Radiant energy – Inspection of solids or liquids by charged particles
Reexamination Certificate
1998-04-15
2001-03-06
Berman, Jack I. (Department: 2818)
Radiant energy
Inspection of solids or liquids by charged particles
Reexamination Certificate
active
06198097
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of Invention
This invention applies to the field of systems and/or various apparatus which are used to inspect and measure surface topology and properties of materials. Such systems are used to measure the variations in surface roughness and to detect the presence of cracks and surface flaws with high spatial resolution. The field also encompasses optical characterization methods and apparatus.
II. Background of the Invention
Conventional scanning surface inspection systems currently use optical scattering techniques which are limited in their application because they use light scattering to measure surface topology. The system being proposed herein is based on the measurement of a small electrical potential difference which appears on any solid body when subjected to illumination by a modulated laser light. This voltage is proportional to the induced change in the surface electrical charge and is capacitively measured on various materials such as conductors, semiconductors, ceramics, dielectrics and biological objects. Experiments are easily repeated, and the amplitude of the detected signal depends on the type of material under investigation, and on the surface properties of the sample.
The design of a measuring system capable of performing photocharge voltage measurements for microscopic characterization of material surfaces is here described. Since the measured quantity, the photocharge voltage (PV) is observed on any kind of material present at the surface of the sample under investigation, e.g. semiconductor, insulator and metal, PV measurements can be easily used to evaluate any morphological variation or discontinuity at the surface, as well as in any spatial variation of the surface charge in a uniform semiconductor area.
The spatial variation of PV can be used to evaluate the surface conditions of the sample even with metalization and the variation of the PV due to the monochromatic bias light are used to characterize the surface states.
The proposed technique is completely contactless and it can be used in a high resolution microscope system. In fact, applications are numerous, from thin film and surface mechanical characterization to in-line nondestructive characterization of semiconductor wafers during the various stages of integrated circuits fabrication.
SUMMARY OF INVENTION
The measurement system proposed herein uses a modified Kelvin probe concept so that spatial variations of the photocharge voltage (PV) can be measured. A modulated laser output is used to optically excite the sample. The output electrical signal from the shielded sample is obtained from the difference in electrical potential. Appropriate instrumentation complete the entire system to precisely, accurately monitor the photocharge voltage.
It is an object of this invention to provide a system for the optical characterization of the surface topology and properties of materials.
It is another object of this invention to provide that the technique remain contactless and be fitted in an high resolution microscope system which can measure the spatial variation of the photocharge voltage (PV) to evaluate the surface conditions of a sample even with metalization. The variation of the PV due to monochromatic bias light is used to characterize the surface states.
It is yet another object of this invention to provide a system with the minimum precautions and constraints in its use.
REFERENCES:
patent: 5105305 (1992-04-01), Betzig et al.
patent: 5393980 (1995-02-01), Yost et al.
patent: 5464977 (1995-11-01), Nakagiri et al.
Abbate Agostino
Das Pankaj K.
Frankel Julius
Berman Jack I.
Moran John F.
Sachs Michael C.
The United States of America as represented by the Secretary of
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