Patent Publication Number: US-2019172839-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. 2017-233281, filed on Dec. 5, 2017; 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 a semiconductor device. 
     BACKGROUND 
     A memory device that has a three-dimensional structure has been proposed in which multiple electrode layers are stacked with an insulating layer interposed. As the number of stacks of electrode layers increases, warp due to internal stress of the electrode layers may be caused. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a semiconductor device according to an embodiment of the invention; 
         FIG. 2  is a schematic cross-sectional view of the semiconductor device according to the embodiment of the invention; 
         FIG. 3  is a schematic cross section perspective view of a portion of the semiconductor device according to the embodiment of the invention; 
         FIG. 4  to  FIG. 13B  are schematic cross-sectional views showing a method for manufacturing the semiconductor device according to the embodiment of the invention; 
         FIG. 14A  is a graph showing the relationship between a fluorine concentration inside a tungsten film and a lattice constant of a tungsten crystal in an unstrained state of the tungsten film, and  FIG. 14B  is a graph showing the relationship between a fluorine concentration inside a tungsten film and an internal stress of the tungsten film; and 
         FIG. 15  is a graph showing the relationship between a nitrogen concentration inside a tungsten film and the internal stress of the tungsten film. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a semiconductor device includes a stacked body, a semiconductor body, and a charge storage portion. The stacked body includes a plurality of electrode layers stacked with an insulator interposed. The semiconductor body extends through the stacked body in a stacking direction of the stacked body. The charge storage portion is provided between the semiconductor body and each of the electrode layers. At least one of the electrode layers is a tungsten film or a molybdenum film including a portion having different fluorine concentration along the stacking direction. 
     Embodiments of the invention will now be described with reference to the drawings. In the drawings, the same components are marked with the same reference numerals; and a detailed description is omitted as appropriate. The drawings are schematic; and the relationships between the thicknesses and widths of portions, the proportions of sizes between portions, etc., are not necessarily the same as the actual values thereof. There are also cases where the dimensions and/or the proportions are illustrated differently between the drawings, even in the case where the same portion is illustrated. 
     In the embodiment, for example, a semiconductor memory device that includes a memory cell array having a three-dimensional structure is described as a semiconductor device. 
       FIG. 1  is a schematic perspective view of the memory cell array  1  according to the embodiment of the invention. 
       FIG. 2  is a schematic cross-sectional view of the memory cell array  1  according to the embodiment of the invention. 
     In  FIG. 1 , two mutually-orthogonal directions parallel to a major surface of a substrate  10  are taken as an X-direction and a Y-direction; and a direction orthogonal to both the X-direction and the Y-direction is taken as a Z-direction (a stacking direction). 
     The memory cell array  1  includes the substrate  10 , a stacked body  100 , a source layer SL provided between the substrate  10  and the stacked body  100 , multiple columnar portions CL, and multiple bit lines BL provided above the stacked body  100 . 
     The substrate  10  is, for example, a silicon substrate. The source layer SL includes a semiconductor layer doped with an impurity and may further include a layer including a metal. An insulating layer may be provided between the substrate  10  and the source layer SL. 
     A separation portion  60  is provided in the stacked body  100 . The separation portion  60  extends in the stacking direction (the Z-direction) and reaches the source layer SL. The separation portion  60  further extends in the X-direction and divides the stacked body  100  into multiple blocks in the Y-direction. The separation portion  60  is formed from an insulating film  61  as shown in  FIG. 2 . 
     The columnar portions CL are formed in substantially circular columnar configurations extending through the stacked body  100  in the stacking direction (the Z-direction). The multiple columnar portions CL have, for example, a staggered arrangement. Or, the multiple columnar portions CL may be arranged in a square lattice along the X-direction and the Y-direction. 
     The multiple bit lines BL are, for example, metal films extending in the Y-direction. The multiple bit lines BL are separated from each other in the X-direction. The upper end portions of semiconductor bodies  20  of the columnar portions CL described below are connected to the bit lines BL via contacts Cb. 
     The stacked body  100  includes multiple electrode layers  70  stacked in a direction (the Z-direction) perpendicular to the major surface of the substrate  10 . The multiple electrode layers  70  are stacked in the Z-direction with an insulating layer (an insulator)  72  interposed. The insulator between the electrode layers  70  may be an air gap. The insulating layer  72  is provided also between the source layer SL and the lowermost electrode layer  70 . 
     An insulating film  42  is provided on the uppermost electrode layer  70 ; and an insulating film  43  is provided on the insulating film  42 . The insulating film  43  covers the upper ends of the columnar portions CL. The columnar portions CL pierce the multiple electrode layers  70  and the multiple insulating layers  72  and reach the source layer SL. 
       FIG. 3  is a schematic cross-sectional perspective view of portions of the columnar portion CL and the stacked body  100 . 
     The columnar portion CL includes a memory film  30 , the semiconductor body  20 , and an insulative core film  50 . The semiconductor body  20  is formed in a pipe-like configuration; and the core film  50  is provided on the inner side of the semiconductor body  20 . The memory film  30  is provided between the semiconductor body  20  and the electrode layer  70 , and surrounds the periphery of the semiconductor body  20 . 
     The semiconductor body  20  is, for example, a silicon film; and the lower end portion of the semiconductor body  20  contacts the source layer SL. The upper end portion of the semiconductor body  20  is connected to the bit line BL via the contact Cb shown in  FIG. 1 . 
     The memory film  30  is a stacked film including a tunneling insulating film  31 , a charge storage film (a charge storage portion)  32 , and a blocking insulating film  33 . The blocking insulating film  33 , the charge storage film  32 , and the tunneling insulating film  31  are provided in order from the electrode layer  70  side between the semiconductor body  20  and the electrode layer  70 . The tunnel insulating film  31  is provided between the semiconductor body  20  and the charge storage film  32 . The charge storage film  32  is provided between the tunnel insulating film  31  and the blocking insulating film  33 . The blocking insulating film  33  is provided between the electrode layer  70  and the charge storage film  32 . 
     The semiconductor body  20 , the memory film  30 , and the electrode layer  70  are included in a memory cell MC. The memory cell MC has a vertical transistor structure in which the electrode layer  70  surrounds the periphery of the semiconductor body  20  with the memory film  30  interposed. 
     In the memory cell MC having the vertical transistor structure, the semiconductor body  20  functions as a channel; and the electrode layer  70  functions as a control gate. The charge storage film  32  functions as a data storage layer that stores charge injected from the semiconductor body  20 . 
     The semiconductor memory device of the embodiment is a nonvolatile semiconductor memory device that can freely and electrically erase/program data and can retain the memory content even when the power supply is OFF. 
     The memory cell MC is, for example, a charge trap memory cell. The charge storage film  32  has many trap sites that trap charge inside an insulative film, and includes, for example, a silicon nitride film. Or, the charge storage portion may be a conductive floating gate surrounded with an insulator. 
     The tunneling insulating film  31  is used as a potential barrier when the charge is injected from the semiconductor body  20  into the charge storage film  32  or when the charge stored in the charge storage film  32  is discharged into the semiconductor body  20 . The tunneling insulating film  31  includes, for example, a silicon oxide film. A stacked film  30   a  that includes the tunneling insulating film  31  and the charge storage film  32  extends to be continuous in the stacking direction of the stacked body  100 . 
     The blocking insulating film  33  prevents the charge stored in the charge storage film  32  from being discharged into the electrode layer  70 . Also, the blocking insulating film  33  prevents back-tunneling of the charge from the electrode layer  70  into the columnar portion CL. 
     The blocking insulating film  33  includes a first blocking film  34  and a second blocking film  35 . The first blocking film  34  is a silicon oxide film. The second blocking film  35  is a metal oxide film (e.g., an aluminum oxide film). The first blocking film  34  is provided between the charge storage film  32  and the second blocking film  35 ; and the second blocking film  35  is provided between the first blocking film  34  and the electrode layer  70 . 
     The blocking insulating film  33  that includes the first blocking film  34  and the second blocking film  35  is provided also between the electrode layer  70  and the insulating layer  72 . 
     The first blocking film  34  is provided between the insulating layer  72  and the second blocking film  35 . The second blocking film  35  is provided between the first blocking film  34  and the electrode layer  70 . 
     A barrier metal  81  is provided between the second blocking film  35  and the electrode layer  70 . The barrier metal  81  is, for example, a metal nitride film. The barrier metal  81  is, more specifically, a titanium nitride film. The barrier metal  81  prevents the mutual diffusion of the elements between the electrode layer  70  and the blocking insulating film  33 . 
     As shown in  FIG. 1 , a drain-side select transistor STD is provided in the upper layer portion of the stacked body  100 ; and a source-side select transistor STS is provided in the lower layer portion of the stacked body  100 . 
     Among the multiple electrode layers  70 , at least the uppermost electrode layer  70  may function as a control gate of the drain-side select transistor STD; and at least the lowermost electrode layer  70  may function as a control gate of the source-side select transistor STS. 
     The multiple memory cells MC are provided between the drain-side select transistor STD and the source-side select transistor STS. The multiple memory cells MC, the drain-side select transistor STD, and the source-side select transistor STS are connected in series via the semiconductor body  20  of the columnar portion CL. The multiple memory cells MC are provided three-dimensionally in the X-direction, the Y-direction, and the Z-direction. 
     In the example shown in  FIG. 3 , the electrode layer  70  includes a first conductive film  70   c  and a second conductive film  70   d . The first conductive film  70   c  is provided at the surface of the barrier metal  81 ; and the second conductive film  70   d  is provided on the inner side of the first conductive film  70   c . The first conductive film  70   c  is provided between the second conductive film  70   d  and the barrier metal  81 . The barrier metal  81  functions as a foundation film of the crystal growth of the first conductive film  70   c.    
     The first conductive film  70   c  and the second conductive film  70   d  are tungsten films. Or, the first conductive film  70   c  and the second conductive film  70   d  are molybdenum films. 
     The lattice constant of the tungsten crystal of the first conductive film  70   c  and the lattice constant of the tungsten crystal of the second conductive film  70   d  are different in the unstrained state. Or, the lattice constant of the molybdenum crystal of the first conductive film  70   c  and the lattice constant of the molybdenum crystal of the second conductive film  70   d  are different in the unstrained state. 
     For example, the analysis and the detection of the lattice constant are possible using XRD (X-ray diffraction), a TEM (transmission electron microscope), or a SEM (scanning electron microscope). Then, it is possible to estimate the value of the internal stress from the lattice constant. 
     The internal stress of the first conductive film  70   c  and the internal stress of the second conductive film  70   d  are different due to such a lattice constant difference. Here, the internal stress being different means that the magnitude (the absolute value) of the internal stress is different. Or, the internal stress being different means that the direction of the internal stress is different. In other words, the magnitude of the internal stress of the first conductive film  70   c  and the magnitude of the internal stress of the second conductive film  70   d  are different. Or, the first conductive film  70   c  has tensile stress; and the second conductive film  70   d  has compressive stress. Or, the first conductive film  70   c  has compressive stress; and the second conductive film  70   d  has tensile stress. 
     For example, the first conductive film  70   c  and the second conductive film  70   d  which are both metal films include a non-metallic element; and the concentration of the non-metallic element inside the first conductive film  70   c  and the concentration of the non-metallic element inside the second conductive film  70   d  are different. Such a non-metallic element concentration difference causes the internal stress of the first conductive film  70   c  and the internal stress of the second conductive film  70   d  to be different. 
     For example, the fluorine concentration in the first conductive film  70   c  which is a tungsten film or a molybdenum film and the fluorine concentration in the second conductive film  70   d  which is a tungsten film or a molybdenum film are different. 
       FIG. 14A  is a graph (experimental results) illustrating the relationship between the fluorine concentration (the average concentration) inside the tungsten film and the lattice constant of the tungsten crystal in the unstrained state of the tungsten film. 
       FIG. 14B  is a graph (experimental results) illustrating the relationship between the fluorine concentration (the average concentration) inside the tungsten film and the internal stress (the tensile stress) of the tungsten film. 
     Results similar to the results shown in  FIGS. 14A and 14B  are obtained also for molybdenum which has a crystal structure similar to that of tungsten. 
     From the results of  FIG. 14A , it can be confirmed that the crystal lattice of tungsten contracts as the fluorine concentration increases. 
     From the results of  FIG. 14B , it can be confirmed that the tensile stress of the tungsten film increases as the fluorine concentration increases. 
     It is considered that the increase of the fluorine concentration causes the crystal lattice of the tungsten to contract; the lattice misfit between the tungsten film and the foundation film increases due to the contraction of the crystal lattice of the tungsten; and the tensile stress of the tungsten film increases. 
     As shown in  FIG. 14B , it can be confirmed that the tensile stress of the tungsten film changes according to the fluorine concentration in the range where the fluorine concentration in the tungsten film is not less than 2×10 17  (atoms/cm 3 ) and not more than 1.5×10 20  (atoms/cm 3 ). Accordingly, the magnitude of the tensile stress of the first conductive film  70   c  can be controlled by controlling the fluorine concentration in the first conductive film  70   c  to be within the range not less than 2×10 17  (atoms/cm 3 ) and not more than 1.5×10 20  (atoms/cm 3 ). Similarly, the magnitude of the tensile stress of the second conductive film  70   d  can be controlled by controlling the fluorine concentration in the second conductive film  70   d  to be within the range not less than 2×10 17  (atoms/cm 3 ) and not more than 1.5×10 20  (atoms/cm 3 ). 
     Or, the nitrogen concentration in the first conductive film  70   c  which is a tungsten layer or a molybdenum layer and the nitrogen concentration in the second conductive film  70   d  which is a tungsten layer or a molybdenum layer are different. 
       FIG. 15  is a graph (experimental results) illustrating the relationship between the nitrogen concentration (the average concentration) inside the tungsten film and the internal stress of the tungsten film. For the vertical axis, a positive numerical value illustrates the magnitude of the tensile stress; and a negative numerical value illustrates the magnitude of the compressive stress. 
     Results similar to the results shown in  FIG. 15  are obtained also for molybdenum which has a crystal structure similar to that of tungsten. 
     From the results of  FIG. 15 , it can be confirmed that the compressive stress of the tungsten film increases as the nitrogen concentration increases. 
     It is considered that the increase of the nitrogen concentration in the tungsten film causes lattice expansion of the tungsten crystal; and the compressive stress of the tungsten film increases. 
     Or, the carbon concentration in the first conductive film  70   c  which is a tungsten layer or a molybdenum layer and the carbon concentration in the second conductive film  70   d  which is a tungsten layer or a molybdenum layer are different. 
     It can be confirmed that the compressive stress of the tungsten film increases as the carbon concentration increases. 
     Or, the oxygen concentration in the first conductive film  70   c  which is a tungsten layer or a molybdenum layer and the oxygen concentration in the second conductive film  70   d  which is a tungsten layer or a molybdenum layer are different. 
     It can be confirmed that the compressive stress of the tungsten film increases as the oxygen concentration increases. 
     The electronegativity of tungsten (W) is 1.7; and the electronegativity of fluorine (F) is 4.0. It is considered that there is a tendency for tensile stress to be generated in the tungsten film due to such an electronegativity difference between tungsten and fluorine. 
     Conversely, the electronegativity of nitrogen (N) is 3.0; the electronegativity of carbon (C) is 2.5; and the electronegativity of oxygen (O) is 3.5. It is considered that there is a tendency for compressive stress to be generated in the tungsten film by adding, to the tungsten film, at least one of nitrogen, carbon, or oxygen having electronegativities smaller than that of fluorine. 
     The warp of the wafer including the stacked body  100  can be suppressed by forming the first conductive film  70   c  and the second conductive film  70   d  which has different internal stresses each other, inside the electrode layer  70 . For example, when one of the first conductive film  70   c  or the second conductive film  70   d  has tensile stress and the other has compressive stress, the tensile stress and the compressive stress cancel; and the warp of the wafer can be suppressed. 
     The electrical resistance of the electrode layer  70  decreases as the concentration of the non-metallic element described above (fluorine, nitrogen, carbon, and oxygen) added to the electrode layer  70  which is a metal layer decreases. For example, the concentration of the non-metallic element inside the first conductive film  70   c  is suppressed to reduce the resistance. In the case where the first conductive film  70   c  has tensile stress, the warp of the wafer can be suppressed by causing the second conductive film  70   d  to have compressive stress that reduces or cancels the tensile stress of the first conductive film  70   c  by adding at least one of nitrogen, carbon, or oxygen to the second conductive film  70   d . In such a case, the greater part of one layer of the electrode layers  70  may be the first conductive film  70   c  having the lower resistance; and the volume of the second conductive film  70   d  may be smaller than the volume of the first conductive film  70   c.    
     A method for manufacturing the semiconductor device shown in  FIG. 3  will now be described with reference to  FIG. 4  to  FIG. 13B . 
     As shown in  FIG. 4 , the source layer SL is formed on the substrate  10 ; and the stacked body  100  that includes multiple sacrificial layers (the first layers)  71  and the multiple insulating layers (the second layers)  72  is formed on the source layer SL. For example, the sacrificial layers  71  are silicon nitride layers; and the insulating layers  72  are silicon oxide layers. 
     The insulating layer  72  is formed on the surface of the source layer SL; and the sacrificial layer  71  is formed on the insulating layer  72 . Thereafter, the processes of alternately stacking the insulating layer  72  and the sacrificial layer  71  are repeated. The insulating film  42  is formed on the uppermost sacrificial layer  71 . 
     As shown in  FIG. 5 , multiple memory holes MH are formed in the stacked body  100 . The memory holes MH are formed by RIE (reactive ion etching) using a not-illustrated mask. The memory holes MH pierce the stacked body  100  and reach the source layer SL. 
     As shown in  FIG. 6 , the stacked film  30   a  is formed conformally on the side surfaces and the bottom surfaces of the memory holes MH. The stacked film  30   a  includes the tunneling insulating film  31  and the charge storage film  32  shown in  FIG. 3 . As shown in  FIG. 7 , a cover silicon film  20   a  is formed conformally on the inner side of the stacked film  30   a.    
     Subsequently, as shown in  FIG. 8 , a mask layer  45  is formed on the stacked body  100 ; and the cover silicon film  20   a  and the stacked film  30   a  that are formed on the bottom surfaces of the memory holes MH are removed by RIE. In the RIE, the stacked film  30   a  formed on the side surfaces of the memory holes MH is protected by being covered with the cover silicon film  20   a . The stacked film  30   a  formed on the side surfaces of the memory holes MH is not damaged by the RIE. 
     After removing the mask layer  45 , a semiconductor film (a silicon film)  20   b  is formed inside the memory holes MH as shown in  FIG. 9 . The semiconductor film  20   b  is formed on the side surface of the cover silicon film  20   a  and the bottom surfaces of the memory holes MH where the source layer SL is exposed. 
     For example, after the cover silicon film  20   a  and the semiconductor film  20   b  are formed as amorphous silicon films, the cover silicon film  20   a  and the semiconductor film  20   b  are crystallized into polycrystalline silicon films by heat treatment. The cover silicon film  20   a  and the semiconductor film  20   b  are included in the semiconductor body  20  described above. 
     As shown in  FIG. 10 , the core film  50  is formed on the inner side of the semiconductor film  20   b . Thus, the columnar portion CL that includes the stacked film  30   a , the semiconductor body  20 , and the core film  50  is formed. 
     The films deposited on the insulating film  42  shown in  FIG. 10  are removed by CMP (chemical mechanical polishing) or etch-back. 
     Subsequently, as shown in  FIG. 11 , the insulating film  43  is formed on the insulating film  42 . The insulating film  43  covers the upper ends of the columnar portions CL. Then, multiple slits ST are formed in the stacked body  100  including the insulating film  43 , the insulating film  42 , the multiple sacrificial layers  71 , and the multiple insulating layers  72  by RIE using a not-illustrated mask. The slits ST pierce the stacked body  100  and reach the source layer SL. 
     Continuing, the sacrificial layers  71  are removed by an etching gas or an etchant supplied through the slits ST. For example, the sacrificial layers  71  which are silicon nitride layers are removed by a solution including phosphoric acid. The sacrificial layers  71  are removed; and air gaps  73  are formed between the insulating layers  72  adjacent to each other in the stacking direction as shown in  FIG. 12  and  FIG. 13A . As shown in  FIG. 12 , the air gap  73  is formed also between the insulating film  42  and the uppermost insulating layer  72 . 
     The multiple insulating layers  72  contact the side surfaces of the multiple columnar portions CL to surround the side surfaces. The multiple insulating layers  72  are supported by such a physical bond with the multiple columnar portions CL; and the air gaps  73  are maintained. 
     As shown in  FIG. 13B , the first blocking film  34 , the second blocking film  35 , and the barrier metal  81  are formed in order on the inner walls of the air gaps  73 . The first blocking film  34 , the second blocking film  35 , and the barrier metal  81  are formed conformally along the upper surface and the lower surface of the insulating layer  72  and the side surface of the columnar portion CL. 
     For example, a silicon oxide film is formed by CVD as the first blocking film  34 ; for example, an aluminum oxide film is formed by CVD as the second blocking film  35 ; and, for example, a titanium nitride film is formed by CVD as the barrier metal  81 . The film formation gases of the CVD are supplied to the air gaps  73  through the slits ST. 
     The air gaps  73  still remain after forming the barrier metal  81 . The electrode layers  70  are filled into the remaining air gaps  73 . First, the first conductive film  70   c  is formed on the surface of the barrier metal  81 ; then, the second conductive film  70   d  is formed on the inner side of the first conductive film  70   c.    
     For example, tungsten films are formed as the first conductive film  70   c  and the second conductive film  70   d  by CVD (Chemical Vapor Deposition) or ALD (Atomic Layer Deposition) using a gas including tungsten fluoride (WF 6 ) and hydrogen (H 2 ). Or, molybdenum films are formed as the first conductive film  70   c  and the second conductive film  70   d  by CVD using a gas including molybdenum fluoride (MoF 6 ) and hydrogen (H 2 ). 
     The fluorine concentrations in the first conductive film  70   c  and in the second conductive film  70   d  can be controlled by the temperature control in the CVD or the ALD. As the temperature increases, the decomposition of tungsten fluoride (WF 6 ) is promoted; and fluorine (F) is exhausted outside the wafer through the slits ST and does not remain easily inside the film. Conversely, as the temperature decreases, tungsten fluoride (WF 6 ) remains easily inside the film without being decomposed. This is similar for the CVD or the ALD forming a molybdenum film using molybdenum fluoride (MoF 6 ). 
     For example, in the case where the temperature when forming the first conductive film  70   c  is set to be higher than the temperature when forming the second conductive film  70   d , the fluorine concentration in the first conductive film  70   c  can be set to be lower than the fluorine concentration in the second conductive film  70   d . This sets the resistance of the first conductive film  70   c  to be lower than the resistance of the second conductive film  70   d . Accordingly, in such a case, it is desirable for the volume of the first conductive film  70   c  to be set to be larger than the volume of the second conductive film  70   d.    
     In CVD or ALD under high-temperature conditions, tungsten fluoride (or molybdenum fluoride) easily becomes a deposit of tungsten (or molybdenum) by decomposing quickly into fluorine and tungsten (or fluorine and molybdenum) when adhering to the surface of the film formation object. Therefore, as the formation of the first conductive film  70   c  continues in a high-temperature process, tungsten fluoride (or molybdenum fluoride) is deposited easily at the vicinity of the opening of the air gap  73  proximal to the slit ST; and the opening of the air gap  73  is plugged easily by the first conductive film  70   c  before the air gap  73  is completely filled with a film. In other words, an unfilled portion of the electrode layer  70  inside the air gap  73  occurs easily; and the resistance of the electrode layer  70  increases. 
     According to the embodiment, after forming the first conductive film  70   c  in a high-temperature process, the film formation is switched to the second conductive film  70   d  in a process having a lower temperature. When using lower-temperature conditions, the deposition of tungsten (or molybdenum) does not occur easily due to the decomposition reaction soon after the tungsten fluoride (or the molybdenum fluoride) adheres to the surface of the film formation object; and the space on the inner side of the first conductive film  70   c  inside the air gap  73  can be filled with the second conductive film  70   d  before the opening of the air gap  73  is plugged. 
     At least one of the multiple electrode layers  70  includes the first conductive film  70   c  and the second conductive film  70   d  which have different fluorine concentrations each other. That is, at least one of the multiple electrode layers  70  includes portions having different fluorine concentrations along the stacking direction or the thickness direction. Fluorine included in the first conductive film  70   c  and the second conductive film  70   d  diffuses in the process accompanying with a heat treatment performed after forming the first conductive film  70   c  and the second conductive film  70   d , and the fluorine concentration near the boundary of the first conductive film  70   c  and the second conductive film  70   d  may change continuously. In the case where the second conductive film  70   d  having the higher fluorine concentration than the first conductive film  70   c  is formed after forming the first conductive film  70   c , the electrode layer  70  can have the profile in which the fluorine concentration increases gradually from the first conductive film  70   c  toward the center in the thickness direction of the second conductive film  70   d.    
     Also, in the CVD or the ALD forming the second conductive film  70   d , for example, nitrogen can be included inside the second conductive film  70   d  by introducing a gas including the element of nitrogen (e.g., N 2 , NH 3 , NO, NO 2 , N 2 O) to the chamber in addition to hydrogen and tungsten fluoride (or molybdenum fluoride). Furthermore, nitrogen can be also included inside the second conductive film  70   d  by using a metal source gas including N such as W 2 (NMe 2 ) 6 , W(NBu) 2 (NMe 2 ) 2 , W(CpEt)(CO) 2 (NO), Mo(NBu) 2 (NMe 2 ) 2 , Mo(NBu) 2 (NEt 2 ) 2 . Here, Me is a methyl group, Bu is a Butyl group, Cp is a Cyclopentadienyl group, Et is a Ethyl group. 
     In these cases, the nitrogen concentration in the second conductive film  70   d  is higher than the nitrogen concentration in the first conductive film  70   c . The fluorine concentration of the second conductive film  70   d  formed in a process with a lower temperature than that of the first conductive film  70   c  is higher than the fluorine concentration of the first conductive film  70   c ; and the tensile stress of the second conductive film  70   d  may be larger than that of the first conductive film  70   c . By adding nitrogen to the second conductive film  70   d , the tensile stress of the second conductive film  70   d  can be reduced or canceled; and the warp of the wafer can be suppressed. 
     Also, by setting the carbon concentration in the second conductive film  70   d  to be higher than the carbon concentration in the first conductive film  70   c , the tensile stress of the second conductive film  70   d  can be reduced or canceled; and the warp of the wafer can be suppressed. Or, by setting the oxygen concentration in the second conductive film  70   d  to be higher than the oxygen concentration in the first conductive film  70   c , the tensile stress of the second conductive film  70   d  can be reduced or canceled; and the warp of the wafer can be suppressed. 
     For example, in the CVD or the ALD forming the second conductive film  70   d , carbon can be included inside the second conductive film  70   d  by introducing a gas including carbon element (for example, CO, CO 2 , CH 4 ) to the chamber. Furthermore, carbon can be also included inside the second conductive film  70   d  by using a metal source gas including C such as W(CO) 6 , W 2 (NMe 2 ) 6 , W(NBu) 2 (NMe 2 ) 2 , W(CpEt)(CO) 2 (NO), Mo(NBu) 2 (NMe 2 ) 2 , Mo(NBu) 2 (NEt 2 ) 2 . 
     For example, in the CVD or the ALD forming the second conductive film  70   d , oxygen can be included inside the second conductive film  70   d  by introducing a gas including an oxygen element (for example, CO, CO 2 , NO, NO 2 , N 2 O) to the chamber. Furthermore, oxygen can be also included inside the second conductive film  70   d  by using a metal source gas including 0 such as W(CO) 6 , WF x O y , WOCl 4 , W(CpEt)(CO) 2 (NO). 
     As shown in  FIG. 13B , the first blocking film  34 , the second blocking film  35 , the barrier metal  81 , the first conductive film  70   c , and the second conductive film  70   d  are formed also on the side wall of the slit ST. Among these films, at least the second conductive film  70   d , the first conductive film  70   c , and the barrier metal  81  which are conductive are removed by etching. The physical connection between the electrode layers  70  of different layers is broken. 
     Subsequently, the separation portions  60  are formed by forming the insulating films  61  shown in  FIG. 2  inside the slits ST. 
     Although the internal stress of the first conductive film  70   c  and the internal stress of the second conductive film  70   d  are caused to be different by the difference between the concentrations of the non-metallic element in the embodiments recited above, the internal stress of the first conductive film  70   c  and the internal stress of the second conductive film  70   d  also may be caused to be different by a difference between the crystal grain boundary density of the first conductive film  70   c  and the crystal grain boundary density of the second conductive film  70   d . For example, the crystal grain boundary density can be controlled by controlling the film formation conditions. 
     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 inventions. 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 inventions. The accompanying claims and their equivalents are intended to cover such forms or modification as would fall within the scope and spirit of the inventions.