Multi-spot illumination for improved detection sensitivity

Patent metadata

Field	Value
Publication number	US-9494531-B2
Application number	US-201414455161-A
Country	US
Kind code	B2
Filing date	Aug 8, 2014
Priority date	Aug 9, 2013
Publication date	Nov 15, 2016
Grant date	Nov 15, 2016

Abstract

Methods and systems for minimizing interference among multiple illumination beams generated from a non-uniform illumination source to provide an effectively uniform illumination profile over the field of view of an inspection system are presented. In some examples, a pulsed beam of light is split into multiple illumination beams such that each of the beams are temporally separated at the surface of the specimen under inspection. In some examples, multiple illumination beams generated from a non-uniform illumination source are projected onto spatially separated areas on the surface of the specimen. A point object of interest illuminated by each area is imaged onto the surface of a time-delay integration (TDI) detector. The images are integrated such that the relative position of the illumination areas along the direction of motion of the point object of interest has no impact on the illumination efficiency distribution over the field of view.

First claim

What is claimed is:

1. An inspection system comprising:
a pulsed laser illumination source configured to generate a beam of illumination light;
an optical subsystem that receives the beam of illumination light and splits the beam of illumination light into two or more secondary beams of illumination light, wherein the optical subsystem introduces a temporal delay among the two or more secondary beams of illumination light as the two or more secondary beams illuminate a surface of a specimen under inspection; and
a detector operable to receive a first amount of light collected from the surface of the specimen illuminated by a first of the two or more secondary beams of illumination light, receive a second amount of light collected from the surface of the specimen illuminated by a second of the two or more secondary beams of illumination light, and generate an output value based on an integration of the first and second amounts of light for a period of time that exceeds a sum of a pulse duration of the beam of illumination light and the temporal delay.

2. The inspection system of claim 1 , wherein the temporal delay exceeds a pulse duration of the beam of illumination light generated by the pulsed laser illumination source.

3. The inspection system of claim 2 , wherein the temporal delay is less than a period between successive pulses of the illumination light generated by the pulsed laser illumination source.

4. The inspection system of claim 1 , wherein the optical subsystem includes two parallel mirrors configured to spatially split the beam of illumination light into two half-beams, wherein one half-beam is spatially displaced and temporally delayed with respect to the other.

5. The inspection system of claim 1 , wherein the optical subsystem includes at least one beam splitter and a mirror configured to generate two or more secondary illumination beams from the beam of illumination light, wherein each of the secondary illumination beams are temporally delayed with respect to any other of the secondary illumination beams.

6. The inspection system of claim 1 , wherein the optical subsystem includes a parallel beam plate configured to spatially split the beam of illumination light into four half-beams of approximately equal intensity, wherein each of the four half-beams is temporally delayed with respect to at least one of the others.

7. The inspection system of claim 6 , wherein the parallel beam plate is further configured to emit a first and a second of the four half-beams from a first surface of the parallel beam plate and third and a fourth of the four half-beams from a second surface of the parallel beam plate.

8. The inspection system of claim 1 , wherein the detector is a time-delay integration (TDI) detector.

9. An inspection system comprising:
an illumination source configured to generate a pulsed beam of illumination light;
an optical subsystem that receives the pulsed beam of illumination light and splits the pulsed beam of illumination light into two or more secondary beams of illumination light, wherein the optical subsystem introduces a spatial separation among the two or more secondary beams of illumination light as the two or more secondary beams illuminate a surface of a specimen under inspection; and
a time-delay integration (TDI) detector operable to receive a first amount of light collected from the surface of the specimen illuminated by a first of the two or more secondary beams of illumination light, receive a second amount of light collected from the surface of the specimen illuminated by a second of the two or more secondary beams of illumination light, and generate an output value based on a time-delay integration of the first and second amounts of collected light, wherein an integration time associated with the time-delay integration is at least five times longer than a time between successive pulses.

10. The inspection system of claim 9 , wherein the optical subsystem includes two parallel mirrors configured to spatially split the beam of illumination light into two half-beams, wherein one half-beam is spatially displaced with respect to the other.

11. The inspection system of claim 9 , wherein the optical subsystem includes at least one beam splitter and a mirror configured to generate two or more secondary illumination beams from the beam of illumination light, wherein each of the secondary illumination beams are spatially displaced with respect to any other of the secondary illumination beams.

12. The inspection system of claim 9 , wherein the optical subsystem includes a parallel beam plate configured to spatially split the beam of illumination light into four half-beams of approximately equal intensity, wherein each of the four half-beams is spatially displaced with respect to at least one of the others.

13. The inspection system of claim 12 , wherein the parallel beam plate is further configured to emit a first and a second of the four half-beams from a first surface of the parallel beam plate and third and a fourth of the four half-beams from a second surface of the parallel beam plate.

14. A method comprising:
generating a pulsed beam of illumination light;
splitting the pulsed beam of illumination light into two or more secondary beams of illumination light with a temporal delay among the two or more secondary beams of illumination light as the two or more secondary beams illuminate a surface of a specimen under inspection;
receiving a first amount of light collected from the surface of the specimen illuminated by a first of the two or more secondary beams of illumination light;
receiving a second amount of light collected from the surface of the specimen illuminated by a second of the two or more secondary beams of illumination light; and
generating an output value based on an integration of the first and second amounts of collected light over a period of time that is at least five times longer than a time between successive pulses of the pulsed beam of illumination light.

15. The method of claim 14 , wherein the splitting the pulsed beam of illumination light into the two or more secondary beams of illumination light involves spatially splitting the beam of illumination light into two half-beams, wherein one half-beam is temporally delayed with respect to the other.

16. The method of claim 14 , wherein the temporal delay exceeds a pulse duration of the pulsed beam of illumination light.

17. The method of claim 16 , wherein the temporal delay is shorter than a period between successive pulses of the pulsed beam of illumination light.

18. A method comprising:
generating a pulsed beam of illumination light;
splitting the pulsed beam of illumination light into two or more secondary beams of illumination light, wherein each area of a surface of a specimen illuminated by each of the two or more secondary beams of illumination light is spatially separated;
receiving a first amount of light collected from the surface of the specimen illuminated by a first of the two or more secondary beams of illumination light;
receiving a second amount of light collected from the surface of the specimen illuminated by a second of the two or more secondary beams of illumination light; and
generating an output value based on a time-delay integration of the first and second amounts of collected light, wherein an integration time associated with the time-delay integration is at least five times longer than a time between successive pulses.

19. The method of claim 18 , wherein the splitting the beam of illumination light

Assignees

• Kla Tencor Corp

Inventors

• Chuang Yung-Ho Alex
• Lu Xiaoxu
• Fielden John
• Maleev Ivan

Classifications

• G01N21/8806

  Specially adapted optical and illumination features · CPC title

• G01J1/04

  Optical or mechanical part {supplementary adjustable parts} · CPC title

• G01N21/9501 Primary

  Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20) · CPC title

• F21Y2115/30

  Semiconductor lasers · CPC title

• F21Y2115/00

  Light-generating elements of semiconductor light sources · CPC title