JP2009087790A - Device and method for measuring electron density, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately and easily measure the density of electrons in plasma. <P>SOLUTION: A tubular member 4 formed of a dielectric material is provided in a range from the sidewall on one side of a plasma generation chamber 2 via a plasma generation region toward the sidewall on the other side. An antenna probe 5 is slid therein which consists of a coaxial cable 51 having an antenna portion 52, and a conductive member 53 provided on the front side in the moving direction of the antenna portion 52 via a gap. A network analyzer 7 is connected to the coaxial cable 51 for finding the absorption frequency of high frequency waves in an axial symmetry mode. In accordance with the absorption frequency, the density of electrons in plasma is computed. The absorption frequency obtained by using the antenna probe 5 is highly reliable, and so the density of electrons can be found with high accuracy. The antenna probe 5 is simply slid inside the tubular member 4, and so it can be easily moved while securing air tightness, resulting in easy measurement. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for measuring electron density in plasma in a plasma generation chamber.

  In a semiconductor device manufacturing process, a semiconductor process using plasma technology is performed for an etching process, a film forming process, and the like. In a plasma processing apparatus that performs such a process, in order to improve in-plane uniformity of processing. In addition, it is required to irradiate the substrate with plasma having a uniform electron density. For this reason, it is necessary to grasp in what state the plasma is generated inside the chamber at the stage of designing and starting up the apparatus, and the importance of measuring the electron density of the plasma is increasing.

  As a method for measuring the electron density of plasma, a method using a plasma absorption probe (PAP) has been proposed (see Non-Patent Document 1). For example, as shown in FIG. 8, the plasma absorption probe 1 used in this method inserts a coaxial cable 11 into a quartz tube 10 whose tip is closed in a spherical shape, and from the tip of the coaxial cable 11, Only the inner conductor 11 a of the coaxial cable 11 is exposed and used as an antenna, and the other end of the cable 11 is connected to the network analyzer 12. At the time of measurement, the plasma absorption probe 1 is inserted into a plasma atmosphere to be measured, and frequency sweeping is performed from the network analyzer 12 to the antenna 11a of the coaxial cable 11 in a band of several MHz to several GHz. While supplying minute electric power, the absorption frequency is obtained.

  That is, when electric power is supplied to the coaxial cable 11, surface waves are excited at the interface between the plasma and the quartz tube 10 by the electromagnetic field around the antenna 11 a, and when the frequency reaches a frequency determined by the electron density of the plasma, A standing wave stands resonantly at the head of the absorption probe 1. The frequency at this time is referred to as an absorption frequency. At this absorption frequency, the power supplied to the antenna 11a of the probe 1 is resonantly absorbed by the plasma, and the power reflected from the plasma and returning to the antenna 11a is reduced. Therefore, the absorption frequency can be grasped by obtaining the frequency at this time.

  The network analyzer 12 measures the ratio (reflectance) of the power of the incident wave to the antenna 11a and the power of the reflected wave reflected by the plasma and returning to the antenna 11a, and the reflectance is determined as the sweep frequency. The spectrum has a function of displaying a spectrum, and the absorption frequency is obtained from this spectrum. On the other hand, a theoretical formula is required that the electron density of plasma is proportional to the square of the absorption frequency, and the electron density can be calculated by measuring the absorption frequency.

  When an electron density distribution of plasma in the chamber is actually created using such a plasma absorption probe 1, the plasma absorption probe 1 is inserted into the chamber and a plurality of measurement positions at the same height in the chamber. The electron density is determined at each measurement position. However, it is difficult and cumbersome to position the plasma absorption probe 1 at a plurality of measurement positions in a state in which the airtightness in the chamber is ensured and the heights are aligned. In the development stage and start-up stage of the device, the electron density is measured many times at the same position, and an electron density distribution is created and compared with each other. Since it is difficult to move the plasma absorption probe 1, it is difficult to ensure high reproducibility of the measurement position. If measurement is performed with the plasma absorption probe 1 moved with high positional accuracy, a considerable amount of time is required. There is a problem that it takes time and effort.

  In order to solve this problem, for example, as shown in FIG. 9, an insulating tube 14 made of, for example, quartz is horizontally bridged between mutually opposing side walls of a chamber 13 that performs plasma processing, and the tip is placed inside this. A method is being studied in which a coaxial cable 11 configured as an antenna 11a made of an inner conductor is inserted, the coaxial cable 11 is moved inside the insulating tube 14, and the electron density at each position is obtained.

  Here, the plasma processing apparatus shown in FIG. 9 will be briefly described. In FIG. 9, reference numeral 13 denotes a vacuum chamber. Inside the vacuum chamber 13, a mounting table 15 for mounting a substrate is provided. A processing gas supply unit 16 that forms an upper electrode for plasma generation is provided so as to face the mounting table 15. Then, a processing gas is supplied from the processing gas supply unit 16 into the vacuum chamber 13, and the inside of the vacuum chamber 13 is evacuated by a vacuum pump (not shown), while high frequency power is applied from the high frequency power supply 17 to the processing gas supply unit 16. As a result, plasma of the processing gas is formed in the space above the substrate, whereby the plasma processing is performed on the substrate. In the figure, reference numeral 18 denotes a seal member for moving the coaxial cable 11 in a state where airtightness in the vacuum chamber 13 is ensured.

  In this method, the coaxial cable 11 may be moved back and forth in the X direction in FIG. 9 in the insulating tube 14, so that it is easy to ensure high reproducibility of the measurement position, and the electron density can be measured with stable position accuracy. It can be performed. However, this method has a problem that although an approximate electron density distribution can be grasped, the electron density cannot be accurately calculated. This is because the tip of the quartz tube 10 is closed in the plasma absorption probe 1 shown in FIG. 8, whereas the insulating tube 14 is opened in the configuration shown in FIG.

  That is, in the method of measuring the electron density of plasma using the plasma absorption probe 1 shown in FIG. 8, a theoretical formula for obtaining the absorption frequency is derived. In this theoretical formula, the high frequency around the antenna is a closed region. The absorption frequency is given as a function of the probe 1 shape and material. Therefore, in the above theoretical formula, the distance d1 of the tip of the plasma absorption probe 1 shown in FIG. 8, the outer diameter a1 and inner diameter b1 of the quartz tube, the dielectric constant of the plasma, the dielectric constant of the quartz tube 10 and the dielectric constant of the vacuum atmosphere. Comes as a proportional constant. On the other hand, in the configuration shown in FIG. 9, since the insulating tube 14 is open and the distance d1 cannot be obtained, an accurate absorption frequency cannot be calculated using the theoretical formula.

  In the theoretical formula, the absorption frequency is calculated on the premise of a high-frequency mode propagating in an axial symmetry. At this time, when the tip of the quartz tube 10 is closed like the plasma absorption probe 1 shown in FIG. 8, the vicinity of the antenna 11a becomes a narrow region, so that it can be considered that the high frequency propagates axially. When the vicinity of the antenna 11a is opened as in the configuration shown in FIG. 6, the high frequency propagates non-axisymmetrically, so that an accurate absorption frequency cannot be calculated using the theoretical formula from this viewpoint.

  By the way, in the network analyzer 12, even in the apparatus having the configuration shown in FIG. 9, there is a spectrum peak that is regarded as an absorption frequency. In the non-axisymmetric propagation mode, a plurality of frequency absorption regions are generated. This is because the plurality of absorption frequencies are collected and appear as one peak in the spectrum, and this absorption frequency is not an accurate absorption frequency. As described above, in the configuration of FIG. 9, the absorption frequency cannot be obtained with high accuracy. Therefore, it is difficult to accurately calculate the electron density obtained as a function of the absorption frequency. Accordingly, since the electron density distribution is also inaccurate, there is a problem that the measured electron density distribution is wobbled or there is no physical basis for the calculated electron density.

  By the way, Patent Document 1 describes a technique for obtaining an electron density by, for example, spanning an insulator tube between sidewalls facing each other in a chamber and inserting an antenna probe therein. However, also in this literature 1, since the front-end | tip of an insulator tube is open | released, the above-mentioned problem generate | occur | produces and cannot solve the subject of this invention.

Sugai, Jpn.J.Appl.Phys.Vol.38 (1999) pp.5262-5266 JP 2005-228727 A

  The present invention has been made under such circumstances, and an object thereof is to provide a technique capable of easily and easily measuring the electron density of plasma.

For this reason, the electron density measuring apparatus of the present invention is an electron density measuring apparatus that measures the electron density of plasma in a plasma generation chamber in which plasma is generated.
A tubular member made of a dielectric material provided from the side wall on one side of the plasma generation chamber toward the side wall on the other side through the plasma generation region;
A coaxial cable provided with an antenna portion that is slidably provided inside the tubular member and is configured to expose the inner conductor from the tip thereof;
A conductive member that is provided on the front side in the traveling direction of the antenna portion via a gap, and that slides inside the tubular member;
A drive mechanism for moving the coaxial cable forward and backward in the tubular member;
While being connected to the rear end side of the coaxial cable and sweeping the frequency, a high frequency is incident on the antenna unit,
The reflected wave corresponding to the high frequency is received through the antenna unit, and the relationship between the high frequency reflectivity and the frequency is obtained, and from this relationship, the high frequency is absorbed in the plasma in a resonant manner in the high frequency axisymmetric mode. Means for determining the frequency;
And an electron density calculator that calculates the electron density in the plasma based on the absorption frequency.

  Here, the coaxial cable and the tubular member are connected by a connecting member, and in the region along the inner periphery of the tubular member, the occupation ratio in the circumferential direction of the connecting member is a high-frequency generated along the outer periphery of the tubular member. You may comprise so that it may be a magnitude | size which does not disturb axisymmetric mode. In this case, the connecting member can be configured as a plurality of linear members extending in the axial direction of the tubular member.

  Furthermore, in this invention, you may make it provide the electron density distribution preparation part which calculates | requires electron density distribution from the positional information on the several measurement position inside the said tubular member, and the electron density in the said measurement position. Further, the tubular member is preferably provided so as to pass through a central portion of the plasma generation chamber, and a gap between the antenna portion and the conductive member is preferably set to 2 mm or more and 20 mm or less.

The electron density measuring method of the present invention is an electron density measuring method for measuring the electron density of plasma in a plasma generating chamber in which plasma is generated.
An antenna portion configured by exposing an inner conductor from a tip of a tubular member made of a dielectric material provided from one side wall of the plasma generation chamber toward the other side wall through a plasma generation region. A step of sliding a coaxial cable provided with a conductive member provided through a gap on the front side in the traveling direction of the antenna unit, and advancing and retracting to a measurement position in the tubular member;
While sweeping the frequency to the coaxial cable, a high frequency is incident on the antenna unit, and a reflected wave corresponding to the high frequency is received through the antenna unit, and a relationship between the high frequency reflectivity and the frequency is obtained. From this relationship, a step of obtaining an absorption frequency at which the high frequency is resonantly absorbed by the plasma in the high frequency axisymmetric mode;
And a step of calculating an electron density in the plasma based on the absorption frequency.

  Moreover, in this invention, the process of calculating | requiring the electron density distribution in plasma based on the positional information on the several measurement position inside the said tubular member, and the electron density in the said measurement position may be further included.

  Furthermore, the storage medium of the present invention is a storage medium storing a computer program used in an electron density measuring device for measuring electron density in plasma, and the program includes a group of steps for executing the electron density measuring method. It is characterized by being assembled.

  According to the present invention, since the conductive member is provided on the front side in the traveling direction of the antenna portion via the gap, the high frequency incident on the antenna portion is reflected by the conductive member when measuring the electron density. The Thereby, the advance of high frequency is suppressed by the conductive member on the front side of the antenna portion, and a closed region can be formed around the antenna portion. Therefore, the high frequency around the antenna portion resonates in the closed region, and the high frequency propagates along the outer circumference of the tubular member and the conductive member in an axially symmetric mode. it can. For this reason, the reliability of the absorption frequency obtained by the absorption frequency measuring unit is increased, and the electron density in the plasma can be obtained with high accuracy. In addition, the coaxial cable and conductive member are slid in the tubular member, so the coaxial cable can be easily moved while maintaining the hermeticity of the plasma generation chamber during measurement. Can be made. For this reason, it is possible to easily measure the electron density in a state where the plasma generation state is stable and high reproducibility of the measurement position is ensured.

  Hereinafter, embodiments of the present invention will be described by taking as an example the case where the present invention is applied to an electron density measuring apparatus of a system that generates plasma using a planar antenna. Briefly explaining the configuration of this apparatus, reference numeral 2 in the figure is a plasma generation chamber (vacuum chamber) that is hermetically sealed in a cylindrical shape and grounded, and a semiconductor wafer as a substrate is contained in the inside thereof. A mounting table 21 serving as a mounting unit for mounting W (hereinafter referred to as “wafer W”) is provided. A gas introduction pipe 22 is provided on the side wall of the plasma generation chamber 2, and a gas supply system 23 is connected to the other end of the gas introduction pipe 22. Further, a vacuum exhaust means 25 is connected to the bottom of the plasma generation chamber 2 via an exhaust path 24.

  The ceiling of the plasma generation chamber 2 is open, and the opening is hermetically closed by a top plate 26 made of a dielectric. The antenna unit 3 is provided so as to be in close contact with the H.26. The antenna unit 3 constitutes a planar antenna. The lid 31, a disk-shaped planar antenna member (slot plate) 32 in which a large number of slots are formed, the planar antenna member 32, the lid 31, , And a lower surface of the planar antenna member 32 is connected to the top plate 26. The lid 31 is grounded.

  The antenna unit 3 configured as described above is connected to a microwave generator 35 by a coaxial waveguide 34, and for example, a microwave having a frequency of 2.45 GHz or 8.3 GHz is supplied. At this time, the waveguide 34 A outside the coaxial waveguide 34 is connected to the lid 31, and the center conductor 34 B is connected to the planar antenna member 32 through an opening formed in the slow phase plate 33. In the planar antenna member 32, a large number of slot pairs 36 for generating circularly polarized waves are formed, for example, concentrically or spirally along the circumferential direction.

  Further, between one side wall 2A of the plasma generation chamber 2 and a side wall 2B facing the side wall 2A, a tubular member 4 made of a dielectric material such as quartz or zirconia is provided between the side walls 2A and 2B. It is stretched horizontally between them. In this example, for example, as shown in FIG. 2, the plasma generation chamber 2 is formed in a circular shape in plan view, so that the tubular member 4 passes through the central portion of the plasma generation chamber 2 so as to pass through the central portion of the plasma generation chamber 2. It is provided to extend along the diameter. Here, since the central portion of the mounting surface of the wafer W of the mounting table 21 is provided so as to be aligned with the central portion of the plasma generation chamber 2, the tubular member 4 is located above the wafer W on the mounting table 21. On the side, it is provided so as to extend along the diameter of the wafer W.

  The tubular member 4 is hollow so that an antenna probe 5 to be described later can slide therein, the cross-sectional shape in the vertical direction is circular, and the outer diameter a is shown in FIG. Is set to about 2 to 6 mm, for example, and the inner diameter b is set to about 1 mm, for example. The tubular member 4 has one end connected to the inner wall of the one side wall 2A and the other end connected to the inner wall of the side wall 2B facing the side wall 2A.

  For example, as shown in FIG. 3, the antenna probe 5 includes an antenna portion 52 configured to expose the inner conductor 51 a from the tip of the coaxial cable 51, and a predetermined gap from the tip of the antenna portion 52 to the front side. An example conductive member 53 made of, for example, copper or the like is provided so that it can be slid inside the tubular member 4 integrally with the coaxial cable 51. The conductive member 53 is formed in a columnar shape, for example, and the coaxial cable 51 and the conductive member 53 are connected by a connecting member 54 formed of, for example, copper.

  The connecting member 54 is provided so as to form a high-frequency propagation space radiated from the antenna portion 52 between the coaxial cable 51 and the conductive member 53, and extends along the inner periphery of the tubular member 4. In this region, the occupying ratio of the connecting member 4 in the circumferential direction is set to a size that does not disturb the high-frequency axisymmetric mode generated along the outer periphery of the tubular member 4.

  For example, the connecting member 54 is composed of a plurality of, for example, two linear members extending in the axial direction of the tubular member 4 and connects, for example, the outer conductor 51 b of the coaxial cable and the peripheral side of the end portion of the conductive member 53. For example, the size is about 30 mm. Since the antenna probe 5 slides inside the tubular member 4, there is almost no gap between the coaxial cable 51 and the conductive member 53 and the inner surface of the tubular member 4, for example, 0. A slight gap of about 1 mm or less is formed.

  Thus, the conductive member 53 provided on the front side of the antenna portion 52 is made of a conductive material so that the high frequency from the antenna portion 52 of the coaxial cable 51 is reflected by the conductive member 53 as described later. This is to form a state in which the high-frequency progression is suppressed on the front side of the conductive member 53. The connecting member 54 only needs to have a size that does not prevent the high frequency from the antenna unit 52 from propagating in an axially symmetric mode and entering the plasma generation chamber 2 via the tubular member 4. The material may be a material that reflects high frequency or a material that transmits light.

  Here, with respect to the sizes of the tubular member 4 and the antenna probe 5, for example, when measuring the electron density of the vacuum chamber 2 having a size for processing a 12-inch wafer W, the outer diameter a of the tubular member 4 is 2 mm. -6 mm, the inner diameter b is 1 mm to 4 mm, the outer diameter of the coaxial cable 51 of the antenna probe 5 is 1 mm to 4 mm, the length c of the antenna part 52 is 1 mm to 10 mm, and the distance between the antenna part 52 and the conductive member 53 It is preferable to set d to 1 mm to 10 mm, the length e of the conductive member 53 to 20 mm to 30 mm, and the outer diameter of the conductive member 53 to about 1 mm to 4 mm.

  The coaxial cable 51 is configured to be moved forward and backward by the drive mechanism 6 to a plurality of measurement positions inside the tubular member 4. The drive mechanism 6 includes, for example, a base 61 extending in the X direction in FIG. 1, a ball screw mechanism 62 provided therein, and a motor 63, and the base end (rear end) side of the coaxial cable 51 is driven. The portion 64 is connected by the ball screw mechanism 62, and is thus configured to move along the base 61. The drive of the motor 63 of the drive mechanism 6 is controlled by the control unit 8 described later. The coaxial cable 51 is inserted into the tubular member 4 through the side wall 2A, and a sealing member 27 for maintaining the degree of vacuum in the vacuum chamber 2 is provided at the insertion site of the side wall 2A. Yes.

  Further, the proximal end side of the coaxial cable 51 is connected to a network analyzer 7 that forms an absorption frequency measurement unit. The network analyzer 7 is connected to the rear end side of the coaxial cable 51 and makes a high frequency incident on the antenna unit 52 while sweeping the frequency, and a reflected wave corresponding to the high frequency is transmitted through the antenna unit 52. This is a means for obtaining the relationship between the high-frequency reflectivity and the frequency, and obtaining the absorption frequency at which the high-frequency is resonantly absorbed by the plasma in the high-frequency axisymmetric mode. The reflectivity of the high frequency is calculated from the power of the incident wave incident on the antenna unit 52 and the power of the reflected wave reflected by the plasma and returning to the antenna unit 52 (power of the reflected wave) / (power of the incident wave). In the network analyzer 7, the frequency characteristic of the reflectance is displayed as a spectrum. There are a plurality of peaks in this spectrum. Among these peaks, the peak at the highest frequency is the peak due to the high-frequency axisymmetric mode, and the frequency corresponding to this peak is obtained as the absorption frequency. The absorption frequency thus obtained from the network analyzer 7 is output to the control unit 8 described later.

  The electron density measuring device 2 is configured to be controlled by the control unit 8. The control unit 8 is composed of a computer, for example, and includes a CPU, a program, and a memory. In the program, a command (each step) is incorporated so that a control signal is sent from the control unit 8 to each part of the electron density measuring device and a predetermined measurement process is performed. This program is stored in a storage unit such as a computer storage medium such as a flexible disk, a compact disk, a hard disk, or an MO (magneto-optical disk) and installed in the control unit.

  Here, the part relating to the electron density measurement incorporated in the program will be described. Based on the absorption frequency obtained by the network analyzer 7, the electron density calculation unit 81 for calculating the electron density, the measurement position, and the electron corresponding to the measurement position A data acquisition unit 82 that stores the density in association with each other as a table, and an electron density distribution generation unit 83 that generates an electron density distribution based on the measurement position and the electron density stored in the data acquisition unit 82. Yes.

  In the electron density calculation unit 81, for example, the electron density (Ne) is calculated based on the absorption frequency by the following equation.

Ne [m ⁻³ ] = A × (f _abs [GHz]) ²
Here, A is a proportionality constant determined by the shape and material of the antenna probe 5, and _fabs is a numerical value representing the absorption frequency when the high frequency propagates in an axially symmetric mode in GHz units.

  Further, the measurement position of the antenna probe 5 is grasped by, for example, the number of rotations of the motor 63 of the drive mechanism 6, and a plurality of measurement values set in advance by outputting a command from the control unit 8 to the motor 63. The antenna probe 5 is sequentially moved so that the tip of the antenna unit 52 is positioned at the positions (P1 to Pn), and the absorption frequency is measured. Here, the measurement position is a position provided at predetermined intervals along the diameter of the plasma generation chamber 2. As described above, the diameter direction of the plasma generation chamber 2 is aligned with the diameter direction of the wafer W. For example, the measurement position is set so as to include a region outside the outer edge of the wafer W. Further, the electron density distribution creating unit 83 graphs the relationship between the electron density and the measurement position, with the vertical axis representing the electron density and the horizontal axis representing the measurement position selected in the diameter direction of the wafer W.

  Then, the electron density measuring method of this invention is demonstrated using FIG.4 and FIG.5. First, the inside of the plasma generation chamber 2 is evacuated to a predetermined pressure, and a processing gas, for example, argon gas is supplied at a predetermined flow rate through the gas supply path 21 to maintain the inside of the plasma generation chamber 2 at a predetermined process pressure. . On the other hand, when a high frequency (microwave) of 2.45 GHz is supplied from the microwave generator 35, the microwave propagates through the coaxial waveguide 34 in the TM mode, the TE mode, or the TEM mode, and the planar antenna of the antenna unit 3. While reaching the member 32 and propagating radially from the central portion of the planar antenna member 32 toward the peripheral region via the inner conductor 34B of the coaxial waveguide, microwaves from the slot pair 36 pass through the top plate 26. And is emitted toward the plasma generation chamber 2 on the lower side. The microwave energy excites high-density plasma in the plasma generation chamber 2. At this time, the antenna probe 5 keeps the tip of the antenna portion 52 at the measurement position P1 closest to the side wall portion 2A into which the antenna probe 5 is inserted (step S1).

  After the plasma is stabilized, power is supplied to the antenna probe 5 from the network analyzer 7 and the network analyzer 7 obtains the absorption frequency at the measurement position P1. In other words, as described above, the network analyzer 7 supplies the antenna probe 5 with a minute electric power of, for example, about 10 mW while sweeping the frequency. If it does in this way, a high frequency (incident wave) will inject into the antenna part 52, and this high frequency will inject toward plasma via the tubular member 4 comprised with the dielectric material. Then, the reflected wave reflected by the plasma reaches the antenna section 52 through the tubular member 4, and its power is measured by the network analyzer 7. Thus, in the network analyzer 7, the frequency characteristic of the reflectance is displayed as a spectrum, and a frequency in a mode in which a high frequency propagates in an axial symmetry is obtained as an absorption frequency (step S2).

  Next, the control unit 8 calculates the electron density from the above theoretical formula based on the obtained absorption frequency in the electron density calculation unit 81 (step S3), and associates the calculated electron density with the measurement position as data. Store in the acquisition unit 82. Next, the antenna probe 5 is moved to the next measurement position P2 (see FIG. 5), the absorption frequency is measured, the electron density is calculated, and the electron density at all measurement positions is obtained. Thus, an electron density distribution is created (step S4).

  With such a method, it is possible to easily measure the electron density with high accuracy. The reason why the electron density can be measured with high accuracy is that the absorption frequency can be accurately obtained as will be apparent from the examples described later. The reason for this will be described. In the antenna probe 5 of the present invention, the conductive member 53 is provided on the front side in the moving direction of the antenna portion 52, and the gap between the antenna portion 5 and the conductive member 53 during measurement is made constant. Therefore, it can be considered that the structure is physically the same as that of the plasma absorption probe 1 shown in FIG.

  That is, when the plasma absorption probe 1 and the antenna probe 5 are compared in FIG. 6, the antenna probe 5 is provided with the conductive member 53 through the gap on the front side of the antenna portion 52, and the high frequency from the antenna portion 52 is Since it is reflected by the conductive member 53 and does not travel to the front side of the conductive member 5, when viewed from the high frequency, the tip is closed as in the case of the plasma absorption probe 1, and as in the case of the probe 1. The distance d of the probe tip is obtained.

  Here, the absorption frequency observed by the plasma absorption probe 1 corresponds to the frequency at which the standing wave of the surface wave is resonantly excited on the head of the probe 1, and the distance of the head of the probe 1 is d1. Then, resonance occurs when the condition of λ = 2d1 is satisfied. The standing wave of the surface wave stands at the interface between the outer surface of the quartz tube 1 and the outer plasma atmosphere when a high frequency is radiated from the antenna 11a.

  On the other hand, in the antenna probe 5, by providing the conductive member 53 on the front side of the antenna portion 52 through a gap, a closed region is formed around the antenna portion, where high frequency resonates. When a distance d corresponding to the distance d1 is obtained and a high frequency is radiated from the antenna portion 52, a standing wave of a surface wave is generated at the interface between the outer surface of the tubular member 4 and the conductive member 53 and the outer plasma atmosphere. Therefore, it can be considered that the structure is the same as that of the plasma absorption probe 1.

  Further, since the distance d around the antenna portion 52 of the antenna probe 5 is a narrow region of about 10 mm, the high frequency of the axially symmetric mode propagates and, as will be apparent from the embodiments described later, by the network analyzer 7. The absorption frequency in the axially symmetric mode can be obtained from the obtained reflectance spectrum. Since this absorption frequency is highly reliable and matches the absorption frequency obtained by the theoretical formula in the plasma absorption probe 1, the electron density calculated based on this absorption frequency is also highly accurate data.

  Here, as will be apparent from the examples described later, by changing the length of the distance d of the head of the antenna probe 5, the peak position and peak size in the reflectance spectrum change. Thus, by adjusting the length of the distance d, it is possible to obtain a spectrum having an appropriate peak size due to the axially symmetric mode, improving the S / N ratio of the absorption frequency, and more reliable. A high absorption frequency can be obtained. However, if the distance d between the antenna portion 52 and the conductive member 53 is too long, it does not propagate in the high-frequency axisymmetric mode from the antenna portion 52, and if it is too short, the received signal becomes small. It is preferable to set it to 20 mm or less.

  In the measurement, the antenna probe 5 is slid inside the tubular member 4 and is positioned at a predetermined measurement position. Therefore, the antenna probe 5 is maintained in a state in which the airtightness of the plasma generation chamber 2 is maintained. The electron density can be measured while ensuring a stable plasma generation state. Further, for example, by providing the tubular member 4 horizontally in the plasma generation chamber 2, the antenna probe 5 can be moved in a state where the height is uniform only by sliding the antenna probe 5 inside the tubular member 4. Therefore, it is easy to ensure good reproducibility of the measurement position, whereby the electron density can be measured with stable position accuracy, and the creation of a highly reliable electron density distribution is facilitated. In addition, since a highly accurate electron density distribution can be created, it is easy to analyze the plasma state and adjust the apparatus when designing and starting up the apparatus based on this.

  Here, since the tubular member 4 is provided so as to pass through the central portion of the plasma generation chamber 4, the electron density distribution obtained by this method is the electron density distribution in the diameter direction of the plasma generation chamber 4. Since the generation chamber 2 is considered to have substantially the same electron density distribution in any radial direction, the electron density distribution in the radial direction of the plasma generation chamber 4 can be obtained by obtaining the electron density distribution in the one radial direction. Can be applied.

  In the above example, since the coaxial cable 51 and the conductive member 53 are connected by the connecting member 54, the gap between the coaxial cable 51 and the conductive member 53 does not change during the movement. Measurement can be performed in a state where the distance d of the head of the antenna probe 5 is constant, and also from this point, measurement of the electron density with high accuracy can be easily performed.

(Experimental example)
Examples carried out to confirm the effects of the present invention will be described below. In the following experiment, the frequency characteristic of the reflectance was obtained by the network analyzer 7 by changing the distance d of the head of the antenna probe 5 using the electron density measuring apparatus shown in FIG.

  Here, the shape of the antenna probe 5 is such that the outer diameter a of the tubular member 4 is 3 mm, the inner diameter b is 2 mm, the outer diameter of the coaxial cable of the antenna probe 5 is 0.9 mm, the length c of the antenna portion 52 is 3 mm, and the conductivity. The length e of the member 53 is 30 mm, the outer diameter of the conductive member 53 is 0.9 mm, the width of the connecting member 54 is 0.1 mm, the distance d of the head of the antenna portion 52 is 3 mm, the tubular member 4 is quartz, The conductive member 53 was made of copper and the connecting member 54 was made of copper (Example 1). When the distance d between the heads of the antenna portion 52 is 6 mm and the antenna probe 5 is the same as in the first embodiment (second embodiment), the conductive member 53 is not used and the other is the same as in the first embodiment. A similar experiment was also performed when the antenna probe (Comparative Example 1) was used.

  The results are shown in FIG. 7 as solid lines for Example 1, dashed lines for Example 2, and dotted lines for Comparative Example 1. In FIG. 7, the vertical axis represents the reflectance, and the horizontal axis represents the sweep frequency. As a result, for Example 1 and Example 2, a peak of the absorption frequency due to the axially symmetric mode is recognized, and this absorption frequency matches the absorption frequency obtained by the theoretical formula using the plasma absorption probe 1. Was confirmed. Thereby, it is understood that the absorption frequency obtained by using the antenna probe 5 of the present invention has high reliability. The first peak and the second peak were found for Example 1, and the first to third three peaks were found for Example 2. Of these, the peak at the highest frequency was the high frequency. The first peak is a peak attributed to the axially symmetric propagation mode.

  Further, it is recognized that the absorption frequency in the axially symmetric mode and the peak size thereof are different by changing the distance d, and the peak position and size of the spectrum can be adjusted by adjusting the distance d, and the absorption It is understood that the S / N ratio of the frequency can be improved.

  Further, in Example 1 where the distance d is small, the peak of the absorption frequency is larger than that in Example 2, and in Comparative Example 1 where the distance d is very long, no peak due to the axially symmetric mode is seen. When the length becomes longer, the high frequency radiated from the antenna section 52 becomes difficult to propagate in the axially symmetric mode, and it is recognized that when the conductive member 53 is not provided, the high frequency cannot propagate in the axially symmetric mode.

  In the present invention, since the gap between the coaxial cable 51 and the conductive member 53 only needs to be constant at the measurement position, the coaxial cable 51 and the conductive member 53 are not connected by the connecting member 54. You may make it move the inside of the tubular member 4 mutually independently. Further, both end sides of the tubular member 4 are not necessarily connected to the side wall portion of the plasma generation chamber 2 and need not be closed by this, and the distal end side (side facing the insertion portion of the coaxial cable 5) of the tubular member 4 is It may be closed before the side wall. Furthermore, the electron density measuring apparatus of the present invention can be applied to an apparatus that generates plasma by other methods such as generating plasma by a parallel plate method.

It is sectional drawing which shows the electron density measuring apparatus which concerns on one embodiment of this invention. It is a top view which shows a part of said electron density measuring apparatus. It is sectional drawing and a perspective view which show the antenna probe provided in the said electron density measuring apparatus. It is process drawing which shows the said electron density measuring method. It is sectional drawing for demonstrating the electron density measuring method performed in the said electron density measuring apparatus. It is sectional drawing for comparing the antenna probe and plasma absorption probe of this invention. It is a characteristic view which shows the frequency characteristic of the reflectance in the experiment example performed in order to confirm the effect of the said electron density measuring apparatus. It is sectional drawing which shows a plasma absorption probe. It is sectional drawing which shows the conventional electron density measuring apparatus.

Explanation of symbols

2 Plasma generation chamber 4 Tubular member 5 Antenna probe 51 Coaxial cable 52 Antenna unit 53 Conductive member 54 Connecting member 6 Drive mechanism 7 Network analyzer 8 Control unit 81 Electron density calculation unit 82 Data acquisition unit 83 Electron density distribution creation unit

Claims (9)

In an electron density measurement device that measures the electron density of plasma in a plasma generation chamber in which plasma is generated,
A tubular member made of a dielectric material provided from the side wall on one side of the plasma generation chamber toward the side wall on the other side through the plasma generation region;
A coaxial cable provided with an antenna portion that is slidably provided inside the tubular member and is configured to expose the inner conductor from the tip thereof;
A conductive member that is provided on the front side in the traveling direction of the antenna portion via a gap, and that slides inside the tubular member;
A drive mechanism for moving the coaxial cable forward and backward in the tubular member;
While being connected to the rear end side of the coaxial cable and sweeping the frequency, a high frequency is incident on the antenna unit,
The reflected wave corresponding to the high frequency is received through the antenna unit, and the relationship between the high frequency reflectivity and the frequency is obtained, and from this relationship, the high frequency is absorbed in the plasma in a resonant manner in the high frequency axisymmetric mode. Means for determining the frequency;
An apparatus for measuring electron density in plasma, comprising: an electron density calculator for calculating electron density in plasma based on the absorption frequency.   The coaxial cable and the tubular member are connected by a connecting member, and in the region along the inner periphery of the tubular member, the occupation ratio in the circumferential direction of the connecting member is axisymmetric with respect to the high frequency generated along the outer periphery of the tubular member. 2. The electron density measuring device according to claim 1, wherein the electron density measuring device has a size that does not disturb the mode.   3. The electron density measuring device according to claim 2, wherein the connecting member is a plurality of linear members extending in the axial direction of the tubular member.   The electron density distribution creation part which calculates | requires electron density distribution by the positional information on the several measurement position inside the said tubular member, and the electron density in the said measurement position is provided. The electron density measuring apparatus described in 1.   The electron density measuring device according to claim 1, wherein the tubular member is provided so as to pass through a central portion of the plasma generation chamber.   The electron density measuring device according to claim 1, wherein an interval between the antenna unit and the conductive member is set to 2 mm or more and 20 mm or less. In an electron density measurement method for measuring the electron density of plasma in a plasma generation chamber in which plasma is generated,
An antenna portion configured by exposing an inner conductor from a tip of a tubular member made of a dielectric material provided from one side wall of the plasma generation chamber toward the other side wall through a plasma generation region. A step of sliding a coaxial cable provided with a conductive member provided through a gap on the front side in the traveling direction of the antenna unit, and advancing and retracting to a measurement position in the tubular member;
While sweeping the frequency to the coaxial cable, a high frequency is incident on the antenna unit, and a reflected wave corresponding to the high frequency is received through the antenna unit, and a relationship between the high frequency reflectivity and the frequency is obtained. From this relationship, a step of obtaining an absorption frequency at which the high frequency is resonantly absorbed by the plasma in the high frequency axisymmetric mode;
Calculating the electron density in the plasma based on the absorption frequency.   8. The electron according to claim 7, further comprising a step of obtaining an electron density distribution in the plasma based on position information of a plurality of measurement positions inside the tubular member and an electron density at the measurement position. Density measurement method. A storage medium storing a computer program used in an electron density measuring device for measuring electron density in plasma,
A storage medium, wherein the program has a set of steps so as to execute the electron density measurement method according to claim 7 or claim 8.

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