Chapter 7.15
Hfvapor (Idonus HF VPE-100 / 150)
(hfvapor)
1.0
Title
hfvapor -
Idonus HF VPE-100 / 150)
2.0
Purpose
The
HF Vapor Phased Etching apparatus consists of a reaction chamber and a wafer
holder. A heating element is integrated in the wafer holder. It controls the temperature
of the substrate to be etched. Wafer clamping can be achieved in two ways:
Wafers can be clamped mechanically using the clamping ring. The screwing is
done from the backside of the apparatus, which is never in direct contact with
the HF vapor. The three nuts are easy to handle with protection gloves. The
other option is electrostatic clamping. Single chips (larger than 5 x 5 mm2)
as well as wafers can be clamped to the heating element. A large area of the
backside of the wafer is protected from etching. Liquid HF is filled into the
reaction chamber. The reaction chamber is closed with the wafer holder. HF
evaporates at room temperature and the etching process starts spontaneously.
The etch rate is controlled by the wafer temperature that can be adjusted from
35ºC to 60ºC. After processing, the acid can be stored in the reservoir for
reuse in a sealable container. Liquid transfer is simply done by lowering the
reservoir.
3.0
Scope
Included in Section 2.0.
4.0
Applicable Documents
Additional
information is available on http://www.idonus.com/.
5.0
Definitions & Process Terminology
5.1
General
Description
The
VPE apparatus consists of
a container, a wafer holder with
connection cable, a controller
box, and a mechanical
clamping ring.
5.2
Container
The
container is a system composed of a reaction chamber and a reservoir. The reservoir
has the function to store HF acid when the HF VPE apparatus is not in operation and
allows a simple and safe
transfer of the acid in and out of the reaction chamber. The
working principle
of the reservoir and the container is called communicating vessels. When the
reservoir is in high position, (i.e., the reservoir handle is pulled up) the
liquid can flow into the reaction chamber (if the valve is open). If the reservoir
is in low position, (i.e., reservoir handle
is down) the liquid flows from the reaction chamber into the reservoir. The valve is open if the
tap is vertical and closed if the tap is horizontal. The tap can be turned in both
directions and does not
have a stopper. Always cover the HF VPE apparatus with the lid if it is not in operation.
5.3
Wafer Holder
The
wafer holder consists of
a heating plate,
a handle
with connection cable,
a mechanical clamp ring, and an electrostatic chuck. The connecting
cable is waterproof if it is connected to the socket. The standard mechanical
clamp ring is able to clamp 150 mm (6”) wafers. The wafers are held by 6 clips.
Three nuts fix the
wafer mechanically to provide a good thermal contact to the heating plate (use only
minimal torque then tightening these nuts to prevent breaking the clamp’s
threaded studs). The
electrostatic clamping is realized by an optional bipolar electrostatic chuck. The
high voltage to drive the electrostatic chuck is created inside the wafer holder. Flat, conductive
substrates can be clamped by the electrostatic chuck. Due to its design, a wafer as
well as multiple chips can be clamped. The chips have to be placed in order to cross two electrodes. The wafer holder with
electrostatic chuck is waterproof and can be rinsed with water. Do not rinse for
more than 15 minutes.
5.4
Controller Box
The front side consists of main
switch, temperature
controller (see separate manual for the special functions of the temperature
controller), socket
for connection to wafer holder, and switch for electrostatic clamping. Potentiometer can adjust
electrostatic clamping force
Controller box
backside has a
socket
for power supply and a
fuse. The front panel
of the controller box is spray water
resistant. The controller box should not come in contact with any
liquid. Spray water resistant mounting is achieved if the controller box
is integrated
into the workbench. The backside of the front panel has to be sealed to your
workbench.
5.4.1
Operating
the Temperature Controller
The
display shows the process value.
5.4.1.1
Operating Level: The set point SP is input here. On
active set point switching via the logic input, SP 1 or SP 2 appears in the display.
When the ramp function is active, the ramp set point SPr is displayed. With
activated timer function, the timer value t i or the timer start value t i 0 is
shown. The set point is altered dynamically using the i and d keys. The setting
will be accepted automatically after approx. 2 sec.
5.4.1.2
Parameter Level: The set points, the limit value of
the limit comparator, the controller parameters and the ramp slope are
programmed here.
5.4.1.3
Configuration Level: The basic functions of the
controller are set here. In order to make the settings, it is necessary to
change to the configuration level A via the parameter y:0 (parameter level).
5.4.1.4
Timer Level: The current timer value (only when the timer has been
started) and the timer start value are altered here. The parameters at this
level are marked with an underscore in the display.
5.4.1.5
Time-Out: If no operation occurs, the controller returns
automatically to normal display after approx. 30 sec (exception: with timer
functions starting via power ON, the timer value is displayed). If the timer
value is displayed at the operating level, time-out is not active.
6.0
Safety
6.1
General Safety Instructions
6.1.1 Working at the hfvapor
tool should be considered equivalent to working at one of the Microlab sinks. Therefore,
as with all Microlab sink operations, lab members must wear acid resistant
gloves, face shield and acid resistant apron when operating or servicing the
hfvapor tool. Lab members should be especially attentive to residual
HF acid from preceding etching processes, opening the reaction chamber during
operation, condensation
of HF acid on parts of the apparatus or the substrate.
6.1.2 If you encounter a spill
at a sink of an unknown solution, first check the pH. The pH test strips can be
found in plastic dispensers located at sink432C adjacent to hfvapor.
Color charts with reading
instructions are laminated and posted by these dispensers. The pH test
strips are calibrated to read from 0-14 pH. If the spill solution is strongly acidic (or strongly basic),
use a sink deck hose to flush the solution into the sink. If it is near neutral
or you have finished flushing, use a Techni-cloth to wipe and dry the surface.
When finished, rinse the Techni-cloth and dispose of it.
6.1.3 During operation of the apparatus HF acid evaporates at room temperature. Therefore,
risks associated with the tool are associated with HF acid liquid and HF acid
vapor. Exposure to HF acid vapor is minimized by housing the tool in a
ventilated hood enclosure. All reservoir filling and emptying operations should
be performed in this or one of the other exhausted sinks in the old lab to
prevent any exposure to HF acid vapor.
6.1.4 HF burns are particularly hazardous. An
insidious aspect of HF burns is that there may not be any discomfort until long
after exposure. These burns are extremely serious and may result in tissue
damage as fluoride ions diffuse through tissue. If you contact HF, flush the
area well and be sure to work under and around
your fingernails. Under fingernails and cuticles are the main areas
people receive burns, having washed off the HF without washing under their
nails. If washed off within a few minutes of exposure, HF will
do no harm. Remember, HF may not produce any burning sensation
until after it has already done damage. You should have a physician examine all
HF burns.
6.2
First Aid for HF Burns to the Skin
6.2.1
Remove
contaminated clothing.
6.2.2
Flush
with cold water for 15 minutes.
There is safety shower and eyewash immediately behind you when
operating hfvapor. There is also immediate running water available at sink432C
or the black utility sink across the room.
6.2.3
Gently
massage calcium gluconate ointment into skin.
There is a container of this material
in the plastic dispenser mounted on the front of sink 432C.
6.2.4
Report
any HF burns to the office during work hours or call Bob Hamilton at
644-3329.
6.2.5
Seek
medical attention at
6.3
Electrostatic Chuck
Damage and Safety Concerns
6.3.1
When the electrostatic chuck’s isolation layer or the chuck itself is
damaged (cracked or shorted), do not operate the machine, as electrocution may
occur. Turn off the main switch on the
controller box, disconnect the chuck (handler) and report the fault on the
wand.
7.0
Statistical/Process Data
N/A
8.0
Available Process,
Gases, Process Notes
N/A
9.0
Operating Procedure
Etching and filling
or emptying the reservoir must be done by a qualified user. If HF acid leakage is observed execute the
following steps. Execute the steps with extreme care.
·
Empty the container (see
Section 9.3, Emptying Procedure)
·
Rinse the container with
water (see Section 9.4, Cleaning Procedure).
·
Contact our technical support
for assistance and repair.
9.1
Etching Procedure of Oxide
Before you start
working with the apparatus make sure that the safety requirements are
accomplished. Following, the etching procedure for thermal SiO2 is described.
9.1.1
Wear protective clothing,
gloves and glasses
9.1.2
Make sure the reservoir
is filled with HF. If not, ask the responsible person for service (SERVICE
MODE).
9.1.3
Connect the connection
cable of the wafer holder to the socket of the controller box.
9.1.4
Switch the main power
switch of the controller box ON.
9.1.5
Program the temperature
controller to the desired temperature.
To do this press
the P button once and select the desired temperature with the ↑ and ↓
buttons. The selectable temperature range lies between 35 and 60ºC (90ºF to
140ºF). Thermal SiO2 should be etched at temperatures around 40ºC (104ºF).
Decreasing the temperature of the substrate increases the etch rate. If your
etch rate is too slow decrease carefully the temperature.
9.1.6
Wait until the desired
temperature is reached (1-5 min). The temperature of the heating plate is
indicated on the temperature controller.
9.1.7
Place the mechanical
clamping ring in front of you so that the bolts are facing upward.
9.1.8
Place your wafer on the
ring so that the surface to be etched faces down.
9.1.9
Place the wafer holder
over the clamping ring and fit the bolts into the holes of the wafer holder.
9.1.10
Use the three nuts to fix
the clamping ring.
Do not overturn the
plastic screws. Overturning the screws may result in damage of the screws, the
clamping ring or the wafer.
9.1.11
Electrostatic clamping
can be used additionally to the clamping ring or alone. If wafers are clamped
by electrostatic force only a minimal force is required. If a too high force is applied, the removal of
the wafer can become critical due to residual fixed charges present in the
dielectric isolation of the electrostatic chuck. These fixed charges disappear slowly without any
further action.
Note: “DO NOT USE ADHESIVE MATERIAL/TAPES ON THE
E-CHUCK.” Kapton tape and/or other material
should not be used to hold samples/wafer on the chuck. This will damage the E-chuck. For
small sample/s that cannot properly bridge the conductive path on the E-chuck, simply place it/them in kitty corners of the conductive path
where it makes a few loops (sharp turns) confined to small areas.
9.1.12
Place the wafer holder in
front of you so that the electrostatic chuck is facing upward.
9.1.13
Place your wafer or chip
on the electrostatic chuck so that the surface to be etched is facing you.
9.1.14
Switch the power for the
electrostatic chuck to ON position. Adjust the force by turning the
potentiometer.
9.1.15
Make sure your wafer is
fixed.
9.1.16
Place the wafer holder on
the reaction chamber with the wafer facing down.
9.1.17
Lift reservoir handle up.
9.1.18
Turn the security pin to
fix the reservoir in high position.
9.1.19
Open the valve (tap
vertical).
9.1.20
Start your timer. The
etching process starts immediately.
9.1.21
30-40 seconds before the
processing time is finished release the security pin and push down the
reservoir handle to place reservoir in low position. Now the acid flows into
the reservoir.
9.1.22
When the process time is
finished, lift the wafer holder and place it besides the container with the
wafer facing down. The wafer holder may be contaminated with condensed HF. Do
not touch the wafer holder of any other parts that were in contact with the
wafer holder.
9.1.23
Loosen the three nuts.
9.1.24
Lift carefully the wafer
holder from the clamping ring. The wafer may stick to the holder and release
whole you are handling the holder. Usually, the wafer releases within several
seconds from the wafer holder.
9.1.25
Take the wafer off the
clamping ring. Do not touch the wafer. If the SiO2 is etched at too low
temperatures HF may condense on the wafer surface. If any other material is
present on the wafer, HF may diffuse in the material or react with it forming
another dangerous chemical.
9.1.26
Releasing the wafer after
usage of the electrostatic clamping. Place the wafer holder so that the wafer
is facing you and switch OFF the electrostatic clamp.
9.1.27
Take the wafer off the
heating plate. Do not touch the wafer holder; it may be contaminated with HF.
Use soft tweezers, which do not scratch the dielectric layer isolating the
electrodes of the electrostatic chuck! Rinse the tweezers after usage.
9.1.28
Close the valve (tap
horizontal) after the HF acid has flown into the reservoir.
9.1.29
Close the reaction
chamber by placing the lid onto the reaction chamber
9.1.30
Rinse the wafer holder,
clamping ring and bolts with water and dry them after rinsing.
9.1.31
Switch OFF the controller
box.
9.2
Filling Procedure of the Reservoir
SERVICE MODE
operations mainly cover the filling and exchange of the HF acid, the cleaning
and maintenance of the HF VPE apparatus.
9.2.1
Wear protective clothing,
gloves and glasses.
9.2.2
Make sure the reservoir
is empty by lifting the handle into high position and open the valve. Secure
the reservoir using the security pin.
9.2.3
Open the lid. Condensed
HF may be present on the lid. Do not touch the lid or any other surface coming
in contact with the lid. Rinse the eventually contaminated surfaced with water
after filling the reservoir.
9.2.4
If the reaction chamber
is filled with HF acid refer to Emptying
Procedure of the Reservoir. Carefully fill
the HF acid into the reaction chamber. Do not overfill! The HF acid level
should be about 5 mm under the border of the reaction chamber (see following
figure). In case of an overflow, pump the excess acid using a HF resistant
pump. Should any acid drip besides the container, refer to the section.
9.2.5
Put the reservoir into
low position by releasing the pin and pushing down the handle. The acid flows
into the reservoir. If it does not flow move the handle up and down a few
times. If it still does not flow a slight vacuum, applied to the gas exhaust,
helps to fill the reservoir for the first time. E.g. a pipette pump is
sufficient to run this process. Release the vacuum right after the acid starts
flowing.
9.2.6
Close the valve after all
acid has flown into the reservoir (tap in horizontal position).
9.2.7
Close the reaction
chamber with the lid.
9.2.8
Indicate that the reservoir
is filled and ready for use.
9.3
Emptying Procedure of the Reservoir
Emptying of the
reservoir is necessary if the HF acid is used many times or contaminated.
Typically the HF acid can be reused for 10 to 100 etching processes, depending on
the etching duration of the individual etchings. If you want to remove the HF
VPE apparatus from your wet bench you need to have it serviced, the emptying
procedure must be followed by the Cleaning
Procedure described in the next section.
9.3.1
Wear protective clothing,
gloves and glasses.
9.3.2
Lift the handle into high
position and open the valve. Secure the reservoir using the security pin.
9.3.3
Open the lid. Condensed
HF may be present on the lid. Do not touch the lid or any other surface coming
in contact with the lid. Rinse the eventually contaminated surfaced with water
after filling the reservoir.
9.3.4
Use a HF resistant pump
to evacuate the HF acid out of the reaction chamber into your HF waste
container.
9.3.5
Close the valve and cover
the reaction chamber by the lid.
Cleaning the
container is done after emptying the reservoir. The reservoir, all tubing and
reaction chamber can be rinsed with water through the rinsing hose. A
connecting tube is delivered with the HF VPE apparatus. You need to connect the
rinsing hose to your water supply. Use only moderate pressures below 0.5 bar to
rinse the HF VPE apparatus! Higher pressures can harm the apparatus or eject
diluted HF acid in vertical direction and causing HF burns.
9.4.1
Screw connection tube
into hole beside the reaction chamber.
9.4.2
Connect the connection
tube with the rinsing hose on the HF VPE apparatus.
9.4.3
Connect the other side of
the connection tube with your water supply.
9.4.4
Tilt the container in a washbasin
or use your laboratory pump to suck out the water from the reaction chamber
(see following figures).
9.4.5
Rinse the container with
water for at least 30 minutes.
9.5
Cleaning or Replacing the Net
If the net at the
bottom of the reservoir is dirty or broken it has to be taken out for cleaning
or replacement. The net is only fixed in a slot and due to the bigger size of
the net. It can be lifted by taking it with fine tweezers and then bend it.
Note: Remove the net only after Cleaning Procedure of the
container. Rinse net with water until it is clean or if it is broken replace
it. To fit the net in, place a side in the slot and press it in.
10.0
Regular Service and Troubleshooting
Guidelines
10.1
Regular
Service
The following list is an
overview about regular services, which must be executed by a Microlab staff.
10.2
Troubleshooting
If you have any difficulties operating the
device please report to
FAULT. The
list below is should be carried out in SERVICE MODE by a qualified user.
11.0 Figures
& Schematics
N/A
12.0 Appendices
12.1 List of
Abbreviations
HF VPE HF Vapor Phased Etching
SP Set Point
12.2 PID
parameter Values after optimization at 40°C on 3/11/06
|
PID Parameter
|
Settings |
|
sp |