Etching method

Abstract

The etching method is a method of etching a metal oxide film in a laminate including a base and the metal oxide film formed on a surface thereof by atomic layer etching, and includes a first step of introducing an oxidizable compound selected from at least one of an alcohol compound, an aldehyde compound, and an ester compound in a processing atmosphere in which the laminate is housed, and a second step of introducing an oxidizing gas in the processing atmosphere after the first step.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for etching a metal oxide film by an atomic layer etching method. BACKGROUND

[0002] In manufacturing devices such as semiconductor devices, it is necessary to form a fine pattern. In order to obtain a fine pattern, it is first necessary to form a high-quality thin film, for example, using an atomic layer deposition method (sometimes referred to as an ALD (Atomic Layer Deposition) method) as a manufacturing process. In order to make the high-quality thin film formed by the ALD method thinner, it is necessary to etch it, but in this case, it is required to control the etching amount at several nanometers.

[0003] As a technique for achieving such etching, an atomic layer etching method (sometimes referred to as an ALE (Atomic Layer Etching) method) has been attracting attention. The ALE method is a technique for etching a film containing metal atoms formed on a substrate at the atomic layer level by an etching gas. Such a technique based on the ALE method is described, for example, in Patent Documents 1 to 3.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: U.S. Patent Application Publication No. 2012 / 0048831

[0007] Patent Document 2: U.S. Patent Application Publication No. 2018 / 0047577

[0008] Patent Document 3: Japanese Patent Application Publication No. 2018-186269 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] In Patent Document 1, an ALE method using chlorine gas as an etching gas is disclosed. In Patent Document 2, an ALE method using hydrogen fluoride gas and a boron-containing gas as etching gases is disclosed. However, these etching gases not only damage the film containing metal atoms formed on the substrate, but also damage the substrate, surrounding members. In addition, stainless steel materials are used in large quantities in semiconductor manufacturing devices, and there is a problem that the etching gas corrodes such stainless steel materials.

[0011] In Patent Document 3, an ALE method using formic acid vapor as an etching gas is disclosed. However, formic acid vapor is also highly corrosive to metals, and sometimes damages the substrate, stainless steel materials, and the like of semiconductor manufacturing devices.

[0012] Therefore, an object of the present application is to provide a method for etching a metal oxide film by an ALE method without damaging a substrate, a stainless steel material of a semiconductor manufacturing apparatus, or the like.

[0013] Means for solving the problem

[0014] As a result of intensive studies by the present inventors and others, it has been found that by using an ALE method having a specific procedure, a metal oxide film can be etched without damaging a substrate, a stainless steel material of a semiconductor manufacturing apparatus, or the like.

[0015] That is, the present application is an etching method for etching a metal oxide film in a laminate including a substrate and the metal oxide film formed on a surface thereof by an atomic layer etching method, having: a first step of introducing an oxidizable compound selected from at least one of an alcohol compound, an aldehyde compound, and an ester compound in a processing atmosphere in which the laminate is housed; and a second step of introducing an oxidizing gas in the processing atmosphere after the first step.

[0016] Effects of the invention

[0017] According to the present application, a metal oxide film can be etched at high productivity without damaging a substrate, a stainless steel material of a semiconductor manufacturing apparatus, or the like. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a schematic diagram showing an example of an apparatus used in the etching method of the present application.

[0019] Figure 2 is a schematic diagram of an apparatus used in the etching method of the comparative example. DETAILED DESCRIPTION

[0020] The etching method of the present application has: a process of introducing an oxidizable compound selected from at least one of an alcohol compound, an aldehyde compound, and an ester compound into a processing atmosphere of a chamber or the like in which a laminate including a base and a metal oxide film formed on a surface thereof is housed (oxidizable compound introduction process); and a process of introducing an oxidizing gas into the processing atmosphere after the oxidizable compound introduction process (oxidizing gas introduction process). As the etching method of the present application, as needed, there is provided a process of exhausting the gas in the processing atmosphere of the chamber or the like between the oxidizable compound introduction process and the oxidizing gas introduction process and after the oxidizing gas introduction process (exhaust process). The etching method of the present application sequentially performs the oxidizable compound introduction process, the exhaust process, the oxidizing gas introduction process, and the exhaust process as one cycle, and by repeating the cycle, the metal oxide film can be etched to a desired thickness. The etching method of the present application can also be implemented in combination with thin film formation using the ALD method, in which case, the laminate can be implemented without being taken out of the processing atmosphere of the chamber or the like. Further, in the etching method of the present application, since the amount of generation of the etching gas can be controlled by the adsorption amount of the oxidizable compound, the etching method of the present application can be suitably used for an etching process requiring fine processing.

[0021] Next, each process of the etching method of the present application will be described.

[0022] (Oxidizable compound introduction process)

[0023] The oxidizable compound introduction process is a process of introducing an oxidizable compound selected from at least one of an alcohol compound, an aldehyde compound, and an ester compound into a processing atmosphere of a chamber or the like in which a laminate including a base and a metal oxide film formed on a surface thereof is housed.

[0024] The oxidizable compound can be introduced into the processing atmosphere in either a liquid state or a gas state, and after the introduction, the oxidizable compound in the gas state is preferably allowed to act (chemisorption) on the metal oxide film. At this time, the laminate can be heated or the processing atmosphere can be heated. In the case where the oxidizable compound in the gas state is introduced into the processing atmosphere, the oxidizable compound is vaporized by heating and / or depressurization in a container in which the oxidizable compound is stored or a connecting portion connecting the container and the chamber, and is introduced into the processing atmosphere. In the case where the oxidizable compound in the gas state is introduced, as needed, a non-reactive gas such as argon, nitrogen, or helium can be used as a carrier gas. In the case where the oxidizable compound in the liquid state is introduced into the processing atmosphere, the introduced oxidizable compound in the liquid state is vaporized by heating and / or depressurization in the processing atmosphere.

[0025] The pressure in the processing atmosphere during the oxidizing compound introduction step is preferably 1 Pa to 10,000 Pa, more preferably 10 Pa to 1,000 Pa. In addition, from the viewpoint of being able to etch the metal oxide film at high productivity in the subsequent oxidizing gas introduction step, the temperature in the processing atmosphere is preferably 100°C to 500°C, more preferably 150°C to 400°C, and particularly preferably 200°C to 350°C.

[0026] As the alcohol compound, there can be mentioned alkyl alcohols such as methanol, ethanol, propanol, isopropanol, butanol, sec-butanol, isobutanol, t-butanol, pentanol, isopentanol, t-amyl alcohol, and the like; ether alcohols such as 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-methoxy-l-methylethanol, 2-methoxy-l, l-dimethylethanol, 2-ethoxy-l, l-dimethylethanol, 2-isopropoxy-l, l-dimethylethanol, 2-butoxy-l, l-dimethylethanol, 2-(2-methoxyethoxy)-l, l-dimethylethanol, 2-propoxy-l, l-diethylethanol, 2-sec-butoxy-l, l-diethylethanol, 3-methoxy-l, l-dimethylpropanol, and the like; dialkylamino alcohols such as dimethylaminoethanol, ethylmethylaminoethanol, diethylaminoethanol, dimethylamino-2-pentanol, ethylmethylamino-2-pentanol, dimethylamino-2-methyl-2-pentanol, ethylmethylamino-2-methyl-2-pentanol, diethylamino-2-methyl-2-pentanol, and the like.

[0027] As the aldehyde compound, there can be mentioned formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, pentanal, hexanal, heptanal, octanal, nonanal, decanal, benzaldehyde, and the like.

[0028] As the ester compound, there can be mentioned methyl butyrate, methyl salicylate, ethyl formate, ethyl butyrate, ethyl acetate, ethyl hexanoate, pentyl acetate, isoamyl acetate, pentyl valerate, pentyl butyrate, octyl acetate, and the like.

[0029] From the viewpoint of being able to etch the metal oxide film at high productivity in the subsequent oxidizing gas introduction step, as the oxidizing compound, an alcohol compound is preferable, an alcohol compound having a carbon number of 1 to 5 is more preferable, and methanol, ethanol, and t-butanol are particularly preferable. In addition, from the viewpoint of not causing damage to the substrate, stainless steel material of a semiconductor manufacturing apparatus, and the like, the oxidizing compound preferably does not contain a fluorine atom.

[0030] The synthesis method of the above-mentioned alcohol compound, aldehyde compound, and ester compound is not particularly limited, and a general synthesis method of the alcohol compound, aldehyde compound, and ester compound known per se can be used for the synthesis. In addition, a product commercially available as a reagent can also be used.

[0031] In the oxidizable compound used in the present application, it is preferred that impurity metal element components, impurity halogen components such as fluorine, and impurity organic components are not contained as much as possible. In terms of the impurity metal element components, it is preferred that each element is 100 ppb or less, more preferably 10 ppb or less, and the total amount is 1 ppm or less, more preferably 100 ppb or less. In particular, in the case of use as a gate insulating film, a gate film, and a barrier layer of LSI, it is necessary to reduce the contents of alkali metal elements and alkaline earth metal elements which have an influence on the electrical characteristics of the etched metal oxide film. In terms of the impurity halogen components, it is preferred that the content is 100 ppm or less, more preferably 10 ppm or less, and most preferably 1 ppm or less. In terms of the impurity organic components, it is preferred that the total amount is 500 ppm or less, more preferably 50 ppm or less, and most preferably 10 ppm or less.

[0032] In addition, in the oxidizable compound used in the present application, in order to reduce or prevent particle contamination of the etched metal oxide film, it is preferred that particles are not contained as much as possible. Specifically, in particle measurement in a liquid phase using a light scattering type liquid particle detector, the number of particles of 0.3 μm or more is preferably 100 or less in 1 mL of the liquid phase, the number of particles of 0.2 μm or more is more preferably 1000 or less in 1 mL of the liquid phase, and the number of particles of 0.2 μm or more is most preferably 100 or less in 1 mL of the liquid phase.

[0033] The material of the substrate is not particularly limited, and examples thereof include silicon; ceramics such as silicon nitride, titanium nitride, tantalum nitride, titanium oxide, titanium nitride, ruthenium oxide, zirconium oxide, hafnium oxide, and lanthanum oxide; glass; and metal. The shape of the substrate can be plate-like, spherical, fibrous, or scale-like. The surface of the substrate can be planar or three-dimensional such as a groove structure.

[0034] The method of forming the metal oxide film is not particularly limited, and examples thereof include sputtering, ion plating, coating thermal decomposition, MOD method such as sol-gel method, CVD method, and ALD method. From the viewpoint of less impurities in the film and stable etching rate, it is preferred that the metal oxide film is formed by the ALD method. Instead of the metal oxide film, a laminate including a metal film formed on the surface of the substrate by the above-described method can be used. In the case of using the laminate including the metal film, the metal film is oxidized by an oxidizing gas such as oxygen or ozone before the oxidizable compound introduction step. As the oxidizing gas used here, oxygen or ozone is preferred. After the metal film is oxidized, it is preferred that the inside of the processing atmosphere is purged with an inactive gas such as argon or nitrogen to remove the oxidizing gas from the processing atmosphere as much as possible, and then the oxidizable compound introduction step is performed.

[0035] The thickness of the metal oxide film is not particularly limited, and is usually 0.1 nm to 100 nm.

[0036] The kind of metal constituting the metal oxide film is not particularly limited, and examples thereof include titanium, aluminum, zirconium, copper, cobalt, molybdenum, ruthenium, germanium, magnesium, tin, hafnium, scandium, gallium, iron, and zinc. The metal constituting the metal oxide film can be one kind or two or more kinds.

[0037] (exhausting process)

[0038] After the oxidizable compound introduction process, the gaseous oxidizable compound that is not adsorbed on the surface of the metal oxide film is exhausted from the chamber. At this time, it is desirable to completely exhaust the gaseous oxidizable compound from the chamber, but it is not necessarily completely exhausted. As the exhausting method, for example, a method of purging the inside of the chamber with a non-reactive gas such as helium, nitrogen, or argon, a method of exhausting by reducing the pressure in the chamber, a method of combining these, or the like can be given. The degree of pressure reduction at the time of pressure reduction is preferably in the range of 0.01 Pa to 300 Pa, and more preferably in the range of 0.01 Pa to 100 Pa.

[0039] (oxidizing gas introduction process)

[0040] The oxidizing gas introduction process is a process of introducing an oxidizing gas into the processing atmosphere after the above-described exhausting process. The mechanism of etching is not clear, but it is considered that the oxidizing gas reacts with the oxidizable compound chemisorbed on the metal oxide film to generate an etching gas in situ, and the metal oxide film is etched. At this time, the stack can be heated or the processing atmosphere can be heated. At the time of introduction of the oxidizing gas, a non-reactive gas such as argon, nitrogen, or helium can also be used as a carrier gas as necessary.

[0041] The pressure in the processing atmosphere at the time of the oxidizing gas introduction process is preferably in the range of 1 Pa to 10,000 Pa, and more preferably in the range of 10 Pa to 1,000 Pa. In addition, from the viewpoint of being able to etch the metal oxide film at a high productivity, the temperature in the processing atmosphere is preferably in the range of 100°C to 500°C, more preferably in the range of 150°C to 400°C, and particularly preferably in the range of 200°C to 350°C.

[0042] As the oxidizing gas used in the present application, oxygen, ozone, water vapor, hydrogen peroxide, nitric oxide, and nitrous oxide can be given. The oxidizing gas used in the present application can be one kind or two or more kinds. In addition, from the viewpoint of not causing damage to the substrate, stainless steel materials of semiconductor manufacturing apparatuses, and the like, the oxidizing gas preferably does not contain a fluorine atom.

[0043] In the case where the oxidizing gas used in the present application is one kind, from the viewpoint of being able to etch the metal oxide film at a high productivity, oxygen, ozone, or water vapor is preferable, and ozone is more preferable. In the case where the oxidizing gas used in the present application is two or more kinds, from the viewpoint of being able to etch the metal oxide film at a high productivity, it is preferable to contain ozone and another oxidizing gas.

[0044] (Exhaust process)

[0045] After the aforementioned oxidizing gas introduction process, unreacted oxidizing gases and byproduct gases are discharged from the chamber. Ideally, all oxidizing gases and byproduct gases should be completely discharged from the chamber, but complete discharge is not always necessary. The exhaust method and the pressure reduction during depressurization are the same as those used in the exhaust process following the introduction of the oxidized compound.

[0046] Regarding the apparatus for implementing the etching method of the present invention, it is possible to use, such as Figure 1 The apparatus shown includes a chamber capable of introducing oxidizing gas, gaseous oxidized compound, and carrier gas into the system, and capable of purging gas to exhaust the system. Alternatively, the etching method of the present invention can also be performed in the film-forming chamber of a known ALD device. It should be noted that the oxidizing gas and gaseous oxidized compound can be introduced into the film-forming chamber of the ALD device through their respective ports, or through a spray head.

[0047] In conventional etching methods, substrate corrosion can lead to contamination of substrate components and halogen contamination. Furthermore, depending on the type of etchant, the metal oxide film may sometimes be partially reduced. In contrast, the etching method of this invention suppresses these phenomena, resulting in a high-purity, high-quality metal oxide film. Therefore, the metal oxide film of this invention is preferably used in the manufacture of various semiconductor devices requiring high-purity metal oxide films.

[0048] Example

[0049] The present invention will now be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples, etc.

[0050] [Example 1]

[0051] Methanol is used as the oxidized compound, and ozone gas is used as the oxidizing gas. Figure 1 The apparatus shown performs atomic layer etching of a molybdenum oxide film formed on a silicon wafer under the following conditions and procedures. The film thickness change before and after atomic layer etching was confirmed by fluorescence X-ray analysis and scanning electron microscopy. The change in film thickness before and after etching was measured, and the results showed that the molybdenum oxide film thickness decreased by 20.5 nm, and the etchable film thickness per cycle was 0.68 nm. Furthermore, no corrosion of the stainless steel material used in the apparatus was confirmed.

[0052] (condition)

[0053] Laminated composite: A product in which a molybdenum oxide film is formed on a silicon wafer.

[0054] Reaction temperature (silicon wafer temperature): 275℃

[0055] Oxidizable compound: methanol

[0056] Oxidizing gas: ozone

[0057] (Procedure)

[0058] A series of procedures consisting of (1) to (4) below was repeated as one cycle for 30 cycles.

[0059] (1) The oxidizable compound vaporized at 23°C, 100 Pa was introduced into the chamber, and the oxidizable compound was adsorbed on the surface of the molybdenum oxide film for 5 seconds under a system pressure of 100 Pa.

[0060] (2) The unadsorbed oxidizable compound was discharged from the chamber by argon purge for 60 seconds.

[0061] (3) The oxidizing gas was introduced into the chamber, and etching was performed for 20 seconds under a system pressure of 100 Pa.

[0062] (4) The unreacted oxidizing gas and byproduct gas were discharged from the chamber by argon purge for 60 seconds.

[0063] [Example 2]

[0064] Atomic layer etching was performed in the same manner as in Example 1 except that ethanol was used instead of methanol as the oxidizable compound. The change in film thickness before and after atomic layer etching was measured, and as a result, it was found that the film thickness of the molybdenum oxide film was thinned by 17.0 nm, and the film thickness that could be etched per 1 cycle was 0.57 nm. In addition, no corrosion of the stainless steel material used in the apparatus was confirmed at all.

[0065] [Example 3]

[0066] Atomic layer etching was performed in the same manner as in Example 1 except that a product in which a cobalt oxide film was formed on a silicon wafer was used as the laminate, and t-butyl alcohol was used instead of methanol as the oxidizable compound. The change in film thickness before and after atomic layer etching was measured, and as a result, it was found that the film thickness of the cobalt oxide film was thinned by 15.5 nm, and the film thickness that could be etched per 1 cycle was 0.52 nm. In addition, no corrosion of the stainless steel material used in the apparatus was confirmed at all.

[0067] [Example 4]

[0068] Atomic layer etching was performed in the same manner as in Example 1 except that acetaldehyde was used instead of methanol as the oxidizable compound. The change in film thickness before and after atomic layer etching was measured, and as a result, it was found that the film thickness of the molybdenum oxide film was thinned by 14.5 nm, and the film thickness that could be etched per 1 cycle was 0.48 nm. In addition, no corrosion of the stainless steel material used in the apparatus was confirmed at all.

[0069] [Example 5]

[0070] Except for using the product with a titanium oxide film formed on a silicon wafer as the laminate and using ethyl acetate instead of methanol as the oxidizing compound, atomic layer etching was performed in the same manner as in Example 1. The change in film thickness before and after atomic layer etching was measured, and the results showed that the titanium oxide film thickness decreased by 14.0 nm, and the etchable film thickness per cycle was 0.47 nm. Furthermore, no corrosion of the stainless steel material used in the apparatus was confirmed.

[0071] [Example 6]

[0072] Except for using a product with a copper oxide film formed on a silicon wafer as the laminate and using tert-butanol instead of methanol as the oxidizing compound, atomic layer etching was performed in the same manner as in Example 1. The change in film thickness before and after atomic layer etching was measured, and the results showed that the copper oxide film thickness decreased by 15.0 nm, and the etchable film thickness per cycle was 0.50 nm. Furthermore, no corrosion of the stainless steel material used in the apparatus was confirmed.

[0073] [Comparative Example 1]

[0074] Hydrogen fluoride was used as the etching gas. Figure 2 The apparatus shown performs atomic layer etching of a molybdenum oxide film formed on a silicon wafer under the following conditions and procedures. The film thickness change before and after atomic layer etching was confirmed by fluorescence X-ray analysis and scanning electron microscopy. The change in film thickness before and after atomic layer etching showed that the molybdenum oxide film thickness decreased by 8.5 nm, and the etchable thickness per cycle was 0.28 nm. However, corrosion of the stainless steel material used in the apparatus was confirmed.

[0075] (condition)

[0076] Laminated composite: A product in which a molybdenum oxide film is formed on a silicon wafer.

[0077] Reaction temperature (silicon wafer temperature): 275℃

[0078] Etching gas: Hydrogen fluoride

[0079] (Process)

[0080] The series of processes consisting of (1) to (2) below is considered as 1 cycle, and is repeated for 30 cycles.

[0081] (1) Introduce etching gas into the chamber and etch for 20 seconds at a system pressure of 100 Pa.

[0082] (2) Unreacted etching gas and byproduct gas are removed from the chamber by purging with argon gas for 60 seconds.

[0083] [Comparative Example 2]

[0084] Atomic layer etching was performed in the same manner as in Comparative Example 1 except that formic acid vapor was used instead of hydrogen fluoride as the etching gas. The change in film thickness before and after atomic layer etching was measured, and as a result, it was found that the film thickness of the molybdenum oxide film was thinned by 7.5 nm, and the film thickness that could be etched per 1 cycle was 0.25 nm. However, corrosion of the stainless steel material used in the apparatus was confirmed.

[0085] From the above results, according to the present application, damage to the stainless steel material used in a semiconductor manufacturing apparatus or the like does not occur, and the metal oxide film formed on the substrate can be etched at high productivity.

Claims

1. An etching method of etching a metal oxide film in a laminate comprising a substrate and the metal oxide film formed on a surface thereof by an atomic layer etching method, comprising: a first step of introducing an oxidizable compound selected from at least one of an alcohol compound, an aldehyde compound and an ester compound into a processing atmosphere in which the laminate is housed; and a second step of introducing an oxidizing gas into the processing atmosphere after the first step, wherein the oxidizing gas is at least one selected from oxygen, ozone, water vapor, hydrogen peroxide, nitric oxide and nitrous oxide, wherein the oxidizable compound and the oxidizing gas do not contain a fluorine atom, wherein a temperature in the processing atmosphere is 150°C or higher in the first step or the second step, wherein a metal constituting the metal oxide film is at least one metal selected from titanium, aluminum, zirconium, copper, cobalt, molybdenum, ruthenium, germanium, magnesium, tin, hafnium, scandium, gallium, iron and zinc, wherein the oxidizable compound is an alcohol compound having 1 to 5 carbon atoms, and wherein the metal oxide film is etched by the etching method according to any one of claims 1 to 4.

5. A metal oxide film etched by the etching method according to any one of claims 1 to 4. ​ ​ ​ 2. The etching method according to claim 1, wherein, ​ 3. The etching method according to claim 1 or 2, wherein, ​ 4. The etching method according to claim 1 or 2, wherein, ​ ​

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