Abstract:
Provided are an anodic bonding structure, a fabricating method thereof, and a method of manufacturing an optical scanner using the same. Provided anodic bonding structure having a substrate and a glass substrate arranged above the substrate, includes at least one dielectric and at least one metal layer deposited between the substrate and the glass substrate, with a dielectric arranged uppermost, wherein the uppermost dielectric and the glass substrate are anodic bonded. Provided method of fabricating an anodic bonding structure having a substrate and a glass substrate arranged above the substrate, includes an act of depositing at least one dielectric and at least one metal layer between the substrate and the glass substrate, with dielectric arranged uppermost, and an act of anodic bonding the uppermost dielectric with the glass substrate. In the provided structure of depositing the metal layer and the dielectric between the substrate and the glass substrate, the dielectric and the glass substrate or the dielectric and the metal layer are anodic bonded so that a stable performance is attained to manufacture various micro-electromechanical systems (MEMS) devices.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application claims the priority of Korean Patent Application No. 2002-10469, filed Feb. 27, 2002 in the Korean Intellectual Property Office, which is incorporated herein in its entirety by reference.  
         [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an anodic bonding structure, a fabricating method thereof, and a method of manufacturing an optical scanner using the same, and more particularly, to an anodic bonding structure of a dielectric and a glass substrate or a dielectric and a metal layer, a fabricating method thereof, and a method of manufacturing an optical scanner using the same.  
         [0004]     2. Description of the Related Art  
         [0005]     Anodic bonding is a technique of bonding a silicon substrate widely used in the fabrication of a micro sensor device and a glass substrate having a thermal expansion coefficient similar to that of a silicon substrate. Pyrex glass, i.e., Corning glass 7740, generally used in an anodic bonding process includes predetermined amounts of sodium (Na) and potassium (K) so that when the Pyrex glass is heated at a temperature of over 200° C., elements are charged and easily moved by a voltage. When a silicon substrate and a glass substrate are aligned and a voltage of over 600 V is applied to the substrates, movable charges move rapidly. Thus, strong dielectric charges occur on the interfaces of the silicon substrate and the glass substrate to bond the silicon substrate with the glass substrate. A plurality of micro-electromechanical systems (MEMS) processes use an anodic bonding method that realizes a stable silicon structure.  
         [0006]      FIG. 1  is a sectional view of a conventional anodic bonding structure. A conventional anodic bonding structure is formed of a substrate  13  placed on a base plate  11  and a glass substrate  15  installed above the substrate  13 . When the structure is heated at the above-described temperature, and a cathode and an anode are connected to an upper portion of the glass substrate  15  and a lower portion of the base plate  11 , respectively, to apply the above-described voltage, charged ions move between the substrate  13  and the glass substrate  15  to perform a strong anodic bonding.  
         [0007]     An anodic bonding process may be used in a method of manufacturing an optical scanner. In a conventional method of manufacturing an optical scanner, only thin silicon substrates are used, thereby an automation process is difficult. Also, a torsion bar is driven in an unstable manner and is easily broken, and the yield is lowered. Although a silicon substrate and a glass substrates are bonded to obtain a stable device, it is impossible to obtain the perfect torsion bar. Therefore, a silicon on insulator (SOI) substrate has been used to stably realize a bonding structure; however, an electrical isolation problem within the SOI substrate occurs.  
       SUMMARY OF THE INVENTION  
       [0008]     To solve the above-described problems, it is an objective of the present invention to provide an anodic bonding structure of a dielectric and a glass substrate or a dielectric and a metal layer, and an optical scanner stably operated by using the anodic bonding structure to electrically connect the upper and lower surfaces of a silicon on insulator (SOI) substrate.  
         [0009]     To accomplish the objective of the present invention, an anodic bonding structure including a substrate and a glass substrate arranged above the substrate, includes at least one dielectric and at least one metal layer deposited between the substrate and the glass substrate, with a dielectric arranged uppermost, wherein the uppermost dielectric and the glass substrate are anodic bonded.  
         [0010]     Here, it is preferable that metal layers and dielectrics are alternately arranged between the substrate and the glass substrate, wherein the uppermost dielectric anodic bonds with the glass substrate.  
         [0011]     It is preferable that at least one metal layer includes a first metal layer and a second metal layer, and at least one dielectric includes a first dielectric and a second dielectric. Here, the first metal layer, the first dielectric, the second metal layer, and the second dielectric are alternately arranged between the substrate and the glass substrate, wherein the second dielectric anodic bonds with the glass substrate.  
         [0012]     Furthermore, at least one dielectric includes a first dielectric and a second dielectric, and the first dielectric, the metal layer, and the second dielectric are alternately arranged between the substrate and the glass substrate, wherein the second dielectric anodic bonds with the glass substrate.  
         [0013]     To accomplish the objective of the present invention, an anodic bonding structure including a substrate and a glass substrate arranged above the substrate, includes a dielectric formed under the glass substrate. Furthermore, at least one dielectric and at least one metal layer deposited between the substrate and the dielectric, with a metal layer arranged uppermost, wherein the dielectric formed under the glass substrate and the uppermost metal layer are anodic bonded.  
         [0014]     Moreover, at least one metal layer includes a first metal layer and a second metal layer, and at least one dielectric includes a first dielectric and a second dielectric. The first metal layer, the first dielectric, the second metal layer, and the second dielectric formed under the glass substrate are alternately arranged between the substrate and the glass substrate, wherein the second metal layer and the second dielectric are anodic bonded.  
         [0015]     It is preferable that the substrate is formed of silicon and the dielectric is formed of silicon oxide.  
         [0016]     It is preferable that the metal layer includes a gold (Au) layer and a chrome (Cr) layer.  
         [0017]     To accomplish the objective of the present invention, a method of fabricating an anodic bonding structure having a substrate and a glass substrate arranged above the substrate, includes an act of depositing at least one dielectric and at least one metal layer between the substrate and the glass substrate, with dielectric arranged uppermost, and an act of anodic bonding the uppermost dielectric with the glass substrate.  
         [0018]     To accomplish the objective of the present invention, a method of fabricating an anodic bonding structure having a substrate and a glass substrate arranged above the substrate, includes an act of forming a dielectric under the glass substrate, an act of depositing at least one dielectric and at least one metal layer between the substrate and the dielectric, with a metal layer arranged uppermost, and an act of anodic bonding the uppermost metal layer with the dielectric under the glass substrate.  
         [0019]     It is preferable that the act of anodic bonding further includes an act of heating at about 300 to 400° C. and applying a pressure of about 800 to 1200 N and a voltage of about 800 to 2000 V to the anodic bonding structure.  
         [0020]     It is preferable that the substrate is formed of silicon and the dielectric is formed of silicon oxide.  
         [0021]     It is preferable that the metal layer includes an Au layer and a Cr layer.  
         [0022]     To accomplish the objective of the present invention, a method of manufacturing a top structure of an optical scanner including a rectangular frame, torsion bars extended from the frame and located with a separation region therebetween, a rectangular scanning mirror connected to the torsion bars and arranged at a central portion, and driving comb electrodes formed on the lower surface of the scanning mirror, the method includes an act of sequentially depositing a first substrate, a dielectric, and a second substrate, an act of performing a photolithography process on the upper surface of the second substrate to form the scanning mirror and a lower frame of the frame, an act of forming pin holes in the scanning mirror and the lower frame, and depositing a metal layer on the scanning mirror and the upper surface of the lower frame, an act of depositing a dielectric on the upper surface of the metal layer, and anodic bonding the dielectric on the upper surface of the lower frame with a glass substrate, an act of polishing the first substrate and patterning the upper surface of the frame which will be an upper frame to coat a metal layer on the upper surface of the upper frame, and an act of forming the upper frame and the torsion bars by etching the first substrate into a predetermined pattern for penetrating a portion corresponding to the separation region and forming the driving comb electrodes on the lower surface of the scanning mirror.  
         [0023]     It is preferable that the act of anodic bonding further includes an act of heating at about 300 to 400° C. and applying a pressure of about 800 to 1200 N and a voltage of about 800 to 2000 V.  
         [0024]     It is preferable that the first and second substrates are formed of silicon and the dielectric is formed of silicon oxide.  
         [0025]     It is preferable that the metal layer includes an Au layer and a Cr layer.  
         [0026]     The present invention provides an anodic bonding structure between a dielectric and a glass substrate and an anodic bonding structure between a dielectric and a metal layer to manufacture various devices using micro-electromechanical systems (MEMS) process. In addition, an optical scanner having stable performance is provided by using the MEMS process.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The above objective and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
         [0028]      FIG. 1  is a sectional view illustrating a conventional anodic bonding structure;  
         [0029]      FIG. 2A  is a sectional view illustrating an anodic bonding structure according to a first embodiment of the present invention;  
         [0030]      FIG. 2B  is a sectional view illustrating an anodic bonding structure according to a second embodiment of the present invention;  
         [0031]      FIG. 2C  is a sectional view illustrating an anodic bonding structure according to a third embodiment of the present invention;  
         [0032]      FIG. 2D  is a sectional view illustrating an anodic bonding structure according to a fourth embodiment of the present invention;  
         [0033]      FIG. 3A  is a scanning electron microscopy (SEM) photograph of an anodic bonding structure according to the first embodiment of the present invention;  
         [0034]      FIG. 3B  is an SEM photograph of an anodic bonding structure according to the second embodiment of the present invention;  
         [0035]      FIG. 4  is a sectional view illustrating the structure of an optical scanner manufactured by a method of manufacturing an optical scanner according to the present invention;  
         [0036]      FIG. 5  is a perspective view illustrating an optical scanner manufactured by a method of manufacturing an optical scanner according to the present invention; and  
         [0037]      FIGS. 6A through 6K  are sectional views illustrating a method of manufacturing an optical scanner according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]      FIGS. 2A through 2D  are sectional views illustrating anodic bonding structures according to first through fourth embodiments of the present invention. In the anodic bonding structures according to the first through third embodiments of the present invention, a glass substrate and an uppermost dielectric in a stack structure of metal layers and dielectrics between a substrate and the glass substrate are anodic bonded.  
         [0039]     With reference to  FIG. 2A , a metal layer  21  is deposited on the upper surface of a substrate  23  and a dielectric  22  is formed on the upper surface of the metal layer  21 . Here, the dielectric  22  and a glass substrate  25  are anodic bonded to form an anodic bonding structure according to a first embodiment of the present invention.  
         [0040]     With reference to  FIG. 2B , a first metal layer  31  is deposited on the upper surface of a substrate  33  and a first dielectric  32  is formed on the upper surface of the first metal layer  31 . Thereafter, a second metal layer  31 ′ is deposited on the upper surface of the first dielectric  32  and a second dielectric  32 ′ is formed on the upper surface of the second metal layer  31 ′. Here, the second dielectric  32 ′ and a glass substrate  35  are anodic bonded to form an anodic bonding structure according to a second embodiment of the present invention.  
         [0041]     With reference to  FIG. 2C , a first dielectric  42  is formed on the upper surface of a substrate  43 , a metal layer  41   5 is deposited on the upper surface of the first dielectric  42 , and a second dielectric  42 ′ is formed on the upper surface of the metal layer  41 . Thus, an anodic bonding structure according to a third embodiment of the present invention is formed.  
         [0042]     Unlike the anodic bonding structures according to the first through third embodiments of the present invention, a second dielectric is preformed under a glass substrate in an anodic bonding structure according to a fourth embodiment of the present invention. Thus, the second dielectric under the glass substrate and an uppermost metal layer in a stack structure of metal layers and dielectrics on the upper surface of a substrate are anodic bonded.  
         [0043]     With reference to  FIG. 2D , a second dielectric  52 ′ is preformed on the lower surface of a glass substrate  55 . A first metal layer  51  is deposited on the upper surface of a substrate  53 , a first dielectric  52  is formed on the upper surface of the first metal layer  51 , and a second metal layer  51 ′ is deposited on the upper surface of the first dielectric  52 . Here, the second metal layer  51 ′ and the second dielectric  52 ′ are anodic bonded to form an anodic bonding structure according to a fourth embodiment of the present invention.  
         [0044]     It is preferable that the anodic bonding processes take place at a temperature of about 300 to 400° C. and a pressure of about 800 to 1200 N and a voltage of about 800 to 2000 V is applied to the substrates during the processes.  
         [0045]     Components of the anodic bonding structures according to the first through fourth embodiments of the present invention will now be described in detail.  
         [0046]     Silicon substrates are generally used for the substrates  23 ,  33 ,  43 , and  53 ; however, gallium (Ga) substrates, substrates of nitride group compound, or of arsenic (As) group compound may be used while substrates in which more than two materials are stacked can be used for the substrates  23 ,  33 ,  43 , and  53 .  
         [0047]     Gold (Au), chrome (Cr), and any materials having metal properties can be used for the metal layers  21 ,  31 ,  31 ′,  41 ,  51 , and  51 ′. Here, the metal layers  21 ,  31 ,  31 ′,  41 ,  51 , and  51 ′ are deposited by a physical deposition method, such as sputtering, or a chemical deposition method, such as chemical vapor deposition (CVD).  
         [0048]     The dielectrics  22 ,  32 ,  32 ′,  42 ,  42 ′,  52 , and  52 ′ are formed of silicon oxide (SiO 2 ) or nitride group compound and formed by a chemical deposition method, such as CVD.  
         [0049]     In the anodic bonding structures according to the first through third embodiments of the present invention, the dielectrics  22 ,  32 ′, and  42 ′ and the glass substrates  25 ,  35 , and  45  are anodic bonded. In the anodic bonding structure according to the fourth embodiment of the present invention, the dielectric  52 ′ and the metal layer  51 ′ are anodic bonded.  
         [0050]     In order to manufacture such an anodic bonding structure, appropriate numbers of the metal layers  21 ,  31 ,  31 ′,  41 ,  51 , and  51 ′ and the dielectrics  22 ,  32 ,  32 ′,  42 ,  42 ′,  52 , and  52 ′ are sequentially deposited. Thereafter, the substrates  23 ,  33 ,  43 , and  53  and the glass substrates  25 ,  35 ,  45 , and  55  are heated at about  300  to 400° C. and a voltage of about 800 to 2000 V are applied to the substrates  23 ,  33 ,  43 , and  53  and the glass substrates  25 ,  35 ,  45 , and  55 . As a result, the dielectrics  22 ,  32 ′, and  42 ′ and the glass substrates  25 ,  35 , and  45  are anodic bonded or the dielectric  52 ′ and the metal layer  51 ′ are anodic bonded.  
         [0051]      FIG. 3A  is a scanning electron microscopy (SEM) photograph of an anodic bonding structure including a silicon substrate  23 , a metal layer  21 , a dielectric  22  of silicon oxide (SiO 2 ), and a glass substrate  25 , according to the first embodiment of the present invention.  FIG. 3B  is an SEM photograph of an anodic bonding structure including a silicon substrate  33 , a first metal layer  31 , a first dielectric  32  of silicon oxide, a second metal layer  31 ′, a second dielectric  32 ′ of silicon oxide, and a glass substrate  35 , according to the second embodiment of the present invention. The conditions for manufacturing such a structure are a temperature of about 400° C., a pressure of 1200 N, a cathode voltage of about −1500 V, and a bonding time of about 5 minutes.  
         [0052]      FIG. 4  is a sectional view illustrating the top structure of an optical scanner manufactured by the above-described anodic bonding structure and the fabricating method thereof, and  FIG. 5  is a perspective view illustrating the optical scanner.  
         [0053]     Referring to  FIGS. 4 and 5 , a top structure of an optical scanner manufactured by a method of manufacturing an optical scanner according to the present invention, includes a rectangular frame  80 , torsion bars  61 ′ extended from the frame  80  and located in the frame  80  with a separation region  73  therebetween, a rectangular scanning mirror  66 ″ located at a central portion and connected to the torsion bars  61 ′, and driving comb electrodes  61 ″ formed under the scanning mirror  66 ″.  
         [0054]     The frame  80  is divided to an upper frame  81  and a lower frame  83 . The upper frame  81  is formed of a glass substrate  68 , a dielectric (SiO 2 )  67  anodic bonded with the lower surface of the glass substrate  68 , and a metal layer (Au and Cr)  66  located on the lower surface of the dielectric  67 . Here, an anodic bonding structure in the frame  80  is the anodic bonding structure according to the first embodiment of the present invention.  
         [0055]     It is preferable that the anodic bonding process takes place at a temperature of about 300 to 400° C. and a pressure of about 800 to 1200 N and a voltage of about 800 to 2000 V is applied to the anodic bonding structure during the process.  
         [0056]     The lower frame  83  is formed of a first substrate (Si)  61 , a metal layer (Au and Cr)  66 ′ deposited under the first substrate  61 , a dielectric (SiO 2 )  62  located on the upper surface of the first substrate  61 , and a second substrate (Si)  63  arranged on the upper surface of the dielectric  62  and extended to the torsion bars  61 ′.  
         [0057]     Furthermore, the scanning mirror  66 ″ is formed by depositing a metal layer (Au and Cr)  66  on the upper surface of the second substrate  63  to reflect light.  
         [0058]     Pinholes are formed at a central portion of the frame  80  and two portions of the scanning mirror  66 ″ to penetrate the second substrate  63 , and the metal layer  66  is deposited into the pinholes. Thus, the first substrate  61 , the second substrate  63 , the torsion bar  61 ′ and driving comb electrodes  61 ″ are all electrically connected.  
         [0059]     Moreover, the first substrate  61 , the dielectric  62 , and the second substrate  63  are formed in a silicon on insulator (SOI) wafer  60  structure. The SOI wafer  60  allows the scanning mirror  66 ″ to stably drive, thereby improving the performance of the optical scanner.  
         [0060]     A method of manufacturing an optical scanner according to the present invention will now be described with reference to drawings.  
         [0061]     An upper structure of an optical scanner according to the present invention is formed by an anodic bonding structure according to the first embodiment of the present invention. Here, a metal layer  66  is deposited on a second substrate  63  formed of silicon, a dielectric  67  is formed on the upper surface of the metal layer  66 , and the dielectric  67  and a glass substrate  68  are anodic bonded, in  FIG. 6H .  
         [0062]      FIGS. 6A through 6K  are sectional views illustrating a method of manufacturing a top structure of an optical scanner according to the present invention.  
         [0063]     Referring to  FIG. 6A , a first substrate  61  formed of a silicon wafer having a thickness of about 500 μm is prepared and the surface of the first substrate  61  is oxidized to form a dielectric  62  formed of silicon oxide having a thickness of about 1 μm. Thereafter, a second substrate  63  formed of a silicon wafer having a thickness of about 15 μm is formed on the upper surface of the dielectric  62 . Thus, an SOI wafer  60  is formed.  
         [0064]     A photoresist layer  64 , such as AZ7220, is coated on the upper surface of the SOI wafer  60 , and then the photoresist layer  64  is exposed and developed by using a predetermined mask. Consequently, the SOI wafer  60  having a patterned photoresist layer  64  as shown in  FIG. 6B  is formed.  
         [0065]     The second substrate  63  is etched by an inductively coupled plasma reactive ion etch (ICPRIE) process. The silicon oxide dielectric  62  formed under the second substrate  63  having a thickness of about 15 μm, stops the etch. Therefore, the torsion bar  61 ′ having a thickness of about 15 μm and a portion to be a scanning mirror  66 ″ are formed as shown in  FIG. 6C .  
         [0066]     Referring to  FIG. 6D , a photoresist layer  65  is coated again and photolithography process is performed on the photoresist layer  65  to form hole patterns. As shown in  FIG. 6E , the second substrate  63  is etched by the ICPRIE process and the silicon oxide dielectric  62  is etched by a reactive ion etch (RIE) process.  
         [0067]     Referring to  FIG. 6E , a pinhole penetrates the central portion of the frame  80  to contact the surface of the first substrate  61 . Furthermore, the pinholes are formed on left and right sides of the portion to be the scanning mirror  66 ″ to penetrate to the first substrate  61 .  
         [0068]     As shown in  FIG. 6F , Cr to be used as an adhesion layer is deposited on the upper surfaces of the scanning mirror  66 ″ portion and the frame  80  to a thickness of about 300 Å, and Au to be used as a reflection later is deposited on the Cr to a thickness of about 3000 Å so as to form a metal layer  66 . Accordingly, the first substrate  61  and the second substrate  63  of the SOI wafer  60  are electrically connected.  
         [0069]     Referring to  FIG. 6G , a silicon oxide dielectric  67  having a thickness of about 5000 Å is deposited by CVD and patterned on the upper surface of the metal layer  66  formed of Au and Cr. The structure is turned upside down, and then a glass substrate  68 , for example, Pyrex glass, is anodic bonded with the silicon oxide dielectric  67 , as shown in  FIG. 6H .  
         [0070]     Referring to  FIG. 61 , the silicon substrate  61  having a thickness of about 500 μm is polished to a thickness of about 100 μm by a chemical mechanical polishing (CMP) process. In addition, a metal layer (Au and Cr)  66 ′ to be used as a fuse bonding layer to the lower structure is deposited and patterned.  
         [0071]     Referring to  FIG. 6J , a photoresist layer  69 , such as AZ4620, is coated on the structure and patterned by a conventional photolithography method. Thus, an upper photoresist pattern of comb structure  69 ′ and metal layer  69  are formed as shown in  FIG. 6J .  
         [0072]     When the first substrate  61  is etched by the ICPRIE process, a separation region  73  between the frame  80  and the scanning mirror  66 ″ is penetrated. Furthermore, the torsion bars  61 ′ extended from the second substrate  63  are formed so that the structure as shown in  FIG. 6K  is completed.  
         [0073]     Since an anodic bonding structure and a fabricating method thereof according to the present invention, anodic bonds a glass substrate with a dielectric or a dielectric with a metal layer, micro-electromechanical systems (MEMS) structures, such as condensers, cantilevers, sensors, and inductors of novel type, can be manufactured and eventually applied to a packaging process. In a method of manufacturing an upper structure of an optical scanner by using an anodic bonding structure and a fabricating method thereof, an optical scanner is stably manufactured and driven. As a result, the overall performance of the optical scanner can be improved.  
         [0074]     It is noted that the present invention is not limited to the preferred embodiments described above, and it is apparent that variations and modifications by those skilled in the art can be effected within the spirit and scope of the present invention defined in the appended claims.  
         [0075]     For example, those skilled in the art may realize various combinations of dielectrics and metal layers stacked between a substrate and a glass substrate. Accordingly, the scope of the present invention is not defined by the preferred embodiments; however, the scoped of the present invention will be defined by the appended claims.  
         [0076]     As described above, an anodic bonding structure and a fabricating method thereof allow various combinations of dielectrics and metal layers stacked between a substrate and a glass substrate so that a novel device can be obtained.