VAS Ellipsometer Standard Operating Procedure

Updated on 6/6/2019

Contents

1 Cold Start

2 Initialization

3 Calibrate System

3.1 Align 25 nm SiO2 Standard Sample

3.2 Z-axis Translation Alignment

3.3 Calibration

4 Preparation for Measurement

5 Spectroscopic Scan

6 Analysis using a model fitting

6.1 Dielectric, Si, and other substrates

6.2 Cauchy model fitting for transparent film

6.2 Global fitting for thick films

6.3 Pt-by-Pt model fitting for a semi-transparent material

6.4 General Oscillator (Genosc) model fitting

7 Fitting Raw Data With Calculation

7.1 Substrate

7.1.1 Glass substrate

7.1.2 Semi-transparent substrate

7.1.3 Opaque substrate

7.2 Single layer

7.2.1 A transparent film on Si wafer

7.2.2 A partially absorbing film on Si wafer

7.2.3 A transparent or partially absorbing film on Si wafer

7.2.4 An absorbing film on glass

7.3 Multilayer

7.3.1 Multi-Layer Strategies

7.3.2 Pt/SiO2/Si wafer

7.3.3 a-Si/SiO2/Si wafer

7.3.4 TiO2/SiO2/Si wafer

7.3.5 crystalline-Si/SiO2/Si wafer

7 Advanced Fitting

7.1 Surface Roughness

7.2 Index Grading

7.3 Surface Roughness + Index Grading

7.4 Non-ideality on Data

8 Transmittance and Reflectance Measurements

8.1 Transmittance Measurement

8.2 Reflectance Measurement

9 WVASE messages on fitting

10 MSE check

11 Correlation matrix

12 Measurement on Another Sample

13 Supplement Documents

1. Cold Start

If the system is shut down, then turn on the power to the controller and monochromator (the PC is always on).

1. Turn on the control module.

2. Turn on the monochromator

• Note: If the controller is off, then the monochromator cannot be turned on.
• The power should be turned on according to the number on the picture.

2. Initialization

• Note: When the system is booted, the initialization of the system must be done. Once the initialization is done, you do not have to do it again.

1. Double-click on the WVASE32 logo to open the software.

2. The following windows appear.

• Note: If these windows do not appear, or if you need to find a "hidden" window, use the "Window" on the top-right of screen.

3. Click the "Initialize" from the "Hardware" window.

4. The following dialog box shows up. Type your name in the box, and click "OK".

• You do not have to register your name.

5. The following message appears in the "Hardware" window when the system is initialized.

3. Calibrate System

• Note: When the system is booted, the calibration of the system must be done. Once the calibration is done, you do not have to do it again.

3.1 Align 25 nm SiO2 Standard Sample

1. Load the 25 nm thick SiO2 standard sample on the vacuum chuck.

2. Choose "Align Sample" from the drop-down menu of "Acquire Data" in the menu.

3. The following dialog box appears. Click "OK".

4. The sample chuck is automatically rotated to the alignment position, and the following screen is shown.

5. Adjust the red cross hairs to the center, using the two knobs behind the sample chuck.

6. Once the cross hair is aligned at the center, press the "ESC" key on the keyboard.

3.2 Z-axis Translation Alignment

1. The following dialog box appears. Click "OK".

2. The sample chuck is automatically rotated to the Z-axis translation alignment position.

3. The following screen appears.

4. Adjust the intensity to be maximum, using the micrometer.

5. When maximizing the intensity, press the "ESC" key on the keyboard.

3.3 Calibration

1. Choose "Calibrate System" from the drop-down menu of "Acquire Data" in the menu, which is shown on the "Hardware" window.

2. The following dialog box appears. Click "OK".

3. The calibration is automatically carried out.

4. When the calibration is done, the following message shows up in the "Hardware" window.

4. Preparation for Measurement

1. Replace the 25 nm thick SiO2 standard sample by your sample.

• Note: A Small Vacuum Chuck is also available.

2. Repeat the "Align Sample" and "Z-axis Translation Alignment" procedures shown above.

• Note:
  • This procedure is always required when replacing the sample.
  • You do not have to repeat the calibration.

5. Spectroscopic Scan

1. Choose "Spectroscopic Scan" from the drop-down menu of "Acquire Data" in the menu, which is shown on the "Hardware" window.

2. The "VASE Scan" dialog box appears.

• See the detail of VASE Scan dialog box.
• You can create your scanning recipe in the VASE dialog box.

3. Click the "Open Settings" button to load the standard scan settings.

4. The following file directory appears. Choose the recipe from the file directory.

5. Enter a comment, if necessary. Click "OK".

6. Spectroscopic scanning starts. The result of scanning is shown in the "Experimetal Data" and "Graph" windows.

7. Save the data, if necessary.

8. Close the "Hardware" window.

6. Analysis using a model fitting

6.1 Dielectric, Si, and other substrates

• Glass substrate
• Si substrate
• Other substrates

6.2 Cauchy model fitting for transparent film

• A transparent film on Si wafer

6.2 Global fitting for thick films

• Global fitting of thick SiO2 film

6.3 Pt-by-Pt model fitting for a semi-transparent material

• Semi-transparent substrate
• A partially absorbing film on Si wafer

6.4 General Oscillator (Genosc) model fitting

Genosc model fitting ensures Kramers-Kronig consistency between e1 and e2 in the analysis (see Kramers-Kronig Relation).

• A transparent or partially absorbing film on Si wafer

7. Fitting Raw Data With Calculation

7.2.4 An absorbing film on glass

• Example of combination of spectroscopic ellipsometry and transmission spectroscopy
• See Acquisition of Intensity Transmittance Data.

7.3 Multilayer

• We assume that you are familiar with the single layer analysis shown above.

7.3.1 Multi-Layer Strategies

7.3.2 Pt/SiO2/Si wafer

7.3.3 a-Si/SiO2/Si wafer

7.3.4 TiO2/SiO2/Si wafer

7.3.5 crystalline-Si/SiO2/Si wafer

8. Advanced Fitting

8.1 Surface Roughness

• Add "srough.mat" on top of the layer structure.
• This model layer is designed for the surface roughness.
• Ellipsometer is sensitive to the boundary condition between air and the top surface.

8.2 Index Grading

• Optical properties can vary with depth into a film.
• This is modeled by dividing film into ‘slices’ where optical constants can vary between each.
• Convert the model layer to SimpleIndexGrade.

8.3 Surface Roughness + Index Grading

8.4 Non-ideality on Data

• "Model Options" dialog box is opened to set non-ideality.

8. Transmittance and Reflectance Measurements

9.1 Transmittance Measurement

• The tool will measure air as the background and a film on glass as the sample. So, the glass should be transparent in the spectral range measured (a cheap glass shows an optical absorption in the UV range).

9.2 Reflectance Measurement

• See Chapter 12.10 in the VASE manual.

10. WVASE messages on fitting

11. MSE check

• MSE (Mean Squared Error) must be minimized during the fitting.
• MSE sometimes falls into local minima.

12. Correlation matrix

• You can check correlation between parameters.

13. Measurement on Another Sample

If you want to make a measurement on another sample, open the Hardware window, and repeat the procedure from "Preparation for measurement" shown above.

14. Supplemental Documents