Metrological scanning probe microscope

Abstract

This invention relates to a metrological scanning probe microscope system combining an SPM which employs an optical lever arrangement to measure displacement of the probe indirectly with another SPM which measures the displacement of the probe directly through the use of an interferometric detection scheme.

What is claimed is: 
     
       1. An atomic force microscope system that operates to characterize a sample, comprising:
 an atomic force microscope probe having a cantilever with a tip;   an objective lens which allows optical viewing in an area near the sample, the objective lens operable to direct a light beam to a surface of the cantilever and to obtain a return beam from the surface,   
       the return beam being indicative of movement of the cantilever; 
       a first optical beam positioning unit, comprising: 
       a rotatable steering mirror that is rotatable in two orthogonal axes that are parallel to a reflecting surface of the steering mirror; 
       a light source emitting a first beam directed at the steering mirror, where the first beam has a first wavelength; 
       the steering mirror controlled to reflect the first beam on the surface of the cantilever opposite the tip, by pitching and yawing the steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the first beam is reflected from the mirror; 
       a first mirror receiving the first beam from the first optical beam positioning unit and directing the first beam to the objective lens; 
       said first mirror receiving a reflection of the first beam from the surface of the cantilever, and 
       a first photodetector detecting a first light power of the first light beam reflected form the surface of the cantilever; 
       a second optical beam positioning unit, comprising: 
       a second light source emitting a second beam at a second wavelength different than the first wavelength; 
       a second rotatable steering mirror, that is rotatable in two orthogonal axes that are parallel to a reflecting surface of the rotatable steering mirror, 
       the second steering mirror controlled to reflect the second beam on the surface of the cantilever opposite the tip by pitching and yawing the second steering mirror and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the second beam is reflected from the mirror; and 
       a second mirror receiving the second beam from the second optical beam positioning unit and directing the second beam to the objective lens; and 
       a second photodetector detecting a second light power of the second light beam reflected form the surface of the cantilever; 
       where both the first beam and the second beam are reflected from the surface of the cantilever; and 
       wherein said system is used for a functionality other than measuring probe displacement of the cantilever. 
     
     
       2. The system as in  claim 1  wherein said First beam is at a red end of the optical spectrum and the second beam is at a blue end of the optical spectrum. 
     
     
       3. The system as in  claim 2 , wherein the first mirror and the second mirror are each selectively reflective of different optical spectra. 
     
     
       4. The system as in  claim 1 , wherein the first and second steering mirror have physical pivots in three-dimensional space which are tuned to set a desired relationship between an axial position of the focus and an angular orientation of the reflected light beam which are geometrically constrained to move along a defined surface. 
     
     
       5. The system as in  claim 1 , wherein the system combines the first beam and the second beam to measure interferometrically at least one object of interest. 
     
     
       6. A metrological scanning probe microscope system with two optical beam positioning units operating to characterize a sample, comprising:
 a scanning probe microscope with a scanning probe microscope probe having a cantilever, with a tip at one end of the cantilever;   a laser doppler vibrometer with a first laser;   an objective lens which is located to carry out optical viewing in an area of the cantilever,   
       the objective lens directing light beams from the scanning probe microscope and the laser doppler vibrometer to a surface of the cantilever opposite the tip and obtains a return beam from the cantilever indicative of the movement of the cantilever; 
       a first dichroic window which: 
       receives a beam from the scanning probe microscope and in turn directs the beam to the objective lens, and 
       passes a beam from the laser doppler vibrometer which beam is directed to the objective lens; 
       a first optical beam positioning unit, comprising:
 said scanning probe microscope which comprising: 
 
       a light source emitting a first beam; 
       a polarizing beamsplitter and quarter-waveplate which receive said first beam and direct said first beam outside the first optical beam positioning unit to said first dichroic window; and
 a quarter-waveplate and polarizing beamsplitter which receive from the objective lens the return beam from the cantilever indicative of the movement of the cantilever and direct the beam to a photodetector; 
 
       a second optical beam positioning unit, which comprises: 
       said laser doppler vibrometer emitting laser light; 
       a second dichroic mirror which reflects said laser light to said dichroic window outside the second optical beam positioning unit; 
       where the photodetector detects a position of the light beam on the probe and the probe's deflection or oscillation; and 
       where the second optical beam positioning unit measures information about the probe interferometrically. 
     
     
       7. The system as in  claim 6 , wherein the first dichroic mirror is infrared. 
     
     
       8. An atomic force microscope system that operates to characterize a sample, comprising:
 an atomic force microscope probe having a cantilever with a tip;   an objective lens which allows optical viewing in an area near the sample, the objective lens operable to direct a light beam to a surface of the cantilever and to obtain a return beam from the surface, the return beam being indicative of movement of the cantilever;   a first optical beam positioning unit, comprising:   a rotatable steering mirror that is rotatable in two orthogonal axes that are parallel to a reflecting surface of the steering mirror;   a light source emitting a first beam directed at the steering mirror, where the first beam has a first wavelength;   the steering mirror controlled to reflect the first beam on the surface of the cantilever opposite the tip, by pitching and yawing the steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the first beam is reflected from the mirror; and   a first mirror receiving the first beam from the first optical beam positioning unit and directing the first beam to the objective lens;   said first mirror receiving a reflection of the first beam from the surface of the cantilever;   a second optical beam positioning unit, comprising:   a second light source emitting a second beam at a second wavelength different than the first wavelength;   a second rotatable steering mirror, that is rotatable in two orthogonal axes that are parallel to a reflecting surface of the rotatable steering mirror,   the second steering mirror controlled to reflect the second beam on the surface of the cantilever opposite the tip by pitching and yawing the second steering mirror and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the second beam is reflected from the mirror; and   a second mirror receiving the second beam from the second optical beam positioning unit and directing the second beam to the objective lens.   
     
     
       9. An atomic force microscope, comprising:
 an atomic force microscope probe having a cantilever with a tip;   a first optical beam positioning unit, comprising:
 a first light source arranged to emit a first beam of light having a first wavelength onto a surface of the cantilever; and 
 a first steering mirror rotatable in two orthogonal axes that are parallel to a reflecting surface of the first steering mirror and controlled to reflect the beam from the light source on the surface of the cantilever opposite the tip, by pitching and yawing the first steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the beam is reflected from the first steering mirror; 
   a tip deflection detector which monitors light of the first wavelength that reflects from the surface of the cantilever, the tip deflection detector for measuring deflections of the probe;   a second optical beam positioning unit, comprising:
 a second light source arranged to emit a second beam of light having a second wavelength onto the cantilever, the second beam forming a spot on the surface of the cantilever that induces photothermal oscillations of the cantilever, wherein a location of the spot on the surface of the cantilever is adjustable, and wherein the location of the spot affects the drive amplitude of the cantilever; and 
 a second steering mirror rotatable in two orthogonal axes that are parallel to a reflecting surface of the second steering mirror and controlled to reflect the beam from the light source on the surface of the cantilever opposite the tip, by pitching and yawing the second steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the beam is reflected from the second steering mirror; and 
   a spot positioner comprising an optical assembly that adjusts the location of the spot to control the bending of the cantilever.   
     
     
       10. An atomic force microscope according to claim 9, wherein the spot positioner adjusts the location of the spot to increase the amplitude of a bending mode of the cantilever. 
     
     
       11. An atomic force microscope according to claim 9, wherein the spot positioner adjusts the location of the spot to increase one of a torsional or normal vibration response of the cantilever, while decreasing the other of the torsional or normal response of the cantilever. 
     
     
       12. An atomic force microscope according to claim 9, wherein the spot positioner adjusts the location of the spot based on the response of one or more eigenmodes of oscillation for the cantilever. 
     
     
       13. An atomic force microscope according to claim 9, wherein the second beam induces sub-resonance bending of the cantilever. 
     
     
       14. An atomic force microscope according to claim 9, wherein the power of the second beam affects the amplitude of oscillation and wherein the spot positioner controls the amplitude of a bending mode of the cantilever by adjusting the power of the second beam at each of a plurality of different locations on the surface of the cantilever. 
     
     
       15. An atomic force microscope according to claim 9, wherein the surface of the cantilever comprises two or more materials of different thermal coefficients to enhance said photothermal oscillation of the probe. 
     
     
       16. An atomic force microscope, comprising:
 an atomic force microscope probe having a cantilever with a tip;   a first optical beam positioning unit, comprising:
 a first light source arranged to emit a first beam of light having a first wavelength onto the tip of the cantilever; and 
 a first steering mirror rotatable in two orthogonal axes that are parallel to a reflecting surface of the first steering mirror and controlled to reflect the beam from the light source on the surface of the cantilever opposite the tip, by pitching and yawing the first steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the beam is reflected from the first steering mirror; 
   a probe temperature detector which monitors light of the first wavelength that reflects from the tip of the cantilever in order to measure the deflection of the cantilever, wherein the probe temperature detector infers the temperature of the probe from the deflection of the cantilever;   a second optical beam positioning unit, comprising:
 a second light source arranged to emit a second beam of light having a second wavelength onto the cantilever, the second beam forming a spot on the surface of the cantilever that heats the cantilever, wherein a location of the spot on the surface of the cantilever is adjustable; and 
 a second steering mirror rotatable in two orthogonal axes that are parallel to a reflecting surface of the second steering mirror and controlled to reflect the beam from the light source on the surface of the cantilever opposite the tip, by pitching and yawing the second steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the beam is reflected from the second steering mirror; and 
   a spot actuator that adjusts the location of the spot to control the temperature of the tip of the cantilever.   
     
     
       17. An atomic force microscope according to claim 16, wherein the spot actuator adjusts the power of the second beam to control the temperature of the tip of the cantilever. 
     
     
       18. An atomic force microscope according to claim 16, further comprising a sample arranged to contact the cantilever tip, wherein the spot actuator adjusts the temperature of the tip in order to induce thermally activated changes in the sample. 
     
     
       19. An atomic force microscope according to claim 18, wherein said thermally activated changes comprise inducing photochemical, photovoltaic, photothermal, pyroelectric or other light sensitive changes to specific portions of the sample. 
     
     
       20. An atomic force microscope according to claim 18, wherein the thermal conductivity of the probe is patterned through selective doping in order to allow heat to flow to the tip of the cantilever more readily than to flow to a base of the probe. 
     
     
       21. An atomic force microscope according to claim 20, wherein a metallic coating is patterned on the probe. 
     
     
       22. An atomic force microscope according to claim 21, wherein only an end of the cantilever comprising the tip is coated. 
     
     
       23. An atomic force microscope according to claim 16, wherein the cantilever is hollow. 
     
     
       24. An atomic force microscope according to claim 16, wherein the probe temperature detector infers the temperature of the probe by measuring the change in the resonant frequency of the probe while changing the power of the second light beam. 
     
     
       25. A method for cleaning a probe of an atomic force microscope system, the atomic force microscope system comprising:
 an atomic force microscope probe having a cantilever with a tip;   a first optical beam positioning unit, comprising:
 a first light source for emitting a first beam of light of a first wavelength onto the cantilever; and 
 a first steering mirror rotatable in two orthogonal axes that are parallel to a reflecting surface of the first steering mirror and controlled to reflect the beam from the light source on the surface of the cantilever opposite the tip, by pitching and yawing the first steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the beam is reflected from the first steering mirror; and 
 a first photodetector which monitors light of the first wavelength that reflects from the surface of the cantilever, the first photodetector for measuring deflection of the probe; and 
   a second optical beam positioning unit, comprising:
 a second light source for emitting a second beam of light of a second wavelength onto the cantilever; and 
 a second steering mirror rotatable in two orthogonal axes that are parallel to a reflecting surface of the second steering mirror and controlled to reflect the beam from the light source on the surface of the cantilever opposite the tip, by pitching and yawing the second steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the beam is reflected from the second steering mirror; and 
   the method comprising operating the second light source to heat the tip of the cantilever in order to modify a tip coating or to break down, thermally modify or remove contaminations that have adhered to the tip.   
     
     
       26. A method according to claim 25, wherein the second beam forms a spot on the surface of the cantilever, wherein a location of the spot on the surface of the cantilever is adjustable. 
     
     
       27. A method according to claim 25, wherein the second light source is further configured form a spot on the surface of the cantilever that induces photothermal oscillations of the cantilever. 
     
     
       28. An atomic force microscope that operates to characterize a sample, comprising:
 an atomic force microscope probe having a cantilever with a tip;   a first optical beam positioning unit, comprising:
 a first light source arranged to emit a first beam of light having a first wavelength onto a surface of the cantilever; and 
 a first steering mirror rotatable in two orthogonal axes that are parallel to a reflecting surface of the first steering mirror and controlled to reflect the beam from the light source on the surface of the cantilever opposite the tip, by pitching and yawing the first steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the beam is reflected from the first steering mirror; 
   a sensor assembly which monitors light of the first wavelength that reflects from the surface of the cantilever;   a second optical beam positioning unit, comprising:
 a second light source arranged to emit a second beam of light having a second wavelength onto the cantilever, the second beam forming a spot on the surface of the cantilever that induces photothermal bending of the cantilever, wherein a location of the spot on the surface of the cantilever is adjustable, and wherein the second beam induces sub-resonance bending of the cantilever; and 
 a second steering mirror rotatable in two orthogonal axes that are parallel to a reflecting surface of the second steering mirror and controlled to reflect the beam from the light source on the surface of the cantilever opposite the tip, by pitching and yawing the second steering mirror, and controlling a physical pivot where the two orthogonal axes intersect to coincide with a point of incidence where the beam is reflected from the second steering mirror; and 
   wherein the sensor assembly measures tip-sample force-distance characteristics in response to the sub-resonance bending of the cantilever.   
     
     
       29. An atomic force microscope according to claim 28, wherein the sensor assembly measures tip-sample force-distance characteristics for tracking sample topography. 
     
     
       30. An atomic force microscope according to claim 28, wherein the sensor assembly measures tip-sample force-distance characteristics for measuring mechanical parameters of the sample. 
     
     
       31. An atomic force microscope according to claim 28, wherein the sensor assembly measures tip-sample force-distance characteristics for measuring an electromechanical response of the sample.