Chapter 7.2
Lam2 Silicon Oxide Etcher
(Lam2)
1.0
Title
Lam2 Silicon Oxide Etcher
2.0
Purpose
Lam2 is an automatic, cassette-to-cassette, single wafer plasma etcher for silicon oxide etching.
3.0 Scope
This document describes the general operation of Lam2. It also covers the recipe loading/modifying procedures and how to set up the automatic endpoint detection.
4.0
Applicable Documents
4.1 Chapter 7.0 of
the Microlab Manual (Lam Etchers Overview)
4.2 AutoEtch
Plasma Etch System, Operation and Maintenance Manual, Lam Research, 1989.
(There is a copy in the Microlab office.)
5.0
Definitions & Process
Terminology
5.1 Plasma
Etcher: An etcher that uses the radical gas atoms/molecules,
generated by plasma, as the main etchants to remove the thin film material on a
substrate or the substrate itself.
5.2 Etch Rate (ER): The rate of the thin film being etched away, usually in A/minute.
5.3 Etch Non-Uniformity: A measure of the etch uniformity. It is defined as (max ER – min ER)/(2 X average ER), usually in %.
5.4 Isotropic/Anisotropic Etch: An etch process that has the same ER in all directions is isotropic. An etch process that etches in the direction perpendicular to the substrate surface is anisotropic. A plasma etcher, e.g. Lam2 usually etches more anisotropically.
5.5 Etch Selectivity: The ratio of ERs between the etched thin film and the underlying substrate/thin film.
5.6 Over-Etch: An optional second etch step with etch chemistry that maximizes the etch selectivity. It removes the residual film due to previous etch non-uniformity with minimum damage to the underlying substrate/film. The etch rate is usually lower in this step.
5.7 Automatic Endpoint Detector: An optical device that traces the light emitted by the etch byproduct in the plasma. It can be programmed to end the etch process at a specified condition. Lam2 uses Channel B (520 nm) to monitor the amount of CO species in the plasma.
5.8 Lam1-PC: A PC used for loading etch recipes to Lam2.
Control Panel and CRT
5.9 START button: Starts the process.
5.10 STOP button: Stops the wafers in the entrance cassette from being sending into the system.
5.11 RECIPE button: Displays, on the CRT, the recipe currently loaded in the system.
5.12 STATUS button: Displays, on the CRT, the current status of the system. It also includes the current process parameters and wafer location.
5.13 PARAMETER button: Displays, on the CRT, the menus of the operating parameters of the system and the automatic endpoint detector.
5.14 OPTIONS button: For diagnostic/maintenance purposes only.
5.15 Arrow keys: Move the cursor on the CRT.
5.16 [FIELD SELECT] button: Toggles options available in the highlighted fields where the cursor at on the CRT.
5.17 LOAD/SAVE buttons: Currently not used.
6.0 Safety
6.1 RF Radiation Hazard: Lam2 uses a 13.56 MHz Radio Frequency power supply as a plasma generator. If suspect RF power leakage, stop etch process by pressing the red emergency stop button.
6.2 UV/Strong light Hazard: The plasma emits UV/Strong light. Do not look straight into the plasma for a long period of time.
6.3 Toxic Gas Hazard: Although Lam1 uses non-toxic gases, however, the etch byproducts may be toxic/reactive. Stop etch process if suspect a vent leakage.
6.4 All applicable safety rules described in the Microlab Lab Manual Chapter 1.2 should be followed.
7.0
Statistical/Process Data
7.1 Microlab web page
(under Processing/Process
Monitoring Tests).
7.2 Problem and
comment section under the equipment section of the Wand.
7.3 Wand equipment
enable message for Lam2.
8.0 Available
Processes, Gases, and Process Notes
8.1
Standard Oxide Recipe (SIO2ET): Used for etching silicon oxide.
8.2
Process Monitor Recipe (SIO2MON): Same as the
SIO2ET recipe without the over-etch step.
Used for process monitor test.
8.3
Clean Recipe (CLEAN): Used to clean the process chamber. It is
performed monthly by the process staff only. The cleaning process erodes the
upper graphite electrode. Excessive electrode erosion will have adversely
impact on etch rate and uniformity.
Process Gases:
8.4
CF4: Main etch gas.
8.5
CHF3: Secondary etch gas, also used to form
sidewall polymer.
8.6
He: Used to increase the etch uniformity.
8.7
O2: Used in the O2CLEAN recipe to clean
organic contamination in the chamber.
8.8
C2F6: Not connected to the system.
Process Notes:
8.9
Lam2 uses high RF power (850W). For long etch process, the
electrode temperature may increase which may cause photo-resist burning. It is
recommended that the user break a long etch step into several 3~5 minute
segments and insert a cooling step in between. It is reported that if the electrode
temperature exceeds 20ºC, significant photo-resist burning occurs.
8.10 Lam2 can be used
to etch thick silicon nitride film with a slightly lower etch rate than
oxide. The user needs to perform the
etch rate test since nitride etch on Lam2 is not included in the regular
process monitor.
8.11 After etching, it
is recommended that you dip your wafers in 100:1 HF for 30 seconds to remove
any sputtered oxide contamination caused by plasma.
8.12
Do not press [OPTION] button on the control panel. The operation
overwrites the safety interlocks built in the system. It is for staff use only.
8.13
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
Enable Lam2 on the WAND.
9.2 Download a recipe using
Lam1-PC.
9.2.1 Make sure that
Lam2 is at IDLE state. No process is running.
9.2.2 On Lam1-PC, press
ESC several times until the “Control Menu” is on the monitor.
9.2.3 Select number 6:
“Send Rec”, then press ENTER. The monitor will show a list of
recipes.
9.2.4 Enter the
number/alphabet of the recipe of your choice, and then press ENTER. The
monitor will display: “Recipe download successfully.” If not, see troubleshooting section in this chapter.
9.2.5 Press ENTER,
the monitor will display a blank chart for endpoint tracing when the wafer is
being etched.
9.3 Modify a recipe
downloaded from Lam1-PC or create a new recipe.
Usually the standard recipes are
sufficient for silicon oxide etching. If you need a new recipe for your own
special application, please consult the process staff first.
9.3.1 Press RECIPE button
on the control panel. The CRT will display the current recipe stored in the
system memory. Every column represents a process step.
9.3.2
Use the arrow keys to move the cursor to the field you want to
modify. Use the numeric keys to enter the new value. If you make a mistake, use
CE key to erase the entry. Afterwards, You must use an arrow key to move
the cursor out of the field for the entry to be stored in the system memory.
9.3.3
To change the pressure unit, move the cursor to the pressure unit
brackets, then press [Field Select] button to toggle between [MTORR] and
[TORR].
9.3.4
Use the same method to toggle entries in the COMPL
field. There are 5 entries you can
choose.
9.3.4.1 TIME: The step will
complete after the time entered in the WAIT field. The process then
advances to the next step.
9.3.4.2 Stability OR TIME: The step will complete and the process advances to the next step
when all the parameters in the step reach their set points within the time
limit entered in the MAX field. Otherwise, an alarm will sound. If the
alarm sounds, move the CRT cursor to the MANUAL ENDPT: [OFF] field, wait
till all parameters reach their set points, then press [FIELD SELECT]
button to advance to the next step. If one or more parameter won’t reach their
set points after a few minutes, see Section 10.0
for troubleshooting. To avoid frequent false alarm, enter reasonable time, at
least 30 seconds, in the MAX field.
9.3.4.3 TIME & ENDPT: The step will
complete and the process advances to the next step when the Automatic Endpoint
Detection conditions are met or after the time entered in the WAIT
field.
9.3.4.4 OVERETCH: The step will
complete after the percentage, entered in the “%” filed, of time of the
previous etch step.
9.3.4.5 RECIPE: Signifies this
is the end of the recipe. All parameters in this step and after are ignored.
9.3.5 Use the copy
feature list on the bottom line of the recipe page. This feature is especially
useful when you plan to delete a step from the recipe. Since there is not
delete step feature in the system, you will have to copy the next step to the
step you plan to delete. Then repeat the copy operation till you reach the last
step in the recipe. The copy feature is also useful for creating a recipe with
several cycles of the same steps.
9.3.5.1 Move the cursor
to the STEP# field and enter the step number to be copied and the step number
to copy to.
9.3.5.2 Move the cursor
to the [COPY] field and press [FIELD SELECT] button. Both of the
step numbers in the STEP# filed will be increased automatically.
9.3.5.3 Press [FIELD
SELECT] repeatedly as many time as you plan for the recipe.
9.4 Set up automatic
endpoint detection (You can skip this section when using standard recipe.)
9.4.1 Press the PARAMETER
Button. Then press the [FIELD SELECT] button a few times until the CRT
display the endpoint setup page. There are four endpoint steps you can set up.
Unless you plan to etch multi-layers in one recipe, you only need to set up
one.
9.4.2 Move the cursor
to the SAMPLING INPUT. Press the [FIELD SELECT] button until [B
ONLY] is selected. Lam2 uses the channel of the automatic endpoint
detector.
9.4.3 Move the cursor
to the next line. Enter the number of the main etch step. It is the step that
has the [TIME & ENDPT] in the COMPL field.
9.4.4 Move the cursor
to the next line. Enter the DELAY time. The automatic endpoint detector
disregard any signal in this first period of the etch step because the plasma
just starts and is stabilizing. The normal DELAY time is 15 seconds.
9.4.5 Move the cursor
to the next line. Enter the NORMALIZE time. The automatic endpoint
detector collects and averages the tracer signal from the plasma in this second
period of the etch step. The averaged (normalized) signal strength is used as
the base for endpoint triggering. Lam2 standard recipes use 5 seconds NORMALIZE
time.
9.4.6 Move the cursor
to the next line. Enter the TRIGGER AT PERCENTAGE of the normalized
value. When the tracer signal reaches the percentage, the end point is
triggered and the etch step completes and the process advances to the next
step. To prevent under-cutting the substrate, the endpoint is set to trigger at
90%.
9.5
Processing Wafers
Contrary to Lam1, it is not recommended
that you run O2CLEAN recipe on Lam2 to clean the etch chamber. However, if
Lam2 has been idle for more than 8 hours, you should run 3 dummy wafers to
“warm up” the system.
9.5.1 Download the
recipe using Lam1-PC by following Section 9.2. Press
the RECIPE button to check the recipe. Modify the recipe by following Section 9.3 if needed. Press the STATUS button to
display the system status.
9.5.2
Load wafers into the blue cassette with flat toward the front.
Load the cassette onto the entrance indexer (left side) with the cassette’s H
bar sitting in the center slot. Load an empty cassette on to the exit indexer
(right side). The cassette will be lowered into the exit indexer.
9.5.3
Press START button. The entrance indexer will send one
wafer (start from the lowest one in the cassette) into the system. The wafer
will first go into the entrance load lock, then the main etch chamber. You can
watch the wafer movement and the system status from the CRT. (Press STATUS
button if needed.)
9.5.4
Once the wafer is in the main etch chamber, the recipe starts.
When it reaches the etch step, Lam1-PC monitor will show the endpoint trace
signal from automatic endpoint detector. (If not, press enter or space bar on
the Lam1-PC keyboard.)
9.5.5
If you want to stop the current recipe step manually, move the
cursor to the [MAN EP] field, then press the [FIELD SELECT]
button. The recipe will advance to the next step.
9.5.6
Once the recipe completes, the wafer will move to the exit load
lock, then the exit indexer. The whole process will repeat itself automatically
until the last wafer on the entrance indexer is processed. After the last wafer
goes into the exit indexer, tilt the indexer toward you to about 45 degrees
then release it to vertical. The exit indexer will rise. When it stops, you can
remove the cassette to get your wafers. If you try to remove the cassette when
it is still at down in the indexer, you may damage the sensor that monitors the
position of the cassette.
9.5.7
If you decide to stop processing some wafers still in the entrance
indexer, press the STOP button. The entrance indexer will stop sending
wafer into the system. However, the wafer(s) already in the system will finish
the recipe and return to the exit indexer.
10.1 Lam1-PC problems
10.1.1 If you or someone
hit option 7 on the control menu by mistake, the PC monitor will switch
to the WINDOW 3.1 interface. Use [CTL]+[TAB] keys to highlight the Lam2
icon, then press enter. The PC monitor will switch back to the control menu.
10.1.2 You can reboot the
Lam1-PC by holding [ALT]+[CTL]+[DEL] keys together. After reboot, it will
prompt you for some setup value. Enter q for the prompt. It will ask you
for the password. Enter lam1-pc. Wait till the control menu shows
up on the monitor.
10.1.3 If Lam1-PC
displays “Unable to send recipe” message, press the PARAMETERS button on
the Lam2 control panel. Use the [FIELD SELECT] button to toggle the [PARAMETERS]
field to the LAM LINK. Make sure that the Lam link field is ACTIVE
and the baud rate is 9600. Try down load the recipe again using Lam1-PC.
10.2 Process Problems
10.2.1 The entrance
indexer does not send wafer into the system after the START button is
pressed.
Check the STATUS page on the CRT by pressing the STATUS
button on the control panel.
10.2.1.1 If the recipe has
already started running, move the cursor to the [MAN EP] field, then
press [FIELD SELECT] button repeatedly till the system returns to the IDLE
state.
Press [PARAMETERS] button.
Move the cursor to the PARAMETERS field. Press [FIELD SELECT] button
repeatedly to toggle the field to [MACHINE]. Move the cursor to the START
BUTTON field. Press [FIELD SELECT] button repeatedly to toggle the
field to [LOAD & PROCESS]. Move the cursor out of the field.
If the system alarms for WAFERS IN
SYSTEM, move the cursor to WAFERS IN SYSTEM ALARM RESET field, then
press [FIELD SELECT] button to clear the alarm.
10.2.1.2 If the recipe has
not started, check that the cassette sit properly on the entrance indexer.
10.2.1.3 Report problem on
WAND if the above procedures do not solve the problem.
10.2.2 The system fails
to stabilize at the STABILITY OR TIME step.
10.2.2.1 Wait for a
minute. If all process parameters have stabilized, move the cursor to the MAN
EP Field on the STATUS page, press [FIELD SELECT] button to
advance the recipe to the next step. If the problem appears often, increase the
time in the MAX field of the step in the recipe.
10.2.2.2 If some of the
process parameters do not stabilize after 2 minutes, move the cursor to the MAN
EP Field on the STATUS page, press [FIELD SELECT] button
repeatedly till the recipe ends. Report the problem on ‘WAND’.
10.2.3 The system
displays ‘RF’ alarms.
10.2.3.1 Press [PARAMETERS]
button. Move the cursor to the PARAMETERS field. Press [FIELD
SELECT] button repeatedly to toggle the field to [MACHINE]. Move the
cursor to the RF ALARM RESET field, then press [FIELD SELECT]
button.
10.2.3.2 Press [STATUS]
button. Move the cursor to the MAN EP field, then press [FIELD
SELECT] button repeatedly till the recipe ends.
10.2.3.3 Load a dummy wafer
to the entrance cassette and start the recipe. If the RF alarm occurs
again, repeat Section 10.2.3.1-2, then report problem on WAND. If the
dummy wafer goes through without problem, it is your wafer that causes the
problem
10.2.4 The recipe has
finished but the wafer does not come out of the system.
10.2.4.1 Press [STOP]
button. Remove all wafers from both cassettes.
10.2.4.2 Report the
problem on WAND. Do not try to find the lost wafer yourself. You may
create more damage.
10.2.4.3 Leave a wafer
holder or a box with a note on the top of the system if you want the staff to
save your wafer (or pieces of your wafer).
10.2.5 The endpoint
trace signal on the Lam1-PC monitor is too small or just a flat line.
10.2.5.1 Make sure that
your wafer has large enough etch area that generates trace signal for the detector.
If so you can change the graph setting using Lam1-PC ‘control menu’.
10.2.5.2 If the situation
does not improve, try using a dummy wafer. If the dummy wafer behaves the same,
the window of the detector may need cleaning. Report the problem on WAND.
11.0 Figures And
Schematics
Lam2 Control Panel
12.0 Appendices
12.1
Standard Oxide Recipe (SIO2ET)
|
|
Step #1 |
Step #2 |
Step #3 |
|
PRESSURE [TORR] |
2.8 |
2.8 |
3.0 |
|
RF TOP [WATTS] |
0 |
850 |
0 |
|
GAP [CM] |
0 |
0.38 |
0.40 |
|
CF4 [SCCM] |
0 |
0 |
0 |
|
HELIUM [SCCM] |
120 |
120 |
110 |
|
OXYGEN [SCCM] |
0 |
0 |
0 |
|
CHF3 [SCCM] |
30 |
30 |
35 |
|
CF4 [SCCM] |
90 |
90 |
30 |
|
COMPL |
[STABILITY OR
TIME] |
[TIME &
ENDPOINT] |
[STABILITY OR
TIME] |
|
MAX/WAIT [MIN:SEC] |
00:30 |
1:00 |
00:30 |
|
|
Step #4 |
Step #5 |
Step #6 |
|
PRESSURE [TORR] |
3.0 |
0 |
0 |
|
RF TOP [WATTS] |
700 |
0 |
0 |
|
GAP [CM] |
.40 |
1.35 |
1.35 |
|
CF4 [SCCM] |
0 |
0 |
0 |
|
HELIUM [SCCM] |
110 |
0 |
0 |
|
OXYGEN [SCCM] |
0 |
0 |
0 |
|
CHF3 [SCCM] |
35 |
0 |
0 |
|
CF4 [SCCM] |
30 |
0 |
0 |
|
COMPL |
[OVERETCH] |
[TIME] |
[RECIPE] |