(lam4)
1.0 Title
LAM4 Poly-Silicon
Rainbow Etcher (for 4-inch wafers only)
2.0 Purpose
LAM4 is a fully automated,
single wafer, plasma/RIE etcher for poly-silicon film, silicon nitride film,
and deep bulk silicon etching on 4-inch wafers. It can also etch germanium and
germanium/silicon mixed films.
3.0 Scope
This document provides the following information:
►
General operation
procedures of LAM4.
►
Recipe loading,
editing, and saving to the floppy/hard drive.
►
User level trouble
shooting.
►
Setup and monitor etch
endpoint trace.
4.0 Applicable
Documents
4.1
Rainbow 4420 Operations
and Maintenance Manual, Lam Research Inc. (copy in Office).
4.2
Microlab Online Manual Chapter 7.0
(LAM Etcher Overview).
4.3
Material Safety Data Sheets for O2, Cl2,
HBr, Ar, He, SF6, and CHF3 (copy in Lobby).
5.0 Definitions
& Process Terminology
5.1
Plasma/RIE Etcher: This kind of etcher uses gas radicals
formed in the plasma generated by RF power to etch film on the wafer. The wafer
is placed on the grounded electrode, for the plasma etcher, to reduce radiation
damage on the devices. For RIE etcher the wafer is placed on the powered
electrode that induces ion bombardments on the wafer to increase etch rate and
anisotropy.
5.2
Etch Rate: The thickness of the film etched per unit time, usually in Ε/minute.
5.3
Etch Uniformity: It is defined as (maximum etch rate
minimum etch rate)/(maximum etch rate + minimum etch rate), usually in %.
5.4
Etch Selectivity: The etch rate ratio between two
different films/substrate.
5.5
Etch Anisotropy: The degree of anisotropy is defined by 1
(lateral etch rate/vertical etch rate). A value zero means isotropic etching
and one is perfect anisotropic.
5.6
Endpoint Detection: Lam4 monitors the light emitted by the
etch by-product in the plasma for endpoint detection. When the light intensity
reaches a preset value, the etch process step stops. Usually, the process
continues on an over-etch step to remove the residue materials.
6.0
Safety
Follow the general safety guidelines in the lab as well as the
specific safety rules as per follow:
6.1
RF Power Hazard: LAM4 uses a 13.56MHz, 1250W RF power
generator. Never touch a RF power cord when the RF power is on. Do not look at
the plasma for long period time.
6.2
Chemical Hazard: All gases used by LAM4 are confined in
the gas delivery system and the vacuum chambers. However, if you sense bleach
or other un-usual smell, it indicates there is a leak in the system, or problem
in the ventilation. Stop the etch process and evacuate the area. Inform
Microlab staff immediately
6.3
Pinch Hazard. The wafer cassette elevators may pinch your fingers. Load/unload
with caution.
6.4
It is required that you consult the process staff before creating
a new recipe or modifying old ones.
7.0
Statistical/Process Data
7.1
Microlab web page (coming soon).
7.2
Problem and comment section under equipment section of the wand.
8.0
Available Process, Gases, Process Notes
8.1
LAM4 can only process 4-inch wafers. Use LAM5 for four-inch
wafers.
Available
Processes
8.2
Oxide break through using SF6.
8.3
Poly-silicon etch using Cl2.
8.4
Poly-silicon etch using Cl2./HBr mixture for improved
selectivity over oxide.
8.5
Germanium and Germanium/Silicon alloy etch (under development).
Available Gases
8.6
O2: Not used in the standard recipes. Can be used to improve
selectivity over oxide.
8.7
Cl2: Main etch gases for silicon.
8.8
HBr: Used to improver selectivity over oxide.
8.9
Ar: Not connected.
8.10
He: Used to improve etch uniformity, and for wafer backside cooling.
8.11
SF6: Used to break through oxide film.
8.12
CHF3: Not used in the standard recipes.
Process Notes
8.13
If the system has not been used for over eight hours, please run
two dummy wafers through the system to make sure the system is in working
condition.
8.14
Dummy wafers with poly-silicon on top of oxide are provided to
condition the etch chamber. Please do not etch through the oxide layer, since
it makes rework of the dummies impossible.
8.15
Please hard bake/UVbake the process wafer and make sure there is
no residual photo-resist on the backside of the wafer. Otherwise, the wafer may
stick to the helium clamp or the lower electrode, and will not be unloaded
after etching.
8.16
SF6 etches poly-silicon fast and isotropically. If it
is used over 10 seconds in the oxide break-through step, the sidewall profile
of the poly-silicon will be affected.
8.17
The endpoint trace signal depends on the etch area (area not cover
by photo-resist). It is recommended that you adjust the endpoint detection
parameters in the recipe to suit your special requirements.
8.18
LAM4 uses a clamp to hold the wafer on the lower electrode, and
flows helium gas on the backside of the wafer for cooling, during the etch
process. The clamp is attached to the upper electrode. If the gap between two
electrodes is over 1.0 cm, the clamp will not be effective, and the wafer may
be pushed away from the bottom electrode when the backside helium is turned on.
In this case, the wafer may be damaged by the robot movements or lost in the
chamber.
8.19
The backside helium flow is determined by the wafer backside
roughness and the helium clamp pressure specified in the recipe. Higher
backside pressure results in better wafer cooling. However, pressure over 10
Torrs may shatter a delicate wafer.
8.20
Inspect the
backside of all your wafers, post lithography step for any contaminant, surface
irregularly or traces of developer that may look like liquid on backside of the
wafer/s. Such contaminants can lead into process issued explained, next.
8.21
If your
process recipe does not stabilize, indicating pressure problems, chances are
that there is an excess helium flow (backside clamp issues); therefore, you
need to abort the recipe. Do not just
let process gases flow; gas flows and the chamber pressure typically stabilize
within 20-30 seconds. End the process if gas/pressure stabilization cannot be
achieved within 3 minutes, max. To end the process use EP CHM command explained
in Section 9.4.4, and inspect the backside of your wafer
for any possible contamination that may inhibit proper backside cooling (He
clamp).
8.22
DO NOT
ETCH ANY TYPE OF GLASS SUBSTRATES (PYREX 7740) IN LAM ETCHER
(LAM1-5). Refer to Chapter
1.3, MOD 31 (Section
V-B) for more details.
9.0
Equipment Operation
9.1
General LAM4 Information
LAM4 is a Rainbow Poly-silicon Etcher, model 4400, manufactured by
Lam Research Inc. It operation is fully automatic. Although it processes one
wafer in the etch chamber at a time, the wafer transport is continuous, which
means that there are possibly up to four wafers in the system at a time. The
front view of LAM4 is shown in Section 11.1.
When the process starts, the wafers
shuttle picks up a wafer from the cassette on the entrance elevator and carries
it to the spinner to align the wafers position and flat orientation, so that
every process wafer will sit at exactly the same location on the bottom
electrode during the etch process. The wafer is then picked up by a robot arm
and moves into the entrance load lock. Then load lock is pumped down to prevent
room air from contaminate the etch chamber. Afterwards, the wafer is sent into
the etch chamber for processing. When the process finishes, the wafers is sent
to the exit load lock. After pump and purge cycles to remove the toxic gases
from the etch process, the wafer is sent to the cassette on the exit elevator.
9.2
LAM4 Operator Interface
LAM4 Operator interface consists of system control switches, a keyboard
panel, and a 13 CRT monitor (see Section 11.2).
9.2.1
System Control Switches
·
ON button to turn on the system AC power.
·
OFF button to turn off the system AC power.
·
ACTUATORS switch that controls the 24VDC power supply for the robot system.
·
CONTROL DISABLE key knob that enables or disables the ON
and OFF of the ACTUATORS switch.
·
EMERGENCY OFF a large, red, mushroom shaped button that turns off the AC power
of the system completely.
§
In addition, there are three lights above the control panel that
indicate the status of the system:
·
MAIN ON to indicate that power to the system is available.
·
FRONT CONTROL to indicate that the front panel is active.
·
AC ON to indicate that the ON button has been pressed and the system is
running.
9.2.2
Keyboard Panel
The interface panel next to the CRT enables the user to see and
utilize the various CRT display pages. It consists of a membrane keypad with
touch keys and a floppy diskette drive. There are four arrow keys on the panel
(up, down. left, and right) that allow the user to move the cursor in any of
the four directions on the display pages. The numerical keys allow the user to
input values when writing recipes or when modifying parameters.
The interface panel also contains the following keys:
·
SEL is the field select key used to activate a highlighted field on a
display page or to enable a command.
·
START key starts the wafer loading sequence once a recipe has been
loaded into the system.
·
STOP key prevents the send cassette from sending additional wafers
into the system. It does not stop the processing of wafers that have already
been in the system.
·
CLR key is used to clear information entered into the numerical
fields.
·
ENTER key is used to enter the numerical information into the system
RAM (random access memory).
·
LOAD key loads a recipe into the system memory from the floppy
diskette in the disk drive. If there is no diskette present in the floppy
drive, the recipe will be loaded from the system hard drive.
·
SAVE key saves a recipe onto the floppy diskette in the disk drive. If
there is no diskette present in the floppy drive, the recipe is saved to the
system hard drive.
·
MENU key brings up the Main Menu page on the CRT display.
9.3
System Control Menu
Upon system initialization or whenever the MENU key on the
interface panel has been pressed, the Main Menu page is displayed on the CRT.
This page displays the current date and the revision number of the software. It
also contains a menu of all primary display pages, each of which is prefaced by
a number. Pressing the numerical key corresponding to the desired primary
display page will bring that page onto the CRT. Most of the primary pages have
associated sub-menus. The following lists the 9 primary pages available from
the Main Menu by pressing the number key in front of the page name.
1. STATUS 2. RECIPE 3. DMC 4.
MARCO 5. CONFIG
6. ALARM 7. PLOT 8.
UTILITY 9. PM/DIAG
Users should not access Pages 3. DMC, 4. MARCO, and 5. CONFIG, which
are reserved for maintenance and process staff use. Incorrect entries on these
pages may damage the wafers being processed and the system.
9.4
STATUS Page (see Section 11.3)
STATUS page is used to monitor the system status and manually
control the etch process. A graphic representation of the operating system and
the position of wafers within the system is displayed on the left side of the
CRT. During a process, the user can pictorially follow the wafer as it leaves
the send cassette, moves through the system, and is finally deposited in the
receive cassette. On the right side of the CRT display are values for the
chamber pressure, RF power, gap setting, electrode temperatures, and gas flow
set points selected for the recipe step in progress. The user can compare these
values with actual monitored values that are updated every 0.5 second. The DC
bias and RF reflected power are also monitored, but they cannot be specified in
the process recipe. A helium clamp pressure field also appears.
There are six commands on the STATUS page:
9.4.1 Options There are three modes of system operation
when the START key is pressed. The selected option always displayed on the
right up corner of the CRT monitor.
9.4.1.1 0 = Load and Process
This is the normal mode of operation. A wafer will be loaded into
the system for processing.
9.4.1.2 1 = Chamber
Process
This option is reserved for process and maintenance staff. The
etch process will start without loading a wafer from the entrance cassette.
Doing so without other special set up will damage the system.
If the Chamber Process option is selected, and you press
the START button by mistake, press 4 (EP CHM) repeatedly until the
process ends. Change the OPTIONS back to Load and Process option.
9.4.1.3 2 = Wafer Clean
Out
The option does not start the etch process at all. The system will
start unloading all the wafers in the system. This option should be used after
system computer reset and power failure.
9.4.2
Recipe Changes the CRT
display to the RECIPE page (see Section 9.5).
9.4.3 Alarm Changes the CRT display to the ALARM page
(see Section 9.6)
9.4.4 EP CHM Ends the current process step and start the following step of
the current recipe. If there is no process running, the message No Process
Active will appear.
9.4.5
Halt Halts the wafer
transport in the system. It will not stop the etch process if the process is
running. Use EP CHM or ABORT command to stop a running process.
Once this command is executed, the display for this command changes to RESUME.
Select it (5 key) got resume wafer transport.
9.4.6
ABORT Stops the entire etch process and wafer transport. The CRT
monitor will display a Red Alarm which needs to be cleared on the ALARM Page (Section 9.6)
9.5
RECIPE Page (see Section 11.4)
RECIPE page is used to program a new or edit an old process
recipe. A recipe can have twenty programmable steps maximum. Each step is
capable of storing values for the chamber pressure, the RF power, and a
specified electrode gap as well as the gas flows for 8 individual process
gases. Step completion is also programmable and six options are available.
System parameters applicable for the whole recipes, not individual recipe steps,
are listed on the right-hand side of the Recipe page. These parameters are the
electrode temperatures, the chiller temperature, and etc.
There are eight commands on the RECIPE page:
9.5.1
EDIT This command moves cursor to the top of the first recipe step,
so you can start editing. Use the arrow keys to move the cursor.
9.5.2 COPY Use this
command to copy recipe steps. When this command is selected, the CRT displays
the message COPY Form 1 To 2. Use the arrow keys to move the cursor to the
numerical fields of the message and input appropriate step numbers. Move the
cursor back to the COPY field, then press ENTER key.
9.5.3
TOL The TOL command is used to set the process parameter tolerance
in each recipe step. The default used in the standard recipes is 10%.
9.5.4
PARAM Used to set the system parameters, e.g. electrode temperature,
listed on the right side of the recipe steps.
9.5.5
CLEAR This command clears all numerical values in the displayed
recipe.
9.5.6
STATUS Returns to the STATUS page.
9.5.7
ALARM Changes the display to the ALARM page.
ALARM page to display system alarms. Three different classes of
alarms can occur on the Rainbow: red alarms, white alarms, and warnings. Red
and white alarms generate the flashing word
< < < <
ALARM > > > >
at the top of whatever CRT page is displayed. Warnings generate
the flashing word
< < < <
WARNING > > > >
if no red or white alarms are present. Users can find out the
nature and description of an alarm or warning by selecting the Alarm page or by
selecting the ALARM command on the Status and Macro pages.
Red alarms indicate an emergency condition or a process abort.
Wafer transport cannot be started while a red alarm is active. These alarms
appear on the Alarm page in red and have to be manually cleared, even the
condition for the alarm is corrected. Red alarms include chamber recipe hard
tolerance and RF alarms. When hard tolerances are exceeded in a recipe step
that has the RF power on, the recipe is terminated. The Alarm page identifies
the recipe value or parameter that exceeded tolerance.
White alarms do not abort the chamber process. Depending on the
alarm, they either continue to hold a recipe in the stability step or allow the
recipe to complete. Movement and processing of further wafers is suspended.
These alarms appear on the Alarm page in white and clear themselves
automatically when the condition causing the alarm has been corrected. White
alarms include wafer transport alarms, soft tolerance alarms, and stability
alarms.
Warnings have no effect on the system operation, but are given as
information only. The appear on the Alarm page in cyan.
There are seven commands on the ALARM page:
9.6.1
CLR ONE This command does not fix any malfunction of the system. It only
clears the one alarm on the display. If the condition causing the alarm has
been corrected, either by the system itself or by the staff, the alarm
disappears from the display. Otherwise, the alarm repeats itself.
9.6.2
CLR ALL Clears all alarms displayed at once. If all problems have been
corrected, the ALARM page displays the message This machine is in perfect
running order. The system will automatically unload the wafer that was in
the chamber during the aborted process and begin to load a new wafer.
9.6.3
AUDIBLE/SILENT Toggles the alarm audible or silent.
9.6.4
DESCRIBE Displays a one-line description of an alarm. It prompts for
entering an alarm number.
9.6.5
LOG Displays the alarm history in a table format, which includes
the alarm number, time occurs, and action taken.
9.6.6
RETURN Returns to the whatever page before the ALARM page was
selected.
9.7
PLOT Page (see Section 11.5)
PLOT page is used to track and plot the analog and digital system
signals on a graph in order to chart signal movement, such as endpoint traces.
Two separate signals can be tracked at the same time and charted on two
separate pilots. The Plot page displays two graph grids with their chosen setup
parameters.
9.7.1
TREND When this command is activated, the display shows the TREND
page. The right side of the page lists all commonly used process parameters,
e.g. endpoint channels, gas flows, pressure, RF power and etc. Press 1
(EDIT) to activate the cursor. Use the arrows keys to move the cursor to the
name field and enter the number corresponding to the process parameter to be
plotted. Make sure the mode field is Manual. Press 2 (PLOT) to
return to the PLOT page.
9.7.2
SETUP A Used to set up the offset and range of the upper plot page. If
no set up correctly, the signal trace may look like a straight line or not
showed at all.
9.7.3
SETUP B Same as above. Used to set up the offset and range of the lower
plot page.
9.7.4
MAN EP Use this command to override the automated endpoint triggering
set up in the process step. It works the same as the EP CHM command on the
STATUS page.
9.8
UTILITY Page
UTILITY page is used for file management, including recipe files
and data files. When selected, it lists all the recipes names stored in the
floppy diskette and the hard drive. It has commands to copy, move, and delete
files.
9.9
PM/DIAG Page
PM/DIAG page can be used to display the wafer count and RF time,
check the leak-back rate of the process chamber, verify the flow rates for the
mass flow controllers, and setup the automatic chamber and gas panel pump/purge
routines.
9.10
Available Recipes
9.10.1
400 Main etch using Cl2, 25% over etch.
9.10.2
440 Main etch using Cl2, no over etch
9.10.3
500 Main etch using Cl2, 25% over etch using HCl/HBr
mixture.
9.10.4
200 Nitride etch using SF6 (Under development).
9.10.5 6xxx Germanium and
Germanium/Silicon alloy (Under development).
9.11 Processing a run
(Loading recipe and wafers)
Loading a Recipe
9.11.1
Enable LAM4 on the WAND.
9.11.2
Check the system status is Load and Process Idle, displayed
on the upper-right corner of the CRT monitor. If not, go to the STATUS page,
select 1 (OPTION), then 0 (Load and Process).
9.11.3
Press the LOAD button. Enter the recipe # when prompted. If
there is a diskette in the floppy drive, the recipe will be loaded from it.
Otherwise, the recipe will be loaded from the hard drive. If there is no such
recipe stored in the system, the message Recipe cannot be loaded will
appear. In such case, you can go to the UTILITY page to find out what recipes
are stored in the system.
9.11.4
Modify the recipe, if necessary, based on your special
requirement. Refer to Section 12.1 on how
to write/modify a process recipe. Go back to STATUS when you finish
editing.
Load Wafers and Run a Process Recipe
9.11.5
Load you wafers into the blue cassette. The flat direction is not
important because LAM4 is equipped with a flat finder. However, make sure that
your wafers sit all the way to the back end of the cassette. Wafers extrude out
of the front end of the cassette may exceed the adjusting limit of the flat finder
and cause a system red alarm.
9.11.6
Load the cassette onto the entrance elevator (left side facing the
system). Make sure the cassette sits firmly and the H-Bar sits in the center
slot on the elevator.
9.11.7
Press START button to start the process. First the system
initials the electronics. It takes about a minute. Then the wafer shuttle will
pick up the wafer that sits on the lowest slot of the cassette and send it into
the system.
9.11.8
You can now monitor the wafer movement and etch process on the CRT
monitor. Or go to the PLOT page to monitor the endpoint traces. You can
skip to next recipe step by using EP CHM command on STATUS page,
or MAN EP on the PLOT page, if needed. You can also abort the
entire recipe by using ABORT command on the STATUS page. The STOP
button on the control panel only stops the wafer transport. It has not effect
on the etch process currently running in the process chamber.
Unload Wafers After Process Ends
9.11.9
After process completes, the wafer is sent to the exit load lock, then
the exit cassette (right side facing the system). To remove the cassette, first
make sure that the robot arm has retracted fully into the exit load lock. Tilt
the cassette toward you for about 30 degrees, then return it to the upright
position. The elevator will rise. When the elevator stops, you can remove the
cassette and examine your wafers. Do not remove the cassette when the elevator
is moving. Doing so may damage the sensor on the elevator.
10.0
Troubleshooting Guidelines
10.1
Shuttle Vacuum Problem
10.1.1
Cause: Cassette not set
properly on the elevator, wafer cross-slotted in the cassette.
Solution: Carefully adjust the wafer/cassette so that
the bottom of the wafer and the shuttle arm have a good contact to achieve
vacuum for wafer transfer.
10.1.2
Cause: Equipment mal-function.
Solution: The vacuum used
to hold the wafer is generated by a large flow of nitrogen (Venturi effect).
Initially, the nitrogen flow may not reach the set point to create enough
vacuum. Wait one minute. Then try clearing the alarm on the ALARM page. If no
success, report on WAND.
10.2
Gas Stabilization Problem
10.2.1
Cause: The time set in the gas
stabilization step of the recipe is too short.
Solution: Increase the gas stabilization time.
10.2.2
Cause: The gas cylinder is
empty or valve closed.
Solution: Report on the WAND.
10.2.3 Cause: Contaminant on the backside of wafers.
Solution: End point (EP CHM command) out of
the stabilization step and bring your wafers out to check their backside for
any possible contamination or irregularity that may have caused the "He
clamp" failure and/or process pressure problems.
Note: DO
NOT just run the stabilization step, if gas and chamber pressure do not
stabilize within a three (3) minutes time, max.
10.3
RF Problem
10.3.1
Cause: Problematic wafer or
improper recipe settings.
Solution: The system
minimizes the RF reflected by matching the impedance of the RF generator
circuits and the etch chamber. A problematic wafer or some non-standard process
settings may change the impedance between the electrodes, that the system could
not match it. If this is case, abort the process then clear the alarm. After
the wafer unloaded, load a clean dummy wafer and run a standard recipe. If the
problem repeats, then it is the equipment problem. Otherwise, it is the problem
of the wafer or the non-standard recipe.
10.3.2
Cause: Equipment problem.
Solution: Report the problem on WAND.
10.4&n