Determining the presence of defects in thin film structures
AssigneeMassachusetts Institute of Technology
InventorsKeith A. Nelson, John A. Rogers
Life of this patent
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Abstract
The invention features a method for detecting a subsurface defect in a thin film structure. The method includes: optically generating an acoustic wave in a first spatial region of the film; optically measuring a time-dependent reflection of the acoustic wave from subsurface features in the film to produce a time-dependent signal; and analyzing the signal to detect an existence of the defect. The optically measuring step can include measuring the diffraction of a probe beam from the reflected acoustic wave. The analyzing step can include comparing the measured signal to a reference signal for defect-free structure.
Claims16
A method for detecting a subsurface defect in a thin film, comprising:
- optically generating an acoustic wave in the film by exciting the film with a pair of crossed excitation pulses;
- diffracting light from a time-dependent reflection of the acoustic wave caused by subsurface features in the film to produce a time-dependent signal;
- and
- analyzing the time-dependent signal to detect an existence of the defect based on the time-dependent reflection.
A method for detecting a subsurface defect in a thin film, comprising:
- optically generating an acoustic wave in a first spatial region of the film;
- optically measuring a time-dependent reflection of the acoustic wave from subsurface features in the film to produce a time-dependent signal;
- and
- analyzing the signal to detect an existence of the defect by comparing the signal to a reference signal for a defect-free film, wherein comparing comprises:
- normalizing a portion of the signal to a corresponding portion of the reference signal, wherein the portions each comprise values at a series of time points;
- calculating a difference in the values of the portions at each of the time points;
- and
- summing squares of the differences to determine an effective value for the similarity of the film to the defect-free film.
A method for detecting a subsurface defect in a thin film, comprising:
- optically generating an acoustic wave in a first spatial region of the film;
- optically measuring a time-dependent reflection of the acoustic wave from subsurface features in the film to produce a time-dependent signal;
- and
- analyzing the signal to detect an existence of the defect by comparing the signal to a reference signal for a defect-free film, wherein comparing comprises:normalizing a portion of the signal to a corresponding portion of the reference signal, wherein the portions each comprise values at a series of time points;
- Fourier transforming each of the portions to produce transformed portions comprising values at a series of frequency points;
- calculating a difference in the values of the transformed portions at each of the frequency points;
- and
- summing squares of the differences to determine an effective value for the similarity of the film to the defect-free film.
Dependencies are inferred from the claim text.