Chapter 6.08
(aln)
1.0
Title
AMS Aluminum
Nitride sputtering process
2.0
Purpose
This document has specific operation and process information about
ALN.
3.0
Scope
ALN is dedicated to sputter-deposit high quality PIEZOELECTRIC aluminum
nitride (AlN) films. It is important to
note that this tool should be used primarily to obtain PIEZOELECTRIC films.
Whenever a dielectric coating is needed, it is recommended to use other
sputtering tools such as Novellus. The system is set up for deposition on 4”
wafers. The tool has capability to deposit on 6” wafers, but a hardware change
is required (parts are stored on aln shelf).
The systems uses a dual AC target technology developed at AMS. The use of a dual target technology avoids
disappearing anode problem generally experienced using standard DC or RF
sputtering tools.
The system consists of a:
►
Cassette module where the wafers are
loaded and transferred into the process module by an automatic transfer system.
►
Process module where the actual AlN
deposition occur. DC and AC power supplies and switches are located underneath
the process module.
►
PC unit running AMS software for tool
control. RF matching power supplies and turbo pump controller are installed
underneath the PC unit. Communications between the tool and the PC unit is
performed through Ethernet connection. The control unit can be accessed
remotely by AMS to provide support.
The two modules are separated by a gate valve. Each module has its
own rough and turbo pumps, which can be controlled separately.
N2 purifier is installed so that 99.9999% pure nitrogen
can be supplied to the system.
4.0
Applicable
Documents
4.1
Vendor Manuals: Refer to hardcopy stored in the Microlab
lobby
4.2
Vendor Website: www.tegal.com/
4.3 Vendor: Murali Narasimhan
51
Phone: 408-383-5700
Cell: 408-460-5793
Fax: 408-432-6330
mnarahimhan at tegal.com
5.0 Definitions and Process Terminology
5.0
Process
Chamber: contains two
99.9999% pure Al targets and shields.
Wafers are held facing down.
Target should be purchased at MRC, a Division of Praxair Surface
Technologies, Inc. (CUSTOMER SERVICE DEPT, 542 Route 303,
5.1
Cassette or
Transfer Module: contains 25
slots cassette where wafers are loaded and an automatic transfer arm system.
5.2
Gate Valve: separates process chamber from cassette
module.
5.3
PC Unit: has AMS software installed in order to control
tool operation. Software interface is very user-friendly and works like any
Microsoft application.
6.0
Safety
6.1
Intense light will be emitted from the
plasma.
6.2
Use new gloves when you work within the
chamber, or when handling parts entering
the chamber.
6.3
Make sure the gate valve is closed anytime
you are venting the cassette module.
7.0
Statistical/Process
Data
7.1
Piezoelectric AlN films have been
deposited on Si and Pt on LSN substrates.
Power: 7kW
Flow rate: N2 ~42 sccm Ar ~ 10
sccm
Dep. Rate: ~ 700 Ĺ/min
Rocking curves: ~ 1.3 FWHM on both
substrates
8.0 Available Process, Gases, Process Notes
Available
Processes
8.0
Exclusively
high-quality PIEZOELECTRIC AlN films on patterned substrates or substrates
having resistivity above 10Ω/cm. In case a deposition on un-patterned
substrates or having resistivity below 10Ω/cm a hardware change is needed
8.1
Available
Recipes
8.1.1
1-3 µm AlN on
Pt+LSN substrates (same recipe can be used for Moly electrodes or any other
high melting temperature pattern metal)
8.1.1
1-3 µm AlN on Si
8.1.2
20-100 nm AlN on
Si, Pt+LSN and SiO2 substrates
8.1.3
Burn-in process:
performed by staff anytime process chamber is vented.
Please, remember that for any deposition
of AlN a dummy wafer is required and used to deposit Al and poison the
target. Remember that no more than 5 µm
of Al should be deposited on each side of the dummy wafer. Replace the dummy wafers anytime you deposit
more than 5um per side and strip them at sink 8 (aluminum bath).
Available Gases
8.2
99.9999 % pure N2 and A
Process Notes
8.3
TMAH, commonly
found in most developers, has been found to attack aluminum and aluminum
nitride. This can occur even at low concentrations. Shipley’s Microposit CD-30 Developer may be used with aluminum
nitride processes. This specific developer will not attack aluminum nitride.
8.4
Material
Restrictions: Si, SiGe,
poly-Ge, SiO2, Pt, and silicon nitride (low stress of stoichiometric) are the
only materials currently allowed
in ALN. Processing other materials requires the express permission of staff.
Photoresist is NEVER allowed inside the chamber. Other substrates
such as pure quartz, sapphire, or silicon carbide will be considered but
must be reviewed with staff before processing. Pyrex or any other
non-pure quartz substrates are NEVER allowed inside the chamber. Other metal
contacts such as Mo and Al will be considered but must be reviewed with staff
before processing.
9.0
Equipment
Operation
9.1
Enable
equipment.
9.2
Verify that tool
software is on and properly working (no interlocks enabled). If not or in case
of communication errors, click first on red icon (stops AMS server) and then on
green icon (start AMS). Finally click on AMS Client and enter the AMS software. You might still have to clear interlock
problems. You can do that in the PM1 unit screen.
9.3
Check base
pressure in the process and cassette modules (pressure should read ~ 1E-7 Torr
unless recently vented). Verify that gate valve is closed (both on computer
screen and by checking the gate valve itself).
Vent cassette module. Load wafers (make sure no particles are on the
wafer and that the wafer is facing down); wafers should be all aligned with the
major flat facing the outside of the cassette. Load cassette making sure that edge
of cassette is touching the two setscrews on the elevator and wafers are pushed
all the way inside the cassette. A misalignment in the cassette will cause
wafer-handling problems and ultimately damage your wafer and transfer arm.
9.4
Pump cassette
module.
9.5
Go to PM1 and
edit time in the recipe you want to run. Time is the only parameter you are
allowed to change in order to change film thickness. Change only the time
during which the actual deposition is happening (generally step 10 and 11 of
the recipe). After consulting with superusers and process staff you might
change gas flow rate in order to control film stress.
9.6
Return to unit
view and set up wafer flow and process sequence. The flow sets the recipe that
is executed on each wafer. The sequence set the flow that is executed for each
wafer in the cassette.
9.7
Make sure the
base pressure in the cassette module is below 5E-6 Torr. If not, do not start
process and report a fault.
9.8
Start process by
clicking on start process in the main unit view. A wizard guides you through
the steps needed to start the process. Select the sequence name, the wafer you
want to process (can click and unclick the desired wafers) and verify the
correct sequence. Before starting the
sequence (by clicking finish), make sure that the selection “vent when process
is done” is not selected.
9.9
Watch first
wafers going in the process chamber and monitor deposition to make sure that no
faults occurred. You can leave and return when the deposition is done,
otherwise report a fault on the wand.
9.10
When process is
done a large green icon pops up on the screen acknowledging the successful
completion of the process. Close the icon and vent the cassette module (make
sure that the gate valve is closed).
9.11
Take wafers out
of the cassette and pumpdown system.
10.0
Troubleshooting
10.1
In case a
temperature or communication interlock is on, make sure that no problems
occurred to the tool and reset interlock in the PM1 screen
10.2
In case the
water flow, vacuum or cover interlocks are on, report promptly on the
wand. If the tool is running without
water the pumps will be seriously damaged. If a vacuum interlock is on the main
chamber was brought to atmosphere a burn-in process is needed.
10.3
In case you have
an ”AC or DC power supply threshold exceeded” error, do not attempt to proceed
further. Report problem on the wand.
Be sure to know…
1. Which
are the most important components of the tool
2. What
kind of wafer substrates you are allowed to run
3. What
is the limitation on the wafer resistivity and what kind of hardware
implication it has
4. Venting
operation
5. Wafer
Loading
6. Interlocks
and troubleshooting
7. Allowed
recipes and recipe changes
8. Sequence,
flow, recipe structure
9. Gas
flow change
10. Starting
procedure