JP2024094581A - Method for forming silicon oxide film - Google Patents

Abstract

The present invention provides a method for forming a silicon oxide film having excellent uniformity by atomic layer deposition using a silicon compound having excellent heat resistance.
[Solution] A method for forming a silicon oxide film, comprising: a preparation step of preparing a substrate in a reactor; a first introduction step of introducing at least one silicon compound into the reactor; a first purging step of purging the reactor with a purge gas; a second introduction step of introducing an oxygen source into the reactor; and a second purging step of purging the reactor with the purge gas, wherein the first introduction step to the second purging step are repeatedly performed until silicon oxide of a desired thickness is deposited on the surface of the substrate, the first introduction step to the second purging step are performed at a temperature of 300°C or higher and 800°C or lower and at a pressure of 7.6 Pa or higher and 100 kPa or lower, and the average roughness of the thickness of the formed silicon oxide film is 10% or less relative to the thickness of the formed silicon oxide film.
[Selected Figure] Figure 1

Description

This disclosure relates to a method for forming a silicon oxide film.

In recent years, with the trend toward 3D NAND flash memory cells, there is a demand for high-temperature (650°C or higher) silicon oxide film deposition to form high-quality insulating films with high adhesion and good coverage.

Chemical vapor deposition (CVD) is the main method used to form silicon oxide films at high temperatures. However, because CVD is a film formation method that utilizes chemical reactions and thermal decomposition, it is not suitable for forming films with high adhesion and good coverage. In addition, it cannot be used to form films on fine patterns, and cannot be used in fine areas.

Therefore, the formation of silicon oxide films using atomic layer deposition (ALD), which allows for the formation of high-quality films at high temperatures, has been investigated (for example, Patent Documents 1 and 2).

Patent No. 6262702 International Publication No. 2021/050368

The objective of this disclosure is to provide a method for forming a silicon oxide film with excellent thickness uniformity by atomic layer deposition using a silicon compound with excellent heat resistance.

前記式（１）中、
Ｒ^１およびＲ^２は、それぞれ独立に、メチル基またはエチル基であり、
Ｒ^３は、メチル基、エチル基、下記式（２）で表される基または下記式（３）で表される基であり、
Ｒ^４は、下記式（２）で表される基または式（３）で表される基である。

前記式（２）および前記式（３）中、
Ｒ^５～Ｒ^１０は、それぞれ独立に、水素原子、メチル基またはエチル基である。 [1] a preparation step of preparing a substrate in a reactor;
A first introduction step of introducing at least one silicon compound represented by the following formula (1) into the reactor;
a first purging step of purging the reactor with a purge gas;
a second introducing step of introducing an oxygen source into the reactor;
A second purge step of purging the reactor with the purge gas,
The first introducing step through the second purging step are repeatedly performed until a desired thickness of silicon oxide is deposited on the surface of the substrate;
The first introduction step to the second purging step are carried out at a temperature of 300° C. or more and 800° C. or less and a pressure of 7.6 Pa or more and 100 kPa or less,
A method for forming a silicon oxide film, wherein the average roughness of the thickness of the formed silicon oxide film is 10% or less with respect to the thickness of the formed silicon oxide film.

In the formula (1),
R ¹ and R ² are each independently a methyl group or an ethyl group;
^R3 is a methyl group, an ethyl group, a group represented by the following formula (2), or a group represented by the following formula (3),
^R4 is a group represented by the following formula (2) or a group represented by the following formula (3).

In the formula (2) and the formula (3),
R ⁵ to R ¹⁰ each independently represent a hydrogen atom, a methyl group, or an ethyl group.

前記式（１）中、
Ｒ^１およびＲ^２は、それぞれ独立に、メチル基またはエチル基であり、
Ｒ^３は、メチル基、エチル基、下記式（２）で表される基または下記式（３）で表される基であり、
Ｒ^４は、下記式（２）で表される基または式（３）で表される基である。

前記式（２）および前記式（３）中、
Ｒ^５～Ｒ^１０は、それぞれ独立に、水素原子、メチル基またはエチル基である。 [2] a preparation step of preparing a substrate having a grooved surface in a reactor;
A first introduction step of introducing at least one silicon compound represented by the following formula (1) into the reactor;
a first purging step of purging the reactor with a purge gas;
a second introducing step of introducing an oxygen source into the reactor;
A second purge step of purging the reactor with the purge gas,
The first introducing step through the second purging step are repeatedly performed until a desired thickness of silicon oxide is deposited on the surface of the substrate;
The first introduction step to the second purging step are carried out at a temperature of 300° C. or more and 800° C. or less and a pressure of 7.6 Pa or more and 100 kPa or less,
The silicon oxide film is
Formula (i): |t ₁ -t ₂ |/t ₁ ≦0.2
Fulfilling the relationship,
In the formula (i),
_t1 denotes the thickness of the silicon oxide film (nm) on top of the trench;
_t2 represents the thickness of the silicon oxide film (nm) at the bottom of the trench.

In the formula (1),
R ¹ and R ² are each independently a methyl group or an ethyl group;
^R3 is a methyl group, an ethyl group, a group represented by the following formula (2), or a group represented by the following formula (3),
^R4 is a group represented by the following formula (2) or a group represented by the following formula (3).

In the formula (2) and the formula (3),
R ⁵ to R ¹⁰ each independently represent a hydrogen atom, a methyl group, or an ethyl group.

[3] In the formula (1),
R ¹ and R ² are methyl groups;
The ^R3 is a methyl group or a group represented by the formula (3),
The R ⁴ is a group represented by the formula (3),
The method for forming a silicon oxide film according to [1] or [2], wherein R ⁸ to R ¹⁰ each independently represent a hydrogen atom, a methyl group, or an ethyl group.

[4] In the formula (1),
R ¹ to R ³ each represent a methyl group;
The R ⁴ is a group represented by the formula (3),
The method for forming a silicon oxide film according to [1] or [2], wherein R ⁸ to R ¹⁰ are hydrogen atoms.

[5] In the formula (1),
The R ¹ and R ² are methyl groups;
The R ³ and R ⁴ are groups represented by the formula (2),
The method for forming a silicon oxide film according to [1] or [2], wherein R ⁵ to R ⁷ are each independently a hydrogen atom, a methyl group, or an ethyl group.

[6] In the formula (1),
R ¹ to R ³ each represent a methyl group;
The R ⁴ is a group represented by the formula (2),
The method for forming a silicon oxide film according to [1] or [2], wherein R ⁵ to R ⁷ are hydrogen atoms.

The present disclosure provides a method for forming a silicon oxide film with excellent thickness uniformity by atomic layer deposition using a silicon compound with excellent heat resistance.

FIG. 1 is a schematic flow chart of a method for forming a silicon oxide film in the present disclosure. FIG. 2 is a conceptual diagram showing an example of a silicon oxide film formed on a substrate in the first embodiment. FIG. 3 is a conceptual diagram showing an example of a film forming apparatus applicable to the method of forming a silicon oxide film in the present disclosure. FIG. 4 is a conceptual diagram illustrating an example of a substrate in the second embodiment. FIG. 5 is a conceptual diagram showing an example of a silicon oxide film formed on a substrate in the second embodiment. 6 is a graph showing the relationship between the supply amount of silicon compounds No. 1 and No. 2 in Test Example 1 and the growth rate of a silicon oxide film. 7 is a graph showing the relationship between the film formation temperature and the growth rate of the silicon oxide film for No. 1 and No. 2 in Test Example 2. FIG. 8 is a photograph showing the thickness of the silicon oxide film in each of the portions (a) of the upper portion, (b) of the middle portion, and (c) of the lower portion in the groove of the substrate of Test Example 3.

Embodiments of the present disclosure are described below. However, the following description does not limit the scope of the claims.

[Embodiment 1]
<Method of forming silicon oxide film>
The method for forming a silicon oxide film of this embodiment includes a preparation step of preparing a substrate in a reactor, a first introduction step of introducing at least one silicon compound represented by the following formula (1) into the reactor, a first purge step of purging the reactor with a purge gas, a second introduction step of introducing an oxygen source into the reactor, and a second purge step of purging the reactor with a purge gas. The first introduction step to the second purge step are repeatedly performed until silicon oxide of a desired thickness is deposited on the surface of the substrate. The first introduction step to the second purge step are performed at a temperature of 300° C. to 800° C. and a pressure of 7.6 Pa to 100 kPa. The average roughness of the thickness of the formed silicon oxide film is 10% or less with respect to the thickness of the formed silicon oxide film.

In formula (1), ^R1 and ^R2 are each independently a methyl group or an ethyl group; ^R3 is a methyl group, an ethyl group, a group represented by the following formula (2) or a group represented by the following formula (3); and ^R4 is a group represented by the following formula (2) or the above formula (3).

In formula (2) and formula (3), R ⁵ to R ¹⁰ each independently represent a hydrogen atom, a methyl group, or an ethyl group.

Figure 1 is a schematic flow chart of the method for forming a silicon oxide film in this embodiment. Each step of the method for forming a silicon oxide film is described below.

There are two types of ALD: thermal ALD and plasma ALD. In this disclosure, we use thermal ALD, which is capable of forming high-quality films in high-temperature regions.

(Preparation process)
The preparation step is a step of preparing a substrate in a reactor.

The substrate used in the present disclosure is not particularly limited as long as it is a substrate capable of growing the precursor silicon compound, and examples of the substrate include ceramic substrates such as silicon substrates, silicon oxide substrates, and silicon nitride substrates. Of these, it is preferable to use a silicon substrate or a silicon oxide substrate from the viewpoint of forming a high-quality film.

A barrier film may be formed on the substrate in advance. Examples of the barrier film include titanium nitride and tantalum nitride.

(First introduction step)
The first introduction step is a step of introducing at least one silicon compound represented by the above formula (1) into a reactor. This step is a step of adsorbing the silicon compound, which is a precursor, onto a substrate.

The silicon compound may be introduced into the reactor by a carrier gas. Here, the carrier gas refers to an inert gas that promotes the supply of the silicon compound to the reactor. The carrier gas and the silicon compound do not react with each other. Examples of the carrier gas include hydrogen (H ₂ ), helium (He), nitrogen (N ₂ ), neon (Ne), and argon (Ar).

In the above formula (1), ^R1 and ^R2 are each independently a methyl group or an ethyl group, ^R3 is a methyl group, an ethyl group, a group represented by the following formula (2) or a group represented by the following formula (3), and ^R4 is a group represented by the above formula (2) or a group represented by the above formula (3).

Such compounds can be useful precursors for forming silicon oxide films. Examples of silicon compounds represented by formula (1) include those having a structure represented by formula (4) below.

In formula (4), R ¹¹ is a methyl group or an ethyl group, R ¹² is any one of the structures represented by formula (5) below, and R ¹³ is any one of the structures represented by formula (6) below. R ¹¹ in formulas (5) and (6) below is also the same group as above.

As the silicon compound represented by the above formula (1), from the viewpoint of heat resistance and film-forming properties, a silicon compound having a structure represented by the following formula (7) is preferred, and a silicon compound represented by the following formula (8) is more preferred.

This process may be carried out for a time and flow rate that allows the silicon compound to be adsorbed onto the substrate. This process may be carried out for a time of, for example, 0.1 seconds or more and 1000 seconds or less. The silicon compound in this process may be introduced into the reactor at a flow rate of, for example, 1 sccm or more and 2000 sccm or less. The flow rate unit "sccm (Standard Cubic Centimeter per Minute)" refers to "mL/min" under standard conditions (0°C, 101.3 kPa).

(First purge step)
The first purge step is a step of purging the reactor with a purge gas after the first introduction step, and is a step of removing excess silicon compound that was not adsorbed on the substrate in the first introduction step.

As the purge gas, an inert gas capable of removing the precursor silicon compound can be used. The purge gas does not react with the silicon compound. Examples of such an inert purge gas include the same gas as the carrier gas described above.

This process may be carried out for a time and at a flow rate that allows excess silicon compounds to be removed. This process may be carried out for a time of, for example, 0.1 seconds or more and 1000 seconds or less. The purge gas in this process may be introduced into the reactor at a flow rate of, for example, 10 sccm or more and 2000 sccm or less.

In this process, the reactor may be vacuum purged before being purged with the purge gas. The vacuum purging may be carried out for a period of time ranging from 0.1 seconds to 1000 seconds, for example.

This process may be performed multiple times. When this process is performed multiple times, the time, flow rate, and purge gas used for each process may be the same or different. Vacuum purging may also be performed between each process. For example, the processes may be performed in the order of purging with purge gas, vacuum purging, and purging with purge gas.

(Second introduction step)
The second introduction step is a step of introducing an oxygen source into a reactor, and is a step of forming a silicon oxide film by reacting the oxygen source with the silicon compound, which is a precursor adsorbed on the substrate.

The oxygen source is not particularly limited, but examples thereof include water, oxygen ( _O2 ), peroxide, oxygen plasma, ozone ( _O3 ), nitric oxide ( _N2O ), nitrogen dioxide ( _NO2 ), carbon monoxide (CO), carbon dioxide ( _CO2 ), and combinations thereof.

This process may be carried out for a time and at a flow rate that allows the silicon compound and the oxygen source to react. This process may be carried out for a time of, for example, 0.1 seconds or more and 100 seconds or less. The oxygen source in this process may be introduced into the reactor at a flow rate of, for example, 1 sccm or more and 2000 sccm or less.

(Second purge step)
The second purge step is a step of purging the reactor with a purge gas after the second introduction step, which is a step of removing the oxygen source that has not reacted with the silicon compound in the second introduction step.

The purge gas used in this process, the duration of this process, and the flow rate of the purge gas are the same as those in the first purge process described above, so details are omitted.

In this process, the reactor may be vacuum purged before being purged with the purge gas. The vacuum purging may be carried out for a period of time ranging from 0.1 seconds to 1000 seconds, for example.

This process may be performed multiple times. When this process is performed multiple times, the time, flow rate, and purge gas used for each process may be the same or different. In addition, vacuum purging may be performed between each process.

(From the first introduction step to the second purge step)
The first introduction step, the first purge step, the second introduction step, and the second purge step are performed at a temperature of 300° C. or more and 800° C. or less. When the first introduction step to the second purge step are performed at a temperature of 300° C. or more and 800° C. or less, a film with high adhesion and good coverage can be formed. The first introduction step to the second purge step are preferably performed at a temperature of 500° C. or more and 750° C. or less, and more preferably at a temperature of 650° C. or more and 750° C. or less.

The first introduction step through the second purge step are carried out at a pressure of 7.6 Pa or more and 100 kPa or less. When the first introduction step through the second purge step are carried out at a pressure of 7.6 Pa or more and 100 kPa or less, a film with high adhesion and good coverage can be formed. It is preferable that the first introduction step through the second purge step are carried out at a pressure of 10 Pa or more and 1 kPa or less.

The first introduction step through the second purge step are repeated. By repeatedly performing the first introduction step through the second purge step, a silicon oxide film of the desired thickness can be obtained.

Figure 2 is a conceptual diagram showing an example of a silicon oxide film formed on a substrate in this embodiment. In this application, the thickness of the silicon oxide film 3 means the thickness (in Figure 2, "t") (nm) of the silicon oxide film 3 deposited on the surface 2 of the substrate 1. The desired thickness is, for example, 0.1 nm to 100 nm, and preferably 3 nm to 50 nm.

The thickness of the silicon oxide film 3 deposited on the surface 2 of the substrate 1 is measured by X-ray reflectometry (XRR). The thickness of the silicon oxide film 3 is measured using an X-ray reflectometry (XRR) under the following conditions, for example.
[conditions]
X-ray source: CuK _α ray Output: 45 kv, 40 mA
Measurement range: 0 to 6°
Step width: 0.002 mm
Scanning speed: 0.05°/min

In this embodiment, the average roughness (Ra) of the thickness of the formed silicon oxide film 3 is 10% or less of the thickness of the formed silicon oxide film 3. Ra is measured by XRR, similar to the thickness of the silicon oxide film 3. It can be said that the smaller the value of Ra, the less unevenness in the thickness of the silicon oxide film 3 and the more uniform the film thickness. Ra is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less.

<Film forming equipment>
An example of a film forming apparatus applicable to the method for forming a silicon oxide film in the present embodiment will be described with reference to Fig. 3. The film forming apparatus 10 includes at least a reactor 11 for accommodating a substrate W as an object to be processed, a precursor gas supply line 14 for supplying a silicon compound as a precursor, a purge gas supply line 15 for supplying a purge gas, an oxygen source supply line 16 for supplying an oxygen source, and an exhaust line 17 for exhausting the atmosphere in the reactor 11.

The reactor 11 has an airtight structure that allows the inside of the reactor 11 to be isolated from the outside air. The reactor 11 is configured in such a way that the substrate W can be accommodated in a horizontal position using a boat or the like. The reactor 11 may be equipped with a heating mechanism (not shown) that can heat the substrate W accommodated therein to a predetermined temperature. There are no particular limitations on the heating mechanism, but a known mechanism such as a heater can be used.

The precursor supply unit 12 has the function of supplying the precursor to the reactor 11. The precursor supply unit 12 stores a liquid or solid precursor. In addition, the precursor supply unit 12 is connected to a carrier gas supply path 13 for introducing a carrier gas. The flow rate of the carrier gas supplied from the carrier gas supply path 13 can be controlled by an MFC (Mass Flow Controller).

A precursor gas supply path 14 is provided between the precursor supply unit 12 and the reactor 11. This allows a precursor gas, which is a vaporized liquid or solid precursor stored in the precursor supply unit 12, to be supplied to the reactor 11. In addition, a needle valve 19 and an on-off valve 20 are provided in the precursor gas supply path 14. The needle valve 19 adjusts the flow rate of the gas flowing through the precursor gas supply path 14. The on-off valve 20 controls the supply or stop of the gas flowing through the precursor gas supply path 14.

The purge gas supply line 15 has the function of supplying purge gas to the reactor 11. The purge gas supply line 15 is connected to the reactor 11. The flow rate of the supplied purge gas can be controlled by an MFC. An on-off valve 21 is provided in the purge gas supply line 15. The on-off valve 21 controls the supply or stop of the purge gas flowing through the purge gas supply line 15.

The oxygen source supply line 16 has the function of supplying the oxygen source to the reactor 11. The oxygen source supply line 16 is connected to the reactor 11. The flow rate of the supplied oxygen source can be controlled by an MFC. An on-off valve 22 is provided in the oxygen source supply line 16. The on-off valve 22 controls the supply or stop of the oxygen source flowing through the oxygen source supply line 16.

The exhaust line 17 has the function of exhausting the atmosphere in the reactor 11. The exhaust line 17 is connected to the reactor 11. A pressure sensor (not shown) as a pressure detection unit that detects the pressure in the reactor 11, an APC (Automatic Pressure Control Valve) valve 18 as a pressure control unit that controls the pressure in the reactor 11, and a vacuum pump (not shown) as a vacuum exhaust device are connected to the exhaust line 17. The opening and closing of the APC valve 18 is controlled by PID (Proportional-Integral-Differential Controller) control based on the measurement of the pressure sensor while the vacuum pump is operating. This allows the pressure in the reactor 11 to be adjusted as desired.

The exhaust gas discharged from the exhaust passage 17 may contain toxic gases, flammable gases, etc. Therefore, the exhaust passage 17 may be provided with a water washing scrubber, sulfuric acid scrubber, caustic scrubber, dry detoxification device, etc., so that the exhaust gas can be rendered harmless and released into the atmosphere.

[Embodiment 2]
<Method of forming silicon oxide film>
The method for forming a silicon oxide film of this embodiment includes a preparation step of preparing a substrate having a grooved surface in a reactor, a first introduction step of introducing at least one silicon compound represented by the following formula (1) into the reactor, a first purge step of purging the reactor with a purge gas, a second introduction step of introducing an oxygen source into the reactor, and a second purge step of purging the reactor with a purge gas. The first introduction step to the second purge step are repeatedly performed until silicon oxide of a desired thickness is deposited on the surface of the substrate. The first introduction step to the second purge step are performed at a temperature of 300° C. to 800° C. and a pressure of 7.6 Pa to 100 kPa. The silicon oxide film satisfies the relationship of the following formula (i).
Formula (i): |t ₁ -t ₂ |/t ₁ ≦0.2...Formula (i)
In formula (i), _t1 represents the thickness of the silicon oxide film (nm) at the top of the groove, and _t2 represents the thickness of the silicon oxide film (nm) at the bottom of the groove.

In formula (1), ^R1 and ^R2 are each independently a methyl group or an ethyl group; ^R3 is a methyl group, an ethyl group, a group represented by the following formula (2) or a group represented by the following formula (3); and ^R4 is a group represented by the following formula (2) or the above formula (3).

In formula (2) and formula (3), R ⁵ to R ¹⁰ each independently represent a hydrogen atom, a methyl group, or an ethyl group.

The method for forming a silicon oxide film according to this embodiment will be described below. Note that descriptions that overlap with those of embodiment 1 will be omitted.

Figure 4 is a conceptual diagram showing an example of a substrate in this embodiment. The substrate 1 may have a surface 7 having a groove 4. The groove 4 has a side wall surface 5 and a bottom wall surface 6. Examples of the groove 4 include a hole, a via, a trench, and a contact. One or more grooves 4 may be provided on the surface 7 of the substrate 1.

The width of the groove 4 ("h ₁ " in FIG. 4) is, for example, 10 nm or more and 500 nm or less. The depth of the groove 4 ("h ₂ " in FIG. 4) is, for example, 100 nm or more and 10 μm or less.

The ratio of the depth of groove 4 to the width of groove 4 (hereinafter referred to as the "aspect ratio") may be, for example, 10 or more, or may be 20 or more, or may be 50 or more. The aspect ratio may be, for example, 1000 or less, 500 or less, or 100 or less.

When multiple grooves 4 are provided, the width, depth and aspect ratio of each groove 4 may be the same or different.

In the first introduction step, the precursor silicon compound is also adsorbed into the groove 4. Other points are the same as in embodiment 1. In addition, the first purge step, the second introduction step, and the second purge step are also the same as in embodiment 1.

5 is a conceptual diagram showing an example of a silicon oxide film formed on a substrate in this embodiment. The thickness of the silicon oxide film 3 deposited on the surface 7 of the substrate 1 is calculated in the same manner as in embodiment 1. The thickness of the silicon oxide film 3 deposited in the groove 4 is calculated, for example, as follows. That is, the substrate is cut perpendicular to the groove 4 at an arbitrary position and processed with a focused ion beam (FIB). After FIB processing, the cut surface is photographed with a transmission electron microscope (TEM). The TEM conditions are as follows. The substrate 1 and the silicon oxide film 3 are distinguished by binarizing the TEM image. The binarization is performed at a threshold value that can properly separate the substrate 1 and the silicon oxide film 3. The thickness of the silicon oxide film 3 is calculated from the TEM image. The arithmetic average of the thicknesses of the silicon oxide film 3 measured in multiple images may be considered as the thickness of the silicon oxide film 3.
[TEM conditions]
Magnification: 750,000 times Acceleration voltage: 200 kV
Magnification accuracy: ±10%

In this embodiment, the silicon oxide film 3 formed satisfies the relationship of the following formula (i).
|t ₁ -t ₂ |/t ₁ ≦0.2... formula (i)
In formula (i), t ₁ indicates the thickness (nm) of the silicon oxide film 3 at the top of the groove 4, and t ₂ indicates the thickness (nm) of the silicon oxide film 3 at the bottom of the groove 4. It can be said that the smaller the value of formula (i), the smaller the difference in film thickness between the top and bottom of the groove 4, and the better the film thickness uniformity. |t ₁ -t ₂ |/t ₁ may be 0.15 or less, 0.10 or less, 0.05 or less, or 0.01 or less. |t ₁ -t ₂ |/t ₁ is preferably 0.10 or less, more preferably 0.05 or less, and even more preferably 0.01 or less.

From the viewpoint of the uniformity of the thickness of the silicon oxide film 3, it is preferable that _t1 and _t2 are substantially the same as t, and it is more preferable that they are the same as t.

Here, the upper part of the groove 4 in this embodiment refers to the uppermost region when the groove 4 is divided into three equal parts in the depth direction and divided into three regions, and the lower part of the groove 4 refers to the lowermost region when the groove 4 is divided into three equal parts in the depth direction and divided into three regions. _t1 may be a thickness measured in a portion or region of a certain length from the surface 7 of the substrate 1. _t2 may be a thickness measured in a portion or region of a certain length from the bottom wall surface 6 of the groove 4.

In this embodiment, it is preferable that the silicon oxide film 3 to be formed satisfies the relationship of the following formula (ii).
|t ₁ -t ₃ |/t ₁ ≦0.2...formula (ii)
In formula (ii), t ₃ represents the thickness (nm) of the silicon oxide film 3 in the middle part of the groove 4. It can be said that the smaller the value of formula (ii), the smaller the difference in film thickness between the upper part and the middle part of the groove 4, and the more excellent the film thickness uniformity. |t ₁ -t ₃ |/t ₁ may be 0.15 or less, 0.10 or less, 0.05 or less, or 0.01 or less. |t ₁ -t ₃ |/t ₁ is preferably 0.10 or less, more preferably 0.05 or less, and even more preferably 0.01 or less.

From the viewpoint of uniformity of the thickness of the silicon oxide film 3, _t3 is preferably approximately the same as t, and more preferably is the same as t.

Here, the intermediate portion of the groove 4 in this embodiment refers to the intermediate region when the groove 4 is divided into three equal regions in the depth direction. _t3 may be a thickness measured in a portion or region of a certain length from the surface 7 of the substrate 1.

In this embodiment, it is preferable that the silicon oxide film 3 to be formed satisfies the relationship of the following formula (iii).
|t ₂ -t ₃ |/t ₂ ≦0.2 ... formula (iii)
It can be said that the smaller the value of formula (iii), the smaller the difference in film thickness between the upper and middle parts of the groove 4, and the better the film thickness uniformity. |t ₂ -t ₃ |/t ₂ may be 0.15 or less, 0.10 or less, 0.05 or less, or 0.01 or less. |t ₂ -t ₃ |/t ₂ is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.01 or less.

t ₁ , t ₂ and t ₃ are measured in the same manner as the TEM measurement described above.

The following examples are provided. However, the following examples are not intended to limit the scope of the claims.

<Apparatus>
In this example, the following equipment was used. Gas chromatograph is abbreviated as "GC" and gas chromatograph mass spectrometer is abbreviated as "GC-MS." In addition, in this example, a film formation apparatus having the configuration shown in FIG. 3 was used.
GC: Shimadzu Corporation, GC-2025AF
GC-MS: Shimadzu Corporation, MSQP2020NX
TEM: Hitachi High-Tech Corporation, H-9500
XRR measuring device: X'Pert PRO manufactured by Malvern Panalytical

<Reagents>
In this example, the following reagents were used. Note that N-trimethylsilylimidazole is abbreviated as "TMS imidazole."
Pyrazole: manufactured by Tokyo Chemical Industry Co., Ltd. Ammonium sulfate: manufactured by Hayashi Pure Chemical Industries, Ltd. Hexamethyldisilazane: manufactured by TCI Corporation TMS imidazole: manufactured by TCI Corporation

<Silicon Compounds>
In this example, trimethylsilylpyrazole (hereinafter abbreviated as "TMS pyrazole") represented by the above formula (8) and TMS imidazole were used. The method for preparing TMS pyrazole is as follows. Note that TMS pyrazole is compound No. 1 and TMS imidazole is compound No. 2.

(Preparation)
51.5 g of pyrazole and a very small amount of ammonium sulfate were added to the flask bottom and dried under vacuum. Then, 62.0 g of hexamethyldisilazane was added and refluxed under nitrogen atmosphere for 12 hours under reflux conditions. The mixture after reflux was filtered through a filter to recover a light yellow liquid. The resulting liquid was then purified in a glove box by vacuum distillation. Analysis using the above-mentioned GC-MS confirmed that the product was TMS pyrazole. Furthermore, analysis using the above-mentioned GC confirmed that the purity was 99.0%.

(Minimum bond dissociation energy)
The minimum bond dissociation energy (MBDE) between the prepared TMS pyrazole and TMS imidazole was calculated. Here, MBDE indicates the minimum value among BDEs, which are the energy required to break a specific chemical bond, and corresponds to the BDE of the weakest bond in a molecule, and the higher the energy value, the better the heat resistance. MBDE was calculated using Gaussian 16, a quantum chemistry calculation program manufactured by Gaussian. The bond dissociation energy between silicon and the methyl group bonded to silicon was MBDE. The results are shown in Table 1.

As can be seen from Table 1, the MBDE values of TMS pyrazole and TMS imidazole were high. This indicates that TMS pyrazole and TMS imidazole have excellent heat resistance.

<Test Example 1>
Atomic layer deposition of silicon oxide film was performed using the prepared TMS pyrazole and TMS imidazole. Specifically, a silicon substrate was placed in the reactor of the film forming apparatus. The substrate was flat and had no grooves. Each compound was introduced into the reactor with _N2 gas, which was a carrier gas. The reactor was purged with N2 gas, which was a purge gas. _O3 , which was an oxygen source, was introduced into the reactor. The reactor was purged with _N2 gas, which was a purge _gas . In the case of TMS pyrazole, the first introduction step was performed for 3 seconds, 11.7 seconds, 21.9 seconds, 80.2 seconds, and 282.9 seconds, and 100 cycles were performed under the conditions shown in Table 2 below. In the case of TMS imidazole, the first introduction step was performed for 15.2 seconds, 90 seconds, 223.5 seconds, 364.6 seconds, and 104 seconds, and 100 cycles were performed under the conditions shown in Table 2 below.

The growth rate of silicon oxide films using TMS pyrazole and TMS imidazole was calculated. Here, the growth rate indicates the growth of silicon oxide films relative to the amount of silicon compound supplied, and is an index of ALD. If the growth rate of silicon oxide films becomes saturated with an increase in the supply amount, it can be said that a silicon oxide film is being formed by ALD. The growth rate was calculated from the amount of film deposited per cycle. The results are shown in Figure 6.

The results in Figure 6 confirm that as the supply amount of TMS pyrazole and TMS imidazole increases, the growth rate curve becomes flat, i.e., reaches saturation. This shows that a silicon oxide film is formed by ALD using TMS pyrazole and TMS imidazole.

<Test Example 2>
As in Test Example 1, atomic layer deposition of silicon oxide film was performed using the above-prepared TMS pyrazole and TMS imidazole, but the conditions were changed from those in Test Example 1. That is, in the case of TMS pyrazole, the time of the first introduction step was set to 161.7 seconds, and the temperatures of each step were set to 200°C, 300°C, 350°C, 500°C, 650°C, and 700°C. In addition, in the case of TMS imidazole, the time of the first introduction step was set to 37.9 seconds, and the temperatures of each step were set to 200°C, 300°C, 400°C, 500°C, 650°C, and 700°C. Other conditions of this test were performed under the conditions in Table 3 below, with 100 cycles for each step.

The film thickness and Ra of the silicon oxide films formed using TMS pyrazole and TMS imidazole were measured using the XRR measuring device described above, and the growth rate was calculated. The XRR conditions were as described above. The results are shown in Table 4 and Figure 7.

From the results of Table 4 and Figure 7, the growth rate at 200°C for both TMS pyrazole and TMS imidazole was slower than the growth rate at other temperature ranges. In other words, it is considered difficult to form a silicon oxide film using TMS pyrazole and TMS imidazole at 200°C. Furthermore, for both TMS pyrazole and TMS imidazole, the Ra was all 10% or less at temperatures other than 200°C, which means that a uniform silicon oxide film was formed.

<Test Example 3>
As in Test Example 1, atomic layer deposition of a silicon oxide film was performed using the TMS pyrazole prepared above, but the conditions were changed from those in Test Example 1. That is, a silicon substrate was used as the substrate, which had a plurality of grooves (holes) with a width of 150 nm and a depth of 3000 nm, and on the surface and holes of the substrate, a titanium nitride film of about 15 nm had been formed in advance. Each process was performed for 296 cycles under the conditions in Table 5 below. In Table 5, the first and second purge processes were performed in the order of vacuum purge ("vacuum" in Table 5), purge with purge gas ("gas" in Table 5), purge with purge gas, vacuum purge, and purge with purge gas.

The thickness of the silicon oxide film was calculated by cutting the substrate perpendicular to the hole at an arbitrary position, processing it with an FIB, photographing the cut surface with the above-mentioned TEM, and binarizing the TEM image. The TEM conditions were as described above. The measurement locations for the silicon oxide film were the top of the hole (depth from the substrate surface 0 nm to 1000 nm), the middle part (depth from the substrate surface 1000 nm to 2000 nm), and the bottom part (distance from the bottom wall of the hole 0 nm to 1000 nm). Photographs of each measurement location are shown in Figure 8.

8, the film thickness of the silicon oxide film was 18.6 nm at the upper portion (t ₁ ), 18.9 nm at the middle portion (t ₃ ), and 18.7 nm at the lower portion (t ₂ ). Substituting these values into the left-hand sides of the above formulas (i) to (iii), the results were 0.005 for formula (i), 0.016 for formula (ii), and 0.011 for formula (iii). These results show that there is little difference in film thickness between the upper, middle, and lower portions of the hole, i.e., the film thickness uniformity is excellent.

The thickness (t) of the silicon oxide film deposited on the flat portion of the substrate was measured to be 20.0 nm. The relationship between the thickness of the silicon oxide film on the flat portion of the substrate and the thickness of the hole was confirmed by applying the thickness of the silicon oxide film and the thickness of the upper, middle and lower portions to the following formula (iv).
|t-t _1-3 |/t≦0.2...formula (iv)

In the case of _t1 , formula (iv): 0.07, in the case of _t2 , formula (iv): 0.065, and in the case of _t3 , formula (iv): 0.055. From these results, it can be said that there is little difference in film thickness between the flat part of the substrate and each part of the hole, that is, the film thickness uniformity is excellent.

In this example, it has been confirmed that TMS imidazole has an MBDE value equivalent to that of TMS pyrazole, the results of Test Example 1 show that a silicon oxide film is formed by ALD, and the results of Test Example 2 show that a uniform silicon oxide film is formed on a flat substrate. Therefore, even when atomic layer deposition is performed on a substrate having multiple grooves using TMS imidazole, it is believed that a uniform silicon oxide film is formed, similar to that of TMS pyrazole.

As described above, the method for forming a highly uniform silicon oxide film by atomic layer deposition using the heat-resistant silicon compound disclosed herein is directly related to innovations in semiconductor manufacturing and can contribute to the smart society, which is expected to become more widespread in the future, including electric vehicles and energy efficiency, and to some of the activities toward the Sustainable Development Goals (SDGs).

The embodiments and examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 substrate, 2 surface, 3 silicon oxide film, 4 groove, 5 side wall surface, 6 bottom wall surface, 7 surface, 10 film formation device, 11 reactor, 12 precursor supply section, 13 carrier gas supply path, 14 precursor gas supply path, 15 purge gas supply path, 16 oxygen source supply path, 17 exhaust path, 18 APC valve, 19 needle valve, 20, 21, 22 on-off valve.

Claims (6)

providing a substrate in a reactor;
A first introduction step of introducing at least one silicon compound represented by the following formula (1) into the reactor;
a first purging step of purging the reactor with a purge gas;
a second introducing step of introducing an oxygen source into the reactor;
A second purge step of purging the reactor with the purge gas,
The first introducing step through the second purging step are repeatedly performed until a desired thickness of silicon oxide is deposited on the surface of the substrate;
The first introduction step to the second purging step are carried out at a temperature of 300° C. or more and 800° C. or less and a pressure of 7.6 Pa or more and 100 kPa or less,
A method for forming a silicon oxide film, wherein the average roughness of the thickness of the formed silicon oxide film is 10% or less with respect to the thickness of the formed silicon oxide film.

In the formula (1),
R ¹ and R ² are each independently a methyl group or an ethyl group;
^R3 is a methyl group, an ethyl group, a group represented by the following formula (2), or a group represented by the following formula (3),
^R4 is a group represented by the following formula (2) or a group represented by the following formula (3).

In the formula (2) and the formula (3),
R ⁵ to R ¹⁰ each independently represent a hydrogen atom, a methyl group, or an ethyl group. providing a substrate having a grooved surface in a reactor;
A first introduction step of introducing at least one silicon compound represented by the following formula (1) into the reactor;
a first purging step of purging the reactor with a purge gas;
a second introducing step of introducing an oxygen source into the reactor;
A second purge step of purging the reactor with the purge gas,
The first introducing step through the second purging step are repeatedly performed until a desired thickness of silicon oxide is deposited on the surface of the substrate;
The first introduction step to the second purging step are carried out at a temperature of 300° C. or more and 800° C. or less and a pressure of 7.6 Pa or more and 100 kPa or less,
The silicon oxide film is
Formula (i): |t ₁ -t ₂ |/t ₁ ≦0.2
Fulfilling the relationship,
In the formula (i),
_t1 denotes the thickness of the silicon oxide film (nm) on top of the trench;
_t2 represents the thickness of the silicon oxide film (nm) at the bottom of the trench.

In the formula (1),
R ¹ and R ² are each independently a methyl group or an ethyl group;
^R3 is a methyl group, an ethyl group, a group represented by the following formula (2), or a group represented by the following formula (3),
^R4 is a group represented by the following formula (2) or a group represented by the following formula (3).

In the formula (2) and the formula (3),
R ⁵ to R ¹⁰ each independently represent a hydrogen atom, a methyl group, or an ethyl group. In the formula (1),
The R ¹ and R ² are methyl groups;
The ^R3 is a methyl group or a group represented by the formula (3),
The R ⁴ is a group represented by the formula (3),
3. The method for forming a silicon oxide film according to claim 1, wherein R ⁸ to R ¹⁰ each independently represent a hydrogen atom, a methyl group or an ethyl group. In the formula (1),
R ¹ to R ³ each represent a methyl group;
The R ⁴ is a group represented by the formula (3),
3. The method for forming a silicon oxide film according to claim 1, wherein said R ⁸ to R ¹⁰ are hydrogen atoms. In the formula (1),
The R ¹ and R ² are methyl groups;
The R ³ and R ⁴ are groups represented by the formula (2),
3. The method for forming a silicon oxide film according to claim 1, wherein said R ⁵ to R ⁷ are each independently a hydrogen atom, a methyl group or an ethyl group. In the formula (1),
R ¹ to R ³ each represent a methyl group;
The R ⁴ is a group represented by the formula (2),
3. The method for forming a silicon oxide film according to claim 1, wherein said R ⁵ to R ⁷ are hydrogen atoms.

Images