Optical inspection device and method

Patent metadata

Field	Value
Publication number	US-11536648-B2
Application number	US-201917258674-A
Country	US
Kind code	B2
Filing date	Jul 15, 2019
Priority date	Jul 13, 2018
Publication date	Dec 27, 2022
Grant date	Dec 27, 2022

Abstract

The optical inspection device is used for inspecting a planar object surface for the presence of particles and/or defects. A light source supplies light to the planar object surface of the object at a grazing angle. An image sensor receives light due to scattering from particles and defects on the object surface. The optical axis of the objective is at non-zero angles with the normal to the planar object surface and a direction or directions of specular reflection of the light from the light source by the planar object surface. A detection surface of the image detection device and the optical axis of the objective is in a Scheimpflug configuration. The light source and image sensor are located outside a space extending perpendicularly from the planar object surface, on opposite sides of that space. The image sensor comprises an objective and an image detection device. The device may further comprise a microscope or spectrometer to access the object surface through said space.

First claim

The invention claimed is:

1. A method of inspecting a pellicle mounted above a photolithographic reticle for presence of particles and/or defects, the method comprising:
lighting a top surface of the pellicle, under a grazing angle or range of grazing angles through a polarizer configured to light the top surface of the pellicle with transverse-electric (TE) polarization, from a light source located outside a space extending perpendicularly from the top surface of the pellicle;
imaging the top surface of the pellicle through an objective onto a detection surface of an image detection device,
wherein an optical axis of the objective is at non-zero angles with respect to normal to the top surface of the pellicle and at a direction or directions of specular reflection of the light from the light source by the top surface of the pellicle,
wherein the detection surface and the optical axis of the objective are in a Scheimpflug configuration to focus the top surface of the pellicle onto the detection surface,
wherein the image detection device and the objective are located outside said space, and
wherein said space is located between the objective and the light source.

2. The method according to claim 1 , wherein the objective is a telecentric objective.

3. The method according to claim 1 , wherein a controller coupled to an output of the image detection device:
detects a pixel in a first image detected by the image detection device, where an intensity of the image at the pixel exceeds a predetermined threshold value;
causes a positioning device to move a microscope to a position where the microscope forms a second image of a part of the top surface of the pellicle that contains an area of the top surface of the pellicle that the objective images onto said pixel, or to successive positions where the microscope successively forms second images that together contain said area, the second image or second images being formed with a greater magnification of the object surface than the first image; and
captures said second image or said second images from said microscope.

4. The method according to claim 3 , wherein the first image images the object surface in its entirety and the second image or images image over less than twice the size of said area of the top surface of the pellicle that the objective images onto said pixel.

5. The method according to claim 1 , wherein a controller coupled to an output of the image detection device:
detects a pixel in a first image detected by the image detection device, where an intensity of the image at the pixel exceeds a predetermined threshold value;
causes a positioning device to move an aperture of a spectrometer system to a position where the spectrometer system captures light from a part of the top surface of the pellicle that contains an area of the top surface of the pellicle that the objective images onto said pixel, or to successive positions where the spectrometer system successively captures light from sub-areas that together contain said area; and
reads a spectrum from the spectrometer system.

6. The method according to claim 1 , wherein the angle between the optical axis of the objective and the normal to the top surface of the pellicle is at least thirty degrees.

7. The method according to claim 1 , wherein the object is a transparent planar layer, and
wherein the method comprises lighting and imaging with a further light source and/or a further image detection device on an opposite side of a plane within which the layer lies.

8. The method according to claim 1 , wherein the lighting and imaging are performed, for a plurality of different orientations of the object relative to the light source and the image detection device, around a rotation axis perpendicular to the top surface of the pellicle.

9. An optical inspection device for inspecting a pellicle mounted above a photolithographic reticle for presence of particles and/or defects, the optical inspection device comprising:
an object location, with the photolithographic reticle placed on the object location, wherein the pellicle is mounted above the photolithographic reticle for placing an object;
a light source configured to supply light to the top surface of the pellicle, at a grazing angle or range of grazing angles, the light source being located outside a space extending perpendicularly from the top surface of the pellicle;
a polarizer, positioned between the light source and the top surface of the pellicle, that is configured to light the top surface of the pellicle with transverse-electric (TE) polarization; and
an image sensor comprising an objective and an image detection device,
wherein an optical axis of the objective is at non-zero angles with respect to normal to the top surface of the pellicle and at a direction or directions of specular reflection of the light from the light source by the top surface of the pellicle,
wherein a detection surface of the image detection device and the optical axis of the objective are in a Scheimpflug configuration to focus the top surface of the pellicle onto the detection surface,
wherein the image detection device and the objective are located outside said space, and
wherein said space is located between the objective and the light source.

10. The optical inspection device according to claim 9 , wherein the objective is a telecentric objective.

11. The optical inspection device according to claim 9 , wherein the light source comprises a collimator.

12. The optical inspection device according to claim 9 , comprising:
a microscope comprising a further image detection device, located to capture images formed by the microscope, the microscope being configured to capture images of parts of the object surface with a greater magnification of the object surface than the image sensor;
a positioning system coupled to the microscope, configured to move the microscope relative to the object surface;
a controller coupled to the image detection device, the further image detection device and the positioning device, wherein the controller comprises a program of instructions for the controller that, when executed by the controller, cause the controller to:
read a first image from the image detection device;
select a pixel in the first image wherein the intensity exceeds a predetermined threshold;
control the positioning system dependent on the pixel that has been selected, to move the microscope to a position where the microscope images a part of object surface that contains an area which maps to the selected pixel or to successive positions where the microscope successively forms second images that together contain said area; and
read and store an image of said part of object surface from the further image sensor.

13. The optical inspection device according to claim 12 , wherein the first image images the object surface entirely and the second images image over less than twice the size of said area.

14. The optical inspection device according to claim 9 , comprising:
a spectrometer system, having an aperture for capturing light for spectrometry;
a positioning system coupled to the spectrometer system, configured to move the aperture relative to the object surface;
a controller coupled to the image detection device, the spectrometer system and the positioning device, the controller comprising a program of instructions for the controller, which when executed by the controller causes the controller to:
read a first image from the image detection device;
select a pixel in the first image wherein the intensity exceeds a predetermined threshold;
control the positioning system

Assignees

• TNO
• Nederlandse Organisatie Voortoegepast Natuurwetenschappelijk Onderzoek Tno

Inventors

• Van Der Zwan Bertram Adriaan
• Oostrom Sjoerd
• Speet Bart Gerardus

Classifications

• G01N21/31 Primary

  Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry {(G01N21/72 takes precedence)} · CPC title

• G01N21/95

  characterised by the material or shape of the object to be examined (G01N21/89 - G01N21/91, G01N21/94 take precedence) · CPC title

• G01N2201/02

  Mechanical · CPC title

• G02B21/365

  Control or image processing arrangements for digital or video microscopes (G02B21/361, G02B21/362 take precedence) · CPC title

• G01N21/8806 Primary

  Specially adapted optical and illumination features · CPC title