FILM THICKNESS MEASUREMENT (SCI FilmTek 2000)

PREPARED BY:
FILM THICKNESS MEASUREMENT
(SCI FilmTek 2000)
Steve Franz DATE
Lab Manager
1
04/01/03

1.0 SCOPE
FILMTEK 2000 THICKNESS MEASUREMENT
This document establishes the procedures for film thickness measurements
using the Filmtek 2000 in the Nanoelectronics laboratory.
2.0 APPLICABLE DOCUMENTS
Filmtek logbook and maintenance log
FilmTek Operations Manual
3.0 MATERIALS AND EQUIPMENT
FilmTek 2000
FilmTek Si reference wafer
Tweezers
4.0 INTRODUCTION
The FilmTek 2000 is a spectrophotometer capable of measuring a reflected
beam from the UV (280nm) through the visible and near IR (1700nm). Based
on software integrated into the FilmTek computer, film thicknesses and
refractive indexes of multiple layers can be measured. In some cases, extinction
coefficients and even bandgap or doping can be measured. Care must be
taken, however, since for some cases eg numerous multiple thin layers, a
unique solution may not exist and another measurement technique must be
used. Examples of films that can be measured include: very thin oxides or
nitrides, polymer films, silicon on oxide (SOI) film stacks, III-V heterostructures,
porous Si films etc..
4.1 Principal of Operation
A light source of the desired wavelength range is used to shine light at normal
incidence through a focussing system to form a spot on the sample surface. The
reflected beam is sent through the appropriate optical path to the detector. A
beam splitter, usable only in the visible, is used to display the image on a video
screen. The splitter must be removed from the optical path for UV
measurements. There are 3 detectors selectable by software; one for each
wavelength range. There are also 3 light sources used for our system: a
deuterium lamp for UV wavelengths, a halogen lamp for visible and IR
wavelengths and a microscope lamp for visible and IR wavelengths. The
halogen lamp is usually not needed and should be left off.
Absolute reflection data is obtained by comparing sample reflection to the
measured reflection of a user supplied reference substrate. Using a generalized
material models in combination with advanced global optimization algorithms
and power spectral density analysis, FilmTek can simultaneously determine:
Multiple layer thickness
Indices of refraction [ n(λ) ]
Extinction (absorption) coefficients [ k(λ) ]
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The parameters that are solved for, along with the layer structure of the sample
being measured, are stored in recipes. The FilmTek computer contains many
commonly used recipes and the user can modify these recipes and create new
recipes. The measurement sequence is initiated by clicking a single button in
the FilmTek Main Window. The spectrophotometer scans the sample over a
predefined range of wavelengths. The software generates a corrected spectrum
based on a previously stored reference scan, and then performs a regression
on the unknown parameters to fit the simulated reflection and power spectral
density to the their observed values. The resulting thin film parameters along
with the measured and modeled spectra are then displayed for the user to
examine.
FilmTek can precisely measure virtually all translucent films ranging in
thickness from less than 100 angstroms to approximately 50 microns. Typical
applications include:
Semiconductor and dielectric materials
Computer disks
Optical antireflection coatings
Coated glass
Electro-optical materials
Laser mirrors
Multilayer optical coatings
Thin Metals
5.0 SYSTEM SET UP AND OPERATION
5.1.1 Turning on the system
The computer and microscope lamp should be left on but the Deuterium lamp
and Halogen lamp should be left off when not in use. You only need to use the
Deuterium lamp if you need to use UV wavelengths. You only need to use the
Halogen lamp if you are using visible or IR AND you are not getting enough
signal from the microscope lamp. To turn on the various lamps (see Fig 1):
Fig 1. Filmtek Lamp Power Supply
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5.1.2 Deuterium Lamp (UV)
To turn on the deuterium lamp (UV only):
NOTE: The LED below the lamp switch is green if the power is on.
1 Verify that the main power is on (green LED labeled power).
2 Turn off the halogen lamp if it is on (red button) and
3 Press the blue button and wait 10 seconds. The green LED below
the blue (deuterium ) lamp switch should come on; if not press the blue
switch again. If you need to turn back on the halogen lamp, simply
press the red button.
4 If the Deuterium LED turns on red, press the blue button again.
NOTE: Both lamps should be warmed up for 10 minutes before using.
To turn off the deuterium lamp :
Simply press the blue button and the green LED should go out indicating
the lamp is off. The lamp should be left off when not in use to prolong its
life.
5.1.3 Halogen Lamp (Visible & IR)
To turn on the halogen lamp simply press the red button and the green
LED should come on. To turn it off, press the red button again. Normally
the halogen lamp may be left off since the microscope lamp contains
enough energy for the visible and IR spectrum.
5.2 Microscope Set Up
Fig 2. Filmtek 2000 Microscope
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CAUTION: Adjust ONLY those knobs discussed below. Do NOT tamper with any
other knobs or filters.
1 Make sure the appropriate light source is on (section 5.1.1 and 5.1.2)
and that the microscope lamp is on as well (Fig 2). The field diaphragm
and aperture should be closed down all the way (levers down).
2 To image a sample, place a sample on the stage and select one of the
silver objectives by rotating it into position. Do NOT use the black
objective for viewing an image; this is only to be used for taking
measurements in the UV range.
3 Make sure the UV-Vis shutter is in the “in” position. It is also labeled
BF/DF on the microscope body.
4 All images are viewed on the TV monitor which is left on. Adjust the focus
knob located at the base of the microscope. If your sample has no
features, focus to get a sharp image of the field diaphragm edge.
5 The lamp on/off switch is located at the rear base of the microscope and
should be left on. Lamp intensity may be adjusted by the knob at the
bottom left of the scope (Fig 2). This should be adjusted to get the
appropriate signal level as discussed in section 5.1.5.
5.3 Computer Set Up
The computer is usually left on but may need to be woken up from the sleep
mode by pressing a key. It may also be rebooted following standard Windows
procedures. No password is required. The system runs on Windows XP and has
both a CDROM drive (top bay) and CD-Write drive (bottom bay) as well as a
standard floppy drive. Data may be exported as ascii text files or graphic
metafiles to CD or floppy depending on file size.
5.4 System Operation
1 From the Windows desktop, double click on the Filmtek icon to start the
program. The program opens with the main window as shown in Fig 3.
Fig 3. Startup screen for Filmtek Program
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2 Unless you will use a stored recipe and don’t need to make any changes,
you will need to log in as a power user. To do so, click on “Security” on
the pull down menu and select “Log-in”. Type in User Name: SCI and
the password located on the cover of the FilmTek manual. Also select
“Power user” (Fig 4).
Fig 4. Log in screen
3 Click the recipe pull down menu at the bottom right of the screen and
scroll to the desired program.
Programs will have a descriptive name for the film and substrate to be
measured as well as a suffix UV, vis (visible) or ir for the appropriate
wavelength range. The microscope must be set up correctly for the
wavelength range being measured as well. If the desired recipe does not
exist contact lab staff or the appropriate engineer to assist in designing a
program. In some cases samples may need to be sent to SCI for initial
characterization. In all cases a known standard must be used to
insure that meaningful measurements are being taken.
4 Make sure the appropriate lamp is on (section 5.1.1 and 5.1.2). The
microscope lamp should always be on for sample viewing and as a
visible/ir source.
5 Choose the appropriate objective lens (silver for visible/IR, black for UV)
and position the light beam over the center hole in the wafer stage with
NO SAMPLE.
6 If you are using UV also make sure the UV-vis shutter is “out”. For visible
and IR it should be “in”.
7 For IR, choose “Calibration”->”NIR Settings” and click the enable box at
the bottom left. The integration time may be changed here as well (see
step 11).
8 Press the “Background” button in the toolbar (2 nd button from the left). A
graph with a red line at 0 should be displayed.
This step is to zero the machine taking into account ambient and stray light. It
should be done hourly or whenever a recipe is changed.
9 Place the SCI silicon reference wafer shiny side up on the microscope
stage and position the wafer under one of the visible (silver) objectives.
Focus on a clean spot on the wafer so that the field diaphragm presents a
nice sharp edge. UV-vis shutter should be in.
10 For UV: Select the black objective lens, pull out the UV-vis shutter and
press “Reference” on the toolbar (leftmost icon-Fig 3). For visible/IR:
Simply press “Reference” on the toolbar (leftmost icon-Fig 3). Press
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“Rescale” to update the graph.
This step calibrates the reflectance axis to a known standard (eg silicon)
so that it correctly reads in % instead of counts. . It should be done hourly
or whenever a recipe is changed. Other standards can be used eg glass
or other semiconductors but the program must be set up explicitly for this
in advance. The SCI manual discusses this in more detail.
11 A spectrum for the reference reflectance will be displayed as shown in
Fig 5 for visible and Fig 6 for UV. The counts should be between 1000-
2000 (for a silicon reference). To adjust signal strength for visible/IR,
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Fig 5. Visible spectra for silicon reference wafer properly scaled.
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Fig 6. UV spectra for silicon reference wafer properly scaled.
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the lamp intensity may be adjusted or the integration time may be
adjusted (for UV, only the integration time may be adjusted).
Select “Calibration” in the pull down menu and then choose “Data
Collection”. Select “Integration time”. Decrease the time to reduce the
count or increase the time to increase the count. Excessively noisy
signals may be improved by increasing “Samples to Average” or
increasing “Data Smoothing”. Verify also that the appropriate detector is
selected: UV= detector 1 and Visible = detector 2.
The real time signal from the detector may be checked any time by
clicking on the “Signal” button (2 nd from right in Fig 3). It may be
necessary to refresh the display by pressing “Data” or “Graph” and then
pressing “Signal” a 2 nd time. To check that the displayed signal is real
time, rotate the objective to block the light and after a few seconds delay,
the display should go to 0; if not, you must refresh the display.
12 Remove the silicon reference wafer and put it in the covered wafer
holder.
13 Place the sample to be measured on the stage and position the stage
under the appropriate objective lens (silver for visible/IR, black for UV).
14 With the UV-vis shutter in, focus so that the field diaphragm edge is in
focus.
15 For Visible/IR, press “Measure” button on the toolbar to initiate
measurement. For UV, pull shutter out and make sure black objective is
in place. Press “Measure”.
16 After a few seconds, a blue curve for the measured values is displayed
along with the red simulated curve. If Autosolve is enabled (usually the
case), it is not necessary to press “Solve” again.
17 The fitted parameters appear in 3 columns along the right side of the
display: name of parameter, initial value and final solution. Also the n and
k at a predetermined wavelength for a predetermined layer (usually layer
1 at 632 nm) are shown.
18 The root mean square error RMSE is shown at the bottom and if it is
greater than a preprogrammed limit, an error message will be displayed.
In general, you want the RMSE to be small ( “Save Data” and give it a descriptive
name. Use the default “Data” folder that pops up. Recipes, data and
modeling parameters must be in the proper default folders or the
program won’t be able to access them. Data can be saved as editable,
formatted text by using the report feature (see Filmtek manual).
20 If there is a problem with the data, you can try changing parameters in the
layers/settings dialog box (“Setup”->”Model/Layers Settings”). You can
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try extending the range of the film thicknesses, adding a layer (eg native
oxide or interfacial layer) or changing the parameter to be fitted. Press
“Solve” after making the changes and compare the curves and RMSE
again.
Care should be taken in adjusting materials or modeling parameters. It is
possible to get a good fit but the wrong result since there are so many
parameters which can be used to fit the curve. See the appropriate lab staff or
superuser if you are having serious problems.
21 When finished using the machine, remove your sample, close the
program and turn off the deuterium or halogen lamp if no one else is
planning on using the machine.
22 Fill in the log book and enter any problems in the comments section.
6.0 RECIPES
6.1 General
In general it is recommended that you get help for generating new recipes but in
some cases, for example for a thicker or thinner film, an existing recipe may be
modified fairly simply to make the measurement. In that case it should be saved
under a new descriptive name with the appropriate tag: vis for visible, uv or ir
(“File”->”Save Recipe as”. A more complete discussion of recipes and
parameters is given in the Filmtek operation manual but some suggested
guidelines are:
1 Try to limit the Film Thickness to the smallest range possible. Generally,
from the reflection spectrum one can deduce what limits should be used.
• If there are a number of maxima and minima in the spectrum, the film
thickness is greater than 1000 Angstroms. The more swings in the
spectrum, the thicker the film is. If the spectrum does exhibit maxima and
minima, be sure to use Thick Film Optimization techniques.
• If the spectrum is monotonic either the film is thin (< 100 nm) or highly
absorbing. If the film is highly absorbing, film thickness may not be
determinable.
2 When fitting on index and the material is known, if available, start with a
model which describes the material. For example, if it is known that the
material is Aluminum, start with a Material Model that describes
Aluminum. Also use constrained optimization on the Material
Coefficients. In the appendix of the Filmtek manual, there is a table
showing SCI Model Material Coefficients for many common materials.
3 Use as few fitted parameters as possible to solve the problem.
4 If the spectrum does exhibit maxima and minima, be sure to use Thick
Film Optimization techniques.
5 When fitting on index and it is known that the film has no absorption, use
the SCI Material Model and set the High Dielectric Constant to 1, the
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damping coefficient to zero, the Vibrational Frequency to zero, and do not
fit on any of these parameters.
6 When solving for an unknown dielectric material which does exhibit
absorption in part of the spectrum, it sometimes best to solve the problem
in parts. The procedure is as follows:
• Limit the wavelength range to that part of the spectrum where the film is
transparent.
• Use the SCI Material Model with a single oscillator. Set the High
Dielectric Constant to 1, the damping coefficient to zero, the Vibrational
Frequency to zero, and do not fit on any of these parameters. Solve for
thickness, Amplitude and Center Energy.
• Include the entire wavelength range.
• Solve again, fitting only on Vibrational Frequency, Damping Coefficient,
and High Dielectric constant.
• Next, fit on all parameters.
• If the fit is not satisfactory, add another oscillator fitting on all
parameters. Starting values for another oscillator are :
Value Max Min
High Dielectric Constant 1 3 1
Damping Coefficient 025 1 0
Amplitude 15 30 0
Center Energy 7 30 2
Vib. Freq. 1 5 0
7 For very thin films, it is usually best to use the UV wavelength range to get a
sufficient number of cycles (interference fringes). Don’t use UV for highly
absorptive thick layers or a thick film stack where the beam cannot penetrate
to the desired interfaces.
8 For some III-V heterostructures or SOI layers, IR may be a good choice. In
this case the light can penetrate to the various interfaces but the substrate’s
backside may play a role in the reflected signal and may need to be
accounted for. The reference for example should have the same type
backside (eg polished vs rough) as the sample. The backside reflections
can be included or excluded in the checkbox in the Layers/Settings dialog
box but is not used in calculating the curve.
6.2 The Model Window/Changing Parameters
In the Model Window, the known and unknown film properties of the sample to
be measured are specified. The properties set in the Model Window include :
Number of layers
Thickness of known layers (if any)
Maximum thickness of each layer
Minimum thickness of each layer
Material model or NK file for each layer
Material model or NK file for the substrate
Enable surface roughness measurement (FilmTek 2000 only)
Enable the use of Thick Films Optimization Techniques (Fitting on Power
Spectral Density, Filmtek 1000 and FilmTek 2000)
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Materials may be defined by equation/dispersion formulas (models) or by an NK
file. The available material models include: Sellmeier, Cauchy, Cauchy
Exponential (which is highly recommended for glasses), Drude, Lorentz
Oscillator, and Drude+Lorentz Oscillator. In addition to the above-mentioned
material models, FilmTek provides two new generalized dispersion formulas
(SCI and Tauc Lorentz Model) which apply to metals, amorphous and
crystalline semiconductors, and dielectric materials. The SCI Model is the
only material model you will ever need to model any material . The
Tauc Lorentz model is very useful when it is desired to solve for the band gap
energy.
If the material type is other than NK, the index of refraction values are calculated
from the coefficients of the model equation. These coefficients may be edited in
the Coefficient Table along with their respective maximum and minimum values.
In FilmTek the user may fit on the coefficients of an equation based material
model but not directly on the NK values.
The Model/Layer Setting Window is shown below. Each individual parameter is
described below.
Fig 7. Model Layer/SettingsWindow
Number of Layers: This combo box is used to select the number of layers in
the stack. The first layer is the layer next to the substrate. The film stack can be
composed of up to five layers. Zero is selected to specify that no films are on top
of the substrate (zero layers).
Include Substrate Backside:
The user can choose to include or exclude reflections from the second surface
(backside) of the substrate. To include backside reflections simply click on the
box with the mouse and input the substrate thickness in the first row third
column of the layer configuration table (substrate thickness is always specified
in mm).
Note: Since phase information is physically not meaningful for incoherent
layers, the calculation of ellipsometric parameters are completely unaffected by
this check box. FilmTek will always ignore the backside reflection in calculating
ellipsometric data. When collecting ellipsometric data, the backside reflection
should be minimized.
Note: One can not fit on the thickness of the substrate. To handle this problem
when the substrate thickness is unknown, make the substrate material VOID or
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air and set the material of the first layer to the substrate material. Also set the
thickness units of layer 1 to mm, which makes layer 1 a massive or incoherent
layer.
6.3 Layer Configuration
This table is a spreadsheet with eight columns and up to six rows. Each row
represents a different layer in the film stack. The layer number is displayed in
the column zero. Columns one to eight are:
Fit on Thick. : The first column contains a check box labeled ‘Fit’. Checking
this box will cause the layer thickness to be solved for when the measure or
solve button is pressed in the main window.
Thick. : The second column displays the starting layer thickness.
Thick Max. : The third column displays the maximum layer thickness.
Thick Min.: The fourth column displays the minimum layer thickness.
Thick Units: The fifth column is used to display the thickness units of the
associated layer. The user should only select “mm” for layers that are
massive (very thick layers that should be treated as incoherent layers such
as glass substrates).
Material File: The sixth column is used to display the material file name of
the associated layer. To load a previously saved NK file or one of the files
supplied with FilmTek click on the combo-box and select one of the listed
material files. Please note that if the Material Model is not NK, then the
Material Model and not the displayed NK file give the nk values. To make
the Material File active, check to see that the Material Model is NK.
Fit on NK: The seventh column contains a check box labeled ‘Fit’. Checking
this box will cause the layer material model coefficients to be solved for
when the measure or solve button is clicked in the main window. Note that
in FilmTek the user fits on the coefficients of the equation based material
models rather than directly on the NK values. The Fit on NK button is
disabled whenever the selected Material Model is NK. A utility to convert
NK files to an equation based material model can be accessed from the
main window (Find Coefficients under the Utilities pull down menu).
Material Model: The last column is used to display the material model for
the associated layer.
6.4 Coefficient Table
In the Coefficient Table the user may edit the coefficients of equation-based
materials along with their respective maximum and minimum values . The
number of coefficients necessary to fully describe the material depends on the
particular material model. The Cauchy material model has six coefficients : An,
Bn, Cn, Ak, Bk, Ck. The Sellmeier, on the other hand, has only three
coefficients. In addition to specifying the coefficients along their maximum and
minimum values, in the Coefficient Table the user also specifies which
coefficients will be allowed to vary.
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The fitted coefficients are defined by checking the small check box in the
second column next to the parameter value to be fitted. It is important to note
that the checked coefficient is not fitted on unless the Fit on NK button located
in the Layer Configuration Table is also checked.
7.0 Sample Problems
7.1 Determining The Thickness of Thick Films (Polyimide on SiO2 on
Silicon:
Problem: To determine the thickness of polyimide on silicon oxide on silicon.
Spectroscopic reflection data at normal incidence (angle of incidence = 0°) is
supplied for this problem on the SCI CD ’22 um Polymide on sio2 (2um) on
Si.tar”.
Fig 8. Layer data for polyimide on SiO2 on silicon
Select thick film optimization option (5 th button from left labeled FFT). Click on
the “OK” button after filling in the data to return to the main window. Load the
data file (Data->Open “22 ¨µm Polyimide on sio2 on si.tar”) and click “Solve”.
The solved data graph is displayed as shown in Fig 9.
Fig 9. Solution to polyimide/SiO2/Si
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To verify number of films, select PSD/FFT button to display the power spectra as
shown in Fig 10.
Fig 10. Power Spectral Density for polyimide problem
The 2 peaks correspond to the SiO2 and Polyimide films.
7.2 Determining the Thickness and Index of SiO2 on Silicon
Problem: To determine the thickness and real index of refraction (n) of silicon
oxide on silicon. Spectroscopic reflection data at normal incidence (angle of
incidence = 0°) is supplied for this problem in “\data\SiO2.tar”. A 13nm SiO2 film
was grown on a silicon substrate. For this example we will load a previously
defined recipe.
Load the SiO2 Recipe by clicking on the combo box labeled Recipe in the lower
right corner of the main window. The Fitted Parameters table is automatically
updated to reflect the unknown variables in the SiO2 recipe. The main window
will appear as shown below.
Fig 11 Main window for SiO2/Si problem
To view or edit the Model click on the Model command button in the tool bar or
select Model/Layer Settings from the Setup pull down menu in the Main
Window. This will bring up the Model/Layer window shown in Fig 12. The first
row in the layer configuration table shows the substrate material (Si) name and
the material model (NK file). The settings for the first layer (SiO2) are shown in
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the second row, Labeled “Layer #1”. The ‘Fit’ check-box of Row 2 is checked to
allow the thickness of Layer 1 to vary during the optimization. The initial
thickness of the SiO2 is 50nm with a minimum and maximum thickness
constraints of 0 and 600nm.To view the model coefficients of SiO2 click on any
cell in the second row Labeled “Layer #1”. The SiO2 coefficient table is now
visible. The material model (dispersion formula) used for SiO2 in this example
is SCI. The extinction coefficient (k) for SiO2 is zero (for wavelength range
between 200nm-4000nm). To set k=0, both the Damping Coefficient and
Vibrational Frequency have been set to zero. Since no changes are made click
on the Cancel button to go back to the main window.
Fig 12. Model layer window for SiO2 problem.
To load the Spectroscopic reflection data (SiO2.tar file) select Open from the
Data pull down menu in the Main Window. This will launch a Windows Common
Dialog Box requesting input of the target file name to be loaded. Select SiO2.tar
file name. The reflection data will now be loaded. The measured and simulated
reflection data will automatically be displayed in the data graph in the main
window .
To begin the optimization click on the Solve Command Button located on the
tool bar or select Solve from the Measure pull down menu in the Main Window.
When the optimization is complete, the Fitted Parameters Table will show both
the initial and final values of the unknown thin film parameters. The final SiO2
thickness is 29.96nm.To re-scale the graph, click on the Rescale Command
Button located in the tool bar. The measured and simulated data is shown in Fig
13.
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Fig 13. Measured and simulated SiO2 reflection data.
To view the SiO2 NK values click on NK Graph Command Button located on the
tool bar or select NK Graph from the View pull down menu in the Main Window.
To view the substrate (Si) NK values click on the combo box labeled Display in
the lower right corner of the main window and select Substrate.
Fig 14. N and K spectra of SiO2 and Si.
7.3 Determining The Thickness of a Multi-layer Structure (Silicon on
Insulator –SOI):
Problem: To determine the thickness of Layer 1 (Buried Oxide SiO2), Layer 2
(Silicon) and Layer 3 (Gate Oxide SiO2). Spectroscopic reflection data at
normal incidence (angle of incidence = 0°) is supplied for this problem in
“\data\SiO2 On SOI.tar”. The expected film thicknesses are Substrate/390nm
SiO2/209nm Si /12nm SiO2.
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To define/build a new Recipe Load the Default Recipe by clicking on the combo
box labeled Recipe in the lower right corner of the main window. This resets the
recipe to the default recipe and the main window will appear as shown below.
To edit the Model click on the Model command button in the tool bar or select
Model/Layer Settings from the Setup pull down menu in the Main Window. This
produces the Model/Layer dialog box shown below.
Fig 15. Inputting data in the Modeling/Layer Window
To change the number of layers from 1 to 3 layers click on the combo box
labeled Number of Layers and select 3. The Model/Layer dialog box will
automatically update the layer list as shown above. The first row in the layer
configuration table shows the substrate material (Si) name and material model
(NK file). The settings for the layer 1-3 are shown in rows 2-4. First we need to
change the material of layer 1 from Si2N3 to SiO2. Click on row 2 column 6
(labeled "Material File") and select SiO2. A dialoge box will automatically pop
and ask if you would like to load the SiO2 Coefficients form a previously defined
material file. Select OK. Similarly set the Material of layer two and three to Si
and SiO2 respectively.
Fig 16. Model layers window for SOI problem.
In this example we will not fit on the index of SiO2. To simplify the recipe set the
SiO2 material model to NK.
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Fig 17 Model layers window for SOI problem (cont’d).
Change the starting thickness of layer one to 430 (nm) and the maximum
thickness to 500 (nm). Set the starting thickness of layer two to 290nm, the
maximum thickness to 400 (nm) and the minimum thickness to 100 (nm).
Similarly set the starting thickness of layer three to 20nm, the maximum
thickness to 100 (nm) and the minimum thickness to 0 (nm).
To solve for the thickness of layers 1-3 the ‘Fit’ check-box (column 1) of Row 2-4
should be checked. To save the new recipe click on File: Save As from the pull
down menu and save the file (SiO2 on Si) for future use. Click the OK button to
accept the changes in the Model/Layers Settings.
Fig 18. Saving the recipe
Before proceeding, we will check the Data Collection Parameters. Select Data
Collection Parameters from the Calibration pull down menu in the Main
Window. This will launch a Data Collection Parameters Dialog Box. The “Limit
Number of Wavelength” parameter is set to 100. In order to speed up the
optimization process, this parameter is used to limit the maximum number of
experimental/measured points. The program automatically selects the
appropriate wavelengths, which are uniformly distributed in frequency space.
Since this example has many oscillations in the data, we will increase the
number of wavelengths from 100 to 300. This will increase the resolution of our
data set.
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Fig 19 Checking Data collection parameters
Now we are ready to load the data. To load the spectroscopic reflection data
(SiO2 on SOI.tar file) select Open from the Data pull down menu in the Main
Window. This will launch a Windows Common Dialog Box requesting input of
the target file name to be loaded. Select SiO2 on SOI.tar file name, the
reflection data will be loaded.
Fig 20. Loading Data File.
The measured and simulated reflection data will automatically be displayed in
the data graph in the main window. Click on Data Table to view the
spectroscopic data you have loaded.
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Fig 21. Data for SOI.
Click on the Solve Button to find the thicknesses of Layer 1-3. The thicknesses
of layer 1-3 are now shown in column 2 (labeled "Final Solution").
Fig 22 Final Solution for SOI example
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