JP5034245B2 - Plasma discharge treatment apparatus and plasma discharge treatment method - Google Patents

Description

The present invention relates to a plasma discharge treatment apparatus and a plasma discharge treatment method, in particular, a plasma discharge using the plasma discharging treatment gas containing N ₄ ⁺ ions used in the plasma discharge treatment carried out at a pressure in the vicinity of atmospheric pressure The present invention relates to a processing apparatus and a plasma discharge processing method.

  In recent years, as a method and apparatus for performing various processes such as thin film deposition, etching, cleaning, hydrophilization, and hydrophobization on the surface of a substrate, a mixed gas such as a discharge gas, a source gas, and a reactive gas is generated by discharge between counter electrodes. Development of a technique for generating a plasma discharge treatment gas and performing a plasma discharge treatment using the gas has been underway.

  Conventionally, as a plasma discharge treatment method, a raw material gas or the like is mixed with a discharge gas composed of a rare gas such as helium or argon, and introduced into a discharge space between opposing electrodes under a low pressure of about several Pa. The method of performing is known (for example, refer patent documents 1-3 etc.). However, in such processing under low pressure, a high degree of airtightness of the apparatus is required, and a pressure reducing means such as a pump is required for pressure reduction. There was a problem.

  Therefore, in recent years, the above problems have been solved, and surface treatment performance under higher pressure conditions has been improved, that is, for example, the expectation for improvement in film formation rate, etc. The following plasma discharge treatment methods have been developed (see, for example, Patent Documents 4 and 5). In recent years, a cheaper nitrogen gas has been used as a discharge gas in place of a conventional rare gas (see, for example, Patent Documents 6 and 7).

  However, when discharging to nitrogen gas under a pressure near atmospheric pressure, it is necessary to increase the electric field strength for starting the discharge as compared with noble gas, etc. Then, the discharge between the electrodes easily shifted to arc discharge, and a predetermined discharge treatment could not be performed.

Therefore, the occurrence of arc discharge is avoided by applying an electric field in which two high-frequency electric fields are superimposed on the discharge space between the counter electrodes (see Patent Document 6) or by applying a pulsed electric field (see Patent Document 7). How to do is known. By adopting these methods, the occurrence of arc discharge is avoided even in nitrogen gas discharge under a pressure near atmospheric pressure, and a sufficiently stable discharge state can be obtained.
JP 2000-36255 A JP 2000-38888 A JP 2000-277495 A JP 2000-72903 A JP 2000-82595 A JP 2004-68143 A JP 2002-155370 A

  However, in these methods, although the discharge state is stable, the so-called plasma density of the plasma discharge treatment gas in the discharge space, that is, the density of electrons, ions, excited molecular species, etc. in the gas may be low, which is sufficient In some cases, the plasma discharge treatment is not always performed satisfactorily, such as when a high-quality film is not formed.

  Therefore, when processing is performed using a plasma discharge processing gas that uses nitrogen gas as a discharge gas under a pressure close to atmospheric pressure, processing conditions that can provide good results and control conditions for the plasma discharge processing apparatus are established. Was strongly desired.

Therefore, the present invention can perform a satisfactory process in various plasma discharge processes such as thin film deposition and cleaning performed under a pressure near atmospheric pressure using a plasma discharge process gas using nitrogen gas as a discharge gas. and an object thereof is to provide a plasma discharge treatment apparatus and a plasma discharge treatment method using the plasma discharge processing gas.

In order to solve the above-described problem, the plasma discharge processing apparatus according to claim 1 is:
A pair of electrodes disposed opposite to each other;
Voltage applying means for applying a voltage to the pair of electrodes;
A gas supply means for supplying a mixed gas containing a discharge gas and a reaction gas containing nitrogen as a main component between the pair of electrodes;
With
The gas supply means supplies the mixed gas between the pair of electrodes under a pressure near atmospheric pressure, and the voltage application means supplies a periodically changing voltage between the pair of electrodes. By applying an electric field that periodically changes between a pair of electrodes, a discharge is generated between the pair of electrodes via the mixed gas, and the mixed gas is turned into plasma, so that the time average density is 8.0 × 10 8. A plasma discharge treatment gas containing N ₄ ⁺ ions in a range of ¹⁶ to 1 × 10 ²⁰ [m ⁻³ ] is generated, and a plasma discharge treatment is performed on the substrate using the generated plasma discharge treatment gas. It is characterized by.

The plasma discharge processing apparatus according to claim 2 ,
A pair of electrodes disposed opposite to each other;
Voltage applying means for applying a voltage to the pair of electrodes;
A gas supply means for supplying a mixed gas containing a discharge gas and a reaction gas containing nitrogen as a main component between the pair of electrodes;
With
The gas supply means supplies the mixed gas between the pair of electrodes under a pressure near atmospheric pressure, and the voltage application means supplies a periodically changing voltage between the pair of electrodes. By applying an electric field that periodically changes between a pair of electrodes, a discharge is generated between the pair of electrodes via the mixed gas, and the mixed gas is turned into plasma, and the time average density is 1.2 × 10 6. A plasma discharge treatment gas containing N ₄ ⁺ ions in a range of ¹⁷ to 1 × 10 ¹⁹ [m ⁻³ ] is generated, and a plasma discharge treatment is performed on the substrate using the generated plasma discharge treatment gas. It is characterized by.

The plasma discharge treatment apparatus according to claim 3 is:
A pair of electrodes disposed opposite to each other;
Voltage applying means for applying a voltage to the pair of electrodes;
A gas supply means for supplying a mixed gas containing a discharge gas and a reaction gas containing nitrogen as a main component between the pair of electrodes;
With
The gas supply means supplies the mixed gas between the pair of electrodes under a pressure near atmospheric pressure, and the voltage application means supplies a periodically changing voltage between the pair of electrodes. By applying an electric field that periodically changes between a pair of electrodes, a discharge is generated between the pair of electrodes via the mixed gas, and the mixed gas is turned into plasma, and the time average density is 2.0 × 10 6. A plasma discharge treatment gas containing N ₄ ⁺ ions in a range of ¹⁷ to 4 × 10 ¹⁷ [m ⁻³ ] is generated, and the substrate is subjected to plasma discharge treatment using the generated plasma discharge treatment gas. It is characterized by.

The plasma discharge processing method according to claim 4 comprises:
A plasma discharge treatment method performed by applying an electric field that periodically changes between a pair of electrodes under a pressure near atmospheric pressure,
A gas mixture containing a discharge gas containing nitrogen as a main component and a reaction gas is supplied between the pair of electrodes, and an electric field that periodically changes is applied between the pair of electrodes, whereby the pair of electrodes is interposed via the gas mixture. A plasma discharge containing N ₄ ⁺ ions having a time average density in the range of 8.0 × 10 ¹⁶ to 1 × 10 ²⁰ [m ⁻³ ] by causing discharge between the electrodes of the mixture to be plasmatized. A processing gas is generated, and a plasma discharge process is performed on the substrate using the generated plasma discharge processing gas.

The plasma discharge processing method according to claim 5 comprises:
A plasma discharge treatment method performed by applying an electric field that periodically changes between a pair of electrodes under a pressure near atmospheric pressure,
A gas mixture containing a discharge gas containing nitrogen as a main component and a reaction gas is supplied between the pair of electrodes, and an electric field that periodically changes is applied between the pair of electrodes, whereby the pair of electrodes is interposed via the gas mixture. A plasma discharge containing N ₄ ⁺ ions having a time average density in the range of 1.2 × 10 ¹⁷ to 1 × 10 ¹⁹ [m ⁻³ ] by causing a discharge between the electrodes of the mixture to be plasmatized. A processing gas is generated, and a plasma discharge process is performed on the substrate using the generated plasma discharge processing gas.

The plasma discharge treatment method according to claim 6 comprises:
A plasma discharge treatment method performed by applying an electric field that periodically changes between a pair of electrodes under a pressure near atmospheric pressure,
A gas mixture containing a discharge gas containing nitrogen as a main component and a reaction gas is supplied between the pair of electrodes, and an electric field that periodically changes is applied between the pair of electrodes, whereby the pair of electrodes is interposed via the gas mixture. A plasma discharge containing N ₄ ⁺ ions having a time average density in the range of 2.0 × 10 ¹⁷ to 4 × 10 ¹⁷ [m ⁻³ ] by causing a discharge between the electrodes of the mixture to be plasmatized. A processing gas is generated, and a plasma discharge process is performed on the substrate using the generated plasma discharge processing gas.
Invention according to claim 7, in the plasma discharge treatment method according to any one of claims 6 claims 4, a time average density of the N ₄ ⁺ ions, by varying the value of the current density control It is characterized by doing.

According to the first to third aspects of the present invention, the plasma discharge treatment gas is introduced into the discharge space under a pressure near atmospheric pressure, and is periodically applied to, for example, the counter electrode or one of the counter electrodes. By applying a changing voltage, the plasma is generated by a periodically changing electric field generated in the discharge space. At that time, N ₄ ⁺ ions are contained in the plasma discharge treatment gas at a time average density of 8.0 × 10 ¹⁶ [m ⁻³ ] or more. At that time, the time average density of N ₄ ⁺ ions is more preferably 1.2 × 10 ¹⁷ [m ⁻³ ] or more, and further preferably 2.0 × 10 ¹⁷ [m ⁻³ ] or more.

According to the invention described in claims 4 to 6 , the predetermined plasma discharge treatment is performed using the plasma discharge treatment gas thus generated.
According to the invention described in claim 7 , in the plasma discharge processing method, the peak value of the current density having a good correlation with the time average density of N ₄ ⁺ ions in the plasma discharge processing gas is changed. To control the density of N ₄ ⁺ ions in the plasma discharge processing gas.

According to the invention described in claims 1 to 6 , the time average density is 8.0 × 10 ¹⁶ [m ⁻³ ] or more, more preferably 1.2 × 10 ¹⁷ [m ⁻³ ] or more, and further preferably. Generates plasma discharge treatment gas containing N ₄ ⁺ ions of 2.0 × 10 ¹⁷ [m ⁻³ ] or more, and performs various plasma discharge treatments using the gas, thereby containing nitrogen gas as a main component. Even with the plasma discharge treatment gas, it is possible to carry out a good treatment that is practical for use under a pressure near atmospheric pressure.

It is unclear whether N ₄ ⁺ ions themselves are directly involved in the plasma discharge treatment, but the time average density is an index indicating the high plasma density of the plasma discharge treatment gas and the stability of the plasma state. Instead of adjusting the control parameters of the plasma discharge processing apparatus empirically or by trial and error as in the prior art, the time average density of N ₄ ⁺ ions in the plasma discharge processing gas is used as in the present invention. Is 8.0 × 10 ¹⁶ [m ⁻³ ] or more, more preferably 1.2 × 10 ¹⁷ [m ⁻³ ] or more, and even more preferably 2.0 × 10 ¹⁷ [m ⁻³ ] or more. By controlling the control parameters of the discharge treatment apparatus, it is possible to perform a good plasma discharge treatment.

According to the seventh aspect of the present invention, in the plasma discharge processing method, the control parameter of the plasma discharge processing apparatus is adjusted to improve the time average density of N ₄ ⁺ ions in the plasma discharge processing gas. By varying the peak value of the current density having the correlation, it is possible to easily set the time average density of N ₄ ⁺ ions in the plasma discharge processing gas, and the effect of the invention according to the claim can be efficiently performed. It will be possible to perform well.

  Embodiments of a plasma discharge treatment gas, a plasma discharge treatment gas generation method, and a plasma discharge treatment method according to the present invention will be described below with reference to the drawings.

(About plasma discharge treatment equipment)
First, a plasma discharge processing apparatus in which a plasma discharge processing gas according to the present embodiment is generated and plasma discharge processing is performed using the gas will be described. The plasma discharge processing apparatus performs plasma discharge processing using the plasma discharge processing gas immediately after generating the plasma discharge processing gas as described below, or at the same time as generating the plasma plasma discharge processing gas. It also has the function of a plasma generator.

  As shown in FIG. 1, the plasma discharge treatment apparatus 10 of the present embodiment includes a first electrode 11 and a second electrode 12 that are counter electrodes, and a voltage applying unit that applies a voltage to the two electrodes 11 and 12. ing. In addition to this, the plasma discharge processing apparatus 10 is provided with a gas supply means for supplying a mixed gas, an electrode temperature adjusting means, a control means, and the like, although not shown.

  A first power supply 15 and a second power supply 16 are connected to the first electrode 11 and the second electrode 12 via a first filter 13 and a second filter 14, respectively. The first filter 13 facilitates the passage of current from the first power supply 15 to the first electrode 11, and at the same time grounds the current from the second power supply 16 so that the current to the first power supply 15 is difficult to pass. Designed to. The second filter 14 functions similarly with respect to the second power supply 16 and the second electrode 12.

  The first electrode 11 and the second electrode 12 are supplied with periodically changing voltages from the first power source 15 and the second power source 16, respectively, whereby an electric field generated between the two electrodes. Changes periodically.

  The interelectrode distance between the first electrode 11 and the second electrode 12 is normally set to about 1 mm, but the interelectrode distance is variable by a moving means (not shown). Above both electrodes, a gas supply means (not shown) for supplying a mixed gas G composed of a discharge gas, a raw material gas and a reactive gas to the discharge space 17 between the two electrodes is disposed. When the mixed gas G is introduced from the gas supply means into the discharge space 17 where a high-frequency electric field is generated between the first electrode 12 and the second electrode 12, a discharge occurs between the two electrodes via the mixed gas G, and the mixed gas G Is converted into plasma to generate plasma discharge processing gas G °.

  The plasma discharge processing gas G ° is ejected in the form of a jet below the discharge space 17 and is composed of the lower surfaces of the first electrode 11 and the second electrode 12 and the base material F supported by the support plate 18 from the back surface side. The treatment space to be filled is filled with the plasma discharge treatment gas G °, and a surface treatment such as forming or etching a thin film near the treatment position 19 on the surface of the substrate F is performed. The treated exhaust gas after the discharge treatment is discharged from an exhaust port (not shown).

  Note that at least the surfaces of the first electrode 11, the second electrode 12, and the support plate 18 that are in contact with the mixed gas G and the plasma discharge processing gas G ° are covered with dielectrics 20, 21, and 22, respectively. As the dielectrics 20, 21, and 22, ceramics such as alumina and silicon nitride, or glass lining materials such as silicate glass and borate glass are preferably used.

  It is also possible to configure so that a voltage is applied to the support plate 18 or the support plate 18 is grounded. Further, the first electrode 11 and the second electrode 12 are subjected to the two-frequency discharge as described above. Instead of this, for example, either the first electrode 11 or the second electrode 12 can be configured to be grounded.

  In addition to the above configuration example, the plasma discharge processing apparatus can be configured as shown in FIG. 2, for example. In this configuration example, the plasma discharge processing apparatus 30 includes a first power source 33 and a second power source 34 that apply voltages to the first electrode 31 and the second electrode 32 that are counter electrodes, and the two electrodes 31 and 32. ing. In FIG. 2, the filter interposed between the electrode and the power source is not shown, but is provided as appropriate.

  The first electrode 31 and the second electrode 32 are supplied with periodically changing voltages from the first power supply 33 and the second power supply 34, respectively, so that an electric field generated between the two electrodes is generated. It changes periodically. The applied voltage, frequency, and output density are the same as those in the above configuration example, and can be appropriately changed to appropriate values. The interelectrode distance between the first electrode 31 and the second electrode 32 is variable by a moving means (not shown).

  A gas supply device 36 for supplying a mixed gas composed of a discharge gas, a raw material gas and a reactive gas to a discharge space 35 formed between both electrodes is disposed on one side in the horizontal direction of both the power sources 33 and 34. In addition, the gas supply device 36 is provided with a nozzle 37 for ejecting the mixed gas into the discharge space 35. In the discharge space 35, a high-frequency electric field is generated between the first electrode 31 and the second electrode 32. When a mixed gas is introduced from the gas supply device 36, a discharge occurs between the two electrodes, and the mixed gas is It is converted into plasma to generate plasma discharge processing gas.

  In the plasma discharge processing apparatus 30 of this configuration example, the base material F is movable in the horizontal direction in the discharge space 35 while being supported from the back side by the second electrode 32. Therefore, at the same time as the plasma discharge treatment gas is generated in the discharge space 35, the substrate F is exposed to the plasma discharge treatment gas. Unlike the above configuration example, the plasma discharge treatment gas Generation and plasma discharge treatment using the same are performed simultaneously.

  Although not shown, like the above, at least the surfaces of the first electrode 31 and the second electrode 32 that are in contact with the mixed gas or the plasma discharge processing gas may be covered with a dielectric. In this case, the material of the dielectric is the same as that in the configuration example. It is also possible to configure so that either the first electrode 31 or the second electrode 32 is grounded.

  The plasma discharge processing apparatuses 10 and 30 described above are the simplest apparatus to which the plasma discharge processing gas or the like of the present embodiment is applied, and the plasma discharge processing gas or the like of the present embodiment is in another form. This is also applied to the plasma discharge processing apparatus.

(About plasma discharge treatment gas)
The plasma discharge processing gas according to this embodiment uses a plasma discharge processing apparatus as illustrated in FIG. 1 or FIG. 2, and generates an electric field between a pair of electrodes arranged opposite to each other under a pressure near atmospheric pressure. Generated with periodic changes. The plasma discharge treatment gas contains nitrogen as a main component as a discharge gas, and the gas contains N ₄ ⁺ ions having a time average density of 8.0 × 10 ¹⁶ [m ⁻³ ] or more.

As shown in Examples described later, if the time average density of N ₄ ⁺ ions in the plasma discharge treatment gas is 8.0 × 10 ¹⁶ [m ⁻³ ] or more, the substrate surface is cleaned, the thin film is formed, etc. In this plasma discharge process, it is possible to perform a process that is sufficiently practical.

The time average density of N ₄ ⁺ ions contained in the plasma discharge treatment gas is preferably 8.0 × 10 ¹⁶ to 1 × 10 ²⁰ [m ⁻³ ], more preferably 1.2 × 10. ^{17 ~1 × 10 19 [m -3} ], more preferably ^{2.0 × 10 17 ~4 × 10 17} [m -3]. The lower limit values of these numerical ranges are shown in the examples described later, and the upper limit value is an approximate value determined in consideration of cost effectiveness in an actual machine.

In addition, since it is difficult to actually measure the density of N ₄ ⁺ ions in the plasma discharge processing gas, plasma simulation is used to define the density value. In addition, since the density of N ₄ ⁺ ions changes with time depending on the electric field between the electrodes that changes periodically, the time average of the density of N ₄ ⁺ ions calculated by the plasma simulation is obtained. density of ₄ ⁺ ions are defined.

Therefore, the N ₄ ⁺ ion density or time average density in the present invention is not an actual measurement value but a value obtained by a plasma simulation described below.

In the present invention, computational fluid dynamics (CFD) software “CFD-ACE +” (manufactured by CFD Research, USA) is used for the simulation. In addition, the reaction data when obtaining the N ₄ ⁺ ion density, that is, reaction constants, etc. are described in IA Kossyi et al., “Kinetic scheme of the non-equilibrium discharge in nitrogen-oxygen mixture”, Plasma Sources Sci. Technol. 1 (1992) 207-220 (British Physical Society, Reference 1), and P. Segur and F. Massines, “The role of numerical modeling to understand the behavior and to predict the existence of an atmospheric pressure glow discharge controlled by a dielectric barrier. “Proc. 13th Int. Conf. On Gas Discharges and their Applications, Glasgow, 2000, 15. (Reference 2).

Here, calculation of N ₄ ⁺ ion density by the computational fluid dynamics software will be described. In the discharge spaces 17 and 35 between the electrodes of the plasma discharge treatment apparatuses 10 and 30, elementary reactions as shown in the following formulas (1) to (9) are generated only by elementary reactions involving electrons.
Elastic collision: e + A → e + A (1)
Electronic excitation: e + A → e + A ^* (2)
Vibration excitation: e + A → e + A (vib) (3)
Rotation excitation: e + A → e + A (rot) (4)
Dissociation: e + AB → e + A + B (5)
Ionization: e + A → e + e + A ⁺ (6)
Electron attachment: e + A → A ⁻ (7)
Dissociative adhesion: e + AB → A + B ⁻ (8)
Superelastic collision: e + A ^* → e + A (9)

Here, A is a neutral gas molecule or atom such as a discharge gas or source gas, or a radical derived therefrom, and A ^* indicates that the molecule is in an electronically excited state. In the discharge space, various elementary reactions such as elementary reactions between electrons and ions, elementary reactions between neutral molecules, atoms and radicals or between them and ions, and elementary reactions between ions occur.

In addition, under the pressure near atmospheric pressure, the contribution of the three-body reaction becomes more important than in the conventional case of low pressure. For example, assuming that the plasma discharge treatment gas is composed of only nitrogen gas, at low pressure,
N ₂ (a ′ ¹ Σ _u ⁻ ) + N ₂ (a ′ ¹ Σ _u ⁻ ) → N ₄ ⁺ + e (10)
N ₂ (A ³ Σ _u ⁺ ) + N ₂ (a ′ ¹ Σ _u ⁻ ) → N ₄ ⁺ + e (11)
The elementary reaction represented by is the main production reaction of N ₄ ⁺ ions.

However, under the pressure near atmospheric pressure, collisions between nitrogen molecules in excited states such as N ₂ (a ′ ¹ Σ _u ⁻ ) and N ₂ (A ³ Σ _u ⁺ ) and other nitrogen molecules frequently occur. Even if excited nitrogen gas is generated, energy is lost due to collision and it is deactivated very quickly, so that the contribution to the N ₄ ⁺ ion generation in the equations (10) and (11) is reduced. .

On the other hand, under the pressure near atmospheric pressure, N ₂ ⁺ + 2N ₂ → N ₄ ⁺ + N ₂ (12) compared with the case of low pressure.
The probability of the occurrence of the three-body reaction indicated by is greatly increased, and it is considered that N ₄ ⁺ ions are mainly generated by this reaction.

N ₄ ⁺ ions are mainly nitrogen molecules and nitrogen atoms present in a large amount in the plasma discharge treatment gas, or, for example, oxygen molecules and oxygen atoms when oxygen molecules are mixed as a reactive gas. , steal electrons from the other collide with NO _X, split into two N ₂ lost from the gas. In addition, there is a path that is combined with electrons existing in the gas to become two N ₂ and lost from the gas.

In the simulation, based on these elementary reactions in the discharge space and secondary electron emission that occurs when positive ions collide with the negative electrode, the one-dimensional plasma solves the following governing equation: The density of N ₄ ⁺ ions and the like are calculated by performing simulation. Note that the source gas in the plasma discharge processing gas is ignored in the simulation of the present invention.

Here, y is the space one-dimensional direction, that is, the position in the direction toward the other electrode from one electrode, n _e electron density, J _e is the electron flux, S _e is the electron generation and extinction section, mu _e is the mobility of electrons, D _e denotes the diffusion coefficient of electrons, the subscript (i) denotes the density and flux such as in the case of ions. N _n is the density of neutral particles (radicals and excited particles), D _n is the diffusion coefficient of neutral particles, ε _e is the average electron energy, Q is the electron energy flux, E is the electric field, and k _loss is the electron energy loss. The rate coefficient, N _gas, means gas density.

The (20) relationship is established between the average electron energy epsilon _e and the electron temperature T _e. The electric field E is obtained from the negative gradient obtained by solving the equation (21), which is a Poisson equation, with respect to the potential φ. The constants e, k, and ε ₀ mean elementary charge, Boltzmann constant, and vacuum dielectric constant, respectively.

  In addition, the electron density is obtained from the equations (13) and (14), the ion density is obtained from the equations (13) and (15), and neutral particles (excited particles and radicals) are obtained from the equations (16) and (17). The density is calculated from the formulas (18) and (19), the average electron energy, the electron temperature from the formula (20), and the potential from the formula (21).

In the plasma simulation, the voltage applied to the electrodes, the frequency of the voltage, the electrode spacing, the relative permittivity of the dielectric covering the electrodes, and the thickness of the dielectric are varied in the plasma discharge processing apparatus. To determine the density of N ₄ ⁺ ions. Further, the electron mobility μ _e and the diffusion coefficient D _e necessary for solving the governing equation, that is, the so-called electron swarm parameter, are obtained by using the software “ Input to the Boltzmann equation analysis program of “CFD-ACE +”.

When the governing equation is solved in this way, the time-varying density of N ₄ ⁺ ions in the plasma discharge treatment gas is calculated as illustrated in FIGS. 3 (A) to 3 (D). In the present invention, as described above, the time average of the calculated density of N ₄ ⁺ ions is obtained, and the density of N ₄ ⁺ ions is defined by the time average. 3A to 3D show the N ₄ ⁺ ion density for each 1/4 period of the voltage frequency having a higher frequency among the voltages applied to the two electrodes of the plasma discharge processing apparatus. To (D) in order, and the solid line indicates the density of N ₄ ⁺ ions. The dotted line in the figure is the electron density.

(Method for generating gas for plasma discharge treatment)
Next, a method for generating the plasma discharge processing gas of this embodiment will be described.

  When a voltage having a predetermined frequency is applied to the first electrode and the second electrode, which are counter electrodes of the plasma discharge processing apparatus, an electric field in which two high-frequency electric fields are superimposed is formed in the discharge space between both electrodes.

  By this electric field, electrons are emitted from the negative electrode side to the discharge space, and when the electrons move from the negative electrode side to the positive electrode side, they collide with gas molecules in the discharge space and are excited to the gas molecules (the above formulas (2) to (4) )), Dissociation (see the above formula (5)) or ionization (see the above formula (6)), and directly by ionization, or as shown in the above formulas (10) and (11) In addition, the electrons further proliferate indirectly through the reaction of the excited molecular species. Further, positive ions generated in the discharge space are attracted to and collide with the negative electrode by electrostatic force, and secondary electrons are emitted into the discharge space by the collision. On the other hand, electrons reach the positive electrode facing each other or are taken into gas molecules by electron attachment (see the above formula (7)) or dissociative attachment (see the above formula (8)) to generate negative ions. Lost from.

  In addition, the positive and negative ions, radicals, and excited molecular species generated by the elementary reaction may react with each other in addition to the reaction with such electrons, or in the discharge space as shown in the equation (12). It is converted into other ions and molecular species through reaction with neutral molecules present in large quantities. They return to the original ions, etc. through the reverse reaction, or react with other ions, radicals, neutral molecules, etc., and are converted into other molecules.

  In this way, a stable discharge state is obtained by repeatedly generating and annihilating electrons and ions through elementary reactions and reactions between molecular species other than electrons as shown in the equations (1) to (9). A gas for plasma discharge treatment is formed.

At that time, the (10) to (12) N ₄ ⁺ ions temporally density during plasma discharge treatment gas throughout the reaction shown changes in the expression generated, on the one hand, N ₄ ⁺ ions thereof By being lost from the plasma discharge processing gas due to the reverse reaction, as shown in FIGS. 3A to 3D, the gas continues to exist in the plasma discharge processing gas while repeating increase and decrease periodically.

The amount of N ₄ ⁺ ions generated, that is, the time average density, is a control parameter in the plasma discharge processing apparatus, the applied voltage to the electrodes, the frequency of the voltage, the electrode interval, the dielectric constant of the dielectric covering the electrodes, It can be controlled by varying the thickness of the dielectric. In the present invention, the gas supplied to the discharge space is a gas containing nitrogen, and preferably a gas containing 50% by volume or more of nitrogen.

According to the research by the inventors, as shown in Examples described later, the time average density of N ₄ ⁺ ions in the plasma discharge processing gas is, for example, the current density in the dielectric covering the electrodes. It is known that the correlation with the peak value of is good, and the density of N ₄ ⁺ ions in the plasma discharge processing gas can be controlled by changing the peak value of the current density.

The current density in the dielectric can be obtained by solving the Poisson equation of the equation (21) for the dielectric using the software “CFD-ACE +”. At this time, since the boundary condition periodically varies, the current density obtained as a solution also varies with time. When the peak value is varied by changing control parameters such as applied voltage and voltage frequency, the time average density of N ₄ ⁺ ions generated in the plasma discharge processing gas can be varied.

The reason why the time average density of N ₄ ⁺ ions in the plasma discharge processing gas shows a good correlation with the peak value of the current density in the dielectric covering the electrode is only the result of simulation. Although it is difficult to clarify clearly, it can be estimated as follows.

When attention is paid to one electrode of the pair of counter electrodes, the current density in the dielectric reaches a peak once each on the positive side and the negative side during one cycle of the voltage applied to the electrode. When the current density reaches a positive or negative peak, electrons pass through the dielectric from the electrodes and are emitted into the discharge space, and proliferate in the discharge space as described above. Therefore, as shown by the dotted lines in FIGS. 3 (B) and 3 (D), the electron density is maximized, and the amount of N ₄ ⁺ ions generated due to this electron density is larger than the lost amount. Density increases.

On the other hand, at a time when the current density is not a peak, particularly at a time close to 0, the electrons remaining in the discharge space reach the counter electrode, and as shown in FIGS. Becomes very small. However, since N ₄ ⁺ ions are much heavier than electrons and cannot easily move in the discharge space, the amount lost from the discharge space is larger than the amount produced and the density is reduced. A relatively large amount remains in the discharge space.

The value of the time average density of N ₄ ⁺ ions, but density of N ₄ ⁺ ions at the time and other peaks of such current density is all reflected, the peak value of the current density, Figure 3 Since it is closely related to the electron density in the discharge space involved in the generation of N ₄ ⁺ ions as shown in (A) and (C), the result shows a good correlation with the time average density of N ₄ ⁺ ions. It is thought to show.

(Plasma discharge treatment method)
As described above, in the plasma discharge processing apparatus, the gas G ° is injected onto the substrate F immediately after the plasma discharge processing gas G ° is generated between the counter electrodes as in the plasma discharge processing apparatus 10 shown in FIG. Alternatively, as in the plasma discharge treatment apparatus 30 shown in FIG. 2, the plasma discharge treatment gas is generated between the counter electrodes, and at the same time, the substrate F inserted in the discharge space is exposed to the plasma discharge treatment gas. Thus, the plasma discharge treatment of the substrate F is performed.

This is an example of a process of forming a SiO ₂ thin film on the surface of the substrate F using nitrogen gas, oxygen gas and tetraethoxysilane (hereinafter referred to as TEOS) as the discharge gas, reactive gas and source gas, respectively. I will explain it.

As described above, in the process of forming the plasma discharge treatment gas in the discharge space, the discharge from the electrodes causes electrons and gas molecules to react in the discharge space to generate various ions, radicals, excited molecular species, etc. Is done. Among them, when an electron collides with an oxygen molecule, an oxygen atom is generated by a dissociation reaction (see the above formula (5)) or a dissociative attachment reaction (see the above formula (8)). When this oxygen atom collides with the TEOS molecule, the TEOS molecule is decomposed into a film precursor molecule and a decomposition molecule. Film precursor molecules are generated in this way or through other generation processes and deposited on the substrate surface to form a SiO ₂ thin film.

(effect)
As described above, according to the plasma discharge processing gas, the plasma discharge processing gas generation method, and the plasma discharge processing method of the present embodiment, the time average density is 8.0 × 10 ¹⁶ [m ⁻³ ] or more. Preferably, plasma discharge treatment gas containing N ₄ ⁺ ions of 1.2 × 10 ¹⁷ [m ⁻³ ] or more, more preferably 2.0 × 10 ¹⁷ [m ⁻³ ] or more is generated and used By performing the plasma discharge treatment, it is possible to perform a good and practical treatment as shown in the following examples.

According to the inventors' consideration, the N ₄ ⁺ ion density or time average density is an index indicating the density of electrons, ions, excited molecular species, etc. in the plasma discharge treatment gas, that is, the so-called plasma density. Conceivable.

Further, it is considered that N ₄ ⁺ ions are generated as a result of various reactions in a plasma state which is self-formed by the above-described electron proliferation and annihilation, generation and annihilation of ions, radicals, and excited molecular species. Therefore, the presence of N ₄ ⁺ ions at a high density is considered to mean that the plasma discharge processing gas is in a state of being stably self-formed. Therefore, the density of N ₄ ⁺ ions is considered to be an index indicating the stability of the plasma state of the plasma discharge treatment gas.

And, as in the following example, the time average density of N ₄ ⁺ ions and the result of the plasma discharge treatment have a correlation, that is, if the time average density of N ₄ ⁺ ions is high, the processing result is good and low. In view of the fact that it shows a failure relationship, plasma discharge treatment gas in a plasma state in which a large amount of N ₄ ⁺ ions are present is in a stable and high plasma density plasma state. In the plasma discharge treatment gas in which only a small amount of N ₄ ⁺ ions are present, the plasma state is not stable or the plasma discharge treatment is performed with sufficient reforming of the raw material gas. Since the density is low, it is considered that the material gas cannot be sufficiently reformed and the plasma discharge treatment cannot be performed accurately. It is.

According to the present invention, instead of adjusting the control parameters of the plasma discharge processing apparatus empirically or by trial and error as in the prior art, as described above, the stability of the plasma state of the plasma discharge processing gas and the plasma The time average density of N ₄ ⁺ ions serving as an index of density is 8.0 × 10 ¹⁶ [m ⁻³ ] or more, more preferably 1.2 × 10 ¹⁷ [m ⁻³ ] or more, and further preferably 2.0 ×. By controlling the control parameters of the plasma discharge processing apparatus so as to be 10 ¹⁷ [m ⁻³ ] or more, it becomes possible to perform good plasma discharge processing.

Example 1
In Example 1, an experiment was conducted to clean contaminants such as organic substances adhering to the surface of the glass substrate for electronic components.

  In the experiment, a mixed gas was prepared by mixing 99.95% by volume of nitrogen gas as a discharge gas and 0.05% by volume of oxygen gas as a reactive gas for removing pollutants, as shown in FIG. It introduced into the discharge space between electrodes from the gas supply apparatus of the plasma discharge processing apparatus 10.

In the plasma discharge treatment apparatus 10, the surface of the metal electrode is covered with alumina having a relative dielectric constant of 7.67, the distance between the electrodes is set to 0.5 mm, and a sine wave voltage having a frequency of 150 kHz and an amplitude of 5000 V is applied to the first electrode. . In addition, the time average density of N ₄ ⁺ ions of the plasma discharge treatment gas in the discharge space was changed by changing the frequency and amplitude of the sine wave voltage applied to the second electrode. The quality of the cleaning result was evaluated by analyzing the amount of residual carbon on the surface of the glass substrate after the treatment using X-ray photoelectron spectroscopy.

The experimental results are shown in FIG. In FIG. 4, the time average density of N ₄ ⁺ ions is shown on the vertical axis, and the peak value of current density is shown on the horizontal axis. Further, in the simulation for obtaining the time average density of N ₄ ⁺ ions, calculation was performed with 99.95% by volume of nitrogen and 0.05% by volume of oxygen. Moreover, about evaluation, it evaluated based on the following reference | standard.
◎ Contaminants were successfully removed.
○ Pollutants were removed within a practical range.
× Pollutant removal was insufficient.

(Evaluation of Example 1)
In the experiment of Example 1, the removal of contaminants was insufficient when the time average density of N ₄ ⁺ ions in the plasma discharge treatment gas was 5.0 × 10 ¹⁶ [m ⁻³ ], but 1.2% In the case of × 10 ¹⁷ [m ⁻³ ] or more, the removal of the contaminants was performed at least within a practical range, and it was good in the range of 2.0 × 10 ¹⁷ [m ⁻³ ] or more.

(Example 2)
In Example 2, an experiment was performed in which a functional thin film of SiO ₂ was formed on the surface of a PET (polyethyleneterephthalate) film. This thin film constitutes an antireflection film, and its refractive index was evaluated.

  In the experiment, a mixed gas was prepared by mixing 79.5% by volume of nitrogen gas as a discharge gas, 20% by volume of oxygen gas as a reactive gas, and 0.5% by volume of TEOS as a source gas, and the plasma discharge shown in FIG. The gas was introduced into the discharge space between the electrodes from the gas supply device 36 of the processing device 30.

In the plasma discharge treatment apparatus 30, the surface of the metal electrode is covered with alumina having a relative dielectric constant of 7.67, the distance between the electrodes is set to 0.5 mm, and a sine wave voltage having a frequency of 150 kHz and an amplitude of 5000 V is applied to the second lower electrode. Applied. Further, the frequency and amplitude of the sine wave voltage applied to the upper first electrode are changed, and the time average density of the N ₄ ⁺ ions of the plasma discharge treatment gas in the discharge space is changed to change the formation and refractive index of the thin film. evaluated.

The experimental results are shown in FIG. In FIG. 5, the time average density of N ₄ ⁺ ions is shown on the vertical axis, and the peak value of current density is shown on the horizontal axis. In the simulation for obtaining the time average density of N ₄ ⁺ ions, the calculation was performed assuming that 80% by volume of nitrogen and 20% by volume of oxygen. Moreover, about evaluation, it evaluated based on the following reference | standard.
◎ Film formation and refractive index are good.
○ Film formation is good and the refractive index is practical.
× No film was formed.

(Evaluation of Example 2)
In the experiment of Example 2, when the time average density of N ₄ ⁺ ions in the plasma discharge treatment gas is 7.1 × 10 ¹⁶ [m ⁻³ ], the generation of particles on the film is large and the film is effective. Not formed. In addition, when the time average density of N ₄ ⁺ ions is 8.0 × 10 ¹⁶ [m ⁻³ ] and 1.4 × 10 ¹⁷ [m ⁻³ ], a thin film of SiO ₂ is favorably formed on the film. The refractive index is practically acceptable, and both the film formation and the refractive index are good in the range of 2.0 × 10 ¹⁷ [m ⁻³ ] or more.

In addition, the current density peak value when the time average density of N ₄ ⁺ ions in the plasma discharge treatment gas is 7.1 × 10 ¹⁶ [m ⁻³ ] and 8.0 × 10 ¹⁶ [m ⁻³ ]. Are close to 743 [Am ⁻² ] and 745 [Am ⁻² ] in the apparatus of this embodiment, respectively, but the evaluation of the film formation experiment was divided into “x” and “◯”. As described above, the result of Example 2 is that the time of N ₄ ⁺ ions in the plasma discharge treatment gas that fluctuates due to the difference in the current density peak value, rather than the difference in the current density peak value, at least regarding the success or failure of the film formation. This greatly depends on the difference in average density, and is considered to indicate that the density around 8.0 × 10 ¹⁶ [m ⁻³ ] is critical.

It is the schematic which shows the structural example of a plasma discharge processing apparatus. It is the schematic which shows another structural example of a plasma discharge processing apparatus. Is a graph displaying the N ₄ ⁺ ion density per 1/4 the cycle of the frequency of the voltage applied to the electrode of the plasma discharge treatment apparatus. 4 is a graph showing experimental results of Example 1. 6 is a graph showing experimental results of Example 2.

Explanation of symbols

10 Plasma discharge treatment equipment
11 First electrode (a pair of electrodes)
12 Second electrode (a pair of electrodes)
15 1st power supply (voltage application means)
16 Second power source (voltage application means)
G Gas mixture G ° Plasma discharge treatment gas

Claims (7)

A pair of electrodes disposed opposite to each other;
Voltage applying means for applying a voltage to the pair of electrodes;
A gas supply means for supplying a mixed gas containing a discharge gas and a reaction gas containing nitrogen as a main component between the pair of electrodes;
With
The gas supply means supplies the mixed gas between the pair of electrodes under a pressure near atmospheric pressure, and the voltage application means supplies a periodically changing voltage between the pair of electrodes. By applying an electric field that periodically changes between a pair of electrodes, a discharge is generated between the pair of electrodes via the mixed gas, and the mixed gas is turned into plasma, so that the time average density is 8.0 × 10 8. A plasma discharge treatment gas containing N ₄ ⁺ ions in a range of ¹⁶ to 1 × 10 ²⁰ [m ⁻³ ] is generated, and a plasma discharge treatment is performed on the substrate using the generated plasma discharge treatment gas. A plasma discharge treatment apparatus. A pair of electrodes disposed opposite to each other;
Voltage applying means for applying a voltage to the pair of electrodes;
A gas supply means for supplying a mixed gas containing a discharge gas and a reaction gas containing nitrogen as a main component between the pair of electrodes;
With
The gas supply means supplies the mixed gas between the pair of electrodes under a pressure near atmospheric pressure, and the voltage application means supplies a periodically changing voltage between the pair of electrodes. By applying an electric field that periodically changes between a pair of electrodes, a discharge is generated between the pair of electrodes via the mixed gas, and the mixed gas is turned into plasma, and the time average density is 1.2 × 10 6. A plasma discharge treatment gas containing N ₄ ⁺ ions in a range of ¹⁷ to 1 × 10 ¹⁹ [m ⁻³ ] is generated, and a plasma discharge treatment is performed on the substrate using the generated plasma discharge treatment gas. A plasma discharge treatment apparatus. A pair of electrodes disposed opposite to each other;
Voltage applying means for applying a voltage to the pair of electrodes;
A gas supply means for supplying a mixed gas containing a discharge gas and a reaction gas containing nitrogen as a main component between the pair of electrodes;
With
The gas supply means supplies the mixed gas between the pair of electrodes under a pressure near atmospheric pressure, and the voltage application means supplies a periodically changing voltage between the pair of electrodes. By applying an electric field that periodically changes between a pair of electrodes, a discharge is generated between the pair of electrodes via the mixed gas, and the mixed gas is turned into plasma, and the time average density is 2.0 × 10 6. A plasma discharge treatment gas containing N ₄ ⁺ ions in a range of ¹⁷ to 4 × 10 ¹⁷ [m ⁻³ ] is generated, and the substrate is subjected to plasma discharge treatment using the generated plasma discharge treatment gas. A plasma discharge treatment apparatus. A plasma discharge treatment method in which an electric field that changes periodically is applied between a pair of electrodes for plasma discharge treatment under a pressure near atmospheric pressure,
A gas mixture containing a discharge gas containing nitrogen as a main component and a reaction gas is supplied between the pair of electrodes, and an electric field that periodically changes is applied between the pair of electrodes, whereby the pair of electrodes is interposed via the gas mixture. A plasma discharge containing N ₄ ⁺ ions having a time average density in the range of 8.0 × 10 ¹⁶ to 1 × 10 ²⁰ [m ⁻³ ] by causing discharge between the electrodes of the mixture to be plasmatized. A plasma discharge treatment method comprising: generating a treatment gas, and performing a plasma discharge treatment on a substrate using the generated plasma discharge treatment gas. A plasma discharge treatment method performed by applying an electric field that periodically changes between a pair of electrodes under a pressure near atmospheric pressure,
A gas mixture containing a discharge gas containing nitrogen as a main component and a reaction gas is supplied between the pair of electrodes, and an electric field that periodically changes is applied between the pair of electrodes, whereby the pair of electrodes is interposed via the gas mixture. A plasma discharge containing N ₄ ⁺ ions having a time average density in the range of 1.2 × 10 ¹⁷ to 1 × 10 ¹⁹ [m ⁻³ ] by causing a discharge between the electrodes of the mixture to be plasmatized. A plasma discharge treatment method comprising: generating a treatment gas, and performing a plasma discharge treatment on a substrate using the generated plasma discharge treatment gas. A plasma discharge treatment method performed by applying an electric field that periodically changes between a pair of electrodes under a pressure near atmospheric pressure,
A gas mixture containing a discharge gas containing nitrogen as a main component and a reaction gas is supplied between the pair of electrodes, and an electric field that periodically changes is applied between the pair of electrodes, whereby the pair of electrodes is interposed via the gas mixture. A plasma discharge containing N ₄ ⁺ ions having a time average density in the range of 2.0 × 10 ¹⁷ to 4 × 10 ¹⁷ [m ⁻³ ] by causing a discharge between the electrodes of the mixture to be plasmatized. A plasma discharge treatment method comprising: generating a treatment gas, and performing a plasma discharge treatment on a substrate using the generated plasma discharge treatment gas. The plasma discharge treatment method according to any one of claims 4 to 6 , wherein the time average density of the N ₄ ⁺ ions is controlled by changing a value of a current density.

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