Plasma processing apparatus

Abstract

The objective of this invention is to suppress the decrease in the etching rate of the substrate and reduce the energy of ions irradiated onto the inner wall of the processing chamber. According to one embodiment of the invention, a plasma processing apparatus includes a DC power supply to generate a negative DC voltage applied to the lower electrode of the workpiece stage. In plasma processing using this apparatus, a radio frequency signal is supplied to excite the gas in the processing chamber to generate plasma. Furthermore, to attract ions from the plasma to the substrate on the workpiece stage, a negative DC voltage from the DC power supply is periodically applied to the lower electrode. The percentage of the period during which the DC voltage is applied to the lower electrode in each cycle is set to 40% or less.

Description

Technical Field

[0001] Embodiments of the present invention relate to a plasma processing method and a plasma processing apparatus. Prior Art

[0002] Plasma processing devices are used in the manufacture of electronic components. Generally, plasma processing devices include a processing chamber body, a workpiece table, and a radio frequency power supply. The processing chamber body provides the internal space as a processing chamber. The processing chamber body is grounded. The workpiece table is arranged in the processing chamber and is configured to support a substrate placed on the upper surface. The workpiece table includes a lower electrode. In order to excite the gas in the processing chamber, the radio frequency power supply supplies a radio frequency signal. In the plasma processing device, ions are accelerated by the potential difference between the potential of the lower electrode and the potential of the plasma, and the accelerated ions are irradiated to the substrate.

[0003] In a plasma processing device, a potential difference is also generated between the processing chamber body and the plasma. When the potential difference between the processing chamber body and the plasma is large, the energy of the ions irradiated to the inner wall of the processing chamber body becomes higher, and particles are released from the processing chamber body. The particles released from the processing chamber body may contaminate the substrate placed on the workpiece table. In order to prevent the generation of such particles, a technology is proposed in Patent Document 1, which uses an adjustment mechanism to adjust the capacitance of the processing chamber to the ground. The adjustment mechanism described in Patent Document 1 is configured to adjust the area ratio of the anode and cathode facing the processing chamber, that is, the A / C ratio. [Prior Technical Literature] [Patent Document]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2011-228694 Summary of the invention

[0005] [Problems to be solved by the invention] The present invention is a plasma processing device that is constructed by supplying a radio frequency signal for biasing a lower electrode. In order to increase the energy of ions irradiated to a substrate and thus increase the etching rate of the substrate, a radio frequency signal for biasing is supplied to the lower electrode. When the potential of the plasma increases, the potential difference between the plasma and the processing chamber body increases, and the energy of ions irradiated to the inner wall of the processing chamber body increases. In this context, it is necessary to suppress the etching rate of the substrate from decreasing and to reduce the energy of ions irradiated to the inner wall of the processing chamber body. [Technical means to solve the problem]

[0006] According to one aspect of the present invention, a plasma processing method that can be performed in a plasma processing device is provided. The plasma processing device includes a processing chamber body, a workpiece stage, a radio frequency power supply, and one or more direct current power supplies. The processing chamber body provides the internal space as a processing chamber. The workpiece stage is arranged in the processing chamber body. The workpiece stage includes a lower electrode. The workpiece stage is configured to support a substrate placed on its upper surface. The radio frequency power supply is configured to supply a radio frequency signal to excite the gas supplied to the processing chamber. One or more direct current power supplies are configured to generate a direct current voltage with a negative polarity and apply it to the lower electrode. A plasma processing method in one aspect includes: (i) a step of supplying a radio frequency signal from the radio frequency power supply in order to generate plasma of the gas supplied to the processing chamber, and (ii) a step of applying a direct current voltage with a negative polarity to the lower electrode from one or more direct current power supplies in order to attract ions in the plasma to the substrate. In the step of applying the direct current voltage, the direct current voltage is periodically applied to the lower electrode, and the proportion of the period of applying the direct current voltage to the lower electrode in each period is set to be less than 40%.

[0007] The ratio of the period in which the negative DC voltage is applied to the lower electrode in each cycle, that is, the etching rate of the substrate is less dependent on the working ratio. On the other hand, when the working ratio is small, especially when the working ratio is less than 40%, the etching rate of the processing chamber body is greatly reduced. That is, the energy of the ions irradiated to the inner wall of the processing chamber body becomes smaller. Therefore, according to a type of etching processing method, the etching rate of the substrate can be suppressed and the energy of the ions irradiated to the inner wall of the processing chamber body can be reduced.

[0008] In one embodiment of the present invention, the above ratio, that is, the working ratio, is set to be less than 35%. According to this embodiment, the energy of the ions irradiated to the inner wall of the processing chamber body can be further reduced.

[0009] In one embodiment, a plasma processing device includes a plurality of DC power supplies as one or more DC power supplies. The DC voltage applied to the lower electrode in each cycle is formed by a plurality of DC voltages sequentially output from the plurality of DC power supplies. According to this embodiment, the load of each of the plurality of DC power supplies is reduced.

[0010] In a plasma processing method according to one embodiment of the present invention, a radio frequency signal is supplied during a period when a DC voltage is applied, and the supply of the radio frequency signal is stopped during a period when the DC voltage is stopped. In a plasma processing method according to another embodiment, the supply of the radio frequency signal is stopped during a period when a DC voltage is applied, and the radio frequency signal is supplied during a period when the DC voltage is stopped.

[0011] The present invention also provides another type of plasma processing device. The plasma processing device comprises: a processing chamber body, a workpiece stage, a radio frequency power supply, one or more direct current power supplies, a switching unit and a controller. The processing chamber body provides the internal space as a processing chamber. The workpiece stage is arranged in the processing chamber body. The workpiece stage includes a lower electrode. The workpiece stage is configured to support a substrate placed on its upper surface. The radio frequency power supply is configured to supply a radio frequency signal to excite the gas supplied to the processing chamber. One or more direct current power supplies are configured to generate a direct current voltage with a negative polarity and apply it to the lower electrode. The switching unit is configured to stop applying the direct current voltage to the lower electrode. The controller is configured to control the switching unit. In order to attract ions in the plasma of the gas generated in the processing chamber to the substrate, the controller controls the switching switch so that the negative direct current voltage from one or more direct current power supplies is periodically applied to the lower electrode and the ratio of the period in each cycle during which the direct current voltage is applied to the lower electrode is set to be less than 40%.

[0012] In one embodiment of the present invention, the controller controls the switching unit so that the above ratio, that is, the working ratio, is set below 35%.

[0013] In one embodiment of the present invention, a plasma processing device has a plurality of DC power supplies as one or more DC power supplies. A controller controls a switching unit so that a DC voltage applied to a lower electrode in each cycle is formed by a plurality of DC voltages sequentially output from the plurality of DC power supplies.

[0014] In one embodiment of the present invention, the controller controls the RF power supply so that the RF signal is supplied during the period of supplying the DC voltage and the RF signal is stopped during the period of stopping the application of the DC voltage. In another embodiment, the controller controls the RF power supply so that the RF signal is stopped during the period of applying the DC voltage and the RF signal is supplied during the period of stopping the application of the DC voltage. [Effects of the invention]

[0015] As described above, the etching rate of the substrate can be suppressed from decreasing and the energy of the ions irradiated to the inner wall of the processing chamber body can be reduced. Simple diagram description

[0016] FIG. 1 is a schematic diagram showing a plasma processing device according to an embodiment. [FIG. 2] is a diagram showing an implementation form of a power supply system and a control system of the plasma processing apparatus shown in FIG. 1. [Figure 3] is a diagram showing the circuit configuration of the DC power supply, switching unit, RF filter and matching device shown in Figure 2. FIG. 4 is a timing chart showing a plasma processing method according to an embodiment of the present invention performed using the plasma processing apparatus shown in FIG. 1 . [Figure 5] (a) and (b) are time diagrams showing the potential of plasma. [Figure 6] Figure 6 (a) and (b) are time charts related to the plasma processing method of another embodiment. [Fig. 7] is a diagram showing a power supply system and a control system of a plasma processing apparatus according to another embodiment. [Fig. 8] is a diagram showing a power supply system and a control system of a plasma processing apparatus according to yet another embodiment. FIG. 9 is a timing chart showing a plasma processing method according to an embodiment of the present invention performed using the plasma processing apparatus shown in FIG. 8 . [Fig. 10] is a diagram showing a power supply system and a control system of a plasma processing apparatus according to yet another embodiment. [Fig. 11] is a circuit diagram showing an example of a waveform shaper. [Figure 12] Figure 12(a) is a curve chart showing the relationship between the working ratio obtained by the first evaluation test and the etching amount of the sample silicon oxide film adhered to the surface of the top plate 34 on the side of the processing chamber 12c, and Figure 12(b) is a curve chart showing the relationship between the working ratio obtained by the first evaluation test and the etching amount of the sample silicon oxide film adhered to the side wall of the processing chamber body 12. FIG. 13 is a graph showing the relationship between the duty ratio obtained in the first evaluation test and the etching amount of the sample silicon oxide film placed on the electrostatic chuck 20. FIG. [Figure 14] Figure 14(a) is a curve chart showing the etching amount of the sample silicon oxide film pasted on the surface of the top plate 34 on the side of the processing chamber 12c obtained by the second evaluation test and the comparison test respectively, and Figure 14(b) is a curve chart showing the etching amount of the sample silicon oxide film pasted on the side wall of the processing chamber body 12 obtained by the second evaluation test and the comparison test respectively. Implementation

[0017] Hereinafter, various embodiments will be described in detail with reference to the drawings. In addition, the same or equivalent parts are annotated with the same figure numbers on each drawing.

[0018] Fig. 1 is a schematic diagram showing a plasma processing apparatus according to an embodiment. Fig. 2 is a diagram showing an embodiment of a power supply system and a control system of the plasma processing apparatus shown in Fig. 1. The plasma processing apparatus 10 shown in Fig. 1 is a capacitive coupling type plasma processing apparatus.

[0019] The plasma processing device 10 includes a processing chamber body 12. The processing chamber body 12 has a substantially cylindrical shape. The processing chamber body 12 provides the internal space as a processing chamber 12c. For example, the processing chamber body 12 is made of aluminum. The processing chamber body 12 is connected to a ground potential. A plasma-resistant film is formed on the inner wall surface of the processing chamber body 12, that is, the wall surface defining the processing chamber 12c. The film may be a ceramic film such as a film formed by anodizing treatment or a film formed of yttrium oxide. In addition, a channel 12p is formed in the processing chamber body 12. When the substrate W is moved into the processing chamber 12c or when the substrate W is moved out of the processing chamber 12c, the substrate W passes through the channel 12p. In order to open and close the channel 12p, a gate valve 12g is provided along the side wall of the processing chamber body 12.

[0020] In the processing chamber 12c, the support portion 15 extends upward from the bottom of the processing chamber body 12. The support portion 15 has a substantially cylindrical shape and is formed of an insulating material such as ceramic. A work table 16 is arranged on the support portion 15. The work table 16 is supported by the support portion 15. The work table 16 is configured to support the substrate W in the processing chamber 12c. The work table 16 includes a lower electrode 18 and an electrostatic chuck 20. In one embodiment, the work table 16 further includes an electrode plate 21. The electrode plate 21 is formed of a conductive material such as aluminum and has a substantially disc shape. The lower electrode 18 is disposed on the electrode plate 21. The lower electrode 18 is formed of a conductive material such as aluminum and has a substantially disc shape. The lower electrode 18 is electrically connected to the electrode plate 21.

[0021] A flow path 18f is provided in the lower electrode 18. The flow path 18f is a flow path for a heat exchange medium. The heat exchange medium uses a liquid refrigerant or a refrigerant (chlorofluorocarbon refrigerant) that cools the lower electrode 18 by gasification. The heat exchange medium is supplied to the flow path 18f from a cooling unit provided outside the processing chamber body 12 through a pipe 23a. The heat exchange medium supplied to the flow path 18f returns to the cooling unit through a pipe 23b. That is, the heat exchange medium is supplied to the flow path 18f so as to circulate between the flow path 18f and the cooling unit.

[0022] The electrostatic chuck 20 is disposed on the lower electrode 18. The electrostatic chuck 20 has a body formed of an insulator and a film-shaped electrode disposed in the body. The electrodes of the electrostatic chuck 20 are electrically connected to a DC power supply. When a voltage is applied from the DC power supply to the electrodes of the electrostatic chuck 20, an electrostatic attraction is generated between the substrate W placed on the electrostatic chuck 20 and the electrostatic chuck 20. The substrate W is adsorbed to the electrostatic chuck 20 and held by the electrostatic chuck 20 by the generated electrostatic attraction. A focusing ring FR is disposed on the peripheral area of ​​the electrostatic chuck 20. The focusing ring FR has a substantially annular shape and is formed, for example, of silicon. The focusing ring FR is disposed so as to surround the edge of the substrate W.

[0023] The plasma processing apparatus 10 is provided with a gas supply line 25. The gas supply line 25 supplies a heat transfer gas, such as helium gas, from a gas supply mechanism to a space between the upper surface of the electrostatic chuck 20 and the back surface (lower surface) of the substrate W.

[0024] The cylindrical portion 28 extends upward from the bottom of the processing chamber body 12. The cylindrical portion 28 extends along the outer periphery of the support portion 15. The cylindrical portion 28 is formed of a conductive material and has a substantially cylindrical shape. The cylindrical portion 28 is connected to the ground potential. An insulating portion 29 is provided on the cylindrical portion 28. The insulating portion 29 has insulating properties and is formed of, for example, quartz or ceramic. The insulating portion 29 extends along the outer periphery of the workpiece stage 16.

[0025] The plasma processing device 10 further includes an upper electrode 30. The upper electrode 30 is disposed above the workpiece stage 16. The upper electrode 30 and the member 32 together seal the upper opening of the processing chamber body 12. The member 32 has insulating properties. The upper electrode 30 is supported on the upper part of the processing chamber body 12 through the member 32. When the first RF power supply 61 described later is electrically connected to the lower electrode 18, the upper electrode 30 is connected to the ground potential.

[0026] The upper electrode 30 includes a top plate 34 and a support 36. The lower surface of the top plate 34 defines the processing chamber 12c. The top plate 34 is provided with a plurality of gas exhaust holes 34a. Each of the plurality of gas exhaust holes 34a penetrates the top plate 34 in the plate thickness direction (in the vertical direction). The top plate 34 is not limited, and is formed of silicon, for example. Alternatively, the top plate 34 may be a structure in which a plasma-resistant film is provided on the surface of an aluminum substrate. The film may be a ceramic film such as a film formed by anodization or a film formed of yttrium oxide.

[0027] The support body 36 is a component that detachably supports the top plate 34. The support body 36 can be formed of a conductive material such as aluminum. A gas diffusion chamber 36a is provided inside the support body 36. A 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. A gas inlet 36c for introducing gas into the gas diffusion chamber 36a is formed in the support body 36, and the gas inlet 36c is connected to a gas supply pipe 38.

[0028] The gas supply pipe 38 is connected to the gas source group 40 through the switch valve group 42 and the flow controller group 44. The gas source group 40 includes a plurality of gas sources. The switch valve group 42 includes a plurality of switch valves. The flow controller group 44 includes a plurality of flow controllers. The plurality of flow controllers of the flow controller group 44 are respectively mass flow controllers or pressure-controlled flow controllers. The plurality of gas sources of the gas source group 40 are connected to the gas supply pipe 38 through the switch valves corresponding to the switch valve group 42 and the flow controllers corresponding to the flow controller group 44. The plasma processing apparatus 10 can select one or more gas sources from the plurality of gas sources of the gas source group 40 and supply the gas to the processing chamber 12c at individually adjusted flow rates.

[0029] A buffer plate 48 is provided between the cylindrical portion 28 and the side wall of the processing chamber body 12. For example, the buffer plate 48 may be formed of a ceramic in which yttrium oxide or the like is coated on an aluminum substrate. A plurality of through holes are formed in the buffer plate 48. Below the buffer plate 48, an exhaust pipe 52 is connected to the bottom of the processing chamber body 12. The exhaust pipe 52 is connected to an exhaust device 50. The exhaust device 50 has a pressure controller such as an automatic pressure control valve and a vacuum pump such as a turbomolecular pump, which can reduce the pressure of the processing chamber 12c.

[0030] As shown in FIG. 1 and FIG. 2 , the plasma processing apparatus 10 further includes a first RF power source 61. The first RF power source 61 is a power source for generating a first RF signal, which is used to excite the gas in the processing chamber 12 c to generate plasma. The first RF signal has a frequency in the range of 27 to 100 MHz, for example, a frequency of 60 MHz. The first RF power source 61 is connected to the lower electrode 18 through the first matching circuit 65 of the matcher 64 and the electrode plate 21. The first matching circuit 65 is a circuit for matching the output impedance of the first RF power source 61 with the impedance of the load side (the lower electrode 18 side). In addition, the first RF power source 61 may not be electrically connected to the lower electrode 18 or may be connected to the upper electrode 30 through the first matching circuit 65.

[0031] The plasma processing apparatus 10 further includes a second RF power source 62. The second RF power source 62 is a power source for generating a second RF signal for biasing, which is used to attract ions to the substrate W. The frequency of the second RF signal is lower than the frequency of the first RF signal. The frequency of the second RF signal is a frequency in the range of 400kHz to 13.56MHz, for example, 400kHz. The second RF power source 62 is connected to the lower electrode 18 through the second matching circuit 66 of the matcher 64 and the electrode plate 21. The second matching circuit 66 is a circuit for matching the output impedance of the second RF power source 62 with the impedance of the load side (lower electrode 18 side).

[0032] The plasma processing device 10 further includes a DC power supply 70 and a switching unit 72. The DC power supply 70 is a power supply that generates a negative DC voltage. The negative DC voltage is used as a bias voltage to attract ions to the substrate W placed on the workpiece stage 16. The DC power supply 70 is connected to the switching unit 72. The switching unit 72 is connected to the lower electrode 18 through the RF filter 74. In the plasma processing device 10, any one of the DC voltage generated by the DC power supply 70 and the second RF signal generated by the second RF power supply 62 is selectively supplied to the lower electrode 18.

[0033] The plasma processing apparatus 10 further includes a controller PC. The controller PC is configured to control the switching unit 72. The controller PC may be configured to further control one or both of the first RF power source 61 and the second RF power source 62.

[0034] In one embodiment, the plasma processing device 10 may also include a main control unit MC. The main control unit MC is a computer, which includes a processor, a memory device, an input device, and a display device, and controls various parts of the plasma processing device 10. Specifically, the main control unit MC executes a control program stored in the memory device, and controls various parts of the plasma processing device 10 according to the recipe data stored in the memory device. The plasma processing device 10 performs the processing specified by the recipe data through such control.

[0035] 2 and 3. FIG3 is a diagram showing the circuit configuration of the DC power supply, the switching unit, the RF filter and the matching device shown in FIG2. The DC power supply 70 is a variable DC power supply that generates a negative DC voltage and applies it to the lower electrode 18.

[0036] The switching unit 72 is configured to stop applying the DC voltage from the DC power supply 70 to the lower electrode 18. In one embodiment, the switching unit 72 includes a field effect transistor (FET) 72a, a FET 72b, a capacitor 72c, and a resistor 72d. FET 72a is, for example, an N-channel MOSFET. FET 72b is, for example, a P-channel MOSFET. The source of FET 72a is connected to the negative electrode of the DC power supply 70. The negative electrode of the DC power supply 70 and the source of FET 72a are connected to one end of the capacitor 72c. The other end of the capacitor 72c is connected to the source of FET 72b. The source of FET 72b is grounded. The gate of FET 72a and the gate of FET 72b are connected to each other. A pulse control signal from the controller PC is supplied to a node NA connected between the gate of FET 72a and the gate of FET 72b. The drain of FET 72a is connected to the drain of FET 72b. The node NB connected between the drain of FET 72a and the drain of FET 72b is connected to the RF filter 74 through the resistor element 72d.

[0037] The RF filter 74 is a filter for reducing or blocking RF signals. In one embodiment, the RF filter 74 has an inductor 74a and a capacitor 74b. One end of the inductor 74a is connected to the resistor 72d. One end of the inductor 74a is also connected to one end of the capacitor 74b. The other end of the capacitor 74b is grounded. The other end of the inductor 74a is connected to the matcher 64.

[0038] The matching device 64 includes a first matching circuit 65 and a second matching circuit 66. In one embodiment, the first matching circuit 65 includes a variable capacitor 65a and a variable capacitor 65b, and the second matching circuit 66 includes a variable capacitor 66a and a variable capacitor 66b. One end of the variable capacitor 65a is connected to the other end of the inductor 74a. The other end of the variable capacitor 65a is connected to the first RF power supply 61 and one end of the variable capacitor 65b. The other end of the variable capacitor 65b is grounded. One end of the variable capacitor 66a is connected to the other end of the inductor 74a. The other end of the variable capacitor 66a is connected to the second RF power supply 62 and one end of the variable capacitor 66b. The other end of the variable capacitor 66b is grounded. One end of the variable capacitor 65a and one end of the variable capacitor 66a are connected to the terminal 64a of the matching device 64. The terminal 64a of the matching device 64 is connected to the lower electrode 18 through the electrode plate 21.

[0039] The control by the main control unit MC and the controller PC is described below. The following description refers to FIG. 2 and FIG. 4. FIG. 4 is a time chart related to a plasma processing method of an embodiment performed using the plasma processing apparatus shown in FIG. 1. The horizontal axis in FIG. 4 represents time, and the vertical axis in FIG. 4 represents the power of the first RF signal, the DC voltage applied to the lower electrode 18 from the DC power supply 70, and the control signal output by the controller PC. In FIG. 4, the power of the first RF signal is at a high level, indicating that the first RF signal is supplied in order to generate plasma. The power of the first RF signal is at a low level, indicating that the supply of the first RF signal is stopped. In addition, in FIG. 4, the DC voltage is at a low level, indicating that a negative DC voltage is applied to the lower electrode 18 from the DC power supply 70, and the DC voltage is 0V, indicating that no DC voltage is applied to the lower electrode 18 from the DC power supply 70.

[0040] The main control unit MC specifies the power and frequency of the first RF signal to the first RF power supply 61. In addition, in one embodiment, the main control unit MC specifies the time point of starting to supply the first RF signal and the time point of ending to supply the first RF signal to the first RF power supply 61. During the period when the first RF signal is supplied by the first RF power supply 61, gas plasma is generated in the processing chamber. That is, in order to generate plasma, the step S1 of supplying the RF signal from the RF power supply is performed during this period. In addition, in the example of FIG. 4, the first RF signal is continuously supplied during the plasma processing method of one embodiment.

[0041] The main control unit MC specifies the frequency and duty ratio of the cycle in which the negative-polarity DC voltage from the DC power supply 70 is applied to the lower electrode 18 to the controller PC. The duty ratio is the ratio of the period ("T1" in FIG. 4) in which the negative-polarity DC voltage from the DC power supply 70 is applied to the lower electrode 18 within one cycle ("PDC" in FIG. 4). The duty ratio is set to be less than 40%. In one embodiment, the duty ratio is set to be less than 35%.

[0042] The controller PC generates a control signal in response to the frequency and duty ratio specified by the main control unit MC. The control signal generated by the controller PC may be a pulse signal. As shown in FIG4 , in one example, the control signal generated by the controller PC has a high level during period T1 and a low level during period T2. Period T2 is a period other than period T1 within one cycle PDC. Alternatively, the control signal generated by the controller PC may have a low level during period T1 and a high level during period T2.

[0043] In one embodiment, a control signal generated by the controller PC is applied to the node NA of the switching unit 72. When the control signal is applied, the switching unit 72 connects the DC power supply 70 and the node NB to each other during the period T1, so that the negative DC voltage from the DC power supply 70 is applied to the lower electrode 18. On the other hand, the switching unit 72 disconnects the DC power supply 70 from the node NB during the period T2, so that the negative DC voltage from the DC power supply 70 is not applied to the lower electrode 18. Thus, as shown in FIG. 4, the negative DC voltage from the DC power supply 70 is applied to the lower electrode 18 during the period T1, and the application of the negative DC voltage from the DC power supply 70 to the lower electrode 18 is stopped during the period T2. That is, in one embodiment of the plasma processing method, step S2 of periodically applying the negative DC voltage from the DC power supply 70 to the lower electrode 18 is performed.

[0044] Here, refer to FIG. 5(a) and FIG. 5(b). FIG. 5(a) and FIG. 5(b) are time diagrams showing the potential of plasma. During period T1, a negative DC voltage from a DC power supply 70 is applied to the lower electrode 18, so that positive ions in the plasma move toward the substrate W. Therefore, as shown in FIG. 5(a) and FIG. 5(b), during period T1, the potential of the plasma becomes low. On the other hand, during period T2, the negative DC voltage from the DC power supply 70 is stopped from being applied to the lower electrode 18, so that the movement of positive ions becomes less, and mainly the electrons in the plasma move. Therefore, during period T2, the potential of the plasma becomes high.

[0045] In the time chart shown in FIG5(a), the duty ratio is smaller than that in the time chart shown in FIG5(b). If the conditions for generating plasma are the same, the total amount of positive ions and the total amount of electrons in the plasma are independent of the duty ratio. That is, the ratio of area A1 to area A2 shown in FIG5(a) becomes the same as the ratio of area A1 to area A2 shown in FIG5(b). Therefore, if the duty ratio is small, the potential PV of the plasma during period T2 becomes small.

[0046] The etching rate of the substrate W is less dependent on the duty ratio, that is, the ratio of the period T1 during which the negative polarity DC voltage is applied to the lower electrode 18 in each cycle PDC. On the other hand, when the duty ratio is small, especially when the duty ratio is below 40%, the potential of the plasma becomes smaller, and thus the etching rate of the processing chamber body 12 is greatly reduced. Therefore, by setting the above-mentioned duty ratio for periodically applying the negative polarity DC voltage to the lower electrode 18 to below 40%, the etching rate of the substrate W can be suppressed from decreasing, and the energy of the ions irradiated to the inner wall of the processing chamber body 12 can be reduced. As a result, the generation of particles from the processing chamber body 12 is suppressed. When the duty ratio is below 35%, the energy of the ions irradiated to the inner wall of the processing chamber body 12 can be further reduced.

[0047] Hereinafter, another embodiment will be described. FIG. 6(a) and FIG. 6(b) are time charts related to another embodiment of the plasma processing method. The horizontal axis of each of FIG. 6(a) and FIG. 6(b) represents time. The vertical axis of each of FIG. 6(a) and FIG. 6(b) represents the power of the first RF signal and the DC voltage applied to the lower electrode 18 from the DC power supply 70. In each of FIG. 6(a) and FIG. 6(b), the power of the first RF signal is at a high level, indicating that the first RF signal is supplied to generate plasma, and the power of the first RF signal is at a low level, indicating that the supply of the first RF signal is stopped. In addition, in each of FIG. 6(a) and FIG. 6(b), the DC voltage is at a low level, indicating that a negative DC voltage is applied to the lower electrode 18 from the DC power supply 70, and the DC voltage is 0V, indicating that no DC voltage is applied to the lower electrode 18 from the DC power supply 70.

[0048] In the embodiment shown in FIG6(a), a negative DC voltage from a DC power supply 70 is periodically applied to the lower electrode 18, or a first radio frequency signal is periodically supplied in order to generate plasma. In the embodiment shown in FIG6(a), the negative DC voltage from the DC power supply 70 is applied to the lower electrode 18 synchronously with the supply of the first radio frequency signal. That is, the first radio frequency signal is supplied during the period T1 when the DC voltage from the DC power supply 70 is applied to the lower electrode 18, and the supply of the first radio frequency signal is stopped during the period T2 when the DC voltage from the DC power supply 70 is stopped.

[0049] In the embodiment shown in FIG6(b), a negative polarity DC voltage from a DC power supply 70 is periodically applied to the lower electrode 18, or a first radio frequency signal is periodically supplied in order to generate plasma. In the embodiment shown in FIG6(b), the phase of the first radio frequency signal is reversed relative to the phase of the negative polarity DC voltage from the DC power supply 70 periodically applied to the lower electrode 18. That is, the first radio frequency signal is stopped during the period T1 when the DC voltage from the DC power supply 70 is applied to the lower electrode 18, and the first radio frequency signal is supplied during the period T2 when the DC voltage from the DC power supply 70 is stopped.

[0050] In the embodiment shown in FIG6(a) and the embodiment shown in FIG6(b), the control signal from the controller PC is applied to the first RF power supply 61. The first RF power supply 61 starts supplying the first RF signal at the time when the control signal from the controller PC rises (or falls), and stops supplying the first RF signal at the time when the control signal from the controller PC falls (or rises). In the embodiment shown in FIG6(a) and the embodiment shown in FIG6(b), the generation of unexpected RF signals caused by intermodulation distortion is suppressed.

[0051] Several other embodiments of plasma processing apparatus are described below. FIG. 7 is a diagram showing a power supply system and a control system of a plasma processing apparatus of another embodiment. As shown in FIG. 7 , the difference between the plasma processing apparatus 10A of another embodiment and the plasma processing apparatus 10 is that the first RF power supply 61 includes a controller PC. That is, the controller PC in the plasma processing apparatus 10A is a part of the first RF power supply 61. On the other hand, in the plasma processing apparatus 10, the controller PC is separated from the first RF power supply 61 and the second RF power supply 62. In the plasma processing apparatus 10A, the controller PC is a part of the first RF power supply 61, so the above-mentioned control signal (pulse signal) from the controller PC is not sent to the first RF power supply 61.

[0052] FIG8 is a diagram showing a power supply system and a control system of a plasma processing apparatus according to another embodiment. The plasma processing apparatus 10B shown in FIG8 includes a plurality of DC power supplies 701 and 702 and a plurality of switching units 721 and 722. The plurality of DC power supplies 701 and 702 are respectively the same power supplies as the DC power supply 70, and are configured to generate a negative DC voltage and apply it to the lower electrode 18. The plurality of switching units 721 and 722 have the same configuration as the switching unit 72. The DC power supply 701 is connected to the switching unit 721. The switching unit 721 is configured to stop applying the DC voltage from the DC power supply 701 to the lower electrode 18, similarly to the switching unit 72. The DC power supply 702 is connected to the switching unit 722. The switching unit 722 is configured to stop applying the DC voltage from the DC power supply 702 to the lower electrode 18, similarly to the switching unit 72.

[0053] FIG9 is a time chart showing a plasma processing method according to an embodiment performed using the plasma processing apparatus shown in FIG8. The horizontal axis in FIG9 represents time, and the vertical axis in FIG9 represents the synthesized DC voltage (i.e., the DC voltage applied to the lower electrode 18), the DC voltage of the DC power supply 701 (i.e., the DC voltage applied to the lower electrode from the DC power supply 701), and the DC voltage of the DC power supply 702 (i.e., the DC voltage applied to the lower electrode from the DC power supply 702). As shown in FIG9, in the plasma processing apparatus 10B, the DC voltage applied to the lower electrode 18 in each cycle PDC is formed by a plurality of DC voltages sequentially output from a plurality of DC power supplies 701 and 702. That is, in the plasma processing apparatus 10B, the DC voltage applied to the lower electrode 18 in each cycle PDC is generated by the temporal synthesis of a plurality of DC voltages sequentially output from a plurality of DC power supplies 701 and 702. According to the plasma processing apparatus 10B, the load of each of the plurality of DC power supplies 701 and 702 is reduced.

[0054] In the plasma processing apparatus 10B, the controller PC supplies a control signal to the switching unit 721, and the control signal is a control signal having a high level (or a low level) during the period when the DC voltage from the DC power supply 701 is applied to the lower electrode 18, and having a low level (or a high level) during the period when the DC voltage from the DC power supply 701 is not applied to the lower electrode 18. In addition, the controller PC supplies a control signal to the switching unit 722, and the control signal is a control signal having a high level (or a low level) during the period when the DC voltage from the DC power supply 702 is applied to the lower electrode 18, and having a low level (or a high level) during the period when the DC voltage from the DC power supply 702 is not applied to the lower electrode 18. That is, control signals (pulse signals) having different phases are respectively supplied to a plurality of switching units connected to a plurality of DC power supplies.

[0055] FIG. 10 is a diagram showing a power supply system and a control system of a plasma processing apparatus according to another embodiment. The plasma processing apparatus 10C shown in FIG. 10 is different from the plasma processing apparatus 10 in that it further includes a waveform shaper 76. The waveform shaper 76 is connected between the switching unit 72 and the radio frequency filter 74. The waveform shaper 76 shapes the waveform of the DC power source output from the DC power source 70 via the switching unit 72, that is, the DC voltage having a negative polarity value and a 0V value alternately. Specifically, the waveform shaper 76 shapes the waveform of the DC voltage so that the waveform of the DC voltage applied to the lower electrode 18 has a substantially triangular waveform. The waveform shaper 76 is, for example, an integrating circuit.

[0056] FIG. 11 is a circuit diagram showing an example of a waveform shaper 76. The waveform shaper 76 shown in FIG. 11 is constituted by an integrating circuit and includes a resistor 76a and a capacitor 76b. One end of the resistor 76a is connected to the resistor 72d of the switching unit 72, and the other end of the resistor 76a is connected to the radio frequency filter 74. One end of the capacitor 76b is connected to the other end of the resistor 76a. The other end of the capacitor 76b is grounded. In the waveform shaper 76 shown in FIG. 11, a delay occurs when the DC voltage output from the switching unit 72 rises and falls due to a time constant determined by the resistance value of the resistor 76a and the electrostatic capacitance value of the capacitor 76b. Therefore, according to the waveform shaper 76 shown in FIG. 11, a voltage having a waveform similar to a triangular wave can be applied to the lower electrode 18. According to the plasma processing apparatus 10C having such a waveform shaper 76, the energy of ions irradiated to the inner wall of the processing chamber body 12 can be adjusted.

[0057] Various embodiments have been described above, but the present invention is not limited to the above embodiments, and various deformation modes can be formed. For example, the plasma processing device of the above various embodiments may not have the second RF power supply 62. That is, the plasma processing device of the above various embodiments may have a single RF power supply.

[0058] In addition, in the above-mentioned various embodiments, the application or stop of the negative polarity DC voltage from the DC power supply to the lower electrode 18 is switched by the switching unit, but if the DC power supply itself is constructed to switch the output or stop the output of the negative polarity DC voltage, then the switching unit is not required.

[0059] In addition, the structural features of the various embodiments described above can be applied in any combination. Furthermore, the plasma processing device of the various embodiments described above is a capacitive coupling type plasma processing device, but the modified plasma processing device can also be an inductive coupling type plasma processing device.

[0060] In addition, when the duty ratio is high, the energy of the ions irradiated to the inner wall of the processing chamber body 12 becomes larger. Therefore, by setting the duty ratio to a high value, for example, setting the duty ratio to a value greater than 40%, the inner wall of the processing chamber body 12 can be cleaned.

[0061] Next, an evaluation test performed on the plasma processing method used in the plasma processing apparatus 10 will be described.

[0062] (1st Assessment Test)

[0063] In the first evaluation test, the sample with the silicon oxide film was attached to the surface of the top plate 34 of the plasma processing device 10 on the processing chamber 12c side and the side wall of the processing chamber body 12, and the sample with the silicon oxide film was placed on the electrostatic chuck 20, and plasma processing was performed under the following conditions. In addition, in the first evaluation test, the duty ratio of the negative polarity DC voltage periodically applied to the lower electrode 18 was used as a variable parameter.

[0064] <Conditions of Plasma Treatment in the First Evaluation Test> ･Pressure of processing chamber 12c: 20mTorr (2.66Pa) ･The flow rate of gas supplied to the processing chamber 12c C 4F 8 gas: 24sccm O2 gas: 16sccm Ar gas: 150sccm ･1st RF signal: 100MHz, 500W continuous wave ･A negative DC voltage is applied to the lower electrode 18 Voltage value:-3000V Frequency:200kHz ･Processing time: 60 seconds

[0065] In the first evaluation test, the etching amount (film thickness reduction) of the sample silicon oxide film adhered to the surface of the top plate 34 on the processing chamber 12c side, the etching amount (film thickness reduction) of the sample silicon oxide film adhered to the side wall of the processing chamber body 12, and the etching amount (film thickness reduction) of the sample silicon oxide film placed on the electrostatic chuck 20 were measured. FIG. 12(a) is a graph showing the relationship between the working ratio obtained in the first evaluation test and the etching amount of the sample silicon oxide film adhered to the surface of the top plate 34 on the processing chamber 12c side. FIG. 12(b) is a graph showing the relationship between the working ratio obtained in the first evaluation test and the etching amount of the sample silicon oxide film adhered to the side wall of the processing chamber body 12. FIG. 13 is a graph showing the relationship between the working ratio obtained in the first evaluation test and the etching amount of the sample silicon oxide film placed on the electrostatic chuck 20.

[0066] As shown in FIG. 13 , the etching amount of the sample silicon oxide film placed on the electrostatic chuck 20 is very little dependent on the working ratio. In addition, as shown in FIG. 12 (a) and FIG. 12 (b), when the working ratio is less than 35%, the etching amount of the sample silicon oxide film adhered to the surface of the top plate 34 on the side of the processing chamber 12c and the etching amount of the sample silicon oxide film adhered to the side wall of the processing chamber body 12 become very small. Therefore, by the first evaluation test, it was confirmed that the etching rate of the substrate is very little dependent on the working ratio of the period during which the negative polarity DC voltage is applied to the lower electrode 18 in each cycle PDC. In addition, in the case of a small working ratio, especially in the case of a working ratio of less than 35%, it was confirmed that the etching rate of the processing chamber body 12 was greatly reduced, that is, the energy of the ions irradiated to the inner wall of the processing chamber body 12 became smaller. In addition, from the graphs of Figures 12(a) and 12(b), it can be inferred that if the working ratio is below 40%, the energy of the ions irradiated to the inner wall of the processing chamber body 12 becomes very small.

[0067] (Second Assessment Test)

[0068] In the second evaluation test, the sample with the silicon oxide film was adhered to the surface of the top plate 34 of the plasma processing device 10 on the side of the processing chamber 12c and the side wall of the processing chamber body 12, and the sample with the silicon oxide film was also placed on the electrostatic chuck 20, and plasma processing was performed according to the conditions shown below.

[0069] <Conditions of Plasma Treatment in the Second Evaluation Test> ･Pressure of processing chamber 12c: 20mTorr (2.66Pa) ･The flow rate of gas supplied to the processing chamber 12c C 4F 8 gas: 24sccm O2 gas: 16sccm Ar gas: 150sccm ･1st RF signal: 100MHz, 500W continuous wave ･A negative DC voltage is applied to the lower electrode 18 Voltage value:-3000V Frequency:200kHz Working ratio: 35% ･Processing time: 60 seconds

[0070] In addition, in the comparative test, the sample with the silicon oxide film was attached to the surface of the top plate 34 of the plasma processing device 10 on the processing chamber 12c side and the side wall of the processing chamber body 12, and the sample with the silicon oxide film was placed on the electrostatic chuck 20, and the plasma treatment was performed under the conditions shown below. In addition, the conditions of the second radio frequency signal in the comparative test were set so that the etching amount (film thickness reduction amount) of the silicon oxide film of the sample placed on the electrostatic chuck 20 after the plasma treatment of the second evaluation test and the plasma treatment of the comparative test was substantially the same.

[0071] <Comparative Evaluation Test Conditions for Plasma Treatment> ･Pressure of processing chamber 12c: 20mTorr (2.66Pa) ･The flow rate of gas supplied to the processing chamber 12c C 4F 8 gas: 24sccm O2 gas: 16sccm Ar gas: 150sccm ･1st RF signal: 100MHz, 500W continuous wave ･2nd RF signal: 400kHz, 2500W continuous wave ･Processing time: 60 seconds

[0072] In the second evaluation test and the comparative test, the etching amount (film thickness reduction) of the sample silicon oxide film attached to the surface of the top plate 34 on the processing chamber 12c side and the etching amount (film thickness reduction) of the sample silicon oxide film attached to the side wall of the processing chamber body 12 were measured respectively. FIG. 14(a) is a graph showing the etching amount of the sample silicon oxide film attached to the surface of the top plate 34 on the processing chamber 12c side obtained in the second evaluation test and the comparative test respectively, and FIG. 14(b) is a graph showing the etching amount of the sample silicon oxide film attached to the side wall of the processing chamber body 12 obtained in the second evaluation test and the comparative test respectively. In the graph of FIG. 14(a), the horizontal axis represents the distance from the center of the processing chamber 12c in the radial direction of the measurement position in the sample attached to the surface of the top plate 34 on the processing chamber 12c side, and the vertical axis represents the etching amount of the sample silicon oxide film attached to the surface of the top plate 34 on the processing chamber 12c side. In the curve graph of Figure 14(b), the horizontal axis represents the distance in the vertical direction from the surface of the top plate 34 on the side of the processing chamber 12c of the measurement position in the sample pasted on the side wall of the processing chamber 12c, and the vertical axis represents the etching amount of the silicon oxide film of the sample pasted on the side wall of the processing chamber 12c.

[0073] As shown in FIG. 14(a) and FIG. 14(b), in the second evaluation test in which a negative polarity DC voltage is periodically applied to the lower electrode 18, the etching amount of the sample silicon oxide film adhered to the surface of the top plate 34 on the processing chamber 12c side and the sample silicon oxide film adhered to the side wall of the processing chamber body 12 becomes very small compared to the comparative test using the second radio frequency signal. Therefore, compared to the case of using the second radio frequency signal, i.e., the radio frequency signal for bias, it is confirmed that by periodically applying a negative polarity DC voltage to the lower electrode 18, the energy of the ions irradiated to the substrate on the electrostatic chuck 20 can be suppressed from decreasing and the energy of the ions irradiated to the wall surface of the processing chamber body 12 and the wall surface of the upper electrode 30 can be greatly reduced.

[0074] 10,10A,10B,10C: Plasma treatment device 12: Processing chamber body 12c: Processing room 12g: Gate valve 12p: Channel 15: Supporting part 16: Workpiece table 18: Lower electrode 18f: Flow path 20: Electrostatic chuck 21: Electrode plate 23a,23b:Piping 25: Gas supply pipeline 28:Tubular part 29: Insulation 30: Upper electrode 32: Component 34: Top plate 34a: discharge hole 36: Support body 36a: Gas diffusion chamber 36b: Gas hole 36c: Gas inlet 38: Gas supply pipe 40: Gas source group 42: Switch valve group 44: Traffic controller group 48: Buffer plate 50: Exhaust 52: Exhaust pipe 61: No. 1 RF power supply 62: Second RF power supply 64:Matcher 64a:Terminal 65: 1st matching circuit 65a, 65b, 66a, 66b: variable capacitor 66: Second matching circuit 70,701,702: DC power supply 72,721,722: Switching unit 72a,72b:FET 72c,74b,76b: Capacitor 72d,76a: Resistor element 74: RF filter 74a: Inductor 76: Waveform Shaper A1, A2: Area FR: Focus ring MC: Main Control Unit NA,NB:Node PC: Controller PDC: Cycle PV: Potential S1, S2: Steps T1, T2: Period W: substrate

Claims

1. A plasma processing apparatus comprising: a processing chamber body providing a processing chamber; a radio frequency power supply supplying a radio frequency signal for exciting a gas supplied to the processing chamber; a worktable disposed within the processing chamber body and including a lower electrode and an electrostatic chuck; a switching unit electrically connected to the worktable and including a first transistor and a second transistor connected in series; a DC power supply electrically connected to the switching unit; and a controller electrically connected to the first transistor and the second transistor; the controller controlling the switching unit by periodically switching control signals applied to the first transistor and the second transistor, such that a state of applying a DC voltage from the DC power supply to the worktable and a state of not applying a DC voltage from the DC power supply to the worktable are periodically repeated; the supply of the radio frequency signal is stopped during the period when the DC voltage is applied to the worktable, and the radio frequency signal is supplied during the period when the DC voltage is stopped from being applied to the worktable.

2. The plasma processing apparatus as described in claim 1, wherein, The first transistor is a first field-effect transistor; the second transistor is a second field-effect transistor having a channel polarity different from that of the first field-effect transistor.

3. The plasma treatment apparatus as described in claim 2, wherein, The controller is electrically connected to the gate of the first field-effect transistor and the gate of the second field-effect transistor.

4. The plasma processing apparatus as described in any one of claims 1 to 3, wherein, An RF filter is configured between the switching unit and the worktable.

5. The plasma treatment apparatus as described in claim 4, wherein, The switching unit includes a resistive element electrically connected to the first transistor and the second transistor; the radio frequency filter is disposed between the resistive element and the worktable.

6. The plasma processing apparatus as described in any one of claims 1 to 3, wherein, The controller controls the switching unit to set the proportion of the period during which the DC voltage is applied to the worktable in each cycle, which includes a state in which the DC voltage from the DC power supply is applied to the worktable and a state in which the DC voltage from the DC power supply is not applied to the worktable, to be less than 40%.

7. The plasma treatment apparatus as described in claim 6, wherein, The controller controls the switching unit to set the proportion of the period in each cycle, which includes a state where the DC voltage from the DC power supply is applied to the worktable and a state where the DC voltage from the DC power supply is not applied to the worktable, to be less than 35%.

8. The plasma processing apparatus as described in any one of claims 1 to 3, wherein, The radio frequency signal is supplied during the period when the DC voltage is applied to the worktable, and the supply of the radio frequency signal is stopped during the period when the DC voltage is stopped applied to the worktable.

9. The plasma processing apparatus as described in any one of claims 1 to 3, wherein, This DC voltage has a negative polarity.

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