Abstract:
A manufacturing method for a vertical transistor of random-access memory, having the steps of: defining an active region on a semiconductor substrate; forming a shallow trench isolation structure outside of the active region; etching the active region and forming a gate dielectric layer and a positioning gate thereon, forming a word line perpendicular to the positioning gate; forming spacing layers on the outer surfaces of the word line; implanting ions to the formed structure in forming an n-type and a p-type region on opposite sides of the word line with the active region; forming an n-type and a p-type floating body respectively on the n-type and p-type region; forming a source line perpendicular to the word line and connecting to the n-type floating body; forming a bit line perpendicular to the source line and connecting to the p-type floating body. Hence, a vertical transistor with steady threshold voltage is achieved.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The instant disclosure relates to a memory device and manufacturing method thereof: more particularly, to a vertical transistor for random-access memory and manufacturing method thereof. 
         [0003]    2. Description of Related Art 
         [0004]    For the mainstream IC processing, the most common transistor is the MOSFET (metal-oxide-semiconductor field-effect transistor). Like typical transistors, the current flows through the channel region of the MOSFET. In particular, n-type MOSFET (nMOSFET, nMOS) is provided with conducting electrons, whereas p-type MOSFET (pMOSFET, pMOS) uses conducting “holes” for operation. 
         [0005]      FIG. 1  shows a typical p-type MOSFET (pMOS), which comprises an n-type substrate  1   a , a gate  2   a , and two spacers  3   a . As a source and a drain, a first doping area  11   a  and a second doping area  12   a  are disposed on the n-type substrate  1   a . An oxide film  13   a  is disposed on the n-type substrate  1   a . The gate  2   a  is disposed on the oxide layer  13   a , and the spacers  3   a  are disposed on the sides of the gate  2   a  over the oxide layer  13   a . The source, drain, and the gate  2   a  of the above-described pMOS are arranged horizontally, which occupy more surface of the n-type substrate  1   a . Thus, the packing density of the semiconductor element is restricted. In addition, after repeated read or write access operation, electric charge accumulation tends to occur. The threshold voltage V t  becomes more fluid, rendering the pMOS to be less stable. 
       SUMMARY OF THE INVENTION 
       [0006]    The instant disclosure encompasses a vertical transistor for random-access memory and manufacturing method thereof. The disclosed vertical transistor can maintain a steady threshold voltage and improve packing density of semiconductor elements. 
         [0007]    In one aspect, the instant disclosure encompasses a manufacturing method of vertical transistor for random-access memory. The manufacturing steps include: defining an active region of a semiconductor substrate and forming a shallow trench isolation structure outside the active region; etching the active region, forming a gate dielectric layer and a positioning gate therein, and forming a word line perpendicular to the positioning gate and forming spacing layers on the outer surface of the word line; implanting ions to form an n-type region and a p-type region respectively for the active region on opposite sides of the word line; covering the above-described structure with an insulating layer: removing the insulating layer partially to form a source line pattern by the self-align contact (SAC) technique; forming two floating bodies by epitaxial deposition and implanting with ions to form an n-type floating body on the n-type region of the active region and a p-type floating body on the p-type region of the active region, and covering the above-described structure with an insulating layer; removing the insulating layer corresponding to the n-type floating body by the self-align contact technique, and forming a source line perpendicular to the word line and connecting to the n-type floating body; covering the above-described structure with an insulating layer and removing the insulating layer corresponding to the p-type floating body by the self-align contact technique; forming a bit line perpendicular to the source line and connecting to the p-type floating body. 
         [0008]    In another aspect, the instant disclosure encompasses a vertical transistor for random-access memory fabricated by the above-described manufacturing method. 
         [0009]    Based on the above, the transistor fabricated by the manufacturing method of vertical transistor for random-access memory can maintain a steady threshold voltage (V t ) and improve packing density by significantly reducing the occupied space of the transistor in the horizontal direction. 
         [0010]    In order to further appreciate the characteristics and technical contents of the instant disclosure, references are hereunder made to the detailed descriptions and appended drawings in connection with the instant disclosure. However, the appended drawings are merely shown for exemplary purposes, rather than being used to restrict the scope of the instant disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a schematic view of a metal-oxide-semiconductor field-effect transistor (MOSFET) of the related art. 
           [0012]      FIGS. 2-1  and  2 - 2  show a flow diagram of the instant disclosure. 
           [0013]      FIG. 3A  shows a top view for a manufacturing step S 101  of the instant disclosure. 
           [0014]      FIG. 3B  shows a sectional view of  FIG. 3A . 
           [0015]      FIG. 4A  shows a top view for a manufacturing step S 102  of the instant disclosure. 
           [0016]      FIG. 4B  shows a sectional view of  FIG. 4A . 
           [0017]      FIG. 5A  shows a top view for a manufacturing step S 103  of the instant disclosure. 
           [0018]      FIG. 5B  shows a sectional view of  FIG. 5A . 
           [0019]      FIG. 6A  shows a top view for a manufacturing step S 104  of the instant disclosure. 
           [0020]      FIG. 6B  shows a sectional view of  FIG. 6A . 
           [0021]      FIG. 7A  shows a top view for a manufacturing step S 105  of the instant disclosure. 
           [0022]      FIG. 7B  shows a sectional view of  FIG. 7A . 
           [0023]      FIG. 8A  shows a top view for a manufacturing step S 106  of the instant disclosure. 
           [0024]      FIG. 8B  shows a sectional view of  FIG. 8A . 
           [0025]      FIG. 9A  shows a top view for a manufacturing step S 107  of the instant disclosure. 
           [0026]      FIG. 9B  shows a sectional view of  FIG. 9A , 
           [0027]      FIG. 10A  shows a top view for a manufacturing step S 108  of the instant disclosure. 
           [0028]      FIG. 10B  shows a sectional view of  FIG. 10A . 
           [0029]      FIG. 11A  shows a top view for a manufacturing step S 109  of the instant disclosure. 
           [0030]      FIG. 11B  shows a sectional view of  FIG. 11A . 
           [0031]      FIG. 12  shows a sectional view of disposing a planar transistor on an edge region B of the instant disclosure. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    Please refer to FIGS.  2 - 1 - 11 B, wherein  FIGS. 2-1  and  2 - 2  show a flow diagram of the instant disclosure, while  FIGS. 3A-11B  show plan views of the instant disclosure. 
         [0033]      FIGS. 2-1  and  2 - 2  correspond to  FIGS. 3A to 11B , wherein  FIGS. 2-1  and  2 - 2  refer to a manufacturing method of vertical transistor for random-access memory. 
         [0034]      FIGS. 3A and 3B  are graphical illustrations of step S 101  and represent a part of a memory device. The part of the memory device is made up by a plurality of unit regions. For the instant embodiment, a unit region A is selected for explanation purpose.  FIG. 3A  is a top view for part of the memory device, and  FIG. 3B  is a sectional view of  FIG. 3A . 
         [0035]    First, an active region  11  of a semiconductor substrate  1  of the unit region A is defined. Next, the semiconductor substrate  1  is etched to form trenches  12 . Dielectric material is deposited to fill the trenches  12  to create shallow trench isolation (STI) structure  13 . Chemical-mechanical planarization/polishing (CMP) is used to remove the excess for smoothing the surface. Ions are implanted to the semiconductor substrate  1 , forming an n-type region for the lower portion thereof and a p-type region for the upper portion thereof. 
         [0036]    The material for the semiconductor substrate  1  can be epitaxial layer, silicon, gallium arsenide, gallium nitride, strained silicon, germanium silicide, silicon carbide, diamond, or other materials. 
         [0037]    The aforementioned STI structure  13  is formed by the shallow trench isolation process, which is a widely used technique by people in the semiconductor industry, therefore is not described in details herein. When implanting the ions, the ions can be zinc (Zn 2+ ), fluorine (F − ), nitrogen (N − ), oxygen (O 2− ), carbon (C 4+ ), argon (Ar + ), boron (B + ), phosphorus (P + ), arsenic (As + ), or antimony (Sb 2+ ). However, for industrial applications, the ions are not limited thereto. 
         [0038]    Please refer to  FIGS. 4A and 4B , which correspond to step S 102 .  FIG. 4A  is a top view of the unit region A, while  FIG. 4B  is a sectional view of  FIG. 4A . For step S 102 , the active region  11  of the unit region A is etched to a pre-determined depth for forming a vertical positioning groove  14  and defined by sidewall portions  15 . The sidewall portions  15  act as the channel region for current flow, and the thickness thereof significantly affects the transistor operation. Next, a gate dielectric layer  2  is disposed onto the formed structure of the unit region A. 
         [0039]    Next, a positioning gate  3  is disposed adjacent to the gate dielectric layer  2  to fill the vertical positioning groove  14  of the unit region A. The positioning gate  3  can be made of polysilicon, tungsten, platinum, titanium nitride, tantalum, tantalum nitride, chromium, alloy, or other applicable materials. In addition, the positioning gate  3  is at least partially surrounded by the sidewall portions  15 . Specifically, channel regions are formed by the sidewall portions  15  at the front, rear, or in all directions of the positioning gate  3 . The electric charge level of the positioning gate  3  controls the conductivity of the sidewall portions  15 . 
         [0040]    A word line  4  is formed perpendicularly to the positioning gate  3  of the unit region A. A protective layer  41  is disposed on the word line  4 , wherein the protective layer  41  can be made of silicon nitride (SiN). A dielectric layer is disposed on the formed structure and anisotropic etching is applied to form spacing layers  42 . The word line  4  is not limited in length according to the figures, wherein other unit regions can share the same word line  4  in its path. 
         [0041]    Please refer to  FIGS. 5A and 5B , which corresponds to step S 103 .  FIG. 5A  shows a top view of the unit region A, wherein  FIG. 5B  is a sectional view of  FIG. 5A . After forming the word line  4 , ions are implanted to the formed structure before or after forming the spacing layers  42 . Thus, an n-type region is formed on one side of the sidewall region  15  of the active region  11  of the unit region A. In other words, the n-type region and a p-type region are formed oppositely on the sidewall portions  15  of the active region  11  of the word line  4 . 
         [0042]    Please refer to  FIGS. 6A and 6B , which corresponds to step S 104 .  FIG. 6A  shows a top view of the unit region A, wherein  FIG. 6B  is a sectional view of  FIG. 6A . Insulating material is deposited to cover the formed structure of the unit region A from step S 103 , thus forming a insulating layer  5 . Next, chemical-mechanical polishing/planarization (CMP) is applied to even the upper surface of the insulating layer  5  and the protective layer  41  (silicon nitride). 
         [0043]    The above-described deposition process can be physical vapor deposition (PVD) or chemical vapor deposition (CVD). For industrial applications, the deposition technique is not limited thereto. The insulating material can be oxidized substance or other insulating materials. 
         [0044]    Please refer to  FIGS. 7A and 7B , which corresponds to step S 105 .  FIG. 7A  shows a top view of the unit region A, wherein  FIG. 7B  is a sectional view of  FIG. 7A . Self-align contact (SAC) process is used to remove the insulating layer  5  partially, for forming the source line pattern. In other words, the portion of the insulating layer  5  above the sidewall portions  15  of the active region  11  of the unit region A and adjacent to the spacing layers  42  are removed accordingly. Since SAC is a common technique used among semiconductor personnel, detailed description is omitted herein. 
         [0045]    Please refer to  FIGS. 8A and 8B , which corresponds to step S 106 .  FIG. 8A  shows a top view of the unit region A, wherein  FIG. 8B  is a sectional view of  FIG. 8A . Next to the spacing layers  42  of the active region  11  of the unit region A, epitaxial deposition process is applied to from two floating bodies  6 . Then, ions are implanted to the floating bodies  6  in similar fashion as sidewall portions  15  of the active region  11 . In other words, an n-type floating body  61  and a p-type floating body  62  are formed adjacent to the respective spacing layer  42  on the sidewall portions  15  of the active region  11 . 
         [0046]    Insulating material is deposited over the above-described structure of the unit region A. Again using the CMP process, the upper surface of the insulating layer  5  is smoothed and evenly leveled for the unit region A. 
         [0047]    Please refer to  FIGS. 9A and 9B , which corresponds to step S 107 .  FIG. 9A  shows a top view of the unit region A, wherein  FIG. 9B  is a sectional view of  FIG. 9A . Self-align contact (SAC) technique is applied to remove the insulating layer  5  formed in the step S 106  partially. More specifically, self-align contact process is used to remove the portion of insulating layer  5  corresponding to the n-type floating body  61 . Then, polysilicon is deposited onto the upper portion of the n-type floating body  61  to form a source line contact end  63 . Next, a source line  7  is formed perpendicularly to the word line  4  and connected to the source line contact  63 . The source line  7  is not limited in length according to the figures, wherein other unit regions can share the same source line  7  in its path by connecting each source line contact end  63  to the source line  7 . 
         [0048]    Please refer to  FIGS. 10A and 10B , which corresponds to step S 108 .  FIG. 10A  shows a top view of the unit region A, wherein  FIG. 10B  is a sectional view of  FIG. 10A . Insulating material is deposited onto the formed structure of the unit region A from step S 107 . CMP technique is applied to smooth the surface of the deposited material in forming an insulating layer  8 . Again. SAC technique is used to remove the portion of insulating layer  8  corresponding to the p-type floating body  62 . Polysilicon is deposited to fill the void left by the removed insulating material corresponding to the p-type floating body  62 , thus forming an n-type bit line contact end  64 . In other words, the n-type bit line contact end  64  is an extension of the p-type floating body  62 . 
         [0049]      FIG. 11A  shows a top view of the unit region A, wherein  FIG. 11B  is a sectional view of  FIG. 11A . A bit line  9  is formed perpendicularly to the source line  7  and connected to the n-type bit line contact end  64 , thus the vertical transistor is formed. In addition, the bit line  9  is not limited in length by the figures, which can be shared by other unit regions via connecting to each n-type bit line contact end  64 . 
         [0050]    Based on the vertical transistor fabricated by the above-described method, a planar transistor  10  can also be disposed at the peripheral region B of the unit region A (as in  FIG. 12 ). For example, when forming the above-described word line  4 , the planar transistor  10  can be further formed at one side of the word line  4 . Thus, when operating the memory device, voltage can be applied to the planar transistor  10 , along with the source line  7  and bit line  9  of the vertical transistor. By modulating the applied voltage of the source line  7 , the electric charge quantity of the transistor is controlled accordingly for maintaining a steady threshold voltage (V t ). 
         [0051]    In addition, the word line  4 , source line  7 , and bit line  9  of the instant disclosure is formed respectively according to the above-described method. However, the fabrication sequence can be adjusted and not limited thereto. For example, the bit line  9  can be formed first, followed by forming the source line  7  and disposing it above the bit line  9 . 
         [0052]    Comparing to related art, the transistor fabricated by the manufacturing method of vertical transistor for random-access memory is added with the source line  7  to adjust the applied voltage for controlling the electric charge quantity, hence keeping a steady threshold voltage (V t ). In addition, the disclosed transistor is a vertical type, which can significantly reduce the occupied space in the horizontal direction, thus improving packing density of semiconductor elements. 
         [0053]    The descriptions illustrated supra set forth simply the preferred embodiments of the instant disclosure; however, the characteristics of the instant disclosure are by no means restricted thereto. All changes, alternations, or modifications conveniently considered by those skilled in the art are deemed to be encompassed within the scope of the instant disclosure delineated by the following claims.