JP6504989B2 - Etching method - Google Patents

Description

  Embodiments of the present invention relate to an etching method, and in particular, a first region having a multilayer film configured by alternately stacking a silicon oxide film and a silicon nitride film, and silicon oxide of the first region. The present invention relates to a method of simultaneously etching a second region including a silicon oxide film having a film thickness larger than the film thickness.

  A NAND flash memory device having a three-dimensional structure is known as a type of semiconductor device. In the manufacture of a NAND-type flash memory device having a three-dimensional structure, a multilayer film formed by alternately providing a silicon oxide film and a silicon nitride film is etched to form deep holes in the multilayer film. A process is performed. Such etching is described in Patent Document 1 below.

  Specifically, Patent Document 1 describes a method of etching a multilayer film by exposing an object to be treated having a mask on the multilayer film to plasma of a processing gas.

US Patent Application Publication No. 2013/0059450

  The target object to be etched has a first region having a multilayer film configured by alternately providing a silicon oxide film and a silicon nitride film, and a thickness of the silicon oxide film in the first region. And a second region including a silicon oxide film having a large thickness. There is a need to etch such objects to simultaneously form spaces such as holes and / or trenches in both the first region and the second region.

  As a method of simultaneously forming a space in the first area and the second area, an object to be processed having a mask providing an opening on both the first area and the second area is prepared, and processing of the plasma processing apparatus is performed. It is conceivable to etch the first region and the second region by generating a plasma of a processing gas comprising fluorocarbon gas and hydrofluorocarbon gas in the vessel.

  However, in the etching using the plasma of such a processing gas, the width of the space formed in the second region may be wide in a part of the space in the depth direction. That is, the perpendicularity of the side wall surface defining the space formed by the etching of the second region may be low.

  In order to suppress a decrease in verticality of the sidewall surface, a first step of generating plasma of a first processing gas containing a fluorocarbon gas and a hydrofluorocarbon gas in a processing container of a plasma processing apparatus, and in the processing container A method of alternately repeating the second step of generating a plasma of a second processing gas containing hydrogen gas, hydrofluorocarbon gas, and nitrogen gas is conceivable. In this method, the etching can be advanced while protecting the side walls defining the space by carbon and / or hydrocarbon generated from the second process gas.

  As described above, in the method of alternately performing the first step and the second step, when the first step and the second step are continuously performed, the first process gas and the second process gas are processed. And a period of time during which plasma is generated occurs in a mixed state. As a result, deposits are excessively formed on the mask, the width of the mask opening may be narrowed, and in some cases, the mask opening may be blocked. As a result, a situation may occur in which a space with high verticality can not be formed in the first area and the second area.

  As a measure to avoid the generation of plasma in a mixed state of two process gases used respectively in the two steps, it is conceivable to provide a gas replacement period between the execution periods of the two steps. In the gas replacement period, the processing gas in the processing container is replaced with the processing gas used in the next step without generating plasma. Then, plasma is generated after the gas replacement period has elapsed. However, the gas replacement period, that is, the period during which plasma is not generated is a factor that reduces the throughput.

  Therefore, a silicon oxide film having a first region having a multilayer film configured by alternately stacking a silicon oxide film and a silicon nitride film, and a film thickness larger than the film thickness of the silicon oxide film of the first region. And performing a second step of generating a plasma of the first processing gas and a second step of generating the plasma of the second processing gas in succession in the technique of simultaneously etching the second region including It is desired to suppress the reduction in the verticality of the side wall surface formed by etching.

  In one aspect, a method is provided for simultaneously etching a first region and a second region of a workpiece. The first region has a multilayer film formed by alternately stacking a silicon oxide film and a silicon nitride film. The second region includes a silicon oxide film having a film thickness larger than that of the silicon oxide film in the first region. The object has a mask that provides an opening over the first region and the second region. This method comprises: (i) a first step of generating plasma of a first processing gas containing a fluorocarbon gas and a hydrofluorocarbon gas in a processing container of a plasma processing apparatus in which an object to be processed is prepared; (ii) processing Generating a plasma of a second process gas comprising hydrofluorocarbon gas and nitrogen gas in a vessel. In this method, a plurality of sequences each including a first step and a second step are performed. That is, the first process and the second process are alternately repeated. In this method, the first and second steps are performed sequentially. In this method, the execution period of the second step includes a first period including the start time of the second step, a second period following the first period, and a second period following the second period and the end time of the second step Including 3 periods. In the second period, hydrogen gas is further included in the second process gas. In the first period immediately after the execution period of the first step and in the third period immediately before the execution period of the first step, the ratio of the flow rate of hydrogen gas to the flow rate of the second processing gas is the first in the second period It is set to a ratio lower than the ratio of the flow rate of hydrogen gas to the flow rate of the processing gas of 2. In one embodiment, a high frequency for generating plasma is continuously used over the execution period of the first step and the execution period of the second step.

  The basic etching principle of the method according to one aspect is as follows. That is, by the execution of the first step, both the first region and the second region are etched. In the second step, the fluorine produced by the dissociation of the hydrofluorocarbon gas combines with hydrogen to reduce the amount of fluorine. In addition, carbon, hydrocarbons, fluorine-containing hydrocarbons and the like generated from hydrofluorocarbons adhere to the side wall surfaces that define the space formed by etching. Thereby, the side wall surface formed by the etching is protected. Also, the amount of carbon and / or hydrocarbons deposited on the mask is reduced by the activated species of nitrogen. Therefore, according to this method, the closure of the opening of the mask is suppressed, and the verticality of the sidewall surface formed by etching, in particular, the sidewall surface formed by etching the second region is improved.

  Further, in the method according to one aspect, the first step and the second step are continuously performed without providing a period in which plasma is not generated for gas replacement. Thus, the throughput is improved. Also, in the first period immediately after the execution period of the first step and in the third period immediately before the execution period of the first step, the ratio of the flow rate of hydrogen gas to the flow rate of the second processing gas is low. It is set. Thereby, the amount of hydrogen gas mixed in the first process gas is reduced. As a result, the decrease in the amount of fluorine generated from the first process gas is suppressed. In addition, excessive formation of hydrocarbons and fluorine-containing hydrocarbons that can be deposited on the mask is suppressed. Therefore, the reduction of the mask aperture and / or the mask occlusion is suppressed. Therefore, the decrease in the verticality of the side wall surface defining the space formed in the first region and the second region is suppressed.

  In one embodiment, the second process gas may further include nitrogen gas in the first period immediately after the execution period of the first step and the third period immediately before the execution period of the first step. In this embodiment, the amount of deposit on the mask is reduced by the activated species of nitrogen.

  In one embodiment, the flow rate of hydrogen gas is lower than the flow rate of hydrogen gas in the second period in the first period immediately after the execution period of the first step and in the third period immediately before the execution period of the first step It may be set to the flow rate. Alternatively, in the first period immediately after the execution period of the first step and in the third period immediately before the execution period of the first step, dilution with nitrogen gas reduces the flow rate of the hydrogen gas to the flow rate of the second process gas. The percentage may be set to a low percentage.

  In one embodiment, the execution period of the first step includes a fourth period including the start of the first step, a fifth period following the fourth period, and a fifth period followed by the end of the first step. Oxygen gas is further included in the first processing gas in the fifth period, including six periods. The fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences, and the sixth period immediately before the execution period of the second step of the at least part of the plurality of sequences. In the period, the ratio of the flow rate of oxygen gas to the flow rate of the first processing gas may be set to be lower than the ratio of the flow rate of oxygen gas to the flow rate of the first processing gas in the fifth period. In this embodiment, by adjusting the time lengths of the fourth and fifth periods, it is possible to adjust the amount of deposit on the mask and to adjust the width of the opening of the mask.

  In one embodiment, the first processing is performed in a fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences and in a sixth period immediately before the execution period of the second step in the plurality of sequences. The gas may further include nitrogen gas. In this embodiment, the amount of deposit on the mask is reduced by the activated species of nitrogen.

  In one embodiment, the fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences, and the execution period of the second step of the at least part of the plurality of sequences. In the sixth period immediately prior to the flow rate of oxygen gas may be set to a flow rate lower than the flow rate of oxygen gas in the fifth period. Alternatively, the fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences, and immediately before the execution period of the second step of the at least part of the plurality of sequences. In the sixth period, the ratio of the flow rate of oxygen gas to the flow rate of the first process gas may be set to a low rate by dilution with nitrogen gas.

  In one embodiment, the fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences, and the execution period of the second step of the at least part of the plurality of sequences. The first process gas may further include a fluorine-containing gas in a sixth period immediately before the heat treatment. According to this embodiment, the amount of deposit on the mask can be adjusted, and the etching rate can be improved.

  In one embodiment, the execution time length of the first step may be set to a time length longer than the execution time length of the second step. The second step is mainly used to protect the sidewall surface, and the contribution to the etching of the step is relatively small. According to this embodiment, since the execution time length of the second step contributing to the protection of the side wall surface is set shorter than the execution time length of the first step contributing to the etching, the first region and the second region The throughput of etching is increased.

  In another aspect, a method is provided for simultaneously etching a first region and a second region of the above-described workpiece. The method includes a first step of generating a plasma of a first processing gas containing a fluorocarbon gas and a hydrofluorocarbon gas in a processing container of a plasma processing apparatus in which an object to be processed is prepared; And a second step of generating a plasma of a second process gas containing gas, nitrogen gas, and hydrogen gas. In this method, a plurality of sequences each including a first step and a second step are performed. Each of the plurality of sequences further includes an intermediate step of generating a plasma of an inert gas including helium gas in the processing vessel between the first step and the second step. In each sequence, the first process, the intermediate process, and the second process are continuously performed. In one embodiment, a radio frequency is continuously used to generate the plasma over multiple sequences. The principle of etching in this method is similar to the principle of etching in the method according to one aspect described above. Furthermore, in this method, the first process and the second process are performed by providing a period for generating plasma of the inert gas without providing a period for not generating plasma for replacement of the gas. It is possible to prevent the generation of plasma in the state in which the processing gas and the second processing gas are mixed. This suppresses the formation of excess deposits on the mask. Therefore, according to this method, the reduction of the opening of the mask and / or the closure of the mask are suppressed, and the verticality of the side wall surface formed by etching, particularly the side wall surface formed by etching the second region is improved. Be done. The inert gas may further contain nitrogen gas.

  In one embodiment, the second process gas may further comprise nitrogen trifluoride gas. Nitrogen trifluoride gas can contribute to the adjustment of the amount of etching of the mask and the amount of hydrocarbons. In one embodiment, the second process gas may further comprise carbonyl sulfide gas. The product containing sulfur (S) generated by dissociation of the carbonyl sulfide gas contributes to the protection of the mask and can contribute to the adjustment of the opening width of the mask. Also, in one embodiment, the second process gas may further comprise a hydrocarbon gas. The hydrocarbon gas can serve as a hydrocarbon source for the protection of the side wall surface. In one embodiment, the mask may be a mask made of carbon, for example, a mask made of amorphous carbon.

  As described above, the first region having the multilayer film configured by alternately stacking the silicon oxide film and the silicon nitride film, and the film thickness larger than the film thickness of the silicon oxide film of the first region In the technique of simultaneously etching the second region including the silicon oxide film, the first step of generating plasma of the first processing gas and the second step of generating plasma of the second processing gas are continuously performed Also, it is possible to suppress the decrease in the verticality of the side wall surface formed by the etching.

3 is a flow chart illustrating an etching method according to an embodiment. It is sectional drawing which illustrates the to-be-processed object to which the etching method shown in FIG. 1 is applied. It is a figure which shows roughly an example of the plasma processing apparatus which can be used for implementation of the method shown in FIG. It is a figure which shows an example of the some gas in the method shown in FIG. 1, and a high frequency timing chart. It is sectional drawing which shows an example of the state of the to-be-processed object of the middle stage in execution of the method shown in FIG. It is sectional drawing which shows an example of the state of the to-be-processed object of the middle stage in execution of the method shown in FIG. It is sectional drawing which shows an example of the state of the to-be-processed object after execution of the method shown in FIG. It is a flowchart which shows the etching method concerning another embodiment. It is a figure which shows an example of the timing chart regarding the method shown in FIG.

  Hereinafter, various embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be denoted by the same reference numerals.

  FIG. 1 is a flow chart showing an etching method according to one embodiment. The method MT shown in FIG. 1 is a method of etching both the first region and the second region to form a space such as a hole or a trench. This method MT can be used, for example, in the manufacture of a NAND flash memory having a three-dimensional structure.

  FIG. 2 is a cross-sectional view illustrating a target to which the etching method shown in FIG. 1 is applied. An object to be processed (hereinafter, referred to as “wafer W”) illustrated in FIG. 2 includes an underlayer UL, a first region R1, a second region R2, and a mask MSK. Underlayer UL can be, for example, a layer made of polycrystalline silicon provided on a substrate. The first region R1 and the second region R2 are provided on the underlayer UL.

  The first region R1 is composed of a multilayer film. The multilayer film is configured by alternately providing the silicon oxide film IL1 and the silicon nitride film IL2. In the first region R1, the thickness of the silicon oxide film IL1 is, for example, 5 nm to 50 nm, and the thickness of the silicon nitride film IL2 is, for example, 10 nm to 75 nm. In one embodiment, in the first region R1, a total of 24 or more layers of the silicon oxide film IL1 and the silicon nitride film IL2 may be stacked.

  The second region R2 is a region including a silicon oxide film having a film thickness larger than that of the silicon oxide film IL1 of the first region R1. In one embodiment, the second region includes a partial region R21 and a partial region R22. Some of the plurality of silicon nitride films IL2 in the first region R1 extend into the partial region R21 in the direction orthogonal to the stacking direction of the multilayer film. As shown in FIG. 2, the plurality of silicon nitride films IL2 extending from the first region R1 into the partial region R21 terminate in the partial region R21 so as to have a step-like shape. The portion other than the silicon nitride film IL2 of the partial region R21 is formed of the silicon oxide film IL1. The partial region R22 is formed of a single layer silicon oxide film IL1. The thickness of the second region R2 configured in this manner is substantially the same as the thickness of the first region R1.

  A mask MSK is provided on the first region R1 and the second region R2. In the mask MSK, an opening for forming a space such as a hole or a trench in the first region R1 and the second region R2 is formed. The mask MSK can be made of, for example, amorphous carbon. Alternatively, the mask MSK may be composed of an organic polymer.

  In the method MT, first, a wafer W as shown in FIG. 2 is prepared in the processing container of the plasma processing apparatus. FIG. 3 is a view schematically showing an example of a plasma processing apparatus that can be used to carry out the method shown in FIG.

  The plasma processing apparatus 10 shown in FIG. 3 is a capacitively coupled plasma etching apparatus, and includes a substantially cylindrical processing container 12. The processing container 12 is made of, for example, aluminum, and the inner wall surface thereof is anodized. The processing container 12 is grounded for security. A passage 12 g for carrying in and out the wafer W is provided on the side wall of the processing container 12. The passage 12g can be opened and closed by a gate valve 54.

  On the bottom of the processing container 12, a substantially cylindrical support 14 made of an insulating material is provided. The support portion 14 extends in the vertical direction from the bottom of the processing container 12 in the processing container 12. The support portion 14 supports the mounting table PD in the processing container 12.

  The mounting table PD has a lower electrode 16 and an electrostatic chuck 18. The lower electrode 16 includes a first member 16a and a second member 16b in one embodiment. The first member 16a and the second member 16b both have a substantially disc shape, and are made of a conductor such as aluminum. The second member 16 b is provided on the first member 16 a and is electrically connected to the first member 16 a.

  A first high frequency power supply 62 is connected to the first member 16 a via a matching unit 66. The first high frequency power supply 62 is a power supply that generates a high frequency for plasma generation, and generates a frequency of 27 to 100 MHz, and in one example, a high frequency of 40 MHz. The matching unit 66 has a circuit for matching the output impedance of the first high frequency power supply 62 and the input impedance on the load side (lower electrode 16 side). The first high frequency power supply 62 may be connected to the upper electrode 30 via the matching unit 66.

  In addition, a second high frequency power supply 64 is connected to the first member 16 a via a matching unit 68. The second high frequency power supply 64 is a power supply that generates a high frequency, ie, a high frequency bias, for drawing ions into the wafer W, and generates a frequency in the range of 400 kHz to 13.56 MHz, in one example, a high frequency bias of 3 MHz. The matching unit 68 has a circuit for matching the output impedance of the second high frequency power supply 64 and the input impedance on the load side (lower electrode 16 side).

  A refrigerant channel 24 is formed inside the second member 16b. The refrigerant is supplied to the refrigerant flow path 24 from the chiller unit provided outside the processing container 12 through the pipe 26a, and the refrigerant supplied to the refrigerant flow path 24 is returned to the chiller unit through the pipe 26b. By controlling the temperature of the refrigerant thus circulated, the temperature of the wafer W mounted on the electrostatic chuck 18 is controlled.

  The electrostatic chuck 18 is provided on the second member 16 b. The electrostatic chuck 18 has a structure in which a film-like electrode is disposed between a pair of insulating layers or insulating sheets. A DC power supply 22 is electrically connected to the electrode of the electrostatic chuck 18 via a switch. The electrostatic chuck 18 adsorbs the wafer W by the electrostatic force such as the coulomb force generated by the DC voltage from the DC power supply 22 and holds the wafer W. A heating element such as a heater may be provided in the electrostatic chuck 18.

  A focus ring FR is provided around the electrostatic chuck 18 and on the second member 16 b. The focus ring FR is disposed to improve etching uniformity, and may be made of, for example, quartz.

  Further, a gas supply line 28 is provided to the lower electrode 16 and the electrostatic chuck 18. The gas supply line 28 is configured to supply the heat transfer gas from the heat transfer gas supply mechanism, such as He gas, between the upper surface of the electrostatic chuck 18 and the back surface of the wafer W.

  The plasma processing apparatus 10 also includes an upper electrode 30. The upper electrode 30 is disposed to face the mounting table PD above the mounting table PD. Lower electrode 16 and upper electrode 30 are provided substantially in parallel with each other, and processing space S for performing plasma processing on wafer W is defined between mounting table PD and lower electrode 16. .

  The upper electrode 30 is supported on the top of the processing container 12 through the insulating shielding member 32. The upper electrode 30 can include a top 34 and a support 36. The top plate 34 faces the processing space S, and provides a plurality of gas discharge holes 34 a. The top plate 34 can be made of a low resistance conductor or semiconductor with low Joule heat.

  The support 36 detachably supports the top plate 34 and is made of, for example, a conductive material such as aluminum. The support 36 may have a water cooling structure. Inside the support 36, a gas diffusion chamber 36a is provided. A plurality of gas flow holes 36b communicating with the gas discharge holes 34a extend downward from the gas diffusion chamber 36a. Further, the support 36 is formed with a gas inlet port 36c for introducing the processing gas into the gas diffusion space 36a, and a gas supply pipe 38 is connected to the gas inlet port 36c.

A gas source group 40 is connected to the gas supply pipe 38 via a valve group 42 and a flow rate controller group 44. The gas source group 40 includes a plurality of gas sources. The plurality of gas sources include a fluorocarbon gas source, a hydrofluorocarbon gas source, a hydrogen gas (H ₂ gas) source, and a nitrogen gas (N ₂ gas) source. In one embodiment, the plurality of gas sources are a source of oxygen gas (O ₂ gas), a source of nitrogen trifluoride gas (NF ₃ gas), a source of carbonyl sulfide gas (COS gas), and a hydrocarbon It may further include a source of gas. The fluorocarbon gas, for _example, C 4 _{F 6 gas,} C 4 _{F 8} gas, one or more fluorocarbon gases such as CF ₄ gas may be used. For example, CH ₂ F ₂ gas may be used as the hydrofluorocarbon gas. Further, as the hydrocarbon gas, for example, CH ₄ gas is used. The plurality of gas sources may further include a source of any rare gas such as He gas, Ne gas, Ar gas, or Kr gas, a source of boron trichloride gas (BCl ₃ gas), or a source of SF ₆ gas. Good.

  The valve group 42 has a plurality of valves. Further, the flow rate controller group 44 includes a plurality of flow rate controllers such as a mass flow controller (MFC). The plurality of gas sources of the gas source group 40 are connected to the gas supply pipe 38 via corresponding flow controllers included in the flow controller group 44 and corresponding valves included in the valve group 42, respectively. In the plasma processing apparatus 10, the gas from the gas source selected from the plurality of gas sources reaches the gas diffusion chamber 36a from the gas supply pipe 38, and the processing space S passes through the gas flow holes 36b and the gas discharge holes 34a. Is discharged.

  The plasma processing apparatus 10 further includes a DC power supply unit 70. The DC power supply unit 70 is connected to the upper electrode 30. The DC power supply unit 70 can generate a negative DC voltage and apply the DC voltage to the upper electrode 30.

  The plasma processing apparatus 10 may further include a ground conductor 12a. The ground conductor 12 a has a substantially cylindrical shape, and is provided so as to extend upward from the side wall of the processing container 12 above the height position of the upper electrode 30.

In the plasma processing apparatus 10, the deposition shield 46 is detachably provided along the inner wall of the processing container 12. The depot shield 46 is also provided on the outer periphery of the support portion 14. The deposition shield 46 prevents adhesion of the etching by-product (deposition) to the processing container 12 and can be configured by coating an aluminum material with a ceramic such as Y ₂ O ₃ .

On the bottom side of the processing container 12, an exhaust plate 48 is provided between the support 14 and the inner wall of the processing container 12. The exhaust plate 48 can be configured, for example, by coating an aluminum material with a ceramic such as Y ₂ O ₃ . The exhaust plate 48 is formed with a large number of through holes. An exhaust port 12 e is provided in the processing container 12 below the exhaust plate 48. An exhaust device 50 is connected to the exhaust port 12 e via an exhaust pipe 52. The exhaust device 50 has a pressure control valve and a vacuum pump such as a turbo molecular pump, and can reduce the pressure in the processing container 12 to a desired pressure.

  A conductive member (GND block) 56 is provided on the inner wall of the processing container 12. The conductive member 56 is attached to the inner wall of the processing container 12 so as to be positioned at substantially the same height as the wafer W in the height direction. The conductive member 56 is DC-connected to the ground, and exhibits an abnormal discharge preventing effect. The conductive member 56 may be provided in the plasma generation region, and the installation position thereof is not limited to the position shown in FIG.

  The plasma processing apparatus 10 may further include a control unit Cnt. The control unit Cnt can be a computer device including a processor, a storage unit, an input device, a display device, and the like, and can control each unit of the plasma processing apparatus 10. In this control unit Cnt, the operator can perform an input operation of a command to manage the plasma processing apparatus 10 and the like using the input device, and the operation status of the plasma processing apparatus 10 is visualized by the display device. Can be displayed. Furthermore, in the storage unit of the control unit Cnt, a control program for controlling various processes executed by the plasma processing apparatus 10 by a processor, and for causing each unit of the plasma processing apparatus 10 to execute processing according to the processing conditions. Programs, that is, processing recipes are stored. In one embodiment, the control unit Cnt controls each part of the plasma processing apparatus 10 according to the processing recipe created for the implementation of the method MT.

  In the plasma processing apparatus 10, the processing gas from the selected gas source among the plurality of gas sources of the gas source group 40 is supplied to the processing space S, and the pressure of the processing space S is set to a predetermined pressure by the exhaust device 50. Set to Also, the high frequency from the first high frequency power supply 62 is supplied to the lower electrode 16, and the high frequency bias from the second high frequency power supply 64 is supplied to the lower electrode 16. Thereby, the processing gas is excited in the processing space S. Then, plasma processing such as etching of the wafer W is performed by active species such as radicals and ions.

The description of the method MT will be continued with reference to FIG. 1 again. Hereinafter, FIGS. 4 to 7 will be referred to together with FIG. FIG. 4 is a diagram showing an example of some gas and high frequency timing charts in the method shown in FIG. The vertical axis in FIG. 4 represents the ratio of the flow rate of hydrogen gas (H ₂ gas) to the flow rate of the _second process gas, the ratio of the flow rate of oxygen gas (O ₂ gas) to the flow rate of the first process gas, and nitrogen It represents the flow rate of gas (N ₂ gas) and the flow rate of fluorine-containing gas in the first process gas. The vertical axis in FIG. 4 represents the supply of high frequency, and the high level of high frequency supply represents that the high frequency is supplied, and the low level of high frequency supply is: It indicates that the high frequency is not supplied. FIG.5 and FIG.6 is sectional drawing which shows an example of the state of the to-be-processed object of the middle stage in execution of the method shown in FIG. Moreover, FIG. 7 is sectional drawing which shows an example of the state of the to-be-processed object after execution of the method shown in FIG. In the following description, the method MT will be described by using the plasma processing apparatus 10 as an example.

  In the method MT, as described above, first, the wafer W is loaded into the processing container 12 of the plasma processing apparatus 10. The wafer W is mounted on the mounting table PD and held by the electrostatic chuck 18. Then, in the method MT, a plurality of sequences SQ each including the process ST1 and the process ST2 are executed. That is, the process ST1 and the process ST2 are alternately repeated.

  In the process ST1, a plasma of the first process gas is generated in the process container 12, and in the process ST2, a plasma of the second process gas is generated in the process container 12. In the method MT, the step ST1 and the step ST2 are continuously performed. That is, plasma is generated even in a period in which a state in which the first processing gas used in step ST1 and the second processing gas used in step ST2 are mixed in the processing container 12 is formed. . In one embodiment, plasma is generated continuously over the execution period of process ST1 and the execution period of process ST2. Specifically, as shown in FIG. 4, a high frequency for generation of plasma is continuously used. More specifically, in the embodiment using the plasma processing apparatus 10, the high frequency power from the first high frequency power supply 62 is continuously supplied to the lower electrode LE over the execution period of the step ST1 and the execution period of the step ST2.

The first process gas used in step ST1 includes fluorocarbon gas and hydrofluorocarbon gas. In one example, the first process gas may include, as a fluorocarbon gas, one or more fluorocarbon gases such as C ₄ F ₆ gas, C ₄ F ₈ gas, and CF ₄ gas. Also, the first process gas may include CH ₂ F ₂ gas as a hydrofluorocarbon gas.

As shown in FIG. 4, an execution period P1 of each step ST1 is a period P _1a (in FIG. 4, time period t ₁ to time t ₂ , time t ₇ to time t ₈ , and time t ₁₃ to time t ₁₄ ) Period P _1b (in FIG. 4, time t ₂ to time t ₃ and time t ₈ to time t ₉ ), and period P _{1 c} (in FIG. 4, time t ₃ to time t ₄ and time t ₉ to time t ₁₀ ) are included. The period P _1a is a period including the start time of the process ST ₁ . The period P 1 _b is a period following the period P ₁ a. The period P _{1 c} is a period following the period P _{1 b} and is a period including the end of the process ST 1. The period P _1a , the period P _1b , and the period P _1c have a predetermined length of time. In one embodiment, the time length of the period P _{1 b} is set to be longer than the time lengths of the period P _{1 a} and the period P _{1 c} .

In period P 1 _{b of} step ST1, the first process gas further includes oxygen gas (O ₂ gas). On the other hand, period P _1a immediately after execution period P2 of process ST2 (in FIG. 4, time t ₇ to time t ₈ and time t ₁₃ to time t ₁₄ ), and a period immediately before execution period P2 of process ST2 At P _1c (in FIG. 4, at time t ₃ to time t ₄ and time t ₉ to time t ₁₀ ), the ratio of the flow rate of oxygen gas to the flow rate of the first process gas is the first process in period P 1 _b The ratio is set to be lower than the ratio of the flow rate of oxygen gas to the flow rate of gas.

In one embodiment, in the period P _1a immediately after the execution period P2 of the process ST2 and in the period P _1c immediately before the execution period P2 of the process ST2, the flow rate of oxygen gas is smaller than the flow rate of oxygen gas in the period P _1b Or set to zero. In this embodiment, the first processing gas may include nitrogen gas in a period P _1a immediately after the execution period P2 of the process ST2 and a period P _1c immediately before the execution period P2 of the process ST2.

In another embodiment, the flow rate of the oxygen gas in the period P _1a immediately after the execution period P2 of the process ST2 and the period P _1c immediately before the execution period P2 of the process ST2 is the flow rate and the substance of the oxygen gas in the period P _1b It may be the same flow rate. In this embodiment, in the period _{P 1c} immediately before the period _{P 1a} and the execution period P2 step ST2 immediately after the execution period P2 of step ST2, the nitrogen gas is included in the first process gas. Thereby, the ratio of the flow rate of the oxygen gas to the flow rate of the first processing gas is relatively low in the period P _1a immediately after the execution period P2 of the process ST2 and the period P _1c immediately before the execution period P2 of the process ST2 Set to

In one embodiment, the fluorine-containing gas is added to the first processing gas in period P _1a immediately after execution period P2 of step ST2 and period P _1c immediately before execution period P2 of step ST2. The fluorine-containing gas is, for example, one or more of NF ₃ gas, CF ₄ gas, and SF ₆ gas. The fluorine-containing gas added in the period P _1a immediately after the execution period P2 of the process ST2 and the period P _1c immediately before the execution period P2 of the process ST2 is the same as the fluorocarbon gas contained in the first process gas. In this case, the flow rate of the fluorocarbon gas is increased in period P _1a immediately after the execution period P2 of step ST2 and period P _1c immediately before the execution period P2 of step ST2.

In step ST 1, the first process gas is supplied into the process container 12. In step ST1, the ratio of the flow rate of the oxygen gas to the flow rate of the first process gas supplied into the process container 12 in each of the period P _1a , the period P _1b , and the period P _1c is as described above. Adjusted. Further, in the process ST1, the pressure of the processing space S is set to a predetermined pressure by the exhaust device 50. Further, in the process ST 1, the high frequency power from the first high frequency power supply 62 and the high frequency bias from the second high frequency power supply 64 are supplied to the lower electrode 16.

In step ST1, as shown in FIG. 5, the first processing gas is excited, and active species such as generated ions and / or radicals cause the first regions R1 and second regions to be exposed in the portion exposed from the mask MSK. Region R2 is etched. Also, in step ST1, a deposit containing carbon, for example, a deposit such as a fluorocarbon and / or a hydrocarbon is formed on the wafer W from the first process gas, and the generated deposit is at least for a period P It is moderately removed by the activated species of oxygen generated in _1b . Therefore, blocking of the opening of the mask MSK due to such a deposit is suppressed.

The second process gas used in step ST2 includes hydrofluorocarbon gas and nitrogen gas (N ₂ gas). As the hydrofluorocarbon gas of the second process gas, for example, CH ₂ F ₂ gas is used. In one embodiment, the second process gas may further include at least one of nitrogen trifluoride gas (NF ₃ gas), carbonyl sulfide gas (COS gas), and hydrocarbon gas.

As shown in FIG. 4, an execution period P2 of each step ST2 is a period P _2a (in FIG. 4, time t ₄ to time t ₅ and time t ₁₀ to time t ₁₁ ), period P _2b (in FIG. 4). , Time t ₅ to time t ₆ , and time t ₁₁ to time t ₁₂ ), and period P _2c (in FIG. 4, time t ₆ to time t ₇ and time t ₁₂ to time t ₁₃ ). It is. The period _P2a is a period including the start time of the process ST2. The period P 2 _b is a period following the period P ₂ a. The period P _{2 c} is a period following the period P _{2 b} and is a period including the end of the process ST 2. The period P _2a , the period P _2b , and the period P _2c have a predetermined time length. Further, in one embodiment, the time length of the period P _2b is set to be longer length than the time length of the period P _2a and period P _2c.

In period P 2 _{b of} step ST 2, hydrogen gas (H ₂ gas) is further included in the second process gas. On the other hand, the immediately preceding period _{P 2c} execution period P1 of the period _{P 2a} and step ST1 immediately after the execution period P1 step ST1, the ratio of the flow rate of the hydrogen gas to the flow rate of the second process gas, the at period _{P 2b} The ratio is set to be lower than the ratio of the flow rate of hydrogen gas to the flow rate of the processing gas of 2.

In one embodiment, in the period P _2a immediately after the execution period P1 of the process ST1 and in the period P _2c immediately before the execution period P1 of the process ST1, the flow rate of hydrogen gas is smaller than the flow rate of hydrogen gas in the period P _2b Or set to zero. In this embodiment, in the period P _2c just before the execution period P1 of the period P _2a and step ST1 immediately after the execution period P1 step ST1, may be nitrogen gas included in the first processing gas.

In another embodiment, the flow rate of hydrogen gas in period P ₂ a immediately after execution period P 1 of step ST 1 and period P _{2 c} immediately before execution period P 1 of step ST 1 substantially corresponds to the flow rate of hydrogen gas in period P 2 _b . The same flow rate may be used. In this embodiment, in the period _{P 2c} just before the execution period P1 of the period _{P 2a} and step ST1 immediately after the execution period P1 step ST1, the nitrogen gas is included in the second process gas. Thereby, in the period P ₂ a immediately after the execution period P 1 of the process ST 1 and the period P _{2 c} immediately before the execution period P 1 of the process ST 1, the ratio of the flow rate of hydrogen gas to the flow rate of the second processing gas is relatively low Set to

In step ST 2, the second process gas is supplied into the process container 12. Also, in step ST2, the ratio of the flow rate of hydrogen gas to the total flow rate of the second process gas supplied into the processing vessel 12 in each of the period P _2a , the period P _2b , and the period P _2c is as described above. To be adjusted. Further, in the process ST2, the pressure of the processing space S is set to a predetermined pressure by the exhaust device 50. Further, in step ST 2, the high frequency from the first high frequency power supply 62 and the high frequency bias from the second high frequency power supply 64 are supplied to the lower electrode 16.

In this step ST2, the second process gas is excited. The hydrofluorocarbon in the second process gas dissociates into fluorine, hydrogen, carbon, and hydrocarbons. The fluorine produced by the dissociation of the hydrofluorocarbon combines with the hydrogen produced by the dissociation of the hydrogen gas in the period P 2 _b . Therefore, in the process ST2, the amount of fluorine contributing to the etching is reduced. In addition, carbon and / or hydrocarbon generated by dissociation of hydrofluorocarbon adhere to the sidewall surface SW defining the space formed by etching and the surface MS of the mask MSK, as shown in FIG. Form the object DP. Thereby, side wall surface SW is protected. Also, the width of the opening provided by the mask MSK is adjusted. Although more carbon and / or hydrocarbon adheres to the surface MS of the mask MSK than the side wall surface SW, carbon and / or hydrocarbon attached to the surface MS of the mask MSK are reduced by the active species of nitrogen Be done. Therefore, blocking of the opening of the mask MSK is suppressed.

  When the second processing gas contains nitrogen trifluoride gas, the fluorine produced by the dissociation of nitrogen trifluoride etches the first region R1 and the second region R2, but the amount of fluorine Is reduced by bonding with hydrogen, the amount by which the first region R1 and the second region R2 are etched in the step ST2 is smaller than the amount by which the first region R1 and the second region R2 are etched in the step ST1. In addition, nitrogen generated by dissociation of nitrogen trifluoride contributes to adjustment of the etching amount of the mask MSK and hydrocarbons deposited on the mask MSK.

  Also, when the second processing gas contains carbonyl sulfide gas, a product containing sulfur (S) generated by dissociation of carbonyl sulfide is deposited on the mask MSK to protect the mask MSK. Contribute to the adjustment of the opening width of the mask MSK. In addition, when the second processing gas contains a hydrocarbon gas, the hydrocarbon gas contributes as a hydrocarbon source for protection of the sidewall surface SW.

  In the method MT, after the execution of the sequence SQ including the step ST1 and the step ST2, it is determined in the step STJ whether or not the stop condition is satisfied. It is determined that the stop condition is satisfied when the number of times of execution of the sequence SQ has reached a predetermined number. If it is determined in step STJ that the stop condition is not satisfied, sequence SQ is executed again from step ST1. On the other hand, if it is determined in step STJ that the stop condition is satisfied, method MT ends. In this manner, in the method MT, by performing a plurality of sequences SQ, as shown in FIG. 7, the first region R1 and the second region R2 are etched until the space reaches the surface of the underlayer UL. .

  As described above, in the method MT, the first region R1 and the second region R2 are etched in the step ST1. Then, the deposit DP is formed on the side wall surface SW formed by the etching in the process ST2. Thus, in the method MT, the etching of the first region R1 and the second region R2 and the formation of the deposit DP for protection of the sidewall surface SW are alternately performed, so that the lateral direction of the sidewall surface SW (film Shaping in the direction orthogonal to the thickness direction is suppressed. In particular, the protection of the side wall surface SW by the deposit DP is effective in the second region R2 which is easily scraped in the lateral direction in the etching of the process ST1. Therefore, according to method MT, it is possible to improve the verticality of sidewall surface SW formed by etching.

  In the method MT according to one embodiment, the execution time length of the process ST1 in the sequence SQ may be set to a time length longer than the execution time length of the process ST2 in the sequence SQ. The process ST1 is used to etch the first region R1 and the second region R2 as described above. On the other hand, as described above, step ST2 is mainly used for protection of sidewall surface SW, and the contribution to etching in step ST2 is relatively small. Therefore, by setting the execution time length of the process ST1 to a time length longer than the execution time length of the process ST2, the throughput of etching of the first region R1 and the second region R2 is increased.

In addition, in the method MT, the process ST1 and the process ST2 are continuously performed without providing a period in which plasma is not generated for gas replacement, so that the throughput is improved. Furthermore, in the period P ₂ a immediately after the execution period P 1 of the process ST 1 and the period P _{2 c} immediately before the execution period P 1 of the process ST 1, the ratio of the flow rate of hydrogen gas to the flow rate of the second processing gas is set to a low rate. Ru. Thereby, the amount of hydrogen gas mixed in the first process gas is reduced. As a result, the decrease in the amount of fluorine generated from the first process gas is suppressed. In addition, excessive formation of hydrocarbons and fluorine-containing hydrocarbons that can be deposited on the mask MSK is suppressed. Therefore, the reduction of the opening of the mask MSK and / or the blocking of the mask MSK is suppressed. Therefore, even if step ST1 and step ST2 are continuously performed, the decrease in verticality of the sidewall surface SW that defines the space formed in the first region R1 and the second region R2 is suppressed.

As described above, in one embodiment, in the period P _2c just before the execution period P1 of the period P _2a and step ST1 immediately after the execution period P1 step ST1, the nitrogen gas is further included in the second process gas. In this embodiment, the amount of deposit on the mask MSK is reduced by the activated species of nitrogen.

Further, as described above, in one embodiment, the oxygen gas relative to the flow rate of the first processing gas in the period P _1a immediately after the execution period P2 of the process ST2 and the period P _1c immediately before the execution period P2 of the process ST2. The ratio of the flow rate is set to be lower than the ratio of the flow rate of oxygen gas to the flow rate of the first processing gas in period P _{1 c} . In this embodiment, by adjusting the time length of the period P _1a and period P _1c, to adjust the amount of the deposit on the mask MSK, it is possible to adjust the width of the opening of the mask MSK.

Further, as described above, in one embodiment, the first process gas further includes nitrogen gas in period P _1a immediately after execution period P2 of step ST2 and period P _1c immediately before execution period P2 of step ST2. It may be done. In this embodiment, the amount of deposit on the mask MSK is reduced by the activated species of nitrogen.

Further, as described above, in one embodiment, the first process gas further includes a fluorine-containing gas in period P _1a immediately after execution period P2 of step ST2 and period P _1c immediately before execution period P2 of step ST2. It may be included. According to this embodiment, the amount of deposit on the mask MSK can be adjusted, and the etching rate can be improved. In addition, it is possible to adjust the width of the opening formed in the first region R1 and the second region R2.

  The execution order of the process ST1 and the process ST2 in each sequence SQ is not limited to the execution order shown in FIG. That is, in each sequence SQ, the process ST2 may be performed first, and then the process ST1 may be performed.

In addition, the ratio of the flow rate of the oxygen gas in the first process gas does not have to be set to a low ratio in the periods P _{1 a} and P _{1 c} of all the sequences SQ. That is, the period P _1a immediately after the execution period P2 of the step ST2 of the partial sequence among the plurality of sequences SQ, and the execution period P2 of the step ST2 of the partial sequence of the plural sequences SQ In the period P _{1 c} , the ratio of the flow rate of the oxygen gas in the first process gas may be set to a low ratio. For example, a period P _1a immediately after the execution period P2 of the step ST2 of one or more sequences included in the first half of the plurality of sequences SQ in the execution order or one or more sequences included in the second half in the execution order; In a period P _{1 c} immediately before the execution period P 2 of the step ST 2 of one or more sequences included in the first half in the first half of the execution order or the second half of the sequence in the second half of the execution order The percentage may be set to a low percentage. Similarly, a period P _1a immediately after the execution period P2 of the step ST2 of one or more sequences included in the first half in the execution order or one or more sequences included in the second half in the execution order, and one in the first half in the execution order The first processing gas may further include nitrogen gas in a period _P1c immediately before the execution period P2 of the step ST2 of one or more sequences included in the second half of the above sequence or execution order. Similarly, a period P _1a immediately after the execution period P2 of the process ST2 of one or more sequences included in the first half in the execution order or one or more sequences included in the second half in the execution order; The fluorine-containing gas may be further included in the first processing gas in a period _P1c immediately before the execution period P2 of the step ST2 of one or more sequences included in the second half of the above sequence or execution order.

  Moreover, in the example shown in FIG. 4, the plasma is continuously generated over the execution period of the process ST1 and the execution period of the process ST2. That is, high frequency is continuously used for generation of plasma over the execution period of process ST1 and the execution period of process ST2. However, plasma may be generated intermittently in each of the execution period of step ST1 and the execution period of step ST2. That is, in each of the execution period of step ST1 and the execution period of step ST2, the period in which the plasma is generated and the period in which the plasma is not substantially generated may be alternately repeated. For example, in each of the execution period of step ST1 and the execution period of step ST2, a pulse-modulated high frequency may be used as a high frequency for plasma generation. Also, the high frequency bias may be pulse modulated in synchronization or phase inversion with the pulse modulated high frequency.

  Hereinafter, an etching method according to another embodiment will be described. FIG. 8 is a flow chart showing an etching method according to another embodiment. FIG. 9 is a diagram showing an example of a timing chart related to the method shown in FIG. In FIG. 9, the horizontal axis represents time, and the vertical axis represents the flow rate of the first processing gas, the flow rate of the inert gas, and the flow rate of the second processing gas. Further, in FIG. 9, the vertical axis represents the supply of high frequency, and the high level of high frequency supply represents that the high frequency is supplied, and the low level of the high frequency supply is , Indicates that high frequency is not supplied. Hereinafter, with respect to the method MT2 illustrated in FIG. 8, points different from the method MT will be described.

  In the method MT2, a plurality of sequences SQ2 each including a process ST1 and a process ST2 are performed. In step ST1, plasma of the first processing gas is generated in the processing container 12. The first process gas includes a fluorocarbon gas and a hydrofluorocarbon gas, as in the first process gas used in step ST1 of the method MT. Also, the first process gas may further include oxygen gas.

In step ST2, plasma of the second processing gas is generated in the processing container 12. The second process gas includes a hydrofluorocarbon gas and a nitrogen gas (N ₂ gas) as in the second process gas used in step ST2 of the method MT. In addition, the second process gas further includes hydrogen gas.

  In the method MT2, each of the multiple sequences SQ2 further includes the step STi. Process STi is performed between process ST1 and process ST2. Process STi is performed in execution period Pi before execution of process ST2 in execution period P2 after execution of process ST1 in execution period P1. In step STi, plasma of an inert gas is generated in the processing container 12. The inert gas includes helium gas. Also, the inert gas may further include nitrogen gas. In addition, after execution of process ST2, process STi may be further performed in the period before execution of process ST1 of next sequence SQ2.

  In the method MT2, after execution of the sequence SQ2 each time, it is determined in step STJ2 whether or not the stop condition is satisfied. The stop condition is determined to be satisfied when the number of times of execution of the sequence SQ2 has reached a predetermined number. If it is determined in step STJ2 that the stop condition is not satisfied, sequence SQ2 is executed again from step ST1. On the other hand, if it is determined in step STJ2 that the stop condition is satisfied, method MT2 ends.

  In each of the plurality of sequences SQ2, step ST1, step STi, and step ST2 are continuously performed. In one embodiment, plasma is continuously generated over the execution period P1 of step ST1, the execution period Pi of step STi, and the execution period P2 of step ST2. That is, the high frequency for generating the plasma is continuously used over the multiple sequences SQ2. Plasma may be intermittently generated in each of the execution period P1 of the process ST1 and the execution period P2 of the process ST2.

  Also in the method MT2, as in the method MT1, the first region R1 and the second region R2 are etched by execution of the step ST1. Then, the deposit DP is formed on the side wall surface SW formed by the etching in the process ST2. Therefore, according to method MT2, it is possible to improve the verticality of sidewall surface SW formed by etching.

  In addition, in the method MT2, the first process is performed by providing a period Pi for generating a plasma of an inert gas between the step ST1 and the step ST2 without providing a period for not generating a plasma for gas replacement. The generation of plasma in the state where the gas and the second processing gas are mixed is prevented. This suppresses the generation of excess deposits on the mask MSK. Therefore, according to the method MT2, the reduction of the opening of the mask MSK and / or the blocking of the mask are suppressed, and the verticality of the side wall surface formed by etching, particularly the side wall surface formed by etching the second region R2. Is improved.

  Further, the rare gas contained in the inert gas used in the step STi is helium gas, and the atomic weight thereof is smaller than the atomic weight of the other rare gas atoms. Therefore, the removal of mask MSK by the ions generated in step STi is suppressed. In one embodiment, the inert gas used in step STi includes nitrogen gas. This reduces the amount of deposit on the mask MSK by the activated species of nitrogen. Therefore, the reduction of the opening of the mask MSK and / or the blocking of the mask is suppressed.

  Although various embodiments have been described above, various modifications can be made without being limited to the above-described embodiments. For example, method MT and method MT2 may be performed using any plasma processing apparatus, such as an inductively coupled plasma processing apparatus or a plasma processing apparatus using surface waves such as microwaves.

  DESCRIPTION OF SYMBOLS 10 ... Plasma processing apparatus, 12 ... Processing container, PD ... Mounting base, 16 ... Lower electrode, 18 ... Electrostatic chuck, 30 ... Upper electrode, 40 ... Gas source group, 50 ... Exhaust apparatus, 62 ... 1st high frequency power supply , 64: second high frequency power supply, Cnt: control unit, W: wafer, MSK: mask, R1: first region, R2: second region, IL1: silicon oxide film, IL2: silicon nitride film, DP: deposit .

Claims (15)

A method of simultaneously etching a first region and a second region of an object to be processed, the first region having a multilayer film formed by alternately laminating a silicon oxide film and a silicon nitride film, The second region includes a silicon oxide film having a film thickness larger than that of the silicon oxide film of the first region, and the object provides an opening over the first region and the second region. And the method has
A first step of generating a plasma of a first processing gas containing a fluorocarbon gas and a hydrofluorocarbon gas in a processing container of the plasma processing apparatus in which the object is prepared;
A second step of generating a plasma of a second processing gas containing hydrofluorocarbon gas and nitrogen gas in the processing vessel;
Including
A plurality of sequences each including the first step and the second step are performed,
The first step and the second step are continuously performed,
The execution period of the second step includes a first period including the start time of the second step, a second period following the first period, and a second period following the second period and a finish period of the second step Including 3 periods,
Hydrogen gas is further included in the second process gas in the second period;
In the first period immediately after the execution period of the first step and the third period immediately before the execution period of the first step, the ratio of the flow rate of hydrogen gas to the flow rate of the second processing gas is The ratio is set to be lower than the ratio of the flow rate of hydrogen gas to the flow rate of the second processing gas in the second period,
Method.   The second process gas further includes nitrogen gas in the first period immediately after the execution period of the first step and the third period immediately before the execution period of the first step. The method described in.   In the first period immediately after the execution period of the first step, and in the third period immediately before the execution period of the first step, the flow rate of the hydrogen gas is the flow rate of the hydrogen gas in the second period The method according to claim 1 or 2, which is set to a lower flow rate. The execution period of the first step is a fourth period including the start time of the first step, a fifth period following the fourth period, and the end period of the first step following the fifth period. Including six periods,
In the fifth period, the first process gas further includes oxygen gas,
The fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences, and the execution period of the second step of at least a part of the plurality of sequences. The ratio of the flow rate of oxygen gas to the flow rate of the first processing gas is lower than the ratio of the flow rate of oxygen gas to the flow rate of the first processing gas in the fifth period in the sixth period immediately before Set,
The method according to any one of claims 1 to 3.   The fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences, and the execution period of the second step of at least a part of the plurality of sequences. 5. The method of claim 4, wherein the first process gas further comprises nitrogen gas in the sixth period immediately prior to.   The fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences, and the execution period of the second step of at least a part of the plurality of sequences. 6. The method according to claim 4, wherein the flow rate of the oxygen gas is set to a flow rate lower than the flow rate of the oxygen gas in the fifth period in the sixth period immediately before the.   The fourth period immediately after the execution period of the second step of at least a part of the plurality of sequences, and the execution period of the second step of at least a part of the plurality of sequences. The method according to any one of claims 4 to 6, wherein the first process gas further comprises a fluorine-containing gas in the sixth period immediately before the.   The method according to any one of claims 1 to 7, wherein a high frequency for generating plasma is continuously used during the execution of the first step and the execution of the second step. A method of simultaneously etching a first region and a second region of an object to be processed, the first region having a multilayer film formed by alternately laminating a silicon oxide film and a silicon nitride film, The second region includes a silicon oxide film having a film thickness larger than that of the silicon oxide film of the first region, and the object provides an opening over the first region and the second region. And the method has
A first step of generating a plasma of a first processing gas containing a fluorocarbon gas and a hydrofluorocarbon gas in a processing container of the plasma processing apparatus in which the object is prepared;
A second step of generating a plasma of a second processing gas containing a hydrofluorocarbon gas, a nitrogen gas, and a hydrogen gas in the processing vessel;
Including
A plurality of sequences each including the first step and the second step are performed,
Each of the plurality of sequences further includes an intermediate step of generating a plasma of an inert gas including helium gas in the processing vessel, between the first step and the second step.
Method.   10. The method of claim 9, wherein the inert gas further comprises nitrogen gas.   The method according to any one of claims 1 to 10, wherein the execution period of the first step is longer than the execution period of the second step.   The method according to any one of the preceding claims, wherein the second process gas further comprises nitrogen trifluoride gas.   The method according to any one of the preceding claims, wherein the second process gas further comprises carbonyl sulfide gas.   14. The method of any one of the preceding claims, wherein the second process gas further comprises a hydrocarbon gas.   The method according to any one of the preceding claims, wherein the mask is a mask made of carbon.

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