Abstract:
A method for fabricating a crown-shaped capacitor includes providing a first dielectric layer with a protective pillar formed thereover, including a first conductive layer, a protective layer, and a mask layer. A second conductive layer is formed over a sidewall of the protective pillar. A first capacitance layer and a third conductive layer are formed over the first dielectric layer. A sacrificial layer is formed over the third conductive layer. The sacrificial layer, the third conductive layer, the first capacitance layer, the second conductive layer, and the mask layer above the protective layer are partially removed. The second conductive layer and the third conductive are removed to form a recess adjacent to the first capacitance layer. The protective layer is removed and an opening is formed to expose the first and second conductive layers. A second capacitance layer and a fourth conductive layer are formed in the opening. The sacrificial layer is removed to expose the third conductive layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority of Taiwan Patent Application No. 98145470, filed on Dec. 29, 2009, the entirety of which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to fabrication of semiconductor memory devices, in particular to a method of fabricating a crown-shaped capacitor for semiconductor memory devices. 
         [0004]    2. Description of the Related Art 
         [0005]    A dynamic random access memory (DRAM) device is a kind of a volatile memory device. Digital data storage in a DRAM device is executed by charges and discharges of a capacitor in the DRAM device. When power supplied to the DRAM device is turned off, the data stored in the memory cell of the DRAM device completely disappears. A memory cell in the DRAM device typically includes at least one field effect transistor (FET) and one capacitor. The capacitor is used for storing signals in the cells of the DRAM device. Commonly used capacitors today, are trench capacitors and crown-shaped capacitors. 
         [0006]    With the size of DRAM device memory cells shrinking, the technological development to maintain the appropriate charge capacitance of capacitors has fallen behind that of the technological development to shrink memory cells. Namely, as the size of the capacitor in a memory cell is reduced, a predetermined charge capacitance is still required for reliable storage of signals. 
         [0007]    Thus, methods for fabricating smaller capacitors, capable of maintaining or increasing storage capacitance, are desired. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Methods for fabricating crown-shaped capacitors applicable in semiconductor memory devices, for example dynamic random access memory (DRAM) devices, are provided with improved capacitance and structural strength. 
         [0009]    An exemplary method for fabricating a crown-shaped capacitor comprises providing a first dielectric layer with a conductive contact disposed therein. A protective pillar is formed over the first dielectric layer, wherein the protective pillar physically contacts the conductive contact and comprises a first conductive layer, a protective layer, and a mask layer sequentially disposed over the conductive contact. A second conductive layer is formed over a side of the protective pillar, wherein the second conductive layer physically contacts the first conductive layer, the protective layer and the mask layer. A first capacitance layer and a third conductive layer are conformably formed over the first dielectric layer to cover the conductive contact, the first dielectric layer, the second conductive layer, and the mask layer. A sacrificial layer is formed over the third conductive layer. The sacrificial layer, the third conductive layer, the first capacitance layer, the second conductive layer, and the mask layer above the protective layer are partially removed. The second conductive layer and the third conductive adjacent to the protective layer are removed to form a recess adjacent to the first capacitance layer. The protective layer is removed to form an opening, wherein the opening exposes the first conductive layer and a side surface of the second conductive layer not in contact with the first capacitance layer. A second capacitance layer and a fourth conductive layer are conformably formed in the opening, wherein the second capacitance layer fills the recess adjacent to the first capacitance layer and physically contacts the first capacitance layer. The sacrificial layer is removed to expose a sidewall surface of the third conductive layer not in contact with the first capacitance layer. A fifth conductive layer is formed to cover the fourth conductive layer, the second capacitance layer, and the third conductive layer. 
         [0010]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0012]      FIGS. 1-4  are cross sections showing a method for fabricating a crown-shaped capacitor according to an embodiment of the invention; and 
           [0013]      FIGS. 5-11  are cross sections showing a method for fabricating a crown-shaped capacitor according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0015]    Exemplary methods for fabricating a crown-shaped capacitor are described below with reference to  FIGS. 1-11 . 
         [0016]      FIGS. 1-4  are cross sections of an exemplary method for fabricating a crown-shaped capacitor. Herein, the exemplary method is a method known by the inventors and is used as a comparative example to comment on the problems found by the inventors, but is not used to restrict the scope of the invention. 
         [0017]    As shown in  FIG. 1 , a semiconductor structure is first provided, and the semiconductor structure may be located in a memory cell region (not shown) of a semiconductor memory device, such as a structure located in a memory cell region of a dynamic random access memory (DRAM) device. The semiconductor structure comprises a plurality of conductive contacts  12  embedded in a dielectric layer  10 , and portions of the dielectric layer  10  above the conductive contacts  12  are removed to partially expose a top surface of each of the conductive contacts  12 . Herein, the semiconductor structure may further comprise a substrate (not shown) and a plurality of transistors (not shown) formed on the semiconductor substrate, and the conductive contacts  12  respectively electrically contacts one of the transistors formed on the semiconductor substrate. For simplicity, the semiconductor structures are merely illustrated with the dielectric layer  10  and the conductive contacts  12  embedded therein, and the underlying semiconductor substrate and transistors which are known to those skilled in the art are omitted. Herein the dielectric layer  10  comprises materials such as updoped silicon glass (USG), phosphorus silicon glass (PSG), boron phosphorus silicon glass (BPSG), TEOS oxide, silicon nitride or insulating materials such as silicon oxide. The conductive contacts  12  comprise conductive materials such as doped polysilicon or metals such as tungsten. Next, a sacrificial layer  14  and a support layer  16  are blanketly formed over the dielectric layer to cover the dielectric layer  10  and the conductive contacts  12 . The sacrificial layer  16  comprises materials such as polysilicon, updoped silicon glass (USG), phosphorus silicon glass (PSG), or boron phosphorus silicon glass (BPSG), TEOS oxide, silicon nitride or insulating materials such as silicon oxide, and preferably comprises polysilicon. A predetermined etching selectivity should be provided between the materials in the passivation layer  14  and the dielectric layer  10  to benefit subsequent processes. The support structure  16  comprises materials such as silicon nitride. 
         [0018]    Referring to  FIG. 1 , photolithography and etching processes (both not shown) are performed to form a plurality of trenches  18  in the support layer  16  and the sacrificial layer  14 . As shown in  FIG. 1 , the trenches  18  are aligned with one of the conductive contacts  12 , respectively, and protrude downward and through the support layer  16  and the sacrificial layer  14 , thereby exposing the conductive contacts  12  thereunder. Herein, the trenches  18  are pillar-like trenches and may have a circular or oval top view. After formation of the trenches  18 , a first conductive layer  20  is conformably formed over the support layer  16  and the sacrificial layer  14 . The first conductive layer  20  is also formed in each of the trenches  18  and covers the exposed surfaces of the support layer  16 , the sacrificial layer  14 , and the conductive contacts  12 . The first conductive layer  20  comprises materials such as Ru, TaN, TiN, Pt, doped polysilicon or metal silicides, and can be formed by deposition processes such as chemical vapor deposition. Therefore, the first conductive layer  20  can be conformably formed over the surfaces of the support layer  16 , the sacrificial layer  14 , and the conductive contact  12 . 
         [0019]    In  FIG. 2 , an etching process (not shown), for example a dry etching process, is then performed to remove portions of the first conductive layer  20  above the support layer  16  to expose the support layer  16 . Next, another photolithography and etching process is performed to partially remove the support layer  16  by use of a mask having predetermined patterns thereon (not shown). Herein, taking the removal of the support layer  16  located at the most left side and the most right side thereof as an example, following, the sacrificial layer  14  under the support substrate  16  is exposed. Next, another etching process, for example a wet etching process, is performed to entirely remove the sacrificial layer  14  (shown in  FIG. 1 ), thereby leaving a patterned first conductive layer  20   a  originally formed in the trenches  18  and the support layer  16  connected with the first conductive layers  20   a  over the dielectric layer  10  and the conductive contacts  12 . 
         [0020]    As shown in  FIG. 2 , at this time, a space  22  is formed between the first conductive layers  20   a , and the conductive contact  12 , the dielectric layer  10  and the support layer  16  adjacent thereto. The space  20  exposes opposite surfaces A and B of the first conductive layer  20   a , wherein the surface A of the first conductive layer  20   a  is a surface originally located in the trench  18 , and the surface B is a surface of the first conductive layer  20   a  originally contacting the sacrificial layer  14  (see  FIG. 1 ). 
         [0021]    As shown in  FIG. 3 , a capacitance layer  24  and a second conductive layer  26  are sequentially and conformably formed on exposed surfaces of the first conductive layer  20   a  and the second conductive layer  26  exposed by each space  22 . Herein, the capacitance layer  24  and the second conductive layer  26  are conformably formed on surface A and B of the first conductive layer  20   a , but does not fill the space  22 , respectively. The capacitance layer  24  comprises nitrogen-containing materials such as silicon nitride, or silicon oxynitride, or high-k dielectric materials (i.e. a dielectric material having a dielectric constant greater than the dielectric constant of the silicon nitride) such as Al 2 O 3 , ZrO 2 , BST (BaSrTiO 3 ) or STO (SrTiO 3 ), BST, STO, Ta 2 O 5 , or HfO 2 , and the second conductive layer  26  comprises materials such as Ru, TaN, TiN, Pt, doped polysilicon, or metal silicides. The capacitance layer  24  and the second conductive layer  26  may be formed by deposition processes such as chemical vapor deposition, to thereby conformably form the above mentioned film layers over the first conductive layer  20   a  and the support layer  16 . 
         [0022]    In  FIG. 4 , a layer of conductive material is blanketly formed over the structure shown in  FIG. 3  to fill each of the spaces  22  and cover the second conductive layer  26 . Next, a planarization process (not shown) is performed to planarize the above conductive materials and a third conductive layer  28  is formed above the structure shown in  FIG. 3 . The third conductive layer  28  fills each of the spaces  22  and the film structure thereof is a solid structure. Herein, the third conductive layer  28  comprises conductive materials such as Ru, TaN, TiN, Pt, doped polysilicon or metal silicides. 
         [0023]    Accordingly, the description of fabricating an exemplary crown-shaped capacitor is substantially finished. The crown-shaped capacitor shown in  FIG. 4  comprises the capacitance layer  24  formed on the opposite surfaces A and B of the first conductive layer  20   a , and the second conductive layer  26 , such that the fabricated crown-shaped capacitor may have increased capacitance and thereby is applicable in a crown-shaped capacitor with reduced size and a maintained or an increased capacitance level. 
         [0024]    However, during the fabrication processes described in  FIGS. 1-4 , such as during the processes described in  FIG. 2 , the stereo structure composed of the patterned first conductive layer  20   a  and the support layer  16  is a hollow structure having a plurality of spaces  22  formed therebetween, and the hollow structure is supported by the dielectric layer  10 , the first conductive layer  20   a  with a relatively thin thickness, and the support layer  16  with a relatively thicker thickness, thereby having poor mechanical strength. Thus, in the processes such as the wet etching process for removing the sacrificial layer  14  and/or the deposition processes for forming the capacitance layer  24  and the second conductive layer  26 , the hollow structure may collapse due to the striking of process fluids used in the processes with ?, which ? in sequential process, thereby affecting process reliably and yield of the obtained crown-shaped capacitor shown in  FIG. 4 . 
         [0025]    Therefore, due to the above process reliably issues in the method for fabricating the crown-shaped capacitor shown in  FIGS. 1-4 , an improved method for fabricating a crown-shaped capacitor is provided to fabricate a crown-shaped capacitor with increase capacitances and improved structure strength. 
         [0026]      FIGS. 5-11  are cross sections showing another exemplary method for fabricating a crown-shaped capacitor of the invention. 
         [0027]    In  FIG. 5 , a semiconductor structure is first provided, and the semiconductor structure is located in a memory cell region (not shown) of a semiconductor memory device, such as a structure located in a memory cell region of a DRAM device. The semiconductor structure comprises a plurality of conductive contacts  104  disposed in a dielectric layer  102 . Herein, the semiconductor structure may further comprise a substrate (not shown) and a plurality of transistors (not shown) formed on the semiconductor substrate, and the conductive contacts  104  respectively electrically contacts one of the transistors formed on the semiconductor substrate. For simplicity, the semiconductor structure is illustrated with the dielectric layer  102  and the conductive contacts  104  disposed therein, and the underlying semiconductor substrate and transistors which are known to those skilled in the art are omitted. Herein, the dielectric layer  102  comprises materials such as updoped silicon glass (USG), phosphorus silicon glass (PSG), boron phosphorus silicon glass (BPSG), TEOS oxide, silicon nitride or insulating materials such as silicon oxide. The conductive contacts  104  comprise conductive materials such as doped polysilicon or metals such as tungsten. Next, a conductive layer  106 , a protective layer  108  and a mask layer  110  are sequentially formed over the dielectric layer  102 . The conductive layer  106  has a thickness of about 100-400 Å and comprises materials such as Ru, TiN, TaN, Pt, doped polysilicon, or metal silicides. The protective layer  108  has a thickness of about 10000-25000 Å, and comprise materials such as updoped silicon glass (USG), phosphorus silicon glass (PSG), boron phosphorus silicon glass (BPSG), TEOS oxide, silicon nitride or insulating materials such as silicon oxide, and preferably comprises polysilicon. A predetermined etching selectivity should be provided between the materials of the protective layer  108  and the underlying dielectric layer  102  to benefit subsequent processes, and the mask layer  110  comprise materials such as silicon nitride and has a thickness of about 8000-15000 Å. 
         [0028]    In  FIG. 6 , photolithography and etching processes (both not shown) are performed to pattern the conductive layer  106 , the protective layer  108 , and the mask layer  110  to form a plurality of protective pillars  114 . Herein, the protective pillars  114  respectively align with one of the underlying conductive contacts  104 . The protective pillars  104  may have a circular or oval top view. As shown in  FIG. 6 , each protective pillar  114  is formed by a patterned conductive layer  106   a , a patterned protective layer  108   a  and a patterned mask layer  110   a  sequentially stacked over one of the conductive contacts  104 , and the protective pillars  114  are separated from each other by a space  112  formed therebetween. 
         [0029]    In  FIG. 7 , a layer of conductive material is conformably formed over the structure shown in  FIG. 6 , and an etching process (not shown) is then performed to form a conductive layer  116  on sidewalls of the protective pillars  114 . The conductive layer  116  is formed over the conductive contacts  104  and physically contacts the conductive layer  106   a , the protective layer  108   a  and the mask layer  110   a  in the protective pillar  114 . After formation of the conductive layer  116 , a capacitance layer  118  and a conductive layer  120  are sequentially formed over the dielectric layer  102 . Herein, the capacitance layer  118  and the conductive layer  120  are sequentially formed over surfaces of the conductive layer  116 , the mask layer  110   a , the conductive contact  104  and the dielectric layer  102 , but does not fill the spaces  112  (see  FIG. 6 ). The capacitance layer  118  comprises nitrogen-containing materials such as silicon nitride, silicon oxynitride or high-k dielectric materials (i.e. a dielectric material having a dielectric constant greater than the dielectric constant of the silicon nitride) such as Al 2 O 3 , ZrO 2 , BST, STO, Ta 2 O 5 , or HfO 2 . The capacitance layer  118  and the conductive layer  120  have a thickness of about 50-130 Å and 30-100 Å, respectively, and can be formed by deposition processes such as chemical vapor deposition or atomic layer deposition. 
         [0030]    In  FIG. 8 , an insulating material is blanketly formed over the structure shown in  FIG. 7  to cover the conductive layer  120  and fill the spaces between the conductive layer  120 . Next, a planarization process (not shown) is performed to planarize the insulating materials and to remove materials of the conductive layer  120  and the capacitance layer  118  above a surface of the mask layer  110   a  of the protective pillars  114 . Next, an etching process (not shown) is performed to remove the mask layer  110   a  in each of the protective pillars  114 , thereby exposing the protective layer  108   a  in the protective pillars  114 . For the etching process, a dry or wet etching process can be used such that portions of the insulating materials, the conductive layer  120 , the capacitance layer  118  and the conductive layer  116  adjacent to the mask layer  110   a  are also removed during removal of the mask layer  110   a , thereby partially etched conductive layers  116   a  and  120   a , and partially etched capacitance layer  118   a  and the sacrificial layer  122  are formed over the dielectric layer  102 . Herein, after the etching process is performed, a surface of the sacrificial layer  122  is slightly below the surfaces of the above film layers. 
         [0031]    In  FIG. 9 , an etching process (not shown), for example a wet etching process, is performed, to remove portions of the conductive layers  116   a  and  120   a  adjacent to both sides of the capacitance layer  118   a , thereby forming recesses  126  between the protective layer  108   a , the capacitance layer  118   a  and the sacrificial layer  122 . Next, another etching process (not shown), for example a dry or wet etching process, is performed to remove the protective layer  108   a  and form openings  124 . The openings  124  expose the conductive layer  106   a  under the protective layer  108   a  and the conductive layer  116   a  at a side thereof. 
         [0032]    In  FIG. 10 , a layer of capacitance material and a layer of conductive material are conformably formed over the structure shown in  FIG. 9 . Next, an etching process (not shown), for example a dry etching process, is performed to respectively form a capacitance layer  128  and a conductive layer  130  over the conductive layer  120   a  and the capacitance layer  118   a . The capacitance layer  128  back fills the recesses  126  formed between the protective layer  108   a , the capacitance layer  118   a  and the sacrificial layer  122  and forms in the openings  124 , thereby physically contacting the capacitance layer  118   a  between the conductive layer  116   a  and  120   a , and the conductive layer  106   a  and  116   a  in the openings  124 . Herein, the capacitance layer  128  comprises nitrogen-containing dielectrics such as silicon nitride, oxynitride, or high-k dielectric materials such as Al 2 O 3 , ZrO 2 , BST, STO, Ta 2 O 5 , or HfO 2 , and the conductive layer  130  comprises conductive materials such as Ru, TaN, TiN, Pt, doped polysilicon or metal silicides. The capacitance layer  128  and the conductive layer  130  have a thickness of about 50-130 Å and 30-100 Å, respectively, and can be formed by deposition processes such as chemical vapor deposition or atomic layer deposition. 
         [0033]    In  FIG. 11 , an etching process (not shown), for example a wet etching process, is performed to remove the sacrificial layer  122  and expose the conductive layer  120   a . After removal of the sacrificial layer  122 , a conductive material is blanketly formed over the conductive layer  120   a , the conductive layer  130 , and the capacitance layer  128 . Next, a planarization process (not shown) is performed to planarize the above conductive materials, thereby forming a planar conductive layer  132 . The conductive layer  132  comprises conductive materials such as Ru, TaN, TiN, Pt, doped polysilicon or metal silicides. 
         [0034]    Accordingly, another description of fabricating an exemplary crown-shaped capacitor is substantially finished. The crown-shaped capacitor shown in  FIG. 11  mainly comprises a bottom electrode composed of a conductive layer  106   a  and two conductive layers  116   a  disposed over the conductive contacts  104 , two independent top electrodes made of the conductive layers  120   a  and  130 , and a capacitance layer made of the capacitance layers  116   a  and  128  formed on the bottom electrode from both side surfaces thereof and between the conductive layers  120   a  and  130   a . Thus, the fabricated crown-shaped capacitor may have increased capacitance and is applicable in crown-shaped capacitors with reduced sizes, while maintaining or increasing capacitance levels thereof. 
         [0035]    Moreover, through the processes illustrated in  FIGS. 5-11 , and described above, due to formation of the protective pillars  114  and the sacrificial layer  122 , the conductive layers  116   a  and  106   a  for the bottom electrode, the conductive layers  130  and  122   a  for the top electrode, and the capacitances  116   a  and  128  for the capacitance layer are all structurally supported by the protective pillar  114  and the sacrificial layer  122  during fabrication thereof. Thus, the main film layers composing the crown-shaped capacitor will not be formed with a hollow structure as that illustrated in the process shown in  FIGS. 1-4 , such that the main film layers for composing the crown-shaped capacitor shown in  FIG. 11  will not be affected by process fluids in etching processes and in deposition processes and by particles formed in sequential processes, thereby ensuring process reliably and yield of the crown-shaped capacitor shown in  FIG. 11 . 
         [0036]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.