Chapter 5.33
Rapid Thermal Annealing
With AG Heatpulse 610 RTA
System (MOS Clean)
(heatpulse3)
Heatpulse3 is a MOS clean tool with a designated chamber (Device) for activation anneal processes in the VLSI area. As a rule, no metalized wafers or non-MOS clean wafers are permitted in this chamber. Also no wafers with photoresist should enter this or any other RTA system in the lab.
This
manual chapter covers the general description of Heatpulse3 RTA system,
operation procedure, available processes, recipe set up/programming and some
trouble shooting guidelines at the end.
5.1
QDR - Quick dump rinse (DI water)
5.2
SRD - Spin rinse dry (DI water and N2 purge)
5.3
RTA - Rapid Thermal annealing, high temperature short time
anneal
6.1
In
the event that user smells ammonia (NH3) in the vicinity of
Heatpulse3, it is most likely coming from the tool. The labmember should
immediately turn the gas flow knob to off position (gas control panel on the
wall behind the chamber), notify the maintenance staff during business hours,
and report the problem on wand.
6.2
Do
not operate the tool at temperatures above 1100oC. The maximum
process time is 3 minutes.
6.3
Do
not touch chamber wall or dummy/process wafers that have just been unloaded
from the chamber, as they will be at elevated temperatures. The standby
temperature is at around 200oC; hence dummy wafers are hot and can
burn you.
6.4
Do
not use the system if chamber wall temperature is higher than process equipment
cooling water set point (Max. ~20oC). Cooling water system will have
to be checked by staff before system can be used.
6.5
Do
not use Heatpulse3 when another user is operating Heatpulse4 since the two RTA
systems share the same common gas distribution system. If you are using a gas other than N2,
make sure that the Heatpulse4 knob is off and the Heatpulse3 knob is on
(located above the gas flow knobs).
N/A
8.0 Available Processes, Gases,
Process Notes
Important
Note: Heatpulse chambers may be replaced or cleaned in HF from time to time.
This changes the light transmission characteristics of the port used by the
pyrometer to control process temperature. Members will need to perform their
own calibration procedure to determine the correct offset needed for their
critical runs, as per explained in Appendix -1.
8.1
Available Processes
8.1.1
Heatpulse3
uses one dedicated chamber (device) assigned to MOS clean activation anneal
processes. Additional chambers may be available in heatpulse3, as a back up to
other systems (Heatpulse2 or Heatpulse4) upon staff approval.
8.1.2
No
silicidation process is allowed in Heatpulse3.
8.1.3
Silicide
processing should be performed in heatpulse4.
8.2
Pre- RTA Wafer Cleaning
Wafers need to receive
proper cleaning before they can enter the Heatpulse3 system, as following:
8.2.1
New
out of the box Si, SOI and 100% quartz wafers
need to receive sink6 clean.
8.2.2
MOS clean wafers need to receive sink6 clean.
8.2.3
Non-MOS clean wafers - NOT ALLOWED.
8.2.4
Metal wafers (wafers with
metal layers on them) - NOT ALLOWED
8.2.5
NO Photoresist - NOT ALLOWED.
8.3
Maximum Operating Temperature (and other related precautions)
8.3.1
Annealing
at temperatures up to 1100oC from 1 sec to 180 sec (3 minutes) are
allowed in Heatpulse3 system. Contact staff for suggestions and updates, if
help with high temperature anneal processing is needed.
8.3.2
Check and make sure proper cooling of the chamber
has occurred, before starting to anneal your next wafer by touching the side panels on the Heatpulse3 machine. Make
sure it is always around room temperature before starting the next run. Cool
down time is approximately 5 minutes.
8.4
Process Gases Available
8.4.1
These
gases are available on Heatpulse3: N2,
NH3, O2, Ar, and N2/H2.
8.4.2
Ammonia
can be used only with superuser and staff permission/training.
Important Note: For critical processes, members need to perform their own temperature calibration procedure, and determine the correct temperature offset, as per explained in Appendix -1.
9.1
Loading Your Wafers
9.1.1
Make
sure dedicated chamber and paddle are installed for your specific application.
9.1.2
Clean
your wafers in the appropriate sink/s prior to RTA step, as per instructions
outlined in Section 8.2 of the process notes section, above.
9.1.3
Enable
equipment on WAND.
9.1.4
Make
sure the system is powered ON and the correct chamber is labeled on the tool
"device" for MOS activation anneal process.
9.1.5
Standby
temperature (indicator on the upper left corner) should be in the neighborhood
of 20.0oC (actual 200oC). The display is offset from the
actual reading by a decimal point, i.e. 20.0oC actually means 200oC.
9.1.6
Make
sure PC is running and is on main menu.
9.1.7
It
is recommended that users use a dedicated pair of clean Teflon tweezers when
loading/unloading wafers in Heatpulse3. It is advised to use 2 Teflon tweezers
so not to drop the wafers.
DO
NOT USE METAL TWEEZERS and DO NOT USE TWEEZERS BELONGING TO HEATPULSE4 FOR THIS
TOOL!
9.1.8
Turn
the knob to the left of the door to show approximately 20 mm of N2
gas. This will purge the chamber while
you load your wafers.
9.1.9
It
is recommended that you run at least 2 dummy runs to test the recipe
stabilization.
9.1.10
Carefully
open the chamber door by lowering the lever.
9.1.11
Pull
lever towards you to bring forward the wafer tray. There is always a dummy
wafer in the chamber. There are three prongs that are used to support the wafer
in the chamber. Carefully remove the dummy wafer and place the process wafer
over the 3 prongs and return the door to the closed position. Users should
minimize the time that the door is kept open.
Be sure not to touch the thermocouple on the quartz holder, if TC is
available in the tool at the time of your processing (please note, most
processes rely on pyrometer).
9.1.12
Be
careful not to touch the quartz holder while loading your wafer. Anything that
touches the quartz may melt and contaminate the chamber. Wafer orientation does
not matter in the chamber.
9.1.13
Choose
desired gas on the gas control panel on the wall behind the chamber. Nitrogen
(N2) is the default gas, but oxygen and Argon are also available. NH3
is available only with permission from the superuser. Turn gas flow knob on.
9.1.14
Let
system N2 purge for at least 3 minutes (to lower background oxygen levels).
9.2
Creating and Running Recipes
9.2.1
Press
the "Process for Engineer"
button on the Main Menu.
9.2.2
Select
the recipe to be edited from the Recipe Files list
9.2.3
Press
Recipe Edit to go to the Recipe Edit
Screen where recipes can be modified.
9.2.4
Users
can create new recipes by hitting the Recipe
New or F7 button. In case the software would ask to save in the old or the
new format, make sure to select the old format to avoid compatibility issues.
9.2.5
Use
the up, down arrows or the mouse to select the desired step. Begin with step 1 to define the recipe step
by step. Commands can be seen on the
bottom of the screen for further clarification.
9.2.6
Move
to the Step Function column. Choose
between Ramp (R), Steady (S), Delay (D) and Finish (F) functions. Recipe
editing is generally explained to the user during qualification. Please contact
a superuser before adding new recipes. Make sure to apply the temperature
offset for each temperature setting in the recipe.
9.2.6.1
Ramp (R): The ramp step occurs in the cycle when the
temperature rises or falls from one temperature to another temperature in a
given time. Ramp rates should not exceed 50oC/sec as damage to the
tool or to the wafer might occur.
9.2.6.2
Steady (S): The steady step occurs in the cycle when the
temperature is kept at a constant/steady-state temperature for a specified
time.
9.2.6.3
Delay (D): The delay step occurs during the cycle when the
lamps in the chamber are off (no heating occurs) and the purge gas is flowing
through the system. This step is most commonly used at the beginning or the end
of the cycle. The initial delay purges any gases from the process chamber
before heating the wafer. The final delay cools down the chamber before the
user can remove the wafer. The recipe always has to start with this step.
9.2.6.4
Intensity (Intn): The constant intensity step can be used instead of
the steady step. This indicates a
constant intensity of the lamp (between 0 and 80%) instead of a constant
temperature.
9.2.6.5
Finish (F): The fourth step is the last step of the process. The
user can begin purging the process gases.
9.2.7
In
each of the steps, the user can specify the Time (s) and Temperature (oC)
or Intensity (%) columns. A Steady
Intensity Factor can also be specified (between 0.01and 20) to compensate
for undershooting or overshooting during temperature ramp. A larger Steady
Intensity Factor will cause a larger overshoot and a smaller one will cause
an undershoot. In annealing above 450oC,
you should write a two-step process. The first should ramp to 450oC
and stay in the delay step for 30 s; then ramp to the desired temperature. The
first step is applied to avoid thermal shock to the wafer.
9.2.8
Members
can select pyrometer or thermocouple mode of controlling the temperature in the
recipe. In case the pyrometer is used, make sure to have 77.04 set up for the
emissivity. DO NOT USE non-silicon wafers with the pyrometer.
9.2.9
Click
the Recipe Validate or F10 button to check if the recipe is
okay. Press OK to validate the recipe.
9.2.10
Press
Save to save the validated recipe
9.2.11
Press
Exit to go to the Process Menu.
9.2.12
Press
Start Process to run your
process. The Recipe Graph window should
pop up, displaying the ideal and actual temperatures of your run.
9.3
Unloading Wafers
9.3.1
Turn off all the process gases except N2 by
turning the gas knob position off. Turn the N2 gas back on, if
necessary. Only one gas knob can be open a time.
9.3.2
Wait until the chamber cools down to at least 200oC
before unloading the sample.
9.3.3
Return the dummy wafer on the prongs and close the
door
9.3.4
Exit out of the software to the Main Menu.
9.3.5
Return the heatpulse3 and heatpulse4 valves so that
they both have N2 flowing in their chambers.
9.3.6
Disable the equipment on WAND.
9.4
Operational Instructions for Ammonia Process in Heatpulse3
This process is only allowed during regular business hours (8:00 AM-5:00 PM, Monday -Friday). If ammonia odor is smelled, immediately close the gas valve. Do not attempt to flow flammable gases (NH3, H2/N2) and oxidizing gasses (O2, N2O), simultaneously. Please keep it in mind that excess ammonia flow (> 2 liter/min.), could shut off the gas fuse at the cylinder cabinet, and hence abort other member's processes in Tystar9 and Tystar17.
9.4.1
Check
ammonia source to make sure the gas fuse (red button) is down.
9.4.2
Turn
valve in CV1, to open.
9.4.3
Enable
Heatpulse3 on WAND, check standby temp, chamber wall temp.
9.4.4
Run
your desired recipe once on dummy wafer, just using N2 gas.
9.4.5
Make
sure that external ammonia valve is off, and then open the chamber.
9.4.6
With
clean Teflon tweezers, unload dummy and load wafer, close chamber.
9.4.7
Put
"danger" hang tag on handle of Heatpulse3.
9.4.8
Turn
gas flow knob to 50 mm and let N2 flow for 2 minutes.
9.4.9
Turn
gas flow knob to 20 mm, turn N2 off at external valve, and slowly
turn ammonia on at external valve. If ammonia odor is smelled, close the valve
immediately. Make sure gas flow is still at 20 mm.
9.4.10
Let
ammonia flow for 2 minutes.
9.4.11
Run
recipe.
9.4.12
During
cool down, turn ammonia off at external valve, and N2 on at the
external valve. Turn gas flow knob to 50 mm.
9.4.13
Let
N2 flow for 5 minutes.
9.4.14
Visually
check to make sure that the ammonia external valve is really off, and
gently opening the chamber, by making sure that no smell of ammonia
is present.
9.4.15
Remove
the wafer and replace it with a dummy.
After final wafer, turn off
ammonia at valve in CV1.
9.4.16
Check
and make sure the gas fuse (red button) at ammonia source is still down.
10.0
Troubleshooting Guidelines
10.1
Chamber
wall temperature > 15ºC. Please contact staff for refilling cooling water, after
which the wall temperature should gradually come down to 15ºC.
10.2
Error
messages show up after starting recipe – reboot the PC by pressing RESET on
front.
10.3
PC
turned OFF. Turn
10.4
System
reboot – If a system reboot is necessary, please turn power OFF on the unit,
turn OFF PC, and then restart unit and then restart PC.
11.0
Figures & Schematics
Please refer vendor supplied documentation is kept
near system.
12.0
Appendices
12.1 Temperature Correction by Oxide Growth on
Test Wafers
12.1.1 Reason for Temperature Correction
(Determining the Temperature Offset Needed)
The chamber and the wafer
holder plate in Heatpulse devices may occasionally need cleaning to remove the
accumulated contamination on their surfaces. During this process the
quartz-ware is dipped into a 25:1 HF bath, which reduces the thickness of a
window used by the pyrometer to monitor/control the chamber temperature. A
pyrometer in heatpulse3 is used to control the diffusion/anneal processes at
high temperatures and by looking at the light emitted from the backside of the
wafer in the chamber. This means light transmission characteristics of the port
(thickness of above noted window) can easily impact the temperature measurement,
therefore, members will need to determine the offset needed to arrive at a
correct process temperature (actual) for a new and/or a cleaned up chamber, as
per procedure explained in the following sections.
Members also need to pay
close attention to any film layers deposited on the backside of their wafers,
which can easily impact the emissive pyrometer readings. Such film may need to
be removed before RTA processing. Substrate materials other than silicon
(Germanium, SiC, SiGe) can also impact the pyrometer reading. The emissivity
value needed for silicon substrates (entered in the software) is 77.04
(standard silicon wafers used in the Microlab).
12.1.2 Wafer Preparation for Calibration
(Determining Required Temperature Offset)
Temperature offset is determined
by oxide growth on silicon substrates. The test wafer needs to receive piranha
clean at sink6 for 10 minutes to remove possible organic contamination,
followed by a quick dump rinse (QDR). Next, HF dip the wafer until its surface
dewets, followed by a QDR /N2 gun dry, and a quick move into the
heatpulse3 machine.
12.1.3 Wafers Oxidation and Temperature
Offset Measurement
This process is done by
measuring oxide layer grown on P-type clean wafers and comparing them with known
previous data to determine the temperature offset required by a new or cleaned
up chamber. The cleaning steps and specifically wafer transfer into the chamber
shall be done as quickly as possible to avoid thermal oxide growth.
Heatpulse Recipe Setup
The historical data in the range of 750ºC - 1050ºC
with the smallest intervals of 50ºC are available, which can be used to
determine the correct offset. Follow the
instruction for the recipe set up and operation of heatpulse machine for the
oxidation test. Make sure to have plenty of N2 to purge the chamber
when you introduce the test wafer into
the chamber. Switch to O2 for the oxidation growth process set at 20
sccm.
Use standard recipes available for different
processing temperatures i.e. OX_950.RCP for the 950ºC oxidation process. Set up a new recipe with your desired
oxidation temperature, if an standard recipe for a particular target
temperature is not available. See below 850ºC oxidation recipe as a template to
set up your own recipe, if needed.
|
Step No. |
Step Temp Func |
Time (seconds) |
Temp (ºC) |
Steady Intn Factor |
|
1 2 3 4 5 6 |
Delay Ramp Steady Ramp Steady Ramp |
5 10 30 15 180 30 |
0 450 450 850 850 500 |
1 1 1 1 1 1 |
Table 1 - Standard Recipe Set-Up
There is a suggested warm-up
step to avoid thermal shock to the wafer. This should be set at 450ºC for 30
seconds prior to the oxidation step. Do not exceed the ramp up rate of 50ºC/sec
as it could harm the machine, also could result in sliplines or dislocations on
your wafers. Intensity factors needs to be adjusted to avoid temperature
overshooting or undershooting at a particular step. Usually a value between 1.2
and 1.6 is used at each steady phase to
better control the temperature during the RTA process. The main oxidation step
is set to run for 180 sec, and after this step no ramp-down rate is defined,
simply call up a temperature value for
the machine to cool down to. The wafer should be removed after the chamber
temperature has dropped below 200 °C shown on an external display just to the
left of the chamber door. The number shown on this red display needs to be
multiplied by 10 for the actual reading.
After
running the oxidation recipe (at least two different temperatures), measure the
oxide thickness on the Sopra ellipsometer machine. An oxide-temperature curve
can then be generated with preferably 3 or more data points, consequently
compared with previous graphs to determine the correct temperature offset
needed to process current runs. The curve fitting can be accomplished by trying
out different offset values to force the new curve to match an old curve with a
known offset value. This will result in temperature delta (offset) and a sign
associated with it to accurately process the run by either increasing or
decreasing the temperature entries in the recipe, as per following examples:
I.e.
offset value of -70 ºC(minus 70ºC) for a 850ºC process will require entering 780ºC in the recipe.
I.e.
offset value of +70ºC (plus 70ºC) for a 850ºC process
will require entering 920ºC in the recipe.
Note: It is highly recommended that members run
their own calibration test any time they need to process wafers that need exact
RTA temperature. This is because a small drift in the electronic circuitry
and/or chamber pressure (N2) can change the actual temperature by 30°C - 50°C Therefore, do not solely rely on the offset value
determined earlier for a particular tool post. Calibration data reported after
a chamber clean or chamber change may drift over time.
12.1.4
Thin
Film Measurement (Sopra)
The thickness
of the oxide layers grown for above temperature calibration can precisely be
measured with ellipsometry technique on our Sopra machine. The standard
equipment initialization and measurement should be followed, as in Sopra manual
Chapter 8.32.
a. Show Screen - Wavelength = 380 nm
Analyzer angle =
45º
Incident angle =
75º
Check linearity
and polarization box
Check attenuator1 and attenuator2 box
Click the run button and adjust the
count if necessary to go over 106
.
Microspot usage is not
necessary for this case. The standard polarizer angle of 75° was used at frequency range of 290 nm to 800 nm.
To measure the curve, incremental steps of 20 nm is suggested.
b. Parameter Screen - Check and if necessary enter parameters
(sub-screens), as in Sopra manual.
c. Click measurement on the GESPACQ screen. Click
run on the next screen to start data collection.
d. Oxide
thickness can be determined by using WINNELLI software to analyze the collect
measured values. The first method of data analysis tan(psi) and cos(delta)
should be used for this purpose, which is specially suited for thin film layer
measurements.
12.1.5 Calibration Data (curve fitting as a
final step)
Newly
collected oxide data from the Sopra machine can be plotted alongside previous
(old) data for curve fitting purposes, and ultimately determining the
temperature offset value. Table 2 below, shows historical data in different
shaded color columns with the measured oxide values shown on the right side.
These oxide values corresponding to temperature values entered in the recipe at
the time the test was performed (far left columns in centigrade and their
equivalent Kelvin values in the column just to the right of it). The |ΔT|
values shown on the top left columns for these shaded areas are generated based
on the shift required to move the curves to a correct baseline and overlapping
the old curves in figure for each new or additional data set. These
corresponding temperature values after the shift (true temperatures based on
baseline oxide data) are also shown in the columns just to the left of the
measured thicknesses for each data set (Kelvin) in the shaded areas.
In the cases
discussed above, ΔT required to
move the curves to a baseline position was a positive 80ºC or 120ºC
(added) shift. This means temperature setting that was used in the recipe
produced thicker oxide film than expected baseline curves (each recipe entry in
far left column, clear area). Therefore, the true offset to process the run
needed to have a negative value, as we had overshot by the ΔT, while
running the test wafers for all cases, below.
Therefore, members had to make a -80ºC adjustment to process temperature entered
into the recipe for runs after 9/13/05, and -120ºC for runs performed after 7/7/05.
i.e. for a process that required a 900ºC they would have entered 820ºC,
after 9/13/05.
|
|
|
|
9/13/05 |
|
7/7/05 |
|
3/9/06 |
|
Recipe entered
T [C] |
Recipe
values T [K] |
|ΔT| value of 80ºC T [K] |
Film
Thickness [A] |
|ΔT| value of 120ºC T [K] |
Film
Thickness [A] |
Offset value of + 80ºC T [K] |
Film
Thickness [A] |
|
750 |
1023 |
1103 |