Atomic layer etching method for metal oxide film

Abstract

Disclosed is an atomic layer etching method of a metal oxide film, in which the metal oxide film is formed on a predetermined lower film on a substrate. An atomic layer etching method according to an embodiment includes a fluorination step in which a fluorinated surface layer is formed by supplying a fluorine-containing gas to react with a surface of a metal oxide film; and a chemical etching step in which the fluorinated surface layer is removed by supplying a chemical etching gas to the substrate, in which a portion of the metal oxide film is removed by repeating a cycle including the fluorination step and the chemical etching step a predetermined number of times to remove a portion of the metal oxide film. And the fluorine-containing gas reacts with the lower film to form a non-volatile passivation film.

Description

Technical Field

[0001] The present invention relates to a semiconductor etching process, and more particularly to an atomic layer etching (ALE) process of a metal oxide film having high etching selectivity to an underlying film. Background Art

[0002] As the ultra-high integration and ultra-miniaturization of semiconductor devices continue to advance, not only the thickness of the film is getting smaller and smaller, but also the line width (critical dimension, CD) of the pattern is getting smaller and smaller. For example, the thickness of the conductive film or dielectric film of the transistor constituting the dynamic random access memory (DRAM) device becomes thinner, and the line width is also reduced to 5nm or less. When manufacturing semiconductor devices with such ultra-fine and ultra-thin patterns, it is not only difficult to achieve atomic-level control using existing physical / chemical processes or plasma processes, but also it will cause problems such as surface damage. Therefore, in the deposition process and etching process, the demand for atomic-scale processing is also increasing.

[0003] The Atomic Layer Deposition (ALD) process and the Atomic Layer Etching (ALE) process are known as manufacturing processes for semiconductor devices that can control the thickness of the film in units of atomic layers or molecular layers. However, when the thickness of the film deposited using the ALD process is very thin, there will be a problem that it is difficult to meet the physical properties required for the film. This is because when the deposited film is a certain thickness or less, the crystallinity of the deposited film is poor, resulting in poor physical properties such as leakage current characteristics. In order to prevent the degradation of these physical properties, the thickness of the deposited film needs to be at a certain level or higher, but if the thickness of the film becomes thicker, it becomes difficult to ensure the required dielectric constant or capacitance.

[0004] Therefore, in order to reduce the film thickness to a certain level or lower while satisfying the required physical properties, after forming a film with good crystallinity to a predetermined thickness or more by using a deposition process, it is necessary to make the film thinner by removing the deposited film in atomic layer or molecular layer units using an ALE process. For example, in Korean Patent Publication No. 2019-0136438 "Thin Film Formation Method" (Patent Document 1), a method of forming a thin film with excellent crystallinity by forming a zirconium oxide film or an aluminum oxide film by using an ALD process and then etching by an ALE process is disclosed.

[0005] However, when etching a thin film using the above-mentioned ALE process, a problem may occur that other films that should not be etched are etched or damaged while etching the film to be etched. If unnecessary etching or surface damage to other films occurs during the etching process, defects in semiconductor devices may occur. In particular, when the process gas is plasmatized to ensure reactivity, the possibility of this problem increases.

[0006] For example, in the manufacture of capacitors and the like of certain semiconductor devices (e.g., DRAM devices), a process for forming a high dielectric metal oxide film having excellent crystallinity and a thin thickness by sequentially applying a deposition process (e.g., an ALD process) and an ALE process is proposed. At this time, in a deposition process such as ALD, a metal oxide film is deposited on a predetermined lower film (e.g., a titanium nitride film (TiN)). And, an ALE process is applied to thin the deposited metal oxide film.

[0007] In such a process sequence, during the ALE process, there is a possibility that the surface of the metal oxide film may be damaged and / or the lower film may be etched together. In particular, in Korean Patent Publication No. 2019-0142407 "In-situ Selective Deposition and Etching for Advanced Patterning Applications" (Patent Document 2), it is disclosed that in the ALE process using the same etching gas, in addition to metal oxide films such as zirconium oxide films and hafnium oxide films, titanium nitride films are also used as one of the etching objects. Accordingly, in the case of the ALE process using the etching gas, while etching the metal oxide film, it is also easy to etch and remove the titanium nitride film at the bottom thereof.

[0008] [Prior Technical Literature]

[0009] (Patent Document 1) Korean Patent Publication No. 2019-0136438

[0010] (Patent Document 1) Korean Patent Publication No. 2019-0142407 Summary of the invention

[0011] Technical issues

[0012] The present invention provides an atomic layer etching (ALE) process, wherein when a single or composite metal oxide film such as a zirconium oxide film, a hafnium oxide film and a hafnium zirconium oxide film is etched by the ALE process, the etching of the underlying film will not be caused, and the surface damage of the metal oxide film serving as the etching target film will not be caused.

[0013] Solutions to the problem

[0014] One embodiment of the present invention is an atomic layer etching method for a metal oxide film, wherein the metal oxide film is formed on a predetermined lower film on a substrate, and the method includes: a fluorination step, wherein a fluorine-containing gas is supplied to react with the surface of the metal oxide film to form a fluorinated surface layer; and a chemical etching step, wherein the fluorinated surface layer is removed by supplying a chemical etching gas to the substrate, wherein a portion of the metal oxide film is removed by repeating a cycle including the fluorination step and the chemical etching step a predetermined number of times, and the fluorine-containing gas reacts with the lower film to form a non-volatile passivation film.

[0015] According to one aspect of the embodiment, the fluorine-containing gas may be in a non-plasma state, and the process temperature of the fluorination step may be 200° C. to 500° C. Preferably, the process temperature of the fluorination step may be 300° C. to 400° C.

[0016] According to another aspect of the embodiment, the fluorine-containing gas may include one or more gases selected from the group consisting of HF gas, NF3 gas, F3NO gas and FNO gas, and the lower film may be a titanium nitride film. At this time, the HF gas may be anhydrous HF gas. In addition, the non-volatile passivation film may include one or more of titanium difluoride (TiF2) and titanium trifluoride (TiF3). In addition, the chemical etching gas may include one or more gases selected from the group consisting of TiCl4 gas and SiCl4 gas.

[0017] According to another aspect of the embodiment, the metal oxide film may include one or more oxide films selected from the group consisting of a hafnium oxide film, a zirconium oxide film, and a hafnium-zirconium composite oxide film.

[0018] Effects of the Invention

[0019] According to the above-mentioned embodiments of the present invention, in the etching process of the metal oxide film using the atomic layer etching (ALE) process, a gas that reacts with the lower film of the metal oxide film to form a non-volatile passivation layer and / or a gas whose molecular size is relatively large is used as a fluorine-containing gas, so that the reactivity can be controlled and the diffusion of the gas through the grain boundaries of the metal oxide film, etc. can be suppressed, so that the metal oxide film can be etched with high selectivity relative to the lower film. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A and Figure 1B They are transmission electron microscope photos showing test results according to the existing plasma atomic layer etching (ALE) process.

[0021] Figure 1C and Figure 1D Each of them is a transmission electron microscope photograph showing the experimental results of the existing plasma ALE process at low temperature.

[0022] Figure 1E A transmission electron microscope photograph showing test results based on a conventional thermal plasma ALE process.

[0023] Figure 2 FIG. 1 is a diagram schematically illustrating an etching process according to a conventional ALE process.

[0024] Figure 3 FIG. 4 is a diagram schematically illustrating an ALE etching process according to an embodiment of the present invention.

[0025] Figure 4 FIG. 4 is a flow chart showing a method for atomic layer etching of a metal oxide film according to an embodiment of the present invention.

[0026] FIG. 5A to FIG. 5C To schematically illustrate the Figure 4 The cross-sectional views of the states during each process of the atomic layer etching method are shown.

[0027] Figure 6 FIG. 4 is a transmission electron microscope photograph showing an experimental result of an ALE etching process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The terms and words used in this specification are selected in consideration of their functions in the embodiments, and the meanings of the terms may vary according to the intention or convention of the present invention, etc. Therefore, when the terms used in the embodiments described below are specifically defined in this specification, the definition should be followed, and if there is no specific definition, it should be interpreted with the meaning generally recognized by those skilled in the art.

[0029] Atomic Layer Etching (ALE) is a film etching technology that utilizes a sequential self-limiting reaction. Since it reacts only on the surface of the film to be etched, it is possible to control etching in atomic layer units. When etching high-dielectric metal oxide films such as hafnium oxide films, zirconium oxide films, and hafnium-zirconium composite oxide films used as high-dielectric films for semiconductor devices (e.g., dynamic random access memory (DRAM)) by applying the ALE process, not only is the self-limiting property for etching in atomic layer units required, but it must also not cause surface damage to the metal oxide film and / or not etch its underlying film. In other words, it must be possible to control the reactivity of the ALE process relative to the metal oxide film (etching in atomic layer units), and it must also show high etching selectivity to the underlying film.

[0030] In the etching process of metal oxide film using ALE process, at least two reaction mechanisms are known. The first reaction mechanism is direct chlorination reaction, in which the metal oxide film is removed by directly reacting the metal oxide film with a chlorine-containing gas. In this case, the chlorine-containing gas can be supplied in a non-plasma state or a plasma state. In the former case, even if the process temperature is increased to 500 ° C, the reactivity is low, resulting in the metal oxide film not being easily etched. On the contrary, in the latter case, the metal oxide film is easily etched due to its high reactivity in proportion to the process temperature, but the chlorine-containing gas in the plasma state has extremely high reactivity, making it difficult to control etching in atomic layer units.

[0031] In the second reaction mechanism, the surface of the metal oxide film is modified by reacting it with a fluorine-containing gas, i.e., fluorination is performed, and then the metal oxide film can be converted into a substance that can evaporate at a relatively low temperature by ligand exchange using a chemical etching gas, thereby removing the metal oxide film. In this case, the fluorine-containing gas can also be supplied in a non-plasma state (hereinafter referred to as 'thermal ALE') or a plasma state (hereinafter referred to as 'plasma ALE'). However, as will be described later, in the case of plasma ALE, the reactivity of the plasmatized gas is relatively greater than when it is supplied in a non-plasma state, resulting in surface damage to the metal oxide film and / or difficulty in controlling the etching of atomic layer units.

[0032] However, in the case of the second reaction mechanism, as disclosed in Korean Patent Publication No. 2019-0142407 (Patent Document 1), depending on the type of fluorine-containing gas and / or chemical etching gas used, the problem of the lower film being etched together with the metal oxide film may occur, which will be explained in more detail based on the following experimental results.

[0033] Figure 1A and Figure 1B The two are transmission electron microscope (TEM) photos showing that when the zirconium oxide film is etched using the plasma ALE process, the titanium nitride film underneath is also etched. Figure 1A The case where plasma NF3 gas is used as the fluorine-containing gas and TiCl4 gas is used as the chemical etching gas is shown, and Figure 1B A case where plasma CF 4 gas is used as the fluorine-containing gas and TiCl 4 gas is used as the chemical etching gas is shown.

[0034] Reference Figure 1A It can be seen that when the ALE process cycle of supplying plasma NF3 gas for 30 seconds and then supplying TiCl4 gas for 30 seconds is repeated 5 times, 10 times and 15 times respectively, the thickness of the ALE layer is about The zirconium oxide film is etched to a thickness of approximately and During this period, the titanium nitride film underneath is also etched and removed. Figure 1B It can be seen that when the ALE process cycle of supplying plasma CF4 gas for 30 seconds and then supplying TiCl4 gas for 30 seconds is repeated 5 times, 10 times and 15 times respectively, when the thickness is about The zirconium oxide film is etched to a thickness of approximately and During the process, after 10 cycles, the titanium nitride film underneath was also etched and removed.

[0035] and, Figure 1C and Figure 1D 3 and 4 are TEM photographs showing a phenomenon that, when a zirconium oxide film is etched using plasma ALE, a titanium nitride film thereunder is also etched, wherein the process temperature is set to about 300° C. Figure 1C To illustrate the case where plasma NF3 gas is used as the fluorine-containing gas and DMAC gas is used as the chemical etching gas, and Figure 1D This illustrates the case where plasma CF4 gas is used as the fluorine-containing gas and DMAC gas is used as the chemical etching gas.

[0036] Reference Figure 1CIt can be seen that when the ALE process cycle of supplying plasma NF3 gas for 30 seconds and then supplying DMAC gas for 30 seconds is repeated 5 times, the thickness of the ALE layer is about The zirconium oxide film is etched to a thickness of approximately During the period, the titanium nitride film at the bottom is also etched and removed. Figure 1D It can be seen that when the ALE process cycle of supplying plasma CF4 gas for 30 seconds and then supplying DMAC gas for 30 seconds is repeated 5 times, 10 times and 15 times respectively, when the thickness is about The zirconium oxide film is etched to a thickness of approximately and During the process, after 10 cycles, the titanium nitride film underneath was also etched and removed.

[0037] and, Figure 1E TEM photograph showing the phenomenon that when a zirconium oxide film is etched using thermal ALE, a titanium nitride film thereunder is also etched, wherein ClF3 gas is used as a fluorine-containing gas and TiCl4 gas is used as a chemical etching gas. Figure 1E , it can be seen that when the ALE process cycle of supplying ClF3 gas for 10 seconds and then supplying TiCl4 gas for 10 seconds is repeated 5 times, 10 times, and 15 times, respectively, the titanium nitride film also begins to be etched after about 10 cycles and is almost completely removed after 15 cycles. However, Figure 1E In the test case of , even if the ALE cycle is repeated 15 times, the thickness is about The zirconium oxide film was hardly etched either, which is presumably because the ligand exchange reaction of the generated ZrF4 did not occur smoothly in the low-temperature process of 300°C.

[0038] Figure 2 To schematically illustrate the process in which the lower film is also etched when a metal oxide film (eg, a zirconium oxide film) is etched using a conventional ALE process, as shown in FIG. Figures 1A to 1E The test results are shown in Figure 2 In the above, A, B, C, and D all represent by-products produced in the corresponding reactions. Figure 2, it can be seen that when plasma NF3 gas, plasma CF4 gas or ClF3 gas is used, it reacts with the zirconium oxide film to form TiF4 (boiling point: about 400°C or higher), and then when TiCl4 gas or DMAC gas is supplied as a chemical etching gas, TiF4 is replaced by a ligand to TiCl4 (boiling point: about 136°C or higher) that can evaporate at a relatively low temperature, and therefore, the titanium nitride film is also etched together with the zirconium oxide film. In this way, the reason why the titanium nitride film as the lower film of the zirconium oxide film is etched is that the zirconium oxide film reacts with the fluorine-containing gas to form TiF4 and cannot function as a passivation film.

[0039] Based on the above test results, it is expected that a material (fluorine-containing gas and / or chemical etching gas) that reacts with the metal oxide film but can block the reaction with the lower film (e.g., titanium nitride film) and / or inhibits the reactivity can increase the etching selectivity. More specifically, when the diffusion of the gas through the grain boundary of the metal oxide film is inhibited or reduced, the fluorine-containing gas can be blocked or inhibited from contacting the titanium nitride film as its lower film. And, by controlling the reactivity of the fluorine-containing gas, a passivation film is formed even if it reacts with the lower film, thereby preventing or inhibiting the titanium nitride film from being etched by the chemical etching gas. As will be described later, according to the present invention, when using a gas with a relatively large particle size, such as HF gas, NF3 gas, F3NO gas and FNO gas, etc. as a fluorine-containing gas, the diffusion of the gas through the grain boundary of the metal oxide film can be blocked or inhibited, and a passivation film can be formed by controlling the reactivity, thereby preventing or reducing the etching of the film located below it, such as the titanium nitride film. Furthermore, by using a material that generates byproducts having sufficient vapor pressure after reaction, such as TiCl4 gas and SiCl4 gas, as a chemical etching gas, a decrease in the etching rate of the metal oxide film or etching stop due to residual reaction byproducts in the process chamber can be prevented.

[0040] Figure 3 To schematically illustrate a process in which, when a metal oxide film (eg, a zirconium oxide film) is etched using a thermal ALE process using HF gas as a fluorine-containing gas, the titanium nitride film at the bottom thereof does not react with the fluorine-containing gas and is not etched. Figure 3 In the above formula, A, B, C, and D all represent reaction by-products. Figure 3 , when HF gas is used as the fluorine-containing gas, it reacts with the zirconium oxide film to form ZrF4, but does not react with the titanium nitride film thereunder, or the reaction is suppressed. Therefore, it can be seen that when TiCl4 gas is subsequently supplied as a chemical etching gas, ZrF4 is removed by being replaced by a ligand with highly volatile ZrCl4, but the titanium nitride film does not react with TiCl4 and is not etched.

[0041] Furthermore, according to an embodiment of the present invention, when the reactivity of the fluorine-containing gas can be controlled, by creating an atmosphere with a relatively insufficient amount of fluorine, even if the fluorine-containing gas reacts with the titanium nitride film, a relatively large amount of TiF2 and / or TiF3 can be generated instead of TiF4. However, the boiling points of TiF2 and TiF3 are 2152° C. and 1400° C., respectively, and are hardly volatile at the ALE process temperature (e.g., 400° C. or lower). As a result, by applying the reaction products between the fluorine-containing gas and the titanium nitride film, namely TiF2 and Ti F3, as a passivation layer, it is possible to block additional reactions of the titanium nitride film with the fluorine-containing gas in subsequent cycles. Therefore, according to an embodiment of the present invention, the metal oxide layer can be etched with high selectivity relative to the titanium nitride film.

[0042] Figure 4 The flowchart of the atomic layer etching method of the metal oxide film according to one embodiment of the present invention is shown in FIG. FIG. 5A to FIG. 5C To schematically illustrate the Figure 4 The cross-sectional views of the states during each process of the atomic layer etching method are shown.

[0043] Reference Figure 4 and Figure 5A In step S1, a body to be processed 1 is prepared, which is formed with a metal oxide film 30, and the metal oxide film 30 is formed on a predetermined material film (lower film 20) on a substrate 10. For example, this step may be a process of loading the body to be processed 1 onto a support inside a process chamber for performing an ALE process. Alternatively, in an apparatus for performing an atomic layer deposition (ALD) process and an ALE process in situ, this step may correspond to a process of preparing to start an ALE process after completing a process of depositing a metal oxide film 30 on a lower film 20 on a substrate 10 using an ALD process in a process chamber. The body to be processed 1 schematically simulates a structure in the manufacture of a semiconductor device (e.g., DRAM), and the upper surface of the metal oxide film 30 becomes a surface to be processed, and the surface to be processed is etched and removed in atomic layer units by a subsequent ALE process.

[0044] Here, the substrate 10 may be a semiconductor wafer, such as a silicon wafer, but is not limited thereto. Furthermore, the lower film 20 does not necessarily need to be formed directly on the substrate 10, and one or more material films may be inserted therein. The inserted material film may be an insulating film and / or a conductive film, and there is no particular limitation on its type or the number of films. For example, the lower film 20 is a part of a capacitor device constituting a DRAM, and may be a titanium nitride film formed on the upper side of a conductive film used as a lower electrode.

[0045] According to the present embodiment, the metal oxide film 30 may be selected from the group consisting of, for example, HfO2, ZrO2, HfZrO2, Al2O3, Y2O3, La2O3, Ta2O5, and a combination thereof. Preferably, the metal oxide film 30 may also be selected from the group consisting of HfO2, ZrO2, HfZrO2, and a combination thereof. Preferably, the metal oxide film 30 is a crystallization-stable film so as to be able to exhibit at least high dielectric properties, and in particular, even if a certain portion of the metal oxide film 30 is etched and removed by the ALE process described later, the crystallinity of the film is preferably maintained.

[0046] According to the present embodiment, there is no particular limitation on the method of forming the metal oxide film 30. For example, the metal oxide film 30 may be a film formed by a known ALD process, or may be a film formed using other deposition processes (e.g., Plasma Enhanced Chemical Vapor Deposition (PECVD)) instead of the ALD process. Also, there is no particular limitation on the thickness of the metal oxide film 30, but it must be greater than the thickness of the film ultimately left by the ALE process (e.g., less than 5 nm in the case of a high dielectric oxide film for a capacitor during DRAM). For example, the thickness of the metal oxide film 30 may be greater than 5 nm and 30 nm or less.

[0047] Reference Figure 4 and Figure 5B In step S2, a process gas including a fluorine-containing gas is supplied into the process chamber to perform a fluorination process on the metal oxide film 30. The fluorine-containing gas may be HF gas, NF3 gas, F3NO gas, FNO gas or a combination thereof. In this step, the surface of the metal oxide film 30 is fluorinated by the supplied fluorine-containing gas to form a fluorinated surface layer 31. For example, a zirconium oxide film (ZrO2) may be fluorinated to form a fluorinated surface layer 31 of ZrF4, a hafnium oxide film (HfO2) may be fluorinated to form a fluorinated surface layer 31 of HfF4, and a hafnium zirconium composite oxide film (HfZrO2) may be fluorinated to form a fluorinated surface layer 31 of HfZrF4.

[0048] In contrast, in step S2, the fluorine-containing gas does not react with the lower film 20 or at least suppresses its reactivity. This is because, as described above, when a gas whose molecular size is relatively large, for example, HF gas, NF3 gas, F3NO gas, or FNO gas is used as the fluorine-containing gas, its diffusion to the titanium nitride film of the lower film 20 as the metal oxide film 30 can be blocked or suppressed.

[0049] According to the present embodiment, preferably, the fluorine-containing gas is supplied in a gaseous state rather than a non-plasma state. As described above, this is because the fluorine-containing gas in a plasma state is highly reactive and easily reacts with the lower film 20 of the metal oxide film 30. In this case, the surface of the lower film 20 can be completely fluorinated (for example, in the case of a titanium nitride film, it is fluorinated to TiF4) and removed by the chemical etching gas supplied in the subsequent process (step S3). The gasified fluorine-containing gas can be supplied alone, or can be supplied together with a carrier gas such as argon or nitrogen.

[0050] When the fluorine-containing gas is supplied, the interior of the process chamber may be set to a temperature of 200° C. to 500° C. to induce a reaction with the metal oxide film 30 or to increase the reaction rate. For example, by heating the object to be processed including the substrate 10 via the substrate support and / or using a carrier gas having a desired temperature, the internal temperature of the process chamber may be brought to a desired temperature range. Preferably, the internal temperature of the process chamber is 300° C. to 400° C. If the process temperature is lower than 300° C., the process may take a long time due to low reactivity, whereas, when the process temperature is higher than 400° C., the possibility that the fluorine-containing gas significantly reacts with the lower film to generate a fluoride (e.g., TiF4) having a relatively high volatility increases.

[0051] According to one aspect of this embodiment, among the fluorine-containing gases, preferably, HF gas is gasified from anhydrous fluoric acid.

[0052] According to one aspect of the present embodiment, when the reactivity of the fluorine-containing gas is controlled by a low temperature process (e.g., 400° C. or lower), even if the fluorine-containing gas reacts with the lower film 20 (e.g., titanium nitride film), the fluoride formed as a result of the reaction is a compound such as TiF2 or TiF3, which is a compound having a higher boiling point than TiF4. This is because, in step S2, when the reactivity of the fluorine-containing gas is suppressed, a sufficient amount of the fluorine-containing gas is not supplied in the reaction with the titanium nitride film. Therefore, in step S2, when the fluorine-containing gas reacts with the lower film 20 (e.g., titanium nitride film), a non-volatile passivation layer is formed by TiF2 and / or TiF3 having a relatively high boiling point. And, since the generated non-volatile passivation layer is attached to the exposed surface of the titanium nitride film, it is possible to block the HF gas from contacting and reacting with the titanium nitride film in a subsequent process.

[0053] Furthermore, although not shown in the figure, after the fluorine-containing gas is supplied to the process chamber, a purge process is additionally performed in which a purge gas for discharging unreacted excess fluorine-containing gas, reaction byproducts, and carrier gas is supplied to the process chamber. As the purge gas, an inert gas such as nitrogen or argon can be used. If the carrier gas in step S2 and the purge gas in the purge step are the same inert gas, the purge process can be performed by only stopping the supply of the silicon precursor while the carrier gas is supplied to the vacuum chamber, without adding a means of supplying only the purge gas.

[0054] Reference Figure 4 and Figure 5C In step S3, chemical etching gas is supplied to the process chamber to replace the fluorine in the fluorinated surface layer 31 with other elements (e.g., chlorine) to remove. At this time, the compound of the fluorinated surface layer 31, such as ZrF4, Hf F4 and / or HfZrF4, etc., can be replaced by a ligand to become ZrCl4, HfCl4 and / or HfZrCl4, etc. The reaction product in such step S3, i.e., ZrCl4, HfCl4 and / or HfZrCl4, etc., has a lower boiling point than the reactant, i.e., ZrF4, HfF4 and / or HfZrF4, etc., and therefore has a higher volatility. Therefore, the fluorinated surface layer 31 replaced by chlorine can be removed by etching.

[0055] According to one aspect of the present embodiment, there is no particular limitation on the type of chemical etching gas. For example, the chemical etching gas may be DMAC, TiCl4, etc. Because these chemical etching gases generate byproducts having sufficient vapor pressure compared to other gases, the generated byproducts remaining in the fluorinated surface layer 31 can be reduced, thereby preventing the fluorinated surface layer 31 from being etched by the byproducts. Preferably, the chemical etching gas is TiCl4.

[0056] Subsequently, although not shown in the figure, the remaining chemical etching gas, reaction byproducts, carrier gas, etc. are exhausted to the outside of the process chamber by supplying a purge gas to the inside of the process chamber. Thus, one cycle of the atomic layer etching (ALE) process for etching the metal oxide film 30 is completed, leaving the metal oxide film 32 with a reduced thickness.

[0057] Then, the ALE process including steps S2 and S3 is repeated a predetermined number of times until the metal oxide film 32 is etched to a desired thickness. At this time, as the number of repetitions of the cycle increases, the amount of the metal oxide film 32 etched and removed increases, and finally a metal oxide film with a desired thickness is left.

[0058] Figure 6TEM photograph showing the phenomenon that the titanium nitride film underneath is also etched when the zirconium oxide film is etched using thermal ALE according to an embodiment of the present invention, wherein HF gas is used as the fluorine-containing gas and TiCl4 gas is used as the chemical etching gas. The temperatures of the process chambers are set at 300° C. and 400° C., respectively. Figure 6 , it can be seen that when the cycle of the ALE process of supplying HF gas for 1 second and then supplying TiCl4 gas for 2 seconds is repeated 20 times, the zirconium oxide film is etched, but the titanium nitride film is hardly etched. However, when the temperature of the process chamber is 400°C, the etching rate of the zirconium oxide film is shown to be higher than when the temperature of the process chamber is 300°C.

[0059] As described in detail above, in an embodiment of the present invention, when etching a metal oxide film such as a hafnium oxide film, a zirconium oxide film and / or a hafnium zirconium composite oxide film, a thermal ALE process is applied to control the etching rate of the metal oxide film and prevent the material (e.g., titanium nitride film) below it from being etched. In particular, in the thermal ALE process, the surface is modified by using a fluorine-containing gas, and then the modified surface layer is removed using a chemical etching gas. HF gas, NF3 gas, F3NO gas and FNO gas are used as fluorine-containing gases, and TiCl4 and SiCl4 are used as chemical etching gases. It can be seen from the above test results that the fluorine-containing gas used in the thermal ALE process is different from other materials, and it can not only inhibit its diffusion through the grain boundary of the metal oxide film to the lower film, but also form a passivation film by controlling the reactivity. Therefore, according to an embodiment of the present invention, the metal oxide film can be etched with high selectivity relative to the lower film, so that the lower film can be prevented or inhibited from being etched.

[0060] Although the present invention has been described in detail with reference to the preferred embodiments, the present invention is not limited to the above-described embodiments, and those skilled in the art can make various modifications within the scope of the technical idea of ​​the present invention.

[0061] Industrial Applicability

[0062] The present invention can be used in semiconductor manufacturing processes.

Claims

1. A method for atomic layer etching of a metal oxide film, wherein: The metal oxide film is formed on a predetermined lower film on a substrate, and the method includes: a fluorination step in which a fluorinated surface layer is formed by supplying a fluorine-containing gas to react with the surface of the metal oxide film; and a chemical etching step, wherein the fluorinated surface layer is removed by supplying a chemical etching gas to the substrate, wherein a portion of the metal oxide film is removed by repeating a cycle including the fluorination step and the chemical etching step a predetermined number of times, and The fluorine-containing gas reacts with the underlying film to form a non-volatile passivation film.

2. The method according to claim 1, wherein: The fluorine-containing gas is in a non-plasma state, and the process temperature of the fluorination step is 200° C. to 500° C.

3. The method according to claim 2, wherein: The process temperature of the fluorination step is 300°C to 400°C.

4. The method according to claim 1, wherein: The fluorine-containing gas includes one or more gases selected from the group consisting of HF gas, NF3 gas, F3NO gas and FNO gas, and The lower film is a titanium nitride film.

5. The method according to claim 4, wherein: The HF gas is anhydrous HF gas.

6. The method according to claim 4, wherein: The non-volatile passivation film includes one or more of titanium difluoride (TiF2) and titanium trifluoride (TiF3).

7. The method according to claim 4, wherein: The chemical etching gas includes one or more gases selected from the group consisting of TiCl 4 gas and SiCl 4 gas.

8. The method according to claim 1, wherein: The metal oxide film includes one or more oxide films selected from the group consisting of a hafnium oxide film, a zirconium oxide film, and a hafnium-zirconium composite oxide film.

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