JP2005135746A - Plasma density information measuring probe, plasma density information measuring device, and plasma processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain plasma density more precisely by improving measuring precision of an absorption frequency by the plasma. <P>SOLUTION: On a measuring probe to be inserted into a plasma PM, an external conductor 43c of a coaxial cable 43 inserted into a tube 41 which is an dielectrics is grounded at the outside of a chamber 10, and a circular noise reduction element (ferrite core) 50 is passed through the coaxial cable 43 between its grounded site 49 and an antenna 42. By this, noise components picked up by the antenna 42 and transferred through the coaxial cable 43 are reduced, and an S/N ratio of a reflective power signal generated by the plasma PM as an object to be measured can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a plasma density information measuring probe and a plasma density information measuring apparatus for measuring plasma density information used in a semiconductor device manufacturing process and the like, and a plasma processing apparatus using such a measuring apparatus.

Various processes using plasma are widely adopted in the manufacturing process of semiconductor devices. Typical examples include plasma CVD (chemical vapor deposition) for forming a thin film on the wafer and plasma etching for partially removing the SiO ₂ film formed on the wafer. As a basic configuration of a processing apparatus using such plasma, a processing gas is introduced into a vacuum atmosphere chamber, a high-frequency voltage is applied to an electrode disposed in the chamber, and the processing gas is converted into plasma by this high-frequency electric field. It has become.

  For example, in a plasma etching apparatus, a wafer to be processed is placed in the plasma formed as described above, and a film on the wafer is etched by a chemical reaction of radicals activated by the plasma. Since the state of the plasma generated in the chamber is not necessarily constant, it is very important to accurately grasp plasma density information in real time in order to control the etching rate. Conventionally, various methods such as the Langmuir probe method are known as plasma density measurement methods, but there are problems such as being unsuitable for continuous measurement over a long period of time or complicated measurement. It was.

  On the other hand, as methods that are simpler and can accurately measure the plasma density for a relatively long period of time, those disclosed in Patent Documents 1 and 2 are known in recent years. FIG. 13 is a block diagram of the main part of this measuring apparatus. A measurement probe 102 for measuring plasma density is installed so as to be inserted into a chamber 101 which is a plasma processing chamber. The measurement probe 102 includes an antenna 105 that radiates power, a coaxial cable 104 that transmits measurement power to the antenna 105, and a cylindrical dielectric tube 103 with a closed end. A coaxial cable 104 is inserted into the antenna 105, and an antenna 105 is connected to the tip.

  The measurement power generated by the measurement power supply 107 installed outside the chamber 101 is supplied to the antenna 105 through the coaxial cable 102 via the directional coupler 108 and directed from the antenna 105 toward the plasma PM in the chamber 101. Is emitted. A part of this radiated power is absorbed by a load due to plasma PM (referred to as plasma load), but most of it is reflected and returns to the antenna 105, and returns to the circuit unit side through the coaxial cable 104. That is, the surface wave by the plasma PM is excited on the surface of the tube 103 by the measurement power radiated toward the plasma PM, and the plasma load is absorbed or reflected depending on whether or not a standing wave is generated. Plasma density information can be obtained based on the degree of reflection or absorption of the measurement power.

  More specifically, the measurement power source 107 performs frequency scanning in a predetermined frequency range. When the measurement power is reflected by the plasma PM, the reflected power returns from the measurement probe 102. The directional coupler 108 detects this reflected power and sends it to the output unit 109. Since the frequency information during scanning is sequentially sent from the measurement power source 107 to the output unit 109, the frequency dependence of the reflectance of the measurement power can be obtained based on both pieces of information. In other words, at the same frequency, the calculation processing of [measured power detection reflection amount] / [total measurement power output amount] is performed to obtain the measurement power reflectivity, and the reflectivity corresponds to the scanning frequency. And plot. Then, from the graph, an absorption frequency at which strong absorption of the measurement power is caused due to the plasma density is derived. Since this absorption frequency has a certain correlation with the plasma density (electron density), the plasma density information can be calculated from the absorption frequency.

  However, the measurement probe 102 having the conventional configuration as described above has the following problems. That is, the antenna 105 of the measurement probe 102 receives not only the reflected power by the plasma PM for the radiation of its own measurement power but also various other electromagnetic waves. For example, high-frequency power supplied into the chamber 101 for plasma excitation or other electromagnetic waves other than that is received, and these are superimposed on the reflected power wave and enter the circuit unit. If the S / N ratio of the signal component representing the reflected power decreases due to such a noise component, it becomes difficult to derive the absorption frequency with high accuracy, and the detection accuracy of the plasma density decreases.

  In addition, although the antenna 105 and the coaxial cable 104 serving as a transmission line are connected to a noise source (such as an electrode (not shown) in the chamber 101) through a tube 103 that is a dielectric, the antenna 105 and the noise source are coupled in high frequency. Resulting in. As a result, noise derived through the coaxial cable 104 is scattered to the outside of the chamber 101, which causes malfunction of not only its own measuring instrument but also other measuring instruments. Further, when the shield portion of the coaxial cable 104 is grounded outside the chamber 101 in order to prevent such unnecessary radiation noise, a high-frequency current flows through the shield portion, and the coaxial cable 104 may generate heat and cause damage.

Japanese Patent Laid-Open No. 2000-100598 Japanese Patent Laid-Open No. 2000-100599

  The present invention has been made to solve these problems, and its main purpose is to improve the measurement accuracy of plasma density information by reducing undesired noise and to improve durability by suppressing heat generation. It is to provide a plasma density information measuring probe capable of improving the performance, a plasma density information measuring apparatus using the probe, and a plasma processing apparatus using such a measuring apparatus.

The plasma density information measurement probe according to the first invention, which has been made to solve the above-mentioned problems, includes an antenna unit that is arranged in a plasma atmosphere and that receives electric power caused by the plasma from the outside, and an electric power received by the antenna unit A transmission line for transmitting to the measurement unit, a plasma density information measurement probe for measuring plasma density information based on the amount of power received by the antenna unit,
A shield portion provided in at least a part of the transmission line along the transmission line is electrically grounded at a predetermined position, and a magnetic material is provided so as to surround the transmission line between the grounded portion and the antenna portion. It is characterized by that.

Similarly, a plasma density information measurement probe according to the second invention, which has been made to solve the above-mentioned problems, is provided in an antenna part that is arranged in a plasma atmosphere and receives electric power caused by the plasma from the outside, and the antenna part receives the plasma part. A transmission line for transmitting the measured power to the measurement unit, and a plasma density information measurement probe for measuring plasma density information based on the amount of power received by the antenna unit,
A shield part provided at least in a part of the range along the transmission line is electrically grounded at a predetermined position, and a noise absorber is provided so as to surround the transmission line between the grounded part and the antenna part. It is characterized by providing.

Embodiments and effects of the invention

  In the plasma density information measuring probe according to the first and second inventions, the antenna unit installed in the plasma atmosphere receives signal power caused by plasma, and this signal power is transmitted to the measurement unit through the transmission line. However, since not only the signal power derived from the plasma load but also high frequency power for plasma excitation and various other electromagnetic waves jump into the antenna section, the power due to these noise components is superimposed on the target signal power and transmitted. Go through the track.

  In the plasma density information measurement probe according to the first aspect of the invention, the magnetic body provided so as to surround the transmission line acts as an inductance particularly on the high-frequency signal component, and when viewed from the antenna part side (that is, the noise generation source side). Cause impedance mismatch. Therefore, the noise component conducted through the transmission line is blocked in the vicinity of the magnetic body, reflected, and returned to the antenna unit side. Thereby, the noise component reaching the measurement unit is reduced, and the S / N ratio of the target signal power is improved. Therefore, plasma density information can be measured with high accuracy. Moreover, the impedance by a magnetic body can suppress the high frequency current which flows through the shield part of a transmission line, and can suppress the heat_generation | fever resulting from this high frequency current.

  On the other hand, in the plasma density information measurement probe according to the second invention, when a noise component is conducted to the transmission line, an induced current is induced in the noise absorber provided so as to surround the transmission line, and the resistance component The electrical energy is converted into thermal energy. Thereby, the noise component conducted through the transmission line is attenuated, and the noise component reaching the measurement unit is reduced. Therefore, as in the first invention, the S / N ratio of the target signal power is improved, so that the plasma density information can be measured with high accuracy. Further, the high frequency current flowing through the shield part of the transmission line can be suppressed by the resistance component of the noise absorber, and heat generation due to the high frequency current can be suppressed.

  When plasma is generated in a vacuum chamber, the chamber itself is set to an electrical ground potential, and the shield part of the plasma density information measurement probe according to the present invention is electrically grounded by connecting it to the chamber at a predetermined position. It can be set as the structure to do.

  As one embodiment of the plasma density information measuring probe according to the first and second inventions, the transmission line is an inner conductor of a coaxial cable and the shield part is an outer conductor, and the outer conductor is grounded at a predetermined position. In addition, the magnetic body or the noise absorber can be provided around the coaxial cable between the grounded portion and the antenna portion.

  As another embodiment of the plasma density information measuring probe according to the first and second inventions, the transmission line is an inner conductor of a coaxial cable and the shield portion is a tubular tube provided further outside the coaxial cable. A magnetic conductor or a noise absorber in a gap between the grounding portion and the antenna portion and between the inner surface of the tubular conductor and the outer surface of the coaxial cable. It is good also as a structure which provided the body around.

  In the plasma density information measurement probe according to the first and second inventions, for example, a hollow magnetic core can be used as the magnetic body or the noise absorber, and specifically, it is called a ferrite core, a ferrite bead, or the like. Use noise countermeasure parts. Such parts have a wide variety of characteristics and sizes, and are easily available in various forms such as those housed in resin cases and split sleeve types. Therefore, it is possible to effectively reduce noise by selecting appropriate components according to the form of the plasma density information measurement probe or according to the frequency band of the noise component in question.

  In the plasma density information measurement probe according to the second aspect of the invention, the temperature of the noise absorber itself increases due to heat converted from noise. If this temperature becomes too high, not only the noise absorbing action is lowered, but also the case of the noise absorber itself or the thermal insulation or damage of the insulation coating of the coaxial cable or the like may be caused. Therefore, in order to avoid such a problem, it is preferable to further include a cooling means for cooling the noise absorber. As cooling means, forcibly supplying air to the noise absorber for air cooling, or providing a heat sink made of cooling fins or a material with good thermal conductivity in thermal contact with the noise absorber. It is possible to use a device that assists spontaneous air cooling, or that uses a refrigerant or the like instead of air cooling.

  In addition, as the noise absorber has a higher resistivity determined by its size, magnetic permeability, and the like, the noise absorbing action is larger, but the temperature rise is larger. Therefore, especially when the noise absorber can only be air-cooled from the direction of the grounding part, the noise absorber is composed of a plurality of resistor elements having different resistivities, and the resistance from the antenna side toward the grounding part is increased. Preferably, the resistor elements are arranged so that the rate increases. According to this, since a larger amount of heat is generated in the resistor element located on the grounded part side with high cooling efficiency, it becomes easy to suppress the temperature rise as the entire noise absorber.

  The plasma density information measuring probe according to the first and second inventions does not have an active function for plasma such as emitting electric power, but passively receives a signal coming from the plasma atmosphere to the measuring unit. However, it is suitable for a configuration having both a function of actively releasing power for measurement and a function of receiving power derived therefrom. That is, in the plasma density information measuring probe according to the first and second inventions, a part of the antenna part and the transmission line is accommodated in a cylindrical body having a closed end made of a dielectric, and the probe is passed through the transmission line. Power for measurement is supplied to the antenna unit, and reflected power from the plasma load is received by the antenna unit with respect to the radiated power radiated into the plasma from the antenna unit through the cylindrical body. It can be set as the structure which measures plasma density information based on absorption.

  In this configuration, when the measurement power is supplied to the antenna unit through the transmission line, the measurement power is released from the antenna unit. Since plasma surface waves are excited by plasma on the surface of the cylindrical body that is a dielectric, the measurement power emitted from the antenna unit is coupled to the plasma load via the surface of the cylindrical body, thereby Absorption or reflection by the load occurs. The reflected power is received by the antenna unit and returned to the measurement unit via the transmission line. Since the measurement power receives particularly strong absorption at a specific frequency according to the plasma density, the plasma density information can be obtained by scanning the frequency of the measurement power and examining the reflection amount or the reflectance. At this time, since the S / N ratio of the reflected power signal is good, the absorption frequency can be obtained accurately, and therefore the plasma density information can be calculated with high accuracy.

  That is, a plasma density information measuring apparatus using the plasma density information measuring probe includes a measurement power source for supplying measurement power of a predetermined frequency to the antenna unit through the transmission line, and a plasma power from the antenna unit by the measurement power. Based on the power detection means for receiving the reflected power from the plasma load with respect to the radiated power radiated to the antenna and detecting the reflected power returned through the transmission line, the measurement power and the reflected power Processing means for obtaining the degree of reflection or absorption by the plasma load and calculating the plasma density information from the relation between the degree of reflection or absorption and the frequency of the power for measurement can be provided.

  As described above, according to the plasma density information measuring apparatus, since the plasma density information at that time can be accurately grasped, the plasma processing speed can be controlled or kept constant in various plasma processing apparatuses. Very useful to do. That is, a plasma processing apparatus according to the present invention is a plasma processing apparatus using the plasma density information measuring apparatus described above, and includes a plasma processing chamber that contains a processing target inside and has a plasma generating means for generating plasma. The plasma density information measurement probe has at least the tip inserted into the plasma processing chamber.

  Here, the plasma treatment may be various treatments using plasma such as plasma etching, plasma CVD, and plasma cleaning. According to this configuration, since such plasma processing can be controlled with high accuracy, there are advantages such as improved processing accuracy and improved processing efficiency.

  Hereinafter, a plasma etching apparatus will be described as an example of a plasma processing apparatus to which a plasma density information measuring apparatus using a plasma density information measuring probe according to the present invention is applied.

  FIG. 1 is a block diagram of the main part of the plasma etching apparatus according to the first embodiment. The chamber 10 which is an etching chamber as a plasma processing chamber is a cylindrical body made of stainless steel, for example, and is electrically grounded. A mounting table 12 for mounting a work W to be etched is also provided as an electrode at the bottom of the chamber 10, and a discharge electrode 11 for plasma generation is provided in the upper part of the chamber 10 so as to face this. Has been placed. The discharge electrode 11 is supplied with high-frequency power for plasma generation generated by the excitation power source 17 via the impedance matching unit 18. The excitation power control unit 19 receives a signal from an electron density calculation unit 36 described later, and controls the impedance matching unit 18 to adjust the plasma density in the chamber 10. The magnitude of the high-frequency power generated by the excitation power source 17 is, for example, about 1 to 3 kW, and the frequency is, for example, a frequency between an RF band typified by 13.56 MHz and a microwave band of about 900 MHz to 2.45 GHz. It is. Of course, the magnitude and frequency of the high-frequency power are not limited to this.

  An exhaust pipe 13 is connected to the chamber 10, and the gas in the chamber 10 is discharged to the outside by the operation of the exhaust pump 14. On the other hand, a gas supply pipe 15 is also connected to the chamber 10, and a gas controlled by the flow rate control valve 16 is supplied into the chamber 10. The inside of the chamber 10 is maintained at an appropriate gas pressure by evacuation by the exhaust pump 14. Specifically, the gas pressure may be about several to several tens of mTorr, for example. The types of gas supplied are argon, nitrogen, oxygen, fluorine-based, chlorine-based, and the like, and the flow rate is preferably about 10 to 100 mL / min.

  The plasma etching apparatus includes an electron density measuring unit 20 for measuring an electron density, which is plasma density information, with high accuracy. The electron density measuring unit 20 includes a measurement probe 21 that protrudes into the chamber 10 through the wall surface of the chamber 10, and a probe control / electrical device that is provided outside the chamber 10 and is electrically connected to the measurement probe 21. And a processing unit 22.

  The probe control / processing unit 22 includes a frequency-scannable measurement oscillator 31, a directional coupler 32, an attenuator 33, a filter 34, a plasma absorption frequency deriving unit 35 that calculates an absorption frequency by the plasma PM, An electron density calculator 36 for calculating the electron density, that is, the plasma density from the plasma absorption frequency, and a display 37 for displaying the result are provided. Here, the indicator 37 is provided for monitoring and can be omitted.

  The measurement oscillator 31 scans a high frequency signal of about 10 mW in a frequency range of about 100 kHz to 3 GHz. The measurement signal output from the measurement oscillator 31 is sent to the measurement probe 21 through the directional coupler 32, the attenuator 33, and the filter 34. The measurement power by the measurement signal is radiated from the measurement probe 21 toward the plasma PM, but not all of it is absorbed by the plasma load. In many cases, most of the measurement power is not absorbed by the plasma load. Reflect and come back. The reflected power returns to the probe control / processing unit 22, passes through the filter 34 and the attenuator 33, reaches the directional coupler 32, is detected, and is sent to the plasma absorption frequency deriving unit 35. When the measurement oscillator 31 performs frequency scanning, the plasma absorption frequency deriving unit 35 obtains the absorption frequency by the plasma PM, and the electron density calculation unit 36 calculates the electron density as the plasma density information from the absorption frequency. Therefore, the electron density calculator 36 outputs the actual electron density of the plasma PM generated in the chamber 10 at that time as plasma density information.

  FIG. 2 is a schematic cross-sectional view showing the configuration of the measurement probe 21, and FIG. 3 is a schematic perspective view of the main part centering on the coaxial cable 43 that is a part of the measurement probe 21. In FIG. 2, a tube 41 is a cylindrical body whose front end located in the chamber 10 is closed and whose rear end is open to the atmosphere. The tube 41 is made of a dielectric, specifically, quartz, ceramics, tempered heat-resistant glass, or the like. . Inside the tube 41, a coaxial cable 43 provided with an antenna 42 for radiating measurement power at the tip is inserted from the open rear end face. The coaxial cable 43 is a conventionally known single-core coaxial cable. Actually, a sheath insulator 43a and an outer conductor (shield wire) 43b are cut by a predetermined length at the end of the coaxial cable 43, and the inner side The inner insulator 43c and the inner conductor (core wire) 43d are projected, and the projected inner conductor 43d functions as the antenna 42. That is, in this embodiment, the inner conductor 43d of the coaxial cable 43 corresponds to the transmission line in the present invention, and the outer conductor 43b corresponds to the shield portion in the present invention. Of course, the antenna 42 may have other shapes such as a loop shape.

  A metal holder 46 is fixed to the chamber 10, and the coaxial cable 43 is connected to an external coaxial cable 48 via a connector 47 fixed to the holder 46. In the connecting portion 49 by the connector 47, the outer conductor 43 b of the coaxial cable 43 is electrically connected to the chamber 10 via the holder 46. That is, it can be considered that the outer conductor 43b of the coaxial cable 43 is grounded (that is, has a potential of 0 V) at the connecting portion 49. Therefore, here, the connecting portion 49 is referred to as a ground contact portion.

  In the measurement probe 21, a plurality of noise reduction elements 50, which are annular ferrite cores, are connected in the tube 41 between the grounding portion 49 and the tip of the measurement probe 21 so that the coaxial cable 43 is inserted inside. Provided. As is well known, the ferrite core is a ceramic mainly composed of iron oxide and has a function of reducing noise by its inductance. In this case, the magnetic field generated by the current flowing through the coaxial cable 43 is absorbed and converted into heat, and the signal transmitted through the coaxial cable 43 from the antenna 42 side due to impedance mismatching. It also has the effect of reducing noise by reflection. That is, in this embodiment, the noise reduction element 50 corresponds to the magnetic body and the noise absorber in the present invention.

  As described above, the measurement power is radiated from the antenna 42 to the plasma PM, and the reflected power is returned to the antenna 42. The antenna 42 is not only the reflected power but also the electromagnetic wave derived from the high frequency power for plasma excitation. In addition to various noises in a wide frequency band. If these noise components are transmitted to the probe control / processing unit 22 as they are, the S / N ratio of the signal level due to the target reflected power is deteriorated. On the other hand, in the configuration of the measurement probe 21, the noise component passing through the coaxial cable 43 can be reduced by the noise reduction element 50 and the grounding of the outer conductor 43 b of the coaxial cable 43 at the ground portion 49.

  As a result, it is possible to suppress the noise of the electromagnetic wave incident on the antenna 42 from reaching the probe control / processing unit 22 through the line, and the signal S / N with respect to the target frequency (scanned frequency). The ratio is improved. Thereby, the absorption frequency can be obtained with higher accuracy in the absorption spectrum in which the frequency is plotted on the horizontal axis and the amount of absorption is plotted on the vertical axis as described later.

  However, since noise reduction elements such as ferrite core generate heat when reducing noise, if this heat is not properly dissipated to the outside, the noise reduction effect will be reduced or the outer sheath of the coaxial cable will be damaged by heat. There is a risk of In the configuration of this embodiment, the tube 41 is closed on the antenna 42 side and heat is not easily dissipated, and the open end surface side of the tube 41 has a much better heat dissipation efficiency. Therefore, noise reduction elements 50 having different resistivities are prepared and arranged so that the resistivities sequentially increase from the antenna 42 side toward the root side of the tube 41. The higher the resistivity, the higher the noise reduction effect, but the greater the amount of heat generated. However, by arranging the elements as described above, the heat generated by the noise reduction elements arranged on the antenna 42 side, which is particularly difficult to dissipate heat. The amount can be reduced. Thereby, the local abnormal temperature rise of the noise reduction element can be prevented, the noise reduction effect can be maintained, and damage to the coaxial cable or the like can be prevented.

  Next, the operation when performing the etching process in this apparatus will be described with reference to the flowchart of FIG. First, it is assumed that the excitation power supply 17 is operating as an initial state, the gas is supplied into the chamber 10 at a predetermined flow rate, and the plasma PM is already generated.

  The measurement oscillator 31 generates a measurement signal while scanning the frequency in the range of, for example, 100 kHz to 2.5 GHz (step S1). Thereby, measurement power is radiated from the antenna 42 of the measurement probe 21 via the coaxial cable 43. As described above, this radiated power is absorbed or reflected by the surface wave of the plasma PM, and the reflected power returns to the probe control / processing unit 22 via the coaxial cable 43, contrary to the power supply. This reflected power is sent to the plasma absorption frequency deriving unit 35 via the filter 34, the attenuator 33, and the directional coupler 32 (step S2).

  The plasma absorption frequency deriving unit 35 calculates the reflectance by calculating (reflected power amount) / (total output amount of measurement power) for the same frequency, and based on the frequency information given from the measurement oscillator 31. . By performing the above calculation at each frequency in the scanning frequency range, the relationship between the frequency and the reflectance is acquired (step S3). An example of the relationship between the frequency and the reflectance thus obtained is shown in FIG. In FIG. 5, peaks Pa and Pb in which the reflectance is greatly reduced are observed. This is an absorption point where strong absorption of the measurement power is caused by the plasma density, and the frequencies fa and fb corresponding to the peak top are obtained. This is the absorption frequency (step S4).

  In the example of FIG. 5, there are two peaks, and two absorption frequencies are obtained correspondingly. Thus, in many cases, there are a plurality of absorption frequencies. All of these absorption frequencies have a correlation with plasma density information such as electron density. In particular, the absorption frequency proportional to the square of the electron density is called the plasma surface wave resonance frequency. Is a particularly useful physical quantity. Since the electron density varies locally even in the same plasma atmosphere, the tip of the measurement probe 21 is located near the surface of the substrate W in order to obtain more accurate plasma density information that contributes to processing on the substrate W. It is desirable to perform the measurement as described above by arranging the parts.

  The electron density calculator 36 calculates the electron density from the absorption frequency obtained as described above (step S5). The calculation result of the electron density (herein referred to as the actual electron density) is sent to the excitation power control unit 19, and the excitation power control unit 19 obtains the difference between the actual electron density and the target value of the electron density, and the difference The impedance matching unit 18 is controlled based on the above. Specifically, when the difference between the actual electron density and the target value is larger than the allowable value (No in step S6), the discharge is performed by changing the tuner position of the impedance matching unit 18 according to the difference, for example. The power supplied to the electrode 11 is increased or decreased (step S8). Then, until the difference between the actual electron density and the target value converges within the allowable value (Yes in step S6), the process returns to step S1 and the adjustment of the excitation power is repeated.

  After the plasma density reaches a desired state in this way, the substrate W is put into the chamber 10 and set on the mounting table 12, and a predetermined voltage is applied to the mounting table 12, whereby ions in the plasma PM are applied. Etching (or other surface treatment) is performed by bringing the electrons into contact with the substrate W (step S7). Even when the target value of the plasma density changes with time, the plasma density can be appropriately controlled by continuously monitoring the plasma density information during etching.

  In the process as described above, the measurement probe 21 according to the present embodiment radiates the measurement power toward the plasma PM, and receives the reflected power and controls the probe via the coaxial cable 43. The data is transmitted to the unit 22. At that time, not only the reflected power that is the original measurement target but also high-frequency power for plasma excitation and other various signals jump into the antenna 42. These are noise components for the detection of reflected power for density measurement, but the noise of the signal input to the probe control / processing unit 22 is greatly suppressed by the noise removal action of the noise reduction element 50 as described above. The S / N ratio of the signal with respect to the target frequency is improved. Thereby, the plasma absorption frequency can be obtained with higher accuracy, and as a result, the calculation accuracy of the electron density is improved and the controllability of the plasma density is improved.

  Next, a plasma density information measuring probe according to a second embodiment of the present invention will be described. FIG. 6A is an external view showing the configuration of the movable portion of the measurement probe 21 according to the second embodiment, and FIGS. 6B and 6C are external views showing the configuration of the state in which the movable portion is inserted into the guide portion. FIG. 7 is a schematic cross-sectional view inside the tube. In addition, the same code | symbol is attached | subjected about the location same as the structure by the said Example, or the description is abbreviate | omitted unless it requires especially.

  In this second embodiment, the tube 41 of the movable part is composed of a tip part 41a made of quartz glass whose tip side is a dielectric, and a base part 41b made of metal, and the tip part 41a houses the antenna inside. A small diameter portion 41a1 having a small diameter (here, the outer diameter is Φ2 mm) and a large diameter portion 41a2 having a larger diameter (here, the outer diameter is Φ6 mm) are formed. Further, the outer diameter of the base 41b is Φ11 mm, and the outer diameter of the coaxial cable inserted into the tube 41 is as narrow as Φ1 mm. At the base of the tube 41, a gripping part 60 is fixed for the analyst to grip when the movable part is inserted into and removed from a guide part described later. The gripping part 60 has an outer cylindrical shape with a scale cut in the longitudinal direction. The scale pipe 61 is fixed.

  The movable part having the above configuration is inserted into an outer cylindrical guide part 62 having a function of guiding the movable part into the chamber 10. When the measurement probe 21 is inserted into the chamber 10, the guide part 62 is connected to the tube 41 and the scale. It moves together with the tube 61, and the flange 62a comes into contact with the outer wall of the chamber 10 and stops as shown in FIG. When the measurement probe 21 is pushed in as it is, the tube 41 is further inserted into the chamber 10 together with the coaxial cable 43. Since the insertion length of the movable portion into the chamber 10 is known from the scale of the scale tube 61 at the rear end portion of the guide portion 62, the movable portion can be inserted to an appropriate position.

  In the second embodiment, the metal tube 42b corresponds to the shield part in the present invention. That is, the grip 60 that is electrically connected to the metal tube 42b is electrically connected to the grounded chamber 10, whereby the grip 60 is a grounding part in the present invention. As shown in FIG. 7, a plurality of noise reduction elements 50 such as ferrite cores are provided around the coaxial cable 43 inside the metal tube 42b located on the antenna 42 side of the grounding portion. As a result, as in the first embodiment, various noises superimposed on the reflected power signal received by the antenna 42 are attenuated during transmission through the coaxial cable 43. Of course, the noise reduction element 50 may be provided around the coaxial cable 43 not only inside the metal tube 42b but also inside the tip portion 41a on the tip side.

  Next, experimental results for demonstrating the noise reduction effect of the configuration of the present invention will be described. FIG. 8 is a schematic diagram showing the configuration of the experimental system, and FIGS. 9 and 10 are perspective views showing a method of arranging the noise reduction elements at locations indicated by C1 and C2 in FIG. In this experiment, for the sake of simplicity, a noise reduction element is installed not on the inside of the measurement probe 21 but on the coaxial cable 48 that connects the measurement probe 21 and the probe control / processing unit 22. That is, as shown in FIG. 8, the coaxial cable 43 was inserted into a tubular insulating tube 70 made of synthetic resin, and the outer side thereof was covered with a shield member 71 made of aluminum foil. The shield member 71 is grounded in the filter 34, and a ferrite core 50b through which the insulating tube 70 passes is provided at a position C2 between the grounded portion and the measurement probe 21 (that is, the antenna 42) as shown in FIG. From that position, a ferrite bead 50a through which the coaxial cable 48 passes is provided inside the insulating tube 70 as shown in FIG. 9 at a position C1 on the measurement probe 21 side.

As the measurement conditions, the maximum power of plasma excitation power is 20 mT and 2700/1350 W. At this time, (1) No ferrite beads (FB) and ferrite cores (FC) (2) Only ferrite beads (FB) are installed (3) The relationship between the absorption frequency and the reflectance was measured with both the ferrite beads (FB) and the ferrite core (FC) installed. The result is shown in FIG. As can be seen from FIG. 11, when the FB is provided compared to the case without the FB and FC, the improvement effect of the S / N ratio is seen, and the S / N ratio is further improved by using the FC together. . When compared at the peak top of the drop in reflectance, the S / N ratio is improved by about 1.5 to 2 dB when FB and FC are used in combination, compared to the case without FB and FC. This can be presumed to be due to the fact that noise transmitted through the coaxial cable 48 is reduced by FB and FC.

  FIG. 12 shows the evaluation results of the measurement probe durability under a certain condition when the ferrite core is not used (a), when it is used (b), and when it is optimized (c). Indicates. As shown in FIG. 12A, when the ferrite core is not used, the absorption waveform is completely broken when 8 minutes and 45 seconds elapse from the start of measurement. This is because the high-frequency current flowing through the shield portion generates heat and the measurement probe is damaged. On the other hand, when a ferrite core is used, as shown in FIG. 12B, an absorption peak can be confirmed even when 10 minutes have elapsed from the start of measurement, and the measurement probe is operating normally. I understand that. Further, in the configuration in which the number of ferrite cores is increased or optimized with respect to the noise frequency, the absorption rate of the absorption peak is also measured when 10 minutes have elapsed from the start of measurement, as shown in FIG. It can maintain almost the same level as the start. Thus, it can be seen that the ferrite core suppresses heat generation, thereby increasing the durability of the measurement probe and improving the reliability.

  The plasma density information measurement probe according to the present invention can be variously modified in addition to the above description.

  For example, the material and shape of the noise reduction element can be selected as appropriate. That is, as a material for the noise reduction element, ferrite is generally used, but in addition to this, an amorphous alloy such as iron or cobalt can be used. Since such a material has higher magnetic permeability than ferrite, a higher noise absorption effect can be expected. In addition, since the frequency band particularly effective for noise reduction is determined by the magnetic characteristics and size of the noise reduction element, it is appropriately selected according to the frequency band dominant to the noise component for plasma density information measurement, such as the frequency of the plasma excitation power. It is preferable to select the characteristics and size. Further, when a plurality of noise reduction elements are used side by side as in the above embodiment, it is also effective to combine noise reduction elements having different main noise reduction frequency bands. Furthermore, in order to obtain a high noise reduction effect, it is also effective to wrap the coaxial cable (transmission line) around the annular noise reduction element a plurality of times.

  On the other hand, heat generation becomes a problem when the noise reduction effect is increased as described above. Heat generation causes two problems, that is, deterioration of the noise absorption effect and damage to the coaxial cable or the like. One method that can be taken as the former solution is to use a material having as high a Curie point as possible as the material of the noise reduction element. Thereby, even if the temperature rises due to heat generation, the magnetism is hardly lost and the noise absorbing effect can be maintained.

  On the other hand, as the latter solution, it is necessary to have a configuration capable of promoting heat dissipation from the noise reduction element as much as possible. One method uses the difference in resistivity of a plurality of noise reduction elements as described above. In addition, a so-called cooling fin that promotes heat radiation from the noise reduction element may be used. For example, in the case of a double shield structure as in the second embodiment and the outer shield member (in the above example, the metal tube 42b) is exposed, the shield member can have a function of a cooling fin. it can. That is, by closely contacting the noise reduction element and the shield member, and preferably using a high thermal conductivity member as the shield member, the heat generated by the noise reduction element is quickly released to the outside through the shield member. can do. Of course, a member corresponding to the cooling fin may be provided separately from the shield member. In order to further promote heat dissipation, a blower such as a small fan that feeds air toward the noise reduction element itself or the cooling fin may be provided, or water or other refrigerants are used. A forced circulation cooling device may be provided.

  In addition, it is obvious that points other than those described above are included in the scope of the claims of the present invention even if they are appropriately changed, modified, or added within the scope of the present invention.

The block diagram of the principal part of the plasma etching apparatus using the plasma density information measuring apparatus by 1st Example of this invention. FIG. 2 is a schematic cross-sectional view showing a configuration of a measurement probe in FIG. 1. The schematic perspective view of the principal part centering on the coaxial cable which is a part of measurement probe in FIG. The flowchart which shows the operation | movement at the time of performing an etching process with the plasma etching apparatus by a present Example. The figure which shows an example of the relationship between the frequency of the electric power for a measurement obtained with the plasma etching apparatus by a present Example, and a reflectance. FIG. 6B is an external view showing the configuration of the movable portion of the measurement probe according to the second embodiment of the present invention, and FIG. 7B is an external view showing the configuration of the state in which the movable portion is inserted into the guide portion. FIG. 7 is a schematic cross-sectional view in the tube of the measurement probe shown in FIG. 6. Schematic which shows the structure of the experimental system which demonstrates the effect by the structure of this invention. The perspective view which shows the arrangement | positioning method of the noise reduction element in the location shown by C1 in FIG. The perspective view which shows the arrangement | positioning method of the noise reduction element in the location shown by C2 in FIG. The figure which shows the result of having actually measured the relationship between an absorption frequency and a reflectance by the experimental system shown in FIG. The figure which shows the evaluation result of the heat_generation | fever suppression effect by a ferrite core under a certain fixed condition. The block diagram of the plasma density information measuring apparatus known conventionally.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Chamber 11 ... Discharge electrode 12 ... Mounting stage 13 ... Exhaust pipe 14 ... Exhaust pump 15 ... Gas supply pipe 16 ... Flow control valve 17 ... Excitation power supply 18 ... Impedance matching device 19 ... Excitation power control part 20 ... Electron density Measuring unit 21 ... Measuring probe 22 ... Probe control / processing unit 31 ... Measuring oscillator 32 ... Directional coupler 33 ... Attenuator 34 ... Filter 35 ... Plasma absorption frequency deriving unit 36 ... Electron density calculating unit 37 ... Display 41 ... Tube 41a ... tip 41a1 ... small diameter part 41a2 ... large diameter part 41b ... base 42 ... antenna 42b ... metal tube 43 ... coaxial cable 43a ... outer insulator 43b ... outer conductor 43c ... inner insulator 43d ... inner conductor 46 ... holder 47 ... Connector 48 ... Coaxial cable 49 ... Grounding part (connecting part)
50 ... Noise reduction element 50a ... Ferrite bead 50b ... Ferrite core 60 ... Grasping part 61 ... Scale pipe 62 ... Guide part 62a ... Flange W ... Workpiece (substrate)

Claims (11)

An antenna unit that is arranged in a plasma atmosphere and receives the electric power caused by the plasma from the outside, and a transmission line that transmits the electric power received by the antenna unit to the measurement unit, the amount of electric power received by the antenna unit A plasma density information measuring probe for measuring plasma density information based on
A shield portion provided in at least a part of the transmission line along the transmission line is electrically grounded at a predetermined position, and a magnetic material is provided so as to surround the transmission line between the grounded portion and the antenna portion. A probe for measuring plasma density information. An antenna unit that is arranged in a plasma atmosphere and receives the electric power caused by the plasma from the outside, and a transmission line that transmits the electric power received by the antenna unit to the measurement unit, the amount of electric power received by the antenna unit A plasma density information measuring probe for measuring plasma density information based on
A shield part provided at least in a part of the range along the transmission line is electrically grounded at a predetermined position, and a noise absorber is provided so as to surround the transmission line between the grounded part and the antenna part. A plasma density information measuring probe characterized by being provided.   The transmission line is an inner conductor of a coaxial cable and the shield portion is an outer conductor, and the outer conductor is grounded at a predetermined position, and the outer side of the coaxial cable is between the ground portion and the antenna portion. 3. The plasma density information measuring probe according to claim 1, further comprising a magnetic body or a noise absorber.   The transmission line is an inner conductor of a coaxial cable, and the shield part is a tubular conductor provided on the outer side of the coaxial cable. The tubular conductor is grounded at a predetermined position, and the grounded portion and the antenna are grounded. 3. The plasma density information measurement according to claim 1, wherein the magnetic body or the noise absorber is provided around a gap between the inner portion and the inner surface of the tubular conductor and the outer surface of the coaxial cable. probe.   5. The plasma density information measuring probe according to claim 1, wherein the magnetic body or the noise absorber is a hollow magnetic core.   The plasma density information measuring probe according to claim 2, further comprising a cooling unit for cooling the noise absorber.   6. The noise absorber is composed of a plurality of resistor elements having different resistivity, and the resistor elements are arranged so that the resistivity increases from the antenna portion side toward a grounded portion. The plasma density information measurement probe according to any one of the above.   A part of the antenna part and the transmission line is housed in a cylindrical body having a closed end made of a dielectric material, supplying measurement power to the antenna part through the transmission line, and the cylindrical part from the antenna part The plasma density information is measured on the basis of reflection or absorption by the plasma load received by the antenna unit with respect to the radiated power radiated into the plasma through the body. The plasma density information measurement probe according to any one of 1 to 7.   The plasma density information measuring probe according to claim 8, wherein the magnetic body or the noise absorber is provided inside the cylindrical body.   A plasma density information measuring apparatus using the plasma density information measuring probe according to claim 8 or 9, wherein a measuring power source for supplying measuring power of a predetermined frequency to the antenna unit through the transmission line, and the measuring power source Power detection means for receiving reflected power from the plasma load with respect to the radiated power radiated into the plasma from the antenna unit by the power and detecting the reflected power returned through the transmission line, and measurement power And processing means for calculating the plasma density information from the relationship between the degree of reflection or absorption and the frequency of the measurement power. Plasma density information measuring device.   11. A plasma processing apparatus using the plasma density information measuring apparatus according to claim 10, further comprising: a plasma processing chamber having a plasma generating means for containing a processing object inside and generating plasma, and measuring the plasma density information A plasma processing apparatus, wherein at least a tip of a probe is inserted into the inside of the plasma processing chamber.

Images