Pattern inspection apparatus and pattern inspection method
A pattern inspection apparatus includes a secondary electron image acquisition mechanism to include a deflector deflecting multiple primary electron beams and a detector detecting multiple secondary electron beams, and acquire a secondary electron image corresponding to each of the multiple primary electron beams by scanning a target object with a pattern thereon with the multiple primary electron beams by the deflector, and detecting the multiple secondary electron beams from the target object by the detector, a storage device to store individual correction kernels each generated for individually adjusting a secondary electron image corresponding to each primary electron beam concerning a reference pattern to be commensurate with a reference blurred image, and a correction circuit to correct, by correspondingly using the individual correction kernel, the secondary electron image corresponding to each primary electron beam acquired from the inspection target object.
1. A pattern inspection apparatus comprising:
a secondary electron image acquisition mechanism configured to include a deflector which deflects multiple primary electron beams and a detector which detects multiple secondary electron beams, and to acquire a secondary electron image corresponding to each primary electron beam of the multiple primary electron beams by scanning a surface of a target object, on which a pattern has been formed, with the multiple primary electron beams by using the deflector, and detecting the multiple secondary electron beams emitted from the surface of the target object by using the detector;
a storage device configured to store individual correction kernels each of which is generated for individually adjusting a secondary electron image corresponding to the each primary electron beam with respect to a reference pattern to be commensurate with a reference blurred image;
a correction circuit configured to correct, by correspondingly using the individual correction kernel, the secondary electron image corresponding to the each primary electron beam acquired from the target object to be inspected;
a comparison circuit configured to compare an inspection image configured by at least a portion of the secondary electron image having been corrected and a reference image; and
a reference blurred image generation circuit configured to generate the reference blurred image by performing blur processing corresponding to an index value for blurring, with respect to the secondary electron image of the reference pattern acquired in a state where a focus position of a reference primary electron beam selected from the multiple primary electron beams is set on the surface of the target object.
2. The apparatus according to claim 1 further comprising:
a determination circuit configured to determine the index value for blurring, based on a blur index which is estimated from at least one of secondary electron images of an evaluation pattern of respective primary electron beams of the multiple primary electron beams, the secondary electron images of the evaluation pattern of the respective primary electron beams being acquired at a position obtained by shifting the focus position of the reference primary electron beam, selected among the multiple primary electron beams, from the surface of the target object.
3. The apparatus according to claim 2 , wherein the index value for blurring is determined based on a secondary electron image of an evaluation pattern of a primary electron beam having a maximum beam diameter, in the secondary electron images of the evaluation pattern of the respective primary electron beams.
4. The apparatus according to claim 2 , further comprising:
a blur index estimation circuit configured to estimate a blur index individually based on the secondary electron images of the evaluation pattern of the respective primary electron beams, where the secondary electron images of the evaluation pattern of the respective primary electron beams are acquired at each of positions obtained by variably shifting the focus position of the reference primary electron beam; and
a distribution generation circuit configured to generate a distribution of the blur index of the each primary electron beam, where the blur index of the each primary electron beam is estimated at each of the positions obtained by shifting the focus position of the reference primary electron beam,
wherein, referring to the distribution of the blur index of the each primary electron beam, the index value for blurring is determined based on a maximum value of the blur index of the each primary electron beam at a shifted position where the maximum value of the blur index is minimum compared with other maximum values of the blur index value at other shifted positions.
5. The apparatus according to claim 3 , wherein a beam diameter of a primary electron beam, expressed by a full width at half maximum, corresponding to the index value for blurring is one of ½ and less than ½ of a defect size.
6. A pattern inspection method comprising:
acquiring a secondary electron image corresponding to each primary electron beam of multiple primary electron beams by scanning a surface of a target object, on which a pattern has been formed, with the multiple primary electron beams, and detecting multiple secondary electron beams emitted from the surface of target object;
correcting the secondary electron image corresponding to the each primary electron beam acquired from the target object to be inspected, by reading from a storage device an individual correction kernel, which correspondingly adjusts each secondary electron image corresponding to the each primary electron beam with respect to a reference pattern to be commensurate with a reference blurred image, to perform the correcting by correspondingly using the individual correction kernel;
comparing an inspection image configured by at least a portion of the secondary electron image having been corrected and a reference image so as to output a compared result; and
generating the reference blurred image by performing blur processing corresponding to an index value for blurring, with respect to the secondary electron image of the reference pattern acquired in a state where a focus position of a reference primary electron beam selected from the multiple primary electron beams is set on the surface of the target object.
7. The method according to claim 6 further comprising:
determining the index value for blurring, based on a blur index which is estimated from at least one of secondary electron images of evaluation pattern of respective primary electron beams of the multiple primary electron beams, each acquired at a position obtained by shifting the focus position of the reference primary electron beam, selected among the multiple primary electron beams, from the surface of the target object.
8. The method according to claim 7 , wherein the index value for blurring is determined based on a secondary electron image of an evaluation pattern of a primary electron beam having a maximum beam diameter, in the secondary electron images of the evaluation patterns of the respective primary electron beams.
9. The method according to claim 7 , further comprising:
estimating a blur index individually based on the secondary electron images of the evaluation pattern of the respective primary electron beams, where the secondary electron images of the evaluation pattern of the respective primary electron beams are acquired at each of positions obtained by variably shifting the focus position of the reference primary electron beam; and
generating a distribution of the blur index of the each primary electron beam, which is estimated at the each of the positions obtained by shifting the focus position of the reference primary electron beam,
wherein, referring to the distribution of the blur index value of the each primary electron beam, the blur index value for blurring is determined based on a maximum value of the blur index value of the each primary electron beam at a shifted position where the maximum value of the blur index value is minimum compared with other maximum values of the blur index value at other shifted positions.
10. The method according to claim 8 , wherein a beam diameter of a primary electron beam, expressed by a full width at half maximum, corresponding to the index value for blurring is one of ½ and less than ½ of a defect size.