Abstract:
A semiconductor device includes a substrate, a semiconductor layer formed on the substrate, and an optically functional portion formed by using at least a portion of the semiconductor layer. The optically functional portion performs light emission or light reception. The semiconductor device further includes a first driving electrode that is electrically connected to a semiconductor layer on a surface of the optically functional portion, and the first driving electrode drives the optically functional portion. The semiconductor device further includes an encapsulating electrode that is formed on the semiconductor layer to surround periphery of the optically functional portion, and electrically connected to the first driving electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2007-067152 filed Mar. 15, 2007. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    This invention relates to a semiconductor device and an optical apparatus. 
         [0004]    2. Related Art 
         [0005]    As light sources for data communication using optical fibers or the like or for a data processing apparatus such as a copier, surface emitting semiconductor lasers, i.e., Vertical-Cavity Surface-Emitting Laser diodes (hereinafter referred to as VCSEL), which consume less power and can be easily arranged in two dimensional arrays, have been used. 
         [0006]    A typical mounting example of a semiconductor device of a related art is shown in  FIGS. 11A to 11C . As shown in  FIG. 11A , a semiconductor device  10  includes a light emitting portion  12  such as a VCSEL and a p-side electrode  14  and an n-side electrode  16  of the light emitting portion  12 . As shown in  FIG. 11B  or  FIG. 11C , in the semiconductor device  10 , the light emitting portion  12  and the electrodes  14  and  16  face a mounting substrate  18 . The electrodes  14  and  16  are connected to a wiring pattern of the mounting substrate  18 . The surrounding or the entirety of the light emitting portion  12  is encapsulated with a resin  20  to obtain a semiconductor device module. However, in general, the resin  20  has moisture permeability, and thus for devices, in which moisture is not desirable, a more highly hermetic encapsulation is needed to ensure reliability. 
         [0007]    As shown in  FIG. 12A , to improve hermeticity of the light emitting portion  12  of the semiconductor device  10 , there is a method in which an encapsulating electrode  22  is formed to surround the electrodes  14  and  16  of the light emitting portion  12 , and the encapsulating electrode  22  is connected to the mounting substrate  18 . In this case, the encapsulating electrode  22  becomes an obstacle when the wiring pattern connected to the electrodes  14  and  16  is extracted from the surface of the mounting substrate. 
         [0008]    The present invention aims to provide a semiconductor device in which hermeticity of an optically functional portion such as a light emitting portion or a light receiving portion can be enhanced, and a wiring can be extracted from a mounting substrate surface, and an optical apparatus using the semiconductor device. 
       SUMMARY 
       [0009]    An aspect of the present invention provides a semiconductor device that includes a substrate, a semiconductor layer formed on the substrate, and an optically functional portion formed by using at least a portion of the semiconductor layer. The optically functional portion performs light emission or light reception. The semiconductor device further includes a first driving electrode that is electrically connected to a semiconductor layer on a surface of the optically functional portion, and the first driving electrode drives the optically functional portion. The semiconductor device further includes an encapsulating electrode that is formed on the semiconductor layer to surround periphery of the optically functional portion, and electrically connected to the first driving electrode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0011]      FIG. 1A  is a plan view of a VCSEL according to an example of the present invention; 
           [0012]      FIG. 1B  is a cross sectional view taken along line A-A of  FIG. 1A ; 
           [0013]      FIG. 2  is a cross sectional view taken along line B-B of  FIG. 1A ; 
           [0014]      FIG. 3  is a cross sectional view of a semiconductor device that is flip-chip mounted on a mounting substrate; 
           [0015]      FIG. 4A  is a cross sectional view of a semiconductor device module; 
           [0016]      FIG. 4B  is a perspective view of a semiconductor device module viewed from above thereof; 
           [0017]      FIG. 5  shows a modified example of a semiconductor device of a first example; 
           [0018]      FIGS. 6A to 6C  show a process for fabricating a semiconductor device of a first example, in cross section take along line A-A of  FIG. 1A ; 
           [0019]      FIGS. 7A to 7C  show a process for fabricating a semiconductor device of a first example, in cross section take along line A-A of  FIG. 1A ; 
           [0020]      FIGS. 8A to 8C  show a process for fabricating a semiconductor device of a first example, in cross section take along line B-B of  FIG. 1A ; 
           [0021]      FIGS. 9A to 9C  show a process for fabricating a semiconductor device of a first example, in cross section take along line B-B of  FIG. 1A ; 
           [0022]      FIGS. 10A and 10B  show a semiconductor device module applied to a living object sensor; 
           [0023]      FIGS. 11A to 11C  show a configuration of a semiconductor device module of a related art; and 
           [0024]      FIGS. 12A and 12B  show a configuration of a semiconductor device module of a related art. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Referring to the accompanying drawings, exemplary embodiments for implementing the present invention will be described. Shown herein is an example in which one light emitting portion and one light receiving portion are monolithically formed on a substrate. 
         [0026]      FIG. 1A  is a plan view of a semiconductor device according to a first example of the present invention, and  FIG. 1B  is a cross sectional view taken along line A-A of  FIG. 1A .  FIG. 2  is a cross sectional view taken along line B-B of  FIG. 1A . In  FIG. 1A , an electrode formed on the surface of a semiconductor device is indicated by a hatch pattern for ease of understanding. 
         [0027]    A semiconductor device  100  of this example has an n-type semiconductor layer  110  on an n-type substrate and a p-type semiconductor layer  120  overlaid thereon. In the p-type semiconductor layer  120 , two ring shaped grooves  130 - 1  and  130 - 2  are formed. The grooves  130 - 1  and  130 - 2  have a depth ranging from the p-type semiconductor layer  120  to the n-type semiconductor layer  110 . A cylindrical post structure (hereinafter referred to as post) PI is defined by the groove  130 - 1 , and a light emitting portion  140  is formed in the post P 1 . By the groove  130 - 2 , a cylindrical post P 2  is formed, and a light receiving portion  150  is formed in the post P 2 . In addition, as shown in  FIG. 2 , a groove  130 - 3  is formed for connecting an n-side driving electrode  200  described later to the n-type semiconductor layer  110 . 
         [0028]    The light emitting portion  140  may be an LED or a VCSEL. In a case of a VCSEL, the n-type semiconductor layer  110  and the p-type semiconductor layer  120  may compose a vertical resonator with Distributed Bragg Reflectors (DBRs), and may include an active layer in the vertical resonator. 
         [0029]    On the p-type semiconductor layer  120  excepting top portions of the posts P 1  and P 2 , an insulating layer  172  of SiOx or the like is formed. On the p-type semiconductor layer  120  exposed at a top portion of the post P 1 , a p-side driving electrode  160  is formed, and the p-side driving electrode  160  is ohmic-contacted to the p-type semiconductor layer  120 . The p-side driving electrode  160  has an annular shape, and a round-shaped opening  162  is formed at a center portion of the p-side driving electrode  160 . The opening  162  functions as a window for emitting light. 
         [0030]    An annular encapsulating electrode  170  is formed such that it surrounds outer periphery of the post P 1  or the light emitting portion  140 . The encapsulating electrode  170  is formed on the p-type semiconductor layer  120  outside of the groove  130 - 1  through the insulating layer  172 . The encapsulating electrode  170  includes an internal connection electrode  174  extending such that a portion of the annular electrode conforms along the groove  130 - 1  and being connected to the p-side driving electrode  160 , and an external connection electrode  176  for making a connection with outside of the semiconductor device. Preferably, the p-side driving electrode  160  and the encapsulating electrode  170  are made of a same metal material, and patterned simultaneously. 
         [0031]    On the p-type semiconductor layer  120  exposed at a top portion of the post P 2 , a p-side driving electrode  180  is formed. The p-side driving electrode  180  is ohmic-contacted to the p-type semiconductor layer  120 . The p-side driving electrode  180  has an annular shape, and a round-shaped opening  182  is formed at a center portion of the p-side driving electrode  180 . The opening  182  functions as a window for emitting light. 
         [0032]    An annular encapsulating electrode  190  is formed such that it surrounds outer periphery of the post P 2  or the light receiving portion  150 . The encapsulating electrode  190  is formed on the p-type semiconductor layer  120  outside of the groove  130 - 2  through the insulating layer  172 . The encapsulating electrode  190  includes an internal connection electrode  194  extending such that a portion of the annular electrode conforms along the groove  130 - 2  and being connected to the p-side driving electrode  180 , and an external connection electrode  196  for making a connection with outside of the semiconductor device. Preferably, the p-side driving electrode  180  and the encapsulating electrode  190  are made of a same metal material, and patterned simultaneously. 
         [0033]    On the outer periphery of the semiconductor device  100 , the n-side driving electrode  200  is formed. As shown in  FIG. 2 , the n-side driving electrode  200  is routed on the p-type semiconductor layer  120  through the insulating layer  172 , and extends to a bottom portion of the groove  130 - 3 . The extension of the n-side driving electrode  200  is electrically connected to the n-type semiconductor layer  110  through a contact hole  202  formed in the insulating layer  172  at a bottom portion of the groove  130 - 3 . The n-side driving electrode  200  becomes a common n-side electrode to the light emitting portion  140  and to the light receiving portion  150 . 
         [0034]    As shown in  FIG. 1B , the p-side driving electrode  160  at the top portion of the post P 1  is slightly lower than the encapsulating electrodes  170  and  190 . The difference is equivalent to the film thickness of the insulating layer  172  formed on the p-type semiconductor  120 . In addition, the p-side driving electrode  180  at the top portion of the post P 2  is lower than the p-side driving electrode  160  at the top portion of the post P 1 . By forming the p-side driving electrodes  160  and  180  lower than the encapsulating electrodes  170  and  190 , when the semiconductor device is flip-chip mounted on a mounting substrate, the p-side driving electrodes  160  and  180  can be spaced apart from the mounting substrate such that stress would not applied onto the light emitting portion  140  and the light receiving portion  150 . However, the p-side driving electrodes  160  and  180  are not necessarily formed lower than the encapsulating electrodes  170  and  190 , and all electrodes may be in a same plane. 
         [0035]      FIG. 3  is a cross sectional view of a semiconductor device module (optical apparatus) in which the semiconductor device shown in  FIGS. 1A and 1B  is mounted. A semiconductor device module  102  includes a mounting substrate  210  and the semiconductor device  100  that is flip-chip mounted onto the mounting substrate  210 . For the mounting substrate  210 , a material that has optical transparency, for example, a glass substrate, may be used. On a surface  212  of the mounting substrate  210 , wiring patterns made of a transparent metal material such as ITO is formed. The posts P 1  and P 2  of the semiconductor device  100  face the mounting substrate  210 . The encapsulating electrodes  170  and  190  are connected to a corresponding wiring pattern through the external connection electrodes  176  and  196 . The n-side driving electrode  200  is connected to a corresponding wiring pattern. The connection of the electrodes may be performed by soldering reflow, for example. 
         [0036]    For the semiconductor device module, the semiconductor device  100  may be encapsulated with a thermosetting resin, for example. By this process, the strength of connection between the semiconductor device  100  and the mounting substrate  210  can be enhanced, and the semiconductor device  100  can be protected. Alternatively, a resin may encapsulate a portion of the semiconductor device  100 , or encapsulate a portion of the semiconductor device  100  and the mounting substrate  210 . 
         [0037]      FIG. 4A  shows a semiconductor device module viewed from backside thereof in which an electronic circuit is mounted on a mounting substrate.  FIG. 4B  is a schematic perspective view of a semiconductor device module when viewed from above thereof. As shown in  FIG. 4A , on the surface  212  of the mounting substrate  210 , wiring patterns  220 ,  222 ,  224 , and  226  are formed. The wiring patterns  222  and  224  are connected to the external connection electrodes  176  and  196  of the semiconductor device  100 , in other words, connected to the p-side driving electrodes  160  and  180  through the encapsulating electrodes  170  and  190 , and the wiring patterns  220  and  226  are connected to the n-side driving electrode  200 . 
         [0038]    The wiring pattern  220  is connected to an output terminal on a negative electrode side of a driving circuit  230 , and the wiring pattern  222  is connected to an output terminal on a positive electrode side of the driving circuit  230 . The wiring pattern  224  is connected to an input terminal on a positive electrode side of a control circuit  232 , and the wiring pattern  226  is connected to an input terminal on a negative electrode side of the control circuit  232 . The control circuit  232  is connected to the driving circuit  230  via a wiring pattern  234 . 
         [0039]    When the driving circuit  230  applies a driving current to the light emitting portion  140  through the wiring patterns  220  and  222 , the light emitting portion  140  emits light from the opening  162  as shown in  FIG. 4B . The light passes through the mounting substrate  210 , and is injected into an optical component such as a lens, mirror, or optical fiber. A portion of the light emitted from the light emitting portion  140  is received by the light receiving portion  150  through the opening  182 . The light receiving portion  150  outputs an electrical signal that corresponds to the amount of received light or the intensity of received light. The electrical signal is provided to the control circuit  232  through wiring patterns  224  and  226 , and the control circuit  232  may perform a control to keep the output of the light emitting portion  140  constant, for example. 
         [0040]    As such, according to an example, the light emitting portion  140  and the light receiving portion  150  can be hermetically sealed by forming the encapsulating electrodes  170  and  190  to surround the outer periphery of the light emitting portion  140  and the light receiving portion  150 , and by connecting the encapsulating electrodes  170  and  190  to the mounting substrate  210 . In addition, by electrically connecting the encapsulating electrodes  170  and  190  to the p-side driving electrodes  160  and  180 , the p-side driving electrodes  160  and  180  can be extracted to a surface of the substrate through the encapsulating electrodes  170  and  190 . Moreover, by integrally forming the light emitting portion  140  and the light receiving portion  150  on a substrate, and forming p-side and n-side driving electrodes on the surface, flip-chip mounting can be achieved. 
         [0041]    In the examples described above, as shown in  FIG. 1A , the n-side driving electrode  200  is formed on the outer periphery of the semiconductor device  100 ; however, for example, as shown in  FIG. 5 , a rectangular n-side electrode pad  200 A may be formed instead. In addition, in the examples described above, the n-type semiconductor layer is formed on the n-type substrate; however, an n-type semiconductor layer may be formed on an insulating substrate, and a p-type semiconductor layer may be formed thereon. Of course, the configuration of n-type and p-type may be vice versa. 
         [0042]    Moreover, in the examples described above, the light emitting portion  140  and the light receiving portion  150  are formed on the n-type substrate; however, the elements to be formed on a substrate are not limited to these elements. For example, plural posts arranged in two dimensional arrays may be formed on a substrate, and a light emitting portion may be formed in each of the posts, and an encapsulating electrode may be formed to surround each of the light emitting portions. Each of the light emitting portions may be a VCSEL or an LED. 
         [0043]    In addition, in the examples described above, to define the area of the light emitting portion  140  or the light receiving portion  150 , the cylindrical post is formed by the ring shaped groove; however, the shape of the groove may be rectangular or other shapes. Moreover, the mounting substrate does not necessarily pass light in its entire region, and only the region that corresponds to a light emitting portion or a light receiving portion may have optical transparency. 
         [0044]    A method for fabricating a semiconductor device of an example will be described hereinafter.  FIGS. 6A to 6C  and  FIGS. 7A to 7C  show a process for the semiconductor device shown in  FIG. 1A  in cross section take along line A-A.  FIGS. 8A to 8C  and  FIGS. 9A to 9C  show a process in cross section take along line B-B of  FIG. 1A . 
         [0045]    As shown in  FIG. 6A  and  FIG. 8A , the n-type semiconductor layer  110  and the p-type semiconductor layer  120  are overlaid on an insulating substrate or an n-type semiconductor substrate by epitaxial growth. In a case where the light emitting portion is a VCSEL, an active layer or a current confining layer is formed between the n-type semiconductor layer  110  and the p-type semiconductor layer  120 , and the semiconductor layers  110  and  120  are made to be DBRs. For example, by Metal Organic Chemical Vapor Deposition (MOCVD), an n-type GaAs buffer layer, an n-type DBR in which 40.5 periods of Al 0.9 Ga 0.1 As and Al 0.12 Ga 0.88 As, each having a film thickness of ¼ of the wavelength in the medium, an undoped quantum well active layer, a p-type DBR in which 30 periods of Al 0.9 Ga 0.1 As and Al 0.15 Ga 0.85 As, each having a film thickness of ¼ of the wavelength in the medium, are sequentially stacked on a GaAs substrate. The lowermost layer of the p-type semiconductor layer  120  may be a current confining layer made of AlAs, and the topmost layer thereof may be a GaAs contact layer having a high carrier concentration. 
         [0046]    Then, as shown in  FIG. 6B  and  FIG. 8B , a mask M is formed on the semiconductor layer  120  by a photolithography process. By using the mask M, the semiconductor layer is anisotropically etched to form the grooves  130 - 1 ,  130 - 2 , and  130 - 3  on the substrate. The depth of the grooves is within the p-type semiconductor layer  120 . By the groove  130 - 1 , the post P 1  for forming a light emitting portion is formed, and by the groove  130 - 2 , the post P 2  for forming a light receiving portion is formed. The groove  130 - 3  is used for the area to connect an n-side driving electrode described later to the n-type semiconductor layer  110 . 
         [0047]    Then, as shown in  FIG. 6C  and  FIG. 8C , only the mask that covers the top portion of the post P 2  is removed, and the semiconductor layer is etched again. By this etching, a portion of the p-type semiconductor layer of the post P 2  is removed, and the post P 2  becomes lower than the post P 1 . In addition, the grooves  130 - 1 ,  130 - 2  and the groove  130 - 3  are etched, and the depth of the etching reaches the n-type semiconductor layer  110 . In a case where the height of the post P 1  is to be made lower, the mask that covers the top portion of the post P 1  is removed, and then the etching described above is performed. 
         [0048]    As shown in  FIG. 7A  and  FIG. 9A , after the mask M is removed, the insulating layer  172  is formed on the entire surface of the substrate to electrically insulate the p-type semiconductor layer  120  and the n-type semiconductor layer  110  in the grooves  130 - 1 ,  130 - 2 , and  130 - 3 . Then, as shown in  FIG. 7B  and  FIG. 9B , the mask M is formed onto the area excepting top portions of the post P 1  and P 2 , and an etching is performed by using the mask. By this etching, the insulating layer  172  at top portions of the posts P 1  and P 2  are etched out, and the p-type semiconductor layer  120  on the surface is exposed. In addition, at a bottom portion of the groove  130 - 3 , the contact hole  202  is formed in the insulating layer  172 , and the n-type semiconductor layer  110  is exposed. 
         [0049]    Then, the mask M is removed, and an electrode  240  is formed on the entire surface of the substrate as shown in  FIG. 7C  and  FIG. 9C . The electrode  240  is then patterned, and the p-side driving electrodes  160  and  180 , the encapsulating electrodes  170  and  190 , and the n-side driving electrode  200  are formed as shown in  FIG. 1A . 
         [0050]    In a case where the light emitting portion  140  is a VCSEL, after the process of  FIG. 6C  and  FIG. 8C , an oxidizing process is performed. By the oxidizing process, the lowermost layer of the p-type semiconductor layer  120 , an AlAs layer, may be oxidized for a specified distance from a side surface of the post P 1  to obtain a current confining layer. 
         [0051]    An application example of a semiconductor device module according to an example is now described.  FIG. 10A  shows an example of a configuration in which a semiconductor device module is applied to a living object sensor. On the mounting substrate  210  of a semiconductor device module  104 , wiring patterns  220 ,  222 ,  224 , and  226  are formed. Each of the wiring patterns  220 ,  222 ,  224 , and  226  is connected to the n-side driving electrode  200 , encapsulating electrode  170  (p-side driving electrode  160 ), encapsulating electrode  190  (p-side driving electrode  180 ), and n-side driving electrode  200  of the semiconductor device  100 , respectively. The wiring patterns  220  and  222  are connected to a driving circuit  250 , and the wiring patterns  224  and  226  are connected to an amplifier  254 . The driving circuit  250  drives the light emitting portion  140  in response to an input signal from an input circuit  252 , and irradiates a living object  260  with light L 1  having a wavelength of λ from the light emitting portion  140 . The living object may be a human body, for example. Light L 2  reflected off the living object  260  is received by the light receiving portion  150 , and its electrical signal is amplified by the amplifier  254 , and outputted from an output circuit  256 . From this output signal, information regarding the bloodstream can be measured, for example. 
         [0052]    In a case where a semiconductor device module is applied to a living object sensor as described above, each of the light emitting portion  140  and the light receiving portion  150  is encapsulated in the mounting substrate  210  by the encapsulating electrodes  170  and  190 , and thus leakage of light from the light emitting portion  140  to the light receiving portion  150 , or leakage of light received by the light receiving portion  150  to the light emitting portion  140  can be prevented, and a more accurate measurement can be performed. 
         [0053]    A semiconductor device according to an aspect of the present invention and a semiconductor device module using the semiconductor device can be used in fields such as optical data processing, optical high speed data communication, living object sensor, or the like. 
         [0054]    The foregoing description of the examples has been provided for the purposes of illustration and description, and it is not intended to limit the scope of the invention. It should be understood that the invention may be implemented by other methods within the scope of the invention that satisfies requirements of a configuration of the present invention.