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Interferometric process and apparatus for the measurement of the etch rate of opaque surfaces

  • US 4,147,435 A
  • Filed: 06/30/1977
  • Issued: 04/03/1979
  • Est. Priority Date: 06/30/1977
  • Status: Expired due to Term
First Claim
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1. An interferometer system for determining the etch rates of an opaque material and an overlying transparent layer which partially masks the opaque material comprising:

  • a light source having a wavelength λ

    ,means for dividing the light into two parallel beams one of which is directed onto the free surface of the opaque material and the other of which is directed onto the transparent layer in a direction perpendicular to the surfaces of the layers,a first detector means located in the path of the interfering reflected beams returning from the surface of the transparent layer and from the underlying surface of the opaque material to measure and record the change in light intensity of the interfering reflected beams as a function of time with one period of oscillation of the light intensity corresponding to a thickness change in the transparent layer of λ

    /2n where n is the refractive index of the transparent layer,a second detector means located in the path of the interfering reflected beams returning from the free surface of the opaque material and from the underlying surface of the opaque material to measure and record the change in light intensity of the interfering reflected beams as a function of time with one period of oscillation of the light intensity corresponding to the removal of an opaque layer thickness of λ

    /2-Δ

    X(n-1), where Δ

    X is the thickness change of the transparent layer during the same period of time.

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