Abstract:
A semiconductor structure includes a substrate having thereon at least one conductive region; a plurality of cylinder-shaped electrodes disposed on the substrate, wherein each of the cylinder-shaped electrodes has a horizontal portion that is in direct contact with the at least one conductive region and a vertical sidewall portion connecting the horizontal portion; an upper support structure comprising a first lattice structure that is situated in a first horizontal level that is lower than a tip portion of each of the cylinder-shaped electrodes; and a lower support structure comprising a second lattice structure that interlocks middle portions of the cylinder-shaped electrodes.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a semiconductor structure. More specifically, the present invention relates to a capacitor or a cylinder-shaped storage node structure of a capacitor, which can be applicable to high-density dynamic random access memory (DRAM) devices. 
     2. Description of the Prior Art 
     As the level of integration continues to increase in integrated circuitry, electronic components are formed to increasing the smaller dimensions. One type of component utilized in integrated circuitry is a capacitor. It is well known that capacitors may serve as charge storage elements of dynamic random access memory (DRAM) devices. 
     Capacitors are becoming increasingly tall and thin in an effort to reduce the footprint of individual capacitors, and thereby conserve semiconductor real estate. Current capacitor dimensions are approaching the limits attainable by conventional processing, and it is desired to develop new processing so that capacitors may be scaled to increasingly thinner dimensions. 
     A common capacitor construction is a so-called container-shaped storage node device. The container-shaped storage nodes are first formed within densely-packed, high-aspect-ratio holes etched into a template or support structure. After removing the template layer, a dielectric material and a capacitor cell plate are formed on the container. Unfortunately, high aspect-ratio container-shaped storage nodes are structurally weak, and subject to toppling, twisting and/or breaking from an underlying base. 
     To avoid toppling of high aspect-ratio container-shaped storage node, a lattice methodology has been developed. Typically, a single lattice layer is provided to retain the uppermost position of the container-shaped electrodes. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a semiconductor structure includes a substrate having thereon at least one conductive region; a plurality of cylinder-shaped electrodes disposed on the substrate, wherein each of the cylinder-shaped electrodes has a horizontal portion that is in direct contact with the at least one conductive region and a vertical sidewall portion connecting the horizontal portion; an upper support structure comprising a first lattice structure that is situated in a first horizontal level that is lower than a tip portion of each of the cylinder-shaped electrodes; and a lower support structure comprising a second lattice structure that interlocks middle portions of the cylinder-shaped electrodes. The upper support structure and the lower support structure prevent the cylinder-shaped electrodes from toppling. 
     According to one embodiment, the upper support structure further comprises an annular spacer disposed around the tip portion of each of the cylinder-shaped electrodes. The annular spacer may comprise silicon oxide or polysilicon. 
     According to one embodiment, the annular spacer, the upper support structure, and the lower support structure have substantially the same pattern. 
     According to one embodiment, the first lattice structure and the second lattice structure comprise silicon nitride. 
     According to one embodiment, discontinuous gaps are dispersed around each of the cylinder-shaped electrodes. 
     According to one embodiment, the semiconductor structure further comprises a capacitor dielectric layer conformally covers the cylinder-shaped electrodes, the upper support structure, and the lower support structure. A capacitor electrode is disposed on the capacitor dielectric layer. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated in and constitute apart of this specification. The drawings illustrate some of the embodiments and, together with the description, serve to explain their principles. In the drawings: 
         FIGS. 1-6  are cross-sectional views schematically depicting a process flow for manufacturing a capacitor structure in accordance with one embodiment of present invention; and 
         FIG. 7  is a top view showing the pattern of the annular spacer, the discontinuous gaps, and the openings in the template structure, wherein the cross-section in  FIG. 3  is taken along line I-I′ in  FIG. 7 . 
     
    
    
     It should be noted that all the figures are diagrammatic. Relative dimensions and proportions of parts of the drawings are exaggerated or reduced in size, for the sake of clarity and convenience. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments. 
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are given to provide a thorough understanding of the invention. It will, however, be apparent to one skilled in the art that the invention may be practiced without these specific details. Furthermore, some well-known system configurations and process steps are not disclosed in detail, as these should be well-known to those skilled in the art. 
     Likewise, the drawings showing embodiments of the apparatus are semi-diagrammatic and not to scale and some dimensions are exaggerated in the figures for clarity of presentation. Also, where multiple embodiments are disclosed and described as having some features in common, like or similar features will usually be described with like reference numerals for ease of illustration and description thereof. 
     The terms “semiconductive substrate,” “semiconductor construction” and “semiconductor substrate” used herein include any construction comprising semiconductive materials, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials), and semiconductive material regions (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. 
     The term “horizontal” as used herein is defined as a plane parallel to the conventional major plane or surface of the semiconductor substrate, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms, such as “on”, “above”, “below”, “bottom”, “top”, “side” (as in “sidewall”), “higher”, “lower”, “over”, and “under”, are defined with respect to the horizontal plane. 
       FIGS. 1-6  are cross-sectional views schematically depicting a process for manufacturing a capacitor structure in accordance with one embodiment of present invention. As shown in  FIG. 1 , a substrate  10  is provided to serve as a base for forming devices, components, or circuits. The substrate  10  may comprise, consist essentially of, or consist of monocrystalline silicon, and may be referred to as a semiconductor substrate, or as a portion of a semiconductor substrate. Although the substrate  10  in this embodiment is shown to be homogenous, the substrate  10  may comprise numerous materials in some embodiments. For instance, the substrate  10  may correspond to a semiconductor substrate containing one or more materials associated with integrated circuit fabrication. In such embodiments, such materials may correspond to one or more of refractory metal materials, barrier materials, diffusion materials, insulator materials, etc. 
     According to the embodiment, at least one conductive region  12  is disposed in the substrate  10 . For example, the conductive region  12  may be a source/drain doping region, a contact, or a landing pad. In a case that the conductive region  12  is a landing pad, for example, a contact plug (not shown) may be disposed underneath the landing pad to couple the landing pad to a source/drain doping region. Initially, a top surface  12   a  of the conductive region  12  may be covered by a stop layer  18 , for example, an etching stop layer. In a later stage, as described herein below, the top surface  12   a  of the conductive region  12  will be revealed. According to the embodiment, the stop layer  18  may include but not limited to silicon nitride or silicon oxy-nitride. 
     Atop the stop layer  18 , a template structure  20  is provided. According to the embodiment, the template structure  20  may comprise a first sacrificial layer  22  that is directly deposited onto the stop layer  18 , a first lattice layer  24  on the first sacrificial layer  22 , a second sacrificial layer  26  on the first lattice layer  24 , a second lattice layer  28  on the second sacrificial layer  26 , and a capping top layer  29  on the second lattice layer  28 . According to the embodiment, the first sacrificial layer  22  and the second sacrificial layer  26  may comprise the same dielectric material, for example, silicon oxide, borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), fluorosilicate glass, or spin-on-dielectric (SOD). The first lattice layer  24  and the second lattice layer  28  may comprise the same dielectric material, for example, silicon nitride. 
     According to the embodiment, the composition of the first sacrificial layer  22  and the second sacrificial layer  26  may be different from the composition of the first lattice layer  24  and the second lattice layer  28  to exhibit adequate etching selectivity. The capping top layer  29  may comprise a dielectric layer that can be removed selectively from the underlying second lattice layer  28 . For example, the capping top layer  29  may comprise silicon oxide. According to the embodiment, the total thickness of the template structure  20  may range between 15000 angstroms and 20000 angstroms, for example. 
     Still referring to  FIG. 1 , a photolithographic process and a dry etching process are carried out to forma cluster of densely packed openings  30  extending through the entire thickness of the template structure  20 . According to the embodiment, each of the openings  30  may have a diameter that is close to or beyond the exposure limit of the lithographic process utilized to define the pattern of the each of the openings  30 . The openings  30  correspond to the underlying conductive region  12 . Each of the openings  30  at least exposes a portion of the top surface  12   a  of each of the conductive region  12 . 
     As shown in  FIG. 2 , cylinder-shaped storage nodes  42  are formed within the densely-packed, high-aspect-ratio openings  30 , respectively. To form the cylinder-shaped storage nodes  42 , a conformal conductive layer (not explicitly shown) such as a titanium nitride film is deposited over the substrate  10 . The conformal conductive layer covers the top surface of the capping top layer  29  and the interior surfaces of the openings  30 . A chemical mechanical polishing (CMP) process may be carried out to remove excess conductive layer outside the openings  30  from the top surface of the capping top layer  29 . At this point, the top surface of the capping top layer  29  is revealed. A sacrificial layer  43  such as photoresist, polysilicon, or SOD may be provided on the conductive layer and into the openings  30  prior to the CMP process. Each of the cylinder-shaped storage nodes  42  comprises a horizontal bottom portion  42   a  and a cylinder-shaped vertical sidewall  42   b  that is connected to the horizontal bottom portion  42   a . According to the embodiment, the height of the aforesaid cylinder-shaped vertical sidewall  42   b  is substantially equal to the total thickness of the template structure  20 . 
     As shown in  FIG. 3 , subsequently, an annular spacer  52  is formed around the uppermost portion of each of the cylinder-shaped storage nodes  42 . The annular spacers  52  are formed on the second lattice layer  28 . Discontinuous gaps  60  are formed between the annular spacers  52 . To form the annular spacer  52 , the capping top layer  29  is first removed from the top surface of the second lattice layer  28 . A conformal spacer material layer (not explicitly shown) is deposited over the substrate  10 . An anisotropic dry etching process is then performed to etch the conformal spacer material layer until the top surface of the second lattice layer  28  is exposed, thereby forming the annular spacer  52 . According to the embodiment, the composition of the annular spacer  52  may be different from the composition of the second lattice layer  28  to exhibit adequate etching selectivity. For example, the annular spacer  52  may comprise silicon oxide, silicon oxy-nitride, silicon carbide, or polysilicon, and the second lattice layer  28  may comprise silicon nitride. An exemplary layout of the annular spacer  52 , the discontinuous gaps  60 , and the openings  30  is illustrated in  FIG. 7 . As shown in  FIG. 7 , there are six gaps  60  dispersed along the periphery of each of the openings  30 . The cross-section in  FIG. 3  is taken along line I-I′ in  FIG. 7 . 
     As shown in  FIG. 4 , after forming the annular spacers  52  and the discontinuous gaps  60 , an anisotropic dry etching process is carried out to selectively etch the exposed second lattice layer  28  through the discontinuous gaps  60 , thereby forming lattice structure  28   a  and through holes  62 . The annular spacers  52  are used as an etching hard mask. The pattern of the lattice structure  28   a  and through holes  62  is substantially identical to that of the annular spacers  52  and the discontinuous gaps  60  as shown in  FIG. 7  when viewed from the above. The through holes  62  expose a portion of the second sacrificial layer  26 . Subsequently, by way of the through holes  62 , an etching process such as a wet etching process is performed to remove the second sacrificial layer  26 . The annular spacers  52  and the lattice structure  28   a  together constitute an upper support structure  102  that bridges the uppermost portions of the cylinder-shaped storage nodes  42 . 
     As shown in  FIG. 5 , likewise, using the annular spacers  52  as an etching hard mask, another anisotropic dry etching process is carried out to etch the first lattice layer  24  via the through holes  62 , thereby forming lattice structure  24   a  and through holes  64 . The pattern of the lattice structure  24   a  and through holes  64  is substantially identical to that of the annular spacers  52  and the discontinuous gaps  60  as shown in  FIG. 7  when viewed from the above. Subsequently, by way of the through holes  62  and  64 , an etching process such as a wet etching process is performed to remove the first sacrificial layer  22 . The lattice structure  24   a  acts as a lower support structure  104  that interlocks the middle portions of the cylinder-shaped storage nodes  42 . Thereafter, the sacrificial layer  43  is removed. In some cases, the annular spacers  52  may be removed together with the sacrificial layer  43 . 
     As shown in  FIG. 6 , subsequently, a capacitor dielectric layer  44  is deposited on the interior surface and outer surface of the cylinder-shaped storage nodes  42 . The capacitor dielectric layer  44  may also cover the upper support structure  102 , the lower support structure  104 , and a top surface of the stop layer  18 . Finally, a capacitor electrode  46  is deposited over the substrate on the capacitor dielectric layer  44 . The capacitor electrode  46  may act as a capacitor cell plate and, as shown in  FIG. 6 , may completely fill the central portion of each of the cylinder-shaped storage nodes  42  and the space therebetween. 
     According to the embodiment, the capacitor dielectric layer may comprise any suitable composition or combination of compositions, such as silicon nitride, silicon dioxide, high k or ultra-high k materials. The capacitor electrode material  44  may comprise any suitable composition or combination of compositions, such as one or more of various metals (for instance, titanium, tungsten, etc.), metal-containing compositions (for instance, metal nitride, metal silicide, etc.) and conductively-doped semiconductor materials (for instance, conductively-doped silicon, conductively-doped germanium, etc.). The capacitor dielectric layer  44  and capacitor electrode  46  may be formed utilizing any suitable methods, including, for example, one or more of atomic layer deposition (ALD), chemical vapor deposition (CVD), and physical vapor deposition (PVD). 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.