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ECE 344 Equipment Instructions for:

The ELLIPSOMETER

Manufacturer: Gaertner

Model: L117

As described in Section 5.10.2 of Anner's Planar Processing Primer, ellipsometers are an accurate means of measuring thicknesses and refractive indicies of transparent films.

Quantities Used.
Measurement Procedure.
Using the software to determine thickness.

Quantities Used later on

Measurement Procedure.

  1. Turn on laser using the on-off key if it's not on already; the indicator light should come on immediately. For best results allow 15 min. for laser warm up. The beam attenuator should be closed during warm up for safety.
  2. Set the analyzer and polarizer to the desired angle of incidence (70 deg. recommended). Both should be set to the same angle and clamped in place.
  3. Place the wafer to be measured on the sample stage. Experimentally, it has been shown that for ECE 344 purposes, the wafers may be left in their carriers with the lid off. The sample stage will normally be left at the proper height for this. For more accurate measurements the wafer should be held flat on the sample stage by vacuum and the stage height adjusted accordingly.
  4. Open the beam attenuator. Looking through the microscope, you should see the laser spot in the center.
  5. Use the x-y adjustment knobs to position the desired measurement point under the crosshairs. The laser spot on the wafer is about 25 microns vertically and 86, 42, or 30 microns horizontally for 70, 50, or 30 deg. angle of incidence, respectively. Turn off the illuminator if used.
  6. Adjust the gain knob to give an extinction meter reading between 150 and 200.
  7. Rotate the analyzer (right drum) slowly in the red numbered region (0-90 deg.) to get a minimum reading on the meter.
  8. Then rotate the polarizer (left drum) slowly in the red region (315-135 deg.) to get a lower minimum meter reading. The numerical value of the meter reading is not important, only that it be a minimum. However, the meter is most sensitive between 25 and 100 (above 100 it is logarithmic), so fine adjustments of the polarizer and analyzer are easiest with the gain adjusted to give a meter reading in the 25 to 100 range.
  9. Return to the analyzer (right hand) and slowly rotate the drum to give a new minimum. This should be within the red region (0 to 90 deg.). If the new minimum is out of this range, rotate the polarizer (left hand) to a new setting in the red region and search for a new minimum.
  10. Return to the polarizer (left hand) and slowly rotate to give a lower meter reading. (The meter gain may be adjusted to keep the meter reading between 25 and 100.)
  11. Work back and forth between analyzer and polarizer to get the lowest possible meter reading. The analyzer and polarizer readings correspond to extinction. Adjust the gain so your minimum is is in the 25 to 100 range as you work. The sensitivity seems highest near 100.
  12. Record the analyzer and polarizer settings, A1 and P1, respectively.
  13. Turn the gain down to its lowest setting (counterclockwise).
  14. Set the polarizer to P1 + 90 deg.
  15. Set the analyzer to 180 - A1 deg.
  16. Again work back and forth between analyzer and polarizer (increasing the gain as before) to get the lowest possible meter readings (extinction).
  17. Record the polarizer and analyzer settings for the second extinction, P2 and A2. To obtain accurate measurements, these values should not differ by more than 4 deg. from the values computed in 13 and 14.

Using the software to determine thickness.

Loading the Software:

The easiest way to start the software is by selecting "Ellipsometer" from the ECE 344 customized root menu. Otherwise
  1. log into one of the machines in lab (like vdpauw.ece.uiuc.edu)
  2. if you are running remotely, you need to display on the terminal you are sitting at.
  3. then type the rest in the 344 machine's xterm:
You will be prompted:

"For Film program press f7/For substrate program press f8."

When you need to get from the substrate program to the general program, or restart either program, press RESET (SHIFT-BREAK), and then function key f3 (RUN).

Using Manual Substrate Program SubP:

Note: For ECE 344 purposes, you may go directly to the General Program GP9. However, to be most accurate, you should make use of this program first.

This program is used to find the refractive index values of a substrate so that the data can be analyzed with the General Program GP9. The General Program defaults to typical values for silicon substrates when no values are supplied by the user. The refractive index of silicon varies depending on quality and doping, so for more accurate results when using silicon substrates, the index values should be found with this program, and used in the general program GP9.

Note: Measurements must be made on bare substrates.

DATA ENTRY: Angle of incidence F, analyzer and polarizer readings A1, P1, A2 and P2, or PSI and DEL, where PSI = {180deg-(A2-A1)}/2, and DEL = 360deg-(P1+P2).

DATA OUTPUT: Ns, Ks, PSI and DEL.

INSTRUCTIONS:

  1. Select NO PRINTING or PRINTING mode using the function keys as prompted.
  2. Enter DATE and/or RETURN.
  3. Enter the value of F if different from the value displayed (usually 70deg) and/or RETURN.
  4. Enter analyzer and polarizer readings A1 and P1 as prompted. (If PSI and DEL values are used, press RETURN when prompted for A1, and then enter PSI and DEL values as prompted.)
  5. When A1 and P1 have been entered, the program displays values for A2 and P2 which should be within a couple degrees of your readings.  Press RETURN and then enter your values for A2 and P2 as prompted.
  6. The program will then prompt "A1=?" again. At this point you can enter an additional set or sets of data and the values will be averaged in the final computation. When you are done entering data, just press RETURN at this prompt.
  7. The program now prompts "RTD=90?" This is the retardation angle, a parameter adjustable on some ellipsometers, but not the L117, for which it is always 90deg. Unless you are taking data on another ellipsometer where RTD ­ 90deg, press RETURN to continue. This initiates the calculation, followed by a beep and the data output. Record the values for use in the general program.
  8. Normally one would proceed on to the general program, but here is how to quit the program.
Note: The ENTER key can be used in place of the RETURN key if desired.

Using General Program GP9:

This program can analyze two-layer or single-layer, absorbing or non-absorbing (transparent) films, as described earlier. Refer to the earlier section "Modes of Operation" to select the mode you wish to use, and determine which parameters, if any, you need to fix. The program mode of operation is determined by parameters that are fixed (in step 4 or 10 below), and by parameters for which there are no values entered. For transparent layers, always press RETURN when prompted for K. When working with single layers, always press RETURN when prompted for the layer 2 thickness. As the program steps through the necessary segments to initialize the required parameters for the calculation, it identifies each segment with a function key label (such as f1). After this initialization process is done, function key labels are displayed along the bottom of the screen. These are used to reenter the initialization process as required to change the program parameters and mode.

DATA ENTRY: Substrate refractive index Ns and Ks, top layer refractive index Nf and Kf, layer 2 thickness, layer 2 refractive index N2 and K2, angle of incidence F, top layer expected thickness, and analyzer and polarizer readings A1, P1, A2 and P2, or PSI and DEL, where PSI = {180deg-(A2-A1)}/2, and DEL = 360deg- (P1+P2).

NOTE:  For properly made measurements, A2 ~ 180-A1, and P2 ~ P1+90. If your readings are not within a couple degrees of the displayed estimates, check that you entered your values properly or repeat the measurement. Note that both A1 and P1 must always lie in the red portion of the scales.

DATA OUTPUT: Substrate refractive index Ns and Ks, angle of incidence F, analyzer and polarizer readings A1, P1, A2 and P2, and/or PSI and DEL, fixed input values, expected thickness, computed thickness and index values. For transparent films, a listing of all possible thicknesses is optional.

INSTRUCTIONS:

  1. Select NO PRINTING or PRINTING mode using function keys as prompted.
  2. ECE 344 students should simply press RETURN until prompted for EXPECTED THICKNESS and skip to the next numbered step. Otherwise:
  3. The prompt "f5: Expected Thickness?" is then displayed. This always refers to the top layer (the only layer if in the single- layer mode). Enter the expected thickness in Angstroms. For absorbing films, you can press RETURN with no entry to display the thickness range choices for selection. See the "Notes on Thickness" section for more information.
  4. ECE 344 students will normally go on to the next step, but if you did not fix both Nf and Kf in step 2, and you are not in the single-layer transparent film mode, "f3: Fix Kf or Nf:" now appears with the instructions: Fix the desired parameter as indicated.
  5. The program now beeps, and is ready to accept ellipsometer data. Enter analyzer and polarizer readings A1 and P1 as prompted. (If PSI and DEL values are used, press RETURN when prompted for A1, and then enter PSI and DEL values as prompted.) To enter the program at this point later, use function key f4 (A1/P1).
  6. When A1 and P1 have been entered, the program displays values for A2 and P2 which should be within a couple degrees of your readings.    Press RETURN and then enter your values for A2 and P2 as prompted.
  7. The program will then prompt "A1=?" again. At this point you can enter an additional set or sets of data and the values will be averaged in the final computation. When you are done entering data, just press RETURN at this prompt.
  8. The program now prompts "RTD=90?" This is the retardation angle, a parameter adjustable on some ellipsometers, but not the L117, on which it is always 90deg. Unless you are taking data on another ellipsometer where RTD ­ 90deg, press RETURN to continue. This initiates the calculation, followed by a beep and the data output. You're DONE!
Note: The ENTER key can be used in place of the RETURN key if desired.

   For properly made measurements, A2 ~ 180deg-A1, and P2 ~ P1+90deg. If your readings are not within a couple degrees of the displayed estimates, check that you entered your values properly or repeat the measurement. Note that both A1 and P1 must always lie in the red portion of the scales.

After the calculation is done, the following function key labels appear across the bottom of the screen: 

   f1     f2     f3   f4   f5       f6       f7    f8

Nf & Kf PHI Fix NfKf A1/P1 EXP THK SAMPLE LISTING PRT/DISP
Function keys f1 through f5 are used to enter the program at the indicated points, as described above. Function key f6 (SAMPLE) allows you to display and print out a sample name and/or number (such as Wafer #15). Function key f7 (LISTING) prints out all the possible thicknesses for several periods for transparent film layers. Function key f8 (PRT/DISP) switches between PRINTING and NO PRINTING modes.

Quitting the program.

  1. Press RESET (SHIFT-BREAK).
  2. Type "bye"

ECE 344 home page.

equipment/Ellipsometer/Instructions.html
This screen was created by Mike Fitzimmons - U of Illinois ECE Dept. - mikef@uiuc.edu
E-mail comments and suggestions to ece344@uiuc.edu

Warning! This is the archived 1999 Fabweb site! Here is the latest site