Abstract:
An optical inspection device of a device-under-test is disclosed, said device comprising a light source, an image rotator, a parabolic reflector, and one or more detectors, wherein said light source provides a light beam traveling through said image rotator and reflecting off said parabolic reflector to a device-under-test and thereby creating diffracted light beams off said device-under-test, and said diffracted light beams reflecting off said parabolic reflector and travels through said image rotator and are received by the detectors.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority from a provisional patent application entitled “Image Rotation devices and Their Applications” filed on Jul. 31, 2006, having an application No. 60/834,048. This application is incorporated herein by reference in its entirety. 
     
     FIELD OF INVENTION 
       [0002]    The present invention relates to the inspection and measurement systems, and in particular, to optical inspection and measurement of devices-under-test (“DUT”) such as semiconductor devices and/or wafers. 
       BACKGROUND 
       [0003]    Optical silicon wafer inspections collect and analyze optical signals generated from areas of interest on a wafer in order to determine the quality of the wafer from the fabrication process. Information in these areas can be collected in one method, the x-y 2-dimensional scanning method, by doing 2-dimensional scanning in the x-y plane, or in another method, the rotation method, by rotating the wafer around its center axis and linear moving the wafer in 1-dimension. The x-y 2-dimensional scanning method can be used for both patterned and unpatterned wafers. The rotation method is potentially fast and requires less space. However, because the pattern of interest rotates as well while the wafer is rotating, it would be difficult to use the rotation method for patterned wafers and thus the application of the rotation method is mostly limited for unpatterned wafers. 
         [0004]    It would be desirable to have inspection systems utilizing the rotation method that rotate a wafer around its center axis and linear moving in 1-dimension in the inspection of a patterned wafer, where inspection includes optical patterned silicon wafer inspection, defect review, critical dimension measurement, and other relevant applications. 
       SUMMARY OF INVENTION 
       [0005]    An object of the present invention is to provide methods and devices that utilize a rotation method in the inspection of DUT. 
         [0006]    Another object of the present invention is to provide methods and devices that utilize a rotation method in the inspection of patterned DUT. 
         [0007]    Another object of the present invention is to provide methods and devices that utilize a rotation method in the inspection of a DUT where the DUT is moved by rotating along its center axis. 
         [0008]    Briefly, the present invention discloses an optical inspection device, comprising a light source, an image rotator, a parabolic reflector; and one or more detectors, wherein said light source provides a light beam traveling through said image rotator and reflecting off said parabolic reflector to a device-under-test and thereby creating diffracted light beams off said device-under-test, and said diffracted light beams reflecting off said parabolic reflector and travels through said image rotator and are received by the detectors. 
         [0009]    An advantage of the present invention is that it provides methods and devices that utilize a rotation method in the inspection of DUT. 
         [0010]    Another advantage of the present invention is that it provides methods and devices that utilize a rotation method in the inspection of patterned DUT. 
         [0011]    Another advantage of the present invention is that it provides methods and devices that utilize a rotation method in the inspection of a DUT where the DUT is moved by rotating along its center axis. 
     
     
       DRAWINGS 
         [0012]    The following are further descriptions of the invention with reference to figures and examples of their applications. 
           [0013]      FIG. 1  illustrates a side view of a presently preferred embodiment of the present invention. 
           [0014]      FIG. 2   a ,  2   b ,  2   c  and  2   d  are top-views of the light source, and the detectors at the top of the image rotator and at the top of the parabolic reflector. 
           [0015]      FIG. 3   a  shows one option of an all-reflective image rotator. 
           [0016]      FIG. 3   b  is a side-view of  FIG. 3   a , where the image rotator rotates around the axis. 
           [0017]      FIG. 4  shows an alternate embodiment of the present invention with a normal incidence angle. 
           [0018]      FIG. 5  shows another alternate embodiment of the present invention with an image detection array and one or more lenses. 
           [0019]      FIG. 6  shows an alternate embodiment of the embodiment 2 (shown in  FIG. 4 ) where the optical image rotator is replaced with an array of detectors. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    The presently preferred embodiment of the present invention may comprise of the following elements:
       1. One or more mirrors or lenses or a parabolic reflector, such as the parabolic reflector previously disclosed in non-provisional patent application Ser. No. 11/735,979, where the parabolic reflector may be stationary or may rotate with an image rotator;   2. An image rotator, such as an image rotator described below or combinations thereof: (1) a Dove prisms image rotator; (2) a reflective image rotator such as one disclosed in non-provisional patent application Ser. No. 11/747,173; or (3) an image sensor array with electronic or digital signal processing to perform image rotations;   3. A light source, providing for an oblique angle incidence with a relative stationary azimuth angle to pattern a rotating wafer. A light source using a normal (or near normal) angle of incidence can be used as well. The light source itself can be a broad band light source, monochromic light source, or others. Options to use variable spectral filters, variable polarizers, variable intensity control, variable position control, and variable spot dimension and shape control can be added. Light sources for auto-focusing can be provided as well;   4. One or more detectors, a detector can be provided in a single area, or spot optical detectors with stationary positions can be provided after an image rotator. A detector array after an image rotator can be used as well, or used with or without an image rotator. A detector can be used with optional variable spectral filters, variable polarization analyzers, variable position control, variable intensity neutral filters, and variable aperture control, etc. A detector can be used for auto-focusing as well; and   5. A computer for (a) synchronization of motions; (b) storage of data; (c) signal processing and data analysis; and/or (d) other purposes.       
 
         [0026]    Mechanical motion(s) of the presently preferred embodiment may include the following: a silicon wafer may rotate in an x-y plane around a wafer center; an optical image rotator (if any) may be rotated; the relative position of an optical setup and the silicon wafer may be moved in a pre-defined direction; and other motions. 
         [0027]    Applications of the present invention may include the following inspection items: (a) defect inspection with DUT rotation; (b) defect review with DUT rotation; (c) optical critical dimension measurement with DUT rotation; (d) other optical metrology with DUT rotation; and (e) other relevant applications. 
       Embodiment 1 
       [0028]      FIG. 1  illustrates a side view of a presently preferred embodiment of the present invention. The collimated beam from light source  1  passes through an image rotator  5  and reflects from the mirror surface spot  7  of the parabolic reflector  6 , then focuses on the focal point  8  of the wafer  12  (or any device-under-test). The mirror surface spot  9  reflects the specular beam into the image rotator  5  and reaches the specular beam detector  2 . The mirror surface spot  10  reflects its diffracted light from the focal spot  8  into the image rotator  5  and reaches its corresponding detector  3 . The mirror surface spot  11  reflects its diffracted light from the focal spot  8  into the image rotator  5  and reaches its corresponding detector  4 . The wafer  12  rotates clockwise in an x-y plane around its center and moves along the x-axis. The image rotator rotates counter-clockwise to completely de-rotate the pattern on the focal spot  8  of wafer  12 . In addition, the specular beam detector  2  can provide auto-focusing function. 
         [0029]      FIG. 2   a ,  2   b ,  2   c  and  2   d  are top-views of the light source and the detectors at the top of the image rotator and at the top of the parabolic reflector (see  FIG. 1 ) corresponding to four sample wafer rotation angles. 
         [0030]    In  FIG. 2   a , top figure, the dashed-line  13   a  represents the rotation angle of the image rotator  5   a  where a mirror image in the lower part of the figure is folded symmetrically along the axis  13   a .  FIG. 2   a , bottom figure, shows a top-view of the parabolic reflector  6   a , which can be stationary. On the top of the image rotator, there are four components: there is a light source  1   a , and light detectors  2   a ,  3   a  and  4   a . On the surface of the mirror, there are four-interested light reflecting spots. They are incident light  7   a  detected by light spots  9   a ,  10   a  and  11   a . Because of the image rotator, on the surface of the parabolic reflector  6   a , light spots  7   a ,  9   a ,  10   a  and  11   a  are in corresponding mirror image positions of  1   a ,  2   a ,  3   a , and  4   a  along line  13   a . A light travels through  1   a  through the image rotator  5   a  to the mirror spot  7   a  and the focal spot  8   a  on the wafer surface. The specular beam is reflected through  9   a  through the image rotator to reach the corresponding detector  2   a . The diffracted spot  10   a  is mirrored back to the detector  3   a , and the other diffracted spot  11   a  is mirrored back to its detector  4   a.    
         [0031]    In  FIG. 2   b , the image rotator rotates to a 45-degree position as shown by line  13   b , corresponding to a wafer 90-degree rotation. Because of the image rotator, on the surface of the parabolic reflector  6   b , the spots  7   b ,  9   b ,  10   b  and  11   b  are in corresponding mirror image positions of  1   b ,  2   b ,  3   b , and  4   b  along line  13   b.    
         [0032]    In  FIG. 2   c , the image rotator rotates to a 90-degree position as shown by line  13   c , corresponding to a wafer 180-degree rotation. Because of the image rotator, on the surface of the parabolic reflector  6   c , the spots  7   c ,  9   c ,  10   c  and  11   c  are in corresponding mirror image positions of  1   c ,  2   c ,  3   c , and  4   c  along line  13   c.    
         [0033]    In  FIG. 2   d , the image rotator rotates to a 135-degree position as shown by line  13   d , corresponding to a wafer 270-degree rotation. Because of the image rotator, on the surface of the parabolic reflector  6   d , the spots  7   d ,  9   d ,  10   d  and  11   d  are in corresponding mirror image positions of  1   d ,  2   d ,  3   d , and  4   d  along line  13   d.    
         [0034]    As shown in  FIGS. 2   a ,  2   b ,  2   c , and  2   d , as the wafer rotates 360-degree, the image rotator rotates 180-degree to de-rotate (or adjust) images of the wafer, where the light source, the detectors, and the parabolic reflector are kept stationary. The light source shown in the figures is chosen as having an oblique angle incidence. Other angles of incidence can be chosen as well such as a normal (or near normal) angle incidence configured as positioning the light source along the center of the rotation axis of the image rotator. 
         [0035]      FIG. 3   a  shows one option of an all-reflective image rotator, where image  14  is an original image and image  15  is its rotated mirror image, and  16 ,  17  and  18  are mirrors.  FIG. 3   b  is a side-view of  FIG. 3   a , where the image rotator rotates around the axis. 
       Embodiment 2 
       [0036]      FIG. 4  shows an alternate embodiment of the present invention where the light source provides a light beam with a normal (or near normal) incidence angle. In  FIG. 4 , a light source  19  directly focuses on the wafer surfaces, and a circular mirror (with an opening in the center of the mirror) or a half mirror  20  reflects the diffracted lights through the image rotator  5 , and the diffracted lights are detected by detectors such as detector  21  and detector  22 . Note that the detector(s) detects the DUT at the same relative azimuth angle to the patterns on the DUT even though the DUT is being rotated. 
         [0037]    Furthermore, in yet another alternate embodiment, the locations of the light source and the detectors can be interchanged such that the light source is provided at the place of the detectors and the detectors are provided at the place of the light source. 
       Embodiment 3 
       [0038]      FIG. 5  shows another alternate embodiment of the present invention with a light source  23 , an image detection array  23  (the light source and the detector can be in the same housing), lenses  24  and  25 , or a lens  25  alone (light sources are not shown). 
       Embodiment 4 
       [0039]      FIG. 6  shows an alternate embodiment of the embodiment 2 (shown in  FIG. 4 ) where the optical image rotator is replaced with an array of detectors. The de-rotation of wafer images is performed with digital processing techniques or software techniques. 
         [0040]    While the present invention has been described with reference to certain preferred embodiments, it is to be understood that the present invention is not limited to such specific embodiments. Rather, it is the inventor&#39;s contention that the invention be understood and construed in its broadest meaning as reflected by the following claims. Thus, these claims are to be understood as incorporating not only the preferred embodiments described herein but all those other and further alterations and modifications as would be apparent to those of ordinary skilled in the art.