Chapter
7.3
(lam3)
1.0
Title
Lam3 Aluminum RIE Etcher
2.0
Purpose
Lam3 is an automatic, cassette-to-cassette, single wafer RIE etcher for aluminum film etching.
3.0
Scope
This document describes the general operation of Lam3. 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 RIE 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. In addition, the process wafers sits on the RF powered electrode, hence a large electrical bias will attract positive charged ion in the plasma to bombard the wafer surface. The added ion bombardment will increase the etch rate and make etch byproduct more volatile.
5.2 Powered Load Lock (PLL): Lam3 used the exit load lock to passivate the etched aluminum surface. It uses CF4/ O2 plasma to replace the Cl residue on the etch surface and in the photo-resist. It also results in a protective film on the aluminum surface.
5.3 Etch Rate (ER): The rate of the thin film being etched away, usually in A/minute.
5.4 Etch Non-Uniformity: A measure of the etch uniformity. It is defined as (max ER – min ER)/(2 X average ER), usually in %.
5.5 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. Lam1 usually etches more anisotropically.
5.6 Etch Selectivity: The ratio of ERs between the etched thin film and the underlying substrate/thin film.
5.7 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.
5.8 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. However, Lam3 Endpoint Detector is not working.
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: Moves 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: Used to load/save a recipe from/to the recipe cartridge. Please do not save any modified recipe into the cartridge. It will erase the standard recipe
6.0 Safety
6.1 RF Radiation Hazard: Lam3 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 General Information/Process
Monitoring Tests).
7.2
Problem and comment section under the equipment section of the
Wand.
7.3
Wand equipment enable message for Lam3.
8.0 Available
Processes, Gases, and Process Notes
8.1 Standard
Aluminum Recipe Used for etching Aluminum.
8.2 Clean
Recipe: Used to clean the process chamber. It is a simple N2 plasma recipe. However, you have to enter it manually.
Process Gases
8.3
Cl2: Main etch gas
8.4
BCl3: Used for etching native Al2O3.
8.5
N2: Used to increase the etch uniformity.
Also used in chamber cleaning recipe.
8.6
CHCl3: Secondary etch gas, also used to form
sidewall polymer.
8.7
SF6: not connected.
8.8
CF4: Used in the PLL for creating fluorine plasma.
This plasma passivates the exposed aluminum surface by exchanging the chlorine,
in the residual etch byproduct, for the fluorine. This is an important process
step since the chlorine will form hydrochloric acid with moisture in the air,
and hence corrodes the aluminum film.
8.9
O2: Used in the PLL to help creating plasma.
It may erode some photo-resist. Also
available in the Reactor chamber to use in place of N2 for alternative metal etching.
Process Notes
8.10
Due to the high electrode temperature (over 60ºC), ion
bombardments during etch process, and the post etch PLL passivation, the
photo-resist burning/erosion has been a major problem for LAM3. It is
recommended to use UVBAKE to harden the photo-resist or hard bake wafers at
least 24 hours in VRW oven before etching.
8.11
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.
8.12 A N2/O2 toggle
switch is located behind Lam3. N2 is a
standard process gas for Aluminum etching; O2 is being used for alternative
metal etching development.
***Note: Aluminum
will not etch if the N2/O2 toggle is set for O2. If your Aluminum is not etching, check to make sure to the toggle
is or re-positioned for N2.
Locate the N2/O2 toggle switch by walking into the adjacent Tystar
service chase to the right of Lam3.
Look down and left, on the backside of Lam3 you will find a 2-way valve
labeled for N2 and O2 on opposite ends.
The standard toggle position is towards N2 flow for Aluminum etching, but
for other metal etching, the toggle may be switched to O2. This valve substitutes O2 for N2 in the main
reactor chamber, only one of these gases will flow through the MFC at a given
time. When your etching is complete (if
using O2), toggle back to the standard N2 position, and run a few dummy wafers
with a standard recipe to purge lines of residual O2 for N2.
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
9.2
Download a recipe using RECIPE CARTRIDGE.
9.2.1
Make sure that Lam3 is at IDLE state. No process is
running.
9.2.2
Insert the RECIPE CARTRIDGE in to the slot on the left side
of the control panel.
9.2.3
Press LOAD button to load the recipe.
9.2.4
Press RECIPE button. Check the recipe on the monitor.
9.2.5
Remove the RECIPE CARTRIDGE.
9.3
Modify a Recipe
Usually the standard recipes are
sufficient for aluminum 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. Different from LAM1 and LAM2, the recipe has two pages, REACTOR
and AIRLOCK (PLL). You can use the FIELD SELECT button to toggle
them.
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. (Endpoint detector is not
working on LAM3 currently.)
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 [A ONLY] is selected. Lam1 uses 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. Lam1 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 80%.
9.5
Processing Wafers
If Lam3 has been idle for more than 8
hours, you should run 3 dummy wafers to “warm up” the system. You can use a
Nitrogen plasma recipe to do chamber clean is necessary. The clean recipe needs
to be entered manually.
9.5.1
Download the recipe by following Section 9.2
or enter it manually. 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 (right side) with the cassette’s H
bar sitting in the center slot. Load an empty cassette on to the exit indexer
(left 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.
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 PLL for
passivation, then to 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 RECIPE CARTRIDGE Problem
If you cannot load recipe from the RECIPE
CARTRIDGE by following Section 9.2, report the problem
on the WAND. The CARTRIDGE may be defective and need to be replaced.
However, you can enter the recipe manually and process your wafers.
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 hold or 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
Aluminum is not etching but machine seems to be working properly
10.2.5.1
Check N2/O2 toggle switch behind machine as described in Section 8.12
11.0
Figures & Schematics
N/A
12.0
Appendices
12.1 Standard
Aluminum Recipe (REACTOR)
|
|
Step #1 |
Step #2 |
Step #3 |
|
PRESSURE [TORR] |
250 |
250 |
250 |
|
RF TOP [WATTS] |
0 |
250 |
250 |
|
BCl3 [SCCM] |
50 |
50 |
50 |
|
N2 [SCCM] |
50 |
50 |
50 |
|
Cl2 [SCCM] |
30 |
30 |
20 |
|
CHCl3 [SCCM] |
30 |
30 |
35 |
|
SF6 [SCCM] |
0 |
0 |
0 |
|
COMPL |
[STABILITY OR
TIME] |
[TIME &
ENDPOINT] |
[OVERETCH] |
|
MAX/WAIT [MIN:SEC] |
00:30 |
3:00 |
50% |
|
|
Step #1 |
Step #2 |
|
PRESSURE [TORR] |
0 |
0 |
|
RF TOP [WATTS] |
0 |
0 |
|
BCl3 [SCCM] |
0 |
0 |
|
N2 [SCCM] |
100 |
0 |
|
Cl2 [SCCM] |
0 |
0 |
|
CHCl3 [SCCM] |
0 |
0 |
|
SF6 [SCCM] |
0 |
0 |
|
COMPL |
[TIME] |
[RECIPE] |
|
MAX/WAIT [MIN:SEC] |
00:10 |
00:00 |
12.2 Standard Aluminum Recipe (AIRLOCK/PLL)
|
|
Step #1 |
Step #2 |
|
PRESSURE [TORR] |