JP2001230100A - Negative electrode for arc plasma source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for arc plasma source which can make the ionization level of gas material high and enables to form a layer of simple chemical composition when used for a deposition device. SOLUTION: The negative electrode 1 for arc plasma source comprises a negative electrode body 2 having a gas outlet tube 3 which extends concentrically with the electrode. The nitrogen gas guided by this gas outlet tube 3 is emitted from a gas outlet opening 3a toward a positive electrode 5. An arc having a sufficiently long positive column is formed between the thermion radiation surface 2a and the positive electrode 5 and silicon is emitted from the negative electrode body 2. A great part of the emitted nitrogen gas molecules enter this positive column and move for a sufficient distance without deviating from this positive column and are ionized. As a result, an arc plasma containing nitrogen gas ion and silicon ion are generated. This arc plasma passes through the positive electrode 5 and forms a silicon nitric layer after arriving at a deposited material 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a cathode for an arc plasma source for supplying at least one of electrons and ions using an arc plasma.

[0002]

2. Description of the Related Art In the formation of functional materials including semiconductors, fine ceramics, and the like, it is necessary to deposit a thin film having characteristics such as corrosion resistance, high strength, and low friction on the surface as a surface treatment. Further, in order to achieve 0.1-micron wiring in a super-integrated circuit, metal embedding of a fine groove (a groove having a width of 0.1 μm or a hole having a diameter) is required. In a film forming apparatus that performs these processes, an ion supplier that supplies ions serving as a material for forming a film is an essential component that influences these processes.

[0003] Cathodic arcs are attracting attention in a wide area as an ion supplier having the above-mentioned characteristics such as corrosion resistance, high strength, and low friction, and for depositing a thin film at high speed. This cathodic arc will be described. When an arc is ignited in a high vacuum (pressure <1 × 10 ⁻⁵ Torr) using a cathode formed of a material such as ultra-high melting point metal such as tungsten or molybdenum or graphite, the cathode surface is formed. An ultra-high temperature point-like region called a spot is generated, and the cathode spot emits thermoelectrons, and at the same time, vapor such as metal or graphite is released and ionized, thereby generating a highly pure plasma completely ionized. Furthermore, the plasma generated by this cathodic arc (arc plasma)
For example, by supplying a gas material such as nitrogen or oxygen,
These ions are ionized, and a film of a nitride, an oxide, or the like can be deposited on the surface of the deposition target material at a high speed.

[0004] As an ion supplier provided in a film forming apparatus for depositing a film such as a nitride or an oxide on the surface of a film-forming material at a high speed, for example, an ion supply for an arc plasma source is provided in a vacuum vessel. A cathode and an anode are provided, and a gas inlet for introducing a gas material such as nitrogen or oxygen is provided on a wall of the container, a vacuum container is filled with the gas material, and the gas material is mixed into the arc plasma. There are various ion supply devices.

[0005]

As described above, in the configuration of the ion supply device in which the gas material is supplied into the arc plasma through the gas inlet provided in the vacuum vessel, the gas material is used. Most of the gas molecules
They cannot enter the plasma and they are not ionized. Therefore, the degree of ionization of the gas cannot be increased.
Under such conditions, the chemical composition of the thin film becomes complicated due to the mixture of several types of compounds, which is practically undesirable. As a result, when the gas material is mixed, a new configuration of the ion feeder for achieving a high ionization degree is required.

Accordingly, an object of the present invention is to provide an arc / plasma source capable of increasing the degree of ionization of a gaseous material and producing a film having a simple chemical composition when used in a film forming apparatus. To provide a cathode for use.

[0007]

In order to achieve the above object, a cathode for an arc plasma source according to claim 1 of the present invention is opposed to an anode at a predetermined distance so as to emit electrons. A cathode body for generating an arc plasma so as to extend between the anode and the anode, and a gas emission surface extending inside the cathode body and emitting gas to the thermionic emission surface. And a gas discharge tube for discharging a gas material into the arc plasma from the gas discharge port and ionizing by the arc plasma.

[0008] By adopting a structure in which the gas material is discharged into the arc plasma from the gas discharge port, most of the released gas material can be directly incident on the arc plasma. Therefore, the degree of ionization of the gas material can be increased.

In the arc plasma source cathode according to a second aspect of the present invention, the cross section of the gas discharge tube has a polygonal or multiple shape so as to increase the surface area of the inner peripheral surface of the gas discharge tube. It is characterized in that it has a square shape.

As described above, in proportion to the surface area of the cathode,
The number of secondary electrons emitted from the cathode surface increases, and the gas material is more efficiently ionized. Therefore, the degree of ionization of the gas material can be further increased.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A cathode for an arc plasma source according to an embodiment of the present invention will be described with reference to FIGS. 1 (a) and 1 (b). FIG. 1A is a longitudinal sectional view showing a configuration of a cathode for an arc plasma source. FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A. In the figure, reference numeral 1 denotes a cathode for an arc / plasma source. The cathode 1 has a cathode main body 2 made of a material such as ultra-high melting point metal such as tungsten or molybdenum or graphite. The cathode body 2 has a cylindrical shape so as to form a gas discharge tube 3 extending concentrically therein. This gas discharge pipe 3
Is one end face of the cathode main body 2 and extends concentrically with the cathode main body 2 so as to penetrate from the thermoelectron emission surface 2a for emitting thermoelectrons to the other end surface. Is provided. The cross-sectional shape (gas flow cross-sectional shape) of the gas discharge tube 3 is circular as shown in FIG. Thus,
Both end surfaces of the cathode main body 2 are formed in an annular shape, and the one end surface defining the thermionic emission surface 2a is formed flat.

The other end of the gas discharge tube 3 is connected to a gas material supply source (not shown). In the present embodiment, a connection member 4 having a supply path coaxial with the gas discharge pipe 3 and connected to a gas introduction pipe 4a extending from the gas material supply source is connected to the gas material supply source.

The gas material supplied from the gas material supply source is introduced from the gas introduction pipe 4a, guided by the gas discharge pipe 3, and discharged from the gas discharge port 3a in a direction toward the gas discharge pipe 3. . When the arc is ignited under a high vacuum, an ultra-high temperature spot-like area called a cathode spot is generated on the thermoelectron emission surface 2a, and the cathode spot emits thermoelectrons and causes the cathode body 2 to move. The vapor of the forming material is released. The vapor is ionized by the thermoelectrons, and an arc plasma having ions of the material constituting the cathode main body 2 is generated. The released gas material enters the arc plasma and is ionized by thermionic electrons.

Next, a first modification of the present embodiment will be described with reference to FIG. FIG. 1C shows the state of FIG.
It is a cross-sectional view of the cathode for an arc plasma source, cut and shown similarly to (b) of FIG. In the drawing, reference numerals 2 'and 3' indicate a cathode main body and a gas discharge tube, respectively. The difference from the above embodiment is that in the embodiment, the gas flow cross-sectional shape is
Although it is circular as shown in FIG. 1 (b), in the present modification, it is star-shaped as shown in FIG. 1 (c). In order to quantitatively compare the difference between the circular shape and the star shape, in the present embodiment and the present modified example, the present modified example is made such that the flow rates of the gas materials passing through the gas discharge tubes 3 and 3 ′ are substantially equal. The example gas release tube 3 'is configured. That is, the volume (gas flow volume) surrounded by the inner peripheral surface of the gas discharge tube 3 'of the present modification and both end surfaces of the cathode main body 2' is equal to the gas flow volume of the present embodiment. That is, the area (gas flow cross-sectional area) of the gas flow cross-sectional shape of the present modification is equal to the gas flow cross-sectional area of the present embodiment. Therefore, according to the figure, the gas discharge tube 3 'of this modification has a star-shaped area indicating the gas discharge tube 3' of FIG. 1C equal to the circular area of FIG. 1B. It is configured to be.

Next, the relationship between the cross-sectional shape of the gas flow and the number of secondary electrons emitted from the surface of the cathode main body 2 (the number of emitted secondary electrons) will be described. First, secondary electrons will be described.
Vapor ions ionized by thermionic electrons in the above-described arc plasma collide with the surface of the cathode body 2. Electrons are emitted by the impact of this collision. This is a secondary electron. These secondary electrons also help ionize the gaseous material, similar to thermoelectrons. As the surface area of the cathode body 2 increases, the surface area on which ions collide increases, and as a result,
By increasing the number of secondary electron emissions, the gaseous material is more ionized. On the other hand, the gas flow cross-sectional shape will be described.
When changing the gas flow cross-sectional shape while keeping the gas flow volume constant, the surface area of the inner peripheral surface of the gas discharge tube is minimized when the gas flow cross-sectional shape is circular. From these two explanations, when the gas flow cross-sectional shape is circular as in the present embodiment, the number of secondary electron emissions is minimum, and as in this modification, the gas flow cross-sectional shape is star-shaped. In some cases, it can be inferred that the secondary electron emission number is larger than that of a circular shape. Therefore, by forming the gas flow cross section into a star shape, the flow rate of the gas material can be secured and the degree of ionization can be further increased.

Next, a second modification will be described with reference to FIG. FIG. 1D is a cross-sectional view of the cathode for the arc plasma source cut and shown in the same manner as FIG. 1B. In the figure, reference numerals 2 "and 3" indicate a cathode main body and a gas discharge tube, respectively. The difference from the present embodiment is that the cross-sectional shape of the gas flow has a star-shaped corner (a star shape) as shown in FIG. Similarly to the comparison between the circular area in FIG. 1B and the star area in FIG. 1C in the description of the first modification, the gas discharge tube 3 ″ of this modification is The star-shaped area indicating the gas discharge tube 3 ″ in FIG. 1D is configured to be equal to the circular area in FIG. 1B.

By making the gas flow cross section into a star shape, the flow rate of the gas material can be ensured and the degree of ionization can be further increased.

In the first and second modifications, the gas flow cross-sectional shapes are a polygonal star and a polygonal corner, respectively, but the present invention is not limited to this. However, the shape may be, for example, another n-sided shape or a shape obtained by removing the corner of the n-sided shape. in this case,
The shape may be a triangle, a rectangle, a hexagon, or a shape obtained by removing a corner of a triangle, a rectangle, or a hexagon.

In the present embodiment, the gas discharge tube is formed concentrically with the cathode main body so as to penetrate from one end surface to the other end surface of the cathode main body, but the present invention is not limited to this. For example, the gas discharge tube may be formed so as to extend parallel to the central axis of the cathode main body, or may be formed non-parallel to the central axis of the cathode main body. Also, the gas discharge tube may not be straight over the entire length,
Bending at a position at a distance of about 1 times or more, preferably about 5 times or more, the average radius of the gas flow cross-sectional shape (average distance from the center of gravity of the gas flow cross-sectional shape to the contour) from the thermionic emission surface (About 15 ° or more, preferably about 90 °), and may be formed to penetrate the side surface of the cathode main body.

In the present embodiment, the cathode main body has a cylindrical shape, but the present invention is not limited to this. For example, it may have a hexagonal prism shape.

In the present embodiment, the cathode body is formed of a material such as ultra-high melting point metal such as tungsten or molybdenum or graphite, but the present invention is not limited to this. For example, it may be formed of copper, aluminum or titanium.

Next, with reference to FIG. 2, an example of an ion supplier using the arc plasma source cathode 1 according to the embodiment of the present invention will be described. FIG. 2 is a schematic diagram showing a configuration of the ion supply device. In this example, the same components as those of FIGS. 1A and 1B illustrating the present embodiment are denoted by the same reference numerals, and description thereof will be omitted. In this ion supply device, an anode 5 is disposed in a direction toward the gas discharge tube 3 so as to face the thermoelectron emission surface 2a of the cathode 1 for an arc / plasma source at a predetermined interval. A circuit having a DC power supply 6 for applying a voltage between them and supplying electric power for igniting an arc is arranged at the two poles 1 and 5.

Next, the ionization process of the gas material which is the material of the supplied ions will be described. As in the present embodiment, a gas material supplied from a gas material supply source (for example, a nitrogen gas, an oxygen gas, or the like. Here, for simplicity of description, an argon gas will be described below).
Is guided by the gas discharge tube 3 and is discharged in a direction toward the anode 5 from the gas discharge port 3a. As a result, a gas flow (gas flow) is formed between the thermionic emission surface 2a and the anode 5. When the DC power supply 6 is operated to ignite the arc, the space between the thermionic emission surface 2a and the anode 5
An arc having a positive column 7 having a length L is formed, and most of the gas flow enters the positive column 7 from the cathode side end face 7a of the positive column 7, and flows through the positive column 7 in the longitudinal direction. Flows along. Most of the gas material discharged from the gas discharge tube 3 is ionized in the positive column 7. This allows
Arc plasma is generated.

Here, the gas material (Al which is a monoatomic molecule)
Consider the conditions for achieving complete ionization of (gon gas).
Now, the density n_e, Temperature T_eGroup of electrons
Degree T _gArgon gas molecules that constitute the gas material
Mean that the molecule is ionized by electrons
Free travel_iAsk for. Average electron velocity v_eAnd argon
Average velocity of gas molecules v_gAre v_e= (8kT_e/ Πm_e)^1/2 v_g= (8kT_g/ Πm_g)^1/2 It is. Where k, m_e, And m_gIs Boltzma respectively
Parameters, the mass of electrons, and the mass of gas molecules. This
Where T_e= 2 × 10⁵⁰K and T_g= 1 × 10
³⁰Assuming the speed as K, v_e= 2.78 × 10⁶ms^-1 v_g= 2.64 × 10²ms^-1 Becomes v_g≪v_eTherefore, the collision of electrons
Mean free path l _iIs σ_iIs the ionization cross section, l_i= (N_eσ_i)^-1・ V_g/ V_e Given by n_e= 5 × 10¹⁹m^-3 σ_i= 2 × 10^-20m² Gives l_i= 9.5 × 10^-5m = 95 μm. Argon gas molecules have this mean free path l_i=
Always travel in the electron ensemble for a distance sufficiently longer than 95 μm
If the ionization degree of argon gas is completely ionized (about 95%)
Can be close to.

Therefore, the conditions for achieving complete ionization of the gas material are such that the gas molecules always travel in the positive column for a distance sufficiently longer than the mean free path required for ionization of the gas molecules constituting the gas material. That is.

The ion supplier shown in FIG. 2 is configured to satisfy this condition. That is, when the length L of the positive column 7 is L> l _i = 95 μm, preferably L> 3l
_i = 285 μm (this means that the gas molecules have a distance of 3 l _i ,
If you always move in the positive column, this is because it is always ionized. ), The ion supplier is configured.

With the above configuration,
Most of the gas flow enters the positive column 7 from the cathode side end face 7a of the positive column 7, and the gas molecules travel through the positive column for a distance sufficiently longer than the mean free path required for ionization of the gas molecules to occur. It is possible to do. Therefore, in the ion supplier using the arc plasma source cathode of the present invention, the degree of ionization of the gas material can be increased.

When a general gas material is used, the length between the thermionic emission surface 2a and the end surface 7a and the length between the anode 5 and the end surface 7b on the anode side of the positive column 7 are: l Same as _i
m order. When the length between the poles 1 and 5 and the diameter of the thermionic emission surface 2a are sufficiently larger than the μm order, the length in the μm order can be ignored. As a result, thermionic emission surface 2
a and the end face 7a, and the anode 5 and the end face 7b can be considered to be close to each other, and thus the entire arc can be considered to be substantially composed of a positive column. Therefore, it can be considered that almost all of the gas flow discharged from the gas discharge port 3a is incident on the end face 7a. Furthermore, the length of l _i can be ignored compared to the length and width of the positive column 7. As a result, it can be considered that the ionization of the gas occurs in the vicinity of the gas outlet 3a. Therefore, when the length between the poles 1 and 5 and the diameter of the thermionic emission surface 2a are sufficiently larger than the μm order, it is estimated that almost all of the released gas material is ionized.

Next, an example of a film forming apparatus using the arc plasma source cathode 1 in the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic diagram showing a film forming apparatus. In this example, the same components as those in FIG. 1 illustrating the embodiment of the present invention are denoted by the same reference numerals, and description thereof is omitted. In this film forming apparatus, the cathode main body 2 is formed of silicon in order to form a silicon nitride film as a deposited thin film. A line segment drawn between the arc plasma source cathode 1 and the anode 5 ′ extends with the gas discharge tube 3 and has an intersection at the gas discharge port 3 a with a half line having the gas discharge port 3 a as one end, The anode 5 ′ is such that their angle is not 0 °, preferably 45 °,
It is located with respect to the cathode 1 for the arc plasma source.
Also, between the poles 1 and 5 ', a macroparticle filter 8 which is a curved coil for generating a magnetic field such that an arc is formed in an arc between them is located. In addition, the curve along the arc and the anode 5 '
The anode 5 ′ and the macroparticle filter 8 are positioned so that the disk surrounded by the ring is orthogonal to the center of the disk.

As described in the example of the ion supply device, the length between the poles 1 and 5 'and the order of the diameter of the thermionic emission surface 2a depend on the length between the thermionic emission surface 2a and the end face 7a. If it is sufficiently larger than the order of the mean free path required for ionization, almost all of the gas flow emitted from the gas outlet 3a is ionized near the gas outlet 3a. In order to satisfy such conditions, the cathode 1 for the arc plasma source, the anode 5 'and the macroparticle filter 8 are used.
And are arranged.

From the cathode 1 for the arc plasma source to the anode 5 '
On the extension of the arc extending in the direction opposite to the arc plasma source cathode 1, at a predetermined distance from the anode 5 ',
The film-forming material 9 is located. Furthermore, the film-forming material 9 is disposed so that an extension of the arc and a surface on which the film of the film-forming material 9 is formed are orthogonal to each other on this surface. A circuit having a DC power supply 10 for applying a voltage between them and igniting an arc is provided between the electrodes 1 and 5 ′, and these circuits are provided between the anode 5 ′ and the film-forming material 9. A circuit having a DC power supply 11 for supplying electric power for generating an electric field from the anode 5 ′ toward the film-forming material 9 is provided therebetween.

The ionization process of a gas material (nitrogen gas) will be described. The nitrogen gas is released from the gas discharge tube 3 and the DC power supply 10 is operated, for example, by using an igniter (igniter).
When the arc is ignited using, for example, the positive column 7 'is formed over almost the entire area of the arc that extends curvedly between the thermionic emission surface 2a and the anode 5'. The nitrogen gas molecules incident on the positive column 7 'are ionized in the vicinity of the gas outlet 3a and become nitrogen ions. The cathode surface is heated to a high temperature by the impact of nitrogen ions or the like supplied from the positive column 7 ′ to the cathode,
Simultaneously with the emission of thermoelectrons, the silicon of the cathode material evaporates and is ionized in the positive column to become silicon ions. Through such a process, an arc plasma having nitrogen ions and silicon ions is generated.

The process of film formation is as follows. Since the electron density of the positive column 7 'is very high, the electric conductivity of the positive column 7' is extremely high. As a result, an electric field which accelerates the silicon ions toward the cathode is very close to the cathode surface. Except negligible, the arc plasma can easily diffuse near the anode. Arc plasma moat over the annular anode also occurs.

When the DC power supply 11 is operated and a negative voltage is applied to the film-forming material 9 with respect to the anode 5 ′, ions in the arc plasma that have crossed the anode due to diffusion are accelerated and the film-forming material 9 is accelerated. Reach 9. Since the ions are composed of two types, silicon and nitrogen, they react on the film-forming material 9 to form a silicon nitride thin film.

The role of the macro particle filter 8 will be described. Depending on the configuration of the device and operating conditions, particles in which tens of thousands of atoms are bonded, so-called,
Macro particles scatter and degrade the film quality. The charged ions in the arc plasma move in an arc shape due to the magnetic field generated by using the macroparticle filter 8, but the electrically neutral macroparticles travel straight. Therefore, it is possible to prevent the macro particles from reaching the film-forming material 9.

Also in such a film forming apparatus, it is realized that most of the gas flow enters the positive column, and gas material molecules move along the positive column for a sufficient distance. Accordingly, in the film forming apparatus using the arc plasma source cathode of the present invention, the degree of ionization of the gas material can be increased.

It should be noted that the present invention is not limited to the above-described embodiment and the examples of the ion supply device and the film forming apparatus to which the present invention is applied, and various modifications and changes may be made without departing from the spirit of the invention. Of course, the application is possible.

[Brief description of the drawings]

FIG. 1A is a longitudinal sectional view showing a configuration of an arc plasma source cathode according to an embodiment of the present invention;
1B is a cross-sectional view taken along line AA of FIG. 1A, and FIGS. 1C and 1D are first and second modifications of the embodiment of the present invention. FIG. 3 is a cross-sectional view showing a cathode for an arc plasma source in an example.

FIG. 2 is a schematic diagram showing a configuration of an example of an ion supplier using an arc plasma source cathode according to the embodiment.

FIG. 3 is a schematic diagram illustrating a configuration of an example of a film forming apparatus using a cathode for an arc / plasma source according to an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cathode for arc / plasma source 2 Cathode body 3 Gas discharge tube

Claims (2)

[Claims] 1. An arc plasma is provided so as to emit electrons and to extend between the anode and the anode, the thermoelectron emission surface being disposed so as to face the anode at a predetermined interval. A cathode body for extending the inside of the cathode body, having a gas emission port on the thermionic emission surface, emitting a gas material from the gas emission port into the arc plasma, and A gas discharge tube for ionization, comprising: a cathode for an arc plasma source. 2. The gas discharge tube according to claim 1, wherein the cross section of the gas discharge tube has a polygonal shape or a shape having corners of a polygon so as to increase a surface area of an inner peripheral surface of the gas discharge tube. The cathode for an arc plasma source of claim 1.