Characterizing of silicon-germanium areas on silicon

Semiconductor device manufacturing: process – With measuring or testing

Reexamination Certificate

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Details

C378S073000, C378S072000

Reexamination Certificate

active

06238941

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for characterizing silicon-germanium areas obtained by epitaxial growth on portions of a single-crystal silicon substrate.
2. Discussion of the Related Art
There exists a growing tendency in microelectronics to use areas of a silicon-germanium heterocrystal (Si
x
Ge
1−
) obtained by epitaxial growth on surface portions of a silicon substrate, the other portions of which are masked. Such Si
x
Ge
1−x
areas are used, in particular, as a base for bipolar transistors to obtain improved speed characteristics and provide devices with good radiofrequency performance.
SUMMARY OF THE INVENTION
The present invention provides a novel method in which, rather than trying to adjust a measured curve, a distinct model is used. The present invention provides for linearly combining a model corresponding to a single-crystal silicon substrate alone with a conventional model corresponding to the superposition of a uniform SiGe layer on a silicon substrate. These models are combined by assigning a weight to the model corresponding to the complex structure, this weighting factor substantially corresponding to the surface ratio between the surface occupied by the single-crystal SiGe regions and the total layer surface.
More specifically, the present invention provides a method for characterizing a structure including single-crystal silicon-germanium areas on a single-crystal silicon substrate, including the steps of:
measuring the X-ray diffraction spectrum of the structure,
simulating the diffraction spectrum of a single-crystal silicon substrate,
simulating the diffraction spectrum of a single-crystal silicon substrate entirely coated with a single-crystal SiGe layer,
adding the simulated spectrums while assigning them weights
a
and
1
-
a
to obtain a sum spectrum,
comparing the sum spectrum with the measured spectrum and adjusting the simulation parameters and weight
a
to reduce the distance between the sum spectrum and the measured spectrum,
after optimizing, adopting the simulation parameters as the measurement parameters.
According to an embodiment of the present invention, weight
a
is chosen at an initial value, before optimizing, which is substantially equal to the ratio between the surface area occupied by the SiGe areas and the total surface area of a silicon wafer.


REFERENCES:
patent: 5442676 (1995-08-01), Fewster
patent: 5530732 (1996-06-01), Takemi
patent: 6081579 (2000-06-01), Nagano et al.
French Search Report from French Patent Application No. 99/11142, filed Sep. 2, 1999.
Christ T., et al.: “Analysis Of Light Emitting Diodes By X-Ray Reflectivity Measurements”, Thin Solid Films, Ch, Elsevier-Sequoia S.A. Lausanne, vol. 302, No. 1-2, Jun. 20, 1997, pp. 214-222.

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