Abstract:
One embodiment described relates to a multiple electron beam apparatus. Multiple columns are arranged in a row configured to generate multiple electron beams. A mechanism is included for translating a substrate so as to be impinged upon by the multiple electron beams. A direction of the substrate translation and a direction of the row of columns are at a skew angle.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present invention claims the benefit of U.S. Provisional Patent Application No. 60/678,866, entitled “Skew-Oriented Multiple Electron Beam Apparatus and Method,” filed May 4, 2005 by inventor David L. Adler, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to microscopic inspection methods and apparatus. The present invention relates more particularly to automated inspection systems for semiconductor manufacturing. 
     2. Description of the Background Art 
     A variety of methods have been used to examine microscopic surface structures of semiconductors. These have important applications in the field of semiconductor integrated circuit (IC) fabrication, where microscopic defects at a surface layer make the difference between a good or bad IC. For example, holes or vias in an intermediate insulating layer often provide a physical conduit for an electrical connection between two outer conducting layers. If one of these holes or vias becomes clogged, it will be impossible to establish this electrical connection. Automated inspection of the semiconductors is used to ensure a level of quality control in the manufacture of the integrated circuits. 
     An example of a conventional electron beam (e-beam) apparatus for an inspection system is described in U.S. Pat. No. 5,578,821, issued to Meisberger et al (the Meisberger patent). The disclosure of the Meisberger patent is hereby incorporated by reference in its entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction of a multitude of integrated circuit dies for manufacture on a semiconductor wafer. 
         FIG. 2  is a schematic diagram illustrating elements of a multiple e-beam apparatus with multiple e-beam columns in accordance with an embodiment of the invention. 
         FIG. 3  is a schematic diagram illustrating a perpendicular orientation of a single row of e-beam columns with respect to a translation direction of a semiconductor wafer. 
         FIG. 4  is a flow chart of a method of multi-beam inspection utilizing a perpendicular orientation. 
         FIG. 5  is a flow chart of a method of multi-beam lithography utilizing a perpendicular orientation. 
         FIG. 6  is a schematic diagram illustrating a skew orientation of a row of e-beam columns with respect to a translation direction of a semiconductor wafer in accordance with an embodiment of the invention. 
         FIG. 7  is a schematic diagram illustrating a skew orientation of a translation direction of a semiconductor wafer with respect to a row of e-beam columns in accordance with an embodiment of the invention. 
         FIG. 8  is a flow chart of a method of multi-beam inspection utilizing a skew orientation in accordance with an embodiment of the invention. 
         FIG. 9  is a flow chart of a method of multi-beam lithography utilizing a skew orientation in accordance with an embodiment of the invention. 
         FIG. 10  is a schematic diagram illustrating a skew orientation of two rows of e-beam columns with respect to a translation direction of a semiconductor wafer in accordance with an embodiment of the invention. 
         FIG. 11  is a schematic diagram illustrating elements of a multiple e-beam apparatus with a row of e-beam columns in accordance with an alternate embodiment of the invention. 
     
    
    
     SUMMARY 
     One embodiment of the invention pertains to a multiple electron beam apparatus. Multiple columns are arranged in a row configured to generate multiple electron beams. A mechanism is included for translating a substrate so as to be impinged upon by the multiple electron beams. A direction of the substrate translation and a direction of the row of columns are at a skew angle. 
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic depiction of a multitude of integrated circuit dies for manufacture on a semiconductor wafer. The semiconductor wafer  102  typically comprises a silicon wafer. The wafer  102  may be, for example, two hundred millimeters (200 mm) or three hundred millimeters (300 mm) in diameter. On the surface of the wafer  102 , numerous integrated circuit dies  104  are manufactured thereon. The integrated circuits may comprise, for example, microprocessors, memories, digital logic, analog circuits, and other circuitry. 
       FIG. 2  is a schematic diagram illustrating elements of a multiple e-beam apparatus with multiple e-beam columns in accordance with an embodiment of the invention. The illustrated apparatus  200  includes four columns (a, b, c, d) which may scan four electron beams over a corresponding four areas ( 202   a ,  202   b ,  202   c ,  202   d ) of a specimen being examined. While four columns are shown in  FIG. 2  for purposes of ease of illustration, a multitude of such columns may be implemented, with the specific number depending on the system specifications. 
     In the embodiment illustrated, each column includes at least a source, a condensor lens system, a scan deflector, and an objective lens. The sources, one for each column, generate incident electron beams ( 204   a ,  204   b ,  204   c ,  204   d ). In one embodiment, each of the sources may comprise an electron source. The electron source may be implemented, for example, using a field emission electron gun and a condenser lens system. 
     The incident beams are controllably scanned by scan deflectors ( 206   a ,  206   b ,  206   c ). These scan deflectors may, for example, be electrostatic deflectors. A microcontroller system may be configured to control the deflectors so as to scan the e-beams in accordance with an inspection plan (for an inspection system) or in accordance with a writing pattern (for a lithography system). 
     The incident beams subsequently travel to objective lenses ( 208   a ,  208   b ,  208   c ,  208   d ). Each objective lens may comprise, for example, a configuration of electromagnetic pole pieces. Alternatively, one or more of the objective lenses may be electrostatic (rather than magnetic). The objective lenses focus the incident beams onto the specimen. 
     Due to impingement of the multiple incident beams onto the specimen, electrons are emitted from the surface of the specimen. The scattered electrons ( 210   a ,  210   b ,  210   c ,  201   d ) generated by the impingement are detected by detection systems. 
       FIG. 3  is a schematic diagram illustrating a perpendicular orientation  300  of a row  200  of e-beam columns with respect to a translation (scan) direction  306  of a semiconductor wafer  102 . The e-beam columns in the row  200  are arranged along a line in a direction  304  which is perpendicular to the scan direction  306  of the wafer  102 . 
     As shown in  FIG. 3 , the columns are spaced by a column spacing distance  310 , while the dies  104  of the wafer  102  are spaced by a die spacing distance  308 . In this example, the die spacing  308  is shorter than the column spacing  310 . In other words, there is a mismatch between the die spacing and the column spacing. 
     Because the column spacing  310  is not commensurate with the die spacing  308 , inefficiencies and complications are introduced into the system. In an inspection system, the “care areas” on each die according to the desired inspection plan are not efficiently scanned simultaneously by all columns or beams. In other words, some columns may be aligned with a “care area” while other columns may not be aligned with (i.e. may miss) the “care area”. In an e-beam writing system, different deflection control signals are sent to the various columns to accomplish the desired writing pattern. 
       FIG. 4  is a flow chart of a method  400  of multi-beam inspection utilizing a perpendicular orientation. In this method  400 , because the perpendicular angle between the scan direction  306  and the line of columns  304 , a different control signal is determined  402  for each particular beam so as to implement the desired die inspection plan. This is because of the mismatch between the die spacing  308  and the column spacing  310 . The mismatch means that different columns are at different locations relative to the dies  104  on the wafer  102 , so that different control signals are needed for the different columns. 
     Hence, when a wafer with dies is scanned (translated)  404  under the multiple beam inspector with such a perpendicular orientation, then the scanning of multiple beams is controlled  406  according to different control signals. In other words, the scanning for each beam is controlled  406  according to a particular control signal specific for that column. This introduces inefficiencies and complications into the inspection system. For example, inspection “care areas” are not efficiently scanned simultaneously by the multiple beams. 
       FIG. 5  is a flow chart of a method  500  of multi-beam lithography utilizing a perpendicular orientation. In this method  500 , because the perpendicular angle between the scan direction  306  and the line of columns  304 , a different control signal is determined  502  for each particular beam so as to achieve the desired die writing pattern. This is because of the mismatch between the die spacing  308  and the column spacing  310 . The mismatch means that different columns are at different locations relative to the dies  104  on the wafer  102 , so that different control signals are needed for the different columns. 
     Hence, when a wafer with dies is scanned (translated)  504  under the multiple beam e-beam lithography system with such a perpendicular orientation, then the scanning of the multiple beams is controlled according to the different control signals. In other words, the scanning for each beam is controlled  506  according to a particular control signal specific for that column. This introduces inefficiencies and complications into the e-beam lithography system. For example, the data path from a desired writing pattern to control signals for the columns becomes more complicated. 
       FIG. 6  is a schematic diagram illustrating a skew orientation  600  of a row  200  of e-beam columns with respect to a translation (scan) direction  606  of a semiconductor wafer  102  in accordance with an embodiment of the invention. The e-beam columns in the row  200  are arranged along a line in a direction  604  which is skew or non-perpendicular to the scan direction  606  of the wafer  102 . 
     As shown in  FIG. 6 , the columns are spaced by a column spacing distance  310 , while the dies  104  of the wafer  102  are spaced by a die spacing distance  308 . In this example, the die spacing  308  is shorter than the column spacing  310 . In other words, there is a mismatch between the die spacing and the column spacing. 
     However, because of the skew orientation, the projected column spacing  608  may be made to match the die spacing  308 . The skew angle  607  may be determined to be equal to ninety degrees plus the inverse cosine of the die spacing  308  divided by the column spacing  310 . In other words, consider that the die spacing  308  is d, the column spacing  310  is c, and the skew angle  607  is θ. θ=90°+cos −1 (d/c). 
     Because the projected column spacing  608  is commensurate with the die spacing  308 , efficiencies and simplifications are introduced into the system. In an inspection system, the “care areas” per die according to the desired inspection plan may be efficiently scanned simultaneously by the multiple columns or beams. In an e-beam writing system, substantially the same deflection control signals may be sent to multiple columns sent to accomplish the desired writing pattern per die. 
       FIG. 7  is a schematic diagram illustrating a skew orientation  700  of a translation (scan) direction  706  of a semiconductor wafer  102  with respect to a row  200  of e-beam columns in accordance with an alternate embodiment of the invention. The e-beam columns in the row  200  are arranged along a line in a direction  704  which is skew or non-perpendicular to the scan direction  706  of the wafer  102 . 
     As shown in  FIG. 7 , the columns are spaced by a column spacing distance  310 , while the dies  104  of the wafer  102  are spaced by a die spacing distance  308 . In this example, the die spacing  308  is shorter than the column spacing  310 . In other words, there is a mismatch between the die spacing and the column spacing. 
     However, because of the skew orientation, the projected column spacing  708  may be made to match the die spacing  308 . The skew or non-perpendicular angle  707  may be determined to be equal to ninety degrees plus the inverse cosine of the die spacing  308  divided by the column spacing  310 . In other words, consider that the die spacing  308  is d, the column spacing  310  is c, and the skew angle  707  is θ. θ=90°+cos −1 (d/c). 
     Because the projected column spacing  708  is commensurate with the die spacing  308 , efficiencies and simplifications are introduced into the system. In an inspection system, the “care areas” per die according to the desired inspection plan may be efficiently scanned simultaneously by the multiple columns or beams. In an e-beam writing system, substantially the same deflection control signals may be sent to multiple columns sent to accomplish the desired writing pattern per die. 
       FIG. 8  is a flow chart of a method  800  of multi-beam inspection utilizing a skew orientation in accordance with an embodiment of the invention. In this method  800 , because the skew angle  607  between the scan direction  606  and the line of columns  604 , a substantially the same control signal may be determined  802  for multiple beams so as to implement the desired die inspection plan. This is because of the projected column spacing  608  matches the die spacing  308 . The match means that multiple columns are at a same location relative to the dies  104  on the wafer  102 , so that substantially the same control signal may be sent to the multiple columns. 
     Hence, when a wafer with dies is scanned (translated)  804  under the multiple beam inspector with such a skew orientation, then the scanning of multiple beams may be controlled  806  according to substantially the same control signal. This introduces efficiencies into and simplifies the inspection system. For example, inspection “care areas” may be efficiently scanned simultaneously by the multiple beams. 
       FIG. 9  is a flow chart of a method  900  of multi-beam lithography utilizing a skew orientation in accordance with an embodiment of the invention. In this method  900 , because the skew angle  607  between the scan direction  606  and the line of columns  604 , substantially the same control signal may be determined  902  for multiple beams so as to achieve the desired die writing pattern. This is because of the match between the die spacing  608  and the projected column spacing  608 . The match means that multiple columns are at a same location relative to the dies  104  on the wafer  102 , so that substantially the same control signal may be used for the multiple columns. 
     Hence, when a wafer with dies is scanned (translated)  904  under the multiple beam e-beam lithography system with such a skew orientation, then the scanning of the multiple beams may controlled according to substantially the same control signal. This introduces efficiencies into and simplifies the e-beam lithography system. For example, the data path from a desired writing pattern to control signals for the columns becomes simplified. 
       FIG. 10  is a schematic diagram illustrating a skew orientation  1000  of two rows  1002  of e-beam columns with respect to a translation (scan) direction  1006  of a semiconductor wafer  102  in accordance with an embodiment of the invention. For this example, note that the size of the die  1001  is smaller than the die size in the previous examples. The e-beam columns in the rows  1002  are arranged along a direction  1004  which is skew or non-perpendicular to the scan direction  1006  of the wafer  102 . 
     As shown in  FIG. 10 , the columns are spaced by a column spacing distance  310 , while the dies  1001  of the wafer  102  are spaced by a die spacing distance  1008 . In this example, because of the skew orientation, the projected column spacing  1010  between a column in one row and a next column in the other row may be made to match the die spacing  1008 . 
       FIG. 11  is a schematic diagram illustrating elements of a multiple e-beam apparatus with multiple e-beam columns in accordance with an alternate embodiment of the invention. The illustrated apparatus  1100  includes three columns (a, b, c) and forms three multi-pixel e-beam spots ( 1102   a ,  1102   b ,  1102   c ) onto a specimen being examined. While three columns are shown in  FIG. 11  for purposes of ease of illustration, a multitude of such columns may be implemented, with the specific number depending on the system specifications. 
     In the embodiment illustrated, each column includes at least a source, a beam separator, and an objective lens. The sources, one for each column, generate incident multi-pixel beams ( 1104   a ,  1104   b ,  1104   c ). In one embodiment, each of the sources may comprise an electron source. The electron source may be implemented, for example, using a field emission electron gun and a condenser lens system. 
     The multi-pixel incident beams travel through beam separator devices ( 1106   a ,  1106   b ,  1106   c ). These beam separators separate the incident beams ( 1104   a ,  1104   b ,  1104   c ) from the scattered beams ( 1110   a ,  1110   b ,  1110   c ). Each beam separator may comprise, for instance, a magnetic beam separator that bends the incident beam to be directed along the optical axis to the normal of the surface to be inspected. Alternatively, other types of beam separators may be used, for example, those in a prism type configuration. 
     The incident beams subsequently travel from the separator devices to objective lenses ( 1108   a ,  1108   b ,  1108   c ). Each objective lens may comprise, for example, a configuration of electromagnetic pole pieces. Alternatively, one or more of the objective lenses may be electrostatic (rather than magnetic). The objective lenses focus the incident beams onto the two multiple-pixel areas ( 1102   a ,  1102   b ,  1102   c ) of the specimen. 
     In contrast to a typical scanning electron beam column where one single-pixel beam is scanned across an area, the columns in  FIG. 11  impinge multiple-pixel incident beams onto the specimen and detect scattered electrons from the multiple pixels. This is advantageous in that data may be obtained in parallel from the multiple pixels within each beam spot. Moreover, the use of a multitude of such multi-pixel beams (instead of just one multi-pixel beam) further increases the efficiency such that the throughput of an inspector may be further improved by approximately a factor of two. 
     Due to impingement of the multiple incident beams onto the multiple-pixel areas ( 1102   a ,  1102   b ,  1102   c ), electrons are emitted from the surface of these areas. In a low energy electron microscopy (LEEM) type embodiment, the incident electrons are decelerated between the objective lenses and the specimen to a relatively low energy of one hundred electron volts (eV) or less, prior to impingement onto the specimen. The low-energy electrons interact with and reflect from the surface of the specimen. The reflected electrons are considered to be the scattered electrons. The scattered electrons from the multi-pixel areas are then re-accelerated as they return to the objective lenses. 
     Subsequently, the scattered electron beams ( 1110   a ,  1110   b ,  1110   c ) travel from the objective lenses to the two beam separators. The beam separators redirect the scattered electron beams to corresponding multi-pixel detection systems. Each multi-pixel detection system may be implemented, for example, with a charged-coupled device (CCD) array or other type of detector array. 
     While the e-beam columns of  FIG. 2  comprise scanning electron beam columns, the e-beam columns of  FIG. 11  comprise projection electron beam columns. 
     Embodiments of the invention may apply for various scanning beam or probe systems in which it is desirable to either write or collect information on a fixed pattern. 
     Applicants believe that without such a skew arrangement to make the die spacing and projected column spacing commensurate with each other, a sample inspection with a multi-beam system may not be much faster than a sample inspection with a single beam system. 
     An alternative of changing the column spacing mechanically may be done, but it may be more difficult and not as reliable. Instead, the skew angle of the present invention may be accomplished by rotating a column plate (a plate on which the multiple columns are on) so as to move the columns as a single unit. 
     The above-described diagrams are not necessarily to scale and are intended be illustrative and not limiting to a particular implementation. The above-described invention may be used in an automatic inspection or review system and applied to the inspection or review of semiconductor wafers and similar substrates in a production environment. In an alternate embodiment, the above-described invention may also be utilized for electron beam lithography applications. 
     In the above description, numerous specific details are given to provide a thorough understanding of embodiments of the invention. However, the above description of illustrated embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific details, or with other methods, components, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the invention. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
     These modifications may be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.