Abstract:
An improved method for fabricating a capacitor capable of reducing defects introduced as a result of complicated processes required to separate the bottom electrodes of the capacitors is provided to thereby enhance the yield of the resulting semiconductor devices. The method comprises forming an insulating film on a substrate; selectively etching the insulating film to open regions for the formation of the bottom electrode; depositing a conductive layer on the substrate including the opened regions; forming a photoresist pattern; and then, preferably in a single etch chamber, completing the process by removing the conductive layer in the peripheral circuit region; etching back the photoresist pattern to expose the conductive layer in the cell region; etching back the conductive layer to form the bottom electrodes; and removing any residual photoresist.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for the fabrication of capacitor and, more particularly, to a method for fabricating a capacitor that is capable of reducing defects incurred during the separation of capacitor. 
     DESCRIPTION OF THE PRIOR ART 
     FIGS. 1A to  1 C are schematic cross-sectional views illustrating a prior art method for the fabrication of capacitor. 
     As shown in FIGS. 1A, an interlayer insulating film  12  is disposed on a semiconductor substrate  11  obtained by a predetermined process, followed by the deposition of an interlayer insulating film  12  that is selectively etched to form a contact hole for a storage node of the capacitor. Next, a conductive layer is disposed on the whole surface including the contact hole, and a storage node contact plug  13  is formed using an etchback process or a chemical-mechanical polishing (CMP) process. Wherein the storage node contact plug  13  is connected to the semiconductor substrate  11  through the contact hole and has a double layered structure. 
     In an ensuing step, a capacitor oxidation film  14  is formed on the whole surface, including the storage node contact plug  13 , and a mask for defining the capacitor is then formed thereon. Subsequently, the capacitor oxidation film  14  is selectively etched using the mask to thereby expose a portion on which a bottom electrode of the capacitor is to be formed (i.e., a portion to which the storage node contact plug  13  is exposed). Thereafter, the interlayer insulating film  12  and the capacitor oxidation film  14  in a peripheral circuit region II are selectively etched to form an alignment key box pattern  15 . 
     After the above step, a polysilicon layer  16 , for the bottom electrode is formed on the whole surface including the exposed portion. A mask  17  is disposed thereon through the use of a photosensitive film serving to expose the peripheral circuit region II. 
     As shown in FIG. 1B, the polysilicon  16  in the peripheral circuit region II is etched using the mask  17 , after which a distinct bottom electrode  16   a  is formed using the CMP process. In this case, a photosensitive film  17   a  remains within the contact hole in the bottom electrode  16   a.    
     As shown in FIG. 1C, the photosensitive film  17   a  remaining within the bottom electrode  16   a  is then removed. 
     The prior art method suffers from a drawback, in that, it employs the chemical mechanical polishing process for the separation of the capacitors, resulting in an excessive height loss of the capacitor and various defects resulting from various causes, e.g., slurry residue, broken portions of the capacitor structure, dishing, and particles, which, in turn, deteriorates the yield of the resulting semiconductor device. 
     In addition, the prior art method must utilize four distinct pieces of equipment such as equipment for removal of the polysilicon in the peripheral circuit region II, equipment for the chemical-mechanical polishing, equipment for stripping away the photosensitive film and equipment for the wet etch. As a result of the need for these various pieces of equipment and the associated handling, the prior art process suffers from a shortcoming in that it increases the number of defect sources and increases the process time, both of which tend to deteriorate the yield of semiconductor device. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a method for fabricating capacitors that is capable of reducing defects introduced as the result of the complicated process during the separation of capacitor, to thereby enhance the yield of the resulting semiconductor device. 
     In accordance with a preferred embodiment of the present invention, there is provided a method for the fabrication of capacitor, comprising the steps of: forming an insulating film on a semiconductor substrate in which a cell region and a peripheral circuit region are defined; selectively etching the insulating film, followed by opening a region in which a bottom electrode will be formed; depositing a conductive layer for the bottom electrode on the whole surface, including the opened region; forming a photosensitive film pattern that exposes the peripheral circuit region; removing the conductive layer in the peripheral circuit region using the photosensitive film as a mask; applying an etchback process to the photosensitive film to expose the conductive layer in the cell region; applying an etchback process to the conductive layer until the insulating film covered with the conductive layer is exposed, to thereby form a distinct bottom electrode; and stripping away the remaining photosensitive film. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
     FIGS. 1A to  1 C are cross-sectional views illustrating a prior art method for the fabrication of capacitor; and 
     FIGS. 2A to  2 E are cross-sectional views illustrating a method for fabricating a capacitor in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 2A to  2 E are schematic cross-sectional views illustrating a method for fabricating a capacitor in accordance with a preferred embodiment of the present invention. 
     As shown in FIG. 2A, an interlayer insulating film  22  is deposited on a semiconductor substrate  21  obtained by a predetermined process. The interlayer insulating film  22  is then selectively etched to form a contact holes for storage nodes. Next, a conductive layer is deposited the whole surface including the contact holes, followed by a selective removal process that is applied to the conductive layer to form a storage node contact plug  23 , which is connected to the semiconductor substrate  21  through the contact hole. In this case, the storage node contact plug  23  is formed only the cell region I in which the capacitors will be formed. 
     Before the formation of the storage node contact plug  23 , word lines (not shown) are formed on the semiconductor substrate  21 , followed by the formation of source-drain regions using an impurity ion implantation using the wordline pattern as an implant mask. In an ensuing step, a first contact plug (not shown) is formed to provide a vertical connection between an impurity junction layer and the wordlines. Next, a wordline insulating film (not shown) is formed on the first contact plug followed by a bit line pattern (not shown) is formed thereon. After the above step, formed is a contact hole to which the first contact plug is exposed. And then, a conductive layer for forming the plug is formed the whole surface including the contact hole, followed by a second contact plug to be connected to The first contact plug is formed using a chemical-mechanical polishing process until the wordline insulating film is exposed. 
     In this case, the second contact plug represents the storage node contact plug  23  and the interlayer insulating film  22  represents the wordline insulating film. 
     In a subsequent step, a capacitor oxidation film  24  having a thickness range of 8,000 Å to 18,000 Å is formed on the whole surface, including the storage node contact plug  23 . The capacitor oxidation film  24  is preferably formed from either tetraethylorthosilicate (TEOS) or boron phosphorus silicate glass (BPSG) material. The capacitor oxidation film  24  is then selectively etched to open a region at which a bottom electrode will be formed and expose the storage node contact plug  23 . The capacitor oxidation film  24  and the interlayer insulating film  22  in the peripheral circuit region II are also selectively etched to form an alignment key box pattern  25 . 
     A polysilicon layer for forming the bottom electrode  26  ranging in thickness from 400 Å to 600 Å is then formed on the whole surface, including the opened region. Next, a photosensitive film pattern  27  is formed to expose the peripheral circuit region II to remove the polysilicon of the alignment key box pattern  25 , wherein the peripheral circuit region II causes a lifting up of the bottom electrode during a wet etching of the capacitor oxidation film  24  exposing the subsequent bottom electrode. In this case, the photosensitive film  27  is formed so that it is applied to the whole surface including the polysilicon for bottom electrode  26 , followed by exposing and developing the photosensitive film  27 , thereby exposing the peripheral circuit region II. 
     As shown in FIG. 2B, the semiconductor substrate  21  on which the photosensitive film  27  is formed is introduced to an isotropic etcher. In the isotropic etcher, a pressure of 300 to 1000 mTorr is maintained, a properly mixed gas of CF 4 , NF 3  as a main etching gas and O 2  as a feed gas is introduced, and a downstream microwave power of 700 W to 1800 W and a radio frequency bias power of 50 W to 100 W are applied. 
     First, the polysilicon for bottom electrode  26  in the peripheral circuit region II is etched using the isotropic etcher under conditions that provide a selection ratio for the capacitor oxidation film  24  of 4:1 to 10:1. In this case, the etching of the polysilicon for bottom electrode  26  is performed in condition that the microwave power (MW), radio frequency bias power (RF), pressure, CF 4 , O 2 , NF 3 , chamber sidewall temperature and chamber bottom temperature are 900-1600 W, 0-450 W, 500-1000 mtorr, 20-100 sccm, 500-1000 sccm, 20-40 sccm, 10-90° C. and 10-90° C., respectively. 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Parameter 
                 Preferred Value 
               
               
                   
                   
               
             
             
               
                   
                 Microwave Power 
                 900-1600 W 
               
               
                   
                 RF Bias Power 
                   0-450 W 
               
               
                   
                 Pressure (Chamber) 
                 500-1000 mTorr 
               
               
                   
                 CF 4  Flow 
                  20-100 sccm 
               
               
                   
                 O 2  Flow 
                 50-1000 sccm 
               
               
                   
                 NF 3  Flow 
                  20-40 sccm 
               
               
                   
                 Chamber Sidewall Temp 
                 10-90° C. 
               
               
                   
                 Chamber Bottom Temp 
                 10-90° C. 
               
               
                   
                   
               
             
          
         
       
     
     For example, applying the isotropic etching to the polysilicon  26  under conditions of 1000 W(MW)/150 W(RF)/700 mTorr/200 CF 4 /100 O 2 /70° C. 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Parameter 
                 Value 
               
               
                   
                   
               
             
             
               
                   
                 Microwave Power 
                 1000 W 
               
               
                   
                 RF Bias Power 
                  150 W 
               
               
                   
                 Pressure (Chamber) 
                 700 mTorr 
               
               
                   
                 CF 3  Flow 
                 200 sccm 
               
               
                   
                 O 2  Flow 
                 100 sccm 
               
               
                   
                 NF 3  Flow 
                  0 sccm 
               
               
                   
                 Chamber Sidewall Temp 
                 70° C. 
               
               
                   
                 Chamber Bottom Temp 
                 70° C. 
               
               
                   
                   
               
             
          
         
       
     
     and an etching rate with 7,340 Å/minute ±7%, with the polysilicon  26  having a thickness 500 Å and the alignment key box pattern  25  having a depth of 15,000 Å even if an etch target is set to a thickness of 5,000 Å A it is possible to completely remove the polysilicon  26  within the align key box pattern  25 . 
     As shown in FIG. 2C, in the same isotropic etcher, an etchback process is then conducted to remove the majority of the photosensitive film  27  while allowing some photosensitive film ( 27   a ) to remain within the contact holes in the polysilicon  26 . In this case, a point at the photosensitive film is exposed only in the contact holes is determined through the use of an end point detector, under condition that a temperature in the chamber, a flow meter of oxygen, RF power and non-uniformity are maintained in the ranges of 20 to 90° C., 200 to 600 sccm, 100 to 450 W and less than 3%, respectively 
     For example, using a recipe with 420 W(RF)/400 O 2 /300 mT/70° C.(W)/60° C.(E), the etching rate of 6,690 Å/minute ±7% is applied. Wherein the 70° C.(W) represents the temperature of the chamber sidewall and the 60° C.(E) represents the temperature of the chamber bottom on which the wafer is disposed. 
     As mentioned above, in the same equipment used to remove the polysilicon  26  in the peripheral circuit region II, it is possible to improve the uniformity of the etchback for the photosensitive film  27  by only using the oxygen and the RF bias power, and achieve delicate control of the etching rate of the photosensitive film using a process temperature of 70° C. and the end point detection. 
     The preceding step is then followed by applying an etchback process to a portion of the polysilicon  26  which is exposed by the etchback for the photosensitive film  27  in the same chamber, to form a distinct bottom electrode  26   a  as shown in FIG.  2 D. The etchback process using a mixed gas of NF 3 /CF 4 /He is introduced under conditions that provide an etch selection ratio between the polysilicon  26  and the photosensitive film  27   a  remaining at the contact hole is in the range of 1:1 to 3:1 and that between the capacitor oxidation film  24  and the photosensitive film  27   a  is in the range of 0.8:1 to 1.5:1. 
     In this case, the microwave power, the RF power and the pressure are in the ranges of 900 to 1600 W, 0 to 450 W and 500 to 1000 mTorr, respectively. Further, the NF 3 , the CF 4  and H 2  are in the ranges of 10 to 40 sccm, 20 to 100 sccm and 500 to 1000 sccm, respectively. 
     At an ensuing step, the photosensitive film  27   a  remaining in the contact hole in the bottom electrode  26   a  is stripped away under conditions in which the microwave power is in the range of 1000 to 1800 W, a mixed gas or a distinct gas of O 2  and N 2  is introduced, a temperature in heating lamp in the chamber ranges from 200° C. to 280° C., a temperature of the chamber wall is about 70° C. During the strip away of the photosensitive film  27   a  , the pressure, O 2  and N 2  are preferably in the ranges of 500 to 1000 mTorr, 1000 to 4000 sccm and 100 to 400 sccm, respectively. 
     After the above step, as shown in FIG. 2E, a wet etch process is than applied to the capacitor oxidation film  24  to expose the bottom electrode  26   a . The wet etch process uses a amine solvent ACT™ or H 2 SO 4 :H 2 O 2 =50:1 at a temperature ranging from 100° C. to 120° C., for 10 to 20 minutes followed by a buffered oxide etchant (BOE) with a ratio of 300:1 for 2 to 10 seconds. 
     As demonstrated above, the present invention has the ability to implement an etching process for a polysilicon, an etchback process for a photosensitive film, an etchback process for polysilicon for separating a bottom electrode, and a stripping process for the photosensitive film, in a single piece of equipment, thereby providing a simplified process, decreased defects and improved yield. 
     Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.