Abstract:
A method for fabricating a crown capacitor is able to form a deep UV photoresist layer having a cylindrical structure by using only one mask. A conductive layer, the main structure of a bottom electrode, is formed on the sidewall of the deep UV photoresist layer by performing a silylation process. A fairly small and high cylindrical structure is formed by the invention, so that the crown capacitor can be used in DRAM having a storage capacity higher than 64 MB. Also, there is no problem of registration because only one mask is used.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [1]    1. This application claims the priority benefit of Taiwan application serial no. 87115742, filed Sep. 22, 1998, the full disclosure of which is incorporated herein by reference.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [2]    2. 1. Field of the Invention  
           [3]    3. The present invention relates to a method of fabricating a capacitor. More particularly, the present invention relates to a method for fabricating a crown capacitor used in DRAM.  
           [4]    4. 2. Description of the Related Art  
           [5]    5. In conventional DRAM having a storage capacity less than 1 MB, it is a customary practice to use a two-dimensional capacitor called a planar-type capacitor as the data storage capacitor. One drawback in the planar-type capacitor, however, is that it requires quite a large chip area to implement. Therefore, the planar-type capacitor is not suitable for high-integration DRAM. In DRAM having a storage capacity higher than 4 MB, a three-dimensional capacitor such as a stacked-type capacitor is used as the data storage capacitor. A crown capacitor is a kind of stacked-type capacitor.  
           [6]    6.FIGS. 1A through 1C are schematic, cross-sectional diagrams used to depict the steps in conventional method for fabricating a crown capacitor.  
           [7]    7. Referring to FIG. 1A, a substrate  20  having a MOS structure is provided, wherein the MOS structure includes a drain region  24 . An inter-layer dielectric layer  26  is formed on the substrate  20 . A contact hole  28  is formed in the inter-dielectric layer  26  to expose the drain region  24 . A conductive layer  30  is formed on the inter-layer dielectric layer  26  and fills the contact hole  28 . The thickness of the conductive layer  30  on the inter-layer dielectric layer  26  is about 6000Å.  
           [8]    8. Referring to FIG. 1B, an opening  32  is formed in the conductive layer  30  and corresponds to the contact hole  28 . The step of forming the opening  32  includes performing an anisotropic etching process to remove a portion of the conductive layer  30  by controlling the duration of etching. The depth of etching is about 4000 to 5000Å.  
           [9]    9. Referring to FIG. 1C, an anisotropic etching process is performed to remove a portion of the conductive layer  30  by using the inter-layer dielectric layer  26  as a stop layer. Therefore, a bottom electrode  34  is made from the remaining conductive layer  30 . A dielectric layer  36  is formed on the bottom electrode  34  and an upper electrode  38  is formed on the dielectric layer  36 .  
           [10]    10. In conventional process for fabricating DRAM whose channel length is below 0.35 μm, two masks are used to form the bottom electrode of the crown capacitor. As the integration of DRAM is increased, the critical dimension of the crown capacitor is reduced. It is hard to meet the demands of the critical dimension of the crown capacitor by using conventional process, because the tolerance of the registration between the two masks is reduced.  
         SUMMARY OF THE INVENTION  
         [11]    11. Accordingly, the present invention provides a method for fabricating a crown capacitor useing only one mask to meet the demand of the critical dimension of the crown capacitor.  
           [12]    12. To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for fabricating a crown capacitor. The method for fabricating this crown capacitor includes the following steps. A substrate having a MOS structure is provided. The MOS structure includes a drain region. An inter-layer dielectric layer is formed on the substrate. A contact hole is formed in the inter-layer dielectric layer to expose the drain region. A first conductive layer is formed on the inter-layer dielectric layer and fills the contact hole. A first, deep UV photoresist layer and a hard mask layer are formed in sequence on the first conductive layer. A second, deep UV photoresist layer is formed on a portion of the hard mask layer and corresponding to the contact hole. A portion of the hard mask layer is removed. The second deep UV photoresist layer and a portion of the first deep UV photoresist layer are removed. A second, conductive layer is formed on the sidewall of the first, deep UV photoresist layer by performing a silylation process. A portion of the first conductive layer exposed by the first, deep UV photoresist layer and the second conductive layer is removed by performing an anisotropic etching process, and a portion of the top of the second conductive layer is removed in the same step. A bottom electrode of the crown capacitor is made from the remaining first conductive layer and the remaining second conductive layer. Then, the hard mask layer and the remaining first, deep UV photoresist layer are removed in sequence. A dielectric layer is formed on the bottom electrode. Finally, an upper electrode is formed on the dielectric layer.  
           [13]    13. To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides another method for fabricating a crown capacitor. The method for fabricating this crown capacitor includes the following steps. A substrate having a MOS structure is provided, wherein the MOS structure includes a drain region. An inter-layer dielectric layer is formed on the substrate. A contact hole is formed in the inter-layer dielectric layer to expose the drain region. A first conductive layer is formed on the inter-layer dielectric layer and fills the contact hole. A deep UV photoresist layer is formed on the first conductive layer. The deep UV photoresist layer is patterned, thus the remaining deep UV photoresist layer having cylindrical structure corresponds to the contact hole. A second conductive layer is formed on the top and the sidewall of the remaining deep UV photoresist layer by performing a silylation process. A portion of the first conductive layer exposed by the second conductive layer and the deep UV photoresist layer is removed, and a portion of the second conductive layer is removed in the same step. A bottom electrode of the crown capacitor is made from the remaining first conductive layer and the remaining second conductive layer. Then, the remaining deep UV photoresist layer is removed. A dielectric layer is formed on the bottom electrode. An upper electrode is formed on the dielectric layer.  
           [14]    14. It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [15]    15. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,  
         [16]    16.FIGS. 1A through 1C are schematic, cross-sectional diagrams used to depict steps in conventional method for fabricating a crown capacitor;  
         [17]    17.FIGS. 2A through 2D are schematic, cross-sectional diagrams used to depict steps in a method according to the invention for fabricating a crown capacitor; and  
         [18]    18.FIGS. 3A through 3E are schematic, cross-sectional diagrams used to depict steps in another method according to the invention for fabricating a crown capacitor.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [19]    19. 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.  
         [20]    20. The invention provides a new fabricating method for a crown capacitor as shown in FIGS. 2A through 2D.  
         [21]    21. Referring to FIG. 2A, a substrate  60  having a MOS structure is provided, wherein the MOS structure includes a drain region  64 . An inter-layer dielectric layer  66  is formed on the substrate  60 . A contact hole  68  is formed in the inter-dielectric layer  66  to expose the drain region  64 . A conductive layer  70  is formed on the inter-layer dielectric layer  66  and fills the contact hole  68 . Preferably, the thickness of the conductive layer  70  on the inter-layer dielectric layer  66  is about 1000 to 2000Å. A deep UV photoresist layer  72  is formed on the conductive layer  70 . A hard mask layer  74  is formed on the deep UV photoresist layer  72 . The hard mask layer  74  includes silicon oxide or silicon nitride formed by plasma enhanced chemical vapor deposition. Moreover, the step of forming the hard mask layer  74  includes performing a silylation process to form a silicon layer on the deep UV photoresist layer  72  and then performing a plasma oxidation process to transform the silicon layer into a silicon oxide layer. A deep UV photoresist layer  76  is formed on the hard mask layer  74  at a location corresponding to the contact hole  68 . The step of forming the deep UV photoresist layer  76  includes coating a thin deep UV photoresist layer over the hard mask layer  74  and then removing a portion of the thin deep UV photoresist layer. The remaining portion of the thin deep UV photoresist layer which forms the deep UV photoresist layer  76  is aligned with the contact hole  68 . The dimension, shape, and planar area of the deep UV photoresist layer  76  can be controlled by choosing proper processing conditions.  
         [22]    22. Referring to FIG. 2B, a hard mask layer  78  is formed. The step of forming the hard mask layer  78  includes performing a dry etching process to remove a portion of the hard mask layer  74  exposed by the deep UV photoresist layer  76 . The remaining portion of the hard mask layer  74  forms the hard mask layer  78 . A deep UV photoresist layer  80  having cylindrical structure is formed by using the hard mask layer  78  as a mask. The step of forming the deep UV photoresist layer  80  includes performing an etching process such as oxygen plasma etching to remove the deep UV photoresist layer  76  and a portion of the deep UV photoresist layer  72  exposed by the hard mask layer  78 . The remaining portion of the deep UV photoresist layer  72  forms the deep UV photoresist layer  80 .  
         [23]    23. Referring to FIG. 2C a conductive layer  82  is formed on the sidewall of the deep UV photoresist layer  80  by performing a silylation process. The inter-layer dielectric layer  66  is used as a stop layer. An anisotropic etching process is performed to remove a portion of the conductive layer  70  exposed by the deep UV photoresist layer  80  and the conductive layer  82 . In the same step, a portion of the top of the conductive layer  82  is removed. Thus, a bottom electrode  84  of a crown capacitor is made from the remaining conductive layer  70  and the remaining conductive layer  82 . [Please describe the process with clear sentences in proper order.]  
         [24]    24. Referring to FIG. 2D, the hard mask layer  78  is removed, and the deep UV photoresist layer  80  is removed by dry etching or wet etching. A dielectric layer  86  is formed on the bottom electrode  84  and an upper electrode  88  is formed on the dielectric layer  86 .  
         [25]    25. The invention provides another new fabricating method for a crown capacitor as shown in FIGS. 3A through 3E.  
         [26]    26. Referring to FIG. 3A, a substrate  160  having a MOS structure is provided, wherein the MOS structure includes a drain region  164 . An inter-layer dielectric layer  166  is formed on the substrate  160 . A contact hole  168  is formed in the inter-dielectric layer  166  to expose the drain region  164 . A conductive layer  170  is formed on the inter-layer dielectric layer  166  and fills the contact hole  168 . The thickness of the conductive layer  170  on the inter-layer dielectric layer  166  is about 1000 to 2000Å. A deep UV photoresist layer  172  is formed on the conductive layer  170 .  
         [27]    27. Referring to FIG. 3B, a portion of the deep UV photoresist layer  172  is removed by an anisotropic etching process. Thus, the remaining portion of the deep UV photoresist layer  172  forms the deep UV photoresist layer  180  aligned with the contact hole  168 . The shape and dimension of the deep photoresist layer  180  can be controlled by adjusting the condition of the etching process. Preferably, the photoresist layer  180  has a cylindrical structure.  
         [28]    28. Referring to FIG. 3C, a conductive layer  182  is formed on the top and the sidewall of the deep UV photoresist layer  180  by performing a silylation process. Referring to FIG. 3D, the inter-layer dielectric layer  166  is used as a stop layer. An anisotropic etching process is performed to remove a portion of the conductive layer  170  exposed by the deep UV photoresist layer  180  and the conductive layer  182 . A portion of the conductive layer  182  on the top of the deep UV photoresist layer  180  is also removed in the same step to expose the top surfce of the photoresist layer  180 . Thus, a bottom electrode  184  of a crown capacitor is made from the remaining conductive layer  170  and the remaining conductive layer  182 .  
         [29]    29. Referring to FIG. 3E, the deep UV photoresist layer  180  is removed by dry etching or wet etching. A dielectric layer  186  is formed on the bottom electrode  184  and an upper electrode  188  is formed on the dielectric layer  186 .  
         [30]    30. According to the foregoing, only one mask is used in the invention to form the deep UV photoresist layer having cylindrical structure, thus the registration problem in conventional method is avoided and the process is simplified.  
         [31]    31. 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.