Chapter 7.5
Lam5 Poly-Si TCP Etcher
(Lam5)
1.0
Title
Lam5
Poly-Si TCP (Transformer Coupled Plasma) Etcher
2.0
Purpose
Lam5 is an automatic, cassette-to-cassette, TCP etcher for Poly-Silicon
etching. The system operates under an upgraded GUI software, Envision®. Lam5 is capable of etching deep sub-micron
features with near vertical sidewalls and extremely high selectivity over the
underlying oxide. The robot is set up for 6-inch wafer. Carrier or pocket
wafers can be used to process 4-inch wafers or samples of other sizes (see
Process Notes, Section
8.3, for details).
3.0
Scope
This document describes
the general operations of Lam5, editing recipe, setting up graphs to monitor
endpoint signals, and basic trouble shooting procedures.
4.0
Applicable Documents
4.1
Microlab Online Manual Chapter 7.0,
Lam Etchers Overview.
4.2
TCP 9400/9400SE System Operation,
Envision, Lam Research, 1997
4.3
TCP 94400 Operation and
Maintenance Manual, Lam Research, 1989
5.0
Definitions & Process Terminology
5.1
TCP Etcher: The TCP etcher has an
upper TCP coil and lower electrode powered up simultaneously during etch
process. The TCP coil generates high density plasma, while the plasma bias can
be independently controlled by the powered lower electrode. It usually operates
at tens milli-torr process pressure range to etch deep sub-micron features.
5.2
Automatic Endpoint Detector: An
optical device that traces the light emitted from the etch byproduct in the
plasma. It can be programmed to end the etch process at a specified condition.
Lam5 uses Channel A (405 nm for poly-silicon) and Channel B (520nm for silicon
oxide) to monitor the amount of SiCl and CO species respectively.
5.3
Etch Rate (ER): The thickness of the film etched per unit time, usually in Å/minute.
5.4
Etch Non-Uniformity: A measure of the etch uniformity. Microlab process monitoring sites
defines as (max ER – min ER)/(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.
Lam5 usually etches more anisotropically.
5.6
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.
5.7
Etch Selectivity: The ratio of ERs between the etched thin film and the underlying
substrate/thin film.
5.8
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.
5.9
Pocket Wafer: A six-inch wafer with a 4-inch pocket
(recessed etched area), which enables one to load 4-inch wafer into a
6-inch process tool.
5.10
Kapton Tape: A special polyimide tape with
silicon adhesive on it, which is ideal for high temperature application, and
can withstand temperature range of –100ºF to + 500ºF.
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: LAM 5 uses two 13.56MHz,
1250W RF power generators. 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 process gases used by
LAM 5 are confined in the gas delivery system and the vacuum chambers. However,
if you smell bleach or other un-usual
odor, stop the etch process and evacuate the area. Inform Microlab staff
immediately. There may be a leak in the system, or problem in the
ventilation.
6.3
Pinch Hazard: The wafer cassette
elevators may pinch your fingers. Load/unload wafer cassette 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/Processing/Process Monitor.
7.2
WAND equipment enable message for
Lam5.
7.3
Problem and comment section under
the equipment section of WAND.
8.0
Available Processes, Gases,
Process Notes
8.1
Available Processes
8.1.1
Recipe 5001: Anisotropic Poly-Si Etch.
The same process parameters (steps) used for the Main Etch part (steps) of the
5003 recipe. This is also used for ASML zero mark (PM Mark) etching.
8.1.2
Recipe 5002: Poly-Si etching can be
accomplished with a high degree of selectivity over a thin underlying oxide
with 5002 recipe. The same process parameter are used for the Over Etch part
(steps) of the 5003 recipe.
Note: small amount of O2 is added to improve poly to oxide selectivity
8.1.3
Recipe 5003: Standard Poly-Si Etch with
native oxide break through, main etch, and over etch steps. This recipe
provides a faster etch rate with the main etch steps followed by a slower, but
highly selective (poly to oxide) Over Etch steps.
8.1.4
Recipe 5004: Native oxide break
through/etch using Cl2 chemistry.
8.1.5
Recipe 5005: Native oxide break
through/etch using CF4 chemistry.
The oxide break through steps are used in the 5003 recipe.
8.1.6
Recipe 6001: Anisotropic Poly-SiC
Etch.
8.2
Process Gases
8.2.1
Cl2: Used in Poly-Si main etch
for high etch rate.
8.2.2
CF4: Used for native oxide
break through and oxide etch.
8.2.3
CHF3: Currently not used, but
can be used with CF4 for oxide etch.
8.2.4
SF6: Currently not used, but
can be used for isotropic oxide etch.
8.2.5
HBr: Used in Poly-Si main and over
etch to improve selectivity over oxide.
8.2.6
O2: Used in Poly-Si over etch
in conjunction with HBr for high selectivity.
8.2.7
He: Used as diluent to improve etch
uniformity. Also used in He Clamp to improve the wafer backside cooling,
8.2.8
O2high: can be used for chamber
cleaning.
8.3.1
Glass substrates (including Pyrex) are not allowed in lam5. This means deposited films on top of the glass substrate/s, as well as
glass substrate itself, must not be
etched in lam5. See Chapter 1.3
- MOD 31, as well as Chapter 1.5 for more details on processing
glass substrates in lam etchers.
8.3.2
The over-etch step selectivity
and length of time to clear main etch residue depends on the device designs.
Most Lam5 users customized their over-etch steps to fit their own designs.
8.3.3
Lam5 uses a mechanical clamp,
attached to the upper electrode, to secure the wafer on the lower electrode.
Helium gas then flows on the backside of the wafer to cool it uniformly. The backside of the wafer needs be smooth,
free of particles and/or any etch patterns. Otherwise, the excess leakage
of helium from the backside of the wafer could create process pressure
stabilization and helium clamp pressure stabilization and abort the process.
Note: the lower electrode is domed
.050” center to edge. when the wafer is clamped down, it is domed as well.
8.3.4
Use a 6-inch pocket wafers, with
a 4-inch recessed etched area, to blank etch of a 4-inch wafers or smaller
samples without using adhesive. Do not use packet wafer to carry photo-resist
patterned wafer/samples. Photo-resist
on the wafer will be burnt because the pocket wafer hinders heat conduction
between the etch wafer/samples and the water-cooled electrode.
Attach patterned 4-inch
wafer or smaller samples to a clean carrier wafer by using adhesive such
as; Kapton tape (small amount place on
top at the edges of sample to hold the sample down), cool grease (very thin
layer at the bottom), or double-side heat tape. If you re-use a carrier wafer,
make sure that the glue residue from previous etch sessions are thoroughly
cleaned. Such residues could easily contaminate the etch chamber and change the
etch process.
Note: Do not use Lam5 Dummies as carrier wafers for processing your
4-inch or smaller substrate in this
tool. Use your own carrier wafers instead to prevent cross contamination.
8.3.5
You can save a file name, e.g. a
customized recipe on the Lam5 system hard drive for your future use or as a
backup. Please note that the file name
DOES NOT have the old 8-character limit
imposed by the old DOS system, however, file name still can not contain any
special character/s or space/s. Please start the file name with your login name
followed by an underscore “_”,
e.g. "ferrari_polyetch1". This will aid you find your file (recipe
name) in the directory, much quicker and the job of administrating the tool
much easier for the staff to manage.
9.0
Equipment Operation
9.1
System Description
Lam5 is a fully automatic etcher.
All operations, except wafer cassette loading/and unloading, are controlled by
Envision, a UNIX Graphical User Interface (GUI) software package. The system is
operated by the keyboard with trackball and a CRT display on the front of the
etcher. Do not touch any other hardware
switches. On the CRT display, the GUI screen is divided into three major
areas: Header (top), Control/Info Pages (center), Page Group Buttons (bottom).
See Figure 11.1.
9.1.1
Header – The header contains the followings:
►
Wafer Transfer Button: When
clicked, it pauses or resumes wafer transport. It does not affect the etch
process in the etch chamber.
►
Non-edit field for Time/Date, Machine Status, and Alarm Status: During normal operation, the Machine Status should show only Load
and Process Idle, Load and Process Active, or Wafer clean out.
►
Help Button: Provides limited help on
the tool.
►
Security Button (pad lock icon): Click
this button to login/out the system.
9.1.2
Control/Info Pages – There are total of 9
control/info pages available on the Envision system. These pages can be
selected by invoking the desired menu options (page buttons) available at the
bottom of the screen. Only 5 of these pages are accessible by a qualified Lam5
user, as per follows:
►
Operate Page: Select recipe and
start/stop wafer loading.
►
Process Page: Monitor wafer movement
and etch chamber process parameters. Manually End-Point a process step, or
abort the whole process.
►
Recipe Page: Write new recipe or edit
existing recipe.
►
Data Log Page: Monitor endpoint signal
traces.
►
Alarm Page: View and clear/purge
alarms.
Note: Diagnose, Maintain, Setup, and Library pages can be viewed by users.
Only Equipment staff is allowed to change the system setting on these pages.
9.1.3
Page Buttons – These are the 9 page buttons discussed earlier located at the bottom of the screen. Click a button to
select/display the corresponding control/info page. There is a Menu button on
the left lower corner. Click it to access to the sub-pages of the displayed
control/info page.
9.2
System Operation
9.2.1
Enable Lam5 on the WAND. Check
with equipment staff if there is a problem reported when you enable Lam5.
9.2.2
On the GUI screen of Lam5, check
the header line. It should read “Load and Process Idle: Host: LOCAL“, and the alarm
status below should read “All system normal”. Do not use Lam5 if the header
line reads otherwise. You will need to log in before accessing various
control/info screens and be able to etch your wafers, as per follows:
9.2.3
Click [Security] Button (padlock icon) to open the User Login Window.
Enter the ID (currently set as "labmember") followed by the return
key, and again return on the Password
field (no password is required for this access level). This will log you into
the machine. The security button located at the top right of the screen will changes from "no
user" to "labmember".
9.2.4
Load wafers to be processed in a
blue cassette and load the cassette onto the entrance indexer (left side). Make
sure the “H bar” on the bottom of the cassette sit properly in the slot at the
center of the indexer. The indexer will lower to the first wafer position of
the cassette.
Note: Wafer flat needs not be aligned.
Lam5 has an automatic flat finder for alignment. Make sure the wafers seat all
the way to the end of the slots. A sticking out wafer will cause problem for
the flat finder.
9.2.5
Load another blue cassette on the
receiving indexer (right side). It will lower to the last empty slot position.
If a cassette already loaded on the receiving indexer and it is in the up position,
tilt it toward you about 30 degrees and then release. It will start lowing
down.
9.2.6
Click [Operate] Page Button, the screen displays the Control Panel page (Figure 11.1). If not, click [Menu] Button on the right lower corner, and select Control Panel.
On the left side of the [Start]
Button, make sure that “Load and Process” is selected (white bullet means
selected; grey means not).
9.2.7
Click [Select Recipe] Button, and select the recipe you plan to use.
Note: Do not
overwrite the standard recipes, if modifications are to be made, then save as a
different recipe/name, as prescribed in Section 9.3.2.
9.2.8
Click [Start] Button to start the etch process. The header line change
from Load and Process Idle to Load and Process Active.
9.2.9
Click [Process] Page Button to monitor the wafer transport and etch
process (Figure 11.2). If the screen does not display the
Main Chamber Page, click [Menu] Button
on the right lower corner, and select Main Chamber. During the etch process,
you can select to perform the following tasks:
►
Click [Manual Endpoint] Button to skip to next recipe step.
►
Click [Abort Process] Button to skip to the end of the recipe.
Note: End point can be monitored in Data Log page.
9.2.10
If you want to change the etch
time or select a new recipe for the next and following wafers, click [Pause Transport] Button on the top
left corner of the screen. The wafer in the main etch chamber will continue and
complete its original process.
Refer
to Section 9.3 to change the etch time. Repeat Section 9.2.6 - 9.2.7 to select
a new recipe or the saved recipe with the new etching time.
Click [Resume Transport] Button to resume processing the wafer paused
in the load lock or load station.
9.2.11
If a system alarm occurs during
the process, refer to Section 9.5 for responding actions.
9.2.12
After the process is complete,
and the last wafer is loaded into the receiving cassette, the receiving indexer
will rise up. If not, make sure the robot arm has retracted, then tilt the
cassette it toward you about 30 degrees and then release. It will start rising
up. Wait till the indexer stop, and then remove the cassette to unload your
wafers.
9.2.13
Click [Security] Button (padlock icon) to log out. Disable Lam5 on the
WAND.
9.3
Recipe Editing/Writing
9.3.1
Click [Recipe] Page Button to access the recipe editor page (Figure 11.3).
Below
the header, there are two buttons: one for Module selection (only PM1 9400
available) and the other for Page selection. Make sure [Recipe] shows on the button. If not, Click the Button and select
“Recipe” from the pull-down menu.
On the
right hand side of the screen, there are 8 buttons for recipe file managements,
e.g. copy, delete, and etc. It is recommended that you modify an existing
recipe for your process, instead of writing new one from scratch.
9.3.2
Click [Open] Button to open an existing recipe, or click [New] Button to write a new recipe. If
you are writing a new recipe, enter the recipe name in the Recipe field, and a
line of description in the Comment field.
Note: A
recipe, created by lab member, should start with the member’s login name,
followed by an underscore, then the remaining of the recipe name. Important!
Any recipes not saved this way will be deleted.
9.3.3
You can enter/edit the process
variables in every process steps. The basic variables use in the standard
recipes are:
►
Pressure – the minimum pressure
depends on the total gas flow.
►
TCP RF - upper electrode power.
►
Bias RF - lower electrode power.
►
Gap – 5.8 cm for all recipes
►
Process Gas Flows – Only Cl2,
HBr, CF4, O2, and He are used.
►
He Clamp – 4 Torr for all the
recipes
►
Completion – There are 6 options
for this field.
Stabl: If the process condition
is stabilized within the time specified in the Time field below, the recipe
advanced to next step. Otherwise, the recipe holds and the system alarms. You
have to clear the alarm (Section 9.5) to continue.
Time: The recipe step will run
the whole length of time specified in the Time field below.
EndPt: The recipe step will run till the Endpoint condition specified in
the Endpoint fields (explained at the end of this section) is reached. If the
Endpoint condition is not reached within the time period specified in the Time
field below, the system alarms. You have to clear the alarm (Section 9.5) to
continue.
EndPt2: not used.
OverEtch: The recipe step will
run the percentage, specified in the Time field below, of the length of time of
the previous EndPt step.
Recipe: This entry terminates the
recipe. This process step and following steps will not be executed.
►
Time (sec): The maximum length of
time the recipe step will run. In case for the over-etch, it set the percentage
of time of the previous EndPt time.
Note: Do
not select “Recipe Params” from the pull-down menu. The Recipe parameter page
set up the chamber temperature, the lower electrode temperature and other
machine parameters. The chamber and lower electrode temperature are controlled
by two separate chillers in the service area. If you need to change these
temperatures, contact equipment staff.
The followings setup Endpoint
Trigger in the Main Etch Step (EndPt step)
►
Channel: The automatic Endpoint
detector channel. Enter “A” for poly-silicon etch.
►
Delay: In this time period, the
endpoint signal is ignored due to plasma stabilization, and etc.
►
Norm (sec): In this time period,
the endpoint signal readings is normalized (averaged).
►
Norm Value: The system will shift
the normalized endpoint signal reading to a number that is easy for
calculation, e.g. 5000 in the standard recipes.
►
Trigger (%): If the endpoint
signal falls below this percentage of the norm value, the recipe step ends and
continue on next step.
Note: Do
not select “EndPoint2” from the pull-down menu since it is not used in Lam5.
9.3.4
Process variable tolerance
set ups
There two types of tolerances can
be set in a recipe: hard tolerance, and soft tolerance. If a process variable
exceeds the hard tolerance, the system will alarm and the recipe step will abort
and you have to clear the alarm (Section 9.5) to continue. If a process
parameter exceeds the soft tolerance, the system will just alarm and continue.
The default tolerance setting for all steps in a recipe is 10% for both soft
and hard tolerance.
To change the tolerance of a
process variable, click the [Recipe]
button next to the work “Page”, and select [Recipe
Tolrnc] from the pull-down menu. You can now change the variable tolerance
of process variables.
It is recommended to increase
tolerance of Pressure in the recipe
step that plasma strikes. When the plasma strikes, the pressure jumps up a few
mtorr for a very short of time. If the pressure was below 20 mtorr, the
pressure increase will exceed the 10% hard tolerance.
9.3.5
Save the recipe to the hard drive
by click [Save] Button on the right
side of the screen. Do not over-write the standard recipes on the hard drive.
If you are saving a modified standard recipe, click [Save As] Button. And save the recipe with the a new name that
starts with you login name.
Note: Only the recipes saved on the hard drive can
be selected on [Operate] page. If
you have modified a recipe but have not saved it on the hard drive, you will be
running the un-modified version of the recipe when you select it on [Operate] page.
9.4
Endpoint Signal Tracing
9.4.1
Click [Datalog] Page Button and the Graph Page shows on the screen (Figure 11.4). If not, Click [Menu] Button, then select “Graph”.
9.4.2
On the lower left corner of the
Graph page, there are four signal channel fields, i.e. A, B, C and D, that you
can select. Select a channel, then click [Load
Config] Button below the field. A window with all the preset signal channel
configurations will pop up. Select the signal, e.g. Endpoint Channel A, TCP RF,
and etc. Do the same for other signal channels.
9.4.3
Click [Manual On] Button below the graph to start the signal tracing. The
signal traces will show up when the recipe is running in the process chamber.
9.4.4
On the top and bottom of the Y
axis, you can enter the range each tracing signal. Adjust the range according
to you preference.
9.4.5
If you are satisfied with your
set up and plan to use the same set up in the future, Click [Save Set] Button on the lower left
corner. Save the set up with the name started with your login. In the future,
you can load the same setup by clicking [Load
Set] button, and then select the set up you saved.
9.5
Responding to An Alarm
9.5.1
Alarm Indicator Symbols – There
are three type of alarm symbols with a brief message displayed in the second
line of the header area of each page screen.
►
Green Circle: All system Normal.
►
Red Triangle: Indicates an
emergency condition, process abort by user, or a process variable exceeding
hard tolerance. Wafer transport suspended; and the alarm must be cleared by the
user.
►
Yellow Square: Indicates a less
severe condition. The wafer in the process chamber will either hold at a
stabilization step, or complete the etch step. However, the wafer transport
will be suspended until the alarm condition has been corrected and the alarm
cleared itself.
9.5.2
Viewing alarm Status and Clearing
Alarms – Click [Alarm] Page Button,
the alarm status page will show up (Figure 11.5). If not,
Click [menu] Button, then select
“Status” from the popup menu. There are 4 buttons on the lower right side of
the page.
►
Clear: Select the alarm line you
want to delete, and then click this button to clear the alarm one at a time.
►
Clear All: Click this button to
clear all the alarms. However, problems that can not cleared by the system will
show up as a new alarm.
Note: Cleared alarms remain displayed, but appeared dimmed.
►
Purge: Click this button to
remove all the cleared alarm from screen.
►
Enable/Disabled: Click this
button to toggle between audible and silent alarm modes.
10.0 Trouble
Shooting Guidelines
10.1 Wafer In The Entrance
Cassette Not Picked Up By The Wafer Shuttle
10.1.1
Cause: The wafer cassette is not loaded properly.
Solution: Adjust the cassette slightly to correct the
problem. Do not lift the cassette because the wafer shuttle is in the cassette.
10.1.2
Cause: The wafer is not loaded properly, e.g. cross
slots, in the wafer cassette.
Solution: Report the problem on WAND, or ask help from the
equipment staff. Do not try to remove wafer cassette or wafer from the
cassette. Doing so may bend the wafer shuttle stuck in the cassette.
10.2 Load Point Vacuum Alarm
10.2.1
Cause: Wafer back side too rough or contaminate
with particles/film.
Solution: Ask equipment staff to remove the wafer for you.
10.2.2
Cause: Wafer Shuttle vacuum problem
Solution: Wait a few seconds, this problem usually clears
itself. If not, Report on WAND.
10.3 Chamber/Electrode
Temperature Out of Tolerance Alarm
10.3.1
Cause: Previous user may set a different
temperature.
Solution: Wait for a few minutes for the temperature to
stabilize. If not stabilizing, report on WAND.
10.3.2
Cause: The chiller is not working. This is the case
if the temperature is at or cooling toward room temperature.
Solution: Report the problem on WAND. The equipment staff
will check the chiller.