JP7709871B2 - Etching method and plasma processing apparatus - Google Patents

Description

An exemplary embodiment of the present disclosure relates to an etching method and a plasma processing apparatus.

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 plasma processing apparatus is described in JP 2009-187975 A (hereinafter referred to as "Patent Document 1").

The plasma processing apparatus described in Patent Document 1 further includes a radio frequency generator and a DC negative pulse generator. The radio frequency generator applies a radio frequency voltage to the substrate holding electrode. The radio frequency generator alternately switches the radio frequency voltage on and off. The DC negative pulse generator applies a DC negative pulse voltage to the substrate holding electrode in accordance with the on and off timing of the radio frequency voltage. In the plasma processing apparatus described in Patent Document 1, the energy of the ions supplied to the substrate is maximum when the DC negative pulse voltage is applied to the substrate holding electrode. The energy of the ions supplied to the substrate is minimum when the DC negative pulse voltage is not applied to the substrate.

JP 2009-187975 A

This disclosure provides a technique for improving the verticality of openings formed in a film and the selectivity of etching the film relative to etching the mask.

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

According to one exemplary embodiment, the verticality of the openings formed in the film and the selectivity of etching the film relative to etching the mask are increased.

1 is a flow diagram of an etching method according to an exemplary embodiment. 2 is a partially enlarged cross-sectional view of an example of a substrate to which the etching method shown in FIG. 1 is applied; 1 is a schematic diagram illustrating a plasma processing apparatus according to an exemplary embodiment; Each of (a) to (d) of FIG. 4 is a diagram showing an example of a change in a voltage pulse over time. 2 is a partially enlarged cross-sectional view of an example of a substrate to which the etching method shown in FIG. 1 is applied. 1 is a graph showing the relationship between four time intervals and the selectivity ratio obtained in a first experiment. 11 is a graph showing the relationship between the depth of an opening formed in film EF and the maximum width of an opening in film FB, obtained in a first experiment. 13 is a graph showing the relationship between the depth of an opening formed in film EF and the maximum width of an opening in film FA, obtained in a first experiment. 11 is a graph showing the relationship between the duty ratio of a pulse NP and the etching rate of a film FA, obtained in a first experiment. 11 is a graph showing the relationship between the duty ratio of a pulse NP and the etching rate of a mask MK, obtained in a first experiment.

Various exemplary embodiments are described below.

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

In the above embodiment, when the depth of the opening formed in the film of the substrate is shallow, the absolute value of the negative potential of the substrate is relatively small, so the film is etched using ions having a relatively low energy. Also, when the depth of the opening formed in the film of the substrate is deep, the absolute value of the negative potential of the substrate is relatively large, so the film is etched using ions having a relatively high energy. Ions having a relatively low energy used when the depth of the opening is shallow suppress the etching of the mask, so as to increase the selectivity of the etching of the film relative to the etching of the mask. Also, ions having a relatively low energy used when the depth of the opening is shallow can suppress the deterioration of the verticality of the opening formed in the film. Also, ions having a relatively high energy used when the depth of the opening is deep increase the etching rate of the film, so as to increase the selectivity of the etching of the film relative to the etching of the mask. Also, ions having a relatively high energy used when the depth of the opening is deep increase the verticality of the opening formed in the film. Therefore, according to the above embodiment, the verticality of the opening formed in the film and the selectivity of the etching of the film relative to the etching of the mask are increased.

In one exemplary embodiment, the pulse may be a negative voltage pulse or a negative DC voltage pulse. 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 trend as etching of the film progresses.

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

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

In one exemplary embodiment, in step (b), the duty ratio of the pulse may be reduced at least once to have a decreasing tendency in accordance with the progress of etching of the film. In one exemplary embodiment, in step (b), the duty ratio of the pulse may be reduced to have a ratio of 15% or more and 20% or less. According to this embodiment, it is possible to further suppress etching of the mask while suppressing a decrease in the etching rate of the film.

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

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

According to another exemplary embodiment, 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 on the substrate placed on the substrate support. The etching step includes a step (a) of generating a plasma of a processing gas in a chamber of the plasma processing apparatus. The etching step further includes a step (b) of etching the film by periodically applying a pulse of voltage 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 reduced at least once so as to have a decreasing trend according to the progress of etching of the film. In one exemplary embodiment, the pulse may be a negative voltage pulse or a negative DC voltage pulse.

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 from polycrystalline silicon.

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

Various exemplary embodiments will be described in detail below with reference to the drawings. Note that the same or equivalent parts in each drawing will be given the same reference numerals.

Figure 1 is a flow diagram of an etching method according to one exemplary embodiment. The etching method shown in Figure 1 (hereinafter referred to as "Method MT") is performed to etch a film on a substrate.

2 is a partially enlarged cross-sectional view of an example of a substrate to which the etching method shown in FIG. 1 is applied. The substrate W shown in FIG. 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 to be transferred to the film EF. The mask MK may be made of 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 made of polycrystalline silicon.

The film EF may be a single layer film or may be a multi-layer 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.

In method MT, a plasma processing apparatus is used to etch a film on a substrate. FIG. 3 is a schematic diagram of a plasma processing apparatus according to an exemplary embodiment. In method MT, the plasma processing apparatus 1 shown in FIG. 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.

In one embodiment, the chamber 10 may include a chamber body 12. The chamber body 12 has a generally cylindrical shape. The internal space 10s is provided in 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 may be a film made of a ceramic such as aluminum oxide or yttrium oxide.

The sidewall 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 sidewall of the chamber body 12.

The plasma processing apparatus 1 further includes a substrate support 16. The substrate support 16 is configured to support a substrate W in the chamber 10. The substrate W may have a substantially disk-like 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.

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 made of a conductive material such as aluminum. The electrode plate 19 has a substantially disk 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 made of a conductive material such as aluminum. The lower electrode 18 has a substantially disk shape, and its central axis is the axis AX. The lower electrode 18 is electrically connected to the electrode plate 19.

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

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 body and an electrode. The body is made of a dielectric material. The electrostatic chuck 20 and its body each have a substantially disk shape, and their central axis is the axis AX. The electrode is a conductive film provided within the 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 attractive force is generated between the electrostatic chuck 20 and the substrate W. Due to the generated electrostatic attractive force, the substrate W is attracted to the electrostatic chuck 20 and held by the electrostatic chuck 20.

The substrate support 16 may support an edge ring ER mounted on its periphery. The edge ring ER may be formed from silicon, silicon carbide, or quartz. The substrate W is positioned on the electrostatic chuck 20 and within the area enclosed by the edge ring ER.

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 the gap between the upper surface of the electrostatic chuck 20 and the rear surface (lower surface) of the substrate W.

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 periphery of the support 15. The cylindrical portion 28 is formed from 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 from a material having insulating properties. The insulating portion 29 is formed from a ceramic such as quartz. The insulating portion 29 has a substantially cylindrical shape. The insulating portion 29 extends along the outer periphery of the electrode plate 19, the outer periphery of the lower electrode 18, and the outer periphery of the electrostatic chuck 20.

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 on the upper part of the chamber body 12 via a member 32. The member 32 is made of an insulating material. The upper electrode 30 and the member 32 close the upper opening of the chamber body 12.

The upper electrode 30 may include a top plate 34 and a support 36. The bottom surface of the top plate 34 is the bottom surface on the side of the internal space 10s and defines the internal space 10s. The top plate 34 may be formed from a low-resistance conductor or semiconductor with little Joule heat. In one embodiment, the top plate 34 is formed from 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 the plate thickness direction.

The support 36 detachably supports the top plate 34. The support 36 is made 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 are respectively connected to the plurality of gas discharge holes 34a. 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.

The gas source group 40 is connected to the gas supply pipe 38 via the valve group 41, the flow rate controller group 42, and the valve group 43. The gas source group 40, the valve group 41, the flow rate controller group 42, and the valve group 43 constitute a gas supply section GS. The gas source group 40 includes a plurality of gas sources. The gas sources of the gas source group 40 include a plurality of gas sources. Each of the valve group 41 and the valve group 43 includes a plurality of opening and closing valves. The flow rate controller group 42 includes a plurality of flow rate controllers. Each of the plurality of flow rate controllers of the flow rate controller group 42 is a mass flow controller or a pressure-controlled flow rate 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 opening and closing valve of the valve group 41, a corresponding flow rate controller of the flow rate controller group 42, and a corresponding opening and closing valve of the valve group 43.

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 may be a plate-shaped member. The baffle member 48 is formed, for example, by forming a corrosion-resistant film on the surface of a member made of aluminum. The corrosion-resistant film may be a film made 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 pressure adjustment valve and a vacuum pump such as a turbomolecular pump.

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 generating plasma. The high-frequency power HF has a first frequency. The first frequency is, for example, within a 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 device 61m and an electrode plate 19 in order to supply the high-frequency power HF to the lower electrode 18. The matching device 61m has a matching circuit. The matching circuit of the matching device 61m has a variable impedance. The impedance of the matching circuit of the matching device 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 does not have to be electrically connected to the lower electrode 18, and may be connected to the upper electrode 30 via the matching device 61m. The high-frequency power supply 61 constitutes a plasma generating unit of one embodiment.

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 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, i.e., the time interval during 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 a range of 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 period, i.e., the duty ratio, may be 20% or less.

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

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 emission of the plasma through a window 74 provided in the side wall of the chamber body 12. The window 74 is made of an optically transparent material such as quartz.

The plasma processing apparatus 1 further includes a control unit 80. The control unit 80 is a computer equipped with 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 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. Under the control of the control unit 80, a process specified by the recipe data, for example, method MT, is executed in the plasma processing apparatus 1.

Method MT will be described below with reference to FIG. 1 again. In the following description, method MT will be described using an example in which it is applied to a substrate W shown in FIG. 2 using a plasma processing apparatus 1. Note that the substrate to which method MT is applied may be a substrate different from the substrate shown in FIG. 2. Also, a plasma processing apparatus different from plasma processing apparatus 1 may be used in method MT.

As shown in FIG. 1, the method MT includes steps STp and STe. In step STp, the substrate W is placed on the substrate support 16. Step STe is performed while the substrate W is placed on the substrate support 16. In step STe, the film EF is etched. Step STe includes steps ST1 and ST2. Step ST1 and ST2 are performed while the substrate W is placed on the substrate support 16 in the chamber 10.

In step ST1, plasma of a processing gas is generated in a chamber of a plasma processing apparatus. The processing gas is selected according to the type of film EF to be etched. When the film EF includes a silicon oxide film and/or a silicon nitride film, the processing gas may include a fluorocarbon gas. The processing gas may include at least one of a rare 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 in the chamber by energy provided by a plasma generating unit. As a result, plasma is generated in the chamber.

When the plasma processing apparatus 1 is used, the control unit 80 controls the gas supply unit GS to supply a processing gas into the chamber 10 in the process ST1. The control unit 80 also controls the exhaust unit 50 to set the pressure in the chamber 10 to a specified pressure. The control unit 80 also controls the high frequency power supply 61 to supply high frequency power HF. Under the control of the control unit 80, plasma is generated from the processing gas in the chamber 10. The frequency of the high frequency power HF during the execution of the process STe may be constant. The frequency of the high frequency power HF during the execution of the process STe may be, for example, 40 MHz.

Step ST2 is performed when the plasma generated in step ST1 is present in the chamber. Step ST2 can be performed simultaneously with the generation of plasma in step ST1. Step ST2 includes step ST21. In step ST21, a pulse NP is applied to the lower electrode of the substrate support. Step ST21 is repeated periodically. That is, in step ST2, a pulse NP is applied periodically to the lower electrode of the substrate support. In step ST2, ions from the plasma are supplied to the substrate, thereby etching the film EF.

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

In step ST2, one or more parameters of the pulse NP are each changed according to the progress of etching of the film EF. Each of the one or more parameters of the pulse NP is changed at least once during the repetition of step ST21. Each of the one or more parameters of the pulse NP may be changed stepwise or gradually during the repetition of step ST21. The 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.

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

Each of FIG. 4(a) to FIG. 4(d) is a diagram showing an example of the change in the voltage pulse over time. In FIG. 4(a), a gradual 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.

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 in accordance with the progress of 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 in accordance with the progress of etching of the film EF.

The duty ratio of the pulse NP may be reduced at least once in step ST2 so as to have a decreasing tendency in accordance with the progress of etching of the film EF. The duty ratio of the pulse NP may be reduced stepwise or gradually in step ST2 so as to have a decreasing tendency in accordance with the progress of etching of the film EF. In FIG. 4(c), a stepwise reduction 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 reduced 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 reduced every cycle.

In one embodiment, the duty ratio of the pulse NP may be reduced in step ST2 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 at different times.

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

In one embodiment, in addition to step ST21, step ST2 may include step ST22. Step ST2 may further include step ST2a and step 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 reaches a predetermined number. The predetermined number may be specified as part of the recipe data. If it is determined that the stop condition is not satisfied in step ST2a, then a determination is made for step ST2b.

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

On the other hand, if it is determined in step ST2b that one or more parameters of the pulse NP should be changed, the process proceeds to step ST22. In one example, if the number of consecutive pulses NP of the same level are output (i.e., the number of consecutive periods in which the pulse NP of the same level is output) reaches a predetermined number, the process proceeds to step ST22. In another example, if it is determined that the type of film being etched has been changed from the emission intensity of each of the multiple wavelengths of light acquired by the analyzer 72, the process proceeds to step ST22. For example, if the film EF includes a stack of a silicon oxide film and a silicon nitride film, the emission intensity of a wavelength of 483 nm is high when the silicon oxide film is etched, and the emission intensity of a wavelength of 387 nm is high when the silicon nitride film is etched. If the film EF includes a stack of a silicon oxide film and a silicon nitride film, the emission intensity of the light of these wavelengths is observed to identify the timing at which the type of film being etched is changed, and step ST22 is performed at that timing.

In step ST22, the parameter of the pulse NP to be changed is changed. If the voltage level of the pulse NP is a parameter to be changed, the level is changed in step ST22. For example, if the voltage of the pulse NP has negative polarity, the absolute value of the voltage of the pulse NP is increased in step ST22. If the duty ratio of the pulse NP is a parameter to be changed, the duty ratio is decreased in step ST22. The change value of the parameter of the pulse NP to be changed may be specified as part of the recipe data. After step ST22, the process proceeds to step ST21.

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

In the method MT, when the depth of the opening formed in the film EF of the substrate W is shallow, the absolute value of the negative potential of the substrate W is relatively small, so the film EF is etched using ions having a relatively low energy. Also, when the depth of the opening formed in the film EF of the substrate W is deep, the absolute value of the negative potential of the substrate W is relatively large, so the film EF is etched using ions having a relatively high energy. Ions having a relatively low energy used when the depth of the opening is shallow suppress the etching of the mask MK, thereby increasing the selectivity of the etching of the film EF relative to the etching of the mask MK. Also, ions having a relatively low energy used when the depth of the opening is shallow can suppress the deterioration of the verticality of the opening formed in the film EF. Also, ions having a relatively high energy used when the depth of the opening is deep increase the etching rate of the film EF, thereby increasing the selectivity of the etching of the film EF relative to the etching of the mask MK. Also, ions having a relatively high energy used when the depth of the opening is deep increase the verticality of the opening formed in the film EF. Therefore, method MT improves the verticality of the openings formed in film EF and the selectivity of etching film EF relative to etching mask MK.

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

When the duty ratio of the periodically applied pulse 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 relative to the etching of the mask MK is improved. Furthermore, when the duty ratio of the pulse NP is decreased to have a ratio of 15% or more and 20% or less, it is possible to further suppress the etching of the mask MK while suppressing the decrease in the etching rate of the film EF.

Although various exemplary embodiments have been described above, various additions, omissions, substitutions, and modifications may be made without being limited to the exemplary embodiments described above. In addition, elements in different embodiments may be combined to form other embodiments.

For example, the first period and the second period may be alternately repeated, and the power level of the high frequency power HF in the second period may be set to be 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. Note that, when the film to be 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, i.e., the pulse frequency, may be 2 kHz. When the film to be etched in the method MT is a silicon nitride film, the pulse frequency may be 5 kHz or more and 10 kHz or less.

In addition, in the method MT, any plasma processing apparatus may be used as long as one or more parameters of the pulse NP periodically applied to the lower electrode of the substrate support can be changed. Examples of such 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 surface waves such as microwaves.

Below, we will explain various experiments that were conducted to evaluate Method MT. This disclosure is not limited to these experiments.

(First experiment)

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 of 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 a plurality of sample substrates was etched under different conditions of the etching time (time length of step ST2) and the absolute value of the negative DC voltage of the pulse NP. Other conditions for steps ST1 and ST2 are shown below.
<Conditions of Step ST1 and Step ST2>
High frequency power HF: 40MHz, 1500W
Second frequency of pulse NP: 400 kHz
Pulse NP duty ratio: 15%
Processing gas: mixed gas containing fluorocarbon gas, _O2 gas, and argon gas

In the first experiment, the selectivity in four time intervals from the start of etching was obtained from the etching results of the film EF of each sample substrate. The four time intervals were 0 to 60 seconds, 60 to 120 seconds, 120 to 180 seconds, and 180 to 240 seconds, based on the start of etching. The selectivity 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 selectivity is shown in FIG. 6. As shown in FIG. 6, when the time elapsed 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 selectivity can be obtained by using a pulse NP of a negative DC voltage with a small absolute value. In addition, when the time elapsed 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 selectivity can be obtained by using a pulse NP of a negative DC voltage with a large absolute value. From this, it was confirmed that a high selectivity ratio can be obtained by increasing the absolute value of the voltage of the pulse NP at least once in step ST2 so that the absolute value of the voltage of the pulse NP has an increasing tendency.

In the first experiment, the relationship between the depth of the opening formed in the film EF and the maximum width of the opening in the film FA (Bowing CD) and the maximum width of the opening in the film FB (Bowing CD) was obtained from the etching results of the film EF of each sample substrate. Figure 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 in the film FB (Bowing CD). Figure 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 in the film FA (Bowing CD). As shown in Figures 7 and 8, when the depth of the opening formed in the film EF was shallow, the dependency 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 greater 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 in step ST2 so that the absolute value of the voltage of the pulse NP has an increasing tendency, it is possible to obtain a high selectivity as well as a high perpendicularity of the opening of the film EF.

(Second experiment)

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 different conditions of the absolute value of the voltage of the pulse NP and the duty ratio. Other conditions for the process ST1 and the process ST2 are shown below.
<Conditions of Step ST1 and Step ST2>
High frequency power HF: 40MHz, 1500W
Second frequency of pulse NP: 400 kHz
Processing gas: mixed gas containing fluorocarbon gas, _O2 gas, and argon gas

In the second experiment, the relationship between the duty ratio of the pulse NP and the etching rate of the film FA and the etching rate of the mask MK was obtained from the etching results of multiple sample substrates. FIG. 9 shows the relationship between the duty ratio of the pulse NP and the etching rate of the film FA. FIG. 10 shows the relationship between the duty ratio of the pulse NP and the etching rate of the mask MK. As shown in FIG. 10, the etching rate of the mask MK decreased with the decrease in the duty ratio of the pulse NP. As shown in FIG. 9, the decrease in the etching rate of the film FA with the decrease in the duty ratio of the pulse NP was small as long as the duty ratio of the pulse NP was decreased within the range of 20% to 15%. Therefore, it was confirmed that the selectivity was increased when the duty ratio of the periodically applied pulse NP had a decreasing tendency. In addition, 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 when the duty ratio of the pulse NP was decreased to have a ratio of 20% or more and 15% or less.

From the foregoing, it will be understood that the various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the appended claims.

1...plasma processing apparatus, 10...chamber, 16...substrate support, 18...lower electrode, 61...high frequency power supply, 62...bias power supply.

Claims (16)

A chamber;
a substrate support disposed within the chamber;
a gas supply configured to supply a process gas into the chamber;
a plasma generating unit configured to generate a plasma from the process gas in the chamber;
a bias power supply electrically connected to the substrate support and configured to periodically apply a voltage pulse to the substrate support with a period including a first period during which a voltage pulse is applied to the substrate support and a second period during which the 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;
Equipped with
The period has a time length that is the inverse of a frequency within a range of 1 kHz to 27 MHz,
The control unit is
(a) controlling the gas supply unit and the plasma generating unit to generate plasma from the processing gas in the chamber;
(b) controlling the bias power supply to periodically apply the one voltage pulse to the substrate support during the period to supply ions in the plasma to a substrate on the substrate support to etch a film on the substrate;
In the control of (b), the bias power supply is controlled so as to change the voltage level of the one voltage pulse at least once in the repetition of the period so that the absolute value of the negative potential of the substrate has an increasing tendency in accordance with the progress of etching of the film.
The plasma processing apparatus is configured as follows. the one voltage pulse is a negative voltage pulse or a negative DC voltage pulse;
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 period in (b) so that the absolute value of the voltage of the one voltage pulse has an increasing tendency according to the progress of etching of the film.
The plasma processing apparatus according to claim 1 . 3 . The plasma processing apparatus according to claim 1 , wherein 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 in the step (b). The plasma processing apparatus of any one of claims 1 to 3, wherein in (b), the control unit is configured to control the bias power supply so as to reduce the duty ratio of the one voltage pulse at least once in the repetition of the period so that the duty ratio of the one voltage pulse has a decreasing tendency in accordance with the progress of etching of the film. 5. The plasma processing apparatus of claim 4, wherein the control unit is configured to control the bias power supply to reduce the duty ratio of the one voltage pulse in the repetition of the period so that the duty ratio of the one voltage pulse has a ratio of 15% or more and 20% or less in (b). 6. The plasma processing apparatus according to claim 4, wherein the control unit is configured to control the bias power supply so as to reduce the duty ratio of the one voltage pulse stepwise or gradually in the repetition of the period in (b). The plasma processing apparatus of any one of claims 1 to 6 , wherein in (b), the control unit is configured to control the bias power supply so as to change the level of the voltage of the one voltage pulse in a stepwise or gradual manner during the repetition of the period. A chamber;
a substrate support disposed within the chamber;
a gas supply configured to supply a process gas into the chamber;
a plasma generating unit configured to generate a plasma from the process gas in the chamber;
a bias power supply electrically connected to the substrate support and configured to periodically apply a voltage pulse to the substrate support with a period including a first period during which a voltage pulse is applied to the substrate support and a second period during which the 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;
Equipped with
The period has a time length that is the inverse of a frequency within a range of 1 kHz to 27 MHz,
The control unit is
(a) controlling the gas supply unit and the plasma generating unit to generate plasma from the processing gas in the chamber;
(b) controlling the bias power supply to periodically apply the one voltage pulse to the substrate support during the period to supply ions in the plasma to a substrate on the substrate support to etch a film on the substrate;
In the control of (b) , the bias power supply is controlled so that the duty ratio of the one voltage pulse has a decreasing tendency in accordance with the progress of etching of the film, and the duty ratio of the one voltage pulse is reduced at least once in the repetition of the period.
The plasma processing apparatus is configured as follows . 9. The plasma processing apparatus of claim 8, wherein the one voltage pulse is a negative voltage pulse or a negative DC voltage pulse. The plasma processing apparatus according to claim 1 , wherein the film includes a silicon-containing film. The plasma processing apparatus of claim 1 , wherein the film comprises a silicon-containing dielectric film. 10. The plasma processing apparatus according to claim 1, wherein the film includes a silicon oxide film. The plasma processing apparatus of claim 12 , wherein the film further comprises a silicon nitride film. 14. The plasma processing apparatus of claim 12 , wherein the substrate further comprises a mask on the film , the mask being made of polycrystalline silicon. placing a substrate on a substrate support disposed within a chamber of a plasma processing apparatus, the substrate having a film and a mask disposed on the film;
Etching the film on the substrate placed on the substrate support ;
Including,
The step of etching the film includes:
(a) generating a plasma from a process gas in the chamber;
(b) periodically applying a voltage pulse to the substrate support, the voltage pulse including a first period during which the voltage pulse is applied to the substrate support and a second period during which the voltage pulse is not applied to the substrate support, to supply ions from the plasma to the substrate, thereby etching the film;
Including,
The period has a time length that is the inverse of a frequency within a range of 1 kHz to 27 MHz,
In the etching method (b), the voltage level of the one voltage pulse is changed at least once in the repetition of the period so that the absolute value of the negative potential of the substrate has an increasing tendency according to the progress of etching of the film. placing a substrate on a substrate support disposed within a chamber of a plasma processing apparatus, the substrate having a film and a mask disposed on the film;
Etching the film on the substrate placed on the substrate support ;
Including,
The step of etching the film includes:
(a) generating a plasma from a process gas in the chamber;
(b) periodically applying a voltage pulse to the substrate support, the voltage pulse including a first period during which the voltage pulse is applied to the substrate support and a second period during which the voltage pulse is not applied to the substrate support, to supply ions from the plasma to the substrate, thereby etching the film;
Including,
The etching method according to (b), wherein the duty ratio of the one voltage pulse in the repetition of the period is reduced at least once so as to have a decreasing tendency in accordance with the progress of etching of the film.