A metrology tool for semiconductor wafers is disclosed which combines modulated reflectivity measurement with junction photovoltage measurements. The tool includes an intensity modulated pump beam for periodically exciting the sample. A separate probe beam is used to monitor changes in optical reflectivity of the sample. In addition, capacitive electrodes are provided to measure modulated changes in the voltage across the electrodes. These measurements are combined to evaluate the wafer. These measurement can be particularly useful in characterizing ultrashallow junctions.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of JPV type system found in the prior art.
FIG. 2 is a schematic diagram of a combination system formed in accordance with the subject invention.
Claims
1. An apparatus for evaluating a semiconductor sample comprising:
a light source for generating an intensity modulated pump beam;optics for directing the pump beam onto the sample in a manner to periodically excite a region of the sample and create an electron hole plasma;a light source for generating a probe beam which is directed to the sample within the periodically excited region;a photodetector for monitoring modulated changes in the reflected probe beam induced by the periodic excitation and generating first output signals in response thereto;a pair of capacitive electrodes positioned close to and spaced from the sample surface and near the periodically excited region;a circuit for measuring the modulated changes in the voltage across the electrodes induced by the periodic excitation and generating second output signals in response thereto; anda processor for analyzing the sample based on a combination of the first and second output signals.
2. An apparatus as recited in claim 1, wherein said photodetector measures changes in the modulated power of the probe induced by changes in optical reflectivity of the sample in response to the periodic excitation.
3. An apparatus as recited in claim 1, wherein one of said electrodes is transparent and said pump and probe beams are directed through said transparent electrode to the sample.
4. An apparatus as recited in claim 3, wherein said optics function to focus the pump and probe beams collinearly on the sample.
5. An apparatus as recited in claim 1, wherein said processor evaluates the characteristics of an ultrashallow junction based on the first and second output signals.
6. A method apparatus for evaluating a semiconductor sample comprising the steps of:
directing an intensity modulated pump beam to the surface of the sample in a manner to periodically excite a region of the sample and create an electron hole plasma;monitoring the modulated changes of a reflected probe beam induced by the periodic excitation and generating first output signals in response thereto;measuring the modulated changes in the voltage across a pair of electrodes positioned close to and spaced from the surface of the sample in the periodically excited region, said measured modulated changes being induced by the periodic excitation and generating second output signals in response thereto;analyzing the sample based on a combination of the first and second output signals; andstoring the results of the analysis.
7. A method as recited in claim 6, wherein the step of measuring the modulated changes of the probe beam is performed by measuring the modulated changes in the power of the probe beam induced by changes in optical reflectivity of the sample in response to the periodic excitation.
8. A method as recited in claim 6, wherein one of said electrodes is transparent and said pump and probe beams are directed through said transparent electrode to the sample.
9. A method as recited in claim 8, further including the step of focusing the pump and probe beams collinearly on the sample.
10. A method as recited in claim 6, wherein the characteristics of an ultrashallow junction are evaluated based on the first and second output signals.
Patent Application
20070188761
