Semiconductor device manufacturing method, substrate processing method, substrate processing apparatus, and process

Abstract

The process includes: (a) nitriding the inner surface of a concave structure formed on a substrate and modifying at least a portion of the inner surface into a nitrided layer; and (b) oxidizing the inner surface containing the nitrided layer and modifying the inner surface into an oxide layer; in (a), the thickness distribution of the nitrided layer on the inner surface is set such that the thickness distribution of the oxide layer on the inner surface is a desired distribution.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a semiconductor device, a substrate processing method, a substrate processing apparatus, and a program. Prior Art

[0002] As one of the steps in the manufacturing process of a semiconductor device, a process of forming an oxide layer on the inner surface of a concave structure formed on a substrate is sometimes performed (for example, see Patent Document 1). Prior Art Literature Patent Literature

[0003] Patent Document 1: International Publication No. 2016 / 125606 Summary of the Invention

[0004] Problems to be solved by the invention

[0005] The present disclosure aims to provide a technology that can achieve a desired thickness distribution for the thickness of an oxide layer formed on the inner surface of a concave structure formed on a substrate. Means of solving problems

[0006] According to one aspect of the present disclosure, a technology is provided, which has: (a) nitriding the inner surface of the concave structure formed on the substrate and converting at least a portion of the inner surface into a nitride layer; and (b) oxidizing the inner surface including the nitride layer and converting the inner surface into an oxide layer; In (a), the thickness distribution of the nitride layer on the inner surface is such that the thickness distribution of the oxide layer on the inner surface becomes a desired distribution. Effects of the Invention

[0007] According to the technology provided by the present disclosure, the thickness of the oxide layer formed on the inner surface of the concave structure formed on the substrate can be set to a desired thickness distribution. Simple diagram description

[0008] FIG. 1 is a schematic diagram of a substrate processing apparatus 100 preferably used in one embodiment of the present disclosure, and is a longitudinal sectional view showing a processing furnace 202 portion. FIG. 2 is an explanatory diagram illustrating the principle of plasma generation in a substrate processing apparatus 100 preferably used in one embodiment of the present disclosure. FIG. 3 is a schematic diagram showing the structure of a controller 221 included in a substrate processing apparatus 100 preferably used in one embodiment of the present disclosure, and is a block diagram showing a control system of the controller 221 . FIG4(a) is a partially enlarged cross-sectional view of a wafer 200 having a trench 301 formed therein. FIG4(b) is a partially enlarged cross-sectional view of the wafer 200 after at least a portion of the inner surface of the trench 301 has been converted into a nitride layer 401. FIG4(c) is a partially enlarged cross-sectional view of the wafer 200 during the conversion of the inner surface of the trench 301, including the nitride layer 401, into an oxide layer 402. FIG4(d) is a partially enlarged cross-sectional view of the wafer 200 after the inner surface of the trench 301, including the nitride layer 401, has been converted into an oxide layer 402. Implementation Method

[0009] <One aspect of the present disclosure>

[0010] The following describes one aspect of the present disclosure primarily with reference to Figures 1 to 3 and Figures 4(a) to 4(d). The figures used in the following description are schematic, and the dimensional relationships and proportions of the elements shown in the figures are not necessarily consistent with actual dimensions. Furthermore, the dimensional relationships and proportions of the elements shown in multiple figures are not necessarily consistent.

[0011] (1) Configuration of substrate processing apparatus As shown in FIG1 , substrate processing apparatus 100 includes a processing furnace 202 for accommodating wafers 200 as substrates and performing plasma processing. Processing furnace 202 includes a processing container 203 that forms a processing chamber 201. Processing container 203 includes a dome-shaped upper container 210 as a first container and a bowl-shaped lower container 211 as a second container. The processing chamber 201 is formed by covering the lower container 211 with the upper container 210. The upper container 210 is made of a non-metallic material such as alumina (Al2O3) or quartz (SiO2), while the lower container 211 is made of aluminum (Al), for example.

[0012] A gate valve 244, serving as a loading / unloading port (parting valve), is provided on the lower sidewall of the lower container 211. By opening gate valve 244, wafers 200 can be loaded into or unloaded from the processing chamber 201 through loading / unloading port 245. By closing gate valve 244, the airtightness within the processing chamber 201 is maintained.

[0013] As shown in Figure 2, the processing chamber 201 includes a plasma generation space 201a and a substrate processing space 201b, which communicates with the plasma generation space 201a and processes the wafer 200. The plasma generation space 201a is the space where plasma is generated, and is, for example, the space above the lower end of the resonance coil 212 (the single-dotted dashed line in Figure 1) within the processing chamber 201. Meanwhile, the substrate processing space 201b is the space where plasma processing is performed on the substrate, and is the space below the lower end of the resonance coil 212.

[0014] A susceptor 217 serving as a substrate placement portion for placing the wafer 200 is disposed at the center of the bottom side of the processing chamber 201. The susceptor 217 is made of a non-metallic material such as aluminum nitride (AlN), ceramic, or quartz.

[0015] The heater 217b is integrally embedded in the susceptor 217 as a heating mechanism. By supplying power to the heater 217b via the heater power adjustment mechanism 276, the surface of the wafer 200 can be heated to a predetermined temperature within a range of 25°C to 1000°C, for example.

[0016] The susceptor 217 is electrically insulated from the lower container 211. An impedance-adjusting electrode 217c is provided within the susceptor 217. The impedance-adjusting electrode 217c is grounded via a variable impedance mechanism 275, which serves as an impedance adjustment unit. The variable impedance mechanism 275 includes a coil, a variable capacitor, and other components. By controlling the inductance and resistance of the coil and the capacitance of the variable capacitor, the impedance of the impedance-adjusting electrode 217c can be varied within a range from approximately 0Ω to the parasitic impedance of the processing chamber 201. This allows the potential (bias) of the wafer 200 during plasma processing to be controlled via the impedance-adjusting electrode 217c and the susceptor 217.

[0017] A susceptor lift mechanism 268 is provided below the susceptor 217 for raising and lowering the susceptor. The susceptor 217 is provided with through-holes 217a. Support pins 266 are provided on the bottom surface of the lower container 211, serving as supports for the wafers 200. At least three through-holes 217a and three support pins 266 are positioned facing each other. When the susceptor 217 is lowered by the susceptor lift mechanism 268, the support pins 266 pass through the through-holes 217a without contacting the susceptor 217. This allows the wafers 200 to be held from below.

[0018] A gas supply head 236 is provided above the processing chamber 201, that is, above the upper container 210. The gas supply head 236 includes a cap-shaped cover 233, a gas inlet 234, a buffer chamber 237, an opening 238, a shield plate 240, and a gas outlet 239, and is configured to supply gas into the processing chamber 201. The buffer chamber 237 functions as a dispersion space for dispersing the reaction gas introduced from the gas inlet 234.

[0019] The downstream end of the gas supply pipe 232a for supplying nitrogen-containing gas, the downstream end of the gas supply pipe 232b for supplying oxygen-containing gas, and the gas supply pipe 232c for supplying inert gas are connected and merged into a gas inlet 234. Gas supply pipe 232a is provided with, in order from the upstream side, a nitrogen-containing gas supply source 250a, a mass flow controller (MFC) 252a serving as a flow control device, and a valve 253a serving as an on-off valve. Gas supply pipe 232b is provided with, in order from the upstream side, an oxygen-containing gas supply source 250b, an MFC 252b serving as a flow control device, and a valve 253b serving as an on-off valve. Gas supply pipe 232c is provided with, in order from the upstream side, an inert gas supply source 250c, an MFC 252c serving as a flow control device, and a valve 253c serving as an on-off valve. Valve 243a is located downstream of the confluence of gas supply pipes 232a, 232b, and 232c, and is connected to the upstream end of gas inlet 234. By opening / closing valves 253a-253c and 243a, the flow rates of the various gases can be adjusted by MFCs 252a-252c, and nitrogen-containing gas, oxygen-containing gas, and inert gas can be supplied into processing chamber 201 via gas supply pipes 232a, 232b, and 232c, respectively.

[0020] The nitrogen-containing gas supply system primarily consists of the gas supply head 236 (cover 233, gas inlet 234, buffer chamber 237, opening 238, shield plate 240, gas outlet 239), gas supply pipe 232a, MFC 252a, and valves 253a and 243a. The oxygen-containing gas supply system primarily consists of the gas supply head 236, gas supply pipe 232b, MFC 252b, valves 253b and 243a. The inert gas supply system primarily consists of the gas supply head 236, gas supply pipe 232c, MFC 252c, and valves 253c and 243a.

[0021] An exhaust port 235 for exhausting the interior of the processing chamber 201 is provided on the side wall of the lower container 211. The upstream end of the exhaust pipe 231 is connected to the exhaust port 235. An APC (Auto Pressure Controller) valve 242, a valve 243b, and a vacuum pump 246 are provided in the exhaust pipe 231 in this order from the upstream side as a pressure regulator (pressure regulating unit).

[0022] The exhaust section mainly comprises an exhaust port 235, an exhaust pipe 231, an APC valve 242, and a valve 243b, and may include a vacuum pump 246.

[0023] A spiral resonant coil 212 is installed on the outer periphery of the processing chamber 201, that is, outside the sidewall of the upper container 210, so as to surround the processing chamber 201. An RF (radio frequency) sensor 272, a high-frequency power supply 273, and a frequency matching unit 274 (frequency control unit) are connected to the resonant coil 212. A shielding plate 223 is installed on the outer periphery of the resonant coil 212.

[0024] High-frequency power source 273 is configured to supply high-frequency power to resonant coil 212. RF sensor 272 is provided on the output side of high-frequency power source 273. RF sensor 272 is configured to monitor information about the traveling wave and reflected wave of the high-frequency power supplied from high-frequency power source 273. Frequency matcher 274 is configured to match the frequency of the high-frequency power output from high-frequency power source 273 based on information about the reflected wave power monitored by RF sensor 272 to minimize reflected waves.

[0025] Both ends of the resonant coil 212 are electrically grounded. One end of the resonant coil 212 is grounded via a movable joint 213. The other end of the resonant coil 212 is grounded via a fixed ground wire 214. A movable joint 215 is provided between the two ends of the resonant coil 212, allowing the position at which the resonant coil 212 receives power from the high-frequency power supply 273 to be arbitrarily set.

[0026] The excitation unit (plasma generator) primarily consists of the resonant coil 212, RF sensor 272, and frequency matcher 274. This excitation unit excites the gases supplied from the nitrogen-containing and oxygen-containing gas supply systems. A high-frequency power supply 273 and shielding plate 223 may also be included in the excitation unit.

[0027] The following supplementary description will be given of the operation of the excitation unit and the properties of the generated plasma with reference to FIG. 2 .

[0028] The resonant coil 212 is configured to function as a high-frequency inductively coupled plasma (ICP) electrode. The winding diameter, winding pitch, and number of windings of the resonant coil 212 are set to generate a standing wave of a predetermined wavelength, allowing resonance in the full-wavelength mode. The electrical length of the resonant coil 212, specifically the length of the electrode between the electrodes and the ground, is adjusted to an integer multiple of the wavelength of the high-frequency power supplied from the high-frequency power supply 273. These configurations, the power supplied to the resonant coil 212, and the magnetic field strength generated by the resonant coil 212 are appropriately determined based on the external shape of the substrate processing apparatus 100 and the processing content. For example, the coil diameter of the resonant coil 212 is set to 200 to 500 mm, and the number of windings is set to 2 to 60.

[0029] High-frequency power supply 273 includes a power supply control unit and an amplifier. The power supply control unit is configured to output a predetermined high-frequency signal (control signal) to the amplifier based on power and frequency output conditions preset via an operation panel. The amplifier is configured to amplify the control signal received from the power supply control unit and output the high-frequency power to resonant coil 212 via a transmission line.

[0030] The frequency matcher 274 receives a voltage signal related to the reflected wave power from the RF sensor 272 and performs correction control to increase or decrease the frequency (oscillation frequency) of the high-frequency power output by the high-frequency power source 273 so that the reflected wave power is minimized.

[0031] With the above configuration, the induced plasma excited in the plasma generating space 201a becomes high-quality plasma with little capacitive coupling to the inner walls of the processing chamber 201 or the susceptor 217. In the plasma generating space 201a, plasma having an extremely low potential and forming a ring shape in plan view is generated.

[0032] As shown in Figure 3, the controller 221, serving as a control unit, is configured as a computer comprising a CPU (Central Processing Unit) 221a, RAM (Random Access Memory) 221b, a storage device 221c, and an I / O port 221d. The RAM 221b, the storage device 221c, and the I / O port 221d are configured to exchange data with the CPU 221a via an internal bus 221e. For example, a touch panel, mouse, keyboard, operation terminal, etc. can be connected to the controller 221 as an input / output device 225. For example, a display can be connected to the controller 221 as a display unit.

[0033] The memory device 221c is composed of, for example, a flash memory, an HDD (hard disk drive), a CD-ROM, etc. The memory device 221c stores a process recipe in a readable manner. The process recipe records the control program for controlling the operation of the substrate processing device 100, the sequence or conditions for substrate processing, etc. The process recipe is combined into a program that enables the substrate processing device 100 to execute each sequence in the substrate processing process described later and obtain the predetermined results through the controller 221 configured as a computer, and functions as a program. Hereinafter, the process recipe, control program, etc. are collectively referred to as a program. When the term "program" is used in this specification, it can include only the process recipe alone, only the control program alone, or a combination of the process recipe and the control program. The RAM 221b is configured as a memory area (work area) that temporarily stores programs or data read by the CPU 221a.

[0034] The I / O port 221d is connected to the above-mentioned MFCs 252a~252c, valves 253a~253c, 243a, 243b, gate valve 244, APC valve 242, vacuum pump 246, heater 217b, RF sensor 272, high-frequency power supply 273, frequency matcher 274, base lifting mechanism 268 and impedance variable mechanism 275, etc.

[0035] The CPU 221 a is configured to read out and execute a control program from the memory device 221 c , and to read out a process recipe etc. from the memory device 221 c in response to input of an operation command etc. from the input / output device 225 . Then, as shown in FIG1 , the CPU 221 a is configured to control the following various actions based on the contents of the read process recipe: adjustment of the opening of the APC valve 242 via the I / O port 221 d and signal line A, opening and closing of the valve 243 b, starting and stopping of the vacuum pump 246, raising and lowering of the susceptor lifting mechanism 268 via the signal line B, adjustment of the amount of power supplied to the heater 217 b by the heater power adjustment mechanism 276 based on the temperature sensor via the signal line C (temperature adjustment action), adjustment of the impedance value by the variable impedance mechanism 275, opening and closing of the gate valve 244 via the signal line D, operation of the RF sensor 272, the frequency matcher 274, and the high-frequency power supply 273 via the signal line E, flow rate adjustment of various gases by the MFCs 252 a to 252 c via the signal line F, and opening and closing of the valves 253 a to 253 c and 243 a.

[0036] The controller 221 is not limited to a dedicated computer and can also be a general-purpose computer. For example, an external storage device (e.g., a magnetic disk such as a magnetic tape, a floppy disk or a hard disk, an optical disk such as a CD or DVD, a magneto-optical disk such as an MO, or a semiconductor memory such as a USB memory or a memory card) 226 storing the aforementioned program can be prepared, and the program can be installed on a general-purpose computer using this external storage device 226, thereby forming the controller 221 of this embodiment. Furthermore, the method for providing the program to the computer is not limited to providing it via the external storage device 226. For example, the program can be provided using communication means such as the internet or a dedicated line, rather than via the external storage device 226. Furthermore, the storage device 221c or the external storage device 226 constitutes a computer-readable recording medium. Hereinafter, these are collectively referred to as recording media. In this specification, when the term "recording medium" is used, the recording medium may include only the storage device 221c, only the external storage device 226, or both.

[0037] (2) Substrate processing engineering An example of a substrate processing sequence for processing a wafer 200 serving as a substrate, one of the steps in a semiconductor device manufacturing process using the substrate processing apparatus 100, will be described primarily using Figures 4(a), 4(b), 4(c), and 4(d). Specifically, an example of a sequence for forming an oxide layer on the inner surface of a concave structure formed on the surface of the wafer 200 will be described. In the following description, the operation of each component of the substrate processing apparatus 100 is controlled by the controller 221.

[0038] The following steps are performed in the substrate processing sequence of this aspect: Step a) of nitriding the inner surface of the concave structure formed on the wafer 200 to convert at least a portion of the inner surface into a nitride layer, and Step b) of oxidizing the inner surface including the nitride layer to convert the inner surface into an oxide layer.

[0039] In step a, the thickness distribution of the nitride layer on the inner surface is adjusted so that the thickness distribution of the oxide layer on the inner surface, that is, the thickness distribution of the oxide layer formed in step b, becomes the desired distribution.

[0040] When the term "wafer" is used in this specification, it can mean "the wafer itself" or "a laminate of a wafer and a predetermined layer or film formed on its surface." In this specification, when the term "surface of the wafer" is used, it can mean "the surface of the wafer itself" or "the surface of a predetermined layer, etc. formed on the wafer." In this specification, when it is stated that "a predetermined layer is formed on the wafer," it means that the predetermined layer is directly formed on the surface of the wafer itself, or it means that the predetermined layer is formed on a layer formed on the wafer. The use of the term "substrate" in this specification is synonymous with the use of the term "wafer."

[0041] (Wafer loading) With the susceptor 217 lowered to the predetermined transfer position, the gate valve 244 is opened, and the wafer 200 to be processed is loaded into the processing chamber 201 by a transfer robot (not shown). The wafer 200 loaded into the processing chamber 201 is supported horizontally on support pins 266 protruding from the surface of the susceptor 217. After the wafer 200 is loaded into the processing chamber 201, the transfer robot's arm is withdrawn from the processing chamber 201, and the gate valve 244 is closed. The susceptor 217 is then raised to the predetermined processing position, and the wafer 200 to be processed is transferred from the support pins 266 onto the susceptor 217. Wafers can be loaded while the interior of the processing chamber 201 is purged with an inert gas or the like.

[0042] As described above, a concave structure such as a groove or hole is pre-formed on the surface of the wafer 200 being processed. In this embodiment, as shown in FIG4(a), a groove 301 pre-formed on the surface of the wafer 200 as an example of a concave structure will be described. Furthermore, as an example, the inner surface of the groove 301 in this embodiment is formed by a Si layer formed of Si monomer (single crystal Si, polycrystalline Si, or amorphous silicon).

[0043] (Pressure adjustment and temperature adjustment) Next, the processing chamber 201 is evacuated by vacuum pump 246 to the desired processing pressure. The pressure within the processing chamber 201 is measured by a pressure sensor, and the APC valve 242 is feedback-controlled based on this pressure information. Furthermore, the wafer 200 is heated by heater 217b to the desired processing temperature. Once the processing chamber 201 reaches the desired processing pressure, or the temperature of the wafer 200 reaches and stabilizes, the nitriding process (described later) begins. The vacuum pump 246 remains in operation until the wafers are unloaded, as will be described later.

[0044] Afterwards, proceed with steps a and b below.

[0045] [Step a: Nitriding treatment] In step a, nitrogen-containing gas is excited by plasma and supplied to the wafer 200 in the processing chamber 201 .

[0046] Specifically, valve 253a is opened to allow nitrogen-containing gas to flow into gas supply pipe 232a. The nitrogen-containing gas is regulated by MFC 252a and supplied into processing chamber 201 via buffer chamber 237 and exhausted from exhaust port 235. At this time, nitrogen-containing gas is supplied from above wafer 200 (nitrogen-containing gas supply). At this time, inert gas can be supplied into processing chamber 201 via buffer chamber 237 by opening valve 243c.

[0047] At this time, high-frequency (RF) power is applied to the resonant coil 212 from the high-frequency power supply 273. This generates an induced plasma having a ring-shaped shape in plan view at height positions corresponding to the upper and lower grounding points and the electrical midpoint of the resonant coil 212 within the plasma generation space 201a. The excitation of the induced plasma activates the nitrogen-containing gas and generates nitride species. Nitride species include at least one of excited N atoms (N*) and ionized N atoms. Furthermore, * represents free radicals. This also applies to the following description. Furthermore, when a gas containing hydrogen (H) is used as the nitrogen-containing gas, the nitride species also include at least one of excited NH radicals (NH*) and ions containing N and H. In this case, reactive species such as excited H atoms (H*) and ionized H atoms may also be generated. These reactive species can also be considered part of the nitride species.

[0048] Examples of processing conditions in this step are as follows: Processing temperature: room temperature ~ 1000℃, preferably 650~900℃ Processing pressure: 1~100Pa, preferably 3~10Pa Nitrogen-containing gas supply flow rate: 0.1~10slm, preferably 0.15~0.5slm Nitrogen-containing gas supply time: 10~600 seconds, preferably 20~50 seconds Inert gas supply flow rate: 0~10slm RF power: 100~5000W, preferably 500~3500W RF frequency: 800kHz~50MHz.

[0049] In this specification, numerical ranges such as "650-900°C" refer to ranges that include both lower and upper limits. Therefore, for example, "650 to 900°C" means "above 650°C and below 900°C." This applies similarly to other numerical ranges. Furthermore, in this specification, "process temperature" refers to the temperature of wafer 200 or the temperature within process chamber 201, and "process pressure" refers to the pressure within process chamber 201. Furthermore, "gas supply flow rate: 0 slm" indicates that no gas is being supplied. This also applies to the following description.

[0050] Under the above-described processing conditions, plasma-excited nitrogen-containing gas is supplied to wafer 200, thereby providing nitride seeds to the inner surface of trench 301. The inner surface of trench 301 is nitrided by the supplied nitride seeds, and at least a portion of the inner surface is converted into a nitride layer 401 (see FIG. 4( b )).

[0051] As an example, the thickness distribution of the nitride layer 401 can be a distribution that gradually becomes thinner from the opening 301a of the trench 301 toward the bottom 301b (see FIG4(b)). As another example, the inner surface near the opening 301a of the trench 301 can be modified into the nitride layer 401, while the inner surface near the bottom 301b can not be modified into the nitride layer 401 (see FIG4(b)). This thickness distribution of the nitride layer 401 is possible because the nitride species supplied to the inner surface of the trench 301 preferentially reacts with the inner surface near the opening 301a and is consumed, with the supply of the nitride species gradually decreasing from the opening 301a toward the bottom 301b. Furthermore, the nitride species supplied to the inner surface of the trench 301 is deactivated while moving from the vicinity of the opening 301a to the bottom 301b, and the supply of the nitride species gradually decreases from the opening 301a toward the bottom 301b.

[0052] For example, the thickness of the nitride layer 401 at the opening 301a of the trench 301 can be set to 1 to 3 nm. As will be described later, the thickness of the nitride layer 401 has the effect of controlling (suppressing) the oxidation rate in step b, regardless of its size (thickness). However, to significantly achieve this effect of controlling (suppressing) the oxidation rate, the thickness of the nitride layer 401 is preferably set to 1 nm or greater. If the thickness is less than 1 nm, this effect in step b may not be fully achieved.

[0053] In this step, the processing pressure is set to a relatively high pressure to maintain the aforementioned thickness distribution of the nitride layer 401. Specifically, the processing pressure at which the nitride layer 401 formed by performing step a has a uniform thickness distribution across the entire inner surface of the trench 301 is defined as "first pressure." The processing pressure is then set to a second pressure that is higher than the first pressure. By increasing the processing pressure in this manner, the mean free path of the nitride species within the processing chamber 201 can be shortened, and the probability of the nitride species reaching the vicinity of the bottom 301b of the trench 301 can be reduced. As a result, the thickness distribution of the nitride layer 401 can be more reliably achieved, with the thickness gradually decreasing from the opening 301a of the trench 301 toward the bottom 301b.

[0054] After the nitriding process is completed, valve 253a is closed, the supply of nitrogen-containing gas into the processing chamber 201 is stopped, and the supply of RF power to the resonant coil 212 is stopped. Then, the processing chamber 201 is evacuated to remove any remaining gas and other gases. At this point, valve 253c is opened to supply an inert gas into the processing chamber 201. This inert gas acts as a purge gas, purging (purging) the interior of the processing chamber 201.

[0055] As nitrogen-containing gases, for example, in addition to nitrogen gas (N₂), hydrogen nitride gases such as ammonia (NH₃) gas, diazene (N₂H₂) gas, hydrazine (N₂H₄) gas, and N₃H₄ gas can be used. At least one of these gases can be used as the nitrogen-containing gas. Furthermore, as the nitrogen-containing gas, a mixture of nitrogen-containing gas and hydrogen-containing gas, such as a mixture of N₂ gas and hydrogen (H₂) gas, can be used.

[0056] When a gas containing hydrogen is used as the nitrogen-containing gas, the nitridation rate of a single film such as a Si film tends to be higher than the nitridation rate of an oxide film such as a SiO film, compared to when a gas not containing hydrogen is used as the nitrogen-containing gas. Therefore, if a native oxide film with uneven thickness, i.e., a variation in thickness, is formed on the inner surface of the trench 301, the influence of the native oxide film may make it difficult to control the thickness distribution of the nitride layer 401 formed on the surface of the wafer 200. In this case, using a gas not containing hydrogen (e.g., N₂ gas) as the nitrogen-containing gas can suppress the influence of the native oxide film, thereby improving the controllability of the thickness distribution of the nitride layer 401 formed on the surface of the wafer 200, which is preferable.

[0057] As an inert gas, for example, a rare gas such as N2 gas, argon (Ar) gas, helium (He) gas, neon (Ne) gas, or xenon (Xe) gas can be used. One or more of these can be used as an inert gas. This also applies to each step described below.

[0058] [Step b: Oxidation treatment] In step b, plasma-excited oxygen-containing gas is supplied to the wafer 200 in the processing chamber 201 .

[0059] Specifically, valve 253b is opened to allow oxygen-containing gas to flow into gas supply pipe 232b. The flow rate of oxygen-containing gas is regulated by MFC 252b, supplied into processing chamber 201 via buffer chamber 237, and exhausted from exhaust port 235. At this time, oxygen-containing gas is supplied from above wafer 200 (oxygen-containing gas supply). At this time, valve 243c can be opened to supply inert gas into processing chamber 201 via buffer chamber 237.

[0060] At this time, RF power is applied to resonant coil 212 from high-frequency power supply 273. This excites induced plasma in the same manner as in step a. The excitation of the induced plasma activates the oxygen-containing gas, generating oxidizing species. Oxidizing species include at least one of excited O atoms (O*) and ionized O atoms. When a gas containing H is used as the oxygen-containing gas, oxidizing species also include at least one of excited OH radicals (OH*) and ions containing O and H. Furthermore, in this case, reactive species such as excited H atoms (H*) or ionized H atoms may also be generated. These reactive species can also be considered part of the oxidizing species.

[0061] Examples of processing conditions in this step are as follows: Processing temperature: room temperature ~ 1000℃, preferably 650~900℃ Processing pressure: 1~1000Pa, preferably 100~200Pa Oxygen-containing gas supply flow rate: 0.1~10slm, preferably 0.2~0.5slm Oxygen-containing gas supply time: 10 to 400 seconds, preferably 20 to 50 seconds. The other treatment conditions are the same as those when the nitrogen-containing gas is supplied in step a.

[0062] Under the above-described processing conditions, plasma-excited oxygen-containing gas is supplied to the wafer 200, thereby supplying oxidizing species to the inner surface of the trench 301. The supplied oxidizing species oxidizes the inner surface of the trench 301, including the nitride layer 401, and converts it into an oxide layer 402 (see FIG. 4( c )).

[0063] At this time, the nitride layer 401 can be converted into the oxide layer 402 throughout the entire thickness of the nitride layer 401. Preferably, within the inner surface of the trench 301, the nitride layer 401 and a predetermined region deeper than the nitride layer 401 in the thickness direction and not converted into the nitride layer 401 (the underlying region where N is not diffused) can be converted into the oxide layer 402. In other words, the inner surface converted into the nitride layer 401 by performing step a and the inner surface not converted into the nitride layer 401 even after performing step a are converted into the oxide layer 402.

[0064] At this time, the thickness distribution of the oxide layer 402 gradually becomes thicker from the opening 301a of the trench 301 to the bottom 301b. Preferably, the thickness distribution at the bottom 301b becomes the largest (see FIG. 4(d)).

[0065] One reason for this is that the rate (oxidation rate) of converting silicon nitride (SiN) to silicon oxide (SiO) is slower than the rate (oxidation speed) of converting silicon (Si) to silicon oxide (SiO). In other words, the oxidation of Si alone is more selective and efficient than the oxidation of SiN.

[0066] Another possible reason is that the thickness distribution of the nitride layer 401 formed in step a gradually decreases from the opening 301a to the bottom 301b of the trench 301. Furthermore, it is preferable that the inner surface near the bottom 301b of the trench 301 is not converted into the nitride layer 401.

[0067] For these reasons, the oxidation rate of the opening 301a of the trench 301 becomes lower than the oxidation rate of the bottom 301b of the trench 301. The oxidation rate on the inner surface of the trench 301 is, for example, the smallest at the opening 301a of the trench 301 and gradually increases from the opening 301a toward the bottom 301b.

[0068] As a result, for example, in step b, the thickness distribution of the oxide layer 402 can be adjusted so that it gradually thickens from the opening 301a to the bottom 301b of the trench 301, and the thickness of the oxide layer 402 can be the thickest at the bottom 301b of the trench 301. In other words, in step a, the thickness distribution of the nitride layer 401 can be adjusted so that in step b, the thickness distribution of the oxide layer 402 gradually thickens from the opening 301a to the bottom 301b of the trench 301, and / or the thickness distribution of the oxide layer 402 can be the thickest at the bottom 301b of the trench 301. In this case, the thickness of the oxide layer 402 at the bottom 301b of the trench 301 can be set to, for example, 5 to 7 nm.

[0069] Furthermore, for example, the thickness distribution of the oxide layer 402 formed in step b can be made uniform across the entire inner surface of the trench 301. In other words, the thickness distribution of the nitride layer 401 can be adjusted in step a so that the thickness distribution of the oxide layer 402 formed in step b is uniform across the entire inner surface of the trench 301.

[0070] After the oxidation process is completed, the valve 253b is closed, the supply of the oxygen-containing gas into the process chamber 201 is stopped, and the supply of the RF power to the resonance coil 212 is stopped.

[0071] As the oxygen-containing gas, for example, oxygen (O2) gas, ozone (O3) gas, O2 gas + hydrogen (H2) gas, water vapor (H2O), hydrogen peroxide (H2O2) gas, etc. can be used. One or more of these can be used as the oxygen-containing gas.

[0072] To enhance the oxidizing ability of the oxygen-containing gas and reliably oxidize the outermost surface of the trench 301, it is preferable to use an oxygen-containing gas that contains hydrogen (H) in addition to oxygen (O). For example, O₂ gas + H₂ gas can be used. In this case, by increasing the ratio of H to O in the oxygen-containing gas, the selectivity of the oxidation treatment for Si monomers can be improved. In other words, the ratio of the oxidation rate RSi when converting Si to SiO relative to the oxidation rate RSiN when converting SiN to SiO (RSi / RSiN) can be increased. This makes it easier to control the thickness distribution of the oxide layer 402 formed by performing step b, for example, it is easier to increase the thickness of the oxide layer 402 at the bottom 301b of the trench 301.

[0073] (Post-purification, restore atmospheric pressure) After step b is completed, the processing chamber 201 is vacuum-exhausted to remove any remaining gases and other substances from the processing chamber 201. Subsequently, the gaseous substances and other substances remaining in the processing chamber 201 are removed from the processing chamber 201 using the same processing sequence and processing conditions as the above-described purge (post-purge). The atmosphere in the processing chamber 201 is then replaced with the purge gas, and the pressure in the processing chamber 201 is returned to normal pressure (returning to atmospheric pressure).

[0074] (Wafer removal) Subsequently, the susceptor 217 descends to a predetermined transfer position, and the wafer 200 is transferred from the susceptor 217 to the support pins 266. Afterwards, the gate valve 244 is opened, and a transfer robot (not shown) is used to move the processed wafer 200 out of the processing chamber 201. This concludes the substrate processing process of this embodiment.

[0075] (3) Effects of this aspect According to this aspect, one or more of the following effects can be obtained.

[0076] (a) Step a is performed before step b, and the thickness distribution of the nitride layer 401 formed by performing step a is set to a predetermined distribution, so that the thickness distribution of the oxide layer 402 formed by performing step b can be set to a desired distribution.

[0077] For example, in step a, the inner surface (particularly the sidewalls) near the opening 301a of the trench 301 is converted into the nitride layer 401, while the inner surface near the bottom 301b of the trench 301 is not converted into the nitride layer 401. Thus, the thickness distribution of the oxide layer 402 formed by performing step b can be configured such that the thickness near the bottom 301b is greater than the thickness near the opening 301a. Furthermore, in step a, the inner surface (particularly the sidewalls) of the trench 301 is converted into the nitride layer 401, while the inner surface near the bottom 301b of the trench 301 is not converted into the nitride layer 401, so that the thickness distribution becomes gradually thinner from the opening 301a to the bottom 301b. Consequently, the thickness distribution of the oxide layer 402 formed by performing step b can be configured such that it gradually thickens from the opening 301a of the trench 301 toward the bottom 301b, reaching its thickest position at the bottom 301b.

[0078] Furthermore, for example, in step a, while the entire inner surface of the trench 301 (including the sidewalls and bottom) is converted into the nitride layer 401, the thickness distribution of the nitride layer 401 is set to a predetermined distribution in which the thickness gradually becomes thinner from the opening 301a to the bottom 301b of the trench 301. This allows the thickness distribution of the oxide layer 402 formed by performing step b to be uniform across the entire inner surface of the trench 301.

[0079] (b) In step a, the nitrogen-containing gas is excited by applying energy such as plasma, heat, or light to generate nitride species, which are then supplied to wafer 200. This effectively forms nitride layer 401. Furthermore, by utilizing the short lifetime of the generated nitride species, the controllability of the thickness distribution of nitride layer 401 formed by performing step a is improved, thereby further improving the controllability of the thickness distribution of oxide layer 402 formed by performing step b.

[0080] (c) In step b, energy is imparted by plasma, heat, light, etc. to excite the oxygen-containing gas to generate oxidizing species, and the oxidizing species are provided to the wafer 200, thereby effectively forming the oxide layer 402.

[0081] (d) In steps a and b, by respectively exciting the nitrogen-containing gas and the oxygen-containing gas with plasma, the nitride layer 401 and the oxide layer 402 can be formed at relatively low temperatures. This can reduce the thermal history of the wafer 200.

[0082] (e) In step a, by using a gas that does not contain H as the nitrogen-containing gas, the influence of the natural oxide film having an uneven thickness formed on the inner surface of the trench 301 can be suppressed, and the controllability of the thickness distribution of the nitride layer 401 formed on the inner surface of the trench 301 can be improved, thereby improving the controllability of the thickness distribution of the oxide layer 402.

[0083] (f) In step b, by using a gas containing H as the oxygen-containing gas, the oxidizing ability of the oxygen-containing gas can be enhanced, thereby improving the efficiency of the oxidation treatment.

[0084] In this case, by increasing the ratio of H (number of H atoms) to O (number of O atoms) contained in the oxygen-containing gas, the selectivity of oxidation of Si monomer (non-nitride) relative to oxidation of SiN (nitride) can be increased (i.e., the aforementioned R Si / R SiN ratio can be increased). Therefore, for example, if the thickness of nitride layer 401 formed on bottom 301b of trench 301 in step a is very small, or if nitride layer 401 is formed so as not to form nitride layer 401, increasing the ratio of H can further selectively increase the thickness of oxide layer 402 formed on bottom 301b. Similarly, for example, if nitride layer 401 is formed in step a with a thickness distribution that gradually decreases from opening 301a toward bottom 301b, increasing the ratio of H can further increase the thickness gradient of oxide layer 402, which increases from opening 301a toward bottom 301b.

[0085] Therefore, for the trench 301 in which the nitride layer 401 is formed with a predetermined thickness distribution in step a, the thickness distribution of the oxide layer 402 can be further controlled by adjusting the ratio of the H component in step b. In other words, by adjusting the ratio of the H component in step b, the controllability of the thickness distribution of the oxide layer 402 formed by performing step b can be improved.

[0086] (g) In step b, by converting the nitride layer 401 into the oxide layer 402 throughout the entire thickness of the nitride layer 401 , it is possible to substantially eliminate any residual nitrogen in the oxide layer 402 .

[0087] Preferably, in step b, in the inner surface of the trench 301, the nitride layer 401 and a predetermined area that is deeper than the nitride layer 401 in the thickness direction of the nitride layer 401 and has not been modified into the nitride layer 401 (the bottom area in which N is not diffused) are respectively modified into the oxide layer 402, thereby more reliably preventing N from remaining in the oxide layer 402.

[0088] (h) Even when a predetermined substance (gaseous substance, liquid substance) is arbitrarily selected from the above-mentioned oxygen-containing gas group, nitrogen-containing gas group, and inert gas group and used, the above-mentioned effects can be obtained in the same manner.

[0089] (4) Modification The substrate processing sequence in this aspect can be modified to the following variations. These variations can be combined in any manner. Unless otherwise specified, the processing order and processing conditions in each step of each variation can be the same as those in each step of the aforementioned substrate processing sequence.

[0090] (Variation 1) In step a, by setting the process pressure to a relatively low pressure, the amount of nitride species generated can be reduced, and the thickness distribution of the nitride layer 401 can be controlled, thereby controlling the thickness distribution of the oxide layer 402. Specifically, the process pressure can be set to a third pressure that is lower than the "first pressure" mentioned in the description of the above aspect.

[0091] This modification also achieves the same effects as the above-described embodiment. Furthermore, according to this modification, the amount of nitride seeds supplied to wafer 200 is reduced, and most of the nitride seeds are consumed near opening 301a of trench 301, preventing the nitride seeds from reaching bottom 301b. As a result, the thickness distribution of nitride layer 401 can be easily adjusted to gradually decrease from opening 301a of trench 301 toward bottom 301b.

[0092] (Variation 2) In step a, by setting the RF power relatively low, the amount of nitride species generated can be reduced, and the thickness distribution of the nitride layer 401 can be controlled, thereby controlling the thickness distribution of the oxide layer 402. Specifically, in order to achieve a uniform thickness distribution of the nitride layer 401 formed by performing step a across the entire inner surface of the trench 301, the RF power value can be set to a second power value lower than the first power value.

[0093] This modification also achieves the same effects as the above-described embodiment. Furthermore, according to this modification, the amount of nitride seeds supplied to wafer 200 is reduced, and most of the nitride seeds are consumed near opening 301a of trench 301, preventing the nitride seeds from reaching bottom 301b. As a result, the thickness distribution of nitride layer 401 can be easily adjusted to gradually decrease from opening 301a of trench 301 toward bottom 301b.

[0094] (Variation 3) In step a, by relatively shortening the supply time of the nitrogen-containing gas, the amount of nitride seed supplied to wafer 200 can be reduced, thereby controlling the thickness distribution of nitride layer 401 and, in turn, the thickness distribution of oxide layer 402. Specifically, the supply time required to achieve a uniform thickness distribution of nitride layer 401 formed by performing step a across the entire inner surface of trench 301 is referred to as the "first supply time." The supply time can be set to a second supply time that is shorter than the first supply time.

[0095] This modification also achieves the same effects as the above-described embodiment. Furthermore, according to this modification, the amount of nitride seeds supplied to wafer 200 is reduced, and most of the nitride seeds are consumed near opening 301a of trench 301, preventing the nitride seeds from reaching bottom 301b. As a result, the thickness distribution of nitride layer 401 can be easily adjusted to gradually decrease from opening 301a of trench 301 toward bottom 301b.

[0096] (Variation 4) In step a, by using ionized N atoms or other ions as nitride seeds to supply wafer 200, the thickness distribution of nitride layer 401, and thus the thickness distribution of oxide layer 402, can be controlled. Specifically, by adjusting variable impedance mechanism 275, the potential (bias) of wafer 200 in step a is controlled via impedance adjustment electrode 217c and susceptor 217. This adjusts the nitride distribution of the ion components of the nitride seeds introduced into trench 301, thereby achieving a desired thickness distribution of nitride layer 401.

[0097] This modified example also achieves the same effects as the aforementioned embodiment. Furthermore, since the mean free path of ionized N atoms and other ions is relatively short even when the processing pressure is reduced, they tend to react preferentially on the inner surface near the opening 301a of the trench 301. As a result, the thickness distribution of the nitride layer 401 can be easily adjusted to gradually decrease from the opening 301a toward the bottom 301b of the trench 301.

[0098] (Variant 5) In step a, by relatively increasing the flow rate of the nitrogen-containing gas, the thickness distribution of the nitride layer 401, and thus the thickness distribution of the oxide layer 402, can also be controlled. Specifically, the flow rate at which the thickness distribution of the nitride layer 401 formed by performing step a is uniform across the entire inner surface of the trench 301 is referred to as the "first flow rate." The flow rate can be set to a second flow rate that is greater than the first flow rate. The flow rate of the nitrogen-containing gas can be adjusted, for example, by controlling the flow rate of the nitrogen-containing gas supplied to the processing chamber 201.

[0099] This modification also achieves the same effects as the above-described embodiment. Furthermore, according to this modification, by increasing the flow rate of the nitride seed, the flow rate of the nitride seed near the bottom 301b is relatively reduced compared to the flow rate of the nitride seed near the opening 301a, allowing preferential nitriding of the inner surface near the opening 301a of the trench 301. As a result, the thickness distribution of the nitride layer 401 can be easily adjusted to gradually decrease from the opening 301a of the trench 301 toward the bottom 301b.

[0100] <Other aspects of the present disclosure> The above has specifically described the aspects of the present disclosure. However, the present disclosure is not limited to the above aspects and can be modified in various ways without departing from the scope of the present disclosure.

[0101] In the above embodiment, a portion of the inner surface of the trench 301 is converted into the nitride layer 401 in step a. However, the present disclosure is not limited thereto. For example, the entire inner surface of the trench 301 may be converted into the nitride layer 401. In this case, the same effects as those of the above embodiment can be achieved.

[0102] While the above aspects illustrate the use of plasma to excite nitrogen-containing and oxygen-containing gases, the present disclosure is not limited thereto. For example, nitrogen-containing and oxygen-containing gases can also be excited using heat or light. In this case, the same effects as in the above aspects can be achieved. Furthermore, damage to wafer 200 and the like caused by plasma can be avoided.

[0103] While the groove 301 is described as an example of a concave structure in the above embodiment, the present disclosure is not limited thereto. For example, a hole may be formed on the surface of the wafer 200 as the concave structure. Furthermore, the concave structure may be configured so that the width increases from the opening 301a toward the bottom 301b (so that the distance between the opposing inner surfaces gradually increases). Furthermore, the width may be configured so that the width narrows from the opening 301a toward the bottom 301b (so that the distance between the opposing inner surfaces gradually decreases). In these cases, the same effects as those of the above embodiment can be achieved.

[0104] Although not described in the above aspects, the present disclosure can use a wafer 200 having a trench 301 with an aspect ratio of 10 or greater, or 20 or greater. According to the present disclosure, even when a wafer 200 with such a high aspect ratio is used, the same effects as those of the above aspects can be obtained.

[0105] In the above embodiment, the inner surface of trench 301 is described as being composed of a Si layer formed from Si monomers, but the present disclosure is not limited thereto. For example, the inner surface of trench 301 may also be composed of a silicon-containing material (Si compound) such as silicon carbide (SiC) or silicon germanium (SiGe). Furthermore, the inner surface of trench 301 may also be composed of a metal containing aluminum (Al), titanium (Ti), hafnium (Hf), or zirconium (Zr), or a compound thereof. However, the inner surface of trench 301 is preferably different from these oxides and nitrides.

[0106] In the above embodiment, an example is described in which the nitridation process (step a) and the oxidation process (step b) are performed sequentially within a single process chamber (i.e., process chamber 201), but the present disclosure is not limited thereto. For example, after the substrate is nitrided (step a), the substrate is moved from the process chamber where the nitridation process has been performed to a transfer chamber that is not open to the atmosphere. Thereafter, the substrate may be moved into another process chamber and subjected to the oxidation process (step b).

[0107] The above aspects describe an example of performing substrate processing using, for example, a single-substrate processing apparatus that processes one or more substrates at a time. However, the present disclosure is not limited to the above aspects and can also be appropriately applied to a batch-type substrate processing apparatus that processes multiple substrates at a time.

[0108] Even when using these substrate processing devices, each process can be performed under the same processing sequence and processing conditions as the above-mentioned aspects or modified examples, thereby obtaining the same effects as the above-mentioned aspects or modified examples.

[0109] 200: Wafer (substrate) 301: Groove (concave structure) 401: Nitride layer 402: Oxide layer

Claims

1. A substrate processing method comprising: (a) performing a nitriding treatment on the inner surface of a concave structure formed on a substrate, thereby modifying a portion of the underlying layer constituting the inner surface into a nitriding layer; and (b) performing an oxidation treatment on the inner surface, thereby modifying the nitriding layer and another portion of the underlying layer not modified into the nitriding layer into an oxide layer; wherein in (b), the oxidation rate of the nitriding layer is lower than the oxidation rate of the other portion of the underlying layer not modified into the nitriding layer.

2. The substrate processing method of claim 1, wherein in (a), the thickness distribution of the aforementioned nitride layer is such that the thickness on the opening side of the aforementioned concave structure is greater than the thickness on the bottom side.

3. A substrate processing method comprising: (a) performing a nitriding treatment on the inner surface of a concave structure formed on a substrate, thereby modifying a portion of the bottom layer constituting the inner surface into a nitriding layer; and (b) performing an oxidation treatment on the inner surface, thereby modifying the nitriding layer and another portion of the bottom layer not modified into the nitriding layer into an oxide layer; wherein in (a), the thickness distribution of the nitriding layer is configured to gradually thin from the opening side of the concave structure towards the bottom side.

4. The substrate processing method of claim 2, wherein in (a), the aforementioned nitride layer is formed on the entire aforementioned inner surface.

5. The substrate processing method of claim 1, wherein in (b), the thickness distribution of the aforementioned oxide layer is such that the thickness of the bottom side of the aforementioned concave structure is greater than the thickness of the opening side.

6. The substrate processing method of claim 1, wherein in (b), the thickness distribution of the aforementioned oxide layer is such that the thickness of the bottom side of the aforementioned concave structure is greater than the thickness of the opening side.

7. The substrate processing method of claim 1, wherein in (b), the thickness distribution of the aforementioned oxide layer is set to be uniformly distributed on the sidewalls of the entire aforementioned inner surface.

8. The substrate processing method of claim 2, wherein in (b), the thickness distribution of the aforementioned oxide layer is set to be uniformly distributed on the sidewalls of the entire aforementioned inner surface.

9. A substrate processing method according to any one of claims 1 to 8, wherein in (a), a nitrogen-containing gas is excited to generate a nitride seed, and the nitride seed is supplied to the substrate.

10. The substrate processing method of claim 9, wherein in (a), the aforementioned nitrogen-containing gas is excited by plasma or heat.

11. The substrate processing method of claim 9, wherein the aforementioned nitrogen-containing gas is a gas that does not contain hydrogen.

12. The substrate processing method of any one of claims 1 to 8, wherein the aforementioned underlying layer contains silicon.

13. A substrate processing method according to any one of claims 1 to 8, wherein in (b), an oxygen-containing gas is excited to generate an oxide seed, and the oxide seed is supplied to the substrate.

14. A substrate processing method as claimed in any one of claims 1 to 8, wherein in (b), oxygen-containing gas is excited by plasma or heat.

15. The substrate processing method of claim 13, wherein in (b), the thickness distribution of the oxide layer is controlled by adjusting the ratio of hydrogen to oxygen contained in the oxygen-containing gas.

16. A method for manufacturing a semiconductor device, comprising: (a) nitriding an inner surface of a concave structure formed on a substrate to modify a portion of a subsurface constituting the inner surface into a nitrided layer; and (b) oxidizing the inner surface to modify the nitrided layer and another portion of the subsurface not modified into the nitrided layer into an oxide layer; wherein in (b), the rate at which the nitrided layer is oxidized is lower than the rate at which the other portion of the subsurface not modified into the nitrided layer is oxidized.

17. A substrate processing apparatus comprising: a nitrogen-containing gas supply system for supplying nitrogen-containing gas to a substrate; an oxygen-containing gas supply system for supplying oxygen-containing gas to the substrate; an excitation unit for exciting the gas supplied from the nitrogen-containing gas supply system and the oxygen-containing gas supply system; and a control unit configured to control the nitrogen-containing gas supply system, the oxygen-containing gas supply system, and the excitation unit to perform the following processes: (a) supplying a nitride seed generated by exciting the nitrogen-containing gas to the substrate having a concave structure formed on its surface, thereby modifying a portion of the bottom layer constituting the inner surface of the concave structure into a nitride layer; and (b) supplying an oxide seed generated by exciting the oxygen-containing gas to the substrate, thereby modifying the nitride layer and another portion of the bottom layer not modified into the nitride layer into an oxide layer; wherein in (b), the rate at which the nitride layer is oxidized is lower than the rate at which the other portion of the bottom layer not modified into the nitride layer is oxidized.

18. A program for substrate processing, wherein a computer causes a substrate processing apparatus to perform the following sequence: (a) nitriding a portion of the underlying layer constituting the inner surface of a concave structure formed on a substrate to modify the inner surface into a nitrided layer; and (b) oxidizing the inner surface to modify the nitrided layer and another portion of the underlying layer not modified into the nitrided layer into an oxide layer; wherein in (b), the oxidation rate of the nitrided layer is lower than the oxidation rate of the other portion of the underlying layer not modified into the nitrided layer.

19. A method for manufacturing a semiconductor device, comprising: (a) performing a nitriding treatment on the inner surface of a concave structure formed on a substrate, thereby modifying a portion of the bottom layer constituting the inner surface into a nitriding layer; and (b) performing an oxidation treatment on the inner surface, thereby modifying the nitriding layer and another portion of the bottom layer not modified into the nitriding layer into an oxide layer; wherein in (a), the thickness distribution of the nitriding layer is configured to gradually thin from the opening side of the concave structure to the bottom side.

20. A substrate processing apparatus comprising: a nitrogen-containing gas supply system for supplying nitrogen-containing gas to a substrate; an oxygen-containing gas supply system for supplying oxygen-containing gas to the substrate; an excitation unit for exciting the gas supplied from the nitrogen-containing gas supply system and the oxygen-containing gas supply system; and a control unit configured to control the nitrogen-containing gas supply system, the oxygen-containing gas supply system, and the excitation unit to perform the following processes: (a) supplying a nitride seed generated by exciting the nitrogen-containing gas to the substrate on which a concave structure is formed, thereby modifying a portion of the bottom layer constituting the inner surface of the concave structure into a nitride layer; and (b) supplying an oxide seed generated by exciting the oxygen-containing gas to the substrate, thereby modifying the nitride layer and another portion of the bottom layer not modified into the nitride layer into an oxide layer; wherein in (a), the thickness distribution of the nitride layer is configured to gradually thin from the opening side of the concave structure to the bottom side.

21. A program for substrate processing, wherein a computer causes a substrate processing apparatus to perform the following sequence: (a) nitriding a portion of the bottom layer constituting the inner surface of a concave structure formed on a substrate to convert it into a nitrided layer; and (b) oxidizing the inner surface to convert the nitrided layer and another portion of the bottom layer not converted into the nitrided layer into an oxide layer; wherein in (a), the thickness distribution of the nitrided layer is set to a distribution that gradually thins from the opening side of the concave structure to the bottom side.

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