Abstract:
The invention provides a manufacturing method of a glass-sealed package, and a glass substrate used for the glass-sealed package, whereby an amount of warp in a glass substrate is reduced to improve processing accuracy in a subsequent step in which the glass substrate is combined (such as by anodic bonding) with another glass substrate provided with a thin film. The front side of the glass substrate includes a region where the cavities used to house electronic devices such as semiconductor IC chips and crystal blanks are not formed. The region devoid of the cavities is provided in the formed of a frame to reduce an amount of warp in the glass substrate.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2009-039334 filed on Feb. 23, 2009, the entire content of which is hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a manufacturing method of a glass-sealed package used for electronic devices such as semiconductor devices and crystal vibrators, and to a glass substrate used for such glass-sealed packages. 
       BACKGROUND ART 
       [0003]    A manufacturing method of a glass substrate used for semiconductor devices such as image sensors is known as described in JP-A-2006-282480 and as illustrated in  FIG. 5 . 
         [0004]    This publication describes providing grooves  502  on a glass substrate  501  so that the amount of warp in a thin-film attached glass substrate before being cut into individual pieces by methods such as dicing is reduced to substantially the same level as that in a thin-film attached glass substrate obtained when the glass substrate  501  having a thin film  503  is cut at the positions of the grooves  502 . In this way, the glass substrate and a semiconductor wafer having a plurality of semiconductor elements can be combined with each other with improved processing accuracy for these elements. 
       SUMMARY OF THE INVENTION 
       [0005]    However, the substrate warps, convex on the grooved side, when hollow spaces such as the grooves are formed in large numbers in the glass substrate without any space. When the amount of warp in the substrate is excessive, the registration accuracy suffers in the alignment performed in the step of combining the substrate with another substrate (such as by anodic bonding). In other words, processing accuracy suffers. This may lead to problems such as a failure to combine the substrates. 
         [0006]      FIGS. 3A and 3B  show schematic illustrations of a substrate provided with large numbers of grooves, or cavities as they are called, in which semiconductor devices such as semiconductor IC chips and crystal blanks are contained. 
         [0007]      FIG. 3A  illustrates a glass substrate. A plurality of cavities  302  for housing electronic devices is formed on a flat circular wafer, a glass substrate portion  301 . The glass substrate portion  301  also includes a cutoff portion, an orientation flat  303 , at an end. The cutting line A-A cuts across the cavities  302  formed on the glass substrate portion  301 , parallel to the straight cut of the orientation flat  303 . The cutting line B-B cuts across the cavities  302  formed on the glass substrate portion  301 , perpendicular to the straight cut of the orientation flat  303 .  FIG. 3B  represents the A-A cross section of the glass substrate portion  301 , and the B-B cross section of the glass substrate portion  301 . 
         [0008]    It was found through experiment that the substrate warps, convex on the hollow space side, when grooves such as the cavities  302  are formed over the surface of the glass substrate portion  301  without any space, as illustrated in the A-A cross section and B-B cross section of  FIG. 3B . 
         [0009]    It is an object of the present invention to reduce an amount of warp in the substrate and to thereby improve the stability and accuracy of combining the substrate with another substrate. 
         [0010]    In order to solve the foregoing problems, the present invention reduces an amount of warp in the substrate by providing a street portion, a region devoid of cavities, extending in a straight line from one end to the other end of the substrate in the form of a frame (a portion where the array pitch is wider than in other portions including the cavities), instead of providing the cavities over the whole surface of the glass substrate portion. 
         [0011]    By the provision of the street portion, the registration accuracy can be stably maintained in the alignment performed in the mating step of combining the substrate with another substrate (such as by anodic bonding). That is, high accuracy and high stability can be realized at the same time. 
         [0012]    As described above, an amount of warp in the glass substrate can be reduced with a manufacturing method of a glass-sealed package of the prevent invention, and with a glass substrate of the present invention. It is therefore possible to realize high registration accuracy and high stability in, for example, the alignment performed in the mating step, thus producing a high-quality glass-sealed package. 
         [0013]    The number of street portions can be optimized according to the size of the substrate so as to minimize a loss in the number of products. In this way, the cost of the product can be minimized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIGS. 1A and 1B  are schematic diagrams of a glass substrate according to a First Embodiment of the present invention. 
           [0015]      FIGS. 2A and 2B  are schematic diagrams of a glass substrate according to a Second Embodiment of the present invention. 
           [0016]      FIGS. 3A and 3B  are schematic diagrams of a glass substrate not provided with a frame in a region of cavities. 
           [0017]      FIG. 4  is a flow chart representing a flow of a manufacture of a piezoelectric vibrator of an embodiment of the present invention. 
           [0018]      FIG. 5  is a cross sectional view of a conventional glass substrate. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Two embodiments of the present invention are described below. These embodiments relate to a glass-sealed package and a glass substrate used for, for example, crystal vibrators (not shown). 
       First Embodiment 
       [0020]      FIGS. 1A and 1B  are diagrams representing a First Embodiment of a glass substrate of the present invention. 
         [0021]    As illustrated in  FIG. 1A , a glass substrate of the present invention includes a glass substrate portion  101 , cavities  104  in which elements such as semiconductor chips and crystal blanks are housed by being mounted, and an orientation flat  105 , which is a cutoff portion formed at one end of the glass substrate portion  101 . To reduce warping of the substrate, street portions  102  and  103  are formed in portions of the glass substrate portion  101  where the cavities  104  are formed. The cavities  104  are not formed in the street portions  102  and  103 . The street portion  102  is perpendicular to the orientation flat  105 , and passes the central portion of the glass substrate portion  101 . The street portion  103  is parallel to the orientation flat  105 , and passes the central portion of the glass substrate portion  101 . The street portions  102  and  103  are formed in a straight line from one end to the other end of the glass substrate portion  101 . The cutting lines A-A and B-B drawn parallel and perpendicular to the orientation flat  105  correspond to the A-A cross section and B-B cross section, respectively, of  FIG. 1B  described below. 
         [0022]      FIG. 1B  shows the A-A cross section and B-B cross section. The A-A cross section and B-B cross section show the cavities  104  formed on the glass substrate portion  101 . The A-A cross section also shows the street portion  102  where the cavities  104  are not formed. The B-B cross section also shows the street portion  103  where the cavities  104  are not formed. 
         [0023]    A manufacturing method of the glass substrate  101  will be described later in detail with reference to the flow chart of  FIG. 4 . 
         [0024]    In the present invention, the street portions  102  and  103  provided as shown in the First Embodiment serve as frames (framework) to reduce warping of the glass substrate  101 . 
         [0025]    The following describes a method for manufacturing a piezoelectric vibrator as a glass-sealed package in which a piezoelectric vibrating piece is housed in the cavities as an electronic device, using the glass substrate  101  of the First Embodiment. 
         [0026]    For convenience, the glass substrate  101  provided with the cavities  104  will be referred to as a lid substrate, and the glass substrate without the cavities as a base substrate. The glass-sealed package of an embodiment of the present invention is realized by combining the lid substrate and the base substrate with an object placed in between. 
         [0027]    The following describes a method for manufacturing a plurality of piezoelectric vibrators at once using the base substrate and the lid substrate, with reference to the flow chart of  FIG. 4 . 
         [0028]    First, an electronic device (piezoelectric vibrator in this embodiment) is fabricated in an electronic device fabrication step (S 10 ). Specifically, a crystal of a Lumbered quartz bar stone is sliced at a predetermined angle to provide a wafer of a constant thickness. The wafer is then coarsely processed by lapping, and optionally mirror finished such as by polishing to obtain a constant thickness. After appropriately processing the wafer by treatment such as washing, a metal film is deposited and patterned on the wafer by techniques such as photolithography and metal masking to form excitation electrodes on the piezoelectric vibrating piece, and inner electrodes, used to mount the piezoelectric vibrating piece, on the other glass substrate provided with no cavities. This completes the fabrication of a plurality of piezoelectric vibrating pieces. 
         [0029]    Then, a lid substrate fabrication step is performed for the glass substrate  101  to make it usable for anodic bonding (S 20 ). First, the glass substrate  101  made of soda-lime glass is polished to a predetermined thickness, and after washing, a disk-shaped glass substrate  101  is formed from which the work-affected layer on the outermost surface has been removed by etching or the like (S 21 ). This is followed by a depression forming step in which a plurality of cavities  104  is formed by methods such as etching and embossing in the row and column directions on the bonding face of the glass substrate  101  (S 22 ). Note that the rigidity of the glass substrate  101  with the cavities  104  is provided by the street portions  102  and  103  having no cavities  104  and formed in a straight line from one end to the other end of the lid substrate. The street portion  102  or the street portion  103  are formed perpendicular or parallel to the orientation flat  105 , respectively. The street portions  102  and  103  are defined by an area of a straight line devoid of the cavities  104 . 
         [0030]    Concurrently with, or before or after this step, a base substrate fabrication step is performed in which the other glass substrate—the base substrate not provided with the cavities  104  and used to mount the piezoelectric vibrating piece—is fabricated to make it usable for anodic bonding (S 30 ). First, soda-lime glass is polished to a predetermined thickness, and after washing, a disk-shaped base substrate wafer is formed from which the work-affected layer on the outermost surface has been removed by etching or the like (S 31 ). This is followed by a through electrodes forming step in which pairs of through electrodes used to connect the piezoelectric vibrating piece to external terminal electrodes are formed in the base substrate wafer (S 32 ). As with the glass substrate  101 , the rigidity of the substrate is provided by the street portions  102  and  103 , a region devoid of the through electrodes, provided in the form of streets crossing at the center of the glass substrate for the base substrate wafer. 
         [0031]    Next, conductive material is patterned on the upper surface of the base substrate wafer to form a bonding film (bonding film forming step; S 33 ) and the inner electrodes electrically connected to the through electrodes, respectively (inner electrodes forming step; S 34 ). 
         [0032]    The through electrodes are substantially flush with the upper surface of the base substrate wafer, as described above. Accordingly, the inner electrodes patterned on the upper surface of the base substrate wafer are closely in contact with the through electrodes without any gap or space. This ensures conductivity between one of the inner electrodes and one of the through electrodes, and between the other inner electrode and the other through electrode. This completes the second wafer fabrication step. 
         [0033]    In  FIG. 4 , the inner electrodes forming step (S 34 ) is performed after the bonding film forming step (S 33 ); however, the bonding film forming step (S 33 ) may be performed after the inner electrodes forming step (S 34 ), or these steps may be performed simultaneously. The same effect can be obtained regardless of the order of the steps. Accordingly, the order of these steps may be changed appropriately, as needed. 
         [0034]    Then, the piezoelectric vibrating pieces fabricated as above are bonded to the upper surface of the base substrate wafer via their respective inner electrodes (mount step; S 40 ). First, bumps are formed on the inner electrodes, using gold wires. 
         [0035]    Then, with the basal portion of the piezoelectric vibrating piece placed on the bumps, the piezoelectric vibrating piece is pressed against the bumps while heating the bumps to a predetermined temperature. In this way, the bumps provide mechanical support for the piezoelectric vibrating piece, and the electrodes formed on the piezoelectric vibrating piece are electrically connected to the inner electrodes. Further, the bump bonding of one of the electrodes of the piezoelectric vibrating piece on one of the bumps, and the bump bonding of the other electrode of the piezoelectric vibrating piece on the other bump supports the piezoelectric vibrator parallel to the base substrate. As a result, the piezoelectric vibrating piece is supported by being suspended above the base substrate wafer. Here, the pair of excitation electrodes of the piezoelectric vibrating piece conducts to the pair of through electrodes, respectively. 
         [0036]    After the piezoelectric vibrating piece is mounted, a mating step is performed in which the lid substrate is mated with the base substrate wafer (S 50 ). Specifically, the wafers are aligned in position using reference marks or the like (not shown) as a marker. As a result, the piezoelectric vibrating piece mounted as above is housed in the cavity  104  surrounded by the wafers. After the mating step, the mated two wafers are placed in an anodic bonding machine to perform a bonding step in which the two wafers are anodically bonded together under application of a predetermined voltage in an atmosphere of a predetermined temperature in a vacuum (S 60 ). 
         [0037]    In the anodic bonding, a predetermined voltage is applied between the bonding film and the glass substrate. This causes an electrochemical reaction at the interface between the bonding film and the glass substrate, anodically bonding the two with tight adhesion. 
         [0038]    Next, a cutting step is performed in which the wafer unit bonded as above is cut into individual piezoelectric vibrators (S 80 ). As a result, a plurality of bilayer, surface-mounted piezoelectric vibrators is manufactured at once, each sealing the piezoelectric vibrating piece in the cavity  104  formed between the anodically bonded base substrate and lid substrate. 
         [0039]    This is followed by a testing step to check for defects (S 90 ). Specifically, measurement is made to check properties of the piezoelectric vibrating piece, such as resonant frequency, resonant resistance, and drive level characteristics (excitation power dependence of resonant frequency and resonant resistance). Other properties, such as insulation resistance characteristics are also checked. The piezoelectric vibrator is then subjected to an appearance test to check the dimensions, quality, and other conditions of the product. The manufacture of the piezoelectric vibrator is finished upon completion of the checking. 
         [0040]    The formation of the grooves  502  to reduce warping of the substrate has been proposed, as described in an embodiment of the foregoing related art JP-A-2006-282480 and as illustrated in  FIG. 5 . However, the substrate warps, convex on the cavity  302  side, when such grooves are formed over the whole surface of the glass substrate as illustrated in  FIGS. 3A and 3B . The warping of the substrate becomes even worse when the surface is polished in the polishing step. 
         [0041]    The street portions  102  and  103  provided as illustrated in the drawings of the First Embodiment of the present invention serve as frames (framework) to reduce warping of the glass substrate. 
       Second Embodiment 
       [0042]    The Second Embodiment is described below with reference to  FIGS. 2A and 2B . 
         [0043]    As illustrated in  FIG. 2A , a glass substrate of the present invention includes a glass substrate portion  201 , cavities  204  in which elements such as semiconductor chips and crystal blanks are housed by being mounted, and an orientation flat  205 , which is a cutoff portion formed at one end of the glass substrate portion  201 . To reduce warping of the substrate, street portions  202  and  203  are formed to partially replace the region where the cavities  204  are formed. The cavities  204  are not formed in the street portions  202  and  203 . The street portions  202  are provided in a plurality, perpendicular to the orientation flat  205  and separating the cavities  204 . The street portions  203  are provided in a plurality, parallel to the orientation flat  205  and separating the cavities  204 . The street portions  202  and  203  are formed in a straight line from one end to the other end of the glass substrate portion  201 . The cutting lines C-C and D-D drawn parallel and perpendicular to the orientation flat  205  correspond to the C-C cross section and D-D cross section, respectively, of  FIG. 2B  described below. 
         [0044]      FIG. 2B  shows the C-C cross section and D-D cross section. The C-C cross section and D-D cross section show the cavities  204  formed on the glass substrate portion  201 . The C-C cross section also shows the street portions  202  where the cavities  204  are not formed. The D-D cross section also shows the street portions  203  where the cavities  204  are not formed. 
         [0045]    A way to reduce the cost is to increase the number of chips that can be obtained from one substrate. This is achieved by increasing the size of the glass substrate. For such large substrates, single street portions such as the street portions  102  and  103  provided perpendicular and parallel to the orientation flat  105  as in the First Embodiment are not sufficient to reduce the warping of the substrate. 
         [0046]    The warp in the substrate can then be reduced by increasing the number of street portions as in the street portions  203  and  204  shown in  FIGS. 2A and 2B . However, in this case, the number of cavities  204  becomes smaller. In other words, the number of chips per substrate is reduced. Thus, the number of street portions  203  and  204  is optimized taking into consideration the cost determined by the size of the glass substrate and the number of chips per substrate. 
         [0047]    With the street portions  202  and  203  that form a grid, warping of the substrate can be reduced even for large glass substrates. 
         [0048]    The subsequent steps, including the polishing step, are performed as in the First Embodiment. 
         [0049]    The manufacturing method of a plurality of piezoelectric vibrators is also in accordance with the flow chart described in the First Embodiment with reference to  FIG. 4 . 
         [0050]    It should be noted that the present invention is not limited to the foregoing First and Second Embodiments. The circular substrate with an orientation flat may be rectangular or polygonal. Further, the base substrate and the lid substrate may be combined using a technique that enables combining of a glass lid substrate with a conductive substrate, using a conductive substrate for the base substrate. 
         [0051]    Further, the foregoing described the cavities  104  formed only in the lid substrate; however, the cavities  104  may be formed only in the base substrate, or in both of the lid substrate and the base substrate. 
         [0052]    The width of the street portions  102 ,  103 ,  202 , and  203  is not necessarily required to match the width of one cavity, and can be increased or decreased under different conditions. When forming a plurality of street portions, the width of each street portion may be varied. 
         [0053]    For example, though not illustrated, the street portion that is wide at the central portion of the glass substrate and that becomes narrower away from the central portion is also intended to be within the scope of the present invention. 
         [0054]    A glass substrate of the present invention is suitable as the member used to mount and package electronic devices such as semiconductor IC chips, crystal blanks, and sensor elements.