Etching method and semiconductor element manufacturing method

Abstract

Provided is an etching method by which an etching object having silicon nitride can be selectively etched compared to a non-etching object. This etching method comprises an etching step in which an etching gas, which contains a fluorine compound having at most 3 carbon atoms and having, in a molecule, at least one bond among a carbon-oxygen double bond and an ether bond, is brought into contact with a member to be etched having an etching object and a non-etching object in the presence of plasma, and the etching object is selectively etched compared to the non-etching object. The concentration of the fluorine compound in the etching gas is 0.5-40 vol%, and the etching object has silicon nitride.

Description

Etching method and semiconductor device manufacturing method

[0001] The present invention relates to an etching method and a method for manufacturing a semiconductor device.

[0002] In semiconductor manufacturing processes, perfluorocompound gases such as carbon tetrafluoride (CF4) and sulfur hexafluoride (SF6) have been used as etching gases in dry etching systems and chamber cleaning gases in chemical vapor deposition (CVD) systems. These perfluorocompounds are stable compounds with a large impact on global warming (high global warming potential), raising concerns about the adverse environmental impacts of their release into the atmosphere. Therefore, there is a need for the development of alternative gases with low global warming potential. For example, Patent Documents 1 and 2 propose fluorocarbon gases having at least one unsaturated bond as gases with a relatively low global warming potential.

[0003] Japanese Patent Publication No. 1998 No. 223614 Japanese Patent Publication No. 6079649

[0004] Although the fluorocarbon gases disclosed in Patent Documents 1 and 2 can be used to etch silicon-containing films such as silicon films, silicon dioxide films, silicon nitride films, and metal silicides, Patent Documents 1 and 2 do not mention whether silicon nitride films can be selectively etched. An object of the present invention is to provide an etching method and a method for manufacturing a semiconductor device that can selectively etch an etching target containing silicon nitride compared to a non-etching target.

[0005] In order to solve the above problems, one aspect of the present invention is as follows: [1] to

[11] . [1] An etching method comprising an etching step of contacting an etching gas containing a fluorine compound having 3 or less carbon atoms and having at least one of a carbon-oxygen double bond and an ether bond in the molecule with a member to be etched, the member having an etching object that is to be etched with the etching gas and a non-etching object that is not to be etched with the etching gas, in the presence of plasma, to selectively etch the etching object compared to the non-etching object, wherein the concentration of the fluorine compound in the etching gas is 0.5% by volume or more and 40% by volume or less, and the etching object comprises silicon nitride.

[0006] [2] The etching method according to [1], wherein the non-etching object comprises at least one selected from the group consisting of silicon oxide, photoresist, and amorphous carbon. [3] The etching method according to [1] or [2], wherein the etching step is performed under a pressure condition of 1 Pa or more and 3 kPa or less.

[0007] [4] The etching method according to any one of [1] to [3], wherein the etching step is carried out at a temperature of 0° C. to 200° C. [5] The etching method according to any one of [1] to [4], wherein the concentration of the fluorine compound in the etching gas is 1% by volume to 30% by volume.

[0008] [6] The etching method according to any one of [1] to [5], wherein the etching gas is a mixed gas containing the fluorine compound and a dilution gas. [7] The etching method according to [6], wherein the dilution gas is at least one gas selected from nitrogen gas, helium, argon, neon, krypton, and xenon. [8] The etching method according to any one of [1] to [5], wherein the etching gas is a mixed gas containing the fluorine compound, a rare gas, and nitrogen gas, and the concentration of the nitrogen gas in the etching gas is 10% by volume or less.

[0009] [9] The etching method according to [8], wherein the etching gas is a mixed gas containing the fluorine compound, a rare gas, a nitrogen gas, and an oxygen-containing gas other than the fluorine compound.

[10] The etching method according to any one of [1] to [9], wherein the fluorine compound is at least one selected from the group consisting of carbonyl fluoride, oxalyl fluoride, and hexafluoropropylene oxide.

[0010]

[11] A method for manufacturing a semiconductor element using the etching method according to any one of [1] to

[10] , wherein the member to be etched is a semiconductor substrate having the etching object and the non-etching object, and the method for manufacturing a semiconductor element includes a processing step of removing at least a part of the etching object from the semiconductor substrate by the etching.

[0011] According to the present invention, an etching target having silicon nitride can be selectively etched compared to a non-etching target.

[0012] 1 is a schematic diagram of an example of an etching apparatus for explaining an embodiment of an etching method according to the present invention. 2 is a diagram illustrating the etched members used in Examples 1 to 27 and Comparative Examples 1 to 5. 3 is a diagram illustrating the etched members used in Examples 28 to 35.

[0013] An embodiment of the present invention will be described below. Note that this embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications and improvements can be made to this embodiment, and such modifications and improvements can also be included in the present invention.

[0014] The etching method according to this embodiment includes an etching step of contacting an etching gas containing a fluorine compound with a member to be etched, which has an etching target that is to be etched by the etching gas and a non-etching target that is not to be etched by the etching gas, in the presence of plasma, to selectively etch the etching target compared to the non-etching target.

[0015] The fluorine compound has three or less carbon atoms and at least one of a carbon-oxygen double bond (carbonyl group) and an ether bond in the molecule. The concentration of the fluorine compound in the etching gas is 0.5% by volume or more and 40% by volume or less. Furthermore, the etching target contains silicon nitride.

[0016] When the etching gas is brought into contact with the material to be etched, the fluorine compound in the etching gas reacts with the silicon nitride in the material to be etched, causing etching of the material to proceed. In contrast, the material to be etched does not react much with the fluorine compound, so etching of the material to be etched hardly proceeds. Therefore, the etching method according to this embodiment allows selective etching of the material to be etched compared to the material to be etched.

[0017] Furthermore, the etching method according to this embodiment can selectively etch an etching target having silicon nitride without using perfluorocompound gases such as carbon tetrafluoride and sulfur hexafluoride, which have high global warming potentials. Therefore, the etching method according to this embodiment can reduce the environmental load caused by the use of etching gases and suppress the adverse effects on global warming.

[0018] In the present invention, etching means removing part or all of the etching target material of the etched member to process the etched member into a predetermined shape (e.g., a three-dimensional shape) (e.g., processing a film-like etching target material made of silicon nitride of the etched member to a predetermined film thickness), and also means removing residues and deposits made of the etching target material from the etched member to clean it.

[0019] The etching method according to the present embodiment can be used in the manufacture of semiconductor devices. That is, the method for manufacturing a semiconductor device according to the present embodiment is a method for manufacturing a semiconductor device using the etching method according to the present embodiment, in which the member to be etched is a semiconductor substrate having an etching target and a non-etching target, and the method includes a process of removing at least a part of the etching target from the semiconductor substrate by etching.

[0020] For example, in the etching method according to this embodiment, etching of silicon nitride (e.g., Si3N4) proceeds more quickly than etching of silicon oxide (e.g., SiO2). By utilizing this characteristic, the etching method according to this embodiment can be used in the manufacture of semiconductor elements such as 3D-NAND flash memories and logic devices.

[0021] For example, by applying the etching method according to this embodiment to a laminate formed by alternately stacking silicon oxide films and silicon nitride films, in which through-holes extending in the stacking direction and penetrating the laminate are formed (see FIG. 3 ), the silicon nitride film exposed on the inner surface of the through-hole is selectively and isotropically etched, thereby forming a structure in which the end of the silicon oxide film protrudes into the through-hole. The process for forming a structure having such a structure can be used as a structure for a semiconductor device, and is therefore used in the manufacture of semiconductor devices such as 3D-NAND flash memories and logic devices.

[0022] The process of forming the above structure by etching has conventionally been carried out using a chemical solution containing phosphoric acid or the like, but etching using an etching gas is superior to etching using a chemical solution in terms of fine processing capability. Therefore, the etching method according to this embodiment is expected to contribute to further miniaturization and higher integration of semiconductor elements.

[0023] Similarly, when the non-etching object itself is used as a structure of a semiconductor element, a material that does not substantially react with a fluorine compound or reacts extremely slowly with a fluorine compound is used as the non-etching object, specifically, at least one material selected from silicon oxide (e.g., SiO), photoresist, and amorphous carbon (C) can be used.

[0024] Furthermore, as described above, the etching method according to this embodiment can also be used for cleaning. For example, after a process of forming a film made of a silicon nitride-containing material on a substrate or a process of etching a film of a silicon nitride-containing material formed on a substrate is performed in a chamber, the silicon nitride-containing deposits adhering to the inner surface of the chamber can be removed and cleaned using the etching method according to this embodiment. In such cleaning, the chamber corresponds to the member to be etched, which is a constituent element of the present invention, and the deposits correspond to the etching target, which is a constituent element of the present invention.

[0025] The etching method and semiconductor device manufacturing method according to this embodiment will be described in more detail below. The etching according to this embodiment can be achieved by plasma etching. The type of plasma source used in plasma etching is not particularly limited, and a commercially available device may be used. Examples of suitable plasma sources include high-frequency discharge plasmas such as inductively coupled plasma (ICP) and capacitively coupled plasma (CCP), and microwave discharge plasmas such as electron cyclotron resonance plasma (ECRP).

[0026] Alternatively, the plasma may be generated in a separate plasma generation chamber (i.e., remote plasma may be used) in which the chamber containing the material to be etched is separate from the plasma generation chamber. Etching using remote plasma may enable etching of silicon nitride-containing etching targets with high selectivity. Note that an etching method in which etching is performed inside a chamber using plasma of an etching gas generated outside the chamber by a plasma source is sometimes referred to as "remote plasma etching."

[0027] [Etching Gas] The etching gas is a gas containing a fluorine compound having 3 or less carbon atoms and having at least one of a carbon-oxygen double bond and an ether bond in the molecule. Examples of functional groups having a carbon-oxygen double bond include a carbonyl group (-(C=O)-) and a formyl group (-(C=O)H). The ether bond (-O-) may be a cyclic ether bond. The type of fluorine compound is not particularly limited as long as it satisfies the above requirements, and examples thereof include formyl fluoride, carbonyl fluoride, oxalyl fluoride, 2,2,2-trifluoroacetyl fluoride, 2,2-difluoroacetyl fluoride, 2-fluoroacetyl fluoride, acetyl fluoride, 2,2,3,3,3-pentafluoropropanoyl fluoride, 2,2,3,3-tetrafluoropropanoyl fluoride, 2,3,3,3-tetrafluoropropanoyl fluoride, 3,3,3-trifluoropropanoyl fluoride, 2, ... , 3,3-trifluoropropanoyl fluoride, 2,2,3-trifluoropropanoyl fluoride, 2,2-difluoropropanoyl fluoride, 2,3-difluoropropanoyl fluoride, 3,3-difluoropropanoyl fluoride, 2-fluoropropanoyl fluoride, 3-fluoropropanoyl fluoride, propanoyl fluoride, perfluoroisopropanoyl fluoride, hexafluoroacetone, hexafluoropropylene oxide, tetrafluoroethylene oxide, trifluoromethyl ether, and the like. These fluorine compounds may be used alone or in combination of two or more. Among these fluorine compounds, from the viewpoints of ease of handling and availability, at least one selected from carbonyl fluoride (COF), oxalyl fluoride ((COF)), and hexafluoropropylene oxide (CFO) is more preferred. Many of the fluorine compounds having 4 or more carbon atoms and at least one of a carbon-oxygen double bond and an ether bond in the molecule are undesirable because they have low volatility and are difficult to handle as etching gases.

[0028] The etching gas is a mixed gas containing a fluorine compound gas and other types of gases, and the concentration of the fluorine compound in the etching gas must be 0.5% by volume or more and 40% by volume or less, preferably 1% by volume or more and 30% by volume or less, and more preferably 2% by volume or more and 30% by volume or less.

[0029] When plasma etching is performed with the fluorine compound concentration in the etching gas within the above range, an etching target having silicon nitride can be selectively etched compared to a non-etching target. For example, the etching selectivity, which is the ratio of the etching rate of the etching target to the etching rate of the non-etching target, is likely to be 5 or more. The etching selectivity is preferably 5 or more, more preferably 7 or more, and even more preferably 10 or more.

[0030] An inert diluent gas can be used as another gas that constitutes the etching gas together with the fluorine compound gas. That is, the etching gas can be a mixed gas containing the fluorine compound and the diluent gas. The diluent gas can be at least one selected from nitrogen gas (N), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).

[0031] In particular, when the etching gas contains a small amount of nitrogen gas, i.e., when the etching gas is a mixed gas containing a fluorine compound, a rare gas, and nitrogen gas, the etching rate of silicon nitride may be improved. The concentration of nitrogen gas in the etching gas is, for example, preferably 10% by volume or less, more preferably 5% by volume or less, and even more preferably 3% by volume or less. The rare gas is at least one selected from helium, neon, argon, krypton, and xenon.

[0032] Furthermore, when the etching gas contains a rare gas and a small amount of nitrogen gas, the addition of an oxygen-containing gas may improve the etching rate of silicon nitride and the etching selectivity. Here, the oxygen-containing gas is a compound that is gaseous under standard conditions and has an oxygen atom in its molecule, other than the above-mentioned fluorine compounds. Examples of oxygen-containing gases include oxygen gas (O), ozone (O), nitric oxide (NO), nitrogen dioxide (NO), nitrous oxide (NO), sulfur dioxide (SO), sulfur trioxide (SO), carbon monoxide (CO), and carbon dioxide (CO). In particular, from the viewpoint of ease of handling, oxygen gas, nitric oxide, nitrogen dioxide, nitrous oxide, sulfur dioxide, and carbon dioxide are preferred, and oxygen, nitric oxide, and nitrous oxide are more preferred.

[0033] The volume ratio of the oxygen-containing gas to the nitrogen gas in the etching gas (oxygen-containing gas / nitrogen gas) is preferably 0.1 to 2, more preferably 0.15 to 1, and even more preferably 0.2 to 0.6. When the volume ratio of the nitrogen gas to the oxygen-containing gas is within the above range, the effect of improving the etching rate of silicon nitride and the effect of improving the etching selectivity are easily obtained.

[0034] [Pressure Conditions of Etching Step] The pressure conditions of the etching step in the etching method according to this embodiment are not particularly limited, but are preferably from 1 Pa to 3 kPa, more preferably from 3 Pa to 2 kPa, and even more preferably from 10 Pa to 1.5 kPa. If the pressure conditions are within the above range, plasma can be easily generated stably.

[0035] For example, the member to be etched can be placed in a chamber and etched while passing an etching gas through the chamber, and the pressure inside the chamber during the passage of the etching gas can be set to 1 Pa or more and 3 kPa or less. The flow rate of the etching gas can be set appropriately so that the pressure inside the chamber is kept constant, depending on the size of the chamber and the capacity of the exhaust equipment for reducing the pressure inside the chamber.

[0036] [Temperature Conditions for Etching Step] The temperature conditions for the etching step in the etching method according to this embodiment are not particularly limited, but are preferably 0°C or higher and 200°C or lower, more preferably 5°C or higher and 170°C or lower, and even more preferably 20°C or higher and 150°C or lower. If the temperature conditions are within the above range, the fluorine compound can exist in a gaseous state, and the etching rate of silicon nitride is likely to be higher. Here, the temperature in the temperature conditions refers to the temperature of the member to be etched, but the temperature of a stage that supports the member to be etched and is installed in the chamber of the etching apparatus can also be used.

[0037] Fluorine compounds hardly react with non-etching targets such as silicon oxide, photoresist, and amorphous carbon at temperatures of 200° C. or less. Therefore, when a member to be etched is etched by the etching method according to this embodiment, it is possible to selectively etch a target having silicon nitride without substantially etching the non-etching target. Therefore, the etching method according to this embodiment can be used, for example, in a method of processing a target having silicon nitride into a predetermined shape by using a patterned non-etching target as a resist or mask.

[0038] Furthermore, if the temperatures of the etching object and the non-etching object are 200° C. or less, the etching selectivity is likely to be high. For example, the etching selectivity, which is the ratio of the etching rate of the etching object having silicon nitride to the etching rate of the non-etching object, is likely to be 5 or more.

[0039] [Member to be etched] The member to be etched by the etching method according to this embodiment has an etching target and a non-etching target, but it may also be a member having a portion formed of an etching target and a portion formed of a non-etching target, or a member formed of a mixture of an etching target and a non-etching target. The member to be etched may also have something other than an etching target or a non-etching target. The shape of the member to be etched is not particularly limited, and may be, for example, a plate, foil, film, powder, or lump. An example of a member to be etched is the semiconductor substrate mentioned above.

[0040] [Object to be etched] The object to be etched has silicon nitride, but may be formed only from silicon nitride, may have a portion formed only from silicon nitride and a portion formed from another material, or may be formed from a mixture of silicon nitride and another material.

[0041] Silicon nitride refers to a compound containing silicon and nitrogen in any ratio, and an example thereof is Si3N4. The purity of silicon nitride is not particularly limited, but is preferably 30 mass% or more, more preferably 60 mass% or more, and even more preferably 90 mass% or more. The shape of the object to be etched is not particularly limited, and may be, for example, a plate, foil, film, powder, or block.

[0042] [Substances not to be etched] The substances not to be etched do not substantially react with the fluorine compound or react very slowly with the fluorine compound, so that etching hardly progresses even when etching is performed by the etching method according to this embodiment. The substances not to be etched are not particularly limited as long as they have the properties described above, but examples include silicon oxide, photoresist, amorphous carbon, titanium nitride, metals such as copper, nickel, and cobalt, and oxides and nitrides of these metals. Among these, silicon oxide, photoresist, and amorphous carbon are more preferred from the viewpoints of ease of handling and availability.

[0043] Photoresist refers to a photosensitive composition whose physical properties, including solubility, change when exposed to light, an electron beam, or the like. Examples include photoresists for g-line, h-line, i-line, KrF, ArF, F2, and EUV. The composition of the photoresist is not particularly limited as long as it is one commonly used in semiconductor manufacturing processes, but examples include compositions containing a polymer synthesized from at least one monomer selected from linear olefin, cyclic olefin, styrene, vinylphenol, acrylic acid, methacrylate, epoxy, melamine, and glycol.

[0044] Furthermore, the non-etching object can be used as a resist or mask to suppress etching of the etching object by the etching gas. Therefore, the etching method according to the present embodiment can be used in a method of processing the etching object into a predetermined shape (e.g., processing a film-like etching object of a member to be etched to a predetermined film thickness) by using the patterned non-etching object as a resist or mask, and is therefore suitable for use in the manufacture of semiconductor devices. Furthermore, since the non-etching object is hardly etched, etching of portions of the semiconductor device that should not be etched can be suppressed, and the loss of properties of the semiconductor device due to etching can be prevented.

[0045] The non-etched material remaining after patterning can be removed by a removal method commonly used in semiconductor device manufacturing processes, such as ashing using an oxidizing gas such as oxygen plasma or ozone, or dissolving and removing using chemicals such as APM (a mixture of aqueous ammonia and hydrogen peroxide), SPM (a mixture of sulfuric acid and hydrogen peroxide), or organic solvents.

[0046] Next, an example of the configuration of an etching apparatus capable of carrying out the etching method according to this embodiment and an example of an etching method using the etching apparatus will be described with reference to Fig. 1. The etching apparatus in Fig. 1 is a remote plasma etching apparatus that performs remote plasma etching. First, the etching apparatus in Fig. 1 will be described.

[0047] The etching apparatus of FIG. 1 includes a chamber 10 in which etching is performed, a remote plasma generator 20 which is a plasma generation source, a stage 11 which supports a member 12 to be etched inside the chamber 10, a thermometer 14 which measures the temperature of the member 12 to be etched, an exhaust pipe 13 which exhausts gas from inside the chamber 10, a vacuum pump 15 which is connected to the exhaust pipe 13 and reduces the pressure inside the chamber 10, and a pressure gauge 16 which measures the pressure inside the chamber 10.

[0048] 1 also includes an etching gas supply unit that supplies an etching gas into the chamber 10. This etching gas supply unit includes a fluorine compound gas supply unit 1 that supplies a fluorine compound gas, a rare gas supply unit 2 that supplies a rare gas, a nitrogen gas supply unit 3 that supplies nitrogen gas, a fluorine compound gas supply pipe 7 that connects the fluorine compound gas supply unit 1 and the chamber 10, a rare gas supply pipe 8 that connects the rare gas supply unit 2 to an intermediate portion of the fluorine compound gas supply pipe 7, and a nitrogen gas supply pipe 9 that connects the nitrogen gas supply unit 3 to an intermediate portion of the rare gas supply pipe 8.

[0049] 1 has a remote plasma generator 20 outside the chamber 10. More specifically, the etching apparatus of Fig. 1 has the remote plasma generator 20 at a position between the chamber 10 and the connecting portion of the fluorine compound gas supply pipe 7 with the rare gas supply pipe 8.

[0050] Furthermore, the fluorine compound gas supply pipe 7 is provided with a fluorine compound gas pressure control device 17 that controls the pressure of the fluorine compound gas, and a fluorine compound gas flow rate control device 4 that controls the flow rate of the fluorine compound gas. Furthermore, the rare gas supply pipe 8 is provided with a rare gas pressure control device 18 that controls the pressure of the rare gas, and a rare gas flow rate control device 5 that controls the flow rate of the rare gas. Furthermore, the nitrogen gas supply pipe 9 is provided with a nitrogen gas pressure control device 19 that controls the pressure of the nitrogen gas, and a nitrogen gas flow rate control device 6 that controls the flow rate of the nitrogen gas.

[0051] When a fluorine compound gas is supplied to the chamber 10 as an etching gas, the fluorine compound gas is sent from the fluorine compound gas supply unit 1 to the fluorine compound gas supply pipe 7, and the fluorine compound gas is supplied to the remote plasma generator 20 via the fluorine compound gas supply pipe 7.

[0052] Furthermore, when a mixed gas of a fluorine compound gas, a rare gas, and a nitrogen gas is supplied as the etching gas, the fluorine compound gas is sent from the fluorine compound gas supply unit 1 to the fluorine compound gas supply pipe 7, and the rare gas and nitrogen gas are sent from the rare gas supply unit 2 and the nitrogen gas supply unit 3 to the fluorine compound gas supply pipe 7 via the rare gas supply pipe 8 and the nitrogen gas supply pipe 9, respectively, so that the mixed gas is supplied to the remote plasma generator 20 via the fluorine compound gas supply pipe 7.

[0053] The fluorine compound gas or mixed gas is converted into plasma in the remote plasma generator 20 and supplied into the chamber 10. The remote plasma generator 20 and the chamber 10 may be directly connected or may be connected via piping. The configurations of the fluorine compound gas supply unit 1, the rare gas supply unit 2, and the nitrogen gas supply unit 3 are not particularly limited and may be, for example, gas bombs or cylinders. Furthermore, the fluorine compound gas flow rate controller 4, the rare gas flow rate controller 5, and the nitrogen gas flow rate controller 6 may be, for example, mass flow controllers or flow meters.

[0054] When the etching gas is supplied to the chamber 10, it is preferable to supply the etching gas while maintaining the pressure of the etching gas (i.e., the value of the fluorine compound gas pressure control device 17 in FIG. 1) at a predetermined value. That is, the supply pressure of the etching gas is preferably 1 Pa or more and 0.2 MPa or less, more preferably 10 Pa or more and 0.1 MPa or less, and even more preferably 50 Pa or more and 50 kPa or less. When the supply pressure of the etching gas is within the above range, the etching gas is smoothly supplied to the chamber 10, and the load on the components of the etching apparatus of FIG. 1 (for example, the various devices and piping) is small.

[0055] Furthermore, from the viewpoint of uniformly etching the surface of the member to be etched 12, the pressure of the etching gas supplied into the chamber 10 is preferably from 1 Pa to 80 kPa, more preferably from 10 Pa to 50 kPa, and even more preferably from 100 Pa to 20 kPa. If the pressure of the etching gas in the chamber 10 is within the above range, a sufficient etching rate can be obtained and the etching selectivity ratio is likely to be high.

[0056] The pressure in the chamber 10 before the etching gas is supplied is not particularly limited as long as it is equal to or lower than the supply pressure of the etching gas. For example, -5 The pressure is preferably 1 Pa or more and less than 10 kPa, and more preferably 1 Pa or more and 2 kPa or less.

[0057] The differential pressure between the supply pressure of the etching gas and the pressure inside the chamber 10 before the etching gas is supplied is preferably 0.5 MPa or less, more preferably 0.3 MPa or less, and even more preferably 0.1 MPa or less. If the differential pressure is within the above range, the etching gas can be smoothly supplied to the chamber 10.

[0058] When the etching gas is supplied to the chamber 10, it is preferable to supply the etching gas while maintaining the temperature of the etching gas at a predetermined value. That is, the supply temperature of the etching gas is preferably 0°C or higher and 150°C or lower. The temperature of the member 12 to be etched during etching is preferably 0°C or higher and 200°C or lower, more preferably 5°C or higher and 170°C or lower, and even more preferably 20°C or higher and 150°C or lower. Within this temperature range, etching of the etching target (particularly silicon nitride) of the member 12 to be etched proceeds smoothly, the load on the etching apparatus is small, and the life of the etching apparatus is likely to be extended.

[0059] The etching processing time (hereinafter sometimes referred to as "etching time") can be set arbitrarily depending on the degree to which the etching target of the member to be etched 12 is desired to be etched, but considering the production efficiency of the semiconductor device manufacturing process, it is preferably within 60 minutes, more preferably within 40 minutes, and even more preferably within 20 minutes. Note that the etching processing time refers to the time during which the plasmatized etching gas is brought into contact with the member to be etched 12 inside the chamber 10.

[0060] The etching method according to this embodiment can be performed using a general plasma etching apparatus used in semiconductor device manufacturing processes, such as the etching apparatus shown in Fig. 1, and the configuration of the etching apparatus that can be used is not particularly limited. For example, the positional relationship between the fluorine compound gas supply pipe 7 and the member to be etched 12 is not particularly limited as long as it allows the etching gas to contact the member to be etched 12. Furthermore, as for the configuration of the temperature adjustment mechanism for the chamber 10, it is sufficient to be able to adjust the temperature of the member to be etched 12 to a desired temperature. Therefore, the temperature adjustment mechanism may be directly provided on the stage 11, or an external temperature adjuster may be used to heat or cool the chamber 10 from outside the chamber 10.

[0061] 1 may be made of any material that is resistant to corrosion by the fluorine compound used and that can be depressurized to a predetermined pressure. For example, metals such as nickel, nickel-based alloys, aluminum, stainless steel, platinum, copper, and cobalt, ceramics such as alumina, and fluororesins may be used for the parts that come into contact with the etching gas.

[0062] Specific examples of nickel-based alloys include Inconel (registered trademark), Hastelloy (registered trademark), Monel (registered trademark), etc. Furthermore, examples of fluororesins include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyvinylidene fluoride (PVDF), Teflon (registered trademark), Viton (registered trademark), Kalrez (registered trademark), etc.

[0063] The present invention will be described in more detail below with reference to examples and comparative examples. Example 1 An etching apparatus having substantially the same configuration as the etching apparatus shown in Fig. 1 was used to etch a member to be etched. The member to be etched used in Example 1 will be described with reference to Fig. 2.

[0064] A 1 μm-thick silicon nitride film 22 was formed on a square silicon substrate 21 with sides of 2 inches (manufactured by KST World Co., Ltd.), and a rectangular silicon dioxide substrate 23 with dimensions of 1 inch x 2 inches was bonded to the silicon nitride film 22 using grease (Demnum Grease L-200 manufactured by Daikin Industries, Ltd.), and the laminate produced in this manner was used as the member to be etched. As shown in FIG. 2, the silicon dioxide substrate 23 was bonded so as to cover approximately half of the silicon nitride film 22. The silicon nitride film 22 was the object to be etched, and the silicon dioxide substrate 23, which was not to be etched, was used as a resist.

[0065] Furthermore, comparative laminates were fabricated by replacing the silicon nitride film 22, which was the etching target, with a film of silicon dioxide, photoresist, or amorphous carbon, which was the non-etching target, in the above-mentioned etched member. The above-mentioned etched member and these three comparative laminates were placed side by side on a stage inside the chamber of an etching device, and the stage temperature was set to 20°C.

[0066] Next, carbonyl fluoride gas at a flow rate of 30 mL / min and argon at a flow rate of 970 mL / min were mixed to form a mixed gas, which was used as the etching gas. This etching gas was then supplied into the chamber at a flow rate of 1000 mL / min and circulated for 3 minutes to perform remote plasma etching. The pressure inside the chamber during the flow of the etching gas was set to 500 Pa. Furthermore, an intelligent remote plasma source, ASTRON Paragon (registered trademark), manufactured by MKS Japan Co., Ltd., was used as the remote plasma generator, with a source power of 100 W. This etched the exposed portion of the silicon nitride film 22 of the etched member that was not covered by the silicon dioxide substrate 23. After the flow of the etching gas was completed, the inside of the chamber was replaced with argon.

[0067] After etching was completed, the chamber was opened and the etched member was removed. The silicon dioxide substrate 23 was removed from the removed etched member, and the adhesive surface was washed with ethanol to remove grease. Then, using an atomic force microscope VN-8010 manufactured by Keyence Corporation, the size of the step between the cover surface 22a of the silicon nitride film 22 that was covered by the silicon dioxide substrate 23 and not etched and the etched surface 22b of the silicon nitride film 22 that was not covered by the silicon dioxide substrate 23 and was etched was measured. The silicon nitride etching rate (nm / min) was calculated by dividing the measured step size (nm) by the etching time (min). The results are shown in Table 1.

[0068] The same procedure was performed on the three control laminates as on the etched members, and the etching rates (nm / min) of silicon dioxide, photoresist, and amorphous carbon were calculated by dividing the step size (nm) by the etching time (min). Furthermore, the ratio of the etching rate of the non-etched object to the etching rate of silicon nitride (etching selectivity) was calculated. The results are shown in Table 1.

[0069] The conditions for measuring the size of the step using an atomic force microscope are as follows: Measurement pressure: atmospheric pressure (101.3 kPa) Measurement temperature: 28° C. Measurement atmosphere: air Scanning range: width 80.0 μm, height 20.0 μm, angle 0°

[0070]

[0071] Examples 2 to 15 Remote plasma etching was performed in the same manner as in Example 1, with the etching target being a silicon nitride film and the non-etching targets being silicon dioxide, photoresist, and amorphous carbon, under the etching conditions (etching gas composition, stage temperature, pressure in the chamber, etching time, and source power of the remote plasma generator) shown in Table 1. The etching rates of the etching target and the non-etching target were calculated, and the etching selectivity was calculated from these values. The results are shown in Tables 1 and 2.

[0072]

[0073] Comparative Example 1 Remote plasma etching was performed in the same manner as in Example 1, except that the etching gas was a mixed gas of sulfur hexafluoride gas and argon, the source power of the remote plasma generator was 400 W, and the etching time was 1 minute. The etching rates of the etching target and the non-etching target were calculated, and the etching selectivity was calculated from these values. The results are shown in Table 2.

[0074] Comparative Example 2 Etching was performed in the same manner as in Example 1, except that the etching gas was a mixture of carbonyl fluoride gas at a flow rate of 300 mL / min and argon gas at a flow rate of 700 mL / min, the stage temperature was 150° C., the source power of the remote plasma generator was 0 W (i.e., no plasma was generated), and the etching time was 30 minutes. The etching rates of the etching target and the non-etching target were calculated, and the etching selectivity was calculated from these values. The results are shown in Table 2.

[0075] Comparative Example 3 Remote plasma etching was performed in the same manner as in Example 1, except that the etching gas was a mixed gas of carbonyl fluoride gas at a flow rate of 800 mL / min and argon gas at a flow rate of 200 mL / min, and the source power of the remote plasma generator was 400 W. The etching rates of the object to be etched and the object not to be etched were calculated, and the etching selectivity was calculated from these values. The results are shown in Table 2.

[0076] Examples 16 to 27 Etching was performed on the member to be etched and the comparative laminate in the same manner as in Example 1, except that a plasma of an etching gas was generated in a chamber using an ICP etching system RIE-200iP manufactured by Samco Inc., and etching was performed in the chamber using the plasma of the etching gas, and the etching conditions (etching gas composition, stage temperature, pressure in the chamber, etching time, source power and bias power of the plasma generator) were as shown in Table 3. Then, in the same manner as in Example 1, the etching rates of the etching target and the non-etching target were calculated, and the etching selectivity was calculated from the values. The results are shown in Table 3.

[0077]

[0078] Comparative Example 4 Plasma etching was performed in the same manner as in Example 16, except that the etching gas was a mixed gas of sulfur hexafluoride gas and argon, and the bias power of the plasma generator was set to 80 W. The etching rates of the etching target and the non-etching target were calculated, and the etching selectivity was calculated from these values. The results are shown in Table 3.

[0079] Comparative Example 5 Plasma etching was performed in the same manner as in Example 16, except that the etching gas was a mixed gas of carbonyl fluoride gas at a flow rate of 40 mL / min and argon gas at a flow rate of 10 mL / min. The etching rates of the etching target and the non-etching target were calculated, and the etching selectivity was calculated from these values. The results are shown in Table 3.

[0080] Example 28 The etched member used in Example 28 will be described with reference to FIG. 3 . The etched member in FIG. 3 has a structure in which 30 layers of 35-nm-thick silicon nitride films 32 and 35-nm-thick silicon oxide films 33 are alternately stacked on a silicon substrate 31 (for convenience, FIG. 3 shows a structure in which 5 layers are alternately stacked). The etched member in FIG. 3 also has a structure in which a 300-nm-thick amorphous carbon film 35 is further stacked on the top silicon oxide film 33. Here, the silicon nitride film 32 and the silicon oxide film 33 are the etching target, and the amorphous carbon film 35 is the non-etching target. Furthermore, the etched member in FIG. 3 has a through-hole 34 with a diameter of 100 nm that penetrates the 30 silicon nitride films 32, the 30 silicon oxide films 33, and one amorphous carbon film 35 in the stacking direction.

[0081] This member to be etched was placed on the stage of an etching apparatus having a configuration substantially similar to that of the etching apparatus in FIG. 1, and the stage temperature was set to 20°C. Next, carbonyl fluoride gas at a flow rate of 30 mL / min was mixed with argon at a flow rate of 970 mL / min to form a mixed gas, which was used as an etching gas. This etching gas was then converted into plasma by remote plasma generation and supplied into the chamber, where it was circulated for 3 minutes to perform remote plasma etching. The pressure inside the chamber during the flow of the etching gas was set to 500 Pa. After the flow of the etching gas was completed, the inside of the chamber was replaced with argon.

[0082] The chamber was opened and the member to be etched was removed. In the etched member, the portion of the silicon nitride film 32 exposed to the inner surface of the through-hole 34 was etched, and in particular, the silicon nitride film 32 was etched preferentially compared to the silicon oxide film 33, so that part of the inner surface of the through-hole 34 expanded radially outward.

[0083] The portion of the silicon oxide film 33 exposed on the inner surface of the through hole 34 is less susceptible to etching than the silicon nitride film 32, and the amorphous carbon film 35 is hardly etched at all, resulting in a structure in which the ends of the silicon oxide film 33 and the amorphous carbon film 35 protrude into the through hole 34.

[0084] The removed etched member was cut, and the cross sections of the 30 silicon nitride films 32 and the 30 silicon oxide films 33 were each analyzed using a scanning electron microscope. Specifically, for each of the 30 silicon nitride films 32, the radial distance between the portion of the silicon nitride film 32 exposed to the inner surface of the through hole 34 and the portion of the amorphous carbon film 35 exposed to the inner surface of the through hole 34 was measured. Furthermore, for each of the 30 silicon oxide films 33, the radial distance between the portion of the silicon oxide film 33 exposed to the inner surface of the through hole 34 and the portion of the amorphous carbon film 35 exposed to the inner surface of the through hole 34 was measured.

[0085] That is, the etching causes the inner surface of the through hole 34 to expand radially outward, increasing the radius of the through hole 34, and the difference in radius was measured. This was then divided by the etching time to calculate the relative etching rates of silicon nitride and silicon oxide with respect to amorphous carbon. The etching rate of amorphous carbon was calculated by comparing the diameter of the through hole 34 before and after etching, but almost no change in diameter was observed.

[0086] The average value and standard deviation of the etching rates of the 30 silicon nitride films 32 and silicon oxide films 33 were calculated to evaluate the uniformity of the relative etching rates in the in-plane direction (direction parallel to the film surface) and whether the relative etching rates varied depending on the position in the film stacking direction. The results are shown in Table 4.

[0087]

[0088] (Examples 29 to 31) Plasma etching was performed in the same manner as in Example 28, under the etching conditions (etching gas composition, stage temperature, pressure in the chamber, etching time, and source power of the plasma generator) shown in Table 4. Then, in the same manner as in Example 28, the relative etching rates of silicon nitride and silicon oxide to amorphous carbon were calculated, and the average value and standard deviation of each etching rate were calculated. The results are shown in Table 4.

[0089] Examples 32 to 35 Etching was performed on the same etched member as in Example 28 using an ICP etching system RIE-200iP manufactured by Samco Corporation. The bias power of the plasma generator was set to 0 W, and other etching conditions (etching gas composition, stage temperature, pressure in the chamber, etching time, and source power of the plasma generator) were as shown in Table 5. Then, as in Example 28, the relative etching rates of silicon nitride and silicon oxide to amorphous carbon were calculated, and the average value and standard deviation of each etching rate were calculated. The results are shown in Table 5.

[0090]

[0091] The results of Examples 1 to 3 show that when the source power was 400 W, the etching rate of silicon nitride was higher than when the source power was 100 W or 800 W. On the other hand, etching of the non-etching target hardly progressed regardless of the source power. The results of Examples 4 to 6 suggest that there is a point in the concentration of carbonyl fluoride in the etching gas where the etching rate of silicon nitride becomes maximum. On the other hand, etching of the non-etching target hardly progressed regardless of the concentration of carbonyl fluoride in the etching gas.

[0092] The results of Examples 7 and 8 show that etching of silicon nitride proceeds without any problems even when the pressure inside the chamber is set to 100 Pa or 1500 Pa. On the other hand, etching of non-etching objects hardly proceeds. The results of Examples 9 and 15 show that increasing the stage temperature improves the etching rate of silicon nitride, which is the etching object, and silicon oxide, photoresist, and amorphous carbon, which are non-etching objects.

[0093] The results of Examples 10 and 11 show that even when oxalyl fluoride or hexafluoropropylene oxide is used as the etching gas, etching of silicon nitride proceeds, but etching of non-etching objects hardly proceeds. The results of Examples 12 and 13 show that when a mixed gas of carbonyl fluoride, argon, and nitrogen gas is used as the etching gas, the etching rate of silicon nitride is improved. Furthermore, etching of non-etching objects also proceeded slightly. The reason for the improvement in the etching rate of silicon nitride is thought to be that the addition of nitrogen gas promotes the dissociation of fluorine atoms from carbonyl fluoride.

[0094] The results of Example 14 show that the etching rate and etching selectivity of silicon nitride are further improved when a mixed gas containing oxygen gas in addition to carbonyl fluoride, argon, and nitrogen gas is used as the etching gas. It is believed that the addition of oxygen gas further promotes the dissociation of fluorine atoms from carbonyl fluoride.

[0095] The results of Comparative Example 1 show that when sulfur hexafluoride is used as the etching gas, both silicon nitride and non-etching objects are etched. The results of Comparative Example 2 show that under conditions where plasma is not generated, etching of silicon oxide, photoresist, and amorphous carbon proceeds at the same rate as silicon nitride, making selective etching of silicon nitride difficult. The results of Comparative Example 3 show that when the concentration of carbonyl fluoride in the etching gas is too high, etching of silicon oxide, photoresist, and amorphous carbon proceeds along with silicon nitride.

[0096] The results of Examples 16 to 27 demonstrate that it is possible to selectively etch silicon nitride compared to non-etching targets, even when using an ICP etching apparatus. It also demonstrates that the etching rate of silicon nitride is improved when the bias power is increased or when a mixed gas containing nitrogen gas is used as the etching gas. It also demonstrates that the etching rate of silicon nitride is further improved when a mixed gas containing nitrogen gas and oxygen gas is used as the etching gas. On the other hand, when the source power is increased, the concentration of carbonyl fluoride in the etching gas is decreased, or oxalyl fluoride or hexafluoropropylene oxide is used as the etching gas, no significant effect is observed on the etching rates of silicon nitride and non-etching targets.

[0097] The results of Comparative Example 4 show that when sulfur hexafluoride is used as the etching gas, silicon nitride is etched as well as silicon oxide, photoresist, and amorphous carbon, which are non-etching targets.The results of Comparative Example 5 show that when the concentration of carbonyl fluoride in the etching gas is too high, silicon nitride is etched as well as silicon oxide, photoresist, and amorphous carbon, which are non-etching targets.

[0098] The results of Examples 28 to 35 demonstrate that etching a laminated film of amorphous carbon, silicon nitride, and silicon oxide can selectively etch the silicon nitride layer. The ratio of the standard deviation of the silicon nitride etching rate to the average value was approximately 2 to 7%, indicating that etching of the 30 layers of silicon nitride film 32 proceeded almost uniformly, regardless of the position in the stacking direction of the silicon nitride film 32. In contrast, the etching rates of silicon oxide and amorphous carbon were smaller than the etching rate of silicon nitride under all conditions. Furthermore, the standard deviation of the silicon oxide etching rate was 3 or less under all conditions.

[0099] 1... Fluorine compound gas supply unit 2... Rare gas supply unit 3... Nitrogen gas supply unit 4... Fluorine compound gas flow rate control device 5... Rare gas flow rate control device 6... Nitrogen gas flow rate control device 7... Fluorine compound gas supply pipe 8... Rare gas supply pipe 9... Nitrogen gas supply pipe 10... Chamber 11... Stage 12... Member to be etched 13... Exhaust pipe 14... Thermometer 15... Vacuum pump 16... Pressure gauge 17... Fluorine compound gas pressure control device 18... Rare gas pressure control device 19... Nitrogen gas pressure control device 20... Remote plasma generator 21... Silicon substrate 22... Silicon nitride film 23... Silicon dioxide substrate 31... Silicon substrate 32... Silicon nitride film 33... Silicon oxide film 34... Through hole 35... Amorphous carbon film

Claims

1. An etching gas containing a fluorine compound having at least one of a carbon-oxygen double bond and an ether bond in the molecule and having 3 or less carbon atoms is brought into contact with an etched member having an object to be etched by the etching gas and a non-etching object that is not an object to be etched by the etching gas in the presence of plasma, and an etching step of selectively etching the object to be etched compared to the non-etching object is provided. The concentration of the fluorine compound in the etching gas is 0.5% by volume or more and 40% by volume or less, and the object to be etched has silicon nitride. An etching method.

2. The etching method according to claim 1, wherein the non-etching object has at least one selected from silicon oxide, photoresist, and amorphous carbon.

3. The etching method according to claim 1 or 2, wherein the etching step is performed under a pressure condition of 1 Pa or more and 3 kPa or less.

4. The etching method according to any one of claims 1 to 3, wherein the etching step is performed under a temperature condition of 0 ° C or more and 200 ° C or less.

5. The etching method according to any one of claims 1 to 4, wherein the concentration of the fluorine compound in the etching gas is 1% by volume or more and 30% by volume or less.

6. The etching method according to any one of claims 1 to 5, wherein the etching gas is a mixed gas containing the fluorine compound and a dilution gas.

7. The etching method according to claim 6, wherein the dilution gas is at least one selected from nitrogen gas, helium, argon, neon, krypton, and xenon.

8. The etching gas is a mixed gas containing the fluorine compound, a rare gas, and nitrogen gas, and the concentration of the nitrogen gas in the etching gas is 10% by volume or less. The etching method according to any one of claims 1 to 5.

9. The etching method according to claim 8, wherein the etching gas is a mixed gas containing, in addition to the fluorine compound, a rare gas, and nitrogen gas, an oxygen-containing gas other than the fluorine compound.

10. The etching method according to any one of claims 1 to 9, wherein the fluorine compound is at least one selected from carbonyl fluoride, oxalyl fluoride, and hexafluoropropylene oxide.

11. A method of manufacturing a semiconductor device using the etching method according to any one of claims 1 to 10, wherein the member to be etched is a semiconductor substrate having the object to be etched and the object not to be etched, and the method includes a processing step of removing at least a part of the object to be etched from the semiconductor substrate by the etching.

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