OPTICAL INSPECTION SYSTEM AND METHOD

• US 20100231902A1
• Filed: 03/01/2010
• Published: 09/16/2010
• Est. Priority Date: 04/04/2008
• Status: Active Grant

• Current Assignee: Nanda Technologies GmbH (Onto Innovation Inc.)
• Original Assignee: Nanda Technologies GmbH (Onto Innovation Inc.)
• Inventors: Chhibber, Rajeshwar, Markwort, Lars, Eckerl, Klaus, Harendt, Norbert
• Granted Patent: US 8,072,591 B2
• Time in Patent Office: Days
• US Class Current: 356/237.200
• CPC Class Codes: G01N 2021/8825 Separate detection of dark field and bright field
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14

Abstract

A wafer inspection system has a bright field imaging beam path and a dark field imaging beam path to obtain bright field images and dark field images of a full 300 mm wafer. The optical system provides for telecentric imaging and has low optical aberrations. The bright field and dark field beam paths are folded such that the system can be integrated to occupy a low volume with a small foot print.

Claims

1. An inspection system comprising:

optics;

an object support for mounting an object in a region of an object plane of the optics;

a dark-field illumination light source; and

an image detector having a radiation sensitive substrate disposed in a region of an image plane of the optics;

wherein the optics provide an imaging beam path and a dark-field illumination beam path and comprises an objective lens, and a projection lens arranged

such that the following elements are arranged in the imaging beam path in the following order;

the object plane, the objective lens, and the radiation sensitive substrate, and

such that the following elements are arranged in the dark-field illumination beam path in the following order;

the dark-field light source, the projection lens and the object plane,

wherein an orientation of chief rays of the illumination beam path varies across an object field imaged onto the radiation sensitive substrate by less than 5°

;

wherein an orientation of chief rays of the imaging beam path varies across the object field by less than 5°

;

wherein a numerical aperture of the imaging beam path on a side of the object plane is less than 0.1;

wherein a numerical aperture of the illumination beam path on a side of the object plane is less than 0.1; and

wherein at least one of the following relations is fulfilled;

i) the object field diameter is greater than 200 mm and a total extension of the imaging beam path from the object plane to the image plane is less than 1100 mm;

ii) the total extension of the imaging beam path from the object plane to the image plane divided by the object field diameter is less than 6.0; and

iii) the diameter of the object field is greater than 0.6 times the object diameter.

2. The inspection system according to claim 1 further comprising a beam dump arranged in the dark field illumination beam path downstream of the object plane such that a portion of an illumination beam reflected at the object plane is receivable by the beam dump.

3. The inspection system according to claim 2 wherein the beam dump comprises first and second light absorbing portions, and wherein the first light absorbing portion of the beam dump is made of an absorbing material providing a transmission of incident light within a range from 1×

10<sup>−

7</sup> to 0.8 at a thickness of 1 mm.

4. The inspection system according to claim 3 wherein the second light absorbing portion of the beam dump is arranged to receive a portion of the illumination beam reflected from the first light absorbing portion.

5. The inspection system according to claim 3 wherein the first light absorbing portion is arranged to receive the portion of the illumination beam reflected from the object on a surface shaped such that pairs of surface normals intersecting the surface at spaced apart locations converge.

6. The inspection system according to claim 3 wherein a surface of the material of the first light absorbing structure of the beam dump carries an anti-reflective coating.

7. The inspection system according to claim 6 wherein a reflectivity of the surface of the material of first structure of the beam dump is less than 0.01.

8. The inspection system according to claim 1 wherein the projection lens is a single non-cemented lens element having two surfaces, wherein the surface having the larger surface curvature fulfils the relation that a free diameter of the lens divided by a radius of curvature of the lens surfaces is greater than 0.5.

9. The inspection system according to claim 1 wherein a lens surface of the projection lens closest to the object plane is a convex surface having a radius of curvature less than 2 m.

10. The inspection system according to claim 1 wherein a lens surface of the projection lens closest to the dark-field light source is a substantially flat surface having a radius of curvature greater than 10 m.

11. The inspection system according to claim 1 wherein the object diameter is greater than 200 mm.

12. The inspection system according to claim 11 wherein the object diameter is greater than or equal to 300 mm.

13. The inspection system according to claim 1 wherein the object comprises a semiconductor wafer.

14. The inspection system according to claim 13 wherein the semiconductor wafer comprises a 300 mm wafer.

15. A method of inspecting an object, the object having a substantially flat surface having a diameter of more than 250 mm and carrying periodic structures, the method comprising:

placing the object at a measuring position of an inspection system;

illuminating the surface of the object with dark-field illumination light such that directions of incidence of individual rays of the dark-field illumination light vary across the surface of the object by less than 5°

; and

imaging the surface of the object using imaging light emerging from the surface of the object under directions varying across the surface of the object by less than 5°

.

16. The method according to claim 15 further comprising rotating the object about an axis orthogonal to the flat surface of the object based on an analysis of an image of the surface.

17. The method according to claim 15 wherein the placing of the object at the measuring position comprises rotating the object to a predetermined rotational position about an axis orthogonal to the flat surface of the object.