Film forming method and film forming device for boron nitride film

Abstract

In this film forming method for a boron nitride film, a sequence is performed a desired number of times, the sequence including supplying, to a substrate placed in a chamber, plasma and a raw material gas containing a compound having a BN bond in a molecule and then supplying, to the substrate, only plasma without supplying the raw material gas. At such time, the desired boron nitride film, from between a hexagonal boron nitride film and an amorphous boron nitride film, is formed through adjustment of the film formation conditions.

Description

Boron nitride film forming method and film forming apparatus

[0001] The present disclosure relates to a method and apparatus for forming a boron nitride film.

[0002] Known techniques for forming a boron nitride (BN) film include those described in Patent Documents 1 to 3, for example.

[0003] Patent Document 1 describes a method for forming a hexagonal BN (h-BN) film on the surface of a substrate by plasma CVD using plasma generated from a boron-containing gas and a nitrogen-containing gas in a plasma generation region located away from the substrate. Patent Document 2 describes a method for forming a film having a borazine ring skeleton and containing boron and nitrogen on a substrate by simultaneously supplying a borazine-based gas containing a ligand to the substrate and a ligand desorption gas that desorbs the ligand to the substrate, the steps being performed intermittently under conditions that maintain the borazine ring skeleton in the borazine-based gas. Patent Document 3 describes a method for producing a hard film made of hydrogen-treated amorphous boron nitride (a-BN:H) with an ion kinetic energy of 50 to 300 eV per ion, the method comprising the steps of depositing a film on a substrate by condensation at a temperature below about 200°C from an ion flow generated from a gaseous precursor made of borazine.

[0004] JP 2020-147826 A JP 2016-63007 A JP 8-41633 A

[0005] The present disclosure provides a method and apparatus for depositing a boron nitride film that can deposit both a hexagonal boron nitride film and an amorphous boron nitride film.

[0006] A method for forming a boron nitride film according to one aspect of the present disclosure includes performing a sequence including supplying a source gas containing a compound having a BN bond in its molecule and plasma to a substrate placed in a chamber, and subsequently supplying the plasma to the substrate without supplying the source gas, a desired number of times, and adjusting the film formation conditions during the sequence to form a desired boron nitride film from among a hexagonal boron nitride film and an amorphous boron nitride film.

[0007] According to the present disclosure, a method and apparatus for forming a boron nitride film are provided that are capable of forming both a hexagonal boron nitride film and an amorphous boron nitride film.

[0008] 1 is a timing chart showing a standard process of a BN film formation method according to an embodiment; FIG. 2 is a timing chart showing a pre-plasma process of a BN film formation method according to an embodiment; FIG. 3 is a timing chart showing a pre-flow process of a BN film formation method according to an embodiment; FIG. 4 is a timing chart showing a film formation method by alternately supplying a source gas containing a borazine-based compound and plasma; FIG. 5 is a diagram for explaining a case where a BN film is used as an underlayer of a photoresist when etching is performed after forming a protective film only on the photoresist after exposure and development; FIG. 6 is a diagram showing the relationship between Depo time and GPC calculated from the film thickness measured by Ellipso and the film thickness measured by TEM when film formation is performed by changing the supply time (Depo time) of the source gas and plasma in step ST2; and FIG. 7 is a diagram showing FT-IR spectra of BN films formed by changing the pressure and temperature. 1 is a graph with pressure on the horizontal axis and temperature on the vertical axis, showing a correlation diagram indicating whether an h-BN film or an a-BN film will be formed depending on the pressure and temperature when the Depo Time is set to 2 seconds. 2 is a graph with pressure on the horizontal axis and temperature on the vertical axis, showing a correlation diagram indicating whether an h-BN film or an a-BN film will be formed depending on the pressure and temperature when the Depo Time is set to 4 seconds. 3 is a cross-sectional view showing an example of a film formation apparatus.

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings.

[0010] <Background and Overview> First, the background and overview will be explained. BN film is an insulating film with excellent properties, and its application to various uses is being considered. In particular, BN film has attracted attention as a low-dielectric-constant insulating film (low-k insulating film) that can achieve a k value of 3 or less.

[0011] Known BN films include h-BN films and amorphous BN films (a-BN films). Both have low k values, but they have different characteristics. For example, a-BN films have a lower k value than h-BN films and are expected to have high density and high breakdown voltage, but h-BN films have higher etching resistance than a-BN films. Therefore, it is extremely effective to selectively fabricate h-BN films and a-BN films to obtain BN films with the desired characteristics.

[0012] The above-mentioned Patent Document 1 describes the formation of an h-BN film by CVD, and Patent Document 3 describes the formation of an amorphous BN, i.e., an a-BN film, but no consideration is given at all to selectively forming an h-BN film or an a-BN film. Furthermore, the BN film formation method described in Patent Document 2 focuses on the film formation rate of the BN film, and does not consider the crystallinity of the formed BN film.

[0013] Therefore, in the present disclosure, a BN film is formed by repeating a sequence including a step of supplying a source gas containing a compound having a BN bond in its molecule and plasma to a substrate placed in a chamber, followed by a step of subsequently supplying plasma to the substrate without supplying the source gas, a desired number of times. Then, by adjusting one or more of the film formation conditions, such as the temperature during film formation, the pressure in the chamber, the time for the step of supplying the source gas and plasma, and the flow rate of the source gas, a desired BN film, either an h-BN film or an a-BN film, is formed. In other words, by adjusting the film formation conditions when forming the BN film using this sequence, it is possible to selectively form an h-BN film or an a-BN film.

[0014] Furthermore, with typical CVD deposition, the deposited BN film is likely to be insufficiently nitrided, which can lead to poor film quality, such as poor water resistance and surface smoothness. In contrast, deposition using the above sequence ensures sufficient nitriding, resulting in a high-density, high-quality BN film. In particular, deposition under high-pressure conditions can yield an h-BN film with good crystallinity, high density, and excellent water resistance and surface smoothness.

[0015] Specific Embodiments Figure 1 is a timing chart showing a standard process of a BN film formation method according to one embodiment. In the BN film formation method according to this embodiment, a substrate is placed in a chamber of a film formation apparatus, and steps ST1, ST2, ST3, and ST4 are performed in a desired cycle (X1 cycle) as shown in Figure 1. The substrate is not particularly limited, but may be a semiconductor substrate, for example. The semiconductor substrate may be, for example, a substrate made of a semiconductor such as Si, or a substrate made of a semiconductor on which a desired film is formed.

[0016] In step ST1, a purge gas is supplied to the chamber in which the substrate is placed to purge the chamber. At this time, in preparation for the flow of the source gas, the source gas may be flowed through an exhaust line or filled into a fill tank. The purge gas may be an inert gas, and a rare gas such as Ar gas or He gas is preferably used. A plasma gas, which will be described later, may also be supplied simultaneously.

[0017] In step ST2, a source gas containing a compound having a BN bond in its molecule (source gas) and plasma are supplied to the substrate in the chamber, thereby causing the source gas to be adsorbed onto the substrate and activating the source gas with the plasma to promote the adsorption.

[0018] The use of a compound having a BN bond in its molecule as a source gas facilitates the formation of a BN film. Examples of compounds having a BN bond in their molecules include borazine-based compounds and aminoborane-based compounds.

[0019] The borazine-based compound is borazine (B) having a structure represented by the following formula (1): ３ H ６ N ３ ) as a basic compound. That is, the borazine-based compound is a compound having a basic skeleton of a borazine ring in which three B and three N atoms are alternately bonded, which constitutes borazine, and may be, for example, an organic borazine compound in which some or all of the H atoms in borazine are substituted with organic ligands. The organic borazine compound may be an alkylborazine compound using an alkyl group as the organic ligand, and for example, trimethylborazine (TMB) having the structure shown in the following formula (2) can be used. The source gas containing the borazine-based compound functions as a B source and an N source for the BN film.

[0020]

[0021] Aminoborane compounds are compounds based on aminoborane, as shown in the following formula (3). The number of N bonded to B may be 1 to 3. The bond of B that is not bonded to N and the bond of N that is not bonded to B may be bonded to H or an alkyl group. An example of an aminoborane compound is tris(dimethylamino)borane, as shown in the following formula (4).

[0022]

[0023] As long as the plasma is supplied to the substrate, it may be generated within the chamber or may be remote plasma, in which plasma generated elsewhere is introduced into the chamber. The plasma generation method is not particularly limited, but capacitively coupled plasma obtained by applying radio frequency (RF) power to parallel plate electrodes to form a radio frequency electric field in the processing space in which the substrate is placed can be used. Other plasmas such as inductively coupled plasma and microwave plasma can also be used. The gas that generates the plasma is not particularly limited, and examples thereof include nitrogen (N ２ ) plasma, hydrogen (H ２ ) plasma, ammonia (NH ３ ) plasma may be used. ２ Plasma, H ２ Plasma, NH３ The plasma may contain a rare gas such as Ar. ２ When plasma is used, N ２ The plasma also functions as a nitrogen source for the BN film. The purge gas may also be used as the plasma gas. In particular, when forming an h-BN film, it is preferable to use plasma with energy that does not destroy the basic structure of the source gas.

[0024] In step ST3, after step ST2, the supply of the source gas is stopped and only plasma is supplied. This promotes the adsorption of the source gas and promotes the reaction of the source gas adsorbed on the substrate to BN. Step ST3 is performed consecutively after step ST2. The plasma used in this step may be the same as that used in step ST2.

[0025] In step ST4, a purge gas is supplied into the chamber to purge any remaining gases in the chamber. The purge gas may be an inert gas, and preferably a rare gas such as Ar gas or He gas.

[0026] By performing the sequence of steps ST1 to ST4 as described above, a thin BN unit film is formed, and by repeating this sequence a desired number of times (X1 cycles), a BN film having a desired thickness is formed.

[0027] As described above, in the standard process, the sequence of steps ST1 to ST4 is performed a desired number of times. However, as shown in FIG. 2, a pre-plasma process may be used in which a pre-plasma step (step ST5) is added to perform plasma treatment on the substrate prior to step ST2. This step ST5 is performed to improve the surface smoothness of the BN film to be formed. The pre-plasma step of step ST5 is not particularly limited, but may be performed in the same manner as step ST3. Furthermore, in step ST5, similar to the purging of step ST1, the source gas may be flowed into the exhaust line or the source gas may be filled into a fill tank in preparation for the flow of the source gas.

[0028] In the example of FIG. 2, a thin BN unit film is formed by a sequence of steps ST1, ST5, ST2, ST3, and ST4, and a BN film having a desired thickness is formed by repeating this sequence a desired number of times (X2 cycles).

[0029] 3, instead of step ST1 of the standard process, a preflow process may be used in which a preflow step (step ST6) is performed prior to step ST2 to supply a source gas to the substrate. The preflow step of step ST6 is performed by supplying the same source gas as in step ST2 without using plasma. This preflow step of step ST6 is performed to improve the step coverage of the BN film to be formed. In step ST6, a purge gas such as a rare gas may be supplied together with the source gas. Furthermore, a plasma generating gas may also be supplied.

[0030] In the example of FIG. 3, a thin BN unit film is formed by the sequence of steps ST6, ST2, ST3, and ST4, and by repeating this sequence a desired number of times (X3 cycles), a BN film having a desired thickness is formed.

[0031] In this embodiment, each of the processes shown in FIGS. 1 to 3 includes a sequence including step ST2, in which a source gas and plasma are supplied, and step ST3, in which only plasma is supplied. When performing this sequence a desired number of times, the desired BN film, either an h-BN film or an a-BN film, is formed by adjusting one or more of the deposition conditions, such as the temperature, pressure, the time of step ST2 (deposition time), and the flow rate of the source gas. That is, by employing a deposition technique that repeats a sequence including step ST2 and the subsequent step ST3, it is possible to selectively produce either an h-BN film or an a-BN film by adjusting the deposition conditions. By adjusting the deposition conditions, the crystalline state of the BN film can be varied not only to produce substantially 100% h-BN or substantially 100% a-BN, but also to produce a mixture of h-BN crystals and random BN (a-BN), and the degree of crystallinity of the h-BN can be selected by adjusting the mixture ratio. The a-BN film does not necessarily have to be a complete a-BN film; it may also contain a small amount of h-BN as long as it has the properties of an a-BN film.

[0032] This will be explained in detail below. A method for chemically forming a film by sequential gas supply, such as ALD, is generally known, in which the adsorption and reaction of source gases are alternately performed. In the case of forming a BN film, a method can be considered in which, as shown in FIG. 4 , source gases containing compounds with BN bonds in their molecules and plasma are alternately supplied to repeat the adsorption and reaction. That is, after purging the chamber (step ST101), the source gas supply (step ST102), purging (step ST103), plasma supply (step ST104), and purging (step ST105) are performed a desired number of times (X' cycles). Because no plasma is used when supplying the source gas in step ST102, a constant amount of source gas, approximately one molecular weight, is adsorbed onto the substrate surface. The adsorbed source gas is then activated by the plasma in step ST104, and reacts to form a BN film. Since the adsorbed source gas contains compounds with BN bonds, a two-dimensional h-BN film is likely to be formed. In particular, when the compound having a BN bond is a borazine-based compound, the ligand is removed while maintaining the basic skeleton of the borazine-based compound, making it easier to form an h-BN film with a two-dimensional structure.

[0033] Thus, in film formation using alternate supply, the BN film formed is mainly h-BN film, and it is difficult to form a-BN film. Furthermore, because compounds having BN bonds, such as borazine-based compounds, in the adsorbed source gas are activated by plasma, the compounds having BN bonds in the film react with each other, making it difficult for the source gas supplied in the next cycle to adsorb. This results in a low film formation rate (GPC).

[0034] In contrast, in this embodiment, when a source gas containing a compound having a BN bond in its molecule is supplied, plasma is supplied to activate the compound having a BN bond, promoting the adsorption and reaction of the source gas. The subsequent supply of plasma alone further promotes the reaction. Therefore, by adjusting the film formation conditions, the adsorption and reaction states of the source gas can be changed to adjust the amount of h-BN crystals and random BN (a-BN), allowing the desired BN film to be formed, either an h-BN film or an a-BN film. In other words, it is possible to selectively produce an h-BN film or an a-BN film. Furthermore, by promoting the adsorption and reaction of the source gas in this manner, the film formation rate (GPC) can be increased.

[0035] The film formation conditions at this time include the time for supplying the source gas and plasma in step ST2 (source gas adsorption time (depo time)), the source gas supply amount, pressure, and temperature. As described above, the film formation conditions are adjusted to selectively produce h-BN films and a-BN films. By adjusting the film formation conditions, the crystalline state can be changed to not only nearly 100% h-BN and nearly 100% a-BN, but also to a mixture of h-BN crystals and random BN (a-BN), and the degree of crystallinity of the h-BN can be selected by adjusting the mixture ratio.

[0036] Among the film formation conditions, with regard to the depo time, if the depo time is short, it is possible to form h-BN, a two-dimensional material with a honeycomb crystal structure, while maintaining the BN bond of the source gas. In particular, when a source gas containing a borazine-based compound is used, it is possible to form h-BN, a two-dimensional material with a honeycomb crystal structure, while maintaining the basic skeleton of the borazine-based compound. In contrast, as the depo time increases, the reaction of the compound with BN bonds is greatly promoted, causing disorder in the h-BN crystal, resulting in a transition to a film formation mode of a-BN, which does not have clear crystallinity. In other words, it is possible to produce h-BN films and a-BN films differently depending on the depo time.

[0037] Regarding the supply amount of the source gas, if the supply amount is small, h-BN can be formed while maintaining the BN bond, or when a borazine-based compound is used, while maintaining its basic skeleton. However, as the supply amount of the source gas increases, the reaction of the borazine-based compound is greatly promoted, and similarly, the h-BN crystal becomes disordered, resulting in a transition to a-BN film formation mode.

[0038] Regarding pressure, crystallinity is disrupted by lowering the pressure, and h-BN films can be formed under high pressure conditions, while a-BN films can be formed under low pressure conditions, making it possible to selectively produce either h-BN or a-BN films.Regarding temperature, crystallinity is disrupted by lowering the pressure, and h-BN films can be formed under high pressure conditions, while a-BN films can be formed under low pressure conditions, making it possible to selectively produce either h-BN or a-BN films.

[0039] Furthermore, in this embodiment, the adsorption and reaction of the source gas is promoted in this way, which results in sufficient nitridation, resulting in a BN film with high density and good film quality. In particular, by depositing the film at a temperature of 250°C or higher and under high pressure conditions, for example, 6 Torr (800 Pa) or higher, an h-BN film with good crystallinity, high density, and excellent water resistance and surface smoothness can be obtained.

[0040] The h-BN film thus produced can be used as an underlayer for photoresist (PR) in photolithography. In particular, as shown in FIG. 5 , it is suitable for use as an underlayer for photoresist when etching is performed after forming a protective film only on the exposed and developed photoresist. Specifically, as shown in FIG. 5( a), a BN film 101 is formed as an underlayer for photoresist (PR) 102 on a hard mask (e.g., SOC, SOG) 105 on a Si substrate 104. Then, as shown in FIG. 5( b), a pattern is formed in the photoresist 102 by exposure and development. As shown in FIG. 5( c), a protective film 103 is formed only on the photoresist 102, and etching is performed in this state. Forming the protective film 103 improves the etching resistance of the photoresist 102, and since a line width can be obtained even with a small exposure dose, throughput during EUV exposure is improved. The underlying photoresist 102 used in forming the protective film 103 is preferably a metal oxide resist (MOR), which has heat and plasma resistance against the heat, plasma, and other factors that occur during the formation of the protective film 103. However, if the BN film 101 used for such applications is incompletely nitrided, the following problems arise: The BN film is etched by the developer (water), causing the BN film 101 to peel off; and, due to its high surface roughness and low density, photoresist residue is likely to remain after development, impairing the selectivity of the protective film and affecting the pattern shape. In contrast, the BN film formed according to this embodiment is sufficiently nitrided, resulting in good film quality and high density. By forming the BN film under high-pressure conditions, an h-BN film with properties suitable for the above applications can be obtained. In other words, under high pressure conditions (for example, 6 Torr (800 Pa) or higher), an h-BN film can be obtained that has good crystallinity (lateral orientation), high density, high etching resistance (water resistance) to the developer (water), and low surface roughness (high surface smoothness). As a result, photoresist residue is less likely to remain after development, making it less likely to affect the pattern shape.

[0041] Next, we will explain the experiments in which the film formation conditions were actually adjusted. In the following experiments 1 to 5, the film formation conditions were adjusted to confirm the distinction between the formation of h-BN films and a-BN films, and in experiment 6, the manufacturing conditions for a BN film suitable as an underlayer for a photoresist were confirmed.

[0042] In Experiment 1, the supply time of the source gas and plasma (Depo time) in step ST2 was changed to confirm whether h-BN films and a-BN films could be fabricated by the standard process shown in Figure 1. Note that here, TMB was used as the source gas and N was used as the plasma. ２ 10 described later, the pressure was 8 Torr (1066 Pa), the temperature was 400° C., the flow rate of TMB was 20 sccm, and the RF power was 400 W. The time for steps ST1 and ST4 was 3 seconds, and the time for step ST3 was 4 seconds.

[0043] FIG. 6 shows the relationship between the deposition time and the GPC results obtained from the film thickness measured by Ellipso and the film thickness measured by TEM. As shown in this figure, it can be seen that the GPC results increase rapidly when the deposition time is 2 seconds or more. This is due to the significant acceleration of the TMB reaction. However, as the deposition time increases, the measurement accuracy of the GPC results obtained from the film thickness measured by Ellipso decreases. This suggests that the h-BN crystals become disordered as the deposition time increases. The crystalline state of the film cross section was observed by TEM for deposition times of 2 seconds, 3 seconds, and 4 seconds. As a result, it was confirmed that at 2 seconds, the film almost entirely had a lateral structure specific to h-BN crystals, but at 3 seconds, a random structure (amorphous) was also observed, with the lateral structure being partial, and at 4 seconds, the film almost entirely had a random structure. That is, when the deposition time is 2 seconds, the entire film becomes an h-BN film, but when it is 3 seconds, the h-BN crystal is maintained but the crystallinity decreases, and when it is 4 seconds, the entire film becomes a-BN. From this, it was confirmed that the h-BN crystal can be made amorphous by extending the deposition time, and it is possible to produce h-BN films and a-BN films separately.

[0044] In Experiment 2, the pressure in step ST2 was changed to 4 Torr (533 Pa), 6 Torr (800 Pa), and 8 Torr (1066 Pa), and the formation of h-BN films and a-BN films was confirmed by the standard process shown in Figure 1. Note that here, TMB was used as the source gas and N was used as the plasma. ２ 10 described later, the temperature was set to 400° C., the flow rate of TMB was set to 20 sccm, and the RF power was set to 400 W. The time for steps ST1 and ST4 was set to 3 seconds, the time for step ST2 was set to 2 seconds, and the time for step ST3 was set to 4 seconds.

[0045] The crystalline state of the cross section of the BN film formed under these pressure variations was observed using a TEM. As a result, it was confirmed that at a pressure of 8 Torr (1066 Pa), the film was almost entirely composed of h-BN crystals in a lateral structure, whereas at 6 Torr (800 Pa), a random structure (amorphous) was also observed, with the lateral structure being partial. At 4 Torr (533 Pa), the film was almost entirely composed of random structure. That is, at a pressure of 8 Torr (1066 Pa), the film was almost entirely composed of h-BN, whereas at 6 Torr (800 Pa), the h-BN crystal structure was maintained but the crystallinity decreased. At 4 Torr (533 Pa), the film was composed of a-BN. This confirms that it is possible to selectively produce h-BN and a-BN films by varying the pressure.

[0046] In Experiment 3, the pressure and temperature in step ST2 were changed to confirm whether h-BN films and a-BN films could be fabricated using the standard process shown in Figure 1. Note that here, TMB was used as the source gas and N was used as the plasma. ２ 10 described later, the flow rate of TMB was set to 20 sccm and the RF power was set to 400 W. The time for steps ST1 and ST4 was set to 3 seconds, the time for step ST2 was set to 4 seconds, and the time for step ST3 was set to 4 seconds. The pressures were set to 1.5 Torr (200 Pa) and 8 Torr (1066 Pa), and the temperatures were set to 200°C and 400°C.

[0047] The crystalline state of the cross section of the BN film formed by changing the pressure and temperature in this way was observed by TEM. As a result, when the pressure was 8 Torr (1066 Pa) and the temperature was 400°C, a lateral structure indicating h-BN crystals was partially observed, but when the pressure was 8 Torr (1066 Pa) and the temperature was 200°C, when the pressure was 1.5 Torr (200 Pa) and the temperature was 400°C, and when the pressure was 1.5 Torr (200 Pa) and the temperature was 200°C, it was confirmed that the structure was almost entirely random. In addition, the FT-IR spectrum of the film formed under these conditions was obtained. As a result, as shown in Figure 7, when the pressure was 8 Torr (1066 Pa) and the temperature was 400°C, the wave number was 1380 cm －１ While a clear h-BN peak was observed around this temperature, the peak was significantly reduced when the pressure was 8 Torr (1066 Pa) and the temperature was 200°C, when the pressure was 1.5 Torr (200 Pa) and the temperature was 400°C, and when the pressure was 1.5 Torr (200 Pa) and the temperature was 200°C. This means that h-BN crystals appeared only when the pressure was 8 Torr (1066 Pa) and the temperature was 400°C, while when the pressure was 1.5 Torr (200 Pa) and the temperature was 200°C, almost no h-BN crystals crystallized, resulting in a-BN. This confirms that it is possible to produce h-BN and a-BN films by varying the pressure or temperature.

[0048] In Experiment 4, the temperature, pressure, TMB flow rate, and deposition time were changed in the preflow process shown in Figure 3 to confirm whether h-BN films and a-BN films could be fabricated. ２10 described later, RF power was set to 400 W, the time for step ST6 was set to 3 seconds, the time for step ST3 was set to 8 seconds, and the time for step ST4 was set to 3 seconds. The temperature, pressure, TMB flow rate, and deposition time were set to the following conditions for cases 1 to 3. Case 1: Temperature: 400°C, Pressure: 8 Torr (1066 Pa), TMB flow rate: 10 sccm, Deposition time: 4 seconds. Case 2: Temperature: 400°C, Pressure: 1.5 Torr (200 Pa), TMB flow rate: 200 sccm, Deposition time: 1 second. Case 3: Temperature: 200°C, Pressure: 1.5 Torr (200 Pa), TMB flow rate: 20 sccm, Deposition time: 1 second.

[0049] The crystalline state of the cross section of the BN films formed under the conditions of Cases 1 to 3 was observed by TEM. As a result, it was confirmed that in Case 1, almost the entire film had a lateral structure indicating h-BN crystals, while in Case 2, a random structure (amorphous) was also observed and the lateral structure was partial, and in Case 3, almost the entire film had a random structure. That is, in the case of the preflow process, as in the standard process of Experiments 1 to 3, it was confirmed that h-BN films and a-BN films could be produced separately by adjusting the temperature, pressure, and deposition time, and that h-BN films and a-BN films could be produced separately by adjusting the TMB flow rate.

[0050] In Experiment 5, the deposition time, pressure, and temperature in step ST2 were changed to investigate in detail whether an h-BN film or an a-BN film was formed when a BN film was formed by the standard process shown in Figure 1. Here, similarly, TMB was used as the source gas and N was used as the plasma. ２ Using plasma, the film formation apparatus shown in FIG. 10 (described later) was used, with the pressure varied from 1.5 to 8 Torr (200 to 1066 Pa), the temperature varied from 200 to 400° C., and the deposition time was set to two levels: 2 seconds and 4 seconds. The TMB flow rate was 20 sccm, and the RF power was 400 W. The time for steps ST1 and ST4 was 3 seconds, and the time for step ST3 was 4 seconds.

[0051] The FT-IR spectrum of the BN film formed under the above-mentioned conditions was measured. －１ The height of the h-BN peak near the 1380 cm of the film formed by the alternate supply method, which was confirmed to be entirely h-BN, was used to determine whether the BN film was an h-BN film or an a-BN film. －１ When the peak height of h-BN in the vicinity is taken as 1, a film having a peak height of less than 0.2 is defined as an a-BN film.

[0052] 8 and 9 are correlation diagrams showing whether an h-BN film or an a-BN film is formed depending on the pressure and temperature, with the horizontal axis representing pressure and the vertical axis representing temperature. Fig. 8 shows the results for a deposition time of 2 seconds, and Fig. 9 shows the results for a deposition time of 4 seconds. As shown in these figures, it was confirmed that it is possible to produce either an h-BN film or an a-BN film by adjusting the deposition time, pressure, and temperature. As shown in Figs. 8 and 9, the a-BN region increases as the deposition time increases. Specifically, when the deposition time is 2 seconds as shown in FIG. 8, h-BN films are obtained in the pressure range of 1.5 to 8 Torr (200 to 1066 Pa) and the temperature range of 200 to 400°C. On the other hand, when the deposition time is 4 seconds as shown in FIG. 9, the range in which h-BN films can be obtained is narrowed to a pressure of 5 Torr or more and a temperature of 350°C or more.

[0053] 8 and 9, the h-BN peak height is greater than 0.2 near the boundary with a-BN, but it is believed that a large amount of random crystals is mixed in. The ratio of h-BN crystals is thought to increase the further away from the boundary with a-BN. Figures 8 and 9 suggest that by setting the Depo time to 2 seconds or more and 4 seconds or less, the ratio of h-BN to a-BN can be adjusted as desired within the pressure range of 8 Torr (1066 Pa) or less and the temperature range of 200 to 400°C.

[0054] 8 also suggests that when the deposition time is 2 seconds and the pressure is 8 Torr or less, an h-BN film is obtained at 200° C. or more, whereas when the pressure is 8 Torr (1066 Pa) or more, an h-BN film is obtained even at 200° C. or less. This indicates that when the deposition time is 2 seconds or less and the pressure is 8 Torr (1066 Pa) or more, an h-BN film is obtained even at 200° C. or less.

[0055] 9 also suggests that when the deposition time is 4 seconds and the pressure is 6 Torr (800 Pa) or higher, an a-BN film is obtained at 350° C. or lower, whereas when the pressure is 6 Torr (800 Pa) or lower, an a-BN film is obtained even at 350° C. or higher. This indicates that when the deposition time is 4 seconds or longer and the pressure is 6 Torr (800 Pa) or lower, an a-BN film is obtained even at a temperature of 350° C. or higher.

[0056] In Experiment 6, TDMAB was used as the source gas and NH ３ The standard process shown in Fig. 1 was carried out using a SiO2 / Ar plasma with the deposition apparatus shown in Fig. 10 (described later). The time for step ST2 was set to 2 seconds and the time for step ST3 was set to 4 seconds. As a result, it was confirmed that an h-BN film with good crystallinity could be obtained at a temperature of 250°C or higher and a pressure of 6 Torr (800 Pa) or higher.

[0057] The crystallinity, surface smoothness, water resistance, and film density of BN films formed by the above-described standard process (step ST2: 2 seconds, step ST3: 4 seconds) and a process in which CVD is performed without performing the cycle of steps ST1 to ST4 (no-cycle process) were actually evaluated. Here, the temperature was set to 300°C, and the no-cycle process was performed at two pressure levels: 2 Torr (266 Pa) and 6 Torr (800 Pa), while the standard process was performed at a pressure of 6 Torr (800 Pa). Crystallinity was confirmed by TEM, surface smoothness (surface roughness) was evaluated by the arithmetic mean height Sa (nm) obtained from SEM images and AFM images, water resistance was evaluated by the surface roughness (Sa (nm)) after water etching, and film density was determined by XRR (X-ray reflectivity measurement).

[0058] The evaluation of these BN films yielded the following results. The BN film formed by the non-cycling process at a pressure of 2 Torr (266 Pa) was confirmed to be a-BN film with random orientation, and its surface roughness was too large to capture roughness of about 10 nm, making it impossible to accurately determine Sa. The film density was 1.91 g / cm. ３ The water resistance of this BN film was not evaluated because the surface roughness was too great.

[0059] The BN film formed by the non-cycling process at a pressure of 6 Torr (800 Pa) was confirmed to be a laterally oriented h-BN film, but the surface roughness was relatively large with Sa of 0.26 nm, and after water etching, Sa increased to 0.30 nm, confirming poor water resistance. The film density was 1.92 g / cm ３ This was slightly higher than that of the BN film at a pressure of 2 Torr (266 Pa).

[0060] The BN film formed in the standard process at a pressure of 6 Torr (800 Pa) was confirmed to be a laterally oriented h-BN film with good crystallinity, and its surface roughness was confirmed to be small (highly smooth), with a surface roughness of 0.22 nm. Furthermore, the surface roughness after water etching was 0.21 nm, and no increase in surface roughness was observed due to water etching, confirming high water resistance. Furthermore, the film density was 1.94 g / cm. ３ was a high value.

[0061] As described above, Experiment 6 confirmed that by employing a method of repeating a cycle including Steps ST2 and ST3 and setting the pressure at 6 Torr (800 Pa) or higher, sufficient nitridation was achieved, sufficient lateral orientation was achieved, and an h-BN film with good crystallinity and high film density was obtained. It was also confirmed that the h-BN film obtained in this manner had reduced surface roughness (higher smoothness) and improved water resistance. In other words, it was confirmed that the h-BN film produced in this manner is suitable for use as an underlayer for a photoresist when a protective film is formed only on the exposed and developed photoresist and then etched.

[0062] <Film Forming Apparatus> Next, an example of a film forming apparatus that can be applied to the implementation of the above-described BN film forming method will be described.

[0063] 10 is a cross-sectional view showing an example of a film formation apparatus. The film formation apparatus 100 includes a chamber 1, a mounting table 2, a shower head 3, an exhaust unit 4, a gas supply mechanism 5, a plasma generation unit 6, and a control unit 7, and forms a BN film on a substrate W. The substrate W is not particularly limited, and may be, for example, a semiconductor substrate such as a Si substrate.

[0064] The chamber 1 is made of a metal such as aluminum and has a substantially cylindrical shape. A loading / unloading port 11 for loading and unloading a substrate W is formed in a side wall of the chamber 1, and the loading / unloading port 11 can be opened and closed by a gate valve 12. A circular exhaust duct 13 with a rectangular cross section is provided above the main body of the chamber 1. A slit 13a is formed along the inner peripheral surface of the exhaust duct 13. An exhaust port 13b is formed in the outer wall of the exhaust duct 13. A ceiling wall 14 is provided on the upper surface of the exhaust duct 13 to close the upper opening of the chamber 1. The space between the ceiling wall 14 and the exhaust duct 13 is airtightly sealed by a seal ring 15.

[0065] The mounting table 2, on which the substrate W is placed in a horizontal position, is disk-shaped and sized to accommodate the substrate W, and is supported by a support member 23. The mounting table 2 is made of a ceramic material such as aluminum nitride (AlN) or a metal material such as aluminum or a nickel-based alloy, and has a heater 21 embedded therein for heating the substrate W. A cover member 22 is provided on the mounting table 2 to cover the side surface.

[0066] A support member 23 that supports the mounting table 2 extends from the center of the bottom surface of the mounting table 2 below the chamber 1 through a hole formed in the bottom wall of the chamber 1, and its lower end is connected to a mounting table lifting mechanism 24. The mounting table lifting mechanism 24 enables the mounting table 2 to be raised and lowered via the support member 23 between a processing position shown by a solid line and a transfer position shown by a dot-dash line below that position where a substrate can be transferred. In addition, a flange 25 is attached to the support member 23 below the chamber 1, and a bellows 26 that separates the atmosphere inside the chamber 1 from the outside air and expands and contracts as the mounting table 2 is raised and lowered is provided between the bottom surface of the chamber 1 and the flange 25.

[0067] Three substrate support pins 27 (only two shown) are provided near the bottom surface of the chamber 1, protruding upward from a lift plate 27a. The substrate support pins 27 can be raised and lowered via the lift plate 27a by a substrate support pin lift mechanism 28 provided below the chamber 1, and are inserted into through holes 2a provided in the mounting table 2 at the transfer position, so that they can be protruded and retracted relative to the upper surface of the mounting table 2. By raising and lowering the substrate support pins 27 in this manner, the substrate W is transferred between the substrate transfer mechanism (not shown) and the mounting table 2. A bellows 28a is provided between the bottom surface of the chamber 1 and the substrate support pin lift mechanism 28.

[0068] The showerhead 3 supplies a process gas into the chamber 1 in a shower-like manner. The showerhead 3 is disposed opposite the mounting table 2 and has approximately the same diameter as the mounting table 2. The showerhead 3 includes a shower body 31 fixed to the ceiling wall 14 of the chamber 1 and a shower plate 32 connected below the shower body 31. A gas diffusion space 33 is formed between the shower body 31 and the shower plate 32. A gas inlet hole 36 is provided to penetrate the center of the shower body 31 and the ceiling wall 14 of the chamber 1 and is connected to this gas diffusion space 33. The shower plate 32 has gas outlet holes 34. When the mounting table 2 is in the processing position, a processing space S is formed between the shower plate 32 and the mounting table 2.

[0069] The exhaust unit 4 includes an exhaust pipe 41 connected to the exhaust port 13b of the exhaust duct 13, an automatic pressure control (APC) valve 42 connected to the exhaust pipe 41, and an exhaust mechanism 43 having a vacuum pump. During processing, gas inside the chamber 1 reaches the exhaust duct 13 through the slit 13a and is exhausted from the exhaust duct 13 through the exhaust pipe 41 by the exhaust mechanism 43 of the exhaust unit 4.

[0070] The gas supply mechanism 5 supplies the gas used for film formation to the shower head 3, and supplies a source gas containing a compound having a BN bond in its molecule, a plasma gas, and a purge gas. In this example, TMB, a borazine-based compound, is used as the source gas containing a compound having a BN bond in its molecule, and N is used as the plasma gas. ２ In this example, Ar gas is used as the purge gas, but as described above, the compound having a BN bond in its molecule may be other borazine compounds or aminoborane compounds, and the plasma gas and purge gas are not limited to these.

[0071] The gas supply mechanism 5 includes a TMB gas supply source 51 that supplies TMB gas as a raw material gas, and a N ２ Gas supply N ２ The chamber includes a gas supply source 52, a first Ar gas supply source 53, and a second Ar gas supply source 54 for supplying Ar gas as a purge gas.

[0072] One end of a TMB gas line 55 is connected to the TMB gas supply source 51, and a valve 55a, a fill tank 55b, and a flow rate regulator 55c are disposed in the TMB gas line 55 in this order from the downstream side. ２ The gas supply source 52 contains N ２ One end of the gas line 56 is connected to ２ The gas line 56 is provided with a valve 56a, a fill tank 56b, and a flow rate regulator 56c in this order from the downstream side. ２ The gas line 56 is connected to one end of a common line 59 , and the other end of the common line 59 is connected to the gas inlet hole 36 of the showerhead 3 .

[0073] One end of a first Ar gas line 57 is connected to the first Ar gas supply source 53, and a valve 57a and a flow rate adjuster 57c are provided in the first Ar gas line 57, in that order from the downstream side. The other end of the first Ar gas line 57 is connected to a TMB gas line 55 downstream of a valve 54a. One end of a second Ar gas line 58 is connected to the second Ar gas supply source 54, and a valve 58a and a flow rate adjuster 58c are provided in the second Ar gas line 58, in that order from the downstream side. The other end of the second Ar gas line 58 is connected to a N ２ The valves 57a and 58a are connected downstream of the valve 56a of the gas line 56. During the film formation process, the valves 57a and 58a are always open, and Ar gas as a purge gas is supplied from the first Ar gas line 57 and the second Ar gas line 58 to the TMB gas line 55, the N ２ It is constantly supplied into the chamber 1 via a gas line 56 .

[0074] The valves 55a and 56a are configured as high-speed on-off valves that open and close the corresponding gas lines at high speed, while the valves 57a and 58a are normal on-off valves.

[0075] Fill tanks 55b and 56b contain TMB gas and N ２The gas is temporarily stored in the fill tanks 55b and 56b before being supplied to the chamber 1. By storing the gas in the fill tanks 55b and 56b, the pressure inside the fill tanks 55b and 56b can be increased to a predetermined level, and then the valves 55a and 56a can be opened to discharge the gas into the chamber 1. This allows a large flow rate of gas to be stably supplied to the chamber 1.

[0076] The flow rate adjusting units 55c, 56c, 57c, and 58c are configured by, for example, mass flow controllers, and adjust and control the flow rates of the gases flowing through the corresponding gas lines.

[0077] The plasma generation unit 6 has a power supply line 61 connected to the shower body 31 of the shower head 3, and a matching box 62 and a radio frequency (RF) power supply 63 connected to the power supply line 61. When radio frequency (RF) power is supplied from the RF power supply 63 to the shower head 3, a radio frequency (RF) electric field is formed in the processing space S between the shower head 3 and the mounting table 2, and this RF electric field generates N ２ When the mounting table 2 is made of a ceramic material, an electrode is embedded in the mounting table 2, and an RF electric field is formed between the shower head 3 and the electrode.

[0078] The control unit 7 is configured as a computer and includes a main control unit with a CPU, an input device, an output device, a display device, and a storage device (storage medium). The main control unit controls components of the film formation apparatus 100, such as valves, flow rate regulators, automatic pressure control valves, heaters, and lifting mechanisms. The storage device stores parameters for various processes executed by the film formation apparatus 100. The storage device also includes a storage medium that stores programs for controlling processes executed by the film formation apparatus 100, i.e., process recipes. The main control unit calls up a predetermined process recipe stored in the storage medium and causes the film formation apparatus 100 to perform a predetermined operation based on the process recipe.

[0079] In the film forming apparatus 100 configured as described above, first, the gate valve 12 is opened, and a transfer device (not shown) loads a substrate W into the chamber 1 through the load / unload port 11, and the substrate W is placed on the mounting table 2. The transfer device is retracted, and the mounting table 2 is raised to the processing position. Then, the gate valve 12 is closed, and the chamber 1 is evacuated, and the heater 21 heats and controls the temperature of the mounting table 2 (substrate temperature) to a desired temperature.

[0080] In this state, the actual film formation process is started. When the above-mentioned standard process is performed, first, Ar gas is supplied as a purge gas from the first Ar gas supply source 53 and the second Ar gas supply source 54 to the processing space S via the first Ar gas line 57 and the second Ar gas line 58 and the shower head 3, thereby purging the inside of the chamber 1 in step ST1 (step ST1). At this time, N 2 as a plasma gas is supplied. ２ Alternatively, preparation for supply may be made by filling a fill tank with TMB gas, which is a raw material gas, or by letting it flow through an exhaust line.

[0081] Next, TMB gas and N ２ Plasma is supplied (step ST2). Specifically, N ２ Gas supply source 52 to N ２ N as a plasma gas is introduced into the processing space S via the gas line 56 and the shower head 3. ２ While the gas is being supplied, RF power is supplied from the RF power source 63 of the plasma generating unit 6 to the shower head 3. As a result, N ２ Furthermore, TMB gas, which is a source gas, is supplied from the TMB gas supply source 51 to the processing space S via the TMB gas line 55 and the shower head 3. As a result, the substrate W is exposed to the TMB gas and N ２ Plasma is supplied, and TMB gas is adsorbed onto the substrate W, and the TMB gas is ２ The adsorption is promoted by activation with plasma.

[0082] After step ST2 is completed, N ２While the plasma generation is continued, the valve 55a is closed to stop the TMB gas, and the N ２ Only plasma is supplied (step ST3), which promotes the adsorption of TMB gas and the reaction of TMB gas with BN.

[0083] Next, the RF power from the RF power supply 63 is turned off, and the valve 56a is closed to ２ The gas supply is stopped, and the chamber 1 is purged while Ar gas is still being supplied (step ST4).

[0084] By repeating the sequence of steps ST1 to ST4 as many times as desired, a BN film having a desired thickness is formed.

[0085] In the case of the above-described pre-plasma process, after step ST1, N ２ A step of supplying plasma (step ST5) is performed. Specifically, N 2 is supplied as a plasma gas to the processing space S. ２ With the gas being supplied, RF power is supplied from the RF power source 63 of the plasma generating unit 6 to the shower head 3 .

[0086] Next, in this state, TMB gas is supplied to the processing space S to perform step ST2, and then the supply of TMB gas is stopped to perform step ST3. Next, the RF power from the RF power source 63 is turned off, and N ２ The supply of gas is stopped, and the chamber 1 is purged with Ar gas in step ST4.

[0087] By repeating the sequence of steps ST1, ST5, ST2, ST3, and ST4 as many times as desired, a BN film having a desired thickness is formed.

[0088] In the case of the above-described preflow process, instead of step ST1, Ar gas (or Ar gas and N ２ A pre-flow step (step ST6) is performed in which TMB gas is supplied to the processing space S in addition to the N gas. Next, RF power is supplied to the shower head 3 to ２Plasma is generated and step ST2 is performed. Then, the TMB gas is stopped and step ST3 is performed. Then, the RF power is turned off and N ２ The supply of gas is stopped, and the purging of step ST4 is performed while keeping the supply of Ar gas.

[0089] By repeating the sequence of steps ST6, ST2, ST3, and ST4 as many times as desired, a BN film having a desired thickness is formed.

[0090] In both processes, the raw material gases TMB gas and N ２ Step ST2 of supplying plasma and subsequent step N ２ Therefore, as described above, by repeating this sequence and adjusting one or more of the film formation conditions, such as the temperature, pressure, the time for step ST2 (deposition time), and the flow rate of the source gas, it is possible to selectively form an h-BN film or an a-BN film.

[0091] Although the embodiments have been described above, the disclosed embodiments should be considered to be illustrative and not restrictive in all respects. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0092] For example, in the above embodiment, the standard process, the pre-plasma process, and the pre-flow process have been described as examples of film formation techniques, but the present invention is not limited to these as long as the basic sequence includes a step of supplying a source gas containing a compound having a BN bond in its molecule and plasma to a substrate, and a subsequent step of supplying plasma to the substrate.

[0093] 10 is merely an example of a film formation apparatus, and is not particularly limited as long as it sequentially performs step ST2 of supplying raw material gas and plasma to the substrate and step ST3 of supplying plasma to the substrate, and may be a single-wafer type or a batch type. Furthermore, the film formation apparatus 100 of FIG. 10 illustrates an example in which RF power is supplied to the shower head 3 to generate capacitively coupled plasma between the shower head 3 and the mounting table 2, but this is not limiting and various types of plasma, such as inductively coupled plasma and microwave plasma, may be used. Furthermore, remote plasma may be used in which plasma generated at another location is transported to the substrate.

[0094] The above-described embodiments also include the following aspects: "A method for forming a boron nitride film, comprising: performing a sequence including the steps of supplying a source gas containing a compound having a BN bond in its molecule and plasma to a substrate placed in a chamber, and subsequently supplying plasma to the substrate without supplying the source gas, a desired number of times, and adjusting the pressure within the chamber as a film formation condition during the sequence."

[0095] 1; chamber; 2; mounting table; 3; shower head; 4; exhaust section; 5; gas supply mechanism; 6; plasma generation unit; 7; control section; 51; TMB gas supply source; 52; N ２ Gas supply sources 53, 54; Ar gas supply source 100; film forming apparatus 101; BN film 102; photoresist 103; protective film, W; substrate

Claims

1. A method for forming a boron nitride film, comprising: supplying a source gas containing a compound having a BN bond in its molecule and plasma to a substrate placed in a chamber; and subsequently supplying plasma to the substrate without supplying the source gas, the sequence including the steps being repeated a desired number of times, and by adjusting the film formation conditions during the process, a desired boron nitride film is formed from either a hexagonal boron nitride film or an amorphous boron nitride film.

2. The method of forming a boron nitride film as described in claim 1, wherein the film formation conditions are one or more of the temperature during film formation, the pressure in the chamber, the time for supplying the raw material gas and plasma, and the flow rate of the raw material gas.

3. The plasma is N ２ Plasma, H ２ Plasma, NH ３ 2. The method for forming a boron nitride film according to claim 1, wherein the method is either a plasma or a gas.

4. A method for forming a boron nitride film according to any one of claims 1 to 3, wherein the sequence comprises purging the chamber, then supplying the source gas and the plasma to the substrate, subsequently supplying the plasma to the substrate without supplying the source gas, and then purging the chamber.

5. A method for forming a boron nitride film according to any one of claims 1 to 3, wherein the sequence comprises purging the chamber, then supplying a plasma to the substrate, then supplying the source gas and the plasma to the substrate, subsequently supplying the plasma to the substrate without supplying the source gas, and then purging the chamber.

6. A method for forming a boron nitride film according to any one of claims 1 to 3, wherein the sequence comprises: supplying the source gas to the substrate; then supplying the source gas and the plasma to the substrate; subsequently supplying the plasma to the substrate without supplying the source gas; and then purging the chamber.

7. A method for forming a boron nitride film according to any one of claims 1 to 3, wherein the compound having a BN bond in its molecule is a borazine-based compound.

8. A method for forming a boron nitride film according to any one of claims 1 to 3, wherein the compound having a BN bond in the molecule is an aminoborane compound.

9. The method for forming a boron nitride film according to claim 7, wherein the borazine-based compound is an alkylborazine compound.

10. The borazine compound is trimethylborazine, and the plasma is N ２ The method for forming a boron nitride film according to claim 9, wherein the method is plasma.

11. The method for forming a boron nitride film according to claim 10, wherein the film forming conditions are that the time for supplying the source gas and the plasma is 4 seconds or more, the pressure in the chamber is 6 Torr or less, and an amorphous boron nitride film is formed even at a temperature of 350° C. or more.

12. A method for forming a boron nitride film as described in claim 10, wherein the film forming conditions are that the time for supplying the source gas and the plasma is 2 seconds or less, the pressure in the chamber is 8 Torr or more, and a hexagonal boron nitride film is formed even at a temperature of 200° C. or less.

13. A method for forming a boron nitride film as set forth in claim 10, wherein the film forming conditions include a supply time of the source gas and the plasma of 2 sec or more and 4 sec or less, a pressure of the chamber of 8 Torr or less, and a temperature in the range of 200 to 400° C., and a boron nitride film is formed in which the ratio of hexagonal boron nitride to amorphous boron nitride is arbitrarily adjusted.

14. The aminoborane compound is tris(dimethyl)aminoborane, and the plasma is NH ３ The method for forming a boron nitride film according to claim 8, wherein the method is plasma.

15. The method for forming a boron nitride film according to claim 14, wherein a hexagonal boron nitride film is formed under film formation conditions of a temperature of 250° C. or higher and a pressure in the chamber of 6 Torr or higher.

16. The method for forming a boron nitride film according to claim 2, wherein the film formation condition is such that the pressure inside the chamber is adjusted to form a hexagonal boron nitride film having excellent surface smoothness and water resistance.

17. A film formation apparatus comprising: a chamber for accommodating a substrate; a gas supply mechanism for supplying into said chamber a raw material gas containing a compound having a BN bond in its molecule and a gas for generating plasma; an exhaust mechanism for exhausting the inside of said processing vessel; a plasma generation unit for generating plasma; a heating mechanism for heating said substrate; and a control unit, wherein said control unit performs a sequence including supplying the raw material gas and plasma to a substrate placed in said chamber and subsequently supplying plasma to said substrate without supplying said raw material gas a desired number of times, and at that time, controls said gas supply mechanism, said exhaust mechanism, said plasma generation unit and said heating mechanism by adjusting film formation conditions so that a desired boron nitride film is formed from a hexagonal boron nitride film or an amorphous boron nitride film.

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