Film forming method

In Example 1, an effect imparted to an amorphous carbon film when a TiO 2 film as a metal oxide film is formed through a PEALD method on the amorphous carbon film as a base film having a predetermined pattern was evaluated by observing a cross-sectional shape of the amorphous carbon film. In addition, in Example 1, the TiO 2 film was formed through the PEALD method in the processing container 10 adjusted to 0.5 Torr (67 Pa). In addition, in the oxidation step, high frequency power of 13.56 MHz was applied from a high frequency power supply. In addition, the cross-sectional shape was observed using a scanning electron microscope (SEM) and a scanning transmission electron microscope (STEM).

FIG. 6 is a diagram illustrating a cross-sectional shape of a metal oxide film formed by a film forming method in Example 1. The leftmost diagram in FIG. 6 is a STEM photograph when a TiO 2 film having a thickness of 15 nm was formed using TiCl 4 as a metal-containing gas. The second diagram from the left side is a STEM photograph when a TiO 2 film having a thickness of 1 nm was formed using TDMAT as a metal-containing gas, and thereafter a TiO 2 film having a thickness of 14 nm was formed using TiCl 4 as a metal-containing gas. The third diagram from the left side is a STEM photograph when a TiO 2 film having a thickness of 3 nm was formed using TDMAT as a metal-containing gas, and thereafter a TiO 2 film having a thickness of 12 nm was formed using TiCl 4 as a metal-containing gas. The fourth diagram from the left side is a STEM photograph when a TiO 2 film having a thickness of 5 nm was formed using TDMAT as a metal-containing gas, and thereafter a TiO 2 film having a thickness of 10 nm was formed using TiCl 4 as a metal-containing gas. The rightmost diagram is a STEM photograph when a TiO 2 film having a thickness of 15 nm was formed using TDMAT as a metal-containing gas.

As illustrated in FIG. 6 , when forming the TiO 2 film having a thickness of 15 nm on the amorphous carbon film using TiCl 4 , the pattern of the amorphous carbon film is etched so that corner portions thereof are rounded. From this result, it can be understood that the amorphous carbon film is damaged when the TiO 2 film having a thickness of 15 nm, for example, using TiCl 4 .

On the other hand, when forming the TiO 2 film using TDMAT on the amorphous carbon film, and thereafter forming the TiO 2 film using TiCl 4 thereon, the amorphous carbon film is hardly etched. From this result, it can be understood that damage to the amorphous carbon film may be reduced by forming the TiO 2 film using TDMAT and thereafter forming the TiO 2 film using TiCl 4 . In addition, even when forming a TiO 2 film having a thickness of 15 nm on the amorphous carbon film using TDMAT, the amorphous carbon film is hardly etched. However, from the viewpoint of film quality controllability, material costs, and productivity, a TiO 2 film may be formed using TDMAT on the amorphous carbon film, and thereafter a TiO 2 film may be formed using TiCl 4 thereon.

In addition, when the TiO 2 film formed using TDMAT has a thickness of 3 nm or 5 nm, a portion of the film is peeled off due to a difference in stress of the TiO 2 film having a different metal-containing gas specie. From this result, the thickness of the TiO 2 film formed using TDMAT may be 1 nm or less.

In Example 2, an effect imparted to an amorphous carbon film when a TiO 2 film as a metal oxide film is formed through a PEALD method on the amorphous carbon film as a base film having a predetermined pattern was evaluated by observing a cross-sectional shape of the amorphous carbon film. In addition, in Example 2, the TiO 2 film was formed through the PEALD method in the processing container 10 adjusted to 2 Torr (267 Pa). In addition, in the oxidation step, high frequency power of 13.56 MHz was applied from a high frequency power supply in the same manner as in Example 1. In addition, the cross-sectional shape was observed using a STEM.

FIG. 7 is a diagram illustrating a cross-sectional shape of a metal oxide film formed by a film forming method in Example 2. The leftmost diagram in FIG. 7 is a STEM photograph when a TiO 2 film having a thickness of 15 nm was formed using TiCl 4 as a metal-containing gas. The center diagram is a STEM photograph when a TiO 2 film having a thickness of 1 nm was formed using TDMAT as a metal-containing gas, and thereafter a TiO 2 film having a thickness of 14 nm was formed using TiCl 4 as a metal-containing gas. The right diagram is a STEM photograph when a TiO 2 film having a thickness of 3 nm was formed using TDMAT as a metal-containing gas, and then a TiO 2 film having a thickness of 12 nm was formed using TiCl 4 as a metal-containing gas.

As illustrated in FIG. 7 , when forming the TiO 2 film having a thickness of 15 nm on the amorphous carbon film using TiCl 4 , the pattern of the amorphous carbon film is etched so that the line width thereof is reduced. From this result, it can be understood that the amorphous carbon film is damaged when the TiO 2 film having a thickness of 15 nm, for example, using TiCl 4 .

On the other hand, when forming the TiO 2 film on the amorphous carbon film using TDMAT, and thereafter forming the TiO 2 film using TiCl 4 thereon, the amorphous carbon film is hardly etched. From this result, it can be understood that damage to the amorphous carbon film may be reduced by forming the TiO 2 film using TDMAT and thereafter forming the TiO 2 film using TiCl 4 .

In addition, when the TiO 2 film formed using TDMAT has a thickness of 1 nm, peeling is not observed in the TiO 2 film. In addition, even when the thickness of the TiO 2 film formed using TDMAT is 3 nm, peeling is hardly observed in the TiO 2 film. From these results, the thickness of a TiO 2 film formed using TDMAT may be preferably 3 nm, and more preferably, may be 1 nm or less.

Second Embodiment

(Film Forming Apparatus)

An exemplary film forming apparatus that carries out a film forming method of a second embodiment will be described. FIG. 8 is a schematic diagram illustrating an exemplary film forming apparatus that carries out a film forming method of a second embodiment.

As illustrated in FIG. 8 , the film forming apparatus of the second embodiment is configured as a capacitively coupled (parallel plate type) plasma film forming apparatus. The film forming apparatus includes the substantially cylindrical processing container 10 .

The processing container 10 is formed of, for example, aluminum of which the surface is anodized. The processing container 10 is grounded. The placing table 12 is provided inside the processing container 10 .

The placing table 12 supports the wafer W as an exemplary workpiece placed thereon. The placing table 12 is grounded via an impedance adjustment circuit 22 , and also functions as a lower electrode. The impedance adjustment circuit 22 includes a variable inductor 24 and a capacitor 26 connected to each other in series and is capable of adjusting the impedance between the placing table 12 and a ground by adjusting the variable inductor 24 . The shower head 14 is provided above the placing table 12 so as to be opposite parallel to the placing table 12 .

The shower head 14 supplies a gas into the processing container 10 , and also functions as an upper electrode. A plurality of gas supply units 16 d and 16 e are connected to the shower head 14 . In addition, the high frequency power supply 18 is connected to the shower head 14 .

The gas supply unit 16 d introduces a metal-containing gas and Ar gas into the shower head 14 . The first metal-containing gas is a Ti containing gas (Ti precursor) such as, for example, TDMAT or TiCl 4 .

The gas supply unit 16 e introduces an oxidizing gas and Ar gas into the shower head 14 . The oxidizing gas is, for example, O 2 gas.

The gas introduced from the gas supply units 16 d and 16 e into the shower head 14 is discharged into the processing container 10 through a number of gas holes (not illustrated) formed in the lower surface of the shower head 14 .

The high frequency power supply 18 is a power supply for exciting plasma, and applies high frequency power to the shower head 14 . The frequency of the high frequency power may be set to a frequency suitable for generating plasma in the processing container 10 , for example, 380 kHz to 60 MHz.

The exhaust port 20 is provided in the bottom portion of the processing container 10 , and exhausts the gas supplied from the shower head 14 into the processing container 10 .

When a plasma processing is performed in this film forming apparatus, the wafer W is placed on the placing table 12 . In addition, a gas is supplied into the processing container 10 from the plurality of gas supply units 16 d and 16 e , and the pressure inside the processing container 10 is reduced by the exhaust port 20 . Then, the gas supplied into the processing container 10 is excited by the high frequency power applied from the high frequency power supply 18 to the shower head 14 . Thus, plasma is generated in the processing container 10 , and the wafer W is processed by radicals and/or ions from the plasma.

Meanwhile, a time average potential (plasma potential) of the plasma generated in the processing container 10 is higher than a time average potential of the processing container 10 and a time average potential of the placing table 12 . When the time average potential of the placing table 12 is higher than the time average potential of the processing container 10 , a potential difference between a time average potential in the vicinity of the wafer W and the plasma potential decreases, and the energy of ions incident on the wafer W decreases. On the other hand, when the time average potential of the placing table 12 is lower than the time average potential of the processing container 10 , the potential difference between the time average potential in the vicinity of the wafer W and the plasma potential increases, and the energy of ions incident on the wafer W increases.

In this film forming apparatus, since the impedance between the placing table 12 and the ground may be adjusted by the impedance adjustment circuit 22 , the time average potential of the placing table 12 may be controlled. Thus, the time average potential of the placing table 12 may vary relative to the time average potential of the processing container 10 , which enables adjustment of the energy of ions incident on the wafer W placed on the placing table 12 . For example, when the impedance adjustment circuit 22 sets a high impedance between the placing table 12 and the ground, the time average potential of the placing table 12 becomes higher than the time average potential of the processing container 10 . Thus, the energy of ions incident on the wafer W placed on the placing table 12 is reduced.

(Film Forming Method)

Next, with respect to the film forming method of the second embodiment, a case where a TiO 2 film as an exemplary metal oxide film is formed on a base film having a predetermined pattern formed on the wafer W using the above-described film forming apparatus will be described by way of example. FIG. 9 is a flowchart for explaining the film forming method of the second embodiment.

As illustrated in FIG. 9 , the film forming method of the second embodiment includes a third metal oxide film forming step S 30 and a fourth metal oxide film forming step S 40 . The third metal oxide film forming step S 30 is a step of forming a third metal oxide film on a base film by alternately supplying a third metal-containing gas having no halogen and a plasmatized oxidizing gas. The fourth metal oxide film forming step S 40 is a step of forming a fourth metal oxide film on the third metal oxide film by alternately supplying a fourth metal-containing gas and a plasmatized oxidizing gas.

FIG. 10 is a diagram for explaining the third metal oxide film forming step S 30 . As illustrated in FIG. 10 , in the third metal oxide film forming step S 30 , a series of operations including an adsorption step S 31 , a purge step S 32 , an oxidation step S 33 , and a purge step S 34 are defined as one cycle, and the number of cycles is controlled to form a TiO 2 film having a desired film thickness. In addition, in the third metal oxide film forming step S 30 , the impedance between the placing table 12 and the ground is adjusted to a first impedance Z 1 by adjusting the impedance adjustment circuit 22 .

The adsorption step S 31 is a step of supplying the metal-containing gas into the processing container 10 and adsorbing the metal-containing gas on the base film in a state where the impedance between the placing table 12 and the ground is adjusted to the first impedance Z 1 . In the adsorption step S 31 , TiCl 4 as an example of the metal-containing gas and Ar gas are supplied from the gas supply unit 16 d into the processing container 10 , and O 2 gas and Ar gas are supplied from the gas supply unit 16 e . Thus, the TiCl 4 is adsorbed on the base film. The adsorption step S 31 may be set to, for example, 0.05 seconds to 0.5 seconds.

The purge step S 32 is a step of purging the excessive metal-containing gas in the processing container 10 . In the purge step S 32 , the supply of TiCl 4 from the gas supply unit 16 d is stopped while the supply of O 2 gas and Ar gas from the gas supply unit 16 e is continued. Thus, for example, the excessive TiCl 4 in the processing container 10 is purged. The purge step S 32 may be set to, for example, 0.3 seconds to 1.0 second.

The oxidation step S 33 is a step of supplying the oxidizing gas into the processing container 10 and oxidizing the TiCl 4 adsorbed on the base film. In the oxidation step S 33 , high frequency power (e.g., 450 kHz) is applied to the shower head 14 by the high frequency power supply 18 while the supply of O 2 gas and Ar gas from the gas supply unit 16 e is continued. Thus, plasma of O 2 gas and Ar gas is generated, and the TiCl 4 adsorbed on the base film is oxidized. The oxidation step S 33 may be set to, for example, 0.3 seconds to 1.0 second.

The purge step S 34 is a step of purging the excessive plasmatized O 2 gas and Ar gas, for example, in the processing container 10 . In the purge step S 34 , the high frequency power applied to the shower head 14 from the high frequency power supply 18 is interrupted while the supply of O 2 gas and Ar gas from the gas supply unit 16 e is continued. Thus, the excessive plasmatized O 2 gas and Ar gas in the processing container 10 are purged. The purge step S 34 may be set to, for example, 0.1 seconds to 1.0 second.

In this manner, by defining a series of operations including the adsorption step S 31 , the purge step S 32 , the oxidation step S 33 , and the purge step S 34 as one cycle, and controlling the number of cycles, a TiO 2 film having a desired film thickness (e.g., 1 nm) may be formed.

FIG. 11 is a diagram for explaining the fourth metal oxide film forming step S 40 . As illustrated in FIG. 11 , in the fourth metal oxide film forming step S 40 , a series of operations including an adsorption step S 41 , a purge step S 42 , an oxidation step S 43 , and a purge step S 44 are defined as one cycle, and the number of cycles is controlled so as to form a TiO 2 film having a desired film thickness. In addition, in the fourth metal oxide film forming step S 40 , the impedance between the placing table 12 and the ground is adjusted to a second impedance Z 2 lower than the first impedance Z 1 by adjusting the impedance adjustment circuit 22 .

The adsorption step S 41 is a step of supplying the metal-containing gas into the processing container 10 and adsorbing the metal-containing gas on the third metal oxide film. In the adsorption step S 41 , TiCl 4 as an example of the metal-containing gas and Ar gas are supplied from the gas supply unit 16 d into the processing container 10 , and O 2 gas and Ar gas are supplied from the gas supply unit 16 e . Thus, the TiCl 4 is adsorbed on the TiO 2 film as the third metal oxide film. The adsorption step S 41 may be set to, for example, 0.05 seconds to 0.5 seconds.

The purge step S 42 is a step of purging the excessive fourth metal-containing gas in the processing container 10 . In the purge step S 42 , the supply of TiCl 4 from the gas supply unit 16 d is stopped while the supply of O 2 gas and Ar gas from the gas supply unit 16 e is continued. Thus, for example, the excessive TiCl 4 in the processing container 10 is purged. The purge step S 42 may be set to, for example, 0.3 seconds to 1.0 second.

The oxidation step S 43 is a step of supplying the oxidizing gas into the processing container 10 and oxidizing the TiCl 4 adsorbed on the third metal oxide film. In the oxidation step S 43 , high frequency power (e.g., 450 kHz) is applied to the shower head 14 by the high frequency power supply 18 while the supply of O 2 gas and Ar gas from the gas supply unit 16 e is continued. Thus, plasma of O 2 gas and Ar gas is generated, and the TiCl 4 adsorbed on the third metal oxide film is oxidized. The oxidation step S 43 may be set to, for example, 0.3 seconds to 1.0 second.

The purge step S 44 is a step of purging, for example, the excessive plasmatized O 2 gas and Ar gas in the processing container 10 . In the purge step S 44 , the high frequency power applied to the shower head 14 from the high frequency power supply 18 is interrupted while the supply of O 2 gas and Ar gas from the gas supply unit 16 e is continued. Thus, the excessive plasmatized O 2 gas and Ar gas in the processing container 10 are purged. The purge step S 44 may be set to, for example, 0.1 seconds to 1.0 second.

In this manner, by defining a series of operations including the adsorption step S 41 , the purge step S 42 , the oxidation step S 43 , and the purge step S 44 as one cycle, and controlling the number of cycles, a TiO 2 film having a desired film thickness (e.g., 14 nm) may be formed.

FIG. 12 is a schematic cross-sectional view of a metal oxide film formed by the film forming method illustrated in FIG. 9 . As illustrated in FIG. 12 , according to the film forming method of the second embodiment, by the third metal oxide film forming step S 30 , a TiO 2 film 202 as the third metal oxide film is formed so as to cover the base film 101 having a predetermined pattern formed on the wafer W. In addition, by the fourth metal oxide film forming step S 40 , a TiO 2 film 203 as the fourth metal oxide film is formed so as to cover the TiO 2 film 202 .

As described above, according to the film forming method of the second embodiment, first, a TiO 2 film is formed on an amorphous carbon film in a state where the impedance adjustment circuit 22 sets a high impedance between the placing table 12 and the ground. Subsequently, a TiO 2 film is formed in a state where the impedance adjustment circuit 22 sets a low impedance between the placing table 12 and the ground. This makes it possible to reduce the energy of ions incident on the amorphous carbon film at the initial stage of film formation in which the surface of the amorphous carbon film is exposed. As a result, ion shocks on the surface of the amorphous carbon film may be prevented. That is, damage to the amorphous carbon film may be reduced.

In addition, while the TiO 2 film is formed, the surface of the amorphous carbon film is already covered with another TiO 2 film. Therefore, even if the energy of ions incident on the amorphous carbon film increases, the TiO 2 film formed at the initial stage functions as a protective film against ions incident on the amorphous carbon film, which prevents the surface of the amorphous carbon film from being roughened. Thus, it is possible to select various conditions including a condition under which the energy of ions incident on the amorphous carbon film increases during film formation. As a result, it is possible to easily form a metal oxide film having a desired film quality (e.g., film density, wet etching rate, or dry etching rate). That is, high film quality controllability is obtained.

In Example 3, an effect imparted to an amorphous carbon film when a TiO 2 film as a metal oxide film is formed through a PEALD method on the amorphous carbon film as a base film having a predetermined pattern was evaluated by observing a cross-sectional shape of the amorphous carbon film. In addition, in Example 3, the TiO 2 film was formed through the PEALD method in a state where the impedance between the placing table 12 and the ground is adjusted to 0Ω or 292Ω. In addition, in the oxidation step, high frequency power of 450 kHz was applied from a high frequency power supply. In addition, the cross-sectional shape was observed using a STEM.

FIG. 13 is a diagram illustrating a cross-sectional shape of a metal oxide film formed by a film forming method in Example 3. The left diagram in FIG. 13 is a STEM photograph when a TiO 2 film was formed on an amorphous carbon film in a state where the impedance between the placing table 12 and the ground is adjusted to 0Ω. The right diagram in FIG. 13 is a STEM photograph when a TiO 2 was film formed on an amorphous carbon film in a state where the impedance between the placing table 12 and the ground is adjusted to 292Ω.

As illustrated in FIG. 13 , when the TiO 2 film is formed on the amorphous carbon film in the state where the impedance between the placing table 12 and the ground is adjusted to 0Ω, a pattern of the amorphous carbon film is etched so that the line width is reduced. From this result, it can be understood that the amorphous carbon film is damaged when the TiO 2 film is formed on the amorphous carbon film in the state where the impedance between the placing table 12 and the ground is adjusted to 0Ω.

On the other hand, when forming the TiO 2 film on the amorphous carbon film in a state where the impedance between the placing table 12 and ground is adjusted to 292Ω, the amorphous carbon film is hardly etched. From this result, it can be understood that damage to the amorphous carbon film may be reduced by forming the TiO 2 film on the amorphous carbon film in the state where the impedance between the placing table 12 and the ground is adjusted to 292Ω.

In the second embodiment, a case where the same metal-containing gas is used in the third metal oxide film forming step S 30 and the fourth metal oxide film forming step S 40 has been described above by way of example, but the present disclosure is not limited thereto. For example, it is possible to use different metal containing gas in the third metal oxide film forming step S 30 from that in the fourth metal oxide film forming step S 40 as in the first embodiment.

In the above embodiments, a semiconductor wafer has been described as an example of a workpiece, but the semiconductor wafer may be a silicon wafer or a compound semiconductor wafer such as, for example, GaAs, SiC, or GaN. In addition, the workpiece is not limited to the semiconductor wafer, and may be, for example, a glass substrate or a ceramic substrate for use in a flat panel display (FPD) such as, for example, a liquid crystal display device.

From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.