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Method and apparatus for real-time monitoring of plasma etch uniformity

  • US 9,847,262 B2
  • Filed: 12/03/2015
  • Issued: 12/19/2017
  • Est. Priority Date: 12/22/2014
  • Status: Active Grant
First Claim
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1. A method for monitoring an etch uniformity of a plasma etching process for removing a layer of material from a substrate, wherein the plasma etching process is a capacitively coupled plasma etching process, comprising:

  • providing a substrate covered by a layer to be etched, wherein the substrate is placed on a powered electrode;

    generating a plasma in an area between the layer to be etched and a counter-surface comprising a grounded electrode mounted opposite the layer and substantially parallel to the layer, whereby material is progressively removed from the layer in a plasma etching process, the plasma emitting light, wherein no other light source is provided besides the plasma, wherein light striking a surface of the grounded electrode is partially reflected towards the layer, wherein light striking the layer is partially reflected from a top surface of the layer and partially refracted through the layer towards the substrate, and wherein the refracted light reflects from a substrate surface and is refracted once again at the top surface of the layer, where the refracted light combines with the reflected light to form an interference pattern due to a difference in optical paths of the reflected light and the refracted light, wherein the interference patterns are primarily due to light beams which have undergone multiple reflections off the grounded electrode, wherein a size and a material of the counter-surface, a size and a material of the substrate and the layer, and a distance between the layer and the counter surface are each configured so that the light interference patterns are primarily due to reflections of light beams taking place in the area between the layer and the counter-surface, and wherein the light beams are directed according to a Brewster angle of the material of the counter-surface;

    measuring, by an optical emission spectroscopy detector at a lateral location with respect to the area, one or more spectral components of light emitted from the area wherein the emission spectroscopy detector comprises a lens coupled to an optical fiber that is coupled to a spectrometer, wherein the lens is arranged to receive light from a totality of the top surface of the layer from a plurality of directions, wherein the light emitted from the area passes through a polarization filter before entering the optical detector, wherein the filter is configured to admit only light with a given polarization into the optical detector, wherein the polarization filter is configured so that only s-polarized light passes the polarization filter;

    arranging the counter-surface relative to the layer so that the optical detector detects oscillations of at least one of the one or more spectral components as a function of time, the oscillations being caused by detected light interference patterns which change due to the progressive removal of the material from the layer; and

    deriving, from the oscillations, an indication about an etch uniformity of the plasma etching process.

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