Abstract:
The present invention belongs to the technical field of optical interconnection and relates to a photo detector, in particular to a photo detector consisting of tunneling field-effect transistors.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention belongs to the technical field of optical interconnection and relates to a photo detector, in particular to a photo detector consisting of tunneling field-effect transistors. 
     2. Description of Related Art 
     Compared with the traditional aluminum, copper has the following advantages: 1, the resistivity of copper is smaller (Cu: 1.7 μΩ/cm, Al: 3 μΩ/cm; 2, the parasitic capacitance of the copper interconnection is smaller than that of the aluminum interconnection; 3, due to low resistance, the power consumption of the copper interconnection is smaller than that of the aluminum interconnection; 4, the electro-migration resistance of copper is better than that of aluminum (Cu&lt;10 7  A/cm 2 , Al&lt;10 6  A/cm 2 ), connection cavities generated by electro-migration are avoided, so that the reliability of the device is improved. Therefore, devices adopting copper interconnections are able to meet the requirements of high frequency, high integration, large power, large capacitance and long service life; and the traditional aluminum interconnection process is gradually replaced by the copper interconnection process. 
     With the further development of integrated electronic device technology, the power consumption and delay of copper interconnections also has gradually failed to meet demands, so the pursuit of technology with lower power consumption and faster interconnection is the future development trend. Compared with copper interconnections, optical interconnections have the advantages of high bandwidth and low loss, and have no problems in crosstalk, matching, and electromagnetic compatibility. The single-chip optical interconnection has been widely applied at present; in the future, the optical interconnection stands a good chance to replace the copper interconnection. 
     In the optical interconnection technology, the photo detector converts the optical signals and the electric signal plays the main role. Usually, the photo detector consists of p-i-n diodes. The basic structure is shown in the  FIG. 1 : a blocking layer (intrinsic layer), namely i layer  100   b,  is added between the p area  100   a  and the n area  100   c  of the common photoelectric diode, and light reaches the p area via an anti-reflection film  104 . With a protective film  102  and electrodes  101 ,  103 , when a high reverse bias is applied to the pn node, the blocking layer of the pn node produces photon-generated carriers under the light, and the photon-generated carriers are driven by the external bias to drift directionally so as to produce photo-generated current. 
     Due to the thick blocking layer, the node capacitance of the p-i-n diode changes are small and the blocking electric field becomes thicker, which enlarges the area for light absorption and light conversion, so the quantum efficiency is improved and the wavelength sensitivity is increased at the same time. However, the thickening of the blocking layer influences the response speed of the photo detector to a large extent, and the p-i-n diode requires a higher bias to make ionizing collisions appear in the diode, so the power consumption is increased. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention aims to provide a photo detector with low product energy consumption and fast response speed. 
     To fulfill the mentioned aim, the present invention provides a photo detector consisting of tunneling field-effect transistors. The structure of the photo detector comprises: 
     a semiconductor substrate; 
     Tunneling field-effect transistor formed on the semiconductor substrate; 
     and a fiber and reflection layer formed on the tunneling field-effect transistor. 
     Moreover, the tunneling field-effect transistor has a vertical channel structure, comprising a drain region of a first doping type formed underneath the vertical channel, a resource region of a second doping type formed above the vertical channel, and gate regions formed on two sides of the vertical channel. 
     Moreover, the angle between the reflection layer and the surface of the semiconductor substrate is 30-60 degrees, and the light rays in the fiber are able to pass through the reflection layer and then reach the source region of the tunneling field-effect transistor, so the photon-generated carriers arc produced. 
     The present invention also provides a method for manufacturing a photo detector consisting of a tunneling field-effect transistor. The method comprises the following steps: Provide a semiconductor substrate; 
     Perform ion injection to form a doped region of a first doping type in the semiconductor substrate; 
     Form a hard mask layer; 
     Form a first photoresist layer; 
     Mask, expose and etch to form a vertical channel structure of a device; 
     Strip the first photoresist layer; 
     Form a first insulating film layer; 
     Form a first conductive film layer; 
     Form a second photoresist layer; 
     Mask, expose and etch the first conductive film layer to form a gate electrode; 
     Perform ion injection to form a drain region of a second doping type; 
     Strip the second photoresist layer; 
     Etch part of the first insulating film layer and etch to remove the rest hard mask; 
     Form a second insulating film layer and etch the second insulating film layer; 
     Form a third insulating film layer and etch the second insulating film layer to form a contact hole; 
     Form a second conductive film layer and etch the second conductive film layer to form an electrode; 
     Form a lower cladding of a fiber; 
     Form a core layer of the fiber; 
     Form an upper cladding of the fiber; 
     Etch the upper cladding, the core layer and the lower cladding of the fiber to form a slope of 45 degrees; 
     and form a reflective layer. 
     Furthermore, the semiconductor substrate may be single-crystalline silicon, polycrystalline silicon or Silicon on the insulator (SOI). The hard mask is made from silicon nitride. The first insulating film may be made from one or mixture of several of SiO 2 , HfO 2 , HfSiO 2 , HfSiON, SiON and Al 2 O 3 . The second and third insulating films are made from silicon dioxide or silicon nitride. The first conductive film is made of metals such as TiN, TaN, RuO 2  and Ru or doped polycrystalline silicon. The second conductive film is made of aluminum, tungsten, or other metal materials. The reflective layer is made of a metal material such as aluminum or silver. 
     Furthermore, the first doping type is an n type, and the second doping type is a p type. Or, the first doping is a p type, and the second doping type is an n type. 
     In this invention, the tunneling field-effect transistor (TFET) is integrated with the fiber, the TFET with the vertical channel is used as the photo detector to detect light, so the required bias is low, the energy consumption is reduced, and the output current and the sensitivity of the photo detector are improved. Meanwhile, the invention also adopts an autocollimation technology to manufacture the photo detector consisting of the TFET, so the process is more stable and the production cost is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a sectional view of the p-i-n photo detector of the prior art. 
         FIG. 2  is a sectional view of the photo detector in one embodiment provided by the present invention. 
         FIGS. 3 to 15  are process flow for manufacturing the photo detector in the embodiment as shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is further described in detail by combining the attached drawings and the embodiments. In the figure, to facilitate description, the layer thickness and region thickness are amplified, but the sizes do not represent the actual dimensions. The figures fail to reflect the actual dimensions of the device accurately, but show the mutual positions of the regions and the structures, specifically the vertical and horizontal neighborhood of the structures. 
     The reference drawing provides schematic views of an ideal embodiment of the present invention. The embodiment of the present invention shall not be limited to the specific shapes of the regions as shown in the figure, but shall comprise all shapes, like deviations caused by manufacturing. For example, an etched curve is usually characterized by a bend or roundness and smoothness. But in this embodiment, all curves are represented by rectangles. The figure is schematic and shall not be considered as a limit of the present invention. Meanwhile, in the below description, the term “substrate” may be considered to comprise a semiconductor substrate being processed or other films prepared on the semiconductor substrate. 
       FIG. 2  illustrates an embodiment of the photo detector consisting of the tunneling field-effect transistor, which is a sectional view along the length direction of the channel of the device. As shown in  FIG. 2 , the photo detector is formed on a silicon substrate  201 , comprising a TFET portion, a fiber portion and a reflection layer  214 . The TFET comprises a source region  202 , a drain region  207 , a gate dielectric layer  205  and a gate electrode  206 , and a metal electrode  210  is connected to the position of the source region  202 . The fiber comprises a lower cladding  211 , a core layer  212  and an upper cladding  213 ,  208  and  209  represent insulation dielectric layers, for example silicon diode. Light rays in the fiber are able to reach the source region  202  of the TFET after being reflected by the reflection layer  214 , to produce the photon-generated carriers. When appropriate voltage is applied to the TFET, the TFET is switched on, and then the photon-generated carriers drift directionally to produce a photon-generated current. The gate voltage of the TFET makes the electric field in the channel rise, so the photon-generated carriers further perform collision ionization. Such phenomenon amplifies the photon-generated current, therefore this kind of devices still have high optical sensitivity under the condition of low voltage at the source region and drain region. 
     The photo detector consisting of the tunneling field-effect transistor is capable of being manufactured by many methods. The following is the process flow of one embodiment for manufacturing the photo detector as shown in  FIG. 2 . 
     First, provide a silicon substrate  201  and then perform n-type ion injection to form an n-type doped region  202  in the silicon substrate  201 , as shown in  FIG. 3 . Second, deposit a layer of hard mask  203 , for example made from silicon nitride, deposit a photoresist layer, perform masking, exposure and development to form a required pattern, etch the hard mask  203  and the silicon substrate  201  to form a vertical channel structure of a device, and strip the photoresist to obtain a product as shown in  FIG. 4 . 
     Third, deposit an insulating film  205 , a conductive film  206  and a photoresist layer in turn, perform masking, exposure and etching on the conductive film  206  to form a gate electrode of the device, and strip the photoresist to obtain a product a shown in  FIG. 5 , wherein the insulating film  205  is one or two layers in the silicon dioxide and high-k material layers, and the conductive film  206  may be the doped polycrystalline silicon. 
     Fourth, perform p-type ion injection to form a drain region  207  of the device, as shown in  FIG. 6 . 
     After the drain region  207  is formed, etch to remove part of the insulating film  205  and the rest hard mask  203  to form a structure as shown in  FIG. 7 .  FIG. 8  is a top view of the TFET portion  200  of the structure as shown in  FIG. 7 . 
     Five, deposit an insulating film  208  which may be made from silicon nitride and etch the silicon diode film  208 , as shown in  FIG. 9 .  FIG. 10  is a top view of the TFET portion  200  of the structure as shown in  FIG. 9 . 
     The process for manufacturing the photo detector of the present invention is described on the basis of the TFET portion  200  of the structure as shown in  FIG. 3   f.    
     First, deposit an insulating film  209  which may be made from silicon dioxide, etch the silicon dioxide film to form a contact hole, deposit a conductive film  210  which may be made of aluminum, and etch the conductive film  210  to form a metal electrode, as shown in  FIG. 11 . 
     Second, form a lower cladding  211 , a core layer  212  and an upper cladding  213  of a fiber in turn, wherein the reflectivity of both the upper cladding  213  and the lower cladding  211  is smaller than that of the core layer  212 , as shown in  FIG. 12 .  FIG. 13  is a top view of the structure as shown in  FIG. 12 ; 
     Third, etch the upper cladding  213 , the core layer  212  and the lower cladding  211  of the fiber to form a slope of 45 degrees, deposit a silver metal and then etch the sliver layer to form a reflection layer  214  of the device, as shown in  FIG. 14 .  FIG. 15  is a top view of the structure as shown in  FIG. 14 ; 
     As mentioned above, a plurality of embodiments with great different may be constructed. It should be noted that, except those defined in the attached claims, the present invention is not limited to the embodiments in the description.