JP3688173B2 - Probe for measuring plasma density information - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film element manufacturing process, a probe for measuring plasma density information in plasma used in a particle beam source, an analyzer, and the like, and more particularly to a technique for easily measuring plasma density information over a long period of time.
[0002]
[Prior art]
In recent years, plasma has been actively used. In the manufacturing process of the thin film element, for example, high-frequency plasma generated by high-frequency power (high-frequency power) having a frequency in the RF band of about 10 MHz to a frequency in the microwave band typified by 2.45 GHz is used, and etching or CVD ( Chemical vapor deposition) processing is performed. In such a plasma application technology, it is very important for performing appropriate processing to sufficiently grasp information on plasma density (plasma density information) that shows the characteristics of generated plasma well. In the case of a typical plasma consisting of monovalent positive ions and electrons, the electron density is usually equal because the positive ion density and the electron density are substantially equal due to the inherent properties of the plasma that remain electrically neutral. Is called plasma density.
[0003]
Conventionally, as a method for measuring the electron density in plasma, there are a Langmuir probe method, a microwave interference measurement method, and a relatively recently developed electron beam irradiation type plasma vibration probe method.
[0004]
In the Langmuir probe method, the current that flows through the metal probe when a metal probe is directly exposed to the plasma and a DC bias voltage or a DC bias voltage superimposed with a high-frequency voltage is applied to the metal probe. In this method, the electron density is obtained based on the value.
[0005]
In the microwave interferometry method, a window facing the plasma is provided on the wall of the plasma generation chamber, and microwaves (for example, monochromatic laser light) are incident on the plasma from one window and pass through the plasma. In this method, the microwave emitted from the other window is detected, and the electron density is obtained based on the phase difference between the incident and outgoing microwaves.
[0006]
The electron beam irradiation type plasma vibration method is a method of obtaining an electron density based on a frequency of plasma vibration generated when a heat filament is placed in a chamber and an electron beam is irradiated from the heat filament to the plasma.
[0007]
[Problems to be solved by the invention]
However, when the Langmuir probe method is applied to reactive plasma, there is a problem that measurement cannot be continued for a long time (that is, the lifetime is short). This is because dirt made of an insulating film adheres to the surface of the metal probe being measured in a short time, and the current value flowing through the metal probe fluctuates, so that accurate measurement cannot be performed immediately. In order to remove dirt attached to the surface of the metal probe, a method of applying a negative bias voltage to the metal probe and removing the spatter by ions, and a method of evaporating and removing the dirt by making the metal probe red-heated have been tried. The effect is thin and the problem cannot be solved.
[0008]
Further, the microwave interferometry method has a problem that the measurement is not easy to perform. This is because it is necessary to adjust a large and expensive device and a difficult microwave transmission path, and since the phase difference between the incident and outgoing microwaves is small, accurate measurement is difficult. In addition, the microwave interferometry method has a drawback that only an average density is obtained and there is no spatial resolution.
[0009]
Further, in the case of the electron beam irradiation type plasma vibration probe method, there is a problem that the measurement is interrupted due to disconnection of the hot filament in addition to the concern of contamination of the plasma atmosphere by tungsten evaporated from the hot filament. In particular, in the case of plasma using oxygen or chlorofluorocarbon gas, it is difficult to say that the hot filament is suitable for practical use because the hot filament is easily broken and the filament needs to be frequently exchanged.
[0010]
Therefore, the present applicant has previously filed Japanese Patent Application No. 11-058636 in order to solve the above problems. This Japanese Patent Application No. 11-058636 (hereinafter abbreviated as “prior invention” where appropriate) adopts the following configuration and provides an effect.
[0011]
[Principle of prior invention]
FIG. 8 is a partial longitudinal sectional view showing a configuration of an example of a probe for measuring plasma density information according to the previous invention (hereinafter abbreviated as “measurement probe” as appropriate).
As shown in FIG. 8, the measurement probe 101 is provided in the chamber 102 with the tip of the measurement probe 101 inserted. The chamber 102 has reactive plasma (hereinafter abbreviated as “plasma” as appropriate) PM generated by a high-frequency power source.
[0012]
The measurement probe 101 has a closed end and a rear end open to the atmosphere (outside air). The loop antenna 103 and the coaxial cable 104 are housed in the tube 105 so that the loop antenna 103 comes first. Furthermore, by pulling or pushing the coaxial cable 104 with respect to the longitudinal direction of the tube 105, the measurement probe 101 can easily change the length L from the root of the loop antenna 103 to the tip of the tube 105. it can.
[0013]
The power incident from the high-frequency oscillator is transmitted by the measurement probe 101 and is emitted from the loop antenna 103 and absorbed by the plasma load or reflected and returned. FIG. 9 shows the measurement of the change in the reflectance of the high-frequency power with respect to frequency (100 kHz to 3 GHz) at each tip length L.
[0014]
The place where the reflectance greatly decreases is an absorption peak (hereinafter referred to as “absorption point” where appropriate) where strong absorption of high-frequency power occurs due to the plasma density. In the curves Ra to Rf of FIG. 9, several absorption points Pa to Pd showing that there is strong absorption of the high frequency power on the plasma load side appear. The frequency at the positions of the absorption points Pa to Pd is the plasma absorption frequency. Since the plasma absorption frequency has a certain correlation with the plasma density, useful plasma density information can be obtained. When the plasma absorption frequency is the surface wave resonance frequency f, the electron density n in the plasma is substantially equivalent to the plasma density. _e The plasma density information can be obtained by calculating.
[0015]
As shown in FIG. 10, only the absorption point Pa having the lowest frequency appears at the same frequency position even if the tip length L changes. Thus, the plasma absorption frequency independent of the tip length L is the plasma surface wave resonance frequency f. Even if the absorption point appears on the lowest frequency side, if the tip length L is changed, the one whose frequency is displaced is not the plasma surface wave resonance frequency. That is, in the previous invention, in order to confirm whether or not the absorption point appearing on the lowest frequency side is the plasma surface wave resonance frequency, the tip length L is measured for measurement.
[0016]
When the plasma surface wave resonance frequency f is thus obtained, as described above, the electron plasma angular frequency ω _p And electron density n of plasma PM _e That is, plasma density n _p However, since it is easily calculated, it is easy to grasp the characteristics of the generated plasma PM.
[0017]
In the case of the prior invention, since the tube 105 is interposed between the loop antenna 103 and the coaxial cable 104 and the plasma PM, foreign matter or the like does not enter the plasma PM from the loop antenna 103 or the coaxial cable 104, and the plasma is cleaned. Sex can be secured. Further, the tube 105 is interposed, thereby preventing the loop antenna 103 and the coaxial cable 104 from being damaged by the plasma PM. In addition, even if dirt made of an insulating film adheres thinly to the surface of the tube 105 during measurement, the measurement system does not substantially change because the insulating film is a dielectric, and measurement due to dirt on the insulating film. There will be no variation in results. Therefore, plasma density information can be measured over a long period of time.
[0018]
In addition, since the high frequency power is supplied from the loop antenna 103 through the tube 105 and the absorption phenomenon of the resonant high frequency power that is easy to measure is captured, the plasma density information can be measured very easily. Furthermore, since it is a hot filament-less system, there is no need to worry about atmospheric contamination by evaporated tungsten and it is not necessary to replace the hot filament.
[0019]
Before explaining the problem of the prior invention, a supplementary explanation will be given regarding the plasma absorption frequency.
As shown in FIGS. 9 and 10, the plasma absorption point most dependent on the tip length L among the plasma absorption points Pa to Pd is Pb. In this specification, the plasma absorption point Pb is defined as a zero-order absorption point or MAIN ABS (Absorption). The absorption point that depends on the tip length L next to the absorption point Pb is Pc. The absorption point Pc is defined as a primary absorption point. In the same manner, the absorption point is defined as a high-order absorption point (higher order, lower order is defined as lower order).
[0020]
When defined as described above, the higher the order, the less the absorption point depends on the tip length L. Note that the frequency of the absorption point of the highest order (infinity order, ∞ order) is the plasma surface wave resonance frequency. The ∞ order absorption point is Pa, and Pa is constant regardless of the tip length L as described above. When the tip length L is brought close to 0, both the high-order absorption point and the low-order absorption point converge at the absorption point Pa at the surface wave resonance frequency.
[0021]
On the other hand, although not theoretically explained yet, as shown in FIG. 9, the absorption point tends to decrease as the order increases in the experiment. Therefore, the ∞ order absorption point Pa has the smallest absorption. On the contrary, the lowest absorption point, that is, the zeroth absorption point has the largest absorption.
[0022]
[Problems to be solved by the present invention]
However, the above-described prior invention also has the following problems.
As described above, MAIN ABS (0th order absorption point) tends to be large. However, in fact, the high-order absorption points that are important in calculating the plasma density, especially the (∞ order) absorption points Pa at the plasma surface wave resonance frequency, have a wide half-value width and tend to have a low absorption level. It is difficult to read the resonance frequency.
[0023]
As described above, when the tip length L is brought close to 0, both the high-order absorption point and the low-order absorption point converge to the absorption point Pa at the surface wave resonance frequency. Therefore, in order to read the absorption point Pa, it is only necessary to look at the absorption point when the tip length L = 0. However, in order to actually set the tip length L = 0, the antenna must be made as short as possible. In addition, if the antenna is shortened, the sensitivity is deteriorated, which is impossible in practice.
[0024]
Further, it is assumed that the absorption point appearing on the lowest frequency side considered to be the plasma surface wave resonance frequency can be read except for the tip length L = 0. However, even in that case, as described above, if the absorption point depends on the tip length L, the frequency is no longer the plasma surface wave resonance frequency. That is, in order to confirm whether or not the absorption point appearing on the lowest frequency side is the plasma surface wave resonance frequency, it is necessary to measure by changing the tip length L. Therefore, the absorption point cannot be determined unless measurement is repeated under different conditions. For this reason, there is a drawback that it requires experience and lacks versatility.
[0025]
For the above reasons, there is a demand for a method that can be read without requiring experience in determining higher-order absorption points. Therefore, the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a plasma density information measuring probe capable of reading the plasma surface wave resonance frequency without moving the length of the tip. And
[0026]
[Means for Solving the Problems]
In the prior invention, as shown in FIG. 8, the dielectric tube inside the surface wave excitation part at the tip of the measurement probe is composed of only a dielectric region such as air. At this time, as shown in FIG. 10, as the tip length L increases, the absorption point shifts to the high frequency side. Further, when the dielectric region is replaced with a conductor region, it is considered that the absorption point shifts to the low frequency side as the tip length L increases.
[0027]
FIG. 11 shows an electron plasma angular frequency ω when a loop antenna is used. _P Of the angular frequency at the absorption point with respect to (ω / ω _P ) Of the change in the length L of the tip portion. Incidentally, the electron plasma angular frequency ω _P Is the surface wave resonance angular frequency ω _SW (Ω _SW = 2πf, f: surface wave resonance frequency) and relative dielectric constant ε, ω _p = Ω _SW X√ (1 + ε).
[0028]
The (plot) points in FIG. 11 are actually measured values for the dielectric region only, and the solid line is the theoretical value. A black circle plot is an actual measurement value of MAIN ABS (0th-order absorption point), and a white circle plot is an actual measurement value of SECOND (first-order absorption point). Similarly, black and white square plots are measured values of THIRD (second order absorption point) and FOURTH (third order absorption point), respectively. Solid lines m = 0, 1, 2, and 3 are theoretical values of zero-order, first-order, second-order, and third-order absorption points, respectively. The broken line is the theoretical value for the conductor region only. Note that when actually measuring only in the conductor region, the entire tip of the probe becomes a conductor region, and electromagnetic waves cannot be emitted from the antenna, which is physically impossible. Therefore, there is no actual measurement value for the conductor region alone.
[0029]
As shown in FIG. 11, the higher the values are, the measured values and the theoretical values, and the dielectric region and the conductor region, as shown in FIG. _P Becomes less dependent on the tip length L. FIG. 11 also shows that as the tip length L increases, the absorption point shifts to the high frequency side when only the dielectric region is present, and the absorption point shifts to the low frequency side when only the conductor region is present.
[0030]
From the above, in a single region, the tip portion length L changes, and shifts to the high frequency side or the low frequency side. Therefore, the present inventor has come up with the idea that the characteristics shifted to the high frequency side or the low frequency side can be canceled out by combining the dielectric region and the conductor region.
[0031]
The present invention created based on the above knowledge has the following configuration.
That is, the plasma density information measuring probe according to the first aspect of the present invention includes a dielectric outer shell having a closed tip, an antenna housed in the dielectric outer shell and radiating high-frequency power, and a dielectric Housed in outer skin Has been Contained in dielectric area and dielectric outer skin Has been With conductor area Including a structure in which a dielectric region and a conductor region are arranged in that order in the direction in which the antenna extends, near the tip of the dielectric outer skin, and the conductor region terminates at the tip of the dielectric outer skin. Have It is characterized by that.
[0032]
According to a second aspect of the present invention, in the plasma density information measuring probe according to the first aspect, the dielectric region is formed of a gas dielectric.
[0033]
According to a third aspect of the present invention, in the plasma density information measuring probe according to the first aspect, the dielectric region is formed of a solid dielectric.
[0034]
According to a fourth aspect of the present invention, in the plasma density information measuring probe according to any one of the first to third aspects, the conductor region is made of a metal.
[0035]
According to a fifth aspect of the present invention, in the plasma density information measuring probe according to any one of the first to fourth aspects, the conductor region is formed of a metal film disposed in a dielectric outer skin. It is characterized by being.
[0036]
According to a sixth aspect of the present invention, there is provided the plasma density information measuring probe according to the first aspect, wherein the center conductor, the central insulator, the outer conductor, and the outer insulation are arranged concentrically in order from the center toward the outer side. It is composed of a coaxial cable consisting of a body, the dielectric sheath is formed of an outer insulator of the coaxial cable, the antenna is formed of the central conductor of the coaxial cable, and the dielectric region is formed of the outer insulator and the outer conductor of the coaxial cable. It is characterized in that it is formed of a central insulator exposed by removing it in the form of a slit, and the conductor region is formed of an outer conductor of a coaxial cable ahead of the slit.
[0037]
The invention according to claim 7 is the plasma density information measuring probe according to any one of claims 1 to 6, wherein the dielectric region and the conductor region are formed in a multilayer structure. To do.
[0038]
[Action]
The operation of the first aspect of the invention will be described.
In the case of only the dielectric region, the absorption point shifts to the high frequency side as the length of the dielectric region increases. Conversely, when only the conductor region is present, the absorption point shifts to the low frequency side as the length of the conductor region increases. Therefore, in order to take advantage of the characteristics of each dielectric region and conductor region, the following configuration is adopted. That is, the antenna is housed in a dielectric outer cover, a dielectric region is further disposed near the tip of the antenna, and a conductor region is disposed closer to the tip of the antenna than the dielectric region. As described above, by combining the dielectric region and the conductor region, the two characteristics that the absorption point shifts to the high frequency side or the low frequency side cancel each other. As a result, the absorption point does not depend on the length of the air layer and the metal layer at the tip of the antenna.
[0039]
According to the second aspect of the present invention, since the dielectric region is formed of a gas dielectric, the thickness, length, etc. can be easily changed. In particular, air is familiar among gas dielectrics and is very easy to handle.
[0040]
According to the third aspect of the present invention, by selecting a solid in the dielectric region, the relative dielectric constant ε of the solid dielectric larger than that of the gas dielectric can be selected up to around 10. By this selection, it is possible to freely adjust the impedance of the transmission system between the high frequency supply side and the load side where the surface waves are excited, thereby suppressing reflection loss.
[0041]
According to the invention described in claim 4, by selecting a metal for the conductor region, processing is simple and high conductivity can be obtained in a wide temperature range. As a result, the probe can function stably even under severe temperature conditions (100 to 500 °) in the chamber.
[0042]
According to the fifth aspect of the present invention, since the conductor region is formed by the metal film disposed in the dielectric outer skin, there is no gap between the metal film and the dielectric outer skin.
[0043]
According to the sixth aspect of the present invention, in the coaxial cable including the central conductor, the central insulator, the outer conductor, and the outer insulator, which are arranged concentrically in order from the center toward the outer side, The conductor (and external insulator) is removed in a slit shape, and the central insulator is exposed in the slit shape. Therefore, the outer insulator of the coaxial cable corresponds to the dielectric outer sheath in the present invention, the central conductor of the coaxial cable corresponds to the antenna in the present invention, and the outer insulator and outer conductor of the coaxial cable are removed in a slit shape. The exposed central insulator corresponds to the dielectric region in the present invention, and the outer conductor of the coaxial cable beyond the slit corresponds to the conductor region in the present invention.
[0044]
According to the seventh aspect of the present invention, the dielectric region and the conductor region are formed in a multilayer structure. Therefore, the surface wave is efficiently absorbed by the conductor layers extending in multiple layers.
[0045]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a probe for measuring plasma density information according to an embodiment. FIG. 2 is a longitudinal sectional view showing a measurement probe when measuring an absorption point. FIG. 3 is a schematic diagram of the plasma processing apparatus according to the embodiment. FIG. 4 is a graph showing the reflectance frequency characteristic of the high frequency power for measuring plasma density information according to the example.
[0046]
First, the configuration and operation of the plasma processing apparatus of the embodiment will be described. Incidentally, the above-described plasma processing apparatus is also used when obtaining the plasma density in the previous invention.
As shown in FIG. 3, the plasma processing system according to the embodiment includes a stainless steel chamber 11 having a diameter of several tens of centimeters having an indoor space S in which plasma PM is generated, and a plasma generating system disposed in the chamber 11. Via a discharge electrode (discharge antenna) 12, a vacuum exhaust pump 14 communicating with the indoor space S of the chamber 11 via an exhaust pipe 13, and a gas supply pipe 16 provided with a flow rate control valve 15. A gas source 17 communicating with the indoor space S of the chamber 11 is provided. In addition, in the chamber 11 of the system of the embodiment, a mounting table (not shown) for a workpiece (workpiece) W, a loading / unloading mechanism (not shown) for the workpiece W, and the like are also provided.
[0047]
The indoor space S of the chamber 11 is evacuated by the vacuum exhaust pump 14, and an appropriate indoor pressure is maintained. Gas is supplied from the gas source 17 at an appropriate flow rate. Examples of the supply gas include argon, nitrogen, oxygen gas, fluorine-based gas, and chlorine-based gas.
[0048]
In addition, a high frequency power source 18 for supplying high frequency power (high frequency power) for plasma generation outside the chamber 11 and a high frequency power for plasma generation supplied to the discharge electrode 12 (hereinafter referred to as “high frequency power for generation” as appropriate). A high-frequency power control unit 19 is provided for controlling (abbreviated “)”.
[0049]
The high frequency power control unit 19 includes an impedance matching unit 20a that adjusts an impedance matching state between the high frequency power supply side and the plasma side, and a plasma density setting unit 20b that sets a target plasma density for plasma generated in the chamber 11. The matching unit controller 20c controls the impedance matching unit 20a according to the difference between the set target plasma density and the actually measured plasma density.
[0050]
In the case of the system of the embodiment, an output power monitor mechanism (not shown) for detecting the output amount of the high frequency power output from the high frequency power source 18 or a high frequency that returns to the power source side without being absorbed on the plasma load side. A reflection power monitor mechanism (not shown) for detecting the amount of power reflection is provided as one means for roughly grasping the plasma generation state.
[0051]
The workpiece W is subjected to an etching process, a CVD (chemical vapor deposition) process, and the like by the plasma PM generated as described above. In the system of the embodiment, as described below, A plasma density information obtaining unit 21 for obtaining density information from time to time is provided. In addition, as shown in FIG. 3, the plasma density information obtaining unit 21 according to the embodiment includes a measurement probe 1 attached to the wall of the chamber 11 and a probe control unit 22 disposed outside the chamber 11. Consists of. First, a specific configuration of the measurement probe 1 will be described.
[0052]
As shown in FIG. 1, the measurement probe 1 according to the embodiment includes a dielectric tube 2 whose tip is closed, and an antenna 3 that radiates high-frequency power is accommodated in the tube 2. A coaxial cable 4 that transmits high-frequency power to the antenna 3 is connected to the rear end of the antenna 3. Furthermore, it is near the tip of the antenna 3 (In other words, near the tip of the tube 2 corresponding to the dielectric outer skin) Is provided with an air layer 5. Further closer to the tip of the antenna 3 than the air layer 5, a metal layer 6 represented by copper or the like is disposed. The tube 2 corresponds to a dielectric outer skin in the present invention, the air layer 5 corresponds to a dielectric region in the present invention, and the metal layer 6 corresponds to a conductor region in the present invention.
[0053]
The thickness t of the air layer 5 along the axis of the tube 2 (hereinafter abbreviated as “the thickness t of the air layer 5” as appropriate) is preferably 1 mm to 10 mm. When the thickness t of the air layer 5 is less than 1 mm, it is difficult to radiate high-frequency power, and when the thickness t of the air layer 5 exceeds 10 mm, the high-frequency power is difficult to diffuse into the metal layer 6. The thickness l of the metal layer 6 along the axial center of the tube 2 (hereinafter abbreviated as “the thickness l of the metal layer 6” as appropriate) is also preferably 1 mm to 10 mm. If the thickness l of the metal layer 6 is less than 1 mm, the effect of the metal layer 6 is small, and if the thickness l of the metal layer 6 exceeds 10 mm, surface waves are not easily transmitted, so it is not necessary to make it 10 mm or more.
[0054]
In this embodiment, a linear antenna is used as the antenna 3 that radiates high-frequency power. However, the loop antenna of the prior invention may be used, and the shape of the antenna is not limited. In FIG. 1, the antenna 3 is connected to the metal layer 6. However, if the high-frequency power radiated by the antenna 3 is sufficiently diffused in the metal layer 6, the antenna 3 is not necessarily connected to the metal layer 6. . In addition, although the dielectric material which forms the tube 2 is not specifically limited, For example, quartz, ceramics, glass, a fluororesin etc. are illustrated. Further, the outside of the antenna 3, the coaxial cable 4, the air layer 5, and the metal layer 6 need not necessarily be covered by the tube 2. If it is coated with a substance formed of a dielectric, it can be used as the measurement probe 1.
[0055]
It has been confirmed by experiments that the measurement probe 1 having the above configuration does not shift the absorption point to the high frequency side or the low frequency side even if the length of the tip of the tube 2 is changed. For the experiment, the measurement probe 1 has a configuration as shown in FIG. That is, the tip air layer 7 is disposed in the tube 2 near the tip of the metal layer 6, and the tip length d of the tip air layer 7 can be easily changed. In addition, in order to distinguish from the front-end | tip part length L in the Example which concerns on a prior invention, the length of the front-end | tip part in a present Example is made into the front-end | tip part length d. The tip length L in the previous invention indicates from the root of the loop antenna 103 to the tip of the tube 105 (prior invention), but the tip length d in this embodiment is the tip of the metal layer 6. The thickness of the air layer 7 at the distal end along the axial center of the tube 2 is shown.
[0056]
Next, a specific configuration of the probe control unit 22 will be described. The probe control unit 22 includes a frequency sweep type high-frequency oscillator 23, a directional coupler 24, an attenuator 25, and a filter 26, which are sequentially supplied to the measurement probe 1 in the order shown in FIG. It is connected. The high frequency oscillator 23 outputs high frequency power for measuring plasma density information at a frequency of 100 kHz to 800 MHz while automatically sweeping. The high frequency power output from the high frequency oscillator 23 is transmitted to the measurement probe 1 via the directional coupler 24 -the attenuator 25 -the filter 26.
[0057]
On the other hand, the high-frequency power for measuring plasma density information (hereinafter abbreviated as “measurement high-frequency power” as appropriate) is not necessarily emitted from the antenna 3 and absorbed by the plasma load, but reflected without being absorbed by the plasma load. There is also a part that comes back. The amount of reflection of the high frequency power that returns without being absorbed by the plasma load is detected by the directional coupler 24 and sent to the plasma absorption frequency finding unit 27. The frequency of the high frequency power for measurement output from the high frequency oscillator 23 is also sequentially sent to the plasma absorption frequency obtaining unit 27.
[0058]
The filter 26 functions to remove high frequency power for plasma excitation mixed into the probe controller 22 via the antenna 3. The attenuator 25 functions to adjust the amount of high frequency power for measurement fed into the measurement probe 1.
[0059]
The plasma absorption frequency obtaining unit 27 obtains the change in the reflectance of the measurement high frequency power with respect to the frequency according to the frequency of the high frequency power and the detected reflection amount of the high frequency power, and calculates the plasma density based on the obtained result. Thus, the plasma absorption frequency at which strong absorption of high frequency power occurs is obtained. That is, the plasma absorption frequency obtaining unit 27 calculates [the detected reflection amount of the high frequency power] / [total output amount of the high frequency power (a constant amount in the embodiment)] to obtain the reflectance of the measurement high frequency power. Then, a process for obtaining a change in the reflectance of the high-frequency power for measurement with respect to the frequency is performed by plotting the frequency corresponding to the ever-changing frequency. The place where the reflectance greatly decreases is an absorption peak or absorption point at which strong absorption of high-frequency power occurs due to the plasma density, and the frequency of the absorption point is the plasma absorption frequency. Further, the plasma absorption frequency obtaining unit 27 performs a process of automatically detecting an absorption point and authorizing and calculating a corresponding frequency as a plasma absorption frequency.
[0060]
The plasma absorption frequency obtained by the plasma absorption frequency obtaining unit 27 is useful plasma density information having a certain correlation with the plasma density. In the case of the embodiment system, the plasma absorption frequency is the surface wave resonance frequency f. The surface wave resonance frequency f is substantially equivalent to the plasma density and the electron density n in the plasma. _e Is useful plasma density information that directly corresponds to
[0061]
Subsequently, a specific measurement example of the absorption point by the measurement probe 1 of the embodiment will be described.
Argon gas is supplied into the chamber, and the pressure in the chamber is adjusted to 20 Pa. 550 W is output from the high frequency power source as the high frequency power for plasma generation. The output high frequency power for plasma generation generates a reactive plasma PM by the discharge electrode in the chamber. The tube 2 is formed of a quartz tube having an outer diameter of 6 mm and a thickness of 1 mm. The coaxial cable 4 is formed of a 50Ω semi-rigid cable. The metal layer 6 is made of copper and has a thickness l of 2 mm. The thickness t of the air layer 5 is 6 mm.
[0062]
First, the measurement probe 1 is set so that the tip portion length d of the tip portion air layer 7 is 1 mm. The high frequency power is output from the high frequency oscillator while sweeping the frequency from 100 kHz to 800 MHz. Then, the reflectivity (expressed in dB) of the high frequency power at that time is measured. In the same manner, the measurement probe 1 is set so that the tip length d is 2 mm, 3 mm, 4 mm, and 5 mm, and the change in the reflectance of the high-frequency power with respect to frequency is measured. The measurement results are as shown in FIG.
[0063]
The place where the reflectance is greatly lowered is an absorption point where strong absorption of high-frequency power occurs due to the plasma density. As shown in FIG. 4, even if the tip length d is changed, the absorption point does not shift to either the high frequency side or the low frequency side. That is, the plasma absorption frequency at the absorption point does not depend on the tip length d. From this, it can be seen that the surface wave does not reach the tip air layer 7, and the high frequency power is absorbed by the plasma only by the air layer 5 and the metal layer 6. On the other hand, although the dispersion | distribution of an absorption point is seen in FIG. 9 which concerns on the measurement result of prior invention, the dispersion | distribution of an absorption point is not seen in FIG. Therefore, the low-order absorption point including the zeroth-order absorption point (MAIN ABS) and the high-order absorption point including the ∞-order absorption point (absorption point at the plasma surface wave resonance frequency) converge. I understand. Furthermore, as compared with FIG. 9 of the previous invention, it can be seen that in FIG. 4, an absorption point having a large Q value is obtained, that is, the absorption point is large. In this specification, loss at resonance, that is, absorption at resonance is defined as a Q value (quality factor).
[0064]
Since the plasma absorption frequency does not depend on the tip length d, it can be seen that the plasma surface wave resonance frequency can be measured without moving the antenna 3. Further, since the high frequency power is absorbed by the plasma only with the air layer 5 and the metal layer 6, it can be seen that the measurement can be performed only with the configuration of FIG. Further, since the low-order and high-order absorption points are converged and the absorption point is large, the absorption point at the plasma surface wave resonance frequency can be easily read.
[0065]
The present invention is not limited to the above embodiment, and can be modified as follows.
(1) In the above embodiment, the air layer 5 is disposed near the tip of the antenna 3, but such a configuration is not necessarily required. Since the air layer 5 corresponds to the dielectric region in the present invention as described above, a dielectric material may be disposed near the tip of the antenna 3. Among the dielectric materials, the gas dielectric is particularly easy to handle, and the thickness and length can be easily changed. In particular, when the dielectric region is formed of the air layer 5 as in the above-described embodiment among the gas dielectrics, the air is close and easy to handle as the measurement probe 1. Among the dielectric materials, the following can be performed in the case of a solid dielectric. That is, the relative dielectric constant ε of the solid dielectric is larger than the relative dielectric constant of the gas dielectric, so that the larger the relative dielectric constant, the higher the Q value and the greater the absorption at resonance. Therefore, since the absorption at the time of resonance in the solid dielectric is larger than the absorption at the time of resonance of the gas dielectric, the plasma absorption frequency at the time of resonance can be easily calculated. Moreover, since it is formed of a solid, it is stable thermally and mechanically. The solid dielectric material is not particularly limited, and examples thereof include quartz, ceramics, glass, and fluororesin.
[0066]
(2) In the case of the embodiment, the metal layer 6 is disposed closer to the tip of the antenna 3 than the air layer 5. However, as described above, since the metal layer 6 corresponds to the conductor region in the present invention, a substance made of a conductor may be accommodated closer to the tip of the antenna 3 than the air layer 5 or the dielectric region. Further, among the conductive materials, the following can be performed in the case of metal. Since processing is easy and high conductivity is obtained in a wide temperature range, the probe can be stably functioned even under severe temperature conditions (100 to 500 °) in the chamber. In addition, although the kind of metal is not specifically limited, For example, copper, aluminum, stainless steel, etc. are illustrated. Further, the conductor material other than the metal is not particularly limited, and for example, carbon or the like can be used as the conductor material.
[0067]
(3) In the case of the embodiment, as shown in FIGS. 1 and 2, the inside of the metal layer 6 is entirely made of metal. However, a metal film may be provided on the inner wall of the tube 2 instead of the metal layer 6. As described above, since the tube 2 corresponds to the dielectric outer skin in the present invention, a metal film may be disposed in the dielectric outer skin. Specifically, as shown in FIG. 5, it can be considered that a metal coating 8 is applied to the inner wall of the tube 2. In the case of the above configuration, since there is no gap between the metal film and the dielectric outer skin, there is stability compared to the case where the conductor region is simply disposed in the dielectric outer skin. .
[0068]
(4) In the case of the embodiment, a coaxial cable 4 that transmits high-frequency power to the antenna 3 from the rear end of the antenna 3 is connected to the tube 2. However, since the covering portion of the coaxial cable 4 is made of an insulating material and made of a dielectric material, it is not necessarily covered by the tube 2. That is, the coaxial cable 4 can be used as the measurement probe 1 by removing the outer conductor and the outer insulator of the coaxial cable 4 in a slit shape. Specifically, as shown in FIG. 6, with respect to the coaxial cable 4, by removing one portion of the outer dielectric insulator 4a and the outer conductor 4b made of a conductor in a slit shape, The measurement probe 1 can be easily made. In FIG. 6, the dielectric region 9 is a portion of the dielectric central insulator 4 c exposed by removing the slit region. The conductor region 10 is a portion of the outer conductor 4b of the coaxial cable 4 ahead of the slit. The center conductor 4d corresponds to the antenna in the present invention, and the external insulator 4a corresponds to the dielectric outer skin in the present invention. If a semi-rigid type coaxial cable is used, the same effect can be obtained as when a slit is provided by cutting the outer conductor and shifting it by several millimeters. In this case, it is necessary to close the end portion of the coaxial cable with a conductor and an insulator. Such processing is very simple and a sufficient effect can be obtained. In the case where the coating portion of the coaxial cable, that is, the external insulator is made of a dielectric material having low heat resistance, the coaxial cable having the above-described configuration may be inserted into the dielectric tube as in the above-described embodiment. .
[0069]
(5) In the case of the embodiment, as shown in FIG. 1, only the air layer 5 and the metal layer 6 are disposed near the tip of the antenna 3. However, as shown in FIG. 7, the dielectric region and the conductor region may be arranged in multiple layers near the tip of the antenna 3. Therefore, the surface wave is absorbed more by the conductor layers extending in multiple layers, so that the Q value is increased. Therefore, the plasma absorption frequency at the time of resonance can be easily calculated.
[0070]
【The invention's effect】
As described above in detail, according to the probe for measuring plasma density information according to the first aspect of the present invention, the dielectric point and the conductor region are provided in the dielectric outer skin, so that the absorption point is low or low. Both characteristics shifted to the frequency side cancel each other. Therefore, even if the length of the tip is changed, the absorption point does not shift. Furthermore, since the low-order and high-order absorption points converge and a high-order absorption point having a large Q value can be obtained, the absorption points at the plasma surface wave resonance frequency can be easily read. As described above, the plasma surface wave resonance frequency can be accurately obtained by only one measurement without changing the length of the tip.
[0071]
According to the probe for measuring plasma density information according to the invention of claim 2, the dielectric region is formed of a gas dielectric. Among the dielectric materials, the gas dielectric is particularly easy to handle, and the thickness and length can be easily changed. In particular, air is familiar among gas dielectrics and is very easy to handle.
[0072]
According to the plasma density information measuring and measuring probe of the invention of claim 3, the dielectric region is formed of a solid dielectric. Since the relative dielectric constant ε of the solid dielectric is larger than that of the gas dielectric, the reflection loss is suppressed. As a result, the Q value is increased and the absorption at the time of resonance is increased. Therefore, since the absorption at the time of resonance in the solid dielectric is larger than the absorption at the time of resonance of the gas dielectric, the plasma absorption frequency at the time of resonance can be easily calculated. Further, since it is formed of a solid and is thermally and mechanically stable, a stable measurement result is always obtained.
[0073]
According to the probe for measuring plasma density information according to the invention of claim 4, by selecting a metal for the conductor portion, processing is simple and high conductivity can be obtained in a wide temperature range. As a result, the probe can function stably even under severe temperature conditions (100 to 500 °) in the chamber. The electron density of the metal is 10 ^{twenty three} / Cm ^Three 10 of the electron density of the plasma measured by the probe. ¹¹ / Cm ^Three Since it is sufficiently larger than the order and the Q value can be maximized, the absorption point can be accurately determined.
[0074]
According to the probe for measuring plasma density information according to the invention of claim 5, since the conductor region is formed of the metal film disposed in the dielectric outer skin, the gap between the metal film and the dielectric outer skin is determined. There are no gaps. Therefore, it is more stable than the case where the conductor region is simply disposed in the dielectric outer skin. Therefore, a stable measurement result can always be obtained.
[0075]
According to the probe for measuring plasma density information according to the invention of claim 6, in the coaxial cable comprising the central conductor, the central insulator, the outer conductor, and the outer insulator in concentric order from the center to the outer side, the coaxial cable The outer conductor and the outer insulator are removed in a slit shape, and the central insulator is exposed by the removal. In the above configuration, the outer insulator of the coaxial cable corresponds to the dielectric outer sheath in the present invention, the central conductor of the coaxial cable corresponds to the antenna in the present invention, and the outer insulator and the outer conductor of the coaxial cable are slit. The central insulator exposed by removing in the shape corresponds to the dielectric region in the present invention, and the outer conductor of the coaxial cable beyond the slit corresponds to the conductor region in the present invention. Therefore, the measurement probe according to the present invention can be easily made by simply cutting and shifting the coaxial cable.
[0076]
According to the probe for measuring plasma density information according to the invention of claim 7, the dielectric region and the conductor region are formed in a multilayer structure. Therefore, since the surface wave is efficiently absorbed by the conductor layers extending in multiple layers, the Q value becomes high.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a probe for measuring plasma density information according to an embodiment.
FIG. 2 is a longitudinal sectional view of a measurement probe used for an example of measuring an absorption point.
FIG. 3 is a schematic view of a plasma processing apparatus according to an embodiment.
FIG. 4 is a graph showing reflectance frequency characteristics of high-frequency power for measuring plasma density information according to an example.
FIG. 5 is a longitudinal sectional view showing a modification of the measurement probe according to the present invention.
FIG. 6 is a longitudinal sectional view showing another modification of the measurement probe according to the present invention.
FIG. 7 is a longitudinal sectional view showing another modification of the measurement probe according to the present invention.
FIG. 8 is a partial longitudinal sectional view showing a configuration of an example of a measurement probe according to the previous invention.
FIG. 9 is a graph showing reflectance frequency characteristics of high-frequency power for measuring plasma density information according to the previous invention.
FIG. 10 is a graph showing the relationship between the plasma absorption frequency and the length of the tip of the tube of the measurement probe according to the previous invention.
FIG. 11 is a theoretical value and an actual measurement value showing a relationship between a ratio of an angular frequency at an absorption point to an electron plasma angular frequency and a tip end length of the antenna.
[Explanation of symbols]
1 ... Measurement probe
2… Tube
3 ... Antenna
4 ... Coaxial cable
4a: External insulator
4b ... outer conductor
4c ... center insulator
4d ... Center conductor
5 ... Air layer
6 ... Metal layer
7 ... Air layer at the tip
8 ... Metal coating
9 ... Dielectric region
10 ... Conductor region
PM ... reactive plasma
t: thickness of the air layer 5
l ... thickness of metal layer 6
d: Length of tip

Claims (7)

A dielectric outer skin whose tip is closed;
An antenna that is housed in a dielectric envelope and radiates high frequency power;
A dielectric region housed in a dielectric skin;
A conductor region housed in a dielectric outer skin ,
It includes a structure in which a dielectric region and a conductor region are arranged in that order in the direction in which the antenna extends, near the tip of the dielectric outer skin, and the conductor region terminates at the tip of the dielectric outer skin. A probe for measuring plasma density information. The probe for measuring plasma density information according to claim 1,
A probe for measuring plasma density information, wherein the dielectric region is formed of a gas dielectric. The probe for measuring plasma density information according to claim 1,
A probe for measuring plasma density information, wherein the dielectric region is formed of a solid dielectric. The probe for measuring plasma density information according to any one of claims 1 to 3,
A probe for measuring plasma density information, wherein the conductor region is made of metal. The probe for measuring plasma density information according to any one of claims 1 to 4,
A probe for measuring plasma density information, wherein the conductor region is formed of a metal film disposed in a dielectric outer skin. The probe for measuring plasma density information according to claim 1 is composed of a coaxial cable composed of a central conductor, a central insulator, an outer conductor, and an outer insulator arranged concentrically in order from the center toward the outside. And
The dielectric skin is formed by the external insulation of the coaxial cable,
The antenna is formed by the central conductor of the coaxial cable,
The dielectric region is formed by the central insulator exposed by removing the outer insulator and outer conductor of the coaxial cable in a slit shape,
The probe for measuring plasma density information, wherein the conductor region is formed by an outer conductor of a coaxial cable ahead of the slit. The probe for measuring plasma density information according to any one of claims 1 to 6,
A probe for measuring plasma density information, wherein a dielectric region and a conductor region are formed in a multilayer structure.

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