Chapter
8.31
Rudolph Ellipsometer
1.0 Title
Rudolph Ellipsometer Operation
2.0 Purpose
Provide the procedures for measuring thickness and/or
refractive index of transparent films using the Rudolph Ellipsometer.
3.0 Scope
The Rudolph
Ellipsometer is a version of the AutoEL II Automatic Ellipsometer (Model
A9822). It is capable of performing ellipsometric measurements at three
wavelengths: 405, 633, and 830 nm. An external PC with the customized DAFIBM
software converts the measured Δ and Φ values
into thickness and refractive index.
This document covers the Initialization
procedure, measurement procedure, and the setup/use of the software DAFIBM (DOS
based) for the calculation of the film thickness and/or refractive index.
4.1
Preliminary Operating Manual, AutoEL II-NIR-3,
A9822.
Double Layer Absorbing Film Calculation
Program (DAFIBM) Manual
(In Office and Laboratory)
4.2
AutoER-II Automatic Ellipsometer Instruction Manual (in Office)
5.0 Definitions & Process
Terminology
5.1
Ellipsometry
Measures the change in polarization of light reflected from
the surface of a sample. The measured values are expressed as Δ and Φ. These
values are related to the ratio of Fresnel reflection coefficients, Rp and Rs
for p- and s- polarized light, respectively. Because ellipsometry measures the
ratio of two values, it can be highly accurate and very reproducible. The ratio
is a complex number, thus it contains phase information, delta, which
makes the measurement very sensitive.
5.2
Refractive Index (n)
The real part of the optical constant of a material. It
defines the phase velocity of light in the material: υ = c / n, where
υ is the speed of light in the material and c is the speed of light in
vacuum
5.3
Extinction Coefficient (k)
The imaginary part of the optical constant of a material. It
is directly related to the absorption of a material. It is related to the
absorption coefficient by: α = 4 π k / λ, where α is the
absorption coefficient and λ is the wavelength of light.
6.0 Safety
Follow the general safety guidelines in the lab.
7.0 Statistical/Process Data
Refer to Appendices.
8.0 Available Processes,
Process Notes
8.1.1
STARTUP: Default
program for DAFIBM software. It can used to measure most of the oxide single
layer films.
8.1.2
GENERAL: General
program for single layer films, e.g. oxide, nitride, and low stress nitride,
and etc.
8.1.3
THINOX: Customized
for measuring thin oxide films.
8.1.4
T17MON: Customized
for measuring TYSTAR17 Low Stress Nitride Monitor wafers (1000 to 1500 Å).
8.1.5
THICKLSN: Customized
for measuring TYLAN18 Low Stress Nitride up to 15000 Å).
8.1.6
There
are several customized programs setup by lab members for their own special
applications
8.2
Process Notes
8.2.1
The Rudolph Ellipsometer is
capable of measuring two-layer film stack. Please consult the process staff for
program setup.
8.2.2
You can set up your own customized
program on the laptop PC. However, if you try to overwrite the standard
programs listed in Section 8.1, the software will abort,
and you have to restart it.
9.0 Equipment Operation
9.1
Equipment Description
The Rudolph Ellipsometer is comprised of the ellipsometer itself and a
laptop PC running DAFIBM software for film thickness and refractive index
calculation. See Section 11.1 for the physical
layout of the ellipsometer and Section 11.2 for the
display screen of the DAFIBM software. The Rudolph Ellipsometer uses a white
visible light source. There is no laser in the system.
9.2
Measurement Procedures
9.2.1
Enable the Rudolph Ellipsometer on
the WAND. It will turn on the light source of the Ellipsometer.
Initialize the Ellipsometer
9.2.2
Make sure the ellipsometer is ON.
If it is OFF, turn the key switch on the lower left side of the ellipsometer
base to turn it on.
9.2.3
Adjust the compensator (left arm)
to the free position (white) and the filter selector (right arm) to the 633 nm
(light red, inner most) position.
9.2.4
Place the 1100 A silicon oxide
sample (in the drawer under the Ellipsometer) on the center of the wafer stage.
Pull the thumb knob on the lower left of the stage, and push the stage to the
inner most position.
The wafer stage slides on a track with 4 fix positions, so
the light beam can reflects on the center, 3 cm, 5 cm, and 6 cm from the center
of the wafer. To move the stage, pull the thumb knob on the lower left of the
stage, then slide it inward/outward. The stage can rotate 360º.
A vacuum switch is located on the right hand side of the
base. Flip the switch down will turn on the vacuum and hold the wafer onto the
stage. To release the wafer from the stage, flip the switch down.
9.2.5
Check the reflected light beam
aligned to the center of the analyzer aperture (tip to the right arm). If not,
turn all three knobs on the bottom of the stage in the same direction to adjust
the height of the stage, so that the reflected light beam aligns with the
analyzer.
9.2.6
Look into the ACT eyepiece
and adjust the three knobs so that the white spot (lighted) is centered in the
circle. You should be able to turn the knobs freely. If you need force to turn
them, they are already at their limit and should not be turned anymore.
9.2.7
Press the RESET button and
the CONT button on the Ellipsometer keyboard. The Display will prompt INITIALIZATION
PROGRAM for about 30 seconds, then DOWN-COMP PRESS CONT OR PROG.
9.2.8
Select a wavelength to perform the
measurement and adjust the compensator (left arm), and Filter (right arm)
accordingly. All standard and most of the customized programs uses 6328Å wave
length.
|
W. L. |
Compensator |
Filter |
Remarks |
|
6328 Å |
Light Red dot |
1 ring |
PC program default |
|
8300 Å |
Dark Red dot |
2 rings |
Need change in PC prog |
|
4050 Å |
Blue dot |
3 rings |
Need change in PC prog |
9.2.9
Depress the PROG button,
then enter one of the following two-digit programs. These are the operating
programs for the Ellipsometer. Usually program
01 is used for best accuracy. These programs are not related to the
programs you are going to select on the laptop PC.
|
Prog # |
# of Zones |
Rel.
Accuracy |
Rel. Speed |
|
01 |
2 |
High |
Slow ~40
seconds |
|
02 |
1 |
Low |
Fast ~15 seconds |
|
03 |
2/1 |
Med |
Med ~25
seconds |
Set Up a
Laptop PC Program
9.2.10
Open the laptop PC and check that
the DAFIBM software is running. If not, go to Section
9.3 to start the software.
9.2.11
Press the space bar on the laptop
PC to move the cursor to Program filename field. Press the [m] key to
enter the program names. Refer to Section 8.1 for
available programs. After typing in the program name, Press the [f] and [l]
keys to load the program from the hard drive, and the [m] key to return
to the Main Menu page.
If you need a new program for your application, refer to Section 4.0 for additional information to set up new
ones, or contact the Process Staff.
9.2.12
If you are not using the default
wavelength 6328 Å, press the space bar to move the cursor to the LAMBDA
field. Press [m] and enter the wavelength you are using (8300 Å or 4050 Å).
9.2.13
Press [g] and the DAFIBM
main menu will disappear from the screen. The laptop PC is now ready to receive
information from the Ellipsometer.
Perform a Measurement
9.2.14
Remove the 1100 A oxide wafer and
put it back into the wafers holder. Place the wafer to be measured onto the
wafer stage. Slide the stage to the desired position.
9.2.15
Press the CONT button on
the Ellipsometer. The Ellipsometer displays MEASURING SAMPLE – PROGRAM NO.
XX.
9.2.16
When the measurement is finished,
the Ellipsometer displays the Delta and Psi. The laptop PC will display the
film thickness and the refractive index.
9.2.17
To do another measurement, repeat
Section 9.2.15 again.
9.2.18
After you have finished taking
measurements, close the laptop PC screen. Disable RUDOLPH on the WAND.
9.3
Start DAFIBM software on
the laptop PC
9.3.1
Turn the laptop PC, and it will
start WINDOWS 98 operation system. Click the Start button on the lower
left of the screen, and select shutdown. Select restart in DOS in the
shutdown option.
Note: please do
not use RUN commands of WINDOWS98 to start the DAFIBM. It only creates
more communication errors.
9.3.2
At the C:\ prompt, type cd
\Rudolph, then press the Enter key. Type in dafibm and press
the Enter key again. The program will start and the screen will display
the main menu
10.0 Troubleshooting Guidelines
10.1
After measurement, the
Ellipsometer displays COMMUNICATION ERROR, and the laptop PC does not
display the measurement results.
Solution: Press the space bar on the laptop PC and it will display the
main menu. Press [g] key and redo the measurement
10.2
The first measurement after
Initialization, the Ellipsometer does not display any result after 1 minute.
Solution: The compensator (left arm) may still at the
free position (white). Set it to the position for the wavelength you have
chosen to do the measurement.
11.0 Figures and Schematics
11.1
Rudolph Ellipsometer
Control Layout
12.0 Appendices
12.1 Measurements (average of three measurements) of the Rudolph
Ellipsometer, Nanoduv, and Nanospec on five oxide wafers.
|
Wafer # |
2 |
16 |
4 |
8 |
13 |
|||||
|
|
Å |
RI |
Å |
RI |
Å |
RI |
Å |
RI |
Å |
RI |
|
Rudolph, Prog #1, 10/21/02 |
||||||||||
|
Ave. |
134 |
1.454 |
208 |
1.473 |
522 |
1.472 |
776 |
1.473 |
1147 |
1.465 |
|
Range % |
5.24 |
3.58 |
0.96 |
0.61 |
0.58 |
0.27 |
0.39 |
0.20 |
0.09 |
0.07 |
|
Rudolph, Prog #2, 10/21/02 |
||||||||||
|
Ave. |
160 |
1.338 |
235 |
1.379 |
540 |
1.451 |
789 |
1.466 |
1151 |
1.465 |
|
Range % |
25.57 |
11.96 |
1.28 |
0.80 |
0.93 |
0.34 |
0.25 |
0.14 |
0.26 |
0.00 |
|
Rudolph, Prog #3, 10/21/02 |
||||||||||
|
Ave. |
111 |
1.750 |
190 |
1.572 |
||||||