Caliper method, system, and apparatus

Abstract

A caliper atomic force microscope (AFM) comprises two AFM probes (each comprised of an oscillator and an attached tip) that operate on a sample in a coordinated manner. The coordinated operation of the AFM probes may be spatially or temporally coordinated. The result of the coordinated operation may be an image of the sample or a dimensional measurement of an unknown sample. The probes of the caliper AFM may be tilted, or the tips may be tilted at a non-orthogonal angle with respect to the probes, so as to enable the tips to access vertical sample surfaces or to enable the tips to touch each other. The tip shapes may include conical, boot-shaped, cylindrical, or spherical and materials from which the tips are fabricated may include silicon or carbon nanotubes. The oscillators may be beveled to allow the tips to operate in close proximity or in contact without interference of the oscillators. The disclosure of the present invention is discussed in terms of an atomic force (van der Waalls) interaction. Other interaction forces are contemplated, such as electrostatic force, magnetic force, and tunneling current. The caliper AFM may be calibrated with the help of a sample with known dimensions or by touching the probe tips. The tip-to-tip calibration enables absolute measurements without the need for a reference artifact, and it enables in-line calibration that may be performed during the measurement process.

1 . A method of calibrating a caliper AFM that has a first tip of a first AFM probe and a second tip of a second AFM probe, the method comprising: 
 taking a measurement of an artifact having a known dimension; and    adjusting the caliper AFM based on the difference between the measurement and the known dimension.    
     
     
         2 . The method of  claim 1 , wherein the taking the measurement comprises: 
 taking a measurement of an artifact having a known dimension, while the tips are in contact with the artifact.    
     
     
         3 . The method of  claim 2 , wherein the taking the measurement comprises: 
 taking a measurement of an artifact having a known dimension, using the extreme lateral points of the tips, while the tips are in contact with the artifact.    
     
     
         4 . The method of  claim 2 , wherein the taking the measurement comprises: 
 taking a measurement of an artifact having a known dimension, using the extreme vertical points of the tips, while the tips are in contact with the artifact.    
     
     
         5 . The method of  claim 1 , wherein the taking the measurement comprises: 
 taking a measurement of an artifact having a known dimension, while the tips are not in contact with the artifact.    
     
     
         6 . The method of  claim 2 , wherein the taking the measurement comprises: 
 taking a measurement of an artifact having a known dimension, using the extreme lateral points of the tips, while the tips are not in contact with the artifact.    
     
     
         7 . The method of  claim 2 , wherein the taking the measurement comprises: 
 taking a measurement of an artifact having a known dimension, using the extreme vertical points of the tips, while the tips are not in contact with the artifact.    
     
     
         8 . The method of  claim 1 , wherein first tip has a first apex, the second tip has a second apex, and the taking the measurement comprises: 
 characterizing the apexes using artifact having a known dimension.    
     
     
         9 . A method of calibrating a caliper AFM that has a first tip of a first AFM probe and a second tip of a second AFM probe, wherein the first AFM probe can move, and wherein the second AFM probe can move, such that the first tip and the second tip coordinate in a caliper manner, the method comprising: 
 at least one calibrating the tips as in  claim 1;  and    at least one measuring the test sample with the caliper AFM.    
     
     
         10 . The method of  claim 9 , wherein the method comprises in-line calibration.  
     
     
         11 . The method of  claim 9 , further comprising: 
 controlling the operation of the method by a logic circuit.    
     
     
         12 . The method of  claim 9 , wherein the controlling comprises: controlling the operation of the method by a logic circuit responsively to the results of past operations of the method.  
     
     
         13 . A method of calibrating a caliper AFM that has a first tip of a first AFM probe and a second tip of a second AFM probe, the method comprising: 
 positioning the tips such that they are at a known tip-to-tip distance for which they have an known interaction;    measuring a measured interaction of the tips; and    adjusting the caliper AFM based on the difference between known interaction and measured interaction.    
     
     
         14 . The method of  claim 13 , 
 wherein the positioning comprises: 
 positioning the tips such that their extreme lateral points are at a known tip-to-tip distance for which they have an known interaction; and  
   wherein the measuring comprises: 
 measuring a measured interaction of the extreme lateral points of the tips.  
   
     
     
         15 . The method of  claim 13 , wherein the measuring comprises: 
 characterizing the each apex with the other apex.    
     
     
         16 . A method of calibrating a caliper AFM that has a first tip of a first AFM probe and a second tip of a second AFM probe, wherein the first AFM probe can move, and wherein the second AFM probe can move, such that the first tip and the second tip coordinate in a caliper manner, the method comprising: 
 at least one calibrating the tips as in  claim 13;  and    at least one measuring a test sample with the caliper AFM.    
     
     
         17 . The method of  claim 16 , wherein the method comprises in-line calibration.  
     
     
         18 . The method of  claim 16 , further comprising: 
 controlling the operation of the method by a logic circuit.    
     
     
         19 . The method of  claim 18 , wherein the controlling comprises: 
 controlling the operation of the method by a logic circuit responsively to the results of past operations of the method.