Microelectronics Research Center

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Plas-Mos Ellipsometer

Table of Contents:
I: Introduction
II: System Components
III: Operating Instructions
IV: Troubleshooting
V: DO's and DON'Ts
VI: Check-off requirements

I. Introduction

Ellipsometry measures the change in polarisation state of light after reflection from the surface of the sample. The experimental data are usually expressed as two parameters and that are related to the Fresnel reflection coefficient Rp and Rs by: These two coefficients contain information related to material optical properties and physical dimensions. Spectroscopic ellipsometry measures this complex ratio as a function of wavelength. The Plas-Mos ellipsometer in the metallization bay is a single-wavelength ellipsometer and it only measures one pair of (Ψ,Δ) at 632.8nm each time. Only two parameters of the film or substrate (refractive index, extinction coefficient or thickness) can be calculated. All other parameters need to be supplied by the user.

II. System Components

  1. He-Ne laser- 632.8nm
  2. Detector
  3. Wafer platform

III. Operating Instructions

  1. Setup
    1. Press Esc until then Engineering Mode menu is displayed. If you are at the Plas-mos logo screen, press "E" for Engineering Mode. If you are prompted for a password, enter "engineer " then press "E" for Engineering Mode.
    2. Press "Y" for Physical Parameters.
    3. Press F2 to choose the mode; if you already know the refractive index of the sample and want the thickness only, chose n-fix mode; otherwise, choose n-float mode for measurement on both the refractive index and thickness.
    4. Press F3 and enter the number of layers you are measuring. (This is probably 1).
    5. For each layer, press the number of the layer and enter the parameters for the layer. You can usually use a thickness of zero. The other values are in the ellipsometer manual in the drawer of the ellipsometer table. Use the 632.8nm parameters
    6. Note: you must know the thickness of the film within half a period (e.g. 1500A for SiO2, etc.) to get accurate results. If you do not, the results you get will not be reliable. Try using the Nanospec, Woollam, or profilometers instead.
    7. Press "S" and enter the parameters for the substrate from the ellipsometer manual.
  2. Loading and Stage Adjustments
    1. Make sure that the beam shutter (switch on left cylinder) is closed (set to black dot).
    2. Place your sample on the sample holder.
    3. Open the beam shutter (turn switch to red dot).
    4. Use the stage height knob on the base of the ellipsometer to raise or lower the sample so that the beam is directed into the center of the detector (cylinder on the right). Once you have the beam directed into the sensor, adjust the height to maximize the intensity shown on the display at the top of the ellipsometer. If the displayed intensity is too high or too low, use the knob at upper end of the sensor to change the display scale.
    5. Use the stage tilt knobs at the base of the stage to maximize the intensity shown on the display at the top of the ellipsometer.
  3. Measurement
    1. Press Esc until the engineering menu is displayed. Press "S" for Single Point Measurement
    2. Press shift-F2 to set the number of measurements to be made
    3. Press F4 to make the measurements
    4. When the measurement results are displayed, you may press any key to return to the Single Point Measurement screen.
  4. Unloading
    1. Close the laser shutter (turn the switch on the left cylinder to the black dot).
    2. Remove your sample.
    3. Log out of the access controller box.

IV. Troubleshooting

Q:The machine does not respond when I hit the keys. What do I do?

A: Check whether you are logged into the machine. If you are logged in and the system is not responding, the system may need to be restarted. DO NOT RESTART THE MACHINE; Contact a staff member immediately.

Q:There is no signal on the intensity indicator. What do I do?

A: Try to turn the knob at the upper end of the sensor to different positions; this will change the display scale. If there is still no signal, this probably means that the reflected laser is not entering the sensor; put a small piece of white paper at the sensor's entrance and locate the laser beam; adjust the height of the stage to direct the laser into the sensor.

Q:The machine keeps popping out "Signal Error." What do I do?

A: Check the signal intensity on the intensity indicator; if it is too high or too low, turn the knob at the upper end of the sensor to different positions and make measurement again; sometimes the computer will adjust the intensity automatically after each measurement; so try another measurement if the first try does not work. If the error persists, the machine may need to be restarted; REPORT THE PROBLEM TO A STAFF MEMBER; DO NOT RESTART THE MACHINE WITHOUT PERMISSION.

V. DO's and DON'Ts

DO

  • Close the laser shutter whenever the measurement is done or before changing the sample.

DO NOT

  • Change any parameters other than those displayed on the recipe page.
  • Leave the laser open when the machine is not in use.

VI. Check-off requirements

To be checked off, you must be able to do, to demonstrate, and must know the following items:

  • Load a sample
  • Adjust intensity
  • Set up single- and double-layer samples
  • Use n-fix and n-fit modes
  • Unload a sample and close machine
  • Set number of measurements
  • Explain theoretical basis of operation, incl. polarization
  • Demonstrate how to handle the following errors:
    • No signal error
    • Keys locking up
    • No signal on intensity indicator