Patent ID: 12237157

DETAILED DESCRIPTION

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

<Plasma Processing Apparatus to which Plasma Measurement Method is Applied>

FIG.1is a cross-sectional view showing an example of a plasma processing apparatus to which a plasma measurement method according to an embodiment is applied.

A plasma processing apparatus100is configured as a plasma processing apparatus for performing plasma processing by radiating electromagnetic waves such as microwaves or the like.

The plasma processing apparatus100includes a processing container (chamber)1accommodating a semiconductor wafer W (hereinafter, simply referred to as “a wafer W”) as a substrate. The plasma processing apparatus100performs plasma processing on the wafer W using surface wave plasma produced near an inner wall surface of a top wall portion in the processing container1by the electromagnetic waves radiated in the processing container1. The plasma processing may be film formation, etching, ashing, or the like. Further, the substrate is not limited to a wafer, and may be another substrate such as an FPD substrate, a ceramic substrate, or the like.

The plasma processing apparatus100includes a plasma source2, a gas supply mechanism6, a probe unit7, and a controller8, in addition to the processing container1.

The processing container1has a substantially cylindrical container body10having an upper opening and a top wall portion20that closes the upper opening of the container main body10. The process container1has a plasma processing space therein. The container body10is made of a metal material such as aluminum, stainless steel, or the like, and is grounded. The top wall portion20is made of a metal material such as aluminum, stainless steel, or the like, and has a disc shape. A seal ring129is disposed on a contact surface between the container body10and the top wall portion20to airtightly seal the inside of the processing container1.

A substrate support11on which the wafer W is placed is disposed in the processing container1. The substrate support11is supported by a cylindrical support member12standing upright from a bottom central portion of the processing container1via an insulating member12a. The substrate support11and the support member12may be made of a metal such as aluminum having an alumite-treated (anodically oxidized) surface or an insulating member (ceramic or the like) having therein an electrode for high frequency. The substrate support11may be provided with an electrostatic chuck for electrostatically attracting and holding the wafer W, a temperature control mechanism, a gas channel for supplying a heat transfer gas to a back surface of the wafer W, or the like.

A high-frequency bias power supply14is connected to the substrate support11through a matching device13. By supplying a high-frequency power from the high-frequency bias power supply14to the substrate support11, ions in the plasma are attracted to the wafer W. The high-frequency bias power supply14may not be provided depending on characteristics of plasma processing.

An exhaust line15is connected to the bottom portion of the processing container1, and an exhaust device16including a vacuum pump is connected to the exhaust line15. When the exhaust device16is operated, the inside of the processing container1is exhausted, whereby the inside of the processing container1is depressurized at a high speed to a predetermined degree of vacuum. A loading/unloading port17for loading/unloading the wafer W and a gate valve18for opening/closing the loading/unloading port17are disposed on a sidewall of the processing container1.

The plasma source2generates electromagnetic waves and radiates the generated electromagnetic waves into the processing container1to produce plasma. The plasma source2includes an electromagnetic wave output unit30, an electromagnetic wave transmission unit40, and an electromagnetic wave radiation mechanism50.

The electromagnetic wave output unit30has an electromagnetic wave oscillator for generating oscillated electromagnetic waves, a pulsing device for turning on and off the oscillated electromagnetic waves in a pulse shape, an amplifier for amplifying the oscillated electromagnetic waves, and a distributor for distributing the amplified electromagnetic waves to a plurality of parts. The electromagnetic wave pulse processed by the pulsing device is distributed to a plurality of parts and outputted. A frequency within a range from 30 kHz to a microwave band, i.e., from 30 kHz to 30 GHz, can be used as a frequency of the electromagnetic wave. A frequency within a range from 500 Hz to 100 kHz can be preferably used as the frequency of the electromagnetic wave pulse.

The electromagnetic wave pulse outputted from the electromagnetic wave output unit30is radiated into the processing container1through the electromagnetic wave transmission unit40and the electromagnetic wave radiation mechanism50. Further, gas is supplied into the processing container1as described later, and the supplied gas is excited by the electric field of the introduced electromagnetic wave. As a result, surface wave plasma is produced.

The electromagnetic wave transmission unit40transmits the electromagnetic wave pulse outputted from the electromagnetic wave output unit30. The electromagnetic wave transmission unit40includes a plurality of amplifiers42, as shown inFIG.2illustrating a cross-section taken along line II-II ofFIG.1, a central electromagnetic wave introducing portion43adisposed at the center of the top wall portion20, and six peripheral electromagnetic wave introducing portions43barranged at equal intervals at the peripheral portion of the top wall portion20. The plurality of amplifiers42amplify the electromagnetic wave pulses distributed by the distributor of the electromagnetic wave output unit30, and are disposed corresponding to the central electromagnetic wave introducing portion43aand the six peripheral electromagnetic wave introducing portions43b. The central electromagnetic wave introducing portion43aand the six peripheral electromagnetic wave introducing portions43bhave a function of introducing the electromagnetic wave pulses outputted from the corresponding amplifier42into the electromagnetic wave radiation mechanism50and a function of matching an impedance.

The central electromagnetic wave introducing portion43aand the peripheral electromagnetic wave introducing portions43bare configured by coaxially arranging a cylindrical outer conductor52and a rod-shaped inner conductor53disposed at the center thereof. The gap between the outer conductor52and the inner conductor53serves as an electromagnetic wave transmission path44to which an electromagnetic wave power is supplied and through which the electromagnetic wave propagates toward the electromagnetic wave radiation mechanism50.

The central electromagnetic wave introducing portion43aand the peripheral electromagnetic wave introducing portions43bare provided with a pair of slags54and an impedance adjusting member140located at the front end thereof. By moving the slags54, the impedance of the load (plasma) in the processing container1is matched with the characteristic impedance of the electromagnetic wave power supply in the electromagnetic wave output unit30. The impedance adjusting member140is made of a dielectric material, and is configured to adjust the impedance of the electromagnetic wave transmission line44by a relative permittivity thereof.

The electromagnetic wave radiation mechanism50includes wave retardation members121and131, slot antennas124and134respectively having slots122and132, and dielectric members123and133. The wave retardation members121and131are disposed at position corresponding to the central electromagnetic wave introducing portion43aon the upper surface of the top wall portion20and positions corresponding to the peripheral electromagnetic wave introducing portions43bon the upper surface of the top wall portion20, respectively. Further, the dielectric members123and133are disposed at position corresponding to the central electromagnetic wave introducing portion43aand positions corresponding to the peripheral electromagnetic wave introducing portions43bin the top wall portion20, respectively. The slots122and132are disposed in a portion of the top wall portion20between the wave retardation member121and the dielectric member123, and a portion of the top wall portion20between the wave retardation member131and the dielectric member133, respectively. The portions where the slots are formed serve as the slot antennas124and134.

Each of the wave retardation members121and131has a disc shape, and is arranged to surround the front end of the inner conductor53. The wave retardation members121and131have a dielectric constant greater than that of a vacuum, and are made of, e.g., quartz, ceramic, a fluorine-based resin such as polytetrafluoroethylene or the like, or a polyimide-based resin. The wave retardation members121and131have a function of making the wavelength of the electromagnetic wave shorter than that in vacuum to make the antenna smaller. The wave retardation members121and131can adjust the phase of the electromagnetic wave by the thicknesses thereof. By adjusting the thicknesses of the wave retardation members121and131so that the slot antennas124and134become “the antinodes” of the standing wave, the reflection is minimized and the radiation energy of the slot antennas124and134is maximized.

Similarly to the wave retardation members121and131, the dielectric members123and133are made of, e.g., quartz, ceramic such as alumina (Al2O3), a fluorine-based resins such as polytetrafluoroethylene or the like, or a polyimide-based resin. The dielectric members123and133are fitted in a space formed in the top wall portion20, and openings are formed at portions corresponding to the dielectric members123and133on the bottom surface of the top wall portion20. Therefore, the dielectric members123and133are exposed to the inside of the processing container1, and function as dielectric windows for supplying electromagnetic wave pulses to a plasma generation space U.

The number of peripheral electromagnetic wave introducing portions43band the number of dielectric members133is not limited to six, and may be two or more and preferably three or more.

The gas supply mechanism6includes a gas supply source61, a gas introducing portion62disposed at the top wall portion20, and gas supply lines63for supplying gas from the gas supply source61to the gas introducing portions62. The gas introducing portion62has a plurality of gas diffusion spaces64arranged in a ring shape at the top wall portion20, and a plurality of gas injection holes65for injecting gas from the gas diffusion spaces64into the processing container1. The gas supplied from the gas supply source61to the gas supply lines63reaches the gas diffusion spaces64of the gas introducing portion62, and is supplied in a shower pattern into the processing container1through the gas injection holes65. The gas may be gas for plasma generation such as Ar gas, or process gas used for processing. The gas supply mechanism6is not limited to the one that injects gas from the top wall portion20in a shower pattern as in this example.

The probe unit7includes probe devices (AC probe)70and a power supply/monitoring portion80, and measures a state of pulsed plasma by applying an AC voltage to plasma via the probe devices70. A plurality of probe devices70are arranged in a circumferential direction on the upper part of the sidewall of the processing container1. A plurality of openings1bare formed on the upper part of the sidewall of the processing container1in a state of being separated from each other corresponding to the portions where the probe devices70are attached. The openings1bmay be continuous to form one opening instead of being separated into the plurality of openings. The power supply/monitoring portion80includes an AC power supply having a variable frequency and a variable voltage, and a monitoring device. The power supply/monitoring portion80and the probe devices70are connected through a coaxial cable81.

The probe device70applies an AC voltage outputted from the AC power supply to the plasma, and transmits a signal (electron current and/or ion current) from the plasma to the monitoring device of the power supply/monitoring portion80.

FIGS.3A and3Bare cross-sectional views showing an example of the probe device70.FIG.3Ais an overall view, andFIG.3Bis an enlarged cross-sectional view showing an area D surrounded by a dashed line. The probe device70includes an antenna portion71attached to the opening1bformed in the sidewall of the processing container1via an O-ring73, an electrode72connected to the antenna portion71, and a dielectric support74that supports the antenna portion71from the surroundings. The antenna portion71has a plate-shaped member71aon the front end side facing the opening1band a rod portion71bextending rearward from the center of the back surface of the plate-shaped member71a. The electrode72is connected to the rear end of the rod portion71b. The coaxial cable81is connected to the electrode72. The shape of the plate-shaped member71ais not particularly limited, and may be, e.g., a disc shape or a rectangular shape.

The plate-shaped member71ais disposed to close the back surface side of the opening1bvia the O-ring73made of a dielectric material such as resin or the like. The front end surface of the antenna portion71and the back surface near the opening1bformed at the wall of the processing container1are separated to form a gap1d. Since the gap1dis formed between the front end surface of the antenna portion71and the wall of the processing container1, the antenna portion71is connected to the wall of the processing container1in a DC manner, thereby preventing a current (stray current) from flowing through the wall of the processing container1. However, if the gap1dis too wide, gas or plasma enters the gap1d, causing problems such as corrosion due to plasma, generation of particles due to gas intrusion, and abnormal discharge. Therefore, the gap1dis set to a width that does not allow plasma or gas to enter.

The surface of the plate-shaped member71aon the front end side of the antenna portion71, which is inside the O-ring73, is covered with the insulating film76, and is insulated from the plasma in a DC manner. Further, an area of the wall surface of the processing container1from at least the side surface of the opening1bthrough the back surface of the opening1bto the O-ring73is covered with an insulating film1c. The insulating film76and the insulating film1care formed by thermal spraying of ceramic such as Y2O3or the like. The insulating films76and1cmay be formed by anodic oxidation of aluminum. By forming the insulating films76and1c, a DC current can be prevented and the plasma resistance can be improved. The surface of the antenna portion71closer to the atmosphere than to the O-ring73and the inner wall surface of the processing container1are coated with the insulating film77. Accordingly, the plasma resistance is further improved.

The surface of the antenna portion71on which the insulating film76is formed is exposed to the plasma generation space U side at a position recessed from the inner wall surface of the processing container1where the opening1bis formed. Since the surface of the antenna portion71is recessed, the influence of the plasma on the probe device70is reduced, and the position of the gap1dwhere particles are generated becomes distant from the wafer W, thereby reducing the influence of the particles. Further, since the surface of the antenna portion71is recessed without being positioned on the same plane as the inner wall surface of the processing container1, it is possible to make it difficult to cause a mode jump of the surface wave plasma propagating on the inner wall surface of the processing container1and avoid an abnormal discharge.

The size of the opening1bis determined by the balance between the sensitivity of the antenna portion71and the adverse effect on the antenna portion71due to the intrusion of plasma or gas. In other words, the larger the size of the opening1b, the higher the sensitivity of the antenna portion71, but since plasma or gas is more likely to enter the antenna portion71side, the antenna portion71is more likely to be corroded, which may deteriorate the performance of the probe device70or cause an abnormal discharge. Further, if the opening1bis enlarged to increase the sensitivity of the probe device70too much, the measurement result may be easily affected by the adhesion of generated reaction products, and the measurement accuracy may be lowered. The shape of the opening1bis not particularly limited, and may be an appropriate shape such as a circle, a rectangle, or the like.

The dielectric support74is made of a resin such as PTFE, and surrounds and supports the antenna portion71. A fixing member1amade of a metal such as aluminum or the like is attached to the back surface side of the dielectric support74to cover the dielectric support74, and the fixing member1ais screwed to the sidewall of the processing container1. Accordingly, the antenna portion71in close contact with the vicinity of the opening1bof the sidewall of the processing container1via the O-ring73and the dielectric support74are fixed. The dielectric support74is divided into a main body74aand an annular member74bdisposed at an outer peripheral portion on the surface side of the plate-shaped member71aof the antenna portion71. However, the dielectric support74may have an integrated structure.

The ratio of a length C of the dielectric support74in the depth direction to a diameter B of the plate-shaped member71ashown inFIG.3Ais preferably within a range of 0.44 to 0.54 from the viewpoint of improving the sensitivity of the probe device70.

Although the plurality of probe devices70are provided in the above example, one probe device70may be provided. Further, although the probe devices70are disposed on the inner wall of the processing container1in the above example, they may be disposed at another position such as the outer peripheral portion of the substrate support11or the inner wall of the top wall portion20.

The controller8controls the operation and processing of each component of the plasma processing apparatus100, such as the gas supply of the gas supply mechanism6, the frequency and output of the electromagnetic wave pulse of the plasma source2, the exhaust by the exhaust device16, the frequency and voltage of the AC power supply applied to the probe device70, the calculation of signal from the monitoring device, and the like. The controller8is typically a computer, and includes a main controller, an input device, an output device, a display device, and a storage device. The main controller has a central processing unit (CPU), a random access memory (RAM), and a read only memory (ROM). The storage device has a computer-readable storage medium such as a hard disk, and is configured to record and read information required for the control. In the controller8, the CPU controls the plasma processing apparatus100by executing a program such as a processing recipe stored in the ROM or the storage medium of the storage device while using the RAM as a work area.

<Processing Operation in Plasma Processing Apparatus>

Next, the operation in the plasma processing apparatus100configured as described above will be described.

First, the gate valve18is opened, and the wafer W held on a transfer arm (not shown) is loaded into the processing container1from the loading/unloading port17and placed on the substrate support11. An empty transfer arm is retracted from the processing container1, and the gate valve18is closed. Next, gas is introduced into the processing container1from the gas supply mechanism6and the processing container1is exhausted by the exhaust device16to adjust a pressure therein. Then, a plasma generating gas such as Ar gas or a processing gas is introduced to produce plasma. The processing gas may be introduced after introducing only the plasma generating gas and igniting the plasma.

In the case of producing plasma, gas is introduced into the processing container1, and an electromagnetic wave pulse processed by a pulsing device is outputted in this example, instead of a continuous electromagnetic wave, from the electromagnetic wave output unit30of the plasma source2. In this case, the electromagnetic wave pulse distributed and outputted from the electromagnetic wave output unit30is amplified by the amplifiers42of the electromagnetic wave transmission unit40, and then transmitted to the central electromagnetic wave introducing portion43aand the peripheral electromagnetic wave introducing portions43b. Then, the electromagnetic wave pulse transmitted thereto is radiated into the processing container1through the wave retardation members121and131of the electromagnetic wave radiation mechanism50, the slots122and132of the slot antennas124and134, and the dielectric members123and133that are the electromagnetic wave transmission windows. In this case, the impedance is automatically matched by moving the slags54, and the electromagnetic wave pulse is supplied in a state where there is substantially no power reflection. The radiated electromagnetic wave pulse propagates as a surface wave on the surface of the top wall portion20. The gas is excited by the electric field of the electromagnetic wave pulse, and pulsed surface wave plasma is produced in the plasma generation space U directly under the top wall portion20in the processing container1. The wafer W is subjected to plasma processing using the pulsed surface wave plasma.

The pulse frequency of the plasma is the same as the frequency of the pulsing device, and the plasma is switched on and off repeatedly at the same cycle as that of the pulsing device. In the pulsed plasma that is switched on and off repeatedly, when the plasma is switched off, the rate of decrease in electron temperature Teis higher than the rate of decrease in electron density Ne, as shown inFIG.4. Therefore, the electron temperature Tecan be lowered while ensuring a high electron density Ne as an average value. Accordingly, the wafer damage can be reduced due to the low electron temperature while maintaining a high processing rate due to the high electron density.

In the plasma processing apparatus100of the present embodiment, the wafer W is disposed in a region distant from the plasma generating region, and the plasma diffused from the plasma generating region is supplied to the wafer W, so that the plasma has essentially a low electron temperature and a high density. In addition, the effect of pulsed plasma is obtained, so that plasma processing with higher electron density and lower electron temperature is further realized.

During such plasma processing, the state of pulsed plasma is measured by applying an AC voltage to the plasma via the probe device (AC probe)70of the probe unit7. At the time of measurement, the AC voltage from the AC power supply of the power supply/monitoring portion80is transmitted to the probe device70via the coaxial cable81, and is applied from the probe device70to the plasma. Then, a signal from the plasma side is transmitted to the monitoring device of the power supply/monitoring portion80via the probe device70, and data including a current value is measured. The measured data is transmitted from the monitoring device to the controller8, and the data consisting of an electron current and an ion current is analyzed by the controller8to obtain the plasma state. For example, the controller8performs Fourier transform (FFT) of the data including the current value to calculate a plasma electron temperature and/or a plasma electron density as the plasma state.

The general measurement of the plasma state is performed as described above, but since the state of pulsed plasma fluctuates in a short time, a data measurement method is important in addition to the above-described procedure. Hereinafter, a method for measuring pulsed plasma will be described.

<Method for Measuring Pulsed Plasma>

Hereinafter, a method for measuring pulsed plasma will be described.

<Conventional Method for Measuring Pulsed Plasma>

First, a conventional method for measuring pulsed plasma will be described.

As a method for measuring plasma, a method using a general Langmuir probe for measuring plasma by applying a DC voltage is used. The Langmuir probe can also be used for the measurement of pulsed plasma. However, the sweep speed of the probe voltage of the Langmuir probe is about 1 sec/10 V, and the peak width (on time) of the pulse is about 100 μs to 10 ms. Therefore, even if the plasma state is measured as it is, the characteristics at the time of pulse-on and the characteristics at the time of pulse-off are mixed, which makes it difficult to analyze it. Accordingly, time-resolved measurement shown inFIGS.5A to5Cis performed. In other words, as shown inFIG.5A, a probe voltage is set for a pulse waveform (dotted line), and a current waveform of plasma is measured with an oscilloscope repeatedly at a plurality of voltages. Then, as shown inFIG.5B, the obtained waveforms are divided by time. Then, as shown inFIG.5C, a graph of I-V characteristics is created for each time. In this case, as shown inFIG.6, the measurement is performed by changing the applied voltage with respect to the time in one cycle of the pulse, as shown by vertical dashed arrows, measurement points are rearranged for each time to obtain a current value I (V, t) as a two-variable function with the voltage V and the time t as variables, and the analysis is performed.

The time-resolved measurement using a Langmuir probe is effective for basic evaluation. Since, however, a DC voltage is applied, when process gas is supplied and the plasma processing is performed, deposits are generated from the process plasma, and the current is disturbed by the deposits, which makes it difficult to apply the above time-resolved measurement. Further, it takes time because it is necessary to change the probe voltage little by little for the measurement. In addition, it is necessary to analyze the measurement results later, which makes real-time analysis impossible.

<General Time-Resolved Measurement Using AC Probe>

Hereinafter, a probe device that measures plasma by supplying an AC voltage, such as the probe device70of the present embodiment, is referred to as “AC probe.” The AC probe applies an AC voltage, and thus can measure a plasma state by allowing current to flow even if deposits are adhered to the surface thereof, and can also be used for the process plasma. Further, the AC probe can perform real-time measurement. Japanese Laid-open Patent Publication No. 2019-46787 discloses that the process plasma state is measured in real-time in the case of performing plasma processing using an AC probe. However, Japanese Laid-open Patent Publication No. 2019-46787 does not disclose the measurement of the state of pulsed plasma.

In the case of measuring the pulsed process plasma state in real-time using an AC probe, if the general time resolved measurement is simply applied, the relationship between the frequency of the pulsed plasma and the AC frequency of the AC probe shown inFIG.7is obtained. In the case of measuring a current value, an AC voltage is applied with respect to the time in one cycle of the pulse to perform the measurement, and the current value data, typically the current value I (V, t) which is a two-variable function, is obtained and analyzed. In this case, the applied voltage is an AC voltage, so that the measurement lines indicated by arrows are inclined as shown inFIG.8. The inclination of the measurement lines corresponds to the frequency of the AC voltage, and the larger the inclination, the higher the frequency. In the actual case, the width of V is smaller than that in the case where a DC voltage is applied.

In this case, as shown inFIG.7, for example, when the frequency of the pulsed plasma is 10 kHz, in order to obtain sufficient measurement points by general time-resolved measurement, a frequency of 200 kHz to 1 MHz, which is higher by about 20 to 100 times, is required as the frequency of the AC voltage in the AC probe. As the frequency increases, it becomes difficult to handle, an increase in signals escaping to stray capacitance occurs, and the cost of the oscillator increases. Further, since the calculation using an AC probe is based on the premise that the plasma does not change in the signal, a sampling frequency of, for example, about 1 MHz, which is high enough to consider that the plasma does not change for about 1 to 10 cycles, is required. Further, signal processing needs to be performed in a very short time of 10 μs per processing. It is extremely difficult to perform data processing in a short time of 10 μs per processing after increasing the AC frequency to 200 kHz to 1 MHz.

<Plasma Measurement Method According to One Embodiment>

In one embodiment, the pulsed process plasma is measured by an AC probe.

However, the current value is measured by deviating the frequency of the AC voltage applied to the plasma from the frequency of the electromagnetic wave pulse processed by the pulsing device, instead of the above-described general time-resolved measurement.

Specifically, the pulsed plasma measurement is performed as follows.

The pulsed plasma measurement of the present embodiment is performed, as described above, by applying an AC voltage from the AC power supply of the power supply/monitoring portion80to the pulsed process plasma using the probe device70, transmitting the signal from the process plasma based on the AC voltage using the probe device70, measuring the data including the current value using the analyzer built in the monitoring device, and analyzing the measured data by the controller8to obtain the pulsed process plasma state.

In this case, by continuously applying an AC voltage having a frequency deviated from the pulse frequency from the AC power supply for a period of a plurality of pulses and superimposing data of different points of the plurality of pulses, it is possible to obtain data of the current value corresponding to the deviation of the cycle within the period of one cycle of the pulse, typically the current value I (V, t) which is a two-variable function. The number of data and the measurement time within the period of one cycle of the pulse at this time change depending on the “deviation” of the frequency of the probe voltage from the electromagnetic wave pulse frequency. Therefore, in the present embodiment, the frequency fprobeof the probe voltage is deviated from the frequency fpulseof the electromagnetic wave pulse so that the number of data required for the measurement of the pulsed process plasma is obtained within allowable time within the period of one cycle of the plurality of pulses of pulsed plasma. AlthoughFIG.9Ashows an example in which fprobemade slightly lower than fpulse, as shown inFIG.9A, a plurality of data corresponding to the pulse-on period can be obtained during 12 pulse cycles.FIG.9Bshows measurement points of a voltage VB among the probe voltages. The data can also be obtained during the pulse-off period.

The data acquisition at this time will be described with reference toFIG.10. InFIG.10, the horizontal axis represents time t in one pulse cycle, and the vertical axis represents a probe voltage (AC voltage) V.FIG.10shows the data of the acquired current value I (V, t) as a two-variable function. Circled numbers inFIG.10indicate the order of data acquisition. As shown inFIG.10, when fprobemade slightly lower than the fpulse, it is possible to acquire data that fills the entire area (t-V area for one pulse cycle) to be measured, which is necessary for plasma measurement. The time required for the data measurement at this time can be calculated by about 1/(fpulse−fprobe), as will be described later. This is the same principal as “beat”.

As described above, fpulseis preferably within a range of 500 Hz to 100 kHz, and fprobeis preferably within a range of 500 Hz to 100 kHz. It is unnecessary that fprobeis extremely higher than fpulseas in the above-described general time-resolved measurement using an AC probe, and fprobemay be less than 10 times fpulse.

Here, letting fprobehave a frequency deviated from fpulsemeans that the ratio between fprobeand fpulseis a simple integer ratio (1:1, 1:2, 2:3, or the like). For example, when fpulseis 10 kHz, fprobeis 11 kHz. In this case, a t-V graph can be drawn at an interval of 1 kHz (=11 kHz-10 kHz). Further, when fpulseis 10 kHz, fprobemay be 5.5 kHz while being deviated from a half thereof, i.e., 5 kHz (corresponding to the case of fpulse=2fprobe) Further, when fpulseis 10 kHz, fprobemay be 15.5 kHz while being deviated from 1.5 times thereof, i.e., 15 kHz (corresponding to the case of 2fpulse=3fprobe).

In the case of a simple integer ratio, e.g., in the case of fpulse=fprobe, in the case of fpulse=2fprobe, and in the case of 2fpulse=3fprobe, it becomes as shown inFIGS.11A,12A, and13A, respectively, there is insufficient data in the pulse cycle, and the area (t-V area for one pulse cycle) to be measured cannot be filled with a satisfactory density as shown inFIGS.11B,12B, and13B, so that the data necessary for accurately obtaining the plasma state cannot be acquired. For example, when the amount of deviation is small as in the case of fpulse=10 kHz and fprobe=10.0001 kHz, the data acquisition interval becomes 0.0001 kHz (i.e., data acquisition once every 10 seconds), which lacks real-time performance, and it takes time to fill the area (t-V area for one pulse cycle) to be measured. However, it may take some time, and in such a case, such a small amount of deviation is acceptable. The measurement time is preferably 10 sec or less.

If data that fills the t-V area for one pulse cycle can be acquired, it is analyzed by dividing it by time as shown inFIG.14. Generally, the measurement point does not necessarily exist on the time axis tanalizeis to be analyzed. In that case, it may be corrected to a value on the axis tanalizeanalyzed by using linear interpolation or spline interpolation.

As described above, in the present embodiment, the frequency fprobeof the probe voltage is deviated from the frequency fpulseof the electromagnetic wave pulse so that the data of the number of current values required for plasma measurement within the period of one pulse cycle, typically the current value I (V, t) which is a two-variable function, can be obtained within the required time. This makes it possible to perform time-resolved measurement without using an AC voltage having a frequency 20 to 100 times higher than the electromagnetic wave pulse frequency, as in the case of simply performing general time-resolved measurement. Accordingly, it is possible to measure the state of pulsed plasma using process gas in real-time relatively easily.

Further, in the plasma measurement method of the present embodiment, although the time required for the measurement per data is relatively long, since it is not necessary to change the voltage conditions for time-resolved measurement as in the case of using the Langmuir probe, the total measurement time can be shortened. Further, since the analyzer is built in the monitoring device of the power supply/monitoring portion80, no additional equipment such as an oscilloscope is required.

Further, a sampling frequency fsampleof the current can also be measured by “deviating” from fpulsein the same manner as fprobe, without making it extremely higher than fpulse. Further, assuming that the upper limit of the allowable time for measurement is Tmax, it is preferable that Tmaxis 10 sec or less.

<Specific Conditions for Plasma Measurement>

Next, specific conditions for pulsed plasma measurement will be described.

First, time required to draw one measurement line in the t-V graph shown inFIG.10will be examined.FIG.15Ashows a case of fprobe>fpulse. Let T0be the time required to draw robe one of these measurement lines. In this case, from f=1/T, the conditions Tprobe<Tpulseand T0=Tprobeare satisfied.FIG.15Bshows the case of fprobe<fpulse. In this case, the conditions Tprobe>Tpulseand T0=Tpulseare satisfied.

These are summarized in the following equation.

T0=min⁡(Tp⁢r⁢o⁢b⁢e,Tpulse)=min⁡(1/fp⁢r⁢o⁢b⁢e,1/fpulse)=1/max⁡(fp⁢r⁢o⁢b⁢e,fpulse)

In the above equation, “min” indicates the minimum value between the two numerical values in parentheses, and “max” indicates the maximum value between the two numerical values in parentheses (the same applies hereinafter).

Next, the case where fprobeand fpulseare substantially equal but slightly different is considered. In this case, in the measurement for a short time, the measurement area is apparently the area of one line on the t-V graph as shown inFIG.16A. If such an area is expanded, several lines are connected. However, if the measurement is continued for a long time, the area on the t-V graph is eventually filled as shown inFIG.16B.

In other words, when the upper limit of the allowable time for measurement is Tmaxand Tmaxis substantially equal to T0(Tmax≈T0), since the measurement line can be drawn only in the area of one line on the t-V graph during Tmaxas shown inFIG.16A, the measurement becomes extremely inaccurate. On the other hand, in the case of Tmax>>T0, the measurement time is long, so that the area on the t-V graph can be filled as shown inFIG.16B, which results in an extremely accurate measurement.

When fprobeis slightly higher than fpulse, the condition T0=Tprobeis satisfied, and if the “deviation” of each measurement line is AT as shown inFIG.17, ΔT=Tpulse−Tprobe. In order to fill the entire area on the t-V graph, it is necessary to draw the number of lines shown by the following Eq. (1), and the time required therefor is expressed by the following Eq. (2).

TpulseΔ⁢T=TpulseTpulse-Tp⁢r⁢o⁢b⁢eEq.(1)TpulseΔ⁢T⁢T0=Tpulsefp⁢r⁢o⁢b⁢efp⁢u⁢l⁢s⁢e-1⁢(=1fp⁢r⁢o⁢b⁢e-fp⁢u⁢l⁢s⁢e)Eq.(2)

The measurement line L shown inFIG.18is a line indicating fprobe/fpulse. The allowable amount of “deviation” of the measurement line is expressed by T0/Tmax. In this case, when the minimum positive integers m and n are taken so as to satisfy the following Eq. (3), this is an approximation with the required accuracy of fprobe/fpulse. In other words, the Eq. (3) is an integer approximation of fprobe/fpulsewith n/m, as shown inFIG.18, the left side of the Eq. (3) indicates how much the line deviates from the line of fprobe/fpulse=n/m each time one line is drawn, and the Eq. (3) is an equation for finding m and n which are a set of minimum positive integers so that the deviation on the left side is within the allowable range.

❘"\[LeftBracketingBar]"fprobefpulse-nm❘"\[RightBracketingBar]"<T0Tmax⁢T0=min⁡(Tpulse,Tp⁢r⁢o⁢b⁢e)Eq.(3)

Next, the above Eq. (3) will be described in detail.

A virtual example in which conditions T0/Tmax=1/100, fprobe/fpulse=1001/1000, and m=n=1 are satisfied is considered. In this case, the Eq. (3) is expressed by the following Eq. (4).

❘"\[LeftBracketingBar]"fprobefpulse-11❘"\[RightBracketingBar]"=11⁢0⁢0⁢0Eq.(4)

At this time, as shown inFIG.19, the measurement line deviates from the 1:1 line only by 1/1000, and the amount of deviation at one time is 1/10 of T0/Tmax=1/100, which is the minimum value of the allowable value. Therefore, the area of the t-V graph cannot be filled during Tmax, and the measurement is extremely inaccurate with fprobe/fpulse=1 (rather, it is almost not established as a measurement).

Considering the case where Tmaxis multiplied by 10 and T0/Tmax=1/1000, as shown inFIG.20, the measurement line deviates from the 1:1 line by 1/1000. Since, however, Tmaxis large and the T0/Tmaxinterval and the interval on the left side of Eq. (4) are substantially the same, it is possible to wait for the deviation of the measurement line to fill the entire area of the t-V graph, and an accurate measurement with fprobe/fpulse=1001/1000 can be established. In this case, however, since 1000 T0=Tmax, the measurement time is barely within the limit.

Next, a trial calculation is performed by actually applying numbers to the above Eq. (3).

Here, fprobe=1000.1 Hz and fpulse=1000 Hz. At this time, since T0=1/(max(fprobe, fpulse)), T0=1/1000.1 sec. For simplicity of explanation, it is approximated to T0=1/1000 sec (the result is almost the same whether or not it is approximated).

At this time, fprobe/fpulse=1000.1/1000=10001/10000=1.0001, and when this is applied to the above Eq. (3), the following Eq. (5) is obtained.

❘"\[LeftBracketingBar]"1.0⁢001-nm❘"\[RightBracketingBar]"<11⁢0⁢0⁢0⁢TmaxEq.(5)

Then, when Tmaxis changed to 0.1 sec, 1 sec, and 10 sec, the above Eq. (5) becomes as follows.

▪⁢Tmax=0.1sec❘"\[LeftBracketingBar]"1.0001-nm❘"\[RightBracketingBar]"<0.0⁢1▪⁢Tmax=1⁢sec❘"\[LeftBracketingBar]"1.0001-nm❘"\[RightBracketingBar]"<0.0⁢01▪⁢Tmax=10⁢sec❘"\[LeftBracketingBar]"1.0001-nm❘"\[RightBracketingBar]"<0.0⁢0⁢0⁢1

When Tmaxis 0.1 sec and 1 sec, the equation is established when n=m=1, and the accurate measurement cannot be performed. On the other hand, when Tmaxis 10 sec, the equation is not established when n=m=1, and larger m and n are required. Assuming that n/m=5002/5001, the left side of the Eq. (5) becomes 0.00009996, which satisfies the equation. In other words, if Tmaxincreases to 10 sec, suddenly large m and n are required. As will be described later, since m and n define the number of measurement lines, when the values of m and n are increased in this way, accurate measurement is realized.

However, since fprobe/fpulse=10001/10000, it is required to satisfy a condition n/m=10001/10000 to completely fill the area of the t-V graph, when n/m=5002/5001, as shown inFIG.21, only half of the area of the t-V graph can be filled.

This is because the left side of the Eq. (3), which is the basis of the Eq. (5), is set as an absolute value. In other words, if the absolute value of the Eq. (5) is simply removed, the result is as follows.
−0.0001<1.0001−(n/m)<0.0001
1<n/m<1.0001+0.0001=1.0002

In other words, the last digit of the maximum value is doubled. In this equation, not 10001/10000 which is close to 1.0001 but 5002/5001 which is close to 1.0002 is the smallest positive integers m and n that satisfy the Eq. (5).

To avoid this, when the above Eq. (3) is divided into the case of fpulse<fprobeand the case of fpulse>fprobe, the following Eq. (6) is obtained. The two equations for each case can be combined into one equation as shown in the following Eq. (7).

·When⁢⁢fpulse<fprobe0≤fp⁢r⁢o⁢b⁢efp⁢u⁢l⁢s⁢e-nm<1fp⁢r⁢o⁢b⁢eTmax·When⁢fp⁢u⁢l⁢s⁢e≥fprobe0≤fp⁢u⁢l⁢s⁢efp⁢r⁢o⁢b⁢e-nm<1fpulse⁢Tmax}Eq.(6)0≤max⁡(fprobe,fpulse)min⁡(fprobe,fpulse)-nm≤1max⁡(fp⁢r⁢o⁢b⁢e,fp⁢u⁢l⁢s⁢e)⁢TmaxEq.(7)

Next, a trial calculation is performed using the above Eq. (7). Here, as in the trial calculation of the above Eq. (3), fprobe=1000.1 Hz, fpulse=1000 Hz, and T0=1/1000 sec.

At this time, fprobe/fpulse=1000.1/1000=10001/10000=1.0001, and when this is applied to the above Eq. (7), the following Eq. (8) is obtained.

0≤1.0⁢0⁢0⁢1-nm<11⁢0⁢0⁢0⁢TmaxEq.(8)

When Tmax10 sec, 1.001−(n/m)<0.0001.

In this case, when n=m=1, the equation is not established, and larger n and m are required. In this case, when n/m=5002/5001, 1.0001−(n/m)=−0.00009996, which is negative, and thus the above Eq. (8) is not satisfied. Therefore, it is necessary to further increase m and n. When m and n are increased until n/m=10001/10000, 1.0001−(n/m)=1.0001−(10001/10000)=0, and the above Eq. (8) is satisfied. In this manner, the expected m and n can be obtained by using the above Eq. (8). In other words, the above Eq. (8) is one of the suitable conditions for the measurement of the pulsed plasma.

In the above description, the case where the fprobeand the fpulseare close to each other has been described as an example in order to clarify the boundary, but even when fprobeand fpulseare not close to each other, m and n satisfying the above Eq. (8) can be obtained in the same manner.

As illustrated inFIG.22, m and n described above appear as the number of points where a plurality of measurement lines intersect the t-line and the V-line of the t-V graph, respectively, and define the number of measurement lines.FIG.22is an example in which m=5 and n=11. The line surrounded by the frame inFIG.22is divided into two, but if the line from the left end to the right end is counted as one, the total number of lines is 11. In other words, in this example, the number of measurement lines N is max(n, m). This corresponds to T0=1/max(fprobe, fpulse) and a higher frequency being used, as described above. In this case, the measurement time until the t-V area is filled is NT0=11Tpulse.

When m and n are small, the number of measurement lines is small and the measurement accuracy is lowered. When the number of measurement lines is 10 or more, sufficient measurement accuracy can be ensured. Therefore, the following Eq. (9) can be mentioned as a suitable measurement accuracy requirement.
max(m,n)≥10  Eq. (9)

Further, the measurement time until the t-V area is filled is expressed by NT0as described above. It is required that NT0is smaller than Tmax. In other words, since N=max(n, m) and T0=1/max(fprobe, fpulse), the following Eq. (10) can be mentioned as a requirement for the measurement time. This equation shows that the measurement time cannot be satisfied if m and n are excessively large.

max⁡(m,n)max⁡(fp⁢r⁢obe,fpulse)<TmaxEq.(10)

As described above, by satisfying the above Eqs. (8), (9), and (10), the optimum m and n can be obtained, and the data required for plasma measurement within the period of one pulse cycle of the pulsed plasma can be more reliably obtained within the required time.

<Signal Processing>

The signal from the plasma side obtained when an AC voltage is applied to the pulsed plasma using the probe device70is sent to the monitoring device. Then, the current value data, typically the current value I (V, t) which is a two-variable function, is measured by the built-in analyzer. The measured data is transmitted to and analyzed by the controller8to measure the state of pulsed plasma. The data analysis at this time is performed by performing Fourier transformation (FFT) on the current value.

In plasma, current flows exponentially with respect to a given voltage. The detected current value includes a fundamental wave component having a fundamental frequency and a harmonic component such as a first harmonic having a wavelength twice that of the fundamental wave, a second harmonic having a wavelength three times higher than that of the fundamental wave, or the like. Therefore, the electron density of the plasma and the electron temperature of the plasma are calculated by using the peaks of the amplitudes of the fundamental wave and the harmonics by FFT. In this case, the electron density and the electron temperature can be calculated by using the formula described in Japanese Laid-open Patent Publication No. 2019-46787.

As described in Japanese Laid-open Patent Publication No. 2019-46787, the measurement results of electrical characteristics such as the electron density and the electron temperature of the plasma when an AC probe (probe device70) is used are equivalent to those of a Langmuir probe which is a DC probe.

OTHER APPLICATIONS

Although the embodiments have been described above, the embodiments of the present disclosure should be considered to be exemplary in all respects and not restrictive. The above-described embodiments may be omitted, replaced, or modified in various forms without departing from the scope of the appended claims and the gist thereof.

For example, in the above embodiment, as a plasma processing apparatus, an apparatus that performs plasma processing by surface wave plasma generated by radiating electromagnetic waves such as microwaves into the processing container from the plurality of electromagnetic wave introducing portions has been exemplified, but the present disclosure is not limited thereto. The electromagnetic wave introducing portion may be one. Further, the plasma processing apparatus is not limited to one that radiates electromagnetic waves to generate plasma, and may be a plasma processing apparatus using various other plasmas such as capacitively coupled plasma (CCP), inductively coupled plasma (ICP), magnetic resonance (ECR) plasma.

Further, in the above-described embodiments, the case where a semiconductor wafer is used as the substrate has been described, but the substrate is not limited to the semiconductor wafer, and may be another substrate such as a flat panel display (FPD) substrate typified by a liquid crystal display (LCD) substrate or a ceramic substrate.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.