Computer-implemented methods and systems for determining a configuration for a light scattering inspection system Number:7,436,505 from the United States Patent and Trademark Office (PTO) owispatent Computer-implemented methods and systems for determining a configuration for a light scattering inspection system are provided. One computer-implemented method includes determining a three-dimensional map of signal-to-noise ratio values for data that would be acquired for a specimen and a potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system. The method also includes determining one or more portions of the scattering hemisphere in which the signal-to-noise ratio values are higher than in other portions of the scattering hemisphere based on the three-dimensional map. In addition, the method includes determining a configuration for a detection subsystem of the inspection system based on the one or more portions of the scattering hemisphere.<H configuration, determining, Computer, implem, 7436505.html, Patent, pto, 7436505

Title: Computer-implemented methods and systems for determining a configuration for a light scattering inspection system

Abstract: Computer-implemented methods and systems for determining a configuration for a light scattering inspection system are provided. One computer-implemented method includes determining a three-dimensional map of signal-to-noise ratio values for data that would be acquired for a specimen and a potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system. The method also includes determining one or more portions of the scattering hemisphere in which the signal-to-noise ratio values are higher than in other portions of the scattering hemisphere based on the three-dimensional map. In addition, the method includes determining a configuration for a detection subsystem of the inspection system based on the one or more portions of the scattering hemisphere.

Patent Number: 7,436,505 Issued on 10/14/2008 to Belyaev, et al.

Inventors: Belyaev; Alexander (Mountain View, CA), Kavaldjiev; Daniel (Milpitas, CA), Murali; Amith (Fremont, CA), Petrenko; Aleksey (Milpitas, CA), Kirk; Mike D. (Los Altos Hills, CA), Shortt; David (Milpitas, CA), Haas; Brian L. (San Jose, CA), Haller; Kurt L. (Pleasanton, CA)
Assignee: KLA-Tencor Technologies Corp. (Milpitas, CA)

Appl. No.: 11/278,624

Filed: April 4, 2006

Current U.S. Class: 356/237.2

Current International Class: G01N 21/00 (20060101)

Field of Search: 356/237.1-237.5,601-623,445-448

References Cited [Referenced By]

U.S. Patent Documents


6201601	March 2001	Vaez-Iravani et al.
6271916	August 2001	Marxer et al.
6538730	March 2003	Vaez-Iravani et al.
6943941	September 2005	Flagello et al.
6950196	September 2005	Fielden et al.
7221501	May 2007	Flagello et al.
7286218	October 2007	Tiemeyer et al.
2007/0252977	November 2007	Baran et al.

Other References

Stokowski, "The Physics of our Enterprise," presented Mar. 11, 1998, 83 pages. cited by other.

Primary Examiner: Pham; Hoa Q
Attorney, Agent or Firm: Baker & McKenzie LLP

Claims

What is claimed is:

1. A computer-implemented method for determining a configuration for a light scattering inspection system, comprising: determining a three-dimensional map of signal-to-noise ratio values for data that would be acquired for a specimen and a potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system; determining one or more portions of the scattering hemisphere in which the signal-to-noise ratio values are higher than in other portions of the scattering hemisphere based on the three-dimensional map; and determining a configuration for a detection subsystem of the inspection system based on the one or more portions of the scattering hemisphere.

2. The method of claim 1, wherein the scattering hemisphere comprises an entire scattering hemisphere of the inspection system.

3. The method of claim 1, wherein said determining the three-dimensional map comprises determining different three-dimensional distributions of light that would be diffusely reflected from the specimen and the potential defect when illuminated by the inspection system and determining the three-dimensional map from the different three-dimensional distributions.

4. The method of claim 1, wherein said determining the three-dimensional map comprises determining a three-dimensional distribution of light that would be diffusely reflected from the specimen when illuminated by the inspection system based on a power spectral density function determined from metrology data for the specimen.

5. The method of claim 1, wherein said determining the three-dimensional map comprises determining a three-dimensional distribution of light that would be diffusely reflected from the specimen when illuminated by the inspection system based on a power spectral density function determined from metrology data for the specimen and information about one or more films that will be present on the specimen and are at least partially transparent to illumination by the inspection system.

6. The method of claim 1, wherein said determining the three-dimensional map comprises determining a three-dimensional distribution of light that would be diffusely reflected from the potential defect based on optical constants of the potential defect and complex indices of the specimen.

7. The method of claim 1, further comprising prior to said determining the one or more portions of the scattering hemisphere, removing one or more portions of the three-dimensional map based on areas of the scattering hemisphere in which the inspection system cannot collect light.

8. The method of claim 1, wherein the configuration comprises positions of one or more detectors in the scattering hemisphere.

9. The method of claim 1, wherein the detection subsystem comprises more than one detector configured to generate signals during inspection of the specimen, and wherein the configuration comprises the signals generated by which of the more than one detector that will be used for detection of the potential defect.

10. The method of claim 1, wherein the configuration comprises one or more parameters of an aperture plate positioned in the scattering hemisphere, and wherein the aperture plate comprises one or more fixed openings.

11. The method of claim 1, wherein the configuration comprises one or more parameters of an aperture plate positioned in the scattering hemisphere, and wherein the aperture plate comprises one or more adjustable openings.

12. The method of claim 1, wherein the configuration comprises one or more parameters of a baffle positioned in the scattering hemisphere.

13. The method of claim 1, wherein the configuration comprises one or more parameters of a linear polarizing filter positioned in the scattering hemisphere.

14. The method of claim 1, wherein the configuration comprises one or more parameters of a linear polarizing filter positioned in the scattering hemisphere, and wherein the linear polarizing filter comprises a plurality of linear polarizing segments.

15. The method of claim 1, wherein the configuration comprises one or more parameters of an electro-optical light filter positioned in the scattering hemisphere.

16. The method of claim 1, further comprising providing signals to a control subsystem of the inspection system that are responsive to the configuration and can be used by the control subsystem to cause the detection subsystem to have the determined configuration.

17. The method of claim 1, further comprising determining a configuration for an additional detection subsystem of the inspection system based on the other portions of the scattering hemisphere such that the additional detection subsystem in the determined configuration is sensitive to changes in the specimen and is not sensitive to the potential defect.

18. The method of claim 1, further comprising performing the method for the specimen and a different potential defect to determine an additional configuration for the detection subsystem, wherein data acquired by the inspection system during different scans of the specimen with the configuration and the additional configuration can be used to classify defects detected in the data.

19. A system configured to determine a configuration for a light scattering inspection system, comprising: a simulation engine configured to determine a three-dimensional map of signal-to-noise ratio values of data that would be acquired for a specimen and a potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system; and a processor configured to determine one or more portions of the scattering hemisphere in which the signal-to-noise ratio values are higher than in other portions of the scattering hemisphere based on the three-dimensional map and to determine a configuration for a detection subsystem of the inspection system based on the one or more portions of the scattering hemisphere.

20. A system configured to determine an inspection system configuration for a specimen, comprising: a light scattering inspection system comprising a control subsystem configured to alter one or more parameters of a detection subsystem of the inspection system; a simulation engine configured to determine a three-dimensional map of signal-to-noise ratio values of data that would be acquired for the specimen and a potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system; and a processor configured to determine one or more portions of the scattering hemisphere in which the signal-to-noise ratio values are higher than in other portions of the scattering hemisphere based on the three-dimensional map, to determine a configuration for the detection subsystem based on the one or more portions of the scattering hemisphere, and to provide signals to the control subsystem that are responsive to the configuration and can be used by the control subsystem to cause the detection subsystem to have the determined configuration.

21. The system of claim 20, wherein the simulation engine is further configured to determine the three-dimensional map based on information about the specimen acquired by a metrology system.

22. The system of claim 20, wherein the simulation engine is further configured to determine the three-dimensional map for different specimens based on information about the different specimens, wherein the processor is further configured to determine the configuration for the detection subsystem for the different specimens and to provide different signals to the control subsystem of the inspection system in real time based on the specimen being inspected by the inspection system, and wherein the different signals are responsive to the configurations and can be used by the control subsystem to cause the detection subsystem to have one of the determined configurations.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to computer-implemented methods and systems for determining a configuration for a light scattering inspection system. Certain embodiments relate to determining a configuration for a detection subsystem of a light scattering inspection system based on a three-dimensional map of signal-to-noise ratio values for data that would be acquired for a specimen and a potential defect on the specimen by the inspection system.

2. Description of the Related Art

The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.

Fabricating semiconductor devices such as logic and memory devices typically includes processing a specimen such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that typically involves transferring a pattern to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a semiconductor wafer and then separated into individual semiconductor devices.

Inspection processes are used at various times during a semiconductor manufacturing process to detect defects on wafers. Inspection has always been an important part of fabricating semiconductor devices such as integrated circuits. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices. For instance, as the dimensions of semiconductor devices decrease, detection of defects of decreasing size has become necessary since even relatively small defects may cause unwanted aberrations in the semiconductor devices.

Often, increased defect detection sensitivity can be achieved by system configurations that result in reduced throughput. For example, the sensitivity of currently available inspection systems can be increased by reducing the size of the spot on the wafer that is illuminated during inspection. The size of the illuminated spot on the wafer may be reduced relatively simply in many currently used inspection systems (e.g., by altering or adding an optical element to the beam forming optics train). Reducing the spot size effectively decreases the amount of light that is scattered from the surface of the wafer relative to the defect scattering, thereby increasing the defect signal-to-noise ratio and the sensitivity of the system. However, reducing the spot size also reduces the throughput of the system since scanning a smaller size spot over an entire wafer surface takes longer than scanning a larger size spot over the wafer surface. Therefore, by varying the spot size, it is possible to trade-off throughput for sensitivity.

Other changes can also or alternatively be made to currently available inspection systems to increase the sensitivity of the inspection systems. For example, the collector of some currently available inspection systems may be altered by changing or adding an aperture to the collector. The aperture may be configured to block light that is scattered from the surface of the wafer while allowing light scattered from a defect to pass through the aperture thereby increasing the defect signal-to-noise ratio and the sensitivity of the system. In another example, the light source of currently available inspection systems may be replaced with a higher power light source. For example, if an inspection system is configured for a laser power of about 350 mW, the laser power of the system can be increased to about 1000 mW. Increasing the power of the light source generally increases the level of light scattered from defects thereby increasing the sensitivity of the system.

To increase the sensitivity of the inspection system, the configuration of the detector of the inspection system may also or alternatively be altered. In particular, in the field of semiconductor wafer inspection with scanning laser light scattering inspection systems, the concept of an optimal detector, one that maximizes the ratio of captured light from defects of interest on the surface to background noise arising from diffuse reflectance of the laser spot on that surface, is known to practitioners of the art. For example, S. Stokowski, "The Physics of Our Enterprise," a presentation given on Mar. 11, 1998, which is incorporated by reference as if fully set forth herein, outlined the process of modeling defect scattering as well as background surface scattering from the power spectral density (PSD) function and included the concept of the optimal detector for 60 nm polystyrene latex (PSL) spheres on bare silicon.

However, heretofore, determining a truly optimized detector required experimental measurements of the spatial distribution of scattered light from a defect and the diffuse scattering pattern from a physical specimen. Based on such data, a configuration can be determined for arrays of optical detectors and/or an aperture in the scattered light collection optics train of any single detector and/or parameters of a variable aperture in the collection optics train (realized, for example, by mechanical baffles and/or liquid crystal display (LCD)-based electronically controlled light values) such that the defect signal to background surface noise ratio is maximized.

Besides the time consuming and error prone experimental measurements that are performed with expensive laboratory equipment unsuited to the semiconductor fab environment, the methods described above are also disadvantageous for end users of the inspection systems who have to select representative wafers and ship them to a remote location (e.g., usually to the facilities of the inspection system manufacturer) for these measurements. Therefore, development cycles for different types of substrates are unacceptably long, and real time optimization of the detector in the fab of the end user is out of the question.

Accordingly, it would be advantageous to develop methods and systems for determining a configuration for a light scattering inspection system without performing measurements of a wafer with the inspection system thereby reducing error in the determined configuration, reducing the time in which the configuration is determined, and increasing the accuracy of the configuration.

SUMMARY OF THE INVENTION

The following description of various embodiments of computer-implemented methods and systems is not to be construed in any way as limiting the subject matter of the appended claims.

One embodiment relates to a computer-implemented method for determining a configuration for a light scattering inspection system. The method includes determining a three-dimensional (3D) map of signal-to-noise ratio (S/N) values for data that would be acquired for a specimen and a potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system. The method also includes determining one or more portions of the scattering hemisphere in which the S/N values are higher than in other portions of the scattering hemisphere based on the 3D map. In addition, the method includes determining a configuration for a detection subsystem of the inspection system based on the one or more portions of the scattering hemisphere.

In one embodiment, the scattering hemisphere includes an entire scattering hemisphere of the inspection system. In another embodiment, determining the 3D map includes determining different 3D distributions of light that would be diffusely reflected from the specimen and the potential defect when illuminated by the inspection system and determining the 3D map from the different 3D distributions.

In an additional embodiment, determining the 3D map includes determining a 3D distribution of light that would be diffusely reflected from the specimen when illuminated by the inspection system based on a power spectral density (PSD) function determined from metrology data for the specimen. In a further embodiment, determining the 3D map includes determining a 3D distribution of light that would be diffusely reflected from the specimen when illuminated by the inspection system based on a PSD function determined from metrology data for the specimen and information about one or more films that will be present on the specimen and are at least partially transparent to illumination by the inspection system. In some embodiments, determining the 3D map includes determining a 3D distribution of light that would be diffusely reflected from the potential defect based on optical constants of the potential defect and complex indices of the specimen.

In one embodiment, prior to determining the one or more portions of the scattering hemisphere, the method includes removing one or more portions of the 3D map based on areas of the scattering hemisphere in which the inspection system cannot collect light. In some embodiments, the configuration includes positions of one or more detectors in the scattering hemisphere. In another embodiment, the detection subsystem includes more than one detector configured to generate signals during inspection of the specimen. In one such embodiment, the configuration includes the signals generated by which of the more than one detector that will be used for detection of the potential defect.

In some embodiments, the configuration includes one or more parameters of an aperture plate positioned in the scattering hemisphere. In one such embodiment, the aperture plate includes one or more fixed openings. In a different such embodiment, the aperture plate includes one or more adjustable openings. In another embodiment, the configuration includes one or more parameters of a baffle positioned in the scattering hemisphere.

In some embodiments, the configuration includes one or more parameters of a linear polarizing filter positioned in the scattering hemisphere. In one such embodiment, the linear polarizing filter includes a plurality of linear polarizing segments. In another embodiment, the configuration includes one or more parameters of an electro-optical light filter positioned in the scattering hemisphere.

In one embodiment, the method includes providing signals to a control subsystem of the inspection system that are responsive to the configuration and can be used by the control subsystem to cause the detection subsystem to have the determined configuration. In another embodiment, the method includes determining a configuration for an additional detection subsystem of the inspection system based on other portions of the scattering hemisphere such that the additional detection subsystem in the determined configuration is sensitive to changes in the specimen and is not sensitive to the potential defect. In a further embodiment, the method is performed for the specimen and a different potential defect to determine an additional configuration for the detection subsystem. In one such embodiment, data acquired by the inspection system during different scans of the specimen with the configuration and the additional configuration can be used to classify defects detected in the data. Each of the embodiments of the method described above may include any other step(s) of any other method(s) described herein.

Another embodiment relates to a system configured to determine a configuration for a light scattering inspection system. The system includes a simulation engine configured to determine a 3D map of S/N values of data that would be acquired for a specimen and a potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system. The system also includes a processor configured to determine one or more portions of the scattering hemisphere in which the S/N values are higher than in other portions of the scattering hemisphere based on the 3D map. The processor is also configured to determine a configuration for a detection subsystem of the inspection system based on the one or more portions of the scattering hemisphere. The system may be further configured as described herein.

An additional embodiment relates to a system configured to determine an inspection system configuration for a specimen. The system includes a light scattering inspection system that includes a control subsystem configured to alter one or more parameters of a detection subsystem of the inspection system. The system also includes a simulation engine configured to determine a 3D map of S/N values of data that would be acquired for the specimen and a potential defect on the specimen by the inspection system across a scattering hemisphere of the inspection system. In addition, the system includes a processor configured to determine one or more portions of the scattering hemisphere in which the S/N values are higher than in other portions of the scattering hemisphere based on the 3D map, to determine a configuration for the detection subsystem based on the one or more portions of the scattering hemisphere, and to provide signals to the control subsystem that are responsive to the configuration and can be used by the control subsystem to cause the detection subsystem to have the determined configuration.

In one embodiment, the simulation engine is configured to determine the 3D map based on information about the specimen acquired by a metrology system. In another embodiment, the simulation engine is configured to determine the 3D map for different specimens based on information about the different specimens. In one such embodiment, the processor is configured to determine the configuration for the detection subsystem for the different specimens and to provide different signals to the control subsystem of the inspection system in real time based on the specimen being inspected by the inspection system. The different signals are responsive to the configurations and can be used by the control subsystem to cause the detection subsystem to have one of the determined configurations. Each of the embodiments of the system described above may be further configured as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description of the preferred embodiments and upon reference to the accompanying drawings in which:

FIG. 1 includes simulated data illustrating one embodiment of a computer-implemented method for determining a configuration for a light scattering inspection system and results acquired using an initial configuration for the inspection system and a configuration for the inspection system determined according to embodiments described herein;

FIG. 2 includes results acquired using an initial configuration for a light scattering inspection system and a configuration for the inspection system determined according to embodiments described herein;

FIGS. 3-5 are schematic diagrams illustrating a side view, a top view, and a perspective view, respectively, of light scattering inspection systems that include a detection subsystem for which a configuration may be determined according to embodiments described herein;

FIGS. 6-7 are schematic diagrams illustrating a cross-sectional view of various embodiments of an aperture plate, one or more parameters of which may be included in a configuration determined according to embodiments described herein;

FIGS. 8-9 are schematic diagrams illustrating a side view of light scattering inspection systems that include a detection subsystem for which a configuration may be determined according to embodiments described herein;

FIG. 10 is a schematic diagram illustrating a cross-sectional view of a linear polarizing filter that includes a plurality of linear polarizing segments and that may be positioned in a scattering hemisphere of a light scattering inspection system;

FIGS. 11-12 are schematic diagrams illustrating a side view of light scattering inspection systems that include one or more detection subsystems for which configurations may be determined according to embodiments described herein;

FIG. 13 is a block diagram illustrating one embodiment of a system configured to determine a configuration for a light scattering inspection system; and

FIG. 14 is a schematic diagram illustrating one embodiment of a system configured to determine an inspection system configuration for a specimen.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term "specimen" generally refers to a wafer. However, although embodiments are described herein with respect to a wafer, it is to be understood that the embodiments described herein may used to determine a configuration for a light scattering inspection system used for any other specimen, and in particular any specimen for which increased defect detection sensitivity is desirable.

As used herein, the term "wafer" generally refers to substrates formed of a semiconductor or non-semiconductor material. Examples of such a semiconductor or non-semiconductor material include, but are not limited to, monocrystalline silicon, gallium arsenide, and indium phosphide. Such substrates may be commonly found and/or processed in semiconductor fabrication facilities.

A wafer may include one or more layers formed upon a substrate. For example, such layers may include, but are not limited to, a resist, a dielectric material, and a conductive material. Many different types of such layers are known in the art, and the term wafer as used herein is intended to encompass a wafer including all types of such layers.

One or more layers formed on a wafer may be patterned. For example, a wafer may include a plurality of dies, each having repeatable pattern features. Formation and processing of such layers of material may ultimately result in completed devices. Many different types of devices may be formed on a wafer, and the term wafer as used herein is intended to encompass a wafer on which any type of device known in the art is being fabricated.

Turning now to the drawings, it is noted that the figures are not drawn to scale. In particular, the scale of some of the elements of the figures is greatly exaggerated to emphasize characteristics of the elements. It is also noted that the figures are not drawn to the same scale. Elements shown in more than one figure that may be similarly configured have been indicated using the same reference numerals.

One embodiment relates to a computer-implemented method for determining a configuration for a light scattering inspection system. The method includes determining a three-dimensional (3D) map of signal-to-noise ratio (S/N) values for data that would be acquired for a specimen and a potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system. In one embodiment, the scattering hemisphere includes an entire scattering hemisphere of the inspection system.

In some embodiments, determining the 3D map includes determining different 3D distributions of light that would be diffusely reflected from the specimen and the potential defect when illuminated by the inspection system and determining the 3D map from the different 3D distributions. One example of such 3D distributions of light are shown in FIG. 1. For example, one embodiment of the computer-implemented method includes determining 3D distribution of light 10 that would be diffusely reflected from a specimen (not shown). 3D distribution of light 10 may be determined using, for example, a surface scatter model. 3D distribution of light 10 is a false color light scattering intensity map that depicts the "detector's eye view" of the wide channel collector of the inspection system (not shown in FIG. 1) described in more detail with reference to FIG. 12. However, it is to be understood that the embodiments described herein can be performed for any inspection system described herein or any other inspection system known in the art.

The specimen is, in this example, a silicon wafer on which a silicon dioxide layer is formed. A polysilicon layer is formed on the silicon dioxide layer. In one example, the polysilicon layer has a thickness of about 800 .ANG. and is relatively rough. Determining a configuration of a light scattering inspection system for such a specimen is particularly advantageous since the background light scattering ("haze") from the grain structure of polysilicon films is known to reduce the achievable sensitivity of unpatterned wafer inspection systems.

In one embodiment, determining the 3D map includes determining 3D distribution of light 10 that would be diffusely reflected from the specimen when illuminated by the inspection system based on a power spectral density (PSD) function determined from metrology data 12 for the specimen. In this manner, the 3D distribution (over the full solid angle of the scattering hemisphere of the inspection system) of the diffusely reflected light from the specimen may be determined using the PSD as input. The metrology data may be, for example, data acquired for the specimen using an atomic force microscope (AFM) or any other suitable metrology system known in the art. The data may be data responsive to roughness of the specimen. The PSD function may be determined from the metrology data using any method and/or algorithm known in the art.

In another embodiment, determining the 3D map includes determining a 3D distribution of light that would be diffusely reflected from the specimen when illuminated by the inspection system based on a PSD function determined from metrology data for the specimen and information about one or more films that will be present on the specimen and are at least partially transparent to illumination by the inspection system. In this manner, if a thin film or stack of films that is semi-transparent or transparent at the wavelength(s) of the inspection system are formed on the specimen, the method takes into account the thickness(es) and complex refractive index (indices) of the film(s).

This embodiment of the computer-implemented method also includes determining 3D distribution of light 14 that would be diffusely reflected from a potential defect on the specimen. 3D distribution of light 14 is a false color light scattering intensity map that depicts the same "detector's eye view" described above. In one example, the potential defect is a polystyrene latex (PSL) sphere. In this example, 3D distribution of light 14 may be determined using a PSL sphere scattering model. In one embodiment, determining the 3D map includes determining a 3D distribution of light that would be diffusely reflected from the potential defect based on optical constants of the potential defect and complex indices of the specimen. For example, for the specimen described above, 3D distribution of light 14 that would be diffusely reflected from the potential defect can be determined based on optical constants of the PSL sphere and complex indices 16 of the specimen that include complex indices (n and k) and thicknesses of bulk silicon, silicon dioxide, and polysilicon. The method can also be performed for defects, such as but not limited to, spherical and non-spherical particles, using optical constants of materials that commonly particulate and deposit on wafers during the semiconductor fabrication process and the complex indices of the substrate and thin film thicknesses (if any). Modeled defects may further include, without limitation, scratches and pits in the substrate surface, thin stains from imperfect drying after wet clean and other wet chemical wafer processing.

In this manner, the embodiments described herein take advantage of advances in highly accurate modeling of light scattering from defects on diffusely reflective surfaces to determine a configuration for a detection subsystem of an inspection system (e.g., optimized detectors) without requiring a physical specimen of a given substrate type. The only experimental data used in embodiments described herein may be the surface roughness of a particular substrate type, the thickness of one or more thin films if formed on the substrate, and experimental or known values of the complex refractive indices of the substrate and thin film materials. In addition, the embodiments described herein take advantage of known and established metrology techniques. For example, surface roughness is easily and often routinely measured during normal wafer fab operations with commercially available AFM systems known in the art. Thin film thicknesses and complex indices of refraction are also routinely measured in the fab with substantially high accuracy using commercially available spectroscopic reflectometry and/or spectroscopic ellipsometry systems known in the art. Examples of systems that may be used to perform the measurements described herein are illustrated in U.S. Pat. No. 6,950,196 to Fielden et al., which is incorporated by reference as if fully set forth herein.

3D distributions of light 10 and 14 may be used to determine 3D map 18 of S/N values for data that would be acquired for the specimen and the potential defect on the specimen by the light scattering inspection system across a scattering hemisphere of the inspection system. For example, 3D map 18 may be determined by dividing 3D distribution 14 by the noise implied by 3D distribution 10.

The method also includes determining one or more portions of the scattering hemisphere in which the S/N values are higher than in other portions of the scattering hemisphere based on the 3D map. In one such example, in 3D map 18 shown in FIG. 1, the S/N values of portions 20 of the 3D map are determined to be higher than in other portions of the 3D map. In particular, portions 20 of the 3D map have the highest S/N values in the map. Therefore, portions 20 may be used to determine the corresponding portions of the scattering hemisphere in which the S/N values will be higher than in other portions of the scattering hemisphere. Although two portions 20 are shown in FIG. 1, it is to be understood that the method may determine that any number of portions (e.g., one, two, three, etc.) of the scattering hemisphere have S/N values that are higher than other portions of the scattering hemisphere. The portion(s) of the scattering hemisphere having the higher S/N values may be located at any position(s) in the scattering hemisphere.

In some embodiments, the 3D map of the S/N values may be considered as the S/N of a hypothetical detector configured to collect light from the complete 3D scattering hemisphere of the inspection system. In this manner, the method may include determining by iterative search and/or other optimization techniques which portions of the hemisphere, if not collected, increase the S/N of the detector relative to the full-hemisphere S/N of the detector. The remaining portion(s) of the scattering hemisphere may then be used to determine the configuration of the inspection system as described further herein. Such a S/N map has not previously been used in such a manner.

As described above, the scattering hemisphere may include an entire scattering hemisphere of the inspection system. In some embodiments, prior to determining the one or more portions of the scattering hemisphere, the method includes removing one or more portions of the 3D map based on areas of the scattering hemisphere in which the inspection system cannot collect light. For example, in a light scattering inspection system, the opto-mechanical configuration of the inspection system usually limits light collection to less than 2.pi. (i.e., the solid angle subtended by a hemisphere) in units of steradian (sr)). Therefore, the optimization described above may be constrained by setting as "uncollectible" those portions of the scattering hemisphere corresponding to the limited collection space of the inspection system. In addition, the optimization may begin with the full hemisphere across which light can be collected by the fixed collector(s) of a particular inspection system. The optimization may then be performed to determine restrictions on this full hemisphere that can be made with elements such as field stops, masks, light valves, etc. to increase the sensitivity of the system. In this manner, the optimization may eliminate a portion or portions of the full scattering hemisphere of an inspection system depending on how the S/N can be optimized for a particular specimen.

In one such example, as shown in FIG. 1, portion 22 of 3D map 18 corresponds to areas of the scattering hemisphere in which the inspection system cannot collect light. The central region of portion 22 of 3D map 18 may correspond to a spatial filter (not shown) of the inspection system that is used to block normal illumination specularly reflected from the specimen and therefore also blocks collection of scattered light in this portion of the scattering hemisphere. The regions of portion 22 extending from the central region may correspond to mechanical components, the position of which prevents light collection in these regions of the scattering hemisphere of the inspection system.

The method also includes determining a configuration for a detection subsystem of the inspection system based on the one or more portions of the scattering hemisphere. For example, as shown in FIG. 1, configuration 24 may be determined based on portions of the scattering hemisphere that correspond to portions 20 of the 3D map. Configuration 24 includes one or more parameters of apertures 26. The parameter(s) of apertures may include, for example, positions of the apertures in the scattering hemisphere, positions of the openings in the apertures, one or more dimensions of the openings, and shape of the openings. In the example shown in FIG. 1, the parameter(s) of apertures 26 may be determined such that the positions of the openings in the apertures correspond to the positions of portions 20 in the 3D map. In this configuration, the detection subsystem may not detect light scattered in portions of the scattering hemisphere other than those corresponding to the openings of the apertures. In other words, the determined optimal configuration realized in practice may be an aperture plate that contains one or more openings that allow scattered light to pass from the specimen to the detector(s) of the inspection system. In this manner, the embodiments described herein can be used to determine an optimal configuration for an aperture plate positioned in the scattering hemisphere of the inspection system for a particular specimen using only nominal film thickness, refractive indices, and metrology data for the specimen as inputs.

The optimal configuration determined above may be further refined by determining the effect that polarizing filter element(s) placed in the path(s) of the detected light will have on the sensitivity of the inspection system. In this manner, in some embodiments, the configuration also includes parameter(s) of one or more linear polarizing filters positioned in the scattering hemisphere. For example, configuration 24 includes one or more parameters of linear polarizing filters 28 disposed in the openings of apertures 26. In this manner, the determined optimal configuration may be realized by positioning linear polarizing filters in the opening(s) of an aperture plate. In some embodiments, the polarizing filter includes a plurality of segments, each of which is a linear polarizing filter arranged azimuthally in the aperture plate openings. Such an embodiment of a polarizing filter (which may be commonly referred to as a "pizza-pie" polarizer) is described further herein. The linear polarizing filters may also be disposed in any location with respect to the openings such that light that passes through the openings also passes through the linear polarizing filters. In other words, the linear polarizing filters do not have to be disposed in the openings, but may be disposed upstream or downstream of the aperture.

As described above, configuration 24 is determined based on the portions of the scattering hemisphere that have higher S/Ns than other portions of the scattering hemisphere. Therefore, the method may be used to determine the optimal inspection system configuration for specimens that include rough films and other specimens described herein. In addition, the method may be used to determine the optimal configuration using a S/N value model and a 3D distribution of light that would be diffusely reflected from the specimen based on AFM data or other metrology data without sample wafers being measured on the light scattering inspection system.

FIG. 1 also illustrates results obtained using a light scattering inspection system in an initial configuration and in a configuration determined according to embodiments described herein. All of the experimental results described herein are not limiting embodiments of the present invention. The results were obtained by inspecting the same wafer with the different configurations. PSL spheres having different sizes were deposited on the wafer prior to inspection. Results 30 were acquired using the SP2 system that is commercially available from KLA-Tencor, San Jose, Calif. In the initial configuration of the SP2 system used to acquire results 30, no aperture plate or mask was positioned in the scattering hemisphere of the system. The numbers shown in results 30 indicate the size of the PSL spheres detected on the wafer. These results indicate that PSL spheres having diameters of 360 nm, 204 nm, 155 nm, 126 nm, and 102 nm were detected, and 83 nm diameter PSL spheres were not detected. Results 32 corresponding to results 30 indicate that the S/N with which the 102 nm PSL spheres were detected on the wafer was about 5. Therefore, the S/N of this configuration of the SP2 system is not sufficient for detection of the 102 nm PSL spheres with relatively good sensitivity. As such, the smallest PSL sphere size that can be detected by the SP2 system in the initial configuration is 126 nm.

Results 34 were acquired using the same SP2 system. However, the configuration of the SP2 system that was used to acquire results 34 included the aperture plate or mask determined as described above and shown in configuration 24. As shown in results 34, in this configuration, the system detected PSL spheres having diameters of 360 nm, 204 nm, 155 nm, 126 nm, 102 nm, and 83 nm. In addition, results 36 corresponding to results 34 indicate that the S/N with which the 102 nm PSL spheres were detected on the wafer was about 22. Results 38 corresponding to results 34 indicate that the S/N with which the 83 nm PSL spheres were detected on the wafer was about 10. Therefore, the configuration of the inspection system determined according to embodiments described herein can be used to detect defects having sizes as small as 83 nm. In this manner, the SP2 system having the configuration determined according to embodiments described herein has at least a 34% improvement in the detectability of PSL spheres compared to the SP2 system having the original configuration.

Using a detection subsystem configuration determined as described herein can produce such dramatic improvements in defect detection capability because larger defects tend to scatter light with a different distribution than smaller defects. In particular, larger defects tend to scatter light asymmetrically. As defect size decreases, the light scatter distribution from the defects tends to become more symmetrical. Therefore, a mask designed for optimal detection of relatively large defects with asymmetric scattering distributions may not be optimal for relatively small defects with relatively symmetric scattering distributions. As such, the embodiments described herein can be used to provide an optimal configuration for a particular defect type having a particular size. In this manner, the embodiments described herein can be used to determine if and what modifications to existing inspection systems can be made to extend the sensitivity of the inspection systems for smaller defect sizes.

The embodiments described herein have a number of advantages over other methods and systems for determining a configuration for an inspection system. For example, as described further above, the embodiments described herein can be used to determine the optimal configuration for an inspection system using input solely from external metrologies such as roughness from AFM, substrate material complex indices, and film thicknesses and complex indices, if present, on the specimen of interest. In this manner, end users of the inspection system do not have to provide physical specimens of the substrate types to the system manufacturer to determine optimal detectors for each substrate type. In addition, inspection system manufacturers do not need to perform time-consuming, error-prone experimental measurements on the physical specimens. Another advantage is that the possibility of determining the inspection system configuration using experimental results for a relatively small sample of specimens that is unrepresentative of the specimen type is reduced since the end user can provide the system manufacturer with AFM and thickness data from multiple wafers over time. Such data can be used to determine an "average" PSD for the specimen type that can be used to determine a "nearly-optimal" configuration that will be robust to normal process variations.

Furthermore, as described further herein, the determined configuration can be used to drive computer-controlled devices to create the optimal configuration in the inspection system. As such, roughness and thickness data can be fed-forward in real time to assure that the optimal configuration is used on an individual wafer basis. Moreover, by using the 3D maps described herein, the iterative optimization can be started from a "reasonable guess" of the optimized configuration, thereby assuring better convergence of the optimization (e.g., the optimization algorithm) in a reasonable amount of time.

FIG. 2 illustrates results obtained for a different specimen using a light scattering inspection system in an initial configuration and in a configuration determined according to embodiments described herein. In this instance, the specimen was a wafer on which a copper film was deposited by electrochemical deposition (ECD). In this manner, the embodiments described herein may be used to determine the optimal inspection system configuration for a copper film. The results were obtained by inspecting the same wafer with the different configurations. PSL spheres having different sizes were deposited on the wafer prior to inspection. Results 40 were acquired using the SP2 system. In the initial configuration of the SP2 system used to acquire results 40, no aperture plate or mask was positioned in the scattering hemisphere of the system. The numbers shown in results 40 indicate the size of the PSL spheres detected on the wafer. These results indicate that PSL spheres having diameters of 304 nm, 204 nm, and 155 nm and, 126 nm diameter PSL spheres were not detected. As such, the smallest PSL sphere size that can be detected by the SP2 system in this configuration is 155 nm.

Results 42 were acquired using the same SP2 system. However, configuration 44 of the SP2 system that was used to acquire results 42 was determined according to embodiments described herein and included an aperture plate or mask having opening 46 and linear polarizer 48 that includes a plurality of linear polarizing segments 50. Such a linear polarizer may be commonly referred to as a "pizza pie" polarizer due to the arrangement of the linear polarizing segments. Illumination beam 52 was used for this configuration. Beam 54 is the light specularly reflected from the wafer.

As shown in results 42, this configuration of the system detected PSL spheres having diameters of 304 nm, 204 nm, 155 nm, and 126 nm. Therefore, the inspection system in the configuration determined according to embodiments described herein can be used to detect defects having sizes as small as 126 nm. In this manner, the SP2 system having the configuration determined according to embodiments described herein has at least a 19% improvement in the detectability of the PSL spheres compared to the SP2 system having the original configuration. As such, the experimental results illustrate a significant improvement in PSL sphere detection sensitivity using a configuration determined according to embodiments described herein. Therefore, configuration 44 may be the optimal inspection system configuration for inspection of wafers on which a copper film has been electrochemically deposited.

As described above, the method embodiments described herein include determining a configuration for a detection subsystem of an inspection system, and the configuration may include parameters of an aperture or mask and parameters of one or more polarizers. The configuration of the detection subsystem that is determined by the embodiments described herein may also or alternatively include other parameter(s) of the detection subsystem. All of the different parameters of the detection subsystem that are described herein may be included in a determined configuration in any combination.

In one embodiment, the configuration determined by the embodiments described herein includes positions of one or more detectors in the scattering hemisphere. The positions of the detector(s) may be defined in any manner known in the art (e.g., by azimuthal, polar, elevation angles, or some combination thereof). One embodiment of a light scattering inspection system for which a configuration may be determined according to embodiments described herein is shown in FIG. 3.

In this embodiment, the inspection system includes light source 56. Light source 56 may include any suitable light source known in the art. Light source 56 may be coupled to one or more optical components (not shown) such that the combination of the light source and the optical component(s) directs light 58 to specimen 60 at an oblique angle of incidence. The optical component(s) may include any suitable optical components known in the art such as reflecting mirrors, acousto-optical deflectors (AODs), etc. Light 58 may be directed to specimen 60 at any suitable oblique angle of incidence.

The inspection system also includes a detection subsystem. The detection subsystem includes collectors 62, 64, and 66. Collectors 62, 64, and 66 may be refractive optical elements. In alternative embodiments, each of the collectors may include one or more refractive optical elements and/or one or more reflective optical elements. Each of the collectors is configured to collect light scattered from the specimen over the same range of azimuthal angles and a different range of polar angles. As used herein, the term "polar angle" is defined as the angle (e.g., angle 68) at which light is scattered from the specimen as measured from normal 70 to the surface of the specimen. As used herein, the term "azimuthal angle" is defined as the angle at which light is scattered from the specimen as measured from the plane of incidence. Therefore, collectors 62, 64, and 66 collect light scattered from the specimen across different two-dimensional (2D) spaces within the scattering hemisphere.

As described above, the collectors collect light scattered at the same range of azimuthal angles but different ranges of polar angles. For example, the collectors may be arranged such that the axis of each collector is centered in the plane of incidence. In this manner, the collection optics of the inspection system may be symmetrical about the plane of incidence. As such, the collectors may be configured in an azimuthal symmetric optical arrangement. In addition, although the axis of collector 64 is shown centered on normal in FIG. 3, the position of the axis of this collector may be offset from normal depending on, for instance, characteristics of the specimen or the defects of interest.

The detection subsystem also includes detectors 72, 74, and 76, which are configured to detect the light collected by collectors 62, 64, and 66, respectively. Detectors 72, 74, and 76 may include any suitable detectors known in the art. Detectors 72, 74, and 76 are configured to generate output signals responsive to the light collected by collectors 62, 64, and 66, respectively, and the output signals may be acquired by or provided to a processor (not shown in FIG. 3), which may be configured to detect defects on specimen 60 using the output signals. The processor may detect the defects using the output signals and any suitable method and/or algorithm known in the art. The processor may be further configured as described herein.

The detection subsystem of the inspection system shown in FIG. 3, therefore, includes collectors 62, 64, and 66 and detectors 72, 74, and 76. The detection subsystem shown in FIG. 3 may, however, include any other components of any other detection subsystem(s) described herein. In addition, although the detection subsystem shown in FIG. 3 includes three collectors and three corresponding detectors, it is to be understood that the detection subsystem may include any suitable number of collectors and corresponding detectors. The number of collectors and the number of detectors included in the detection subsystem may or may not be equal.

In one embodiment, a configuration determined according to embodiments described herein for the detection subsystem shown in FIG. 3 includes position(s) of detector 72, detector 74, detector 76, or some combination thereof. For instance, the configuration may include a range of polar angles and a range of azimuthal angles that define the 2D space within the scattering hemisphere in which one or more of the detectors detect light. The range of azimuthal angles may be constant in this embodiment such that the detection subsystem maintains its symmetry about the plane of incidence. Therefore, determining the configuration may, in this embodiment, include determining the range of polar angles for each, some, or one of detectors 72, 74, and 76 that defines the detection space for the detector(s) in the scattering hemisphere. The position(s) of one or more of the collectors may also be determined as described above or may be determined based on the determined configurations of their corresponding detectors. The inspection system shown in FIG. 3 may be further configured as described herein.

Another embodiment of a light scattering inspection system that includes a detection subsystem for which a configuration may be determined according to embodiments described herein is shown in FIG. 4. In this embodiment, the inspection system includes a light source (not shown). The light source may include any suitable light source known in the art. The light source may be coupled to one or more optical components (not shown) such that the combination of the light source and the optical component(s) directs light 78 to specimen 80 at an oblique angle of incidence. The optical component(s) may include any suitable optical components known in the art such as those described above. Light 78 may be directed to specimen 80 at any suitable oblique angle of incidence.

The inspection system also includes a detection subsystem that includes collectors 82, 84, and 86. Collectors 82, 84, and 86 may be refractive optical elements. In alternative embodiments, each of the collectors may include one or more refractive optical elements and/or one or more reflective optical elements. Collectors 82, 84, and 86 are configured to collect light scattered from the specimen over different ranges of azimuthal angles and different ranges of polar angles. The polar angles may be defined as described above. The azimuthal angle of collector 82 can be defined as angle 88 measured from plane of incidence 90 to axis 92 of collector 82. The range of azimuthal angles across which collector 82 collects light may be defined by angle 88 and characteristics of collector 82. The azimuthal angles of the other collectors and the range of azimuthal angles across which the other collectors collect light may be defined in a similar manner. Therefore, collectors 82, 84, and 86 collect light scattered from the specimen across different 2D spaces within the scattering hemisphere.

The detection subsystem also includes detectors (not shown in FIG. 4), each of which is configured to detect the light collected by one of collectors 82, 84, and 86. The detectors may include any suitable detectors known in the art. The detectors are configured to generate output signals responsive to the light collected by the collectors, and the output signals may be acquired by or provided to a processor (not shown in FIG. 4), which may be configured as described further herein.

The detection subsystem shown in FIG. 4, therefore, includes collectors 82, 84, and 86 and corresponding detectors. The detection subsystem shown in FIG. 4 may, however, include any other components of any other detection subsystem(s) described herein. In addition, although the detection subsystem shown in FIG. 4 includes three collectors, it is to be understood that the detection subsystem may include any suitable number of collectors and corresponding detectors. The number of collectors and the number of detectors included in the detection subsystem may or may not be equal.

In one embodiment, a configuration determined according to embodiments described herein for the detec