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Dual-modulation interferometric ellipsometer

  • US 5,485,271 A
  • Filed: 04/06/1995
  • Issued: 01/16/1996
  • Est. Priority Date: 01/07/1992
  • Status: Expired due to Fees
First Claim
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1. An infrared ellipsometer for measuring a sample, comprising:

  • a) an exciter group including a source, a Michelson interferometer providing a first reference signal, a polarizer, and optical means for aligning said source and the sample, said exciter group generating infrared source energy directed at the sample;

    b) a sample support for supporting the sample;

    c) an analysis group including a polarizer-analyzer, a detector, and optical means for aligning the sample and said detector, said analysis group being aligned for receiving infrared source energy reflected from said sample;

    d) an electro-optical phase modulator, located along a beam path of the infrared source energy, for providing a second reference signal, and modulating at a frequency ω

    ; and

    e) electronic means for controlling said exciter group including the Michelson interferometer, for controlling said electro-optical phase modulator, for receiving signals from said analysis group, and for supplying a measurement result, wherein said electronic means includes;

    1) a pre-amplifier for receiving a signal produced by said detector in said analysis group and for providing a pre-amplifier output signal;

    2) an analog-to-digital converter receiving the pre-amplifier output signal and for providing a digital output signal;

    3) a Fourier analyzer for receiving (A) the digital output signal from said analog-to-digital converter, (B) the first reference signal originating from said Michelson interferometer and (C) the second reference signal originating from said electro-optical phase modulator, for simultaneously extracting the dc component of the digital signal and components of the digital signal at frequencies ω and



    , and for producing values which are representative data of the input signal in response to the first reference signal and the second reference signal;

    4) a register for receiving the values produced by said Fourier analyzer; and

    5) a microcomputer for storing the values produced by said Fourier analyzer, and for generating values of ellipsometer angles of the measurement result by inverse optical Fourier transform.

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