Patent Publication Number: US-2023162977-A1

Title: Substrate processing method and substrate processing apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to a substrate processing method and a substrate processing apparatus. 
     BACKGROUND 
     For example, a substrate processing apparatus that embeds a film in a substrate having irregularities formed therein is known. 
     Patent Document 1 discloses a method for forming a silicon-containing film with which a silicon-containing film is filled in a depression formed on a surface of a substrate, the method including a first film-forming cycle including a first silicon adsorption step of supplying a silicon-containing gas to the substrate and causing the silicon-containing gas to be adsorbed in the depression, a silicon etching step of supplying an etching gas to the substrate and etching a portion of a silicon component of the silicon-containing gas adsorbed in the depression, and a first silicon-containing film deposition step of supplying a reaction gas that reacts with the silicon component to the substrate, causing the reaction gas to react with the silicon component remaining adsorbed in the depression after etching to produce a reaction product, and depositing a silicon-containing film in the depression. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese laid-open publication No. 2017-11136 
     The present disclosure provides some embodiments of a substrate processing method and a substrate processing apparatus, wherein a silicon oxide film is favorably embedded. 
     SUMMARY 
     According to an embodiment of the present disclosure, there is provided a substrate processing method, including forming a silicon oxide film by repeating a cycle a plurality of times, the cycle including: forming an adsorption layer by supplying a silicon-containing gas to a substrate having a depression formed therein and causing the silicon-containing gas to be adsorbed on the substrate; etching at least a portion of the adsorption layer by supplying a shape control gas to the substrate; and supplying an oxygen-containing gas to the substrate and causing the oxygen-containing gas to react with the adsorption layer, wherein a temperature of the substrate is 400° C. or lower. 
     According to some embodiments of the present disclosure, it is possible to provide a substrate processing method and a substrate processing apparatus, wherein a silicon oxide film is favorably embedded. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram illustrating a configuration example of a substrate processing apparatus. 
         FIG.  2    is an example of a time chart showing a film-forming process of a SiO 2  film by a substrate processing apparatus. 
         FIG.  3 A  is an example of a schematic cross-sectional view of a substrate W in each step of the film-forming process. 
         FIG.  3 B  is an example of a schematic cross-sectional view of the substrate W in each step of the film-forming process. 
         FIG.  3 C  is an example of a schematic cross-sectional view of the substrate W in each step of the film-forming process. 
         FIG.  4    is a cross-sectional view illustrating a relationship between a process temperature and a film shape of the SiO 2  film. 
         FIG.  5    is a flowchart showing an example of embedding process of the SiO 2  film. 
         FIG.  6 A  is a schematic diagram describing another embedding method of the SiO 2  film. 
         FIG.  6 B  is a schematic diagram describing another embedding method of the SiO 2  film. 
         FIG.  6 C  is a schematic diagram describing another embedding method of the SiO 2  film. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments in which the present disclosure are implemented will be described with reference to the drawings. In each figure, the same components may be designated with the same reference numerals, and duplicated descriptions may be omitted. 
     Substrate Processing Apparatus 
     A substrate processing apparatus  100  in accordance with the present embodiment will be described using  FIG.  1   .  FIG.  1    is a schematic diagram illustrating a configuration example of a substrate processing apparatus  100 . Further, the substrate processing apparatus  100  is a film-forming apparatus that forms a SiO 2  film on a substrate W having a depression such as a trench, and embeds the SiO 2  film in the depression. 
     The substrate processing apparatus  100  includes a process container  1  formed in a shape of a cylindrical body having a ceiling with an open lower end. The entire process container  1  is formed of, for example, quartz. A ceiling plate  2  formed of quartz is installed in the vicinity of an upper end in the process container  1 , and the region below the ceiling plate  2  is sealed off. A metal manifold  3  formed in a shape of a cylindrical body is connected to the lower end opening of the process container  1  via a sealing member  4  such as an O-ring. 
     The manifold  3  supports the lower end of the process container  1 , and a wafer boat  5  loaded with a number of sheets (e.g., 25 to 150 sheets) of semiconductor wafers (hereinafter referred to as “substrate W”) as substrates in multiple stages is inserted into the process container  1  from below the manifold  3 . In this manner, a number of sheets of substrates W are accommodated substantially horizontally at intervals along a vertical direction in the process container  1 . The wafer boat  5  is formed of, for example, quartz. The wafer boat  5  has three rods  6  (two are shown in  FIG.  1   ), and a number of sheets of substrates W are supported by grooves (not shown) formed in the rods  6 . 
     The wafer boat  5  is placed on a table  8  via a heat insulating tube  7  formed of quartz. The table  8  is supported on a rotating shaft  10  that passes through a metal (stainless steel) cover  9  that opens and closes the lower end opening of the manifold  3 . 
     A magnetic fluid seal  11  is installed at a penetration portion of the rotating shaft  10  to thereby hermetically seal and rotatably support the rotating shaft  10 . A sealing member  12  that maintains airtightness in the process container  1  is provided between a peripheral portion of the cover  9  and the lower end of the manifold  3 . 
     The rotating shaft  10  is attached to a tip of an arm  13  supported by a elevating mechanism (not shown) such as, for example, a boat elevator, and the wafer boat  5  and the cover  9  move up and down integrally and are inserted into and separated from an inside of the process container  1 . In addition, the table  8  may be fixed to the cover  9  such that the substrates W may be processed without rotating the wafer boat  5 . 
     Further, the substrate processing apparatus  100  includes a gas supply  20  that supplies predetermined gases, such as a processing gas and a purge gas, into the process container  1 . 
     The gas supply  20  includes gas supply pipes  21 ,  22 ,  23 , and  24 . The gas supply pipes  21  to  23  are formed of, for example, quartz, and pass through a side wall of the manifold  3  inward, bend upward, and extend vertically. In vertical portions of the gas supply pipes  21  to  23 , a plurality of gas holes  21   g  to  23   g  are formed at predetermined intervals over a length in the vertical direction corresponding to a wafer support range of the wafer boat  5 . The respective gas holes  21   g  to  23   g  discharge gases in a horizontal direction. The gas supply pipe  24  is formed of, for example, quartz, and is made of a short quartz pipe provided through the side wall of the manifold  3 . 
     The gas supply pipe  21  is installed such that a vertical portion (a vertical portion where the gas hole  21   g  is formed) of the gas supply pipe  21  is provided in the process container  1 . A processing gas is supplied to the gas supply pipe  21  from a gas supply source  22   a  via gas piping. The gas piping is provided with a flow controller  21   b  and an on-off valve  21   c . As a result, the processing gas from the gas supply source  21   a  is supplied into the process container  1  via the gas piping and the gas supply pipe  21 . 
     The gas supply pipe  22  is installed such that a vertical portion (a vertical portion where the gas hole  22   g  is formed) of the gas supply pipe  22  is provided in the process container  1 . The processing gas is supplied to the gas supply pipe  22  from the gas supply source  22   a  via the gas piping. The gas piping is provided with a flow controller  22   b  and an on-off valve  22   c . As a result, the processing gas from the gas supply source  22   a  is supplied into the process container  1  via the gas piping and the gas supply pipe  22 . 
     The gas supply pipe  23  is installed such that a vertical portion (a vertical portion where the gas hole  23   g  is formed) of the gas supply pipe  23  is provided in the process container  1 . The processing gas is supplied to the gas supply pipe  23  from the gas supply source  23   a  via the gas piping. The gas piping is provided with a flow controller  23   b  and an on-off valve  23   c . As a result, the processing gas from the gas supply source  23   a  is supplied into the process container  1  via the gas piping and the gas supply pipe  23 . 
     Here, the gas supply source  21   a  supplies a raw material gas containing Si. As the raw material gas, for example, an aminosilane-based gas such as diisopropylaminosilane (DIPAS) may be used. In addition, the raw material gas containing Si is not limited to organic aminosilane, but inorganic silanes, higher-order silanes, and silanols may also be used. 
     The gas supply source  22   a  supplies a shape control gas to be described later. As the shape control gas, for example, chlorine gas (Cl 2  gas) may be used. Further, as the shape control gas, F 2  or CIF 3  gas is also suitable and plasma to which RF is applied may also be used. 
     The gas supply source  23   a  supplies an oxidizing gas. As the oxidizing gas, for example, ozone gas (O 3  gas) may be used. In addition, as the oxidizing gas, O 2  or H 2 O, H 2  and H 2  mixed gases, and the like, may be used, and it may be a radical by RF application or the like. 
     The gas supply pipe  24  is supplied with a purge gas from a purge gas supply source (not shown) via the gas piping. The gas piping (not shown) is provided with a flow controller (not shown) and an on-off valve (not shown). As a result, the purge gas from the purge gas supply source is supplied into the process container  1  via the gas piping and the gas supply pipe  24 . As the purge gas, an inert gas such as, for example, argon (Ar) or nitrogen (N 2 ) may be used. Moreover, although the case where the purge gas is supplied into the process container  1  via the gas piping and the gas supply pipe  24  from the purge gas supply source has been described, the present disclosure is not limited thereto, and the purge gas may be supplied from any of the gas supply pipes  21 ,  22 , and  23 . 
     An exhaust port  40  configured to vacuum-exhaust an interior of the process container  1  is installed at a portion of a side wall of the process container  1  opposite a position where the gas supply pipes  21  to  23  are arranged. The exhaust port  40  is formed to be elongated vertically in correspondence to the wafer boat  5 . An exhaust port cover member  41  formed in a U-shape in cross section so as to cover the exhaust port  40  is provided at a portion of the process container  1  corresponding to the exhaust port  40 . The exhaust port cover member  41  extends upward along the side wall of the process container  1 . An exhaust pipe  42  configured to exhaust the process container  1  through the exhaust port  40  is connected to a lower portion of the exhaust port cover member  41 . A pressure control valve  43  that controls a pressure in the process container  1  and an exhaust apparatus  44  including a vacuum pump and the like are connected to the exhaust pipe  42 , and the interior of the process container  1  is exhausted by the exhaust apparatus  44  through the exhaust pipe  42 . 
     In addition, a heating mechanism  50  formed in a shape of a cylindrical body and configured to heat the process container  1  and the substrates W therein is provided to surround an outer periphery of the process container  1 . 
     In addition, the substrate processing apparatus  100  includes a controller  60 . The controller  60  controls, for example, an operation of each component of the substrate processing apparatus  100 , for example, supply/stop of each gas by opening/closing the on-off valves  21   c  to  23   c , control of the gas flow rate by the flow controllers  21   b  to  23   b , and exhaust control by the exhaust apparatus  44 . Moreover, the controller  60  controls the temperature of the substrates W by the heating mechanism  50 , for example. 
     The controller  60  may be, for example, a computer or the like. Further, program of a computer that performs the operation of each component of the substrate processing apparatus  100  is stored in a storage medium. The storage medium may be, for example, a flexible disk, a compact disk, a hard disk, a flash memory, a DVD, or the like. 
     Embedding of SiO 2  Film 
     Next, an example of substrate processing by the substrate processing apparatus  100  shown in  FIG.  1    will be described.  FIG.  2    is an example of a time chart showing a film-forming process of a SiO 2  film by the substrate processing apparatus  100 . Here, the substrate processing apparatus  100  forms the SiO 2  film on the substrate W and thereby embeds the SiO 2  film in a depression such as a trench formed on the surface of the substrate W. 
     The film-forming process shown in  FIG.  2    is a process of embedding an SiO 2  film in a depression formed on the surface of the substrate W by repeating a cycle a predetermined number of times, the cycle including step S 101  of supplying a raw material gas to the substrate W whose temperature has been adjusted to a predetermined temperature, step S 102  of purging, step S 103  of supplying a shape control gas, step S 104  of purging, step S 105  of supplying an oxidizing gas, and step S 106  of purging. Further,  FIG.  2    shows only one cycle. Moreover, in steps S 101  to S 106 , N 2  gas that is the purge gas is constantly (continuously) supplied from the gas supply pipe  24  during the film-forming process. 
     Step S 101  of supplying a raw material gas is a step of supplying the raw material gas containing Si (shown as Si in  FIG.  2   ) into the process container  1 . In step S 101  of supplying the raw material gas, the raw material gas is supplied into the process container  1  from the gas supply source  21   a  via the gas supply pipe  21  by opening the on-off valve  21   c . 
     Step S 102  of purging is a step of purging the excess raw material gas or the like in the process container  1 . In step S 102  of purging, the supply of the raw material gas is stopped by closing the on-off valve  21   c . As a result, the purge gas constantly supplied from the gas supply pipe  24  purges the excess raw material gas and the like in the process container  1 . 
     Step S 103  of supplying the shape control gas is a step of supplying the shape control gas into the process container  1 . In step S 103  of supplying the shape control gas, the shape control gas is supplied into the process container  1  from the gas supply source  22   a  via the gas supply pipe  22  by opening the on-off valve  22   c . 
     Step S 104  of purging is a step of purging the excess shape control gas or the like in the process container  1 . In step S 104  of purging, the supply of the shape control gas is stopped by closing the on-off valve  22   c . As a result, the purge gas constantly supplied from the gas supply pipe  24  purges the excess shape control gas and the like in the process container  1 . 
     Step S 105  of supplying an oxidizing gas is a step of supplying the oxidizing gas into the process container  1 . In step S 105  of supplying the oxidizing gas, the oxidizing gas is supplied into the process container  1  from the gas supply source  21   a  via the gas supply pipe  21  by opening the on-off valve  21   c . 
     Step S 106  of purging is a step of purging the excess oxidizing gas or the like in the process container  1 . In step S 106  of purging, the supply of the oxidizing gas is stopped by closing the on-off valve  21   c . As a result, the purge gas constantly supplied from the gas supply pipe  24  purges the excess oxidizing gas and the like in the process container  1 . 
     By repeating the cycle described above, a SiO 2  film is formed on the substrate W, and the SiO 2  film is embedded in the depression of the surface of the substrate W. 
     Here, a preferable range of a film-forming condition in the film-forming process are presented below. 
     Substrate temperature: lower than 400° C. (more preferably, 300 to 350° C.) 
     Pressure: 0.1 to 9 Torr   Raw material gas flow rate: 50 to 1000 sccm   Shape control gas flow rate: 0.5 to 5000 sccm   Oxidizing gas flow rate: 500 to 10000 sccm   N 2  gas flow rate: 50 to 5000 sccm   Step S 101  time: 2 to 30 seconds   Step S 102  time: 2 to 30 seconds   Step S 103  time: 0.5 to 10 seconds   Step S 104  time: 2 to 30 seconds   Step S 105  time: 10 to 120 seconds   Step S 106  time: 2 to 60 seconds   

     The film-forming process will be further described with reference to  FIGS.  3 A to  3 C .  FIGS.  3 A to  3 C  are examples of schematic cross-sectional views of the substrate W in each step of the film-forming process. 
     Although not illustrated, the surface of the substrate W is terminated with OH groups before starting step S 101  of supplying the raw material gas. 
     In step S 101  of supplying the raw material gas, by supplying an aminosilane-based raw material gas (precursor gas) into the process container  1  and causing the substrates W in the process container  1  to be exposed to the raw material gas, an aminosilane-based precursor is adsorbed on the surfaces of the substrates W and thus, an adsorption layer of the precursor is formed on the surface of the substrates W. As shown in  FIG.  3 A , the surface of the substrate W becomes —O—Si—H due to the adsorption of the precursor. 
     In step S 103  of supplying the shape control gas, by supplying Cl 2  gas (shape control gas) into the process container  1  and causing the substrates W in the process container  1  to be exposed to the Cl 2  gas, the aminosilane-based precursor adsorbed on the surfaces of the substrates W is etched. That is, at least a portion of the adsorption layer of the precursor formed on the surface of the substrates W is etched. Here, the etching with the Cl 2  gas is performed such that the reaction is limited in a depth direction D. Therefore, the adsorption layer is etched by the Cl 2  gas in the vicinity of the opening of the depression as shown in  FIG.  3 B . On the other hand, the adsorption layer is not etched in the vicinity of an inner side of the depression. 
     In step S 105  of supplying the oxidizing gas, by supplying O 3  gas (oxidizing gas) into the process container  1  and causing the substrates W in the process container  1  to be exposed to O 3  gas such that the O 3  gas reacts with the aminosilane-based precursor adsorbed on the surface of the substrates W, thereby forming an SiO 2  film. That is, the O 3  gas reacts with the adsorption layer of the precursor formed on the surface of the substrates W, thereby forming the SiO 2  film. Here, the adsorption layer of the precursor is etched in the vicinity of the opening of the depression as shown in  FIG.  3 B  described above. Therefore, the adsorption layer and the O 3  gas react with each other to form the SiO 2  film in the vicinity of the inner side of the depression, and the formation of the SiO 2  film is suppressed in the vicinity of the opening of the depression as shown in  FIG.  3 C . 
       FIG.  4    is a cross-sectional view illustrating the relationship between the process temperature and the film shape of the SiO 2  film. Here, the SiO 2  film  810  was formed (embedded) in a depression structure  800  such as a trench of the substrate W under the process condition shown in  FIG.  2    and described above, at the process temperatures of 310, 320, 325, 330, 335, 340, and 350° C. 
     As shown in  FIG.  4   , in the range of the process temperature of 310 to 320° C., a film having a uniform film formation amount (conformal film) near an inlet of the depression and near the inner side of the depression is formed. 
     As shown in  FIG.  4   , in the range of the process temperature of 325 to 335° C., the film formation amount (film formation rate) near the inlet of the depression is smaller than the film formation amount (film formation rate) near the inner side the depression. As a result, the SiO 2  film may be embedded so as to be formed in a V-shape such that a width of the SiO 2  film widens from the inner side toward the opening of the depression. Accordingly, it is possible to suppress the opening from being blocked by the SiO 2  film near the inlet of the depression before embedding the SiO 2  film on the inner side of the depression. In other words, it can be made into a shape that makes it easy to embed the film in the depression. As a result, it is possible to suppress generation of voids or seams. 
     On the other hand, in a case where the process temperature is 340° C. or higher, the film formation of the SiO 2  film is suppressed as shown in  FIG.  4   . 
     As described above, according to the substrate processing apparatus  100  in accordance with the present embodiment, the shape of the SiO 2  film to be formed in the depression of the substrate W can be controlled by controlling the temperature of the substrate W during the film-forming process. Specifically, by controlling the temperature of the substrate W during the film-forming process to 400° C. or lower, the shape of the SiO 2  film to be formed in the depression of the substrate W can be controlled. More preferably, by controlling the temperature of the substrate W during the film-forming process to be within the range of 300 to 350° C., the shape of the SiO 2  film to be formed in the depression of the substrate W can be controlled. 
     Specifically, by setting the temperature of the substrate W during the film-forming process to be within the range of 325 to 335° C., it is possible to form a SiO 2  film in which the film thickness near the opening of the depression is smaller than the film thickness near the inner side of the depression. In addition, by setting the temperature of the substrate W during the film-forming process to be within the range of 320° C. or lower, a conformal SiO 2  film can be formed in the depression. Furthermore, by setting the temperature of the substrate W during the film-forming process to be within the range of 340° C. or higher, it is possible to suppress the film formation of the SiO 2  film in the depression. 
     Next, an example of embedding the SiO 2  film by using the substrate processing apparatus  100  in accordance with the present embodiment will be further described with reference to  FIG.  5   . 
       FIG.  5    is a flowchart showing an example of embedding process of the SiO 2  film. 
     In a first film-forming step shown in step S 201 , the SiO 2  film is embedded such that the depression is V-shaped. Specifically, the film-forming process is performed on the substrate W within the range of the process temperature of 325 to 335° C. (first temperature). 
     In a second film-forming step shown in step S 202 , a conformal SiO 2  film is embedded. Specifically, for example, the film-forming process is performed on the substrate W within the range of the process temperature of 320° C. or lower (300 to 320° C.) (second temperature). Here, since the depression is formed in the V-shape in step S 201 , it is possible to suppress the occurrence of seams or voids when the depression is embedded with the conformal SiO 2  film. In addition, the second film-forming step S 202  is not limited to this, and the steps of supplying and exhausting the shape control gas shown in S 103  and S 104  of  FIG.  2    may be omitted. That is, it may be a process of forming the SiO 2  film by alternately repeating the supply and exhaust of the raw material gas (S 101  and S 102 ) and the supply and exhaust of the oxidizing gas (S 105  and S 106 ). 
     As described above, according to the process shown in  FIG.  5   , since the V shape is formed in the first film-forming step and the conformal film is formed along the V shape in the second film-forming step, a voidless SiO 2  film can be formed in the depression. In addition, since the conformal film is formed onto the V shape, an embedding speed can be improved as the film formation proceeds from the bottom surface and the side wall of the depression. 
       FIGS.  6 A to  6 C  are schematic diagrams describing another embedding method of the SiO 2  film. In the verification of the present disclosure, changes in the coating property inside the trench are checked by vertical movement of the film-forming temperature. This indicates that the vertical movement of the generation position of the V shape can be controlled by the film-forming temperature. In a case where embedding with a V shape proceeds for a certain structure, a desired V-shaped film formation may not be obtained along with a change in an aspect ratio. In this case, the film-forming shape can be adjusted by interrupting the film-forming process for some time and changing the temperature of the substrate. This makes it possible to continue film-forming without taking out the substrate from the inside of the apparatus. 
     In  FIG.  6 A , a SiO 2  film is formed in the film-forming process shown in  FIG.  2    at a process temperature T1 (a third temperature, for example, 335° C.). For example, in the initial state, the depression structure  800  such as a trench has a deeply depressed shape. Here, the SiO 2  film  810  is formed at the process temperature T1 that is higher than process temperatures T2 and T3, which will be described later, in a temperature range in which a film can be formed in a V shape (e.g., the range of 325 to 335° C. for forming a SiO 2  film in which the film thickness near the opening of the depression is smaller than the film thickness near the inner side of the depression). As a result, the SiO 2  film  810  can be embedded by forming the film preponderantly from the bottom of the depression structure  800  to a depth D 1 . When the aspect ratio of the depression structure  800  changes as the SiO 2  film  810  is embedded up to the depth D 1 , the etching becomes more excessive than the film formation, and thus, the embedding is suppressed as the film formation amount decreases. 
     Next, in  FIG.  6 B , a SiO 2  film is formed in the film-forming process shown in  FIG.  2    at the process temperature T2 (a fourth temperature, for example, 330° C.). Here, the SiO 2  film  810  is formed at the process temperature T2 that is lower than the process temperature T1 in a temperature range in which a film can be formed in a V shape. As a result, the SiO 2  film  810  can be embedded by forming a film preponderantly from the bottom of the depression structure  800  to a depth D 2 . Further, since the SiO 2  film  810  has been embedded from the bottom of the depression structure  800  to the depth D 1  at the process temperature T1, the embedding is performed from the depth D 1  to the depth D 2  at the process temperature T2. When the aspect ratio of the depression structure  800  changes as the SiO 2  film  810  is embedded up to the depth D 2 , the etching becomes more excessive than the film formation, and thus, the embedding is suppressed as the film formation amount decreases. 
     Next, in  FIG.  6 C , a SiO 2  film is formed in the film-forming process shown in  FIG.  2    at the process temperature T3 (a fifth temperature, for example, 325° C.). Here, the SiO 2  film  810  is formed at the process temperature T3 that is lower than the process temperature T2 in a temperature range in which a film can be formed in a V shape. As a result, the SiO 2  film  810  can be embedded by forming a film preponderantly from the bottom of the depression structure  800  to a depth D 3 . Further, since the SiO 2  film  810  has been embedded from the bottom of the depression structure  800  to the depth D 2  at the process temperature T2, the embedding is performed from the depth D 2  to the depth D 3  at the process temperature T3. When the aspect ratio of the depression structure  800  changes as the SiO 2  film  810  is embedded up to the depth D 3 , the etching becomes more excessive than the film formation, and thus, the embedding is suppressed as the film formation amount decreases. 
     By sequentially changing the process temperature in this manner, the SiO 2  film can be embedded from the bottom surface of the depression in a bottom-up fashion. As a result, since the SiO 2  film can be embedded in a bottom-up fashion even for depression shapes having a large aspect ratio, the occurrence of voids and seams can be suppressed. Further, by alternately performing the temperature control and film-forming process of the substrate, bottom-up embedding can be continuously realized as in-situ film-forming. 
     Although the substrate processing by the substrate processing apparatus  100  has been described above, the present disclosure is not limited to the above embodiments and the like, and various modifications and improvements can be made within the scope of the subject matter of the present disclosure set forth in the claims. 
     In addition, this application claims priority to Japanese Patent Application No. 2020-46631, filed on Mar. 17, 2020, the entire contents of which are incorporated herein by reference. 
     EXPLANATION OF REFERENCE NUMERALS 
     W: substrate,  100 : substrate processing apparatus,  1 : process container,  2 : ceiling plate,  20 : gas supply,  21  to  24 : gas supply pipes,  21   a  to  23   a : gas supply sources,  44 : exhaust apparatus,  50 : heating mechanism,  60 : controller