Etching method for silicon nitride and production method for semiconductor element

Abstract

Provided is an etching method that is for silicon nitride and that enable selective etching of silicon nitride without using plasma. This etching method for silicon nitride comprises an etching step for placing an etching object (12) that contains silicon nitride, in an etching gas containing a halogen fluoride which is a compound of bromine or iodine and fluorine, and etching the silicon nitride of the etching object (12), under a pressure of 1-80 kPa, without using plasma.

Description

Silicon nitride etching method and semiconductor device manufacturing method

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

[0002] Etching is used for patterning and removing silicon nitride in semiconductor manufacturing processes. For example, Patent Document 1 discloses a method for selectively etching silicon nitride relative to silicon oxide using a plasma gas obtained by plasmatizing a dry etching agent containing 1,3,3,3-tetrafluoropropene. However, etching methods using plasma have the problem of being expensive.

[0003] International Publication No. 2016 / 181723 Japanese Patent Publication No. 6032033 International Publication No. 2016 / 056300

[0004] As an etching method that does not use plasma (hereinafter sometimes referred to as a "plasma-less etching method" or "plasma-less etching"), for example, Patent Document 2 discloses a method for etching a polysilicon film using iodine heptafluoride (IF7). Also, Patent Document 3 discloses a method for etching a silicon compound using an etching gas composition containing a halogen fluoride such as chlorine monofluoride (ClF) as a main component.

[0005] However, Patent Document 2 lists silicon nitride as a mask material, suggesting that the plasmaless etching method disclosed in Patent Document 2 does not etch silicon nitride. Furthermore, the plasmaless etching method disclosed in Patent Document 3 is a method for selectively etching silicon oxide over silicon nitride, but does not disclose that silicon nitride is selectively etched. An object of the present invention is to provide a silicon nitride etching method that can selectively etch silicon nitride without using plasma.

[0006] In order to solve the above problems, one aspect of the present invention is as follows [1] to

[11] : [1] A method for etching silicon nitride, comprising an etching step of placing an etching object containing silicon nitride in an etching gas containing a halogen fluoride, which is a compound of bromine or iodine and fluorine, and etching the silicon nitride of the etching object under a pressure of 1 Pa or more and 80 kPa or less without using plasma.

[0007] [2] The method for etching silicon nitride according to [1], wherein the content of hydrogen fluoride contained in the etching gas is less than 100 ppm by volume. [3] The method for etching silicon nitride according to [1] or [2], wherein the temperature of the object to be etched is 155°C or higher and 500°C or lower. [4] The method for etching silicon nitride according to any one of [1] to [3], wherein the content of the halogen fluoride contained in the etching gas is 1% by volume or higher.

[0008] [5] The method for etching silicon nitride according to any one of [1] to [4], wherein the etching gas is a gas consisting of only the halogen fluoride or a mixed gas consisting of the halogen fluoride and an inert gas. [6] The method for etching silicon nitride according to [5], wherein the inert gas is at least one gas selected from nitrogen gas, helium, argon, neon, krypton, and xenon.

[0009] [7] The method for etching silicon nitride according to any one of [1] to [6], wherein the halogen fluoride is at least one selected from the group consisting of bromine trifluoride, bromine pentafluoride, iodine pentafluoride, and iodine heptafluoride. [8] The method for etching silicon nitride according to any one of [1] to [7], wherein the object to be etched contains the silicon nitride and an etching-resistant material that suppresses etching of the silicon nitride by the etching gas, and the silicon nitride of the object to be etched is selectively etched by the etching gas.

[0010] [9] The method for etching silicon nitride according to [8], wherein the etching-resistant material contains at least one selected from silicon dioxide, photoresist, and amorphous carbon.

[10] The method for etching silicon nitride according to [8] or [9], wherein an etching selectivity, which is the ratio of the etching rate of the silicon nitride to the etching rate of the etching-resistant material, is 10 or more.

[11] A method for manufacturing a semiconductor element, wherein a semiconductor element is manufactured using the method for etching silicon nitride according to any one of [1] to

[10] .

[0011] According to the present invention, silicon nitride can be selectively etched without using plasma.

[0012] 1 is a schematic diagram of an example of an etching apparatus for explaining an embodiment of a silicon nitride etching method according to the present invention.

[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 silicon nitride etching method of this embodiment includes an etching step of placing an etching object containing silicon nitride (e.g., SiN) in an etching gas containing a halogen fluoride, which is a compound of bromine or iodine and fluorine, and etching the silicon nitride of the etching object under a pressure of 1 Pa or more and 80 kPa or less without using plasma.

[0015] Since silicon nitride can be selectively etched without using plasma, there is no need to use expensive plasma generators for etching. Therefore, etching of silicon nitride can be performed at low cost. Furthermore, since plasma is not used, corrosion of the components constituting the etching apparatus and the piping connected to the etching apparatus is less likely to occur.

[0016] In the present invention, etching means removing part or all of the silicon nitride contained in the object to be etched and processing the object to a predetermined shape (e.g., a three-dimensional shape) (e.g., processing the silicon nitride film of the object to be etched to a predetermined film thickness), and also means removing residues and deposits made of silicon nitride from the object to be etched and cleaning it.

[0017] The silicon nitride etching method of this embodiment as described above can be used in the manufacture of semiconductor devices such as 3D-NAND flash memories. For example, by applying the silicon nitride etching method of this embodiment to a laminate formed by alternately stacking silicon dioxide films and silicon nitride films, in which through-holes extending along the stacking direction and penetrating the laminate are formed (see FIG. 2), 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 dioxide film protrudes into the through-hole. The process of 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.

[0018] 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 silicon nitride etching method of this embodiment is expected to contribute to further miniaturization and higher integration of semiconductor elements.

[0019] Similarly, when the etching-resistant material itself, which will be described later, is used as a structure of a semiconductor element, a material that does not substantially react with halogen fluorides or reacts extremely slowly with halogen fluorides is used as the etching-resistant material. Specifically, for example, at least one material selected from silicon dioxide (SiO), photoresist, and amorphous carbon can be used.

[0020] Furthermore, as described above, the silicon nitride etching method of 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 silicon nitride-containing material film 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 by the silicon nitride etching method of this embodiment.

[0021] The silicon nitride etching method of this embodiment will be described in more detail below. [Etching Gas] The etching gas is a gas containing a halogen fluoride, which is a compound of bromine or iodine with fluorine. The type of halogen fluoride is not particularly limited as long as it is a compound of bromine or iodine with fluorine, but at least one selected from bromine monofluoride (BrF), bromine trifluoride (BrF), bromine pentafluoride (BrF), iodine pentafluoride (IF), and iodine heptafluoride (IF) is preferred. Among these halogen fluorides, at least one selected from bromine trifluoride, bromine pentafluoride, iodine pentafluoride, and iodine heptafluoride is more preferred from the standpoints of ease of handling and availability.

[0022] The etching gas may be a gas consisting of only a halogen fluoride, or may be a mixed gas containing a halogen fluoride and other gases. When the etching gas is a mixed gas containing a halogen fluoride and other gases, the content of the halogen fluoride contained in the etching gas is preferably 1% by volume or more, more preferably 5% by volume or more, and even more preferably 10% by volume or more.

[0023] When the etching gas is a mixed gas containing a halogen fluoride and other gases, an inert gas can be used as the other gas. That is, the etching gas may be a mixed gas containing a halogen fluoride and an inert gas. The inert gas may be at least one selected from nitrogen gas (N), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). The content of the inert gas contained in the etching gas is not particularly limited, but can be more than 0% by volume and not more than 99% by volume.

[0024] The hydrogen fluoride content in the etching gas is preferably less than 100 ppm by volume, more preferably less than 50 ppm by volume, which tends to increase the etching selectivity, which is the ratio of the etching rate of silicon nitride to the etching rate of an etching-resistant material, which will be described later.

[0025] [Pressure During Etching] In the etching step of the silicon nitride etching method of this embodiment, the object to be etched is placed in an etching gas, and the silicon nitride of the object to be etched is etched without using plasma, but the etching is performed under a pressure of 1 Pa or more and 80 kPa or less.

[0026] For example, an object to be etched can be placed in a chamber and etched while passing an etching gas through the chamber, with the pressure inside the chamber during the passage of the etching gas being set to 1 Pa or more and 80 kPa or less. The flow rate of the etching gas may 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.

[0027] [Temperature During Etching] In the etching step of the silicon nitride etching method of this embodiment, the object to be etched is placed in an etching gas, and silicon nitride of the object to be etched is etched without using plasma, but it is preferable to perform the etching at a temperature of 155°C or higher and 500°C or lower.

[0028] If the temperature of the etching object is 155°C or higher, the halogen fluoride can exist in a gaseous state and the etching rate of silicon nitride tends to be higher. The temperature of the etching object is preferably 170°C or higher, more preferably 200°C or higher, and even more preferably 250°C or higher. On the other hand, if the temperature of the etching object is 500°C or lower, there are advantages such as being able to heat the object without requiring excessive time and energy, being less likely to damage the equipment and components used in the etching, and being less susceptible to etching of etching-resistant materials.

[0029] Halogen fluorides hardly react with etching-resistant materials such as silicon dioxide and photoresist under conditions where plasma is not generated and at temperatures of 500°C or less. Therefore, when the etching target contains both an etching-resistant material and silicon nitride, the silicon nitride etching method of this embodiment can be used to selectively etch the silicon nitride without substantially etching the etching-resistant material. Therefore, the silicon nitride etching method of this embodiment can be used in methods such as using a patterned etching-resistant material as a mask to process silicon nitride into a predetermined shape.

[0030] Furthermore, if the temperature of the etching object is 500°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 silicon nitride to the etching rate of an etching-resistant material described below, is likely to be 10 or more. The upper limit of the temperature of the etching object is preferably 500°C or less, more preferably 450°C or less, and even more preferably 350°C or less.

[0031] [Etching Object] The etching object to be etched by the silicon nitride etching method of this embodiment contains silicon nitride. That is, the etching object may be a member made only of silicon nitride, a member having a portion made only of silicon nitride and a portion made of another material, or a member made of a mixture of silicon nitride and another material.

[0032] Silicon nitride refers to a compound containing substantially only silicon and nitrogen in any proportion, and examples thereof include 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 entire object to be etched and the shape of the portion of the object to be etched that is made only of silicon nitride are not particularly limited, and may be, for example, a foil, film, powder, or block.

[0033] When the etching object is a component having a portion made only of silicon nitride and a portion made of another material, or when the component is a component made of a mixture of silicon nitride and another material, the other material may be an etching-resistant material that suppresses etching of the silicon nitride by the etching gas. That is, when the etching object contains silicon nitride and an etching-resistant material that suppresses etching of the silicon nitride by the etching gas, the etching-resistant material is used as a mask, and the silicon nitride of the etching object is selectively etched by the etching gas.

[0034] The etching-resistant material is not particularly limited as long as it is a material that does not substantially react with halogen fluorides or reacts extremely slowly with halogen fluorides and can suppress etching of silicon nitride by etching gas, but examples thereof include silicon dioxide, photoresist, amorphous carbon, metals such as nickel and cobalt, and oxides and nitrides of these metals. Among these, silicon dioxide, photoresist, and amorphous carbon are more preferred from the viewpoints of ease of handling and availability.

[0035] 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.

[0036] Next, an example of the configuration of an etching apparatus and an example of a method for etching silicon nitride using the etching apparatus will be described with reference to Figure 1. The etching apparatus in Figure 1 is a plasmaless etching apparatus that does not use plasma. First, the etching apparatus in Figure 1 will be described.

[0037] The etching apparatus of FIG. 1 includes a chamber 10 in which etching is performed, a stage 11 that supports an etching object 12 to be etched inside the chamber 10, a thermometer 14 that measures the temperature of the etching object 12, an exhaust pipe 13 that exhausts gas from inside the chamber 10, a vacuum pump 15 that is connected to the exhaust pipe 13 and reduces the pressure inside the chamber 10, and a pressure gauge 16 that measures the pressure inside the chamber 10.

[0038] 1 also includes an etching gas supply unit that supplies an etching gas into the chamber 10. This etching gas supply unit includes a halogen fluoride gas supply unit 1 that supplies a halogen fluoride gas, an inert gas supply unit 2 that supplies an inert gas, a halogen fluoride gas supply pipe 5 that connects the halogen fluoride gas supply unit 1 and the chamber 10, and an inert gas supply pipe 6 that connects the inert gas supply unit 2 to an intermediate portion of the halogen fluoride gas supply pipe 5.

[0039] Furthermore, a pressure gauge 7 for measuring the pressure of the halogen fluoride gas and a halogen fluoride gas flow rate control device 3 for controlling the flow rate of the halogen fluoride gas are provided in the halogen fluoride gas supply pipe 5. Furthermore, an inert gas pressure control device 8 for controlling the pressure of the inert gas and an inert gas flow rate control device 4 for controlling the flow rate of the inert gas are provided in the inert gas supply pipe 6.

[0040] When halogen fluoride gas is supplied to the chamber 10 as an etching gas, the halogen fluoride gas is sent from the halogen fluoride gas supply unit 1 to the halogen fluoride gas supply pipe 5, and the halogen fluoride gas is supplied to the chamber 10 via the halogen fluoride gas supply pipe 5.

[0041] Furthermore, when a mixed gas of halogen fluoride gas and inert gas is supplied as the etching gas, halogen fluoride gas is fed from the halogen fluoride gas supply unit 1 to the halogen fluoride gas supply pipe 5, and inert gas is fed from the inert gas supply unit 2 to the halogen fluoride gas supply pipe 5 via the inert gas supply pipe 6. As a result, the halogen fluoride gas and the inert gas are mixed in the middle of the halogen fluoride gas supply pipe 5 to form a mixed gas, and this mixed gas is supplied to the chamber 10 via the halogen fluoride gas supply pipe 5.

[0042] The configurations of the halogen fluoride gas supply unit 1 and the inert gas supply unit 2 are not particularly limited, and may be, for example, a bomb or a cylinder. Furthermore, the halogen fluoride gas flow rate control device 3 and the inert gas flow rate control device 4 may be, for example, a mass flow controller or a flow meter.

[0043] When the etching gas is supplied to the chamber 10, it is preferable to supply the etching gas while maintaining the supply pressure of the etching gas (i.e., the value of the pressure gauge 7 in FIG. 1) at a predetermined value. That is, the supply pressure of the etching gas is preferably 1 kPa or more and 1.0 MPa or less, more preferably 10 kPa or more and 0.5 MPa or less, and even more preferably 30 kPa or more and 0.3 MPa 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 (e.g., the various devices and the piping) is small.

[0044] Furthermore, the pressure of the etching gas supplied into the chamber 10 must be 1 Pa or more and 80 kPa or less, and preferably 5 Pa or more and 50 kPa or less, from the viewpoint of uniformly etching the surface of the etching object 12. 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.

[0045] 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.

[0046] 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 1.0 MPa or less, more preferably 0.5 MPa or less, and even more preferably 0.3 MPa or less. If the differential pressure is within the above range, the etching gas is likely to be smoothly supplied to the chamber 10.

[0047] 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 10°C or higher and 150°C or lower. The temperature of the etching target 12 during etching is preferably 155°C or higher and 500°C or lower. Within this temperature range, etching of silicon nitride proceeds smoothly, the load on the etching apparatus is small, and the life of the etching apparatus is likely to be extended.

[0048] The etching treatment time (hereinafter sometimes referred to as "etching time") can be set arbitrarily depending on the degree to which silicon nitride 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 30 minutes. Note that the etching treatment time refers to the time from when the etching gas is introduced into the chamber 10 until the etching gas inside the chamber 10 is exhausted to complete the etching.

[0049] The silicon nitride etching method of this embodiment can be performed using a typical plasmaless etching apparatus used in semiconductor device manufacturing processes, such as the etching apparatus shown in Figure 1, and the configuration of the etching apparatus that can be used is not particularly limited. For example, the positional relationship between the halogen fluoride gas supply pipe 5 and the etching target 12 is not particularly limited as long as it allows the etching gas to contact the etching target 12. Furthermore, as for the configuration of the temperature adjustment mechanism of the chamber 10, it is sufficient to be able to adjust the temperature of the etching target 12 to a desired temperature, so 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.

[0050] The material of the etching apparatus shown in FIG. 1 is not particularly limited as long as it is corrosion-resistant to the halogen fluoride used and can be decompressed to a predetermined pressure. For example, metals such as nickel, nickel-based alloys, aluminum, stainless steel, and platinum, ceramics such as alumina, and fluororesins can be used for the parts that come into contact with the etching gas. Specific examples of nickel-based alloys include Inconel (registered trademark), Hastelloy (registered trademark), and Monel (registered trademark). Examples of fluororesins include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyvinylidene fluoride (PVDF), Teflon (registered trademark), Viton (registered trademark), and Kalrez (registered trademark).

[0051] The present invention will be described in more detail below with reference to examples and comparative examples. Example 1 An etching apparatus having a configuration substantially similar to that of the etching apparatus shown in Figure 1 was used to etch an object to be etched. This object to be etched was a square silicon substrate with sides of 2 inches and a silicon nitride film with a thickness of 1014 nm formed on it, and was manufactured by KST World Corporation.

[0052] The object to be etched was placed on a stage inside the chamber of the etching apparatus, and the temperature of the stage was raised to 155°C. Next, bromine pentafluoride gas at a flow rate of 50 mL / min was mixed with argon at a flow rate of 450 mL / min to form a mixed gas, which was used as an etching gas. This etching gas was then supplied into the chamber at a flow rate of 500 mL / min and allowed to flow for 10 minutes to perform etching. The pressure inside the chamber during the flow of the etching gas was 10 kPa, and the partial pressure of the bromine pentafluoride gas was 1 kPa. When the flow of the etching gas was completed, the heating of the stage was stopped, and the inside of the chamber was replaced with argon.

[0053] The hydrogen fluoride content in the etching gas was measured by infrared spectroscopy and found to be less than 30 ppm by volume. The measurement conditions were as follows: Measurement equipment: Nicolet iS5 (manufactured by Thermo Scientific), Measurement temperature: 60°C, Measurement pressure: 0.01 MPa, Window material: calcium fluoride, Number of integrations: 8, Measurement wavelength range: 1200-4000 cm -1 Peak wavelength used to measure hydrogen fluoride content: 3877 cm -1

[0054] The chamber was opened, the object to be etched was removed, and the thickness of the silicon nitride film was measured. The thickness of the silicon nitride film was measured using an F20 film thickness measurement system manufactured by Filmetrics Inc. The film thickness measurement conditions were as follows: Measurement pressure: atmospheric pressure (101.3 kPa) Measurement temperature: 28°C Measurement atmosphere: air Measurement wavelength range for silicon dioxide: 200 to 1000 nm Measurement wavelength range for silicon nitride: 900 to 1700 nm

[0055] The etching rate of silicon nitride was calculated by substituting the film thickness measurement results into the following formula. The results are shown in Table 1. Etching rate (nm / min) = {film thickness of silicon nitride film before etching (nm) - film thickness of silicon nitride film after etching (nm)} / etching time (min).

[0056]

[0057] Example 2 The etching target was etched in the same manner as in Example 1, except that the stage temperature was set to 220°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1. Example 3 The etching target was etched in the same manner as in Example 1, except that the stage temperature was set to 300°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1. Example 4 The etching target was etched in the same manner as in Example 1, except that the stage temperature was set to 500°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1.

[0058] Example 5 An object to be etched was etched in the same manner as in Example 1, except that no inert gas was mixed into the etching gas, and the etching gas consisted solely of bromine pentafluoride gas, and the stage temperature was set to 300°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1. Example 6 An object to be etched was etched in the same manner as in Example 1, except that nitrogen gas was used as the inert gas, and the stage temperature was set to 300°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1.

[0059] Example 7 The etching target was etched in the same manner as in Example 1, except that a mixed gas of nitrogen gas and argon was used as the inert gas and the stage temperature was set to 300°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1. The mixing ratio of nitrogen gas to argon was 50% by volume:50% by volume. Example 8 The etching target was etched in the same manner as in Example 1, except that the pressure inside the chamber was set to 50 kPa and the stage temperature was set to 300°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1.

[0060] Example 9 The etching target was etched in the same manner as in Example 1, except that the pressure inside the chamber was set to 0.5 kPa and the stage temperature was set to 300°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1. Example 10 The etching target was etched in the same manner as in Example 1, except that the halogen fluoride was changed to iodine heptafluoride and the stage temperature was set to 300°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1.

[0061] Example 11 The etching target was etched in the same manner as in Example 1, except that the flow rate of the bromine pentafluoride gas was 30 mL / min, the flow rate of the argon gas was 970 mL / min, and the stage temperature was 300°C, and the etching rate of silicon nitride was calculated. The results are shown in Table 1. Example 12 The etching target was etched in the same manner as in Example 1, except that the stage temperature was 100°C and the etching time was 100 minutes, and the etching rate of silicon nitride was calculated. The results are shown in Table 1.

[0062] Comparative Example 1 The etching object was etched in the same manner as in Example 1, except that the etching object was a square silicon substrate with sides of 2 inches and a silicon dioxide film with a thickness of 142 nm formed thereon, the stage temperature was set to 300°C, and the etching time was set to 100 minutes. The etching rate of the silicon dioxide was calculated by substituting the film thickness measurement results into an equation similar to the above equation. The results are shown in Table 1. The etching object was manufactured by KST World Co., Ltd. Comparative Example 2 The etching object was etched in the same manner as in Comparative Example 1, except that the stage temperature was set to 500°C, and the etching rate of the silicon dioxide was calculated. The results are shown in Table 1.

[0063] Comparative Example 3 The etching target was a square silicon substrate with sides of 2 inches coated with photoresist (TSCR (registered trademark) manufactured by Tokyo Ohka Kogyo Co., Ltd.), exposed to light, and cured to form a photoresist film with a film thickness of 130 nm. The etching target was etched in the same manner as in Example 1, except that the stage temperature was set to 300° C., and the etching rate of the photoresist was calculated. The results are shown in Table 1.

[0064] Comparative Example 4 The etching target was a square silicon substrate with sides of 2 inches coated with amorphous carbon (manufactured by Merck) to form an amorphous carbon film with a thickness of 150 nm, and the etching rate of the amorphous carbon was calculated in the same manner as in Example 1, except that the stage temperature was set to 300° C.

[0065] Example 13 The etching targets used in Example 1 and Comparative Example 1 were both used as etching targets, and the etching was carried out in the same manner as in Example 1, except that the two etching targets were placed side by side on a stage in a chamber and the stage temperature was set to 300°C, and the etching rates and etching selectivity ratios of silicon nitride and silicon dioxide were calculated. The etching selectivity ratio is (etching rate of silicon nitride) / (etching rate of silicon dioxide). The results are shown in Table 2.

[0066] Example 14 The etching target was etched in the same manner as in Example 13, except that the etching gas contained 1000 ppm by volume of hydrogen fluoride (i.e., a mixed gas obtained by mixing bromine pentafluoride gas at a flow rate of 50 mL / min with argon at a flow rate of 450 mL / min and further adding 1000 ppm by volume of hydrogen fluoride was used as the etching gas), and the etching rates of silicon nitride and silicon dioxide were calculated. The results are shown in Table 2.

[0067] Comparative Example 5 The etching target was etched in the same manner as in Example 13, except that the pressure inside the chamber was set to 100 kPa, and the etching rates of silicon nitride and silicon dioxide were calculated. The results are shown in Table 2.

[0068]

[0069] The results of Examples 1 to 4 show that the etching rate of silicon nitride increases as the stage temperature increases. The results of Example 5 show that the etching rate of silicon nitride is faster when no inert gas is added than when an inert gas is added. This is thought to be because the partial pressure of the halogen fluoride inside the chamber increases, increasing the frequency of contact between the surface of the silicon nitride film and the halogen fluoride, and causing etching to proceed more quickly.

[0070] The results of Examples 6 and 7 show that the results obtained when using nitrogen gas or a mixture of nitrogen gas and argon as the inert gas are equivalent to those obtained when using argon alone as the inert gas. These results suggest that the type of inert gas has almost no effect on etching performance. Furthermore, the results of Example 11 show that the etching rate decreases when the proportion of inert gas in the etching gas is high.

[0071] The results of Examples 8 and 9 show that the etching rate of silicon nitride increases as the pressure inside the chamber increases, whereas the etching rate of silicon nitride decreases as the pressure inside the chamber decreases. These results suggest that the etching rate increases when the partial pressure of halogen fluoride inside the chamber is high, and decreases when the partial pressure is low.

[0072] The results of Example 10 show that etching of silicon nitride is possible even when etching is performed using an etching gas containing iodine heptafluoride. The results of Comparative Examples 1 to 4 show that the etching rates of silicon dioxide, photoresist, and amorphous carbon are extremely slow even when etching is performed using an etching gas containing bromine pentafluoride.

[0073] The results of Example 12 show that, at temperatures below 100°C, when etching is performed using an etching gas containing bromine pentafluoride, the etching rate of silicon nitride is slow, but etching is possible. The results of Example 13 show that silicon nitride is selectively etched without any problems even when silicon nitride and silicon dioxide coexist in the same chamber. The results of Example 14 show that when the hydrogen fluoride content in the etching gas is 1000 volume ppm, the etching selectivity between silicon nitride and silicon dioxide decreases, but etching is possible. The results of Comparative Example 5 show that when the pressure inside the chamber exceeds 80 kPa, the etching selectivity between silicon nitride and silicon dioxide decreases significantly.

[0074] Example 15 The etching object used in Example 15 will be described with reference to Fig. 2. The etching object in Fig. 2 has a structure in which five 100 nm-thick silicon nitride films 32 and five 100 nm-thick silicon dioxide films 33 are alternately stacked on a silicon substrate 31. Furthermore, the etching object in Fig. 2 has a through-hole 34 with a diameter of 100 nm that penetrates the five silicon nitride films 32 and the five silicon dioxide films 33 in the stacking direction.

[0075] This etching object 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 temperature of the stage was raised to 300°C. Next, bromine pentafluoride gas at a flow rate of 10 mL / min was mixed with argon at a flow rate of 90 mL / min to form a mixed gas, which was used as an etching gas. This etching gas was then supplied into the chamber and circulated for 10 minutes to perform etching. The pressure inside the chamber during the flow of the etching gas was 10 kPa, and the partial pressure of the bromine pentafluoride gas was 1 kPa. When the flow of the etching gas was completed, the heating of the stage was stopped, and the inside of the chamber was replaced with argon.

[0076] The chamber was opened and the object to be etched was removed. In the etched object, 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 dioxide film 33, so that part of the inner surface of the through-hole 34 expanded radially outward. The portion of the silicon dioxide film 33 exposed to the inner surface of the through-hole 34 was not etched, so a structure was formed in which the end of the silicon dioxide film 33 protruded into the through-hole 34.

[0077] The removed etching object was cut, and the cross section of the five-layer silicon nitride film 32 was analyzed using a scanning electron microscope. More specifically, for each of the five 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 silicon dioxide film 33 exposed to the inner surface of the through hole 34 was measured. That is, the inner surface of the through hole 34 expands radially outward due to etching, increasing the radius of the through hole 34, and the difference in this radius was measured. This was then divided by the etching time to calculate the relative etching rate of silicon nitride to silicon dioxide.

[0078] The average value and standard deviation of the etching rates of the five silicon nitride films 32 were then calculated to evaluate the uniformity of the relative etching rates, that is, whether the relative etching rates in the in-plane direction of the silicon nitride films 32 (directions parallel to the surfaces of the silicon nitride films 32) vary depending on the position in the stacking direction of the silicon nitride films 32. The results are shown in Table 3.

[0079]

[0080] (Examples 16 to 20) Etching of the etching target was carried out in the same manner as in Example 15, except that any one of the stage temperature, type of halogen fluoride, use or non-use of inert gas, pressure inside the chamber, partial pressure of halogen fluoride, and etching time was changed as shown in Table 3, and the average value and standard deviation of the etching rate of silicon nitride were calculated. The results are shown in Table 3.

[0081] The results of Examples 15 to 20 show that the etching rate of silicon nitride increases by increasing the stage temperature or the partial pressure of the halogen fluoride. Furthermore, the ratio of the standard deviation of the etching rate to the average value of the silicon nitride etching rate is approximately 7 to 13%, which shows that etching of the five silicon nitride films 32 proceeds almost uniformly regardless of the position of the silicon nitride films 32 in the stacking direction.

[0082] By taking advantage of the characteristic that etching of the silicon nitride film proceeds almost uniformly regardless of the position in the stacking direction as described above, it is possible to form, for example, a structure in which the end of the silicon dioxide film protrudes into the through-hole. Such a structure is used as a structure for semiconductor devices such as 3D-NAND flash memories. In other words, the present invention has the technical significance of being applicable to the manufacture of semiconductor devices such as 3D-NAND flash memories.

[0083] DESCRIPTION OF SYMBOLS 1... Halogen fluoride gas supply unit 2... Inert gas supply unit 3... Halogen fluoride gas flow rate control device 4... Inert gas flow rate control device 5... Halogen fluoride gas supply pipe 6... Inert gas supply pipe 7, 16... Pressure gauge 10... Chamber 11... Stage 12... Etching object 13... Exhaust pipe 14... Thermometer 15... Vacuum pump 31... Silicon substrate 32... Silicon nitride film 33... Silicon dioxide film 34... Through hole

Claims

1. An etching method for silicon nitride, comprising an etching step of disposing an object to be etched containing silicon nitride in an etching gas containing a halogen fluoride which is a compound of bromine or iodine and fluorine, and etching the silicon nitride of the object to be etched without using plasma under a pressure of 1 Pa or more and 80 kPa or less.

2. The etching method for silicon nitride according to claim 1, wherein the content of hydrogen fluoride contained in the etching gas is less than 100 volume ppm.

3. The etching method for silicon nitride according to claim 1 or claim 2, wherein the temperature of the object to be etched is 155°C or more and 500°C or less.

4. The etching method for silicon nitride according to any one of claims 1 to 3, wherein the content of the halogen fluoride contained in the etching gas is 1 volume% or more.

5. The etching method for silicon nitride according to any one of claims 1 to 4, wherein the etching gas is a gas consisting only of the halogen fluoride or a mixed gas consisting of the halogen fluoride and an inert gas.

6. The etching method for silicon nitride according to claim 5, wherein the inert gas is at least one selected from nitrogen gas, helium, argon, neon, krypton, and xenon.

7. The etching method for silicon nitride according to any one of claims 1 to 6, wherein the halogen fluoride is at least one selected from bromine trifluoride, bromine pentafluoride, iodine pentafluoride, and iodine heptafluoride.

8. The etching method for silicon nitride according to any one of claims 1 to 7, wherein the object to be etched contains the silicon nitride and an etching-resistant material that suppresses the etching of the silicon nitride by the etching gas, and the silicon nitride in the object to be etched is selectively etched by the etching gas.

9. The etching method for silicon nitride according to claim 8, wherein the etching-resistant material contains at least one selected from silicon dioxide, photoresist, and amorphous carbon.

10. The etching method for silicon nitride according to claim 8 or claim 9, wherein the etching selectivity, which is the ratio of the etching rate of the silicon nitride to the etching rate of the etching-resistant material, is 10 or more.

11. A method for manufacturing a semiconductor device, comprising manufacturing a semiconductor device using the etching method for silicon nitride according to any one of claims 1 to 10.

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