Process monitor and method thereof
First Claim
1. Apparatus for monitoring the change in thickness of an article in at least a portion of one surface thereof while that surface is subjected to a process, said apparatus comprising:
- means for illuminating a portion of said surface with coherent electromagnetic energy;
means for detecting a portion of the energy reflected from said surface and for producing an electrical signal proportional thereto;
means for identifying points in said electrical signal corresponding to points in said process at which a particular relationship obtains between said thickness and the wavelength of said coherent energy;
means for altering said process upon identifying a certain number of said points, andmeans for generating a second signal, proportional to the first derivative with respect to time of said electrical signal, and wherein said means for identifying utilizes said second signal for identifying said points.
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Accused Products
Abstract
A process monitor which is particularly useful for endpoint detection in plasma etching processes does not require the dedication of a test area on the wafer for endpoint detection and also obviates the need for wafer alignment. An improved optical window which does not significantly perturb the RF fields in the plasma chamber is also disclosed. The apparatus reflects laser energy off an area of the wafer comparable to the area of a typical die and extracts the necessary information from the resulting waveform by means of first and second time derivatives.
80 Citations
10 Claims
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1. Apparatus for monitoring the change in thickness of an article in at least a portion of one surface thereof while that surface is subjected to a process, said apparatus comprising:
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means for illuminating a portion of said surface with coherent electromagnetic energy; means for detecting a portion of the energy reflected from said surface and for producing an electrical signal proportional thereto; means for identifying points in said electrical signal corresponding to points in said process at which a particular relationship obtains between said thickness and the wavelength of said coherent energy; means for altering said process upon identifying a certain number of said points, and means for generating a second signal, proportional to the first derivative with respect to time of said electrical signal, and wherein said means for identifying utilizes said second signal for identifying said points. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for monitoring the change in thickness of an article, subjected to a process which acts upon at least one surface of said article, comprising the steps of:
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illuminating a portion of said surface with coherent radiation; detecting radiation reflected from said surface and producing an analog signal proportional thereto; wherein said illuminating detecting steps are carried out at more than one location on said surface to produce several analog signals; and identifying points in said analog signals indicative of predetermined changes in thickness. - View Dependent Claims (9)
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10. A plasma etch process monitor comprising:
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means for illuminating with coherent electromagntic energy a semiconductor wafer;
said means including a first optical window for illuminating a central portion of said wafer and to collect energy reflected therefrom and a second optical window for illuminating an edge portion of said wafer and to collect energy reflected therefrom;means for generating analog signals related to the intensity of the energy reflected from said central portion and the edge portion of said wafer, respectively;
each analog signal having superposed large and small amplitude components;means for identifying maxima of said small amplitude periodic component; and means for altering said etch process upon identifying a certain number of said maxima.
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Specification