Patent Publication Number: US-2023164998-A1

Title: Semiconductor device and method for manufacturing same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-191334, filed Nov. 25, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a semiconductor device and a method for manufacturing the same. 
     BACKGROUND 
     In a three-dimensional semiconductor memory, there can be a problem that the charge stored in the charge storage layer of a memory cell escapes to the outside of the charge storage layer or to another memory cell. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view showing a structure of a semiconductor device of a first embodiment. 
         FIG.  2    is a cross-sectional view showing the structure of the semiconductor device of the first embodiment. 
         FIG.  3    is a cross-sectional view showing details of the structure of the semiconductor device of the first embodiment. 
         FIGS.  4 A and  4 B  are cross-sectional views (1/7) showing a method for manufacturing the semiconductor device of the first embodiment. 
         FIGS.  5 A and  5 B  are cross-sectional views (2/7) showing the method for manufacturing the semiconductor device of the first embodiment. 
         FIGS.  6 A and  6 B  are cross-sectional views (3/7) showing the method for manufacturing the semiconductor device of the first embodiment. 
         FIGS.  7 A and  7 B  are cross-sectional views (4/7) showing the method for manufacturing the semiconductor device of the first embodiment. 
         FIGS.  8 A and  8 B  are cross-sectional views (5/7) showing the method for manufacturing the semiconductor device of the first embodiment. 
         FIGS.  9 A and  9 B  are cross-sectional views (6/7) showing the method for manufacturing the semiconductor device of the first embodiment. 
         FIGS.  10 A and  10 B  are cross-sectional views (7/7) showing the method for manufacturing the semiconductor device of the first embodiment. 
         FIGS.  11 A and  11 B  are cross-sectional views (1/2) showing details of the method for manufacturing the semiconductor device of the first embodiment. 
         FIGS.  12 A and  12 B  are cross-sectional views (2/2) showing details of the method for manufacturing the semiconductor device of the first embodiment; 
         FIGS.  13 A to  13 C  are graphs (1/3) showing examples of an F concentration profile in the semiconductor device of the first embodiment. 
         FIGS.  14 A to  14 C  are graphs (2/3) showing examples of the F concentration profile in the semiconductor device of the first embodiment. 
         FIGS.  15 A to  15 D  are graphs (3/3) showing examples of the F concentration profile and the like in the semiconductor device of the first embodiment. 
         FIG.  16    is a graph related to the F concentration in the semiconductor device of the first embodiment. 
         FIG.  17    is a cross-sectional view showing a structure of a semiconductor device of a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     At least one embodiment provides a semiconductor device capable of preventing charge from escaping from a charge storage layer, and a method for manufacturing the same. 
     In general, according to at least one embodiment, a semiconductor device includes a plurality of electrode layers separated from each other in a first direction, a charge storage layer provided on side surfaces of the plurality of electrode layers via a first insulating film, and a semiconductor layer provided on a side surface of the charge storage layer via a second insulating film. The charge storage layer includes a location having a fluorine concentration of 5.0 × 10 18  atoms/cm 3  or less. A fluorine concentration at an interface between the charge storage layer and the second insulating film is 10 times or more or 1 / 10 or less of a fluorine concentration at an interface between the charge storage layer and the first insulating film. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In  FIGS.  1  to  17   , the same components are designated by the same reference numerals and duplicate descriptions will be omitted. 
     First Embodiment 
       FIG.  1    is a perspective view showing a structure of a semiconductor device of a first embodiment. The semiconductor device of  FIG.  1    includes, for example, a three-dimensional semiconductor memory. 
     The semiconductor device of  FIG.  1    includes a core insulating film  1 , a channel semiconductor layer  2 , a tunnel insulating film  3 , a charge storage layer  4 , a block insulating film  5 , and an electrode layer  6 . The block insulating film  5  includes an insulating film  5   a  and an insulating film  5   b . The electrode layer  6  includes a barrier metal layer  6   a  and an electrode material layer  6   b . The insulating film  5   a , the tunnel insulating film  3 , and the insulating film  5   b  are examples of a first insulating film, a second insulating film, and a third insulating film, respectively. The channel semiconductor layer  2  is an example of a semiconductor layer. 
     In  FIG.  1   , a plurality of electrode layers and a plurality of insulating films are alternately stacked on a substrate, and a memory hole MH is provided in these electrode layers and insulating films.  FIG.  1    shows one electrode layer  6  among these electrode layers. These electrode layers function, for example, as word lines of the three-dimensional semiconductor memory.  FIG.  1    shows X and Y directions parallel to a surface of the substrate and perpendicular to each other, and a Z direction perpendicular to the surface of the substrate. In the present specification, a +Z direction is treated as an upward direction and a -Z direction is treated as a downward direction. The -Z direction may or may not coincide with a direction of gravity. The Z direction is an example of the first direction, and the X direction is an example of a second direction. 
     The core insulating film  1 , the channel semiconductor layer  2 , the tunnel insulating film  3 , the charge storage layer  4 , and the insulating film  5   a  are formed in the memory hole MH and configure a memory cell of the three-dimensional semiconductor memory. The insulating film  5   a  is formed on surfaces of the plurality of electrode layers and the plurality of insulating films in the memory hole MH, and the charge storage layer  4  is formed on a surface of the insulating film  5   a . The charge storage layer  4  can store a signal charge of the three-dimensional semiconductor memory. The tunnel insulating film  3  is formed on a surface of the charge storage layer  4  and the channel semiconductor layer  2  is formed on a surface of the tunnel insulating film  3 . The channel semiconductor layer  2  functions as a channel of the memory cell. The core insulating film  1  is formed in the channel semiconductor layer  2 . 
     The insulating film  5   a  contains, for example, Si (silicon) and O (oxygen). The insulating film  5   a  is, for example, a SiO 2  film (silicon oxide film). The charge storage layer  4  contains, for example, Si (silicon) and N (nitrogen). The charge storage layer  4  is, for example, an insulating film such as a SiN film (silicon nitride film). The tunnel insulating film  3  contains, for example, Si (silicon), O (oxygen), and N (nitrogen), or contains Si (silicon) and O (oxygen). The tunnel insulating film  3  is, for example, a SiON film (silicon oxynitride film) or the SiO 2  film. The channel semiconductor layer  2  contains, for example, Si (silicon). The channel semiconductor layer  2  is, for example, a polysilicon layer. The core insulating film  1  contains, for example, Si (silicon) and O (oxygen). The core insulating film  1  is, for example, the SiO 2  film. 
     The insulating film  5   b , the barrier metal layer  6   a , and the electrode material layer  6   b  are sequentially formed between two insulating films adjacent to each other in the Z direction and formed on a lower surface of an upper insulating film, an upper surface of a lower insulating film, and a side surface of the insulating film  5   a . The insulating film  5   b  contains, for example, Al (aluminum) and O (oxygen). The insulating film  5   b  is, for example, a metal insulating film such as an Al 2 O 3  film (aluminum oxide film). The barrier metal layer  6   a  contains, for example, Ti (titanium) and N (nitrogen). The barrier metal layer  6   a  is, for example, a TiN film (titanium nitride film). The electrode material layer  6   b  contains, for example, W (tungsten). The electrode material layer  6   b  is, for example, a W (tungsten) layer. 
       FIG.  2    is a cross-sectional view showing the structure of the semiconductor device of the first embodiment.  FIG.  2    is a vertical cross-sectional view of an XZ cross-section Sxz shown in  FIG.  1   . 
       FIG.  2    shows a vertical cross-section of the memory hole MH shown in  FIG.  1   . As described with reference to  FIG.  1   , the semiconductor device of at least one embodiment includes a plurality of electrode layers  6  and a plurality of insulating films  8  alternately stacked on a substrate  7  ( FIG.  2   ). As shown in  FIG.  2   , these electrode layers  6  are separated from each other in the Z direction. Each electrode layer  6  includes the barrier metal layer  6   a  and the electrode material layer  6   b  described above. The substrate  7  is, for example, a semiconductor substrate such as a Si (silicon) substrate. Each insulating film  8  is, for example, an SiO 2  film. The plurality of electrode layers  6  and the plurality of insulating films  8  configure a stacked film  9 . 
     The insulating film  5   a , the charge storage layer  4 , the tunnel insulating film  3 , the channel semiconductor layer  2 , and the core insulating film  1  are sequentially formed on a side surface of the stacked film  9  in the memory hole MH, that is, on the side surfaces of the plurality of electrode layers  6  and the plurality of insulating films  8  in the memory hole MH. The barrier metal layer  6   a  and the electrode material layer  6   b  in each electrode layer  6  are sequentially formed on a lower surface of an upper insulating film  8 , an upper surface of a lower insulating film  8 , and the side surface of the insulating film  5   a  via the insulating film  5   b . 
       FIG.  2    shows a plurality of memory cells MC of the semiconductor device of at least one embodiment. As shown in  FIG.  2   , each memory cell MC includes the core insulating film  1 , the channel semiconductor layer  2 , the tunnel insulating film  3 , the charge storage layer  4 , the block insulating film  5 , and the corresponding electrode layer  6 . As shown schematically in  FIG.  2   , each memory cell MC can store the signal charge in the charge storage layer  4 . 
     Next, with reference to  FIG.  2   , fluorine (F) contained in the charge storage layer  4  of at least one embodiment will be described. 
     As schematically shown in  FIG.  2   , the charge storage layer  4  of at least one embodiment contains F atoms as impurity atoms. Before forming the charge storage layer  4  in a chamber, the inside of the chamber may be cleaned with a cleaning gas. This cleaning gas often contains an F component, such as a F 2  (fluorine) gas and a HF (hydrogen fluoride) gas. As a result, when the charge storage layer  4  is formed in the chamber after cleaning the chamber, the F component remaining in the chamber often enters the charge storage layer  4 .  FIG.  2    shows F atoms that enter the charge storage layer  4  in this way. 
     Further, the gas in a FOUP (Front Opening Unified Pod) that carries the substrate  7  may also contain the F component. In this case, the F component in the FOUP may enter the charge storage layer  4 . 
     Due to these reasons, the charge storage layer  4  may contain F atoms. In this case, even if there is no step of using a process gas or a process liquid (for example, a source gas, an oxidizing agent, a reducing agent, an etching solution, etc.) containing F atoms when manufacturing the semiconductor device of at least one embodiment, F atoms enter the charge storage layer  4 . As will be described later, F atoms may also enter a portion other than the charge storage layer  4  (for example, the tunnel insulating film  3  or the insulating film  5   a ) in the semiconductor device of at least one embodiment. 
     When F atoms enter the charge storage layer  4  in this way, a concentration of F atoms in the charge storage layer  4  (hereinafter, referred to as an “F concentration”) is generally high. Generally, the F concentration in the charge storage layer  4  in this case is about 1.0 × 10 20  atoms/cm 3 . When the F concentration in the charge storage layer  4  becomes high, the signal charge is likely to escape from the charge storage layer  4 . As a result, the charge retention characteristics of each memory cell MC may deteriorate. 
       FIG.  2    schematically shows how the signal charge escapes from the charge storage layer  4 . As shown in  FIG.  2   , the signal charge stored in the charge storage layer  4  of each memory cell MC may escape to the outside of the charge storage layer  4  of the memory cell MC or to another memory cell MC. Generally, when F atoms enter the charge storage layer  4 , a shallow trap is generated in the charge storage layer  4 . In this case, if the signal charge in the charge storage layer  4  is captured by the shallow trap, the signal charge is likely to escape to the outside of the charge storage layer  4 . Therefore, when the F concentration in the charge storage layer  4  becomes high, the signal charge is likely to escape from the charge storage layer  4 . 
     Therefore, when manufacturing the semiconductor device of at least one embodiment, a process of reducing the F concentration in the charge storage layer  4  is performed, as will be described later. This makes it possible to prevent the signal charge from escaping from the charge storage layer  4 . 
     The F concentration in the charge storage layer  4  of the present embodiment is set to 5.0 × 10 18  atoms/cm 3  or less, entirely or partially. For example, when the F concentration in the charge storage layer  4  is uniform, the F concentration in all the locations in the charge storage layer  4  is set to the same value of 5.0 × 10 18  atoms/cm 3  or less. On the other hand, when the F concentration in the charge storage layer  4  is non-uniform, the F concentration in all the locations in the charge storage layer  4  may be set to 5.0 × 10 18  atoms/cm 3  or less, or the F concentration in only a part of the charge storage layer  4  may be set to 5.0 × 10 18  atoms/cm 3  or less. Various examples of such F concentration will be described later with reference to  FIGS.  13 A to  15 D . 
     The F concentration in the charge storage layer  4  of at least one embodiment is set to a high concentration at an interface between the charge storage layer  4  and the tunnel insulating film  3  and is set to a low concentration at an interface between the charge storage layer  4  and the insulating film  5   a , for example. For example, an F concentration at the interface between the charge storage layer  4  and the tunnel insulating film  3  is set to be 10 times or more an F concentration at the interface between the charge storage layer  4  and the insulating film  5   a  ( FIG.  13 B , etc.). Such F concentration can be implemented by removing F atoms near the interface between the charge storage layer  4  and the insulating film  5   a . 
     On the other hand, the F concentration in the charge storage layer  4  of at least one embodiment may be set to a low concentration at the interface between the charge storage layer  4  and the tunnel insulating film  3  and may be set to a high concentration at the interface between the charge storage layer  4  and the insulating film  5   a . For example, the F concentration at the interface between the charge storage layer  4  and the tunnel insulating film  3  may be set to 1 / 10 or less of the F concentration at the interface between the charge storage layer  4  and the insulating film  5   a  ( FIG.  13 C , etc.). Such F concentration can be implemented by removing F atoms near the interface between the charge storage layer  4  and the tunnel insulating film  3 . 
     For example, when the F concentration at the interface between the charge storage layer  4  and the tunnel insulating film  3  is a maximum value and the F concentration at the interface between the charge storage layer  4  and the insulating film  5   a  is a minimum value, the F concentration of the former is 10 times or more the F concentration of the latter. In this case, the F concentration of the latter is 1 / 10 or less of the F concentration of the former. In this case, a maximum value of the F concentration in the charge storage layer  4  is 10 times or more a minimum value of the F concentration in the charge storage layer  4 . 
       FIG.  3    is a cross-sectional view showing the details of the structure of the semiconductor device of the first embodiment. 
       FIG.  3    shows a plurality of columnar portions CL having a structure similar to a structure in the memory hole MH shown in  FIG.  2   . The semiconductor device of at least one embodiment includes an interlayer insulating film  11 , a source layer  12 , an interlayer insulating film  13 , a gate layer  14 , an interlayer insulating film  15 , a plurality of memory insulating films  16 , and a plurality of slit insulating films  17 , in addition to components shown in  FIG.  2   . The source layer  12  includes a metal layer  12   a , a lower semiconductor layer  12   b , an intermediate semiconductor layer  12   c , and an upper semiconductor layer  12   d . 
     The interlayer insulating film  11 , the source layer  12 , the interlayer insulating film  13 , the gate layer  14 , the stacked film  9 , and the interlayer insulating film  15  are sequentially formed on the substrate  7 . The interlayer insulating film  11  is, for example, an SiO 2  film. The source layer  12  includes the metal layer  12   a  (e.g., W layer), the lower semiconductor layer  12   b  (e.g., polysilicon layer), the intermediate semiconductor layer  12   c  (e.g., polysilicon layer), and the upper semiconductor layer  12   d  (e.g., polysilicon layer), which are sequentially formed on the interlayer insulating film  11 . The interlayer insulating film  13  is, for example, an SiO 2  film. The gate layer  14  is, for example, the polysilicon layer. The interlayer insulating film  15  is, for example, an SiO 2  film. The insulating film  5   b  in the stacked film  9  is not shown. 
     Each columnar portion CL has a columnar shape extending in the Z direction and is formed in the lower semiconductor layer  12   b , the intermediate semiconductor layer  12   c , the upper semiconductor layer  12   d , the interlayer insulating film  13 , the gate layer  14 , the stacked film  9 , and the interlayer insulating film  15 . Each columnar portion CL includes the memory insulating film  16 , the channel semiconductor layer  2 , and the core insulating film  1  in this order. The memory insulating film  16  in each columnar portion CL includes the above-mentioned insulating film  5   a , the charge storage layer  4 , and the tunnel insulating film  3  in this order (see  FIG.  2   ). The channel semiconductor layer  2  in each columnar portion CL is in contact with the intermediate semiconductor layer  12   c  and is electrically connected to the source layer  12 . 
     Each slit insulating film  17  has a plate-like shape extending in the Z direction and the Y direction and is formed in the upper semiconductor layer  12   d , the interlayer insulating film  13 , the gate layer  14 , the stacked film  9 , and the interlayer insulating film  15 . Each slit insulating film  17  is, for example, an SiO 2  film. 
       FIGS.  4 A to  10 B  are cross-sectional views showing a method for manufacturing the semiconductor device of the first embodiment. 
     First, the interlayer insulating film  11 , the metal layer  12   a , the lower semiconductor layer  12   b , a lower protective film  21 , a sacrifice layer  22 , an upper protective film  23 , the upper semiconductor layer  12   d , the interlayer insulating film  13 , and the gate layer  14  are sequentially formed on the substrate  7  ( FIG.  4 A ). The lower protective film  21  is, for example, an SiO 2  film. The sacrifice layer  22  is, for example, the polysilicon layer. The upper protective film  23  is, for example, an SiO 2  film. 
     Next, a stacked film  9 ′ including a plurality of sacrifice layers  6 ′ and the plurality of insulating films  8  alternately is formed on the gate layer  14 , and the interlayer insulating film  15  is formed on the stacked film  9 ′ ( FIG.  4 B ). Each sacrifice layer  6 ′ is, for example, an SiN film. These sacrifice layers  6 ′ are separated from each other in the Z direction. These sacrifice layers  6 ′ are examples of a first layer. 
     Next, by photolithography and RIE (Reactive Ion Etching), a plurality of memory holes MH are formed in the interlayer insulating film  15 , the stacked film  9 ′, the gate layer  14 , the interlayer insulating film  13 , the upper semiconductor layer  12   d , the upper protective film  23 , the sacrifice layer  22 , the lower protective film  21 , and the lower semiconductor layer  12   b  ( FIG.  5 A ). 
     Next, the memory insulating film  16 , the channel semiconductor layer  2 , and the core insulating film  1  are sequentially formed in these memory holes MH ( FIG.  5 B ). As a result, the plurality of columnar portions CL are formed in these memory holes MH. The memory insulating film  16  is formed by forming the insulating film  5   a , the charge storage layer  4 , and the tunnel insulating film  3  in this order in each memory hole MH (see  FIG.  2   ). At this time, in at least one embodiment, F atoms enter the charge storage layer  4  and the F concentration in the charge storage layer  4  becomes high. 
     Next, a plurality of slits ST are formed in the interlayer insulating film  15 , the stacked film  9 ′, and the gate layer  14  by the photolithography and the RIE ( FIGS.  6 A and  6 B ). The RIE is performed using a first etching gas in the step shown in  FIG.  6 A , and is performed using a second etching gas different from the first etching gas in the step shown in  FIG.  6 B . 
     Next, the upper protective film  23  is removed from a bottom surface of a slit ST by etching ( FIG.  7 A ), a liner layer  24  is formed on a surface of the slit ST ( FIG.  7 B ), and the liner layer  24  is removed from the bottom surface of the slit ST by etching ( FIG.  8 A ). As a result, a side surface of the slit ST is protected by the liner layer  24 , while the sacrifice layer  22  is exposed on the bottom surface of the slit ST. The liner layer  24  is, for example, an SiN film. 
     Next, the sacrifice layer  22  is removed by wet etching using the slit ST ( FIG.  8 B ). As a result, a cavity C 1  is formed between the lower protective film  21  and the upper protective film  23 , and the memory insulating film  16  is exposed on a side surface of the cavity C 1 . 
     Next, the lower protective film  21 , the upper protective film  23 , and the memory insulating film  16  exposed on the side surface of the cavity C 1  are removed by CDE (Chemical Dry Etching) using the slit ST ( FIG.  9 A ). As a result, the upper semiconductor layer  12   d  is exposed on an upper surface of the cavity C 1 , the lower semiconductor layer  12   b  is exposed on a lower surface of the cavity C 1 , and the channel semiconductor layer  2  is exposed on the side surface of the cavity C 1 . 
     Next, the intermediate semiconductor layer  12   c  is formed in the cavity C 1  by forming the intermediate semiconductor layer  12   c  on the surfaces of the upper semiconductor layer  12   d , the lower semiconductor layer  12   b , and the channel semiconductor layer  2 , which are exposed in the cavity C 1  ( FIG.  9 B ) . As a result, the intermediate semiconductor layer  12   c  in contact with the upper semiconductor layer  12   d , the lower semiconductor layer  12   b , and the channel semiconductor layer  2  are formed between the upper semiconductor layer  12   d  and the lower semiconductor layer  12   b . 
     Next, the liner layer  24  in the slit ST and each sacrifice layer  6 ′ in the stacked film  9 ′ are removed by wet etching or dry etching using the slit ST ( FIG.  10 A ) . As a result, a plurality of cavities C 2  are formed between the insulating films  8  in the stacked film  9 ′. These cavities C 2  are examples of a first recess portion. 
     Next, the plurality of electrode layers  6  are formed in these cavities C 2  by CVD (Chemical Vapor Deposition) ( FIG.  10 B ). As a result, the stacked film  9  including the plurality of electrode layers  6  and the plurality of insulating films  8  alternately is formed between the gate layer  14  and the interlayer insulating film  15 . In this way, the plurality of sacrifice layers  6 ′ are replaced with the plurality of electrode layers  6 . In the step shown in  FIG.  10 B , the insulating film  5   b , the barrier metal layer  6   a , and the electrode material layer  6   b  are sequentially formed in each cavity C 2  (see  FIG.  2   ). 
     After that, the slit insulating film  17  is formed in each slit ST. Further, various plug layers, wiring layers, interlayer insulating films, and the like are formed on the substrate  7 . In this way, the semiconductor device shown in  FIG.  3    is manufactured. 
     When manufacturing the semiconductor device of the present embodiment, a process of reducing the F concentration in the charge storage layer  4  is performed between the step shown in  FIG.  10 A  and the step shown in  FIG.  10 B . Details of this process will be described later with reference to  FIGS.  11 A to  12 B . 
       FIGS.  11 A to  12 B  are cross-sectional views showing details of the method for manufacturing the semiconductor device of the first embodiment. 
       FIG.  11 A  shows an insulating film  31  formed at a bottom portion of the slit ST in addition to components shown in  FIG.  10 A . First, after performing the step shown in  FIG.  10 A , annealing is performed using a gas G 1  ( FIG.  11 A ). The annealing shown in  FIG.  11 A  is, for example, thermal annealing using a gas containing N (nitrogen) and O (oxygen) as the gas G 1 . The gas G 1  is, for example, a N 2 O (nitrous oxide) gas. The thermal annealing is, for example, RT (Rapid Thermal) annealing. The gas G 1  is supplied to the charge storage layer  4  through the slit ST and the cavity C 2 . As a result, some of F atoms in the charge storage layer  4  are removed from the charge storage layer  4  by the action of the gas G 1 , and the F concentration in the charge storage layer  4  decreases. As described above, according to at least one embodiment, it is possible to reduce the F concentration in the charge storage layer  4  by the annealing shown in  FIG.  11 A . 
     Next, the insulating film  5   b  is formed in each cavity C 2  ( FIG.  11 B ). The insulating film  5   b  is, for example, an AlO x  film (aluminum oxide film). 
     Next, annealing is performed using a gas G 2  ( FIG.  12 A ). The annealing shown in  FIG.  12 A  is, for example, the thermal annealing using the gas containing N (nitrogen) and O (oxygen) as the gas G 2 . The gas G 2  is, for example, an N 2 O gas. The thermal annealing is, for example, an RT annealing. The gas G 2  is supplied to the charge storage layer  4  through the slit ST and the cavity C 2 . As a result, some of F atoms in the charge storage layer  4  are removed from the charge storage layer  4  by the action of the gas G 2 , and the F concentration in the charge storage layer  4  is further reduced. As described above, according to at least one embodiment, the F concentration in the charge storage layer  4  can be further reduced by the annealing shown in  FIG.  12 A . Further, according to at least one embodiment, the insulating film  5   b  can be modified by the annealing shown in  FIG.  12 A . 
     Next, the barrier metal layer  6   a  and the electrode material layer  6   b  are sequentially formed in each cavity C 2  ( FIG.  12 B ). As a result, the electrode layer  6  is formed in each cavity C 2  via the insulating film  5   b . 
     After that, the slit insulating film  17  is formed in each slit ST. Further, various plug layers, wiring layers, interlayer insulating films, and the like are formed on the substrate  7 . In this way, the semiconductor device shown in  FIG.  3    is manufactured. 
     The gas G 1  may be a gas other than the N 2 O gas or may be a mixed gas containing the N 2 O gas and another gas. For example, the gas G 1  may be a mixed gas containing the N 2 O gas and a H 2  (hydrogen) gas or may be a mixed gas containing the N 2 O gas and a D 2  (deuterium) gas. This also applies to the gas G 2 . 
     Next, the F concentration in the charge storage layer  4  of at least one embodiment will be described with reference to  FIGS.  11 A to  12 B . 
     In at least one embodiment, when the charge storage layer  4  is formed in the step shown in  FIG.  5 B , F atoms enter the charge storage layer  4  and the F concentration in the charge storage layer  4  becomes high. Therefore, immediately before the annealing shown in  FIG.  11 A , the F concentration in the charge storage layer  4  is high. Specifically, immediately before the annealing shown in  FIG.  11 A , the F concentration in the charge storage layer  4  of at least one embodiment is higher than 5.0 x 10 18  atoms/cm 3  at any location in the charge storage layer  4 . For example, immediately before the annealing shown in  FIG.  11 A , the F concentration in the charge storage layer  4  is about 1.0 x 10 20  atoms/cm 3  at any location in the charge storage layer  4 . 
     In at least one embodiment, the F concentration in the charge storage layer  4  is reduced by performing the annealing shown in  FIGS.  11 A and  12 A . As a result, locations having the F concentration of 5.0 x 10 18  atoms/cm 3  or less are generated in the charge storage layer  4 . This makes it possible to prevent the signal charge from escaping from the charge storage layer  4 . The locations having the F concentration of 5.0 x 10 18  atoms/cm 3  or less may be generated after the annealing shown in  FIG.  11 A  or after the annealing shown in  FIG.  12 A . 
     The gases G 1  and G 2  are supplied to the charge storage layer  4  via the insulating film  5   a . Therefore, the F concentration in the charge storage layer  4  decreases mainly near the interface between the charge storage layer  4  and the insulating film  5   a . As a result, the F concentration at the interface between the charge storage layer  4  and the tunnel insulating film  3  becomes 10 times or more the F concentration at the interface between the charge storage layer  4  and the insulating film  5   a  (see  FIG.  13 B  and the like). In at least one embodiment, the F concentration at the interface between the charge storage layer  4  and the insulating film  5   a  is 5.0 x 10 18  atoms/cm 3  or less. 
     In at least one embodiment, only one of the annealing shown in  FIG.  11 A  and the annealing shown in  FIG.  12 A  may be performed. In this case, the annealing shown in  FIG.  11 A  or  FIG.  12 A  is performed so that the locations having the F concentration of 5.0 x 10 18  atoms/cm 3  or less are generated in the charge storage layer  4  by this annealing. 
     Further, the annealing using the N 2 O gas may be performed in the step shown in  FIG.  5 B  instead of the step shown in  FIG.  11 A  and/or  FIG.  12 A . In this case, the annealing using the N 2 O gas is performed after formation of the charge storage layer  4  and before the memory hole MH is completely embedded. The N 2 O gas is supplied to the charge storage layer  4  via the tunnel insulating film  3 . Therefore, the F concentration in the charge storage layer  4  mainly decreases near an inner peripheral surface of the charge storage layer  4 , which is the interface between the charge storage layer  4  and the tunnel insulating film  3 . As a result, the F concentration at the interface between the charge storage layer  4  and the tunnel insulating film  3  is 1 / 10 or less of the F concentration at the interface between the charge storage layer  4  and the insulating film  5   a  (see  FIG.  13 C  and the like). In this case, the F concentration at the interface between the charge storage layer  4  and the tunnel insulating film  3  is 5.0 x 10 18  atoms/cm 3  or less. 
     Further, the annealing using the N 2 O gas may be performed in both the steps shown in  FIG.  11 A  and/or 12A and the step shown in  FIG.  5 B . In this case, the F concentration in the charge storage layer  4  decreases near the inner peripheral surface of the charge storage layer  4  (the interface between the charge storage layer  4  and the tunnel insulating film  3 ) as well as near an outer peripheral surface of the charge storage layer  4  (the interface between the charge storage layer  4  and the insulating film  5   b ). As a result, for example, as shown in  FIG.  13 A , it is possible to implement an F concentration distribution in which a difference in F concentration between the inner peripheral surface of the charge storage layer  4  and the outer peripheral surface of the charge storage layer  4  is smaller than that in  FIGS.  13 B and  13 C . For example, an F concentration distribution of the charge storage layer  4  can be made uniform. 
       FIGS.  13 A to  15 D  are graphs showing examples of an F concentration profile and the like in the semiconductor device of the first embodiment. 
     Example of FIG.  13 A 
       FIG.  13 A  shows an example of an F concentration profile in the charge storage layer  4 . In  FIG.  13 A , a horizontal axis indicates an X coordinate of each location in the charge storage layer  4 , and a vertical axis indicates the F concentration of each location in the charge storage layer  4  on a logarithmic scale (the same applies to  FIG.  13 B  to  FIG.  15 A ).  FIG.  13 A  shows an F concentration profile along an X axis in an XZ cross-section of the charge storage layer  4  passing through a central axis of the memory hole MH (or columnar portion CL) (the same applies to  FIGS.  13 B to  15 A ). 
       FIG.  13 A  shows positions of an interface S 1  between the charge storage layer  4  and the insulating film  5   a , an interface S 2  between the charge storage layer  4  and the tunnel insulating film  3 , and an interface S 3  between the channel semiconductor layer  2  and the tunnel insulating film  3 .  FIG.  13 A  further shows an F concentration K 1  before the annealing shown in  FIGS.   11 A and  12 A  and an F concentration K 2  after the annealing shown in  FIGS.  11 A and  12 A . 
     In the example of  FIG.  13 A , the F concentration K 1  in the charge storage layer  4  before annealing is high. The F concentration K 1  is, for example, 1.0 x 10 20  atoms/cm 3  or more. On the other hand, the F concentration K 2  in the charge storage layer  4  after annealing is low. The F concentration K 2  is, for example, 5.0 x 10 18  atoms/cm 3  or less. Further, the F concentration K 1  and the F concentration K 2  may be uniform in the charge storage layer  4 . Such F concentration profile can be implemented, for example, by performing annealing with the N 2 O gas in both the steps shown in  FIGS.  11 A and/or  12 A  and the step shown in  FIG.  5 B . In this case, the F concentration K 1  represents a concentration before annealing in the step shown in  FIG.  5 B . 
     The horizontal axis in  FIG.  13 A  may be a coordinate other than the X coordinate and may be, for example, a Y coordinate of each location in the charge storage layer  4 . In this case, 
       FIG.  13 A  shows, for example, an F concentration profile along a Y axis in a YZ cross section of the charge storage layer  4  passing through the central axis of the memory hole MH (or columnar portion CL). This also applies to  FIGS.  13 B to  15 A . 
     Example of FIG.  13 B 
       FIG.  13 B  shows the F concentration K 1  in the charge storage layer  4  before the annealing shown in  FIGS.  11 A and  12 A , an F concentration K 3  in the tunnel insulating film  3  before the annealing shown in  FIGS.  11 A and  12 A , and the F concentration K 2  in the charge storage layer  4  and the tunnel insulation film  3  after the annealing shown in  FIGS.  11 A and  12 A . 
     In the example of  FIG.  13 B , the F concentration K 1  in the charge storage layer  4  before annealing is high, and the F concentration K 2  in the tunnel insulating film  3  before annealing is low. The F concentration K 1  is, for example, 1.0 x 10 20  atoms/cm 3  or more. The F concentration K 3  is, for example, 5.0 x 10 18  atoms/cm 3  or less. Meanwhile, the F concentration K 2  after annealing decreases in the charge storage layer  4  and increases in the tunnel insulating film  3 . The F concentration K 2  after annealing has a peak P in the charge storage layer  4 , increases from the interface S 1  to the peak P along the X direction, and decreases from the peak P to the interface S 2 . The location of the peak P is an example of a predetermined location. 
     In the example of  FIG.  13 B , the annealing using the N 2 O gas is performed in the steps shown in  FIGS.  11 A and  12 A . Therefore, the F concentration in the charge storage layer  4  decreases mainly near the interface S 1  between the charge storage layer  4  and the insulating film  5   a . As a result, the F concentration at the interface S 2  between the charge storage layer  4  and the tunnel insulating film  3  becomes 10 times or more the F concentration at the interface S 1  between the charge storage layer  4  and the insulating film  5   a . In the example of  FIG.  13 B , the F concentration at the interface S 1  is 5.0 x 10 18  atoms/cm 3  or less, and the F concentration at the interface S 2  and the peak P is 5.0 x 10 19  atoms/cm 3  or more. The signal charge in the charge storage layer  4  is generally stored near the surface of the charge storage layer  4 . According to the example of  FIG.  13 B , since the F concentration at the interface S 1  decreases, it is possible to suitably store the signal charge near the interface S 1 . Furthermore, SILC (Stress Induced Leakage Current) can be improved by termination by a Si—F bond. 
     In the example of  FIG.  13 B , the F concentration in the tunnel insulating film  3  is increased by annealing. The F concentration in the tunnel insulating film  3  after annealing is, for example, 1.0 x 10 19  atoms/cm 3  or more and 1.0 x 10 20  atoms/cm 3  or less, entirely or partially. The F concentration in the tunnel insulating film  3  can be applied to the examples of  FIGS.  13 A and  13 C to  15 A . 
     In the example of  FIG.  13 B , the F concentration at the interface S 1  may be 5.0 x 10 18  atoms/cm 3  or less, the F concentration at the peak P may be 1.0 x 10 20  atoms/cm 3  or more, and the F concentration at the interface S 2  may be 5.0 x 10 19  atoms/cm 3  or less. 
     Example of FIG.  13 C 
     The F concentration profile shown in  FIG.  13 C  can be implemented by performing the annealing using the N 2 O gas in the step shown in  FIG.  5 B  instead of the steps shown in  FIG.  11 A  and/or  FIG.  12 A . In the example of  FIG.  13 C , the F concentration K 1  in the charge storage layer  4  before annealing is high, and the F concentration K 2  in the charge storage layer  4  after annealing is reduced to have the peak P in the charge storage layer  4 . The F concentration K 1  is, for example, 1.0 x 10 20  atoms/cm 3  or more. The F concentration K 2  increases from the interface S 1  to the peak P and decreases from the peak P to the interface S 2 , along the X direction. 
     In the example of  FIG.  13 C , the annealing using the N 2 O gas is performed in the step shown in  FIG.  5 B . Therefore, the F concentration in the charge storage layer  4  decreases mainly near the interface S 2  between the charge storage layer  4  and the tunnel insulating film  3 . As a result, the F concentration at the interface S 2  between the charge storage layer  4  and the tunnel insulating film  3  is 1 / 10 or less of the F concentration at the interface S 1  between the charge storage layer  4  and the insulating film  5   a . In the example of  FIG.  13 C , the F concentration at the interface S 2  is 5.0 x 10 18  atoms/cm 3  or less and the F concentration at the interface S 1  and the peak P is 5.0 x 10 19  atoms/cm 3  or more. The signal charge in the charge storage layer  4  is generally stored near the surface of the charge storage layer  4 . According to the example of  FIG.  13 C , since the F concentration of the interface S 2  decreases, it is possible to suitably store the signal charge near the interface S 2 . 
     In the example of  FIG.  13 C , the F concentration at the interface S 2  may be 5.0 x 10 18  atoms/cm 3 . or less, the F concentration at the peak P may be 1.0 x 10 20  atoms/cm 3  or more, and the F concentration at the interface S 1  may be 5.0 x 10 19  atoms/cm 3  or less. 
     Example of FIG.  14 A 
       FIG.  14 A  shows the F concentration in the charge storage layer  4  after the annealing shown in  FIGS.  11 A and  12 A . In the example of  FIG.  14 A , the charge storage layer  4  includes a region Ra having an F concentration Ka and a region Rb having an F concentration Kb. Regions Ra and Rb are examples of first and second regions, respectively. The F concentrations Ka and Kb are examples of first and second fluorine concentrations, respectively. 
     The region Ra is located on the insulating film  5   a  side in the charge storage layer  4  and the region Rb is located on the tunnel insulating film  3  side in the charge storage layer  4 . In this example, the F concentration Kb is higher than the F concentration Ka. For example, the F concentration Ka is 5.0 x 10 18  atoms/cm 3  or less, and the F concentration Kb is 5.0 x 10 19  atoms/cm 3  or more. This makes it possible to implement an F concentration profile in which the interface S 1  has a low concentration and the interface S 2  has a high concentration, as in the example of  FIG.  13 B . 
     Examples of FIGS.  14 B and  14 C 
     Both  FIGS.  14 B and  14 C  show the F concentration K in the charge storage layer  4  and the tunnel insulating film  3  after the annealing shown in  FIGS.  11 A and  12 A . In the examples of  FIGS.  14 B and  14 C , the F concentration K in the charge storage layer  4  increases from the interface S 1  to the interface S 2  along the X direction. 
     The F concentration K shown in  FIG.  14 B  has a peak P in the tunnel insulating film  3 . Meanwhile, the F concentration K shown in  FIG.  14 C  has a peak P at the interface S 2  between the charge storage layer  4  and the tunnel insulating film  3 . In both  FIGS.  14 B and  14 C , the F concentration K increases from the interface S 1  to the peak P and decreases from the peak P to the interface S 3 , along the X direction. 
     In the examples of  FIGS.  14 B and  14 C , the F concentration at the interface S 1  is 5.0 x 10 18  atoms/cm 3  or less, and the F concentration at the interface S 2  and the peak P is 5.0 x 10 19  atoms/cm 3  or more. This makes it possible to implement an F concentration profile in which the interface S 1  has a low concentration and the interface S 2  has a high concentration, as in the example of  FIG.  13 B . 
     Examples of FIGS.  15 A and  15 B 
       FIGS.  15 A and  15 B  show the concentrations of F atom, O (oxygen) atom, and N (nitrogen) atom in the same semiconductor device. Specifically,  FIG.  15 A  shows the F concentration K in the insulating film  5   a , the charge storage layer  4 , and the tunnel insulating film  3  after the annealing shown in  FIGS.  11 A and  12 A .  FIG.  15 B  shows the O concentration and the N concentration in the insulating film  5   a , the charge storage layer  4 , and the tunnel insulating film  3  after the annealing shown in  FIGS.  11 A and  12 A . 
     The F concentration profile shown in  FIG.  15 A  is generally the same as the F concentration profile shown in  FIG.  14 B . Specifically, the F concentration K in the insulating film  5   a  and the charge storage layer  4  increases along the X direction. Further, the F concentration K in the tunnel insulating film  3  increases from the interface S 2  to the peak P and decreases from the peak P to the interface S 3 . The F concentration at the interface S 1  is 5.0 x 10 18  atoms/cm 3  or less and the F concentration at the interface S 2  and the peak P is 5.0 x 10 19  atoms/cm 3  or more. In the example of  FIG.  15 A , the F concentration at the interface S 2  is lower than 1.0 x 10 20  atoms/cm 3  and the F concentration at the peak P is about 1.0 x 10 20  atoms/cm 3 . 
       FIG.  15 B  shows the O concentration and the N concentration in the insulating film  5   a , the charge storage layer  4 , and the tunnel insulating film  3 .  FIG.  15 B  further shows positions P 1  and P 2  where the O concentration and the N concentration coincide with each other. The positions of the interfaces S 1  and S 2  can be specified, for example, by specifying the positions P 1  and P 2 . In the example of  FIG.  15 B , a region occupied by the charge storage layer  4  is a region where the N concentration is higher than the O concentration. The N concentration and the O concentration can be measured by using, for example, EELS (Electron Energy Loss Spectroscopy) analysis or SIMS (Secondary Ion Mass Spectrometry) analysis. 
     Examples of FIGS.  15 C and  15 D 
       FIG.  15 C  is a graph for illustrating a method for realizing the concentration profile shown in  FIG.  13 A .  FIG.  15 C  shows a change in the concentration profile when the annealing using the N 2 O gas is performed in both the steps shown in  FIGS.  11 A and/or  12 A  and the step shown in  FIG.  5 B . Specifically, an F concentration K 1 ′ indicates a concentration before performing the steps shown in  FIGS.  11 A,  12 A, and  5 B , and an F concentration K 2 ′ indicates a concentration after performing the steps shown in  FIGS.  11 A,  12 A, and  5 B . It will be understood that in the charge storage layer  4 , the F concentration K 1 ′ generally coincides with the F concentration K 1  and the F concentration K 2 ′ generally coincides with the F concentration K 2 . 
       FIG.  15 D  shows a concentration profile when the annealing using the N 2 O gas is performed in the step shown in  FIG.  5 B  without performing the annealing using the N 2 O gas in the steps shown in  FIGS.  11 A and  12 A . It will be understood that the concentration profile shown in  FIG.  15 D  has a shape substantially symmetrical to that of the concentration profile shown in  FIG.  15 A . 
       FIG.  16    is a graph related to the F concentration in the semiconductor device of the first embodiment. 
     A horizontal axis of  FIG.  16    indicates an F concentration on the surface of the charge storage layer  4 , specifically, the F concentration at the interface between the charge storage layer  4  and the insulating film  5   a . Meanwhile, a vertical axis of  FIG.  16    shows high reliability of the charge storage layer  4 . 
     As a result of the verification, it is found that the reliability of the charge storage layer  4  decreases as the F concentration at the interface between the charge storage layer  4  and the insulating film  5   a  increases, as shown in  FIG.  16   . In addition, it is found that the reliability of the charge storage layer  4  becomes good when the F concentration at the interface between the charge storage layer  4  and the insulating film  5   a  is approximately 5.0 x 10 18  atoms/cm 3  or less. Therefore, it is desirable that the F concentration in the charge storage layer  4  of at least one embodiment is 5.0 x 10 18  atoms/cm 3  or less on the surface of the charge storage layer  4 . 
     As described above, the charge storage layer  4  of at least one embodiment includes a location having the F concentration of 5.0 x 10 18  atoms/cm 3  or less. Further, the F concentration at the interface S 2  between the charge storage layer  4  and the tunnel insulating film  3  of the present embodiment is, for example, 10 times or more or 1 / 10 or less of the F concentration at the interface S 1  between the charge storage layer  4  and the insulating film  5   a . Therefore, according to at least one embodiment, it is possible to prevent the charge from escaping from the charge storage layer  4  by reducing the F concentration on the surface of the charge storage layer  4 . 
     Second Embodiment 
       FIG.  17    is a cross-sectional view showing a structure of a semiconductor device of a second embodiment. 
     The semiconductor device of the second embodiment ( FIG.  17   ) has the same components as the semiconductor device of the first embodiment ( FIG.  3   ). However, a film thickness W 1  of the insulating film  5   a  of the present embodiment varies along the Z direction. Similarly, a film thickness W 2  of the charge storage layer  4  of the present embodiment varies along the Z direction. 
     Specifically, the film thickness W 1  of the insulating film  5   a  is thick in the memory cell MC and thin outside the memory cell MC. On the other hand, the film thickness W 2  of the charge storage layer  4  is thin in the memory cell MC and thick outside the memory cell MC. As a result, as shown in  FIG.  17   , the film thickness W 2  of the charge storage layer  4  of the present embodiment is thicker outside the memory cell MC than in the memory cell MC. A film thickness of the charge storage layer  4  outside the memory cell MC of the present embodiment is thicker by 1 nm or more than the film thickness of the charge storage layer  4  in the memory cell MC. The charge storage layer  4  outside the memory cell MC is an example of a first portion and the charge storage layer  4  in the memory cell MC is an example of a second portion. 
     The semiconductor device of the present embodiment is manufactured by the method shown in  FIG.  3    to 12B, similarly to the semiconductor device of the first embodiment. In this case, when the N 2 O gas is supplied from each cavity C 2  to the charge storage layer  4  by the annealing shown in  FIGS.  11 A and  12 A , the insulating film  5   a  and the charge storage layer  4  on a side of each cavity C 2 , that is, at the same height as each cavity C 2 , are oxidized or expanded. As a result, the film thickness W 1  of the insulating film  5   a  becomes thicker on the side of each cavity C 2 , and the film thickness W 2  of the charge storage layer  4  becomes thinner on the side of each cavity C 2 . As a result, the structure shown in  FIG.  17    is implemented. 
     According to the present embodiment, the charge storage layer  4  has the film thickness W 2  that varies along the Z direction. For example, a maximum film thickness of the charge storage layer  4  provided on an outer periphery of one channel semiconductor layer  2  is thicker by 1 nm or more than a minimum film thickness of the charge storage layer  4 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.