Patent Publication Number: US-2023137865-A1

Title: Film forming method and film forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-179003, filed on Nov. 1, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a film forming method and a film forming apparatus. 
     BACKGROUND 
     Further improvement in capacitor performance is required in an insulating film that constitutes, for example, a DRAM (Dynamic Random Access Memory) as a semiconductor device. Therefore, there is an increasing need for an ultra-high-k film having a dielectric constant of, for example, about 80 to 100 as a material for the insulating film. A crystal of a composite oxide containing strontium (Sr) and titanium (Ti) (hereinafter also referred to as “STO”) is known as a candidate for the ultra-high-k film. 
     For example, there is known a technique in which a first Sr—Ti—O-based film having a thickness of 10 nm or less formed on a Ru film is crystallized by annealing, and then a second Sr—Ti—O-based film is formed and crystallized by annealing. 
     [Prior Art Document] 
     [Patent Document] 
     Patent Document 1: International Publication No. 2009/104621 
     SUMMARY 
     According to the present disclosure, a method of forming a crystalline structure film containing strontium, titanium, and oxygen on a substrate, includes: forming an amorphous structure film on a surface of a titanium nitride film formed on a surface of the substrate, the amorphous structure film containing strontium and oxygen and having a titanium content adjusted so that a content ratio of titanium to strontium based on the number of atoms becomes a value in a range of 0 or more and less than 1.0; and obtaining a crystalline structure film containing strontium, titanium and oxygen and containing titanium diffused from the titanium nitride film by heating the substrate on which the amorphous structure film is formed, at a temperature of 500 degrees C. or higher. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure. 
         FIGS.  1 A and  1 B  are schematic diagrams showing a method of forming a crystalline structure STO film according to a first embodiment. 
         FIG.  2    is a plan view of a film forming apparatus for forming the STO film. 
         FIG.  3    is a vertical cross-sectional side view of a film forming part. 
         FIG.  4    is a vertical cross-sectional side view of a heat treatment part. 
         FIG.  5    is a diagram showing an example of a film forming sequence. 
         FIGS.  6 A- 1 ,  6 A- 2  and  6 B  are schematic diagrams showing a method of forming a crystalline structure STO film according to a second embodiment. 
         FIGS.  7 A to  7 D  are schematic diagrams showing a method of forming a crystalline structure STO film according to a third embodiment. 
         FIG.  8    is a first diffraction spectrum diagram showing XRD analysis results of STO films according to an Example and a Comparative Example. 
         FIG.  9    is a graph showing a layered structure of the STO film. 
         FIG.  10    is a second diffraction spectrum diagram showing XRD analysis results of STO films according to Examples and a Comparative Example. 
         FIGS.  11 A,  11 B and  11 C  are first electron micrographs of surfaces of STO films according to Examples and a Comparative Example. 
         FIGS.  12 A and  12 B  are second electron micrographs of the surfaces of STO films according to an Example and a Comparative Example. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, systems, and components have not been described in detail so as not to unnecessarily obscure aspects of the various embodiments. 
     &lt;First Embodiment&gt; 
     First, a method for forming a crystalline structure STO film according to the present disclosure (hereinafter also referred to as “crystalline STO film”) will be described with reference to  FIGS.  1 A and  1 B .  FIGS.  1 A and  1 B  schematically show a layered structure of films formed on a semiconductor wafer (hereinafter referred to as “wafer”) W, which is a substrate, in a process of forming, for example, a DRAM. In  FIGS.  1 A and  1 B ,  FIGS.  6 A- 1 ,  6 A- 2 , and  6 B , and  FIGS.  7 A to  7 D , structures such as trenches and via holes formed in the wafer W are omitted. 
     As exemplified in  FIG.  1 A , in the wafer W on which the crystalline STO film is formed, a silicon oxide film (SiO film)  82  as a base film and a titanium nitride film (TiN film)  83  for making contact with a silicon wafer  81  through trenches and via holes (not shown) are layered on an upper surface of the main body of the silicon wafer  81 . A crystalline STO film  85 , which is an ultra-high-k film, is formed on the upper surface of the TiN film  83 . 
     As a method of obtaining the crystalline STO film  85 , there is known a technique in which an amorphous structure STO film (hereinafter also referred to as “amorphous STO film”) is formed on a wafer W to be subjected to film formation and the amorphous STO film is converted to a crystalline STO film by heat-treating (annealing) the wafer W. 
     Meanwhile, the inventors of the present disclosure have found that as shown in the experimental results in the later-described Examples, unlike ordinary metals, even if a heat treatment is performed after forming an amorphous STO film on the upper surface of the TiN film  83 , a crystalline STO film may not be formed. In this case, it is also conceivable to adopt a technique in which another amorphous STO film is layered on the upper surface of the amorphous STO film and subjected to a heat treatment to obtain a crystalline STO film in a region not in contact with the TiN film  83  by performing the heat treatment of the another amorphous STO film. However, it was found that even if the crystalline STO film is obtained by this technique, irregularities called blisters may be formed on the surface of the crystalline STO film. 
     The reason that a crystalline STO film cannot be obtained even after a heat treatment is not clear. As for this point, the inventors speculated that if the content of titanium in the vicinity of the interface between the TiN film  83  and the amorphous STO film is high, there may be created conditions that make it difficult for STO crystals to grow. 
     Therefore, in the method of forming a crystalline STO film according to the first embodiment, as shown in  FIG.  1 A , a strontium oxide film (SrO film)  84  is formed on the surface of the TiN film  83  without adding titanium (amorphous STO film forming process). Thereafter, the wafer W, on which the SrO film  84  is formed, is subjected to a heat treatment to diffuse titanium from the TiN film  83  into the SrO film  84 , thereby obtaining a crystalline STO film  85  (crystalline STO film obtaining process,  FIG.  1 B ). 
     For example, when obtaining the crystalline STO film  85  having a thickness in the range of 1 nm to 5 nm, it is preferable to form the SrO film  84  having a thickness of 2 nm to 10 nm. Further, the heat treatment is carried out in an atmosphere of an inert gas such as an argon (Ar) gas or a nitrogen (N 2 ) gas, at a temperature of 500 to 700 degrees C., for example, 630 degrees C., for 5 minutes to 1 hour, for example, 1 hour. 
     Hereinafter, the configuration of an apparatus (film forming apparatus  1 ) for forming the crystalline STO film  85  by performing the above-described process will be described with reference to  FIGS.  2  to  4   . The film forming apparatus  1  is configured, for example, as a multi-chamber system vacuum processing apparatus. As shown in  FIG.  2   , the film forming apparatus  1  includes an atmospheric pressure transfer chamber  22  which is kept at an atmospheric pressure by, for example, an Ar gas. A load port  21  for transferring the wafer W to and from, for example, a carrier C accommodating wafers W is installed in front of the atmospheric pressure transfer chamber  22 . The front wall of the atmospheric pressure transfer chamber  22  is provided with an opening/closing door  27  that is opened when the wafer W is transferred to and from the carrier C. A transfer arm  25  for transferring the wafer W is provided in the atmospheric pressure transfer chamber  22 . Further, an alignment chamber  26  for adjusting the orientation and eccentricity of the wafer W is provided on the left sidewall of the atmospheric pressure transfer chamber  22  when viewed from the load port  21  side. 
     A load lock chamber  23  is connected to the wall surface of the atmospheric pressure transfer chamber  22  opposite to the load port  21 . The load lock chamber  23  has a function of switching the internal atmosphere between an atmospheric pressure atmosphere and a vacuum atmosphere while the wafer W is accommodated therein. For example, two load lock chambers  23  are arranged side by side when viewed from the atmospheric pressure transfer chamber  22  side. A vacuum transfer chamber  24  is arranged behind the load lock chambers  23  when viewed from the atmospheric pressure transfer chamber  22 . The atmospheric pressure transfer chamber  22  and the vacuum transfer chamber  24  are connected to each load lock chamber  23  via a gate valve  29 . 
     A film forming module (film forming part)  101  for forming the SrO film  84  on the upper surface of the TiN film  83  formed on the wafer W, and a heat treatment module (heat treatment part)  102  for forming a crystalline STO film  85  at the interface between the TiN film  83  and the SrO film  84  by heat-treating the wafer W on which the SrO film  84  is formed are connected to the vacuum transfer chamber  24 . In this example, two film forming modules  101  and two heat treatment modules  102  are connected to the vacuum transfer chamber  24 . A transfer arm  28  is provided in the vacuum transfer chamber  24 . The wafer W is delivered among the load lock chamber  23 , the film forming module  101 , and the heat treatment module  102  by the transfer arm  28 . 
     Next, a configuration example of the film forming module  101  for forming the SrO film  84  on the upper surface side of the TiN film  83  by an ALD (Atomic Layer Deposition) method will be described ( FIG.  3   ). For the sake of convenience in description, the film forming module  101  shown in  FIG.  3    is configured to be capable of forming a Sr-rich STO film  86  and an STO upper layer film  87  described in second and third embodiments. The formation of the SrO film  84  is different from the formation of the Sr-rich STO film  86  and the STO upper layer film  87  in that the provision of a Ti raw material gas supply part  62  for supplying a titanium (Ti) raw material gas is omitted or the Ti raw material gas supply part  62  is not used. In the following description, the configuration of the film forming module  101  including the Ti raw material gas supply part  62  will be described. 
     The film forming module  101  includes a processing container  30  that accommodates the wafer W. A loading/unloading port  31  that can be opened and closed by the gate valve  29  described above is formed on a side surface of the processing container  30 . 
     For example, an annular exhaust duct  32  is arranged on an upper portion of the sidewall of the processing container  30 . Furthermore, a top plate  33  is provided on an upper surface of the exhaust duct  32  so as to block the upper opening of the processing container  30 . The processing container  30  is connected to an evacuation part  35  such as a vacuum pump or the like through an evacuation path  34  connected to an exhaust port  331  of the exhaust duct  32 . An APC (auto pressure controller) valve  36  for adjusting an internal pressure of the processing container  30  is installed in the evacuation path  34 . 
     A stage  4  which horizontally supports the wafer W is provided inside the processing container  30 . A heater  41  for heating the wafer W is embedded in the stage  4 . Further, the stage  4  is connected to an elevating mechanism  44  via a column  43  and is configured to be vertically movable by the elevating mechanism  44 . In  FIG.  3   , the stage  4  moved to a wafer delivery position is indicated by a one-dot chain line. In  FIG.  3   , reference numeral  45  denotes support pins for use in delivering the wafer W, and the support pins  45  are configured to be vertically movable by a lifting mechanism  46 . Reference numeral  42  denotes through-holes for the support pins  45 , and reference numerals  47  and  48  denote bellows that expand and contract as the stage  4  and the support pins  45  are moved up and down. 
     A shower head  5  for supplying a processing gas into the processing container  30  is provided in the film forming module  101  so as to face the stage  4 . The shower head  5  has a gas diffusion space  51  therein. The lower surface of the shower head  5  is configured as a shower plate  52  having a large number of gas discharge holes  53 . A gas supply system  6  is connected to the gas diffusion space  51  through a gas introduction hole  54 . 
     The gas supply system  6  includes a Sr raw material gas supply part  61  for supplying a strontium (Sr) raw material gas toward the processing container  30 , a Ti raw material gas supply part  62  for supplying a Ti raw material gas toward the processing container  30 , and an oxidizing gas supply part  63  for supplying an oxidizing gas for oxidizing the Sr raw material and the Ti raw material toward the processing container  30 . 
     The Sr raw material supplied from the Sr raw material gas supply part  61  includes a strontium-containing compound such as Sr(Me5Cp) 2  (bispentamethylcyclopentadienyl strontium), Sr(THD) 2  (strontium bistetramethylheptanedionate), or the like. Further, the Ti raw material supplied from the Ti raw material gas supply part  62  includes a titanium-containing compound such as Ti(Me5Cp)(MeO) 3  (pentamethylcyclopentadienyl titanium trimethoxide), Ti(Me5Cp)(NMe 2 ) 3  (methylcyclopentadienyl titanium trimethoxide), or the like. Moreover, in this example, a highly reactive ozone (O 3 ) gas is used as the oxidizing gas. Alternatively, for example, remote plasma obtained by ionizing an oxygen gas may be supplied as the oxidizing gas. 
     The Sr raw material gas supply part  61  includes a gas source  64  for supplying the strontium (Sr) raw material gas and a strontium gas supply path  641 . The Sr raw material gas source  64  has a function of bringing the above-described Sr raw material into contact with a carrier gas to vaporize or sublime the Sr raw material, and supplying the same as a raw material gas. For example, in the strontium gas supply path  641 , a flow rate adjustment part  642 , a storage tank  643 , and a valve V 1  are installed sequentially from the upstream side. 
     The Ti raw material gas supply part  62  includes a gas source  65  for supplying the Ti raw material gas and a titanium gas supply path  651 . The Ti raw material gas source  65  has a function of bringing the aforementioned Ti raw material into contact with a carrier gas to vaporize or sublime the Ti raw material, and supplying the same as a raw material gas. For example, in the titanium gas supply path  651 , a flow rate adjustment part  652 , a storage tank  653 , and a valve V 2  are installed sequentially from the upstream side. 
     Further, the oxidizing gas supply part  63  includes an O 3  gas source  66  for supplying the oxidizing gas and an O 3  gas supply path  661 . For example, in the O 3  gas supply path  661 , a flow rate adjustment part  662 , a storage tank  663 , and a valve V 3  are installed sequentially from the upstream side. 
     The Sr raw material gas, the Ti raw material gas, and O 3  are temporarily stored in storage tanks  643 ,  653 , and  663 , respectively, and are supplied to the film forming module  101  after being pressurized to a predetermined pressure. The supply and cutoff of the respective gases from the storage tanks  643 ,  653 , and  663  to the film forming module  101  are performed by opening and closing the valves V 1 , V 2 , and V 3 . 
     Further, the gas supply system  6  includes an inert gas supply part for supplying an inert gas to the film forming module  101 . For example, an Ar gas is used as the inert gas. The inert gas supply part in this example includes Ar gas sources  67 ,  68 , and  69 , and Ar gas supply paths  671 ,  681 , and  691 . 
     In this example, the Ar gas supplied from the Ar gas source  67  of the Sr raw material gas supply part  61  is a purge gas for the Sr raw material gas. The Ar gas source  67  is connected to the strontium gas supply path  641  on the downstream side of the valve V 1  through the Ar gas supply path  671 . Further, the Ar gas supplied from the Ar gas source  68  of the Ti raw material gas supply part  62  is a purge gas for the Ti raw material gas. The Ar gas source  68  is connected to the titanium gas supply path  651  on the downstream side of the valve V 2  via the Ar gas supply path  681 . 
     Furthermore, the Ar gas supplied from the Ar gas source  69  of the oxidizing gas supply part  63  is a purge gas for the oxidizing gas. The Ar gas source  69  is connected to the O 3  gas supply path  661  on the downstream side of the valve V 3  via the Ar gas supply path  691 . In  FIG.  3   , reference numerals  672 ,  682 , and  692  indicate flow rate adjustment parts, respectively, and reference numerals V 4 , V 5 , and V 6  indicate valves, respectively. 
     When forming the SrO film  84  (or the Sr-rich STO film  86  described later) on the upper surface of the TiN film  83  by the film forming module  101  shown in  FIG.  3   , the Sr raw material gas supply part  61  corresponds to a first raw material gas supply part, and the Ti raw material gas supply part  62  corresponds to a second raw material gas supply part. 
     Next, the configuration of the heat treatment module  102  will be described with reference to  FIG.  4   . In  FIG.  4   , the components having the same functions as those of the film forming module  101  described with reference to  FIG.  3    may be designated by the same reference numerals as those used in  FIG.  3   , and a duplicate description thereof may be omitted. 
     As shown in  FIG.  4   , the heat treatment module  102  includes a processing container  30 , a stage  4   a  on which a wafer W to be processed is placed, and a shower head  5  installed on a ceiling surface side of the processing container  30  so as to face the stage  4   a.    
     The stage  4   a  of this example is fixedly arranged on a bottom plate of the processing container  30 . The wafer W on which the SrO film  84  has been formed in the film forming module  101  is placed on the stage  4   a . A plurality of support pins (not shown) is provided inside the stage  4   a  so as to be movable up and down. The wafer W is delivered by allowing the support pins to protrude or retract with respect to the upper surface of the stage  4   a.    
     A heater  41  for heating the wafer W to, for example, 630 degrees C. within the temperature range of 500 to 700 degrees C. is provided inside the stage  4   a . A plurality of exhaust ports  331  for evacuating the interior of the processing container  30  is formed in the bottom plate around the stage  4   a.    
     An inert gas supply part  60  for supplying an Ar gas, which is an example of an inert gas, to the processing container  30  is connected to the showerhead  5 . The inert gas supply part  60  includes an Ar gas source  600  and an Ar gas supply path  601 . For example, in the Ar gas supply path  601 , a flow rate adjustment part  602  and a valve V 7  are installed sequentially from the upstream side. 
     The film forming apparatus  1  having the above configuration includes a controller  100  as shown in  FIG.  2   . The controller  100  is configured with a computer including a storage part for storing a program, a memory, and a CPU. The program includes instructions (steps) which are combined so as to output control signals from the controller  100  to the respective parts of the film forming apparatus  1  to form the SrO film  84  on the wafer W and to perform the subsequent heat treatment. The program is stored in the storage part of the computer, such as a flexible disk, a compact disk, a hard disk, an MO disk (magneto-optical disk), a non-volatile memory, or the like. The program is read out from the storage part and installed in the controller  100 . 
     The operation of the film forming apparatus  1  having the configuration described above will be described. First, a carrier C accommodating a plurality of wafers W is transferred to the load port  21  of the film forming apparatus  1 . The SiO film  82  shown in the schematic diagram of  FIG.  1 A  is formed on the upper surface of each wafer W. The wafer W is taken out from the carrier C by the transfer arm  25 , loaded into the alignment chamber  26  through the atmospheric pressure transfer chamber  22 , subjected to alignment, and then loaded into the vacuum transfer chamber  24  through the load lock chamber  23 . 
     Subsequently, the wafer W is transferred to the film forming module  101  by the transfer arm  28 , and the SrO film  84  is formed by an ALD method. The wafer W loaded into the processing container  30  is placed on the stage  4 , and heating of the wafer W is started by raising the temperature of the heater  41  to a temperature within the range of 250 to 400 degrees C. Along with this heating operation, an Ar gas is supplied from the Ar gas sources  67 ,  68 , and  69  into the processing container  30  at preset flow rates. Then, the interior of the processing container  30  is evacuated by the evacuation part  35 , and the opening degree of the valve  36  is adjusted so that the internal pressure of the processing container  30  becomes a target pressure. 
     Subsequently, a process of forming a SrO film  84  is performed based on the film forming sequence of  FIG.  5   . In the case of forming the SrO film  84 , only a cycle of operations  1  to  4  (first cycle) shown in  FIG.  5    is executed. On the other hand, the number of execution times of the cycle of operations  5  to  8  (second cycle) is zero. First, the valve V 1  is opened to supply the Sr raw material gas, and the Ar gas is supplied from the Ar gas sources  67 ,  68 , and  69  at preset flow rates (operation  1 ). By this process, the Sr raw material is adsorbed on the entire surface of the wafer W. 
     Next, the valve V 1  is closed to stop the supply of the Sr raw material gas, while the supply of the Ar gas from the Ar gas sources  67 ,  68 , and  69  is continued. In this manner, purging with the Ar gas is performed to remove the Sr raw material gas remaining in the processing container  30  (operation  2 ). 
     Next, while continuing to supply the Ar gas from the Ar gas sources  67 ,  68 , and  69 , the valve V 3  is opened to supply O 3 , which is an oxidizing gas. By this process, the Sr raw material adsorbed to the wafer W reacts with O 3  to form a thin film of SrO (operation  3 ). When the Sr raw material is composed of an organometallic compound as in the example of the Sr raw material described above, the thin SrO film may contain a component containing carbon (e.g., SrCO 3 , etc.). Subsequently, the valve V 3  is closed to stop the supply of O 3 , while the supply of the Ar gas from the Ar gas sources  67 ,  68 , and  69  is continued. Purging with the Ar gas is performed to remove O 3  remaining in the processing container  30  (operation  4 ). 
     Thus, in the process of forming the SrO film  84 , operations  1  to  4  of alternately supplying the Sr raw material gas and the oxidizing gas while supplying the Ar gas, which is an inert gas, into the processing container  30  is repeated by a predetermined number of cycles to form an SrO film  84  having a desired thickness. An example of the thickness of the SrO film  84  may be 10 nm, which is in the range of 2 nm or more and 10 nm or less. 
     After the formation of the SrO film  84  is completed, the wafer W is unloaded from the film forming module  101  and loaded into the heat treatment module  102  to perform a process of obtaining a crystalline STO film  85 . That is, after the wafer W is placed on the stage  4   a  of the film forming module  101 , the gate valve  29  is closed, and while the interior of the processing chamber  30  is being evacuated, the Ar gas is supplied from the inert gas supply part  60  to regulate the internal pressure of the processing container  30  to a preset pressure. In addition, electric power is supplied to the heater  41  from a power supply part (not shown) to heat the wafer W on the stage  4   a  to, for example, 630 degrees C. in the range of 500 to 700 degrees C. 
     By forming the SrO film  84  on the upper surface side of the TiN film  83 , titanium diffuses from the TiN film  83  side to the SrO film  84  side due to a difference in concentration of titanium. The diffusion of titanium is promoted by heating the wafer W. Meanwhile, even when titanium moves toward the SrO film  84  by diffusion, the concentration of titanium may be lower than that of an amorphous STO film in the related art and may not be high enough to prevent the crystallization of the region containing strontium, titanium, and oxygen. 
     Therefore, by heat-treating the wafer W in which the SrO film  84  is formed on the TiN film  83 , crystallization can be caused to occur in the region of the interface between the TiN film  83  and the SrO film  84  where titanium diffuses toward the SrO film  84 . As a result, a crystalline STO film  85  can be obtained as shown in  FIG.  1 B . 
     For example, in order to obtain the crystalline STO film  85  having a thickness of 1 nm or more and 5 nm or less at the above-described heating temperature, the heat treatment is performed for a processing time of 5 minutes to 1 hour. The SrO film  84  remaining on the upper surface side of the crystalline STO film  85  may be removed by etching or CMP (Chemical Mechanical Polishing) after the wafer W is taken out from the film forming apparatus  1 . 
     After heat-treating the wafer W for a preset period of time in the heat treatment module  102 , the wafer W is taken out from the heat treatment module  102  and is transferred through the vacuum transfer chamber  24 , the load lock chamber  23 , and the atmospheric pressure transfer chamber in the opposite route to that used during the loading. The processed wafer W is accommodated in the original carrier C. 
     According to the film forming apparatus  1  of the present disclosure, the wafer W is heat-treated after the SrO film  84  containing no titanium is formed on the upper surface of the TiN film  83 . As a result, an excessive increase in the titanium content at the interface between the TiN film  83  and the SrO film  84  can be suppressed, and the crystalline STO film  85  can be formed on the upper surface of the TiN film  83 , which has conventionally been difficult to crystallize the amorphous STO film. 
     Here, the film formed on the upper surface of the TiN film  83  to obtain the crystalline STO film  85  by the method described with reference to  FIGS.  1 A and  1 B  is not limited to the SrO film  84  containing no titanium. For example, a strontium (Sr)-rich STO film having a relatively low content ratio of titanium to strontium (based on the number of atoms) may be used. The configuration of the Sr-rich STO film will be exemplified in the second embodiment described below. 
     &lt;Second Embodiment&gt; 
       FIGS.  6 A- 1 ,  6 A- 2  and  6 B  schematically show a method of forming the crystalline STO film  85  according to a second embodiment. In the second embodiment, a SrO film  84   a  (or a Sr-rich STO film  86 ) is formed to have a thickness in the range of 5 nm to 10 nm, which is close to the thickness of the crystalline STO film  85  formed on the upper surface side of the TiN film  83 . The second embodiment is different from the first embodiment in which the interface region of the SrO film  84  is crystallized with the TiN film  83 , in that the entire SrO film  84   a  (or Sr-rich STO film  86 ) is converted into the crystalline STO film  85  by heat treatment. 
     The film forming method of the SrO film  84   a  shown in  FIG.  6 A- 1    is the same as that of the first embodiment except that as compared with the SrO film  84  shown in  FIG.  1 A  (having a thickness of, for example, 2 nm or more and 10 nm or less), the SrO film  84   a  shown in  FIGS.  6 A- 1 , and  6 A- 2    has a thickness in the range of 5 nm to 10 nm. Further, the heat treatment method may also be the same as that of the first embodiment as long as the time for executing the heat treatment capable of converting the entire SrO film  84   a  into the crystalline STO film  85  can be ensured. 
     If the thickness of the titanium diffused from the TiN film  83  falls within a range that spreads over the entire SrO film  84   a  in the thickness direction, the entire SrO film  84   a  may be converted into the crystalline STO film  85  by the same mechanism as the example described in the first embodiment. 
     Further, the film that can be converted into the crystalline STO film  85  by heat treatment is not limited to the SrO film  84  containing no titanium.  FIG.  6 A- 2    shows an example in which the Sr-rich STO film  86  having a relatively low content ratio of titanium to strontium is formed on the upper surface side of the TiN film  83 . The Sr-rich STO film  86  is formed so that the content ratio of titanium to strontium on the basis of the number of atoms is in the range of more than 0 and less than 1.0, preferably more than 0 and less than or equal to 0.7. The thickness range of the Sr-rich STO film  86  is the same as that of the already-described SrO film  84   a.    
     The Sr-rich STO film  86  can be formed by performing all operations  1  to  8  of the film forming sequence shown in  FIG.  5    using the film forming module  101  (provided with the Ti raw material gas supply part  62 ) described with reference to  FIG.  3   . 
     That is, in forming the Sr-rich STO film  86 , the cycle of operations  1  to  4  described above is performed to form a thin SrO film. Then, a cycle including supplying a Ti raw material gas, adsorbing the Ti raw material onto the wafer W (operation  5 ), stopping the supply of the Ti raw material gas, purging the interior of the processing container  30  (operation  6 ), supplying an oxidation gas (O 3 ) (operation  7 ), stopping the supply of the Ti raw material gas, and purging the interior of the processing container  30  (operation  8 ) is executed to form a thin film of TiO. Then, the cycle of operations  1  to  4  (first cycle) and the cycle of operations  5  to  8  (second cycle) are alternately repeated for a plurality of cycles. This makes it possible to form the Sr-rich STO film  86  having a desired thickness. In  FIG.  5   , the number of alternate repetitions of the first cycle and the second cycle is denoted as “Z”. 
     Here, the content ratio of titanium to strontium in the Sr-rich STO film  86  is adjusted by changing the ratio of the number of execution times of the first cycle (denoted as “X” in  FIG.  5   ) to the number of execution times of the second cycle (denoted as “Y” in  FIG.  5   ). 
     Specifically, composition analysis (e.g., secondary ion mass spectrometry, or the like) of the amorphous STO film obtained by changing the cycle ratio “X:Y” is performed in preliminary experiments. Then, within the range where the content ratio of titanium to strontium (based on the number of atoms) is greater than 0 and less than 1.0, the numbers of execution times of the respective cycles X and Y corresponding to the desired content ratio are adopted as the film forming conditions of the actual Sr-rich STO film  86 . 
     As for the Sr-rich STO film  86  formed by the above-described method, just like the case of the SrO film  84   a  shown in  FIG.  6 A- 1   , the entire Sr-rich STO film  86  may be converted into the crystalline STO film  85  by a heat treatment using the heat treatment module  102 . 
     &lt;Third Embodiment&gt; 
     If the crystalline STO film  85  can be formed on the upper surface of the TiN film  83  by the method described in the first and second embodiments, it is possible to use the crystalline STO film  85  as a partition against the TiN film  83  and to form a thicker crystalline STO film. The third embodiment shown in  FIGS.  7 A to  7 D  is an example in which a crystalline STO film is formed by this method. 
       FIGS.  7 A and  7 B  are re-illustration of  FIGS.  6 A- 1  and  6 B , respectively, showing an example in which a SrO film  84   a  is formed on the upper surface of a TiN film  83  and then subjected to a heat treatment to obtain a crystalline STO film  85 . Subsequently, an STO upper layer film  87  having an amorphous structure is formed on the upper surface of the crystalline STO film  85  (see  FIG.  7 C ). 
     The STO upper layer film  87  may be formed using the film forming module  101  including the Ti raw material gas supply part  62  described with reference to  FIG.  3   . The film forming module  101  for forming the STO upper layer film  87  corresponds to the upper layer film forming part of this example. As the upper layer film forming part, the same film forming module  101  as that for forming the SrO film  84  according to the first embodiment and the SrO film  84   a  and the Sr-rich STO film  86  according to the second embodiment may be used. Alternatively, a film forming module  101  other than the film forming module  101  for forming these films  84 ,  84   a , and  86  may be connected to the vacuum transfer chamber  24 . 
     The STO upper layer film  87  is formed to have a thickness of 3 nm or more and 30 nm or less, which is larger than the crystalline STO film  85 . In addition, in the STO upper layer film  87 , the content ratio of titanium to strontium based on the number of atoms may be set to a value of 1.0 or more. Since the STO upper layer film  87  does not make direct contact with the TiN film  83 , the content ratio of titanium to strontium is not limited to the range of 0 or more and less than 1.0 and may be adjusted more freely. For example, when the conditions for obtaining a crystalline STO film having a higher relative dielectric constant is included in the range of the content ratio close to 1.0 or equal to or larger than 1.0, a high-quality STO upper layer film  87  may be formed without being subject to the restrictions for forming the crystalline STO film  85  on the upper surface of the TiN film  83 . As a suitable content ratio in such a case, the STO upper layer film  87  may have the content ratio of titanium to strontium on the basis of the number of atoms falling within the range of 0.8 or more and 1.2 or less. 
     The STO upper layer film  87  formed by the above method may also be converted into a crystalline STO film  88  by a heat treatment using the heat treatment module  102 . The upper layer film heat treatment part that heats the STO upper layer film  87  may be the same heat treatment module  102  as the one that heat-treats the SrO film  84  according to the first embodiment or the SrO film  84   a  and the Sr-rich STO film  86  according to the second embodiment. Alternatively, a heat treatment module  102  other than the heat treatment module  102  for forming the films  84 ,  84   a , and  86  may be connected to the vacuum transfer chamber  24 . 
     In the first to third embodiments described above, the film forming module  101  and the heat treatment module  102 , which are single-substrate modules, are connected to the common vacuum transfer chamber  24 . However, the present disclosure is not limited to the case where the process of forming the amorphous films (the SrO films  84  and  84   a , and the Sr-rich STO film  86 ) and the process of converting the films  84 ,  84   a , and  86  into the crystalline STO film  85  by the heat treatment are performed by the common film forming apparatus  1 . For example, a batch-type processing apparatus, in which a boat holding a large number of wafers W is accommodated and processed in a heating furnace, may be used. The formation of amorphous films and the heat treatment thereof may be performed separately. As for the heat treatment, the wafer W may be heated by, for example, an RTA (Rapid Thermal Annealing) apparatus using an infrared lamp, for a treatment time shorter than the previously described 5 minutes. Further, when forming amorphous films, it may be possible to use a semi-batch type film forming apparatus in which a plurality of wafers W is arranged on a rotary table, revolved around a rotation axis, and allowed to pass through a plurality of processing spaces partitioned from each other to repeat adsorption of a raw material gas and formation of a thin film of SiO or TiO using an oxidizing gas. 
     Alternatively, for example, other modules such as a module for forming the TiN film  83 , and the like may be connected to the vacuum transfer chamber  24  of the film forming apparatus  1  shown in  FIG.  2   . In this case, it is possible to form a layered structure of a plurality of types of films on the wafer W using the common film forming apparatus  1 . 
     It should be considered that the embodiments disclosed herein are illustrative in all respects and not limitative. The embodiments described above may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims. 
     (Experiment 1) 
     In correspondence to the first embodiment, a SrO film  84  was formed on the upper surface side of a TiN film  83  described with reference to  FIGS.  1 A and  1 B . The difference in the film structure with and without a heat treatment was checked. 
     A. Experiment Conditions 
     (Example 1) 
     A TiN film  83  having a thickness of 10 nm was formed on a wafer W, and a SrO film  84  having a thickness of 10 nm was formed on the upper surface of the TiN film  83  by an ALD method based on operations  1  to  4  of  FIG.  5   . A cyclopentadienyl-based strontium compound was used as a Sr raw material, and the heating temperature of the wafer W was set to 350 degrees C. Thereafter, the wafer W was heated to 600 degrees C. under an argon gas supply atmosphere (at a pressure of 400 Pa (3 Torr)) and subjected to a heat treatment for 1 hour. The heat-treated wafer W was subjected to crystal structure analysis by XRD (X-Ray Diffraction) and cross section observation by TEM (Transmission Electron Microscope). 
     (Comparative Example 1) 
     The same analysis as in Example 1 was performed on a wafer W on which a SrO film  84  was formed and not subjected to a heat treatment. 
     B. Experimental Results 
       FIG.  8    shows the results of XRD analysis according to Example 1 and Comparative Example 1. The horizontal axis in  FIG.  8    indicates the X-ray diffraction angle, and the vertical axis in  FIG.  8    indicates the detected X-ray intensity. Further,  FIG.  9    shows the results of summarizing the layered structure of the TiN film  83 , the SrO film  84 , and the crystalline STO film  85  based on the results of TEM observation as a stacked bar graph of the thickness of each layer. 
     According to the XRD analysis results shown in  FIG.  8   , in Example 1 in which the heat treatment is performed after the SrO film  84  is formed, an X-ray diffraction peak was confirmed at the diffraction angle corresponding to the crystal plane of the crystalline STO. This suggests that the crystalline STO film  85  is formed by heat-treating the wafer W after forming the SrO film  84  on the upper surface of the TiN film  83 . On the other hand, in Comparative Example 1, no diffraction peak corresponding to crystalline STO was confirmed. 
     According to the TEM observation results shown in  FIG.  9   , it was confirmed that a layer having a thickness of about 6 nm is formed between the TiN film  83  and the SrO film  84  in Example 1. It can be understood that this layer corresponds to the crystalline STO film  85  which showed the diffraction peak corresponding to the crystal plane of the crystalline STO in the XRD analysis. Even in the TEM observation results of Comparative Example 1, a thin layer of about 3.5 nm was formed between the TiN film  83  and the SrO film  84 . However, considering that the diffraction peak corresponding to the crystal plane of the crystalline STO could not be confirmed by the XRD analysis, it can be understood to be a mixed amorphous layer of SrO and SiN formed when the SrO film  84  was formed. 
     (Experiment 2) 
     In correspondence to the second embodiment, the film type of the film formed on the upper surface side of the TiN film  83  described with reference to  FIGS.  6 A- 1 ,  6 A- 2  and  6 B  was changed to confirm the difference in the film structure after the heat treatment. 
     A. Experimental Conditions 
     (Example 2-1) 
     A SrO film  84   a  was formed under the same conditions as in Example 1, except that the thickness was set to 5 nm. Thereafter, the wafer W was heated to 630 degrees C. under an argon gas supply atmosphere (at a pressure of 400 Pa (3 Torr)) and subjected to a heat treatment for 1 hour. Crystal structure analysis by XRD and surface observation by SEM (Scanning Electron Microscope) were performed on the wafer W after the heat treatment. 
     (Embodiment 2-2) 
     Instead of the SrO film  84   a , a Sr-rich STO film  86  having a content ratio of titanium to strontium of 9.4 (first cycle execution number X: first cycle execution number Y=10:1) was formed by an ALD method based on operations  1  to  8  of  FIG.  5   . This wafer W was analyzed in the same manner as in Example 2-1. 
     (Comparative Example 2-1) 
     An amorphous STO film having a content ratio of titanium to strontium of 1.0 (first cycle execution number X: first cycle execution number Y=2:3) was formed by the same method as in Example 2-1. This wafer W was subjected to the same heat treatment and analysis as in Example 2-1. 
     B. Experimental Results 
       FIG.  10    shows the results of XRD analysis for Examples 2-1 and 2-2 and Comparative Example 2-1. The horizontal and vertical axes in  FIG.  10    are the same as those in  FIG.  8   . SEM photographs of the surfaces of the respective wafers W are shown in  FIGS.  11 A to  11 C . 
     According to the results of the XRD analysis shown in  FIG.  10   , in both Example 2-1 in which the SrO film  84   a  having a thickness of 5 nm was formed and Example 2-2 in which the Sr-rich STO film  86  having a thickness of 5 nm was formed, the diffraction peak corresponding to the crystalline STO was confirmed. From the results of this XRD analysis, it can be seen that the films  84   a  and  86  have been converted into crystalline STO films  85 . On the other hand, in Comparative Example 2-1 having a high content ratio of titanium to strontium, no diffraction peak corresponding to the crystalline STO was confirmed. 
     Further, according to the SEM photographs shown in  FIGS.  11 A and  11 B , the crystalline STO films  85  according to Examples 2-1 and 2-2 obtained by heat-treating the SrO film  84   a  and the Sr-rich STO film  86  have flat surfaces. On the other hand, according to  FIG.  11 C , a large number of protrusions called blisters were formed on the surface of the wafer W according to Comparative Example 2-2 obtained by heat-treating amorphous STO having a content ratio of titanium to strontium of 1.0. Such blisters are generated by partial peeling of the amorphous STO film, and are not desirable because they become a factor causing film peeling and deterioration of film characteristics such as a decrease in a dielectric constant. 
     (Experiment 3) 
     In correspondence to the third embodiment, the film type of the film formed on the lower surface side of the STO upper layer film  87  described with reference to  FIGS.  7 A to  7 D  was changed to confirm the difference in the film structure after the heat treatment. 
     A. Experimental Conditions 
     (Example 3-1) 
     An STO upper layer film  87  having a thickness of 20 nm and a content ratio of titanium to strontium of 1.0 was formed on the upper surface of the crystalline STO film  85  formed by the method described in Example 2-2. The method of forming the STO upper layer film  87  is the same as in Comparative Example 2-1. After forming the STO upper layer film  87 , the wafer W was heated to 630 degrees C. under an argon gas supply atmosphere (at pressure of 400 Pa (3 Torr)) and subjected to a heat treatment for 1 hour. The surface of the wafer W after the heat treatment was observed by SEM. 
     (Comparative Example 3-1) 
     The STO upper layer film  87  was formed and heat-treated under the same conditions as in Example 3-1 except that an amorphous STO film having a content ratio of titanium to strontium of 1.0, which is formed by the method described in Comparative Example 2-1, is heat-treated and then the STO upper layer film  87  was formed on the upper surface of the amorphous STO film. The surface was observed by SEM. 
     B. Experimental Results 
     SEM photographs for Example 3-1 and Comparative Example 3-1 are shown in  FIGS.  12 A and  12 B , respectively. In all experimental results, it was confirmed by XRD analysis that a crystalline STO film  88  was formed after the heat treatment of the STO upper layer film  87 . According to the results shown in  FIG.  12 A , it can be confirmed that when the STO upper layer film  87  is formed on the upper surface of the flat crystalline STO film  85  shown in  FIG.  11 B , the surface of the crystalline STO film  88  after the heat treatment is also flat. On the other hand, according to the results shown in  FIG.  12 B , it can be noted that when the STO upper layer film  87  is formed on the surface of the film having blisters shown in  FIG.  11 C , blisters are also formed on the surface of the crystalline STO film  88  after the heat treatment. 
     According to the present disclosure in some embodiments, it is possible to form a crystalline structure film containing strontium, titanium, and oxygen on a titanium nitride film. 
     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 disclosures. Indeed, the 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 disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.