Abstract:
On a module substrate on which a wiring pattern is formed, an integrated circuit device is mounted via solder bumps so that the front surface thereof faces the module substrate. An optical fiber is seated within a groove formed on the rear surface of the integrated circuit device. Additionally, a photo-detecting device is mounted on the module substrate for receiving light transmitted through the optical fiber. This allows the photo-detecting module to reduce the number of mounted parts and to be fabricated in less time.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photo-detecting module for use as an optical receiver in an optical transmission system. 
     2. Description of the Related Art 
     The photo-detecting module comprises such components as a photo-detecting device for converting received optical signals into electric signals, and an integrated circuit device having a pre-amplifier for extracting the electric signal from the photo-detecting device and the like. As shown in FIG. 1, a prior art photo-detecting module employs separate silicon substrates for the components. Referring to the figure, reference numeral  26  denotes a silicon substrate,  27  a photo-detecting device,  28  an integrated circuit device, and  29  bonding wires. 
     For this reason, when these components constitute a circuit-built-in module, separate rooms are required for respective components as shown in FIG.  1 . In addition, in typical cases, bonding wires are used for connecting an optical segment to an integrated circuit device segment and for connecting the integrated circuit device to the package. The bonding wires are required to be equal to or more than 1 mm in length to provide a room for mounting, thus presenting a problem of inducing deterioration in high-frequency property. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a photo-detecting module that allows the number of mounted parts to be reduced and the time for fabrication to be reduced by using the rear surface of a semiconductor integrated circuit device as a member for seating an optical fiber. Another object is to provide a photo-detecting module that is given an improved high-frequency property by flip-chip mounting a semiconductor integrated circuit device via solder bumps and thus eliminating the need for respective connections to the photo-detecting device using bonding wires. 
     The photo-detecting module according to the present invention comprises a module substrate on which a wiring pattern is formed. An integrated circuit device is mounted on said module substrate via solder bumps so that the front surface thereof where an integrated circuit is provided faces said module substrate. Said integrated circuit device has a groove on the rear surface thereof. An optical fiber is seated within said groove formed on the rear surface of said integrated circuit device. A photo-detecting device is mounted on said module substrate for receiving light transmitted through said optical fiber. 
     Said integrated circuit device and photo-detecting device may be mounted on a block that is used for positioning those in the direction of height. 
     Furthermore, said groove may be formed in the shape of letter V. Also, an optical fiber retainer may hold said optical fiber by sandwiching said optical fiber with said integrated circuit device. 
     According to the present invention, the optical fiber is seated within an optical fiber seat groove provided on the integrated circuit device, and the semiconductor integrated circuit device is flip-chip mounted on the module substrate via solder bumps. Moreover, the photo-detecting device and the semiconductor integrated circuit device are connected to each other by means of a wiring pattern provided on the module substrate. Such use of the rear surface of the semiconductor integrated circuit device as an optical fiber seat member allows the number of mounted parts to be reduced and the time for fabrication to be reduced. In addition, flip-chip mounting of the semiconductor integrated circuit device via solder bumps eliminates the need for respective connections to the photo-detecting device using bonding wires, thus also enabling providing an improved high-frequency property. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing a prior art photo-detecting module. 
     FIG. 2 is a view showing a photo-detecting module according to an embodiment of the present invention. 
     FIG. 3 is a view showing a wiring pattern on the module substrate of the photo-detecting module of FIG.  2 . 
     FIG. 4A is a view showing the light-incident side of a photo-detecting device for use in the photo-detecting module of FIG. 2, and FIG. 4B is a view showing the side of the electrode thereof. 
     FIG. 5 is a detailed view showing a carrier of the photo-detecting device for use in the photo-detecting module of FIG.  2 . 
     FIG. 6 is a view showing an integrated circuit device for use in the photo-detecting module of FIG. 2, and an optical fiber seat groove formed on the back thereof. 
     FIG. 7 is a cross-sectional view showing the photo-detecting module of FIG.  2 . 
     FIG. 8 is a detailed view showing the photo-detecting device of a front-incident type for use in the photo-detecting module of the present invention. 
     FIG. 9 is a cross-sectional view showing a photo-detecting module according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 shows a photo-detecting module according to an embodiment of the present invention. 
     On a module substrate  1 , there are mounted a carrier  3  on which a photo-detecting device  2  is mounted, and a semiconductor integrated circuit device  4 . There is formed an optical fiber seat groove  5  on the semiconductor integrated circuit device  4 . An optical fiber  6  is seated within the optical fiber seat groove  5  and is sandwiched by an optical fiber retainer  7  to be held therebetween. On the module substrate  1 , there are provided electrode patterns such as a signal wire  8  for fixing the semiconductor integrated circuit device  4  for electrical connection, power/GND wires  9 , and control terminal wires  10 . 
     FIG. 3 is a view showing the carrier  3  and the semiconductor integrated circuit device  4  which are indicated by dashed lines and of which wiring patterns extend to the lower portions where the carrier  3  and semiconductor integrated circuit device  4  are mounted. FIG. 2 is a view showing the core portion of the photo-detecting module of the present invention, and no particular limitation is given to the structure and configuration of other surrounding portions. 
     Now, respective components are explained. 
     FIGS. 4A and 4B show the pattern of the photo-detecting device  2 . A photo-detecting device of a rear-incident type is taken as an example. FIG. 4A shows a light-incident side and FIG. 4B shows an electrode side. The light emitted from the optical fiber  6  is allowed to be incident on the light-incident region  11  shown in FIG.  4 A. Photocurrent is outputted from a p electrode  12  shown in FIG. 4B. A solder bump  14  is provided on both p and n electrodes to fixedly mount the photo-detecting device  2  on the carrier  3 . 
     FIG. 5 shows the carrier  3  in detail. 
     The photo-detecting device  2  is provided, on the mount surface thereof, with an electrode  15  located to the photo-detecting device  2 , and is fixed via the solder bump. The electrode  15  is bent to extend to an edge face. On the electrodes of the edge face, there are provided solder bumps  16  for connecting to the module substrate  1 . The photo-detecting device  2  is fixedly positioned with high accuracy to the carrier  3  so as to be coupled to the light emitted from the optical fiber  6  in an optimal manner when a photo-detecting device  2  is assembled with the carrier  3  into a module. 
     FIG. 6 shows the semiconductor integrated circuit device  4  on which the optical fiber seat groove  5  is formed that characterizes the present invention. An integrated circuit device composed of silicon is taken as an example here for explanation. 
     Silicon substrates are employed as material for use in many integrated circuit devices. Taking advantage of the anisotropic etching property of silicon, the silicon substrate is applied to the. highly accurate V-shaped groove substrate for seating an optical fiber. Therefore, a silicon-based semiconductor integrated circuit device is also used as an optical fiber seat substrate. 
     First, a pattern for forming the V-shaped groove is formed on the rear side of a silicon substrate that has gone through the steps of an integrated circuit device. 
     Next, an etching passivation film is formed on the side of integrated circuit device and then a V-shaped groove that is employed as an optical fiber seat groove is formed by etching. After the formation of the V-shaped groove, the etching passivation film is removed to allow solder bumps  22  to be formed on pad electrodes  23 . 
     The use of the V-shaped groove allows the optical fiber to be held at three points on the circumference thereof by means of said V-shaped groove and an optical fiber retainer, thereby positively securing the optical fiber. 
     Although the above explanation was made taking silicon as an example, the present invention is not intended to specify materials or formation method as the requirements for the configuration thereof so long as the integrated circuit device has an optical fiber seat groove formed. 
     FIG. 7 is a cross-sectional view showing a photo-detecting module of the present invention. The carrier  3 , on which the photo-detecting device  2  is mounted, and the optical fiber  6  are mechanically positioned with each other and fixed by a passive alignment mounting technique without optical alignment so as to provide optimal optical properties. The respective electrodes of the module substrate  1 , the photo-detecting device  2 , and the semiconductor integrated circuit device  4  are electrically connected to each other via solder bumps that are formed respectively. In this embodiment, the accuracy in the direction of height depends on that of the solder bumps formed, respectively, which is of the order of a few micrometers. 
     FIG. 8 shows the case where a photo-detecting device  13  of a front-incident type is employed. Like in FIG. 5, an electrode  21  is formed on the mount surface of the photo-detecting device  13  and on the edge face thereof as well, and solder bumps  20  for connecting to the module substrate  1  are formed on the edge face. The difference from FIG. 5 is that a bonding wire  19  is employed for electrical connection. 
     In this embodiment, a single bonding wire is employed to extract signals from the photo-detecting device. However, the bonding wire is only 100 to 200μm in length and deterioration in high-frequency property of this portion is therefore not appreciable, thus never departing from the feature of the present invention. 
     An embodiment shown in FIG. 9 is a mounting structure for providing an improved accuracy in the direction of height. A projecting block  24  is disposed for positioning in the direction of height, and the carrier  3  and the semiconductor integrated circuit device  4  are fixedly mounted by being brought into contact therewith. This configuration provides mounting accuracy of the order of sub-micrometer in the direction of height.