X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1998-12-15
2001-05-01
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S089000
Reexamination Certificate
active
06226348
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The invention relates to the field of measuring thickness of materials. The invention relates further to a technique for processing signal data so that a Fourier transform can be performed more successfully.
B. Related Art
Measuring thickness of layers is of particular usefulness in the semiconductor arts.
In the past, people attempted to use rocking curve outputs of x-ray diffractometers to measure thickness of layers. This was a cumbersome process. First, the user would identify bumps in a rocking curve manually and manually put cursors at adjacent maxima. From the position of the cursors, an angle of difference could be derived. From that one could derive a dominant thickness in the material under observation. What layer was dominant at a particular angle would depend on Bragg angle and selection rules. The user would have to guess based on expectations of thickness of particular layers in the material. That guess would be a starting point of simulation. The simulation parameters would then be altered until they produced a simulation curve matching the measured rocking curve.
Some also tried to Fourier transform the rocking curve to yield a thickness curve, but the results were so noisy as to be useless.
SUMMARY OF THE INVENTION
The object of the invention is to use an x-ray diffractometer to determine the thickness of multiple non-metallic crystalline layers without manual intervention. Another object of the invention is to improve techniques of taking Fourier transforms.
The inventors recognized that the reason that the Fourier transform did not work on the rocking curve was that the average value of the curve was far from zero.
Accordingly, the inventors developed a technique for deriving a result curve from the rocking curve such that the result curve would have an average value near zero. This led to an automated method for determining thickness of multiple layers using an x-ray diffractometer.
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Moore Christopher John Lawrence
Summers James Alexander
Philips Electronics North America Corporation
Porta David P.
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