Etching method

Abstract

Provided is an etching technology which provides high uniformity in the etching amount and has an improved yield of etching processing. This etching method for etching a film layer to be processed which contains titanium carbide and is disposed on a surface of a wafer comprises: a step for supplying a surface of the film layer with reactive particles that contain fluorine and oxygen but do not contain hydrogen, thereby forming a reaction layer on the surface of the film layer; and a step for heating the film layer to detach the reaction layer.

Description

Technical Field

[0001] The present disclosure relates to a method for etching a film layer to be processed containing a metal carbide using plasma, for example, a titanium carbide film.

Background Art

[0002] Driven by the spread of mobile devices represented by smartphones, the high integration of semiconductor devices has been progressing. In the field of semiconductor devices for recording, three-dimensional (3D) NAND flash memories in which memory cells are stacked in multiple layers in the three-dimensional direction are being mass-produced. Also, in the field of semiconductor devices for logic, as the structure of transistors, fin-type FETs (Field Effect Transistors) having a fine three-dimensional structure have become mainstream. Currently, for further improvement in integration density, stacked nanowire-type FETs are entering the stage of practical use.

[0003]

[0004] As such, as the three-dimensionalization of the device structure and the miniaturization of the processing dimensions progress, in the device manufacturing process (manufacturing method of semiconductor devices), the need for an etching technique that combines isotropism and high processing dimension controllability at the atomic layer level is increasing. As such an isotropic etching technique, conventionally, wet etching techniques such as etching of silicon dioxide using an aqueous mixed solution of hydrofluoric acid and ammonium fluoride, etching of silicon nitride using hot phosphoric acid, have been widely used. However, in these conventional wet etching techniques using such chemical solutions, there has been a problem that pattern collapse due to the surface tension of the rinse solution becomes apparent as the pattern is miniaturized.

[0005] On the other hand, metal carbide films such as titanium carbide and titanium aluminum carbide are widely used as work function metals in the aforementioned semiconductor devices. Therefore, etching technology for titanium carbide that combines isotropy, high processing dimensional control at the atomic layer level, and high selectivity is required for the manufacturing process of next-generation semiconductor devices.

[0006] As a conventional technique for etching titanium carbide films using plasma without using chemicals, for example, Japanese Patent Publication No. 01-223733 (Patent Document 1) has been proposed.

[0007] Patent Document 1 discloses a technique for etching away titanium carbide films using CF4 / O2 plasma. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 01-223733 [Overview of the project] [Problems that the invention aims to solve]

[0009] The prior art described in Patent Document 1 had problems because it did not adequately consider the following points.

[0010] In other words, while the technology in Patent Document 1 discloses a technique for etching titanium carbide, it did not consider the conditions for isotropically etching a film to be processed that has been deposited on a pattern, such as in the fabrication process of work function metals. In particular, when conformal etching at the atomic layer level is required in a fine three-dimensional structure, such as in the fabrication process of work function metals for fin-type FETs and multilayer nanowire type FETs, the etching rate differs at the top and bottom of the pattern, and as a result of the etching process, vertical variations in the thickness of the processed object after processing were not considered. Therefore, the technology in Patent Document 1 had the problem that a large distribution in the amount of etching of the film layer to be processed occurred in the vertical (depth) direction of the pattern formed on the film structure, which impaired the yield of the etching process (etching step) of semiconductor devices.

[0011] Furthermore, the technology described in Patent Document 1 involves the continuous etching of a titanium carbide film in response to an increase in etching time. In such a continuous etching process, the amount of etching is adjusted by detecting and adjusting the time elapsed since the start of the etching process. However, adjusting the amount of etching based on the etching time in this manner makes it difficult to precisely control the extremely small amount of etching required in the manufacturing process of next-generation and subsequent fine semiconductor devices, such as etching to an atomic layer level in terms of etching depth (width). This raises concerns that the accuracy and yield of the etching process may be compromised.

[0012] Thus, in the continuous plasma etching technology described in Patent Document 1, the etching amount is non-uniform, reflecting the distribution of radicals, resulting in low uniformity of etching amount in the wafer plane direction and pattern depth direction, and the etching amount must be controlled by the plasma processing time. For this reason, the continuous plasma etching technology described in Patent Document 1 is likely to have limited applicability in next-generation and subsequent device manufacturing processes that require high dimensional control at the atomic layer level.

[0013] The purpose of this disclosure is to provide an etching technology that exhibits high uniformity of etching amount and improved yield of the etching process.

[0014] Other purposes and novel features of this disclosure will become apparent from the description herein and the accompanying drawings. [Means for solving the problem]

[0015] A brief overview of some of the representative disclosures is as follows:

[0016] An etching technique according to one embodiment of the present disclosure is an etching method for etching a film layer to be treated, which contains metal carbides and is disposed on the surface of a wafer, comprising the steps of supplying reactive particles containing fluorine and oxygen but not hydrogen to the surface of the film layer to form a reaction layer containing a bond between metal and fluorine on the surface of the film layer, and heating the film layer to remove the reaction layer. [Effects of the Invention]

[0017] The effects that can be obtained from representative examples of this disclosure are briefly explained below.

[0018] The etching technology of this disclosure enables high uniformity of etching amount and improves the yield of the etching process. For example, when etching a titanium carbide film as a film layer to be processed that contains metal carbides, it is possible to provide an isotropic atomic layer etching technology that enables etching with high uniformity of etching amount in the wafer plane direction and pattern depth direction, as well as high controllability of processing dimensions at the atomic layer level. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a schematic longitudinal cross-sectional view showing the configuration of a plasma processing apparatus according to an embodiment of the present disclosure. [Figure 2]FIG. 2 is a flowchart showing an outline of the flow of an etching process of a film containing titanium carbide pre-formed on a wafer to be processed by the plasma processing apparatus according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a time chart showing changes over time of a plurality of parameters included in the processing conditions during the processing of the wafer according to the embodiment shown in FIG. 1. [Figure 4] FIG. 4 is a cross-sectional view schematically showing an outline of changes in a film structure including a film containing titanium carbide during the processing of the wafer according to the embodiment shown in FIG. 3. [Figure 5] FIG. 5 is a diagram showing the analysis result of the wafer surface according to the embodiment shown in FIG. 1. [Figure 6] FIG. 6 is a diagram showing the reaction time dependence of the amount of surface reaction layer generated according to the embodiment shown in FIG. 1. [Figure 7] FIG. 7 is a diagram showing the heating temperature dependence of the remaining amount of the surface reaction layer according to the embodiment shown in FIG. 1. [Figure 8] FIG. 8 is a graph showing the relationship between the number of cycles and the amount of etching in the etching process performed by the plasma processing apparatus according to the embodiment shown in FIG. 1. [Figure 9] FIG. 9 is a graph showing the relationship between the number of cycles and the amount of etching in the etching process performed by the plasma processing apparatus according to the embodiment shown in FIG. 1, and is a diagram showing the results when the wafer temperature is changed. [Figure 10] FIG. 10 is a longitudinal sectional view schematically showing changes in the film structure when plasma etching according to the technology of the present disclosure is performed on a fine and high aspect ratio film structure formed on a sample on a substrate such as a semiconductor wafer to be processed. [Figure 11] FIG. 11 is a longitudinal sectional view schematically showing changes in the film structure when plasma etching according to the conventional technology is performed on a fine and high aspect ratio film structure formed on a sample on a substrate such as a semiconductor wafer to be processed.

MODE FOR CARRYING OUT THE INVENTION

[0020] Embodiments of this disclosure will be described below with reference to the drawings. In the following description, the same reference numerals will be used for the same components, and repeated descriptions may be omitted. In addition, the drawings may be more schematic than the actual embodiments in order to make the explanation clearer, but they are merely examples and do not limit the interpretation of this disclosure.

[0021] In the process of forming work function metals in the manufacturing of semiconductor devices, such as fin-type FETs, a technique is required to etch a titanium carbide film deposited on a fine fin structure with a high aspect ratio isotropically and with high precision at the atomic layer level. Therefore, the Disclosers investigated, as an example, the case of performing conventional plasma etching on a structure as shown in Figure 11.

[0022] Figure 11 is a schematic longitudinal cross-sectional view showing the change in the film structure when a predetermined structure, in which multiple fin structures are formed adjacent to each other on a substrate such as a semiconductor wafer, is subjected to conventional plasma etching. Figures 11(a) to (c) show three stages of the film structure's shape as it changes after etching.

[0023] Figure 11(a) shows the film structure before the plasma etching process has started. The film structure is formed on the surface of a fin structure 902 formed on a substrate structure 901, with a titanium carbide film 903 to be processed and a mask 904 protecting the parts of the titanium carbide film 903 that are not to be processed. Figure 11(b) shows the state after etching of the titanium carbide film 903 has progressed. In Figure 11(b), a plasma is formed using tetrafluoromethane (CF4) and oxygen (O2) gas (hereinafter referred to as CF4 / O2 gas) to etch the titanium carbide film 903 of the film structure in Figure 11(a). Then, a fluorine-containing reactive species 905 in the plasma is supplied into the groove 911 of the film structure and reacts with the surface of the titanium carbide film 903 while the wafer temperature is maintained at room temperature. As a result, the reaction product 906 containing titanium fluoride is removed upward, and etching of the titanium carbide film 903 has progressed. Figure 11(c) shows the state after the etching of the titanium carbide film 903 using the plasma described above has been stopped. In this example, the fin structure 902 is made of silicon and is pre-formed on the substrate structure 901, and its surface is coated with hafnium oxide or titanium nitride, which are not shown.

[0024] In our investigation, we found the following: As shown in Figure 11(b), we attempted to uniformly etch only the titanium carbide film 903 inside the high-aspect-ratio groove 911, where the surface of the fin structure 902 is covered with a titanium carbide film 903, forming the side walls on both sides. However, because we did not use a low wafer temperature that would suppress the volatilization of the reaction product 906, the surface reaction layer was not retained on the surface of the titanium carbide film 903, and it was confirmed that etching proceeded continuously due to the continuous desorption caused by the volatilization of the reaction product 906. On the other hand, the reaction species 905 supplied from the plasma formed above the sample enters the groove 911 from above into its interior and is consumed by the titanium carbide film 903 deposited near the opening at the upper end of the groove 911. Therefore, the amount of reaction species 905 that reaches the titanium carbide film 903 in the lower region 9111 (bottom of the groove 911) is small. Therefore, as shown in Figure 11(c), the distribution of etching amount of the titanium carbide film 903 becomes non-uniform in the vertical direction of the groove 911. Consequently, the etching amount of the titanium carbide film 903 is large near the opening of the upper part 9112 of the groove 911, and small at the lower part 9111 of the groove 911. As a result, etching of the titanium carbide film 903 using conventional techniques results in a non-uniform distribution of etching amount of the titanium carbide film 903, which may lead to a decrease in the yield of sample processing or semiconductor device manufacturing.

[0025] Thus, in conventional plasma etching technology, the etching amount of the titanium carbide film 903 is non-uniform, reflecting the distribution of radicals. This results in low uniformity of etching in the wafer plane and pattern depth directions, and the etching amount of the titanium carbide film 903 must be controlled by the plasma processing time. For this reason, the application of conventional continuous plasma etching technology is likely to be limited in next-generation and beyond device manufacturing processes that require high dimensional control at the atomic layer level.

[0026] The Disclosers attempted to etch titanium carbide films using plasma from various gases. As a result, they found the following (1)-(3). (1) A surface reaction layer mainly composed of titanium-fluorine (Ti-F) bonds is formed on the surface of a titanium carbide film by supplying a plasma of a gas containing fluorine and oxygen but not hydrogen. (2) The amount of the surface reaction layer produced is self-saturating (self-limiting). (3) The surface reaction layer is removed by heating.

[0027] This disclosure is based on these new findings ((1)-(3)). Specifically, the etching method for titanium carbide films (the film layer to be treated) is as follows: Step 1) A plasma is formed using a gas containing methane tetrafluoride (CF4) and oxygen (O2), and reactive particles containing fluorine and oxygen but not hydrogen are supplied from the plasma to the surface of the titanium carbide film to be etched, thereby forming a surface reaction layer on the surface of the titanium carbide film (also called the surface reaction layer formation step). Second step) Next, a step of removing the surface reaction layer by heating (or a step of detaching the surface reaction layer by heating) (also called the surface reaction layer removal step), We will implement this.

[0028] These two processes (the first and second processes) are treated as a single cycle, and by repeating this cycle multiple times, the desired amount of titanium carbide film etching is achieved.

[0029] With the above configuration, the surface reaction layer formation process and the surface reaction layer removal process are self-saturating, thereby suppressing non-uniformity of the etching amount in the in-plane direction of the wafer and in the depth direction of the film structure pattern such as grooves or holes. Furthermore, the thickness of the titanium carbide film removed in one cycle can be adjusted with high precision at the atomic layer level, and the amount of etching obtained by repeating the cycle can be adjusted by the number of repeating cycles, thus improving the dimensional accuracy of semiconductor devices formed by etching stacked titanium carbide films.

[0030] Figure 10 is a schematic longitudinal cross-sectional view showing the changes in a film structure when a fine, high-aspect-ratio film structure formed on a sample on a substrate such as a semiconductor wafer is subjected to plasma etching using the technology of this disclosure. Figures 10(a) to (c) show three stages of the shape of the film structure as it changes after etching.

[0031] Figure 10(a) shows a film structure in which a titanium carbide film 903 to be treated and a mask 904 protecting the parts of the titanium carbide film 903 not to be treated are formed on the surface of a fin structure 902 formed on a substrate structure 901, and the plasma etching process has not yet been started. Figure 10(b) shows the film structure in which, in order to etch the titanium carbide film 903 of the film structure in Figure 10(a), a plasma of a mixed gas containing tetrafluoride methane (CF4) and oxygen (O2) is formed, and reactive particles containing fluorine and oxygen but not hydrogen are supplied from the plasma to the surface of the titanium carbide film 903 to be etched that are not covered by the mask 904, thereby forming a surface reaction layer on the surface of the titanium carbide film 903 to be etched. Next, this surface reaction layer is removed (desorbed) by heating. In other words, the process involves forming a surface reaction layer (first step) and desorbing the surface reaction layer by heating (second step). These two processes (the first and second processes) are treated as a single cycle, and by repeating this cycle multiple times, the desired amount of titanium carbide film etching is achieved.

[0032] As a result, as shown in Figure 10(c), the titanium carbide film 903 that is not covered by the mask 904 can be selectively removed by etching. Furthermore, since the gas of this disclosure does not contain hydrogen, it does not etch nitride films such as titanium nitride. With the gas of this disclosure, titanium nitride oxide is formed on the surface of the titanium nitride, and etching stops.

[0033] In contrast, when a mixed gas of methane trifluoride (CHF3) and oxygen (O2) containing hydrogen is used, for example, a surface reaction layer such as ammonium titanium fluoride is formed on the surface of the titanium nitride. During the heating step, this surface reaction layer such as ammonium titanium fluoride volatilizes, resulting in etching of the titanium nitride. However, this presents a problem: it cannot be applied to processes that selectively etch titanium carbide against titanium nitride, such as the fabrication process of work function metals. A more detailed explanation of Figures 10(a)-(c) can be found in the explanation of Figures 4(a)-(c) described later.

[0034] In the following embodiments, an etching process that involves repeatedly performing a set of steps (Step 1 and Step 2) that include a step for forming a self-saturating surface reactive layer (Step 1) and a step for removing the surface reactive layer (Step 2) is referred to as atomic layer etching. In these embodiments, "atomic layer" etching is not limited to atomic layer etching in the narrow sense, where the etching amount per cycle is equivalent to the thickness of a layer composed of a single atom of the material constituting the target film. Even if the etching amount per cycle is on the order of nanometers or larger, any process in which each step tends to be self-saturating, i.e., self-limiting, with respect to processing time, is referred to as atomic layer etching. In addition, terms such as "digital etching," "self-limiting cycle etching," "atomic level etching," and "layer-by-layer etching" can also be used for equivalent processes.

[0035] The following describes embodiments of this disclosure with reference to the drawings. [Examples]

[0036] Examples of the present disclosure will be described below with reference to Figures 1 to 9. In these examples, the following etching technique will be described. First, a step (first step) is performed in which a surface reaction layer is formed on the surface of the titanium carbide film to be processed by plasma formed using a mixed gas consisting of methane tetrafluoride (CF4), oxygen (O2), and argon (Ar). Then, a step (second step) is performed in which the surface reaction layer is removed by wafer heating using an infrared lamp. This is done to isotropically etch the titanium carbide film to be processed, which has been previously formed on a semiconductor wafer such as silicon.

[0037] Figure 1 is a schematic longitudinal cross-sectional view showing the configuration of a plasma processing apparatus according to an embodiment of the present disclosure.

[0038] Processing chamber 1 consists of a base chamber 11, which houses a wafer stage 4 (hereinafter referred to as stage 4) for placing the wafer 2 (hereinafter referred to as wafer 2), the sample to be processed. An ICP (Inductively Coupled Plasma) discharge method is used as the plasma source, and above processing chamber 1 is a plasma source equipped with a quartz chamber 12, an ICP coil 34, and a high-frequency power supply 20. Here, the ICP coil 34 is installed outside the quartz chamber 12.

[0039] A high-frequency power supply 20 for plasma generation is connected to the ICP coil 34 via a matching unit 22. The frequency of the high-frequency power is set to a frequency band of several tens of MHz, such as 13.56 MHz. A top plate 6 is installed on top of the quartz chamber 12. A shower plate 5 is installed on the top plate 6, and a gas dispersion plate 17 is installed below it. The processing gas is introduced into the processing chamber 1 from the outer periphery of the gas dispersion plate 17.

[0040] The processing gas is located within the mass flow controller control unit 51, and the flow rate supplied is adjusted by mass flow controllers 50 installed for each type of gas. In Figure 1, at least methane tetrafluoride (CF4), oxygen (O2), and argon (Ar) are supplied to the processing chamber 1 as processing gases, and mass flow controllers 50-2, 50-3, 50-4, and 50-6 are provided corresponding to each of these gases. However, the supplied gases are not limited to these. The mass flow controller control unit 51 also includes a mass flow controller 50-7 that adjusts the flow rate of He gas supplied between the back surface of the wafer 2 and the upper surface of the dielectric film on the stage 4 on which it is placed, as will be described later.

[0041] The lower part of the processing chamber 1 is connected to an exhaust means 15 by a vacuum exhaust pipe 16 to reduce the pressure inside the processing chamber 1. The exhaust means 15 is composed of, for example, a turbomolecular pump, a mechanical booster pump, or a dry pump. A pressure regulating means 14 is installed upstream of the exhaust means 15. The pressure regulating means 14 adjusts the flow rate of internal gas and plasma 10 particles discharged from the processing chamber 1 by the operation of the exhaust means 15 by increasing or decreasing the flow path cross-sectional area, which is the cross-sectional area of ​​the vacuum exhaust pipe 16 in a plane perpendicular to the axial direction. The pressure regulating means 14 is composed of multiple plate-shaped flaps that have an axis in a direction transverse to the flow path and rotate around that axis, and plate members that move axially within the flow path to adjust the pressure in the processing chamber 1 and the discharge area 3.

[0042] An infrared lamp unit for heating the wafer 2 is installed between Stage 4 and the quartz chamber 12 that constitutes the ICP plasma source. The infrared lamp unit mainly consists of an infrared lamp 62, a reflector 63 that reflects infrared light, and a light-transmitting window 74. A circular (ring-shaped) lamp is used for the infrared lamp 62. The light emitted from the infrared lamp 62 is assumed to be mainly light in the visible light to infrared light region. Here, such light is referred to as infrared light. In the configuration shown in Figure 1, three infrared lamps 62-1, 62-2, and 62-3 are installed as the infrared lamp 62, but two or four rotations may also be used. A reflector 63 is installed above the infrared lamp 62 to reflect the infrared light downwards.

[0043] An infrared lamp 62 is connected to an infrared lamp power supply 64, and a high-frequency cut filter 25 is installed in between to prevent noise from the high-frequency power used for plasma generation generated by the high-frequency power supply 20 from flowing into the infrared lamp power supply 64. In addition, the infrared lamp power supply 64 is equipped with a function that allows the power supplied to infrared lamps 62-1, 62-2, and 62-3 to be controlled independently of each other, so that the radial distribution of the heating amount of the wafer 2 can be adjusted.

[0044] In the center of the infrared lamp unit, a gas channel 75 is formed for directing the gas supplied from the mass flow controller 50 into the quartz chamber 12 towards the processing chamber 1. A slit plate (ion shielding plate) 78 with multiple holes is installed in this gas channel 75 to shield ions and electrons generated in the plasma generated inside the quartz chamber 12, allowing only neutral gas and neutral radicals to pass through and irradiate the wafer 2.

[0045] Stage 4 has a coolant channel 39 formed inside for cooling Stage 4, and the coolant is circulated and supplied by a chiller 38. In addition, electrostatic adsorption electrodes 30, which are plate-shaped electrode plates, are embedded in Stage 4 in order to fix the wafer 2 to Stage 4 by electrostatic adsorption, and a DC (Direct Current) power supply 31 for electrostatic adsorption is connected to each of them.

[0046] Furthermore, in order to efficiently cool the wafer 2, He gas can be supplied between the back surface of the wafer 2 placed on the stage 4 and the stage 4. In addition, to prevent damage to the back surface of the wafer 2 even when heating or cooling is performed while the wafer 2 is electrostatically adsorbed by the electrostatic adsorption electrode 30, the wafer-holding surface of the stage 4 is coated with a resin such as polyimide. A thermocouple 70 for measuring the temperature of the stage 4 is installed inside the stage 4, and this thermocouple 70 is connected to a thermocouple thermometer 71.

[0047] Furthermore, optical fibers 92-1 and 92-2 for measuring the temperature of wafer 2 are installed at three locations: near the center of wafer 2 (also referred to as the wafer center), near the radial middle of wafer 2 (also referred to as the wafer middle), and near the outer edge of wafer 2 (also referred to as the wafer outer edge). Optical fiber 92-1 guides infrared light from the external infrared light source 93 to the back surface of wafer 2 and irradiates the back surface of wafer 2. On the other hand, optical fiber 92-2 collects the IR light that has been transmitted and reflected from wafer 2 among the infrared light irradiated by optical fiber 92-1 and transmits it to the spectrometer 96.

[0048] The external infrared light generated by the external infrared light source 93 is transmitted to the optical path switch 94 for turning the optical path on and off. Then, it is split into multiple paths by the optical distributor 95 (three paths in Figure 1), and irradiated to different locations on the back side of the wafer 2 via three optical fibers 92-1.

[0049] Infrared light absorbed and reflected by wafer 2 is transmitted to spectrometer 96 via optical fiber 92-2, and wavelength-dependent data of the spectral intensity is obtained by detector 97. The obtained wavelength-dependent data of the spectral intensity is then sent to calculation unit 41 of control unit 40, where the absorption wavelength is calculated, and the temperature of wafer 2 can be determined based on this. In addition, an optical multiplexer 98 is installed in the middle of optical fiber 92-2, allowing switching between measuring the light at the wafer center, wafer middle, or wafer periphery for spectral measurement. As a result, calculation unit 41 can determine the temperature of the wafer center, wafer middle, and wafer periphery separately.

[0050] In Figure 1, 60 is a container covering the quartz chamber 12, and 81 is an O-ring for vacuum sealing between the stage 4 and the bottom surface of the base chamber 11.

[0051] The control unit 40 controls the on / off switching of the high-frequency power supply from the high-frequency power supply 20 to the ICP coil 34. It also controls the mass flow controller control unit 51 to adjust the type and flow rate of gas supplied from each mass flow controller 50 into the quartz chamber 12. In this state, the control unit 40 further activates the exhaust means 15 and controls the pressure regulating means 14 to adjust the pressure inside the processing chamber 1 to the desired level.

[0052] Furthermore, the control unit 40 operates the DC power supply 31 for electrostatic adsorption to electrostatically adsorb the wafer 2 onto the stage 4, and operates the mass flow controller 50-7 that supplies He gas between the wafer 2 and the stage 4, while controlling the infrared lamp power supply 64 and chiller 38 so that the temperature of the wafer 2 is within a predetermined temperature range. At this time, the control unit 40 controls the infrared lamp power supply 64 and chiller 38 so that the temperature of the wafer 2 is within a predetermined temperature range based on the temperature inside the stage 4 measured by the thermocouple thermometer 71, and the temperature distribution information of the wafer 2 obtained by the calculation unit 41 based on the spectral intensity information of the wafer 2 near the center, near the radial middle, and near the outer edge of the wafer 2 measured by the detector 97. The temperature range is preferably -40°C to 0°C. A typical temperature is -20°C. Here, if the wafer temperature is below -40°C, the time required to lower the wafer temperature to that temperature in the temperature cycling process performed in the etching process becomes longer, and the time required for the etching process becomes longer, which is undesirable because it reduces the throughput, which is the number of wafers processed per unit time. On the other hand, if the wafer temperature rises above 0°C, the volatilization of titanium fluoride contained in the surface reaction layer generated during plasma processing progresses, leading to the problem that the reaction cannot be self-saturated.

[0053] The processing flow of the wafer 2 carried out by the plasma processing apparatus 100 of this embodiment will be explained using Figure 2. Figure 2 is a schematic flowchart of the etching process of a titanium carbide film pre-formed on a wafer, carried out by the plasma processing apparatus according to the embodiment of this disclosure.

[0054] In Figure 2, before processing of the wafer 2 begins, the wafer 2, which has a film structure including a film layer to be processed, including a titanium carbide film, pre-arranged on its surface, is placed on the stage 4 in the processing chamber 1, and is held on the stage 4 by the electrostatic force formed by the supply of DC power from the DC power supply 31 to the electrostatic adsorption electrode 30.

[0055] After the start of processing, in step S201, a gas containing fluorine and oxygen but not hydrogen is introduced into processing chamber 1. Examples of gases that can be used include methane tetrafluoride (CF4) / oxygen (O2) or nitrogen trifluoride (NF3) / oxygen (O2). Alternatively, a mixed gas obtained by diluting these gases with argon (Ar) or nitrogen (N2) may be used. Furthermore, the wafer temperature in step S201 is kept constant by the temperature control function of stage 4 on which wafer 2 is placed. When using nitrogen trifluoride (NF3) or nitrogen (N2), mass flow controllers 50-1 and 50-8 for nitrogen (N2) or mass flow controller 50-5 for nitrogen trifluoride (NF3) are used.

[0056] Next, in step S202, plasma 10 is generated inside the discharge region 3 using the above gas, and reactive particles (also called reactive particles) such as radicals (active species) of fluorine (F) are generated when atoms or molecules of the gas containing fluorine and oxygen but not hydrogen in the plasma 10 are activated.

[0057] In step S203, reactive particles are supplied to the surface of the wafer 2 through the gas channel 75 and the through-holes of the slit plate 78, and adhere to the surface of the film layer containing the titanium carbide film. The reactive particles react with the material on the surface of the attached film layer to form a surface reaction layer of a thickness determined by the conditions for generating the plasma 10 and the processing conditions such as the temperature of the stage 4. At this time, the surface reaction layer formed on the surface of the film layer containing the titanium carbide film contains at least titanium-fluorine (Ti-F) bonds.

[0058] Subsequently, in step S204, after the control unit 40 confirms that a surface reaction layer of a predetermined thickness has been formed by a film thickness detector (not shown) or by checking the passage of a predetermined time, the pressure regulating means 14 increases the flow path cross-sectional area of ​​the vacuum exhaust pipe 16 to increase the exhaust volume and significantly reduces the pressure inside the processing chamber 1. Then, the gas containing fluorine and oxygen but no hydrogen that was supplied into the processing chamber 1 is rapidly exhausted. This completes the surface reaction layer formation process. At this time, an inert gas such as Ar may be supplied into the processing chamber 1 to replace the gas containing fluorine and oxygen but no hydrogen, thereby promoting the discharge of the gas containing fluorine and oxygen but no hydrogen.

[0059] Next, in step S205, the infrared lamp 62 is turned on, and the surface of the wafer 2 is heated in a vacuum state by the light (infrared light) emitted from the infrared lamp 62. The irradiation time of the infrared light at this time is, for example, 20 seconds, and the maximum temperature reached on the surface of the wafer 2 at that time is, for example, 120°C. The pressure in the processing chamber 1 during heating is, for example, 1 × 10⁻⁶ -3 The temperature was set to Pa. At this time, the temperature of wafer 2 rises at a rate of approximately 7°C / second as the irradiation time of the infrared lamp increases, and this temperature rise causes the surface reaction layer to volatilize from the surface and be removed (desorbed) from the surface of the film layer. The infrared lamp 62 is turned off when the temperature of wafer 2 has risen to a predetermined temperature, which is confirmed by the temperature detection mechanism (92-97, 41) or after a predetermined time has elapsed, as confirmed by the control unit 40.

[0060] Examples of volatile reaction products include titanium fluoride (TiF4) and carbon dioxide (CO2). These reaction product particles detached from the wafer 2 are discharged from the processing chamber 1 to the outside by the operation of the pressure regulating means 14 or the exhaust means 15, which evacuates the inside of the processing chamber 1, or by the resulting flow of particles inside the processing chamber 1. Subsequently, in step S206, the gas containing the reaction products is exhausted from the inside of the processing chamber 1 to the outside of the processing chamber 1.

[0061] One cycle consisting of the above steps S201 to S206 is completed. During this cycle, the surface reaction layer formed on the surface of the titanium carbide film due to the reaction with the plasma is removed (desorbed), so the titanium carbide film is removed by the thickness of the surface reaction layer, and the thickness of the titanium carbide film becomes thinner. This change in film thickness is the etching amount per cycle.

[0062] After this, the control unit 40 receives the output from a film thickness detector (not shown) and determines from the results obtained whether the desired etching amount has been reached, or whether the termination conditions, including the number of cycles for which the desired etching amount has been derived from prior tests, have been met (step S207). If it is determined that the conditions are met (S207: yes), the etching process of the film layer including the titanium carbide film is terminated. If it is determined that the conditions are not met (S207: no), the process returns to step S201 and the cycle (S201-S206) is performed again. In this embodiment, the cycle (S201-S206) is repeated until the desired etching amount is obtained.

[0063] The following describes the operation sequence when etching a film layer containing a titanium carbide film on a wafer 2 using the plasma processing apparatus 100 of this embodiment, with CF4 / O2 / Ar as the reaction layer formation gas, using Figures 3 and 4. Figure 3 is a time chart showing the changes over time of several parameters included in the processing conditions during wafer processing according to the embodiment shown in Figure 1. In Figure 3, the parameters are shown from top to bottom as gas supply flow rate, high-frequency power supply power, infrared lamp power, electrostatic adsorption, and wafer surface temperature.

[0064] Figure 4 is a schematic cross-sectional view illustrating the changes in the film structure, including the film layer containing the titanium carbide film, during the processing of a wafer according to the embodiment shown in Figure 3. In particular, Figure 4 schematically shows the structure near the surface of the titanium carbide film 402 and its changes in a film structure in which the titanium carbide film 402 is laminated and arranged adjacent to the underlayer film 401 of the wafer 2.

[0065] First, at time t0 during processing as shown in Figure 3, in response to a command signal from the control unit 40, a wafer 2, which has a pre-formed film structure consisting of a base film 401 and a titanium carbide film 402 to be etched, as shown in Figure 4(a), is transported into the processing chamber 1 via a transport port (not shown) provided in the processing chamber 1 and placed on the stage 4. Subsequently, power from the DC power supply 31 is supplied to the electrostatic adsorption electrode 30, and the wafer 2 is electrostatically adsorbed and held on the dielectric film on the stage 4. Furthermore, in response to a command signal from the control unit 40, the mass flow controller 50-7 of the mass flow controller control unit 51, which is compatible with He gas, adjusts and supplies the flow rate of He gas for wafer cooling to the gap between the back surface of the wafer 2 and the stage 4, and the pressure of the He gas in the gap is adjusted to a value within a predetermined range. As a result, heat transfer between the stage 4 and the wafer 2 is promoted, and the surface temperature of the wafer 2 is brought to a value T1 close to the temperature of the stage 4, where a refrigerant that has been pre-heated to a predetermined temperature by the chiller 38 is supplied to the refrigerant flow path 39 and circulated. In this embodiment, the surface temperature T1 of wafer 2 is set to, for example, -20°C.

[0066] Next, at time t1 shown in Figure 3, the flow rates supplied by the mass flow controllers 50-3 or 50-6 for CF4, 50-2 for O2, and 50-4 for Ar are adjusted in response to a command signal from the control unit 40. As a result, a mixed gas of these multiple types of substances is supplied to the processing chamber 1 as a processing gas at a predetermined flow rate. Simultaneously, the opening of the pressure regulating means 14 is adjusted so that the pressure inside the processing chamber 1 and inside the discharge region 3 of the quartz chamber 12 is within the desired range.

[0067] In this state, at time t2 shown in Figure 3, a predetermined value of W of high-frequency power is supplied from the high-frequency power supply 20 to the ICP coil 34 in response to a command signal from the control unit 40, and plasma discharge is started in the discharge region 3 inside the quartz chamber 12, generating plasma 10 inside the quartz chamber 12. At this time, power is not supplied to the infrared lamp 62 in order to maintain the temperature of the wafer 2 at the same level as before the generation of the plasma 10 while the plasma 10 is being generated.

[0068] In this state, at least a portion of the CF4 / O2 / Ar gas particles are excited, dissociated, or ionized by the plasma 10, forming charged particles such as ions or reactive particles such as active species. The reactive particles such as active species and the neutral gas formed in the discharge region 3 are introduced into the processing chamber 1 through slits or through holes formed in the slit plate 78 and supplied to the surface of the wafer 2. As shown in Figure 4(b), active species 403, including fluorine radicals (F), are adsorbed onto the surface of the titanium carbide film 402 on the wafer 2 and interact with the material of the titanium carbide film 402, forming a surface reaction layer 404. In other words, reactive particles 403 containing fluorine and oxygen but not hydrogen are supplied to the surface of the titanium carbide film 402 to form a surface reaction layer 404 on the surface of the titanium carbide film 402.

[0069] This surface reaction layer 404 is a reaction product mainly containing Ti-F bonds, and a key feature is that when measured by X-ray photoelectron spectroscopy using aluminum Kα rays, it exhibits peaks at bond energies of titanium 2p around 462±2eV (2p 3 / 2) and around 467±2eV (2p 1 / 2). Figure 5 shows the photoelectron spectrum obtained when the surface of the titanium carbide film 402 on which the surface reaction layer 404 is formed is analyzed by X-ray photoelectron spectroscopy using aluminum Kα rays. At the binding energy (eV), peaks at around 462±2eV and 467±2eV, attributable to the surface reaction layer 404 and indicating the presence of Ti-F bonds, are observed. The composition of this surface reaction layer depends on the composition of the gas used and the reaction time. It may consist of elemental fluorine, or a mixture of carbon, fluorine, and titanium in various bonding states, such as carbon fluoride or titanium fluoride. It may also contain titanium carbide oxides or carbon oxides. The bond energy values ​​shown here are calibrated assuming that the position of the carbon 1s peak, which is caused by surface contamination carbon observed on the surface of the initial sample, is 284.5 eV.

[0070] Figure 6 is a graph showing the dependence of the intensity of the titanium 2p peak due to the surface reaction layer 404 on the plasma treatment time. Plasma treatment time refers to the elapsed time since the start of supplying high-frequency power. As shown in Figure 6, the intensity of the titanium 2p peak due to the surface reaction layer 404 increased with the progression of plasma treatment time and showed a tendency to saturate, becoming almost constant after 60 seconds of plasma treatment time. Thus, the self-saturating property of the amount of reaction product generated is very similar to the spontaneous oxidation phenomenon of metal surfaces and silicon surfaces. Because the formation of the surface reaction layer is self-saturating, the amount of surface reaction layer 404 generated per cycle can be kept constant by performing plasma treatment for a time longer than required for saturation. In this embodiment, it took 60 seconds for the amount of surface reaction layer 404 generated to saturate, but the time required for saturation will vary depending on the device parameters such as the distance between the plasma source (12,34) and the wafer 2 and the substrate temperature.

[0071] After the plasma processing time required for the surface reactive layer to saturate has elapsed, at time t3 shown in Figure 3, the output of high-frequency power from the high-frequency power supply 20 is stopped and the supply of processing gas to the discharge region 3 is stopped in response to a command signal from the control unit 40. As a result, the plasma 10 in the discharge region 3 disappears. Between time t3 and time t4, the processing gas and particles such as reactive particles in the processing chamber 1 are exhausted to the outside of the processing chamber 1 via the vacuum exhaust pipe 16 and exhaust means 15, whose opening degree is adjusted by the pressure regulating means 14.

[0072] At time t4, the infrared lamp 62 is turned on in response to a command signal from the control unit 40, and the surface of the wafer 2 is vacuum heated by the light (infrared light) 405 emitted from the infrared lamp 62, as shown in Figure 4(c). The pressure in the processing chamber 1 at this time is, for example, 1 × 10⁻⁶ -3 Assuming Pa, the irradiation time of the infrared lamp 62 was, for example, 20 seconds. The maximum temperature that can be reached on the surface of the wafer 2 is, for example, 120°C. This process is a reaction in which the surface reaction layer 404 is decomposed into a reaction product 406 containing titanium fluoride, and then volatilized or desorbed. This desorption reaction is more advantageous at higher temperatures and lower pressures. The disclosers have found that in order to bring about this desorption reaction, the surface temperature of the wafer 2 must be 50°C or higher, and the pressure in the processing chamber 1 is preferably 10 Pa or less.

[0073] In this embodiment, the maximum temperature achievable on the surface of wafer 2 is 120°C, and the vacuum level of processing chamber 1 is 1 × 10⁻⁶. -3 Although Pa is used, the maximum achievable temperature can be set to an appropriate value in the temperature range of 50°C or higher. The typical temperature range is 50 to 150°C, and the typical pressure range of processing chamber 1 during heating is 1 × 10⁻⁶. -5 The pressure is approximately 10 Pa. Raising the heating temperature to 150°C would increase the heating time, leading to a decrease in throughput (the number of wafers that can be processed per unit time). Therefore, a wafer heating temperature of 150°C or lower is preferable.

[0074] Figure 7 shows a vacuum of 1 × 10⁻⁶. -4This graph shows the change in titanium 2p peak intensity attributable to the surface reaction layer 404 with respect to heating temperature when the surface reaction layer 404 is removed by vacuum heating in Pa. The results show that as the heating temperature increases, the intensity of the titanium 2p peak, which indicates the remaining amount of surface reaction layer 404, decreases. At a heating temperature of 50°C, the surface reaction layer 404 is significantly reduced, and at a heating temperature of 100°C, it is completely eliminated. Therefore, the optimal temperature range for heating is between 50°C and 150°C. In other words, the wafer temperature in the process of removing the surface reaction layer 404 (second step) is preferably between 50°C and 150°C. If the heating temperature is below 50°C, there is a problem of insufficient volatilization of the surface reaction layer 404, resulting in residual material. Furthermore, if the heating temperature is above 150°C, the temperature range for heating and cooling becomes larger, and the time required for heating and cooling increases, leading to a decrease in wafer processing throughput, which is undesirable. Furthermore, in this heating process, only the surface reaction layer 404 formed on the surface of wafer 2 decomposes and volatilizes, while the unreacted titanium carbide film 402 located beneath the surface reaction layer 404 remains completely unchanged. Therefore, only the surface reaction layer 404 portion can be removed. Accordingly, in addition to the process of forming the surface reaction layer 404, the process of removing the surface reaction layer 404 is also self-saturating.

[0075] During this heating process, although the wafer 2 is placed on the wafer stage 4, the supply of helium gas, which is used to increase the heat conduction on the back surface of the wafer 2, is stopped to allow the surface temperature of the wafer 2 to rise rapidly. In this embodiment, the wafer 2 was processed while it remained on the wafer stage 4, but infrared light may also be irradiated onto the wafer 2 while it is not in thermal contact with the wafer stage 4 using a lift pin (not shown) or the like. After the heating time necessary to remove the surface reaction layer 404 has elapsed, the infrared lamp 62 is turned off, and the residual gas in the processing chamber 1 is exhausted to the outside of the processing chamber 1 using the exhaust means 15. Subsequently, the supply of helium gas is restarted to increase the heat conduction between the wafer 2 and the wafer stage 4, and the wafer temperature is cooled to -20°C by the chiller 38, completing the first cycle of processing.

[0076] In response to a command signal from the control unit 40, the infrared lamp 62 is turned off at time t5 as shown in Figure 3. Furthermore, the gas containing reaction product particles and other particles in the processing chamber 1 is exhausted to the outside of the processing chamber 1 via the vacuum exhaust pipe 16 and exhaust means 15, whose opening is adjusted by the pressure regulating means 14. After time t5, as explained in Figure 2, it is determined whether the etching amount or remaining film thickness of the titanium carbide film 402 on the wafer 2 has reached a desired value (corresponding to step S207), and depending on the determination result, the next cycle is started (S201-S206) or the processing of the wafer 2 is terminated.

[0077] To start the next cycle, at any time t6 after time t5, the introduction of CF4 / O2 / Ar gas into the discharge region 3 is started in response to a command signal from the control unit 40, similar to the operation from time t1. In other words, as the next cycle, the process of forming the surface reaction layer 404 as described in Figure 4(b) and the process of desorbing the surface reaction layer by heating as described in Figure 4(c) are performed again. To finish processing the wafer 2, at time t6, the supply of He gas that was supplied to the gap between the back surface of the wafer 2 and the top surface of the stage 4 is stopped, the valve 52 is opened to discharge the He gas from the gap, the pressure in the gap is made to be approximately the same as the pressure in the processing chamber 1, and a process of releasing the electrostatic adsorption of the wafer 2, including the removal of static electricity, is performed. This completes the etching process of the titanium carbide film 402.

[0078] In this embodiment, when an etching amount of 6 nm was required, the above cycle was repeated five times to complete the etching. Figure 8 is a graph showing the relationship between the number of cycles and the amount of etching in the etching process performed by the plasma processing apparatus 100 according to this embodiment shown in Figure 1, and shows the results when the target film is titanium carbide and titanium nitride. The pressure is 50 Pa. In Figure 8, the horizontal axis represents the number of cycles, and the vertical axis represents the etching amount (etching depth) detected using in-situ ellipsometry (polarization analysis method) after the completion of each cycle and before the start of the next cycle.

[0079] As shown in Figure 8, in this example, the etching amount changes almost linearly with increasing cycle count. From Figure 8, it can be seen that the etching amount of the titanium carbide film per cycle in this embodiment is, for example, 1.2 nm / cycle. Furthermore, in this embodiment, etching of titanium nitride did not proceed, and titanium carbide could be selectively etched relative to titanium nitride. Therefore, when a film layer containing titanium carbide and another film layer containing titanium nitride are arranged on the surface of wafer 2, the etching process performed by the plasma processing apparatus 100 according to this embodiment does not proceed with etching of titanium nitride in the other film layers, meaning that titanium carbide in the film layer to be processed can be selectively etched relative to titanium nitride. This is an effect of the gas of this disclosure not containing hydrogen. In the plasma processing process, the gas contains fluorine and oxygen but not hydrogen, so a surface reaction layer such as ammonium titanium fluoride is not formed on the surface of the titanium nitride, and etching of titanium nitride does not proceed.

[0080] Figure 9 is a graph showing the relationship between the number of cycles and the amount of etching in the etching process performed by the plasma processing apparatus 100 according to this embodiment shown in Figure 1, and shows the results when the wafer temperature is changed to -20°C, 0°C, and 20°C. The pressure is 50 Pa. In addition, the plasma irradiation time is changed as a parameter to 60 seconds, 90 seconds, and 120 seconds. As shown in Figure 9, when the wafer temperature is low at -20°C, the amount of etching per cycle does not change even when the plasma irradiation time is changed, and it can be seen that the amount of etching has self-saturation with respect to the plasma irradiation time. On the other hand, when the wafer temperature is relatively high, such as 0°C or 20°C, the amount of etching per cycle increases with increasing plasma irradiation time, and self-saturation of the amount of etching with respect to plasma irradiation time is not observed. This is because when the wafer temperature is 0°C or higher, volatilization of reaction products such as titanium fluoride proceeds during plasma irradiation. From the above results, it was found that the wafer temperature range suitable for the process of this disclosure is in the range of -40°C to 0°C. In other words, the wafer temperature in the process of forming the surface reaction layer 404 is preferably in the range of -40°C to 0°C. The reason why the lower limit of the wafer temperature is -40°C is that if the wafer temperature is lowered to below -40°C, the temperature range for heating and cooling widens, increasing the time required for the process and reducing the throughput of wafer processing, which is undesirable. The appropriate pressure range in the plasma irradiation process is 0.1 Pa to 1000 Pa, and more specifically, the high effectiveness of this disclosure has been confirmed in the range of 1 Pa to 100 Pa.

[0081] As described above, both the step of forming the surface reaction layer 404 (first step) and the step of removing the surface reaction layer 404 (second step) in this embodiment have the property of self-saturating completion. Therefore, in this embodiment, when etching a wafer 2 on which a film structure having a circuit pattern has been pre-formed, the amount of etching on the surface of the titanium carbide film 402 after one cycle is reduced in both the in-plane direction and the depth direction of the wafer 2, making it more uniform.

[0082] Because the above-mentioned self-saturation is utilized, even if the density of reactive particles such as radicals supplied to the wafer 2 has a different distribution depending on the horizontal and depth directions of the upper surface of the wafer 2, excessive or insufficient etching is suppressed, and variations in etching amount are reduced. Furthermore, the total etching amount can be adjusted by increasing or decreasing the number of repetitions of one cycle (the first and second steps) including the first and second steps, and in this embodiment, the etching amount is the etching amount per cycle multiplied by the number of repetitions or the sum of the repetitions. As a result, in this embodiment, compared with conventional continuous plasma etching, the controllability of the dimensions after processing by etching and the yield of the process can be improved.

[0083] As described above, this embodiment provides an isotropic atomic layer etching technology that etches a titanium carbide film with high uniformity in the wafer plane direction and pattern depth direction, as well as high controllability of processing dimensions at the atomic layer level.

[0084] In this embodiment, a titanium carbide film was described as an example of a film layer to be treated that contains metal carbides. However, this disclosure also applies to cases where the titanium carbide film contains oxygen, nitrogen, or both oxygen and nitrogen as other components. Specifically, it can be applied not only to TiC but also to films such as TiCO, TiCN, and TiCNO.

[0085] In the plasma processing apparatus 100 shown in Figure 1, the infrared lamp 62 is positioned outside the vacuum vessel above the processing chamber 1 on the outer periphery of the quartz chamber 12 surrounding the discharge area 3. However, it may also be positioned inside the quartz chamber 12 or the vacuum vessel. Furthermore, the above-described example is explained in detail for the purpose of making this disclosure easy to understand, and is not necessarily limited to having all the configurations described. [Explanation of symbols]

[0086] 1: Processing chamber, 2: Wafer, 3: Discharge area, 4: Stage, 5: Shower plate, 6: Top plate, 10: Plasma, 11: Base chamber, 12: Quartz chamber, 14: Pressure regulating means, 15: Exhaust means, 16: Vacuum exhaust piping, 17: Gas dispersion plate, 20: High-frequency power supply, 22: Matching unit, 25: High-frequency cut filter, 30: Electrostatic adsorption electrode, 31: DC power supply, 34: ICP coil, 38: Chiller, 39: Refrigerant flow path, 40: Control unit, 41: Calculation unit, 50: Mass flow controller, 51: Mass flow controller control unit, 52: Valve, 60: Container, 62: Infrared lamp 63: Reflector, 64: Power supply for infrared lamp, 70: Thermocouple, 71: Thermocouple thermometer, 74: Light transmission window, 75: Gas flow path, 78: Slit plate, 81: O-ring, 92: Optical fiber, 93: External infrared light source, 94: Optical path switch, 95: Optical distributor, 96: Spectrometer, 97: Detector, 98: Optical multiplexer, 100: Plasma processing device, 401: Underlayment film, 402: Titanium carbide film, 403: Active species, 404: Surface reaction layer, 406: Reaction product, 901: Underlayment structure, 902: Fin structure, 903: Titanium carbide film, 904: Mask, 905: Reactant species, 906: Reaction product.

Claims

1. An etching method for etching a film layer containing titanium carbide that is to be treated and is placed on the surface of a wafer, A step of supplying reactive particles containing fluorine and oxygen but not hydrogen to the surface of the film layer to form a reaction layer on the surface of the film layer, A step of heating the film layer to remove the reaction layer, An etching method equipped with [a specific feature].

2. The etching method according to claim 1, An etching method characterized in that the reactive particles containing fluorine and oxygen but not hydrogen are formed from a gas composed of tetrafluoride methane and oxygen.

3. The etching method according to claim 1, An etching method characterized in that, when the film layer to be treated, which contains titanium carbide, and another film layer, which contains titanium nitride, are arranged on the surface of the wafer, the other film layer, which contains titanium nitride, is not etched.

4. The etching method according to claim 1, An etching method characterized in that the amount of reaction layer produced is self-saturating.

5. The etching method according to claim 1, An etching method characterized by repeating the process of forming the reaction layer and removing the reaction layer as a single cycle multiple times.

6. The etching method according to claim 1, An etching method characterized in that the wafer temperature in the step of forming the reaction layer is in the range of -40°C to 0°C.

7. The etching method according to claim 1, An etching method characterized in that the wafer temperature in the step of removing the reaction layer is in the range of 50°C to 150°C.

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