Method for forming thin film

Abstract

To provide a method for forming a thin film which does not leave any reaction product on a substrate.SOLUTION: A method for forming a thin film includes a preparation step of preparing a substrate including a first thin film in a reactor, and an etching step of etching the substrate including the first thin film by atomic layer etching to form a substrate including a second thin film. The etching step further includes a step of introducing a fluorine-containing gas into the reactor to form a fluorinated surface layer on the first thin film, and a step of introducing oxalyl chloride into the reactor to remove a reaction product between the oxalyl chloride and the surface layer and form a substrate including the second thin film. The first thin film and the second thin film include a metal oxide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for forming a thin film. [Background technology]

[0002] In recent years, research and development of device structures and materials has been actively conducted to cope with the increasing integration density and miniaturization of circuit patterns in semiconductor devices. Among these, the use of metal oxides as materials for the gate oxide film of miniaturized transistors has attracted attention.

[0003] In order to manufacture fine transistors, it is necessary to thin the gate oxide film. Methods for forming thin films include, for example, chemical vapor deposition (CVD) and atomic layer deposition (ALD). In some cases, it is required to make the thin films formed by such methods even thinner. In such cases, it is required to control the amount of etching on the nanometer order.

[0004] However, when it comes to dry etching of metal oxides such as zirconium oxide, hafnium oxide, and aluminum oxide, the melting and boiling points of metal halides are high, and plasma etching using halogen-based gases has a high vapor pressure (high volatility), making it difficult to obtain reaction products. In addition, because the bond between the metal and oxygen is strong (high bond energy), these materials are known as difficult-to-etch materials, and microfabrication has been difficult using conventional etching methods. Therefore, the use of atomic layer etching (ALE), an etching method with high controllability at the atomic layer order, has been considered for difficult-to-etch materials (for example, Patent Documents 1-2 and Non-Patent Documents 1-2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2018-500767 [Patent Document 2] JP 2018-26566 A [Non-patent literature]

[0006] [Non-Patent Document 1] Austin M. Cano, Jonathan L. Partridge, and Steven M. George, Thermal Atomic Layer Etching of AL2O3Using Sequential HF and BCl3 Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms, Chemistry of Materials, 2022, 34, 6440-6449. [Non-Patent Document 2] Varun Sharma, Simon D. Elliott, Tom Blomberg, Suvi Haukka, Michael E. Givens, Marko Tuominen, and Mikko Ritala, Thermal Atomic Layer Etching of Aluminum Oxide (AL2O3) Using Sequential Exposures of Niobium Pentafluoride (NbF5) and Carbon Tetrachloride (CCl4): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism, Chemistry of Materials, 2021, 33, 2883-2893. Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the methods described in Patent Documents 1 and 2, the reaction products remain on the substrate, which may deteriorate the performance. Also, in the methods described in Non-Patent Documents 1 and 2, the reaction is not saturated in the ALE reaction step, and the surface is thought to be formed non-uniformly.

[0008] An object of the present disclosure is to provide a method for forming a thin film that does not leave any reaction products on a substrate. [Means for solving the problem]

[0009] [1] a preparation step of preparing a substrate including a first thin film in a reactor; and an etching step of etching the substrate including the first thin film by atomic layer etching to form a substrate including a second thin film, The etching step includes: introducing a fluorine-containing gas into the reactor to form a fluorinated surface layer on the first thin film; introducing oxalyl chloride into the reactor and removing a reaction product between oxalyl chloride and the surface layer to form a substrate including the second thin film; The method for forming a thin film, wherein the first thin film and the second thin film contain a metal oxide.

[0010] [2] The method for forming a thin film according to [1], wherein the metal oxide has a relative dielectric constant of 5 or more and 40 or less.

[0011] [3] The method for forming a thin film according to [1] or [2], wherein the metal oxide is at least one selected from the group consisting of zirconium oxide, hafnium oxide and aluminum oxide.

[0012] [4] The method for forming a thin film according to any one of [1] to [3], wherein the fluorine-containing gas is hydrogen fluoride.

[0013] [5] The method for forming a thin film according to any one of [1] to [4], wherein the etching step is performed repeatedly. Effect of the Invention

[0014] According to the present disclosure, it is possible to provide a method for forming a thin film that does not leave any reaction products on a substrate. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic flow chart showing an example of a method for forming a thin film according to the present disclosure. [Diagram 2] FIG. 2 is a schematic flow chart showing an example of an etching process according to the present disclosure. [Diagram 3] FIG. 3 is a schematic diagram illustrating an example of a substrate including a first thin film in the present disclosure. [Figure 4] FIG. 4 is a schematic diagram illustrating an example of a substrate including a surface layer according to the present disclosure. [Diagram 5] FIG. 5 is a schematic diagram illustrating an example of a substrate including a second thin film in the present disclosure. [Figure 6] FIG. 6 is a conceptual diagram showing an example of an etching apparatus applicable to the thin film forming method according to the present disclosure. [Figure 7] FIG. 7 is a graph showing the relationship between the amount of etching and the temperature in the reactor for each of the substrates No. 1 to 3 in Test Example 1. [Figure 8] FIG. 8 is a graph showing the relationship of the etching rate to the supply time of hydrogen fluoride in Example 1. [Figure 9] FIG. 9 is a graph showing the relationship of the etching rate to the supply time of oxalyl chloride in Example 2. [Figure 10] FIG. 10 is a graph showing the relationship between the etching amount and the number of cycles in the etching process in Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, embodiments of the present disclosure will be described. However, the following description does not limit the scope of the claims.

[0017] <<Method of forming thin film>> The method for forming a thin film of this embodiment includes a preparation step of preparing a substrate including a first thin film in a reactor, and an etching step of etching the substrate including the first thin film by atomic layer etching to form a substrate including a second thin film. The etching step further includes a step of introducing a fluorine-containing gas into the reactor to form a fluorinated surface layer on the first thin film, and a step of introducing oxalyl chloride into the reactor to remove a reaction product between oxalyl chloride and the surface layer to form a substrate including a second thin film. The first thin film and the second thin film include a metal oxide.

[0018] Fig. 1 is a schematic flow chart showing an example of a method for forming a thin film in this embodiment, and Fig. 2 is a schematic flow chart showing an example of an etching process in this embodiment. Each step of the method for forming a thin film will be described below.

[0019] <Preparation process> The preparation step is a step of preparing a substrate 5 including a first thin film in a reactor (see FIG. 3).

[0020] The substrate 1 used in the present disclosure is not particularly limited, but examples thereof include ceramic substrates such as silicon substrates, silicon oxide substrates, and silicon nitride substrates.

[0021] The first thin film 2 includes a metal oxide. The metal oxide is, for example, lithium oxide (Li 2 O), beryllium oxide (BeO), aluminum oxide (Al 2 O 3 ), calcium oxide (CaO), scandium(III) oxide (Sc 2 O 3 ), titanium(IV) oxide (TiO 2 ), vanadium pentoxide (V 2 O 5 ), chromium(II) oxide (CrO), chromium(III) oxide (Cr 2 O 3 ), chromium(IV) oxide (CrO 2 ), manganese(II) oxide (MnO), manganese(III) oxide (Mn 2 O3 ), iron(II) oxide (FeO), iron(III) oxide (Fe 2 O 3 ), cobalt(III) oxide (CoO), zinc oxide (ZnO), strontium oxide (SrO), yttrium(III) oxide (Y 2 O 3 ), zirconium oxide (ZrO 2 ), molybdenum(VI) oxide (MoO 3 ), barium oxide (BaO), lanthanum(III) oxide (La 2 O 3 ), hafnium oxide (HfO 2 ), Tantalum Pentoxide (Ta 2 O 5 ), tungsten(VI) oxide (WO 3 ), hafnium silicate (HfSiO 4 ) etc.

[0022] The metal oxide preferably has a high relative dielectric constant (High-k). When a high-k metal oxide is used, it is possible to increase the capacitance and suppress the leakage current. In the present disclosure, a high relative dielectric constant refers to a relative dielectric constant of 5 or more, and may be 10 or more, or 20 or more. Examples of such metal oxides include Li 2 O(k:9), Al 2 O 3 (k:9), Sc 2 O 3 (k:13), TiO 2 (k:80), SrO(k:13), Y 2 O 3 (k:15), ZrO 2 (k:25), BaO(k:34), La 2 O 3 (k:30), HfO 2 (k:25), Ta 2 O 5 (k:22), WO 3 (k:20), HfSiO 4 Among these, Al is the most popular from the viewpoint of practicality. 2 O 3 , ZrO 2 , HfO2 It is preferable that the metal oxide is at least one selected from the group consisting of: The higher the dielectric constant of the metal oxide, the higher the capacitance, but the smaller the band gap tends to be. If the band gap is small, it may not function as an insulating film. Therefore, the dielectric constant of the metal oxide is preferably 40 or less, more preferably 30 or less.

[0023] The method for forming the first thin film 2 on the substrate 1 is not particularly limited as long as the first thin film 2 is formed on the substrate 1, and examples thereof include CVD, ALD, sputtering, vacuum deposition, plating, etc. Examples of CVD and ALD include plasma CVD, plasma ALD, thermal CVD, thermal ALD, etc. Among these, from the viewpoints of coverage and film formation on fine portions, formation of the first thin film 2 by thermal ALD is preferred.

[0024] The thickness of the substrate 1 is not particularly limited, but is, for example, 0.5 mm or more and 1.0 mm or less. The thickness of the first thin film 2 ("H1" in FIG. 3) is not particularly limited, but is, for example, 1.0 nm or more and 100 nm or less.

[0025] <Etching process> The etching step is a step of etching the substrate 5 including the first thin film by atomic layer etching (ALE) to form the substrate 6 including the second thin film. Here, ALE refers to an etching technique that controls the thickness of a film including a metal oxide formed on a substrate by a surface treatment gas and an etching gas at the atomic layer level. In the present disclosure, ALE refers to supplying a surface treatment gas to the substrate 1 to treat the surface of the first thin film 2 on the substrate 1, purging and removing the remaining surface treatment gas, and then supplying an etching gas to the substrate 1 to react the surface-treated portion (surface layer 3) of the first thin film 2 with the etching gas to remove the reaction product between the surface layer 3 and the etching gas, and purging and removing the remaining etching gas, thereby forming the substrate 6 including the second thin film. In addition, ALE can be performed in combination with the formation of the substrate 5 including the first thin film (e.g., CVD, ALD, etc.) in the above-mentioned preparation step.

[0026] The etching step further includes a step of introducing a fluorine-containing gas into the reactor to form a fluorinated surface layer 3 on the first thin film 2 (first introduction step), and a step of introducing oxalyl chloride into the reactor to remove a reaction product between oxalyl chloride and the surface layer 3 to form a substrate 6 including a second thin film (second introduction step). In addition, the etching step preferably further includes a step of purging the reactor with a purge gas between the first and second introduction steps (first purging step), and a step of purging the reactor with a purge gas after the second introduction step (second purging step).

[0027] (1st introduction process) The first introduction step is a step of introducing a fluorine-containing gas, which is a surface treatment gas, into a reactor to form a fluorinated surface layer 3 on the first thin film 2 (see FIG. 4). In this step, the metal in the metal oxide contained in the first thin film 2 reacts with the fluorine contained in the fluorine-containing gas to form the surface layer 3 containing the fluorinated metal.

[0028] The fluorine-containing gas is not particularly limited as long as it contains fluorine. For example, fluorine (F 2 ), hydrogen fluoride (HF), chlorine trifluoride (ClF 3 ), nitrogen trifluoride (NF 3 ), sulfur hexafluoride (SF 6 ), xenon difluoride (XeF 2 ), trifluoromethane (CHF 3 ), tungsten hexafluoride (WF 6 ), niobium pentafluoride (NbF 5 ), bromine trifluoride (BrF 3 ), bromine pentafluoride (BrF 5 ), iodine pentafluoride (IF 5 ), boron trifluoride (BF 3 ), silicon tetrafluoride (SiF 4 ), carbonyl fluoride (COF 2 ), thionyl fluoride (SOF 2 Among these, F 2 and HF are preferred. 2This is because HF does not leave behind any reaction products as impurities even when it reacts with metal oxides.

[0029] The fluorine-containing gas 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 fluorine-containing gas to the reactor. The carrier gas and the fluorine-containing gas do not react with each other. The carrier gas is, for example, hydrogen (H 2 ), Helium (He), Nitrogen (N 2 ), neon (Ne), argon (Ar), etc.

[0030] This step may be performed for a time and at a flow rate that allows the formation of the surface layer 3. This step may be performed for a time of, for example, 0.1 seconds or more and 1000 seconds or less. The fluorine-containing gas in this step may be introduced into the reactor at a flow rate of, for example, 1 sccm or more and 2000 sccm or less. The unit of flow rate "sccm (Standard Cubic Centimeter per Minute)" indicates "mL / min" under standard conditions (0°C, 101.3 kPa).

[0031] (First purge process) The first purge step is a step of purging the reactor with a purge gas after the first introduction step, which is a step of removing excess fluorine-containing gas that has not reacted in the first introduction step.

[0032] The purge gas may be an inert gas capable of removing the fluorine-containing gas. The purge gas does not react with the fluorine-containing gas. Examples of such an inert purge gas include the same gas as the carrier gas described above.

[0033] This step may be carried out for a time and at a flow rate that can remove excess fluorine-containing gas. This step 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 step may be introduced into the reactor at a flow rate of, for example, 1 sccm or more and 2000 sccm or less.

[0034] In this step, 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 of, for example, 0.1 seconds to 1000 seconds.

[0035] This step may be carried out multiple times. When this step is carried out multiple times, the time, flow rate, and purge gas used in each step may be the same or different. Vacuum purging may be performed between each step. For example, purging with a purge gas, vacuum purging, and purging with a purge gas may be performed in this order.

[0036] (Second introduction process) The second introduction step is a step of introducing oxalyl chloride, which is an etching gas, into a reactor, removing the reaction product between oxalyl chloride and the surface layer 3, and forming a substrate 6 including a second thin film (see FIG. 5). In this step, oxalyl chloride reacts with the surface layer 3 to generate metal chlorides and carbonyl fluoride, which are then removed to form a substrate 6 including a second thin film. The thickness of the second thin film 4 ("H2" in FIG. 5) is smaller than the thickness of the first thin film 2. The thickness of the second thin film 4 is not particularly limited, but is, for example, 0.1 nm or more and less than 100 nm.

[0037] In this step, oxalyl chloride may be introduced into the reactor in either liquid or gaseous form, but it is preferable to react with the surface layer 3 in gaseous form. When oxalyl chloride is introduced into the reactor in liquid form, the introduced oxalyl chloride may be vaporized by heating or reducing the pressure inside the reactor. When oxalyl chloride is introduced into the reactor in gaseous form, oxalyl chloride may be introduced by a carrier gas. The carrier gas used in this step may be the same as the above-mentioned carrier gas.

[0038] This step may be carried out for a time and at a flow rate that allows the oxalyl chloride to react with the surface layer 3. This step may be carried out for a time of, for example, 0.1 seconds or more and 1000 seconds or less. In this step, the oxalyl chloride may be introduced into the reactor at a flow rate of, for example, 1 sccm or more and 2000 sccm or less.

[0039] (Second purge process) The second purge step is a step of purging the reactor after the second introduction step with a purge gas. This step is a step of removing excess oxalyl chloride that did not react in the second introduction step and the above reaction products that were not completely removed.

[0040] The purge gas used in this step is the same as the carrier gas described above. This step may be carried out for, for example, 0.1 seconds or more and 1000 seconds or less. The purge gas in this step may be introduced into the reactor at a flow rate of, for example, 1 sccm or more and 2000 sccm or less.

[0041] (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, for example, at a temperature of 200° C. or more and 450° C. or less. However, the temperature at which each step is performed varies depending on the metal oxide contained in the first thin film 2 used, and is therefore set appropriately depending on the type of metal oxide. In addition, the first introduction step, the first purge step, the second introduction step, and the second purge step are performed, for example, at a pressure of 13 Pa or more and 40,000 Pa or less.

[0042] The first introducing step to the second purging step may be repeatedly performed. By repeatedly performing the first introducing step to the second purging step, a thin film having a desired thickness can be formed.

[0043] (Other processes) The thin film forming method of the present application may include a step of annealing the first thin film 2 (annealing step) between the preparation step and the etching step.

[0044] By annealing the metal oxide contained in the first thin film 2, the metal oxide is crystallized. This is expected to improve the relative dielectric constant of the metal oxide. However, if the thickness of the first thin film 2 is less than 10 nm, the crystallization of the metal oxide may not progress even if the annealing is performed, so it is preferable to perform the annealing treatment when the thickness of the first thin film 2 is 10 nm or more.

[0045] The temperature for carrying out the annealing treatment may be, for example, in the range of 400 to 600° C. The time for carrying out the annealing treatment may be appropriately adjusted depending on the metal oxide used.

[0046] <Etching equipment> An example of an etching apparatus applicable to the thin film forming method of the present embodiment will be described with reference to Fig. 6. The etching apparatus 30 includes at least a reactor 11 for accommodating a substrate including a first thin film as an object to be processed, a fluorine-containing gas supply path 12 for supplying a fluorine-containing gas as a surface treatment gas, a purge gas supply path 13 for supplying a purge gas, a second oxalyl chloride supply path 16 for supplying oxalyl chloride as an etching gas, and an exhaust path 17 for exhausting the atmosphere in the reactor 11.

[0047] The reactor 11 has a sealed structure that allows the inside of the reactor 11 to be isolated from the outside air. The reactor 11 is configured in such a manner that the substrate including the first thin film can be accommodated in a horizontal position using a boat or the like. The reactor 11 may include a heating mechanism (not shown) that can heat the substrate including the first thin film accommodated inside to a predetermined temperature. The heating mechanism is not particularly limited, and for example, a known mechanism such as a heater can be adopted.

[0048] The fluorine-containing gas supply path 12 has a function of supplying a fluorine-containing gas to the reactor 11. The fluorine-containing gas supply path 12 is connected to the reactor 11. The flow rate of the fluorine-containing gas to be supplied can be controlled by an MFC (Mass Flow Controller). An on-off valve 19 is provided in the fluorine-containing gas supply path 12. The on-off valve 19 controls the supply or stop of the fluorine-containing gas flowing through the fluorine-containing gas supply path 12.

[0049] The fluorine-containing gas may be supplied to the reactor 11 by the following method. The etching apparatus 30 may include, for example, a fluorine-containing gas supply unit, a fluorine-containing gas supply path, a carrier gas supply path, and the like. The fluorine-containing gas may be introduced into the fluorine-containing gas supply unit by a carrier gas through the carrier gas supply path. The carrier gas supplied from the carrier gas supply path may be flow-controlled by an MFC. The fluorine-containing gas introduced into the fluorine-containing gas supply unit and stored may be supplied to the reactor 11 through a fluorine-containing gas supply path provided between the fluorine-containing gas supply unit and the reactor 11. The fluorine-containing gas supply path may be provided with a needle valve for adjusting the flow rate of the gas flowing through the fluorine-containing gas supply path, an opening / closing valve for controlling the supply or stop of the gas flowing through the fluorine-containing gas supply path, and the like.

[0050] The purge gas supply path 13 has a function of supplying a purge gas to the reactor 11. The purge gas supply path 13 is connected to the reactor 11. The flow rate of the supplied purge gas can be controlled by an MFC. An on-off valve 20 is provided in the purge gas supply path 13. The on-off valve 20 controls the supply or stop of the purge gas flowing through the purge gas supply path 13.

[0051] The oxalyl chloride supply unit 15 has a function of supplying oxalyl chloride to the reactor 11. Liquid oxalyl chloride is stored in the oxalyl chloride supply unit 15. A first oxalyl chloride supply line 14 for introducing oxalyl chloride is connected to the oxalyl chloride supply unit 15. A second oxalyl chloride supply line 16 is provided between the oxalyl chloride supply unit 15 and the reactor 11. The oxalyl chloride stored in the oxalyl chloride supply unit 15 is vaporized by heating the oxalyl chloride supply unit 15. The vaporized oxalyl chloride is supplied to the reactor 11 through the second oxalyl chloride supply line 16. The second oxalyl chloride supply line 16 is provided with an MFC, a needle valve 22, and an on-off valve 21. The flow rate of the vaporized oxalyl chloride can be controlled by the MFC. The needle valve 22 adjusts the flow rate of the gas flowing through the second oxalyl chloride supply line 16. The on-off valve 21 controls the supply or stop of the gas flowing through the second oxalyl chloride supply line 16.

[0052] In addition, oxalyl chloride may be supplied to the reactor 11 by the following method. The etching apparatus 30 may include, for example, an oxalyl chloride supply unit, an oxalyl chloride supply path, a carrier gas supply path, and the like. Oxalyl chloride may be introduced into the oxalyl chloride supply unit by a carrier gas through the carrier gas supply path. The carrier gas supplied from the carrier gas supply path may be flow-controlled by an MFC. Oxalyl chloride introduced and stored in the oxalyl chloride supply unit may be supplied to the reactor 11 through an oxalyl chloride supply path provided between the oxalyl chloride supply unit and the reactor 11. The oxalyl chloride supply path may be provided with a needle valve for adjusting the flow rate of the gas flowing through the oxalyl chloride supply path, an on-off valve for controlling the supply or stop of the gas flowing through the oxalyl chloride supply path, and the like.

[0053] The exhaust line 17 has a 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 control of the APC valve 18 is performed 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.

[0054] The exhaust gas discharged from the exhaust passage 17 may contain toxic gas, flammable gas, etc. Therefore, the exhaust passage 17 may be provided with a water washing scrubber, a sulfuric acid scrubber, a caustic scrubber, a dry detoxification device, etc., so that the exhaust gas can be made harmless and released into the atmosphere. EXAMPLES

[0055] The following examples are provided to illustrate, but not to limit, the scope of the claims.

[0056] Substrates No. 1 to 3 were prepared as substrates including the first thin film. The first thin film of No. 1 contained ZrO 2 The first thin film of No. 2 is HfO 2 The first thin film of No.3 contains Al as the metal oxide. 2 O 3 The first thin films No. 1 to 3 were formed by thermal ALD and had a thickness of 15 nm. The thickness of the first thin films was measured by X-ray reflectometry (XRR), and an XRR measuring device (Malvern Panalytical's X'Pert PRO MRD) was used.

[0057] <Test Example 1> In order to confirm the effect of oxalyl chloride on the thin film, the following test was carried out. Specifically, each of the substrates No. 1 to 3 was placed in the reactor of the etching apparatus shown in FIG. 6, and the extent to which the first thin film of No. 1 to 3 was etched (etching amount) when only oxalyl chloride was supplied was evaluated under the following conditions. In No. 1, the reactor temperature was set to 200°C, 250°C, 300°C, 350°C, and 400°C, in No. 2, 380°C, 400°C, and 500°C, and in No. 3, 420°C and 500°C. The results are shown in FIG. 7. The etching amount was measured by the above-mentioned XRR measurement device.

[0058] (conditions) Flow rate: 60sccm Pressure: 40Pa Time: 10 minutes As shown in Figure 7, it was confirmed that etching was hardly performed up to 350°C in No. 1, up to 380°C in No. 2, and up to 420°C in No. 3, but etching was clearly performed above the above temperatures. This means that oxalyl chloride etches the first thin film above a certain temperature, that is, during ALE, after removing the surface layer with oxalyl chloride, it etches the first thin film, which is not normally etched, and this may prevent ideal ALE from being performed.

[0059] <Test Example 2> In order to confirm whether any reaction products remain after ALE and whether there is any change in the film composition between the first thin film and the second thin film, ALE was performed using the etching apparatus shown in FIG.

[0060] Specifically, the No. 1 substrate was placed in the reactor of the etching device. HF, a fluorine-containing gas, was introduced into the reactor. N 2 The reactor was purged with N gas. Oxalyl chloride was vaporized by heating to 50-60°C and introduced into the reactor. 2The reactor was purged with gas. Each process was performed 20 cycles under the conditions in Table 1 below. The presence or absence of reaction products remaining on the substrate after ALE, and the film compositions of the first and second thin films were measured by X-ray photoelectron spectroscopy (XPS) (ULVAC-PHI, Quantera SXM) under the following conditions. The results are shown in Table 2.

[0061] (conditions) X-ray source: Monochromated Al (1486.6 eV) Detection area: 100μmφ Detection depth: 4~5nm Take-out angle: 45°

[0062] [Table 1]

[0063] [Table 2]

[0064] As shown in Table 2, F increased slightly after ALE, but chlorine (Cl) derived from oxalyl chloride was not detected, and C did not change significantly before and after ALE. This indicates that no reaction products remain on the substrate even after ALE. In addition, the ratio of O to Zr does not change before and after ALE. This indicates that the film composition does not change even after ALE. In addition, although the quantitative value of F increased after ALE, this is not thought to indicate the presence of residual reaction products.

[0065] <Test Example 3> In order to confirm the etching rate and etching amount by ALE, ALE was performed on the substrate No. 1 using the etching apparatus shown in Figure 6. In the following Examples 1 to 3, HF was used as the fluorine-containing gas and N was used as the purge gas. 2 The gas was heated to 50 to 60° C. to vaporize oxalyl chloride, which was then used.

[0066] Example 1 In each step, the time for the first introduction step was set to 5 seconds, 15 seconds, 20 seconds, 40 seconds, 45 seconds, 60 seconds, and 90 seconds, and 20 cycles were performed under the conditions in Table 1 below.

[0067] [Table 3]

[0068] Example 2 In each step, the time for the second introduction step was set to 60 seconds, 120 seconds, 180 seconds, 240 seconds, 420 seconds, 600 seconds, and 780 seconds, and 20 cycles were performed under the conditions in Table 2 below.

[0069] [Table 4]

[0070] Example 3 Each step was carried out for 5 cycles, 20 cycles, 40 cycles, or 80 cycles under the conditions in Table 3 below.

[0071] [Table 5]

[0072] (etching rate) The etching rate for the first thin film in Examples 1 and 2 was calculated. Here, the etching rate indicates the amount of the thin film etched with respect to the supply time of the fluorine-containing gas or oxalyl chloride, and is an index of ALE. If the etching rate of the thin film becomes saturated with the supply time, it can be said that the thin film is etched by ALE. The etching rate was calculated from the amount of etching per cycle. The results are shown in Figures 8 and 9.

[0073] 8 and 9, it was confirmed that the etching rate curves flattened out, that is, reached a saturated state, with the supply time of HF and oxalyl chloride. This indicates that the thin film was etched by ALE in Examples 1 and 2.

[0074] (etching amount) The etching amount for the first thin film in Example 3 was calculated, and the result is shown in Figure 10. The etching amount was measured by the above-mentioned XRR measurement device.

[0075] As shown in Figure 10, the amount of etching increased in proportion to the increase in the number of cycles of each process. From this, it can be easily estimated how many times the etching process must be repeated to obtain a substrate including a second thin film of the required thickness from a substrate including a first thin film.

[0076] 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 defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0077] 1 substrate, 2 first thin film, 3 surface layer, 4 second thin film, 5 substrate including first thin film, 6 substrate including second thin film, 11 reactor, 12 fluorine-containing gas supply channel, 13 purge gas supply channel, 14 first oxalyl chloride supply channel, 15 oxalyl chloride supply unit, 16 second oxalyl chloride supply channel, 17 exhaust channel, 18 APC valve, 19, 20, 21 on-off valves, 22 needle valve, 30 etching device.

Claims

1. providing a substrate including a first thin film in a reactor; and an etching step of etching the substrate including the first thin film by atomic layer etching to form a substrate including a second thin film, The etching step includes: introducing a fluorine-containing gas into the reactor to form a fluorinated surface layer on the first thin film; introducing oxalyl chloride into the reactor and removing a reaction product between oxalyl chloride and the surface layer to form a substrate including the second thin film; The method for forming a thin film, wherein the first thin film and the second thin film include a metal oxide.

2. 2. The method for forming a thin film according to claim 1, wherein the metal oxide has a relative dielectric constant of 5 or more and 40 or less.

3. 2. The method for forming a thin film according to claim 1, wherein the metal oxide is at least one selected from the group consisting of zirconium oxide, hafnium oxide and aluminum oxide.

4. 2. The method for forming a thin film according to claim 1, wherein the fluorine-containing gas is hydrogen fluoride.

5. The method of forming a thin film according to claim 1 , wherein the etching step is performed repeatedly.

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