Abstract:
A photo sensor has an insulator layer for covering a diode stack, and the insulator layer is made of phtoresist to reduce a side leakage current.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to Taiwan Application Serial Number 96136414, filed Sep. 28, 2007, which is herein incorporated by reference. 
       BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to a method of manufacturing a semiconductor device. More particularly, the present invention relates to a method of manufacturing a photo sensor. 
         [0004]    2. Description of Related Art 
         [0005]    A “Sensor” detects heat, light or magnetic fields and converts the detected physical parameter into electronic signals. By using the signal generated by the sensor, the user can obtain information therefrom. 
         [0006]    According to the above, the data can be produced by a photo sensor that generates a current with light. The photo sensor can be divided into two parts, a transistor and a diode. The mechanism of the photo sensor is that the light is directed to the diode to generate a current, and then the current is amplified from tens to hundreds of times to produce a stronger signal. 
         [0007]    However, in the conventional structure of the photo sensor, the material of the insulating layer used to cover the diode usually is silicon nitride, silicon oxide, or silicon oxy-nitride. Nevertheless, these materials cannot provide good insulation. In addition, since both sides of the diode are easily oxidized into silicon monoxide, the diode cover is degraded and current leakage from the diode through the insulating layer occurs. Furthermore, the conventional material for the insulating layer cannot provide good flatness. Therefore, there is a need to develop a photo sensor to prevent current leakage and to improve the electrical property of the photo sensor. 
       SUMMARY 
       [0008]    The present invention provides a method of manufacturing a photo sensor to simplify the conventional process. 
         [0009]    It is therefore an objective of the present invention to provide a method of manufacturing a photo sensor. First, a substrate having a switching element region and an electronic element region is provided. Next, a gate is formed on the switching element region of the substrate. A gate dielectric layer, a semiconductor layer, and an electrical property enhancement layer are formed in sequence to cover the gate and the substrate. After that, the electrical property enhancement layer and the semiconductor layer are patterned to form a channel region on the gate dielectric layer above the gate. Then, a first conductive layer, a plurality of element function layers and a second conductive layer are formed in sequence to cover the gate dielectric layer and the channel region. Next, the second conductive layer and the element function layers are patterned wherein the element function layers patterned form a diode stack on the first conductive layer of the electronic element region, and the second conductive layer patterned forms a photo-electrode on the diode stack. Furthermore, the first conductive layer is patterned to form a source/drain above the opposite sides of the channel region and expose a part of the electrical property enhancement layer. Then, an insulating layer is formed to cover the source/drain, the diode stack and the photoelectrode wherein the material of the insulating layer is a photoresist. The insulating layer is patterned to form an opening in the insulating layer and the opening exposes the photoelectrode. Moreover, a third conductive layer is formed to cover the insulating layer and the photoelectrode. Finally, the third conductive layer is patterned so that the third conductive layer patterned covers a part of the insulating layer above the source/drain and connects to one side of the photoelectrode near the source/drain along the opening. 
         [0010]    It is another an objective of the present invention to provide a photo sensor having at least one switching element region and an electronic element region on a substrate. The photo sensor comprises a gate, a gate dielectric layer, a channel region, a source/drain, a diode stack, a photoelectrode, a insulating layer and a bias electrode. The gate is disposed on the switching element region of the substrate. The gate dielectric layer covers the gate and the substrate. The channel region is disposed on the gate dielectric layer above the gate. The source/drain is disposed on the opposite sides of the channel region and covers the gate dielectric layer underneath the opposite sides of the channel region. The diode stack is disposed on at least one of the source/drain in the electronic element region. The photoelectrode is disposed on the diode stack. The insulating layer covers the source/drain, the channel region, the diode stack and the photoelectrode, and has an opening to expose a part of the photoelectrode on the diode stack, wherein the material of the insulating layer is a photoresist. The bias electrode is disposed on a part of the insulating layer on the source/drain and connects to one side of the photoelectrode near the source/drain along the opening. 
         [0011]    In the foregoing, compared with the conventional materials such as silicon nitride, silicon oxide or silicon oxynitride used for the insulating layer, the insulating layer made of resin has better insulating effect and less current leakage. Meanwhile, since the insulating layer made of resin can provide better flatness, the surface of the substrate becomes smoother and this is helpful for the later process. 
         [0012]    It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0014]      FIG. 1  is a cross section view of a photo sensor according to one embodiment of the present invention; 
           [0015]      FIGS. 2A-2J  illustrate cross section views of the photo sensor of  FIG. 1  at each manufacturing stage; 
           [0016]      FIG. 3  illustrates a cross section view of the photo sensor having a protective layer according to another embodiment of the present invention; and 
           [0017]      FIG. 4  illustrates the results of the current leakage test for three different diodes. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
         [0019]    Refer to  FIG. 1 .  FIG. 1  illustrates a cross section view of a photo sensor according to one embodiment of the present invention. As show in  FIG. 1 , the photo sensor  100  is arranged on a substrate  102  which can be divided into a switching element region  102  and an electronic element region  104 . The photo sensor  100  comprises a gate  108 , a gate dielectric layer  110 , a channel region  112 , a source/drain  114 , a diode stack  116 , a photo electrode  118 , a insulating layer  120  and a bias electrode  122 . The gate  108  is disposed on the switching element region  104  of the substrate  102  and the gate dielectric layer  110  covers the gate  108  and the substrate  102 . The channel region  112  is disposed on the gate dielectric layer  110  above the gate  108 , and comprises a semiconductor layer  126  and an electrical property enhancement layer  128  disposed on both sides of the semiconductor layer  126 . The source/drain  114  is disposed on the electrical property enhancement layer  128  of the channel region  112  and covers the gate dielectric layer  110  underneath the channel region  112 . 
         [0020]    A diode stack  116  is arranged on one of the source/drain  114  in the electronic element region  106  of the substrate  102  and the photoelectrode  118  is disposed on the diode stack  116 . The insulating layer  120  covers the source/drain  114 , the channel region  112 , the diode stack  116  and both sides of the photoelectrode  118 , and has a opening  124  to expose a part of the photoelectrode  118  on the diode stack  116 . The bias electrode  122  is disposed on a part of the insulating layer  120  on the source/drain  114  and connects to one side  118   a  of the photoelectrode  118  near the source/drain  114  along the opening  124 . 
         [0021]    Next,  FIG. 2A  to  FIG. 2J  illustrate cross section views of the photo sensor  100  of  FIG. 1  described above at each manufacturing stage. As shown in  FIG. 2A , a substrate  102  is provided first, wherein the substrate  102  has a switching element region  104  and an electronic element region  106 . Next, a gate metal layer (not shown) is formed on the substrate and then patterned to form a gate  108  on the switching element region  104  of the substrate  108 . The substrate  102  is a transparent substrate, such as a glass substrate or a plastic substrate. The method used to form the gate metal layer can be physical vapor deposition, and the material used can be for example Mo, Cr, an alloy of Mo and Cr, an alloy of Mo and W, the complex material of Mo—Al—Mo or the complex material of Cr—Al—Cr. The thickness of the gate metal layer is between 2000 Å and 4000 Å. 
         [0022]    Refer to  FIG. 2B , a gate dielectric layer  110 , a semiconductor layer  126 , and an electrical property enhancement layer  128  are formed in sequence on the gate  108  and the substrate  102 . The method used to form these three layers can be chemical vapor deposition wherein the thickness of the gate dielectric layer is between 2500 Å and 4000 Å and is made of silicon nitride. The thickness of the semiconductor layer  126  is between 4000 Å and 1500 Å and the material thereof is amorphous silicon. The thickness of the electrical property enhancement layer  128  is between 1000 Å and 100 Å and the material is doped silicon. 
         [0023]    Refer to  FIG. 2C , the electrical property enhancement layer  128  and the semiconductor layer  126  are patterned to form a channel region  112  on the gate dielectric layer  110  above the gate  108 . 
         [0024]    After that, Refer to  FIG. 2D , a first conductive layer  107 , a plurality of element function layers  116   a ,  116   b ,  116   c  and a second conductive layer  117  are formed in sequence on the gate dielectric layer  110  and the channel region  112 . The element function layers  116   a ,  116   b  and  116   c  are a first doping layer, an intrinsic semiconductor layer, and a second doping layer, respectively. In the embodiment, the method used to form the element function layers  116   a ,  116   b  and  116   c  can be chemical vapor deposition. The element function layer  116   a  is an n-doped silicon layer with thickness between 250 Å and 500 Å. The element function layer  116   b  layer is an amorphous silicon layer with thickness between 4500 Å and 8000 Å. The element function layer  116   c  layer is a p-doped silicon layer with thickness between 110 Å and 200 Å. However, in the embodiment, the element function layers  116   a  and  116   c  are used as exemplified, which can also be p-doped silicon layer and n-doped silicon layer, respectively. The first conductive layer  107  and the second conductive layer  117  can be formed by physical vapor deposition wherein the first conductive layer  107  can be metal, such as copper or the alloy thereof, with thickness between 2000 Å and 4000 Å. The second conductive layer  117  is made of a transparent material, such as indium tin oxide, aluminium zinc oxide, indium zinc oxide, cadmium zinc oxide or the combination thereof, with thickness between 300 Å and 500 Å. In the following process described, the first conductive layer  107  and the element function layer  116   a - 116   c  will further form a source/drain and a diode stack, respectively. 
         [0025]    Refer to  FIG. 2E , the second conductive layer  117  and the element function layers  116   a - 116   c  are patterned so that the element function layers  116   a - 116   c  turns into a diode stack  116  on the first conductive layer  107  of the electronic element region  106 , and the second conductive layer  117  becomes a photoelectrode  118  on the diode stack  116 . Since the photo electrode  118  is made of transparent material, light can directly pass through the photo electrode  118  and then to the diode stack  116  to generate a current, while using the photo sensor  110 . In addition, according to the materials used for the element function layers  116   a - 116   c , it is known that the diode  116  is a PIN diode wherein an amorphous silicon layer is arranged between a p-doped silicon layer and a n-doped silicon layer so that the enlarged depletion region can generate a greater current after being illuminated. 
         [0026]    Refer to  FIG. 2F , the first conductive layer  107  is patterned to form a source/drain  114  above the opposite sides of the channel region  112  and expose a part of the electrical property enhancement layer  128 . The electrical property enhancement layer  128  in the channel region  112  reduces the resistance between the semiconductor layer  126  and the source/drain and  114  to enhance the Ohmic Contact property. The Ohmic Contact property is that the contact resistance between two different materials is small and steady, which will not change as the voltage is changed. Since there is a difference between the energy level of the amorphous silicon material used for the semiconductor layer  126  and that of the metal used for the source/drain  114 , this results in increasing the resistance. Therefore, by arranging a high doped electrical property enhancement layer  128  between the semiconductor layer  126  and the source/drain  114 , electrons can flow between the metal and the semiconductor material much more easily so that the Ohmic Contact property can be improved. Similarly, in the embodiment of the present invention, the Ohmic Contact property between the element function layer  116   b  and the first conductive layer  107 , and between the element function layer  116   b  and the photoelectrode  118  can be improved by the element function layers  116   a  (an n-doped silicon layer) and the element function layers  116   c  (a p-doped silicon layer), respectively. 
         [0027]    Refer to  FIG. 2G , after patterning the first conductive layer  107  is completed, the electrical property enhancement layer  128  is selectively etched to expose a part of the semiconductor layer  126 . 
         [0028]    Next, refer to  FIG. 2H , an insulating layer  120  is formed to cover the source/drain  114 , the channel region  112 , the diode stack  116  and the photoelectrode  118 . After that, the insulating layer  120  is patterned to form an opening  124  in the insulating layer  120  so that a part of the photoelectrode  118  is exposed. In the embodiment, the thickness of the insulating layer  120  is between 0.5 μm and −1.6 μm and can be made of common photoresists, such as phenolic resin, or black matrix photoresist (e.g., the photoresist comprises epoxy resin (Novolac), acrylic resin, etc.). Compared with the conventional material used, such as silicon nitride, silicon oxide, or silicon oxynitride, in this embodiment, the insulating layer  120  made of resin not only provides good impedance ability but also forms better coverage on the side of the diode stack  116  so that the generation of the leakage current can be decreased. 
         [0029]    Refer to  FIG. 2I , the third conductive layer  121  is formed on the second conductive layer  117  in the opening  124  and the insulating layer  120 . The thickness of the third conductive layer  121  is between 2000 Å-and 4000 Å and the material used is metal, such as copper. 
         [0030]    Refer to  FIG. 2J , the third conductive layer  121  is patterned so that the third conductive layer  121  patterned forms a bias electrode  122 . As shown in  FIG. 2J , the bias electrode  122  covers a part of the insulating layer  120  above the source/drain  114  and connects to one side  118   a  of the photoelectrode  118  near the source/drain  114  along the opening  124 . The bias electrode  122  not only provides a bias voltage for the diode stack  126 , but also is an effective shield against the light. 
         [0031]    Furthermore, refer to  FIG. 3 .  FIG. 3  illustrates a cross section view of the photo sensor  100  according to another embodiment of the present invention. In the embodiment, to provide sufficient protection for the photo sensor  100 , a protective layer  123  is formed to cover the insulating layer  120 , the bias electrode  122  and the photoelectrode  118 . Then, the protective layer  123  is patterned so that the protective layer  123  patterned covers the bias electrode  122  and the insulating layer  120  in the electronic element region  106 , and a lighting opening  130  is formed above the diode stack  116  to expose a part of the photoelectrode  118 . In the embodiment, the material used for the protective layer  123  depends on the insulating layer  120 . For example, while the material used for the insulating layer  120  is resin type black matrix photoresist having light shielding function, the protective layer  123  can be made of common photoresist without light shielding function or resin type black matrix photoresist with light shielding function. While the material of the insulating layer  120  is common photoresit without light shielding function, the material used for the protective layer  123  needs to be made of resin type black matrix photoresist with light shielding function to provide better light shield effect. 
         [0032]    To examine whether the photo sensor manufactured by the process above could prevent the leakage current or not, a bias voltage is applied to three kinds of PIN diodes to test the leakage of the current. These three kinds of PIN diodes tested are: (1) PIN diode without an insulating layer; (2) PIN diode with a conventional silicon nitride insulating layer; and (3) PIN diode with a epoxy resin insulating layer. The result is shown in  FIG. 4 . 
         [0033]    Refer to  FIG. 4 .  FIG. 4  illustrates the results of the current leakage test for three different diodes. As shown in  FIG. 4 , the PIN diode without an insulating layer has the greatest leakage current, which is 7.45×10 −9  per unit area (500 μm×500 μm). The conventional PIN diode with a silicon nitride insulating layer has a less leakage current, 1.23×10 −11  per unit area. As to the PIN diode with an epoxy resin insulating layer, it has the fewest leakage current, only 3.4×10 −13 , which is decreased at least 40% compared with that of the conventional diode. 
         [0034]    According to above, compared with the conventional materials such as silicon nitride, silicon oxide or silicon oxynitride used for the insulating layer, the insulating layer made of resin has better insulating effect so that the leakage current can be reduced. Meanwhile, since the insulating layer made of resin can provide better flatness than other materials (e.g., silicon nitride), the surface of the substrate will become smoother and this is helpful for the later process. 
         [0035]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.