Film Thickness Module

The FTG Software Film Thickness Module (FilmThk.exe Version 1.01d) for Windows calculates the thickness of films which exhibit multiple fringes when measured in reflectance or transmittance. The program uses two algorithms: fringe counting and fast Fourier transform. It includes calibration functions, spectral smoothing, and film dispersion.

A more advanced program (included with FilmStar or Scantraq) includes client-server automation facilities based on ActiveX.

Get Acrobat Reader A paper Film Thickness of 'Thick Thin Films' by Spectroscopy (129K) presented at the SVC 1998 meeting in Boston can be downloaded and printed. This is in Adobe Acrobat (.pdf) format.

  1. CLICK HERE to download file FtgFree.exe (1.2M) to your download directory.

  2. Run the program to install the Film Thickness Module and other free FTG Software programs. A password is required during installation. CLICK HERE to obtain a password. 

  3. Users outside the USA should set Windows to recognize ',' as thousands separator, '.' as decimal point and ',' as list separator.

  4. Please contact FTG Software if you have problems and questions.

Getting Started

1. Click File...Open and open Calculation Parameters file fringes.ftp.

2. Click Spectra...Open and open t1500nm.dx

Thickness is automatically calculated by fringe counting. At this point you might like to click Setup...Parameters to see how Calculation Parameters are specified. The next example of a much thicker film uses the fast Fourier transform technique.

4. Click File...Open and open Calculation Parameters file fft.ftp.

5. Click Spectra...Open and open t10um.dx

6. Click Evalulate...Recalculate to calculate film thickness by fast Fourier transform

Setup Menu

Calculation Parameters

1. Setup

Enter the name of a dispersive film file or a constant index value. Dispersive file names are those located in the 'Indices' directory in the Configuration screen. There are two calculation methods: fringe counting and Fourier transform. The latter method is recommended when there are many fringes.

1a. Count fringes

Check if the substrate has a high index or is metallic. Technically this means that a film whose optical thickness at wavelength W is a multiple of a quarter wave optical thickness (QWOT) reduces the reflection at W. You may choose to use some or all peaks for calculating film thickness. This depends on the dispersion of the substrate as well as the film material. You would not, for example, want to include reqions where the substrate index illustrates wild fluctuations.

1a. Inverse FFT (Fast Fourier Transform)

This method finds the peak thickness value corresponding to maximum PSD (Power Spectral Density). It then calculates the center of gravity of that peak using 1 to 11 points. When set to Auto, the number of FFT sampling points is determined by the number of experimental data points. This is always a power of two. For example, if there are 1500 data points, an interpolated array with 2048 points will be created by interpolation.

Setting FFT Plot Range to Automatic utilizes the entire possible range of thickness values. If a false peak is found near zero thickness, set Minimum = 0.1 µm. In most cases it is better to manually select a plot range as the resulting graph will be superior.

1c. Calibration

Enter 1 to 6 thickness sets depending on the calibration data that you have and the accuracy required.

1 set - Constant correction (may be sufficient)
2 sets - Linear correction
3-6 sets - Quadratic correction

2. Film Indices

The Film Indices editor sets up dispersion files. k values are not currently used in the calculation but are included for possible future use. FilmStar users should note that dispersive index files are not compatible. FilmStar INDEX values can be easily inserted by copying and pasting.

Spectra Menu

Open

FTG Software comma-separated .csv format starts with a description line in quotes, followed by the number of points n, followed by n lines. Each line contains wavelength in nanometers and reflectance or transmittance in the range 0 to 1. A file would appear as follows in a text editor.

"Description"
3
400,.2
500,.3
600,.4

J-CAMP .dx is a standard format for transferring spectral data. If your version of J-CAMP does not work, send it by e-mail to FTG Software at info@ftgsoftware.com. One advantage of J-CAMP is that it includes information about the type of measurement. Absorbance values are NOT automatically converted to transmittance. This is because some programs store everything including reflectance in absorbance units.

Paste

Tab-separated spectra copied to the clipboard can be pasted into the Film Thickness Module. The format would look like this in a text editor

400   .2
500   .3
600   .4

This format is equivalent to copying the data to the clipboard in Excel.

Evaluate Menu

Smoothing is supported and may be necessary to remove false peaks resulting from noise or from rapid fringes caused by thin substrates. Try S-G smoothing with order = 2 and number of points = 7.

Double-click on the graph for graph options such as colors or saving as a metafile.

Support

Support is available by contacting us by e-mail. Attach data files (spectral data, calculation parameters, and film indices) illustrating your problem.