Plasma processing device

Abstract

This plasma processing device comprises: a chamber; a substrate support part including a lower electrode; an RF generation unit for generating a pulsed RF signal having a first power level in a first period in each cycle and having a second power level less than the first power level in a second period in each cycle, in order to generate plasma in the chamber; a pulsed voltage generation unit electrically connected to the lower electrode and generating a pulsed voltage signal having a reference voltage level within the first period and a sequence of a plurality of voltage pulses having a first voltage level in the second period, wherein the absolute value of the first voltage level being greater than the absolute value of the reference voltage level; a microwave interferometer for monitoring the electron density of the plasma in the chamber; and a control unit for adjusting the first power level on the basis of the electron density in the first period and adjusting the first voltage level on the basis of the electron density in the second period.

Description

Plasma processing equipment

[0001] The present disclosure relates to a plasma processing apparatus.

[0002] The etching apparatus disclosed in Patent Document 1 is an etching apparatus comprising a substrate electrode that applies high-frequency power to a substrate to be etched, and a source electrode that generates plasma supplied to the substrate electrode, and is also provided with an electron density control means that controls the high-frequency power applied to the source electrode so that the electron density in the plasma supplied to the substrate electrode becomes a predetermined set value, and an ion energy control means that controls the high-frequency power applied to the substrate electrode so that the ion energy in the plasma supplied to the substrate electrode becomes a predetermined set value.

[0003] Japanese Patent Application Laid-Open No. 2004-128236

[0004] The present disclosure provides a plasma processing apparatus capable of suppressing changes in plasma conditions over time.

[0005] According to one aspect of the present disclosure, a plasma processing apparatus includes: a chamber; a substrate support disposed within the chamber and including a lower electrode; an RF generator configured to generate a pulsed RF signal to generate a plasma within the chamber, the pulsed RF signal having a first power level during a first period within each cycle and a second power level during a second period within each cycle that is less than the first power level; a pulsed voltage generator electrically connected to the lower electrode and configured to generate a pulsed voltage signal, the pulsed voltage signal having a sequence of multiple voltage pulses having a reference voltage level during the first period and the first voltage level during the second period, the absolute value of the first voltage level being greater than the absolute value of the reference voltage level; a microwave interferometer configured to monitor an electron density of plasma within the chamber; and a controller configured to adjust the first power level based on the monitored electron density of the plasma during the first period and to adjust the first voltage level based on the monitored electron density of the plasma during the second period.

[0006] According to the present disclosure, it is possible to suppress changes in plasma conditions over time.

[0007] FIG. 1 is a diagram illustrating an example of a plasma processing system according to a first embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view illustrating an example of the configuration of a plasma processing apparatus according to the first embodiment. FIG. 3 is a timing chart illustrating an example of changes in electron density and supply timing of RF power and DC pulses in the first embodiment. FIG. 4 is a timing chart illustrating an example of supply timing of RF power and DC pulses in the first embodiment. FIG. 5 is a timing chart illustrating an enlarged portion of the timing chart illustrated in FIG. 4. FIG. 6 is a timing chart illustrating an example of changes in electron density and supply timing of RF power and DC pulses in the first embodiment. FIG. 7 is a diagram illustrating an example of changes in electron density near the offset period when the amount of deposition is at an appropriate level. FIG. 8 is a diagram schematically illustrating deposition and etching when the amount of deposition is at an appropriate level. FIG. 9 is a diagram illustrating an example of changes in electron density near the offset period when the amount of deposition is insufficient. FIG. 10 is a diagram schematically illustrating deposition and etching when the amount of deposition is insufficient. FIG. 11 is a diagram illustrating an example of changes in electron density near the offset period when the amount of deposition is excessive. FIG. 12 is a diagram schematically illustrating deposition and etching when the amount of deposition is excessive. FIG. 13 is a diagram illustrating an example of a method for adjusting electron density at the start timing of period P1. FIG. 14 is a diagram illustrating an example of a method for adjusting electron density at the start timing of period P1. FIG. 15 is a flowchart illustrating an example of a plasma control process according to the first embodiment. FIG. 16 is a diagram illustrating an example of a timing chart for one cycle of a synchro pulse. FIG. 17 is a diagram illustrating an example of a timing chart for one cycle of an offset pulse. FIG. 18 is a diagram illustrating an example of a timing chart for one cycle of an offset pulse. FIG. 19 is a diagram illustrating an example of a timing chart for one cycle of an offset pulse. FIG. 20 is a graph illustrating an example of a change in electron density during a repetition period in the second embodiment. FIG. 21 is a flowchart illustrating an example of a plasma control process according to the second embodiment.

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the plasma processing apparatus will be described in detail below with reference to the accompanying drawings. However, the disclosed technology is not limited to the following embodiments.

[0009] In etching processes, the power level of the RF power supply (source RF power) is set as one of the process conditions for generating plasma. However, when etching processes are performed over a long period of time, the impedance of the chamber as seen from the RF power supply changes due to wear on parts in the chamber and the accumulation of by-products (deposits) on the parts. If the power level supplied from the RF power supply remains the same, a change in the chamber impedance over time will result in a change in the electron density of the generated plasma. In other words, the plasma condition will change over time. Such changes in the plasma condition over time can cause a decrease in the etching rate and changes in the etching profile (process shift). Therefore, it is desirable to suppress changes in the plasma condition over time.

[0010] First Embodiment [Configuration of Plasma Processing System] FIG. 1 is a diagram illustrating an example of a plasma processing system according to a first embodiment of the present disclosure. In this embodiment, the plasma processing system includes a plasma processing apparatus 1 and a controller 2. The plasma processing system is an example of a substrate processing system, and the plasma processing apparatus 1 is an example of a substrate processing apparatus. The plasma processing apparatus 1 includes a plasma processing chamber 10, a substrate support 11, and a plasma generation unit 12. The plasma processing chamber 10 has a plasma processing space. The plasma processing chamber 10 also has at least one gas supply port for supplying at least one processing gas to the plasma processing space and at least one gas exhaust port for exhausting gas from the plasma processing space. The gas supply port is connected to a gas supply unit 20 (described later), and the gas exhaust port is connected to an exhaust system 40 (described later). The substrate support 11 is disposed in the plasma processing space and has a substrate support surface for supporting a substrate.

[0011] The plasma generating unit 12 is configured to generate plasma from at least one processing gas supplied into the plasma processing space. The plasma generated in the plasma processing space may be capacitively coupled plasma (CCP), inductively coupled plasma (ICP), electron-cyclotron-resonance plasma (ECR), helicon wave plasma (HWP), or surface wave plasma (SWP). Various types of plasma generators may be used, including alternating current (AC) plasma generators and direct current (DC) plasma generators. In one embodiment, the AC signal (AC power) used in the AC plasma generator has a frequency in the range of 100 kHz to 10 GHz. Thus, AC signals include radio frequency (RF) signals and microwave signals. In one embodiment, the RF signal has a frequency in the range of 100 kHz to 150 MHz.

[0012] The control unit 2 processes computer-executable instructions that cause the plasma processing apparatus 1 to perform various processes described in this disclosure. The control unit 2 may be configured to control each element of the plasma processing apparatus 1 to perform various processes described herein. In one embodiment, part or all of the control unit 2 may be included in the plasma processing apparatus 1. The control unit 2 may include a processing unit 2a1, a storage unit 2a2, and a communication interface 2a3. The control unit 2 may be implemented by, for example, a computer 2a. The processing unit 2a1 may be configured to read a program from the storage unit 2a2 and execute the read program to perform various control operations. This program may be stored in the storage unit 2a2 in advance or may be acquired via a medium when needed. The acquired program is stored in the storage unit 2a2 and read from the storage unit 2a2 by the processing unit 2a1 for execution. The medium may be various storage media readable by the computer 2a or a communication line connected to the communication interface 2a3. The processing unit 2a1 may be a CPU (Central Processing Unit). The storage unit 2a2 may include a random access memory (RAM), a read-only memory (ROM), a hard disk drive (HDD), a solid state drive (SSD), or a combination thereof. The communication interface 2a3 may communicate with the plasma processing apparatus 1 via a communication line such as a local area network (LAN).

[0013] The following describes a configuration example of a capacitively coupled plasma processing apparatus as an example of the plasma processing apparatus 1. Fig. 2 is a schematic cross-sectional view showing an example of the configuration of the plasma processing apparatus according to the first embodiment.

[0014] The capacitively coupled plasma processing apparatus 1 includes a plasma processing chamber 10, a gas supply unit 20, a power supply 30, a microwave interferometer 35, and an exhaust system 40. The plasma processing apparatus 1 also includes a substrate support 11 and a gas inlet. The gas inlet is configured to introduce at least one process gas into the plasma processing chamber 10. The gas inlet includes a showerhead 13. The substrate support 11 is disposed within the plasma processing chamber 10. The showerhead 13 is disposed above the substrate support 11. In one embodiment, the showerhead 13 forms at least a portion of the ceiling of the plasma processing chamber 10. The plasma processing chamber 10 has a plasma processing space 10s defined by the showerhead 13, a sidewall 10a of the plasma processing chamber 10, and the substrate support 11. The plasma processing chamber 10 is grounded. The showerhead 13 and the substrate support 11 are electrically insulated from the housing of the plasma processing chamber 10.

[0015] The substrate support 11 includes a main body 111 and a ring assembly 112. The main body 111 has a central region 111a for supporting a substrate W and an annular region 111b for supporting the ring assembly 112. A wafer is an example of a substrate W. The annular region 111b of the main body 111 surrounds the central region 111a of the main body 111 in a plan view. The substrate W is disposed on the central region 111a of the main body 111, and the ring assembly 112 is disposed on the annular region 111b of the main body 111 so as to surround the substrate W on the central region 111a of the main body 111. Therefore, the central region 111a is also called a substrate support surface for supporting the substrate W, and the annular region 111b is also called a ring support surface for supporting the ring assembly 112.

[0016] In one embodiment, the main body 111 includes a base 1110 and an electrostatic chuck 1111. The base 1110 includes a conductive member. The conductive member of the base 1110 can function as a lower electrode. The electrostatic chuck 1111 is disposed on the base 1110. The electrostatic chuck 1111 includes a ceramic member 1111a and an electrostatic electrode 1111b disposed within the ceramic member 1111a. The ceramic member 1111a has a central region 111a. In one embodiment, the ceramic member 1111a also has an annular region 111b. Note that the annular region 111b may also be provided by another member surrounding the electrostatic chuck 1111, such as an annular electrostatic chuck or an annular insulating member. In this case, the ring assembly 112 may be disposed on the annular electrostatic chuck or the annular insulating member, or may be disposed on both the electrostatic chuck 1111 and the annular insulating member. Furthermore, at least one RF / DC electrode coupled to an RF power supply 31 and / or a DC power supply 32, which will be described later, may be disposed within the ceramic member 1111a. In this case, the at least one RF / DC electrode functions as a lower electrode. When a bias RF signal and / or a DC signal, which will be described later, is supplied to the at least one RF / DC electrode, the RF / DC electrode is also called a bias electrode. Note that the conductive member of the base 1110 and the at least one RF / DC electrode may function as multiple lower electrodes. Furthermore, the electrostatic electrode 1111b may function as a lower electrode. Therefore, the substrate support 11 includes at least one lower electrode.

[0017] The ring assembly 112 includes one or more annular members. In one embodiment, the one or more annular members include one or more edge rings and at least one cover ring. The edge rings are formed of a conductive or insulating material, and the cover rings are formed of an insulating material.

[0018] The substrate support 11 may also include a temperature adjustment module configured to adjust at least one of the electrostatic chuck 1111, the ring assembly 112, and the substrate to a target temperature. The temperature adjustment module may include a heater, a heat transfer medium, a flow passage 1110a, or a combination thereof. A heat transfer fluid such as brine or a gas flows through the flow passage 1110a. In one embodiment, the flow passage 1110a is formed in the base 1110, and one or more heaters are disposed in the ceramic member 1111a of the electrostatic chuck 1111. The substrate support 11 may also include a heat transfer gas supply configured to supply a heat transfer gas to a gap between the backside of the substrate W and the central region 111a.

[0019] The showerhead 13 is configured to introduce at least one process gas from the gas supply unit 20 into the plasma processing space 10s. The showerhead 13 has at least one gas supply port 13a, at least one gas diffusion chamber 13b, and multiple gas inlets 13c. The process gas supplied to the gas supply port 13a passes through the gas diffusion chamber 13b and is introduced into the plasma processing space 10s from the multiple gas inlets 13c. The showerhead 13 also includes at least one upper electrode. In addition to the showerhead 13, the gas inlet may also include one or more side gas injectors (SGIs) attached to one or more openings formed in the sidewall 10a.

[0020] The gas supply unit 20 may include at least one gas source 21 and at least one flow controller 22. In one embodiment, the gas supply unit 20 is configured to supply at least one process gas from a corresponding gas source 21 to the showerhead 13 via a corresponding flow controller 22. Each flow controller 22 may include, for example, a mass flow controller or a pressure-controlled flow controller. Additionally, the gas supply unit 20 may include at least one flow modulation device that modulates or pulses the flow rate of the at least one process gas.

[0021] The power supply 30 includes an RF power supply 31 coupled to the plasma processing chamber 10 via at least one impedance matching circuit. The RF power supply 31 is configured to supply at least one RF signal (RF power) to at least one lower electrode and / or at least one upper electrode. This generates a plasma from at least one processing gas supplied to the plasma processing space 10s. Therefore, the RF power supply 31 can function as at least a part of the plasma generation unit 12. Furthermore, by supplying a bias RF signal to the at least one lower electrode, a bias potential is generated on the substrate W, thereby attracting ion components in the formed plasma to the substrate W.

[0022] In one embodiment, the RF power supply 31 includes a first RF generating unit 31a and a second RF generating unit 31b. The first RF generating unit 31a is coupled to at least one lower electrode and / or at least one upper electrode via at least one impedance matching circuit and is configured to generate a source RF signal (source RF power) for plasma generation. In one embodiment, the source RF signal has a frequency in the range of 10 MHz to 150 MHz. In one embodiment, the first RF generating unit 31a may be configured to generate multiple source RF signals having different frequencies. The generated one or more source RF signals are supplied to at least one lower electrode and / or at least one upper electrode. Note that the first RF generating unit 31a is an example of an RF generating unit.

[0023] The second RF generator 31b is coupled to at least one lower electrode via at least one impedance matching circuit and is configured to generate a bias RF signal (bias RF power). The frequency of the bias RF signal may be the same as or different from the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency lower than the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency in the range of 100 kHz to 60 MHz. In one embodiment, the second RF generator 31b may be configured to generate multiple bias RF signals having different frequencies. The generated one or more bias RF signals are supplied to at least one lower electrode. In various embodiments, at least one of the source RF signal and the bias RF signal may be pulsed.

[0024] The power supply 30 may also include a DC power supply 32 coupled to the plasma processing chamber 10. The DC power supply 32 includes a first DC generator 32a and a second DC generator 32b. In one embodiment, the first DC generator 32a is connected to the at least one lower electrode and configured to generate a first DC signal. The generated first DC signal is applied to the at least one lower electrode. In one embodiment, the second DC generator 32b is connected to the at least one upper electrode and configured to generate a second DC signal. The generated second DC signal is applied to the at least one upper electrode.

[0025] In various embodiments, the first and second DC signals may be pulsed. In this case, a sequence of voltage pulses is applied to at least one lower electrode and / or at least one upper electrode. The voltage pulses may have a rectangular, trapezoidal, triangular, or combination thereof pulse waveform. In one embodiment, a waveform generator for generating a sequence of voltage pulses from the DC signal is connected between the first DC generator 32a and at least one lower electrode. Therefore, the first DC generator 32a and the waveform generator constitute a voltage pulse generator. Note that the first DC generator 32a and the waveform generator are examples of a pulsed voltage generator. In the following description, the first DC generator 32a may be referred to as including a waveform generator. When the second DC generator 32b and the waveform generator constitute a voltage pulse generator, the voltage pulse generator is connected to at least one upper electrode. The voltage pulses may have a positive polarity or a negative polarity. The voltage pulse sequence may include one or more positive voltage pulses and one or more negative voltage pulses within one cycle. The first and second DC generators 32 a and 32 b may be provided in addition to the RF power supply 31, or the first DC generator 32 a may be provided instead of the second RF generator 31 b.

[0026] The microwave interferometer 35 is used to measure (monitor) the electron density Ne of the plasma generated in the plasma processing space 10s. The microwave interferometer 35 has electromagnetic horns 36a and 36b, and is attached to the sidewall 10a of the plasma processing chamber 10 at two locations so that the electromagnetic horns 36a and 36b face each other. Microwaves are transmitted from one of the electromagnetic horns 36a and 36b, and received at the other. In the plasma processing space 10s, the line connecting the electromagnetic horns 36a and 36b crosses the plasma. The microwave interferometer 35 measures the electron density Ne of the plasma based on the phase difference between the transmitted microwave and the received microwave. The microwave interferometer 35 outputs the measured electron density Ne to the control unit 2. The control unit 2 controls the RF power supply 31 (first RF generation unit 31 a) based on the input electron density Ne to adjust a first power level of the source RF signal (source RF power) during a first period T1 (to be described later). The control unit 2 also controls the DC power supply 32 (first DC generation unit 32 a and waveform generation unit) based on the input electron density Ne to adjust an offset period De (to be described later) of the first DC signal (DC pulse). Furthermore, the control unit 2 may also control the DC power supply 32 (first DC generation unit 32 a and waveform generation unit) based on the input electron density Ne to adjust a first voltage level of the first DC signal during a second period T1 (to be described later).

[0027] The exhaust system 40 may be connected to, for example, a gas exhaust port 10e provided at the bottom of the plasma processing chamber 10. The exhaust system 40 may include a pressure regulating valve and a vacuum pump. The pressure in the plasma processing space 10s is regulated by the pressure regulating valve. The vacuum pump may include a turbomolecular pump, a dry pump, or a combination thereof.

[0028] [RF Power and DC Pulse] Here, changes in RF power, a first DC signal (DC pulse), and electron density Ne will be described. Note that RF power may have two types of frequencies, with a high-frequency source RF signal also referred to as HF (High Frequency) and a low-frequency bias RF signal also referred to as LF (Low Frequency). In this embodiment, the relationship between HF (hereinafter also referred to as RF (HF)), a DC pulse, and electron density Ne will be described. FIG. 3 is a timing chart showing an example of supply timing of RF power and a DC pulse and changes in electron density in the first embodiment.

[0029] As shown in FIG. 3 , RF power (RF (HF)) and DC pulses are supplied periodically, with one cycle consisting of a first period T1 and a second period T2. RF power is supplied at a first power level (High) during the first period T1, and at a second power level (Low) during the second period T2. DC pulses are supplied at a reference voltage level during an offset period (delay period) De, which will be described later, within the first period T1. Furthermore, DC pulses are supplied as a sequence of multiple voltage pulses having a first voltage level after the offset period De has elapsed, i.e., during the first period T1 excluding the offset period De. Furthermore, DC pulses are supplied at the reference voltage level during the second period T2. Note that in FIG. 3 , for example, the reference voltage level is 0 V, and the first voltage level is a pulse having a negative polarity.

[0030] The electron density Ne increases from the start of the first period T1, peaks when the supply of the DC pulse begins after the offset period De has elapsed, and maintains the first level, albeit with a tendency to decrease slightly. Thereafter, the electron density Ne decreases from the end of the first period T1, i.e., the start of the second period T2, to a second level lower than the first level, and maintains the second level. In the first embodiment, for example, the microwave interferometer 35 measures the electron density Ne at timing 52 within the first period T1. The measured electron density Ne is then used to adjust the first power level of the RF (HF). Alternatively, the microwave interferometer 35 may measure the electron density Ne at timing 53 within the second period T2.

[0031] Next, details of the RF power and DC pulses will be described with reference to FIGS. 4 and 5 . FIG. 4 is a timing chart showing an example of the supply timing of the RF power and DC pulses in the first embodiment. FIG. 5 is a timing chart showing an enlarged portion of the timing chart shown in FIG. 4 . FIG. 5 shows an enlarged view of a range 54 in the timing chart shown in FIG. 4 . As shown in FIG. 4 , in the process of etching a film to be etched on the substrate W, RF power (HF) is supplied, and the film to be etched on the substrate W is etched using plasma generated from a processing gas. The RF power source 31 periodically supplies RF power of "High" and "Low" levels to the substrate support 11 (lower electrode), with the repetition period C shown in FIG. 4 being one cycle. Note that the RF power may also be supplied to the shower head 13 (upper electrode). In the present disclosure, the RF power source 31 (first RF generation unit 31 a) is coupled to the lower electrode and supplies RF (HF) shown in FIG. 4 as RF power.

[0032] In FIG. 4 , "High" (hereinafter also referred to as "high state" or "high") is an example indicating a first power level of RF power. For example, the first power level is greater than 0 W. On the other hand, "Low" (hereinafter also referred to as "low state" or "low") is an example indicating a second power level of RF power. The second power level of RF power is less than the first power level and is 0 W or greater than 0 W.

[0033] The first period T1, in which the RF power is in a high state, and the second period T2, in which the RF power is in a low state, are repeated in this order. Alternatively, the RF power may be in an on state during the first period T1 and an off state during the second period T2, and repeated in this order. Here, the on state is a first power level similar to the high state, and the off state is when the second power level is 0 W. The first period T1 has a duty ratio within a range of 10% to 60% with respect to the repetition period C. The duty ratio indicates the proportion of the first period T1, and is the ratio of the first period T1 to the total time indicated by (first period T1 + second period T2). The repetition period C has a repetition frequency within a range of 0.1 kHz to 50 kHz.

[0034] In the supply of DC pulses shown in FIG. 5, a voltage having a periodic pulse waveform with negative polarity is supplied. The "periodicity" here has two meanings. One refers to the periodicity between the ON state during period P1 in FIG. 4 and the OFF state during period P2 in FIG. 4. In other words, it refers to the periodicity corresponding to the ON and OFF states of a control signal indicating whether or not a DC pulse is supplied. The ON state period P1 corresponds to the first period T1 excluding the offset period De shown in FIG. 5. The OFF state period P2 corresponds to the offset period De and the second period T2. The other refers to the ON and OFF periodicity of the negative pulse waveform shown in FIG. 5 during the first period T1 (period P1) excluding the offset period De.

[0035] The DC power supply 32 sets a first period T1 during which the RF power is in a high state and a second period T2 during which the RF power is in a low state, and keeps the DC pulse in an off state from the start of the first period T1 to the end of an offset period De. The offset period De is within a range of 2% to 7% of the repetition period C. The DC power supply 32 supplies a DC pulse in an on state during the first period T1 after the offset period De has elapsed, i.e., during a period P1 (= T1 - De), and keeps the DC pulse in an off state during a second period T2. In this way, the DC power supply 32 repeats, in this order, a period P1 during which a negative DC pulse is supplied and a period P2 (= De + T2) during which the supply of the negative DC pulse is stopped.

[0036] During period P1 when the DC pulse is in the ON state, the DC pulse further repeats ON (ON: negative value) and OFF (OFF: 0 V) ​​periodically as a voltage pulse sequence (pulse waveform). That is, the absolute value of the first voltage level is greater than the absolute value of the reference voltage level. During period P2, the DC pulse is in the OFF state, that is, the control signal indicating whether or not to supply a DC pulse is in the OFF state. Note that during period P2, a DC pulse having a voltage absolute value smaller than that of the DC pulse during period P1 may be supplied.

[0037] In the pulse waveform of the DC pulse during period P1, if the reciprocal of the on-off cycle (wavelength λ1) of the pulse waveform is defined as pulse frequency f1, then the pulse frequency f1 can be, for example, a frequency in the range of 100 kHz to 1 MHz. Furthermore, the duty ratio of the pulse waveform of the DC pulse during period P1 indicates the proportion of the on-time (t1) of the DC pulse. In other words, the duty ratio of the pulse waveform of the DC pulse during period P1 is the proportion of the on-time to the total time of the on-time (t1) and the off-time (t2) (t1 / (t1+t2)). The DC pulse is not limited to a rectangular wave, and may be a triangular wave, impulse wave, trapezoidal wave, sawtooth wave, or a pulse waveform that is a combination of these.

[0038] Next, the improvement of the mask selectivity and the adjustment of the electron density by providing an offset period will be described with reference to FIGS. 6 to 14. FIG. 6 is a timing chart showing an example of the supply timing of RF power and DC pulses and the change in electron density in the first embodiment. FIG. 6 corresponds to the timing chart of FIG. 3 and is a timing chart expressed using control signals for RF power and DC pulses. As shown in FIG. 6, at the rising edge of the control signal, the control signal for RF power (RF(HF)) becomes "ON", and then, after the offset period De has elapsed, the control signal for the DC pulse becomes "ON". After the period P1 has elapsed, at the falling edge of the control signal, the control signals for RF(HF) and DC pulse simultaneously become "OFF". Note that when RF(HF) is "ON", a first power level "High" is supplied, and when it is "OFF", a second power level "Low" is supplied.

[0039] Here, in the timing chart of the electron density Ne, the offset period De is the period during which by-products (hereinafter referred to as deposits) are deposited on the substrate W, and the period P1 is the etching period. In other words, the deposits deposited on the substrate W during the offset period De protect the mask on the substrate W during etching in the period P1. In other words, it is believed that the mask selectivity is maximized when an appropriate amount of deposits is deposited. Therefore, attention is focused on the offset period De and the first half of the period P1 in the timing chart of the electron density Ne, which are related to the amount of deposits.

[0040] FIG. 7 is a diagram showing an example of changes in electron density near the offset period when the amount of deposition is at an appropriate level. FIG. 8 is a diagram schematically showing deposition and etching when the amount of deposition is at an appropriate level. As shown in range 55a of FIG. 7, when the electron density Ne is at the appropriate level L at the start timing of period P1, as shown in state 56a of FIG. 8, deposits 59 accumulate on the sidewalls of the holes 57 and on the surface 58 of the substrate W, forming a protective film 60 of an appropriate thickness. During period P1, as shown in state 56b of FIG. 8, ions 61 are attracted and the bottom of the holes 57 is etched, while the sidewalls of the holes 57 and the surface 58 of the substrate W are protected by the protective film 60 and are not etched. In other words, since the amount of deposition estimated from the measured electron density Ne is at an appropriate level, the mask selectivity can be improved.

[0041] FIG. 9 is a diagram showing an example of changes in electron density near the offset period when the amount of deposition is insufficient. FIG. 10 is a diagram schematically showing deposition and etching when the amount of deposition is insufficient. As shown in range 55b in FIG. 9 , when the electron density Ne is lower than the appropriate level L at the start timing of period P1, less deposit 63 accumulates on the sidewall of the hole 57 and the surface 58 of the substrate W, as shown in state 62a in FIG. 10 , and a protective film 64 thinner than the protective film 60 is formed. During period P1, as shown in state 62b in FIG. 10 , ions 65 are attracted and the bottom of the hole 57 is etched, but because the protective film 64 is thin, the sidewall of the hole 57 and the surface 58 of the substrate W are also etched, resulting in a decrease in mask selectivity. As shown in range 55b, when the electron density Ne is lower than the appropriate level L at the start timing of period P1, the RF power supply 31 (first RF generator 31a) is controlled to increase the first power level of the RF (HF). The appropriate level L is an example of a target value for the electron density Ne.

[0042] FIG. 11 shows an example of changes in electron density near the offset period when the amount of deposition is excessive. FIG. 12 is a schematic diagram showing deposition and etching when the amount of deposition is excessive. As shown in range 55c of FIG. 11, when the electron density Ne is higher than the appropriate level L at the start timing of period P1, the amount of deposition 67 increases, as shown in state 66a of FIG. 12. In this case, not only does the deposition 67 accumulate on the sidewall of the hole 57 and the surface 58 of the substrate W, but the formed protective film 68 is also etched by the deposition 67, making it thinner than the protective film 60. During period P1, as shown in state 66b of FIG. 12, ions 69 are attracted to etch the bottom of the hole 57, but because the protective film 68 is thin, the sidewall of the hole 57 and the surface 58 of the substrate W are also etched, resulting in a decrease in mask selectivity. As shown in range 55c, when the electron density Ne is higher than the appropriate level L at the start timing of period P1, the RF power supply 31 (first RF generating unit 31a) is controlled so that the first power level of RF (HF) is reduced.

[0043] Furthermore, the electron density Ne may be adjusted by adjusting the length of the offset period De. FIG. 13 illustrates an example of a method for adjusting the electron density at the start timing of the period P1. The range 70 illustrated in FIG. 13 corresponds to the range 55 in FIG. 6 and is an example of adjustment when the electron density Ne at the start timing of the period P1 is less than the appropriate level L, as shown in the range 55b in FIG. 9 . In the example of the range 70, the offset period De is adjusted by adding the additional period De1 to the offset period De to obtain the offset period De'. Note that since the relationship of the first period T1 = the offset period De + the period P1 is satisfied, when the range 70 is adjusted, the period P1' = the period P1 - the additional period De1, and the first period T1 = the offset period De' + the period P1'. In this way, when the electron density Ne at the start timing of the period P1 is less than the appropriate level L, the DC power supply 32 (the first DC generator 32a and the waveform generator) may be controlled to lengthen the offset period De.

[0044] FIG. 14 is a diagram showing an example of a method for adjusting the electron density at the start timing of the period P1. The range 71 shown in FIG. 14 corresponds to the range 55 in FIG. 6 and is an example of adjustment when the electron density Ne at the start timing of the period P1 exceeds the appropriate level L, as shown in the range 55c in FIG. 11 . In the example of the range 71, the offset period De is adjusted by subtracting the shortening period De2 from the offset period De to obtain the offset period De". Note that since the relationship of the first period T1 = the offset period De + the period P1 is satisfied, after adjusting the range 71, the period P1" = the period P1 + the shortening period De2, and the first period T1 = the offset period De" + the period P1". In this way, when the electron density Ne at the start timing of the period P1 exceeds the appropriate level L, the DC power supply 32 (the first DC generating unit 32a and the waveform generating unit) may be controlled to shorten the offset period De. Note that the adjustment of the first power level of the RF (HF) and the adjustment of the offset period De may be combined.

[0045] [Plasma Control Method] Next, an example of a plasma control process in the plasma processing apparatus 1 of the first embodiment will be described. Fig. 15 is a flowchart showing an example of the plasma control process according to the first embodiment. The plasma control process shown in Fig. 15 is realized by the control unit 2 controlling each part of the plasma processing apparatus 1.

[0046] First, the substrate W is loaded into the plasma processing chamber 10 and supported on the substrate support 11. Then, the control unit 2 controls the gas supply unit 20 so that a predetermined flow rate of the processing gas is supplied into the plasma processing chamber 10. Then, the control unit 2 controls the exhaust system 40 to adjust the pressure inside the plasma processing chamber 10. Next, the control unit 2 controls the RF power supply 31 and the DC power supply 32 to supply RF power and DC pulses to the substrate support 11, which serves as the lower electrode. This generates plasma of the processing gas in the plasma processing chamber 10. The control unit 2 controls the microwave interferometer 35 to measure the electron density Ne of the plasma (step S1). The microwave interferometer 35 outputs the measured electron density Ne to the control unit 2. Note that the measurement of the plasma electron density Ne by the microwave interferometer 35 is continued during the plasma processing during adjustment.

[0047] When the electron density Ne measured by the microwave interferometer 35 is input, the control unit 2 controls the RF power supply 31 and the DC power supply 32 so as to adjust at least one of the first power level and the offset period De based on the input electron density Ne (step S2). That is, the control unit 2 adjusts at least one of the first power level and the offset period De, and controls the RF power supply 31 and the DC power supply 32 so that the input electron density Ne becomes the appropriate level L.

[0048] When the plasma processing process is completed, the processed substrate W is unloaded from the plasma processing chamber 10 by a robot arm (not shown).

[0049] In this way, in the first embodiment, at least one of the first power level and the offset period De is adjusted based on the measured electron density Ne, so that it is possible to suppress changes in the plasma condition over time.

[0050] Second Embodiment In the first embodiment, the DC pulse is supplied when the RF power is in a high state, but it may also be supplied when the RF power is in a low state, and this embodiment will be described as a second embodiment. Note that the plasma processing system in the second embodiment is similar to that of the first embodiment except for the timing of supplying the DC pulse, and therefore a description of the overlapping configuration and operation will be omitted.

[0051] In the first embodiment, at least one of the first power level of the first period T1 and the offset period De is adjusted based on the electron density Ne measured in the first period T1. In contrast, in the second embodiment, for example, the first power level of the RF power is adjusted based on the electron density Ne measured in the first period T1, and the first voltage level of the DC pulse is adjusted based on the electron density Ne measured in the second period T2.

[0052] First, the synchro pulse and timing offset pulse (hereinafter also referred to as offset pulse) will be described with reference to FIGS. 16 to 19. FIG. 16 is a diagram showing an example of a timing chart for one cycle of the synchro pulse. As shown in FIG. 16, the synchro pulse is a case where the offset of the DC pulse with respect to the RF power (RF(HF)) is 0°. In addition, in the example of FIG. 16, the duty ratio of the RF(HF) and DC pulse with respect to the repetition period C is 30%. That is, the RF(HF) and DC pulse are simultaneously supplied to the lower electrode (substrate support 11) of the plasma processing chamber 10. Note that, for the offset, the phase is expressed in degrees (angle).

[0053] 17 to 19 are diagrams showing examples of timing charts for one cycle of the offset pulse. The DC pulse shown in FIG. 17 has an offset of 54° relative to the RF (HF). That is, the DC pulse shown in FIG. 17 is a pulse whose phase is delayed by 15% relative to the synchro pulse. In the example of FIG. 17, the duty ratios of the RF (HF) and DC pulses are each 30%. That is, after the RF (HF) starts to be supplied to the lower electrode (substrate support 11) of the plasma processing chamber 10, the DC pulse starts to be supplied to the lower electrode (substrate support 11) of the plasma processing chamber 10 15% of the repetition period C has elapsed. That is, during the repetition period C, the RF (HF) is in a high state and the DC pulse is in an off state, the RF (HF) is in a high state and the DC pulse is in an on state, the RF (HF) is in a low state and the DC pulse is in an on state, and the RF (HF) is in a low state and the DC pulse is in an off state, in that order.

[0054] The DC pulse shown in Figure 18 has an offset of 108° relative to the RF (HF). That is, the DC pulse shown in Figure 18 is a pulse whose phase is delayed by 30% relative to the synchro pulse. In the example of Figure 18, the duty ratios of the RF (HF) and DC pulses are each 30%. That is, after the RF (HF) starts to be supplied to the lower electrode (substrate support 11) of the plasma processing chamber 10, the DC pulse starts to be supplied to the lower electrode (substrate support 11) of the plasma processing chamber 10 after 30% of the repetition period C has elapsed. That is, during the repetition period C, the RF (HF) is in a high state and the DC pulse is in an off state, the RF (HF) is in a low state and the DC pulse is in an on state, and then the RF (HF) is in a low state and the DC pulse is in an off state, in that order.

[0055] The DC pulse shown in FIG. 19 has an offset of −144° relative to the RF (HF). That is, the DC pulse shown in FIG. 19 is a pulse whose phase is 40% advanced (60% delayed) relative to the synchro pulse. In the example of FIG. 19, the duty ratios of the RF (HF) and DC pulses are each 30%. That is, after the RF (HF) starts to be supplied to the lower electrode (substrate support 11) of the plasma processing chamber 10, the DC pulse starts to be supplied to the lower electrode (substrate support 11) of the plasma processing chamber 10 after 60% of the repetition period C has elapsed. That is, during the repetition period C, the RF (HF) is in a high state and the DC pulse is in an off state, the RF (HF) is in a low state and the DC pulse is in an off state, the RF (HF) is in a low state and the DC pulse is in an on state, and the RF (HF) is in a low state and the DC pulse is in an off state, in that order.

[0056] 16 to 19, the period when the RF (HF) is in the high state is the first period T1, and the period when the RF (HF) is in the low state is the second period T2. In the second embodiment, the first power level when the RF (HF) is in the high state is adjusted based on the plasma electron density Ne measured in the first period T1. Also in the second embodiment, the first voltage level when the DC pulse is in the on state is adjusted based on the plasma electron density Ne measured in the second period T2.

[0057] Next, an example of offset pulse adjustment will be described using FIG. 20 . FIG. 20 is a graph showing an example of changes in electron density during a repetition period in the second embodiment. FIG. 20 illustrates changes in electron density Ne when the offset shown in FIG. 18 is 108°. That is, FIG. 20 illustrates changes in electron density Ne during a repetition period C in a period A1 corresponding to the first period T1, a period A2 during the second period T2 during which the DC pulse is in the ON state, and a period A3 during the second period T2 during which the DC pulse is in the OFF state. That is, during period A1, the RF (HF) is in the HIGH state and the DC pulse is in the OFF state; during period A2, the RF (HF) is in the LOW state and the DC pulse is in the ON state; and during period A3, the RF (HF) is in the LOW state and the DC pulse is in the OFF state. A graph 72 in FIG. 20 illustrates an example of changes in electron density Ne during plasma conditions immediately after maintenance, for example. In the graph 72, the electron density Ne in the period A1 rises to about twice the electron density Ne in the period A2.

[0058] At this time, the control unit 2 controls the RF power supply 31 so that the electron density Ne is constant at a target value for the first power level when the RF (HF) is in a high state during the period A1. Furthermore, the control unit 2 controls the DC power supply 32 so that the electron density Ne is constant at a target value for the first voltage level when the DC pulse is in an on state during the period A2. Furthermore, the control unit 2 controls the RF power supply 31 so that the plasma is maintained at a second power level when the RF (HF) is in a low state during the period A3. Note that, during the periods A1 and A2, the first power level of the RF (HF) and the first voltage level of the DC pulse may mutually affect each other. In this case, the first power level of the RF (HF) and the first voltage level of the DC pulse may be adjustable during the periods A1 and A2. That is, the electron density Ne may be controlled to be constant at a target value during each of the periods A1 and A2 by balancing the first power level of the RF (HF) and the first voltage level of the DC pulse. This control method can be applied not only to the offset pulse but also to the sync pulse.

[0059] 20 shows an example of a change in electron density Ne in plasma conditions when, for example, time has passed since maintenance and plasma processing has been performed for a long time in the plasma processing chamber 10. Comparing graph 73 with graph 72, the electron density Ne in period A1 of graph 73 is lower than the target value in graph 72. In this case, the controller 2 controls the RF power supply 31 to increase the first power level of the RF (HF) in period A1 so that the electron density Ne in period A1 becomes the target value (so that it overlaps with graph 72).

[0060] That is, in the first period T1 (period A1), when the electron density Ne is less than the target value, the control unit 2 controls the RF power supply 31 to increase the first power level of the RF (HF). Furthermore, in the first period T1 (period A1), when the electron density Ne exceeds the target value, the control unit 2 controls the RF power supply 31 to decrease the first power level of the RF (HF). Similarly, in the second period T2 (e.g., period A2), when the electron density Ne is less than the target value, the control unit 2 controls the DC power supply 32 to increase the first voltage level of the DC pulse. Furthermore, in the second period T2 (e.g., period A2), when the electron density Ne exceeds the target value, the control unit 2 controls the DC power supply 32 to decrease the first voltage level of the DC pulse.

[0061] [Plasma Control Method] Next, an example of a plasma control process in the plasma processing apparatus 1 according to the second embodiment will be described. Fig. 21 is a flowchart showing an example of the plasma control process according to the second embodiment. The plasma control process shown in Fig. 21 is realized by the control unit 2 controlling each part of the plasma processing apparatus 1.

[0062] First, the substrate W is loaded into the plasma processing chamber 10 and supported on the substrate support 11. Then, the control unit 2 controls the gas supply unit 20 so that a predetermined flow rate of the processing gas is supplied into the plasma processing chamber 10. Then, the control unit 2 controls the exhaust system 40 to adjust the pressure inside the plasma processing chamber 10. Next, the control unit 2 controls the RF power supply 31 and the DC power supply 32 to supply RF power and DC pulses to the substrate support 11, which serves as the lower electrode. This generates plasma of the processing gas in the plasma processing chamber 10. The control unit 2 controls the microwave interferometer 35 to measure the electron density Ne of the plasma (step S11). The microwave interferometer 35 outputs the measured electron density Ne to the control unit 2. Note that the measurement of the plasma electron density Ne by the microwave interferometer 35 is continued during the plasma processing during adjustment.

[0063] When the electron density Ne measured by the microwave interferometer 35 is input, the control unit 2 controls the RF power supply 31 to adjust the first power level based on the electron density Ne measured in the first period T1 among the input electron densities Ne. The control unit 2 also controls the DC power supply 32 to adjust the first voltage level based on the electron density Ne measured in the second period T2 among the input electron densities Ne (step S12). That is, the control unit 2 adjusts the first power level and the first voltage level, and controls the RF power supply 31 and the DC power supply 32 so that the input electron density Ne becomes the target value for each of the first period T1 and the second period T2.

[0064] When the plasma processing process is completed, the processed substrate W is unloaded from the plasma processing chamber 10 by a robot arm (not shown).

[0065] In this way, in the second embodiment, the first power level and the first voltage level are adjusted based on the electron density Ne measured in the first period T1 and the second period T2, respectively, thereby making it possible to suppress changes in the plasma condition over time.

[0066] As described above, according to the second embodiment, the plasma processing apparatus 1 includes a chamber (plasma processing chamber 10), a substrate support 11 disposed within the chamber and including a lower electrode, an RF generator (RF power supply 31), a pulsed voltage generator (DC power supply 32), a microwave interferometer 35, and a controller 2. The RF generator is configured to generate a pulsed RF signal to generate plasma within the chamber, the pulsed RF signal having a first power level during a first period T1 within each cycle (repetition period C) and a second power level during a second period T2 within each cycle that is less than the first power level. The pulsed voltage generator is electrically connected to the lower electrode and configured to generate a pulsed voltage signal, the pulsed voltage signal having a sequence of multiple voltage pulses having a reference voltage level during a first period T1 and a first voltage level during a second period T2, the absolute value of the first voltage level being greater than the absolute value of the reference voltage level. The microwave interferometer 35 is configured to monitor the electron density of the plasma in the chamber. The control unit 2 is configured to adjust the first power level based on the monitored plasma electron density during the first period T1, and adjust the first voltage level based on the monitored plasma electron density during the second period T2. As a result, it is possible to suppress changes in the plasma condition over time.

[0067] Furthermore, according to the second embodiment, when the electron density in the first period T1 is less than the target value, the control unit 2 adjusts the first power level to be larger, thereby adjusting the electron density in the first period T1.

[0068] Furthermore, according to the second embodiment, when the electron density in the first period T1 exceeds the target value, the control unit 2 adjusts the first power level to be smaller, thereby adjusting the electron density in the first period T1.

[0069] Furthermore, according to the second embodiment, when the electron density during the second period T2 is less than the target value, the control unit 2 adjusts the absolute value of the first voltage level to be larger, thereby adjusting the electron density during the second period T2.

[0070] Furthermore, according to the second embodiment, when the electron density during the second period T2 exceeds the target value, the control unit 2 adjusts the absolute value of the first voltage level to be smaller, thereby adjusting the electron density during the second period T2.

[0071] Furthermore, according to the first embodiment, the plasma processing apparatus 1 includes a chamber (plasma processing chamber 10), a substrate support 11 disposed within the chamber and including a lower electrode, an RF generator (RF power supply 31), a pulsed voltage generator (DC power supply 32), a microwave interferometer 35, and a controller 2. The RF generator is configured to generate a pulsed RF signal to generate plasma within the chamber, the pulsed RF signal having a first power level during a first period T1 within each cycle (repetition period C) and a second power level lower than the first power level during a second period T2 within each cycle. The pulsed voltage generating unit is electrically connected to the lower electrode and configured to generate a pulsed voltage signal, the pulsed voltage signal having a reference voltage level during a delay period (offset period De) within a first period T1, a sequence of multiple voltage pulses having a first voltage level during the first period T1 excluding the delay period, and the reference voltage level during a second period T2, the absolute value of the first voltage level being greater than the absolute value of the reference voltage level, and the delay period being within a range of 2% to 7% of the total period of each cycle. The microwave interferometer 35 is configured to monitor the electron density of plasma in the chamber. The control unit 2 is configured to adjust at least one of the first power level and the delay period based on the electron density of plasma monitored during the delay period. As a result, changes in the plasma condition over time can be suppressed.

[0072] Furthermore, according to the first embodiment, when the electron density is less than the target value, the control unit 2 adjusts the first power level to be higher or the delay period to be longer, thereby adjusting the electron density in the first period T1.

[0073] Furthermore, according to the first embodiment, when the electron density exceeds the target value, the control unit 2 adjusts the first power level to be lower or the delay period to be shorter, thereby adjusting the electron density in the first period T1.

[0074] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive, and various omissions, substitutions, and modifications may be made in the above embodiments without departing from the scope and spirit of the appended claims.

[0075] REFERENCE SIGNS LIST 1 Plasma processing apparatus 2 Control unit 10 Plasma processing chamber 11 Substrate support unit 20 Gas supply unit 30 Power supply 31 RF power supply 31a First RF generation unit 31b Second RF generation unit 32 DC power supply 32a First DC generation unit 32b Second DC generation unit 35 Microwave interferometer 40 Exhaust system C Repeating period De Offset period (delay period) T1 First period T2 Second period W Substrate

Claims

1. A plasma processing apparatus comprising: a chamber; a substrate support disposed within the chamber and including a lower electrode; an RF generator configured to generate a pulsed RF signal to generate a plasma in the chamber, the pulsed RF signal having a first power level during a first time period within each cycle and a second power level during a second time period within each cycle that is less than the first power level; a pulsed voltage generator electrically connected to the lower electrode and configured to generate a pulsed voltage signal, the pulsed voltage signal having a sequence of a plurality of voltage pulses having a reference voltage level during the first time period and a first voltage level during the second time period, an absolute value of the first voltage level being greater than an absolute value of the reference voltage level; a microwave interferometer configured to monitor an electron density of a plasma in the chamber; and a controller configured to adjust the first power level based on an electron density of the plasma monitored during the first time period and to adjust the first voltage level based on an electron density of the plasma monitored during the second time period.

2. The plasma processing apparatus according to claim 1, wherein the control unit adjusts the first power level to be larger when the electron density during the first period is less than a target value.

3. The plasma processing apparatus according to claim 1, wherein the control unit adjusts the first power level to be smaller when the electron density during the first period exceeds a target value.

4. The plasma processing apparatus according to claim 1, wherein the control unit adjusts the absolute value of the first voltage level to be larger when the electron density during the second period is less than a target value.

5. The plasma processing apparatus according to claim 1, wherein the control unit adjusts the absolute value of the first voltage level to be smaller when the electron density during the second period exceeds a target value.

6. A chamber; a substrate support disposed within the chamber and including a lower electrode; an RF generator configured to generate a pulsed RF signal to generate a plasma within the chamber, the pulsed RF signal having a first power level during a first period within each cycle and a second power level during a second period within each cycle that is less than the first power level; a pulsed voltage generator electrically connected to the lower electrode and configured to generate a pulsed voltage signal, the pulsed voltage signal having a reference voltage level during a delay period within the first period, a sequence of a plurality of voltage pulses having a first voltage level during the first period excluding the delay period, and having the reference voltage level during the second period, an absolute value of the first voltage level being greater than an absolute value of the reference voltage level, the delay period being in a range of 2% to 7% of a total period of each cycle; and a microwave interferometer configured to monitor an electron density of the plasma within the chamber. a controller configured to adjust at least one of the first power level and the delay period based on an electron density of the plasma monitored during the delay period.

7. The plasma processing apparatus according to claim 6, wherein the control unit adjusts the first power level to be larger or adjusts the delay period to be longer when the electron density is less than a target value.

8. The plasma processing apparatus according to claim 6, wherein the control unit adjusts the first power level to be lowered or the delay period to be shorter when the electron density exceeds a target value.

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