JP5067749B2 - Microwave plasma processing equipment - Google Patents

Description

  In the present invention, plasma is generated by microwave power, and a substrate such as a wafer is subjected to processing such as CVD (chemical vapor deposition), etching, ashing (resist ashing) using plasma. The present invention relates to a processing apparatus.

  In a process for manufacturing a semiconductor, a micromachine, or the like, plasma generated when energy is applied to the reaction gas from the outside is widely used. In recent years, in particular, due to demands for larger diameter wafers, mass production, etc., it has become essential to develop an apparatus capable of performing large-area substrate processing using plasma.

Among them, a microwave surface wave excitation plasma processing apparatus that generates and maintains plasma by surface waves generated by introducing microwave power into a discharge vessel has attracted attention due to the following characteristics. Here, the surface wave means a wave having a characteristic that microwave energy is concentrated in a region near the plasma surface and attenuates in a direction toward the inside of the plasma.
(1) It is not necessary to apply an external magnetic field.
(2) Utilizing microwaves (2.45 GHz), magnetron is inexpensive, impedance matching is easy, electrodes necessary for generating plasma are unnecessary, and so-called electrodeless operation is possible.
(3) Since the plasma is excited by surface waves, it is possible to generate large-area plasma with high uniformity, and high density (> 10 ¹¹ cm ^-3 ) even at low pressure (<100 mTorr (1 Torr = 133 Pa)) Plasma can be obtained.

  FIG. 10 shows an example of a microwave surface wave excitation plasma apparatus. The microwave surface wave excitation plasma device 40 is installed along the waveguide 101, a ring-shaped dielectric antenna 102 made of Teflon (registered trademark) surrounded by the waveguide 101, and the bottom surface of the waveguide 101. A plurality of slots 103, and a circular dielectric window 104 and a metal vacuum vessel 105 installed below the slots 103, and a substrate holder for placing a substrate 106 in the vacuum vessel 105 107, a gas exhaust port 109 for setting the inside of the processing chamber 10 to a required degree of vacuum, and a gas introduction port 108 for supplying a required reaction gas are installed.

  In this microwave surface wave excitation plasma apparatus 40, the microwave introduced from the waveguide 101 forms a standing wave in the dielectric antenna 102, and is installed along the bottom surface of the waveguide 101. And into the vacuum chamber 105 through the dielectric window 104 installed thereunder, and plasma is generated near the dielectric window 104. The plasma spreads from the periphery of the vacuum vessel 105 in which the slot 103 is installed to the center by the surface wave propagating on the boundary surface between the dielectric window 104 and the plasma. Further, the surface wave-excited plasma generated in the vicinity of the dielectric window 104 is configured to spread over the entire vacuum vessel 105 due to a diffusion phenomenon. When performing a process such as CVD on the substrate 106 placed on the substrate holder 107 using the microwave surface wave excitation plasma apparatus 40 having such a configuration, air in the vacuum vessel 105 is discharged from the gas exhaust port 109. After exhausting, the reaction gas is supplied from the gas inlet 108. A microwave generated by a microwave oscillator (not shown) forms a standing wave in the dielectric antenna 102, and is installed in a slot 103 disposed along the bottom surface of the waveguide 101 and in a lower portion thereof. When introduced into the processing chamber 10 through the dielectric window 104, plasma is generated inside the processing chamber 10, and the substrate 106 is subjected to processing such as CVD by the plasma.

  By the way, in order to form a high-quality thin film at high speed by plasma CVD at a low pressure of 1 Torr or less, it is necessary to generate a large amount of radicals necessary for forming the thin film. Since radicals in plasma are mainly generated by electron energy, a high electron temperature is required to generate a large amount of radicals. For this reason, plasma having a high electron temperature is required.

  On the other hand, since ion bombardment to the substrate is a parameter that greatly affects thin film formation, it is necessary to control the sheath voltage of ion acceleration on the front surface of the substrate. Generally, the sheath voltage is controlled by applying a bias voltage to the substrate. However, in order to easily control the sheath potential by applying a bias voltage from the outside, it is advantageous that the plasma electron temperature is low (plasma This is because the ionic current density and the floating potential that enter the substrate surface from are a function of the electron temperature, and they are smaller as the electron temperature is lower.

  As described above, in order to form a high-quality thin film by plasma CVD, high electron temperature plasma is required in the radical generation region and low electron temperature plasma is required in the film formation region.

  The microwave surface wave excitation plasma apparatus 40 configured as shown in FIG. 10 is high in the vicinity of the dielectric window 104 into which microwaves are introduced due to the electric field of the surface wave generated at the interface between the dielectric window 104 and the plasma. Electron temperature plasma is generated. A little away from the dielectric window 104 into the plasma, the electric field of the surface wave is greatly attenuated, and there is a plasma with a low electron temperature mainly governed by the diffusion phenomenon, making it ideal as a CVD device for thin film formation. Has plasma characteristics. As an application example thereof, there is plasma CVD for forming a diamond thin film at a gas pressure of 100 mTorr or less.

The diamond thin film formation technique at a gas pressure of 100 mTorr or less is a technique that has recently been attracting attention because it is expected to have the following advantages over the conventional gas pressure of 10 to 100 Torr.
(1) Since a large-area plasma can be generated, a large-area thin film can be formed.
(2) The substrate temperature required for diamond thin film formation can be lowered.
(3) Since the temperature of the neutral gas is low, mixing of impurities from the wall of the vacuum vessel is reduced.
(4) Independent and precise control of CVD parameters (gas pressure, substrate temperature, power, etc.) is possible.
(5) The nuclear density of diamond increases.
(6) The film thickness can be controlled at the atomic level.
(7) Since various plasma measurement techniques can be used, in-situ measurement of diamond thin film formation is possible.
(8) When forming a diamond thin film for a semiconductor, the impurity doping concentration can be precisely controlled.

  However, at a pressure of 100 mTorr or less, the present condition is that it is difficult to form a diamond thin film due to an increase in graphite components. There is an example of diamond synthesis using ICP (inductively coupling plasma) and ECR (electron cyclotron resonance) plasma at 100 mTorr or less, but it does not grow into a perfect layered film and has not yet reached a practical quality. The cause is considered to be the low radical density and the influence of ion bombardment on the substrate.

  In plasma at a pressure of 100 mTorr or less, a collisionless sheath is formed, and ions from the plasma are accelerated by the sheath potential and collide with the substrate surface as it is. growing. Ion bombardment is known to cause detrimental reactions to growing diamond film formation. In order to suppress ion bombardment in the diamond thin film formation process, a method of applying a positive DC bias voltage to the substrate 106 shown in FIG. 11 to lower the sheath potential is generally used. The microwave surface wave excitation plasma apparatus 50 of FIG. 11 is configured such that a positive DC bias voltage is applied to the substrate 106 by the bias power source 200 and the inner wall of the vacuum vessel 105 serves as an earth electrode.

  However, with this method, increasing the bias voltage also increases the plasma space potential, so the plasma becomes unstable, and arc discharge may occur on the inner wall of the vacuum vessel (discharge vessel). Has its limits.

On the other hand, a method of reducing the sheath potential in the vicinity of the substrate surface using the above-described spatial nonuniformity of the electron temperature of the microwave surface wave excitation plasma processing apparatus 40 shown in FIG. 10 has been developed (Patent Document 1). ). FIG. 12 shows a microwave surface wave excitation plasma processing apparatus disclosed in Patent Document 1. In addition to the basic structure of the microwave surface wave excitation plasma processing apparatus 40 shown in FIG. 10, the microwave surface wave excitation plasma processing apparatus 60 has a specially shaped conductor plate under the dielectric window 104 where the high electron temperature plasma is located. Is made to be an upper electrode 203, and a negative DC bias voltage is applied to the upper electrode 203 by the bias power source 200 to the vacuum vessel 105 and the substrate 106 serving as the ground. In this case, 80% or more of the inner wall of the vacuum vessel 105 of the microwave surface wave excitation plasma processing apparatus 60 is covered with the insulator film 116. In the microwave surface wave excitation plasma processing apparatus 60, a considerable part of the plasma space potential can be controlled, and thereby the sheath potential in the vicinity of the substrate 106 that is grounded can be controlled. Further, the electron density of the plasma in which the substrate 106 is placed and CVD is performed is high, and the electron temperature is low. The microwave surface wave-excited plasma processing apparatus 60 has a perfectly layered flat surface at a pressure of 30 mTorr and a substrate temperature of about 650 ° C. on a mechanically scratched silicon substrate as a pretreatment for promoting nucleation. Nanocrystalline diamond thin film has been successfully formed. In addition, we have succeeded in synthesizing carbon nanomaterials such as carbon nanowalls and carbon nanoparticles by controlling the gas species and plasma space potential. The effectiveness of the negative bias application method for controlling the plasma space potential using the spatial difference of the electron temperature in the surface wave excited plasma has been experimentally confirmed.
JP 2004-119619 A

  However, higher quality diamond film formation, diamond film formation at lower pressure and substrate temperature, sheath potential is controlled and the desired carbon material is synthesized to further control plasma space potential (sheath potential near substrate). There is a need to.

  In addition, during the thin film formation process, it is often necessary to perform the process while changing the plasma space potential. For example, in a process that uses the Bias enhanced nucleation (BEN) method as a pretreatment for promoting diamond nucleation, a negative bias voltage is applied to increase the sheath potential near the substrate as the first step (nucleation stage). An ion bombardment is applied to the surface, and in the second step (growth stage), a positive bias voltage is applied to lower the sheath potential.

  Development of a new plasma space potential (sheath potential near the substrate) control technology that can meet the demands for these plasma processing apparatuses is required.

  On the other hand, the plasma space potential is controlled by a negative bias voltage application method using the electron temperature difference between the surface region near the dielectric window, which is a characteristic of surface wave excitation plasma, and the bulk region where CVD is performed. When the principle is analyzed by the sheath theory, it is understood that the plasma space potential in the vicinity of the substrate can be controlled by changing the surface area ratio of both electrodes in contact with the plasma in addition to the bias voltage.

  The present invention has been made in consideration of the above points, and provides a plasma processing method and apparatus optimal for processing such as thin film formation and etching, enabling generation and control of plasma having excellent characteristics, More specifically, an object of the present invention is to provide a microwave plasma processing apparatus capable of changing the surface area in contact with the plasma of both electrodes installed in the processing chamber outside the processing chamber and controlling the plasma space potential.

  The present invention provides a microwave plasma processing apparatus in which the surface area in contact with the plasma of both electrodes installed in the plasma processing chamber for applying a bias voltage can be controlled outside the processing chamber, thereby controlling the plasma space potential. is there. That is, the present invention is as follows.

  The microwave plasma processing apparatus according to claim 1 of the present invention has a processing chamber for storing a substrate, and a vacuum vessel in which a dielectric window capable of transmitting microwaves is provided in an airtight manner, and a waveguide. An antenna for introducing microwaves propagating through the vacuum chamber into the vacuum vessel and the dielectric window in the processing chamber are installed along the dielectric window, and are electrically insulated from the vacuum vessel and transmit the microwaves. A microwave plasma processing apparatus comprising a conductive plate having a possible part, wherein the inner container is installed in the processing chamber and is electrically insulated from the vacuum container, and the inner container is electrically And a plurality of conductors installed in the inner container, and each of the conductor plate, the inner container, and the plurality of conductors is provided with an electrical lead wire, one of which is the electrical lead wire Contact Other is to have a switch that is is characterized in that in communication with the vacuum chamber outside of the ground circuit.

  In the microwave plasma processing apparatus according to claim 2 of the present invention, the conductor plate includes a plurality of portions that are electrically insulated from each other, and the plurality of portions are provided with electric lead wires, one of which is the electric lead wire. The other switch connected to is connected to a ground circuit outside the vacuum vessel.

  The microwave plasma processing apparatus according to claim 3 of the present invention is characterized by having a power source for applying a bias voltage to the conductor plate.

  The microwave plasma processing apparatus according to claim 4 of the present invention is characterized in that the dielectric window has an annular protrusion on the inside of the processing chamber, and the conductor plate is disposed inside the annular protrusion. .

  According to the microwave plasma processing apparatus of the first aspect of the present invention, the surface area in contact with the plasma of the lower electrode installed in the processing chamber can be changed outside the processing chamber, and by controlling the plasma space potential, Quality, low pressure and low substrate temperature plasma processing is possible.

  According to the microwave plasma processing apparatus of the second aspect of the present invention, the value of the surface area in contact with the plasma of the upper electrode can be changed outside the processing chamber, and by controlling the plasma space potential over a wide range, High quality, lower pressure and lower substrate temperature plasma processing is possible.

  According to the microwave plasma processing apparatus of the third aspect of the present invention, by further applying a bias voltage to the upper electrode, it is possible to control the plasma space potential over a wider range, resulting in higher quality, lower pressure and Plasma processing at a low substrate temperature is possible.

  According to the microwave plasma processing apparatus of the fourth aspect of the present invention, the above effect can be exhibited while suppressing arc discharge.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  A first embodiment of the present invention is shown in FIG. This microwave surface wave-excited plasma processing apparatus 1 includes a cylindrical metal vacuum vessel 105 having an open upper end, and a dielectric window (for example, a hermetically attached microwave window attached to the upper end of the vacuum vessel 105 (for example, (Quartz, alumina, etc.) 104 and a microwave launcher attached to the upper part of the ring-shaped dielectric antenna 102 surrounded by the waveguide 101 and a microwave on the lower surface of the ring-shaped dielectric antenna 102 Has a transmissive slot 103.

  In the vacuum vessel 105, a gas exhaust port 109 for setting the inside of the vacuum vessel 105 to a required vacuum degree, a gas introduction port 108 for supplying a required reaction gas, and an inner wall of the vacuum vessel 105 are electrically connected. A cylindrical inner container 201 having an open upper end that is insulated and installed, a plurality of cylindrical conductors 202 that are electrically insulated from the inner container 201, a substrate 106, and a substrate 106 are mounted. And a conductive plate 203 that is electrically insulated from the inner container 201 and the cylindrical conductor 202 and is attached to the lower surface of the dielectric window 104. Here, the inner container 201 may be a conductor container, a dielectric container, or a container in which the inner wall of the vacuum container 105 is covered with an insulating film. That is, any material can be used as long as it can electrically float the inner wall of the vacuum vessel in contact with the plasma.

  An electric lead wire 210 is attached to the vacuum vessel 105 and the substrate holder 107 to form an earth circuit, and an electric lead wire 210 is provided on the inner vessel 201 and each cylindrical conductor 202, respectively. It is connected to an ON / OFF switch 211, a switch 212, and an earth circuit installed outside. By opening and closing the switches 211 and 212, one of which is connected to the electrical lead and the other connected to the ground circuit, the inner container 201 and the individual cylindrical conductor 202 are electrically grounded or floating (floating potential state, immobile potential) State) is possible. Similarly, one end of the switch 213 is connected to the conductor plate 203 via an electrical lead wire, and the other end of the switch 213 is connected to a ground circuit. When the switch 213 is opened and closed, the conductor plate 203 is electrically grounded or floating. It is configured as possible.

  In the above configuration, using the microwave surface wave excitation plasma processing apparatus 1, the substrate 106 can be subjected to processing such as CVD by the following procedure.

  When performing the CVD process on the substrate 106 placed on the substrate holder 107 in the processing chamber 10 of the microwave surface wave excitation plasma processing apparatus 1, first, the air in the processing chamber 10 is discharged from the gas exhaust port 109. After exhausting, the reaction gas is supplied from the gas inlet 108. Next, when the microwave introduced from the microwave power source (not shown) through the waveguide 101 into the ring-shaped dielectric antenna 102 generates a standing wave, the standing wave is converted into the slot 103. Then, plasma is generated in the vacuum vessel 105 through the dielectric window 104. A CVD process is performed on the substrate 106 by this plasma.

  The plasma generated in the vacuum vessel 105 has a higher electron temperature due to the surface wave near the dielectric window 104 (surface region). On the other hand, the inner container 201 (bulk region) has a low electron temperature. Such a difference in the spatial distribution of the electron temperature is a prominent feature of the microwave surface wave excitation plasma apparatus.

  Even if two electrodes I and II are installed in a plasma having a spatially uniform electron temperature and electron density and the electrodes are electrically connected, no current flows. That is, the electron current and ion current entering the electrode I become the same due to both diffusion phenomena, and the electron current and ion current entering the electrode II are also the same, so the number of electrons and ions flowing from the plasma to both electrodes is balanced. Because. Therefore, the plasma space potential becomes a floating potential and is constant even if the surface area ratio of both electrodes changes.

  However, when the electrode I is installed in the high electron temperature region and the electrode II is installed in the low electron temperature region in the plasma with a large difference in the spatial distribution of electron temperature, such as microwave surface wave excitation plasma, both electrodes are in contact with each other. Due to the difference in plasma electron temperature, a current flows from a plasma region having a high electron temperature to a plasma region having a low electron temperature. That is, an electron current mainly flows from the plasma to the electrode I, and an ion current flows from the plasma to the electrode II. The electron current flowing through the electrode I is limited by the ionic current flowing through the electrode II. If the surface area of the electrode II is increased, the ion current also increases in proportion to the surface area. Therefore, in order to maintain the overall electrical neutrality of the plasma, the electron current flowing to the electrode I is the ion current flowing to the electrode II. You must increase only the amount of increase. As a result, the plasma space potential decreases.

  In the CVD process using the microwave surface wave excitation plasma processing apparatus 1 of the present invention, when the conductive plate 203 is an upper electrode and the inner vessel 201, the cylindrical conductor 202, the substrate holder 107, and the substrate 106 are lower electrodes, The electrode corresponds to the electrode I described above, and the lower electrode corresponds to the electrode II described above. Therefore, the plasma space potential, that is, the sheath potential in the vicinity of the substrate 106 can be controlled by controlling the surface area ratio of the upper electrode and the lower electrode in contact with the plasma by opening and closing the switch 211, the switch 212, and the switch 213. .

  For example, when the switch 213 is closed (hereinafter referred to as an ON state), the switch 211 is opened (hereinafter referred to as an OFF state), and the switches 212a, 212b, 212c, 212d, and 212e are all OFF ( In step 1) of Table 1, the surface area of the lower electrode is minimized, the surface area ratio between the upper electrode and the lower electrode is minimized, and the sheath potential near the substrate 106 is the highest. Next, when the switches 212a, 212b, 212c, 212d, and 212e are sequentially switched from OFF to ON (step 2 in Table 1), the area corresponding to the area of the cylindrical conductor 202 connected to the ON switch is obtained. The surface area of the lower electrode increases, the surface area ratio between the upper electrode and the lower electrode increases correspondingly, and the sheath potential near the substrate 106 decreases. Similarly, if the switch 211 is turned on with all the switches 212 turned on (step 3 in Table 1), the surface area of the lower electrode is increased by the area of the inner container 201, and the surface area ratio of the upper electrode and the lower electrode is increased. Correspondingly increases, and the sheath potential near the substrate 106 further decreases. Here, when the switch 213 is turned OFF (Step 4 in Table 1), no current flows between the upper electrode and the lower electrode regardless of the ON / OFF state of the switch 211 and the switch 212, and the sheath near the substrate 106 is placed. The potential is a floating potential determined by the electron temperature and is minimized.

  By operating the switch in the above procedure, it becomes possible to control the sheath potential in the vicinity of the substrate 106 from the higher one to the lower one in a stepwise manner. Table 1 summarizes the ON / OFF status of each switch at each step.

Experiment (1)
As an application example of this example, the result of forming a diamond thin film at a gas pressure of 30 mTorr is shown below.

  In the conventional technology, in order to increase the diamond nucleation density on the substrate surface, mechanical scratching is performed as a pretreatment for promoting nucleation, and after cleaning the substrate surface, the substrate is placed on the substrate holder in the plasma CVD processing apparatus. Either the diamond thin film is formed or the surface of the substrate is cleaned without scratching, the substrate is placed on the substrate holder in the plasma CVD processing apparatus to generate plasma, and grounding is performed as a pretreatment for promoting nucleation. After applying a negative DC bias voltage to the substrate for several minutes to several tens of minutes to the vacuum vessel to apply ion bombardment to the substrate (bias enhanced nucleation: BEN), it is necessary to form a diamond thin film. It was.

In contrast, in this embodiment, only the surface of the substrate 106 is cleaned without being scratched, and plasma of H ₂ and CO mixed gas is generated in the substrate holder 107 in the microwave surface wave excitation plasma processing apparatus 1. First, after performing the state of step 1 shown in Table 1 for several tens of minutes, the diamond thin film was formed in the state of step 4 (experimental conditions: gas pressure 30 mTorr, substrate temperature 650 ° C.), and the diamond thin film was successfully formed. did.

  In this experiment, by reducing the area of the lower electrode for the first tens of minutes, the plasma space potential is increased and ion bombardment is applied to the substrate surface, so that nucleation promotion pretreatment is performed by means different from conventional BEN treatment. went. That is, in the microwave surface wave excitation plasma processing apparatus 1, BEN processing performed using a conventional DC bias power supply can be performed by simply controlling the switch without using a DC power supply, thus simplifying the preprocessing process. Can be.

  As described above, the microwave surface wave excitation plasma processing apparatus 1 according to the present embodiment includes the processing chamber 10 in which the substrate 106 is accommodated, and a dielectric window 104 capable of transmitting microwaves is airtightly provided in part. A vacuum vessel 105, a dielectric antenna 102 that introduces microwaves propagating through the waveguide 101 into the vacuum vessel 105, and the dielectric window 104 in the processing chamber 10. A microwave plasma processing apparatus comprising a conductive plate 203 having a portion that is electrically insulated from and permeable to microwaves from the vacuum container 105, and is installed in the processing chamber 10 and the vacuum container 105 An electrically insulated inner container 201 and the inner container 201 are electrically insulated and have a plurality of conductors 202 installed in the inner container 201. The conductor plate 203 and the inner container 201 and each of the plurality of conductors 202 have electrical lead wires 210 The switch 211, 212, 213, one of which is connected to the electrical lead 210, is connected to a ground circuit outside the vacuum vessel 105, and is installed in the processing chamber 10. The surface area of the lower electrode in contact with the plasma can be changed outside the processing chamber, and high quality, low pressure and low substrate temperature plasma processing can be performed by controlling the plasma space potential.

  Next, a second embodiment will be described.

  In the second embodiment, when compared with the first embodiment, the conductor plate 203 attached to the lower surface of the dielectric window 104 is formed of a plurality of conductor plates 203a, 203b, 203c, 203d as shown in FIG. The difference is that switches 213a, 213b, 213c, and 213d are respectively provided. By turning ON / OFF the switches 213a, 213b, 213c, and 213d, the surface area of the upper electrode 203 can be changed, whereby the stepwise control of the plasma space potential is possible. Other configurations and effects of the second embodiment are the same as those of the first embodiment.

  As described above, in this embodiment, the conductor plate 203 of the microwave surface wave excitation plasma processing apparatus 1 is a plurality of portions 203a, 203b, 203c, 203d that are electrically insulated from each other, and the plurality of portions are electrically connected. A lead wire 210 is provided, and the other of the switches 213a, 213b, 213c, and 213d connected to the electric lead wire 210 is connected to an earth circuit outside the vacuum vessel 105, Furthermore, the surface area of the upper electrode in contact with the plasma can be changed outside the processing chamber, and plasma processing with higher quality, lower pressure, and lower substrate temperature is possible by controlling the plasma space potential over a wide range.

Next, the third embodiment shown in FIG. 3 with the same reference numerals as those in FIG. 1 will be described.
The microwave surface wave excitation plasma processing apparatus 20 of the third embodiment is provided with a bias power source 200 on the conductor plate 203 as compared with the microwave surface wave excitation plasma processing apparatus 10 of the first embodiment. Is different.

By applying a bias voltage to the conductor plate 203 with a bias power source 200 connected between the switches 213, the plasma space potential can be controlled. For example, when the switch 213 is turned off and the switch 214 is turned on and a negative DC bias is applied to the conductor plate 203, the plasma space potential is controlled, and the sheath potential near the substrate can be lowered to the floating potential or less. Further, for example, the switch 211, the switch 212, and the switch 213 are turned OFF, and the sheath potential near the substrate can be reduced as the surface area of the lower electrode is reduced _.

In the microwave surface wave excitation plasma processing apparatus 20 shown in FIG. 3, when a bias voltage is applied to the conductor plate 203, the opening of the vacuum vessel 105 immediately below the dielectric window 104 is in electrical contact with the plasma. Therefore, arc discharge may occur between the inner wall there and the conductor plate 203. In order to suppress the occurrence of the arc discharge, it is necessary to prevent the opening of the vacuum vessel 105 from being in electrical contact with the plasma by some method. For example, by covering an insulator (for example, an alumina (Al ₂ O ₃ ) film), occurrence of arc discharge can be suppressed. Further, by using the dielectric window 114 provided with the ring-shaped protrusion 114a as shown in FIGS. 4 and 5, the conductor plate 203 is installed in the hole of the ring-shaped protrusion 114a, so that the arc discharge with the discharge vessel wall is prevented. A large bias voltage can be applied while suppressing.

Experiment (2)
As an application example of this example, the result of diamond thin film formation at a gas pressure of 30 mTorr and a substrate temperature of 400 ° C. is shown below.

  In the conventional technology, in order to increase the diamond nucleation density on the substrate surface, mechanical scratching is performed as a pretreatment for promoting nucleation, and after cleaning the substrate surface, the substrate is placed on the substrate holder in the plasma CVD processing apparatus. Either the diamond thin film is formed or the surface of the substrate is cleaned without scratching, the substrate is placed on the substrate holder in the plasma CVD processing apparatus to generate plasma, and grounding is performed as a pretreatment for promoting nucleation. After applying a negative DC bias voltage to the substrate for several minutes to several tens of minutes to the vacuum vessel to apply ion bombardment to the substrate (bias enhanced nucleation: BEN), it is necessary to form a diamond thin film. It was.

In contrast, in this embodiment, only the surface of the substrate 106 is cleaned without scratching, and plasma of H ₂ and CO mixed gas is generated in the substrate holder 107 in the microwave plasma processing apparatus 1. By operating the switch so as to minimize the surface area of the lower electrode (state of step 4 in Table 1), and applying a DC bias voltage of −150 V or more to the conductor plate (upper electrode) 203, a gas pressure of 30 mTorr, Under the experimental conditions with a substrate temperature of 400 ° C., a nanocrystal diamond thin film having a complete layer state was successfully formed by only one CVD step (negative bias applied to the upper electrode). It was confirmed by X-ray diffraction (XRD) that the formed thin film was a nanocrystal diamond thin film.

  The nucleation-promoting pretreatment required by conventional diamond CVD technology is not only a troublesome process but also a problem in the application of diamond thin films to semiconductors and nano-micromachines because the substrate surface is damaged. Yes. Further, in the conventional technique, a substrate temperature of 700 ° C. to 1000 ° C. is required for forming a diamond thin film, and the range of substrate material selection is narrow due to the problem of heat resistance.

  The experimental results of this example show that the present invention is an innovative technology that solves the limitations of the conventional diamond CVD technology.

Experiment (3)
As an application example of the present example, a surface SEM obtained as a result of forming a diamond thin film using a mixed gas composed of 2% CH ₄ and 98% H ₂ by applying a DC voltage of −70 V to the conductor plate 203. Pictures are shown in FIGS. In the case of FIG. 6, all the switches 211, 212a, 212b, 212c, 212d, and 212e of the microwave surface wave excitation plasma processing apparatus 20 are turned OFF. In the case of FIG. All of 212a, 212b, 212c, 212d, and 212e are turned on and CVD is performed. The film forming process was performed for 8 hours.

  In the thin film shown in FIG. 6, grains having an order of about 30 nm are generated on the entire surface of the substrate, and a sheet-like material having a thickness of about 20 nm and a length of several hundreds of nanometers is formed thereon.

  In contrast, the thin film shown in FIG. 7 is uniformly formed on the entire surface of the substrate in such a manner that small sheet-like grains having a thickness of about 20 nm and a length of about 150 nm are thickly overlapped. This is thought to be because carbon grew into seeds, stopped growing at a certain size, and new sheet-like grains grew one after another.

  From this experiment, it was confirmed in this example that the film quality of the diamond thin film can be controlled by changing the area of the lower electrode with a switch and changing the plasma space potential.

  As described above, the microwave surface wave excitation plasma processing apparatus 20 of the present embodiment has a power source for applying a bias voltage to the conductor plate, and further applies a bias voltage to the upper electrode 203. By doing so, the plasma space potential can be controlled in a wider range, and plasma processing with higher quality, lower pressure and lower substrate temperature becomes possible.

  Next, a fourth embodiment will be described.

  Although the microwave surface wave excitation plasma can be generated in devices having various structures, the characteristics of the plasma have similar characteristics regardless of the structure. That is, high electron temperature plasma is generated in the surface region near the dielectric window, and low electron temperature plasma is generated in the bulk region. By understanding this characteristic and applying the present invention, the same effect as the above microwave surface wave excitation plasma processing apparatus can be obtained regardless of the structure of the apparatus.

  A microwave-excited plasma processing apparatus 30 according to a fourth embodiment is shown in FIG. 8 with the same reference numerals as those in FIG. FIG. 9 is a top plan view of the microwave surface wave excitation plasma processing apparatus 30.

  The microwave surface wave excitation plasma processing apparatus 30 according to the fourth embodiment is different from the first embodiment in that the slot 103 is not provided between the dielectric antenna 102 and the microwave introduction dielectric window 104. Different from the surface acoustic wave excitation plasma processing apparatus 10. In this microwave surface wave excitation plasma processing apparatus 30 as well, control of the plasma space potential is recognized by changing the surface area ratio of the electrodes installed in the surface region and the bulk region.

  As described above, the microwave surface wave excitation plasma processing apparatus 30 according to the present embodiment includes the processing chamber 10 in which the substrate 106 is accommodated, and a dielectric window 104 capable of transmitting microwaves is airtightly provided in part. A vacuum vessel 105, a dielectric antenna 102 that introduces microwaves propagating through the waveguide 101 into the vacuum vessel 105, and the dielectric window 104 in the processing chamber 10. A microwave plasma processing apparatus comprising a conductive plate 203 having a portion that is electrically insulated from and permeable to microwaves from the vacuum container 105, and is installed in the processing chamber 10 and the vacuum container 105 An electrically insulated inner container 201 and the inner container 201 are electrically insulated and have a plurality of conductors 202 installed in the inner container 201. The conductor plate 203 and the inner container 201 and each of the plurality of conductors 202 have electrical leads 210 The other of switches 211, 212, and 213 provided and connected to the electrical lead 210 is connected in a circuit to the ground outside the vacuum vessel 105, and is installed in the processing chamber 10. The surface area of the lower electrode in contact with the plasma can be changed outside the processing chamber 10, and high quality, low pressure and low substrate temperature plasma processing can be performed by controlling the plasma space potential.

  As mentioned above, although the Example of this invention was described, this invention is not limited to the said Example, A various deformation | transformation implementation is possible. For example, in the embodiments, a dielectric antenna is used as the antenna, but a slot antenna in which an opening is secured with a dielectric, a metal antenna, or the like can also be used. An apparatus in which the dielectric window and the substrate are turned upside down is also possible. In this case, an electrode called an upper electrode to which a negative bias is applied is called a lower electrode and may be placed on the dielectric window, so that a special support for preventing the fall is not necessary.

  In addition to the diamond thin film such as the nanocrystal diamond thin film shown in the examples, in addition to the control of the gas species and the substrate temperature, by controlling the stepwise plasma space potential using the present invention, the carbon nanotube, It is also possible to synthesize carbon nanomaterials such as carbon nanowalls and carbon nanoparticles.

  The present invention also provides an effective effect in a microwave plasma processing apparatus which performs thin film formation of various materials using conventional plasma, etching, ashing, solid surface treatment, plasma ion implantation, and the like.

It is a figure which shows the microwave surface wave excitation plasma processing apparatus in 1st Example of this invention. It is a figure which shows the conductor plate (upper electrode) of the microwave surface wave excitation plasma processing apparatus in 2nd Example of this invention. It is a figure which shows the microwave surface wave excitation plasma processing apparatus in the 3rd Example of this invention. It is a figure which shows the dielectric material window periphery with the ring-shaped protrusion of the microwave surface wave excitation plasma processing apparatus in the 3rd Example of this invention. It is a figure which shows the dielectric material window with the ring-shaped protrusion of the microwave surface wave excitation plasma processing apparatus in 3rd Example of this invention. It is a figure which shows the surface SEM photograph of the diamond thin film formed with the microwave surface wave excitation plasma processing apparatus in the 3rd Example of this invention. It is a figure which shows the surface SEM photograph of the diamond thin film formed with the microwave surface wave excitation plasma processing apparatus in the 3rd Example of this invention. It is a figure which shows the microwave surface wave excitation plasma processing apparatus in the 4th Example of this invention. It is an upper top view which shows the microwave surface wave excitation plasma processing apparatus in the 4th Example of this invention. It is a figure which shows the microwave surface wave excitation plasma processing apparatus of a prior art example. It is a figure which shows the microwave surface wave excitation plasma processing apparatus of a prior art example. It is a figure which shows the microwave surface wave excitation plasma processing apparatus of a prior art example.

Explanation of symbols

1, 20, 30, 40, 50 Microwave (surface wave excitation) plasma processing equipment
10 Processing chamber
101 waveguide
102 (Dielectric) antenna
103 slots
104 Dielectric window
105 vacuum vessel
106 substrates
107 Board holder
108 Gas inlet
109 Gas outlet
114 Dielectric window with ring-shaped projections
114a Ring-shaped protrusion (annular protrusion)
115 O-ring
116 Insulator film
200 bias power supply
201 inner container
202 Conductor (lower electrode)
203, 203a, 203b, 203c, 203d Conductor plate (upper electrode)
210 Electrical leads
211, 212, 212a, 212b, 212c, 212d, 212e 213, 213a, 213b, 213c, 213d, ON / OFF switch

Claims (4)

A vacuum chamber having a processing chamber for storing a substrate, and a dielectric window capable of transmitting microwaves in part in an airtight manner;
An antenna for introducing a microwave propagating through a waveguide into the vacuum vessel;
The microwave plasma processing apparatus is provided along a dielectric window in the processing chamber, and is electrically insulated from the vacuum vessel and includes a conductor plate having a portion through which the microwave can pass. And
An inner container installed in the processing chamber and electrically insulated from the vacuum container; and a plurality of conductors electrically insulated from the inner container and installed in the inner container. ,
An electrical lead wire is provided for each of the conductor plate, the inner container, and the plurality of conductors, and one of the switches connected to the electrical lead wire is connected to an earth circuit outside the vacuum container. A featured microwave plasma processing apparatus.   The conductor plate is composed of a plurality of portions that are electrically insulated from each other, and the plurality of portions are provided with electric lead wires, and one of the switches connected to the electric lead wire is connected to the ground outside the vacuum vessel. The microwave plasma processing apparatus according to claim 1, wherein the microwave plasma processing apparatus is connected to a circuit.   The microwave plasma processing apparatus according to claim 1, further comprising a power source that applies a bias voltage to the conductor plate.   The microwave according to any one of claims 1 to 3, wherein the dielectric window has an annular protrusion on the processing chamber side, and the conductive plate is installed inside the annular protrusion. Plasma processing equipment.

Images