VASE to Filmetrics
Use VASE results in your Filmetrics measurements at the nanoFAB.
Convert files containing optical constants obtained using variable angle spectroscopic ellipsometry (VASE) into a format compatible with the Filmetrics F50-UV tool.
Use this form to convert a WVASE® .mat file to the .fitnk format used by Filmetrics.
The nanoFAB's Filmetrics F50-UV is a convenient tool to measure the thickness and uniformity of unpatterned films on wafers or other planar specimens, due to its location in the cleanroom, lack of any necessary specimen prepartion, non-destructive nature, and quick turnaround. However, a meaningful measurement can only be obtained if the optical constants—the refractive index n and extinction coefficient k as a function of wavelength—used in the reflectance model accurately represent those of the film being measured. While a library of standard materials exists in the Filmetrics FILMapper software, these may deviate from the optical contants of actual films being used in one's processing, due to differences in stoichiometry, etc.
Accurate optical constants and thickness for one's films can be measured via variable angle spectroscopic ellipsometry (VASE), using either of the nanoFAB's J.A. Woollam ellipsometery tools, but this technique is much slower than the Filmetrics, particularly if a uniformity map is desired. A good workflow is therefore to perform VASE on a film, then import the optical constants into the Filmetrics material library, which can then be used to obtain fast, accurate thickness measurements. Unfortunately, the native material file format output by the WVASE32 software cannot directly be read by the version of FILMapper available in the cleanroom.
To overcome this problem, this webpage may be used to convert WVASE32 .mat files into the .fitnk format used by FILMapper.
- VASE data preparation
- Perform VASE on your film using the WVASE32 software.
- Fit the ellipsometry data, as per usual, using an appropriate model.
- When a good fit has been obtained, save the optical constants in .mat file format:
- Right-click the layer in question in the Model window. Select Optical Constants > > from the drop-down menu.
- Click Save. Click No in the "Save disperson model parameters?" window.
- Enter a file name (.mat extension) and click Save.
- Enter a meaningful description in the "Enter a Comment for the Material File" window and click Ok.
- Upload and convert
- Using the above form, upload your .mat file.
- Select an appropriate material category and click Submit.
- The data will be plotted as a sanity check.
- Download the resulting .fitnk file and copy it to a temporary location on the Filmetrics computer in the cleanroom (e.g., Desktop, Downloads folder). The links to the converted files will be accessible for at least 24 hours.
- In FILMapper, use File > Import > Material… and choose the .fitnk file.
- Delete the .fitnk file from the temporary location.
- Your material may now be used in Filmetrics recipes; it will be listed under the material catetory you chose in the form.