Patent Publication Number: US-2020299840-A1

Title: Substrate Processing Method and Substrate Processing Apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-055096, filed on Mar. 22, 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a substrate processing method and a substrate processing apparatus. 
     BACKGROUND 
     In a semiconductor device manufacturing process, various films are formed on a semiconductor wafer (hereinafter, referred to as a “wafer”) as a substrate, and a wiring pattern is formed on each film. In addition, in order to make the electrical characteristics between the wiring lines of the semiconductor device appropriate, there is a case where a gap (air gap) is formed in each film. In Patent Document 1, an interlayer insulating film is formed by chemical vapor deposition (CVD) on a front surface of a wafer in which a groove having a relatively high aspect ratio is formed. The film formation rate by CVD is higher at the entrance of the groove than at the bottom of the groove. Thus, insulating films are connected to each other at the entrance of the groove during the film formation, so that the above air gap is formed. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2012-054307 
     SUMMARY 
     According to one embodiment of the present disclosure, there is provided a method of processing a substrate, the method including: forming a coating film so as to cover a front surface of the substrate, the substrate having a recess formed in the front surface and in which an organic film is formed; heating the substrate to turn the organic film into a gas, removing the gas from an interior of the recess by causing the gas to pass through the coating film, and forming in the substrate a sealed space surrounded by the recess and the coating film; supplying a processing gas into the sealed space; and irradiating the substrate with a light to activate the processing gas in the sealed space, causing a reaction product gas to pass through the coating film, and removing the reaction product gas, wherein the reaction product gas is generated by a reaction between a residue of the organic film and the activated processing gas in the sealed space. 
    
    
     
       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. 
         FIG. 1A  is a schematic vertical cross-sectional view illustrating a substrate processing step according to an embodiment of the present disclosure. 
         FIG. 1B  is a schematic vertical cross-sectional view illustrating the substrate processing step. 
         FIG. 1C  is a schematic vertical cross-sectional view illustrating the substrate processing step. 
         FIG. 1D  is a schematic vertical cross-sectional view illustrating the substrate processing step. 
         FIG. 2A  is a schematic vertical cross-sectional view illustrating the substrate processing step. 
         FIG. 2B  is a schematic vertical cross-sectional view illustrating the substrate processing step. 
         FIG. 3A  is a schematic vertical cross-sectional view illustrating the substrate processing step. 
         FIG. 3B  is a schematic vertical cross-sectional view illustrating the substrate processing step. 
         FIG. 4  is a plan view illustrating an embodiment of a substrate processing apparatus for performing the substrate processing steps. 
         FIG. 5  is a vertical cross-sectional side view of a film formation module provided in the substrate processing apparatus. 
         FIG. 6  is a vertical cross-sectional side view of a residue removal module provided in the substrate processing apparatus. 
         FIG. 7  is a schematic view illustrating an image of a wafer obtained in an evaluation test. 
         FIG. 8  is a schematic view illustrating an image of the wafer obtained in the evaluation test. 
         FIG. 9  is a graph representing a result of the evaluation test. 
         FIG. 10  is a graph representing a result of the evaluation test. 
         FIG. 11  is a graph representing a result of the evaluation test. 
         FIG. 12  is a graph representing a result of the evaluation test. 
     
    
    
     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. 
     A substrate processing according to an embodiment of the present disclosure will be described with reference to  FIGS. 1A to 1D , and  FIGS. 2A and 2B , which are schematic vertical cross-sectional views of the wafer W. Each of these figures illustrates a state in which a front surface of the wafer W is changed by performing a series of processes on the wafer W. Each of the series of processes is performed in a state in which the wafer W is accommodated in a processing container and a vacuum atmosphere is formed around the wafer W by exhausting the interior of the processing container. 
       FIG. 1A  illustrates the wafer W before the substrate processing. A layer  11  composed of, for example, silicon oxide (SiO 2 ) is formed on the front surface of the wafer W. A recess  12 , which is a pattern for forming wirings on the wafer W, is formed in the layer  11 . First, a film-forming gas for forming an organic film is supplied to the wafer W. As the organic film, for example, a polyurea film  13  as a polymer having a urea bond is formed so as to be buried in the recess  12 . 
     Thereafter, the wafer W is heated to a predetermined temperature so as to depolymerize the polyurea film  13  and remove a limited portion of the front surface of the wafer W. The removal of the limited portion of the front surface is performed such that the polyurea film  13  remains in the recess  12  while the polyurea film  13  is entirely removed in the outside of the recess  12  so as to expose a front surface of the layer  11 . For example, by repeating a cycle including the formation of the polyurea film  13  and the removal of the front surface portion of the polyurea film  13 , the polyurea film  13  is repeatedly deposited in the recess  12 . A film thickness of the polyurea film  13  is increased until the front surface of the polyurea film  13  reaches a desired height.  FIG. 1B  illustrates an example in which the polyurea film  13  is formed such that the height of the front surface thereof is equal to the outer height of the recess  12 . 
     After the above cycle has been performed a predetermined number of times, a film-forming gas for forming a cap film is supplied to the front surface of the wafer W so that a cap film  14  as a coating film is formed so as to cover the front surface of the wafer W. More specifically, the cap film  14  is formed so as to come into contact with the outside of the recess  12  in the layer  11  and the front surface of the polyurea film  13  and to close the recess  12  ( FIG. 1C ). The cap film  14  is made of, for example, SiO 2 . In order to remove the polyurea film  13  remaining in a gas state and a residue generated from the polyurea film  13  from the recess  12  as will be described later, the cap film  14  has a permeability to the gas. A thickness H 1  of the cap film  14  is set to, for example, 10 nm or less so as to have such a gas permeability. In addition, the cap film  14  has transparency to vacuum ultraviolet light (VUV) and relatively high resistance to radicals generated by the VUV (described later) so that the residue can be removed. For example, the gas permeability of the cap film  14  to an oxygen gas used for removing the residue is 1 g/m 2  day or less at normal temperature and in normal pressure atmosphere. 
     After the formation of the cap film  14 , the wafer W is heated to a predetermined temperature, for example, a temperature of 350 degrees C. or higher, so that the polyurea film  13  serving as a sacrificial film is depolymerized and gasified. The generated gas passes through the cap film  14  and is removed from the interior of the recess  12 . By removing the polyurea film  13  from the interior of the recess  12  in this manner, a sealed space  15  is formed as an empty hole surrounded by the recess  12  and the cap film  14 . This sealed space  15  constitutes the air gap described above. While the sealed space  15  is formed in this manner, a portion of the polyurea film  13  is altered to produce an organic residue  16 . The residue  16  remains in the sealed space  15  as, for example, solid foreign matter ( FIG. 1D ). 
     Subsequently, in a state in which the wafer W is heated to, for example, 100 degrees C. to 300 degrees C., for example, an oxygen (O 2 ) gas is supplied to the wafer W as a processing gas for removing the residue  16 , and the front surface of the wafer W is irradiated with, for example, VUV having a wavelength of 172 nm. The O 2  gas passes through the cap film  14  and diffuses in the sealed space  15 . In addition, the VUV is also supplied to the sealed space  15  through the cap film  14 . The O 2  gas, which has diffused in the sealed space  15 , is activated by receiving energy from the VUV. Specifically, oxygen radicals and an ozone gas are generated from O 2  gas. The ozone gas is further decomposed to generate oxygen radicals. The arrows in  FIG. 2A  denote VUV, reference numeral  21  denotes the oxygen gas before activation, and reference numeral  22  denotes the oxygen gas after activation, that is, the oxygen radicals. The oxygen radicals  22  thus generated in the sealed space  15  react with the residue  16 , and the residue  16  is decomposed into water and gases having a relatively small molecular weight, such as carbon dioxide and carbon monoxide. These gases pass through the cap film  14  and are removed from the sealed space  15 . 
     In a case where a partial pressure of the O 2  gas around the wafer W during the above-mentioned VUV irradiation is too low, the amount of generated oxygen radicals is small. Thus, the residue may not be sufficiently removed. Meanwhile, in a case where the partial pressure of the O 2  gas is too high, the amount of VUV to be supplied to the sealed space  15  decreases by being absorbed by the O 2  gas around the wafer W before reaching the sealed space  15 . Thus, the activation effect of the O 2  gas in the sealed space  15  may be weakened. Therefore, as shown in an evaluation test described later, the partial pressure of the O 2  gas around the wafer W during the VUV irradiation may be set to, for example, 1.33×10 3  Pa (10 Torr) to 2.66×10 3  Pa (20 Torr). After the residue  16  is decomposed and removed from the sealed space  15 , the supply of the O 2  gas to the wafer W and the VUV irradiation are stopped, and a series of processes are terminated ( FIG. 2B ). 
     Meanwhile, in removing the residue  16 , it is assumed that, instead of generating the radicals in the sealed space  15  by the VUV irradiation and the supply of the O 2  gas described with reference to  FIG. 2A , radicals were supplied from the outside of the sealed space  15 . However, the radicals generated outside the sealed space  15  are deactivated while passing through the cap film  14  and hardly act on the residue  16 . In addition, it is conceivable to radiate VUV without supplying the O 2  gas to the sealed space  15 , that is, to remove the residue  16 , which is an organic substance, only by the action of VUV without relying on the action of radicals. However, as shown in the evaluation test described later, it is impossible to obtain a sufficient decomposition rate. 
     However, according to the processes described in the above embodiment, after forming the cap film  14 , the polyurea film  13  is gasified and removed from the recess  12  through the cap film  14  by heating, so that the O 2  gas can be supplied into the recess  12  (the sealed space  15 ). Then, after the O 2  gas is supplied into the sealed space  15 , VUV is irradiated so as to generate the radicals in the sealed space  15 . Accordingly, the deactivation of radicals before the radicals acting on the residue  16  is suppressed, which makes it is possible to remove the residue  16  highly reliably and quickly. 
     In addition, by removing the residue  16  as described above, in a process following the series of processes described above, it is possible to prevent the residue  16  from being gasified and affected, for example, when the wafer W is heated. Furthermore, it is possible to prevent electrical characteristics between the wirings formed on the wafer W from being affected due to the residue  16  staying in the sealed space  15 . Therefore, according to the above embodiment, since it is possible to reliably remove the residue  16 , there is an advantage in that it is possible to improve the yield of semiconductor products manufactured from the wafer W. 
     In addition, there is another method of forming the sealed space  15  comprising forming a sacrificial film having higher selectivity to an etching gas than the layer  11  constituting the recess  12 , then forming the above-described cap film, and forming a minute hole in the cap film so as to overlap the recess  12  may be considered. After forming the hole, an etching gas is supplied into the recess  12  through the hole and diffused to remove the sacrificial film. Thereafter, a laminated film is formed on the cap film  14  by CVD such that the hole of the cap film  14  is closed. However, in such a method of forming the sealed space  15 , in order to sufficiently diffuse the etching gas in the recess  12 , the size of the recess  12 , that is, the size of the sealed space  15  may become relatively large. Therefore, according to the above embodiment, there is an advantage in that it is possible to increase a degree of freedom of the size of the sealed space  15 . 
     Meanwhile, the removal of the residue  16  after the formation of the sealed space  15  is not limited to the step illustrated in  FIG. 2A , but may be performed in other steps described below. 
       FIGS. 3A and 3B  illustrate other steps. Specifically, first, an O 2  gas is supplied to the wafer W, and a pressure around the wafer W (internal pressure of the processing chamber) is set to a second pressure, which is relatively high, for example, 1.33×10 4  Pa to 1.33×10 5  Pa. With such a pressure, the O 2  gas efficiently passes through the cap film  14  and is supplied into the sealed space  15 , and the partial pressure of the O 2  gas in the sealed space  15  becomes relatively high ( FIG. 3A ). While the pressure around the wafer W is kept at the second pressure, the VUV is difficult to reach the wafer W by being absorbed to the gas around the wafer W. Thus, the VUV irradiation is not performed. 
     Thereafter, the pressure around the wafer W is set to a first pressure lower than the second pressure, specifically, for example, 1.33×10 Pa to 1.33×10 2  Pa. The wafer W is irradiated with VUV in the state in which the gas around the wafer W is difficult to absorb the VUV due to the decrease in the pressure. At this time, since the partial pressure of the O 2  gas in the sealed space  15  is high as described above, a relatively large number of oxygen radicals  22  are generated, and the residue  16  is more reliably removed ( FIG. 3B ). A difference between the first pressure and the second pressure is, for example, 10 Torr or more. 
     Next, a substrate processing apparatus  3 , which is an embodiment of an apparatus for performing the series of processes illustrated in  FIGS. 1A to 1D ,  FIGS. 2A and 2B  will be described with reference to a plan view of  FIG. 4 . The substrate processing apparatus  3  may perform the process described with reference to  FIGS. 3A and 3B  instead of the process illustrated in  FIGS. 2A and 2B . The substrate processing apparatus  3  includes a normal-pressure transfer chamber  31 , of which the internal atmosphere is set to a normal pressure atmosphere by, for example, dried nitrogen gas. In front of the normal-pressure transfer chamber  31 , loading/unloading ports  32 , each of which is configured to place a carrier C that stores the wafer W therein, are arranged side by side in the left-right direction. Doors  33 , which are respectively opened/closed together with covers of the carriers C, are provided on the front wall of the normal-pressure transfer chamber  31 . Inside the normal-pressure transfer chamber  31 , a first transfer mechanism  34  including an articulated arm for transferring the wafer W is provided. In addition, on the left side wall of the normal-pressure transfer chamber  31  when viewed from the side of the loading/unloading ports  32 , an alignment chamber  35  is provided to adjust the orientation or eccentricity of the wafer W. 
     On the opposite side of the loading/unloading ports  32  in the normal-pressure transfer chamber  31 , for example, two load-lock chambers  36 A and  36  B are disposed so as to be arranged on the left and right. Gate valves  37  are provided between the load-lock chambers  36 A and  36 B and the normal-pressure transfer chamber  31 . A vacuum transfer chamber  38  is arranged via gate valves  39  on the rear side of the load-lock chambers  36 A and  36 B when viewed from the side of the normal-pressure transfer chamber  31 . 
     A polyurea film formation module  5 A, an annealing module  5 B, a cap film formation module  5 C, an annealing module  5 D, and a VUV irradiation module  5 E are connected to the vacuum transfer chamber  38  via gate valves  41 , respectively. The annealing module  5 B is a module that removes an unnecessary portion of the front surface of the polyurea film  13  by heating the wafer W as described above in the filling of the recess  12  with the polyurea film  13 . The annealing module  5 D is a module that removes the polyurea film  13  by heating the wafer W after the formation of the cap film  14 . The vacuum transfer chamber  38  is provided with a second transfer mechanism  42  having two transfer arms configured as articulated arms. The second transfer mechanism  42  delivers the wafers W among the load-lock chambers  36 A and  36 B, the polyurea film formation module  5 A, the annealing modules  5 B and  5 D, the cap film formation module  5 C, and the VUV irradiation module  5 E. 
       FIG. 5  illustrates the polyurea film formation module  5 A. For example, the polyurea film formation module  5 A supplies each of a first film-forming gas containing H6XDA (1,3-bis (aminomethyl) cyclohexane) as diamine, and a second film-forming gas containing H6XDI (1,3-bis (isocyanatomethyl) cyclohexane) as diisocyanate to the wafer W. The polyurea film  13  is formed by vapor deposition polymerization of the H6XDA and H6XDI on the front surface of the wafer W. 
     In  FIG. 5 , reference numeral  51  denotes a processing container, and reference numeral  52  denotes an exhaust mechanism configured to exhaust the interior of the processing container  51  so as to form a vacuum atmosphere. In  FIG. 5 , reference numeral  53  denotes a stage configured to place the wafer W thereon. The stage  53  is provided with a heater for heating the wafer W placed thereon to an appropriate temperature during film formation. In  FIG. 5 , reference numeral  54  denotes a shower head provided to face the stage  53 . In  FIG. 5 , reference numeral  55  denotes a gas supply mechanism  55  connected to the shower head  54 . The gas supply mechanism  55  performs supply and cutoff of various gases with respect to the shower head  54  based on a control signal outputted from a controller  30  to be described later. A large number of ejection holes are formed in a lower surface of the shower head  54 . Each gas supplied from the gas supply mechanism  55  to the shower head  54  is ejected from each ejection hole toward the wafer W on the stage  53 . 
     In the state in which the wafer W placed on the stage  53  is heated to a predetermined temperature, the gas supply mechanism  55  performs a cyclic operation of sequentially supplying, for example, the first film-forming gas, a nitrogen (N 2 ) gas, the second film-forming gas, and a N 2  gas, so that the polyurea film  13  is formed on the wafer W. In addition, the N 2  gas supplied in this cyclic operation is a purge gas for removing unnecessary first film-forming gas and second film-forming gas inside the processing container  51 . 
     Although the annealing modules  5 B and  5 D and the cap film formation module  5 C are not illustrated, these modules have substantially the same configuration as, for example, the polyurea film formation module  5 A. In the annealing modules  5 B and  5 D, the wafer W placed on the stage  53  is heated and annealed in the state in which the N 2  gas is supplied from the shower head  54  and the interior of the processing container  51  is in the N 2  gas atmosphere. In the cap film formation module  5 C, the cap film  14  is formed on the wafer W by CVD by ejecting a film-forming gas for forming the cap film from the shower head  54  instead of the first film-forming gas and the second film-forming gas described above. The cap film formation module  5 C constitutes a coating film formation part, and the annealing module  5 D constitutes a heating part. 
       FIG. 6  illustrates the VUV irradiation module  5 E constituting a gas supply part and a light irradiation part. The VUV irradiation module  5 E includes a processing container  51 , an exhaust mechanism  52 , and a stage  53 , like the polyurea film formation module  5 A. In addition, the exhaust mechanism  52  includes, for example, a valve having a variable opening degree, and a pump configured to exhaust the interior of the processing container  51  via the valve. The degree of opening of the valve constituting the exhaust mechanism  52  varies in response to a control signal outputted from the controller  30  described later. The amount of gas exhausted from the processing container  51  varies depending on the variation in the degree of opening of the valve, so that the internal pressure of the processing container  51  is adjusted. A VUV light source  61  is provided inside the processing container  51  so as to face the stage  53 . Thus, the wafer W on the stage  53  can be irradiated with the VUV through the window  62 . 
     The VUV irradiation module  5 E is provided with a nozzle  63  for ejecting gas into the processing container  51 . One end of a pipe  64  is connected to the nozzle  63 , and the other end of the pipe  64  is branched and connected to each of a N 2  gas supply mechanism  65  and an O 2  gas supply mechanism  66 . Based on a control signal outputted from the controller  30 , the N 2  gas supply mechanism  65  and the O 2  gas supply mechanism  66  respectively perform supply and cutoff of the N 2  gas and the O 2  gas with respect to the nozzle  63 . 
     In the state in which the wafer W placed on the stage  53  is heated to a predetermined temperature and the N 2  gas and the O 2  gas are supplied into the processing container  51 , VUV is irradiated from the light source  61  to the wafer W so as to perform the removal of the residue  16  by the oxygen radicals described above with reference to  FIG. 2A . When the light irradiation is performed in this manner, the N 2  gas and the O 2  gas are supplied from the nozzle  63  such that the partial pressure of the O 2  gas inside the processing container  51  has a value within the range described above. 
     The VUV irradiation module  5 E is also capable of performing the process described with reference to  FIGS. 3A and 3B . In the case of performing the process of  FIGS. 3A and 3B  as described above, the N 2  gas and the O 2  gas are supplied into the processing container  51  from the nozzle  63  in the state in which the internal pressure of the processing container  51  is set to the relatively high second pressure by the exhaust mechanism  52 . Then, when the internal pressure of the processing container  51  is reduced to the first pressure by the exhaust mechanism  52 , the VUV irradiation is performed on the wafer W heated to a predetermined temperature, and thus the residue  16  is removed. 
     Referring back to  FIG. 4 , the substrate processing apparatus  3  includes the controller  30 , which is a computer. The controller  30  includes a program, a memory, and a CPU. The program may be stored in a non-transitory computer-readable storage medium, such as a compact disc, a hard disc, a magneto-optical disc, a memory card, or a DVD, and may be installed on the controller  30 . The controller  30  outputs a control signal to each part of the substrate processing apparatus  3  according to the program, and controls the operation of each part. Specifically, the program incorporates a group of steps so as to control the operation of each transfer mechanism, the opening and closing of the gate valves  37 ,  39 , and  41  and the doors  33 , the operation of each module, and the like in the substrate processing apparatus  3 , and execute the series of processes described above with respect to the wafer W. 
     The operations in the substrate processing apparatus  3  and the transfer path of the wafer W will be described. When the carrier C accommodating the wafer W whose front surface is formed as described with reference to  FIG. 1A , is placed on the loading/unloading port  32 , the first transfer mechanism  34  takes out the wafer W from the carrier C. Then, the wafer W is sequentially transferred to the normal-pressure transfer chamber  31 , the alignment chamber  35 , and the load-lock chamber  36 A. Thereafter, the wafer W is repeatedly transferred between the polyurea film formation module  5 A and the annealing module  5 B by the second transfer mechanism  42  so that the formation of the above-described polyurea film  13  and the removal of the portion of the front surface of the polyurea film  13  are repeatedly performed. Thus, the polyurea film  13  is formed in the recess  12  as illustrated in  FIG. 2B . 
     Thereafter, the wafer W is transferred by the second transfer mechanism  42  to the cap film formation module  5 C where the cap film  14  is formed as illustrated in  FIG. 1C . Subsequently, the wafer W is transferred to the annealing module  5 D where the polyurea film  13  is removed and the sealed space  15  is formed, as described above with reference to  FIG. 1D . Subsequently, the wafer W is transferred by the second transfer mechanism  42  to the VUV irradiation module  5 E where the residue  16  is removed as described above with reference to  FIGS. 2A and 2B . The residue  16  may be removed as described with reference to  FIGS. 3A and 3B . The wafer W from which the residue  16  has been removed is sequentially transferred to the vacuum transfer chamber  38  and the load-lock chamber  36 B by the second transfer mechanism  42 , and is returned to the carrier C by the first transfer mechanism  34 . 
     Incidentally, the layer  11  forming the recess  12  is not limited to being made of SiO 2 , but may be made of, for example, silicon nitride (SiN). The cap film  14  may be made of any material as long as it has light transparency and gas permeability so as to enable the residue  16  to be removed and has relatively highly resistant to radicals generated for removing the residue  16 . That is, the cap film  14  may be made of an inorganic oxide other than the silicon oxide (SiO 2 ). Specifically, the cap film  14  may be made of, for example, aluminum oxide (Al 2 O 3 ) or titanium oxide (TiO 2 ). 
     The processing gas supplied to the sealed space  15  in order to remove the residue  16  is not limited to the oxygen gas, as long as the processing gas is capable of generating radicals for decomposing organic substances as described above. For example, the processing gas may be a gas of a compound that contains oxygen as a constituent element, such as water or ozone, and generates oxygen radicals in the same manner as the oxygen gas. In addition, an example of the radicals that decompose organic substances may include halogen radicals. Therefore, the processing gas may be a gas containing a compound composed of a halogen. Specifically, for example, a fluorine gas or a chlorine gas may be used as the processing gas. 
     In addition, the light to be radiated to the wafer W is not limited to VUV but may be any light as long as it is able to propagate in a vacuum atmosphere, pass through the cap film  14 , and generate radicals in the sealed space  15 . In some embodiments, VUV having a wavelength of 10 nm to 200 nm may be used because it has high transmittance to the cap film  14 , and easily activates the processing gas by applying high energy to the processing gas. 
     The technology described herein is not limited to the embodiment described above, and various modifications, omissions, and substitutions can be made within the scope of the present disclosure. For example, in the above-described embodiment, polyurea was used as a material for forming the sacrificial film, but other organic materials may be used as long as they are thermally-decomposable organic materials. Example of the thermally-decomposable organic materials may include polyurethane, acrylic resin, polyolefin, polycarbonate, polyamide, phenol resin, or a thermally-vaporizable low molecular material, in addition to the polyurea. In addition, the thermally-decomposable organic material may be buried in each recess of a workpiece (substrate) by applying a processing liquid containing the organic material. Further, the cap film  14  may be similarly formed by applying a processing liquid. 
     Although H6XDA and H6XDI are illustrated as examples of materials for forming the polyurea film  13 , the present disclosure is not limited to these materials. For example, the polyurea film  13  may be formed using another known material. In addition, the configuration of the substrate processing apparatus  3  is an example, and is not limited to thereto. For example, each of the annealing modules  5 B and  5 D may be provided with the light source  61  as in the VUV irradiation module  5 E, and may be configured to heat the wafer W by radiating, for example, infrared rays from the light source  61  instead of VUV. In addition, although the polyurea film formation module  5 A for forming a polyurea film has been described to separately supply the first film-forming gas and the second film-forming gas to the wafer W so as to perform film formation, the present disclosure is not limited thereto. As an example, the first film-forming gas and the second film-forming gas may be simultaneously supplied to the wafer W so as to perform the film formation. 
     Evaluation Tests 
     Next, evaluation tests performed in relation to the embodiments described above will be described. 
     Evaluation Test 1 
     As described above with reference to  FIGS. 1A to 1D , the formation of the polyurea film  13  in the recess  12  of the wafer W, the formation of the cap film  14  as SiO 2 , and the annealing process of removing the polyurea film  13  were performed. In such series of processes, after the formation of the cap film  14  and before the annealing process, and after the annealing process, images of vertical cross sections of the wafer W were obtained using a scanning electron microscope (SEM). In addition, the front surface of the wafer W before the annealing process and the front surface of the wafer W after the annealing process were analyzed by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectric spectroscopy (XPS). In the above series of processes, the polyurea film  13  was formed in the recess  12  such that the front surface of the polyurea film  13  is lower than the height outside the recess  12 , and the cap film  14  was formed to have a thickness of 2 nm. 
       FIGS. 7 and 8  are schematic views illustrating images obtained from the wafer W before the annealing process and the wafer W after the annealing process, respectively. As illustrated in these schematic views, it was confirmed that the polyurea film  13  is removed and the sealed space  15  is formed by performing the annealing process. No residue  16  was confirmed in the sealed space  15  from the images. As illustrated in  FIGS. 7 and 8 , the cross-sectional shapes of the cap film  14  before and after the annealing process were different from each other. 
     Comparing infrared absorption spectra (not illustrated) obtained from the wafer W before the annealing process and the wafer W after the annealing process by FT-IR, peaks of absorbance appear at the same wavelength. That is, the presence of the residue  16  after the annealing process was not confirmed from the FT-IR. 
     However, the presence of the residue  16  was confirmed from the analysis results by XPS. Describing the XPS analysis method in detail, SiO 2  constituting the front surface of the wafer W was etched by 10 nm for 100 sec. Therefore, the etching rate was 0.1 nm/sec. A measurement was performed in each cycle with 5 seconds during this etching as one cycle. In a graph of  FIG. 9 , for the sake of avoiding complexity of illustration due to overlapping of waveforms, only the spectrum of a first cycle is displayed. The vertical axis of the graph represents photoelectron emission intensity, and the horizontal axis of the graph represents bonding energy (unit: eV). Looking at the waveform of the graph, a relatively small peak corresponding to the residue  16  for C1s appears around 285 eV. The C1s peaks became smaller in the later cycles. 
     Evaluation Test 2 
     In Evaluation Test 2, the formation of the polyurea film  13  in the recess  12  of the wafer W, the formation of the cap film  14 , and the annealing process of removing the polyurea film  13  were sequentially performed, as in Evaluation Test 1. Thereafter, unlike Evaluation Test 1, the wafer W thus annealed was accommodated in the processing container, heated to 150 degrees C., and air and N 2  gas were supplied into the processing container, and the internal pressure of the processing container was set to 200 Torr (2.66×10 4  Pa). In such a state, the wafer W was irradiated with VUV for 5 minutes, and the XPS-based analysis was performed in the same manner as in Evaluation Test 1. Each of the flow rates of the N 2  gas and the air supplied into the processing container was set to 1 slm. 
     A graph of  FIG. 10  shows the results of Evaluation test 2. As in the graph of  FIG. 9 , the vertical axis and the horizontal axis represent photoelectron emission intensity and bonding energy, respectively. In the graph of  FIG. 10 , no C1s peak was observed in the vicinity of 285 eV. The graph of  FIG. 10  shows only the spectrum of the first cycle, as in the graph of  FIG. 9 , but C1s peaks were not observed in the spectra of other cycles, similarly to the spectra of the first cycle. 
     From the results of Evaluation Tests 1 and 2, it can be seen that the residue  16  generated from the polyurea film  13  slightly remains on the wafer W after the polyurea film  13  was removed by the annealing process. Then, it was confirmed that the residue  16  was removed by performing both the supply of oxygen around the wafer W and the VUV irradiation. Therefore, the effects of the above embodiment were confirmed by Evaluation Tests 1 and 2. 
     Evaluation Test 3 
     In Evaluation Test 3 (3-1 to 3-8), a process of heating the wafer W having a polyurea film formed on the front surface thereof at 150 degrees C. inside the processing container and irradiating the front surface of the wafer W with VUV was performed. This process was performed on the plurality of wafers W. In processing each wafer W, the N 2  gas alone, or both the N 2  gas and air were supplied into the processing container. In addition, for each wafer W, the process was performed while changing the combination of the flow rate of the gas to be supplied into the processing container, the total internal pressure of the processing container, the partial pressure of oxygen, and the processing time. Then, for each of the processed wafers W, a film thickness maintenance rate of the polyurea film (film thickness after the process/film thickness before the process)×100 was calculated. The processing conditions of each of Evaluation Tests 3-1 to 3-8 are as below. Each of Evaluation Tests 3-1 to 3-8 was performed by setting the processing time of the wafer W to 1 minute, 3 minutes, or 5 minutes. 
     In Evaluation Test 3-1, the flow rate of the N 2  gas was set to 0.1 slm, and the total internal pressure of the processing container was set to 0.4 Torr (53.3 Pa). In Evaluation Test 3-2, the flow rate of the N 2  gas was set to 0.1 slm, and the total internal pressure of the processing container was set to 10 Torr (1.33×10 3  Pa). As Evaluation Test 3-3, the flow rate of the N 2  gas was set to 0.1 slm, and the total internal pressure of the processing container was set to 600 Torr (8.00×10 4  Pa). In these Evaluation Tests 3-1 to 3-3, air was not supplied into the processing container. In Evaluation Test 3-4, the flow rate of the N 2  gas was set to 0.1 slm, and the total internal pressure of the processing container was set to 10 Torr. Air was supplied such that the oxygen partial pressure in the processing container become 2 Torr (2.66×10 2  Pa). 
     In the following Evaluation Tests 3-5 to 3-8, the N 2  gas and air were supplied into the processing container. In Evaluation Test 3-5, each of the flow rates of the N 2  gas and the air was set to 1 slm, the total internal pressure of the processing container was set to 100 Torr (1.33×10 4  Pa), and the partial pressure of oxygen in the processing container was set to 10 Torr. In Evaluation Test 3-6, each of the flow rates of the N 2  gas and the air was set to 1 slm, the total internal pressure of the processing container was set to 100 Torr, and the partial pressure of oxygen in the processing container was set to 20 Torr (2.66×10 3  Pa). In Evaluation Test 3-7, each of the flow rates of the N 2  gas and the air was set to 1 slm, the total internal pressure of the processing container was set to 200 Torr (2.66×10 4  Pa), and the partial pressure of oxygen in the processing container was set to 20 Torr. In Evaluation Test 3-8, each of the flow rates of the N 2  gas and the air was set to 1 slm, the total internal pressure of the processing container was set to 600 Torr, and the partial pressure of oxygen in the processing container was set to 60 Torr (7.98×10 3  Pa). 
     The results of Evaluation Tests 3-1 to 3-4, in which the flow rate of the N 2  gas was 0.1 slm, are shown in a bar graph of  FIG. 11 , and the results of Evaluation Tests 3-5 to 3-8, in which each of the flow rates of the N 2  gas and the air was 1 slm, are shown in a bar graph of  FIG. 12 . The vertical axis of the graphs in  FIGS. 11 and 12  represent the above-mentioned film thickness maintenance rate (unit: %). In the graphs, bars without patterns, bars with diagonal lines, and bars with dots are test results obtained when the processing times were 1, 3, and 5 minutes, respectively. 
     As shown in the graphs, in all of Evaluation Tests 3-1 to 3-8, the longer the processing time, the lower the film thickness maintenance rate. That is, it can be seen that the removal of the polyurea film progresses as the processing time becomes longer. However, in Evaluation Tests 3-1 to 3-3, in which no air was supplied, the film thickness maintenance rate at each processing time was a high value of 85% or more, and the removal of the polyurea film was difficult to progress. Comparing Evaluation Tests 3-1 to 3-3 with Evaluation Test 3-4 in which air was supplied, the film thickness maintenance rate in Evaluation Test 3-4 is lower than those in Evaluation Tests 3-1 to 3-3 when the processing times were the same. Also, comparing the results of Evaluation Tests 3-5 to 3-8 in which air was supplied, with the results of Evaluation Tests 3-1 to 3-3, the film thickness maintenance rates in Evaluation Tests 3-5 to 3-8 are lower than those in Evaluation Tests 3-1 to 3-3 when the processing times were the same. 
     From these results, it can be seen that in removing the polyurea film formed on the wafer W by the VUV irradiation, the film thickness maintenance rate is high, that is, the film removal efficiency is low when air does not exist around the wafer W. It may be considered that, when air is supplied, the O 2  gas in the air is activated by VUV and acts on the polyurea film. 
     The residue  16  described in the embodiment is an organic substance similarly to the polyurea film. Thus, it is considered that the removal efficiency deteriorates unless oxygen is supplied during the VUV irradiation. Accordingly, from the results of Evaluation Test 3, it can be seen that it is difficult to completely remove the residue  16  only by the VUV irradiation in the above embodiment, and that it is effective to activate the O 2  gas supplied to the wafer W so as to remove the residue  16 , as described above. 
     Looking at the results of Evaluation Tests 3-4 to 3-8 in which air was supplied into the processing container, the film thickness maintenance rates in Evaluation test 3-4, in which the partial pressure of the oxygen gas was relatively low, and Evaluation Test 3-4, in which the partial pressure of the oxygen gas was relatively high, were high compared to those in Evaluation Tests 3-5 to 3-7. The reason that each of the film thickness maintenance rates in Evaluation Tests 3-4 and 3-8 was relatively high is believed to be due to the fact that sufficient oxygen radicals were not generated and that the partial pressure of the oxygen gas was high and thus VUV was absorbed by the oxygen gas, as described in the embodiment. Meanwhile, in Evaluation Tests 3-5 to 3-7, the film thickness maintenance rates were sufficiently low, and in Evaluation Tests 3-5 to 3-7, a favorable result was obtained in Evaluation Test 3-7 since the film thickness maintenance rate is the lowest. The detailed results of Evaluation Test 3-7 were as follows: when the processing times were 1 minute, 3 minutes, and 5 minutes, the removal rates of polyurea films (removed film thickness/processing time) were 45 nm/min, 28 nm/min and 21 nm/min, respectively. 
     From the results of Evaluation Tests 3-4 to 3-8, it can be seen that there is an appropriate range for the partial pressure of the oxygen gas around the wafer W during the light irradiation. Since Evaluation Tests 3-5 to 3-7 showed good results, it can be seen that the oxygen partial pressure is preferably set to 10 Torr (1.33×10 3  Pa) to 20 Torr (2.66×10 3  Pa). As described above, Evaluation Test 3-7, in which the oxygen partial pressure was set to 20 Torr, showed a more preferable film thickness maintenance rate, but Evaluation Test 3-6, in which the oxygen partial pressure was lower by 10 Torr, also showed a favorable result. Therefore, it is considered that it is possible to obtain a high removal rate even when the oxygen partial pressure is set to 30 Torr (3.99×10 3  Pa), which is higher than 20 Torr by 10 Torr. Therefore, it is considered that the oxygen partial pressure is preferably set to a value of 10 Torr to 30 Torr. 
     According to the present disclosure in some embodiments, when forming a sealed space surrounded by a recess and a film formed on the recess in a substrate, it is possible to prevent foreign matter from remaining in the sealed space. 
     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.