Atomic Layer Etching Method for Metal Oxide Film

Abstract

A method for atomic layer etching of a metal oxide film formed on a predetermined lower film on a substrate is disclosed. The atomic layer etching method according to an embodiment includes a fluorination step of supplying a fluorine-containing gas to react with the surface of the metal oxide film to form a fluorinated surface layer, and a chemical etching step of supplying a chemical etching gas to the substrate to remove the fluorinated surface layer. A cycle including the fluorination step and the chemical etching step is repeated a predetermined number of times to remove a part 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 specifically, to an atomic layer etching (ALE) process of a metal oxide film having a high etching selectivity with respect to a lower film.

Background Art

[0002] As the ultra-high integration and ultra-fine patterning of semiconductor devices continue to progress, not only the thickness of thin films but also the line width (Critical Dimension, CD) of patterns is decreasing. For example, the thickness of the conductive film and dielectric film of the transistor constituting the DRAM device is decreasing, and the line width is also as small as 5 nm or less. In the manufacture of semiconductor devices having such ultra-fine and ultra-thin patterns, it is difficult to control at the atomic level with existing physical / chemical processes and plasma processes, and problems such as surface damage are caused. Therefore, the need for atomic scale processing in both the deposition process and the etching process is increasing more and more.

[0003] As manufacturing processes for semiconductor devices capable of controlling the thickness of thin films in atomic or molecular layer units, an atomic layer deposition (ALD) process and an atomic layer etching process are known. However, when the thickness of the thin film deposited using the ALD process is very thin, there is a problem that it is difficult for the thin film to satisfy the required physical properties. This is because when the thin film is deposited thinly below a certain thickness, the crystallinity of the deposited film is poor, and physical properties such as leakage current characteristics are poor. In order to prevent such deterioration of physical properties, it is necessary for the thickness of the thin film to be above a certain level. However, when the thickness of the thin film increases, it becomes difficult to ensure the required dielectric constant and capacitance.

[0004] Therefore, in order to reduce the thickness of the thin film to a certain level or below while satisfying the required physical properties, it is necessary to form a film with good crystallinity to a thickness of a predetermined value or more using a vapor deposition process, and then remove the vapor-deposited film in atomic layer or molecular layer units using an ALE process to reduce the film thickness. For example, in Korean Patent Publication No. 2019-0136438, "Method for Forming a Thin Film" (Patent Document 1), a method for forming a thin film with excellent crystallinity is disclosed, in which a zirconium oxide film or an aluminum oxide film is formed using an ALD process and then etched using an ALE process.

[0005] However, when etching a thin film using the ALE process described above, problems may occur in that another thin film that should not be etched during the etching of the film to be etched may be etched together or damaged. If unintended etching or surface damage of another thin film occurs during the etching process, it may cause defects in the semiconductor device. In particular, when the process gas is made into plasma to ensure reactivity, the possibility of such problems occurring is even higher.

[0006] For example, in the manufacture of a specific semiconductor device, such as a capacitor of a DRAM device, a process has been proposed in which a vapor deposition process (e.g., an ALD process) and an ALE process are sequentially applied to form a high-k metal oxide film having excellent crystallinity and a thin thickness at the same time. At this time, in a vapor deposition process such as ALD, the metal oxide film is vapor-deposited on a predetermined lower film, for example, a titanium nitride film (TiN). Then, an ALE process is applied to thin the vapor-deposited metal oxide film.

[0007] In such a process sequence, during the progress of the ALE process, damage may be induced on the surface of the metal oxide film and / or a phenomenon may occur in which the underlying film is etched together. In particular, in Korean Patent Publication No. 2019-0142407, "In-situ Selective Deposition and Etching for Advanced Pattening Application" (Patent Document 2), in the ALE process using the same etching gas, in addition to metal oxide films such as zirconium oxide film and hafnium oxide film, titanium nitride film is also disclosed as one of the etching targets. According to this, in the case of the ALE process using the etching gas, while the metal oxide film is being etched, the underlying titanium nitride film is also likely to be etched and removed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The problem to be solved by the present invention is to provide an ALE process that does not induce etching on the underlying film and does not cause surface damage to the metal oxide film, which is the etching target film, when etching a single or composite metal oxide film such as zirconium oxide film, hafnium oxide film, and hafnium zirconium oxide film by the ALE process.

Means for Solving the Problems

[0010] One embodiment of the present invention for solving the above problems is a method for atomic layer etching of a metal oxide film formed on a predetermined lower film on a substrate, including a fluorination step of supplying a fluorine-containing gas to react with the surface of the metal oxide film to form a fluorinated surface layer, and a chemical etching step of supplying a chemical etching gas to the substrate to remove the fluorinated surface layer. A cycle including the fluorination step and the chemical etching step is repeated a predetermined number of times to remove a part of the metal oxide film, and the fluorine-containing gas reacts with the lower film to form a non-volatile passivation film.

[0011] According to one aspect of the above embodiment, the fluorine-containing gas is 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.

[0012] According to another aspect of the above embodiment, 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 may be a titanium nitride film. At this time, the HF gas may be anhydrous HF gas. And the non-volatile passivation film may include one or more of titanium difluoride (TiF2) and titanium trifluoride (TiF3). Further, the chemical etching gas may include one or more gases selected from the group consisting of TiCl4 gas and SiCl4 gas.

[0013] According to another aspect of the above embodiment, the metal oxide film may include one or more oxide films selected from the group consisting of hafnium oxide film, zirconium oxide film, and hafnium zirconium composite oxide film.

Advantages of the Invention

[0014] According to the embodiments of the present invention, in the etching process of the metal oxide film using the ALE process, a gas that reacts with the underlying film of the metal oxide film to form a non-volatile passivation layer is used as the fluorine-containing gas, and / or a gas with a relatively large molecular size is used. Therefore, the reactivity can be controlled, and the diffusion of the gas leading to the grain boundaries of the metal oxide film can be suppressed, making it possible to etch the metal oxide film with a high selectivity with respect to the underlying film.

Brief Description of the Drawings

[0015]

Fig. 1a

Fig. 1b

Fig. 1c

Fig. 1d

Fig. 1e

Fig. 2

Fig. 3

Fig. 4

Fig. 5a

Fig. 5b

Fig. 5c

Fig. 6

Embodiments for Carrying Out the Invention

[0016] 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 terms selected in consideration of the functions in the embodiments, and the meanings of those terms may vary depending on the intention of the invention or conventions, etc. Therefore, the terms used in the embodiments described below should be construed as having the meaning generally recognized by those skilled in the art when there is no specific definition in this specification, and should be construed according to the definition when specifically defined in this specification.

[0017] Atomic layer etching (ALE) is a film etching technique that utilizes sequential self-limiting reactions. Since it reacts only on the surface of the film to be etched, etching control can be achieved in atomic layer units. When etching high-k metal oxide films such as hafnium oxide films, zirconium oxide films, and hafnium zirconium composite oxide films used as high-k films of semiconductor devices, such as DRAM, not only the self-limiting characteristics for atomic layer etching are required, but also it is necessary not to cause surface damage to the metal oxide film and / or not to etch the underlying film. That is, the reactivity of the ALE process with respect to the metal oxide film (etching in atomic layer units) must be controllable, and it is necessary to have a high etching selectivity with respect to the underlying film.

[0018] In the etching process of metal oxide films using the ALE process, at least two reaction mechanisms are known. The first reaction mechanism is a direct chlorination reaction in which the metal oxide film is directly reacted with a chlorine-containing gas to remove the metal oxide film. In this case, the chlorine-containing gas can be supplied in a non-plasma state or in a plasma state. In the former case, even if the process temperature is increased to 500 °C, the reactivity is low and the metal oxide film is difficult to etch. On the other hand, in the latter case, the reactivity increases in proportion to the process temperature, and the metal oxide film is easily etched. However, the chlorine-containing gas in the plasma state is overly reactive, making it difficult to control the etching at the atomic layer unit.

[0019] The second reaction mechanism is to react the metal oxide film with a fluorine-containing gas to modify the surface, that is, to fluorinate it, and then convert it into a substance that can evaporate even at a relatively low temperature by ligand exchange using a chemical etching gas and remove it. Also in this case, the fluorine-containing gas can be supplied in a non-plasma state (hereinafter referred to as "thermal ALE") or in a plasma state (hereinafter referred to as "plasma ALE"). However, as will be described later, in the case of plasma ALE, there are drawbacks that the reactivity of the plasmaized gas is relatively higher than when supplied in a non-plasma state, causing surface damage to the metal oxide film and / or making it difficult to control the etching at the atomic layer unit.

[0020] However, in the case of the second reaction mechanism, as disclosed in Korean Patent Publication No. 2019-0142407 (Patent Document 1), there may be a problem that the underlying film is also etched together with the metal oxide film depending on the type of the fluorine-containing gas and / or the chemical etching gas used. This will be described in more detail based on the experimental results below.

[0021] Figures 1a and 1b are transmission electron microscopy (TEM) photographs showing the phenomenon that when etching a zirconium oxide film using a plasma ALE process, the underlying titanium nitride film is also etched. Here, Figure 1a shows the case where plasma NF3 gas is used as the fluorine-containing gas and TiCl4 gas is used as the chemical etching gas, and Figure 1b shows the case where plasma CF4 gas is used as the fluorine-containing gas and TiCl4 is similarly used as the chemical etching gas.

[0022] Referring to Figure 1a, when the cycles of the ALE process of supplying plasma NF3 gas for 30 seconds and then supplying TiCl4 gas for 30 seconds are repeated 5 times, 10 times, and 15 times respectively, it can be seen that while the zirconium oxide film with a thickness of about 80 Å is etched to a thickness of about 65 Å, 40 Å, and 20 Å, the underlying titanium oxide film is etched and removed. Referring to Figure 1b, when the cycles of the ALE process of supplying plasma CF4 gas for 30 seconds and then supplying TiCl4 gas for 30 seconds are repeated 5 times, 10 times, and 15 times respectively, it can be seen that while the zirconium oxide film with a thickness of about 80 Å is etched to a thickness of about 80 Å, 75 Å, and 62 Å, the underlying titanium oxide film is etched and removed after 10 cycles.

[0023] And Figures 1c and 1d are also transmission electron microscopy (TEM) photographs showing the phenomenon that when etching a zirconium oxide film using plasma ALE, the underlying titanium nitride film is etched, in the case where the process temperature is set to about 300 °C. Figure 1c shows 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 shows the case where plasma CF4 gas is used as the fluorine-containing gas and DMAC gas is used as the chemical etching gas.

[0024] Referring to FIG. 1c, when the cycle of the ALE process of supplying plasma NF3 gas for 30 seconds and then supplying DMAC gas for 30 seconds is repeated 5 times, it can be seen that while the zirconium oxide film with a thickness of about 80 Å is etched to a thickness of about 59 Å, the titanium oxide film below it is etched and removed. Then, referring to FIG. 1d, when the cycles of the ALE process of supplying plasma CF4 gas for 30 seconds and then supplying the DMAC gas to be tested for 30 seconds are repeated 5 times, 10 times, and 15 times respectively, while the zirconium oxide film with a thickness of about 80 Å is etched to thicknesses of about 76 Å, 45 Å, and 19 Å respectively, it can be seen that after 10 cycles, the titanium oxide film below it is etched and removed.

[0025] And FIG. 1e is a transmission electron microscope (TEM) photograph showing the phenomenon that the titanium nitride film below is etched when etching the zirconium oxide film using thermal ALE. As the fluorine-containing gas, ClF3 gas is used, and as the chemical etching gas, TiCl4 gas is used. Referring to FIG. 1e, when the cycles of the ALE process of supplying ClF3 gas for 10 seconds and then supplying TiCl4 gas for 10 seconds are repeated 5 times, 10 times, and 15 times respectively, it can be seen that the titanium oxide film begins to be etched after about 10 cycles and is almost completely removed after 15 cycles. However, in the experimental example of FIG. 1e, even when the ALE cycle is repeated up to 15 times, the zirconium oxide film with a thickness of about 80 Å is hardly etched. This is presumably because the ligand exchange reaction of ZrF4 generated in the low-temperature process at 300 °C does not occur smoothly.

[0026] FIG. 2 schematically shows that when etching a metal oxide film (e.g., zirconium oxide film) using a conventional ALE process as in the experimental results of FIGS. 1a to 1e, the lower films are both etched. In FIG. 2, A, B, C, and D all represent reaction by-products generated in the reaction. Referring to FIG. 2, when using plasma NF3 gas, plasma CF4 gas, or ClF3 gas as the fluorine-containing gas, it reacts with the zirconium oxide film to form TiF4 (boiling point: about 400 °C or higher). Then, when supplying TiCl4 gas or DMAC gas as the chemical etching gas, it can be seen that TiF4 is ligand-substituted with TiCl4 (boiling point: about 136 °C or higher) that evaporates at a relatively low temperature, and the titanium nitride film is also etched together with the zirconium oxide film. Thus, the etching of the titanium nitride film, which is the lower film of the zirconium oxide film, is because the zirconium oxide film reacts with the fluorine-containing gas to form TiF4, and thus it cannot function as a passivation film.

[0027] Based on the above experimental results, it is predicted that a material (fluorine-containing gas and / or chemical etching gas) that reacts with the metal oxide film but blocks and / or suppresses the reaction with the underlying film, such as a titanium nitride film, can increase the etching selectivity. More specifically, if the diffusion of the gas through the grain boundary of the metal oxide film is suppressed or minimized, the fluorine-containing gas can be blocked or suppressed from contacting the underlying titanium nitride film. And by controlling the reactivity of the fluorine-containing gas to form a passivation film even when it reacts with the underlying film, the etching of the titanium nitride film by the chemical etching gas can be prevented or suppressed. As will be described later, according to the present invention, when a gas with a relatively large particle size, such as HF gas, NF3 gas, F3NO gas, FNO gas, etc., is used as the fluorine-containing gas, the diffusion of the gas through the grain boundary of the metal oxide film can be blocked or suppressed, and a passivation film can be formed by reactivity control, preventing or minimizing the etching of the film located below, such as the titanium nitride film. And as the chemical etching gas, by using a material that generates a by-product having a sufficient vapor pressure after the reaction, such as TiCl4 gas, SiCl4 gas, it is possible to prevent the etching rate of the metal oxide film from decreasing or the etching from stopping due to the reaction by-products remaining in the process chamber.

[0028] FIG. 3 is a diagram schematically showing that when etching a metal oxide film (for example, a zirconium oxide film) using a thermal ALE process in which HF gas is used as a fluorine-containing gas, the underlying titanium nitride film does not react with the fluorine-containing gas and is not etched. In FIG. 3, A, B, C, and D all represent reaction by-products. Referring to FIG. 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 or is suppressed from reacting with the underlying titanium nitride film. Therefore, when TiCl4 gas is subsequently supplied as a chemical etching gas, it can be seen that ZrF4 is removed by ligand substitution with highly volatile ZrCl4, while the titanium nitride film does not react with TiCl4 and is not etched.

[0029] According to an embodiment of the present invention, when the reactivity of the fluorine-containing gas can be controlled, by creating an atmosphere in which fluorine is relatively insufficient, even if the fluorine-containing gas reacts with the titanium nitride film, relatively more TiF2 and / or TiF3 rather than TiF4 can be generated. The boiling points of TiF2 and TIF3 are 2152°C and 1400°C, respectively, and they hardly volatilize at the ALE process temperature (for example, 400°C or lower). Therefore, TiF2 and TIF3, which are reaction products of the fluorine-containing gas and the titanium nitride film, act as a passivation layer and can block further reaction between the titanium nitride film and the fluorine-containing gas in subsequent cycles. Therefore, according to an embodiment of the present invention, a metal oxide can be etched with a high selectivity ratio with respect to the titanium nitride film.

[0030] FIG. 4 is a flowchart showing an atomic layer etching method of a metal oxide film according to an embodiment of the present invention, and FIGS. 5a to 5c are cross-sectional views schematically showing the states when each step of the atomic layer etching method shown in FIG. 4 is performed.

[0031] Referring to FIGS. 4 and 5a, a workpiece 1 is prepared in which a metal oxide film 30 is formed on a predetermined material film (lower film) 20 on a substrate 10 (step S1). For example, this step may be a step of loading the workpiece 1 onto a support table inside a process chamber for performing an ALE process. Alternatively, in an apparatus where an ALD process and an ALE process are performed in-situ, this step may correspond to a step of preparing to start the ALE process after completing the step of depositing the metal oxide film 30 on the lower film 20 on the substrate 10 using the ALD process in one process chamber. Such a workpiece 1 schematically represents a structure during the manufacture of a semiconductor element, for example, a DRAM. The upper surface of the metal oxide film 30 becomes the surface to be processed, and the surface to be processed is etched and removed in atomic layer units by a subsequent ALE process.

[0032] Here, the substrate 10 is a semiconductor wafer, which may be, for example, a silicon wafer, but is not limited thereto. And the lower film 20 does not necessarily have to be formed directly on the substrate 10, and one or more material films may be interposed therebetween. The interposed material film may be an insulating film and / or a conductive film, and there are no particular restrictions on its type or the number of film layers. As an example, the lower film 20 may be a titanium nitride film formed on the upper side of a conductive film used as a lower electrode as a part of constituting a capacitor element of a DRAM.

[0033] According to the present embodiment, the metal oxide film 30 can be selected from the group consisting of, for example, HfO2, ZrO2, HfZrO2, Al2O3, Y2O3, La2O3, Ta2O5, and combinations thereof. Preferably, the metal oxide film 30 may be selected from the group consisting of HfO2, ZrO2, HfZrO2, and combinations thereof. The metal oxide film 30 is preferably a film that is crystallographically stabilized so as to have at least high dielectric properties. In particular, it is preferable that the crystallinity of the film is maintained even if a certain portion of the metal oxide film 30 is etched and removed by an ALE process described later.

[0034] According to this embodiment, there is no particular limitation on the method for 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 by another deposition process that is not an ALD process, such as a plasma enhanced chemical vapor deposition (PECVD). The thickness of the metal oxide film 30 is not particularly limited, but it must be greater than the thickness of the film that is finally desired to remain by the ALE process (for example, less than 5 nm in the case of a high dielectric constant oxide film for a capacitor of a DRAM element). For example, the thickness of the metal oxide film 30 may be 5 nm to 30 nm.

[0035] Referring to FIGS. 4 and 5b, a process gas containing a fluorine-containing gas is supplied into the process chamber, and a fluorination process is performed on the metal oxide film 30 (S2). The fluorine-containing gas may be HF gas, NF3 gas, F3NO gas, FNO gas, or a combination thereof. In this process, the surface of the metal oxide film 30a is fluorinated by the supplied fluorine-containing gas to form a fluorinated surface layer 31. For example, a zirconium oxide film (ZrO2) can be fluorinated to form ZrF4, a hafnium oxide film (HfO2) can form a fluorinated surface layer 31 of HfF4, and a hafnium zirconium composite oxide film (HfZrO2) can form a fluorinated surface layer 31 of HfZrF4.

[0036] On the other hand, in step S2, the fluorine-containing gas does not react with the lower film 20 or at least the reactivity is suppressed. This is because, as described above, when a gas having a relatively large molecular size such as HF gas, NF3 gas, F3NO gas or FNO gas is used as the fluorine-containing gas, the diffusion to the titanium nitride film 20 which is the lower film of the metal oxide film 30a is blocked or suppressed.

[0037] According to this embodiment, it is preferable that the fluorine-containing gas is supplied in a vaporized gas state rather than in a plasma state. As described above, the fluorine-containing gas in a plasma state has high reactivity and easily reacts with the lower film 20 of the metal oxide film 30a. In this case, the surface of the lower film 20 is completely fluorinated (for example, in the case of a titanium nitride film, it is fluorinated to TiF4) and is removed by the chemical etching gas supplied in the subsequent step (step S3). The vaporized fluorine-containing gas may be supplied as it is, or may be supplied together with a carrier gas such as argon or nitrogen gas.

[0038] When the fluorine-containing gas is supplied, in order to induce the reaction with the metal oxide film 30 or increase the reaction rate, the inside of the process chamber can be set to a temperature of 200°C to 500°C. For example, by heating the object to be processed including the substrate 10 through the substrate support and / or using a carrier gas at a desired temperature, the temperature inside the process chamber can be made to be within the desired temperature range. Preferably, the temperature inside the process chamber is preferably 300°C to 400°C. However, if the process temperature is lower than 300°C, the reactivity is low and the process time is long, while if the process temperature is higher than 400°C, there is a high possibility that the fluorine-containing gas will surely react with the lower film to generate a fluoride with relatively high volatility (for example, TiF4).

[0039] According to one aspect of this example, among the fluorine-containing gases, the HF gas is preferably vaporized from anhydrous hydrofluoric acid.

[0040] According to one aspect of the present embodiment, when controlling the reactivity of the fluorine-containing gas by a low-temperature process (for example, 400 ° C or lower), even if the fluorine-containing gas reacts with the lower film 20, for example, a titanium nitride film, the fluoride formed as a result of the reaction is a compound such as TiF2 or TiF3, which is a compound with a higher boiling point than TiF4. This is because when the reactivity of the fluorine-containing gas is suppressed in step S2, a sufficient amount of the fluorine-containing gas is not supplied to the reaction with the titanium nitride film. Therefore, in step S2, when the fluorine-containing gas reacts with the lower film 20, for example, a titanium nitride film, a non-volatile passivation layer is formed by relatively high-boiling TiF2 and / or TiF3. And since the produced non-volatile passivation layer adheres to the exposed surface of the titanium nitride film, it is possible to block the subsequent step of HF gas from coming into contact with and reacting with the titanium nitride film.

[0041] Also, although not shown, after supplying the fluorine-containing gas to the process chamber, a purge process of supplying a purge gas for discharging the unreacted excess fluorine-containing gas, reaction by-products, and carrier gas to the process chamber may be further performed. As the purge gas, an inert gas such as nitrogen gas or argon gas can be used. If the carrier gas in step S2 and the purge gas in the purge process are the same inert gas, there is no need to add means for supplying only the purge gas, and the purge process can be performed simply by interrupting the supply of the silicon precursor while supplying the carrier gas to the vacuum chamber.

[0042] Referring to FIGS. 4 and 5c, a chemical etching gas is supplied to the process chamber to replace and remove the fluorine in the fluorinated surface layer 31 with other elements, such as chlorine (S3). At this time, the compounds in the fluorinated surface layer 31, such as compounds like ZrF4, HfF4, and / or HfZrF4, etc., can have their ligands substituted and become ZrCl4, HfCl4, and / or HfZrCl4, etc. The reaction products such as ZrCl4, HfCl4, and / or HfZrCl4, etc. in such step S3 have a lower boiling point and relatively higher volatility than the reactants such as ZrF4, HfF4, and / or HfZrF4, etc. Thereby, the fluorinated surface layer 31 substituted with chlorine can be etched and removed.

[0043] According to one aspect of this embodiment, there is no particular limitation on the type of the chemical etching gas. For example, the chemical etching gas may include DMAC, TiCl4, etc. These chemical etching gases generate by-products having a sufficient vapor pressure compared to other gases, so that the generation of by-products remaining in the fluorinated surface layer 31 is minimized, and it can be prevented that the fluorinated surface layer 31 is etched by the by-products. Preferably, the chemical etching gas is preferably TiCl4.

[0044] Subsequently, although not shown, a purge gas is supplied into the process chamber to exhaust the remaining chemical etching gas, reaction by-products, carrier gas, etc. to the outside of the process chamber. Thereby, one cycle of the atomic layer etching (ALE) process for etching the metal oxide film 30 is completed, and a metal oxide film 32 with a reduced thickness remains.

[0045] Subsequently, until the metal oxide film 32 is etched to a desired thickness, the ALE process cycle including the above-described steps S2 and S3 is repeated a predetermined number of times. 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 remains.

[0046] FIG. 6 is a transmission electron microscope (TEM) photograph showing a phenomenon in which a titanium nitride film at the lower part thereof is etched when etching a zirconium oxide film using a thermal ALE process according to an embodiment of the present invention. In this case, HF gas is used as the fluorine-containing gas, and TiCl4 gas is used as the chemical etching gas. The temperatures of the process chamber are set to 300° C. and 400° C., respectively. Referring to FIG. 6, 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, it can be seen that the zirconium oxide film is etched, but the titanium nitride film is hardly etched. However, the etching rate of the zirconium oxide film is even higher when the temperature of the process chamber is 400° C. than when it is 300° C.

[0047] As described in detail above, in the embodiments 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 in order to control the etching rate of the metal oxide film and prevent etching of a material film below it, for example, a titanium nitride film. In particular, in the thermal ALE process, after the surface is modified using a fluorine-containing gas, the modified surface layer is removed using a chemical etching gas. As the fluorine-containing gas, HF gas, NF3 gas, F3NO gas, and FNO gas are used, and as the chemical etching gas, TiCl4 and SiCl4 are used. As can be seen from the above experimental results, the fluorine-containing gas used in the thermal ALE process, unlike other materials, not only suppresses diffusion to the lower film leading to the grain boundaries of the metal oxide film, but also can form a passivation film by controlling the reactivity. Therefore, according to such an embodiment of the present invention, the metal oxide film can be etched with a high selectivity with respect to the lower film, and it is possible to prevent or suppress the etching of the lower film.

[0048] As described above, the present invention has been described in detail with reference to preferred embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made by those having ordinary knowledge in the art within the scope of the technical idea of the present invention.

Industrial Applicability

[0049] The present invention can be utilized in the manufacturing process of semiconductors.

Claims

1. In a method for atomic layer etching of a metal oxide film formed on a predetermined lower film on a substrate, a fluorination step of supplying a fluorine-containing gas to react with the surface of the metal oxide film to form a fluorinated surface layer, and a chemical etching step of supplying a chemical etching gas to the substrate to remove the fluorinated surface layer, wherein a cycle including the fluorination step and the chemical etching step is repeated a predetermined number of times to remove a part of the metal oxide film, the fluorine-containing gas reacts with the lower film to form a non-volatile passivation film, and the method for atomic layer etching of a metal oxide film is characterized in that.

2. The method for atomic layer etching of a metal oxide film 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 for atomic layer etching of a metal oxide film according to claim 2, wherein the process temperature of the fluorination step is 300°C to 400°C.

4. The fluorine-containing gas contains one or more gases selected from the group consisting of HF gas, NF ３ gas, F ３ NO gas, and FNO gas. The method for atomic layer etching of a metal oxide film according to claim 1, wherein the lower film is a titanium nitride film.

5. The method for atomic layer etching of a metal oxide film according to claim 4, wherein the HF gas is anhydrous HF gas.

6. The non-volatile passivation film contains at least one of titanium difluoride (TiF ２ ), and titanium trifluoride (TiF ３ ). The method for atomic layer etching of a metal oxide film according to claim 4, characterized in that it is as described above.

7. The chemical etching gas is TiCl ４ gas and SiCl ４ The method for atomic layer etching of a metal oxide film according to claim 4, characterized by comprising one or more gases selected from the group consisting of gas.

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

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