Apparatus and method for optical inspection

• US 20070121106A1
• Filed: 10/20/2006
• Published: 05/31/2007
• Est. Priority Date: 11/29/2005
• Status: Active Grant

• Current Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Inventors: Maeda, Shunji, Shibata, Yukihiro
• Granted Patent: US 7,826,047 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 2021/8887 based on image processing techniques
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• 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 21/95607 using a comparative method
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

The present invention provides a variety of optical functions so as to be applicable to various kinds of objects to be inspected. For each of the optical functions, the invention accumulates contrasts (brightness differences), etc. of defects to be detected (DOI) and false defects not to be detected (nuisance), and efficiently selects parameters advantageous for inspection with high sensitivity and low nuisance ratio. A wavelength band, an illumination scheme, and filtering parameters can be selected for an optical system.

Claims

1. An optical inspection apparatus, comprising:

a light source which emits light of a wide wavelength band;

an illumination optical system which irradiates an object to be inspected that is formed on a sample with the light of the wide wavelength band that is emitted from the light source,;

a detection optical system which includes a wavelength separation element and a plurality of image sensors, the wavelength separation element being formed such that reflection light having the wide wavelength band obtained from the object on the sample with which the light has been irradiated by the illumination optical system is separated into reflection lights having a plurality of wavelength bands, each of a plurality of image sensors receiving optical image of each of the reflection lights separated by the wavelength separation element so as to output each of image signals; and

an image processing unit which detects defects of interest;

wherein the image processing unit selects a desired image signal which suppresses detection of false defects according to kind of the object to be inspected, from the image signals obtained from the plurality of image sensors in the detection optical system, and detects the defects of interest by processing the selected image signal.

2. The optical inspection apparatus according to claim 1, wherein

a plurality of objective lenses whose aberration has been corrected for each of the plurality of wavelength bands in the wide wavelength band are each selectably disposed for common use in the illumination optical system and the detection optical system.

3. The optical inspection apparatus according to claim 1, wherein

the illumination optical system further includes:

a bright-field illumination optics that irradiates the sample with the light having the plurality of wavelength bands; and

a dark-field illumination optics that irradiates the sample with the light having the plurality of wavelength bands.

4. The optical inspection apparatus according to claim 1, wherein

the light of the wide wavelength band that is emitted from the light source includes visible light.

5. The optical inspection apparatus according to claim 4, wherein

the illumination optical system further includes a band cutoff filter group constructed such that light of a plurality of any wavelength bands is selected from a wavelength band of visible light by combining a plurality of band cutoff filters which cut off lights of different specific wavelength bands.

6. The optical inspection apparatus according to claim 1, wherein

the light of the wide wavelength band that is emitted from the light source includes visible light and ultraviolet (UV) light.

7. The optical inspection apparatus according to claim 6, wherein

the illumination optical system further includes a band cutoff filter group constructed such that light of a plurality of any wavelength bands is selected from wavelength bands of visible light and UV light by combining a plurality of band cutoff filters which cut off lights of different specific wavelength bands.

8. The optical inspection apparatus according to claim 7, wherein

the illumination optical system further includes a wavelength selection element that selects each of UV light and visible light by switching between the UV light and the visible light.

9. The optical inspection apparatus according to claim 1, wherein:

the illumination optical system further includes a polarizing control optics that controls a polarization state of the irradiated light; and

the detection optical system includes at least an analyzer.

10. The optical inspection apparatus according to claim 1, wherein:

the illumination optical system further includes a polarizing control optics that controls the polarization state of the irradiated light; and

the detection optical system includes an analyzer between the wavelength separation element and each of the image sensors.

11. The optical inspection apparatus according to claim 9, wherein the detection optical system includes a polarizing beam splitter that is selectably disposed, instead of the wavelength separation element.

12. The optical inspection apparatus according to claim 1, further comprising:

an objective lens for common use in the illumination optical system and the detection optical system; and

a controllable or selectable spatial filter disposed at a position conjugate to a pupil of the objective lens in the detection optical system.

13. An optical inspection apparatus, comprising:

a light source which emits light of a wide wavelength band;

an illumination optical system having a wavelength selection optical element which selects light of a desired wavelength band from the light of the wide wavelength band that is emitted from the light source, the illumination optical system being adapted to irradiate an object to be inspected that is formed on a sample with the selected light of the desired wavelength band;

a detection optical system having an image sensor which receives an optical image of reflection light having a desired wavelength band obtained from the object to be inspected on the sample that has been irradiated with the light, so as to output an image signal; and

an image processing unit which detects defects of interest;

wherein;

the wavelength selection optical element selects the light of the desired wavelength band which suppresses detection of false defects according to kind of the object to be inspected; and

the image processing unit detects the defects of interest by processing the image signal obtained from the image sensor in the detection optical system.

17. The optical inspection apparatus according to claim 13, 14, or 15, further comprising:

an objective lens for common use between the two optical systems in the illumination optical system and the detection optical system; and

a spatial filter controllably or selectably disposed at a position conjugate to a pupil of the objective lens in the detection optical system.

14. An optical inspection apparatus, comprising:

a light source which emits light of a wide wavelength band;

an illumination optical system having a wavelength selection optical element which selects light having a plurality of wavelength bands from the light of the wide wavelength band that is emitted from the light source, wherein the illumination optical system irradiates an object to be inspected that is formed on a sample, with the light that has been selected by the wavelength selection optical element;

a detection optical system that includes a wavelength separation element and a plurality of image sensors, the wavelength separation element being formed such that reflection light having the plurality of wavelength bands obtained from the object to be inspected on the sample that has been irradiated by the illumination optical system with the light is separated into reflection lights having a plurality of wavelength bands, and each of the plurality of image sensors receiving optical image of each of the reflection lights that have been separated by the wavelength separation element so as to output each of image signals; and

an image processing unit which detects defects of interest;

wherein;

the wavelength selection optical element of the illumination optical system selects the light of a desired wavelength band which suppresses detection of false defects according to kind of the object to be objected; and

the image processing unit processes an image signal selected from the image signals obtained from each of the image sensors in the detection optical system so as to detect the defects of interest.

15. The optical inspection apparatus according to claim 14, wherein:

the illumination optical system further includes a polarizing control optics adapted to control a polarization state of the irradiated light; and

the detection optical system includes an analyzer between the wavelength separation element and each of the image sensors.

16. An optical inspection apparatus, comprising:

a light source which emits light of a wide wavelength band;

an illumination optical system having a wavelength selection optical element which selects light having a plurality of wavelength bands from the light of the wide wavelength band that is emitted from the light source, wherein the illumination optical system irradiates an object to be inspected that is formed on a sample, with the light that has been selected by the wavelength selection optical element;

a detection optical system which includes a polarizing separation element and a plurality of image sensors, the polarizing separation element being formed such that reflection light having the plurality of wavelength bands obtained from the object to be inspected on the sample that has been irradiated by the illumination optical system with the light is separated into reflection lights having different polarization states, each of the plurality of image sensors receiving optical image of each of the reflection lights that have been separated by the polarizing separation element so as to output each of image signals; and

an image processing unit which detects defects of interest;

wherein;

at least the illumination optical system or the detection optical system further has a polarizing control optics which controls polarization states;

the wavelength selection optical element of the illumination optical system selects the light of a desired wavelength band which suppresses detection of false defects according to kind of the object to be inspected; and

the image processing unit detects the defects of interest by processing an image signal selected from the image signals obtained from each of the image sensors in the detection optical system.

18. An optical inspection method, comprising:

an illumination step of irradiating an object to be inspected that is formed on a sample, with light of a wide wavelength band that is emitted from a light source that emits the light of the wide wavelength band, by an illumination optical system;

a detection step of separating reflection light having a wide wavelength band obtained from the object to be inspected on the sample irradiated with the light in the illumination step, into reflection light having a plurality of wavelength bands, by a wavelength separation element and receiving optical image of the reflection light having each of the wavelength bands separated by the wavelength separation element, by each of a plurality of image sensors so as to output each of image signals; and

an image processing step of detecting defects of interest in an image processing unit;

wherein the image processing step includes the sub-steps of;

selecting a desired image signal which suppresses detection of false defects according to kind of the object to be inspected from the image signals obtained from the plurality of image sensors in a detection optical system; and

detecting the defects of interest by processing the selected image signal.

19. The optical inspection method according to claim 18, wherein, in the illumination step, the illumination optical system uses a bright-field illumination optics adapted to irradiate the object to be inspected with the light having the plurality of wavelength bands and a dark-field illumination optics adapted to irradiate the object to be inspected with the light having the plurality of wavelength bands.

20. The optical inspection method according to claim 18, wherein, in the illumination step, the light of the wide wavelength band emitted from the light source includes visible light.

21. The optical inspection method according to claim 20, wherein, in the illumination step, the illumination optical system includes a band cutoff filter group constructed such that light of a plurality of any wavelength bands is selected from a wavelength band of visible light by combining a plurality of band cutoff filters which cut off lights of different specific wavelength bands.

22. The optical inspection method according to claim 18, wherein:

in the illumination step, a polarizing optics that controls a polarization state of the irradiated light is used as the illumination optical system; and

in the detection step, an analyzer controllably arranged between the wavelength separation element and each of the image sensors is used.

23. An optical inspection method, comprising:

an illumination step of selecting light of a desired wavelength band from the light of a wide wavelength band that is emitted from a light source that emits the light of the wide wavelength band, by a wavelength selection optical element and irradiating an object to be inspected that is formed on a sample, with the selected light of the desired wavelength band;

a detection step of receiving an optical image of reflection light having a desired wavelength band obtained from the object to be inspected on the sample irradiated with the light in the illumination step, by an image sensor so as to output an image signal; and

an image processing step of detecting defects of interest in an image processing unit;

wherein;

in the illumination step, the wavelength selection optical element selects the light of the desired wavelength band which suppresses detection of false defects according to kind of the object to be inspected; and

in the image processing step, the image signal obtained from the image sensor in the detection step is processed so as to detect the defects of interest.

24. An optical inspection method, comprising:

an illumination step of selecting light of a plurality of wavelength bands from light of a wide wavelength band that is emitted from a light source that emits the light of the wide wavelength band, by a wavelength selection optical element and irradiating an object to be inspected that is formed on a sample, with the selected light of the plural wavelength bands;

a detection step of separating reflection light having a plurality of wavelength bands obtained from the object to be inspected on the sample irradiated with the light in the illumination step, into reflection lights having a plurality of wavelength bands and receiving optical image of the reflection light having each of the wavelength bands separated by wavelength separation element, by each of a plurality of image sensors so as to output each of image signals; and

an image processing step of detecting defects of interest in an image processing unit;

wherein;

in the illumination step, the wavelength selection optical element selects the light of the desired wavelength band which suppresses detection of false defects according to kind of the object to be inspected; and

in the image processing step, an image signal selected from the image signals obtained from the image sensors in the detection step is processed so as to detect the defects of interest.

25. An optical inspection method, comprising:

an illumination step of selecting light having a plurality of wavelength bands from the light of a wide wavelength band that is emitted from a light source that emits the light of the wide wavelength band, and irradiating an object to be inspected that is formed on a sample, with the selected light of the plural wavelength bands;

a detection step of separating reflection light having the plurality of wavelength bands obtained from the object to be inspected on the sample irradiated with the light in the illumination step, into reflection lights having a plurality of wavelength bands by a wavelength separation element and receiving optical image of each of the reflection lights that have been separated by the wavelength separation element, by a plurality of image sensors so as to output each of image signals; and

an image processing step of detecting defects of interest in an image processing unit;

wherein;

at least in the illumination step or the detection step, a polarizing control optics which can control a polarization state is used;

in illumination step, the wavelength selection optical element selects light of a desired wavelength band which suppresses detection of a false defect according to kind of the object to be inspected; and

in the image processing step, an image signal selected from the image signals obtained from the image sensors in the detection step is processed so as to detect the defects of interest.