Silicon nitride etching method and semiconductor device manufacturing method

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

[Technical field]

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

[0002] Etching is used for patterning and removing silicon nitride in the manufacturing process of semiconductors. For example, Patent Document 1 discloses a method for selectively etching silicon nitride with respect to silicon oxide using a plasma gas obtained by plasmatizing a dry etching agent containing 1,3,3,3-tetrafluoropropene. However, the etching method using plasma has a problem of being expensive. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 181723 [Patent Document 2] Japanese Patent Publication No. 6032033 [Patent Document 3] International Publication No. 2016 / 056300 Summary of the Invention [Problem to be solved by the invention]

[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). 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 silicon nitride is not etched by the plasmaless etching method disclosed in Patent Document 2. Moreover, the plasmaless etching method disclosed in Patent Document 3 is a method for selectively etching silicon oxide relative to silicon nitride, and does not disclose that silicon nitride is selectively etched. An object of the present invention is to provide a method for etching silicon nitride, which is capable of selectively etching silicon nitride without using plasma. [Means for solving the problem]

[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 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 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 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 in the etching gas is 1 volume % or more.

[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 the halogen fluoride alone, 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 selected from the group consisting of 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 inhibits 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 material selected from the group consisting of silicon dioxide, photoresist, and amorphous carbon.

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

[11] A method for producing a semiconductor element, comprising the steps of: producing a semiconductor element by using the method for etching silicon nitride according to any one of [1] to

[10] . Effect of the Invention

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

[0012] [Figure 1] FIG. 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. [Diagram 2] FIG. 1 is a diagram illustrating the etching objects used in Examples 15 to 20. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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. In addition, 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 the present embodiment includes an etching step in which an object to be etched containing silicon nitride (such as Si3N4) is placed in an etching gas containing a halogen fluoride, which is a compound of bromine or iodine and fluorine, and the silicon nitride of the object to be etched is etched without using plasma under a pressure of 1 Pa or more and 80 kPa or less.

[0015] Since silicon nitride can be selectively etched without using plasma, there is no need to use an expensive plasma generating device for etching. Therefore, etching of silicon nitride can be performed at low cost. In addition, since no plasma is used, corrosion of the components constituting the etching device and the piping connected to the etching device is unlikely 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 be etched into 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 the present embodiment as described above can be used for manufacturing semiconductor elements such as 3D-NAND flash memories. For example, by applying the silicon nitride etching method of the present embodiment to a laminate in which silicon dioxide films and silicon nitride films are alternately stacked, and through-holes extending along the stacking direction and penetrating the laminate (see FIG. 2), the silicon nitride film exposed on the inner surface of the through-hole is selectively and isotropically etched, so that a structure in which the end of the silicon dioxide film protrudes into the through-hole can be formed. The process of forming a structure having such a structure can be used as a structure of a semiconductor element, and is therefore used for manufacturing semiconductor elements 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. Therefore, the silicon nitride etching method of this embodiment is expected to contribute to further miniaturization and high integration of semiconductor elements.

[0019] Similarly, when the etching-resistant material described later is used as a structure of a semiconductor element, a material that does not substantially react with halogen fluorides or reacts very slowly with halogen fluorides is used as the etching-resistant material. Specifically, at least one material selected from silicon dioxide (SiO2), photoresist, and amorphous carbon can be used.

[0020] Furthermore, the silicon nitride etching method of this embodiment can also be used for cleaning, as described above. For example, after a process of forming a film made of a material containing silicon nitride on a substrate or a process of etching the film of the material containing silicon nitride formed on the 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 further detail below. [Etching gas] The etching gas is a gas containing a halogen fluoride, which is a compound of bromine or iodine and fluorine. The type of halogen fluoride is not particularly limited as long as it is a compound of bromine or iodine and fluorine, but at least one selected from bromine monofluoride (BrF), bromine trifluoride (BrF3), bromine pentafluoride (BrF5), iodine pentafluoride (IF5), and iodine heptafluoride (IF7) 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 viewpoint of ease of handling and availability.

[0022] The etching gas may be a gas consisting of halogen fluoride alone, or may be a mixed gas containing halogen fluoride and other gases. When the etching gas is a mixed gas containing halogen fluoride and other gases, the content of 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 consisting of a halogen fluoride and an inert gas. As the inert gas, at least one selected from nitrogen gas (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can be used. The content of the inert gas contained in the etching gas is not particularly limited, but can be more than 0 volume % and 99 volume % or less.

[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. If the hydrogen fluoride content is less than 100 ppm by volume, the etching selectivity, which is the ratio of the etching rate of silicon nitride to the etching rate of an etching-resistant material described later, tends to be high.

[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 in the chamber being 1 Pa to 80 kPa during the passage of the etching gas. The flow rate of the etching gas can be appropriately set so that the pressure in the chamber is kept constant, depending on the size of the chamber and the capacity of the exhaust equipment for reducing the pressure in the chamber.

[0027] [Temperature during etching] In the etching step of the silicon nitride etching method of the present 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 the object to be etched of 155° C. or more and 500° C. or less.

[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 is likely 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 members used in the etching, and being less likely to cause etching-resistant materials to be etched.

[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 has both an etching-resistant material and silicon nitride, the silicon nitride can be selectively etched without etching the etching-resistant material by using the silicon nitride etching method of this embodiment. Therefore, the silicon nitride etching method of this embodiment can be used in a method of processing silicon nitride into a predetermined shape by using a patterned etching-resistant material as a mask.

[0030] Furthermore, if the temperature of the object to be etched is 500° C. or lower, 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 later, is likely to be 10 or higher. The upper limit of the temperature of the object to be etched is preferably 500° C. or less, more preferably 450° C. or less, and even more preferably 350° C. or less.

[0031] [Object to be etched] The etching object to be etched by the silicon nitride etching method of the present embodiment contains silicon nitride. That is, the etching object may be a member made of only silicon nitride, a member having a portion made of only 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 that contains substantially only silicon and nitrogen in any ratio, and can be, for example, Si3N4. The purity of silicon nitride is not particularly limited, but is preferably 30 mass% or more, more preferably 60 mass% or more, and further preferably 90 mass% or more. The shape of the entire etching object and the shape of the part of the etching object that is made only of silicon nitride are not particularly limited, and may be, for example, a foil, a film, a powder, or a lump.

[0033] When the etching object is a member having a portion made of only silicon nitride and a portion made of another material, or when the etching object is a member 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 preferable 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 or an electron beam. Examples of photoresists 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 that is generally used in the semiconductor manufacturing process, and examples of the composition include a composition 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 Fig. 1. The etching apparatus in Fig. 1 is a plasmaless etching apparatus that does not use plasma. First, the etching apparatus in Fig. 1 will be described.

[0037] The etching apparatus of FIG. 1 comprises a chamber 10 in which etching is performed, a stage 11 that supports an object 12 to be etched inside the chamber 10, a thermometer 14 that measures the temperature of the object 12 to be etched, 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 to the inside of the chamber 10. The 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, the halogen fluoride gas supply pipe 5 is provided with 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. Furthermore, the inert gas supply pipe 6 is provided with 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.

[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 piping 5, so that the halogen fluoride gas is supplied to the chamber 10 via the halogen fluoride gas supply piping 5.

[0041] In addition, when a mixed gas of halogen fluoride gas and inert gas is supplied as the etching gas, halogen fluoride gas is sent from the halogen fluoride gas supply unit 1 to the halogen fluoride gas supply pipe 5, and inert gas is sent 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 become a mixed gas, and this mixed gas is supplied to the chamber 10 via the halogen fluoride gas supply pipe 5.

[0042] The configuration of the halogen fluoride gas supply unit 1 and the inert gas supply unit 2 is not particularly limited, and may be, for example, a gas cylinder, etc. Furthermore, as the halogen fluoride gas flow rate control device 3 and the inert gas flow rate control device 4, for example, a mass flow controller, a flow meter, etc. can be used.

[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 further 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 parts of the etching apparatus of FIG. 1 (e.g., the various devices and the piping) is small.

[0044] Moreover, 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 from 1 Pa to less than 10 kPa, and more preferably from 1 Pa to 2 kPa.

[0046] The differential pressure between the supply pressure of the etching gas and the pressure in 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 easily supplied to the chamber 10 smoothly.

[0047] It is preferable that the etching gas be supplied while maintaining the temperature of the etching gas at a predetermined value when it is supplied to the chamber 10. That is, the supply temperature of the etching gas is preferably 10° C. or more and 150° C. or less. The temperature of the etching object 12 during etching is preferably 155° C. to 500° C. Within this temperature range, etching of silicon nitride proceeds smoothly, the load on the etching device is small, and the life of the etching device is likely to be long.

[0048] The etching process 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 process time refers to the time from when the etching gas is introduced into the chamber 10 to when the etching gas inside the chamber 10 is exhausted to finish the etching.

[0049] The silicon nitride etching method of the present embodiment can be performed using a general plasmaless etching apparatus used in the semiconductor device manufacturing process, such as the etching apparatus shown in FIG. 1, and the configuration of the usable etching apparatus is not particularly limited. For example, the positional relationship between the halogen fluoride gas supply pipe 5 and the etching object 12 is not particularly limited as long as the etching gas can be brought into contact with the etching object 12. In addition, as for the configuration of the temperature control mechanism of the chamber 10, since it is only necessary to adjust the temperature of the etching object 12 to an arbitrary temperature, the temperature control mechanism may be directly provided on the stage 11, or the chamber 10 may be heated or cooled from outside the chamber 10 by an external temperature controller.

[0050] The material of the etching apparatus in FIG. 1 is not particularly limited as long as it has corrosion resistance against 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). EXAMPLES

[0051] The present invention will be described in more detail below with reference to examples and comparative examples. Example 1 The etching object was etched using an etching apparatus having a configuration similar to that of the etching apparatus in Figure 1. The etching object 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 device, 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 prepare a mixed gas, which was used as an etching gas. Then, this etching gas was supplied into the chamber at a flow rate of 500 mL / min 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.

[0053] The hydrogen fluoride content in the etching gas was measured by infrared spectroscopy and found to be less than 30 ppm by volume under the following measurement conditions: Measurement equipment: Nicolet iS5 (manufactured by Thermo Scientific) Measurement temperature: 60℃ Measurement pressure: 0.01MPa Window material: Calcium fluoride Number of times: 8 Measurement wavelength range: 1200-4000cm -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 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℃ Measurement atmosphere: Air Silicon dioxide measurement wavelength range: 200-1000nm Silicon nitride measurement wavelength range: 900-1700nm

[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) = {thickness of silicon nitride film before etching (nm) - thickness of silicon nitride film after etching (nm)} / etching time (min)

[0056] [Table 1]

[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 The etching target was etched in the same manner as in Example 1, except that the etching gas was composed only of bromine pentafluoride gas without mixing an inert gas into the etching 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 The etching target 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 mixture ratio of nitrogen gas and 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 changed 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 of the etching object was carried out in the same manner as in Example 1, except that the etching object was a 142 nm-thick silicon dioxide film formed on a 2-inch square silicon substrate, the stage temperature was 300° C., and the etching time was 100 minutes, and the etching rate of silicon dioxide was calculated by substituting the measurement results of the film thickness into an equation similar to the above equation. The results are shown in Table 1. The etching object was manufactured by KST World Corporation. Comparative Example 2 The etching target 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 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 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 was carried out in the same manner as in Example 1, except that the stage temperature was set to 300° C., and the etching rate of the amorphous carbon was calculated. The results are shown in Table 1.

[0065] (Example 13) The etching targets used in Example 1 and Comparative Example 1 were both used as etching targets, and the etching was performed 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 temperature of the stage 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 object was etched in the same manner as in Example 13, except that the etching gas contained 1000 ppm by volume of hydrogen fluoride (that is, the mixed gas was prepared 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 containing 1000 ppm by volume of hydrogen fluoride, to prepare 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 rate of silicon nitride and silicon dioxide was calculated by the same method as in Example 13, except that the pressure inside the chamber was set to 100 kPa. The results are shown in Table 2.

[0068] [Table 2]

[0069] From the results of Examples 1 to 4, it is clear that the etching rate of silicon nitride increases as the stage temperature increases. From the results of Example 5, it can be seen that the etching rate of silicon nitride is faster when no inert gas is added than when an inert gas is added. The reason for this is considered to be that the partial pressure of the halogen fluoride inside the chamber increases, which increases the frequency of contact between the surface of the silicon nitride film and the halogen fluoride, and the etching proceeds more quickly.

[0070] From the results of Examples 6 and 7, it can be seen that the results are the same when nitrogen gas or a mixture of nitrogen gas and argon is used as the inert gas as when only argon is used as the inert gas. This result suggests that the type of inert gas has almost no effect on the etching performance. Moreover, from the results of Example 11, it can be seen that the etching rate decreases when the ratio of the inert gas in the etching gas is high.

[0071] From the results of Examples 8 and 9, it can be seen 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. This result suggests that the etching rate increases when the partial pressure of the halogen fluoride in 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. From the results of Comparative Examples 1 to 4, it is clear that even when etching is performed using an etching gas containing bromine pentafluoride, the etching rates of silicon dioxide, photoresist, and amorphous carbon are extremely slow.

[0073] From the results of Example 12, it is clear that when etching is performed using an etching gas containing bromine pentafluoride at a temperature of 100° C. or less, etching of silicon nitride is possible, although the etching rate is slow. The results of Example 13 show that even if silicon nitride and silicon dioxide coexist in the same chamber, silicon nitride is selectively etched without any problems. From the results of Example 14, it is clear that when the content of hydrogen fluoride in the etching gas reaches 1000 ppm by volume, the etching selectivity ratio between silicon nitride and silicon dioxide decreases, but etching is still possible. From the results of Comparative Example 5, it can be seen that when the pressure inside the chamber exceeds 80 kPa, the etching selectivity ratio between silicon nitride and silicon dioxide is significantly reduced.

[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 layers of silicon nitride films 32 each having a thickness of 100 nm and five layers of silicon dioxide films 33 each having a thickness of 100 nm are alternately laminated on a silicon substrate 31. Furthermore, the etching object in Fig. 2 has a through hole 34 having a diameter of 100 nm that penetrates the five layers of silicon nitride films 32 and the five layers of silicon dioxide films 33 in the lamination direction.

[0075] The object to be etched was placed on a stage of an etching apparatus having a configuration substantially similar to that of the etching apparatus of 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 prepare a mixed gas, which was used as an etching gas. Then, this etching gas was 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 preferentially etched compared to the silicon dioxide film 33, so that a 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 by a scanning electron microscope. More specifically, for each of the five silicon nitride films 32, the radial distance between the part of the silicon nitride film 32 exposed to the inner surface of the through hole 34 and the part 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 spreads outward in the radial direction due to etching, and the radius of the through hole 34 increases, and the difference in the radius was measured. Then, the relative etching rate of silicon nitride to silicon dioxide was calculated by dividing the difference by the etching time.

[0078] Then, the average value and standard deviation of the etching rates of the five silicon nitride films 32 were calculated to evaluate the uniformity of the relative etching rates, that is, whether or not the relative etching rates in the in-plane direction of the silicon nitride film 32 (the direction parallel to the surface of the silicon nitride film 32) change depending on the position in the stacking direction of the silicon nitride film 32. The results are shown in Table 3.

[0079] [Table 3]

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

[0081] From the results of Examples 15 to 20, it is found that the etching rate of silicon nitride increases by increasing the stage temperature or the partial pressure of halogen fluoride. In addition, since the ratio of the standard deviation of the etching rate to the average value of the etching rate of silicon nitride is about 7 to 13%, it is found that the 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 utilizing the characteristic that etching of the silicon nitride film proceeds almost uniformly regardless of the position in the stacking direction as described above, for example, a structure in which the end of the silicon dioxide film protrudes into the through hole can be formed. Such a structure is used as a structure of a semiconductor device such as a 3D-NAND flash memory. In other words, the present invention has the technical significance of being applicable to the manufacture of semiconductor devices such as a 3D-NAND flash memory. [Explanation of symbols]

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

Claims

1. The method comprises an etching step of disposing an etching object containing silicon nitride in an etching gas containing a halogen fluoride, which is a compound of bromine or iodine and fluorine, inside a chamber, 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; The method for etching silicon nitride, wherein the etching gas is supplied into the chamber while maintaining a temperature of the etching gas in the range of 10° C. to 150° C.

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

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

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

5. 5. The method for etching silicon nitride according to claim 1, wherein the etching gas is a gas consisting of the halogen fluoride alone, or a mixed gas consisting of the halogen fluoride and an inert gas.

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

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

8. 8. The method for etching silicon nitride according to claim 1, wherein the object to be etched contains the silicon nitride and an etching resistant material that inhibits 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.

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

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

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

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