Abstract:
One production method for semiconductor devices includes sequentially forming a stopper film and a BPSG film, forming a cylinder etch laminated mask upon the BPSG film, forming openings having a prescribed pattern in the cylinder etch laminated mask, then, using same as a mask, forming a cylinder hole that pierces from the BPSG film to the stopper film in the thickness direction. Next, forming a conductive layer that adjoins the side surfaces of the BPSG film, the stopper film, and a polysilicon film being part of the cylinder etch laminated mask, then removing the polysilicon film and the BPSG film .

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method in which holes having a large aspect ratio are formed in an insulating layer covering a semiconductor substrate. 
       BACKGROUND 
       [0002]    As semiconductor devices have come to have increasingly more components packed into increasingly small packages in recent years, a need has arisen for a process in which holes having a large aspect ratio are formed in the insulating layer covering the semiconductor substrate. For example, Patent Document 1 discloses a process for manufacturing a representative example of a semiconductor memory device (a dynamic random access memory (DRAM) device) in which cylindrical holes for forming cell capacitors are formed in a cylinder interlayer film (see Patent Document 1). 
         [0003]    As the area available for each cell capacitor has decreased in recent years with the increasing miniaturization and the increasing number of components integrated into DRAM devices, the cylinder interlayer film must be formed with a greater film thickness. This causes the aspect ratio of the cylindrical holes formed in the cylinder interlayer film to become extremely large, thereby presenting various problems in the process for forming those cylindrical holes. For example, such devices are prone to material removal defects due to insufficient etching as well as shape defects such as bowing. 
       RELATED ART DOCUMENT 
     Patent Document 
       [0004]    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2007-180493 
       SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
       [0005]    Conventional methods for preventing such defects include using a multilayer cylinder interlayer film, adding a bowing prevention sidewall film, using a multistep etching process, and the like. However, each of these conventional methods entails an increased number of steps in the manufacturing process and makes it difficult to form patterns small enough to necessitate double-patterning of patterns below the limits of lithography resolution. 
       Means for Solving the Problems 
       [0006]    One aspect of the present invention is a method for manufacturing a semiconductor device, including: forming a first insulating layer and a second insulating layer in order; forming a mask layer on top of the second insulating layer; forming openings in a prescribed pattern in the mask layer; forming holes going through the second insulating layer to the first insulating layer in a thickness direction thereof, using the mask layer as a mask; forming conductive layers contacting side surfaces of the mask layer, the second insulating layer, and the first insulating layer; and removing the mask layer and the second insulating layer. 
         [0007]    Another aspect of the present invention is a method for manufacturing a semiconductor device, including: forming a first insulating layer and a second insulating layer in order; forming a first support layer on top of the second insulating layer; forming, in a first pattern in the first support layer, openings that expose portions of the second insulating layer; forming a first mask layer covering the first support layer and exposed portions of the second insulating layer; forming, in the first mask layer and in a prescribed pattern, openings that overlap at least partially with the first pattern; forming holes going through the first support layer and the second insulating layer to the first insulating layer in a thickness direction thereof, using the first mask layer as a mask; forming conductive layers contacting side surfaces of the first mask layer, the first support layer, the second insulating layer, and the first insulating layer; and removing the first mask layer and the second insulating layer. 
         [0008]    Yet another aspect of the present invention is a method for manufacturing a semiconductor device, including: forming a first insulating layer and a second insulating layer in order; forming a first support layer on top of the second insulating layer; forming, in a first pattern in the first support layer, openings that expose portions of the second insulating layer; forming a first mask layer covering the first support layer and exposed portions of the second insulating layer; forming a second support layer on top of the first mask layer; forming, in a second pattern in the second support layer, openings that expose portions of the first mask layer; forming a second mask layer covering the second support layer and exposed portions of the first mask layer; forming, in a prescribed pattern, openings that overlap at least partially with the first pattern and the second pattern and that go through the second mask layer and the second support layer to the first mask layer in a thickness direction thereof; forming holes going through the first support layer and the second insulating layer to the first insulating layer in a thickness direction thereof, using the second mask layer as a mask; forming conductive layers contacting side surfaces of the second support layer, the second mask layer, the first mask layer, the first support layer, the second insulating layer, and the first insulating layer; and removing the second mask layer, the first mask layer, and the second insulating layer. 
       Effects of the Invention 
       [0009]    The present invention makes it possible to reduce the aspect ratio of the holes by using a mask layer and a conductive layer for patterning the first and second insulating layer as-is as a sidewall. This not only reduces the overall etching time but also reduces the occurrence of removal defects and bowing, thereby making it possible to increase yield. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cross-sectional view illustrating a method for manufacturing a semiconductor device according to Embodiment  1  of the present invention.  FIG. 1(   a ) illustrates the semiconductor device prior to patterning, and  FIG. 1(   b ) illustrates the device after patterning. 
           [0011]      FIG. 2  is a cross-sectional view illustrating one step of the method for manufacturing a semiconductor device according to Embodiment 1. 
           [0012]      FIG. 3  is a cross-sectional view illustrating one step of the method for manufacturing a semiconductor device according to Embodiment 1. 
           [0013]      FIG. 4  is a cross-sectional view illustrating one step of the method for manufacturing a semiconductor device according to Embodiment 1. 
           [0014]      FIG. 5  is a cross-sectional view illustrating one step of the method for manufacturing a semiconductor device according to Embodiment 1. 
           [0015]      FIG. 6  is a cross-sectional view illustrating a method for manufacturing a semiconductor device according to Embodiment 2 of the present invention.  FIG. 6(   a ) illustrates the semiconductor device prior to patterning, and  FIG. 6(   b ) illustrates the device after patterning. 
           [0016]      FIG. 7  is a cross-sectional view illustrating one step of the method for manufacturing a semiconductor device according to Embodiment 2. 
           [0017]      FIG. 8  is a cross-sectional view illustrating one step of the method for manufacturing a semiconductor device according to Embodiment 2. 
           [0018]      FIG. 9  is a cross-sectional view illustrating one step of the method for manufacturing a semiconductor device according to Embodiment 2. 
           [0019]      FIG. 10  is a cross-sectional view illustrating one step of the method for manufacturing a semiconductor device according to Embodiment 2. 
           [0020]      FIG. 11  is a cross-sectional view illustrating a method for manufacturing a prototype semiconductor device.  FIG. 11(   a ) illustrates the semiconductor device prior to patterning, and  FIG. 11(   b ) illustrates the device after patterning. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0021]    Preferred embodiments of the present invention will be described in detail below. However, first the problems that arise when forming holes having a large aspect ratio in an insulating layer will be described. 
         [0022]      FIG. 11  is a cross-sectional view illustrating a method for manufacturing a prototype semiconductor device.  FIG. 11(   a ) illustrates the semiconductor device prior to patterning, and  FIG. 11(   b ) illustrates the device after patterning. 
         [0023]    As illustrated in  FIG. 11(   a ), a semiconductor substrate  100  includes active regions separated by an element isolation region  200 . Each active region includes two word lines  300 . These word lines  300  function as the gate electrodes of the cell transistors of the DRAM device. In each cell transistor, one of the source region and the drain region is connected to a bit line  500 , and the other is connected to a capacitive contact plug  700  that serves as an underlying structure. The capacitive contact plug  700  is connected to the lower electrode of a cell capacitor. The capacitive contact plug  700  is formed by filling in a contact hole formed in an interlayer insulating layer  400  with a conductive film. 
         [0024]    Once this cell transistor structure is formed, a stopper film  780 , a BPSG film  790 A, an Si 3 N 4  film  804 ′, an SiO 2  film  790 B, an Si 3 N 4  film  805 ′, and a cylinder etching mask  850  are layered in order covering the cell transistor. The cylinder etching mask  850  includes a polysilicon film  851 , an SiO 2  film  852 , an amorphous carbon film  853 , and a multilayer SiN/SiON film  854  layered in order. Here, the layered films from the stopper film  780  to the Si 3 N 4  film  805 ′ are used to form sidewalls for forming a conductive layer (the lower electrode of the cell capacitor) in a later process. The collective height of these layered films is determined by the height H required for the conductive layer. 
         [0025]    Next, a photoresist  91  is formed on top of these layered films, and the desired pattern is formed in the photoresist  91  using photolithography. Then, the cylinder etching mask  850  is patterned using this patterned photoresist  91  as a mask. Furthermore, the Si 3 N 4  film  805 ′, the SiO 2  film  790 B, the Si 3 N 4  film  804 ′, the BPSG film  790 A, and the stopper film  780  are etched using this patterned cylinder etching mask  850  as a mask. As illustrated in  FIG. 11(   b ), this process forms cylindrical holes  810  that expose the capacitive contact plugs  700 . 
         [0026]    However, in the process depicted in  FIGS. 11(   a ) and  11 ( b ), the layered films ( 805 ′ to  780 ) must be etched through the entire collective height H thereof. This causes the aspect ratio of the holes to become extremely large during the etching process. As a result, the device is prone to removal defects such as that indicated by D 1  in the figure and bowing defects such as those indicated by D 2  in the figure, thereby decreasing the yield of the manufacturing method. 
         [0027]    However, the method for manufacturing a semiconductor device according to the following embodiments of the present invention solves these problems. 
         [0028]      FIG. 1  is a cross-sectional view illustrating a method for manufacturing a semiconductor device according to Embodiment 1 of the present invention.  FIG. 1(   a ) illustrates the semiconductor device prior to patterning, and  FIG. 1(   b ) illustrates the device after patterning. Note that in the figures described below, the same reference characters are used for components that are the same as those illustrated in  FIGS. 11(   a ) and  11 ( b ), and redundant descriptions of those components are omitted here. 
         [0029]    As illustrated in  FIG. 1(   a ), in the present embodiment a stopper film  780 , a BPSG film  790 A, an Si 3 N 4  film  804 ′, and a cylinder etching mask  850  are layered in order covering a cell transistor. The cylinder etching mask  850  includes a polysilicon film  851 , an SiO 2  film  852 , an amorphous carbon film  853 , and a multilayer SiN/SiON film  854  layered in order. 
         [0030]    Here, the stopper film  780  and the BPSG film  790 A are used to form portions of sidewalls for forming a conductive layer in a later process. The collective height H 1  of the stopper film  780  and the BPSG film  790 A is less than the height H required for the conductive layer (the lower electrode of the cell capacitor). The polysilicon film  851  is arranged at the uppermost position of the portions that form the height H. 
         [0031]    Next, a photoresist  91  is formed on top of these layered films, and the desired pattern is formed in the photoresist  91  using photolithography. The portions of the photoresist  91  that are removed during this patterning process are the regions where cylindrical holes  810  will be formed in a later process. Next, the cylinder etching mask  850  is patterned using this patterned photoresist  91  as a mask, thereby exposing the regions of the BPSG film  790 A where the cylindrical holes  810  will be formed. At this time, the polysilicon film  851  of the cylinder etching mask  850  remains with a prescribed height H 2 +α in the regions where the cylindrical holes  810  will not be formed. 
         [0032]    Next, as illustrated in  FIG. 1(   b ), the BPSG film  790 A and the stopper film  780  are etched using the patterned cylinder etching mask  850  as a mask to form the cylindrical holes  810  that expose capacitive contact plugs  700 . During this process, the film thickness of the polysilicon film  851  is reduced by a and becomes equal to H 2 . 
         [0033]    In the method for manufacturing a semiconductor device of the present embodiment, etching the stopper film  780  and the BPSG film  790 A (which have a collective height H 1  that is less than the overall required height H) in this manner reduces the aspect ratio of the holes in comparison with the prototype illustrated in  FIG. 11 . The patterned cylinder etching mask  850  adds a height H 2 , which forms the remainder of the required height H. This configuration prevents removal defects and bowing, thereby making it possible to improve yield. 
         [0034]    Next, the method for manufacturing a semiconductor device according to the present embodiment will be described in more detail with reference to  FIGS. 2 to 5 . 
         [0035]    First, as illustrated in  FIG. 2 , the stopper film  780 , the BPSG film  790 A, the Si 3 N 4  film  804 ′, and a photoresist  92  are layered in order covering the cell transistor. The stopper film  780  is made from silicon nitride and has a thickness of 25 nm, for example. Moreover, the BPSG film  790 A has a thickness of 900 nm, and the Si 3 N 4  film  804 ′ has a thickness of 200 nm, for example As described above, the collective film thickness (height) H 1  of the stopper film  780  and the BPSG film  790 A is less than the height H required for the conductive layer (the lower electrode of the cell capacitor). 
         [0036]    Next, the desired pattern is formed in the photoresist  92  using photolithography. Then, the Si 3 N 4  film  804 ′ is patterned using the patterned photoresist  92  as a mask to form a first support film  804  made from silicon nitride. Note that formation of the first support film  804  is not required in the present invention. However, forming the first support film  804  is extremely effective for preventing collapse of the cylindrical conductive layers that will be described later. 
         [0037]    Next, as illustrated in  FIG. 3 , the photoresist  92  is removed, and the cylinder etching mask  850  is formed over the entire surface covering the first support film  804  and the exposed BPSG film  790 A. As described above, the cylinder etching mask  850  includes the polysilicon film  851 , the SiO 2  film  852 , the amorphous carbon film  853 , and the multilayer SiN/SiON film  854  layered in order. The polysilicon film  851  has a thickness of 500 nm, the SiO 2  film  852  has a thickness of 200 nm, and the amorphous carbon film  853  has a thickness of 200 nm, for example Moreover, the multilayer SiN/SiON film  854  includes an Si 3 N 4  film and an SiON film both having a thickness of 15 nm, for example 
         [0038]    Next, a photoresist  91  is formed on top of the cylinder etching mask  850 , and the desired pattern is formed in the photoresist  91  using photolithography. The portions of the photoresist  91  that are removed during this patterning process are the regions where cylindrical holes  810  will be formed in a later process. Next, the cylinder etching mask  850  is patterned using this patterned photoresist  91  as a mask, thereby exposing the regions of the BPSG film  790 A where the cylindrical holes  810  will be formed. At this time, a portion of the Si 3 N 4  film  804 ′ is also removed, thereby forming the first support film  804 . 
         [0039]    Next, as illustrated in  FIG. 4 , the BPSG film  790 A and the stopper film  780  are etched using the patterned cylinder etching mask  850  as a mask to form the cylindrical holes  810  that expose the capacitive contact plugs  700 . As illustrated in  FIG. 4 , etching the stopper film  780  and the BPSG film  790 A (which have a collective height H 1 ) in this manner reduces the aspect ratio of the holes in comparison with the prototype illustrated in  FIG. 11 . The patterned cylinder etching mask  850  adds a height H 2 , which forms the remainder of the required height H. 
         [0040]    Next, a conductive layer is formed over the entire surface to cover the inner walls and bottom surfaces of the cylindrical holes  810  as well as the top surface of the polysilicon film  851  with a conductive film. Here, the inner walls of the cylindrical holes  810  include the sidewalls of the stopper film  780 , the sidewalls of the BPSG film  790 A, the sidewalls of the first support film  804 , and the sidewalls of the polysilicon film  851 . Next, the conductive film covering the top surface of the polysilicon film  851  is removed, and the polysilicon film  851  and the BPSG film  790 A are removed. As illustrated in  FIG. 5 , this process leaves conductive layers  801  having a height H from the capacitive contact plugs  700  at the bottom. The conductive layers  801  are cylindrical and function as the lower electrodes of the cell capacitor. The conductive layers  801  have an extremely large aspect ratio but are partially supported by the first support film  804  and are thereby prevented from collapsing. 
         [0041]    Next, after forming a capacitive insulating film  802  and upper electrodes  803 , an interlayer insulating film  900  and a protective insulating film  930  are formed to complete the semiconductor device according to the present embodiment. 
         [0042]    In the method for manufacturing a semiconductor device of the present embodiment, the stopper film  780  and the BPSG film  790 A, which have a collective height H 1  that is less than the overall height H required for the conductive layers  801  (the lower electrodes) are etched using the cylinder etching mask  850  (the etching mask for the stopper film  780  and the BPSG film  790 A) as-is for the height H 2 , which forms the remainder of the required height H. In this way, the aspect ratio of the holes created during the etching process is reduced, thereby making it possible to prevent removal defects and bowing as well as to reduce the overall etching time. Moreover, after the cylindrical holes  810  are formed, an additional step for removing the polysilicon film  851  that was used as a mask is not required, thereby reducing the number of steps in the process. 
         [0043]    Next, Embodiment 2 of the present invention will be described. 
         [0044]      FIG. 6  is a cross-sectional view illustrating a method for manufacturing a semiconductor device according to Embodiment 2 of the present invention.  FIG. 6(   a ) illustrates the semiconductor device prior to patterning, and  FIG. 6(   b ) illustrates the device after patterning. Note that in the figures described below, the same reference characters are used for components that are the same as those illustrated in  FIGS. 1(   a ) and  1 ( b ),  FIGS. 2 to 5 , and  FIGS. 11(   a ) and  11 ( b ), and redundant descriptions of those components are omitted here. 
         [0045]    As illustrated in  FIG. 6(   a ), the present embodiment differs from Embodiment 1 in that the polysilicon film  851  is divided into a polysilicon film  851  and a polysilicon film  851 ′ and an Si 3 N 4  film  805 ′ is formed therebetween. The Si 3 N 4  film  805 ′ serves as a second support film  805  during later processes, and the upper surface of the Si 3 N 4  film  805 ′ is positioned at the uppermost position of the height H from the capacitive contact plugs  700 . In the present embodiment, the stopper film  780  and the BPSG film  790 A have a collective film thickness of H 1 . Note that after forming the Si 3 N 4  film  805 ′, the Si 3 N 4  film  805 ′ may be patterned to form the second support film  805  before forming the polysilicon film  851 ′. 
         [0046]    In the present embodiment, the polysilicon film  851 , the Si 3 N 4  film  805 ′, and the polysilicon film  851  are used as a mask when forming the cylindrical holes  810 . The polysilicon film  851 ′ is then removed, and the Si 3 N 4  film  805 ′ is partially removed to form the second support film  805 . In the present embodiment, etching the stopper film  780  and the BPSG film  790 A (which have a collective height H 1  that is less than the overall required height H) in this manner reduces the aspect ratio of the holes formed during the etching process. This prevents removal defects and bowing, thereby making it possible to improve yield. 
         [0047]    Next, the method for manufacturing a semiconductor device according to the present embodiment will be described in more detail with reference to  FIGS. 7 to 10 . 
         [0048]    First, as illustrated in  FIG. 7 , after performing the process described in reference to  FIG. 2 , the cylinder etching mask  850  is formed over the entire surface covering the first support film  804  formed from portions of the Si 3 N 4  film  804 ′ as well as the exposed BPSG film  790 A. As described above, the cylinder etching mask  850  includes the polysilicon film  851 , the Si 3 N 4  film  805 ′, the polysilicon film  851 ′, the SiO 2  film  852 , the amorphous carbon film  853 , and the multilayer SiN/SiON film  854  layered in order. The total film thickness of the polysilicon film  851  and the polysilicon film  851 ′ is 500 nm, for example. Moreover, the Si 3 N 4  film  805  has a thickness of 30 nm, for example 
         [0049]    Next, a photoresist  91  is formed on top of the cylinder etching mask  850 , and the desired pattern is formed in the photoresist  91  using photolithography. The portions of the photoresist  91  that are removed during this patterning process are the regions where the cylindrical holes  810  will be formed in a later process. Next, as illustrated in  FIG. 8 , the cylinder etching mask  850  is patterned using this patterned photoresist  91  as a mask, thereby exposing the regions of the BPSG film  790 A where the cylindrical holes  810  will be formed. At this time, a portion of the Si 3 N 4  film  804 ′ is also removed, thereby forming the first support film  804 . 
         [0050]    Next, as illustrated in  FIG. 9 , the BPSG film  790 A and the stopper film  780  are etched using the patterned cylinder etching mask  850  as a mask to form the cylindrical holes  810  that expose the capacitive contact plugs  700 . As illustrated in  FIG. 9 , etching the stopper film  780  and the BPSG film  790 A (which have a collective height H 1 ) in this manner reduces the aspect ratio of the holes in comparison with the prototype illustrated in  FIG. 11 . The polysilicon film  851  or the polysilicon film  851  and the first support film  804  add a height H 2 , which forms the remainder of the required height H. 
         [0051]    Next, as illustrated in  FIG. 10 , the entire polysilicon film  851 ′ is then removed, and the Si 3 N 4  film  805 ′ is selectively removed to form the second support film  805 . It is preferable that the second support film  805  be formed at different positions than the first support film  804  when viewed in a plan view. Then, the same process described in reference to  FIG. 5  is performed, and a conductive layer is formed over the entire surface. Next, the conductive film covering the top surface of the polysilicon film  851  or the second support film  805  is removed, and the polysilicon film  851  and the BPSG film  790 A are removed. As illustrated in  FIG. 10 , this process leaves conductive layers  801  having a height H from the capacitive contact plugs  700  at the bottom. The conductive layers  801  have an extremely large aspect ratio but are partially supported by the first support film  804  and the second support film  805  and are thereby prevented from collapsing. 
         [0052]    Next, after forming a capacitive insulating film  802  and upper electrodes  803 , an interlayer insulating film  900  and a protective insulating film  930  are formed to complete the semiconductor device according to the present embodiment. 
         [0053]    In the method for manufacturing a semiconductor device according to the present embodiment, in addition to the effect described in Embodiment 1, the conductive layers  801  are also partially supported by the second support film  805 , thereby more effectively preventing the conductive layers  801  from collapsing. Moreover, the height H required for the conductive layers  801  is defined by the top surface of the second support film  805 , thereby making it possible to more accurately control the height H. 
         [0054]    Preferable embodiments of the present invention were described above. However, the present invention is not limited to these embodiments. Various modifications can be made without departing from the spirit of the present invention, and such modifications are included within the scope of the present invention. 
       DESCRIPTION OF REFERENCE CHARACTERS 
       [0000]    
       
           91 ,  91  photoresist 
           100  semiconductor substrate 
           200  element isolation region 
           300  word line 
           400  interlayer insulating layer 
           500  bit line 
           700  capacitive contact plug 
           780  stopper film 
           790 A,  790 B BPSG film 
           801  conductive layer (lower electrode) 
           802  capacitive insulating film 
           803  upper electrode 
           804 ′,  805 ′ Si 3 N 4  film 
           804  first support film 
           805  second support film 
           810  cylindrical hole 
           850  cylinder etching mask 
           851 ,  851 ′ polysilicon film 
           852  SiO 2  film 
           853  amorphous carbon film 
           854  multilayer SiN/SiON film 
           900  interlayer insulating film 
           930  protective insulating film