place.
5.10 Reticle
Gripper: This is a fork like apparatus used by the machine to
automatically grab/transfer reticles back and forth between SMIF pod and the
ASML reticle table.
5.11
5.12 Wafer
Stage: This is the unit that moves the wafer around during alignment and
exposure with extreme positioning accuracy and stability.
5.13 P-
Chuck: Pre-alignment chuck, where wafer gets centered and aligned for
next step (E-chuck).
5.14 E-Chuck: Exposure chuck
(E-chuck) is a part of the wafer stage that will receive and vacuum down the
wafer for alignment and exposure steps.
5.15 PM
Mark: A diffraction grating (4 quadrant of parallel line and spaces)
used for accurately aligning the wafer to reticle (mask). See Figure
1 - M1 Marks.
5.16 Pellicle: A thin
transparent membrane that covers the patterned area of the reticle (mask). This
membrane is pulled over a secure frame, anchored to the chrome side of the mask
at a distance equal to the height of the frame (~ 0.25"). Pellicles
provide good protection against particle/s that would otherwise come into
direct contact with the patterned area of the mask/s. Keeping particles some
distance away (defocused) from the pattern will prevent them from printing as
defects or part of the pattern during the lithography step/s. Adding a pellicle to a mask however creates
reticle handling issues/challenges, as it can easily get damaged and in turn
causes other types of problems. Do not use pellicles, unless you need an
absolute (100%) protection against defects printing in your patterned area of
the mask (memory cells or dense arrays, so on).
6.0
Safety
6.1
Illumination beam coming into the ASML
5500/90 stepper is projected through its lens into the wafer stage (exposure
chuck). This is a very bright laser beam comprised of intense UV/DUV light,
much of which is invisible to the eye. Avoid exposure to this beam at the laser
source, beam guide or in the machine enclosure. Do not defeat any of the
interlocks with the light source on.
6.2
The stepper performs various tasks such as
reticle and stage alignment with a number of low power laser beams. This
includes wafer stage helium neon (HeNe) laser (visible, class 2 633 nm),
alignment HeNe laser (visible class 3b 633 nm), and level sensor GaAlAs laser
diode (not visible class 3b 820 nm). Radiation from these beams can cause eye
and/or skin damage. Avoid direct exposure to these beams.
6.3
Many components in the electronic cabinets
use 220 V AC power, which constitutes a serious hazard. Do not open the
electronics cabinets.
6.4
The stepper has moving parts that are well
enclosed, never the less make sure your hands are off the moving parts, specifically
cassette elevators. Do not leave obstacles along the path of the moving parts
(i.e. broken wafer on the wafer stage).
6.5
Do not place anything other than reticle
SMIF pod on stepper’s reticle loader compartment and other areas identified
with warning signs. Reticle loader compartment is the area to the right of the
operator console (top of the compartment, flat area).
<<<
DO NOT
PLACE ANYTHING ON TOP OF
THE RETICLE LOADER
UNIT! >>>
<< MAKE
SURE CORRECT SIZE AND SHAPE RETICLES (MASKS) ARE USED IN THIS TOOL! >>
6.6
Pay attention to warning signs
posted on different parts of the ASML stepper; beam guide, Cymer laser, reticle
loader and wafer loaders.
Absolutely, do not wipe the reticle stage, the
exposure chuck or the reticle table with regular wipe. Particles can travel
onto the critical parts of the exposure chuck and reticle loader assembly,
hence, greatly degrades the performance of the machine. These parts are very
expensive and can easily be damaged by improper cleaning. Authorized personnel
(ASML representative and trained staff) are the only people allowed to perform
exposure chuck clean up. Notify staff, if there are any problems.
7.0
Statistical/Process
Data
7.0
Process logbook at the station.
7.1
Problem and comment section under
equipment section of the wand.
7.2
Enable message for ASML stepper.
7.3
Process monitoring website (ASML clear
energy): http://microlab2.eecs.berkeley.edu/ProcessMonitor/index.html
8.0
General System
Overview, Available Recipes, & Equipment Material
8.1 System Descriptions and General Information
The ASML 5500/90 is a 5X reduction camera, capable of
stepping and exposing maximum field size of 21 mm × 21 mm on a 6” wafer. This
tool utilizes special type of targets called PM (pre-alignment) marks to
align/expose all layers defined in a specific stepper job. The first
lithography layer often called zero layer prints these PM marks,
which should then be etched into the substrate at the depth of 1200 Å +
120 Å. PM marks provide diffraction-grating needed by the stepper laser system
to accurately position/align subsequent mask layers on the wafers. There are
various styles of PM marks available for different applications. We only use
one type of marks in our facility dictated by our current stepper hardware set
up/capability.
The ASML machine is comprised of the following main units:
8.1.1
Operator Console: This is a unit
that executes the operator commands (includes key board/track ball).
8.1.2
Exposure Unit: This is the unit
that controls the exposure time for a desired dose energy.
8.1.3
Wafer Transport System: This unit
transfers wafers from wafer loader station to pre-align and then over to
exposure chuck, and finally out and back to wafer receiver (exit) station.
8.1.4
Electronic Cabinet: This cabinet
controls the power, as well as various stepper functions.
8.1.5
Temperature Control Unit Cabinet (TCU): This unit
provides controlled temperature cooling water/air to the lens assembly.
8.1.6
Air Conditioning Cabinet (AIRCO): This unit
provides controlled temperature/ conditioned clean air to stage and lamp
compartments.
8.1.7
Excimer Laser: A Cymer 5600
model laser is currently used on our stepper, which utilizes KrF medium (gas)
to generate excimer laser light at λ = 248 nm for wafer exposure (12 mj
max. pulse energy).
8.1.8
Beam Delivery System: This system
comprised of beam expander, some pipes, and mirrors that directs the laser
light into the ASML exposure unit.
8.2
ASML Jobs (Recipes)
The ASML is a very capable and robust machine, however a
reasonable level of training is required to be able to manipulate the machine
and/or perform special application task/s, therefore staff help may be needed
on job set up and/or special application projects. This stepper can be used in
a Mix&Match mode, sharing process layers with other steppers, specifically
GCAWS6 stepper (6" I-line stepper) in the Microlab. This requires special
jobs and a few minor details discussed later in this chapter. Other special
application cases may include combining different layers onto one reticle to
save on the mask fabrication cost (4 field mask), and/or exposing different die
sizes on the same wafer (multiple jobs required). Process staff can help you
with special application requests. However, there are three different standard
die size stepper jobs available for general use as per follows.
Standard Jobs
8.2.1
Members can use one of the
general purpose (predefined) stepper jobs listed in Table 1 to process their
run.
Note: Standard jobs are designed for one layer per
reticle only. Therefore, if you need to place multiple layers onto the same
reticle, then multi-field version of the stepper job is needed.
8.2.2
Make sure your layout can fit inside the
area defined by the standard job/s (die size).
8.2.3
Center your design layout in your mask layout
using the ASML_1field template currently available under the asml
directory in mercury4.
(/home/mercury4/cad/asml/ASML_1field.gds).
8.2.4
Your design should be five times larger on
your mask than your intended field size (die) at the wafer level. This is
because our ASML 5500/90 model is a 5X reduction camera, which can accurately
project your mask image onto the wafer: i.e., a die size of 10 mm x 10 mm at
the wafer level, therefore, consumes an area of 50 mm × 50 mm on your mask
layout (5cm x 5cm).
8.2.5
Standard jobs for different die sizes are
available in the ASML standard_jobs directory.
|
Stepper Job |
Field size (die size on
wafers) |
Number of Available
Layers |
|
SMALL_FIELD_5 ×
5 |
5 mm × 5 mm |
20 |
|
MID_FIELD_10×
10 |
10 mm × 10 mm |
20 |
|
MAX_FIELD_21 ×
21 |
21 mm × 21 mm |
20 |
Table 1 -
Standard (Predefined) Stepper Jobs Available for General Use
Multiple field Jobs (Typically 4 Fields or 4 lithography layers on
the same reticle)
Most members use multiple field masks, typically
4-filed mask/s that combines layout designs from different lithography layers
onto the same mask to save on the mask fabrication cost. Such mask/s (reticles)
can accommodate up to ~ 1 cm2 die size at the wafers level for 4
lithography layers/mask. This can be expanded up to 9 lithography layers on one
mask, at the cost of increased stepper job complexity, and reduced die size
(Not recommended).
8.2.6
Special job needs to be defined by staff
for the multi-field jobs, based on the location of each layer on the mask, and
the die size. This can be copied/modified from other existing jobs or simply
started from scratch, as per your specification. Contact staff for multi-filed
job set up.
8.2.7
A multi-field layout designs can be placed
on the asml_fiducials template, however, 4field version of this template
exists/available under the asml directory in mercury4: /home/mercury4/cad/asml/ASML_4field.gds
8.2.8
It is highly recommended that your layout
quadrants (4Q) are placed at X&Y = |27.34| mm with respect to the center of
the mask or ASML_4field.gds template. X and Y coordinate signs depend on which
quadrant is utilized for a particular layer. Try not to exceed 10.06 mm x 10.06
mm die size at wafers level (50.8 mm x 50.8 mm mask level) for the 4 field
design. This will make it much easier for staff to standardize the general use
version of 4fileds stepper jobs.
8.2.9
It is highly recommended to use the
Mix&Match version of these jobs explained next, even if you do not plan on
using the GCAWS6 stepper in a Mix&Match mode. This will make the GCAWS6
stepper available to you as a back up, with just an additional initial exposure
step at the Zero Layer.
Mix& Match Jobs
8.2.10 These
are jobs that enable members to use the ASML machine for critical layers,
supplemented by the GCAWS6 for the non-critical layers in the run. A 1field and
4 field version of Mix&Match layout
design templates are available
in the mix_match directory: /home/mercury4/cad/mix_match/
8.2.11 All
mix and match jobs require a half degree rotation in the negative direction (-
0.5º) for their ASML stepper layers, including the zero layer (PM marks). This
will facilitate easy (semi-automatic) target alignment at the GCAWS6 station,
where global targets would otherwise, be very difficult to locate, due to stage
hardware differences between the ASML and GCAWS6 steppers. A special template
is available for printing micro-DEFAS alignment marks used by the GCAWS6
stepper's field by field alignment. These targets can be printed and etched
into the silicon at the same time that the ASML PM marks are printed/etched.
Details of Mix&Match processing is outlined in the Mix&Match manual Chapter 4.05,
and later in this chapter.
8.2.12 Mix&Match
jobs for 1-field and 4-field are available in the MIX_MATCH_JOBS directory, and
are listed in Table 2. However, it is highly recommended that members use the
4-field version, as the GCAWS6 die size is limited to 1.5 cm x 1.5 cm (square),
cannot harvest the full benefit of larger field size available on the ASML
stepper. The 1-field template is currently set for 10.06 cm x 10.06 cm die
size.
|
Stepper Job |
Field size (die size on
wafers) |
Number of Available
Layers |
|
MIX_MATCH_1FIELD |
10.06
mm × 10.06 mm |
16 |
|
MIX_MATCH_4FIELD |
10.06
mm × 10.06 mm |
16 |
Table 2 -
Mix&Match Stepper Jobs
8.3
Incoming Reticle inspection, A MUST
DO!
It is very important not to use poor quality reticles on the ASML
stepper and to make sure any reticle (mask) used on this tool complies with the
manufacturer's specification. This means
that if you are ordering masks from outside vendors, make sure they know about
exact reticle specification for our ASML 500/90 stepper (6"X6"
reticle with straight sides). They should have a copy of ASML mask manual
obtained from the ASML Company. A simplified version of the ASML template with
correct plate size, and various alignment mark position are shown in Figure 1. A certified mask making outfit should have a more
detailed copy of the ASML mask template, along with information about proper
mask plate material (quartz), and required size/thicknesses. Some vendor in the
past had made a poor quality mask that resulted in an extensive damage to our
stepper. Therefore, staff has made available an apparatus (template) that can
be used to check the quality (size and shape) of an incoming reticle. Please,
refer to Appendix 2, and make sure that any reticle made by an outside vendor
can pass the go or no go test on this set up currently available
in the GL4 room, next to the UV scope. An incoming reticle should perfectly fit
into this template before it can be used on the ASML stepper.
8.4
Special Notes
8.4.1 PM Marks: ASML PM marks need to be printed as the first
layer on the ASML stepper. These marks can then be etched in Lam5 etcher with 5001
or 5003 recipe (~20 second) and by adjusting the etch time to create 1200 Å +
120 Å deep trenches (PM mark segments).
http://microlab.berkeley.edu/labmanual/chap7/7.5.html
8.4.1
Mask Type: Six–inch quartz at specific thickness (250 mil,
150 mil and 120 mil) are used for the ASML stepper. The UV light transmission
in other media other than quartz will render them useless for the DUV
application (ASML 5500/90). This includes soda lime glass masks, which is
currently used on other exposure tools in the lab. Quartz plates at 250 mil
(0.25-inch) thickness are strongly recommended for high-end application.
8.4.2
ASML Mask Layout: Chapter 3.3
(Appendix II) of the lab manuals (GCA 3600F Pattern Generator) defines the
specifics of the ASML masks, as well as mask preparation and exposure set up on
the pattern generator.
8.4.3
Reticle Alignment Marks: The ASML uses two asterisk shape marks (clear
chrome area at the edges of the mask) to accurately place/align the mask onto
the reticle table. The PM marks explained earlier are also needed, but for
wafer to reticle alignment. Therefore, mask designers will need to incorporate
both these structures in their mask layout design. The easiest route to take is
to follow the instructions defined in Chapter 3.1 of
the lab manual titled Mask Generation Using CAD Software.
8.4.4
ASML Reticles can only be automatically
loaded onto the stepper. This requires
SMIF pod/s to transfer reticles into the ASML Advanced Reticle Management
System (ARMS). The SMIF pod containing the reticle/s needs to be placed on the
SMIF port at the top of ARMS unit (stage with 3 pins on it), then automatically
loaded into the machine by operator command instructions explained in the operation section of this manual.
8.4.5
There are a few reticles at the ASML
station that can only be used by authorized staff and the ASML field engineers.
These are called ASML qualification reticles, which are kept in a
separate SMIF pod. <<< DO NOT USE THESE RETICLES, UNLESS OTHERWISE,
YOU ARE AUTHORIZED/DIRECTED BY Sia Parsa >>>. These reticles must
be kept in their designated SMIF pod at all times, no exception.
8.4.6
The combi reticle used for the ASML zero
layer (PM marks) is to be kept in its dedicated single SMIF pod. Be careful
when using this reticle, as it is very hard to replace!
8.4.7
Asyst reticle loader unit (ALU) in GL4 can
be used to automatically load reticle/s into SMIF pods. Multi reticle SMIF pods are better suited for
reticles with pellicles on them.
Note: Warning!
Be careful when loading reticle/s with pellicle/s in the single SMIF
pod, the 4 prongs in the single SMIF pod can easily puncture the pellicle. Make
sure you approximately center the reticle in the SMIF pod, before lowering it
onto the bottom surface.
8.4.8
Specially made wipe, NOT our regular
tech-cloth can only be used on the ASML stepper. A General use wipe not
suitable for the ASML should never be used on wafer stage, reticle loader and
other critical parts of the machine.
9.0
Operating
Procedure
The ASML 5500/90 can be logged onto at three different
security levels. These are operator, engineering and maintenance levels
(modes). Qualified users are only allowed to operate the machine in the
operator mode. This is sufficient enough to expose wafers or if absolutely
necessary to perform soft shutdown. Do not operate the tool in maintenance or
engineering modes, as you may inadvertently alter the machine’s set up or
potentially damage this very expensive piece of machinery. Special provision
may be made to allow superusers to use the stepper in engineering mode and/or
generate special application jobs.
There are three standard (predefined) and two Mix&Match jobs
available on this tool. Members can expose various size exposure fields with
these jobs. These jobs contain up to 20 layers that can be used to expose all the
layers lab members will need to fabricate their devices. Members need to first
print zero layer (PM marks for ASML , if needed additional global/micro-DEFAS
targets for the Mix&Match process). These marks will need to get etched
into the substrate at initial stages of the fabrication process, refer to lam5 Chapter 7.5
(recipe 5001) for etching information. All subsequent layers will be aligned to
these marks. Make sure not to switch stepper jobs in the middle of your
process, as the location of the PM marks may be different in the other jobs
(you may not be able to align to your initial marks with a different job).
Process staff can help you with your special application job/s, which may
better suite your chip design.
An image quality test routine is regularly performed by staff to
check compensate for possible machine drift (focus/layer registration). The
Appendix shows specification limits for this test, as per ASML’s
recommendations.
Note: Before
exposing any wafer, make sure that the laser gas fill and the Image quality
control (IQC) test has been completed within the past 72 hours (check the log
book next to the operator console for IQC, and laser light indicator for the
laser status). The IQC test generates correct offsets for focus and stage
position. Cymer laser is currently kept ON at all times (bright light at
the console should be on).
DO
NOT ATTEMPT ASML START UP OR SHUT DOWN PROCEDURE, AS IT WILL TURN THE LASER
OFF.
9.1
Logging Onto the Machine and Loading
a Reticle (Mask)
9.1.1
Enable the ASML stepper on the wand.
9.1.2
Type in a user name and password at the
operator console. User name and password for the operator mode logging are OPR
and OPERATOR, respectively.
9.2
Reticle Load/ Unload Procedure
There are two
types of SMIF pods available for loading reticles. Please use the single SMIF
pod, unless you have reticles with pellicles on them, in which case you can
utilize the general purpose multi-slot SMIF pods for your reticles. Be careful
not to damage the thin pellicle layers.
Important Note: NEVER LOAD AN OVERSIZED RETICLE INTO THE
STEPPER!!
Make
sure to check the shape and size of any new reticle, as per instructions noted
in Section 8.3 and the Appendix.
9.2.1
Log onto the ASML (operator mode, see Section 9.1)
9.2.2
Load your reticle/s in the SMIF pod at the
Asyst Loader Unit (ALU) station located at the entrance of the GL4 room (table
top area). Place the SMIF pod on top of the reticle loader (elevator), and
simultaneously press two buttons on the operator control module to open the box
(use both hands).
9.2.3
Wait for the elevator to unlatch (open)
the SMIF pod, and bring the reticle cassette/holder down to its loading
position. Load your reticle in the cassette (multi-slots) or tray (single tray)
and press the same buttons to latch it back up again.
9.2.4
Grab the SMIF pod by the handle on top,
and carry it over to the stepper with your other hand held below the box (extra
precaution to safeguard against accidental unlatching of the SMIF pod).
9.2.5
Place the SMIF pod on the ASML's SMIF
port. Make sure that the three holes located at the bottom of SMIF pod
match the stud positions on top of the stepper’s SMIF port (reticle loader
stage).
9.2.6
Click on the material handle icon, top
menu bar of the screen (main menu or other screens, which all have this option
available).
9.2.7
Select the exchange reticle box,
option #3 on the Material Handling window. See Figure 2.
9.2.8
This will take you to the next material
handling screen shown on Figure 3.
9.2.9
Click on Read 1 icon. This will prompt
the machine to automatically load and read the reticle IDs available in the
pod. No ID will be displayed for the reticles that are not bar-coded (mostly
the ones made internally).
9.2.10
You need to specify an ID for each unnamed
reticle slot by clicking the specify button under the overwrite
reticle ID’s. Type in the desired name/s and make sure to keep track of
your reticle name in a multi-slot SMIF pod case. Once done, click on the apply
button, then accept the screen (top menu bar). See Figure 3.
9.2.11
You can unload the reticles by clicking on
the unlock button on the same screen, later.
Notes:
Do not leave reticles in the machine after you are done exposing
your layer/s. Make sure you have them back in the SMIF pod, then unloaded and
stored away in your reticle storage box.
Do not leave reticles in
the general use Multi-slot SMIF pod, unless special permission is given
for valid reason by the staff. Use the available single SMIF pods instead.
9.3
Printing Pre-alignment (PM) Marks
(Zero Layer)
9.3.1
Log onto the ASML (operator mode, see Section 9.1)
9.3.2
Minimum of two pre-alignment (PM) marks
must be printed, then etched into the substrate (~1200A deep) for all jobs that
require layer to layer alignment (blind stepping one layer does not require any
marks).
9.3.3
Load the Combi reticle on the
stepper, as per Section 9.1.
9.3.4
Click on batch control button
(option #2) in the main menu, see Figure 4.
9.3.5
Click on define batch button
(option #1) in the batch control window, see Figure 5.
9.3.6
Enter proper values in the parameter
fields as per follows (see Figure 6 for more detail).
9.3.6.1
Enter a batch ID, anything that enable you
to later track down a report for this run, if needed.
9.3.6.2
Click on the job name field and
select your job name (recipe) from the pull down directory/jobs list (i.e.
user-data/job directory/standard jobs/)
9.3.6.3
Click on the desired job, i.e. MAX_FIELD_21 × 21, then click on the
accept button at the top of the menu bar. This will take you back to the
previous window (define batch screen) with the correct job shown in it.
9.3.6.4
Click on layer ID, here make sure
to select PM layer from the pull down
list.
9.3.6.5
Enter C in the control mode
field. This will put the stepper in the cassette mode. You can select wafer
mode W instead, for a single wafer processing.
9.3.6.6
Batch size is predefined at 1, unless
you are going to mix different types of wafers in the same cassette, then you
can change it.
9.3.6.7