Inspection tools supporting multiple operating states for multiple detector arrangements

An inspection system can support operation in multiple states. For instance, when inspecting an article, such as a semiconductor wafer, the tool can switch between imaging multiple locations using respective detectors to another operating state wherein multiple detectors operating in multiple imaging modes inspect a single location. An inspection system may combine the use of multiple detectors for multiple locations and the use of multiple viewing angles or modes for the same locations and thereby achieve high throughput. The different imaging modes can comprise, for example, different collection angles, polarizations, different spectral bands, different attenuations, different focal positions relative to the wafer, and other different types of imaging.

BACKGROUND

Many electro-optical semi-conductor inspection systems contain at least two detectors.

One way of arranging these detectors is where every detector views a respective part of the inspected article. For example, U.S. Pat. No. 6,693,664 includes a discussion of an arrangement where there are multiple 2-dimensional detectors which are located at the focal plane of the system's imager to creating a continuous imaging surface. U.S. Pat. No. 7,274,444 includes discussion of an embodiment where the multiple 2-dimensional detectors are located with intervals between them.

An arrangement of line or TDI detectors may also be used, with special optics used so that the line detectors view areas that are side by side (see U.S. Pat. No. 6,366,315).

Another way to inspect articles is to let multiple detectors view the same location in the article, but with different imaging modes. U.S. Pat. No. 7,265,900, for example, discusses an embodiment in which all the detectors view the same area in a wafer but with different collection angles.

SUMMARY

An inspection system configured in accordance with one or more aspects of the present subject matter may be more useful and versatile than existing tools by supporting operation in multiple states. For instance, when inspecting an article, such as a semiconductor wafer, the tool can switch between imaging multiple locations using respective detectors to another operating state wherein multiple detectors image the same location in different imaging modes.

An inspection system may combine the use of multiple detectors for multiple locations and the use of multiple viewing angles or modes for the same locations and thereby achieve high throughput with lower sensitivity and lower throughput with higher sensitivity as needed.

As discussed further below, an electro-optical inspection system can comprise at least two imaging detectors, an illumination system comprising one or more light sources, and a set of imaging optics that relays light from the imaged object to the imaging detectors. Namely, the imaging optics can be positioned on an optical path between the wafer (or other object under inspection) and the detectors. The tool can be configured to operate in at least two “states,” with the state adjusted by varying the composition and/or arrangement of the imaging optics. The term “state” is used to avoid confusion with “mode,” which is used to refer to how the locations are imaged (i.e. imaging mode).

In a first state, (referred to as “multiple location state” below), at least two of the imaging detectors are used to view different physical locations on the article being inspected. The locations may partially overlap or may be completely separated. In the second state (referred to as “multiple imaging state” below), at least two of the imaging detectors view the same location on the article, but with different imaging modes (such as different collecting angles, for example).

Before inspection, according to a manual and/or automatic decision, the state of the inspection apparatus is changed using mechanical, electrical, optical and/or electro-optical control. For example, an operator could select a desired state, or the state could be specified as part of an inspection recipe. At least some of the detectors that are used for imaging when the tool is in the first state are also used for imaging when the tool is in the second state. In some embodiments, all of the detectors that are used for imaging when the tool is in the first state are also used for imaging when the tool is in the second state. Furthermore, some (or all) of the detectors used for imaging when the tool is in the second state are used for imaging when the tool is in the first state.

Put another way, detectors available for use by the tool may be treated as a set and categorized in a first subset if used for imaging in the first state and a second subset if used for imaging the second state. The sets may partially overlap, i.e. some detectors may be used in both states while some detectors are used only in one state. Alternatively, the subsets may fully overlap, with all the detectors used in the first state also used in the second state.

The detectors may comprise any suitable type. For example, in some embodiments, one or more detectors are two-dimensional (i.e. matrix) detectors. In some embodiments, one or more detectors are time delay integration (TDI) detectors. One or more detectors are line detectors in certain embodiments. In yet other embodiments, one or more detectors are photomultiplier tube (PMT) detectors, or may comprise avalanche photodiode detectors.

In some embodiments, some or all of the detectors are repositionable, and the tool is configured to reposition the detectors when changing between the first and second state. Further, the set of variable imaging optics can comprise a plurality of changeable filter elements and a splitting apparatus. In the first state, the splitting apparatus can direct light corresponding to different physical locations of the object under inspection along different optical paths, with each different optical path leading to a respective detector. In the second state, the changeable filter elements can be positioned in appropriate optical paths after the splitting apparatus in order to change the imaging mode of the detector in the path.

Examples of changeable filter elements include, but are not limited to, spatial masks, polarizers, spectral filters, attenuators, or elements (e.g. lens) that change the focus position of the detector relative to the surface of the object under inspection. For example, the objective lens may be focused at a particular point relative to the surface of the object under inspection. One or more changeable filters may adjust the focus of one detector so that light above, on, or below the focus point of the objective lens. Accordingly, different detectors may be focused at different points relative to the surface of the object.

As an example, in some embodiments, the inspection system comprises at least four detectors each operable to selectively image the object at least two modes. The modes may be selected by varying the imaging optics and/or may be a characteristic of the detectors themselves. In the first state, the system images at least four different locations on the object under inspection simultaneously, and in the second state, at least two locations on the object under inspection are imaged simultaneously in at least two modes. As another example, in the first state, the system images at least one location on the object under inspection simultaneously in two different modes.

A method of inspecting an object in an electro-optical inspection system comprising a set of detectors, the method can comprise illuminating the object, imaging at least one location on the object in different modes by using at least two detectors of a first subset of the detectors to image the same location, and imaging at least two different locations on the object, with each location imaged using a respective detector of a second subset of the detectors.

In some embodiments, the method can comprise repositioning at least some of the set of detectors between imaging the same location on the object in different modes and imaging at least two different locations on the object with a respective detector.

Certain embodiments of the method may include, splitting light along different optical paths so as to direct the light from respective locations on the object to the respective detectors when imaging at least two different locations with a respective detector. When imaging at least one location in multiple modes, the method can include positioning a plurality of changeable filter elements in the optical path leading to each detector to adjust the imaging mode of the detector.

In some embodiments in which light from the object is gathered using an objective lens, the method further comprises placing a post-objective lens configured to focus light from different physical locations on the object to respective detectors when imaging at least two different locations each with a respective detector, and replacing the post-objective lens with an optical element comprising multiple lenses so that multiple detectors image the same physical location on the object at different collection angles when the post-objective lens is in place.

In some embodiments in which an optical element in the path comprising multiple lenses is used, the method can comprise selectively placing one of a first and second objective lens in the optical path before the multi-lens optical element. Accordingly, when the first objective lens is in the optical path, the first objective lens and optical element in the path comprising multiple lenses direct light from different locations on the object to different respective detectors, and when the second objective lens is in the optical path, the second objective lens and optical element in the path comprising multiple lenses direct light so that at least two detectors image the same physical location on the object.

In some embodiments, the method comprises illuminating the object multiple times when using at least two detectors to image the same physical location on the object, with the illumination timed so that the respective detectors can image the location at different times.

In some embodiments, the method comprises changing between a state in which one or more locations are imaged in multiple modes to a state in which multiple locations are simultaneously imaged with different respective detectors. The state change can occur at any time. In embodiments in which inspection entails inspecting a plurality of slices extending along an imaging axis, the state can be changed in between slices.

Use of like reference numerals in different features is intended to illustrate like or analogous components.

DETAILED DESCRIPTION

Reference will now be made in detail to various and alternative exemplary embodiments and to the accompanying drawings, with like numerals representing substantially identical structural elements. Each example is provided by way of explanation, and not as a limitation. In fact, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the scope or spirit of the disclosure and claims. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the instant disclosure includes modifications and variations as come within the scope of the appended claims and their equivalents. The use of headings, numberings, and the like is meant to assist the reader of the specification, and not to limit the subject matter.

Before discussing exemplary embodiments of detector arrangements for a multi-state tool,FIGS. 9 and 10will be discussed to place the arrangements in context.FIG. 9is a block diagram showing illumination, imaging, and control components in an exemplary optical inspection tool andFIG. 10is a block diagram showing additional aspects of imaging and illumination in an exemplary optical inspection tool.

In this example,FIG. 9is a schematic diagram illustrating an exemplary embodiment of a system for fast on-line electro-optical detection of wafer defects, whileFIG. 10shows a schematic illustration of an object inspection system utilizing a laser source and a fiber optical delivery bundle in an exemplary inspection tool. For instance, the tool may comprise a Negevtech 3320, 3370, or other model optical inspection tool (available from Negevtech, Ltd. of Rehovot, Israel), modified to support one or more operating states in accordance with one or more aspects of the presently disclosed detector arrangements and methodologies.

Additional details regarding exemplary aspects of an optical inspection system can be found in U.S. patent application Ser. No. 10/345,097, published as US Patent Application No. 2004-0146295 A1, which is incorporated by reference herein for all purposes in its entirety to the extent it is not in conflict with the present subject matter. However, it is to be noted that the detector arrangement principles and multi-state tools discussed below can be used in any suitable inspection system that creates an image of an object at a focal plane.

As shown inFIG. 9, an inspection tool can include a focal plane assembly30comprising pixels from multiple two-dimensional detectors. Focal plane assembly30is configured so that light from an article being inspected is sensed by detectors arranged in accordance with one or more aspects discussed below so that the tool can support multiple operating states. In this example, assembly30is depicted as providing a continuous surface (this may be achieved by physically positioning the detectors near one another and/or by optically forming the surface). It will be recognized that, in different embodiments and depending on the optical configuration and state of the tool, a discontinuous surface may be presented in some instances.

In operation, the dies14of wafer12can be illuminated in any suitable manner, such as by laser light from pulsed illumination system26. Light48represents rays of light scattered, reflected, and diffracted by the wafer. This light can be collected using imaging optics18. In this example, imaging optics18comprise a beam splitter44(used in illuminating wafer12with light from laser system26), focusing lens42, and an objective lens46which may be adjusted using an auto-focus system28(not shown in detail). In this example, focusing lens42focuses light48onto focal plane assembly30and defines the focal plane of imaging optics18. However, the actual content and arrangement of a particular set of imaging optics can vary. Particularly, the imaging optics18shown in this example are simplified for purposes of explaining general principles of an inspection tool. A tool that operates in multiple states can have more complex imaging optics configured in accordance with the present subject matter.

A patterned semiconductor wafer12featuring a plurality of wafer dies14, is placed and aligned on a continuous moving XY translation stage16to impart motion between the wafer and the components used to image the wafer. XY translation stage16moves wafer12typically in a serpentine pattern beneath an optical imaging system18, thereby changing which area of the wafer is in view of the imager. However, movement patterns other than a serpentine pattern could be used. Additionally, the wafer may be moved in a different manner in other embodiments. Furthermore, in some embodiments, the wafer may remain stationary, with apparent motion between the wafer and component(s) used to image the wafer imparted by the use of one or more optical components. For instance, a rotating mirror can be used to move the field of view of imaging optics18in a serpentine (or other) pattern across the wafer. In other embodiments, relative motion may be imparted by moving both the wafer and adjusting optical components.

Movement of XY translation stage16(and therefore movement of wafer12) is synchronized with action of a multi-component camera system by a central control system20via control/data links22, in such a way that wafer12moves the equivalent of one field of view24during a CCD matrix photo-detector frame time. For example, the frame time and motion may be synchronized so that the wafer moves only on the order of about 10−2of a single pixel during exposure to an illumination system26, thereby resulting in little to no image smear or loss of image resolution. Control system20can comprise any suitable type or arrangement of components used to orchestrate the inspection process, including, for example, a microprocessor-based controller, a general-purpose or specialized computer system, and the like.

In this example, illumination system26includes a repetitively pulsed laser32, a laser beam expander34, a laser beam light path36, control/data links38, and a crystal40having non linear optical properties and serving as a ‘second harmonic’ or ‘third harmonic’ generating crystal. This type of illumination system enables ultra fast imaging of a large field of view24, by featuring pulsed laser32for repetitively generating and propagating a highly bright and highly energetic light pulse in an extremely short period of time. Illumination system26is in communication with the central control system20via control/data links38. Of course, detector arrangements in accordance with the present subject matter can be used in any inspection system regardless of the particular type, mode, or manner of illumination.

Briefly,FIG. 10illustrates exemplary components associated with illuminating an object in an inspection system. According to different methods of operation, three alternative modes of illumination can be provided: Bright Field (BF), Side-illuminated Dark Field (DF) and Orthogonal or Obscured Reflectance Dark Field (ODF). Each mode of illumination is used to detect different types of defects in different production process steps. For example in order to detect an embedded defect in a transparent layer, such as silicon oxide, BF illumination may be preferred. In order to detect a small particle on a surface, DF illumination can generally yield better results.

In bright field illumination in general, the illumination is incident on the sample through the same objective lens as is used for viewing the sample.FIG. 10shows a bright field illuminating laser source1300delivering its output beam1015into an optical delivery fiber bundle1021, preferably by means of a laser to fiber coupler1150. This optical fiber bundle1021provides both uniform illumination on the sample and coherence breaking of the laser illumination. In some embodiments, only a single fiber bundle is used, but it is to be understood that a serially-arranged fiber bundle solution may also be suitable. In other embodiments, one or more bundles may be combined with further components, such as a light guide or guides. Discussion of exemplary fiber/light guide combinations can be found in co-pending U.S. patent application entitled “Speckle Reduction Using a Fiber Bundle and Light Guide,” Ser. No. 11/503,859, filed Aug. 14, 2006 published as US20080037933A1 on Feb. 14, 2008, which is incorporated by reference herein for all purposes in its entirety to the extent it is not in conflict with the present subject matter.

From the output termination of the fiber bundle1021, the laser beam is imaged by means of illumination transfer lenses1301,1302onto the objective lens in use1201, which is operative to focus the illumination onto a wafer1100being inspected. Appropriate alternative objective lenses1201′ can be swung into place on an objective revolver1200, as is known in the microscope arts. The illumination returned from the wafer is collected by the same objective lens1201, and is deflected from the illumination path by means of a beam splitter1202, towards a second beam splitter1500, from where it is reflected through the imaging lens1203, which images the light from the wafer onto the detectors of the imager, with one of the detectors represented inFIG. 10at1206. In this example, only a single detector and optical path is shown for purposes of example. In practice, the path of light comprising the split portions of the inspection image will, of course, vary according to the state of the tool, detector arrangement, etc. In this example, the second beam splitter1500is used to separate the light going to the imaging functionality from the light used in the auto-focus functionality, which is directed by means of the auto-focus imaging lens1501to the auto-focus detector1502.

When conventional dark field illumination is required for the imaging in hand, a dark field side illumination source1231is used to project the required illumination beam1221onto the wafer1000. When orthogonal dark field, or obscured reflectance dark field illumination is required for the imaging in hand, an alternative dark field illumination source1230is used to project the required illumination beam1232via the obscured reflectance mirror1240onto the wafer1000orthogonally from above.FIG. 10indicates sources1300,1231, and1230at different locations. However, any or all of sources1300,1230, and1231may comprise the same light source, with the bright field, dark field, and obscured reflectance dark field effects achieved through moving the source(s) and/or redirecting illumination to the appropriate angle using one or more optical components. Further, it is to be understood that other arrangements for laser illumination and/or other illumination methods entirely could be used in conjunction with the present subject matter.

In operation, one or more images of the wafer are obtained and the images are analyzed to determine the presence or absence of a defect or potential defect in the wafer. For example, the tool may include an image analysis system comprising one or more computers or other suitable image processing hardware configured to evaluate the images. In the example ofFIG. 9, an image processing system99includes parallel configured image processing channels90for image grabbing by an image grabber92, an image buffer94, a defect detection unit96, a defect file98, and control/data links101. Image data acquired by focal plane assembly30featuring twenty-four two-dimensional CCD matrix photo-detectors52is processed in parallel, whereby each of the twenty-four CCD matrix photo-detectors52communicates separately, in parallel to the other CCD matrix photo-detectors52of focal plane assembly30, with image grabber92, via twenty-four separate image processing channels90. Instead of processing image data using a single serial channel of 48 megapixels at a CCD frame speed acquisition rate of 60 times per second, resulting in a single channel with a very high, 3 gigapixels per second processing rate, each of the twenty-four separate image processing channels90having about 2 megapixels of image data, acquired at a rate of 60 times per second, is used for processing at a moderate rate of tens of megapixels per second. Image processing system99is in communication with central control system20via control/data links102

As another example, the tool may be connected to suitable hardware for image analysis, or image data may be provided to such hardware in any other manner.

Any suitable type(s) of analysis may be used to determine the presence or absence of defects. For example, the tool may obtain images on a frame-by-frame basis and compare single frames or groups of frames to references. As another example, the tool may analyze images without comparison to other images, such as locating bright spots on a dark area and/or dark spots on a light area. Any suitable comparison/analysis technique(s) may be used, including cell-to-cell comparison, die-to-die comparison, and may be carried out using any suitable software algorithm(s) and/or specialized hardware to analyze and process the images.

The above discussion is for purposes of example only with regard to illumination and imaging techniques. The present subject matter can be utilized in the context of any suitable inspection tool. Next, several different embodiments of detector arranging techniques will be discussed.

FIG. 1Aillustrates an example of imaging performed using two detectors when a tool is operating in the “multiple location” state. In this figure, two locations on the article (100and102) are imaged by two different respective detectors110and112.

The imaging optics between the article and the detectors are not illustrated and may be any suitable arrangement of optical components. For example, arrangements in accordance with one or more aspects of the examples described in the following sections can be used. Although several examples herein pertain to two detectors, it should be understood that more than two detectors may be used.

FIG. 2provides some examples of the relative positioning of locations100and102. For example, the locations on the article may be spaced in one or more directions, such as shown inFIG. 1Aand inFIG. 2A, where the locations are separated by a distance “d.” In some embodiments, the locations are adjacent as shown inFIG. 2B, while in some embodiments, the locations at least partially overlap as shown at “o” inFIG. 2C.

In some embodiments, when locations are separated by a space, the space may be an integer multiplication of the detector size, and particularly may be an even integer multiplication of the detector size. However, in other embodiments, the spacing between locations is any size. Further, not all locations need to be equally spaced or oriented to one another in the same manner. Additionally, the spacing of detectors may or may not correspond to the spacing of the imaged locations.

The locations that are simultaneously imaged on the article at may be arranged in any suitable way, including different spacings in the horizontal and vertical direction (with “horizontal” and “vertical” referring to perpendicular directions relative to the plane of the wafer or other article being imaged).FIG. 3provides several non-limiting examples such as: the vertical array shown at (a) in which locations100,102, and103are arranged vertically; the horizontal array shown at (b) in which locations100,102, and103are arranged horizontally; a two-dimensional dimensional array shown at (c) in which locations100,102, and103are part of an array of other locations. The locations may be spaced, such as the alternating horizontal or vertical arrays shown at (d). Any arbitrary arrangement, and example of which is shown at (e), can be used as well.

The different locations may be spaced apart in the same plane on the article. However, in some embodiments, different locations are additionally or alternatively spaced apart so as to lie in different planes. For example, detectors may be positioned relative to the focal plane of the imaging lens (es) used to image the object. Thus, the detected locations may overlap horizontally and/or vertically while the detectors nonetheless view different parts of the article, such as different layers.

It is also possible to achieve overlap without varying the detector position, so that different parts of different detectors may view the same location on the article. For example, two different detectors may view the image in different magnification.

FIG. 1Billustrates how an object is imaged by detectors in a tool operating in a “multiple imaging” state. In this figure, a single location100′ on the article is imaged by two different detectors110and112. These are the same detectors used for imaging when the tool is operating in the “multiple location” state, but in this example, the detectors are operating in different imaging modes from one another. In the particular example illustrated inFIG. 1B, the detectors are shown to operate using different collecting angles.

The imaging optics between the article and the detectors are not illustrated and may be any suitable optics, for example as described in the next sections. In addition, more than two detectors may be used, of course

In some embodiments, not all detectors that are used in the multiple location state are used in the multiple imaging state. Similarly, some of the detectors that are used in the multiple imaging state may not be used in the multiple location state. Preferably, though, all the detectors used in the multiple location state are used in the multiple imaging state, and all the detectors used in the multiple imaging state are used in the multiple location state.

The different imaging modes may comprise any known kind of imaging mode, for example, but not limited to the following mode differences:

Different collecting angles: Multiple detectors view the same location on the article using different collection angle range (or ranges). The angle range(s) may be totally different or overlapped. In some embodiments, the angle range of one detector may totally contain or may totally be contained in an angle range of another detector.

Different polarization: Multiple detectors view the same location on the article using different polarizations. In some embodiments, the polarizations of detectors viewing the same area are orthogonal.

Different wavelength band: Multiple detectors view the same location on the article but with different wavelength range (or ranges). The wavelength range(s) may be totally different or may overlap. The wavelength range of one detector may totally contain or be contained in a wavelength range of another detector (i.e. one detector may detect a sub-range of a range of wavelengths detected by another detector). Use of a tool supporting “multiple imaging state” operation may be especially useful when using broadband or multiband (multiple wavelengths) illumination and/or imaging is desired. For an example of a tool using broadband or multiband radiation, see U.S. patent application Ser. No. 11/684,191, published as US20070273945A1 on Nov. 29, 2007, which is incorporated by reference herein in its entirety for all purposes to the extent it is not in conflict with the present subject matter. Broadband or multiband wavelengths can be produced by broadband or multiband illumination or due to fluorescence or other non-linear phenomena. Instead of wavelength range, a single wavelength may be used, for all or at least one of the detectors.

Different attenuation: Multiple detectors view the same location on the article after different attenuation. In some embodiments, one “attenuation” is actually null attenuation. Imaging based on light that has been attenuated differently may be used for enhancing the dynamic range of the system.

Different focusing: Multiple detectors view the same location on the article but with different focusing position relative to the article plane. For example, the focus position for one detector may be beneath the article surface while another detector's focus position is on the article surface or above it. By using different focusing, different detectors may be sensitive for different layers on the article, and this may allow different detectors to be used to observe different types of defects.

Of course, the different imaging modes noted above may be used in combination. For example, a tool may support a multi-imaging state where a plurality of detectors view the same location, with the detectors viewing different wavelength ranges and at different focusing from one another.

The tool may support different imaging modes while in the multiple location state. For example, as noted above, the detectors inFIG. 1Aimage different locations. Detector110may have a different attenuation from detector112if, for example, a different dynamic range is needed to inspect area100as compared to area102.

As another example embodiment of a multiple imaging state, two (or more) detectors may view the article in the same imaging mode. This may provide an advantage by reducing the noise, such as by using averaging or other operator between the data from the detector.

In addition to or instead of using different imaging for each detector, a multiple imaging state may be implemented by configuring the tool to provide different illumination for different detectors. For instance, in some embodiments, the different illumination can be applied at different times (preferably with a very short period between them) for different respective detectors. The detectors are opened to receive illumination (by electronic gating for example) or otherwise rendered operable to image the article only at the time of corresponding illumination.

Next, three different exemplary implementations of an inspection apparatus that supports operation in both a multiple location state (or states) and in a multiple imaging state (or states) are described. Specifically, examples of optical configurations are shown. In these examples, optical components and/or detectors are arranged so that the optical path to the detectors and/or the components of the light traveling along the optical path can be managed.

FIG. 4illustrates an example of an embodiment that can be used in a tool so that the tool supports “flexible states.” In this embodiment, a beam splitter118is located in the imaging path between the article12and the detectors114and116. The imaging path includes focusing lens117. For example, the optics shown inFIG. 4could be used to configure a replacement for optics18noted above with regard toFIG. 9, in which focusing lens117could correspond to focusing lens46, imaging lenses124,126would correspond generally to lens42, and so on. Beam splitter118splits part of the image toward Detector114and the other part toward Detector116. Preferably, the beam splitter is 50% transmitting and 50% reflecting, although other percentages could be used in other embodiments.

A changeable filter120is located in the imaging path of detector114and another changeable filter122is located at the imaging path of detector116. These filters are used to change the imaging mode of each detector. After each filter, a focusing lens124and126images the light onto detectors114and116, respectively.

In this example, the two detectors are adjustable, e.g. the location of each detector can be changed up, down, left or right in the corresponding focal plane of its focusing lens. The detectors may be additionally movable perpendicular to the focal plane to move the focus point below or above the article. For example, the detectors may be housed or mounted on tracks or other assemblies which allow the detector location to be varied either manually or via suitable control signals from the inspection tool. The detectors may be moved in any number of directions along straight and/or curved paths as needed.

Multiple Location State

The detector arrangement ofFIG. 4may be operated in the multiple location state as illustrated atFIG. 5A. When the tool is commanded to operate in this state, Detector114views Location A on article12and Detector116views Location B on the article. To execute this state, each detector is moved toward a pre-determined position so it will view the corresponding location on the article. Changeable filters120and122are pulled out or neutralized during this state.

As with the detectors, the filters may be mounted on tracks or assemblies so that the filters can be physically moved (manually or automatically) to adjust the tool state. However, Changeable Filter120and/or122may remain in place, but may otherwise be adjusted so as not to affect light passing through. Accordingly, those filters are not shown inFIG. 5A.

The reflected light from Location A on the article is passed through lens117and transmitted partially by the beam-splitter118(the part reflected by the beam splitter is not illustrated). After the beam splitter, the light is focused on Detector114by lens124. The extreme rays for Detector114are drawn as wide dashed lines.

The reflected light from Location B on the article is also passed through lens117and reflected partially by the beam-splitter118(the transmitted part is not illustrated). After the beam splitter, the light is focused on Detector116by lens126. The middle ray for Detector116is drawn as a narrow dashed line and is indicated at119for purposes of clarity.

Multiple Imaging State

The multiple imaging state is illustrated atFIG. 5B. In this example, in the multiple imaging state, both detectors (Detector114and Detector116) view the same location (Location C) on the article. To execute this state, each detector is moved so it will view Location C on the article, and the changeable filters120,122are put in place or activated. In this example, detectors114and116are moved toward the central position. It will be understood, though, that the particular direction(s) of movement will depend on the original detector locations and desired location for viewing.

Changeable filters120,122may comprise any suitable type of filter which can be used to determine the resulting mode of the detector(s) receiving light that has passed through the filter. The term “changeable” is intended to encompass variable filters whose characteristics can be adjusted in-place, but also to include fixed filters whose functionality can be changed by physical moving the filter (such as by changing the filter position and/or orientation). Thus, changeable filters can include, but are not limited to:

Spatial mask: a spatially changeable filter is located at the Fourier plane of117. This mask can be used to determine the collection angles of each detector. Similarly, the same kind of filter can be located at the Fourier plane of L2.

Polarizers, retarders (e.g., λ/2 plate) or combination thereof: These may be used to determine the polarization of light impinging each detector.

Spectral filters: These may be used to determine/control the wavelength or wavelength bands each detector views.

Attenuators: these may be used to determine the attenuation of the light impinging each detector.

Focusing Element: Any suitable optical element (such as, for example, flat plates or lenses) can be used to change the focus position.

Any of the above may be used in conjunction with one another or any other suitable filtering mechanism to adjust the mode of the respective detector.

The reflected light from Location C on article12is passed through lens117and transmitted partially by the beam-splitter118and reflected partially from it. The transmitted light is filtered by Changeable Filter120, and focused on Detector114by lens124. The extreme rays for Detector114are drawn as wide dashed lines.

The reflected light is filtered by Changeable Filter122, and focused on Detector116by lens126. The middle ray for Detector116is drawn as a narrow dashed line.

As mentioned above, the changeable filters can be configured in any suitable way so as to control their use and effects on light in the optical paths. For example, the filters may be fixed filters or masks. Changing the imaging state is achieved by placing the filter/mask in the optical path or taking it out. As another example, the filters may be mechanically changed. The imaging state is changed mechanically, such as by rotating a polarizer. As another example, the filters may be electronically or electro-mechanically changed. In such filters, the imaging is changed by using an LCD mask or micro shutters array as the spatial mask in the focal plane.

In addition to the lenses124,126, other components may be added between the changeable filter(s) and their respective detectors, such as polarizers, attenuators, spectral filter, etc that are same or different for each optical path. The components may be added before the focusing lenses, after the focusing lenses, or combined with the focusing lenses (for example, a focusing lens with high light absorption may serve as an attenuator as well).

FIGS. 5A and 5Beach are a simplified diagram, and it will be understood that, in some embodiments,117and/or124and/or126may comprise more complicated optics, such as, for example, multiple lenses, doublets, triplets, etc. One or more components of the optics may contain diffractive lenses or graded index lenses.

Part or all of the different imaging may be implemented by repositioning or reconfiguring beam-splitter118instead of or in addition to changing the changeable filters. For example, a polarizing beam splitter may be placed after117instead of using polarizers as the changeable filter.

As another example, the beam splitter may be highly reflective and low transmissive. The detector receiving the transmitted rays would not need an attenuator in such a case. Of course, the beam splitter could by highly transmissive and lowly reflective to reverse the situation.

As another example, instead of using spectral filters, a dichroic beam splitter could be used. Generally speaking, beam splitter characteristics can be changed in any suitable manner to adjust the imaging mode in addition to, or instead of, using the changeable filters.

In this example, light was split to two detectors. Of course, light can be split to more than two detectors using cascaded beam splitters, combination of beam splitters and mirrors, and/or any suitable splitting system.

One Lens/Two Lenses Embodiments

A second exemplary embodiment is illustrated in conjunction withFIGS. 6A and 6B. In this example, a tool supports a multiple location state and a multiple imaging state in which a different collection angle is used for each detector. The two different states are exchanged by switching a single lens132for an optic element134containing or functioning as multiple lenses. In this example, optic element134contains two lenses, and the illustrated switch uses two detectors.

In the multiple location state (FIG. 6A) different locations on article12(Location D and Location E) are imaged on respective detectors128and130.

Rays from the Location D of the article, for example, go through lens117, and are focused by single lens132, which is positioned on the Fourier plane of lens117, onto Detector130. Similarly, rays from Location E are focused on Detector128.

In the multiple imaging state, the tool's optics are configured as shown inFIG. 6B. Location F of article12is imaged on two detectors128and130in two ranges of collection angles. This imaging state is implemented by exchanging single lens132for an optical element134.

Optical element134comprises two adjacent lenses, each with a power equal the power of lens132. Discrete lenses may be used, or optical element134may comprise any suitable material configured to function as multiple lenses. All the rays that reflected from horizontal to bottom direction (HB inFIG. 6B) are imaged by117and the bottom lens of element134to Detector130. All the rays reflected from horizontal to top direction (HT inFIG. 6B) are imaged by117and the top lens of element134to Detector128.

The lenses comprising element134may be arranged in any size or order.FIG. 7illustrates several exemplary configurations of element134when a pair of lenses is used. InFIG. 7, the aperture of single lens132, which is replaced by element134when the tool is in the multiple imaging state, is represented by a dashed line136. In the example illustrated atFIG. 7A, the two lenses (I and11) are side by side, and each of them is a different half of the total aperture. In the example illustrated atFIG. 7B, the two lenses are circular, and each lens is half of the diameter of lens132. In this case the two lenses are also positioned adjacent to one another.

In the example illustrated atFIG. 7C, one lens is larger than the other, in this example, equal to or almost equal to the original size of single lens132. The larger lens (I) comprise a hole in which the second lens (II) is placed. This configuration may require wedges or other optics to direct the light to the detectors.

In the example illustrated atFIG. 7D, non adjacent lenses are shown. Additionally, the lenses have different sizes from one another.

Changing Objective Embodiment

FIG. 8illustrates a configuration of optics in which a multiple location state is achieved by changing the objective lens117. The multiple imaging state of this embodiment is same as the multiple imaging state of the second embodiment ofFIG. 6B. However, in this embodiment, the same optical element134used in the multiple imaging state is also used in the multiple location state.

In contrast to the multiple location state ofFIG. 6A, though, in this embodiment, a different objective lens117′ is used instead of117when the tool is operating in the multiple location state. Additionally, relay lenses135and140are placed in the optical path of each respective detector128,130as shown inFIG. 8.

In this state, Location E is first imaged on the top lens of element134. This lens and the nearby relay lens135image location E on Detector128. Similarly, Location D is imaged onto Detector130via117′, the bottom lens of element134, and a corresponding relay lens140.

In this embodiment, the two detectors may image adjacent areas on the article without shadows between them. For examples of imaging adjacent areas on the article without shadows, see U.S. patent application Ser. No. 11/944,684, entitled “Image Splitting in Optical Inspection Systems” by Dov Furman, Shai Silberstein, Effy Miklatzky, Daniel Mandelik, and Martin Abraham, filed Nov. 26, 2007 and published as US 2008-0137074 A1, which is incorporated by reference herein in its entirety for all purposes to the extent it is not in conflict with the present subject matter.

In various embodiments,117′ may be placed at a different position than117;117′ may have a different power from117; or117′ may be both placed at a different position and may have a different power from117.

To implement the multiple imaging state, in addition to the element134, other components may be added, such as polarizers, attenuators, spectral filter, etc that are same or different for each lens in element134. The components may be added before the lenses, after the lenses, or combined with the lenses (for example, a lens with high light absorption may be served as an attenuator as well).

The components may be added also before, after or in combination of the relay lenses if/when relay lenses are used.117and/or132and/or the relay lenses135,140may be more complicated optics and may comprise, for example, multiple lenses, doublets, triplets, etc. Further, one or more components of the optics may comprise diffractive lenses or graded index lenses.

In some embodiments, instead of two lenses in element134for two detectors, more than two lenses and respective detectors may be used. For example element134may comprise three lenses for imaging three parts on the article to three detectors in the multiple location state, while in a multiple imaging state, three ranges of collection angles are imaged to the three detectors.

Although not shown inFIG. 8, a wedge may be placed after each lens of132or element134in order to direct the output from the lens to a specific detector.

The detector(s) used in an optical inspection tool can comprise any suitable number, type, or combination of light-sensing elements. The underlying sensing can be based on any suitable technology. For instance, in various embodiments, one or more of the following types of detector types can be used: CCD, CMOS, PMT, and/or avalanche photodiode detectors.

The detectors may be of any suitable type. For example, one or more detectors may comprise an area detector, such as a matrix of photo-sensors producing 2 dimensional image data. As another example, one or more detectors can comprise a TDI line detector, i.e. a matrix of photo-sensors which produces 1 dimensional image data. As another example, one or more detectors can comprise a line detector i.e. a line of photo-sensors which produces 1 dimensional image. In certain embodiments, a detector can comprise a “point detector,” where each detector signal represents a pixel.

It will be appreciated that, in some embodiments in which light sensing and imaging is based on point detection, such as when PMT and/or avalanche photodiode detectors are used, the illumination and/or imaging hardware will need to be varied appropriately from the example arrangements discussed above in conjunction withFIGS. 9 and 10. For example, embodiments of a tool using PMT and/or avalanche photodiode detectors can include some sort of scanning mechanism to variably illuminate spots on the wafer or other object(s) under inspection. For instance, a suitable illumination source (such as an argon laser or another laser) can be used in conjunction with an acousto-optical deflector to scan one or more illuminating beams across the wafer or other object(s) under inspection.

As one example of inspecting using a scanning source, a sawtooth pattern in the time domain can be used while the stage moves the wafer orthogonally to the movement of the illuminating beam. The imaging optics can be arranged to appropriately collect light from the illuminating beam as reflected or otherwise scattered by the wafer. Exemplary details of an inspection system including a scanning illumination source can be found in U.S. Pat. No. 5,699,447, which is incorporated by reference herein in its entirety to the extent it does not conflict with the present subject matter. Exemplary discussion of line detection can be found in U.S. Pat. No. 6,724,473, which is incorporated by reference herein in its entirety to the extent it does not conflict with the present subject matter.

When TDI or line detection is used, illumination and relative movement of the wafer should be adjusted accordingly, with the image acquisition hardware/software also suitably configured. For instance, as is known in the art, when TDI detection is used, continuous illumination is applied while the imaging location on the wafer or other object is varied.

Similarly, the hardware/software used for image acquisition/analysis should be appropriately configured for embodiments in which point detection is used. Namely, rather than capturing an entire field of view instantaneously, the imaging hardware images a series of points (which may each comprise one or more pixels) from which the entire image of the wafer can be constructed. In some embodiments in which point detection is used, in the multiple-location state, the tool images multiple points at a given time, while in the multiple imaging state, a given point is imaged by multiple detectors (e.g. two or more point detectors operating in different imaging modes from one another).

In some embodiments, a tool using more than two detectors supports selection between two of the following three states: (1) All the detectors view a different respective location on the article; (2) All the detectors view the same location on the article, but with different imaging modes; and (3) Some of the detectors view the same location with different imaging, while some detectors view different locations from one another.

Preferably in some embodiments, the number of imaging modes in option (3) is the number of detectors divided by the number of viewed locations. In each viewed location, the same image is used for each mode. Thus, a tool could switch between operating in a purely multiple-location state to a mix of multiple locations and multiple modes, for example.

For example, if there are four detectors, the tool can image two different locations at a time while in the multiple imaging state, with each location imaged using two different modes. For instance, the detectors may be assigned as follows: Detector 1—Location I, imaging mode I; Detector 2—Location I, imaging mode II; Detector 3—Location II, imaging mode I; Detector 4—Location II, imaging mode II. Of course, this example may represent a subset of many available detectors and modes.

As another example, a tool with twenty-four detectors may support a “multiple imaging state” in which the tool can image eight different locations simultaneously in three modes.

The inspected article may be any article used in or resulting from a semi-conductor manufacturing process, such as wafers, masks, photomasks and reticles, although the principles discussed herein could be applied to inspection tools regardless of the article under inspection.

In some embodiments, when the detectors view different respective locations on the article, a different imaging mode for each detector may also be used. For example, between two detectors, Detector I may view location I in imaging mode II while Detector II views location II in imaging mode I.

The imaging state of the tool may be changed during an inspection, and not only before inspection, to use the best state for each part of the article. As an example, in a tool with four detectors supporting two different modes, the tool may operate in a multiple imaging state when high sensitivity is needed for some areas of a wafer and image two locations simultaneously in two different modes for each location. In other parts of the wafer where less sensitivity is needed, all four detectors may be used to image different respective locations in a single mode and thereby increase throughput. As mentioned above, while the detectors image different respective areas, the detectors may all operate in the same mode, or one or more detectors may image their respective area(s) in different modes from one another.

In some embodiments, it may be advantageous to change the state in between slices, i.e. after each slice (with a “slice” referring to an inspected section of the article along an imaging axis from start to end). However, if applicable, the states can be changed within inspection of a slice. In any event, the inspection tool can be configured to select appropriate inspection paths, sequences, and the like and thereby address changes in the size, shape, and coverage of its field of view in different states.