System and method for defect detection using multi-spot scanning

Patent metadata

Field	Value
Publication number	US-10386311-B1
Application number	US-201715803789-A
Country	US
Kind code	B1
Filing date	Nov 5, 2017
Priority date	Sep 25, 2012
Publication date	Aug 20, 2019
Grant date	Aug 20, 2019

Abstract

A system that may include a radiation source to generate a beam of coherent radiation; traveling lens optics to focus the beam so as to generate multiple spots on a surface of a sample and to scan the spots together over the surface; collection optics to collect the radiation scattered from the multiple spots and to focus the collected radiation so as to generate a pattern of interference fringes; and a detection unit to detect changes in the pattern of interference fringes.

First claim

The invention claimed is:

1. A method, comprising:
generating, by a radiation source, a beam of coherent radiation;
focusing, by traveling lens optics, the beam to generate multiple spots on a surface of a sample;
scanning the multiple spots together over the surface while varying at least one optical character of at least one spot of the multiple spots in alternation;
collecting, by collection optics, radiation scattered from the multiple spots and focusing the collected radiation to generate a pattern of interference fringes;
detecting, by a detection unit, changes in the pattern of interference fringes;
generating multiple images of non-continuous portions of the surface of the sample representative of near-field radiation in proximity to the surface of the sample, each image of the multiple images is associated with a certain value of the at least one optical character; and
classifying defects on the surface of the sample using the multiple images.

2. The method of claim 1 , wherein the multiple spots comprise a first spot, a second spot, and a third spot, and wherein the traveling lens optics comprise an acousto-optic Bragg cell and an acoustic transducer coupled to the cell adapted to produce first, second, and third frequency-modulated acoustic pulses which travel along a length of the Bragg cell such that, when the beam of radiation passes through the Bragg cell, it is focused by the first, second, and third pulses so as to generate and scan the first, second, and third spots, respectively.

3. The method of claim 2 , wherein the transducer is adapted to vary, in response to receiving a control signal from a controller, a relative timing and phase of the first, second, and third acoustic pulses to control a spacing and relative phase of the first, second and third spots.

4. The method of claim 3 , wherein the second spot is formed between the first and third spots, and wherein the traveling lens optics are adapted to generate the first and third spots as being of a same phase and to generate the second spot as being phase shifted from the first and third spots.

5. The method of claim 3 , wherein the traveling lens optics are adapted to control, in response to receiving the signal transmitted by the controller, at least one of a phase and amplitude of each one of the first, second and third spots to cause the pattern of interference fringes to remain substantially stationary at a certain optical plane regardless of topographic differences between different portions of the surface of the sample.

6. The method of claim 3 , wherein the second spot is formed between the first and third spots, and wherein the traveling lens optics are adapted to vary, in response to receiving a signal transmitted by a controller, a phase differently between the second spot and a phase of the third and first spots while maintaining the second spot between the first and third spots.

7. The method of claim 1 , wherein the collection optics comprise a beam stop which is arranged to block at least one interference fringe of the pattern of interference fringes from impinging on a detector of the detection unit.

8. The method of claim 1 , wherein the traveling lens optics are further adapted to vary, in response to receiving a signal transmitted by a controller, a phase of the at least one spot in alternation between at least three different phase values to generate at least three images of the multiple images, each of the at least three images corresponds to a different phase value.

9. A system, comprising:
a radiation source adapted to generate a beam of coherent radiation;
traveling lens optics adapted to focus the beam to generate multiple spots on a surface of a sample and to scan the multiple spots together over the surface, the traveling lens optics being further adapted to, in response to receiving a signal from a controller, generate the multiple spots and to vary at least one optical character of at least one spot of the multiple spots in alternation;
collection optics comprising an objective lens and a beam splitter, the collection optics being positioned and adapted to collect the radiation scattered from the multiple spots and to focus the collected radiation to generate a pattern of interference fringes;
a detector adapted to detect changes in the pattern of interference fringes; and
processing hardware adapted to:
generate multiple images of non-continuous portions of the surface of the sample representative of near-field radiation in proximity to the surface of the sample, each image of the multiple images is associated with a certain value of the at least one optical character; and
classify defects on the surface of the sample using the multiple images.

10. The system of claim 9 , wherein the multiple spots comprise a first spot, a second spot, and a third spot, and wherein the traveling lens optics comprise an acousto-optic Bragg cell and an acoustic transducer coupled to the cell adapted to produce first, second, and third frequency-modulated acoustic pulses which travel along a length of the Bragg cell such that, when the beam of radiation passes through the Bragg cell, it is focused by the first, second, and third pulses so as to generate and scan the first, second, and third spots, respectively.

11. The system of claim 10 , wherein the transducer is adapted to vary a relative timing and phase of the first, second, and third acoustic pulses to control a spacing and relative phase of the first, second and third spots.

12. The system of claim 11 , wherein the second spot is formed between the first and third spots, and wherein the traveling lens optics are adapted to generate the first and third spots as being of a same phase and to generate the second spot as being phase shifted from the first and third spots.

13. The system of claim 11 , wherein the traveling lens optics are adapted to control at least one of a phase and amplitude of each one of the first, second and third spots to cause the pattern of interference fringes to remain substantially stationary at a certain optical plane regardless of topographic differences between different portions of the surface of the sample.

14. The system of claim 10 , wherein the second spot is formed between the first and third spots, and wherein the traveling lens optics are adapted to vary a phase differently between the second spot and a phase of the third and first spots while maintaining the second spot between the first and third spots.

15. The system of claim 9 , wherein the collection optics further comprise a beam stop which is arranged to block at least one interference fringe of the pattern of interference fringes from impinging on the detector.

16. The system of claim 9 , wherein the traveling lens optics are further adapted to vary a phase of the at least one spot in alternation between at least three different phase values to generate at least three images of the multiple images, each of the at least three images corresponds to a different phase value.

Assignees

• Applied Materials Israel Ltd

Inventors

• Shoham Amir
• Berlatzky Yoav
• Feldman Haim

Classifications

• G01B2290/30

  Grating as beam-splitter · CPC title

• G01N21/95623

  using a spatial filtering method (per se G02B) · CPC title

• G01N21/95607 Primary

  using a comparative method · CPC title