Abstract:
A micro-electro-mechanical system (MEMS) package having a metal sealing member is disclosed. The MEMS package is formed by forming a metal layer on a substrate by patterning so that the metal layer surrounds an MEMS element provided on the substrate; joining a lid to the metal layer; providing a side sealing member on a side surface of the substrate; and covering the lid and the substrate with a metal sealing member, thus hermetically sealing the MEMS element from the external environment.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates, in general, to micro-electro-mechanical system (MEMS) packages with metal sealing members and methods of manufacturing the MEMS packages and, more particularly, to an MEMS package having a metal sealing member, in which an MEMS element provided on a substrate is hermetically sealed from the external environment by forming a metal layer on the substrate by patterning, or forming a spacer on the substrate so as to create an MEMS moving space in which the MEMS element is free to move vertically; joining a lid to the metal layer or the spacer; providing a side sealing member on a side surface of the lid; and covering the lid and the substrate with the metal sealing member. 
   2. Description of the Related Art 
   In recent years, high-capacity communications for broadband service, such as in the Internet or the IMT 2000, have become powerful, so that optical communication techniques including, for example, WDM (wavelength division multiplexing), have been quickly standardized. In relation to the standardization of the optical communication technique, MEMS, which does not depend on wavelength, data rate or signal format and thereby has characteristics of being “optically transparent”, has been proposed and recognized as an innovative technique to supplant electronics, which can accomplish the recent trend of system smallness. 
   In the related art, current applications of MEMS are accelerometers, pressure sensors, inkjet heads, hard disk heads, projection displays, scanners and micro-fluidics. In recent years, interest in the techniques of optical communication elements, having higher operational performance to meet the rapid development in the optical communications field, has increased. 
   Particularly, the interest in the techniques of the optical communication elements is concentrated on spatial light modulators, which have a great number of micromirrors and operate in a specified switching manner such that the micromirrors are actuated by MEMS type actuators. The spatial light modulators use an optical signal processing technique with advantages in that a great amount of data can be quickly processed in a parallel manner, unlike a conventional digital information processing technique, in which a great amount of data cannot be processed in real time. 
   Thus, studies have been actively conducted on the design and production of binary phase only filters, optical logic gates, light amplifiers, image processing techniques, optical devices, and light modulators using the spatial light modulation theory. Of them, the spatial light modulators are applied to fields relating to optical memory units, optical display devices, printers, optical interconnections, and holograms, and studies have been conducted to develop display devices employing the spatial display modulators. 
   However, the MEMS elements have ultra-fine actuators so that the MEMS elements are greatly sensitive to the external environment, including temperature, humidity, micro-dust, vibration and impact, and thereby may frequently commit errors during operation, or may suddenly stop operating. 
   In an effort to allow the MEMS elements to effectively operate without being negatively affected by the environment, the MEMS elements have been sealed in cavities of sealed packages. U.S. Pat. No. 6,303,986 discloses a method and apparatus for sealing MEMS elements using a hermetic lid to provide an MEMS package. 
   Herein below, the construction of the MEMS package disclosed in U.S. Pat. No. 6,303,986, in which the lid glass hermetically seals the MEMS elements from the external environment, will be described with reference to  FIG. 1 . 
     FIG. 1  shows a representative sectional view of the MEMS package in which the transparent lid hermetically seals the MEMS element. As shown in  FIG. 1 , a conductive ribbon  100  having a metallic conductive/reflective covering  102  is formed over an upper surface of a semiconductor substrate  104 , with an air gap  106  defined between the ribbon  100  and the substrate  104 . 
   A conductive electrode  108  is formed on the upper surface of the substrate  104  and covered with an insulation layer  110 . The conductive electrode  108  is placed under the ribbon  100  at a position under the air gap  106 . 
   The conductive/reflective covering  102  extends beyond the region of the mechanically active ribbon  100  and is configured as a bond pad  112  at its distal end. The MEMS package is also passivated with a conventional overlying insulating passivation layer  114  which does not cover the bond pads  112  or the ribbon structures  100  and  102 . 
   Control and power signals are coupled to the MEMS package using conventional wire-bonding structures  116 . 
   Unlike conventional semiconductor manufacturing techniques in which semiconductor elements are packed densely onto the upper surface of a semiconductor substrate, an optical glass is hermetically sealed directly onto the semiconductor substrate in the above-mentioned US patent. Thus, the bond pads  112  are spaced a considerable distance from the ribbon structures  100  and  102 , so that a lid sealing region  118  is provided. A solderable material  120  is formed on the lid sealing region  118 . 
   The hermetic lid  122 , which is joined to the semiconductor substrate, is preferably formed of an optical quality material. Thus, the lid  122  can be used for a variety of purposes including filtering undesired radiation and enhancing or decreasing reflectivity. 
   The lid  122  may be also coated with an optically sensitive material to be used for other purposes without being limited to the above-mentioned purposes. 
   Once the lid  122  is formed to a size appropriate to fit concurrently over the lid sealing region  118 , with a solderable material  124  formed in a ring surrounding the periphery of one surface of the lid  122 , solder  126  is deposited onto the solderable material  124  so that the lid  122  is joined to the semiconductor substrate. 
   Though not shown to scale in the drawing, a significant space exists between the lid  122  and the ribbon structures  100  and  102  to prevent them from interfering with one another. Thus, the ribbon structures  100  and  102  are free to move upwards and downwards. 
   However, in the above-mentioned conventional technique of sealing the semiconductor elements in the above-mentioned MEMS package, the solder must be placed between the substrate and the lid and, thereafter, heat must be applied to the solder through a reflow process at a predetermined temperature so as to bond the lid to the substrate. Thus, the technique undesirably reduces the work speed, causing a reduction in productivity. 
   Another problem of the technique of sealing the semiconductor elements in the MEMS package is that it is impossible to execute a reworking process, such as for adding solder, even when the sealing is not complete due to inaccurate positioning of the solder and/or application of a deficient amount of solder to the junction between the substrate and the lid. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide an MEMS package, in which a metal sealing member is formed on a side surface of a lid that covers an MEMS element provided on a substrate, so that the metal sealing member hermetically seals the MEMS element from the external environment. 
   In order to achieve the above object, according to one aspect of the present invention, there is provided an MEMS package, comprising: a substrate, with an MEMS element provided on a surface of the substrate; a lid joined to the substrate such that the lid covers the MEMS element; a side sealing member provided on a side surface of the substrate and a surface of the lid, thus hermetically sealing the MEMS element from the external environment; and a metal sealing member made of metal, which completely covers both the side sealing member and the substrate having the MEMS element. 
   According to another aspect of the present invention, there is provided an MEMS package, comprising: an element substrate, with an MEMS element provided on a surface of the element substrate; a base substrate on which the element substrate is mounted; a lid joined to the element substrate such that the lid covers the MEMS element; a side sealing member provided on a surface of the base substrate and a side surface of a structure comprising both the element substrate and the lid, thus hermetically sealing the MEMS element from the external environment; and a metal sealing member made of metal, which completely covers both the side sealing member and the lid. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a sectional view illustrating the construction of an MEMS package according to a conventional technique; 
       FIG. 2A  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a first embodiment of the present invention; 
       FIG. 2B  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a second embodiment of the present invention; 
       FIG. 2C  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a third embodiment of the present invention; 
       FIG. 3A  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a fourth embodiment of the present invention; and 
       FIG. 3B  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a fifth embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Below, an MEMS package having a metal sealing member according to the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 2A  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a first embodiment of the present invention. 
   As shown in the drawing, the MEMS package having a metal sealing member according to the first embodiment of the present invention comprises a base substrate  300  on which an MEMS element  310  is provided, a lower bump  331 , an upper bump  332 , a lid glass  320 , a side sealing member  351 , and a metal sealing member  352 . 
   In the first embodiment, the base substrate  300  may be a semiconductor substrate on which an MEMS element is formed, or a package module on which an MEMS element is mounted. 
   In that case, examples of MEMS elements  310  are diffractive, reflective or transmissive light modulating elements, optical elements or display elements used in a variety of optical devices, such as optical memory units, optical displays, printers, optical interconnections, and hologram displays. 
   The lower bump  331  is formed on a lid sealing region  330  of the base substrate  300 . The upper bump  332  is formed on a lid sealing region  330 ′ of the lid glass  320 . 
   The lid glass  320  is joined to the base substrate  300  by means of the lower bump  331  and the upper bump  332 , thus defining an air space which is an MEMS moving space in which the MEMS element  310  is free to move vertically. 
   The lid glass  320  may be coated on one or both sides thereof with an antireflective (AR) coating so that incident light transmissibility of the lid glass  320  can be enhanced. 
   The side sealing member  351  functions as a sealing means for sealing the MEMS element  310  provided on the base substrate  300  from the external environment. Thus, the side sealing member  351  is provided on a surface of the lid glass  320  and a side surface of the base substrate  300 , and forms a flat surface which allows the metal sealing member  352  to be easily formed on the side sealing member  351  through a vapor deposition process. The side sealing member  351  has a solid and strong structure, but may not realize desired sealing efficiency, thus often failing to hermetically or reliably seal the MEMS element  310  from the external environment. Therefore, in the MEMS package according to the first embodiment of the present invention, the metal sealing member  352  is formed through one of a variety of deposition processes, such as a sputtering or vapor deposition process, so that the metal sealing member  352  completely covers the side sealing member  351  and the base substrate  300 , and hermetically and reliably seals the MEMS element  310  from the external environment. 
     FIG. 2B  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a second embodiment of the present invention. 
   As shown in the drawing, the MEMS package having a metal sealing member according to the second embodiment of the present invention comprises a base substrate  300  on which an MEMS element  310  is provided, a lower bump  331 , an upper bump  332 , a lid glass  320 , a side sealing member  351 , a metal sealing member  352 , and an external protective layer  353 . 
   The base substrate  300  is a semiconductor substrate on which an MEMS element is formed. The lower bump  331  is formed on a lid sealing region  330  of the base substrate  300 , while the upper bump  332  is formed on a lid sealing region  330 ′ of the lid glass  320 . 
   The lid glass  320  is joined to the base substrate  300  by means of the lower bump  331  and the upper bump  332 , thus defining an air space which is an MEMS moving space in which the MEMS element  310  formed on the base substrate  300  is free to move vertically. 
   The side sealing member  351  functions as a sealing means for sealing the MEMS element  310 , formed on the base substrate  300 , from the external environment. Thus, the side sealing member  351  is provided on a surface of the lid glass  320  and a side surface of the base substrate  300 , and forms a flat surface which allows the metal sealing member  352  to be easily formed on the side sealing member  351  through a vapor deposition process. The side sealing member  351  has a solid and strong structure, but may not realize desired sealing efficiency, thus often failing to hermetically or reliably seal the MEMS element  310  from the external environment. Therefore, in the MEMS package according to the second embodiment of the present invention, the metal sealing member  352  is formed through one of a variety of deposition processes, such as a sputtering or vapor deposition process, so that the metal sealing member  352  completely covers the side sealing member  351  and the base substrate  300 , and hermetically and reliably seals the MEMS element  310  from the external environment. 
   Unlike the MEMS package according to the first embodiment, the MEMS package according to the second embodiment further comprises the external protective layer  353  which is formed on the metal sealing member  352  using a sealing material such that the layer  353  completely covers the metal sealing member  352  and protects the metal sealing member  352  from the external environment. 
     FIG. 2C  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a third embodiment of the present invention. 
   As shown in the drawing, the MEMS package having a metal sealing member according to the third embodiment of the present invention comprises a base substrate  300  on which an MEMS element  310  is provided, a lower bump  331 , an upper bump  332 , a lid glass  320 , a first side sealing member  351   a , a second side sealing member  351   b , a first metal sealing member  352   a , and a second metal sealing member  352   b.    
   In the third embodiment, the base substrate  300  may be a semiconductor substrate on which an MEMS element is formed, or a package module on which an MEMS element is mounted. 
   In that case, examples of MEMS elements  310  are diffractive, reflective or transmissive light modulating elements, optical elements or display elements, used in a variety of optical devices, such as optical memory units, optical displays, printers, optical interconnections, and hologram displays. 
   The lower bump  331  is formed on a lid sealing region  330  of the base substrate  300 , while the upper bump  332  is formed on a lid sealing region  330 ′ of the lid glass  320 . 
   The lid glass  320  is joined to the base substrate  300  by means of the lower bump  331  and the upper bump  332 , thus defining an air space which is an MEMS moving space in which the MEMS element  310  is free to move vertically. 
   The first side sealing member  351   a  functions as a sealing means for sealing the MEMS element  310  provided on the base substrate  300  from the external environment. Thus, the first side sealing member  351   a  is provided on a surface of the lid glass  320  and a side surface of the base substrate  300 , and forms a flat surface which allows the first metal sealing member  352   a  to be easily formed on the first side sealing member  351   a  through a vapor deposition process. The first side sealing member  351   a  has a solid and strong structure, but may not realize desired sealing efficiency, thus often failing to hermetically or reliably seal the MEMS element  310  from the external environment. Therefore, in the MEMS package according to the third embodiment of the present invention, the first metal sealing member  352   a  is formed through one of a variety of deposition processes, such as a sputtering or vapor deposition process, so that the first metal sealing member  352   a  completely covers the first side sealing member  351   a , and hermetically and reliably seals the MEMS element  310  from the external environment. 
   Unlike the MEMS packages according to the first and second embodiments, each of the side sealing member and the metal sealing member in the MEMS package according to the third embodiment is configured as a multi-layered structure. 
   Described in detail, the first metal sealing member  352   a  is formed on the first side sealing member  351   a . Thereafter, the second side sealing member  351   b  is formed on the first metal sealing member  352   a  using a sealing material. The second side sealing member  351   b  is configured such that the second side sealing member  351   b  protects the first metal sealing member  351   a  and allows the second metal sealing member  352   b  to be easily formed thereon. 
   After the second side sealing member  351   b  is formed on the first metal sealing member  352   a  as described above, the second metal sealing member  352   b  is formed such that the second metal sealing member  352   b  covers both the base substrate  300  and the second side sealing member  351   b . Thus, the MEMS package according to the third embodiment hermetically and reliably seals the MEMS element  310  from the external environment. 
   In each of the first through third embodiments of the present invention, the MEMS element  310  is an optical element, so that the lid glass  320  is required. However, if the MEMS element is not an optical element, the lid glass may be replaced with a conventional substrate. 
     FIG. 3A  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a fourth embodiment of the present invention. 
   As shown in the drawing, the MEMS package having a metal sealing member according to the fourth embodiment of the present invention comprises a base substrate  400 , an element substrate  410 , an MEMS element  420 , a lower bump  431 , an upper bump  432 , a lid  440 , a side sealing member  451 , and a metal sealing member  452 . 
   In the fourth embodiment, the base substrate  400  is a conventional printed circuit board (PCB) to which the element substrate  410  provided with the MEMS element  420  thereon is mounted through a bonding process and which thus functions as a medium. The above-mentioned base substrate  400  is provided with a bond pad (not shown) to which a wire (not shown) to transceive electric signals to and from the outside of the package is connected. 
   The lower bump  431  is formed on a lid sealing region  430  of the element substrate  410 . The upper bump  432  is formed on a lid sealing region  430 ′ of the lid  440 . 
   The element substrate  410  and the lid  440  are joined together by means of the lower bump  431  and the upper bump  432 , thus defining an air space which is an MEMS moving space in which the MEMS element  420  is free to move vertically. 
   The side sealing member  451  functions as a sealing means for sealing a structure, comprising the lid  440  and the element substrate  410  provided with the MEMS element  420  thereon and mounted to the base substrate  400 , from the external environment. Thus, the side sealing member  451  is provided on a surface of the base substrate  400  and a side surface of the structure which comprises the lid  440  and the element substrate  410  having the MEMS element  420 . The side sealing member  451  has a solid and strong structure, but may not realize desired sealing efficiency, thus often failing to hermetically or reliably seal the structure from the external environment. 
   Therefore, in the MEMS package according to the fourth embodiment, the metal sealing member  452  is formed through a vapor deposition process so that the metal sealing member  452  completely covers the surface of the base substrate  400 , a side surface of the side sealing member  451 , and a surface of the lid  440 . Thus, the metal sealing member  452  hermetically and reliably seals the MEMS element  420  from the external environment. 
     FIG. 3B  is a sectional view illustrating the construction of an MEMS package having a metal sealing member according to a fifth embodiment of the present invention. 
   As shown in the drawing, the MEMS package having a metal sealing member according to the fifth embodiment of the present invention comprises a base substrate  400 , an element substrate  410 , an MEMS element  420 , a lower bump  431 , an upper bump  432 , a lid  440 , a side sealing member  451 , a metal sealing member  452 , and an external protective layer  453 . 
   The general shape of the MEMS package according to the fifth embodiment remains the same as that described for the MEMS package according to the fourth embodiment. However, unlike the fourth embodiment, the fifth embodiment further comprises the external protective layer  453  which is formed on the metal sealing member  452  using a sealing material such that the layer  453  completely covers the metal sealing member  452  and protects the metal sealing member  452  from the external environment. 
   In the fourth and fifth embodiments of the present invention, each of the side sealing member and the metal sealing member in the MEMS package may be configured as a multi-layered structure in the same manner as that described for the third embodiment. 
   As is apparent from the above description, the MEMS package according to the present invention hermetically and reliably seals an MEMS element from the external environment using a metal sealing member. 
   Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.