Patent Publication Number: US-2013236283-A1

Title: Method and apparatus for wafer alignment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Korean Patent Application No. 10-2012-0023263 filed on Mar. 7, 2012, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a method and apparatus for wafer alignment. 
     DISCUSSION OF THE RELATED ART 
     During the manufacturing of a semiconductor, the alignment of wafers should be performed. 
     For example, a mechanical alignment method is widely used. In the mechanical alignment method, three exterior points of two wafers to be aligned are appropriately determined according to shapes thereof, and the wafers are moved to be aligned with each other via physical contact on the exterior points. However, when wafers are aligned with each other by using this method, there may be a limit in increasing alignment accuracy due to issues of processes and equipment, and difficulties may arise with wafer alignment due to different wafer shapes. 
     As another method, an alignment key is formed on two wafers to be aligned and the wafers are aligned with each other by using the alignment key. However, this method may require an additional process of forming an alignment key on two wafers. Further, as equipment using an alignment key is relatively expensive, it may be difficult to realize mass production through the use thereof. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention provide a method and apparatus for wafer alignment, able to increase alignment accuracy via simplified processes. 
     According to an exemplary embodiment of the present invention, there is provided a wafer aligning apparatus including: first and second wafer holders supporting first and second wafers, respectively, a holder moving unit configured to move at least one of the first and second wafer holders such that the first and second wafers are pre-aligned and face each other, one or more observing units arranged in a horizontal direction with respect to the pre-aligned first and second wafers and configured to observe edge portions of the first and second wafers in a state in which the first and second wafers are pre-aligned with each other by the holder moving unit and a controlling unit configured to control the holder moving unit to realign the first and second wafers when the edge portions of the first and second wafers are outside of a desired alignment state based on information observed by the one or more observing units. 
     The one or more observing units may include microscopes. 
     The one or more observing units may include a plurality of observing units, and the plurality of observing units are configured to observe the edge portions in different positions. 
     The observing units may be provided to be symmetrical with respect to the pre-aligned first and second wafers. 
     The one or more observing units may be configured to observe observation points on tangents between the one or more observing units and outlines of the pre-aligned first and second wafers. 
     The holder moving unit controlled by the controlling unit may be configured to move the first and second wafer holders in an XYθ direction. 
     The first and second wafers may have the same shape and area, and the desired alignment state may be a state in which cross sections of the edge portions of the upper and lower wafers are positioned on a single straight line. 
     The first and second wafers may be different in terms of at least one of shape and area thereof, and the desired alignment state may be a state in which cross sections of the edge portions of the upper and lower wafers are equally deviated at the edge portions of the upper and lower wafers observed via the plurality of observing units. 
     According to an exemplary embodiment of the present invention, there is provided a method of wafer alignment, including: arranging first and second wafers on first and second wafer holders, pre-aligning the first and second wafers with each other to face each other by moving at least one of the first and second wafer holders, observing edge portions of the first and second wafers by using one or more observing units arranged in a horizontal direction with respect to the pre-aligned first and second wafers and realigning the first and second wafers with each other when the edge portions of the first and second wafers observed by the one or more observing units are outside of a desired alignment state. 
     The one or more observing units may include microscopes. 
     The one or more observing units may include a plurality of observing units, and the plurality of observing units may be configured to observe the edge portions in different positions. 
     The one or more observing units may be provided to be symmetrical with respect to the pre-aligned first and second wafers. 
     The one or more observing units may be configured to observe observation points on tangents between the one or more observing units and outlines of the pre-aligned first and second wafers. 
     The realigning of the first and second wafers may include moving the first and second wafer holders in an XYθ direction. 
     The first and second wafers may have the same shape and area, and the desired alignment state may be a state in which cross sections of the edge portions of the upper and lower wafers are positioned on a single straight line. 
     The first and second wafers may be different in teens of at least one of shape and area thereof, and the desired alignment state may be a state in which cross sections of the edge portions of the upper and lower wafers are equally deviated at the edge portions of the upper and lower wafers observed via the plurality of observing units. 
     In an exemplary embodiment of the present invention, a wafer aligning apparatus is provided. The wafer aligning apparatus includes an upper wafer holder and a lower wafer holder configured to support an upper wafer and a lower wafer, respectively, by a force of vacuum suction, a holder moving unit configured to move at least one of the upper wafer holder and the lower wafer holder in at least one of an upward and downward direction, respectively such that the upper and lower wafers are pre-aligned and face each other, and a plurality of microscopes accommodated in a corresponding one of a plurality of microscope supports and movable therein. The microscopes are arranged in a horizontal direction with respect to the pre-aligned upper and lower wafers so as to be symmetrical with respect to the upper and lower wafers and configured to observe: edge portions of the upper and lower wafers in a state in which the upper and lower wafers are pre-aligned with each other by the holder moving unit. 
     The wafer aligning apparatus further includes a controlling unit operatively connected to the microscopes and configured to receive and read observation data from the microscopes and to control the holding moving unit to move at least one of the upper wafer holder and the lower wafer holder in an XYθ direction based upon the transmitted observation data to thereby realign the upper and lower wafers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention can be understood in further detail from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a wafer aligning apparatus according to an embodiment of the present invention; 
         FIG. 2  is a plan view showing a method of observing upper and lower wafers, which are pre-aligned with each other, via microscopes of the wafer aligning apparatus of  FIG. 1 ; 
         FIG. 3  shows edge portions of the upper and lower wafers, which are observed by the microscopes of the wafer aligning apparatus of  FIG. 1 ; and 
         FIG. 4  shows edge portions of upper and lower wafers, which are observed by microscopes of a wafer aligning apparatus according to an embodiment of the present invention, when the upper and lower wafers are different in terms of shape or area thereof. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     In the drawings, the shapes and sizes of elements may be exaggerated for clarity and the same reference numerals will be used throughout to designate the same or like elements. 
     As used herein, the singular forms, “a”, “an”, and “the” are intended to include plural forms as well, unless the context clearly indicates otherwise. 
       FIG. 1  is a schematic diagram of a wafer aligning apparatus  100  according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the wafer aligning apparatus  100  according to the present embodiment includes, for example, an upper wafer holder  10  and a lower wafer holder  20 , which respectively support upper and lower wafers W 1  and W 2 , a holder moving unit  30 , one or more observing units including a first microscope support  40   a , a second microscope support  40   b  and a microscope set including a first microscope  50   a  and a second microscope  50   b , and a controlling unit  60 . 
     The lower wafer W 2  is positioned on the lower wafer holder  20  and the upper wafer W 1  is held by the upper wafer holder  10  by, for example, the force of vacuum suction. The upper wafer holder  10  may be connected to the holder moving unit  30  so as to be moved in, for example, an XYθ direction according to an operation of the holder moving unit  30 . 
     The first microscope support  40   a  and the second microscope support  40   b  may accommodate the first microscope  50   a  and the second microscope  50   b  and move the first microscope  50   a  and the second microscope  50   b , respectively. The first microscope  50   a  and the second microscope  50   b  are arranged in, for example, a horizontal direction with respect to the pre-aligned upper and lower wafers W 1  and W 2  so as to be symmetrical with respect to the upper and lower wafers W 1  and W 2  and are used to observe alignment states of the upper and lower wafers W 1  and W 2  in the wafer aligning apparatus  100 . 
     For example, throughout this specification, pre-alignment may refer to a state in which wafers are previously aligned with each other by using a common wafer moving method to prepare subsequent processes such as adherence or deposition and may include a state in which two wafers are spaced apart from each other in a perpendicular direction and do not completely contact each other so as to be easily realigned with each other to have a desired alignment state. 
     The controlling unit  60  aligns the upper and lower wafers W 1  and W 2  with each other to have a desired alignment state by recognizing an alignment state of the upper and lower wafers W 1  and W 2 , which are observed by the microscope set, and then moving the upper wafer holder  10  connected to the holder moving unit  30  in the XYθ direction. 
     According to the present embodiment, the wafer aligning apparatus  100  moves the upper wafer holder  10  in, for example, the XYθ direction according to an operation of the holder moving unit  30 . Alternatively, the wafer aligning apparatus  100  may, for example, pre-align the upper and lower wafers W 1  and W 2  with each other by moving at least one of the upper wafer holder  10  and the lower wafer holder  20 . 
     According to an embodiment of the present invention, in a method of wafer alignment by using the wafer aligning apparatus  100 , the upper wafer W 1  is held by the upper wafer holder  10  and then the lower wafer W 2  is seated on the lower wafer holder  20 . Then, the upper wafer holder  10  attached to the holder moving unit  30  may be moved in a downward direction to pre-align the upper wafer W 1  and the lower wafer W 2  with each other. 
     Then, the microscope set accommodated in first and second microscope supports  40   a  and  40   b  may be positioned adjacent to the pre-aligned upper and lower wafers W 1  and W 2  in, for example, a horizontal direction with respect to the upper and lower wafers W 1  and W 2  and may observe edge portions of the upper and lower wafers W 1  and W 2 . Then, observation data is transmitted to the controlling unit  60 . The controlling unit  60  realigns the upper and lower wafers W 1  and W 2  with each other by, for example, reading the transmitted data and moving the upper wafer holder  10  connected to the holder moving unit  30  in the XYθ direction. In this case, the realigned upper and lower wafers W 1  and W 2  are re-observed by the microscope set. Observation data is transmitted to the controlling unit  60 . Then, the controlling unit  60  may realign the upper and lower wafers W 1  and W 2  with each other by, for example, reading the transmitted data and moving the holder moving unit  30  in the XYθ direction. Then, the upper wafer holder  10  is moved in a downward direction such that the upper and lower wafers W 1  and W 2  may contact each other. Subsequent processes such as, for example, adherence or deposition are performed on the aligned upper and lower wafers W 1  and W 2 . 
     According to an embodiment of the present invention, in the method of wafer alignment, the upper wafer holder  10  is moved in, for example, a downward direction toward the lower wafer holder  20  by the holder moving unit  30 . Alternatively, the upper and lower wafers W 1  and W 2  may, for example, be pre-aligned with each other by moving the lower wafer holder  20  in an upward direction toward the upper wafer holder  10  or moving both the upper wafer holder  10  and the lower wafer holder  20  by the holder moving unit  30 . 
     According to the present embodiment, the wafer aligning apparatus  100  realigns the upper and lower wafers W 1  and W 2  with each other by, for example, moving the upper wafer holder  10  in the XYθ direction according to an operation of the holder moving unit  30 . Alternatively, the upper and lower wafers W 1  and W 2  may, for example, be realigned with each other by moving at least one of the upper wafer holder  10  and the lower wafer holder  20 . 
       FIG. 2  is a plan view showing a method of observing the upper and lower wafers W 1  and W 2 , which are pre-aligned with each other, via the microscopes of the wafer aligning apparatus of  FIG. 1 . 
     The microscope set of the wafer aligning apparatus  100  is used to observe edge portions of the upper and lower wafers W 1  and W 2  that are pre-aligned with each other. The edge portions of the upper and lower wafers W 1  and W 2  are observed via the first microscope  50   a  at observation points P 1  and P 2  on tangents between the first microscope  50   a  and the pre-aligned upper and lower wafers W 1  and W 2  and the edge portions of the upper and lower wafers W 1  and W 2  are observed via the second microscope  50   b  at observation points P 3  and P 4  on tangents between the second microscope  50   b  and the pre-aligned upper and lower wafers W 1  and W 2 , such that the alignment state of the upper and lower wafers W 1  and W 2  is determined. 
     When, for example, at least three of the observation points P 1 , P 2 , P 3 , and P 4  are aligned with each other, it may be determined whether the upper and lower wafers W 1  and W 2  are aligned with each other or not, so only the three points may be observed. 
       FIG. 3  shows the edge portions of the upper and lower wafers W 1  and W 2 , which are observed by the microscopes of the wafer aligning apparatus of  FIG. 1 . 
     As shown in  FIG. 3 , when cross sections of the edge portions of the upper and lower wafers W 1  and W 2 , observed at three of the four observation points P 1 , P 2 , P 3 , and P 4 , are positioned on a single straight line (indicated by a dotted line), it may be determined that the upper and lower wafers W 1  and W 2  are aligned with each other. 
       FIG. 4  shows the edge portions of the upper and lower wafers W 1  and W 2 , which are observed by the microscopes of the Wafer aligning apparatus according to an embodiment of the present invention, when the upper and lower wafers W 1  and W 2  are different in terms of at least one of shape and area thereof. 
     As shown in  FIG. 4 , in a case in which the upper and lower wafers W 1  and W 2  are different in terms of at least one of shape and area thereof, when a first cross section A and a second cross section B of the upper and lower wafers W 1  and W 2 , which are obtained by observing the upper and lower wafers W 1  and W 2  at different observation points, are the same, that is, when the upper and lower wafers W 1  and W 2  are equally deviated by an amount equal to ‘d’ in both the first and second cross sections, it may be determined that the upper and lower wafers W 1  and W 2  are aligned with each other. 
     In addition, as shown in  FIGS. 3 and 4 , when the cross sections of the upper and lower wafers W 1  and W 2 , which are observed at three of the four observation points P 1 , P 2 , P 3 , and P 4 , correspond to each other, it may be determined that the upper and lower wafers W 1  and W 2  are aligned with each other. 
     Although two microscopes are used in the present embodiment of the present invention, it noted that exemplary embodiments of the present invention are not limited thereto. For example, alternatively, in an exemplary embodiment, a plurality of microscopes which is greater in number than two microscopes for wafer alignment may be used if necessary. 
     When the wafer aligning apparatus according to the present embodiment of the present invention is used to align wafers with each other, wafers having various shapes may be accurately aligned with each other and the formation of an alignment key is not required to thereby reduce manufacturing costs. 
     As set forth above, according to embodiments of the present invention, a method and apparatus for wafer alignment that can increase alignment accuracy via simplified processes may be provided. 
     According to embodiments of the present invention, the wafers may be aligned with each other, even in the case that the shapes of wafers are different. 
     Having described exemplary embodiments of the present invention, it is further noted that it is readily apparent to those of ordinary skill in the art that various modifications may be made without departing from the spirit and scope of the invention which is defined by the metes and bounds of the appended claims.