Apparatuses and methods for enhanced critical dimension scatterometry

Abstract

Apparatuses and methods for evaluating microstructures on workpieces are disclosed herein. In one embodiment, a scatterometer comprises an irradiation source, an optic member, and an object lens assembly. The irradiation source can be a laser that produces a beam of radiation at a wavelength. The optic member is aligned with the path of the beam and configured to condition the beam (e.g., shape, randomize, select order, diffuse, converge, diverge, collimate, etc.), and the object lens assembly is positioned between the optic member and a workpiece site. The object lens assembly is configured to (a) simultaneously focus the conditioned beam through a plurality of altitude angles to a spot at an object focal plane, (b) receive radiation scattered from a workpiece, and (c) present a distribution of the scattered radiation at a second focal plane. The object lens assembly maintains a sine relationship between the altitude angles and corresponding points on the radiation distribution at the second focal plane. The scatterometer further includes a mask positioned between the optic member and the object lens assembly, and a detector positioned to receive at least a portion of the radiation distribution. The mask is aligned with the path of the beam to block a portion of the conditioned beam. The mask is configured to at least partially separate the zeroth-order diffraction and the higher-order diffractions in the radiation distribution at the second focal plane. The detector is configured to produce a representation of the radiation distribution.

1 . A scatterometer for evaluating microstructures on a workpiece, comprising: 
 an irradiation source for producing a beam of radiation at a wavelength;    a optic member aligned with the path of the beam, the optic member being configured to condition the beam;    an object lens assembly aligned with the path of the beam and positioned between the optic member and a workpiece site, the object lens assembly being configured to (a) receive the conditioned beam, (b) simultaneously focus the conditioned beam through a plurality of altitude angles to a spot at an object focal plane, (c) receive return radiation in the wavelength scattered from a workpiece, and (d) present a radiation distribution of the return radiation at a second focal plane, wherein the object lens assembly maintains a sine relationship between the altitude angles and corresponding points on the radiation distribution at the second focal plane;    a mask positioned between the optic member and the object lens assembly and aligned with the path of the beam to block a portion of the conditioned beam, the mask being configured to at least partially separate the zeroth-order diffraction and the higher-order diffractions in the radiation distribution at the second focal plane; and    a detector positioned to receive the radiation distribution and configured to produce a representation of the radiation distribution.    
   
   
       2 . The scatterometer of  claim 1  wherein the mask comprises a quadrant-shaped aperture through which a section of the conditioned beam can pass.  
   
   
       3 . The scatterometer of  claim 1  wherein the mask comprises an arcuate aperture through which a section of the conditioned beam can pass.  
   
   
       4 . The scatterometer of  claim 1  wherein the mask comprises a semicircular aperture through which a section of the conditioned beam can pass.  
   
   
       5 . The scatterometer of  claim 1  wherein the mask comprises (a) a circular area having quadrants, (b) a first aperture in a first quadrant, and (c) a second aperture in a second quadrant.  
   
   
       6 . The scatterometer of  claim 1  wherein the mask comprises (a) a circular area having quadrants, and (b) a plurality of arcuate apertures in corresponding quadrants.  
   
   
       7 . The scatterometer of  claim 1  wherein the mask comprises an aperture sized such that the mask blocks at least 75 percent of the cross-sectional area of the conditioned beam.  
   
   
       8 . The scatterometer of  claim 1  wherein the mask comprises an aperture sized such that the mask blocks at least 50 percent of the cross-sectional area of the conditioned beam.  
   
   
       9 . The scatterometer of  claim 1  wherein the mask includes an aperture with a straight edge.  
   
   
       10 . The scatterometer of  claim 1  wherein the object lens assembly is configured to focus the conditioned beam to a spot size not greater than 50 μm.  
   
   
       11 . The scatterometer of  claim 1  wherein the irradiation source comprises a laser configured to generate a first beam having a first wavelength and a second beam having a second wavelength different than the first wavelength.  
   
   
       12 . The scatterometer of  claim 1 , further comprising a computer operatively coupled to the detector for receiving a predetermined portion of the representation of the radiation distribution based on the configuration of the mask, wherein the computer includes a database having a plurality of simulated radiation distributions corresponding to different sets of parameters of a microstructure and a computer-operable medium containing instructions that cause the computer to identify a simulated radiation distribution that adequately fits the predetermined portion of the representation of the radiation distribution produced by the detector.  
   
   
       13 . The scatterometer of  claim 1  wherein the first wavelength is between approximately 200 nm and approximately 475 nm.  
   
   
       14 . The scatterometer of  claim 1  wherein the first wavelength is between approximately 375 nm and approximately 475 nm.  
   
   
       15 . The scatterometer of  claim 1  wherein the sine relationship between the altitude angles and the corresponding points on the radiation distribution is represented by the following formula: X=F sin Θ; 
 wherein F is a constant;    wherein X is a displacement in the radiation distribution at the second focal plane; and    wherein Θ is the altitude angle.    
   
   
       16 . A scatterometer for evaluating microstructures on a workpiece, comprising: 
 a radiation source configured to produce a beam of radiation having a first wavelength;    an optical system having a first optics assembly, an object lens assembly, and a mask, wherein the first optics assembly is configured to condition the beam of radiation such that beam is diffuse and randomized, and wherein the object lens assembly is configured to (a) focus the beam at an area of an object focal plane and (b) present a radiation distribution of return radiation scattered from a microstructure in a second focal plane; and    a detector positioned to receive the radiation distribution and configured to produce a representation of the radiation distribution;    wherein the mask is shaped to block a portion of the beam such that a specific diffraction order is at least partially isolated from other diffraction orders in the representation of the radiation distribution.    
   
   
       17 . The scatterometer of  claim 16  wherein the mask is configured to block a portion of the beam such that the zeroth-order diffraction is at least partially separated from the higher-order diffractions in the representation of the radiation distribution.  
   
   
       18 . The scatterometer of  claim 16  wherein the first optics assembly comprises a beam conditioner, and wherein the mask is aligned with the beam and positioned between the beam conditioner and the object lens assembly.  
   
   
       19 . The scatterometer of  claim 16  wherein the mask comprises an aperture through which a section of the beam can pass.  
   
   
       20 . The scatterometer of  claim 16  wherein the mask comprises an aperture sized such that the mask blocks at least 75 percent of the cross-sectional area of the beam.  
   
   
       21 . The scatterometer of  claim 16  wherein the mask comprises an aperture sized such that the mask blocks at least 50 percent of the cross-sectional area of the beam.  
   
   
       22 . The scatterometer of  claim 16 , further comprising a computer operatively coupled to the detector for receiving a predetermined portion of the representation of the radiation distribution based on the configuration of the mask, wherein the computer includes a database having a plurality of simulated radiation distributions corresponding to different sets of parameters of a microstructure and a computer-operable medium containing instructions that cause the computer to identify a simulated radiation distribution that adequately fits the predetermined portion of the representation of the radiation distribution produced by the detector.  
   
   
       23 . A scatterometer for evaluating microstructures on workpieces, comprising: 
 a radiation source configured to produce a beam of radiation having a first wavelength;    an optical system having a first optics assembly, an object lens assembly, and a mask, wherein the first optics assembly is configured to condition the beam of radiation such that beam is diffuse and randomized, wherein the object lens assembly is configured to (a) focus the beam at an area of an object focal plane and (b) present a radiation distribution of return radiation scattered from a microstructure in a second focal plane, and wherein the mask is shaped to block a portion of the beam such that the zeroth-order diffraction is at least partially separated from the higher-order diffractions in the radiation distribution at the second focal plane;    a detector positioned to receive the radiation distribution of the return radiation and configured to produce a representation of the radiation distribution; and    a computer operatively coupled to the detector for receiving a predetermined portion of the representation of the radiation distribution based on the configuration of the mask, wherein the computer includes a database having a plurality of simulated radiation distributions corresponding to different sets of parameters of a microstructure and a computer-operable medium containing instructions that cause the computer to identify a simulated radiation distribution that adequately fits the predetermined portion of the representation of the radiation distribution produced by the detector.    
   
   
       24 . The scatterometer of  claim 23  wherein the first optics assembly comprises a beam conditioner, and wherein the mask is aligned with the beam and positioned between the beam conditioner and the object lens assembly.  
   
   
       25 . The scatterometer of  claim 23  wherein the mask comprises an aperture through which a section of the beam can pass, and wherein the aperture is shaped so that the zeroth-order diffraction is at least partially isolated from the higher-order diffractions in the radiation distribution at the second focal plane.  
   
   
       26 . The scatterometer of  claim 23  wherein the mask comprises an aperture sized such that the mask blocks at least 75 percent of the cross-sectional area of the beam.  
   
   
       27 . The scatterometer of  claim 23  wherein the mask comprises an aperture sized such that the mask blocks at least 50 percent of the cross-sectional area of the beam.  
   
   
       28 . A scatterometer for evaluating microstructures on workpieces, comprising: 
 an irradiation source for producing a first beam of radiation at a first wavelength;    a first optic member aligned with the path of the beam, the first optic member being configured to condition the beam;    an object lens assembly aligned with the path of the beam and positioned between the first optic member and a workpiece site, the object lens assembly being configured to (a) focus the beam at an area of an object focal plane and (b) present an radiation distribution of return radiation scattered from a microstructure at a second focal plane;    means for at least partially separating the zeroth-order diffraction and the higher-order diffractions in the radiation distribution at the second focal plane; and    a detector positioned to receive the radiation distribution and configured to produce a representation of the radiation distribution.    
   
   
       29 . The scatterometer of  claim 28  wherein the means for at least partially separating the zeroth-order diffraction and the higher-order diffractions comprise a mask positioned to block a portion of the conditioned beam.  
   
   
       30 . The scatterometer of  claim 28  wherein the means for at least partially separating the zeroth-order diffraction and the higher-order diffractions comprise a mask aligned with the beam and positioned between the first optic member and the object lens assembly.  
   
   
       31 . The scatterometer of  claim 28  wherein the means for at least partially separating the zeroth-order diffraction and the higher-order diffractions comprise a mask configured to block at least 50 percent of the cross-sectional area of the beam.  
   
   
       32 . A method of evaluating a microstructure on a workpiece, the method comprising: 
 generating a beam having a wavelength;    irradiating a microstructure on a workpiece by passing the beam through an object lens assembly that focuses the beam to a focus area at a focal plane, wherein the focus area has a dimension not greater than 50 μm, and wherein the beam simultaneously is focused through angles of incidence having (a) altitude angles of 0° to at least 15° and (b) azimuth angles of 0° to at least 90°; and    detecting an actual radiation distribution corresponding to radiation scattered from the microstructure with the zeroth-order diffraction at least partially separated from the higher-order diffractions.    
   
   
       33 . The method of  claim 32  wherein irradiating the microstructure comprises blocking a portion of the beam with a mask.  
   
   
       34 . The method of  claim 32  wherein irradiating the microstructure comprises passing a portion of the beam through an aperture in a mask with the aperture sized so that the zeroth-order diffraction is at least partially isolated from the higher-order diffractions in the detected radiation distribution.  
   
   
       35 . The method of  claim 32  wherein irradiating the microstructure comprises passing a portion of the beam through a plurality of apertures in a mask.  
   
   
       36 . The method of  claim 32  wherein irradiating the microstructure comprises blocking at least 75 percent of the cross-sectional area of the beam.  
   
   
       37 . The method of  claim 32  wherein irradiating the microstructure comprises blocking at least 50 percent of the cross-sectional area of the beam.  
   
   
       38 . The method of  claim 32 , further comprising: 
 providing a database having a plurality of simulated radiation distributions corresponding to different sets of parameters of the microstructure; and    identifying a simulated radiation distribution that adequately fits a predetermined portion of the representation of the detected radiation distribution corresponding to the zeroth-order diffraction.    
   
   
       39 . The method of  claim 32  wherein irradiating the microstructure comprises passing a portion of the beam through a quadrant-shaped aperture in a mask.  
   
   
       40 . The method of  claim 32  wherein irradiating the microstructure comprises passing a portion of the beam through an arcuate aperture in a mask.  
   
   
       41 . The method of  claim 32  wherein irradiating the microstructure comprises passing a portion of the beam through a semicircular aperture in a mask.  
   
   
       42 . A method of evaluating a microstructure on a workpiece, the method comprising: 
 providing a workpiece having a microstructure in an area not greater than 50 μm, wherein a critical dimension of a feature in the microstructure is less than approximately 90 nm;    generating a beam of radiation having a wavelength;    passing the beam through (a) a mask that blocks a portion of the beam, and (b) a lens that focuses the beam to a focus area at a focal plane, wherein the focus area has a dimension not greater than 50 μm, and wherein the beam is focused through a range of angles of incidence having simultaneously (a) altitude angles of 0° to at least 15° and (b) azimuth angles of 0° to at least 90°;    detecting a radiation distribution of return radiation scattered from the microstructure with the zeroth-order diffraction at least partially separated from the higher-order diffractions;    providing a database having a plurality of simulated radiation distributions corresponding to different sets of parameters of the microstructure; and    identifying a simulated radiation distribution that adequately fits a predetermined portion of the representation of the detected radiation distribution corresponding to the zeroth-order diffraction.    
   
   
       43 . The method of  claim 42  wherein passing the beam through the mask comprises passing the beam through a plurality of apertures in the mask.  
   
   
       44 . The method of  claim 42  wherein passing the beam through the mask comprises blocking at least 75 percent of the cross-sectional area of the beam with the mask.