Plasma etching device and plasma etching method

Abstract

A plasma etching device comprising a chamber, a gas supply part that supplies gas to the chamber, and a control part, wherein: the gas supply part is provided with a gas box which is for supplying the gas, a gas diffusion chamber inside which the gas from the gas box diffuses, and which introduces the gas into the chamber, and a release part which is for discharging the gas that is in the gas diffusion chamber; the control part performs control including (a) a step for supplying a first gas at a first flow rate from the gas box and generating plasma inside the chamber, and (b) a step for, after stopping the supply of the first gas from the gas box, supplying a second gas at a second flow rate from the gas box, and discharging the inside of the gas diffusion chamber; and in the step (b), the pressure inside the gas diffusion chamber is maintained at greater than or equal to a threshold value which is determined in advance on the basis of a plasma treatment condition, as a pressure at which to maintain the plasma inside the chamber.

Description

Plasma etching apparatus and plasma etching method

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

[0002] Patent Document 1 discloses a method for selectively etching a silicon oxide film on a substrate to be processed having a silicon nitride film and a silicon oxide film on the surface thereof, which method includes a step of intermittently exposing the substrate to at least one of a processing gas containing hydrogen fluoride gas and ammonia gas, and a processing gas containing a compound containing nitrogen, hydrogen, and fluorine, in a vacuum atmosphere, multiple times.

[0003] JP 2015-144249 A

[0004] The technology according to the present disclosure appropriately switches gases during plasma etching.

[0005] One aspect of the present disclosure is a plasma etching apparatus comprising: a chamber; a gas supply unit that supplies a gas to the chamber; and a control unit. The gas supply unit comprises a gas box that supplies the gas; a gas diffusion chamber in which the gas from the gas box is diffused and introduced into the chamber; and an exhaust unit that exhausts the gas from the gas diffusion chamber. The control unit executes control including: (a) supplying a first gas from the gas box at a first flow rate to generate plasma in the chamber; and (b) after stopping the supply of the first gas from the gas box, supplying a second gas from the gas box at a second flow rate while exhausting the gas diffusion chamber. In the (b) step, the pressure in the gas diffusion chamber is maintained at or above a threshold value predetermined based on plasma processing conditions as a pressure for maintaining the plasma in the chamber.

[0006] According to the present disclosure, gas switching can be performed appropriately in plasma etching.

[0007] FIG. 1 is an explanatory diagram showing an example of the configuration of a plasma etching system according to an embodiment; FIG. 2 is a cross-sectional view showing an example of the configuration of a plasma etching apparatus according to an embodiment; FIG. 3 is a schematic diagram showing an outline of the configuration of a gas supply unit according to a first embodiment; FIG. 4 is a schematic diagram showing an outline of one example of the configuration of an exhaust unit; FIG. 5 is a schematic diagram showing an outline of another example of the configuration of an exhaust unit; FIG. 6 is a sequence chart showing flow rate control in a gas supply method; FIG. 7 is a graph showing the pressure of a gas diffusion chamber in a gas supply method; FIG. 8 is a sequence chart showing a modified example of flow rate control in a gas supply method; FIG. 9 is a schematic diagram showing an outline of the configuration of a gas supply unit according to a second embodiment; FIG. 10 is a sequence chart showing flow rate control in a gas supply method; FIG. 11 is a graph showing the pressure of a gas diffusion chamber and a chamber in a gas supply method; FIG. 12 is a sequence chart showing flow rate control in a gas supply method according to a comparative example, and a graph showing pressure values ​​of a gas diffusion chamber or a chamber.

[0008] 2. Description of the Related Art In a semiconductor device manufacturing process, a plasma etching process is performed in which a desired process gas is supplied to a process module containing a semiconductor wafer (hereinafter referred to as a "substrate"), and the substrate is etched with plasma from the process gas.

[0009] Substrates to be processed by plasma etching include those having multiple layers stacked on the surface with different etching selectivities. When processing such substrates, process gases with high selectivities for each layer may be sequentially supplied, and one process gas may be supplied to etch one layer, and then another process gas may be supplied to etch another layer.

[0010] Patent Document 1 discloses a method for selectively etching a silicon oxide film on a substrate to be processed having a silicon nitride film and a silicon oxide film on the surface thereof, which method includes a step of intermittently exposing the substrate to at least one of a processing gas containing hydrogen fluoride gas and ammonia gas, and a processing gas containing a compound containing nitrogen, hydrogen, and fluorine, in a vacuum atmosphere, multiple times.

[0011] On the other hand, when one process gas is exhausted and then another process gas is supplied, the gas diffusion chamber may be exhausted through a shower head by an exhaust device connected to the chamber. In such cases, the flow rate of the process gas at the gas inlet of the shower head may become a rate limiting factor, preventing rapid exhaust of the gas diffusion chamber.

[0012] The present inventors have studied this problem extensively and have come up with the idea of ​​providing an exhaust section that can exhaust the inside of the gas diffusion chamber at a sufficient speed. Furthermore, the present inventors have also studied this problem and found that such an exhaust section has the following problem. Specifically, as shown in Fig. 12 for the comparative example, when switching gases by supplying a first gas, exhausting the first gas through the exhaust section, and then supplying a second gas, the pressure inside the gas diffusion chamber decreases while the exhaust section is exhausting the inside of the gas diffusion chamber, and thus the pressure in the chamber decreases. When the chamber pressure reaches a threshold pressure P necessary to maintain a plasma generation state, ＣＴ If the temperature drops further, the plasma generation state changes and may even cause an extinguishment.

[0013] Therefore, the technology disclosed herein appropriately switches gases during plasma etching. Specifically, after the supply of the first gas is stopped, a second gas is supplied and the gas diffusion chamber is evacuated by an exhaust unit provided in the gas diffusion chamber. The gas supply is controlled so that the pressure in the gas diffusion chamber is equal to or greater than a threshold pressure in the diffusion chamber capable of maintaining plasma in the chamber, or so that the pressure in the chamber is equal to or greater than a threshold pressure in the chamber capable of maintaining plasma in the chamber.

[0014] Hereinafter, the configuration of the substrate processing apparatus according to this embodiment will be described with reference to the drawings. In this specification, elements having substantially the same functional configuration are designated by the same reference numerals, and redundant description will be omitted.

[0015] <Plasma Etching System> FIG. 1 is a diagram illustrating an example of the configuration of a plasma etching system. In one embodiment, the plasma etching system includes a plasma etching apparatus 1 and a control unit 2. The plasma etching system is an example of a substrate processing system, and the plasma etching apparatus 1 is an example of a substrate processing apparatus. The plasma etching apparatus 1 includes a plasma etching chamber 10 (hereinafter referred to as "chamber 10"), a substrate support 11, and a plasma generation unit 12. The chamber 10 has a plasma processing space. The chamber 10 also has at least one gas supply port for supplying at least one processing gas to the plasma processing space and at least one gas exhaust port for exhausting gas from the plasma processing space. The gas supply port is connected to a gas box 21 (described later), and the gas exhaust port is connected to an exhaust system 40 (described later). The substrate support 11 is disposed in the plasma processing space and has a substrate support surface for supporting a substrate.

[0016] The plasma generating unit 12 is configured to generate a plasma PL from at least one processing gas supplied into the plasma processing space. The plasma PL formed in the plasma processing space may be a capacitively coupled plasma (CCP), an inductively coupled plasma (ICP), an electron-cyclotron-resonance (ECR) plasma, a helicon wave plasma (HWP), a surface wave plasma (SWP), or the like. Various types of plasma generators may be used, including alternating current (AC) plasma generators and direct current (DC) plasma generators. In one embodiment, the AC signal (AC power) used in the AC plasma generator has a frequency in the range of 100 kHz to 10 GHz. Thus, AC signals include radio frequency (RF) signals and microwave signals. In one embodiment, the RF signal has a frequency in the range of 100 kHz to 150 MHz.

[0017] The controller 2 processes computer-executable instructions that cause the plasma etching apparatus 1 to perform the various steps described in this disclosure. The controller 2 may be configured to control each element of the plasma etching apparatus 1 to perform the various steps described herein. In one embodiment, part or all of the controller 2 may be included in the plasma etching apparatus 1. The controller 2 may include a processing unit 2a1, a storage unit 2a2, and a communication interface 2a3. The controller 2 may be implemented, for example, by a computer 2a. The processing unit 2a1 may be configured to read a program from the storage unit 2a2 and execute the read program to perform various control operations. The program may be stored in the storage unit 2a2 in advance or may be acquired via a medium when needed. The acquired program is stored in the storage unit 2a2 and read from the storage unit 2a2 by the processing unit 2a1 for execution. The medium may be various storage media readable by the computer 2a or a communication line connected to the communication interface 2a3. The processing unit 2a1 may be a CPU (Central Processing Unit). The storage unit 2a2 may include a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), a solid state drive (SSD), or a combination thereof. The communication interface 2a3 may communicate with the plasma etching apparatus 1 via a communication line such as a local area network (LAN).

[0018] <Plasma Etching Apparatus> An example of the configuration of a capacitively coupled plasma etching apparatus 1 as an example of a substrate processing apparatus will be described below. Fig. 2 is a diagram for explaining an example of the configuration of the capacitively coupled plasma etching apparatus 1.

[0019] The plasma etching apparatus 1 includes a chamber 10 , a substrate support 11 , a gas supply 20 , a power supply 30 and an exhaust system 40 .

[0020] The substrate support 11 is disposed in the chamber 10. The substrate support 11 includes a main body 111 and a ring assembly 112. The main body 111 has a central region 111a for supporting a substrate W and an annular region 111b for supporting the ring assembly 112. A wafer is an example of a substrate W. The annular region 111b of the main body 111 surrounds the central region 111a of the main body 111 in a plan view. The substrate W is disposed on the central region 111a of the main body 111, and the ring assembly 112 is disposed on the annular region 111b of the main body 111 so as to surround the substrate W on the central region 111a of the main body 111. Therefore, the central region 111a is also referred to as a substrate support surface for supporting the substrate W, and the annular region 111b is also referred to as a ring support surface for supporting the ring assembly 112.

[0021] In one embodiment, the main body 111 includes a base 1110 and an electrostatic chuck 1111. The base 1110 includes a conductive member. The conductive member of the base 1110 can function as a lower electrode. The electrostatic chuck 1111 is disposed on the base 1110. The electrostatic chuck 1111 includes a ceramic member 1111a and an electrostatic electrode 1111b disposed within the ceramic member 1111a. The ceramic member 1111a has a central region 111a. In one embodiment, the ceramic member 1111a also has an annular region 111b. Note that the annular region 111b may also be provided by another member surrounding the electrostatic chuck 1111, such as an annular electrostatic chuck or an annular insulating member. In this case, the ring assembly 112 may be disposed on the annular electrostatic chuck or the annular insulating member, or may be disposed on both the electrostatic chuck 1111 and the annular insulating member. Furthermore, at least one RF / DC electrode coupled to an RF power supply 31 and / or a DC power supply 32, which will be described later, may be disposed within the ceramic member 1111a. In this case, the at least one RF / DC electrode functions as a lower electrode. When a bias RF signal and / or a DC signal, which will be described later, is supplied to the at least one RF / DC electrode, the RF / DC electrode is also called a bias electrode. Note that the conductive member of the base 1110 and the at least one RF / DC electrode may function as multiple lower electrodes. Furthermore, the electrostatic electrode 1111b may function as a lower electrode. Therefore, the substrate support 11 includes at least one lower electrode.

[0022] The ring assembly 112 includes one or more annular members. In one embodiment, the one or more annular members include one or more edge rings and at least one cover ring. The edge rings are formed of a conductive or insulating material, and the cover rings are formed of an insulating material.

[0023] The substrate support 11 may also include a temperature adjustment module configured to adjust at least one of the electrostatic chuck 1111, the ring assembly 112, and the substrate W to a target temperature. The temperature adjustment module may include a heater, a heat transfer medium, a flow passage 1110a, or a combination thereof. A heat transfer fluid such as brine or a gas flows through the flow passage 1110a. In one embodiment, the flow passage 1110a is formed in the base 1110, and one or more heaters are disposed in the ceramic member 1111a of the electrostatic chuck 1111. The substrate support 11 may also include a heat transfer gas supply configured to supply a heat transfer gas to a gap between the back surface of the substrate W and the central region 111a.

[0024] The gas supply unit 20, which will be described in detail later, includes a gas box 21, a gas flow path 22, a gas inlet, and an exhaust unit 24. The gas box 21 is configured to supply multiple gases supplied from a gas source at controlled flow rates. The gas flow path 22 is configured to supply the gas supplied from the gas box 21 to the gas inlet. The gas inlet is configured to introduce two or more process gases into the chamber 10. The exhaust unit 24 is configured to exhaust the gases introduced into the gas inlet. The gas inlet includes a showerhead 25. The showerhead 25 is disposed above the substrate support 11. In one embodiment, the showerhead 25 constitutes at least a portion of the ceiling of the chamber 10. The chamber 10 has a plasma processing space 10s defined by the showerhead 25, a sidewall 10a of the chamber 10, and the substrate support 11. The chamber 10 is grounded. The showerhead 25 and the substrate support 11 are electrically insulated from the housing of the chamber 10.

[0025] The showerhead 25 is configured to introduce the processing gas from the gas box 21 into the plasma processing space 10s. The showerhead 25 has at least one gas supply port 25a, at least one gas diffusion chamber 25b, and multiple gas inlets 25c. The processing gas supplied to the gas supply port 25a passes through the gas diffusion chamber 25b and is introduced into the plasma processing space 10s from the multiple gas inlets 25c. The showerhead 25 also includes at least one upper electrode. Note that, in addition to the showerhead 25, the gas introduction unit may also include one or more side gas injectors (SGIs) attached to one or more openings formed in the sidewall 10a.

[0026] The gas box 21 may include at least one gas source 26 and at least one flow controller 27. In one embodiment, the gas box 21 is configured to supply two or more process gases from respective gas sources 26 through respective flow controllers 27 to the showerhead 25. Each flow controller 27 may include, for example, a mass flow controller or a pressure-controlled flow controller. Additionally, the gas box 21 may include at least one flow modulation device that modulates or pulses the flow rate of at least one process gas.

[0027] The power supply 30 includes an RF power supply 31 coupled to the chamber 10 via at least one impedance matching circuit. The RF power supply 31 is configured to supply at least one RF signal (RF power) to at least one lower electrode and / or at least one upper electrode. This generates a plasma PL from at least one processing gas supplied to the plasma processing space 10s. Therefore, the RF power supply 31 can function as at least a part of the plasma generation unit 12. Furthermore, by supplying a bias RF signal to the at least one lower electrode, a bias potential is generated on the substrate W, and ion components in the formed plasma can be attracted to the substrate W.

[0028] In one embodiment, the RF power supply 31 includes a first RF generating unit 31a and a second RF generating unit 31b. The first RF generating unit 31a is coupled to at least one lower electrode and / or at least one upper electrode via at least one impedance matching circuit and is configured to generate a source RF signal (source RF power) for plasma generation. In one embodiment, the source RF signal has a frequency in the range of 10 MHz to 150 MHz. In one embodiment, the first RF generating unit 31a may be configured to generate multiple source RF signals having different frequencies. The generated one or more source RF signals are supplied to at least one lower electrode and / or at least one upper electrode.

[0029] The second RF generator 31b is coupled to at least one lower electrode via at least one impedance matching circuit and is configured to generate a bias RF signal (bias RF power). The frequency of the bias RF signal may be the same as or different from the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency lower than the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency in the range of 100 kHz to 60 MHz. In one embodiment, the second RF generator 31b may be configured to generate multiple bias RF signals having different frequencies. The generated one or more bias RF signals are supplied to at least one lower electrode. In various embodiments, at least one of the source RF signal and the bias RF signal may be pulsed.

[0030] The power supply 30 may also include a DC power supply 32 coupled to the chamber 10. The DC power supply 32 includes a first DC generator 32a and a second DC generator 32b. In one embodiment, the first DC generator 32a is connected to the at least one lower electrode and configured to generate a first DC signal. The generated first DC signal is applied to the at least one lower electrode. In one embodiment, the second DC generator 32b is connected to the at least one upper electrode and configured to generate a second DC signal. The generated second DC signal is applied to the at least one upper electrode.

[0031] In various embodiments, the first and second DC signals may be pulsed. In this case, a sequence of voltage pulses is applied to at least one lower electrode and / or at least one upper electrode. The voltage pulses may have a rectangular, trapezoidal, triangular, or combination thereof pulse waveform. In one embodiment, a waveform generator for generating the sequence of voltage pulses from the DC signal is connected between the first DC generator 32a and at least one lower electrode. Thus, the first DC generator 32a and the waveform generator constitute a voltage pulse generator. When the second DC generator 32b and the waveform generator constitute a voltage pulse generator, the voltage pulse generator is connected to at least one upper electrode. The voltage pulses may have either positive or negative polarity. Furthermore, the sequence of voltage pulses may include one or more positive voltage pulses and one or more negative voltage pulses within one period. The first and second DC generating units 32a and 32b may be provided in addition to the RF power supply 31, or the first DC generating unit 32a may be provided instead of the second RF generating unit 31b.

[0032] The exhaust system 40 may be connected to, for example, a gas exhaust port 10e provided at the bottom of the chamber 10. The exhaust system 40 may include a pressure regulating valve and a vacuum pump. The pressure in the plasma processing space 10s is regulated by the pressure regulating valve. The vacuum pump may include a turbomolecular pump, a dry pump, or a combination thereof.

[0033] (First Embodiment) <Gas Supply Unit> Hereinafter, the gas supply unit 20 according to the first embodiment will be described with reference to Figures 3 to 5. Figure 3 is a schematic diagram showing an outline of the configuration of the gas supply unit 20. Note that in Figure 3, for the sake of convenience, the chamber 10, part of the substrate support unit 11, the plasma generation unit 12, and the like in the plasma etching apparatus 1 are not shown.

[0034] 3, the gas box 21 includes a first gas source 201 that supplies a first gas and a second gas source 202 that supplies a second gas. Each of the first gas source 201 and the second gas source 202 may include a plurality of gas sources. Alternatively, some of the gas sources may be shared by the first gas source 201 and the second gas source. The first gas and the second gas may be known gases that can selectively etch either a silicon nitride film or a silicon oxide film.

[0035] The gas flow path 22 includes a first flow path 211 downstream of the first gas source 201 through which a first gas flows. The gas flow path 22 also includes a second flow path 212 downstream of the second gas source 202 through which a second gas flows. The first flow path 211 and the second flow path 212 merge downstream of these flow paths to form a common flow path 213 through which one of the gases flows. The common flow path 213 according to this embodiment includes a branching structure 214 that distributes the gas so that the pressure in the surface direction is uniform. The common flow path 213 is connected to a plurality of gas supply ports 25a in the shower head 25 at its downstream end relative to the branching structure 214. The first flow path 211 includes a first valve 215 at its end connected to the common flow path 213. The second flow path 212 includes a second valve 216 at its end connected to the common flow path 213.

[0036] In the gas flow path 22 having such a configuration, for example, with the first valve 215 open and the second valve 216 closed, a first gas supplied from the first gas source 201 flows through the first flow path 211 and into the common flow path 213. The first gas is dispersed while flowing through the branching structure 214 of the common flow path 213, and flows from the downstream end of the branching structure 214 into the gas diffusion chamber 25b via the multiple gas supply ports 25a in the shower head 25. The first gas is diffused in the gas diffusion chamber 25b so as to achieve a substantially uniform pressure distribution in the surface direction, and is then introduced into the chamber 10 via the gas inlet 25c.

[0037] The gas diffusion chamber 25b includes a pressure gauge P1. The pressure gauge P1 is configured to measure the pressure inside the gas diffusion chamber 25b and, for example, transmit the measurement value information to the control unit 2.

[0038] The chamber 10 includes a pressure gauge P2. The pressure gauge P2 is configured to measure the pressure inside the chamber 10 and, for example, transmit the measurement value information to the control unit 2.

[0039] The gas diffusion chamber 25b is connected to the exhaust unit 24. The exhaust unit 24 includes an exhaust flow path 221 and a vacuum pump 222. The exhaust flow path 221 has an end connected to the gas diffusion chamber 25b and an end connected to the vacuum pump 222, and is configured to allow gas to flow therethrough. The vacuum pump 222 may include a turbomolecular pump, a dry pump, or a combination thereof. The vacuum pump 222 may also be included in the exhaust system 40.

[0040] In one embodiment, a plurality of exhaust flow paths 221 are provided, and the ends of the exhaust flow paths 221 connected to the gas diffusion chamber 25b are arranged evenly in the circumferential direction in a plan view of the gas diffusion chamber 25b, thereby enabling exhaust from the gas diffusion chamber 25b to achieve an even pressure distribution in the surface direction.

[0041] 4 , the exhaust unit 24 includes a control valve 230 in the exhaust flow path 221. The control valve 230 is configured to be able to control, for example, the opening degree, opening / closing timing, or opening time by the control unit 2 so as to adjust the flow rate of gas flowing through the exhaust flow path 221.

[0042] 5, the exhaust unit 24 includes a tank 240 in the exhaust flow path 221, and a first tank valve 241 and a second tank valve 242 before and after the tank 240. The interior of the tank 240 is configured to be able to maintain a negative pressure relative to the gas diffusion chamber 25b. In one embodiment, the volume of the tank 240 is approximately the same as the volume of the gas diffusion chamber 25b.

[0043] 6 and 7, a gas supply method MT1 for supplying a gas to the chamber 10 using the gas supply unit 20 according to the first embodiment will be described. Fig. 6 is a sequence chart for controlling the flow rate of the first gas or the second gas supplied from the first gas source 201 or the second gas source 202, and the exhaust flow rate from the gas diffusion chamber 25b by the exhaust unit 24, in the gas supply method MT1.

[0044] The gas supply method MT1 is a method that includes switching the gas supplied to the chamber 10 from a first gas to a second gas, or from the second gas to the first gas, and includes the following steps ST11 to ST14.

[0045] In step ST11, a first flow rate F １ The supply of the first gas is started at a first flow rate F to generate the plasma PL, and the supply of the first gas is stopped after a desired duration. １ is the flow rate for maintaining the pressure in the chamber 10 at a desired level in order to maintain the generation of the plasma PL of the first gas in the chamber 10. At this time, the pressure in the gas diffusion chamber 25b is set to a value equal to or greater than the threshold pressure P ＤＴ The pressure in the diffusion chamber is maintained at or above the threshold P ＤＴis a value determined in advance as the pressure in the gas diffusion chamber 25b while the plasma PL is maintained in the chamber 10, based on plasma processing conditions such as the gas species, the frequency or voltage of the RF signal, the temperature in the chamber 10, or the volume of the chamber 10. When the pressure in the gas diffusion chamber 25b is below the diffusion chamber pressure threshold P ＤＴ If the pressure in the diffusion chamber is equal to or greater than the threshold P ＤＴ may be determined experimentally for each plasma processing condition or may be determined by simulation.

[0046] In step ST12, a second gas source 202 is supplied with a second flow rate F ２ The supply of the second gas is started at a second flow rate F ２ More on this later.

[0047] In step ST13, the gas diffusion space 25b is evacuated by the exhaust unit 24 at an exhaust flow rate VAC, which will be described later. During this exhaust, the gas diffusion space 25b is maintained at a desired pressure, as shown in Fig. 7, for reasons that will be described later. After an exhaust time, which will be described later, has elapsed, the exhaust of the gas diffusion space 25b is stopped.

[0048] In step ST14, the flow rate of the second gas supplied from the second gas source 202 is set to a second flow rate F ２ to the third flow rate F ３ and continue for a desired period of time. ３ is the second flow rate F ２ and is a flow rate for maintaining the desired pressure in the chamber 10 in order to maintain the state in which the plasma PL of the second gas is generated in the chamber 10 .

[0049] The switching from the first gas to the second gas is completed by the above steps ST11 to ST14. In steps ST11 and ST14, plasma etching can be performed on the substrate W placed in the chamber 10 using the plasma PL of the first gas or the plasma PL of the second gas, respectively.

[0050] After the step ST14 is performed and the supply of the second gas is stopped, the supply of the first gas is stopped at a fourth flow rate F ４ After the switching to the first gas, the flow rate of the first gas is increased to a fourth flow rate F by a step ST14' similar to the step ST14. ４ to the first flow rate F １ When switching to the first gas, the first flow rate F of the first gas is changed to １ is the third flow rate F of the second gas ３ and a fourth flow rate F of the first gas corresponds to ４ is the second flow rate F of the second gas ２ Thereafter, plasma etching can be continued while switching between the first gas and the second gas a desired number of times.

[0051] Next, the second flow rate F ２ First, the first gas supplied in step ST11 remains in the common flow path 213 and the gas diffusion chamber 25b when the supply is terminated. Thereafter, when the supply of the second gas is started in step ST12, the second gas is sequentially filled into the common flow path 213 and the gas diffusion chamber 25b. At this time, the second gas pushes out the first gas remaining in the common flow path 213 toward the gas diffusion chamber 25b. The first gas thus pushed out is sequentially exhausted in step ST13.

[0052] Consider a comparative example in which the flow rate of the second gas supplied in step ST12 is approximately equal to the exhaust flow rate VAC when the first gas is sequentially exhausted in step ST13. In this comparative example, the flow rate of the first gas pushed out from the common flow path 213 is approximately equal to the exhaust flow rate VAC. Since exhaust is performed from the exhaust unit 24 in step ST13, the flow rate obtained by subtracting the exhaust flow rate VAC from the flow rate of the first gas pushed out from the common flow path 213 becomes the apparent flow rate of the gas supplied to the gas diffusion chamber 25b. This apparent flow rate is calculated by dividing the gas diffusion chamber 25b by the threshold pressure P ＤＴTherefore, the flow rate of the gas introduced into the chamber 10 from the gas diffusion chamber 25b during the process ST13 is reduced. As a result, the pressure in the chamber 10 is reduced, and the threshold P ＣＴ If the pressure in the chamber falls below the threshold P ＣＴ is a value determined in advance based on plasma processing conditions such as the gas species, the frequency or voltage of the RF signal, the temperature inside the chamber 10, or the volume of the chamber 10. ＣＴ If the pressure in the chamber is equal to or greater than this threshold P ＣＴ may be determined experimentally for each plasma processing condition or may be determined by simulation. ＣＴ is 5 mTorr or more.

[0053] In contrast, in the gas supply method MT1 according to the present embodiment, the second gas is supplied at a second flow rate F ２ As a result, the flow rate of the first gas pushed out from the common flow path 213 is equal to the second flow rate F ２ Here, the second flow rate F ２ is the third flow rate F ３ First-out flow rate F Ａｄ and so the third flow rate F ３ In this specification, the "advance delivery" of the second gas means that the second gas is supplied during the exhaust of the first gas in step ST13 (step ST12) prior to step ST14 required for the plasma processing of the substrate W. Ａｄ is a flow rate that is added to the third flow rate during a period overlapping with the exhaust time of step ST13, as shown in FIG. ２ is the third flow rate F ３ and the exhaust flow rate VAC. In the step ST13, exhaust is performed from the exhaust unit 24, so the second flow rate F ２The flow rate obtained by subtracting the exhaust flow rate VAC from the apparent flow rate of the gas supplied to the gas diffusion chamber 25b is the apparent flow rate of the gas supplied to the gas diffusion chamber 25b. By supplying the second gas to the gas diffusion chamber 25b at this apparent flow rate, as shown in FIG. 7, during the execution of step ST13, the gas diffusion chamber 25b is at the threshold P ＤＴ It is maintained above.

[0054] Next, the exhaust flow rate VAC in step ST13 will be described. The exhaust flow rate VAC is set to the second flow rate F ２ The apparent flow rate obtained by subtracting the exhaust flow rate VAC from the second flow rate F is a flow rate that is sufficient to maintain the gas diffusion chamber 25b at a desired pressure. ２ The advance flow rate F included in Ａｄ In this case, the second flow rate F ２ The apparent flow rate obtained by subtracting the exhaust flow rate VAC from the third flow rate F ３ This apparent flow rate is approximately equal to the threshold pressure P ＤＴ It is enough to maintain more than

[0055] Next, the exhaust time in step ST13 will be described. The exhaust time is not particularly limited, but is set to a time required for the first gas filled in the gas diffusion space 25b and the common flow path 213 to be sufficiently exhausted. This exhaust time can be determined based on the sum of the volumes of the gas diffusion space 25b and the common flow path 213, the gas temperature, the exhaust flow rate VAC, the flow rate of the gas introduced from the gas diffusion space 25b into the chamber 10, and the like.

[0056] Next, an example of a method of exhausting air by the exhaust unit 24 in the process ST13 will be described. In the example configuration shown in FIG. 4 including the control valve 230, the start and end of exhaust and the exhaust flow rate VAC are adjusted by controlling the opening and closing, opening degree, and open time of the control valve 230. When the exhaust flow rate VAC is adjusted by the control valve 230, the second flow rate F ２ The advance flow rate F included in Ａｄ is adjusted in conjunction with the adjustment of the exhaust flow rate VAC, and the advance flow rate F ＡｄAlternatively, the exhaust flow rate VAC may be controlled by the control valve 230 so that the pressure value measured by the pressure gauge P1 provided in the gas diffusion chamber 25b is maintained at a desired pressure.

[0057] 5 , the first tank valve 241 is opened when evacuation begins in step ST13. The tank 240 is previously placed under negative pressure relative to the gas diffusion chamber 25b, so that the gas diffusion chamber 25b and the tank 240 communicate with each other when the first tank valve is opened, and the gas in the gas diffusion chamber 25b is evacuated to the tank 240. In one embodiment, in a configuration in which the volume of the tank 240 is substantially the same as the volume of the gas diffusion chamber 25b, if the tank 240 is maintained at a vacuum, all of the gas remaining in the gas diffusion chamber 25b is quickly evacuated to the tank 240 when the first tank valve 241 is opened in step ST13. This allows the remaining gas to be evacuated quickly, enabling rapid gas switching.

[0058] Next, a modified example of the gas supply method MT1 using the gas supply unit 20 according to the first embodiment will be described with reference to Fig. 8. Fig. 8 is a sequence chart relating to control of the flow rate of the first gas or the second gas supplied from the first gas source or the second gas source, and the exhaust flow rate VAC from the gas diffusion chamber 25b in the gas supply method MT1.

[0059] 8 , instead of step ST13, the gas diffusion chamber 25b is constantly evacuated by the exhaust unit 24 during execution of the gas supply method MT1. In this modification, the pressure value measured by the pressure gauge P1 provided in the gas diffusion chamber 25b is referenced, and the exhaust flow rate VAC is controlled by the control valve 230 so that the pressure value is maintained at a desired value. Such control may be a known feedback control based on the pressure value. This allows the gas diffusion chamber 25b to be maintained at a desired pressure.

[0060] Second Embodiment <Gas Supply Unit> A gas supply unit 300 according to a second embodiment will be described below with reference to FIGS. 9 to 11. FIG. 9 is a schematic diagram showing an outline of the configuration of the gas supply unit 300. In FIG. 9, the gas supply unit 300 includes a first gas line 301 and a second gas line 302. For ease of viewing, components of the first gas line 301 are shown with solid lines, and components of the second gas line 302 are shown with dotted lines.

[0061] The configuration of the first gas line 301 is similar to that of the gas supply unit 20 according to the first embodiment. Specifically, the gas box 21 includes a first gas source 311 for supplying a first gas and a second gas source 312 for supplying a second gas in the first gas line 301. The gas flow path 22 includes a first flow path 321 downstream of the first gas source 311 for supplying the first gas. The gas flow path 22 also includes a second flow path 322 downstream of the second gas source 312 for supplying the second gas. The first flow path 321 and the second flow path 322 join downstream to form a common flow path 323 for supplying either one of the gases. The first flow path 321 includes a first valve 325 at the end connected to the common flow path 323. The second flow path 322 also includes a second valve 326 at the end connected to the common flow path 323. The common flow path 323 according to this embodiment constitutes a branching structure 328 that distributes the gas so that the pressure in the surface direction is uniform. The common flow path 323 is connected at the downstream end of the branching structure 328 to a plurality of gas supply ports 25 a in a first gas diffusion chamber 330 in the shower head 25.

[0062] In the first gas line 301 having such a configuration, for example, with the first valve 325 open and the second valve 326 closed, a first gas supplied from the first gas source 311 flows through the first flow path 321 and into the common flow path 323. The first gas is dispersed while flowing through the branching structure 328 of the common flow path 323, and flows from the downstream end of the branching structure 328 into the first gas diffusion chamber 330 via the multiple gas supply ports 25a in the shower head 25. The first gas is diffused in the first gas diffusion chamber 330 so as to achieve a substantially uniform pressure distribution in the surface direction, and is then introduced into the chamber 10 via the gas inlet port 25c in the first gas diffusion chamber 330.

[0063] The first gas diffusion chamber 330 is equipped with a pressure gauge P1. The pressure gauge P1 measures the pressure inside the first gas diffusion chamber 330 and, for example, transmits the measurement value information to the control unit 2. An exhaust unit 24 is also connected to the first gas diffusion chamber 330. The configuration and control method of the exhaust unit 24 are the same as those in the first embodiment.

[0064] The second gas line 302 includes a third gas source 341 that supplies a third gas, and a third flow path 342. The third gas source 341 may include a plurality of gas sources. Also, some of the gas sources may be shared between the first gas source 311 and the second gas source 312. The third flow path 342 includes a branch structure 344, and the downstream end of the branch structure 344 is connected to a plurality of gas supply ports 25a in the second gas diffusion chamber 350 in the shower head 25. For example, the third gas may include a carrier gas that is commonly contained in the first gas or the second gas. For example, the carrier gas may be Ar and / or O. ２ It may contain a gas.

[0065] According to the second gas line 302 having such a configuration, for example, the third gas supplied from the third gas source 341 flows through the branching structure 344 of the third flow path 342, is dispersed, and flows from the downstream end of the branching structure 344 through the multiple gas supply ports 25 a in the shower head 25 into the second gas diffusion chamber 350. The third gas is diffused in the second gas diffusion chamber 350 so that the pressure distribution in the surface direction becomes approximately uniform, and then is introduced into the chamber 10 through the gas inlet port 25 c in the second gas diffusion chamber 350.

[0066] The first gas diffusion chamber 330 and the second gas diffusion chamber 350 in the showerhead 25 are independent of each other in terms of gas flow. That is, the second gas line is configured to be able to supply gas to the chamber 10 without passing through at least the first gas diffusion chamber 330. Because the exhaust unit 24 is connected only to the first gas diffusion chamber 330, exhaust by the exhaust unit 24 is performed only from the first gas diffusion chamber 330, and not from the second gas diffusion chamber 350.

[0067] <Gas Supply Method> Next, a gas supply method MT2 for supplying a gas to the chamber 10 using the gas supply unit 300 according to the second embodiment will be described with reference to Fig. 10. Fig. 10 is a sequence chart for controlling the flow rate of the first gas, the second gas, or the third gas supplied from the first gas line 301 or the second gas line 302, and the exhaust flow rate from the first gas diffusion chamber 330, in the gas supply method MT2.

[0068] The gas supply method MT2 is a method that enables the gas supplied to the chamber 10 to be switched from a first gas to a second gas, or to be appropriately switched from the second gas to the first gas, and includes the following steps ST21 to ST24.

[0069] In step ST21, a first flow rate F １ The supply of the first gas is started at a first flow rate F to generate the plasma PL, and the supply of the first gas is stopped after a desired duration. １is the flow rate for maintaining the pressure inside the chamber 10 at a desired level in order to maintain the state in which the plasma PL of the first gas is generated in the chamber 10.

[0070] In step ST22, the first gas diffusion space 330 is evacuated by the exhaust unit 24 at an exhaust flow rate VAC, which will be described later. During this exhaust, the chamber 10 is evacuated to a pressure exceeding a threshold value P ＣＴ After the evacuation time, which will be described later, has elapsed, the evacuation of the first gas diffusion space 330 is stopped.

[0071] In step ST23, a second flow rate F ２ In one embodiment, the supply of the second gas is started at a second flow rate F ２ is the flow rate for maintaining the desired pressure in the chamber 10 in order to maintain the state in which the plasma PL of the second gas is generated in the chamber 10.

[0072] In step ST24, while the steps ST21 to ST23 are being performed, a third flow rate F ３ A third gas is supplied at a third flow rate F ３ This will be discussed later.

[0073] The switching from the first gas to the second gas is completed by the above steps ST21 to ST24. In steps ST21 and ST23, plasma etching can be performed on the substrate placed in chamber 10 using the plasma PL of the first gas or the plasma PL of the second gas, respectively. After step ST23 is performed and the supply of the second gas is stopped, the second gas can be switched back to the first gas by performing steps ST22 and ST21 in this order while continuing step ST24. Thereafter, plasma etching can be continued while switching between the first gas and the second gas a desired number of times.

[0074] Next, details of step ST24 will be described. First, after the supply of the first gas that has been supplied in step ST21 is completed, in step ST22, the first gas is sequentially exhausted from the common flow path 323 and the first gas diffusion chamber 330. Since no gas is supplied to the first gas diffusion chamber 330 during the execution of step ST22, the pressure value measured by the pressure gauge P1 provided in the first gas diffusion chamber 330 is a vacuum P as shown in the upper part of FIG. ０ approaching.

[0075] Here, in the case of a comparative example in which the third gas is not supplied from the second gas line 302 in the process ST24, the pressure in the chamber 10 decreases until the second gas is supplied in the process ST23, and the threshold P of the pressure in the chamber necessary to maintain the generation state of the plasma PL is reached. ＣＴ If the pressure in the chamber falls below the threshold P ＣＴ The meaning of is the same as that explained in the first embodiment.

[0076] In contrast, in the gas supply method MT2 according to the present embodiment, the third gas is supplied at a third flow rate F ３ 11, the pressure value measured by the pressure gauge P2 provided in the chamber 10 is equal to the threshold P ＣＴ , so that the chamber 10 can be maintained at a sufficient pressure.

[0077] Third flow rate F ３ is a flow rate for maintaining a desired pressure in the chamber 10 in order to maintain a state in which plasma PL is generated from a gas that is a combination of the first gas supplied from the first gas line 301 and the third gas supplied from the second gas line 302 in the chamber 10. In the first gas line 301, the pressure of the first gas introduced into the chamber 10 in step ST22 is reduced. Therefore, the third flow rate F ３ is a flow rate sufficient to create a pressure in chamber 10 that compensates for the reduced pressure. ３is substantially the same as the exhaust flow rate VAC of the first gas exhausted from the first gas diffusion chamber 330 in step ST22. In this case, the third flow rate F ３ Since the third gas is supplied, the pressure in the chamber 10 reaches the threshold pressure P ＣＴ It is maintained above that.

[0078] As a secondary effect, the pressure of the gas filled in the first gas diffusion chamber 330 in the first gas line 301 can be lowered compared to the first embodiment, thereby shortening the time required to evacuate the first gas diffusion chamber 330. Furthermore, by lowering the pressure of the gas filled in the first gas diffusion chamber 330, the risk of abnormal discharge can be reduced.

[0079] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims. For example, the components of the above-described embodiments may be arbitrarily combined. Such an arbitrary combination naturally provides the functions and effects of each of the components involved in the combination, and also provides other functions and effects that are apparent to those skilled in the art from the description of this specification.

[0080] Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that are apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0081] The following configuration examples also fall within the technical scope of the present disclosure: (1) A plasma etching apparatus comprising: a chamber; a gas supply unit that supplies a gas to the chamber; and a control unit, wherein the gas supply unit comprises: a gas box that supplies the gas; a gas diffusion chamber in which the gas from the gas box is diffused and which introduces the gas into the chamber; and an exhaust unit that exhausts the gas inside the gas diffusion chamber, wherein the control unit executes control including the steps of: (a) supplying a first gas from the gas box at a first flow rate to generate plasma in the chamber, and (b) after stopping the supply of the first gas from the gas box, supplying a second gas from the gas box at a second flow rate and exhausting the gas diffusion chamber, wherein in the step (b), the pressure inside the gas diffusion chamber is maintained at or above a threshold value predetermined based on plasma processing conditions as a pressure for maintaining the plasma in the chamber. (2) The plasma etching apparatus according to (1), wherein the control unit further executes control including the steps of: (c) stopping the exhaust of the gas diffusion chamber after the step (b) is executed; and (d) continuing to supply the second gas from the gas box at a third flow rate that is smaller than the second flow rate, and wherein the pressure in the gas diffusion chamber is maintained at or above the threshold value in the steps (c) and (d). (3) The plasma etching apparatus according to (2), wherein the second flow rate is the sum of the third flow rate and an exhaust flow rate when the gas diffusion chamber is evacuated in the step (b).(4) A plasma etching apparatus comprising: a chamber; a gas supply unit that supplies a gas to the chamber; and a control unit, wherein the gas supply unit comprises: a gas box that supplies the gas; a first gas line; and a second gas line, wherein the first gas line comprises: a gas diffusion chamber through which the gas from the gas box is diffused and which introduces the gas into the chamber; and an exhaust unit that exhausts the gas inside the gas diffusion chamber, and the second gas line is configured to be able to supply the gas to the chamber without passing through at least the gas diffusion chamber of the first gas line, and the control unit performs the steps of: (a) supplying a first gas from the gas box through the first gas line at a first flow rate to generate plasma in the chamber; and (b) stopping the supply of the first gas from the gas box through the first gas line, subsequently exhausting the gas diffusion chamber, and subsequently supplying a second gas from the gas box through the first gas line at a second flow rate. (c) supplying a third gas from the gas box through the second gas line at a third flow rate at least during execution of the step (b), wherein in the steps (b) and (c), the pressure in the chamber is maintained at or above a threshold value predetermined based on plasma processing conditions as a pressure for maintaining the plasma in the chamber. (5) The plasma etching apparatus according to (4) above, wherein in the step (b), an exhaust flow rate when exhausting the inside of the gas diffusion chamber through the first gas line is the same as the third flow rate. (6) The plasma etching apparatus according to any one of (1) to (5) above, wherein the exhaust unit includes a tank configured to be able to maintain a negative pressure inside with respect to the gas diffusion chamber, and the control unit evacuates the inside of the gas diffusion chamber by communicating the gas diffusion chamber with the tank. (7) The plasma etching apparatus according to (6) above, wherein a volume of the tank is the same as a volume of the gas diffusion chamber.(8) A plasma etching method using a plasma etching apparatus, the plasma etching apparatus comprising: a chamber; and a gas supply unit that supplies a gas to the chamber, the gas supply unit comprising: a gas box that supplies the gas; a gas diffusion chamber in which the gas from the gas box is diffused and introduced into the chamber; and an exhaust unit that exhausts the gas inside the gas diffusion chamber, the plasma etching method comprising: (a) a step of supplying a first gas from the gas box at a first flow rate to generate plasma in the chamber; and (b) a step of supplying a second gas from the gas box at a second flow rate and exhausting the gas diffusion chamber after stopping the supply of the first gas from the gas box, wherein in the step (b), a pressure inside the gas diffusion chamber is maintained at or above a threshold value that is predetermined based on plasma processing conditions as a pressure for maintaining the plasma in the chamber. (9) The plasma etching method according to (8), further comprising the steps of: (c) stopping the evacuation of the gas diffusion chamber after the step (b); and (d) continuing to supply the second gas from the gas box at a third flow rate lower than the second flow rate, wherein the pressure in the gas diffusion chamber is maintained at or above the threshold value in the steps (c) and (d). (10) The plasma etching method according to (9), further comprising the steps of: (a) stopping the evacuation of the gas diffusion chamber after the step (b); and (b) continuing to supply the second gas from the gas box at a third flow rate lower than the second flow rate.

[0082] F １ First flow rate F １ F ２ Second flow rate F ２ VAC: Exhaust flow rate VAC 1: Plasma etching apparatus 2: Control unit 10: Chamber 20: Gas supply unit 21: Gas box 24: Exhaust unit 25b: Gas diffusion chamber

Claims

1. A plasma etching apparatus, a chamber; a gas supply unit that supplies a gas to the chamber; a control unit, The gas supply unit a gas box for supplying the gas; a gas diffusion chamber in which the gas from the gas box is diffused and which introduces the gas into the chamber; an exhaust unit that exhausts the gas in the gas diffusion chamber, The control unit (a) supplying a first gas from the gas box at a first flow rate to generate a plasma in the chamber; (b) stopping the supply of the first gas from the gas box, and then supplying a second gas from the gas box at a second flow rate while evacuating the gas diffusion chamber; (c) stopping the evacuation of the gas diffusion chamber after the execution of the (b) step; (d) continuing to supply the second gas from the gas box at a third flow rate that is smaller than the second flow rate; the second flow rate is equal to or greater than the sum of the third flow rate and an exhaust flow rate when exhausting the gas diffusion chamber in the step (b), A plasma etching apparatus, wherein in the steps (b), (c), and (d), the pressure in the gas diffusion chamber is set to a pressure at which plasma is maintained in the chamber.

2. 2. The plasma etching apparatus according to claim 1, wherein the second flow rate is the sum of the third flow rate and the exhaust flow rate when exhausting the inside of the gas diffusion chamber in the step (b).

3. A plasma etching apparatus, a chamber; a gas supply unit that supplies a gas to the chamber; a control unit, The gas supply unit a gas box for supplying the gas; a first gas line; a second gas line; The first gas line a gas diffusion chamber through which the gas from the gas box is diffused and which introduces the gas into the chamber; an exhaust unit that exhausts the gas in the gas diffusion chamber, the second gas line is configured to be able to supply the gas to the chamber without passing through at least the gas diffusion chamber of the first gas line; The control unit (a) supplying a first gas from the gas box through the first gas line at a first flow rate to generate a plasma in the chamber; (b) stopping the supply of the first gas from the gas box through the first gas line, subsequently evacuating the gas diffusion chamber, and subsequently supplying a second gas at a second flow rate from the gas box through the first gas line; (c) supplying a third gas at a third flow rate from the gas box to the second gas line at least during the execution of the step (b); an exhaust flow rate when exhausting the inside of the gas diffusion chamber in the first gas line in the step (b) is set to be equal to or smaller than the third flow rate; In the steps (b) and (c), the pressure in the chamber is set to a pressure at which plasma is maintained in the chamber. Plasma etching equipment.

4. 4. The plasma etching apparatus according to claim 3, wherein an exhaust flow rate when exhausting the inside of the gas diffusion chamber in the first gas line in the step (b) is the same as the third flow rate.

5. the exhaust unit includes a tank configured to be able to maintain a negative pressure inside the gas diffusion chamber, 5. The plasma etching apparatus according to claim 1, wherein the control unit evacuates the gas diffusion chamber by connecting the gas diffusion chamber with the tank.

6. 6. The plasma etching apparatus of claim 5, wherein the volume of the tank is the same as the volume of the gas diffusion chamber.

7. A plasma etching method using a plasma etching apparatus, comprising: The plasma etching apparatus includes: a chamber; a gas supply unit that supplies a gas to the chamber; The gas supply unit a gas box for supplying the gas; a gas diffusion chamber in which the gas from the gas box is diffused and which introduces the gas into the chamber; an exhaust unit that exhausts the gas in the gas diffusion chamber, The plasma etching method includes: (a) supplying a first gas from the gas box at a first flow rate to generate a plasma in the chamber; (b) stopping the supply of the first gas from the gas box, and then supplying a second gas from the gas box at a second flow rate while evacuating the gas diffusion chamber; (c) stopping the evacuation of the gas diffusion chamber after the execution of the (b) step; (d) continuing to supply the second gas from the gas box at a third flow rate that is less than the second flow rate; the second flow rate is equal to or greater than the sum of the third flow rate and an exhaust flow rate for exhausting the gas diffusion chamber in the step (b), A plasma etching method, wherein in steps (b), (c), and (d), the pressure in the gas diffusion chamber is set to a pressure at which plasma is maintained in the chamber.

8. 8. The plasma etching method according to claim 7, wherein the second flow rate is the sum of the third flow rate and the exhaust flow rate at which the gas diffusion chamber is exhausted in the step (b).

9. A plasma etching method using a plasma etching apparatus, comprising: The plasma etching apparatus includes: a chamber; a gas supply unit that supplies a gas to the chamber; The gas supply unit a gas box for supplying the gas; a first gas line; a second gas line; The first gas line a gas diffusion chamber through which the gas from the gas box is diffused and which introduces the gas into the chamber; an exhaust unit that exhausts the gas in the gas diffusion chamber, the second gas line is configured to be able to supply the gas to the chamber without passing through at least the gas diffusion chamber of the first gas line; The plasma etching method includes: (a) supplying a first gas from the gas box through the first gas line at a first flow rate to generate a plasma in the chamber; (b) stopping the supply of the first gas from the gas box through the first gas line, subsequently evacuating the gas diffusion chamber, and subsequently supplying a second gas at a second flow rate from the gas box through the first gas line; (c) supplying a third gas at a third flow rate from the gas box to the second gas line at least during the execution of the step (b); an exhaust flow rate when exhausting the inside of the gas diffusion chamber in the first gas line in the step (b) is set to be equal to or smaller than the third flow rate; In the steps (b) and (c), the pressure in the chamber is set to a pressure at which plasma is maintained in the chamber. Plasma etching method.