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Metal etch rate analyzer

  • US 4,260,259 A
  • Filed: 12/29/1978
  • Issued: 04/07/1981
  • Est. Priority Date: 12/29/1978
  • 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

    ,beam splitter means for dividing light from said source into a first beam directed along a first beam path onto the free surface of said opaque material in a direction perpendicular to the opaque surface, and a second beam directed along a second beam path onto the surface of the transparent layer in a direction perpendicular to the transparent surface,said beam splitter means defining a first return light path for the reflected light returning from the surface of the transparent layer and the underlying surface of the opaque material, anda second return light path for the light reflected from the free surface of the opaque layer and from the underlying surface of the opaque material, the first and second return light paths being of substantially equal length,said beam splitter means including a neutral beam splitter oriented at an angle with respect to said light source and the surface of said opaque material to direct light thereon, and first and second beam splitters each oriented at an angle with respect to said neutral beam splitter to define a closed light path for the equal length light paths,a first detector means located in the first return 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 second return path 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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