Pattern invariant focusing of a charged particle beam
First Claim
1. A method for focusing a scanning microscope, comprising;
- scanning a primary charged particle beam across a plurality of first sites of a reference die of a wafer;
detecting a secondary beam of charged particles emitted from the plurality of first sites in response to the primary charged particle beam;
computing first focus scores for the plurality of first sites based on the detected secondary beam;
scanning the primary charged particle beam across a plurality of second sites of a given die of the wafer while modulating a focal depth of the primary charged particle beam, the reference die and the given die having congruent layouts, and wherein the second sites respectively correspond vectorially in location with the first sites of the reference die;
detecting the secondary beam of charged particles emitted from the plurality of second sites in response to the primary charged particle beam;
computing second focus scores for the second sites based on the detected secondary beam emitted therefrom, anddetermining an exact focus of the primary charged particle beam for the second sites in response to the first and the second focus scores.
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Abstract
A method for focusing a scanning microscope, including scanning a primary charged particle beam across first sites of a reference die of a wafer, detecting a secondary beam emitted from the sites, and computing first focus scores for the sites based on the secondary beam. The method includes scanning the primary beam across second sites of a given die of the wafer while modulating a focal depth of the primary beam, the reference die and the given die having congruent layouts, the second sites corresponding vectorially in location with the first sites, and detecting the secondary beam emitted from the second sites in response to the primary beam. The method also includes computing second focus scores for the second sites based on the detected secondary beam emitted therefrom, and determining an exact focus of the primary beam for the second sites using the first and the second focus scores.
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Citations
18 Claims
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1. A method for focusing a scanning microscope, comprising;
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scanning a primary charged particle beam across a plurality of first sites of a reference die of a wafer; detecting a secondary beam of charged particles emitted from the plurality of first sites in response to the primary charged particle beam; computing first focus scores for the plurality of first sites based on the detected secondary beam; scanning the primary charged particle beam across a plurality of second sites of a given die of the wafer while modulating a focal depth of the primary charged particle beam, the reference die and the given die having congruent layouts, and wherein the second sites respectively correspond vectorially in location with the first sites of the reference die; detecting the secondary beam of charged particles emitted from the plurality of second sites in response to the primary charged particle beam; computing second focus scores for the second sites based on the detected secondary beam emitted therefrom, and determining an exact focus of the primary charged particle beam for the second sites in response to the first and the second focus scores. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Apparatus for focusing a scanning microscope, comprising:
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an irradiation module which is configured to scan a primary charged particle beam across a plurality of first sites of a reference die of a wafer, and to scan the primary charged particle beam across a plurality of second sites of a given die of the wafer while modulating a focal depth of the primary charged particle beam, the reference die and the given die having congruent layouts, and wherein the second sites respectively correspond vectorially in location with the first sites of the reference die; an imaging detector which is configured to detect a secondary beam of charged particles emitted from the first sites and the second sites in response to the primary charged particle beam; and a processor which is configured to compute first focus scores for the plurality of first sites and second focus scores for the plurality of second sites based on the detected secondary beam and to determine an exact focus of the primary charged particle beam for the second sites in response to the first and the second focus scores. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification