System and method for reviewing a curved sample edge

The disclosure is directed to a system and method for reviewing a curved edge of a sample. A line scan detector is actuated along an actuation path defined by the edge of the sample to scan a plurality of locations along the sample edge. The scan data is assembled to generate at least one review image of at least a portion of the edge of the sample. In some embodiments a substantially normal angle of incidence is maintained between the sample edge and the scanning illumination. In some embodiments, brightfield and darkfield images may be collected utilizing a common objective with separately operable illumination sources directing illumination along a first and second illumination path to the sample edge for review.

TECHNICAL FIELD

The present disclosure generally relates to field of sample review and more particularly to reviewing a curved edge of a sample.

BACKGROUND

Several methods exist in the art for reviewing a curved edge of a sample, such as a semiconductor wafer. For example, some wafer edge review systems collect a 2-D format image at a small angle off normal to the wafer with illumination at the reflected angle covering a radial zone of possible local wafer surface normal angles. Some other systems include a 2-D camera viewing normal to the wafer edge. In another class of systems a TDI camera with a center pixel normal to the local wafer edge is configured to image the wafer spinning on a radial stage. All of the foregoing systems, however, suffer from a limited depth of focus and/or severe image shading resulting from angle of incidence between illumination and the wafer edge. The depth of focus and shading may limit the usable field of view to very small strips.

SUMMARY

The disclosure is directed to systems and methods that cure deficiencies of the current art to enable collection of high resolution review images over the sample edge. In some embodiments, the systems and methods described below may further extended to applications beyond review imaging such as, but not limited to, inspection over the wafer edge or film review or inspection at a selected angle of incidence in radial slice planes.

In one aspect, the disclosure is directed to a system for reviewing a curved edge of a sample while avoiding field depth of focus problems by line scanning along the wafer edge. The system includes a stage configured to support a sample and at least one illumination source configured to illuminate an edge of the sample with illumination emanating along an illumination path defined by one or more illumination optics. A line scan detector is configured to receive illumination reflected from the edge of the sample along a collection path defined by one or more collection optics. At least one actuator is configured to actuate the line scan detector and the one or more collection optics radially along an actuation path defined by the edge of the sample to scan along the sample edge. A computing system communicatively coupled to the line scan detector is configured to generate at least one review image of at least a portion of the sample edge by assembling line scans associated with illumination received by the line scan detector from a plurality of locations along the edge of the sample.

In another aspect, the disclosure is directed to a system including a first illumination source configured to illuminate an edge of the sample with illumination emanating along a first illumination path and a second illumination source configured to illuminate the edge of the sample with illumination emanating a second illumination path. In some embodiments, the system further includes a beam splitter configured to merge the first illumination path and the second illumination path into a common path leading to the sample edge. The first and second illumination sources may be configured for separately operating to respectively provide for brightfield and darkfield imaging of the sample edge. In some embodiments, a common objective is configured to collect illumination reflected from the sample edge for either type of imaging.

In yet another aspect, the disclosure is directed to a method of reviewing a curved sample edge in accordance with the foregoing systems. The method may include at least the steps of: illuminating an edge of a sample with illumination emanating from a first illumination source along a first illumination path including one or more illumination optics; receiving illumination reflected from the edge of the sample along a collection path including one or more collection optics utilizing a line scan detector; actuating the line scan detector and the one or more collection optics radially along an actuation path defined by the edge of the sample; and generating at least one review image of at least a portion of the edge of the sample utilizing scan data associated with illumination received by the line scan detector from a plurality of locations along the edge of the sample.

In yet another aspect, review images on the top or bottom section of the sample, which are not curved, may be collected utilizing a two dimensional (2-D) sensor (as opposed to the line scan imager). In some embodiments, the line scan function may be achieved utilizing a windowed readout of a 2-D sensor with a minimal number of lines (i.e. on the order of 8 lines). This would allow a 2-D sensor to be in place for rapid imaging of the top and bottom flat wafer sections, and allow fast pseudo line scanning over the edge of the wafer.

DETAILED DESCRIPTION

FIGS. 1 through 4generally illustrate a system100and method200for collecting review images along curved edge102of a sample101, such as a wafer, by line scanning over the sample edge102. Line scanning over the edge of the wafer may allow for improvements in of the required depth of field, the required cone angle of bright field illumination, and thus increase the usable field of view as compared to previously known systems and methods in the art. Accordingly review images may be collected with reduced image shading due to a reduction in the depth of field and illumination limitations common to existing wafer edge review systems. Furthermore, an enhanced field of view may enable review of certain defects of interest, such as edge chips, on a relatively small scale (e.g. order of a millimeter).

FIG. 1illustrates a system100for reviewing an edge102of a sample101, in accordance with an embodiment of the disclosure. The system100includes at least one illumination source104configured to illuminate the sample edge102by providing illumination along an illumination path defined by one or more illumination optics106. The sample101may be supported by a stage configured to actuate the sample101to a selected position (i.e. placing a defect of interest into view). For example, the stage may be mechanically coupled to or include one or more motors, servos, or alternative actuation means configured to spin the sample101about its central axis to place a selected portion of the sample edge102into view.

The system100further includes at least one line scan detector108, such as a polychrome or monochrome line scan camera (e.g. CCD or CMOS linear sensor array). The line scan detector108is configured to receive at least a portion of illumination reflected from the sample edge102along a collection path defined by one or more collection optics110. This line scan camera function can also be achieved by using a 2-D sensor and windowing out a minimal number of lines. In some embodiments, the collection optics110include an objective lens assembly, such as a brightfield objective. A beam splitter112disposed between the collection optics110and the sample edge102may be configured to direct illumination from the illumination path to the sample edge102and direct illumination reflected from the sample edge102back through the collection optics110to the line scan detector108. Placement below the objective110may enable angle of incidence variations; however, the beam splitter112may be alternately disposed between the line scan detector108and the objective110if angle of incidence is maintained substantially uniform while scanning the sample edge102.

As illustrated inFIG. 2, the line scan detector108is configured to scan across at least a portion of the sample edge102by following an actuation path defined by the edge profile. One of more actuators are mechanically coupled to at least the line scan detector108and the collection optics110. In some embodiments, the line scan detector108and the collection optics110are supported by a stage coupled to the one or more actuators. The one or more actuators are configured to radially actuate the line scan detector108and the collection optics110along the actuation path (over and under a portion of the sample101) to enable scanning across the selected portion of the sample edge102.

The one or more actuators may be configured to translate and/or rotate the line scan detector108and the collection optics110along at least three axis (or six degrees of freedom) to enable control of focus and angle of incidence. In some embodiments, the illumination source104and illumination optics106are also coupled to the one or more actuators for scanning convenience. For example, the illumination source104and optics106may be disposed upon the stage supporting the line scan detector108and the collection optics100to enable simultaneous actuation. In some embodiments, a plurality of actuators (e.g. motors/servos) may operate in concert to follow the edge profile while maintaining a substantially uniform level of focus and angle of incidence (e.g. substantially normal incidence). Accordingly, the line scan detector108may be enabled to collect high resolution (e.g. 3 to 5 um pixel resolution) review images of the scanned portion of the sample edge102.

In some embodiments, the system100further includes a second illumination source120configured to provide illumination along a second illumination path to illuminate the sample edge102. A beam splitter122may be configured to merge a first illumination path corresponding the first illumination source104and the second illumination path corresponding the second illumination source120into a common illumination path leading to the sample edge102. Each channel may be configured for imaging the sample edge102according to a different review protocol. For example, the first illumination source104may be configured to illuminate the sample edge102to collect brightfield review images, and the second illumination source120may be configured to illuminate the sample edge102to collect darkfield review images. In either mode of operation, the same collection optics110(e.g. a brightfield objective) may be configured to direct illumination reflected from the sample edge102to the line scan detector108. Accordingly, the line scan detector108may be configured to collect brightfield or darkfield review images of the sample edge102depending upon the illumination source104or120illuminating the sample edge102during a scan.

At least one computing system114communicatively coupled to line scan detector108is configured to process data collected from a plurality of scanned locations along the sample edge102. For example, the computing system114may be configured to generate a review image of at least a portion of the sample edge102by merging multiple line scans. In some embodiments, the computing system114may include at least one processor (e.g. single-core or multiple-core processor) configured to execute program instructions118from at least one carrier medium116, wherein the program instructions118direct the processor to carry out one or more of the steps or functions described herein. The one or more computing systems114may be further configured to control the one or more actuators of the sample stage or the illumination/collection optics to scan a selected portion of the sample edge102, as described above.

In some embodiments, the one or more computing systems114are further configured to control illuminations source104and/or120to provide pulses of illumination to for illumination uniformity and/or focus as the sample edge102is scanned. For example, each illumination source104/120may include at least one light emitting diode (LED) configured to strobe illumination to compensate for variations in illumination intensity that can occur between scanning locations as a result of non-uniform motion along the actuation path.

FIG. 3illustrates another embodiment of the system100including a scatter channel photomultiplier tube124to enable inspection in addition to review of the sample edge102. In some embodiments, the photomultiplier tube124is disposed in place of the second illumination source120(fromFIG. 1), wherein the beam splitter122is configured to direct at least a portion of illumination reflected or scattered from the sample edge102along a scatter channel to the photomultiplier tube124. Alternatively, the scatter channel is incorporated in addition to the first and second illumination channels utilizing an additional beam splitter in series with the first beam splitter122. The one or more computing systems108may be further coupled to the photomultiplier tube124and configured to determine location, size, and/or classification of at least one defect of the sample101utilizing information associated with illumination received by the photomultiplier tube124.

FIG. 4illustrates a method200of reviewing a sample edge102in accordance with the foregoing system100. It is noted, however, that method200may be implemented by alternative or additional means known to the art than those described by the foregoing embodiments of system100. Accordingly, method200should be construed as encompassing any means known now or hereafter for executing one or more of the following steps or functions. Furthermore, method200is not limited to the following steps and may include one or more steps for carrying out any of the functions described above with regard to embodiments of system100.

At step202, an edge102of a sample101is illuminated utilizing at least one illumination source104and/or120. In some embodiments, pulsed illumination is utilized to enable focusing and/or compensation for non-uniform actuation about the sample edge102. At steps204and206, a plurality of line scans are detected by actuating a line scan detector108along an actuation path defined by the sample edge102. In some embodiments, the scans are collected while maintaining a substantially normal angle of incidence with the scanned portion of the sample surface. At step208, the scan data (i.e. 1-D line scans) are assembled into a (2-D) review image of at least a portion of the sample edge102. Accordingly, a high resolution image of the sample edge102is collected by following the edge profile to scan over a plurality of locations along the sample edge.

The foregoing system100and method200provide several advantages over the current art. By scanning over the edge of the wafer with a line array, the angle of incidence to the wafer over a 4 mm wide swath, for example (consistent with a 0.125 NA, 1 um pixel resolution) would only be 0.0089 radians, which is a very small fraction of the basic NA. Shading in a thru the lens illumination would be ˜8% (compared to 100% darkening for the alternate methods at only 2% of this field of view. Addition of under-the-lens illumination allows a slight overfilling of the objective NA, and allows minor misalignment and local surface tilt without any illumination vignetting. Adding a scatter channel option through the same beam splitter path allows for convenience of stage motion for inspection and review. The advantages can be further extended to applications beyond edge review images. For example, the system100and method200described above can be further configured for inspecting a film disposed upon a wafer at an angle, with the angle of incidence in radial slice planes.

It should be recognized that the various steps and functions described throughout the present disclosure may be carried out by a single computing system or by multiple computing systems. The one or more computing systems may include, but are not limited to, a personal computing system, mainframe computing system, workstation, image computer, parallel processor, or any other device known in the art. In general, the term “computing system” may be broadly defined to encompass any device having one or more processors, which execute instructions from at least one carrier medium.

Those having skill in the art will appreciate that there are various vehicles by which processes and/or systems and/or other technologies described herein can be effected (e.g., hardware, software, and/or firmware), and that the preferred vehicle will vary with the context in which the processes and/or systems and/or other technologies are deployed. Program instructions implementing methods such as those described herein may be transmitted over or stored on carrier media. A carrier medium may include a transmission medium such as a wire, cable, or wireless transmission link. The carrier medium may also include a storage medium such as a read-only memory, a random access memory, a magnetic or optical disk, or a magnetic tape.

All of the methods described herein may include storing results of one or more steps of the method embodiments in a storage medium. The results may include any of the results described herein and may be stored in any manner known in the art. The storage medium may include any storage medium described herein or any other suitable storage medium known in the art. After the results have been stored, the results can be accessed in the storage medium and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc. Furthermore, the results may be stored “permanently,” “semi-permanently,” temporarily, or for some period of time. For example, the storage medium may be random access memory (RAM), and the results may not necessarily persist indefinitely in the storage medium.

Although particular embodiments of this invention have been illustrated, it is apparent that various modifications and embodiments of the invention may be made by those skilled in the art without departing from the scope and spirit of the foregoing disclosure. Accordingly, the scope of the invention should be limited only by the claims appended hereto.