Method and apparatus for determining surface characteristics by using SPM techniques with acoustic excitation and real-time digitizing
View Patent ↗By digitizing the UFM signal without using a lock-in amplifier, substantially all of the information initially contained in the UFM output signal may be maintained and may then be used for further data processing. Consequently, any type of model or evaluation algorithm may be used without being restricted to a very narrow bandwidth, as is the case in lock-in based techniques. The digitizing is performed on a real-time basis, wherein a complete UFM curve is digitized and stored for each scan position. In this way, quantitative meaningful values for specific surface-related characteristics with a nanometer resolution may be obtained.
1. A metrology system, comprising:
a scanning probe microscope;
a modulation unit connected to the scanning probe microscope to enable a modulated excitation of a sample;
a signal processing unit connected to said scanning probe microscope to receive an output signal of said scanning probe for a plurality of scan positions defining a two-dimensional region said signal processing unit being configured to digitize and record a frequency spectrum including a plurality of frequency components of a frequency band for each scan position; and
a data processor operable to generate an image of the sample over the two-dimensional region based on the plurality of frequency components of the frequency band.
2. The metrology system of claim 1 , wherein said modulation unit comprises an acoustic modulation unit.
3. The metrology system of claim 2 , wherein said acoustic modulation unit is configured to operate at ultrasonic frequencies.
4. The metrology system of claim 1 , wherein said scanning probe microscope comprises an atomic force microscope.
5. The metrology system of claim 1 , wherein said signal processing unit is configured to digitize and record a full output signal of said scanning probe microscope for each scan position.
6. The metrology system of claim 1 , further comprising a data processor configured to operate on said recorded output data on the basis of one or more predefined evaluation algorithms to extract surface-related information from said recorded output data.
7. The metrology system of claim 6 , wherein said data processor is configured to average said output data for a defined number of scan positions.
8. The metrology system of claim 7 , further comprising an area selector configured to select a region of interest among said plurality of scan positions, said region of interest comprising said defined number of scan positions.
9. The metrology system of claim 1 , further comprising a compensation unit configured to estimate a systematic deviation between recorded output data associated with different scan positions.
10. The metrology system of claim 1 , further comprising a lock-in amplifier connected to receive said output signal, said lock-in amplifier being tuned to a modulation frequency used in said modulation unit.
11. A method, comprising:
scanning a sample surface by a scanning probe at least a plurality of scan positions defining a two-dimensional region to obtain a surface-related output signal at each of said plurality of scan positions;
exciting said sample surface with a modulated signal;
digitizing said output signal including a frequency spectrum including a plurality of frequency components of a frequency band for each of said plurality of scan positions; and
generating an image of the sample over the two-dimensional region based on the plurality of frequency components of the frequency band.
12. The method of claim 11 , further comprising recording said digitized output signal including said plurality of frequency components for each of said plurality of scan positions to store substantially all information included in said output signal at each scan position as output data.
13. The method of claim 12 , further comprising manipulating said output data associated with at least some of the plurality of scan positions to extract at least one surface characteristic of said sample surface.
14. The method of claim 13 , further comprising defining at least one region of interest in said sample surface and processing output data associated with scan positions of said region of interest on the basis of a specified algorithm.
15. The method of claim 14 , wherein said specified algorithm comprises averaging output data belonging to a respective one of said one or more regions of interest.
16. The method of claim 12 , further comprising analyzing said output data with respect to a systematic deviation during scanning said sample surface.
17. The method of claim 12 , further comprising defining a specific algorithm for analyzing said output data after evaluating at least some of said recorded output data with respect to one or more specific criteria.
18. The method of claim 11 , wherein said sample surface is excited on the basis of a modulated acoustic signal.
19. The method of claim 18 , wherein said acoustic signal includes ultrasonic frequencies.
20. The method of claim 11 , wherein said sample surface is excited by at least one of mechanical excitation and radiative excitation.