Etching method and etching apparatus

Abstract

The present invention provides a technology for appropriately etching an oxide film. This etching method includes: a carry-in step in which a substrate that has an oxide film formed on the surface thereof is carried into a chamber; a first measurement step in which, after the carry-in step, the amount of moisture in the chamber is measured in a state in which the pressure in the chamber has been reduced, to acquire a first measurement value; a supply amount determination step in which a supply amount of water vapor is determined on the basis of correspondence relationship data indicating a correspondence relationship between information pertaining to the amount of moisture in the chamber and information pertaining to the amount of water vapor to be supplied into the chamber, and the first measurement value measured in the first measurement step; and an etching step in which, while supplying water vapor into the chamber in the supply amount determined in the supply amount determination step, an etching gas that contains hydrogen fluoride gas is supplied into the chamber to etch the oxide film.

Description

Etching method and etching apparatus

[0001] The present disclosure relates to an etching method and an etching apparatus.

[0002] Substrate processing apparatuses for etching silicon oxide films have been proposed (for example, Patent Document 1). Patent Document 1 describes an etching method that can etch silicon oxide films formed by atomic layer deposition (ALD) or chemical vapor deposition (CVD) with a high selectivity relative to silicon oxide films formed by other methods such as thermal oxidation.

[0003] JP 2019-114628 A

[0004] As described in Patent Document 1, an oxide film on a substrate in a chamber can be etched by supplying hydrogen fluoride gas and water vapor into the chamber. At this time, the hydrogen fluoride gas and water react to generate hydrogen fluoride ions. The hydrogen fluoride ions contribute to etching the oxide film.

[0005] Incidentally, the oxide film on the substrate also contains moisture. The etching gas also reacts with this moisture to etch the oxide film. Therefore, if the moisture content in the oxide film on the substrate is low, etching may be insufficient, while if the moisture content in the oxide film on the substrate is high, etching may be excessive.

[0006] Therefore, an object of the present disclosure is to provide a technique for appropriately etching an oxide film.

[0007] A first aspect is an etching method comprising: a loading step of loading a substrate having an oxide film formed on its surface into a chamber; a first measurement step of measuring the amount of moisture in the chamber after the loading step while the chamber is depressurized to obtain a first measurement value; a supply amount determination step of determining the supply amount of water vapor based on correspondence data indicating a correspondence between information on the amount of moisture in the chamber and information on a supply amount of water vapor to be supplied to the chamber, and the first measurement value measured in the first measurement step; and an etching step of supplying an etching gas containing hydrogen fluoride gas into the chamber while supplying the water vapor into the chamber at the supply amount determined in the supply amount determination step, to etch the oxide film.

[0008] A second aspect is an etching method according to the first aspect, further comprising: a second measurement step of measuring the moisture content in the chamber to obtain a second measurement value when the substrate is not loaded into the chamber and the chamber is depressurized; and a calculation step of calculating the substrate moisture content by subtracting the second measurement value measured in the second measurement step from the first measurement value measured in the first measurement step, and in the supply amount determination step, the supply amount of water vapor is determined based on the correspondence data indicating the correspondence between the substrate moisture content and the supply amount and the substrate moisture content calculated in the calculation step.

[0009] A third aspect is the etching method according to the first or second aspect, wherein the pressure in the chamber in the first measuring step is lower than the pressure in the chamber in the etching step.

[0010] A fourth aspect is an etching method according to the third aspect, wherein in the first measurement step, the pressure in the chamber is measured, and the amount of water in the chamber is measured while the pressure in the chamber is adjusted so that the measured value of the pressure in the chamber approaches a target pressure.

[0011] A fifth aspect is an etching method according to any one of the first to fourth aspects, wherein in the first measurement step, the moisture content in the chamber measured after a predetermined time has elapsed since the substrate was loaded, the peak value of the moisture content, or the convergence value of the moisture content, is obtained as the first measurement value in the time change of the moisture content in the chamber.

[0012] A sixth aspect is an etching method according to any one of the first to fifth aspects, wherein the etching step is carried out when the amount of moisture in the chamber or the change in the amount of moisture over time is equal to or less than a predetermined reference value.

[0013] A seventh aspect is the etching method according to any one of the first to sixth aspects, wherein in the etching step, a CVD oxide film is selectively etched relative to a thermal oxide film on the substrate.

[0014] an etching apparatus including: a chamber; a substrate holder provided in the chamber and supporting or holding a substrate; an etching gas supply unit including an etching gas pipe connected to the chamber and an etching gas valve provided on the etching gas pipe; a water vapor supply unit including a water vapor pipe connected to the chamber and a water vapor valve provided on the water vapor pipe; a pressure reduction unit including a suction pipe connected to the chamber and a suction unit that suctions gas in the chamber through the suction pipe; a moisture sensor that measures a moisture amount in the chamber; a memory unit that stores correspondence data indicating a correspondence between information about the moisture amount in the chamber and information about a supply amount of water vapor to be supplied into the chamber; and a control unit that determines a supply amount of water vapor based on the moisture amount measured by the moisture sensor and the correspondence data when the substrate holder supports or holds the substrate and the pressure reduction unit depressurizes the chamber, and causes the etching gas supply unit to supply the etching gas to the chamber and the water vapor supply unit to supply the water vapor to the chamber at the supply amount.

[0015] According to the first aspect, the first measurement value measured in the first measurement step reflects the amount of moisture in the oxide film of the substrate. That is, the amount of moisture in the oxide film of the substrate is indirectly measured in the first measurement step. Therefore, the supply amount determination step can determine the amount of water vapor to be supplied based on the amount of moisture in the oxide film of the substrate. Therefore, even if the amount of moisture in the oxide film of the substrate varies among multiple substrates, the oxide film can be etched with an etching amount that is more appropriate for each substrate.

[0016] According to the second aspect, the second measurement value, which is the amount of moisture in the chamber when no substrate is loaded, is subtracted from the first measurement value, so that the substrate moisture amount reflects the amount of moisture in the oxide film of the substrate with high accuracy, thereby enabling the oxide film to be etched with a more uniform etching amount.

[0017] According to the third aspect, the first measurement value obtained in the first measurement step reflects the moisture content in the oxide film of the substrate with higher accuracy, and therefore the amount of water vapor supplied can be appropriately determined in accordance with the moisture content in the oxide film of the substrate.

[0018] According to the fourth aspect, the influence of pressure fluctuations in the chamber on the first measurement value can be reduced, so that the first measurement value that reflects the amount of moisture in the oxide film of the substrate with higher accuracy can be obtained.

[0019] According to the fifth aspect, it is possible to obtain a first measurement value that appropriately reflects the amount of moisture in the oxide film of the substrate.

[0020] According to the sixth aspect, the etching process can be performed on the substrate more stably.

[0021] According to the seventh aspect, the CVD oxide film can be etched with a uniform etching amount.

[0022] According to the eighth aspect, even if the amount of moisture in the oxide film of the substrate varies among a plurality of substrates, the oxide film can be etched with an etching amount that is more appropriate for each substrate.

[0023] FIG. 1 is a side view schematically showing an example of the configuration of an etching apparatus. FIG. 2 is a block diagram schematically showing an example of the configuration of a control unit. FIG. 3 is a flowchart showing an example of the operation of the etching apparatus according to the first embodiment. FIG. 4 is a diagram schematically showing an example of the state of the etching apparatus at each step. FIG. 5 is a diagram schematically showing an example of the state of the etching apparatus at each step. FIG. 6 is a graph schematically showing an example of the change in the amount of moisture in a chamber over time. FIG. 7 is a flowchart showing an example of the operation of the etching apparatus according to the second embodiment. FIG. 8 is a diagram schematically showing an example of the state of the etching apparatus at each step. FIG. 9 is a flowchart showing an example of the operation of the etching apparatus according to the third embodiment.

[0024] Hereinafter, the embodiments will be described in detail with reference to the drawings. In the drawings, the dimensions and numbers of parts are exaggerated or simplified as necessary for ease of understanding. Parts having similar configurations and functions are designated by the same reference numerals, and duplicate explanations will be omitted below.

[0025] In the following description, the same components are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions of them may be omitted to avoid duplication.

[0026] Furthermore, in the following description, even if ordinal numbers such as "first" or "second" are used, these terms are used for convenience to facilitate understanding of the contents of the embodiments, and are not limited to the order that may result from these ordinal numbers.

[0027] When expressions indicating relative or absolute positional relationships (e.g., "in one direction," "along one direction," "parallel," "orthogonal," "center," "concentric," "coaxial," etc.) are used, unless otherwise specified, the expressions not only strictly represent the positional relationship but also represent a state in which there is a relative displacement in terms of angle or distance within a range in which tolerance or equivalent functionality is obtained. When expressions indicating an equal state (e.g., "identical," "equal," "homogeneous," etc.) are used, the expressions not only represent a state in which there is strict quantitative equality but also represent a state in which there is a difference in which tolerance or equivalent functionality is obtained, unless otherwise specified. When expressions indicating a shape (e.g., "rectangular shape" or "cylindrical shape," etc.) are used, the expressions not only represent a geometrically strict shape but also represent a shape with, for example, irregularities or chamfers within a range in which equivalent effects are obtained. When the expressions "comprise," "include," "have," "includes," "includes," or "have" are used to describe one component, the expressions are not exclusive expressions that exclude the presence of other components. When the phrase "at least one of A, B, and C" is used, the phrase includes A only, B only, C only, any two of A, B, and C, and all of A, B, and C.

[0028] First Embodiment FIG. 1 is a side view schematically illustrating an example of the configuration of an etching apparatus 1. The etching apparatus 1 is a single-wafer etching apparatus that etches substrates W, such as semiconductor wafers, one by one, and is, for example, a gas-phase etching apparatus that does not use plasma. The etching apparatus 1 can be applied to a part of an apparatus for manufacturing semiconductor devices. Note that the substrate W is not necessarily limited to a substrate for a semiconductor device. The substrate W may also be, for example, a liquid crystal display substrate, a plasma display substrate, an organic electroluminescence (EL) substrate, an FED (Field Emission Display) substrate, an optical display substrate, an organic electroluminescence (EL) substrate, a magneto-optical disk substrate, a photomask substrate, or a solar cell substrate.

[0029] Various oxide films can be formed on the surface of the substrate W in a pre-process before the substrate W is loaded into the etching apparatus 1. For example, a thermal oxide film is formed. In this example, the substrate W is a silicon substrate, and a silicon thermal oxide film is formed on the surface. The thermal oxide film is formed by a method of oxidizing the substrate W from the surface to the inside. Specifically, the substrate W is exposed to oxygen or water vapor in a high-temperature atmosphere, whereby silicon (Si) and oxygen (O ２ ) to chemically react with silicon dioxide (SiO ２ ) thin film (thermal oxide film) is formed.

[0030] Other films are also formed on the surface of the substrate W. Examples of other films include a TEOS (Tetra Ethoxy Silane) film, a BSG (Boron Silicate Glass) film, a PSG (Phospho Silicate Glass) film, and a BPSG (Boron-doped Phospho Silicate Glass) film formed by a chemical vapor deposition (CVD) method, and an oxide film such as an ALD oxide film formed by an atomic layer deposition (ALD) method.

[0031] In the CVD method, for example, the substrate W is exposed to a source gas containing components of a target thin film, and a chemical reaction is induced on the substrate W using heat or plasma. This chemical reaction forms the target thin film on the substrate W. For example, when a BSG film is formed by the CVD method, the source gas contains boron (B).

[0032] In the ALD method, first, a substrate W placed in a chamber is exposed to precursor A. Then, precursor A is removed from the chamber by purging, and the substrate is exposed to another precursor B (e.g., ozone). Then, precursor B is removed from the chamber again by purging. By repeating these processes, a film at the single-molecular level is formed layer by layer. Specifically, when a silicon oxide film is to be formed as an ALD oxide film, aminosilane is used as the source gas (precursor A), and aluminum oxide (Al ２ O ３ When a SiO 2 film is to be formed, trimethylaluminum is used as the source gas.

[0033] In the following description, it is assumed that a thermal oxide film and a CVD oxide film are exposed as silicon oxide films on the surface of the substrate W. Also, as an example, the etching apparatus 1 selectively etches the CVD oxide film of the substrate W relative to the thermal oxide film.

[0034] The etching apparatus 1 includes a chamber 10 , a substrate holder 2 , an etching gas supply unit 3 , a water vapor supply unit 4 , a pressure reduction unit 6 , a moisture sensor 7 , and a control unit 9 .

[0035] The chamber 10 is formed to be hollow and capable of accommodating a substrate W therein. The internal space of the chamber 10 corresponds to a processing chamber in which the substrate W is subjected to an etching process.

[0036] The substrate holder 2 is provided in the chamber 10 and supports or holds the substrate W. In the example of FIG. 1 , the substrate holder 2 supports or holds the substrate W in a horizontal position. Here, "horizontal position" refers to a state in which the substrate W is parallel to a horizontal plane. An oxide film is formed on the upper surface of the substrate W. The substrate W is carried into the chamber 10 from the outside by the transport unit 15 and placed on the substrate holder 2. The substrate holder 2 may hold the substrate W by suction, or may clamp the periphery of the substrate W with multiple chuck pins. Note that the substrate holder 2 does not need to hold the substrate W, and may simply support the substrate W. In other words, the substrate holder 2 may be a mounting table on which the substrate W is placed.

[0037] A temperature regulator (not shown) may be provided inside the substrate holder 2. The temperature regulator adjusts the temperature of the substrate W to a temperature range suitable for processing. The temperature regulator is, for example, a resistance heating type or an optical type heater.

[0038] In the example of Fig. 1, the chamber 10 is connected to a transfer unit 15 through a gate valve 13. The transfer unit 15 includes a transfer chamber (not shown) that forms a transfer chamber, and a transfer robot (not shown) provided in the transfer chamber. The gate valve 13 switches between communication between the chamber 10 and the transfer chamber and disconnection. The gate valve 13 and the transfer unit 15 are controlled by a control unit 9.

[0039] The transport unit 15 receives an unprocessed substrate W from the outside and transports it into the chamber 10 through the gate valve 13. The etching apparatus 1 etches the oxide film on the top surface of the substrate W that has been transported into the chamber 10. The transport unit 15 removes the etched substrate W from the chamber 10 and transports it to the outside. By repeating the same operations thereafter, the etching apparatus 1 can etch a plurality of substrates W one by one.

[0040] The pressure reducing unit 6 reduces the pressure within the chamber 10. The pressure reducing unit 6 includes a suction pipe 61, a pressure adjustment valve 62, and a suction unit 63. The suction pipe 61 connects the chamber 10 to an external exhaust unit (not shown). The upstream port of the suction pipe 61 opens within the chamber 10. In the example of FIG. 1 , the upstream port of the suction pipe 61 is provided at a position adjacent to the substrate holder 2 on the bottom of the chamber 10. The suction unit 63 is provided in the suction pipe 61. The suction unit 63 is controlled by the control unit 9 and sucks gas from the chamber 10 through the suction pipe 61. The suction unit 63 includes, for example, a pump (specifically, a vacuum pump). The pressure adjustment valve 62 is provided in the suction pipe 61. The pressure adjustment valve 62 is controlled by the control unit 9. The control unit 9 can reduce the pressure within the chamber 10 to within a predetermined pressure range by controlling the opening degree of the pressure adjustment valve 62 and the suction unit 63.

[0041] 1, the etching apparatus 1 may be provided with a pressure sensor 71. The pressure sensor 71 measures the pressure inside the chamber 10 and outputs an electrical signal indicating the measurement result to the control unit 9. The pressure sensor 71 is, for example, a resistive film type, a capacitance type, a piezoelectric element type, or an optical type sensor. The control unit 9 controls the pressure adjustment valve 62 so that the pressure value measured by the pressure sensor 71 approaches the target pressure. In this case, the pressure inside the chamber 10 is adjusted to the target pressure with higher accuracy.

[0042] In the example of FIG. 1 , the etching apparatus 1 is also provided with an inert gas supply unit 8. The inert gas supply unit 8 supplies an inert gas into the chamber 10. The inert gas includes, for example, at least one of nitrogen gas and a rare gas. The rare gas is, for example, argon gas. In the example of FIG. 1 , the inert gas supply unit 8 includes an inert gas pipe 81 and an inert gas valve 82. The inert gas pipe 81 is connected to the chamber 10 and an inert gas supply source (not shown). That is, the downstream port of the inert gas pipe 81 opens in the chamber 10, and the upstream end of the inert gas pipe 81 is connected to the inert gas supply source.

[0043] 1, the downstream portion of the inert gas pipe 81 also serves as the etching gas pipe 31 and the water vapor pipe 41, which will be described later. Specifically, the inert gas pipe 81 includes a common pipe 30 and a branch pipe 811, and the common pipe 30 also serves as the etching gas pipe 31 and the water vapor pipe 41. In the example of Fig. 1, the downstream port of the common pipe 30 opens in the ceiling of the chamber 10. The downstream end of the branch pipe 811 is connected to the common pipe 30, and the upstream end of the branch pipe 811 is connected to an inert gas supply source.

[0044] The inert gas valve 82 is provided in the inert gas pipe 81 (specifically, the branch pipe 811). The inert gas valve 82 is controlled by the control unit 9, and switches the flow path of the inert gas pipe 81 between open and closed. When the control unit 9 opens the inert gas valve 82, the inert gas is supplied into the chamber 10 through the inert gas pipe 81. This makes it possible, for example, to increase the pressure inside the chamber 10 with the inert gas. For example, the pressure inside the chamber 10 can be increased to near standard atmospheric pressure.

[0045] The etching gas supply unit 3 supplies an etching gas into the chamber 10. The etching gas supply unit 3 includes an etching gas pipe 31 and an etching gas valve 32. The etching gas pipe 31 is connected to the chamber 10 and an etching gas supply source (not shown). A downstream port of the etching gas pipe 31 opens into the chamber 10. In the example of FIG. 1 , the etching gas pipe 31 is connected to the ceiling of the chamber 10. The etching gas valve 32 is provided on the etching gas pipe 31. The etching gas valve 32 is controlled by the control unit 9 and switches between opening and closing the flow path of the etching gas pipe 31. When the control unit 9 opens the etching gas valve 32, the etching gas is supplied into the chamber 10 through the etching gas pipe 31.

[0046] As will be described later, the etching gas etches the oxide film on the substrate W while reacting with moisture. The etching gas is, for example, hydrogen fluoride (HF) gas. As a more specific example, anhydrous hydrogen fluoride gas is used as the etching gas. The anhydrous hydrogen fluoride gas referred to here is hydrogen fluoride gas that contains almost no moisture, and for example, the moisture content (volume ratio) is several tens (e.g., 10) vol. ppm or less.

[0047] In the example of FIG. 1 , a gas dispersion plate 12 is provided in the chamber 10. The gas dispersion plate 12 has a plate-like shape and is provided with its thickness direction aligned vertically. In the example of FIG. 1 , the periphery of the gas dispersion plate 12 is connected to the inner wall of the chamber 10. The gas dispersion plate 12 is provided between the downstream port of the etching gas pipe 31 and the substrate holder 2. The gas dispersion plate 12 has a plurality of openings 12 a. The openings 12 a penetrate the gas dispersion plate 12 along its thickness direction. The plurality of openings 12 a are arranged in a two-dimensionally dispersed manner in a plan view. The etching gas supplied into the chamber 10 passes through the openings 12 a of the gas dispersion plate 12 and moves toward the substrate W on the substrate holder 2. The gas dispersion plate 12 can function as a flow rectifying plate that rectifies the flow of gas.

[0048] The water vapor supply unit 4 supplies water vapor into the chamber 10. The water vapor supply unit 4 includes a water vapor pipe 41 and a water vapor valve 42. The water vapor pipe 41 is connected to the chamber 10 and a vaporizer 43. In the example of FIG. 1 , the downstream portion of the etching gas pipe 31 is also used as the water vapor pipe 41. Specifically, in the example of FIG. 1 , the etching gas pipe 31 includes a common pipe 30 and a branch pipe 311, and the water vapor pipe 41 includes the common pipe 30 and a branch pipe 411. In other words, the common pipe 30 is used as both the etching gas pipe 31 and the water vapor pipe 41. The downstream port of the common pipe 30 opens in the chamber 10, and the downstream ends of the branch pipes 311 and 411 are connected to the common pipe 30. The upstream end of the branch pipe 311 is connected to an etching gas supply source (not shown), and the upstream end of the branch pipe 411 is connected to the vaporizer 43.

[0049] The vaporizer 43 vaporizes water to generate water vapor and supplies the water vapor to the upstream end of the water vapor pipe 41. In the example of FIG. 1 , a water supply pipe 44 is connected to the vaporizer 43. The upstream end of the water supply pipe 44 is connected to a water supply source (not shown). The vaporizer 43 includes, for example, a tank (not shown). Water (liquid) from the water supply source is supplied to the tank of the vaporizer 43 through the water supply pipe 44. The water may be pure water (in other words, deionized water). The vaporizer 43 also includes, for example, a heater (not shown) that heats the water stored in the tank to evaporate the water. The heater is controlled by the control unit 9.

[0050] 1, a carrier gas pipe 45 is also connected to the vaporizer 34. The upstream end of the carrier gas pipe 45 is connected to a carrier gas supply source (not shown). An inert gas is used as the carrier gas. The carrier gas flowing into the vaporizer 43 through the carrier gas pipe 45 is supplied into the chamber 10 together with the water vapor in the vaporizer 43 through the water vapor pipe 41.

[0051] 1 , the water supply pipe 44 is provided with a flow rate adjustment valve 46, and the carrier gas pipe 45 is provided with a flow rate adjustment valve 47. The flow rate adjustment valve 46 is controlled by the control unit 9 to adjust the flow rate of water flowing through the water supply pipe 44. The flow rate adjustment valve 47 is controlled by the control unit 9 to adjust the flow rate of the carrier gas flowing through the carrier gas pipe 45. Each of the flow rate adjustment valve 46 and the flow rate adjustment valve 47 is, for example, a mass flow controller.

[0052] The water vapor valve 42 is provided in the water vapor pipe 41. Specifically, the water vapor valve 42 is provided in the branch pipe 411. The water vapor valve 42 is controlled by the control unit 9 to switch between opening and closing the flow path of the water vapor pipe 41. When the control unit 9 opens the water vapor valve 42 and causes the vaporizer 43 to vaporize water, the water vapor and carrier gas from the vaporizer 43 are supplied into the chamber 10 through the water vapor pipe 41. Note that the carrier gas itself makes almost no contribution to etching of the substrate W, and therefore the carrier gas will be omitted in the following description.

[0053] The etching gas and water vapor flowing out from the downstream port of the common pipe 30 flow toward the surface (here, the upper surface) of the substrate W on the substrate holder 2. In the example of FIG. 1 , the etching gas and water vapor pass through the opening 12a of the gas dispersion plate 12 and flow toward the substrate W. The etching gas and water vapor react with each other to etch the oxide film on the substrate W. An example of a specific reaction formula is as follows:

[0054] 2HF+H ２ O → HF ２ － +H ３ O ＋ ... (1) SiO ２ +2HF ２ － +2H ３ O ＋ →SiF ４ +4H ２As shown in formula (1), hydrogen fluoride gas, which is an etching gas, reacts with water to generate hydrogen difluoride ions and hydronium, and as shown in formula (2), these ions react with the silicon oxide film to generate silicon tetrafluoride and water vapor, thereby removing the silicon oxide film (e.g., a CVD film).

[0055] The etching rate of an oxide film is largely dependent on the amount of water that reacts with hydrogen fluoride. For example, the greater the amount of water, the higher the etching rate. In addition, in the reaction of formula (1), hydrogen fluoride gas reacts not only with the water vapor supplied into the chamber 10 but also with the moisture contained in the oxide film on the substrate W. Therefore, the greater the amount of water vapor supplied and the amount of moisture in the substrate W, the higher the etching rate.

[0056] On the other hand, the amount of moisture in the oxide film of the substrate W may vary among multiple substrates W. Therefore, if the same amount of water vapor is supplied to multiple substrates W, there is a risk that the degree of etching may vary among the multiple substrates W. In this embodiment, as will be described in detail later, the etching apparatus 1 estimates the amount of moisture in the oxide film of the substrate W and adjusts the amount of water vapor supplied based on the estimated amount of moisture, thereby achieving uniform etching.

[0057] The moisture sensor 7 measures the amount of moisture in the chamber 10 and outputs an electrical signal indicating the measurement result to the control unit 9. Since the amount of moisture in the chamber 10 is mainly the amount of water vapor, it can also be said that the moisture sensor 7 measures the amount of water vapor. The moisture sensor 7 is, for example, a quadrupole mass spectrometer. In this case, the moisture sensor 7 measures the mass of water. As will be described in detail later, the control unit 9 determines the amount of water vapor to be supplied into the chamber 10 based on the measurement result of the moisture sensor 7.

[0058] The control unit 9 controls various components of the etching apparatus 1. FIG. 2 is a block diagram illustrating an example of the configuration of the control unit 9. The control unit 9 is an electronic circuit, and includes, for example, a data processing unit 91 and a storage unit 92. In the specific example of FIG. 2, the data processing unit 91 and the storage unit 92 are connected to each other via a bus 93. The data processing unit 91 may be, for example, an arithmetic processing device such as a central processing unit (CPU). The storage unit 92 may include a non-transitory storage unit (e.g., a read-only memory (ROM)) 921 and a temporary storage unit (e.g., a random access memory (RAM)) 922. The non-transitory storage unit 921 may store, for example, a program that defines the processing to be performed by the control unit 90. The data processing unit 91 executes this program, allowing the control unit 9 to perform the processing defined in the program. Of course, some or all of the processing performed by the control unit 9 may be performed by hardware such as a dedicated logic circuit. Furthermore, multiple units including the data processing unit 91 and the storage unit 92 may be provided. In this case, the functions realized by the control unit 9 may be shared among multiple data processing units 91.

[0059] As shown in Fig. 2, the control unit 9 may be electrically connected to a storage unit 94. The storage unit 94 is a non-transitory storage unit, and may be, for example, a memory or a hard disk. In Fig. 2, the storage unit 94 stores correspondence data D1. The correspondence data D1 will be described in detail later.

[0060] The control unit 9 also has a function of determining the amount of water vapor to be supplied into the chamber 10 based on the measurement result of the moisture sensor 7. This will be described in detail later.

[0061] Next, an example of the operation of the etching apparatus 1 will be described. Fig. 3 is a flowchart showing an example of the operation of the etching apparatus 1 according to the first embodiment, and Figs. 4 and 5 are diagrams schematically showing an example of the state of the etching apparatus 1 at each step. The flow of Fig. 3 is executed by the control unit 9 controlling each component of the etching apparatus 1. Here, it is assumed that the etching gas valve 32, the water vapor valve 42, and the inert gas valve 82 are initially closed.

[0062] 3, first, the pressure reducing unit 6 reduces the pressure in the chamber 10 (step S1: pressure reducing step). Specifically, the control unit 9 opens the pressure adjustment valve 62 and activates the suction unit 63. The operation of the suction unit 63 sucks gas from the chamber 10, reducing the pressure in the chamber 10. FIG. 4A shows an example of the etching apparatus 1 in step S1. In FIG. 4A, the substrate W has not yet been loaded into the chamber 10, and gas in the chamber 10 is sucked through the suction pipe 61. The pressure reducing unit 6 reduces the pressure in the chamber 10 to, for example, less than 1 Torr or a few Pa or less.

[0063] The control unit 9 may control the aperture of the pressure adjustment valve 62 to a predetermined aperture (e.g., maximum aperture). Alternatively, the control unit 9 may feedback-control the aperture of the pressure adjustment valve 62 so that the pressure in the chamber 10 approaches a predetermined first pressure value (first target pressure). For example, the pressure sensor 71 measures the pressure in the chamber 10 at predetermined time intervals and outputs the measured pressure to the control unit 9 at predetermined time intervals. The control unit 9 dynamically adjusts the aperture of the pressure adjustment valve 62 so that the measured pressure approaches the first pressure value. This feedback control allows the decompression unit 6 to adjust the pressure in the chamber 10 to the first pressure value with higher accuracy. The decompression unit 6 adjusts the pressure in the chamber 10 to the first pressure value at least until step S3, described below, is completed.

[0064] Next, the transfer unit 15 loads the substrate W into the chamber 10 (step S2: loading step). That is, in the example of FIG. 3 , the transfer unit 15 loads the substrate W into the chamber 10 in a reduced pressure state where the pressure inside the chamber 10 is reduced. Here, the transfer unit 15 includes a pressure reduction unit (not shown) that reduces the pressure inside the transfer chamber. The configuration of this pressure reduction unit may be similar to that of the pressure reduction unit 6. The pressure reduction unit of the transfer unit 15 reduces the pressure inside the transfer chamber while the transfer robot holds the unprocessed substrate W. The pressure reduction unit can also reduce the pressure inside the transfer chamber to the same level as the pressure inside the chamber 10. Next, the control unit 9 opens the gate valve 13, and the transfer robot of the transfer unit 15 transfers the substrate W to the substrate holder 2. Then, after the transfer robot has transferred the substrate W, the control unit 9 closes the gate valve 13.

[0065] Next, the moisture sensor 7 measures the moisture content in the chamber 10 (step S3: first measurement step). FIG. 4B shows an example of the etching apparatus 1 in step S3. In step S3, the moisture sensor 7 measures the moisture content in the chamber 10 to obtain a first measurement value when the substrate W has already been loaded into the chamber 10 and the chamber 10 is depressurized. When the chamber 10 is depressurized, some of the moisture contained in the oxide film of the substrate W near the surface (top surface) is released into the chamber 10 as gas (i.e., water vapor). The amount of this release increases as the moisture content in the oxide film of the substrate W increases. Therefore, the first measurement value measured by the moisture sensor 7 depends on the moisture content in the oxide film of the substrate W. Specifically, the first measurement value tends to increase as the moisture content in the oxide film of the substrate W increases.

[0066] Fig. 6 is a graph schematically showing an example of the change over time in the moisture content in the chamber 10. Graphs G1 and G2 are shown in Fig. 6 for two substrates W. Graph G1 shows an example of the change over time in the moisture content in the chamber 10 when the moisture content in the oxide film of the substrate W is large, and graph G2 shows an example of the change over time in the moisture content in the chamber 10 when the moisture content in the oxide film of the substrate W is smaller than the moisture content of graph G1.

[0067] In the example of Figure 6, a substrate W is loaded at time t0. When the substrate W is loaded, the moisture content in the chamber 10 initially increases over time. This is because water vapor is released from the substrate W into the chamber 10. In step S3, the pressure reducing unit 6 continues to suck gas from the chamber 10, so the moisture content decreases over time after reaching a peak value Mp. This is thought to be because once moisture is released near the surface of the substrate W, the release slows down. The greater the moisture content in the oxide film of the substrate W, the greater the amount of released moisture. Therefore, as shown in Figure 6, the moisture content in the chamber 10 at each time point is greater in graph G1 than in graph G2.

[0068] Conversely, the larger the first measurement value measured by the moisture sensor 7, the larger the moisture content in the oxide film of the substrate W. In other words, it can be said that the moisture sensor 7 indirectly measures the moisture content in the oxide film of the substrate W.

[0069] Therefore, the control unit 9 determines the amount of water vapor to be supplied into the chamber 10 based on the first measurement value of the moisture sensor 7 (step S4: supply amount determination process). The control unit 9 may determine the supply flow rate of water vapor as the amount of water vapor to be supplied. Because the first measurement value may fluctuate over time, the control unit 9 may determine the supply flow rate based on the first measurement value (moisture content Mt in the figure) of the moisture sensor 7 at a predetermined time Δt after the substrate W is loaded (e.g., the gate valve 13 is closed). Alternatively, the control unit 9 may obtain a peak value Mp or a convergence value Mc of the first measurement value and determine the supply flow rate based on the peak value Mp or the convergence value Mc. The supply flow rate may be a mass flow rate (e.g., g / min) or a volumetric flow rate (e.g., sccm).

[0070] The correspondence between the information on the moisture amount measured by the moisture sensor 7 and the information on the amount of water vapor supplied may be set in advance. The information on the moisture amount may be the moisture amount measured by the moisture sensor 7 itself. The information on the amount of water vapor supplied may be the supply flow rate of water vapor. Such a correspondence is set in advance by simulation or experiment. The correspondence data D1 may be a table. Table 1 is a table showing an example of the correspondence data D1. The correspondence data D1 showing this correspondence is stored in the memory unit 94.

[0071]

[0072] In the example of Table 1, the correspondence data D1 is data indicating the correspondence between the moisture amount measured by the moisture sensor 7, the target value of the etching amount (here, the etching rate), and the supply amount (here, the supply flow rate). Here, the moisture amount in Table 1 may be the moisture amount Mt in the chamber 10 after a predetermined time Δt has elapsed since the substrate W was loaded, or may be the peak value Mp of the moisture amount in the chamber 10, or may be the convergence value Mc of the moisture amount in the chamber 10. In Table 1, moisture amounts M1 to M4 are shown as the moisture amounts, and etching amounts E1 to E4 are shown as the etching amounts. The larger the number of the associated symbol, the larger the moisture amount and the etching amount.

[0073] In Table 1, if the target etching amount is the same, the larger the moisture amount, the smaller the supply flow rate is set. For example, the supply amounts F11 to F14 are set smaller as the number of their symbols increases. On the other hand, if the moisture amount is the same, the higher the target etching amount, the larger the supply rate is set. For example, the supply amounts F11, F21, F31, and F41 are set larger as the number of their symbols increases.

[0074] The etching amount (target) is set in advance, for example, and stored in the memory unit 94. The etching amount may be input to the control unit 9, for example, by the user operating a user interface (not shown). The control unit 9 determines the supply flow rate based on the first measurement value of the moisture sensor 7 measured in step S3, the correspondence data D1 read from the memory unit 94, and the etching amount. The control unit 9 may determine the supply flow rate by appropriately using interpolation processing.

[0075] Next, the etching apparatus 1 adjusts the pressure in the chamber 10 to a second pressure value (second target pressure) (step S5: pressure adjustment step). The second pressure value is higher than the first pressure value and is within a pressure range suitable for etching oxide films. The second pressure value may be, for example, 1 Torr or more and 200 Torr or less, or 10 Torr or more and 200 Torr or less.

[0076] 5A shows an example of the etching apparatus 1 in step S5. As shown in FIG. 5A, the inert gas supply unit 8 supplies inert gas to the chamber 10. That is, the control unit 9 opens the inert gas valve 82. As a result, the pressure in the chamber 10 increases over time. The control unit 9 then controls the pressure adjustment valve 62 so that the pressure measured by the pressure sensor 71 approaches the second pressure value (second target pressure). The pressure reduction unit 6 adjusts the pressure in the chamber 10 to the second pressure value at least until the end of etching.

[0077] Furthermore, a temperature regulator built into the substrate holder 2 regulates the temperature of the substrate W. That is, the temperature regulator regulates the temperature of the substrate W to a temperature range suitable for etching. For example, when a thermal oxide film and a CVD oxide film are exposed on the main surface of the substrate W and the CVD oxide film is to be etched, the temperature regulator regulates the temperature of the substrate W to, for example, 35° C. or higher and 60° C. or lower. This allows the etching apparatus 1 to etch the CVD oxide film with high selectivity relative to the thermal oxide film.

[0078] Note that step S5 may be performed in parallel with step S4, or may be performed between step S3 and step S4.

[0079] Next, the etching apparatus 1 etches the oxide film on the substrate W (step S6: etching process). FIG. 5B shows the etching apparatus 1 in step S6. As shown in FIG. 5B, the etching gas supply unit 3 supplies hydrogen fluoride gas into the chamber 10, while the water vapor supply unit 4 supplies water vapor to the chamber 10 at a supply amount (e.g., a supply flow rate) determined in step S4. For example, the control unit 9 opens the etching gas valve 32 and the water vapor valve 42, and then controls the vaporizer 43 (heater), flow rate control valve 46, and flow rate control valve 47 to adjust the supply flow rate of water vapor. The heater of the vaporizer 43, the flow rate control valve 46, and the flow rate control valve 47 constitute a flow rate control unit that adjusts the supply flow rate of water vapor.

[0080] The hydrogen fluoride gas and water vapor supplied into the chamber 10 flow toward the substrate W through the openings 12a in the gas dispersion plate 12. The hydrogen fluoride gas reacts with the water vapor and the moisture in the oxide film, and the reaction products react with the oxide film, etching the oxide film (see formulas (1) and (2)). This etches the CVD oxide film.

[0081] When the oxide film on the substrate W is sufficiently etched, the etching gas supply unit 3 stops supplying the hydrogen fluoride gas, and the water vapor supply unit 4 stops supplying the water vapor. As an example, when a predetermined etching time has elapsed since the start of step S6, the control unit 9 closes the etching gas valve 32 and the water vapor valve 42. The control unit 9 can measure the time using, for example, a timer circuit (not shown).

[0082] Next, the transfer unit 15 transfers the processed substrate W out of the chamber 10 (step S7: transfer step). Specifically, with the control unit 9 opening the gate valve 13, the transfer robot of the transfer unit 15 takes out the substrate W from the substrate holder 2 and hands over the substrate W to the outside.

[0083] As described above, the moisture sensor 7 measures the moisture content in the chamber 10 after the substrate W has already been loaded and the chamber 10 is depressurized (step S3). Therefore, the first measurement value of the moisture sensor 7 reflects the moisture content in the oxide film of the substrate W. That is, the first measurement value tends to increase as the moisture content in the oxide film increases. Therefore, it can be said that the moisture sensor 7 indirectly measures the moisture content in the oxide film of the substrate W. The control unit 9 then determines the supply amount of water vapor based on the first measurement value (step S4). Specifically, for the same target etching amount, the control unit 9 determines a smaller supply amount as the first measurement value increases. That is, if the moisture content in the oxide film of the substrate W is high, increasing the supply amount of water vapor may result in excessive etching. Therefore, the control unit 9 determines a smaller supply amount of water vapor. This allows the etching apparatus 1 to suppress excessive etching of the substrate W. Conversely, for the same target etching amount, the control unit 9 determines a larger supply amount as the first measurement value decreases. This allows the etching apparatus 1 to suppress insufficient etching of the substrate W. That is, the etching apparatus 1 can more uniformly etch the oxide film on the substrate W regardless of the amount of moisture in the oxide film. In other words, the etching apparatus 1 can suppress variations in etching caused by the amount of moisture in the oxide film. Therefore, the etching apparatus 1 can more uniformly etch each of the multiple substrates W that are sequentially loaded into the etching apparatus 1.

[0084] In the above example, the moisture sensor 7 measures the moisture content in the chamber 10 when the pressure in the chamber 10 is adjusted to a first pressure value (first target pressure) (step S3). Because this first pressure value is lower than the second pressure value in step S6 (etching process), the moisture sensor 7 measures the moisture content in the chamber 10 when the amount of moisture originally present in the chamber 10 is smaller. It is also considered that the lower the pressure in the chamber 10, the greater the amount of moisture released from the substrate W. That is, the amount of moisture released from the substrate W accounts for a larger proportion of the first measurement value of the moisture sensor 7. Therefore, the first measurement value of the moisture sensor 7 reflects the moisture content in the oxide film of the substrate W with higher accuracy. The controller 9 determines the supply amount of water vapor based on this first measurement value, and therefore can determine the supply amount based on the moisture content in the oxide film with higher accuracy. Consequently, the etching apparatus 1 can more effectively suppress etching variations due to the amount of moisture in the oxide film.

[0085] Furthermore, in the above example, when the moisture sensor 7 measures the moisture content (step S3), the control unit 9 controls the pressure regulating valve 62 based on the pressure measured by the pressure sensor 71. This allows the pressure in the chamber 10 to be adjusted to the first pressure value (first target pressure) with higher accuracy. That is, the moisture sensor 7 measures the moisture content in the chamber 10 while the pressure in the chamber 10 is adjusted so that the measured value of the pressure in the chamber 10 measured by the pressure sensor 71 approaches the target pressure. Although the amount of moisture released from the substrate W is thought to depend on the pressure in the chamber 10, the pressure in the chamber 10 is adjusted to the first pressure value with high accuracy, thereby suppressing the influence of pressure fluctuations in the chamber 10 on the first measured value. This allows the first measured value of the moisture sensor 7 to reflect the moisture content in the oxide film on the substrate W with even higher accuracy. Consequently, the control unit 9 can determine the supply amount based on the moisture content in the oxide film with even higher accuracy.

[0086] In the above example, step S1 (decompression step) is performed before step S2 (carry-in step), but it may be performed after step S2.

[0087] Second Embodiment The configuration of the etching apparatus 1 according to the second embodiment is similar to that of the first embodiment. However, the operation of the etching apparatus 1 according to the second embodiment differs from that of the etching apparatus 1 according to the first embodiment. Fig. 7 is a flowchart showing an example of the operation of the etching apparatus 1 according to the second embodiment, and Fig. 8 is a diagram schematically showing an example of the state of the etching apparatus 1 in each step.

[0088] 7 , first, similar to step S1, the pressure reducing unit 6 reduces the pressure in the chamber 10 (step S11: pressure reducing step). For example, the pressure reducing unit 6 adjusts the pressure in the chamber 10 to a first pressure value (first target pressure). As an example, the control unit 9 controls the pressure adjustment valve 62 based on the pressure measured by the pressure sensor 71. This allows the pressure reducing unit 6 to adjust the pressure in the chamber 10 to the first pressure value (first target pressure) with high accuracy.

[0089] Next, the moisture sensor 7 measures the amount of moisture in the chamber 10 to obtain a second measurement value (step S12: second measurement step). Figure 8(a) shows the etching apparatus 1 in step S12. As shown in Figure 8(a), the moisture sensor 7 measures the amount of moisture in the chamber 10 before a substrate W has been loaded into the chamber 10 and the chamber 10 is in a depressurized state. Because the substrate W has not yet been loaded, the second measurement value does not include moisture in the oxide film on the substrate W, but includes moisture originally present in the chamber 10.

[0090] Next, similarly to step S2, the transfer unit 15 transfers the substrate W into the chamber 10 (step S13: transfer step). At this time, the transfer robot transfers the substrate W to the chamber 10 while the pressure reduction unit of the transfer unit 15 reduces the pressure inside the transfer chamber. The pressure inside the transfer chamber may be approximately the same as the pressure inside the chamber 10. As an example, the pressure inside the transfer chamber may be lower than the pressure inside the chamber 10. This makes it possible to suppress the inflow of moisture from the transfer chamber into the chamber 10.

[0091] Next, similar to step S3, the moisture sensor 7 measures the amount of moisture in the chamber 10 to obtain a first measurement value (step S14: first measurement step). Fig. 8B shows the etching apparatus 1 in step S14. The moisture sensor 7 measures the amount of moisture in the chamber 10 after the substrate W has already been loaded into the chamber 10 and the chamber 10 has been depressurized.

[0092] Next, the control unit 9 subtracts the second measurement value measured in step S12 from the first measurement value measured in step S14 to calculate the substrate moisture content (step S15: calculation step). As in the first embodiment, the first measurement value may be the moisture content Mt after a predetermined time Δt has elapsed, the peak value Mp, or the convergence value Mc. The first measurement value includes the amount of moisture originally present in the chamber 10 and the amount of water vapor released from the substrate W, while the second measurement value includes the amount of moisture originally present in the chamber 10. Therefore, by subtracting the second measurement value from the first measurement value, the amount of moisture originally present in the chamber 10 can be substantially canceled out. Therefore, the substrate moisture content obtained by subtracting the second measurement value from the first measurement value reflects the moisture content in the oxide film of the substrate W with higher accuracy.

[0093] Next, the control unit 9 determines the supply amount of water vapor (here, the supply flow rate) based on the substrate moisture content (step S16: supply amount determination step). The correspondence relationship between the substrate moisture content and the supply amount of water vapor may be set in advance. Such a correspondence relationship is set in advance through simulation or experiment. In this case, the correspondence data D1 includes data indicating the correspondence relationship between the substrate moisture content and the supply amount of water vapor. As a more specific example, the correspondence data D1 may be data indicating the correspondence relationship between the substrate moisture content, the target value of the etching amount (here, the etching rate), and the supply amount (here, the supply flow rate). An example of the correspondence data D1 is the same as Table 1. However, the substrate moisture content (i.e., the difference between the first measured value and the second measured value) is used as the moisture content.

[0094] Next, the etching apparatus 1 adjusts the pressure in the chamber 10 to a second pressure value (second target pressure) as in step S5 (step S17: pressure adjustment step). The temperature regulator also adjusts the temperature of the substrate W to a range suitable for etching. Next, as in step S6, the etching apparatus 1 supplies water vapor into the chamber 10 at the supply rate determined in step S16 while supplying etching gas into the chamber 10 (step S18: etching step). This etches the oxide film (e.g., a CVD oxide film) on the substrate W. When the oxide film is sufficiently etched, the etching apparatus 1 stops supplying the etching gas and water vapor, and as in step S7, the transport unit 15 unloads the substrate W (step S19: unloading step).

[0095] As described above, in the second embodiment, the control unit 9 determines the supply amount of water vapor based on the substrate moisture content obtained by subtracting the second measurement value from the first measurement value (step S17). Therefore, the control unit 9 can suppress the influence of moisture originally present in the chamber 10 and determine the supply amount of water vapor more accurately based on the moisture content in the oxide film of the substrate W.

[0096] Third Embodiment The configuration of the etching apparatus 1 according to the third embodiment is similar to that of the first embodiment. However, one example of the operation of the etching apparatus 1 according to the third embodiment differs from that of the first embodiment. In the third embodiment, the etching apparatus 1 starts the etching process (step S6 or step S18) in a state in which the amount of moisture measured by the moisture sensor 7 is stable.

[0097] 9 is a flowchart showing an example of the operation of the etching apparatus 1 according to the third embodiment. In the example of Fig. 9, after the supply amount determination step (step S4 or step S16), the moisture sensor 7 measures the moisture amount in the chamber 10 (step S21: third measurement step).

[0098] Next, the control unit 9 determines whether the moisture content measured in the third measurement step is equal to or less than a predetermined reference value (step S22: determination step). The predetermined reference value may be set in advance. For example, the convergence value Mc of the moisture content when the pressure in the chamber 10 is the first pressure value depends on the substrate W loaded into the chamber 10 and the original moisture content in the chamber 10, but the maximum value of the convergence value Mc can be estimated in advance by experiment, simulation, or the like. Therefore, the predetermined reference value is set to a value slightly larger than the maximum convergence value Mc.

[0099] If the amount of moisture is greater than the predetermined reference value, step S21 is executed again. On the other hand, if the amount of moisture is equal to or less than the predetermined reference value, the etching apparatus 1 executes the pressure adjustment step (step S6 or step S18) and then the etching step (step S7 or step S19).

[0100] As described above, in the third embodiment, the etching process is performed in a state where the amount of moisture in the chamber 10 is stable. Therefore, the etching apparatus 1 can perform the etching process on the substrate W more stably.

[0101] The control unit 9 may determine the amount of change over time in the amount of moisture measured by the moisture sensor 7. For example, the control unit 9 may determine the amount of change over time as the difference between the amount of moisture measured in the previous step S21 and the amount of moisture measured in the current step S21. Then, the control unit 9 may execute the pressure adjustment step and the etching step when the amount of change over time is equal to or less than a predetermined difference reference value.

[0102] Although the etching apparatus 1 and the etching method have been described in detail above, the above description is merely an example in all respects, and this disclosure is not limited thereto. Furthermore, the various modifications described above can be combined and applied as long as they are not mutually inconsistent. It is understood that many modifications not illustrated can be envisioned without departing from the scope of this disclosure.

[0103] For example, although the CVD oxide film is etched in the above specific example, a thermal oxide film may also be etched. For example, this embodiment can also be applied to a case where only a thermal oxide film is exposed on the upper surface of the substrate W.

[0104] Although the correspondence data D1 is a table in the above specific example, it is not necessarily limited to this. The correspondence data D1 may be, for example, a function. Alternatively, the correspondence data D1 may be a parameter in a machine-learned model that outputs the amount of water vapor supply based on the etching amount (target value) and the moisture content.

[0105] REFERENCE SIGNS LIST 10 Chamber 2 Substrate holder 3 Etching gas supply unit 31 Etching gas pipe 32 Etching gas valve 4 Water vapor supply unit 41 Water vapor pipe 42 Water vapor valve 6 Pressure reduction unit 61 Suction pipe 63 Suction unit 7 Moisture sensor 9 Control unit 94 Storage unit D1 Correspondence data S12 Second measurement process (step) S2, S13 Loading process (step) S3, S14 First measurement process (step) S15 Calculation process (step) S4, S16 Supply amount determination process S5, S17 Etching process W Substrate

Claims

1. An etching method comprising: a loading step of loading a substrate having an oxide film formed on its surface into a chamber; a first measurement step of measuring the amount of moisture in the chamber after the loading step while the chamber is depressurized to obtain a first measurement value; a supply amount determination step of determining the supply amount of water vapor based on correspondence data indicating a correspondence between information on the amount of moisture in the chamber and information on the supply amount of water vapor to be supplied to the chamber, and the first measurement value measured in the first measurement step; and an etching step of supplying an etching gas containing hydrogen fluoride gas into the chamber while supplying the water vapor into the chamber at the supply amount determined in the supply amount determination step, to etch the oxide film.

2. An etching method as defined in claim 1, further comprising: a second measurement step of measuring the moisture content in the chamber to obtain a second measurement value while the substrate is not loaded into the chamber and the chamber is depressurized; and a calculation step of calculating the substrate moisture content by subtracting the second measurement value measured in the second measurement step from the first measurement value measured in the first measurement step, wherein the supply amount determination step determines the supply amount of water vapor based on the correspondence data indicating the correspondence between the substrate moisture content and the supply amount and the substrate moisture content calculated in the calculation step.

3. An etching method according to claim 1 or 2, wherein the pressure in the chamber in the first measurement step is lower than the pressure in the chamber in the etching step.

4. An etching method according to claim 3, wherein in the first measurement step, the pressure inside the chamber is measured, and the amount of water inside the chamber is measured while the pressure inside the chamber is adjusted so that the measured value of the pressure inside the chamber approaches a target pressure.

5. An etching method according to claim 1 or 2, wherein in the first measurement step, the moisture content in the chamber measured after a predetermined time has elapsed since the substrate was loaded, the peak value of the moisture content, or the convergence value of the moisture content, in the time change of the moisture content in the chamber, is obtained as the first measurement value.

6. An etching method according to claim 1 or 2, wherein the etching step is carried out when the amount of moisture in the chamber or the amount of change in the amount of moisture over time is equal to or less than a predetermined reference value.

7. An etching method according to claim 1 or 2, wherein in the etching step, a CVD oxide film is selectively etched relative to a thermal oxide film on the substrate.

8. An etching apparatus comprising: a chamber; a substrate holder provided within the chamber for supporting or holding a substrate; an etching gas supply unit including an etching gas pipe connected to the chamber and an etching gas valve provided on the etching gas pipe; a water vapor supply unit including a water vapor pipe connected to the chamber and a water vapor valve provided on the water vapor pipe; a pressure reduction unit including a suction pipe connected to the chamber and a suction unit for sucking gas into the chamber through the suction pipe; a moisture sensor for measuring an amount of moisture within the chamber; a memory unit in which correspondence data indicating a correspondence between information regarding the amount of moisture within the chamber and information regarding an amount of water vapor to be supplied into the chamber is stored; and a control unit that determines the amount of water vapor to be supplied based on the amount of moisture measured by the moisture sensor and the correspondence data when the substrate holder supports or holds the substrate and the pressure reduction unit has reduced the pressure of the chamber, and causes the etching gas supply unit to supply the etching gas to the chamber while causing the water vapor supply unit to supply the water vapor to the chamber at the supply amount.

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