System for measuring periodic structures

Abstract

A periodic structure is illuminated by polychromatic electromagnetic radiation. Radiation from the structure is collected and divided into two rays having different polarization states. The two rays are detected from which one or more parameters of the periodic structure may be derived. In another embodiment, when the periodic structure is illuminated by a poly chromatic electromagnetic radiation, the collected radiation from the structure is passed through a polarization element having a polarization plane. The element and the polychromatic beam are controlled so that the polarization plane of the element are at two or more different orientations with respect to the plane of incidence of the polychromatic beam. Radiation that has passed through the element is detected when the plane of polarization is at the two or more positions so that one or more parameters of the periodic structure may be derived from the detected signals. At least one of the orientations of the plane of polarization is substantially stationary when the detection takes place. To have as small a footprint as possible, one employs an optical device that includes a first element directing a polychromatic beam of electromagnetic radiation to the structure and a second optical element collecting radiation from the structure where the two elements form an integral unit or are attached together to form an integrated unit. To reduce the footprint, the measurement instrument and the wafer are both moved. In one embodiment, both the apparatus and the wafer undergo translational motion transverse to each other. In a different arrangement, one of the two motions is translational and the other is rotational. Any one of the above-described embodiments may be included in an integrated processing and detection apparatus which also includes a processing system processing the sample, where the processing system is responsive to the output of any one of the above embodiments for adjusting a processing parameter.

What is claimed is:  
     
         1 . A method for measuring one or more parameters of a periodic structure, comprising: 
 directing a polychromatic beam of electromagnetic radiation to the structure;    collecting radiation from the beam after it has been modified by the structure;    dividing the collected radiation into two collected rays having different polarization states;    detecting the two rays to provide two outputs; and    deriving the one or more parameters from the two outputs.    
     
     
         2 . The method of  claim 1 , wherein the dividing divides the collected radiation into an ordinary ray and an extraordinary ray, said two rays having substantially orthogonal polarizations.  
     
     
         3 . The method of  claim 1 , wherein the directing includes passing the collected radiation through an optical element having a plane of polarization at an angle different from 0, 90, 180 and 270 degrees to the plane of incidence.  
     
     
         4 . The method of  claim 1 , wherein the dividing includes passing the collected radiation through an optical element having a plane of polarization at an angle of about 0, 45, 90, 135, 180, 225, 270 and 315 degrees to the plane of incidence.  
     
     
         5 . The method of  claim 1 , wherein the directing directs an unpolarized beam to the structure, and wherein the dividing includes passing the collected radiation through an optical element having a plane of polarization at an angle of about 0, 90, 180 and 270 degrees to the plane of incidence.  
     
     
         6 . An apparatus for measuring one or more parameters of a periodic structure, comprising: 
 an instrument directing a polychromatic beam of electromagnetic radiation to the structure;    optics collecting radiation from the beam after it has been modified by the structure;    a device dividing the collected radiation into two collected rays having different polarization states;    detectors detecting the two rays to provide two outputs; and    a processor deriving the one or more parameters from the two outputs.    
     
     
         7 . The apparatus of  claim 6 , wherein the device divides the collected radiation into an ordinary ray and an extraordinary ray, said two rays having substantially orthogonal polarizations.  
     
     
         8 . The apparatus of  claim 6 , wherein the instrument includes an optical element having a plane of polarization at a non-zero angle to the plane of incidence, wherein said plane of polarization is not perpendicular to the plane of incidence.  
     
     
         9 . The apparatus of  claim 6 , wherein the device includes an optical element having a plane of polarization at an angle to the plane of incidence, where the angle is about 0, 45, 90, 135, 180, 225, 270 and 315 degrees.  
     
     
         10 . The apparatus of  claim 6 , wherein the instrument directs an unpolarized beam to the structure, and wherein the device includes an optical element passing the collected radiation, said optical element having a plane of polarization at an angle of about 0, 90, 180 and 270 degrees to the plane of incidence.  
     
     
         11 . The apparatus of  claim 4 , wherein each of said source and said optics has a numerical aperture, and wherein the numerical aperture of the optics is smaller than that of the source.  
     
     
         12 . A method for measuring one or more parameters of a periodic structure, comprising: 
 (a) directing a polychromatic beam of electromagnetic radiation to the structure in a plane of incidence;    (b) collecting radiation from the beam after it has been modified by the structure;    (c) passing the collected radiation through a first polarizing element having a polarization plane at a first angle to the plane of incidence;    (d) detecting the collected radiation passing through the element to provide an output;    (e) altering the first angle between the two planes to a different value and repeating (a), (b), (c) and (d), wherein said different value remains substantially stationary when (a), (b), (c) and (d) are repeated to provide at least an additional output; and    (f) deriving the one or more parameters from the outputs.    
     
     
         13 . The method of  claim 12 , wherein said different stationary value of the angle is one of 0, 45, 90, 135, 180, 225, 270 and 315 degrees.  
     
     
         14 . The method of  claim 12 , wherein said directing includes passing radiation through a second polarizing element having a polarization plane at a second angle to the plane of incidence, said second angle having a value different from 0, 90, 180 and 270 degrees.  
     
     
         15 . The method of  claim 14 , wherein said polarization planes of the two elements are substantially parallel or perpendicular to each other.  
     
     
         16 . An apparatus for measuring one or more parameters of a periodic structure, comprising: 
 a source directing a polychromatic beam of electromagnetic radiation to the structure in a plane of incidence;    optics collecting radiation from the beam after it has been modified by the structure;    a first polarizing element having a polarization plane at a first angle to the plane of incidence passing the collected radiation;    a detector detecting the collected radiation that has passed through the element to provide an output;    an instrument rotating the first element relative to the plane of incidence to alter the value(s) of the first angle to one or more different value(s) that remain substantially stationary when said detector is detecting the collected radiation, so that the detector provides at least one output before and after the first angle is altered; and    a processor deriving the one or more parameters from the outputs.    
     
     
         17 . The apparatus of  claim 16 , wherein said different value of the first angle is one of 0, 45, 90, 135, 180, 225, 270 and 315 degrees.  
     
     
         18 . The apparatus of  claim 16 , said source including a second polarizing element passing radiation to provide said beam, said second element having a polarization plane at a second angle to the plane of incidence, said instrument rotating one or more of the two elements relative to the plane of incidence to alter the value(s) of the first and/or the second angle to one or more different value(s) that remain substantially stationary when said detector is detecting the collected radiation.  
     
     
         19 . The apparatus of  claim 18 , wherein said different value(s) of the first and/or second angle are one of 0, 45, 90, 135, 180, 225, 270 and 315 degrees.  
     
     
         20 . The apparatus of  claim 16 , wherein each of said source and said optics has a numerical aperture, and wherein the numerical aperture of the optics is smaller than that of the source.  
     
     
         21 . The apparatus of  claim 16 , wherein said source includes a second polarizing element having a polarization plane at an angle to the plane of incidence, said second element passing radiation to provide said beam, said angle having a value different from 0, 90, 180 and 270 degrees.  
     
     
         22 . The apparatus of  claim 21 , wherein said polarization planes of the two elements are substantially parallel or perpendicular to each other.  
     
     
         23 . An apparatus for measuring one or more parameters of a periodic structure, comprising: 
 an optical device including a first element directing a polychromatic beam of electromagnetic radiation to the structure in a plane of incidence and a second optical element passing radiation from the beam after it has been modified by the structure, said two elements attached together to form an integrated unit or being an integral unit;    said second element having a plane of polarization; and    at least one detector detecting the collected radiation that has passed through the second element to provide at least one output.    
     
     
         24 . The apparatus of  claim 23 , said plane of polarization is at an angle to the plane of incidence, said angle having a value different from 0, 90, 180, 270 degrees.  
     
     
         25 . The apparatus of  claim 24 , wherein said plane of polarization is at an angle of about 0, 45, 90, 135, 180, 225, 270 or 315 degrees to the plane of incidence.  
     
     
         26 . The apparatus of  claim 23 , wherein the second element divides the radiation from the beam after it has been modified by the structure into an ordinary ray and an extraordinary ray, said two rays having substantially orthogonal polarizations, said apparatus further comprising two detectors, each of the two detectors detecting a corresponding one of the two rays.  
     
     
         27 . The apparatus of  claim 23 , wherein each of said two elements has a numerical aperture, and wherein the numerical aperture of the second element is smaller than that of the first.  
     
     
         28 . The apparatus of  claim 23 , further comprising a processor deriving the one or more parameters from the output.  
     
     
         29 . An apparatus for inspecting a sample having a structure thereon, comprising: 
 (a) a detection system including: 
 a device directing a polychromatic beam of electromagnetic radiation to the structure;  
 optics collecting radiation from the beam after it has been modified by the structure; and  
 at least one detector detecting the collected radiation to provide at least one output;  
   (b) a first instrument causing translational motion of the sample in a first direction; and    (c) a second instrument causing translational motion between the first instrument and the system in a second direction transverse to the first direction.    
     
     
         30 . The apparatus of  claim 29 , said system further including a radiation source.  
     
     
         31 . The apparatus of  claim 29 , said system further including a conduit carrying a collimated beam of radiation.  
     
     
         32 . The apparatus of  claim 29 , further including an optical arrangement directing an incoming radiation beam to the detection system along different optical paths when relative motion is caused between the system and the sample, so that the different optical paths have substantially the same optical path length.  
     
     
         33 . The apparatus of  claim 29 , said arrangement including a radiation reflective element that moves together with the second instrument reflecting radiation towards the device along optical paths that are substantially at 45 degrees to a trajectory of the device when moved by the two instruments.  
     
     
         34 . An apparatus for inspecting a sample having a structure thereon, comprising: 
 (a) a detection system including: 
 a device directing a polychromatic beam of electromagnetic radiation to the structure;  
 optics collecting radiation from the beam after it has been modified by the structure; and  
 at least one detector detecting the collected radiation to provide at least one output;  
   (b) an instrument causing first motion of the sample, and second motion between the first instrument and the system, wherein one of the two motions is translational and the remaining motion is rotational.    
     
     
         35 . The apparatus of  claim 34 , said system further including a radiation source.  
     
     
         36 . The apparatus of  claim 34 , said system further including a conduit carrying a collimated beam of radiation.  
     
     
         37 . The apparatus of  claim 34 , further including an optical arrangement directing an incoming radiation beam to the detection system along different optical paths when relative motion is caused between the system and the sample, so that the different optical paths have substantially the same optical path length.  
     
     
         38 . The apparatus of  claim 34 , said arrangement including a radiation reflective element that moves together with the second instrument reflecting radiation towards the device along optical paths that are substantially at 45 degrees to a trajectory of the device when moved by the two instruments.  
     
     
         39 . An integrated processing and detection apparatus for processing a sample having structures thereon, comprising: 
 (a) a detection system for finding one or more parameters of a structure, wherein the system detects the structure by directing a polychromatic beam of electromagnetic radiation to the structure, collecting radiation from the beam after it has been modified by the structure; said system including:    a device dividing the collected radiation into two collected rays having different polarization states;    detectors detecting the two rays to provide two outputs; and    a processor deriving the one or more parameters from the two outputs; and    (b) a processing system processing the sample, said processing system responsive to said one or more parameters for adjusting a processing parameter.    
     
     
         40 . The apparatus of  claim 39 , said detection system further including a radiation source that provides the polychromatic beam.  
     
     
         41 . The apparatus of  claim 39 , further including a conduit for transmitting radiation to said detection system.  
     
     
         42 . The apparatus of  claim 41 , said conduit including an optical fiber.  
     
     
         43 . The apparatus of  claim 39 , further including an instrument causing relative motion between the detection system and the sample in order to detect an area of the sample, an optical arrangement directing an incoming radiation beam to the detection system along different optical paths when relative motion is caused between the system and the sample, so that the different optical paths have substantially the same optical path length.  
     
     
         44 . The apparatus of  claim 39 , said detection system including one or more reflective optical elements.  
     
     
         45 . An integrated processing and detection apparatus for processing a sample having structures thereon, comprising: 
 (a) a detection system for finding one or more parameters of a structure, wherein the system detects the structure by directing a polychromatic beam of electromagnetic radiation to the structure in a plane of incidence, collecting radiation from the beam after it has been modified by the structure; said detection system including:    a first polarizing element having a polarization plane at a first angle to the plane of incidence passing the collected radiation;    a detector detecting the collected radiation that has passed through the element to provide an output;    an instrument rotating the first element relative to the plane of incidence to alter the value(s) of the first angle to one or more different value(s) that remain substantially stationary when said detector is detecting the collected radiation, so that the detector provides at least one output before and after the first angle is altered; and    a processor deriving the one or more parameters from the outputs.    (b) a processing system processing the sample, said processing system responsive to said one or more parameters for adjusting a processing parameter.    
     
     
         46 . The apparatus of  claim 45 , said detection system further including a radiation source that provides the polychromatic beam.  
     
     
         47 . The apparatus of  claim 45 , further including a conduit for transmitting radiation to said detection system.  
     
     
         48 . The apparatus of  claim 47 , said conduit including an optical fiber.  
     
     
         49 . The apparatus of  claim 45 , said system further including a second instrument causing relative motion between the detection system and the sample in order to detect an area of the sample, said system further including an optical arrangement directing an incoming radiation beam to the detection system along different optical paths when relative motion is caused between the system and the sample, so that the different optical paths have substantially the same optical path length.  
     
     
         50 . The apparatus of  claim 45 , said detection system including one or more reflective optical elements.  
     
     
         51 . An integrated processing and detection apparatus for processing a sample having structures thereon, comprising: 
 (a) a detection system including: 
 a device directing a polychromatic beam of electromagnetic radiation to the structure;  
 optics collecting radiation from the beam after it has been modified by the structure; and  
 at least one detector detecting the collected radiation to provide at least one output;  
   (b) a first instrument causing motion of the sample;    (c) a second instrument causing relative motion between the first instrument and the system so that the beam has access to any location of the sample; and    (d) a processing system processing the sample, said processing system responsive to said at least one output for adjusting a processing parameter.    
     
     
         52 . The apparatus of  claim 51 , said detection system further including a radiation source that provides the polychromatic beam.  
     
     
         53 . The apparatus of  claim 51 , further including a conduit carrying a collimated beam of radiation to the detection system.  
     
     
         54 . The apparatus of  claim 51 , further including an optical arrangement directing an incoming radiation beam to the detection system along different optical paths when relative motion is caused between the system and the sample, so that the different optical paths have substantially the same optical path length.  
     
     
         55 . The apparatus of  claim 51 , said two instruments causing translational motion that are substantially perpendicular to each other, said arrangement including a radiation reflective element that moves together with the second instrument reflecting radiation towards the device along optical paths that are substantially at 45 degrees to a trajectory of the device when moved by the two instruments.