Patent Publication Number: US-2022238335-A1

Title: Method for forming film and processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is based on and claims priority to Japanese Patent Application No. 2021-011976 filed on Jan. 28, 2021, the contents of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The disclosures herein generally relate to a method for forming a film, and a processing apparatus. 
     BACKGROUND 
     A method for forming a silicon nitride film in which ammonia gas, a silane family gas, and a carbon hydride gas are used as process gases, and the silane family gas is intermittently supplied, is known (see, for example, Japanese Unexamined Patent Application Publication No. 2005-012168). 
     SUMMARY 
     According to an embodiment, a method for forming a film includes: forming a SiCN seed layer on a substrate by a thermal ALD (atomic layer deposition), forming a SiN protective layer on the SiCN seed layer by a thermal ALD, and forming a SiN bulk layer on the SiN protective layer by a plasma enhanced ALD. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an outline (1) of an example of a processing apparatus according to an embodiment; 
         FIG. 2  is a diagram illustrating an outline (2) of the example of the processing apparatus according to the embodiment; 
         FIG. 3  is a flow chart illustrating an example of a method for forming a film according to the embodiment; 
         FIGS. 4A to 4C  are cross-sectional views illustrating a process of an example of the method for forming a film according to the embodiment; 
         FIG. 5  is a diagram illustrating an example of a process for forming a SiCN seed layer by a thermal ALD; 
         FIG. 6  is a diagram illustrating an example of a process for forming a SiN protective layer by a thermal ALD; 
         FIG. 7  is a diagram illustrating an example of a process for forming a SiN bulk layer by a plasma enhanced ALD; 
         FIG. 8  is a diagram illustrating another example of a process for forming a SiN bulk layer by a plasma enhanced ALD; 
         FIGS. 9A and 9B  are diagrams illustrating a reaction when a Si/SiCN stack is exposed to NH 3  plasma; 
         FIGS. 10A and 10B  are diagrams illustrating a reaction when a Si/SiCN/SiN protective layer stack is exposed to NH 3  plasma; 
         FIG. 11  is a diagram illustrating a result of evaluating plasma resistance of a SiCN seed layer; and 
         FIG. 12  is a diagram illustrating a result of evaluating a composition of the SiCN seed layer. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, non-limiting exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. In the drawings, the same or corresponding parts or components are designated by the same or corresponding reference numerals, and the description thereof will be omitted. 
     [Processing Apparatus] 
     Referring to  FIGS. 1 and 2 , an example of a processing apparatus according to an embodiment will be described. 
     A processing apparatus  100  includes a processing chamber  1  having a cylindrical shape with a ceiling and an open lower end. The entire processing chamber  1  is formed, for example, of quartz. Near the upper end of the processing chamber  1 , a ceiling plate formed of quartz is provided, thereby sealing the space under the ceiling plate  2 . To an opening of the lower end of the processing chamber  1 , a metal manifold  3  having a cylindrical shape is connected via a sealing member  4  such as an O-ring. 
     The manifold  3  supports the lower end of the processing chamber  1 . A boat  5  is inserted into the processing chamber  1  from below the manifold  3 . The boat  5  has a configuration in which a large number of substrates W (for example, 25 to 150) are mounted in multiple stages. The substrates W are housed substantially horizontally in the processing chamber  1  with spacing from each other along the vertical direction. The boat  5  is formed, for example, of quartz. The boat  5  includes three rods  6  (see  FIGS. 1 and 2 ). The substrates W are supported by grooves (not shown) formed in the rods  6 . The substrate W may be, for example, a semiconductor wafer. 
     The boat  5  is mounted on a table  8  via a heat insulating tube  7  formed of quartz. The table  8  is supported on a rotating shaft  10 . The rotating shaft penetrates a metal (stainless steel) lid  9  that opens and closes the lower end of the manifold  3 . 
     A magnetic fluid seal  11  is provided at the penetrating portion of the rotating shaft  10 . The magnetic fluid seal  11  airtightly seals the rotating shaft  10  and rotatably supports the rotating shaft  10 . A seal member  12  is provided between the periphery of the lid  9  and the lower end of the manifold  3  to maintain the airtightness within the processing chamber  1 . 
     The rotating shaft  10  is mounted to the tip of an arm  13 . The arm  13  is supported by a lifting mechanism (not shown), such as a boat elevator. The boat  5  and the lid  9  are integrally elevated and lowered, and are inserted into and removed from the inside of the processing chamber  1 . The table  8  may be fixed to the lid  9 , and the substrate W may be processed without rotating the boat  5 . 
     The processing apparatus  100  includes a gas supply  20  for supplying a predetermined gas, such as process gas, purge gas, and the like, into the processing chamber  1 . 
     The gas supply  20  includes gas supply lines  21 ,  22 , and  24 . The gas supply lines  21 ,  22 , and  24  are formed, for example, of quartz. The gas supply lines  21  and  22  penetrate the side wall of the manifold  3  inward, then bend upwardly and extend vertically. In each of the vertically-extending portions of the gas supply lines  21  and  22 , a plurality of gas holes  21   a  and  22   a  are formed at predetermined intervals. The gas holes  21   a  and  22   a  are formed in the part of the gas supply lines  21  and  22  that corresponds horizontally to the position where the boat  5  supports the substrates W. The gas holes  21   a  and  22   a  discharge gas horizontally. The gas supply line  24  is, for example, a short quartz tube that is provided through the side wall of the manifold  3 . In the illustrated examples, two gas supply lines  21  and one line each for gas supply lines  22  and  24  are provided. 
     The vertically-extending portion of the gas supply line  21  is provided inside the processing chamber  1 . A silicon-containing gas from a silicon-containing gas source is supplied via a gas line to the gas supply line  21 . The gas line is provided with a flow controller and an open/close valve. Thus, the silicon-containing gas is supplied from the silicon-containing gas source via the gas line and the gas supply line  21  into the processing chamber  1  at a predetermined flow rate. 
     As the silicon-containing gas, one or more gases selected from the group consisting of, for example, hexachlorodisilane (HCD), monosilane (SiH 4 ), disilane (Si 2 H 6 ), dichlorosilane (DCS), hexaethylaminodisilane, hexamethyldisilazane (HMDS), tetrachlorosilane (TCS), disilylanine (DSA), trisilylamine (TSA), and bistertialbutylaminosilane (BTBAS) may be used. 
     A carbon-containing gas from a carbon-containing gas source is also supplied via a gas line to the gas supply line  21 . The gas line is provided with a flow controller and an open/close valve. Thus, the carbon-containing gas is supplied from the carbon-containing gas source via the gas line and the gas supply line  21  into the processing chamber  1  at a predetermined flow rate. 
     As the carbon-containing gas, one or more gases selected from the group consisting of, for example, acetylene (C 2 H 2 ), ethylene (C 2 H 4 ), propylene (C 3 H 6 ), methane (CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), and butane (C 4 H 10 ) may be used. 
     The vertically-extending portion of the gas supply line  22  is provided in a plasma generation space described later. A nitrogen-containing gas from a nitrogen-containing gas source is supplied via a gas line to the gas supply line  22 . The gas line is provided with a flow controller and an open/close valve. Thus, the nitrogen-containing gas is supplied from the nitrogen-containing gas source via the gas line and the gas supply line  22  to the plasma generation space at a predetermined flow rate. The nitrogen-containing gas is formed into a plasma in the plasma generation space, and then supplied into the processing chamber  1 . 
     As the nitrogen-containing gas, one or more gases selected from the group consisting of, for example, ammonia (NH 3 ), diazene (N 2 H 2 ), hydrazine (N 2 H 4 ), and an organic hydrazine compound such as monomethylhydrazine (CH 3 (NH)NH 2 ) may be used. 
     A hydrogen (H 2 ) gas is also supplied from a hydrogen gas source via a gas line to the gas supply line  22 . The gas line is provided with a flow controller and an open/close valve. Thus, the H 2  gas is supplied from the hydrogen gas source via the gas line and the gas supply line  22  to the plasma generation space at a predetermined flow rate. The H 2  gas is formed into a plasma in the plasma generation space, and then supplied into the processing chamber  1 . 
     A purge gas is supplied from a purge gas source via a gas line to the gas supply line  24 . The gas line is provided with a flow controller and an open/close valve. Thus, the purge gas is supplied from the purge gas source via the gas line and the gas supply line  24  into the processing chamber  1  at a predetermined flow rate. As the purge gas, for example, an inert gas such as nitrogen (N 2 ) and argon (Ar) may be used. The purge gas may also be supplied from at least one of the gas supply lines  21  and  22 . 
     A plasma generation mechanism  30  is formed in a part of the side wall of the processing chamber  1 . The plasma generation mechanism  30  forms an NH 3  gas into a plasma, thereby generating active species (reactive species) for nitridation. The plasma generation mechanism  30  forms a H 2  gas into a plasma, thereby generating a hydrogen (H) radical. The plasma generation mechanism  30  forms a Cl 2  gas into a plasma, thereby generating a chlorine (Cl) radical. 
     The plasma generation mechanism  30  includes a plasma compartment wall  32 , a pair of plasma electrodes  33 , a power supply line  34 , an RF power supply  35 , and an insulation cover  36 . 
     The plasma compartment wall  32  is airtightly welded to an outer wall of the processing chamber  1 . The plasma compartment wall  32  is formed, for example, of quartz. The plasma compartment wall  32  has a concave shape in cross-section, and covers an opening  31  formed in the side wall of the processing chamber  1 . The opening  31  is elongated vertically so as to cover vertically all the substrates W supported on the boat  5 . The inner space defined by the plasma compartment wall  32  and communicating with the inside of the processing chamber  1 , is the plasma generation space. The gas supply line  22  is disposed in the plasma generation space. The gas supply line  21  is disposed close to the substrate W, along the inner wall of the processing chamber  1  outside of the plasma generation space. In the illustrated example, two gas supply lines are disposed at positions sandwiching the opening  31 , but the configuration is not limited thereto. For example, only one of the two gas supply lines  21  may be disposed. 
     A pair of plasma electrodes  33 , each having an elongated shape, are disposed facing each other on the outer surface of both sides of the plasma compartment wall  32  along the vertical direction. The power supply line  34  is connected to the lower end of each of the plasma electrodes  33 . 
     The power supply line  34  electrically connects each of the plasma electrodes  33  to the RF power supply  35 . In the illustrated example, one end of the power supply line  34  is connected to the lower end of the plasma electrode  33 , namely, to the lateral portion of the short side of the plasma electrode  33 , and the other end is connected to the RF power supply  35 . 
     The RF power supply  35  is connected to the lower end of each of the plasma electrodes  33  via the power supply line  34 . The RF power supply  35  may supply RF power of, for example, 13.56 MHz, to a pair of plasma electrodes  33 . Accordingly, RF power is applied within the plasma generation space defined by the plasma compartment wall  32 . The nitrogen-containing gas discharged from the gas supply line  22  is formed into a plasma in the plasma generation space to which the RF power is applied, whereby active species for nitridation are generated. The active species are supplied into the processing chamber  1  via the opening  31 . The H 2  gas discharged from the gas supply line  22  is formed into a plasma in the plasma generation space to which RF power is applied, whereby a hydrogen radical is generated. The hydrogen radical is supplied into the processing chamber  1  via the opening  31 . 
     The insulation cover  36  is mounted outside the plasma compartment wall  32  to cover the plasma compartment wall  32 . A coolant passage (not shown) is provided inside the insulation cover  36 . The plasma electrode  33  may be cooled by flowing a cooled coolant, such as N 2  gas, through the coolant passage. A shield (not shown) may be provided between the plasma electrode  33  and the insulation cover  36 , to cover the plasma electrode  33 . The shield is formed of a good conductor such as metal, and is grounded. 
     The side wall of the processing chamber  1  facing the opening  31  is provided with an exhaust port  40  for vacuum exhausting the processing chamber  1 . The exhaust port  40  is elongated vertically, corresponding to the boat  5 . To the portion of the processing chamber  1  where the exhaust port  40  is provided, an exhaust port cover member  41  is attached. The exhaust port cover member  41  is formed in a U-shaped cross section so as to cover the exhaust port  40 . The exhaust port cover member  41  extends upwardly along the side wall of the processing chamber  1 . To the lower portion of the exhaust port cover member  41 , an exhaust line  42  for evacuating the processing chamber  1  via the exhaust port  40  is connected. To the exhaust line  42 , an exhaust apparatus  44  that includes a pressure control valve  43  for controlling the pressure in the processing chamber  1 , a vacuum pump, and the like, is connected. The exhaust apparatus  44  evacuates the processing chamber  1  via the exhaust line  42 . 
     A cylindrical heating mechanism  50  is provided around the processing chamber  1 . The heating mechanism  50  heats the processing chamber  1  and the substrates W inside the processing chamber  1 . 
     The processing apparatus  100  includes a controller  60 . The controller  60  controls, for example, an operation of each part of the processing apparatus  100  to perform a method for forming a film to be described later. The controller  60  may be, for example, a computer or the like. A program for a computer to perform an operation of each part of the 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. 
     [Method for Forming a Film] 
     Referring to  FIGS. 3 to 8 , a method for forming a film according to the embodiment will be described by exemplifying a case where the method is performed by the processing apparatus  100  described above. The method for forming a film according to the embodiment may be performed by an apparatus different from the processing apparatus  100  described above. 
     The method for forming a film according to the embodiment includes Step S 10  of forming a SiCN seed layer by a thermal ALD, Step S 20  of forming a SiN protective layer by a thermal ALD, and Step S 30  of forming a SiN bulk layer by a plasma enhanced ALD, as shown in  FIG. 3 . 
     Step S 10  of forming a SiCN seed layer by a thermal ALD, Step S 20  of forming a SiN protective layer by a thermal ALD, and Step S 30  of forming a SiN bulk layer by a plasma enhanced ALD, are all performed in the processing chamber  1  of the processing apparatus  100 , for example. 
     Step S 10  of forming a SiCN seed layer by a thermal ALD, Step S 20  of forming a SiN protective layer by a thermal ALD, and Step S 30  of forming a SiN bulk layer by a plasma enhanced ALD, are performed in a state where the substrates W are heated to 450° C. to 630° C., for example. 
     In Step S 10  of forming a SiCN seed layer by a thermal ALD, as shown in  FIG. 4A , a SiCN seed layer  101  is formed on the substrate W by a thermal ALD (atomic layer deposition) in which the reaction of a silicon-containing gas, a carbon-containing gas, and a nitrogen-containing gas is caused by heat. In other words, in Step S 10  of forming the SiCN seed layer by the thermal ALD, the SiCN seed layer  101  is formed on the substrate W without forming the silicon-containing gas, the carbon-containing gas, and the nitrogen-containing gas into a plasma. The substrate W may be, for example, a silicon wafer having a SiO 2  film formed on the surface as a base. 
     In the present embodiment, Step S 10  of forming the SiCN seed layer by the thermal ALD includes, as shown in  FIG. 5 , a purge step S 11 , a HCD supply step S 12 , a purge step S 13 , a C 2 H 4  supply step S 14 , a purge step S 15 , and a Th—NH 3  supply step S 16 . The purge step S 11 , the HCD supply step S 12 , the purge step S 13 , the C 2 H 4  supply step S 14 , the purge step S 15 , and the Th—NH 3  supply step S 16  are repeated in this order until the SiCN seed layer  101  of a desired thickness is formed on the substrate W. The number of the repeats may be, for example, from 1 to 20. 
     In the purge step S 11 , the atmosphere in the processing chamber  1  is replaced with a purge gas. Specifically, the atmosphere in the processing chamber  1  is replaced with the purge gas by supplying the purge gas from the gas supply line  24  to the processing chamber  1  while evacuating the processing chamber  1  by the exhaust apparatus  44 . 
     In the HCD supply step S 12 , a HCD gas, which is an example of a silicon-containing gas, is supplied to the substrate W. Specifically, the HCD gas is supplied from the gas supply line  21  into the processing chamber  1 . As a result, the HCD gas adsorbs to the surface of the substrate W. 
     In the purge step S 13 , the atmosphere in the processing chamber  1  is replaced with a purge gas. Specifically, the atmosphere in the processing chamber  1  is replaced with the purge gas by supplying the purge gas from the gas supply line  24  to the processing chamber  1  while evacuating the processing chamber  1  by the exhaust apparatus  44 . 
     In the C 2 H 4  supply step S 14 , a C 2 H 4  gas, which is an example of a carbon-containing gas, is supplied to the substrate W. Specifically, the C 2 H 4  gas is supplied to the substrate W by supplying the C 2 H 4  gas into the processing chamber  1  from the gas supply line  22 . As a result, the HCD gas adsorbed to the surface of the substrate W is carbonized. 
     In the purge step S 15 , the atmosphere in the processing chamber  1  is replaced with a purge gas. Specifically, the atmosphere in the processing chamber  1  is replaced with the purge gas by supplying the purge gas from the gas supply line  24  to the processing chamber  1  while evacuating the processing chamber  1  by the exhaust apparatus  44 . 
     In the Th—NH 3  supply step S 16 , an NH 3  gas, which is an example of a nitrogen-containing gas, is supplied to the substrate W. Specifically, the NH 3  gas is supplied to the substrate W by supplying the NH 3  gas into the processing chamber  1  from the gas supply line  22 . As a result, the HCD gas adsorbed to the surface of the substrate W is nitrided. 
     In Step S 20  of forming a SiN protective layer by a thermal ALD, as shown in  FIG. 4B , a SiN protective layer  102  is formed on the SiCN seed layer  101  by a thermal ALD in which the reaction of a silicon-containing gas and a nitrogen-containing gas is caused by heat. In other words, in Step S 20  of forming the SiN protective layer by the thermal ALD, the SiN protective layer  102  is formed on the SiCN seed layer  101  without forming the silicon-containing gas and the nitrogen-containing gas into a plasma. 
     In the present embodiment, Step S 20  of forming the SiN protective layer by the thermal ALD includes, as shown in  FIG. 6 , a purge step S 21 , a HCD supply step S 22 , a purge step S 23 , and a Th—NH 3  supply step S 24 . The purge step S 21 , the HCD supply step S 22 , the purge step S 23 , and the Th—NH 3  supply step S 24  are repeated in this order until the SiN protective layer  102  of a desired thickness is formed on the SiCN seed layer  101 . The number of the repeats may be, for example, from 5 to 20. 
     The thickness of the SiN protective layer  102  is preferably 2 nm or more. Accordingly, damage to the SiCN seed layer  101  when a SiN bulk layer  103  is formed on the SiN protective layer  102  by the plasma enhanced ALD is greatly reduced. In addition, it is preferable that the SiN protective layer  102  is thin, because the SiN layer formed by the thermal ALD tends to have a poorer film quality compared to the SiN layer formed by the plasma enhanced ALD. The thickness of the SiN protective layer  102  is, for example, 3 nm or less. 
     The purge step S 21 , the HCD supply step S 22 , the purge step S 23 , and the Th—NH 3  supply step S 24  may be the same as the purge step S 11 , the HCD supply step S 12 , the purge step S 13 , and the Th—NH 3  supply step S 16 , respectively. 
     In Step S 30  of forming a SiN bulk layer by a plasma enhanced ALD, as shown in  FIG. 4C , a SiN bulk layer  103  is formed on the SiN protective layer  102  by a plasma enhanced ALD in which the reaction of a silicon-containing gas and a nitrogen-containing gas is assisted by a plasma. 
     In the present embodiment, Step S 30  of forming the SiN bulk layer by the plasma enhanced ALD includes, as shown in  FIG. 7 , a purge step S 31 , a DCS supply step S 32 , a purge step S 33 , and a PE-NH 3  supply step S 34 . The purge step S 31 , the DCS supply step S 32 , the purge step S 33 , and the PE-NH 3  supply step S 34  are repeated in this order until the SiN bulk layer  103  of a desired thickness is formed on the SiN protective layer  102 . 
     The purge step S 31  and the purge step S 33  may be the same as the purge step S 11  and the purge step S 13 , respectively. 
     In the DCS supply step S 32 , a DCS gas, which is an example of a silicon-containing gas, is supplied to the substrate W. Specifically, the DCS gas is supplied into the processing chamber  1  from the gas supply line  21 . As a result, the DCS gas adsorbs to the surface of the substrate W. 
     In the PE-NH 3  supply step S 34 , the substrate W is exposed to a plasma generated from the NH 3  gas, which is an example of a nitrogen-containing gas. Specifically, by supplying the NH 3  gas from the gas supply line  22  into the processing chamber  1 , and by applying an RF power to a pair of plasma electrodes  33  from the RF power supply  35 , the NH 3  gas is formed into a plasma, and active species for nitridation are generated. The active species are supplied to the substrate W. As a result, the DCS gas adsorbed to the surface of the substrate W is nitrided. 
     Step S 30  of forming a SiN bulk layer by plasma enhanced ALD may further include a HRP step S 35  and a purge step S 36 , in addition to the purge step S 31 , the DCS supply step S 32 , the purge step S 33 , and the PE-NH 3  supply step S 34 , as shown in  FIG. 8 . In this case, the purge step S 31 , the DCS supply step S 32 , the purge step S 33 , the HRP step S 35 , the purge step S 36 , and the PE-NH 3  supply step S 34  are repeated in this order until the SiN bulk layer  103  of a desired thickness is formed on the SiN protective layer  102 . The addition of the HRP step S 35  improves the film quality of the SiN bulk layer  103 . 
     In the HRP step S 35 , HRP (Hydrogen Radical Purge) is performed so that the substrate W is exposed to a plasma generated from the H 2  gas. In the present embodiment, by supplying the H 2  gas from the gas supply line  22  into the processing chamber  1 , and by applying an RF power to a pair of plasma electrodes  33  from the RF power supply  35 , the H 2  gas is formed into a plasma, and hydrogen radicals are generated. The hydrogen radicals are supplied to the substrate W. 
     In the purge step S 36 , the atmosphere in the processing chamber  1  is replaced with a purge gas. Specifically, the atmosphere in the processing chamber  1  is replaced with the purge gas by supplying the purge gas from the gas supply line  24  to the processing chamber  1  while evacuating the processing chamber  1  by the exhaust apparatus  44 . 
     As described above, according to the method for forming a film of the present embodiment, the SiN protective layer  102  is formed by the thermal ALD prior to forming the SiN bulk layer  103  by the plasma enhanced ALD on the SiCN seed layer  101 . The SiN protective layer  102  serves to block the plasma when the SiN bulk layer  103  is formed by the plasma enhanced ALD. Accordingly, the film quality of the SiCN seed layer  101  is maintained. That is, damage to the SiCN seed layer  101  can be reduced when forming the SiN bulk layer  103  on the SiCN seed layer  101  using a plasma. 
     In the method for forming a film according to the embodiment described above, a case in which different types of silicon-containing gases are used in Steps S 10  and S 20  versus Step S 30 , has been described. The present disclosure is not limited thereto. For example, in Step S 10 , Step S 20 , and Step S 30 , the same type of silicon-containing gas may be used. For example, in Step S 10 , Step S 20 , and Step S 30 , different types of silicon-containing gases may be used. 
     In the method for forming a film according to the embodiment described above, Step S 10 , Step S 20 , and Step S 30  are all performed in the processing chamber  1 . The present disclosure is not limited thereto. 
     [Mechanism] 
     Referring to  FIGS. 9 and 10 , a mechanism is described in which damage to the SiCN seed layer  101  can be suppressed when the SiN bulk layer  103  is deposited, using a plasma, on the SiCN seed layer  101  that is formed on the substrate W, by the method for forming a film according to the present embodiment. 
     First, with reference to  FIG. 9 , a case where the SiN protective layer  102  is not formed on the SiCN seed layer  101  will be described. As illustrated in  FIG. 9A , when the Si/SiCN stack is exposed to an NH 3  plasma, the stack reacts with active species such as radicals and ions in the plasma. Thus, carbon (C) contained in the SiCN is desorbed (volatilized) as CH x . As a result, the SiCN film thickness is reduced by the amount of region A, as illustrated in  FIG. 9B . 
     Next, with reference to  FIG. 10 , a case where the SiN protective layer  102  is formed on the SiCN seed layer  101  will be described. As illustrated in FIG.  10 A, when the Si/SiCN/SiN protective layer stack is exposed to the NH 3  plasma, the SiN protective layer covering the surface of SiCN prevents the reaction of active species such as radicals and ions in the plasma with the SiCN. Thus, it is possible to prevent carbon (C) contained in SiCN from becoming CH x  and desorbing (volatilizing). The SiN protective layer contains no carbon (C). Accordingly, even when the SiN protective layer is exposed to an NH 3  plasma, carbon loss is not caused, and the SiN protective layer is not appreciably damaged. As a result, damage to SiCN can be reduced. 
     Example 
     With reference to  FIGS. 11 and 12 , an example in which plasma resistance of the SiCN seed layer is evaluated will be described. 
     A SiCN seed layer was formed on a substrate by a thermal ALD. Specifically, the SiCN seed layer was formed on the substrate by performing the process illustrated in  FIG. 5 . 
     Also, a SiCN seed layer was formed on the substrate by a plasma enhanced ALD. Specifically, the Th—NH 3  supply step S 16  in the process illustrated in  FIG. 5  was changed to a step in which the substrate is exposed to a plasma generated from the NH 3  gas, to form a SiCN seed layer on the substrate. 
     Then, the WER (wet etching rate) of each SiCN seed layer formed on the substrate was measured. The WER is the etching rate when the SiCN seed layer is etched with 0.5% DHF (dilute hydrofluoric acid). In addition, a composition of each SiCN layer formed on the substrate was measured. 
       FIG. 11  is a diagram illustrating the result of evaluating plasma resistance of the SiCN seed layer. In  FIG. 11 , the left graph illustrates the WER [Å/min] of the SiCN seed layer (Th—SiCN) formed by the thermal ALD, and the right graph illustrates the WER [Å/min] of the SiCN seed layer (PE-SiCN) formed by the plasma enhanced ALD. 
     As illustrated in  FIG. 11 , WER of the SiCN seed layer formed by the thermal ALD is 1.79, while WER of the SiCN seed layer formed by the plasma enhanced ALD is 7.47. That is, the SiCN seed layer formed by the plasma enhanced ALD is about four times greater in WER than the SiCN seed layer formed by the thermal ALD. From this result, it was shown that the film quality of the SiCN layer deteriorates when the SiCN layer is formed using a plasma. 
       FIG. 12  is a diagram illustrating the result of evaluating a composition of the SiCN seed layer. In  FIG. 12 , the left graph illustrates the composition [%] of the SiCN seed layer (Th—SiCN) formed by the thermal ALD, and the right graph illustrates the composition [%] of the SiCN seed layer (PE-SiCN) formed by the plasma enhanced ALD. 
     As illustrated in  FIG. 12 , the carbon (C) concentration contained in the SiCN seed layer formed by the thermal ALD is approximately 7%, while the carbon (C) concentration of the SiCN seed layer formed by the plasma enhanced ALD is approximately 1%. That is, the SiCN seed layer formed by the plasma enhanced ALD has a significantly lower carbon concentration than the SiCN seed layer formed by the thermal ALD. From this result, it was shown that the concentration of carbon (C) in the SiCN seed layer is reduced when the SiCN layer is formed using a plasma. 
     These results suggest that when the SiCN seed layer is exposed to a plasma, the concentration of carbon (C) contained in the SiCN seed layer decreases, and thus the film quality deteriorates. 
     The embodiments disclosed herein should be considered to be exemplary in all respects and not limiting. The embodiments described above may be omitted, substituted, or modified in various forms without departing from the appended claims and spirit thereof. 
     In the embodiments described above, the processing apparatus is a batch-type apparatus that processes a plurality of substrates at once. The present disclosure is not limited thereto. For example, the processing apparatus may be a sheet-fed apparatus that processes a substrate one by one. For example, the processing apparatus may be a semi-batch apparatus in which a plurality of substrates are disposed on a rotating table in the processing chamber and the substrates are revolved in accordance with the rotation of the rotating table. The substrates are processed by passing through a region in which the first gas is supplied and a region in which the second gas is supplied in turn. 
     According to the present disclosure, damage to a SiCN layer when forming a SiN layer on the SiCN layer using plasma can be reduced.