Etching method

Abstract

A method is provided to prevent the deterioration of the shape of the silicon oxide film portion during etching and to etch the silicon nitride film with high precision with high selectivity for the silicon oxide film. A dry etching method for a silicon nitride film structure, in which a silicon nitride film is pre-formed on a wafer placed in a processing chamber and the ends of the film layers stacked by being sandwiched vertically between a silicon oxide film and forming the sidewalls of a groove or hole, wherein a processing gas is supplied into the processing chamber and a plasma is not used, wherein as a first process, a hydrogen fluoride gas is reacted at a temperature of 30°C or higher and 55°C or lower to form a reaction layer on the silicon nitride film, and then, as a second process, heating is performed at a temperature of 70°C or higher and 110°C or lower without flowing hydrogen fluoride gas to volatilize and remove the reaction layer formed in the first process, and by repeating the first and second processes multiple times, the silicon nitride film is etched in the transverse direction from the ends.

Description

Technology Field

[0001] The present disclosure relates to an etching method, and in particular, to a process technology for isotropic dry etching used in a process for removing silicon nitride films such as semiconductor devices, 3D memory. Background Technology

[0002] In semiconductor devices, further miniaturization and the three-dimensionalization of device structures are progressing due to demands for lower power consumption and increased memory capacity. In the manufacturing of three-dimensional devices, because the structure is three-dimensional and complex, "isotropic etching," which allows etching in the transverse direction as well as the vertical direction, is widely used in addition to "vertical (anisotropic) etching," which performs etching perpendicular to the wafer surface. Conventionally, isotropic etching has been performed by wet treatment using chemical solutions; however, with the advancement of miniaturization, problems such as pattern collapse due to the surface tension of the chemical solution and etching residue in fine gaps have become apparent. Furthermore, the requirement for a large amount of chemical treatment is also a problem. Therefore, in isotropic etching, it has become necessary to replace the conventional wet treatment using chemical solutions with a dry treatment that does not use chemical solutions.

[0003] Since silicon nitride films are widely used in semiconductor devices, there are known examples of dry etching processes that use hydrogen fluoride (HF) gas and do not use plasma. For example, Patent Document 1 describes a method for etching a silicon nitride film without damaging the thermal oxide film by supplying hydrogen fluoride gas at a wafer temperature of 60°C or higher and 200°C or lower. Additionally, Patent Document 2 describes a method for selectively etching a silicon nitride film with respect to a silicon oxide film by supplying hydrogen fluoride gas at a temperature of 10 to 120°C while setting the pressure inside the chamber to 1333 Pa or higher.

[0004] As a known example of adding other components to HF gas, Patent Document 3 describes a method of selectively etching a silicon nitride film by supplying NO gas or / and ozone gas and HF gas. Additionally, Patent Document 4 describes a method of etching a silicon nitride film by contacting a mixed gas containing a fluorinated carboxylic acid and HF gas with a plasma at a temperature below 100°C.

[0005] Regarding etching with a fluorine-containing gas other than HF gas, Patent Document 5 discloses a method of selectively etching a silicon nitride film with respect to a silicon oxide film using ClF3 gas. Additionally, Patent Document 6 discloses a method of selectively etching a silicon nitride film using a fluorine-containing etching gas selected from the group consisting of FNO, F3NO, FNO2, and combinations thereof. Furthermore, Patent Document 7 discloses etching a silicon nitride film without using plasma under a pressure of 1 Pa or more and 80 kPa or less using an etching gas containing a halogen fluoride, which is a compound of bromine or iodine and fluorine.

[0006] Regarding the use of radicals generated by a certain plasma, Patent Document 8 describes a method of selectively etching a silicon nitride film against silicon and / or silicon oxide films by supplying a fluorine-containing gas, an alcohol gas, an O2 gas, and an inert gas in a state excited by an external plasma. Additionally, Patent Document 9 discloses a method for selectively etching a silicon nitride film comprising a process of introducing a gas containing H and F and a process of selectively introducing radicals of an inert gas into a processing space. Furthermore, Patent Document 10 describes selectively etching a silicon nitride film in the transverse direction from a structure in which a silicon nitride film and a silicon oxide film are stacked, using a precursor containing oxygen generated by plasma and a precursor containing fluorine at -20°C or lower.

[0007] In addition, Patent Documents 6 and 10 describe selectively etching a silicon nitride film in the transverse direction from the side wall of a high aspect ratio opening formed in a structure in which a silicon nitride film and a silicon oxide film of a 3D-NAND device, which is a 3D memory, are stacked in multiple layers.

[0008] In addition, Patent Document 11 discloses removing ammonium silicofluoride [(NH4)2SiF6], ammonium fluoride [NH4HF2], etc. formed on a silicon nitride film by heating with a lamp or the like. Prior art literature

[0009] Japanese Patent Publication No. 2008-187105, Japanese Patent Publication No. 2018-207088, Japanese Patent Publication No. 2014-197603, Japanese Patent Publication No. 2019-091890, Japanese Patent Publication No. 2016-58544, Japanese Patent Publication No. 2021-509538, International Publication No. 2021 / 079780, Japanese Patent Publication No. 2015-228433, Japanese Patent Publication No. 2019-012759, U.S. Patent No. 10319603, Japanese Patent Publication No. 2005-161493 The problem to be solved

[0010] For example, in processing stacked films of 3D-NAND flash memory, which is a semiconductor device with a three-dimensional structure, or processing around the gate of a Fin-type FET, a technology is required to etch silicon nitride films with high selectivity and isotropic control at the atomic layer level relative to polycrystalline silicon films or silicon oxide films. Among these, in the 3D-NAND structure, there exists a process for selectively and isotropically etching a small amount of silicon nitride film in the transverse direction from a structure in which silicon oxide films (SiO2 films) and silicon nitride films (SiN) are alternately stacked in multiple layers and deep hole shapes or groove shapes are formed therein.

[0011] As described in the background art, conventional wet etching using aqueous hydrofluoric acid or buffered aqueous hydrofluoric acid has problems such as etching residue in fine gaps and poor controllability of the etching. In addition, in the case of dry etching, it is difficult to etch silicon nitride films with high precision with high selectivity for silicon oxide films, and there was a problem of the shape of the silicon oxide film portion to be left deteriorating.

[0012] The present disclosure is made in consideration of the above problem and provides an etching method that can etch a silicon nitride film with high selectivity and high precision against a silicon oxide film without causing deterioration of the shape of the silicon oxide film to be left. means of solving the problem

[0013] The etching method of the present disclosure is a dry etching method in which a silicon nitride film, which is pre-formed on a wafer placed in a processing chamber, is stacked vertically with a silicon oxide film, and the end portion of the film layer forms the side wall of a groove or hole, wherein a processing gas is supplied into the processing chamber and a plasma is not used. In the first process, a hydrogen fluoride gas is reacted at a temperature of 30°C or higher and 55°C or lower to form a reaction layer on the silicon nitride film. After the first process, in the second process, heating is performed at a temperature of 70°C or higher and 110°C or lower without flowing hydrogen fluoride gas to volatilize and remove the reaction layer formed in the first process. By repeating the first process and the second process multiple times, the silicon nitride film is etched in the transverse direction from the end portion. Effects of the invention

[0014] According to the above etching method, it is possible to prevent the deterioration of the shape of the silicon oxide film portion during etching and to provide a method for etching the silicon nitride film with high precision with high selectivity for the silicon oxide film. Problems, configurations, and effects other than those mentioned above will become apparent from the description of the following embodiments. Brief explanation of the drawing

[0015] FIG. 1a is a graph showing the etching film thickness and selectivity ratio of a silicon nitride film and a silicon oxide film with respect to an IR lamp output irradiated simultaneously with HF supply in a first process according to a first embodiment (stage temperature -30℃, voltage 300Pa, 10 cycles). FIG. 1b is a graph showing the etching film thickness and selectivity ratio of a silicon nitride film and a silicon oxide film with respect to an IR lamp output irradiated simultaneously with HF supply in a first process according to a first embodiment (stage temperature -30℃, voltage 600Pa, 10 cycles). FIG. 1c is a graph showing the etching film thickness and selectivity ratio of a silicon nitride film and a silicon oxide film with respect to an IR lamp output irradiated simultaneously with HF supply in the first process according to the first embodiment (stage temperature -30℃, voltage 900Pa, 10 cycles). FIG. 2a is a graph showing the etching film thickness and selectivity ratio of silicon nitride film and silicon oxide film with respect to IR lamp output irradiated simultaneously with HF supply in the first process according to the second embodiment (stage temperature -20℃, voltage 900Pa, 10 cycles). FIG. 2b is a graph showing the etching film thickness and selectivity ratio of a silicon nitride film and a silicon oxide film with respect to an IR lamp output irradiated simultaneously with HF supply in the first process according to the second embodiment (stage temperature 0°C, voltage 900 Pa, 10 cycles). FIG. 2c is a graph showing the etching film thickness and selectivity ratio of a silicon nitride film and a silicon oxide film with respect to an IR lamp output irradiated simultaneously with HF supply in the first process according to the second embodiment (stage temperature 20℃, voltage 900Pa, 10 cycles). FIG. 2d is a graph showing the etching film thickness and selectivity of silicon nitride film and silicon oxide film with respect to the irradiation time of an IR lamp irradiated in the second process according to the second embodiment (stage temperature 0℃, voltage 900Pa, 10 cycles). FIG. 2e is a graph showing the thickness of the reaction layer on the silicon nitride film with respect to the number of cycles when the IR lamp output irradiated simultaneously with the HF supply is changed in the first process according to the second embodiment. FIG. 3a is a graph showing the etching film thickness and selectivity ratio of the silicon nitride film and the silicon oxide film when the stage temperature of the first process according to the third embodiment is changed. FIG. 3b is a graph showing the thickness of the reaction layer on the silicon nitride film with respect to the number of cycles when the stage temperature of the first process according to the third embodiment is changed. FIG. 4 is a cross-sectional view showing a schematic of an etching apparatus according to a first embodiment. FIG. 5 is a flowchart of an etching method for a silicon nitride film according to an embodiment. FIG. 6 is a flowchart of an etching method for a silicon nitride film according to an embodiment. FIG. 7 is a time chart schematically showing the flow of operation over time of the etching process according to the first embodiment. FIG. 8 is a time chart schematically showing the flow of operations accompanying the time elapsed of the etching process according to the second embodiment. FIG. 9 is a time chart schematically showing the flow of operations accompanying the time elapsed of the etching process according to the third embodiment. FIG. 10a is a partial cross-sectional view illustrating the progress of the etching treatment (before etching) of a stack of silicon nitride and silicon oxide films according to an embodiment. FIG. 10b is a partial cross-sectional view illustrating the progress of the etching treatment (after etching) of a stack of silicon nitride and silicon oxide films according to an embodiment. FIG. 11a is a partial cross-sectional view illustrating the progress of the etching treatment of a stack of silicon nitride and silicon oxide films in a case of poor selectivity according to an example, and shows that the shape of the end portion of the silicon oxide film after etching is round rather than rectangular. FIG. 11b is a partial cross-sectional view illustrating the progress of the etching process of a stack of silicon nitride film and silicon oxide film according to an embodiment, and shows that the corners of the silicon oxide film have fallen off and become triangular. FIG. 12 is a partial cross-sectional view illustrating the progress of the etching treatment of a stack of silicon nitride film and silicon oxide film according to an embodiment, and is a drawing showing that the silicon oxide film portion has a thinned film thickness while the corners of the silicon oxide film maintain a rectangular shape in the case where the selectivity is relatively high. FIG. 13 is a cross-sectional view showing a schematic of an etching device according to a second embodiment. Specific details for implementing the invention

[0016] The present disclosure examines etching using hydrogen fluoride gas (HF) that does not use plasma for each monolayer of silicon nitride film and silicon oxide film formed by plasma CVD (chemical vapor deposition).

[0017] Hereinafter, embodiments of the embodiments will be described in detail with reference to the drawings.

[0018] (Example 1)

[0019] [Overall configuration of etching processing unit 1]

[0020] First, using FIG. 4, a schematic description including the overall configuration of an etching processing apparatus according to Example 1 will be provided. FIG. 4 is a cross-sectional view showing a schematic of an etching apparatus according to a first embodiment. The etching processing apparatus (100) has a processing chamber (1). The processing chamber (1) is formed by a base chamber (11), and a wafer stage (3) for placing a wafer (2) is installed therein. A shower plate (23) is installed at the center of the upper side of the processing chamber (1), and a processing gas is supplied to the processing chamber (1) through the shower plate (23).

[0021] The supply flow rate of the processing gas is adjusted by a mass flow controller (50) installed for each type of gas. Additionally, a gas distributor (51) is installed downstream of the mass flow controller (50), and the flow rate and composition of the gas supplied to the center of the processing room (1) and the gas supplied to the outer periphery are controlled independently, thereby allowing detailed control of the spatial distribution of the partial pressure of the processing gas. Furthermore, in FIG. 4, argon (Ar) gas, nitrogen (N2) gas, helium (He) gas, and hydrogen fluoride (HF) gas are shown as examples, but other processing gases can also be supplied.

[0022] The lower part of the processing chamber (1) is connected to an exhaust means (15) via a vacuum exhaust pipe (16) to reduce the pressure of the processing chamber (1). The exhaust means (15) is configured, for example, by a turbo molecular pump, a mechanical booster pump, or a dry pump. In addition, a pressure regulating means (14) is installed upstream of the exhaust means (15) to adjust the pressure of the processing chamber (1).

[0023] An IR lamp unit (infrared lighting unit) for heating the wafer (2) is installed on the upper part of the wafer stage (3). The IR lamp unit mainly consists of an IR lamp (60), a reflector (61), and an IR light transmission window (72). A circular lamp is used for the IR lamp (60). Also, the light emitted from the IR lamp (60) is to emit light mainly in the infrared region from visible light (here referred to as IR light). In this embodiment, three sets of lamps (60-1, 60-2, 60-3) are installed, but two sets, four sets, etc. are also possible. Above the IR lamp (60), a reflector (61) is installed to reflect the IR light downwards (the installation direction of the wafer (2)). As for the material of the IR transmitting window (72), it is preferable that it does not contain alkali metal ions, transmits light in the infrared region, and has heat resistance, and as a specific material, quartz is preferred.

[0024] An IR lamp power supply (73) is connected to the IR lamp (60), and a high-frequency cut filter (74) is installed in the middle to prevent noise of high-frequency power from entering the IR lamp power supply (73). In addition, the IR lamp power supply (73) has the function of independently controlling the power supplied to the IR lamps (60-1, 60-2, 60-3), and is configured to control the diameter-direction distribution of the heating amount of the wafer (2) (wiring is partially omitted from illustration). A space is formed in the center of the IR lamp unit for installing a shower plate (23) for introducing processing gas.

[0025] A refrigerant flow path (39) for cooling the stage is formed inside the wafer stage (3), and the refrigerant is circulated and supplied by a chiller (38). As for this chiller, in this embodiment, the wafer stage (3) uses one capable of temperature control from -50°C to 50°C. Additionally, as for the method of the wafer stage (3), a proximity cooling method is used here.

[0026] On the surface of the wafer stage (3), protrusions (56) are installed, and the wafer (2) is mounted in a form supported by points by the protrusions (56). The height of the protrusions (56) is preferably, for example, about 0.1 mm to 1.0 mm, and the number of supported points (i.e., the number of protrusions (56)) is preferably 3 points or more. Specifically, 6 points of protrusions (56) with a height of 0.25 mm were used. As for the material of the wafer stage (3), a metal or metal compound with corrosion resistance and high thermal conductivity can be used.

[0027] Because there is a gap between the wafer stage (3) and the wafer (2) due to the protrusion (56), an inert gas such as He, Ar, or N2 is flowed through the entire chamber (11), causing the inert gas to flow through the gap and heat conduction to occur, thereby cooling the wafer (2). Also, regarding the cooling method of the wafer (2), the electrostatic adsorption method shown in Example 2 can be used.

[0028] Additionally, a thermocouple (70) for measuring the temperature of the stage (3) is installed inside the wafer stage (3), and the thermocouple (70) is connected to a thermocouple thermometer (71). With respect to the set temperature of the chiller (38), the temperature of the stage (3) was within ±1℃ of the difference measured by the thermocouple thermometer (71) of the thermocouple (70).

[0029] The proximity cooling stage (3) described above has the advantage of being low-cost because its structure is simple. However, when the chamber (11) is in a vacuum state while idling, the wafer (2) is insulated, so a certain amount of time is required until cooling begins by flowing inert gas. Also, because the distance between the refrigerant from the chiller (38) and the wafer (2) is long, it was found that the actual temperature of the wafer (2) tends to rise relative to the set temperature of the chiller (38). When the temperature was measured during cooling or processing on a wafer to which a thermocouple was applied, it was found that the actual temperature of the wafer (2) was about 5°C higher relative to the set temperature of the chiller (38).

[0030] In addition, as a mechanism for cooling the stage (3) used in the etching processing device (100) of the present embodiment, in addition to circulating a refrigerant, a Peltier element, which is a thermoelectric conversion device, may also be used.

[0031] The etching processing device (100) used in this embodiment can heat the interior of a chamber (11) other than the wafer stage (3) exposed to hydrogen fluoride gas, such as a processing room (1). For example, a temperature of about 40°C to 120°C can be used. By doing so, it is possible to prevent hydrogen fluoride gas from adsorbing inside the chamber (11), thereby making it possible to significantly reduce corrosion inside the chamber (11).

[0032] In this embodiment, for example, HF of 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less) is used at a stage temperature of 40°C to -30°C of the stage (3). Depending on the stage temperature of the stage (3), it is thought that HF ​​may aggregate on the silicon nitride film and become liquefied. Therefore, when using an electrostatic adsorption method, if solidification or liquefaction occurs on the back side of the wafer (2), the seal band of the cooling gas on the back side of the wafer (2) breaks, and a cooling gas such as He leaks, for example, and there is a possibility of an electrostatic chuck error. In contrast to this, the proximity cooling stage (3) shown in FIG. 4 has a gap created by a protrusion (56) between the original wafer stage (3) and the wafer (2), so even when solidification or liquefaction of HF occurs, the wafer stage (3) does not become an error and processing can be performed stably.

[0033] In addition, in the electrostatic adsorption method, since the distance between the wafer (2) and the stage (3) is narrow, when liquefaction of HF occurs, the wafer (2) is prone to sticking to the stage (3) due to surface tension. Therefore, when the wafer (2) is lifted by a pusher pin during de-chewing, there is a problem where the wafer (2) breaks. Regarding this, by using a proximity cooling method with a gap of 0.25 mm between the wafer (2) and the stage (3), the problem of the wafer (2) sticking to the stage (3) due to liquefaction of HF could be reduced.

[0034] As in the present embodiment, when applying a process that utilizes low temperature, condensation may form on components in contact with the ambient atmosphere inside the electrostatic chuck electrode, which is the cooling source, potentially causing a short circuit in electrical circuits such as the power supply section. In this regard, the structure of the proximity cooling stage (3), in which the internal components of the electrode are simplified, has an advantage.

[0035] [Etching Method: Dry Etching Process Flow]

[0036] Next, the flow of the dry etching process using hydrogen fluoride gas without plasma proposed in this embodiment will be explained using FIGS. 4, 5, and 7. FIG. 5 is a flowchart of the etching method of a silicon nitride film according to this embodiment. FIG. 7 is a time chart schematically showing the flow of operation over time of the etching process according to the first embodiment.

[0037] First, the wafer (2) is transported to the processing room (1) through a transport port (not shown) installed in the processing room (1), and then the wafer (2) is placed on a protrusion (56) on the wafer stage (3).

[0038] After that, wafer cooling of step S101 of FIG. 5 is performed by supplying wafer cooling Ar gas to the wafer (2) through a mass flow controller (52), a gas distributor (51), and further through a shower plate (23). Since the Ar gas plays both the role of heat transfer to the wafer (2) and the role of a diluent gas to dilute the HF gas, steps S101 and S102 of FIG. 5 are performed simultaneously here. In addition, the flow rate of the Ar gas can be changed (it can be different flow rates) when cooling the wafer (2) and when using it as a diluent gas. Also, the diluent Ar gas may be allowed to flow continuously or not flow until the etching process is completed. In addition, N2 gas may be used as an inert gas instead of Ar gas.

[0039] Next, as step S103 of FIG. 5, HF gas is supplied to the processing chamber (1) in a predetermined amount and for a predetermined time as a processing gas, and at the same time, heating of the wafer (2) is performed to form a reaction layer on the wafer (2). As a method of heating, heating by an IR (infrared) lamp (60) is performed here. As for the wafer temperature of the wafer (2) obtained as a result of cooling by the stage (3) and heating by the IR lamp (60), for example, 30°C or higher and 55°C or lower is preferred, and 35°C or higher and 50°C or lower is more preferred. As described in the example with changed conditions described later, it is possible to control the film thickness of the reaction layer by the total pressure or HF partial pressure, heating temperature, for example, the output of the IR lamp (60), time, number of repetitions, etc. Furthermore, if the wafer temperature of the aforementioned wafer (2) is lower than, for example, 30°C, the reaction layer cannot be sufficiently formed, so etching is difficult to occur. If the wafer temperature of the aforementioned wafer (2) is, for example, higher than 55°C, the reaction layer may be formed in excess, and when the reaction layer formed in excess is decomposed and volatilized, the adjacent silicon oxide film that is undesirable is etched, so the selectivity of the etching is reduced.

[0040] In this embodiment, the pressure used is preferably, for example, about 10 Pa to 1000 Pa, and also preferably 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), and particularly preferably 100 Pa to 1000 Pa. The higher the pressure, the easier it is for the reaction layer on the silicon nitride film to be formed, and at the same time, the temperature required for formation becomes lower. Even when the pressure is high, by controlling the output of the IR lamp (60), the reaction layer can be formed on the silicon nitride film without affecting the silicon oxide film.

[0041] After forming the reaction layer for a predetermined time, as in step S104 of FIG. 5, the supply of HF gas is stopped, and the HF gas remaining in the gas phase and the reaction product on the silicon nitride film as the reaction layer are exhausted using the exhaust means (15). When vacuum exhaust is performed, it is preferable to set it to, for example, 5 Pa or less. In step S104, the reaction product can be exhausted more efficiently by supplying Ar gas, which is a diluent gas, during and after exhaust. When exhausting while flowing Ar, it is preferable to set it to, for example, 40 Pa or less.

[0042] Next, the reaction layer is removed by heating without flowing HF gas (Step S105 of FIG. 5). Here, the heating temperature is preferably, for example, 70°C to 110°C (70°C or higher and 110°C or lower), and more preferably 70°C to 100°C (70°C or higher and 100°C or lower). As a heating method, an IR lamp (60) was used here. The heating method is not limited to this; for example, it may be a method of heating the wafer stage (3), or a method of separately transporting the wafer (2) to a device that performs only heating to perform the heating treatment. In addition, Ar gas or nitrogen gas may be introduced into the processing chamber (1) when irradiating with the IR lamp (60). Also, the heating treatment may be performed multiple times as needed. After heating, the wafer cooling of Step S106 is performed. Afterwards, the process from step S102 to step S106 is considered as one cycle and repeated N times (N is a positive integer). After repeating the cycle until the required amount of etching is obtained, the etching method of FIG. 4 is terminated.

[0043] FIG. 7 shows a time chart based on the flow of the etching method shown in FIG. 5. A process (step S103) of heating the IR lamp (60) while flowing HF gas and a process (step S105) of heating the IR lamp (60) without flowing HF gas are included in one cycle, and by repeating this N times, etching of the silicon nitride film occurs.

[0044] [Etching Result 1]

[0045] The results of etching using hydrogen fluoride (HF) gas without plasma in this embodiment are shown. By setting the temperature of the stage (3) to -30°C, the etching rate of each single layer of silicon nitride film (PE-SiN) and silicon oxide film (PE-SiO2) formed by plasma CVD was measured.

[0046] Here, as a base wafer (2), a high-resistance substrate (31 Ω cm) with a diameter of 300 mm was used, on which 2 cm square coupon samples of silicon nitride film and silicon oxide film were attached using silicon vacuum grease.

[0047] After placing the wafer (2) into the processing chamber (1) of the etching processing apparatus (100) shown in FIG. 4, etching was performed according to the process flow of the etching method shown in FIG. 5. First, to cool the wafer, Ar was flowed at a flow rate of 1.4 L / min and 900 Pa for 60 seconds. Then, after reaching the set pressure, HF was introduced at a flow rate of 0.40 L / min and Ar as a diluent gas at a flow rate of 0.20 L / min, while simultaneously irradiating with an IR lamp (60) at a predetermined output. Here, the time for introducing HF and irradiating with IR was set to 60 seconds. By doing this, a reaction layer is formed on the silicon nitride film.

[0048] After that, with the exhaust valve in the pressure regulating means (14) open to 100%, exhaust was performed for 120 seconds. Through this exhaust operation, some of the fluorine gas and reaction products are exhausted. Next, with the set temperature of the stage (3) remaining the same, and with Ar flowing at a flow rate of 0.50 L / min, and with the exhaust valve in the pressure regulating means (14) open to 100%, the IR lamp (60) was heated for 30 to 50 seconds at a predetermined lamp intensity. By this, the reaction layer is removed. After that, returning to the beginning, the wafer (2) was cooled with Ar flowing at a pressure of 900 Pa, a flow rate of 1.4 L / min, and for 60 seconds. This series of processes (processes from step S102 to step S106) was performed 10 cycles here according to the flow of FIG. 5.

[0049] FIGS. 1a, 1b, and 1c show the etching film thickness of the silicon nitride film (PE-SiN), the etching film thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film relative to the silicon oxide film obtained after 10 cycles when the output of the IR lamp (60) is varied. FIG. 1a is a graph showing the etching film thickness and selectivity of the silicon nitride film and the silicon oxide film with respect to the IR lamp output irradiated simultaneously with the HF supply in the first process according to the first embodiment (stage temperature -30℃, high pressure 300Pa, 10 cycles). FIG. 1b is a graph showing the etching film thickness and selectivity of silicon nitride film and silicon oxide film with respect to the IR lamp output irradiated simultaneously with HF supply in the first process according to the first embodiment (stage temperature -30°C, high pressure 600 Pa, 10 cycles). FIG. 1c is a graph showing the etching film thickness and selectivity of silicon nitride film and silicon oxide film with respect to the IR lamp output irradiated simultaneously with HF supply in the first process according to the first embodiment (stage temperature -30°C, high pressure 900 Pa, 10 cycles). Here, FIG. 1a, FIG. 1b, and FIG. 1c show experimental results in which the pressure when introducing HF / Ar and performing IR irradiation was changed to 300 Pa, 600 Pa, and 900 Pa, respectively. In addition, IR lamp irradiation to remove the reaction layer formed by the second process (S103) was performed for 50 seconds at 70% output.

[0050] As shown in Fig. 1a, when using 300 Pa, an etching amount of about 15 nm of silicon nitride film (PE-SiN) was obtained in 10 cycles when using an IR output of 60% or more. However, at an IR output of 65% or more, it was found that silicon oxide film (PE-SiO2) also began to be etched, and the selectivity deteriorated.

[0051] As shown in Fig. 1b, when the pressure was increased to 600 Pa, the amount of etching of the silicon nitride film (PE-SiN) increased in proportion to the IR lamp output. As the pressure increased, the amount of etching of the silicon nitride film (PE-SiN) increased overall, and the selectivity for the silicon oxide film (PE-SiO2) increased. However, even in this case, etching of the silicon oxide film (PE-SiO2) began to occur at an IR output of 65% or higher. In addition, as shown in Fig. 1c, when the pressure was increased to 900 Pa, it was found that the amount of etching of the silicon nitride film (PE-SiN) tended to increase as the IR output increased, and the amount of etching increased further.

[0052] A wafer (2) equipped with a thermocouple was used, and the process temperature during lamp irradiation was actually measured by replacing the HF gas with Ar. Table 1a shows the IR lamp output (IR output: 50%, 55%, 60%, 65%) when the stage temperature is -30°C and the temperature of the wafer (2) after 60 seconds. Here, the reached temperature is indicated. A high-resistance substrate is used, similar to the base wafer. The measured temperature was 30°C to 57°C. In addition, temperature measurements were also taken regarding the process of removing the reaction layer, and it was found that the reached temperature was 80°C.

[0053] [Table 1a]

[0054]

[0055] The structure of the film targeted by this embodiment is explained using FIG. 10a and FIG. 10b. FIG. 10a is a partial cross-sectional view for explaining the progress of the etching process (before etching) of a stacked film of silicon nitride and silicon oxide according to the embodiment. FIG. 10b is a partial cross-sectional view for explaining the progress of the etching process (after etching) of a stacked film of silicon nitride and silicon oxide according to the embodiment. The structure of the film targeted by this embodiment is a structure required for a 3D-NAND in which a silicon nitride film (103) and a silicon oxide film (102) are alternately stacked on a substrate (101) as shown in FIG. 10a, and a deep hole shape or a groove shape is formed therein as an opening (104). That is, this configuration is a film structure in which the end of the film layer, which is stacked with the silicon nitride film sandwiched vertically between the silicon oxide film, forms the side wall of the groove or hole. The thickness of the silicon nitride film (103) used here is from several nm to 100 nm, and the thickness of the silicon oxide film (102) is from several nm to 100 nm. In addition, the number of layers stacked is from tens to hundreds of layers. The total thickness (105) of the stacked layers is from several µm to several tens of µm. The width of the opening (104) is from several tens of nm to several hundred nm. By the process of the present embodiment, the silicon nitride film (103) is etched laterally with high selectivity relative to the silicon oxide film (102) as shown in FIG. 10b. The dimension (106) of this etching in the lateral direction is from several nm to several tens of nm.

[0056] FIGS. 11a, FIGS. 11b, and FIGS. 12 are drawings illustrating examples of the shape of the end portion of a silicon oxide film (102) after etching. FIG. 11a is a partial cross-sectional view illustrating the progress of the etching process of a silicon nitride film and a silicon oxide film stacked film when the selectivity is poor according to an embodiment, and the shape of the end portion of the silicon oxide film after etching is rounded rather than rectangular. FIG. 11b is a partial cross-sectional view illustrating the progress of the etching process of a silicon nitride film and a silicon oxide film stacked film according to an embodiment, and the corner of the silicon oxide film is detached and becomes triangular. FIG. 12 is a partial cross-sectional view illustrating the progress of the etching process of a silicon nitride film and a silicon oxide film stacked film according to an embodiment, and when the selectivity is relatively high, the corner of the silicon oxide film maintains a rectangular shape, and the film thickness of the silicon oxide film portion is thinned.

[0057] Here, when etching the silicon nitride film (103) in the transverse direction, the selectivity ratio for the silicon oxide film (102) is 10 or more, more preferably 20 or more. If this selectivity ratio is low, etching of the silicon oxide film (102), which should not originally be etched, occurs simultaneously, so the shape of the end of the silicon oxide film (102) after etching becomes round rather than rectangular, as shown in 111 of FIG. 11a, and has an adverse effect on device performance.

[0058] Empirically, when the selectivity ratio is 10 or more, more preferably 20 or more, a shape closer to a rectangle, as shown in FIG. 10b, is obtained. Also, when the selectivity ratio is less than 5, the shape of the end of the silicon oxide film (102), as shown by 111 in FIG. 11a, is round, which is undesirable.

[0059] Here, the etching characteristics in a fine pattern were evaluated using a sample in which a total of 20 layers of alternating silicon nitride film (103) (film thickness 40 nm) and silicon oxide film (102) (film thickness 40 nm) were formed, and a slit-shaped space (opening (104)) of 200 nm was formed. As experimental conditions, 10 cycles of etching were performed under the conditions shown in FIGS. 1a, 1b, and 1c. The results are shown in Tables 1b, 1c, and 1d. Table 1b shows the etching results at a stage temperature of -30°C and 300 Pa. Table 1c shows the etching results at a stage temperature of -30°C and 600 Pa. Table 1d shows the etching results at a stage temperature of -30°C and 900 Pa. Table 1e shows the symbols and criteria for the evaluation results of the slit samples.

[0060] Consequently, as shown in FIG. 10b, when the etching of the silicon nitride film (103) proceeds with high selectivity in a shape close to a rectangle, as shown in FIG. 11a, there was a case where the selectivity was poor and the leading edge of the silicon oxide film (102) to be left became rounded (indicated by 111). Even when the selectivity was relatively good, as shown in FIG. 11b, the corners of the silicon oxide film (102) were detached and became triangular (indicated by 113), and furthermore, as shown in FIG. 12, even when the corners of the silicon oxide film (102) maintained a rectangular shape, the film thickness of the leading edge portion of the silicon oxide film (102) was thinned (indicated by 112). Figure 112 shows an example of an end portion of a silicon oxide film (102) after etching, in which the corners of the silicon oxide film (102) maintain a rectangular shape while the film thickness of the silicon oxide film (102) portion is reduced. Figure 113 shows an example of an end portion of a silicon oxide film (102) after etching, in which the corners of the silicon oxide film (102) are detached and become triangular. The composition formula of the silicon oxide film is represented as SiO2 or SiO2.

[0061] Thus, Tables 1b, 1c, and 1d show the recess amount (the amount of etching of the silicon oxide film minus the amount of etching of the silicon nitride film), the selectivity ratio from the slit pattern result (the amount of etching from the initial dimensions of the silicon nitride film divided by the amount of etching of the silicon oxide film), and the residual SiO2 thickness (the leading thickness (108) of the silicon oxide film (102) after etching shown in FIG. 12 divided by the initial thickness (107) of the silicon oxide film (102). Here, good etching conditions are a relatively large recess amount, a large selectivity ratio, and furthermore, a residual SiO2 thickness close to 1.

[0062] In addition, to make the evaluation results easier to understand, symbols such as ◎, ○, △, and × were included in Tables 1b, 1c, and 1d. The criteria are shown in Table 1e.

[0063] [Table 1b]

[0064]

[0065] [Table 1c]

[0066]

[0067] [Table 1d]

[0068]

[0069] [Table 1e]

[0070]

[0071] As shown in Tables 1b, 1c, and 1d, in all cases, when the IR lamp output (IR output) is high, the residual SiO2 thickness decreases, so it was found that this is not a suitable condition. Therefore, it was found that even when the selectivity is relatively high, there are cases where the residual SiO2 thickness is low. From the above, it was found that the temperature that satisfies the recess amount, selectivity, and residual SiO2 thickness is 30°C or higher and 55°C or lower.

[0072] In addition, while high temperature and high pressure contribute to increasing the amount of etching of the silicon nitride film (103), it was found that when the temperature is high, the thickness of the residual SiO2 decreases, so the characteristics are good when the pressure is high and the temperature is low.

[0073] (Example 2)

[0074] [Etching Processing Device 2]

[0075] Using FIG. 13, the overall configuration of the etching processing apparatus (200) according to Example 2 of the present embodiment is described in schematic terms. FIG. 13 is a cross-sectional view showing the schematic configuration of the etching apparatus according to the second embodiment. The etching processing apparatus (200) has a processing chamber (1). The processing chamber (1) is composed of a base chamber (11), and a wafer stage (3) for placing a wafer (2) is installed inside it. A plasma source is installed above the processing chamber (1), and an ICP discharge method is used. The ICP plasma source can be used for cleaning the inner wall of the chamber (11) by plasma or for generating reactive gas by plasma. A cylindrical quartz chamber (12) constituting the ICP plasma source is installed above the processing chamber (1), and an ICP coil (20) is installed on the outside of the quartz chamber (12). A high-frequency power source (21) for generating plasma is connected to the ICP coil (20) through a matching device (22). The frequency of the high-frequency power generated from the high-frequency power source (21) is set to use a frequency range of several tens of MHz, such as 13.56 MHz. A top plate (25) is installed on the upper part of the quartz chamber (12). A gas dispersion plate (24) and a shower plate (23) are installed on the lower part of the top plate (25), and the processing gas is introduced into the quartz chamber (12) through the gas dispersion plate (24) and the shower plate (23).

[0076] The supply flow rate of the processing gas is adjusted by a mass flow controller (50) installed for each type of gas. Additionally, a gas distributor (51) is installed downstream of the mass flow controller (50), and the gas distributor (51) is configured to independently control the flow rate and composition of the gas supplied to the center of the quartz chamber (12) and the gas supplied to the outer periphery, thereby enabling detailed control of the spatial distribution of the partial pressure of the processing gas. Also, in FIG. 13, Ar, N2, HF, and O2 are listed as processing gases, but other gases may also be supplied as needed.

[0077] At the bottom of the processing chamber (1), an exhaust means (15) is connected via a vacuum exhaust pipe (16) to reduce the pressure of the processing chamber. The exhaust means (15) is configured, for example, by a turbo molecular pump, a mechanical booster pump, or a dry pump. Additionally, a pressure regulating means (14) is installed upstream of the exhaust means (15) to adjust the pressure of the processing chamber (1).

[0078] An IR lamp unit for heating the wafer (2) is installed on the upper part of the wafer stage (3). The IR lamp unit mainly consists of an IR lamp (60), a reflector (61), and an IR light transmission window (72). A circular lamp is used for the IR lamp (60). In addition, the light emitted from the IR lamp (60) is to emit light mainly in the visible light to infrared light region (here referred to as IR light). In this embodiment, three sets of lamps (60-1, 60-2, 60-3) are installed, but two sets, four sets, etc., may be used. A reflector (61) is installed above the IR lamp (60) to reflect the IR light downwards (in the direction of wafer installation). As for the material of the IR transmission window (72), it is preferable that it does not contain alkali metal ions, transmits light in the infrared light region, and has heat resistance, and specifically, quartz is preferred.

[0079] An IR lamp (60) is connected to an IR lamp power supply (73), and a high-frequency cut filter (74) is installed therein to prevent high-frequency power noise from entering the IR lamp power supply (73). In addition, the IR lamp power supply (73) is equipped with a function that allows the power supplied to the IR lamps (60-1, 60-2, 60-3) to be controlled independently of each other, and the diameter-direction distribution of the heating amount of the wafer (2) can be adjusted (some wiring is omitted from the illustration).

[0080] A channel (27) is formed in the center of the IR lamp unit. In this channel (27), a slit plate (26) with multiple holes is installed to shield ions or electrons generated in the plasma and to allow only neutral gas or neutral radicals to pass through to irradiate the wafer (2). As for the material of the slit plate (26), it is preferable that it does not contain alkali metal ions, etc. and has heat resistance, and specific materials such as alumina or quartz can be used.

[0081] A refrigerant flow path (39) for cooling the stage is formed inside the wafer stage (3), and the refrigerant is circulated and supplied by a chiller (38). As for the chiller (38), in this embodiment, a chiller capable of controlling the temperature of the wafer stage (3) to -50°C to 50°C was used. In addition, to fix the wafer (2) by electrostatic adsorption, a plate-shaped electrode plate (30) is embedded in the stage (3), and a DC power source (31) is connected to each of the electrode plates (30). In addition, to efficiently cool the wafer (2), He gas can be supplied between the back surface of the wafer (2) and the wafer stage (3). Furthermore, to prevent scratches on the back surface of the wafer (2) even when heating and cooling are performed while the wafer (2) is adsorbed, the surface of the wafer stage (3) (the surface facing the wafer (2)) is coated with a resin such as polyimide. Additionally, a thermocouple (70) for measuring the temperature of the stage (3) is installed inside the wafer stage (3), and the thermocouple (70) is connected to a thermocouple thermometer (71).

[0082] Regarding the set temperature of the chiller (38), the temperature of the stage (3) measured by the thermocouple thermometer (71) of the thermocouple (70) was within ±1℃, and the temperature of the wafer (2) measured separately by the thermocouple (70) was within ±3℃ (within ±2℃ for the temperature of the stage (3)).

[0083] In addition, as a mechanism for cooling the stage (3) used in the etching processing device (200) of the present embodiment, in addition to circulating a refrigerant, a Peltier element, which is a thermoelectric conversion device, may also be used.

[0084] In addition, the etching processing device (200) used in this embodiment can heat the interior of a chamber (11) other than the wafer stage (3) exposed to hydrogen fluoride gas, such as a processing room (1). For example, a temperature of about 40°C to 120°C can be used. By doing so, it is possible to prevent hydrogen fluoride gas from adsorbing inside the chamber (11), thereby making it possible to significantly reduce corrosion inside the chamber.

[0085] [Etching Method: Dry Etching Process Flow 2]

[0086] Next, the flow of the etching process using hydrogen fluoride gas without plasma proposed in this embodiment will be explained using FIG. 5, FIG. 8, and FIG. 13 (device drawing). FIG. 5 is a flowchart of the etching method of a silicon nitride film according to this embodiment. FIG. 8 is a time chart schematically showing the flow of operation over time of the etching process according to the second embodiment.

[0087] First, after the wafer (2) is returned to the processing room (1) through a return port (not shown) installed in the processing room (1), the wafer (2) is fixed to the wafer stage (3) by a DC power source (31) for electrostatic adsorption, and the wafer cooling of step S101 of FIG. 5 is performed by supplying a wafer cooling He gas (55) to the back side of the wafer (2). A valve (54) is placed between the He gas (55) and the vacuum exhaust pipe (16).

[0088] Next, as step S102 of FIG. 5, Ar gas for diluting HF gas is supplied to the processing chamber (1) through the mass flow controller (50), the gas distributor (51), and further through the shower plate (23). Until the etching process is completed, the diluting Ar gas may be allowed to flow continuously or may not be allowed to flow. Additionally, N2 gas may be used as an inert gas instead of Ar gas.

[0089] Next, as step S103 of FIG. 5, HF gas was supplied to the processing chamber (1) in a predetermined amount and for a predetermined time as a processing gas, and heating was performed simultaneously to form a reaction layer. As a method of heating, heating by an IR (infrared) lamp (60) was used here. As for the temperature of the wafer (2) obtained as a result of cooling by the stage (3) and heating by the IR lamp (60), for example, 30°C or higher and 55°C or lower is preferred, and 35°C or higher and 50°C or lower is more preferred. As described in the example with changed conditions described later, it is possible to control the film thickness of the reaction layer by the total pressure or HF partial pressure, heating temperature, in this case the lamp output of the IR lamp (60), time, number of repetitions, etc.

[0090] In this embodiment, the pressure used is preferably, for example, about 10 Pa to 1000 Pa, more preferably 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), and particularly preferably 100 Pa to 1000 Pa. The higher the pressure, the easier it is for the reaction layer to be formed on the silicon nitride film (103), and the lower the temperature required for formation. Even when the pressure is increased, by controlling the output of the IR lamp (60), the reaction layer can be formed on the silicon nitride film (103) without affecting the silicon oxide film (102).

[0091] After forming the reaction layer for a predetermined time, as step S104 of FIG. 5, the supply of HF gas is stopped, and the HF gas remaining in the gas phase and the reaction product on the silicon nitride film (103) as the reaction layer are exhausted. In step S104, by supplying Ar gas as a diluent gas during and after exhaust, the reaction product can be exhausted more efficiently.

[0092] Next, heating is performed without flowing HF gas to remove the reaction layer (Step S105 of FIG. 5). Here, the heating temperature is preferably, for example, 70°C to 110°C (70°C or higher and 110°C or lower), and more preferably 70°C to 100°C (70°C or higher and 100°C or lower). As a method of heating, an IR lamp (60) was used here. The heating method is not limited to this; for example, a method of heating the wafer stage (3) or a method of separately transporting the wafer (2) to a device that performs only heating and performing the heating treatment may be used. Additionally, Ar gas or nitrogen gas may be introduced when irradiating with the IR lamp (60). Furthermore, the heating treatment may be performed multiple times as needed. After heating, the wafer cooling of Step S106 is performed. Afterwards, the process from step S102 to step S106 is performed as one cycle and repeated N times (N is a positive integer). After repeating the cycle until the required amount of etching is obtained, the etching method is terminated.

[0093] Figure 8 shows a time chart based on the flow shown in Figure 5. A process of performing IR lamp heating while flowing HF gas (step S103) and a process of performing IR lamp heating without flowing HF gas (step S105) are included in one cycle, and by repeating this N times, etching of the silicon nitride film occurs.

[0094] [Etching Result 2]

[0095] Using the etching processing apparatus (200) shown in FIG. 13 and the process flow of FIG. 5 and FIG. 8 shown above, etching was performed by changing the conditions. In Example 1, the flow rate was fixed at HF / Ar = 0.40 / 0.20 (L / min) and the stage temperature at -30°C, and the experiment was conducted by varying the voltage at 300 Pa, 600 Pa, and 900 Pa. In Example 2, the voltage was fixed at 900 Pa, the flow rates of HF and Ar were kept the same, and the stage temperature of the stage (3) was varied at -20°C, 0°C, and 20°C, and etching was performed using hydrogen fluoride gas without using the plasma of this embodiment, just as in Example 1. In addition, during etching, for example, a voltage of ± 1200 V was applied to electrostatically adsorb the wafer (2) to the stage (3). In addition, to improve the heat conduction of the stage (3), He was flowed from the back side of the wafer (2), for example, to a pressure of 1.0 kPa.

[0096] After setting the flow rate of Ar to 1.0 L / min and the pressure to 900 Pa, HF was introduced at a flow rate of 0.40 L / min and Ar as a diluent gas at a flow rate of 0.20 L / min, while simultaneously irradiating with an IR lamp (60) at a predetermined output. Here, the time for introducing HF and irradiating with IR was set to 60 seconds. By doing this, a reaction layer is formed on the silicon nitride film (103).

[0097] After that, with the exhaust valve in the pressure regulating means (14) open to 100%, exhaust was performed for 120 seconds. Through this exhaust operation, some of the fluorine gas and reaction products are exhausted. Next, while keeping the set temperature of the stage (3) as is, and with Ar flowing at a flow rate of 0.50 L / min, and with the exhaust valve in the pressure regulating means (14) open to 100%, heating was performed with an IR lamp (60) at a predetermined lamp intensity for 30 to 50 seconds. By this, the reaction layer is removed. After that, returning to the beginning, cooling was performed with Ar flowing at a pressure of 900 Pa and a flow rate of 1.4 L / min for 60 seconds. This series of processes (processes from step S102 to step S106) was performed 10 cycles here according to the flow of FIG. 5.

[0098] FIGS. 2a, 2b, and 2c show the etching film thickness of the silicon nitride film (PE-SiN), the etching film thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film relative to the silicon oxide film obtained after 10 cycles when the output of the IR lamp (60) is varied. FIG. 2a is a graph showing the etching film thickness and selectivity of the silicon nitride film and the silicon oxide film with respect to the IR lamp output irradiated simultaneously with the HF supply in the first process according to the second embodiment (stage temperature -20℃, high pressure 900Pa, 10 cycles). FIG. 2b is a graph showing the etching film thickness and selectivity of silicon nitride film and silicon oxide film with respect to the IR lamp output irradiated simultaneously with HF supply in the first process according to the second embodiment (stage temperature 0°C, high pressure 900 Pa, 10 cycles). FIG. 2c is a graph showing the etching film thickness and selectivity of silicon nitride film and silicon oxide film with respect to the IR lamp output irradiated simultaneously with HF supply in the first process according to the second embodiment (stage temperature 20°C, high pressure 900 Pa, 10 cycles). Here, FIG. 2a, FIG. 2b, and FIG. 2c show experimental results in which the temperature of the stage (3) was varied to -20°C, 0°C, and 20°C, respectively. In addition, the IR lamp (60) for removing the reaction layer was irradiated for 40 seconds at 70% output.

[0099] Using a wafer (2) equipped with a thermocouple, the process temperature during lamp irradiation was actually measured by replacing the HF gas with Ar. Table 2a shows the IR lamp output (IR output) and the temperature after 60 seconds when the stage temperature is different. Table 2b shows the temperature after 40 seconds at 70% IR lamp output. As indicated by the temperatures reached in Table 2a, it was found that the temperature ranged from 21°C to 81°C. Additionally, temperature measurements were taken regarding the process of removing the reaction layer, and it was found that the temperatures reached were as shown in Table 2b.

[0100] [Table 2a]

[0101]

[0102] [Table 2b]

[0103]

[0104] As is evident from FIGS. 2a, 2b, and 2c, the greater the output (IR output) of the IR lamp (60), the greater the etching film thickness of the silicon nitride film (PE-SiN). Additionally, as the temperature of the stage (3) increases, the graph of the etching amount of the silicon nitride film (PE-SiN) shifts to the left, indicating that the same etching amount is obtained with a smaller output (IR output) of the IR lamp (60). However, when the temperature of the stage (3) is high, there is a tendency for the etching amount of the silicon oxide film (PE-SiO2) to increase at the higher output of the IR lamp (60), indicating that the selectivity is reduced.

[0105] Here, in the transverse etching of the silicon nitride film (103), the selectivity ratio for the silicon oxide film (102) is 10 or more, more preferably 20 or more. When this selectivity ratio is low, the etching of the silicon oxide film (102), which should not originally be etched, occurs simultaneously, so the shape of the end of the silicon oxide film (102) after etching becomes round rather than rectangular, as shown in 111 of FIG. 11a, which has an adverse effect on device performance.

[0106] Empirically, when the selectivity ratio is 10 or more, more preferably 20 or more, a shape closer to a rectangle, as shown in FIG. 10b, is obtained. Also, when the selectivity ratio is less than 5, the shape of the end of the silicon oxide film (102), as shown in 111 of FIG. 11a, is round, which is undesirable.

[0107] Here, as in Example 1, the etching characteristics in a fine pattern were evaluated using a sample in which a total of 20 layers of alternating silicon nitride film (103) (film thickness 40 nm) and silicon oxide film (102) (film thickness 40 nm) were deposited, and a slit-shaped space of 200 nm was formed. As experimental conditions, etching of the slit sample was performed for 10 cycles under the conditions used in FIGS. 2a, 2b, and 2c. The results are shown in Tables 2c, 2d, and 2e. Table 2c shows the etching results at a stage temperature of -20°C and 900 Pa. Table 2d shows the etching results at a stage temperature of 0°C and 900 Pa. Table 2e shows the etching results at a stage temperature of 20°C and 900 Pa.

[0108] Consequently, as shown in Fig. 10b, when etching proceeds with a shape close to a rectangle with high selectivity, as shown in Fig. 11a, there were cases where the selectivity was poor and the leading edge of the silicon oxide film to be left became rounded. Even when the selectivity was relatively good, as shown in Fig. 11b, the corners of the silicon oxide film were detached and became triangular, and furthermore, as shown in Fig. 12, even when the corners of the silicon oxide film maintained a rectangular shape, the film thickness of the silicon oxide film portion was thinned.

[0109] Thus, Tables 2c, 2d, and 2e show the recess amount (the amount of silicon oxide film etched minus the amount of silicon nitride film etched), the selectivity ratio from the slit pattern result (the amount of silicon nitride film etched from the initial dimensions divided by the amount of silicon oxide film etched), and the residual SiO2 thickness (the thickness of the leading edge of the silicon oxide film after etching shown in FIG. 12 divided by the initial thickness of the silicon oxide film (107). Here, good etching conditions are a relatively large recess amount, a large selectivity ratio, and a residual SiO2 thickness close to 1.

[0110] In addition, to make the evaluation results easier to understand, symbols such as ◎, ○, △, ×, etc. were included in Tables 2c, 2d, and 2e. The criteria are as shown in the aforementioned Table 1e.

[0111] [Table 2c]

[0112]

[0113] [Table 2d]

[0114]

[0115] [Table 2e]

[0116]

[0117] As shown in Tables 2c, 2d, and 2e, when the stage temperature is higher, the output of the appropriate IR lamp (60) becomes smaller. In addition, in any case, when the output of the IR lamp (60) is high, the residual SiO2 thickness becomes smaller, and it was found that this is not suitable as a condition. Therefore, it was found that even when the selectivity ratio is relatively high, there are cases where the residual SiO2 thickness is low. Also, naturally, the selectivity ratio was poor when the IR output was excessively low, such as when the stage temperature was -20℃ and the IR output was 45%. From the above, it was found that the temperature that satisfies the recess amount, selectivity ratio, and residual SiO2 thickness is 30℃ or higher and 55℃ or lower.

[0118] In addition, when comparing the residual SiO2 thicknesses in Tables 2c, 2d, and 2e, it was found that the residual SiO2 thickness was greater when the stage temperature shown in Table 2c was lower (stage temperature -20℃) and smaller when the stage temperature shown in Table 2e was higher (stage temperature 20℃). Therefore, it was found that it is desirable to keep the stage (3) at a low temperature and obtain the necessary reaction temperature from the irradiation of the IR lamp (60).

[0119] The temperature during irradiation by the second IR lamp (60) to remove the reaction layer in the experiment here was in the range of 70°C to 95°C, as shown in Table 2b, but no particularly significant difference was observed in this temperature range. In addition, this time, under conditions of a relatively good performance stage temperature of -20°C and IR output of 55%, the exhaust process (step S104) of the hydrogen fluoride gas and reaction product of FIG. 5 was performed for 120 seconds with the exhaust valve in the pressure regulating means (14) opened 100% while Ar was flowed at 1.4 L / min, rather than vacuum exhaust. As a result, it was found that there was an effect of reducing residue on the fine pattern compared to when vacuum exhaust was performed.

[0120] Next, using the process conditions (stage temperature -20°C) examined in the aforementioned FIG. 2a, the output of the IR lamp (60) of the first process (step S103) for forming the reaction layer was fixed at 55%, and the irradiation time (post IR (70%) time) of the IR lamp (60) (output 70%) of the second process (step 105) for removing the reaction layer was changed to 20 seconds, 30 seconds, 40 seconds, and 50 seconds, and 10 cycles of etching were performed according to the flow of FIG. 5.

[0121] FIG. 2d shows the etching film thickness of the silicon nitride film (PE-SiN), the etching film thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film relative to the silicon oxide film obtained after 10 cycles with respect to the IR lamp irradiation (post-IR) time of reaction layer removal in step S105. FIG. 2d is a graph showing the etching film thickness and selectivity of the silicon nitride film and the silicon oxide film with respect to the irradiation time of the IR lamp irradiated in the second process according to the second embodiment (stage temperature 0°C, high pressure 900 Pa, 10 cycles). As an experimental result, when the IR irradiation for reaction layer removal was 20s, the reaction layer was not removed well, and the film thickness could not be measured by an optical film thickness measuring instrument. As can be seen from FIG. 2d, when the IR irradiation of the reaction layer removal in step S105 was 30s to 50s, no significant difference in the results was observed.

[0122] Here, as in the aforementioned review, the etching characteristics in the fine pattern were evaluated using a sample in which a total of 20 layers of alternating silicon nitride film (103) (film thickness 40 nm) and silicon oxide film (102) (film thickness 40 nm) were deposited, and a slit-shaped space of 200 nm was formed. As for the experimental conditions, etching of the slit sample for 10 cycles was performed under the conditions used in FIG. 2d. The results are shown in Table 2f. Table 2f shows the etching results when the irradiation time of the IR for reaction layer removal (reaction layer removal IR) was changed.

[0123] [Table 2f]

[0124]

[0125] When the IR irradiation time for reaction layer removal (reaction layer removal IR) was 30s, 40s, and 50s, the results were all good. In contrast, when the reaction layer removal IR was 20s, as previously described, the reaction layer was not removed, and etching was not performed well. From these results, it was found that if the temperature for removing the reaction layer is excessively low, the reaction layer is not removed and etching is not performed well.

[0126] As described below, the reaction product is thought to be mainly ammonium silicofluoride [(NH4)2SiF6]. Therefore, a certain temperature is required to decompose and volatilize it. However, since too high a temperature may cause side reactions such as etching the silicon oxide film (102), a minimum necessary temperature is desirable. From the above, as a second temperature for removing the reaction layer, for example, 70°C or higher and 110°C or lower is preferred, and 75°C or higher and 100°C or lower is more preferred.

[0127] [Review of the thickness and composition of the reaction layer]

[0128] Next, an examination was conducted regarding the thickness of the reaction layer. Here, as a condition, the IR irradiation condition for forming the reaction layer (output of the IR lamp (60)) was varied from 30% to 50% with conditions corresponding to the etching conditions shown in FIG. 2c or Table 2e (stage temperature 20°C, 900 Pa, HF / Ar=0.40 / 0.20 L / min, 60 seconds), and a cycle treatment was performed without performing IR irradiation for removing the reaction layer (irradiation time of IR for removing the reaction layer (IR for removing the reaction layer)). Specifically, in the flow of FIG. 5, after exhausting the hydrogen fluoride gas and reaction products (step S104), the process proceeded to the next wafer cooling (step S106) without removing the reaction layer by heating (step S105), and then repeated the cycle starting from the introduction of a diluent gas (S102) (i.e., the sequence S102->S103->S104->S106 was considered as one cycle and repeated multiple times). Samples of silicon nitride films were prepared by performing cycles without IR irradiation for reaction layer removal 2, 5, and 10 times, respectively, and the cross-sections were observed using a scanning electron microscope to measure the film thickness of the reaction layer. The results are shown in FIG. 2e. FIG. 2e is a graph showing the thickness of the reaction layer on the silicon nitride film relative to the number of cycles when the IR lamp output irradiated simultaneously with the HF supply in the first process according to the second embodiment was changed.

[0129] FIG. 2e shows the thickness of the reaction layer with respect to the number of cycles at a stage temperature of 20°C. Data is organized and presented by varying the output of the IR lamp (60) forming the reaction layer from 30% to 50% (here, the IR output is set to 30%, 35%, 40%, 45%, and 50%). The stage temperature with respect to the IR output is summarized in Table 2a. It was found that when the IR output is 30% to 45%, the thickness of the reaction layer tends to saturate with respect to the number of cycles. In contrast, when the IR output is 50%, it was found that the thickness of the reaction layer tends to increase significantly with respect to the number of cycles. When looking at the temperature, it was found that when the temperature is between 40°C and less than 60°C (IR lamp output 30% to 45%), the thickness of the reaction layer tends to saturate, and when the temperature is 70°C (IR lamp output 50%), the reaction layer tends to continue increasing with respect to the number of cycles.

[0130] As shown in Table 2e regarding the etching results of the fine pattern, under the condition of a stage temperature of 20°C, the results were good when the IR output was 35% and 40%. Considering the thickness of the reaction layer mentioned above, if the thickness of the reaction layer generated is too thick (in the case of an IR output of 50%), it is thought that the amount is too large when it is decomposed and volatilized by the second IR irradiation, thereby thinning or degrading the shape of the adjacent silicon oxide film (102). Therefore, it is important to control not only the temperature of the formation and removal of the reaction layer but also the amount of the reaction layer generated. Considering the above-mentioned FIG. 2e, the thickness of the reaction layer is preferably 50 nm or less per 10 cycles, for example. Accordingly, in the first process step S103, it is preferable to form a reaction layer of 5 nm or less per cycle, for example.

[0131] Regarding the above reaction layer, compositional analysis was performed by X-ray photoelectron spectroscopy (XPS). As a result, regarding the surface composition, nitrogen (N1s) exhibited a peak at 402 eV, rather than the 395 eV peak associated with silicon nitride. It was determined that this 402 eV peak is attributed to ammonium salts. Regarding silicon (Si2P), a peak at 103 eV, attributed to silicate, was observed at 99 eV for silicon nitride, indicating hexafluorosilicate SiF6. 2- It is thought that this is the case. In the case of ammonium silicofluoride [(NH4)2SiF6], the elemental ratios are Si=1, F=6, N=2, but the elemental ratios obtained by XPS of the surface of the reaction layer are Si=1, F=4.4, N=1.6, which is close to that. From the above, it is thought that the component formed as the reaction layer is mainly ammonium silicofluoride [(NH4)2SiF6], and that HF ​​or NH3 generated when it decomposes and volatilizes etch the adjacent silicon oxide film depending on the conditions.

[0132] (Example 3)

[0133] [Etching Method: Dry Etching Process Flow 3]

[0134] Next, regarding the etching process using hydrogen fluoride gas without plasma proposed in Example 3 of the present embodiment, a flow that is partially different from Flow 1 of the etching process shown in Example 1 will be explained using FIGS. 4, 6, and 9. FIG. 6 is a flowchart of an etching method for a silicon nitride film according to an embodiment. FIG. 9 is a time chart schematically showing the flow of operation over time of the etching process according to the third embodiment.

[0135] First, the wafer (2) is transported to the processing room (1) through a transport port (not shown) installed in the processing room (1), and then the wafer (2) is placed on a protrusion (56) on the wafer stage (3). In this case, the stage temperature is set to a predetermined temperature of 30°C to 55°C.

[0136] After that, wafer heating is performed by the step S101 of FIG. 6 by supplying Ar gas for heat conduction to the wafer (2) through a mass flow controller (52), a gas distributor (51), and further through a shower plate (23). Since the Ar gas serves as a diluent gas for heat conduction to the wafer (2) and for diluting the HF gas, steps S101 and S102 of FIG. 6 are performed simultaneously. Also, the flow rate of the Ar gas can be changed when heat is conducted to the wafer (2) and when it is used as a diluent gas. Additionally, the diluent Ar gas may be allowed to flow continuously or not flow until the etching process is finished. Also, N2 gas may be used as an inert gas instead of Ar gas.

[0137] Next, as step S103 of FIG. 6, HF gas is supplied to the processing chamber (1) in a predetermined amount for a predetermined time to form a reaction layer. Here, heating by an IR (infrared) lamp as shown in the flowchart of FIG. 5 is not used, and only the temperature of heat transfer by the stage (3) is used. The temperature of the stage (3), i.e., the temperature of the wafer (2), is preferably, for example, 30°C or higher and 55°C or lower, and more preferably 35°C or higher and 50°C or lower. It is possible to control the film thickness of the reaction layer by the temperature of the stage (3), the pressure or partial pressure of HF, time, the number of repetitions, etc.

[0138] In this embodiment, the pressure used is preferably, for example, about 10 Pa to 1000 Pa. In addition, 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less) is preferred, and particularly 300 Pa to 1000 Pa is preferred. The higher the pressure, the easier it is for the reaction layer on the silicon nitride film to form, and at the same time, the temperature required for formation becomes lower.

[0139] After forming the reaction layer for a predetermined time, as in step S104 of FIG. 6, the supply of HF gas is stopped, and the HF gas remaining in the gas phase and the reaction product on the silicon nitride film as the reaction layer are exhausted. In step S104, by supplying Ar gas as a diluent gas during and after exhaust, the reaction product can be exhausted more efficiently.

[0140] Next, heating is performed without flowing HF gas to remove the reaction layer (Step S105 of FIG. 6). Here, the heating temperature is preferably, for example, 70°C to 110°C (70°C or higher and 110°C or lower), and more preferably 70°C to 100°C (70°C or higher and 100°C or lower). As a heating method, an IR lamp (60) was used here. The heating method is not limited to this; for example, a method of heating the wafer stage (3) or a method of separately transporting the wafer to a device that performs only heating to perform the heating treatment may also be used. Additionally, Ar gas or nitrogen gas may be introduced when irradiating with the IR lamp (60). Furthermore, the heating treatment may be performed multiple times as needed. After heating, the wafer (2) of Step S106 is cooled (wafer cooling). Afterwards, the process from step S102 to step S106 is performed as one cycle and repeated N times (N is a positive integer). After repeating the cycle until the required amount of etching is obtained, the flow of FIG. 6 is terminated.

[0141] Figure 9 shows a time chart based on the flow shown in Figure 6. A process of flowing HF gas and Ar (process for forming a reaction layer: S103) and a process of heating with an IR lamp without flowing HF gas (process for decomposing and volatilizing the reaction layer: S105) are in one cycle, and by repeating this N times, etching of the silicon nitride film occurs.

[0142] [Etching Result 3]

[0143] Using the etching processing apparatus (100) used in Example 1 and the etching process flow of FIG. 6, a process was considered in which the temperature of the stage (3) (stage temperature) is set to 20°C to 40°C, and IR heating is not performed in step S103, where HF / Ar is flowed. First, to conduct heat to the wafer (2), Ar was flowed at a flow rate of 1.4 L / min and 900 Pa for 60 seconds. Then, while controlling the pressure at 900 Pa, HF was introduced at a flow rate of 0.40 L / min and Ar as a diluent gas at a flow rate of 0.20 L / min for 60 seconds. By doing this, a reaction layer is formed on the silicon nitride film (103).

[0144] After that, with the exhaust valve in the pressure regulating means (14) open to 100%, exhaust was performed for 120 seconds. Through this exhaust operation, some of the fluorine gas and reaction products are exhausted. Next, the set temperature of the stage (3) was kept the same (20°C to 40°C), and with Ar flowing at a flow rate of 0.50 L / min, with the exhaust valve in the pressure regulating means (14) open to 100%, heating was performed with the IR lamp (60) at 70% output for 30 seconds. By this, the reaction layer is removed. After that, returning to the beginning, the wafer (2) was cooled with Ar flowing at a pressure of 900 Pa and a flow rate of 1.4 L / min for 60 seconds, and the temperature was brought to the same temperature as the stage (3). This series of processes was performed 10 times here according to the flow of FIG. 6.

[0145] FIG. 3a shows the etching film thickness of the silicon nitride film (PE-SiN), the etching film thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film (PE-SiN) relative to the silicon oxide film (PE-SiO2) obtained after 10 cycles when the temperature of the stage (3) is changed. FIG. 3a is a graph showing the etching film thickness and selectivity of the silicon nitride film and the silicon oxide film when the stage temperature of the first process according to the third embodiment is changed.

[0146] As shown in Fig. 3a, it was found that etching of the silicon nitride film (PE-SiN) occurs with only the stage temperature, and the amount of etching of the silicon nitride film (PE-SiN) is proportional to the stage temperature. In addition, etching of the silicon oxide film (PE-SiO2) hardly occurs, and in the case of a single layer, the selectivity ratio was also high.

[0147] Here, as in Examples 1 and 2, the etching characteristics in a fine pattern were evaluated using a sample in which a slit-shaped space of 200 nm was formed on a sample in which a total of 20 layers of alternating silicon nitride film (103) (film thickness 40 nm) and silicon oxide film (102) (film thickness 40 nm) were deposited. As experimental conditions, etching of the slit sample was performed for 10 and 20 cycles under the conditions used in FIG. 3a. The results are shown in Table 3. Table 3 shows the etching results of the fine pattern according to the conditions of FIG. 3a.

[0148] [Table 3]

[0149]

[0150] Thus, Table 3 shows the stage temperature, the number of cycles, the recess amount (the amount of etching of the silicon oxide film minus the amount of etching of the silicon nitride film), the selectivity ratio from the result of the slit pattern (the amount of etching from the initial dimensions of the silicon nitride film divided by the amount of etching of the silicon oxide film), and the residual SiO2 thickness (the thickness (108) of the leading edge of the silicon oxide film (102) after etching shown in FIG. 12 divided by the thickness (107) of the initial silicon oxide film (102). Here, good etching conditions are a relatively large recess amount, a large selectivity ratio, and a residual SiO2 thickness close to 1.

[0151] In addition, to make the evaluation results easier to understand, symbols such as ◎, ○, △, ×, etc. were included in Table 3. The criteria are as shown in the aforementioned Table 1e.

[0152] As a result, it was found that in any case, when the number of cycles was increased and 20 cycles of etching were performed, the selectivity was reduced. In particular, when the number of cycles was high, the edges of the silicon oxide film (102) tended to detach and the tip tended to become triangular, as shown in the shape of 113 in FIG. 11b.

[0153] Although etching of the silicon nitride film (103) is possible by performing a reaction with HF using only the temperature of the stage (3), it was found that the etching by the combination of cooling at the low temperature stage (3) and the IR lamp (60) as shown in Examples 1 and 2 above has superior selectivity and pattern shape. That is, in the first process (step S103) and the second process (step S105), it is preferable to obtain a temperature of 30°C or higher and 55°C or lower as the first process and 70°C or higher and 110°C or lower as the second process by lowering the temperature of the stage (3) on which the wafer (2) is placed to a low temperature of -50°C or higher and 0°C or lower, and then heating with the IR lamp (60) thereon.

[0154] [Review of the thickness of the reaction layer]

[0155] Next, as in Example 2, an examination was conducted regarding the thickness of the reaction layer. Here, under the etching conditions shown in FIG. 3a or Table 3 (stage temperature 20°C to 40°C, 900 Pa, HF / Ar = 0.40 / 0.20 L / min, 60 sec), only the formation of the reaction layer was performed, and the cycle treatment was carried out without IR irradiation for reaction layer removal. Specifically, in the flow of FIG. 6, after exhausting the hydrogen fluoride gas and reaction products (Step S104), the removal of the reaction layer by heating (Step S105) was not performed, and the process proceeded to the next wafer cooling (Step S106). Subsequently, a cycle starting from the introduction of a diluent gas (Step S102) was repeated (i.e., the sequence S101->S102->S103->S104->S106 was considered as one cycle and repeated multiple times). Samples of silicon nitride films were prepared by performing cycles without IR irradiation for the removal of the reaction layer 2, 5, and 10 times, respectively, and the cross-sections were observed using a scanning electron microscope to measure the film thickness of the reaction layer. The results are shown in FIG. 3b. FIG. 3b is a graph showing the thickness of the reaction layer on the silicon nitride film as a function of the number of cycles when the stage temperature of the first process according to the third embodiment is changed.

[0156] Figure 3b shows the thickness of the reaction layer with respect to the number of cycles at stage temperatures of 30°C, 35°C, and 40°C. It can be seen that when the stage temperature is 30°C and 35°C, the thickness of the reaction layer tends to saturate with respect to the number of cycles. When the stage temperature is 40°C, it can be seen that the thickness of the reaction layer tends to increase slightly with respect to the number of cycles.

[0157] As described in Example 2, if the thickness of the reaction layer being generated is excessively thick, the amount is too large when it is decomposed and volatilized by the second IR irradiation to remove it, thereby thinning or degrading the shape of the adjacent silicon oxide film (102). Therefore, it is important to control not only the temperature of the formation and removal of the reaction layer but also the amount of the reaction layer generated. Considering FIG. 2e of the aforementioned Example 2, the thickness of the reaction layer is preferably 50 nm or less in 10 cycles, for example. Accordingly, in the first process step S103, it is preferable to form a reaction layer of 5 nm or less per cycle. Explanation of the symbols

[0158] 1 : Processing Room 2 : Wafer 3: Wafer Stage 11: Base Chamber 12: Quartz chamber 13: Discharge zone 14: Pressure regulating means 15: Exhaust means 16: Vacuum exhaust piping 20: ICP coil 21: High-frequency power supply 22: Matching unit 23: Shower plate 24: High gas dispersion plate 25 : Top plate 26 : Slit plate 27 : Flow path 30 : Electrostatic adsorption electrode 31: DC power supply for electrostatic adsorption 38: Chiller 39: Refrigerant flow path 50: Mass flow controller 51: Gas distributor 54: Valve 55: He gas 56: Protrusion for proximity cooling 60, 60-1, 60-2, 60-3: IR lamps 61: Reflector 64: Power supply for IR lamp 70: Thermocouple 71: Thermocouple thermometer 72: IR light transmission window 73: Power supply for IR lamp 74: High-frequency cut filter 101 : Substrate 102 : Silicon nitride film 103: Silicon oxide film 104: Opening 105 : Laminated film 106: Etching amount of silicon oxide film relative to silicon nitride film 111 : End of silicon oxide film after etching when selectivity is low 112: A drawing showing an example of an end portion of a silicon oxide film after etching, wherein the corners of the silicon oxide film maintain a rectangular shape while the film thickness of a portion of the silicon oxide film is thinned. 113: A drawing showing an example of the end of a silicon oxide film after etching, wherein the corner of the silicon oxide film has detached and formed a triangle.

Claims

Claim 1 An etching method for dry etching a film structure, wherein a silicon nitride film pre-formed on a wafer placed in a processing chamber is stacked by being sandwiched vertically between a silicon oxide film and the ends of the film layers constitute the sidewalls of a groove or hole, by supplying a processing gas into the processing chamber and without using plasma, wherein as a first process, a hydrogen fluoride gas is reacted at a temperature of 30°C or higher and 55°C or lower to form a reaction layer on the silicon nitride film, and after the first process, as a second process, heating is performed at a temperature of 70°C or higher and 110°C or lower without flowing the hydrogen fluoride gas to volatilize and remove the reaction layer formed in the first process, and wherein the first process and the second process are performed by setting the stage on which the wafer is placed to a low temperature of -50°C or higher and 0°C or lower and heating it with an IR lamp, thereby, as a first process, 30°C or higher and 55°C An etching method characterized by obtaining a temperature of 70°C or higher and 110°C or lower as the second process, and repeating the first process and the second process multiple times to etch the silicon nitride film in the transverse direction from the end. Claim 2 An etching method according to claim 1, characterized in that the pressure of the first process is 50 Pa or more and 1000 Pa or less. Claim 3 An etching method according to claim 1 or 2, characterized by including a process of exhausting while flowing inert gas, such as Ar gas or N2 gas, between the first process and the second process. Claim 4 An etching method according to claim 1 or 2, characterized in that the thickness of the reaction layer formed in the first process is greater than 0 nm and less than or equal to 5 nm. Claim 5 delete Claim 6 delete

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