Etching method and semiconductor device manufacturing method

Abstract

Provided is an etching method by which an etching object containing silicon nitride can be selectively etched compared to a non-etching object, while suppressing the generation of particles and variations in etching rate. This etching method comprises an etching step in which an etching gas containing more than 20 vol% of nitrosyl fluoride is brought into contact with a member (12) to be etched, which has an etching object that is to be etched by the etching gas and a non-etching object that is not to be etched by the etching gas, and without using plasma, the etching object is selectively etched in comparison to the non-etching object. The etching object contains silicon nitride.

Description

Technical Field

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

Background Art

[0002] Nitrosyl fluoride (NOF) can be used as an etching gas for etching a silicon material in a semiconductor manufacturing process. For example, Patent Document 1 discloses a method of selectively etching silicon nitride compared to silicon oxide using an etching gas containing nitrosyl fluoride and having a concentration thereof of 0.1 to 20% by volume. Here, silicon nitride is an object to be etched that is the object of etching by the etching gas, and silicon oxide is a non-etching object that is not the object of etching by the etching gas.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When etching is performed using an etching gas having a low concentration of nitrosyl fluoride, in order to increase the ratio of the etching rate of silicon nitride to the etching rate of silicon oxide, that is, the etching selectivity, it is necessary to perform the etching at a high temperature. However, as the etching temperature becomes higher, it becomes difficult to keep the temperature of the etching member having the object to be etched and the non-etching object and the temperature of the etching gas uniform during etching, so there is a possibility that the etching rate of the object to be etched may vary.

[0005] In addition, high etching temperatures could lead to particle generation due to wear and tear of components in the etching apparatus or excessive etching of the material being etched. If these particles adhere to the material being etched, it could cause structural collapse or short circuits in the material, potentially reducing the production yield of semiconductor devices. The present invention aims to provide an etching method that can selectively etch an etchable object containing silicon nitride compared to a non-etchable object, while suppressing particle generation and variations in etching rate, and a method for manufacturing a semiconductor device. [Means for solving the problem]

[0006] To solve the aforementioned problems, one aspect of the present invention is as follows [1] to [7]. [1] An etching method comprising an etching step of bringing an etching gas containing more than 20 volume% of nitrosyl fluoride into contact with a member to be etched, which has an object to be etched by the etching gas and a non-etchable object that is not to be etched by the etching gas, and selectively etching the object to be etched compared to the non-etchable object without using plasma, wherein the object to be etched contains silicon nitride.

[0007] [2] The etching method according to [1], wherein the etching gas contains 30 volume% or more of nitrosyl fluoride. [3] The etching method according to [1] or [2], wherein the etching gas is a gas consisting solely of nitrosyl fluoride, or a mixed gas containing nitrosyl fluoride and a diluent gas. [4] The etching method according to any one of [1] to [3], wherein the non-etching object is at least one of silicon oxide and amorphous carbon.

[0008] [5] The etching method according to [4], wherein the temperature conditions of the etching process are 50°C or higher and 250°C or lower. [6] The etching method according to any one of the items [1] to [5], wherein the etching selectivity ratio, which is the ratio of the etching rate of the object to be etched to the etching rate of the non-etching object, is 10 or more.

[0009] A method for manufacturing a semiconductor device using an etching method described in any one of the items [7] [1] to [6], The member to be etched is a semiconductor substrate having the object to be etched and the object not to be etched, A method for manufacturing a semiconductor device, comprising a processing step of removing at least a portion of the object to be etched from the semiconductor substrate by etching. [Effects of the Invention]

[0010] According to the present invention, it is possible to selectively etch objects containing silicon nitride compared to non-etchable objects while suppressing particle generation and variations in etching rate. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of an example of an etching apparatus illustrating one embodiment of the etching method according to the present invention. [Figure 2] This diagram illustrates the etched members used in the examples and comparative examples. [Modes for carrying out the invention]

[0012] One embodiment of the present invention is described below. This embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications or improvements can be made to this embodiment, and such modified or improved forms may also be included in the present invention.

[0013] The etching method according to this embodiment comprises an etching step in which an etching gas containing more than 20 volume% of nitrosyl fluoride is brought into contact with a member to be etched, which has both an object to be etched by the etching gas and a non-etchable object that is not to be etched by the etching gas, and selectively etches the object to be etched compared to the non-etchable object without using plasma. In the etching method according to this embodiment, the object to be etched contains silicon nitride (SiN).

[0014] When an etching gas is brought into contact with the material to be etched, the silicon nitride-containing material to be etched reacts with the nitrosyl fluoride in the etching gas, causing the etching of the material to proceed. In contrast, non-etchable materials such as resists and masks hardly react with nitrosyl fluoride, so etching of non-etchable materials hardly progresses. Therefore, according to the etching method of this embodiment, the material to be etched can be selectively etched compared to non-etchable materials (i.e., high etching selectivity can be obtained). For example, the etching selectivity ratio, which is the ratio of the etching rate of the material to be etched to the etching rate of the non-etched material, can be set to 10 or more. Preferably, the etching selectivity ratio is 30 or more, and more preferably 50 or more.

[0015] Furthermore, according to the etching method of this embodiment, etching targets containing silicon nitride can be etched at a high etching rate. Furthermore, according to the etching method of this embodiment, the object to be etched can be etched without using plasma, eliminating the need to perform etching using expensive plasma generators. Therefore, etching of the component to be etched can be performed at a low cost.

[0016] Furthermore, according to the etching method of the present embodiment, since etching is performed using an etching gas containing more than 20% by volume of nitrosyl fluoride, the etching selectivity can be increased without setting the etching temperature to a high temperature. Since etching can be performed at a low temperature, it becomes easy to keep the temperature of the etched member and the temperature of the etching gas uniform during etching, and variations in the etching rate of the object to be etched are unlikely to occur.

[0017] Furthermore, since etching can be performed at a low temperature, particles are unlikely to be generated during etching. When etching is performed at a high temperature, particles may be generated due to wear of the members constituting the etching apparatus or excessive etching of the etched member, etc. However, according to the etching method of the present embodiment, since etching can be performed at a low temperature, particles are unlikely to be generated. Therefore, when manufacturing a semiconductor element using the etching method of the present embodiment, the number of particles adhering to the etched member is small, so the production yield of the semiconductor element is high.

[0018] In the present invention, "particle" refers to a small piece having a major axis of 1 nm or more, and usually a small piece having a major axis of 300 nm or less. As long as this requirement is satisfied, there is no particular limitation on the shape of the particle, and it may be, for example, granular, foil-like, film-like,块状, etc. In addition, "etching" in the present invention means removing part or all of the object to be etched contained in the etched member to process the etched member into a predetermined shape (for example, a three-dimensional shape) (for example, processing a film-like object to be etched made of silicon nitride, which the etched member has, to a predetermined film thickness), and also means removing residues and deposits composed of the object to be etched from the etched member for cleaning.

[0019] The etching method according to the above-described 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 that manufactures a semiconductor device using the etching method according to the present embodiment, wherein the member to be etched is a semiconductor substrate having an object to be etched and an object not to be etched, and includes a processing step of removing at least a part of the object to be etched from the semiconductor substrate by etching.

[0020] The etching method according to the present embodiment can be used, for example, in the manufacture of semiconductor devices such as 3D-NAND type flash memories. For example, with respect to a structure in which a through hole extending along the stacking direction and penetrating the stacked layer is formed in a stacked layer formed by alternately stacking a silicon oxide film and a silicon nitride film (see FIG. 2), by applying the etching method according to the present embodiment, since the silicon nitride film exposed on the inner surface of the through hole is selectively and isotropically etched, a structure in which an end portion of the silicon oxide film protrudes into the through hole can be formed. A process for forming a structure having such a structure can be used as a structure of a semiconductor device, and thus is used in the manufacture of semiconductor devices such as 3D-NAND type flash memories.

[0021] The process for forming the above structure by etching has conventionally been performed using a chemical solution containing phosphoric acid or the like, but etching using an etching gas is superior in microfabrication performance to etching using a chemical solution. Therefore, the etching method according to the present embodiment can be expected to contribute to further miniaturization and high integration of semiconductor devices.

[0022] Furthermore, since etching can be performed at low temperatures in the etching method according to this embodiment, it can be used, for example, for the manufacture of semiconductor devices having heat-sensitive circuits. For example, complementary metal oxide semiconductors (CMOS) and the like are susceptible to circuit damage when exposed to high temperatures during etching, but by employing etching according to this embodiment, circuit damage due to heat is less likely to occur.

[0023] Furthermore, when the non-etching target itself is used as a structure for a semiconductor device, the non-etching target is a material that does not substantially react with nitrosyl fluoride or a material that reacts with nitrosyl fluoride very slowly. For example, silicon oxides consisting of silicon (Si) and oxygen (O) (a specific example being silicon dioxide (SiO2)) or amorphous carbon can be used.

[0024] Furthermore, as described above, the etching method according to this embodiment can also be used for cleaning. For example, after performing a process of forming a film made of a silicon nitride-containing material on a substrate, or a process of etching a film made of a silicon nitride-containing material formed on a substrate, 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 object to be etched, which is a constituent element of the present invention.

[0025] Here, we will explain "particles" and "adhered materials." Particles are small fragments mainly generated due to wear and tear of components constituting the etching equipment, and may also include fragments generated due to excessive etching of the material being etched. Therefore, the material of the particles is generated when materials used as components constituting the etching equipment or materials forming the material being etched react during etching. Specific examples include oxides of stainless steel, nickel (Ni), alumina (Al2O3), silicon, yttrium (Y), fluorides, oxyfluorides, and oxynitrides.

[0026] The deposits consist of particles and etching residues that adhere to the side walls of the patterns formed by etching and the inner surface of the chamber in various shapes, and include the aforementioned particles. Therefore, the material of the deposits may include compounds of at least one of nitrogen, oxygen, and fluorine with silicon, materials derived from amorphous carbon, and materials generated due to wear and tear of components constituting the etching apparatus, and may include the material of the aforementioned particles.

[0027] Specific examples of compounds of silicon with at least one of nitrogen, oxygen, and fluorine include silicon nitrides, oxides, oxynitrides, nitrogen fluorides, and oxyfluorides. Specific examples of materials derived from amorphous carbon include elemental amorphous carbon, fluorides, and trinitrides. Specific examples of materials generated due to wear and tear of components constituting the etching apparatus are similar to those for particles and include oxides, fluorides, oxyfluorides, and oxynitrides of stainless steel, nickel, alumina, silicon, yttrium, etc.

[0028] The etching method according to this embodiment will be described in more detail below. [Etching gas] The etching gas is a gas containing nitrosyl fluoride, but it may be a gas consisting only of nitrosyl fluoride, or a mixed gas containing nitrosyl fluoride and other gases. If the etching gas is a mixed gas containing nitrosyl fluoride and other gases, the nitrosyl fluoride content in the etching gas must exceed 20% by volume, but is preferably 30% to 90% by volume, and more preferably 30% to 70% by volume.

[0029] By performing etching with the nitrosyl fluoride content in the etching gas within the above range, materials containing silicon nitride can be selectively etched compared to materials that are not etched. For example, the etching selectivity ratio, which is the ratio of the etching rate of the material to the etching rate of the material that is not etched, can be set to 10 or higher.

[0030] Dilution gases can be used as other gases that make up the etching gas along with nitrosyl fluoride gas. That is, the etching gas can be a mixed gas containing nitrosyl fluoride and a dilution gas. As the diluent gas, an inert gas is preferred, specifically, at least one selected from nitrogen gas (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). The amount of diluent gas contained in the etching gas is not particularly limited, but it may be greater than 0 volume% and less than 80 volume%.

[0031] Furthermore, the content of fluorine gas (F2) and hydrogen fluoride (HF) contained in the etching gas is preferably 100 ppm by volume or less, more preferably 50 ppm by volume or less, and even more preferably 20 ppm by volume or less. When the content of fluorine gas and hydrogen fluoride is 100 ppm by volume or less, the etching selectivity ratio tends to be high.

[0032] [Pressure conditions for the etching process] The pressure conditions for the etching process in the etching method according to this embodiment are not particularly limited, but are preferably 0.1 Pa or more and 80 kPa or less, more preferably 100 Pa or more and 55 kPa or less, and even more preferably 1.3 kPa or more and 40 kPa or less.

[0033] For example, etching can be performed by placing the workpiece to be etched inside a chamber and circulating etching gas through the chamber. The pressure inside the chamber during the circulation of the etching gas can be set to between 0.1 Pa and 80 kPa. The flow rate of the etching gas should be appropriately set according to the size of the chamber and the capacity of the exhaust equipment that reduces the pressure inside the chamber, so as to maintain a constant pressure inside the chamber.

[0034] [Temperature conditions for the etching process] The temperature conditions for the etching process in the etching method according to this embodiment are not particularly limited, but are preferably 50°C to 250°C, more preferably 60°C to 200°C, and even more preferably 70°C to 180°C. If the temperature conditions are within the above range, advantages such as being able to perform etching without requiring excessive time and energy, and being able to suppress variations in etching rate can be easily obtained. Here, the temperature in the temperature conditions is the temperature of the material to be etched, but the temperature of the stage that supports the material to be etched, which is installed in the chamber of the etching apparatus, can also be used.

[0035] Nitrosyl fluoride hardly reacts with non-etchable materials such as silicon dioxide and amorphous carbon under conditions where plasma is not generated and the temperature is below 250°C. Therefore, when the member to be etched has both etchable and non-etchable materials, the etching method according to this embodiment can selectively etch the etchable material without etching the non-etchable material. Thus, the etching method according to this embodiment can be used for methods such as processing the etchable material into a predetermined shape using a patterned non-etchable material as a mask, or for removing the etchable material from a structure having both etchable and non-etchable materials.

[0036] Furthermore, etching selectivity tends to be higher when the temperature of both the etched and unetched objects is 250°C or lower. For example, the etching selectivity ratio, which is the ratio of the etching rate of the etched object to the etching rate of the unetched object, tends to be 10 or higher.

[0037] [Material to be etched] The member to be etched by the etching method according to this embodiment has both an etchable object and a non-etchable object. However, it may also be a member having a portion formed by the etchable object and a portion formed by the non-etchable object, or a member formed by a mixture of the etchable object and the non-etchable object (for example, a non-etchable object with particles of the etchable object attached). Furthermore, the member to be etched may also have components other than the etchable object and the non-etchable object. Furthermore, the shape of the material to be etched is not particularly limited and may be, for example, plate-shaped, foil-shaped, film-shaped, powder-shaped, or lump-shaped. An example of the material to be etched is the semiconductor substrate mentioned above.

[0038] [Object to be etched] The object to be etched contains silicon nitride, but may be made solely of silicon nitride, or may have a portion made solely of silicon nitride and a portion made of another material, or may be made of a mixture of silicon nitride and another material (for example, a material with silicon nitride particles attached to it).

[0039] Silicon nitride refers to a compound that is substantially composed only of silicon and nitrogen, and has silicon and nitrogen in any proportion; an example is Si3N4. The purity of silicon nitride is not particularly limited, but is preferably 30% by mass or more, more preferably 60% by mass or more, and even more preferably 90% by mass or more. Furthermore, the shape of the object to be etched is not particularly limited and may be, for example, plate-shaped, foil-shaped, film-shaped, powder-shaped, or lump-shaped.

[0040] [Non-etchable objects] Non-etchable materials either do not react substantially with nitrosyl fluoride, or react with nitrosyl fluoride very slowly, so even if etching is performed by the etching method according to this embodiment, etching hardly progresses. Non-etchable materials are not particularly limited as long as they have the above-mentioned properties, but examples include silicon dioxide and amorphous carbon. An example of silicon dioxide is silicon dioxide (SiO2).

[0041] The oxygen atom-to-silicon atom ratio (O / Si) of silicon oxide is not particularly limited as long as silicon oxide does not substantially react with nitrosyl fluoride, or its reaction with nitrosyl fluoride is slower than that of silicon nitride, but it is preferably 0.3 to 5, more preferably 0.5 to 4, even more preferably 1 to 3, and particularly preferably 1.2 to 2.5.

[0042] Since non-etchable objects are hardly etched by the etching method according to this embodiment, the etching of etchable objects by the etching gas can be suppressed by the non-etchable objects. Therefore, non-etchable objects can be used as a resist or mask to suppress the etching of etchable objects by the etching gas.

[0043] Therefore, the etching method according to this embodiment can be used to process an object to be etched into a predetermined shape by using a patterned non-etchable object as a resist or mask (for example, processing a film-like object to be etched on the component to be etched to a predetermined film thickness), and is therefore suitably used for the manufacture of semiconductor devices.

[0044] Furthermore, since the non-etched material is hardly etched, the etching of parts of the semiconductor device that should not be etched can be suppressed by the non-etched material, thus preventing the loss of semiconductor device properties due to etching.

[0045] Next, an example of the configuration of an etching apparatus capable of implementing the etching method according to this embodiment, and an example of an etching method using the etching apparatus, will be described with reference to Figure 1. The etching apparatus in Figure 1 is an etching apparatus capable of plasmaless etching without using plasma. First, the etching apparatus in Figure 1 will be described.

[0046] The etching apparatus shown in Figure 1 comprises a chamber 10 in which etching is performed, a stage 11 that supports the workpiece to be etched 12 inside the chamber 10, a thermometer 14 for measuring the temperature of the workpiece to be etched 12, an exhaust pipe 13 for discharging gas from inside the chamber 10, a vacuum pump 15 provided in the exhaust pipe 13 for reducing the pressure inside the chamber 10, and a pressure gauge 16 for measuring the pressure inside the chamber 10.

[0047] Furthermore, the etching apparatus shown in Figure 1 includes an etching gas supply unit that supplies etching gas into the chamber 10, and an analysis unit (not shown) that analyzes particles present inside the chamber 10. The etching gas supply unit includes a nitrosyl fluoride gas supply unit 1 that supplies nitrosyl fluoride gas, a dilution gas supply unit 2 that supplies dilution gas, a nitrosyl fluoride gas supply pipe 5 that connects the nitrosyl fluoride gas supply unit 1 and the chamber 10, and a dilution gas supply pipe 6 that connects the dilution gas supply unit 2 to the middle of the nitrosyl fluoride gas supply pipe 5.

[0048] Furthermore, the nitrosyl fluoride gas supply piping 5 is equipped with a nitrosyl fluoride gas pressure control device 7 for controlling the pressure of the nitrosyl fluoride gas and a nitrosyl fluoride gas flow rate control device 3 for controlling the flow rate of the nitrosyl fluoride gas. Furthermore, the dilution gas supply piping 6 is equipped with a dilution gas pressure control device 8 for controlling the pressure of the dilution gas and a dilution gas flow rate control device 4 for controlling the flow rate of the dilution gas.

[0049] Furthermore, when supplying nitrosyl fluoride gas to the chamber 10 as an etching gas, the nitrosyl fluoride gas is sent from the nitrosyl fluoride gas supply unit 1 to the nitrosyl fluoride gas supply pipe 5, thereby supplying the nitrosyl fluoride gas to the chamber 10 via the nitrosyl fluoride gas supply pipe 5.

[0050] Furthermore, when supplying a mixed gas of nitrosyl fluoride gas and a diluent gas such as an inert gas as the etching gas, nitrosyl fluoride gas is sent from the nitrosyl fluoride gas supply unit 1 to the nitrosyl fluoride gas supply pipe 5, and diluent gas is sent from the diluent gas supply unit 2 to the nitrosyl fluoride gas supply pipe 5 via the diluent gas supply pipe 6. As a result, the nitrosyl fluoride gas and the diluent gas are mixed in the middle of the nitrosyl fluoride gas supply pipe 5 to form a mixed gas, and this mixed gas is supplied to the chamber 10 via the nitrosyl fluoride gas supply pipe 5. However, the nitrosyl fluoride gas and the diluent gas may be supplied to the chamber 10 separately and mixed within the chamber 10.

[0051] The configuration of the nitrosyl fluoride gas supply unit 1 and the dilution gas supply unit 2 is not particularly limited and may be, for example, a cylinder or a gas cylinder. Furthermore, the nitrosyl fluoride gas flow rate control device 3 and the dilution gas flow rate control device 4 may be, for example, a mass flow controller or a flow meter.

[0052] When supplying etching gas to the chamber 10, it is preferable to maintain the etching gas supply pressure (i.e., the value of the nitrosyl fluoride gas pressure control device 7 in Figure 1) at a predetermined value. Specifically, the etching gas supply pressure is preferably 20 kPa or more and 1500 kPa or less, more preferably 40 kPa or more and 700 kPa or less, and even more preferably 60 kPa or more and 400 kPa or less. If the etching gas supply pressure is within the above range, the etching gas will be supplied to the chamber 10 smoothly, and the load on the components of the etching apparatus in Figure 1 (for example, the various devices and the piping) will be small.

[0053] Furthermore, the pressure of the etching gas supplied into the chamber 10 is preferably 0.1 Pa or more and 80 kPa or less, more preferably 100 Pa or more and 55 kPa or less, and even more preferably 1.3 kPa or more and 40 kPa or less. 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 tends to be high.

[0054] The pressure inside the chamber 10 before supplying the etching gas is not particularly limited as long as it is less than or equal to the etching gas supply pressure, or lower than the etching gas supply pressure, but it is preferably 0.1 Pa or more and less than 40 kPa, and more preferably 10 Pa or more and 20 kPa or less.

[0055] The difference between the etching gas supply pressure and the pressure inside the chamber 10 before the etching gas is supplied is preferably 1.5 MPa or less, more preferably 0.6 MPa or less, and even more preferably 0.4 MPa or less. If the difference is within the above range, the etching gas can be supplied to the chamber 10 smoothly.

[0056] When supplying etching gas to the chamber 10, it is preferable to supply the etching gas while maintaining its temperature at a predetermined value. That is, the supply temperature of the etching gas is preferably between 0°C and 250°C. When etching is performed, the temperature of the component to be etched 12 is preferably 250°C or lower. Within this temperature range, the etching of the material to be etched on the component to be etched 12 proceeds smoothly, the load on the etching apparatus is small, and the lifespan of the etching apparatus tends to be extended.

[0057] The etching process time (hereinafter sometimes referred to as "etching time") can be arbitrarily set depending on how much etching is desired on the material to be etched on the component to be etched 12. However, considering the production efficiency of the semiconductor device manufacturing process, it is preferable that the etching process time be within 180 minutes, more preferably within 140 minutes, even more preferably within 90 minutes, and particularly preferably within 60 minutes. The etching process time refers to the time from when the etching gas is introduced into the chamber 10 until the etching gas is exhausted from the chamber 10 to complete the etching.

[0058] The etching method according to this embodiment can be carried out using a general etching apparatus used in semiconductor device manufacturing processes, such as the etching apparatus shown in Figure 1, and the configuration of the usable etching apparatus is not particularly limited. For example, the positional relationship between the nitrosyl fluoride gas supply pipe 5 and the member to be etched 12 is not particularly limited, as long as the etching gas can be brought into contact with the member to be etched 12. Also, regarding the configuration of the temperature control mechanism of the chamber 10, it is sufficient if the temperature of the member to be etched 12 can be adjusted to any desired temperature, so the temperature control mechanism for the member to be etched 12 may be directly mounted on the stage 11, or an external temperature controller may be used to heat or cool the chamber 10 from the outside.

[0059] Furthermore, the material of the etching apparatus shown in Figure 1 is not particularly limited, as long as it has corrosion resistance to nitrosyl fluoride and can be reduced to a predetermined pressure. For example, metals such as nickel, nickel-based alloys, aluminum (Al), stainless steel, platinum (Pt), ceramics such as alumina, or fluororesins can be used for the parts that come into contact with the etching gas.

[0060] Specific examples of nickel-based alloys include Inconel®, Hastelloy®, and Monel®. Examples of fluororesins include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyvinylidene fluoride (PVDF), Viton®, and Kalrez®. [Examples]

[0061] The present invention will be described in more detail below with reference to examples and comparative examples. (Example 1) Etching of the samples to be etched was performed using an etching apparatus having substantially the same configuration as the etching apparatus in Figure 1. The samples to be etched used in Example 1 are described below. Three types of silicon wafers were prepared: one with a silicon nitride film with a thickness of 1000 nm deposited on the surface of a 100 mm diameter disc-shaped silicon wafer (manufactured by Seiren KST Co., Ltd.), one with a silicon oxide film with a thickness of 1000 nm deposited on the surface of a 100 mm diameter disc-shaped silicon wafer (manufactured by Seiren KST Co., Ltd.), and one with an amorphous carbon film with a thickness of 1500 nm deposited on the surface of a 100 mm diameter disc-shaped silicon wafer (manufactured by Seiren KST Co., Ltd.).

[0062] The three types of samples to be etched were then placed side by side on a stage inside the etching apparatus chamber, and the temperature of the stage was raised to 150°C. Next, nitrosyl fluoride gas at a flow rate of 30 mL / min and argon at a flow rate of 60 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 90 mL / min and circulated for 10 minutes to perform etching. The pressure inside the chamber during the circulation of the etching gas was set to 6.7 kPa, and the partial pressure of the nitrosyl fluoride gas was set to 2.2 kPa.

[0063] This process etched the silicon nitride film, silicon oxide film, and amorphous carbon film of the three types of samples to be etched. After the etching gas flow was completed, the stage heating was stopped and the inside of the chamber was replaced with argon. Furthermore, the hydrogen fluoride content in the etching gas was measured using a Thermo Fisher Scientific Nicolet iS5 infrared spectrophotometer and found to be less than 20 ppm by volume. The measurement conditions were as follows:

[0064] Measurement temperature: 60℃ Measured pressure: 0.1 MPa Window material: Calcium fluoride Total number of times: 8 Measurement wavelength range: 1200~4000cm -1 Wavelength of the peak used in the measurement: 3877 cm -1

[0065] After etching was complete, the chamber was opened and the etched samples were removed. The thicknesses of the silicon nitride film, silicon oxide film, and amorphous carbon film were measured, and the number of particles attached to the surfaces of the silicon nitride film, silicon oxide film, and amorphous carbon film was also measured. The film thicknesses of silicon nitride films, silicon oxide films, and amorphous carbon films were measured using the F20 film thickness measurement system manufactured by Filmetrix, Inc. The measurement conditions for the film thicknesses were as follows:

[0066] Measured pressure: Atmospheric pressure (101.3 kPa) Measurement temperature: 28℃ Measurement atmosphere: Air Measurement wavelength range for silicon nitride: 900~1700nm Measurement wavelength range for silicon dioxide: 200~1000nm Measurement wavelength range for amorphous carbon: 800~1200nm

[0067] For silicon nitride films, silicon oxide films, and amorphous carbon films, the etching rates (nm / min) for silicon nitride, silicon oxide, and amorphous carbon were calculated by subtracting the film thickness after etching (nm) from the film thickness before etching (nm) and dividing the result by the etching time (min). Then, the ratio of the etching rate of the etched material (silicon nitride) to the etching rate of the non-etched material (silicon oxide or amorphous carbon) (etching selectivity ratio) was calculated. The results are shown in Table 1.

[0068] Furthermore, the number of particles adhering to the surface of each of the silicon nitride film, silicon oxide film, and amorphous carbon film was measured using a Topcon WM-2500 wafer surface inspection system. As a result, no particles were detected on any of the films. The total number of particles adhering to the surface of the three films is shown in Table 1.

[0069] [Table 1]

[0070] (Examples 2-8 and Comparative Examples 1 and 2) Except for the flow rates of nitrosyl fluoride gas and argon, the stage temperature, and the pressure inside the chamber being as shown in Table 1, the three samples to be etched were performed in the same manner as in Example 1, and the etching rates and their ratios for silicon nitride, silicon oxide, and amorphous carbon were calculated. In addition, the number of particles attached to the surface of the three films was measured in the same manner as in Example 1, and the total number was calculated. The results are shown in Table 1.

[0071] (Example 9) The etched member used in Example 9 will be described with reference to Figure 2. The etched member in Figure 2 has a structure in which 90 layers each of silicon nitride film 32 and silicon oxide film 33 are alternately stacked on a silicon substrate 31 (for convenience, Figure 2 shows a structure in which 4 layers each are alternately stacked). The thickness of each silicon nitride film 32 and silicon oxide film 33 is 35 nm per layer. However, the thickness of the top layer of silicon oxide film 33 is 70 nm.

[0072] Furthermore, the etched member in Figure 2 has a structure in which an amorphous carbon film 35 with a thickness of 1500 nm is further laminated on top of the uppermost silicon oxide film 33. Here, the silicon nitride film 32 is the object to be etched, while the silicon oxide film 33 and the amorphous carbon film 35 are not to be etched. In addition, the etched member in Figure 2 has through holes 34 with a diameter of 200 nm that penetrate the 90 layers of silicon nitride film 32, the 90 layers of silicon oxide film 33, and the 1 layer of amorphous carbon film 35 in the lamination direction.

[0073] The workpiece to be etched was placed on the stage of an etching apparatus having a configuration substantially similar to that of the etching apparatus shown in Figure 1, and the stage temperature was set to 150°C. Next, nitrosyl fluoride gas at a flow rate of 35 mL / min and argon at a flow rate of 65 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 and circulated for 10 minutes to perform etching. The pressure inside the chamber during the circulation of the etching gas was set to 6.7 kPa. After the circulation of the etching gas was completed, the heating of the stage was stopped, and the inside of the chamber was replaced with argon.

[0074] The chamber was opened and the etched component was removed. The etched component showed that the portion of the silicon nitride film 32 exposed on 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 a portion of the inner surface of the through-hole 34 extended radially outward.

[0075] The portion of the silicon oxide film 33 exposed to 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. As a result, a structure was formed in which the edges of the silicon oxide film 33 and the amorphous carbon film 35 protruded into the through-hole 34.

[0076] The extracted etched material was cut, and the cross-sections of the 90-layer silicon nitride film 32 and the 90-layer silicon oxide film 33 were analyzed using a transmission electron microscope. More specifically, for each of the 90-layer silicon nitride film 32, the radial distance between the portion of the silicon nitride film 32 exposed on the inner surface of the through-hole 34 and the portion of the amorphous carbon film 35 exposed on the inner surface of the through-hole 34 was measured. Similarly, for each of the 90-layer silicon oxide film 33, the radial distance between the portion of the silicon oxide film 33 exposed on the inner surface of the through-hole 34 and the portion of the amorphous carbon film 35 exposed on the inner surface of the through-hole 34 was measured.

[0077] Specifically, etching causes the inner surface of the through-hole 34 to expand radially outward, increasing the radius of the through-hole 34. The difference in radius was measured. By dividing this difference by the etching time, the relative etching rates of silicon nitride and silicon oxide with respect to amorphous carbon were calculated. 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.

[0078] The average and standard deviation of the etching rates of the 90-layer silicon nitride film 32 and the 90-layer silicon oxide film 33 were calculated to evaluate whether the relative etching rate in the in-plane direction (direction parallel to the film surface) changed depending on the stacking direction of the film, and to assess the uniformity of the relative etching rate. In addition, it was confirmed whether or not there was any deposit on the side walls (inner surfaces) of the through holes 34. The results are shown in Table 2.

[0079] [Table 2]

[0080] (Examples 10, 11) Except for the flow rates of nitrosyl fluoride gas and argon and the stage temperature being as shown in Table 2, the material to be etched was performed in the same manner as in Example 9, and the average value and standard deviation of the etching rates of silicon nitride and silicon oxide were calculated, respectively. In addition, in the same manner as in Example 9, it was checked whether or not there was any deposit on the side wall of the through hole 34. The results are shown in Table 2.

[0081] (Comparative Examples 3 and 4) Except for the flow rates of nitrosyl fluoride gas and argon, the stage temperature, and the etching gas flow time being 30 minutes, the workpiece to be etched was performed in the same manner as in Example 9, and the average and standard deviation of the etching rates of silicon nitride and silicon oxide were calculated, respectively. In addition, in the same manner as in Example 9, it was checked whether or not there was any deposit on the side wall of the through hole 34. The results are shown in Table 2.

[0082] The results from Examples 1-3 showed that as the proportion of nitrosyl fluoride in the etching gas increased, the etching rate of silicon nitride and the etching selectivity for non-etchable objects improved. Furthermore, after etching, almost no particles adhered to the surfaces of the silicon nitride film, silicon oxide film, and amorphous carbon film on the silicon wafer. This is thought to be because the increased partial pressure of nitrosyl fluoride inside the chamber increased the frequency of contact between the silicon nitride film surface and nitrosyl fluoride, allowing etching to proceed rapidly, while the controlled temperature suppressed the generation of particles caused by chamber wear and tear.

[0083] The results from Examples 2 and 4 show that the etching rate of silicon nitride increases as the internal pressure of the chamber increases. This suggests that the etching rate increases if the partial pressure of nitrosyl fluoride in the chamber is high. The results from Examples 5, 6, and 7 show that the etching rate of silicon nitride increases as the stage temperature rises. On the other hand, the etching rate of silicon nitride decreases when the stage temperature reaches 50°C, indicating that it is preferable to set the etching temperature to 50°C or higher in order to improve process throughput.

[0084] The results from Examples 1, 2, 3, and 8 show that increasing the partial pressure of nitrosyl fluoride in the etching gas tends to slightly increase the number of particles generated, but this is not at a problematic level. The results from Comparative Example 2 show that lowering the partial pressure of nitrosyl fluoride in the etching gas reduces the etching rate of silicon nitride and the etching selectivity ratio of silicon nitride to silicon oxide. In contrast, in Comparative Example 1, where the etching temperature was increased to increase the etching rate of silicon nitride, the generation of particles increased significantly.

[0085] The results from Examples 9, 10, and 11 show that increasing the stage temperature or the partial pressure of nitrosyl fluoride increases the etching rate of silicon nitride. Furthermore, the ratio of the standard deviation of the etching rate to the average etching rate of silicon nitride is approximately 17-20%, indicating that the etching of the 90 silicon nitride films 32 proceeds almost uniformly regardless of the stacking direction of the silicon nitride films 32.

[0086] On the other hand, the results from Comparative Example 3 show that when the nitrosyl fluoride concentration in the etching gas and the etching temperature are low, the etching rate of silicon nitride and the ratio of the etching rate of silicon nitride to the etching rate of silicon oxide decrease significantly. In addition, in Comparative Example 3, deposits were observed on the side walls of the through-holes 34.

[0087] Furthermore, the results from Comparative Example 4 show that when the etching temperature is too high, the ratio of the standard deviation of the etching rate to the average etching rate of silicon nitride is approximately 80%. Specifically, among the 90 silicon nitride films 32, those located near the bottom of the through-holes 34 tended to have a lower etching rate, with the silicon nitride film 32 closer to the bottom of the through-holes 34 tending to have a lower etching rate. In addition, deposits were observed on the side walls of the through-holes 34.

[0088] As described above, by taking advantage of the characteristics that no deposits (adhered materials) remain in the structure after etching, and that the etching of the silicon nitride film proceeds almost uniformly regardless of the stacking direction position, it is possible to form a structure in which, for example, the edges of the silicon oxide film protrude into the through-holes. Such structures are used, for example, as structures for semiconductor devices such as 3D-NAND flash memory. In other words, the present invention has technical significance in that it can be used, for example, in the manufacture of semiconductor devices such as 3D-NAND flash memory. [Explanation of symbols]

[0089] 1. Nitrosyl Fluoride Gas Supply Unit 2. Dilution gas supply unit 3. Nitrosyl Fluoride Gas Flow Control Device 4. Dilution gas flow control device 5. Piping for supplying nitrosyl fluoride gas. 6. Piping for supplying dilution gas 7. Nitrosyl Fluoride Gas Pressure Control Device 8. Dilution gas pressure control device 10 chambers 11... Stages 12. Etching material 13. Exhaust piping 14...Thermometer 15. Vacuum pump 16. Pressure gauge 31. Silicon substrate 32. Silicon nitride film 33. Silicon oxide film 34... Through hole 35. Amorphous carbon film

Claims

1. An etching method comprising an etching step of bringing an etching gas containing 30 volume% or more of nitrosyl fluoride into contact with a member to be etched, which has an object to be etched by the etching gas and a non-etchable object that is not to be etched by the etching gas, and selectively etching the object to be etched compared to the non-etchable object without using plasma, wherein the object to be etched contains silicon nitride.

2. The etching method according to claim 1, wherein the etching gas is a gas consisting solely of nitrosyl fluoride, or a mixed gas containing nitrosyl fluoride and a diluent gas.

3. The etching method according to claim 1 or claim 2, wherein the non-etching target is at least one of silicon oxide and amorphous carbon.

4. The etching method according to claim 3, wherein the temperature conditions of the etching process are 50°C or higher and 250°C or lower.

5. The etching method according to any one of claims 1 to 4, wherein the etching selectivity ratio, which is the ratio of the etching rate of the object to be etched to the etching rate of the non-etching object, is 10 or more.

6. A method for manufacturing a semiconductor device using the etching method described in any one of Claims 1 to 5, The member to be etched is a semiconductor substrate having the object to be etched and the object not to be etched, A method for manufacturing a semiconductor device, comprising a processing step of removing at least a portion of the object to be etched from the semiconductor substrate by etching.

Images