Abstract:
An optical device for receiving a light and changing a transmission direction of the received light is disclosed. The optical device includes a substrate having a surface with which the received light is transmitted in parallel; a layer formed on the surface of the substrate; and a reflecting face formed in the layer, the reflecting face being inclined and reflecting the received light to change the transmission direction of the received light.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a U.S. continuation application filed under 35 USC 111(a) claiming benefit under 35 USC 120 and 365(c) of PCT International Application No. PCT/JP02/09295 filed on Sep. 11, 2002, which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention generally relates to optical devices and methods of manufacturing the optical devices, and more particularly, to an optical device used for optical communication or optical pickup, and a manufacturing method thereof.  
         [0003]     Conventionally, optical devices employing a light waveguide path have been utilized for optical switches. For example, as described in an article, A. Himeno et. al., “Silica-Based Planar Lightwave circuits”, IEEE. J. Selected Topics Quantum Electronics, vol. 4, no. 6, pp. 913, 1998, an optical device using a Mach Zender interferometer circuit to switch light path is known.  
         [0004]     In such an optical device, a part of a signal light is taken out to an upper direction and received by a photodiode (PD), for measuring the amount of light. In order to take out the signal light, the optical device has a recess on a substrate, and the recess has at least one inclination face for reflecting the received signal light.  
         [0005]     In order to form a recess in a layer, dry etching processes such as a reactive ion etching process are normally used. When such a recess with a substantially vertical wall (vertical face) and an inclined wall (inclined face) is formed on the substrate, a mask for etching the inclined portion is required to be inclined also.  
         [0006]     For example, if an etching selective ratio between mask material and etched material is assumed to be 1, the mask generally should have an inclined portion whose angle is the same as that of the material to be etched, as shown in  FIG. 1 .  
         [0007]     In  FIG. 1 , on a substrate  10 , a layer  12  to be etched is formed. On the layer  12 , a mask  14  and a mask  15  are formed. The mask  14  has a vertical face  14   a , and the mask  15  has an inclined face  15   a.    
         [0008]     Instead of inclining the face  15   a  of the mask  15 , a mask  16  may have a step-like face  16   a  by overlaying plural layers with shifting one by one, as shown in  FIG. 2 . The mask  16  having the step-like face  16   a  can be used for etching an inclined face in the layer  12 . However, in order to smooth the step-like face  16   a , the number of steps should be increased, requiring many processes such as multiple times of applying resists, exposing and developing.  
         [0009]     The incrementing of the number of processes worsens mask accuracy, makes inclined faces uneven, and increases manufacturing costs.  
       SUMMARY OF THE INVENTION  
       [0010]     A general object of the present invention is to provide optical devices and methods for manufacturing thereof, which avoid incrementing the number of processes, provide accurate masks, reduce unevenness of inclination faces, and reduce manufacturing costs.  
         [0011]     The above object of the present invention is achieved by an optical device for receiving a light and changing a transmission direction of the received light, comprising: a substrate having a surface with which the received light is transmitted in parallel; a layer formed on the surface of the substrate; and a reflecting face formed in the layer, the reflecting face being inclined and reflecting the received light to change the transmission direction of the received light. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  illustrates a prior art method for forming an inclined face;  
         [0013]      FIG. 2  illustrates another prior art method for forming an inclined face;  
         [0014]      FIG. 3  is a plan view of a mask according to an embodiment of the present invention;  
         [0015]      FIG. 4  is a cross-sectional view of an optical device according to the embodiment of the present invention;  
         [0016]      FIG. 5  is a plan view of a mask according to another embodiment of the present invention;  
         [0017]      FIG. 6  is a cross-sectional view of an optical device according to another embodiment of the present invention;  
         [0018]      FIGS. 7A through 7D  illustrate manufacturing process steps according to the embodiment of the present invention;  
         [0019]      FIGS. 8A and 8B  are a plan view of a mask and a cross-sectional view of an optical device, respectively, according to a further embodiment of the present invention; and  
         [0020]      FIG. 9  is a perspective view of a communication device to which the present invention is applicable. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     The following is a description of embodiments of the present invention, with reference to the accompanying drawings.  
         [0022]     In the embodiments of the present invention, one process of dry etching utilizing the micro loading effect can form a recess with a vertical side wall (vertical face) and an inclined side wall (inclined face). The micro loading effect is an effect that etching rates differ depending on area sizes of regions to be etched in an etching process, that is, the smaller the area size is, the lower the etching rate is. The present inventors found that it is possible to control the micro loading effect by adequately selecting mask shape and thereby obtain an etched inclined face with a desired inclination.  
         [0023]     In order to form such a recess with a vertical face and an inclined face in one process, an opening of a mask is narrowed over an upper portion of the inclined face and widened over a lower portion of the inclined face. In this manner, the difference in the width of the mask opening gives different etching rates of the inclined face. That is, the etching rate becomes higher under the widened opening of the mask, and becomes lower under the narrowed opening of the mask due to the micro loading effect, resulting in an inclined face. This method can drastically reduce process steps required for forming an inclined face, compared with step-like masks.  
         [0024]     In an embodiment shown in  FIG. 3 , a mask  22  is formed, which has a mask opening  20  having a substantially triangle shape. By performing a reactive ion etching (RIE) process on a layer  24  using this mask  22 , a recess  26  with a vertical face  24   a  and an inclined face  24   b  can be formed in the etched layer  24 , as shown in  FIG. 4 . Needless to say, the mask  22  itself does not have to have an inclined portion.  
         [0025]      FIG. 5  is a plan view of a mask according to another embodiment of the present invention. A mask  34  is formed, which has a mask opening  30 , as shown in  FIG. 5 . The mask opening  30  comprises a substantially triangle-shaped main opening  31 , a substantially triangle-shaped dummy opening  32  and a connection opening  33  for connecting the tops of the two triangles  31  and  32 .  
         [0026]     The main opening  31  and the dummy opening  32  have 200 μm long base sides, which are orthogonal to the longitudinal axis of the connection opening  33 . Both ends of the base sides are shaped as circular arcs having a curvature radius of 30 μm, in order to prevent from cracking from these ends when patterning the mask  34 .  
         [0027]     If all the three tops of the main opening  31  are shaped as circular arcs having a curvature radius of 30 μm, it becomes difficult to form by the micro loading effect an inclined face having enough inclination for reflecting. Accordingly, the facing tops of the main opening  31  and the dummy opening  32  are narrowed to 2 μm width and connected by the connection opening  33 .  
         [0028]     In this manner, the width at the top of the main opening  31  can be 2 μm, and it is possible to form by the micro loading effect an inclined face having enough inclination for reflecting, and to prevent cracking. The dummy opening  32  is formed in order to treat the end portion of the connection opening  33 , and therefore it does not have to be a mirror image of the main opening  31 .  
         [0029]      FIG. 6  shows a cross section of the etched layer having a recess with a vertical face and an inclined face formed in accordance with the embodiment of the present invention. On a silicon substrate  40 , a layer  42  to be etched is formed by the CVD method. The layer  42  has a thickness of about 50 μm and is made of mainly SiO 2 . The layer  42  to be etched is provided a light waveguide path  43  therein.  
         [0030]     The mask shown in  FIG. 5  is overlaid on the layer  42  to be etched, and the RIE etching is performed so as to form a recess  44  with a vertical face  42   a  and an inclined face  42   b  in the layer  42  to be etched. The inclination angle of the inclined face  42   b  is 49.8°. The recess  44  is formed by the main opening  31  of the mask  34 . Similarly, the recess  45  having a vertical face  42   c  and an inclined face  42   d  is formed by a dummy opening  32 . The plan view shapes of the recesses  44  and  45  are the same as the shapes of the main opening  31  and the dummy opening  32  of the mask shown in  FIG. 5 .  
         [0031]     A light passing through the light waveguide path  43  is emitted at the vertical face  42   a  into the recess  44  and reflected by the inclined face  42   b  to an upper direction in  FIG. 6 . Applying metal such as Au or Al by vapor deposition onto the inclination face  42   b  improves light reflectivity. After Au is vapor deposited onto the inclined face  42   b , the recess  44  is filled with matching material and a photo diode is mounted along the light axis of the reflected light, then a monitor function is realized for monitoring the light passing through the light waveguide path  43 .  
         [0032]     Next, a manufacturing process in accordance with embodiments of the present invention is explained below.  
         [0033]     First, as shown in  FIG. 7A , on a silicon substrate  50 , a layer  52  to be etched is formed. The layer  52  is made of mainly SiO 2 . The layer  52  to be etched is provided a light waveguide path therein. Further, on the whole top surface of layer  52 , a chromic (Cr) layer  54  is formed as a mask.  
         [0034]     Next, as shown in  FIG. 7B , a resist  56  is formed, and then the resist  56  is partially removed at a mask position. Thereafter, the chromic layer  54  is etched using the resist  56 , to obtain a chromic mask  55  as shown in  FIG. 7C . The mask  55  has, for example, the shape as shown in  FIG. 5 .  
         [0035]     Further, using the mask  55 , the RIE is performed to form a recess  58  having a vertical face and an inclined face as shown in  FIG. 7D .  
         [0036]     In this manner, since the mask can be manufactured by only one process, it becomes possible to avoid increasing process steps, to give accurate masks, to reduce variation in inclination, and to reduce manufacturing cost.  
         [0037]     The above embodiment is explained with respect to refection of the light emitted from the light waveguide path, but the present invention can also be applied to reflection of a light emitted from an optical fiber. It is possible to insert a light source such as a semiconductor laser or an optical diode within the recess, and reflect the light emitted from the light source. This structure can be utilized in a pick up device in CD or DVD players.  
         [0038]     As shown in  FIG. 8A , a mask  62  having a triangle opening  60  whose top is directed to an incident light can also be used for an RIE process. In this case, as shown in  FIG. 8B , a recess  66  with an inclination face  64   b  and a vertical face  64   a  can be formed. Light passing through a light waveguide path  65  can be easily reflected to substrate  68  (lower direction in  FIG. 8B .)  
         [0039]      FIG. 9  is a perspective view of a communication device according to another embodiment of the present invention. On a silicon substrate  70 , a light waveguide path forming layer  72  made of SiO 2  is formed. In the layer  72 , light waveguide paths  73 ,  74  and  75  are formed. Light is input from the outside to one end of the light waveguide path  73 . The other end of the light waveguide path  73  is terminated with a light shielding recess  78 . The light waveguide path  74  emits light to the outside. The light waveguide paths  73  and  74  are arranged close to each other at two locations, where 3 dB couplers  76 ,  77  are formed. Between the 3 dB couplers  76  and  77 , a heating element  79  is provided on the light waveguide path  73 . Whether to drive the heating element  79  as a light switch determines whether to output the light signal from the light waveguide path  74 .  
         [0040]     The light waveguide paths  73  and  75  are placed close to each other at one location and constitute a light coupler  80  there. The coupler  80  divides 1/20 of the light passing through the light waveguide path  73  out to the light waveguide path  75 . One end of the light waveguide path  75  is terminated with a recess  82  as shown in  FIG. 6 . A photo diode (not shown) is mounted over an inclined face of the recess  82 , with a light receiving face of the diode being coaxial to a light reflected by the inclined face. The photodiode  84  can monitor the light transmitting through the light waveguide path  75 .  
         [0041]     It should be noted that the present invention is not limited to the embodiments specifically disclosed above, but other variations and modifications may be made without departing from the scope of the present invention.