Patent Publication Number: US-6656844-B1

Title: Method of forming a protected crown capacitor structure utilizing the outside crown surface to increase capacitance

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to increase the surface area of a crown shaped capacitor structure. 
     (2) Description of Prior Art 
     As performance objectives for semiconductor devices continue to increase efforts to enhance the performance of dynamic random access memory (DRAM), devices, via increases in the surface area of the DRAM capacitor structure, have been ongoing. The greater the surface area of the DRAM capacitor structure, the greater the capacitance, thus allowing the enhanced performance objective to realized. The objective of increasing the surface area for DRAM crown shaped capacitor structures has been successfully addressed by increasing the height of the crown shaped structure. In addition to further increase capacitor surface area the tall, vertical features of the crown shaped capacitor structure are left not embedded, or not located butted to an adjacent insulator region. However continuing to increase only the vertical dimension, or the height of the crown shaped capacitor structure, without increasing the horizontal dimension of this structure, can result in collapse of the tall, unembedded, crown shaped capacitor vertical features, during subsequent fabrication steps. If an insulator layer were retained to butt or embed the DRAM capacitor structure, the outside surfaces of the vertical capacitor features butting the insulator layer would not contribute to the increased surface area objective. 
     This invention will teach novel process sequences allowing DRAM crown shaped capacitor structures to be formed, featuring the tall vertical capacitor features needed to increase device capacitance To maintain the desired height of the vertical features, as well as to protect against collapse of the tall, vertical capacitor features, a matrix of four individual storage node structures underlying a single top plate structure, is formed to provide the needed surface area. Protection against collapse of the tall vertical storage node features is accomplished via only about 50% of the storage node surface butting an adjacent insulator region. Prior art, such as Ching et al, in U.S. Pat. No. 6,168,989, as well as Huang, in U.S. Pat. No. 6,187,624, describe methods of fabricating crown shaped capacitor structures for DRAM devices, however these prior arts do not describe the novel process sequences described in the present invention, which allow increased capacitor surface area to be realized via the use of a matrix of storage node structures, and with each storage node structure comprised with tall, vertical features, protected only on some sides by adjacent insulator regions. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to fabricate crown shaped capacitor structures for DRAM devices. 
     It is another object of this invention to increase the capacitance of the crown shaped capacitor structure via formation of a matrix of storage node structures, with the complete matrix overlaid with a single top plate structure. 
     It is still another object of this invention to form storage node structures comprised with tall, vertical features, with a first group of tall vertical feature surfaces butting an adjacent insulator region, while a second group of tall, vertical feature surfaces of the storage node structures remain are stripped of adjacent insulator. 
     It is still yet another object of this invention to obtain the bare, tall, vertical feature surfaces of the storage node structures via selective removal of insulator regions using a photoresist shape as an etch mask, wherein the photoresist shape is formed in either a positive or in a negative photoresist layer. 
     In accordance with the present invention a method of increasing the capacitance of a crown shaped capacitor structure via formation of a matrix of storage node structures, wherein each storage node structure is in turn comprised of tall, vertical features, and where a group of the surfaces of the tall vertical features are left uncovered by insulator, is described. After formation of source/drain regions in a semiconductor substrate, capacitor openings are formed in an insulator layer, exposing top portions of the underlying source/drain regions. After formation of a matrix of storage node structures, each located in a specific capacitor opening, a photoresist shape, formed in a positive photoresist layer, is used as a mask to allow regions of the insulator layer to be selectively removed, resulting in a matrix of storage node structures, with each storage node structure comprised with tall vertical features, and with a first portion of tall vertical features still butting the adjacent insulator layer, while a second portion of tall, vertical features have been stripped of insulator layer. After formation of a capacitor dielectric layer on exposed, bare portions of storage node structures, a top plate is formed overlying the matrix of storage node structures, resulting in a capacitor structure with increased surface area as a result of the matrix of storage node structures, each comprised with tall, vertical features, and with a portion of the tall, vertical features stripped of adjacent insulator to further increase surface area maintained bare to further. A second iteration of this invention entails the use of the same photolithographic plate used to define the photoresist shape used to strip adjacent insulator from the sides of the tall, vertical features of the storage node matrix in the first iteration of this invention. However in this case a negative photoresist layer is used to define the photoresist masking shape, thus resulting in insulator stripping of a set tall, vertical features, different then the set of tall, vertical features stripped in the first iteration of this invention. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     The object and other advantages of this invention are best described in the preferred embodiment with reference to the attached drawings that include: 
     FIGS. 1B,  2 ,  3 ,  4 B,  5 ,  6 B, and  7 , which schematically, in cross-sectional style, describe key stages of fabrication used to fabricate a capacitor structure comprised of a matrix, or of an array of storage node structures, wherein each storage node structure is comprised with tall, vertical features. 
     FIGS. 1A,  4 A, and  6 A, which schematically show a top view of the capacitor structure at specific stages of fabrication. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The method of fabricating a crown shaped capacitor structure comprised of a matrix of storage node structures, each in turn comprised with tall, vertical features, and with a group of inside and outside surfaces of the vertical features not butted by insulator, will now be described in detail. Semiconductor substrate  1 , comprised of P type, single crystalline silicon, with a &lt;100&gt; crystallographic orientation is used and schematically shown in FIG.  1 B. The transfer gate transistor used with the capacitor structure described in this invention, will not be described. The transfer gate transistor will be comprised of a conducive gate, or word line structure, on an underlying gate insulator layer, with source/drain regions formed in regions of semiconductor substrate  1 , not covered by the gate or word line structure. Insulator layer  2 , comprised of either silicon oxide, or boro-phosphosilicate glass (BPSG), is deposited via low pressure chemical vapor deposition (LPCVD), or plasma enhanced chemical vapor deposition (PECVD), procedures, at a thickness between about 5000 to 20000 Angstroms. If desired insulator layer  2 , can be subjected to a chemical mechanical polishing procedure to planarize the top surface of insulator layer  2 . A photoresist shape, not shown in the drawings, is used as an etch mask to allowing an anisotropic, reactive ion etching (RIE), procedure to define capacitor openings  3 , in insulator  2 . The RIE procedure is performed using CHF 3  as an etchant for insulator layer  2 . The result of these procedures are schematically shown, in cross-sectional style, in FIG.  1 B. The portion of semiconductor substrate  1 , exposed at the bottom of capacitor openings  3 , is comprised with source/drain regions. A top view of the array of capacitor openings  3 , is schematically shown in FIG.  1 A. 
     Formation of storage node structures is next addressed and schematically described, in cross-sectional style, using FIGS. 2-3. Polysilicon layer  4   a , is deposited via LPCVD procedures, at a thickness between about 750 to 1250 Angstroms, coating all surfaces of capacitor openings  3 , as well as coating the exposed source/drain regions located at the bottom of capacitor openings  3 . Polysilicon layer  4   a , is doped in situ, during deposition via the addition of arsine, or phosphine, to a silane ambient. If desired a hemispherical grain (HSG), silicon layer can be formed on polysilicon layer  4   a , to increase the surface area of te subsequent storage node structures. A photoresist layer is applied then etched, or polished back to expose the top surface of polysilicon layer  4   a , in a region in which polysilicon layer  4   a , overlays the top surface of insulator layer  2 , while photoresist plugs  20 , are formed and still remain in capacitor openings  3 . Another chemical mechanical polishing procedure is then employed to selectively remove exposed portions of polysilicon layer  4   a , from the top surface of insulator layer  2 , resulting in storage node structures  4   b , located in capacitor openings  3 . The vertical features of storage node structures  4   b , are between about 5000 to 20000 Angsroms in height, equal to the thickness of insulator layer  2 . If desired removal of exposed portions of polysilicon layer  4   a , can also be accomplished via a selective RIE procedure, using Cl 2  or SF 6  as an etchant for polysilicon. Photoresist plugs  20 , protects the portions of polysilicon layer  4   a , in the capacitor openings, during the selective RIE procedure. Removal of photoresist plugs  20 , is then accomplished via plasma oxygen ashing procedures. 
     The definition of a matrix, or of an array of storage node structures, and the removal of insulator layer  2 , from specific outside surfaces of the tall, vertical features of the storage node structures, are next addressed, in a first iteration of this invention. A positive photoresist layer is applied followed by exposure of regions of the positive photoresist layer through openings in a specific photolithographic plate. After development of the exposed portions of the positive photoresist layer, photoresist shape  5   a , shown schematically in FIG. 4B, is defined. Photoresist shape  5   a , is then used as an etch mask, allowing regions of insulator layer  2 , not covered by photoresist shape  5   a , to be selectively removed, resulting in opened area  6   a , now exposing portions of semiconductor substrate  1 . The selective removal of exposed regions of insulator layer  2 , is accomplished via a RIE procedure using CHF 3  as an etchant for insulator layer  2 , or via a wet etch procedure, using a buffered hydrofluoric acid solution. The etch procedure allows the outside surface of some of the tall, vertical features of storage node structures  4   b , to be bare, and therefore to contribute to the surface area of a subsequent capacitor structure. This is shown schematically, in cross-sectional style in FIG. 4B. A clearer picture of the regions of removed. insulator layer is schematically shown in a top view of FIG.  4 A. It can be seen that for matrix  7 , comprised of four storage node structures  4   b , insulator layer  2 , had been removed from the outside surfaces of storage node structures  4   b , located only inside matrix  7 , while the outside surfaces of these same storage node structures, not located in matrix  7 , are still butting insulator layer  2 . This combination allows additional capacitor surface area, regarding the bare surfaces of the tall, vertical features, while still providing protection against collapse of via the features still butting against insulator layer  2 . Photoresist shape  5   a , is removed via plasma oxygen ashing procedures. 
     The completion of the capacitor structure, featuring a matrix or array of storage node structures, is next addressed and schematically shown, in cross-sectional style, in FIG.  5 . Capacitor dielectric layer  8 , is deposited, overlying all exposed surfaces of storage node structures  4   b . Capacitor dielectric layer  8 , can be a tantalum oxide, silicon oxide, silicon oxynitride, or silicon nitride layer, deposited via plasma vapor deposition (PVD), or via chemical vapor deposition (CVD), procedures, at a thickness between about 40 to 60 Angstroms. A polysilicon layer is next deposited via LPCVD procedures, to a thickness between about 750 to 1250 Angstroms, with the polysilicon layer doped in situ, during deposition, via the addition of arsine, or phosphine to a silane ambient. Photolithographic and RIE procedures, using Cl 2  or SF 6  as an etchant, are used to define polysilicon top plate structure  9 , completely overlying the array of storage node structures. Capacitor structure  21 , comprised of top plate structure  9 , dielectric layer  8 , and storage node structures  4   b , offers increased surface area as a result of uncovered tall, vertical features for some of the outside surfaces, while offering protection against collapse of the storage node structures as a result of some of the outside surfaces of the storage node structure still butting adjacent insulator layer  2 . 
     A second iteration of this invention is next described, featuring a photoresist shape, obtained from exposure and development of a negative photoresist layer, used as a mask to define a storage node matrix. A negative photoresist layer is applied and exposed through clear regions in the same photolithographic plate previously used in the first iteration of this invention. Development procedures now remove only unexposed regions of the negative photoresist layer, thus resulting in the definition of photoresist shape  5   b , shown schematically, in cross-sectional style in FIG.  6 B. Photoresist shape  5   b , is then used as an etch mask allowing exposed regions of insulator layer  2 , to be removed, resulting in outside surfaces of the storage node structures, residing outside of matrix  17 , to be now be bare. Removal of exposed regions of insulator layer  2 , is again accomplished via a selective dry etching procedure using CHF 3  as an etchant, or via a wet etch procedure using a buffered hydrofluoric acid solution as an etchant. This is shown schematically as a top view in FIG.  6 A. This is in contrast to previously described matrix  7 , defined via an etch mask formed via exposure of a positive photoresist layer, where only the outside surfaces of storage node structures located inside the storage node matrix had insulator layer removed. For this iteration the desired, additional surface area is realized from the uncovered surfaces of storage node structures residing outside matrix  17 , while protection against collapse of the storage node structures is preventing by insulator layer  2 , still butting the surfaces of the storage node structures, inside matrix  17 . Photoresist shape  5   b , is removed via plasma oxygen ashing procedures. 
     The completion of the capacitor structure featuring matrix  17 , comprised of an array of storage node structures, is next addressed and schematically shown, in cross-sectional style, in FIG.  7 . Capacitor dielectric layer  8 , again as previously described in the first iteration, comprised of either tantalum oxide, silicon oxide, silicon oxynitride, or silicon nitride, at a thickness between about 40 to 60 Angstroms, is again used to overlay storage node structures  4   b . Top plate structure  9 , again comprised of an in situ doped polysilicon layer, is again defined via photolithographic and RLE procedures, using Cl 2  or SF 6 , as an etchant, resulting in the formation of capacitor structure  22 , comprised with a matrix of storage node structures, with each storage node structure comprised with tall, vertical features, and with the outside surfaces of the storage node structures located inside matrix  17 , butting insulator layer, while leaving the outside surfaces of the storage node structures located outside matrix  17 , bare. 
     While this invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit or scope of the invention.