Etching method and plasma processing apparatus

Abstract

To provide a technology that enhances verticality of an opening formed in a film and selectivity of etching of the film relative to etching of a mask.SOLUTION: The disclosed etching method comprises: a step (a) of generating plasma of a processing gas in a chamber of a plasma processing apparatus. The plasma is generated in a state where a substrate is mounted on a substrate supporting unit which has a bottom electrode within the chamber. The substrate has a film and a mask. The mask is provided on the film. The etching method further comprises: a step (b) of etching the film by periodically applying a negative DC voltage pulse to the bottom electrode to supply ions from the plasma to the substrate. In the step (b), a level of pulse voltage is changed at least one time such that an absolute value of negative potential of the substrate has an increasing trend depending on a procedure of etching of the film.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Exemplary embodiments of the present disclosure relate to an etching method and a plasma processing apparatus.

Background Art

[0002] A plasma processing apparatus is used in plasma processing of a substrate. The plasma processing apparatus includes a chamber and a substrate holding electrode. The substrate holding electrode is provided in the chamber. The substrate holding electrode holds a substrate placed on its main surface. One type of such a plasma processing apparatus is described in Japanese Patent Application Laid-Open No. 2009-187975 (hereinafter referred to as "Patent Document 1").

[0003] The plasma processing apparatus described in Patent Document 1 further includes a high-frequency generator and a DC negative pulse generator. The high-frequency generator applies a high-frequency voltage to the substrate holding electrode. The high-frequency generator alternately switches on and off the high-frequency voltage. The DC negative pulse generator applies a DC negative pulse voltage to the substrate holding electrode according to the on and off timing of the high-frequency voltage. In the plasma processing apparatus described in Patent Document 1, the energy of ions supplied to the substrate is maximized when the DC negative pulse voltage is applied to the substrate holding electrode. The energy of ions supplied to the substrate is minimized when the DC negative pulse voltage is not applied to the substrate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present disclosure provides a technique for enhancing the perpendicularity of an opening formed in a film and the selectivity of etching of the film with respect to etching of a mask.

Means for Solving the Problem

[0006] In one exemplary embodiment, an etching method is provided. The etching method includes a step of placing a substrate on a substrate support provided in a chamber of a plasma processing apparatus. The substrate has a film and a mask. The mask is provided on the film. The etching method further includes a step of etching the film of the substrate placed on the substrate support. The step of etching includes a step (a) of generating plasma of a processing gas in the chamber. The step of etching further includes a step (b) of etching the film by periodically applying a voltage pulse to a lower electrode in the substrate support to supply ions from the plasma to the substrate. In step (b), the level of the pulsed voltage is changed at least once such that the absolute value of the negative potential of the substrate has an increasing tendency according to the progress of the etching of the film.

Advantages of the Invention

[0007] According to one exemplary embodiment, the perpendicularity of the opening formed in the film and the selectivity of the etching of the film with respect to the etching of the mask are enhanced.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

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Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0009] Hereinafter, various exemplary embodiments will be described.

[0010] In one exemplary embodiment, an etching method is provided. The etching method includes a step of placing a substrate on a substrate support provided in a chamber of a plasma processing apparatus. The substrate has a film and a mask. The mask is provided on the film. The etching method further includes a step of etching the film of the substrate placed on the substrate support. The etching step includes a step (a) of generating plasma of a processing gas in the chamber. The etching step further includes a step (b) of etching the film by periodically applying a voltage pulse to a lower electrode in the substrate support to supply ions from the plasma to the substrate. In step (b), the voltage level of the pulse is changed at least once such that the absolute value of the negative potential of the substrate has an increasing tendency according to the progress of the etching of the film.

[0011] In the above embodiment, when the depth of the opening formed in the film of the substrate is shallow, since the absolute value of the negative potential of the substrate is relatively small, the film is etched using ions having relatively low energy. Further, when the depth of the opening formed in the film of the substrate is deep, since the absolute value of the negative potential of the substrate is relatively large, the film is etched using ions having relatively high energy. The ions having relatively low energy used when the depth of the opening is shallow suppress the etching of the mask, thereby increasing the selectivity of the etching of the film with respect to the etching of the mask. Further, the ions having relatively low energy used when the depth of the opening is shallow can suppress the deterioration of the perpendicularity of the opening formed in the film. Further, the ions having relatively high energy used when the depth of the opening is deep increase the selectivity of the etching of the film with respect to the etching of the mask by increasing the etching rate of the film. Further, the ions having relatively high energy used when the depth of the opening is deep increase the perpendicularity of the opening formed in the film. Therefore, according to the above embodiment, the perpendicularity of the opening formed in the film and the selectivity of the etching of the film with respect to the etching of the mask are increased.

[0012] In one exemplary embodiment, the pulse may be a pulse of a negative voltage or a pulse of a negative DC voltage. In step (b), the absolute value of the voltage of the pulse may be increased at least once so that the absolute value of the voltage of the pulse has an increasing tendency according to the progress of the etching of the film.

[0013] In the above embodiment, when the depth of the opening formed in the film of the substrate is shallow, a pulse of a negative voltage having a relatively low absolute value is supplied to the lower electrode, and the film is etched using ions having relatively low energy. Further, when the depth of the opening formed in the film of the substrate is deep, a pulse of a negative voltage having a relatively high absolute value is supplied to the lower electrode, and the film is etched using ions having relatively high energy.

[0014] In one exemplary embodiment, in step (b), the duty ratio of the pulse may be set to 20% or less.

[0015] In one exemplary embodiment, in step (b), the duty ratio of the pulse may be decreased at least once such that it has a decreasing tendency according to the progress of the etching of the film. In one exemplary embodiment, in step (b), the duty ratio of the pulse may be decreased such that it has a ratio of 15% or more and 20% or less. According to this embodiment, it is possible to further suppress the etching of the mask while suppressing the decrease in the etching rate of the film.

[0016] In one exemplary embodiment, in step (b), the duty ratio of the pulse may be decreased stepwise or gradually.

[0017] In one exemplary embodiment, in step (b), the absolute value of the voltage of the pulse may be increased stepwise or gradually.

[0018] An etching method according to another exemplary embodiment includes a step of placing a substrate on a substrate support provided in a chamber of a plasma processing apparatus. The substrate has a film and a mask. The mask is provided on the film. The etching method further includes a step of etching the film of the substrate placed on the substrate support. The step of etching includes a step (a) of generating plasma of a processing gas in a chamber of the plasma processing apparatus. The step of etching further includes a step (b) of etching the film by periodically applying a voltage pulse to a lower electrode in the substrate support to supply ions from the plasma to the substrate. In step (b), the duty ratio of the pulse is decreased at least once such that it has a decreasing tendency according to the progress of the etching of the film. In one exemplary embodiment, the pulse may be a negative voltage pulse or a negative DC voltage pulse.

[0019] In one exemplary embodiment, the film may include a silicon-containing film. The film may include a silicon-containing dielectric film. The film may include a silicon oxide film. The film may further include a silicon nitride film. The mask may be formed of polycrystalline silicon.

[0020] In yet another exemplary embodiment, a plasma processing apparatus is provided. The plasma processing apparatus includes a chamber, a substrate support, a gas supply unit, a plasma generation unit, a bias power supply, and a control unit. The substrate support has a lower electrode and is provided in the chamber. The gas supply unit is configured to supply a processing gas into the chamber. The plasma generation unit is configured to generate plasma from the gas in the chamber. The bias power supply is electrically connected to the lower electrode and is configured to periodically generate voltage pulses. The control unit controls (a) the gas supply unit and the plasma generation unit so as to generate plasma of the processing gas in the chamber. The control unit controls (b) the bias power supply so as to periodically apply a pulse to the lower electrode in order to supply ions from the plasma to a substrate on the substrate support and etch a film of the substrate. In the control of (b), the control unit controls the bias power supply so as to change the voltage level of the pulse at least once such that the absolute value of the negative potential of the substrate has an increasing tendency according to the progress of the film etching. In one exemplary embodiment, the bias power supply may be configured to generate, as a pulse, a negative voltage pulse or a negative DC voltage pulse.

[0021] Hereinafter, various exemplary embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts will be denoted by the same reference numerals.

[0022] FIG. 1 is a flowchart of an etching method according to one exemplary embodiment. The etching method shown in FIG. 1 (hereinafter referred to as "method MT") is performed to etch a film of a substrate.

[0023] Figure 2 is a partially enlarged cross-sectional view of a substrate in an example to which the etching method shown in Figure 1 is applied. The substrate W shown in Figure 2 has a film EF and a mask MK. The film EF is etched in the method MT. The film EF may include a silicon-containing film and / or a silicon-containing dielectric film. The film EF may include a silicon oxide film and / or a silicon nitride film. The mask MK is provided on the film EF. The mask MK has a pattern transferred to the film EF. The mask MK can be formed from any material as long as the film EF is selectively etched with respect to the mask MK. When the film EF includes a silicon oxide film and / or a silicon nitride film, the mask MK may be formed of polycrystalline silicon.

[0024] The film EF may be a single-layer film or a multilayer film. In one embodiment, the film EF may include a film FA and a film FB. The film FB is provided on the film FA, and the mask MK is provided on the film FB. The film FA may be a silicon oxide film, and the film FB may be a silicon nitride film. In one embodiment, the substrate W may further have a base region UR. The film EF may be provided on the base region UR.

[0025] In the method MT, a plasma processing apparatus is used for etching the film of the substrate. Figure 3 is a diagram schematically showing a plasma processing apparatus according to one exemplary embodiment. In the method MT, the plasma processing apparatus 1 shown in Figure 3 can be used. The plasma processing apparatus 1 is a capacitively coupled plasma processing apparatus. The plasma processing apparatus 1 includes a chamber 10. The chamber 10 provides an internal space 10s therein. The central axis of the chamber 10 is an axis AX extending in the vertical direction.

[0026] In one embodiment, the chamber 10 may include a chamber body 12. The chamber body 12 has a substantially cylindrical shape. The internal space 10s is provided within the chamber body 12. The chamber body 12 is made of, for example, aluminum. The chamber body 12 is electrically grounded. A corrosion-resistant film is provided on the inner wall surface of the chamber body 12. The corrosion-resistant film can be a film formed from ceramics such as aluminum oxide and yttrium oxide.

[0027] The side wall of the chamber body 12 provides a passage 12p. The substrate W passes through the passage 12p when being transported between the internal space 10s and the outside of the chamber 10. The passage 12p can be opened and closed by a gate valve 12g. The gate valve 12g is provided along the side wall of the chamber body 12.

[0028] The plasma processing apparatus 1 further includes a substrate support 16. The substrate support 16 is configured to support the substrate W within the chamber 10. The substrate W may have a substantially disc shape. The substrate support 16 may be supported by a support 15. The support 15 extends upward from the bottom of the chamber body 12. The support 15 has a substantially cylindrical shape. The support 15 is formed from an insulating material such as quartz.

[0029] The substrate support 16 includes a lower electrode 18. The substrate support 16 may further include an electrostatic chuck 20. The substrate support 16 may further include an electrode plate 19. The electrode plate 19 is formed from a conductive material such as aluminum. The electrode plate 19 has a substantially disc shape, and its central axis is the axis AX. The lower electrode 18 is provided on the electrode plate 19. The lower electrode 18 is formed from a conductive material such as aluminum. The lower electrode 18 has a substantially disc shape, and its central axis is the axis AX. The lower electrode 18 is electrically connected to the electrode plate 19.

[0030] The lower electrode 18 provides a flow path 18f therein. The flow path 18f is connected to a supply device (e.g., a chiller unit) for a heat exchange medium. This supply device is provided outside the chamber 10. The flow path 18f receives the heat exchange medium supplied from the supply device via the pipe 23a. The heat exchange medium flows through the flow path 18f and is returned to the supply device via the pipe 23b. The supply device constitutes a temperature adjustment mechanism of the plasma processing apparatus 1.

[0031] The electrostatic chuck 20 is provided on the lower electrode 18. The substrate W is placed on the upper surface of the electrostatic chuck 20. The electrostatic chuck 20 has a main body and an electrode. The main body is formed of a dielectric. Each of the electrostatic chuck 20 and its main body has a substantially disk shape, and its central axis is the axis AX. The electrode is a conductive film and is provided in the main body. The electrode is connected to a DC power supply via a switch. When a voltage from the DC power supply is applied to the electrode, an electrostatic attraction force is generated between the electrostatic chuck 20 and the substrate W. Due to the generated electrostatic attraction force, the substrate W is attracted to the electrostatic chuck 20 and held by the electrostatic chuck 20.

[0032] The substrate support 16 may support an edge ring ER mounted on its peripheral portion. The edge ring ER can be formed of silicon, silicon carbide, or quartz. The substrate W is disposed within a region surrounded by the electrostatic chuck 20 and the edge ring ER.

[0033] The plasma processing apparatus 1 may further include a gas supply line 25. The gas supply line 25 supplies a heat transfer gas (e.g., He gas) from a gas supply mechanism to a gap between the upper surface of the electrostatic chuck 20 and the back surface (lower surface) of the substrate W.

[0034] The plasma processing apparatus 1 may further include a cylindrical portion 28 and an insulating portion 29. The cylindrical portion 28 extends upward from the bottom of the chamber body 12. The cylindrical portion 28 extends along the outer circumference of the support 15. The cylindrical portion 28 is formed of a conductive material and has a substantially cylindrical shape. The cylindrical portion 28 is electrically grounded. The insulating portion 29 is provided on the cylindrical portion 28. The insulating portion 29 is formed of a material having insulating properties. The insulating portion 29 is formed of a ceramic such as quartz, for example. The insulating portion 29 has a substantially cylindrical shape. The insulating portion 29 extends along the outer circumference of the electrode plate 19, the outer circumference of the lower electrode 18, and the outer circumference of the electrostatic chuck 20.

[0035] The plasma processing apparatus 1 further includes an upper electrode 30. The upper electrode 30 is provided above the substrate support 16. The upper electrode 30 is supported by the upper portion of the chamber body 12 via a member 32. The member 32 is formed of a material having insulating properties. The upper electrode 30 and the member 32 close the upper opening of the chamber body 12.

[0036] The upper electrode 30 may include a top plate 34 and a support 36. The lower surface of the top plate 34 is the lower surface on the side of the internal space 10s and defines the internal space 10s. The top plate 34 may be formed of a low-resistance conductor or semiconductor with less Joule heat. In one embodiment, the top plate 34 is formed of silicon. The top plate 34 provides a plurality of gas discharge holes 34a. The plurality of gas discharge holes 34a penetrate the top plate 34 in its plate thickness direction.

[0037] The support 36 detachably supports the top plate 34. The support 36 is formed of a conductive material such as aluminum. The support 36 provides a gas diffusion chamber 36a therein. The support 36 further provides a plurality of gas holes 36b. The plurality of gas holes 36b extend downward from the gas diffusion chamber 36a. The plurality of gas holes 36b communicate with the plurality of gas discharge holes 34a respectively. The support 36 further provides a gas inlet 36c. The gas inlet 36c is connected to the gas diffusion chamber 36a. A gas supply pipe 38 is connected to the gas inlet 36c.

[0038] A gas supply pipe 38 is connected to a gas source group 40 via a valve group 41, a flow controller group 42, and a valve group 43. The gas source group 40, the valve group 41, the flow controller group 42, and the valve group 43 constitute a gas supply unit GS. The gas source group 40 includes a plurality of gas sources. The plurality of gas sources of the gas source group 40 include sources of a plurality of gases. Each of the valve group 41 and the valve group 43 includes a plurality of on-off valves. The flow controller group 42 includes a plurality of flow controllers. Each of the plurality of flow controllers of the flow controller group 42 is a mass flow controller or a pressure-controlled flow controller. Each of the plurality of gas sources of the gas source group 40 is connected to the gas supply pipe 38 via a corresponding on-off valve of the valve group 41, a corresponding flow controller of the flow controller group 42, and a corresponding on-off valve of the valve group 43.

[0039] The plasma processing apparatus 1 may further include a baffle member 48. The baffle member 48 is provided between the cylindrical portion 28 and the side wall of the chamber body 12. The baffle member 48 can be a plate-like member. The baffle member 48 is configured, for example, by forming a corrosion-resistant film on the surface of a member formed of aluminum. The corrosion-resistant film can be a film formed of a ceramic such as yttrium oxide. The baffle member 48 provides a plurality of through holes. The bottom of the chamber body 12 provides an exhaust port 12e below the baffle member 48. An exhaust device 50 is connected to the exhaust port 12e via an exhaust pipe 52. The exhaust device 50 has a vacuum pump such as a pressure regulating valve and a turbo molecular pump.

[0040] The plasma processing apparatus 1 further includes a high-frequency power supply 61. The high-frequency power supply 61 is a power supply that generates high-frequency power HF for plasma generation. The high-frequency power HF has a first frequency. The first frequency is, for example, a frequency within the range of 27 to 100 MHz. In one example, the first frequency is 40 MHz. The high-frequency power supply 61 is connected to the lower electrode 18 via a matching unit 61m and an electrode plate 19 in order to supply the high-frequency power HF to the lower electrode 18. The matching unit 61m has a matching circuit. The matching circuit of the matching unit 61m has a variable impedance. The impedance of the matching circuit of the matching unit 61m is adjusted so as to reduce reflection from the load of the high-frequency power supply 61. Note that the high-frequency power supply 61 may not be electrically connected to the lower electrode 18 and may be connected to the upper electrode 30 via the matching unit 61m. The high-frequency power supply 61 constitutes a plasma generation unit of one embodiment.

[0041] The plasma processing apparatus 1 further includes a bias power supply 62. The bias power supply 62 is connected to the lower electrode 18 via the electrode plate 19. The bias power supply 62 is configured to periodically generate a voltage pulse NP. The polarity of the voltage of the pulse NP may be either negative or positive as long as the potential of the substrate W set by applying the pulse NP to the lower electrode 18 is a negative potential. In one embodiment, the bias power supply 62 generates a negative voltage pulse or a negative DC voltage pulse as the voltage pulse NP. The period of the pulse NP, that is, the time interval at which the pulse NP is generated, has a time length that is the reciprocal of the second frequency. The second frequency is lower than the first frequency. The second frequency is, for example, a frequency within the range of 1 kHz to 27 MHz. In one example, the second frequency is 400 kHz. The ratio that the time during which the pulse NP is applied to the lower electrode 18 occupies in the time length of one period, that is, the duty ratio, may be 20% or less.

[0042] In one embodiment, the bias power supply 62 may be connected to the lower electrode 18 via a filter 62f. The filter 62f is a low-pass filter and reduces the high-frequency power HF that can flow into the bias power supply 62.

[0043] In one embodiment, the plasma processing apparatus 1 may further include an analyzer 72. The analyzer 72 performs spectroscopic analysis of the plasma generated in the chamber 10. For example, the analyzer 72 observes the light emission of the plasma through a window 74 provided on the side wall of the chamber body 12. The window 74 is made of an optically transparent member such as quartz.

[0044] The plasma processing apparatus 1 further includes a control unit 80. The control unit 80 is a computer including a processor, a storage device, an input device, a display device, etc., and controls each part of the plasma processing apparatus 1. Specifically, the control unit 80 executes a control program stored in the storage device and controls each part of the plasma processing apparatus 1 based on the recipe data stored in the storage device. The control unit 80 controls, for example, the gas supply unit GS, the exhaust device 50, the high-frequency power supply 61, the bias power supply 62, etc. By the control of the control unit 80, a process specified by the recipe data, for example, the method MT, is executed in the plasma processing apparatus 1.

[0045] Hereinafter, with reference to FIG. 1 again, the method MT will be described. In the following description, the case where the method MT is applied to the substrate W shown in FIG. 2 using the plasma processing apparatus 1 will be taken as an example to describe the method MT. Note that the substrate to which the method MT is applied may be a substrate different from the substrate shown in FIG. 2. Also, in the method MT, a plasma processing apparatus different from the plasma processing apparatus 1 may be used.

[0046] As shown in FIG. 1, the method MT includes a step STp and a step STe. In the step STp, the substrate W is placed on the substrate support 16. The step STe is executed in a state where the substrate W is placed on the substrate support 16. In the step STe, the film EF is etched. The step STe includes a step ST1 and a step ST2. The step ST1 and the step ST2 are executed in a state where the substrate W is placed on the substrate support 16 in the chamber 10.

[0047] In step ST1, plasma of a processing gas is generated inside the chamber of the plasma processing apparatus. The processing gas is selected according to the film type of the film EF to be etched. When the film EF contains a silicon oxide film and / or a silicon nitride film, the processing gas may contain a fluorocarbon gas. The processing gas may contain at least one of a noble gas such as argon gas, an oxygen gas such as O2 gas, and other fluorine-containing gases. In step ST1, the processing gas is excited inside the chamber by the energy provided by the plasma generation unit. As a result, plasma is generated inside the chamber.

[0048] When the plasma processing apparatus 1 is used, in step ST1, the control unit 80 controls the gas supply unit GS to supply the processing gas into the chamber 10. Also, the control unit 80 controls the exhaust device 50 to set the pressure inside the chamber 10 to a specified pressure. Further, the control unit 80 controls the high-frequency power supply 61 to supply the high-frequency power HF. By the control of the control unit 80, plasma is generated from the processing gas inside the chamber 10. Note that the frequency of the high-frequency power HF during the execution of step STe may be constant. The frequency of the high-frequency power HF during the execution of step STe may be, for example, 40 MHz.

[0049] Step ST2 is performed when the plasma generated in step ST1 exists inside the chamber. Step ST2 can be performed simultaneously with the generation of the plasma in step ST1. Step ST2 includes step ST21. In step ST21, the pulse NP is applied to the lower electrode of the substrate support. Step ST21 is repeatedly performed periodically. That is, in step ST2, the pulse NP is periodically applied to the lower electrode of the substrate support. In step ST2, ions from the plasma are supplied to the substrate, whereby the film EF is etched.

[0050] When the plasma processing apparatus 1 is used, the control unit 80 controls the bias power supply 62 so as to periodically apply the pulse NP to the lower electrode 18 in the step ST2. The period in which the pulse NP is applied to the lower electrode 18, that is, the time interval, has a time length that is the reciprocal of the second frequency. The second frequency is, as described above, a frequency in the range of, for example, 1 kHz to 27 MHz. In one example, the second frequency is 400 kHz. The ratio of the time during which the pulse NP is applied to the lower electrode 18 in the time length of one cycle, that is, the duty ratio, may be 20% or less.

[0051] In step ST2, each of one or more parameters of the pulse NP is changed according to the progress of the etching of the film EF. Each of one or more parameters of the pulse NP is changed at least once during the repetition of step ST21. Each of one or more parameters of the pulse NP may be changed stepwise or gradually during the repetition of step ST21. One or more parameters of the pulse NP may include at least one of the voltage level of the pulse NP and the duty ratio of the pulse NP.

[0052] The voltage level of the pulse NP can be changed at least once in step ST2 so that the absolute value of the negative potential of the substrate W has an increasing tendency according to the progress of the etching of the film EF. The voltage level of the pulse NP may be changed stepwise or gradually in step ST2 so that the absolute value of the negative potential of the substrate W has an increasing tendency according to the progress of the etching of the film EF.

[0053] Each of (a) to (d) of FIG. 4 is a diagram showing an example of the time change of the voltage pulse. In FIG. 4(a), a stepwise change in the voltage level of the pulse NP is shown. As shown in FIG. 4(a), in step ST2, the voltage level of the pulse NP may be changed every two or more cycles. In FIG. 4(b), a gradual change in the voltage level of the pulse NP is shown. As shown in FIG. 4(b), in step ST2, the voltage level of the pulse NP may be changed every cycle.

[0054] In one embodiment, in step ST2, the absolute value of the negative voltage or negative DC voltage of the pulse NP may be increased at least once so as to have an increasing tendency according to the progress of the etching of the film EF. In step ST2, the absolute value of the negative voltage or negative DC voltage of the pulse NP may be increased stepwise or gradually so as to have an increasing tendency according to the progress of the etching of the film EF.

[0055] The duty ratio of the pulse NP may be decreased at least once in step ST2 so as to have a decreasing tendency according to the progress of the etching of the film EF. The duty ratio of the pulse NP may be decreased stepwise or gradually in step ST2 so as to have a decreasing tendency according to the progress of the etching of the film EF. In FIG. 4(c), a stepwise decrease in the duty ratio of the pulse NP is shown. As shown in FIG. 4(c), in step ST2, the duty ratio of the pulse NP may be decreased for every two or more cycles. In FIG. 4(d), a gradual change in the duty ratio of the pulse NP is shown. As shown in FIG. 4(d), in step ST2, the duty ratio of the pulse NP may be decreased for every cycle.

[0056] In one embodiment, the duty ratio of the pulse NP may be decreased in step ST2 so as to have a ratio within a range of 15% or more and 20% or less. During the execution of step ST2, the absolute value of the voltage of the pulse NP and the duty ratio of the pulse NP may be changed simultaneously or may be changed at different timings.

[0057] In step ST2, the control unit 80 controls the bias power supply 62 so as to change each of one or more parameters of the pulse NP at least once according to the progress of the etching of the film EF. In step ST2, the control unit 80 can control the bias power supply 62 so as to change the voltage level of the pulse NP at least once such that the absolute value of the negative potential of the substrate W has an increasing tendency according to the progress of the etching of the film EF. When the voltage of the pulse NP has a negative polarity, in step ST2, the control unit 80 may control the bias power supply 62 so as to increase the absolute value of the voltage of the pulse NP at least once such that the absolute value of the voltage of the pulse NP has an increasing tendency according to the progress of the etching of the film EF. In step ST2, the control unit 80 may control the bias power supply 62 so as to decrease the duty ratio of the pulse NP at least once such that the duty ratio of the pulse NP has a decreasing tendency according to the progress of the etching of the film EF.

[0058] In one embodiment, step ST2 may include step ST22 in addition to step ST21. Step ST2 may further include steps ST2a and ST2b. In step ST2a, it is determined whether a stop condition is satisfied. The stop condition is determined to be satisfied, for example, when the number of repetitions of step ST21 has reached a predetermined number. The predetermined number may be specified as part of the recipe data. When it is determined in step ST2a that the stop condition is not satisfied, then the determination in step ST2b is performed.

[0059] In step ST2b, it is determined whether any of one or more parameters of the pulse NP should be changed. The timing of the change of each of one or more parameters of the pulse NP may be defined as part of the recipe data. When it is determined in step ST2b that none of one or more parameters of the pulse NP should be changed, the process proceeds to step ST21.

[0060] On one hand, if it is determined that any one of one or more parameters of the pulse NP should be changed in step ST2b, the process proceeds to step ST22. In one example, when the number of times the same-level pulse NP has been continuously output (i.e., the number of consecutive periods in which the same-level pulse NP has been output) reaches a predetermined number, the process proceeds to step ST22. In another example, when it is determined from the emission intensity of light of each of a plurality of wavelengths acquired by the analyzer 72 that the type of the film being etched has changed, the process proceeds to step ST22. For example, when the film EF includes a stack of a silicon oxide film and a silicon nitride film, the emission intensity of the light with a wavelength of 483 nm is large when the silicon oxide film is being etched, and the emission intensity of the light with a wavelength of 387 nm is large when the silicon nitride film is being etched. When the film EF includes a stack of a silicon oxide film and a silicon nitride film, by observing the emission intensity of the light of these wavelengths, the timing at which the type of the film being etched changes is specified, and step ST22 is performed at such timing.

[0061] In step ST22, the parameter of the pulse NP to be changed is changed. When the level of the voltage of the pulse NP is the parameter to be changed, the level is changed in step ST22. For example, when the voltage of the pulse NP has a negative polarity, the absolute value of the voltage of the pulse NP is increased in step ST22. When the duty ratio of the pulse NP is the parameter to be changed, the duty ratio is decreased in step ST22. Note that the change value of the parameter of the pulse NP to be changed may be defined as part of the recipe data. After step ST22, the process proceeds to step ST21.

[0062] When it is determined that the stop condition is satisfied in step ST2a after the process ST21 is periodically repeated, the process ST2 ends and the method MT ends. FIG. 5 is a partially enlarged cross-sectional view of a substrate in an example where the etching method shown in FIG. 1 is applied. In step ST2, the film EF is etched so as to transfer the pattern of the mask MK thereto. As a result, an opening is formed in the film EF. In step ST2, as shown in FIG. 5, the film EF may be etched so as to partially expose the underlying region UR.

[0063] In the method MT, when the depth of the opening formed in the film EF of the substrate W is shallow, since the absolute value of the negative potential of the substrate W is relatively small, the film EF is etched using ions having relatively low energy. Further, when the depth of the opening formed in the film EF of the substrate W is deep, since the absolute value of the negative potential of the substrate W is relatively large, the film EF is etched using ions having relatively high energy. The ions having relatively low energy used when the depth of the opening is shallow suppress the etching of the mask MK, so that the selectivity of the etching of the film EF with respect to the etching of the mask MK is increased. Further, the ions having relatively low energy used when the depth of the opening is shallow can suppress the deterioration of the perpendicularity of the opening formed in the film EF. Further, the ions having relatively high energy used when the depth of the opening is deep increase the selectivity of the etching of the film EF with respect to the etching of the mask MK by increasing the etching rate of the film EF. Further, the ions having relatively high energy used when the depth of the opening is deep increase the perpendicularity of the opening formed in the film EF. Therefore, according to the method MT, the perpendicularity of the opening formed in the film EF and the selectivity of the etching of the film EF with respect to the etching of the mask MK are increased.

[0064] In one embodiment, the voltage of the periodically applied pulsed NP has a negative polarity. When the absolute value of the voltage of the periodically applied pulsed NP has an increasing tendency, when the depth of the opening formed in the film EF of the substrate W is shallow, a pulsed NP with a negative voltage having a relatively low absolute value is supplied to the lower electrode 18. Therefore, the film EF is etched using ions having relatively low energy. Also, when the depth of the opening formed in the film EF is deep, a pulsed NP with a negative voltage having a relatively high absolute value is supplied to the lower electrode 18, and the film EF is etched using ions having relatively high energy.

[0065] When the duty ratio of the periodically applied pulsed NP has a decreasing tendency, the etching rate of the mask MK decreases as the etching of the film EF progresses. Therefore, the selectivity of the etching of the film EF with respect to the etching of the mask MK is enhanced. Also, when the duty ratio of the pulsed NP is decreased to have a ratio of 15% or more and 20% or less, it becomes possible to further suppress the etching of the mask MK while suppressing the decrease in the etching rate of the film EF.

[0066] As described above, various exemplary embodiments have been described. However, the present invention is not limited to the above-described exemplary embodiments, and various additions, omissions, substitutions, and changes may be made. Also, it is possible to form other embodiments by combining elements in different embodiments.

[0067] For example, the first period and the second period may be alternately repeated and set such that the power level of the high-frequency power HF in the second period is lower than the power level of the high-frequency power HF in the first period. The power level of the high-frequency power HF in the second period may be set to zero. That is, the supply of the high-frequency power HF may be stopped in the second period. Also, the absolute value of the voltage of the pulse NP periodically applied in the second period may be set to be lower than the absolute value of the voltage of the pulse NP periodically applied in the first period. The application of the pulse NP may be stopped in the second period. When the film etched in the method MT is a silicon oxide film, the reciprocal of the time length of one cycle including the first period and the second period, that is, the pulse frequency, may be 2 kHz. When the film etched in the method MT is a silicon nitride film, the pulse frequency may be 5 kHz or more and 10 kHz or less.

[0068] Also, in the method MT, as long as one or more parameters of the pulse NP periodically applied to the lower electrode of the substrate support can be changed, any plasma processing apparatus may be used. Examples of such a plasma processing apparatus include an inductively coupled plasma processing apparatus, an electron cyclotron resonance (ECR) plasma processing apparatus, and a plasma processing apparatus that generates plasma using a surface wave such as a microwave.

[0069] Hereinafter, various experiments conducted for the evaluation of the method MT will be described. The present disclosure is not limited by these experiments.

[0070] (First Experiment)

[0071] In the first experiment, the method MT was applied to a plurality of sample substrates identical to the substrate W shown in FIG. 2 using the plasma processing apparatus 1. In each of the sample substrates, the mask MK was a mask formed from a polycrystalline silicon film. The film FA was a silicon oxide film, and the film FB was a silicon nitride film. In the first experiment, the film EF of the plurality of sample substrates was etched under conditions where the etching time (the time length of step ST2) and the absolute value of the negative DC voltage of the pulse NP were different from each other. Hereinafter, other conditions of step ST1 and step ST2 are shown. <Conditions of step ST1 and step ST2> High-frequency power HF: 40 MHz, 1500 W Second frequency of pulse NP: 400 kHz Duty ratio of pulse NP: 15% Processing gas: Mixed gas containing fluorocarbon gas, O2 gas, and argon gas

[0072] In the first experiment, from the etching results of the film EF of each sample substrate, the selection ratio in four time intervals from the start of etching was obtained. The four time intervals were 0 seconds to 60 seconds, 60 seconds to 120 seconds, 120 seconds to 180 seconds, and 180 seconds to 240 seconds based on the start point of etching. The selection ratio was obtained by dividing the etching rate of the film EF by the etching rate of the mask MK. The relationship between the four time intervals and the selection ratio is shown in FIG. 6. As shown in FIG. 6, when the elapsed time from the start of etching is short, that is, when the opening formed in the film EF is shallow, it was confirmed that a high selection ratio can be obtained by using a pulse NP with a negative DC voltage having a small absolute value. Also, when the elapsed time from the start of etching is long, that is, when the opening formed in the film EF is deep, it was confirmed that a high selection ratio can be obtained by using a pulse NP with a negative DC voltage having a large absolute value. From this, it was confirmed that a high selection ratio can be obtained by increasing the absolute value of the voltage of the pulse NP at least once so that the absolute value of the voltage of the pulse NP has an increasing tendency in step ST2.

[0073] In the first experiment, from the etching results of the film EF on each sample substrate, the relationship between the depth of the opening formed in the film EF and the maximum width of the opening (Bowing CD) in the film FA and the maximum width of the opening (Bowing CD) in the film FB was determined. FIG. 7 is a graph showing the relationship between the depth of the opening formed in the film EF and the maximum width of the opening (Bowing CD) in the film FB. FIG. 8 is a graph showing the relationship between the depth of the opening formed in the film EF and the maximum width of the opening (Bowing CD) in the film FA. As shown in FIGS. 7 and 8, when the depth of the opening formed in the film EF was shallow, the dependence of the Bowing CD of each of the films FA and FB on the absolute value of the voltage of the pulse NP was small. When the depth of the opening formed in the film EF was deep, the larger the absolute value of the voltage of the pulse NP, the smaller the Bowing CD of each of the films FA and FB. From this, it was confirmed that by increasing the absolute value of the voltage of the pulse NP at least once so that the absolute value of the voltage of the pulse NP has an increasing tendency in the step ST2, a high selectivity and a high verticality of the opening of the film EF can be obtained.

[0074] (Second Experiment)

[0075] In the second experiment, the method MT was applied to a plurality of sample substrates using the plasma processing apparatus 1. Each of the plurality of sample substrates used in the second experiment had the same configuration as the sample substrate used in the first experiment. In the second experiment, the film EF of the plurality of sample substrates was etched under conditions with different absolute values of the voltage of the pulse NP and different duty ratios. Hereinafter, other conditions of the step ST1 and the step ST2 are shown. <Conditions of Step ST1 and Step ST2> High-frequency power HF: 40 MHz, 1500 W Second frequency of pulse NP: 400 kHz Processing gas: Mixed gas containing fluorocarbon gas, O2 gas, and argon gas

[0076] In the second experiment, from the etching results of a plurality of sample substrates, the relationships between the duty ratio of the pulsed NP, the etching rate of the film FA, and the etching rate of the mask MK were determined. Fig. 9 shows the relationship between the duty ratio of the pulsed NP and the etching rate of the film FA. Fig. 10 shows the relationship between the duty ratio of the pulsed NP and the etching rate of the mask MK. As shown in Fig. 10, the etching rate of the mask MK decreased in response to the decrease in the duty ratio of the pulsed NP. As shown in Fig. 9, the decrease in the etching rate of the film FA in response to the decrease in the duty ratio of the pulsed NP was small as long as the duty ratio of the pulsed NP was decreased within the range of 20% to 15%. Therefore, it was confirmed that the selectivity was enhanced when the duty ratio of the periodically applied pulsed NP had a decreasing tendency. Also, when the duty ratio of the pulsed NP was decreased to have a ratio of 20% or more and 15% or less, it was confirmed that it was possible to further suppress the etching of the mask MK while suppressing the decrease in the etching rate of the film EF.

[0077] From the above description, it will be understood that the various embodiments of the present disclosure have been described herein for the purpose of illustration, and that various changes can be made without departing from the scope and spirit of the present disclosure. Therefore, the various embodiments disclosed herein are not intended to be limiting, and the true scope and spirit are indicated by the appended claims.

Description of Reference Numerals

[0078] 1... Plasma processing apparatus, 10... Chamber, 16... Substrate support, 18... Lower electrode, 61... High-frequency power supply, 62... Bias power supply.

Claims

1. A chamber, a substrate support provided in the chamber, a gas supply unit configured to supply a processing gas into the chamber, a plasma generation unit configured to generate plasma from the processing gas in the chamber, a bias power supply electrically connected to the substrate support and configured to periodically apply the one voltage pulse to the substrate support in a cycle including a first period in which the one voltage pulse is applied to the substrate support and a second period in which the one voltage pulse is not applied to the substrate support, a control unit configured to control the gas supply unit, the plasma generation unit, and the bias power supply, comprising: the cycle has a time length that is the reciprocal of a frequency within a range of 1 kHz to 27 MHz, the control unit: (a) controls the gas supply unit and the plasma generation unit so as to generate plasma from the processing gas in the chamber, (b) controls the bias power supply so as to periodically apply the one voltage pulse to the substrate support in the cycle in order to supply ions in the plasma to a substrate on the substrate support and etch a film of the substrate, in the control of (b), the bias power supply is controlled so that the level of the voltage of the one voltage pulse is changed at least once in the repetition of the cycle so that the absolute value of the negative potential of the substrate has an increasing tendency according to the progress of the etching of the film, a plasma processing apparatus configured as described above.

2. The one voltage pulse is a pulse of a negative voltage or a pulse of a negative DC voltage, in (b), the control unit is configured to control the bias power supply so that the absolute value of the voltage of the one voltage pulse increases at least once in the repetition of the cycle so that the absolute value of the voltage of the one voltage pulse has an increasing tendency according to the progress of the etching of the film, The plasma processing apparatus according to Claim 1.

3. In (b), the control unit is configured to control the bias power supply so as to set a duty ratio of the one voltage pulse to 20% or less. The plasma processing apparatus according to Claim 1 or 2.

4. The control unit is configured to control the bias power supply so that, in (b), the duty ratio of the one voltage pulse has a decreasing tendency according to the progress of the etching of the film, and the duty ratio of the one voltage pulse is decreased at least once in the repetition of the cycle, according to any one of claims 1 to 3. A plasma processing apparatus.

5. The control unit is configured to control the bias power supply so that, in (b), the duty ratio of the one voltage pulse is decreased in the repetition of the cycle so that the duty ratio of the one voltage pulse has a ratio of 15% or more and 20% or less, according to claim 4. A plasma processing apparatus.

6. The control unit is configured to control the bias power supply so that, in (b), the duty ratio of the one voltage pulse is decreased stepwise or gradually in the repetition of the cycle, according to claim 4 or 5. A plasma processing apparatus.

7. The control unit is configured to control the bias power supply so that, in (b), the level of the voltage of the one voltage pulse is changed stepwise or gradually in the repetition of the cycle, according to any one of claims 1 to 6. A plasma processing apparatus.

8. A chamber, A substrate support provided in the chamber, A gas supply unit configured to supply a processing gas into the chamber, A plasma generation unit configured to generate plasma from the processing gas in the chamber, A bias power supply electrically connected to the substrate support and configured to periodically apply the one voltage pulse to the substrate support in a cycle including a first period in which the one voltage pulse is applied to the substrate support and a second period in which the one voltage pulse is not applied to the substrate support, A control unit configured to control the gas supply unit, the plasma generation unit, and the bias power supply, Comprising, The cycle has a time length that is the reciprocal of a frequency within a range of 1 kHz to 27 MHz, The control unit, (a) controlling the gas supply unit and the plasma generation unit to generate plasma from the processing gas in the chamber, (b) To supply the ions in the plasma to the substrate on the substrate support and etch the film on the substrate, the bias power supply is controlled to periodically apply the one voltage pulse to the substrate support at the period, In the control of (b), the bias power supply is controlled so that the duty ratio of the one voltage pulse is decreased at least once in the repetition of the period so that the duty ratio of the one voltage pulse has a decreasing tendency according to the progress of the etching of the film. A plasma processing apparatus configured as described above.

9. The plasma processing apparatus according to claim 8, wherein the one voltage pulse is a pulse of a negative voltage or a pulse of a negative DC voltage.

10. The plasma processing apparatus according to any one of claims 1 to 9, wherein the film includes a silicon-containing film.

11. The plasma processing apparatus according to any one of claims 1 to 9, wherein the film includes a silicon-containing dielectric film.

12. The plasma processing apparatus according to any one of claims 1 to 9, wherein the film includes a silicon oxide film.

13. The plasma processing apparatus according to claim 12, wherein the film further includes a silicon nitride film.

14. The plasma processing apparatus according to claim 12 or 13, wherein the substrate further includes a mask on the film, and the mask is formed of polycrystalline silicon.

15. A step of placing a substrate on a substrate support provided in a chamber of a plasma processing apparatus, the substrate having a film and a mask provided on the film, the step; A step of etching the film of the substrate placed on the substrate support; Including The step of etching the film includes (a) A step of generating plasma from a processing gas in the chamber; (b) A step of etching the film by periodically applying the one voltage pulse to the substrate support at a period including a first period in which the one voltage pulse is applied to the substrate support and a second period in which the one voltage pulse is not applied to the substrate support, and supplying ions from the plasma to the substrate; Including The period has a time length that is the reciprocal of a frequency within a range of 1 kHz to 27 MHz. An etching method in which, in (b), the level of the voltage of the one voltage pulse is changed at least once in the repetition of the cycle so that the absolute value of the negative potential of the substrate has an increasing tendency according to the progress of the etching of the film.

16. A step of placing a substrate on a substrate support provided in a chamber of a plasma processing apparatus, the substrate having a film and a mask provided on the film, the step, A step of etching the film of the substrate placed on the substrate support, Including, The step of etching the film, (a) A step of generating plasma from a processing gas in the chamber, (b) The film is etched by periodically applying the one voltage pulse to the substrate support in a cycle including a first period in which the one voltage pulse is applied to the substrate support and a second period in which the one voltage pulse is not applied to the substrate support, and supplying ions from the plasma to the substrate, Including, An etching method in which, in (b), the duty ratio of the one voltage pulse is decreased at least once in the repetition of the cycle so as to have a decreasing tendency according to the progress of the etching of the film.

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