Automated selection of X-ray reflectometry measurement locations

Abstract

A computer-implemented method for inspection of a sample includes defining a plurality of locations on a surface of the sample, irradiating the surface at each of the locations with a beam of X-rays, and measuring an angular distribution of the X-rays that are emitted from the surface responsively to the beam, so as to produce a respective plurality of X-ray spectra. The X-ray spectra are analyzed to produce respective figures-of-merit indicative of a measurement quality of the X-ray spectra at the respective locations. One or more locations are selected out of the plurality of locations responsively to the figures-of-merit, and a property of the sample is estimated using the X-ray spectra measured at the selected locations.

1 . A computer-implemented method for inspection of a sample, comprising: 
 defining a plurality of locations on a surface of the sample;    irradiating the surface at each of the locations with a beam of X-rays and measuring an angular distribution of the X-rays that are emitted from the surface responsively to the beam, so as to produce a respective plurality of X-ray spectra;    analyzing the X-ray spectra to produce respective figures-of-merit indicative of a measurement quality of the X-ray spectra at the respective locations;    selecting one or more locations out of the plurality of locations responsively to the figures-of-merit; and    estimating a property of the sample using the X-ray spectra measured at the selected locations.    
   
   
       2 . The method according to  claim 1 , wherein the sample comprises a semiconductor wafer, and wherein estimating the property comprises at least one of detecting a fault and estimating a process parameter in a fabrication process of the semiconductor wafer.  
   
   
       3 . The method according to  claim 1 , wherein the figures-of-merit comprise a measure of information content of the X-ray spectra.  
   
   
       4 . The method according to  claim 3 , wherein the measure of the information content comprises curve lengths of the respective X-ray spectra with the X-ray spectra expressed as reflectivity values as a function of reflection angle.  
   
   
       5 . The method according to  claim 4 , wherein analyzing the X-ray spectra comprises calculating the curve lengths using a curvilinear formula.  
   
   
       6 . The method according to  claim 4 , wherein the X-ray spectra are expressed as logarithms of the reflectivity values as a function of reflection angle.  
   
   
       7 . The method according to  claim 1 , wherein analyzing the X-ray spectra comprises at least one of pre-filtering the X-ray spectra and omitting from the X-ray spectra data points having reflectivities smaller than a predetermined threshold.  
   
   
       8 . The method according to  claim 1 , wherein defining the plurality of locations comprises at least one of accepting a definition of the locations from a user and determining the locations using an automatic pattern recognition process.  
   
   
       9 . The method according to  claim 1 , wherein the sample comprises a patterned wafer, and wherein defining the plurality of locations comprises positioning at least some of the locations on a scribe line of the wafer.  
   
   
       10 . Apparatus for inspection of a sample, comprising: 
 an X-ray source, which is arranged to irradiate a surface of the sample with a beam of X-rays at a plurality of locations on the surface;    a detector assembly, which is arranged to measure a distribution of the X-rays that are emitted from the plurality of the locations responsively to the beam, so as to produce a respective plurality of X-ray spectra; and    a processor, which is arranged to analyze the X-ray spectra to produce respective figures-of-merit indicative of a measurement quality of the X-ray spectra at the respective locations, to select one or more locations out of the plurality of locations responsively to the figures-of-merit, and to estimate a property of the sample using the X-ray spectra measured at the selected locations.    
   
   
       11 . The apparatus according to  claim 10 , wherein the sample comprises a semiconductor wafer, and wherein the processor is arranged to perform at least one of detecting a fault and estimating a process parameter in a fabrication process of the semiconductor wafer by estimating the property.  
   
   
       12 . The apparatus according to  claim 10 , wherein the figures-of-merit comprise a measure of information content of the X-ray spectra.  
   
   
       13 . The apparatus according to  claim 12 , wherein the measure of the information content comprises curve lengths of the respective X-ray spectra with the X-ray spectra expressed as reflectivity values as a function of reflection angle.  
   
   
       14 . The apparatus according to  claim 13 , wherein the processor is arranged to calculate the curve lengths by applying a curvilinear formula.  
   
   
       15 . The apparatus according to  claim 13 , wherein the X-ray spectra are expressed as logarithms of the reflectivity values as a function of reflection angle.  
   
   
       16 . The apparatus according to  claim 10 , wherein the processor is arranged to perform at least one of pre-filtering the X-ray spectra and omitting from the X-ray spectra data points having reflectivities smaller than a predetermined threshold.  
   
   
       17 . The apparatus according to  claim 10 , wherein the processor is arranged to determine the plurality of locations using an automatic pattern recognition process.  
   
   
       18 . The apparatus according to  claim 10 , wherein the sample comprises a patterned wafer, and wherein at least some of the locations in the plurality are located on a scribe line of the wafer.  
   
   
       19 . A cluster tool for producing microelectronic devices, comprising: 
 a deposition station, which is arranged to form a thin-film layer on a surface of a semiconductor wafer; and    an inspection station, comprising: 
 an X-ray source, which is arranged to irradiate the surface of the semiconductor wafer with a beam of X-rays at a plurality of locations on the surface;  
 a detector assembly, which is arranged to measure a distribution of the X-rays that are emitted from the plurality of the locations responsively to the beam, so as to produce a respective plurality of X-ray spectra; and  
 a processor, which is arranged to analyze the X-ray spectra to produce respective figures-of-merit indicative of a measurement quality of the X-ray spectra at the respective locations, to select one or more locations out of the plurality of locations responsively to the figures-of-merit, and to estimate a property of the thin-film layer using the X-ray spectra measured at the selected locations.  
   
   
   
       20 . Apparatus for producing microelectronic devices, comprising: 
 a production chamber, which is arranged to receive a semiconductor wafer;    a deposition device, which is arranged to deposit a thin-film layer on a surface of the semiconductor wafer within the chamber;    an X-ray source, which is adapted to irradiate the surface of the semiconductor wafer in the production chamber with a beam of X-rays at a plurality of locations on the surface;    a detector assembly, which is arranged to measure a distribution of the X-rays that are emitted from the plurality of the locations responsively to the beam, so as to produce a respective plurality of X-ray spectra; and    a processor, which is arranged to analyze the X-ray spectra to produce respective figures-of-merit indicative of a measurement quality of the X-ray spectra at the respective locations, to select one or more locations out of the plurality of locations responsively to the figures-of-merit, and to estimate a property of the thin-film layer using the X-ray spectra measured at the selected locations.