JPH0644099U - Microwave plasma source - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a microwave plasma source capable of generating a plasma with a large area and a high uniformity of density, and without increasing the length of the tapered waveguide. To do. This microwave plasma source has a convex lens shape as an example of a radio wave lens for converting a spherical wave of a microwave 14 into a plane wave in a portion inside an opening of a tapered waveguide 10 and in front of a dielectric window 8. The dielectric lens 20 including the dielectric 22 is provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to, for example, a plasma processing apparatus that performs etching, film formation, etc. using plasma, or a microwave plasma source used as an ion source that extracts an ion beam from plasma.

[0002]

[Prior art]

 A conventional example of this type of microwave plasma source is shown in FIG. This microwave plasma source includes a plasma generation container 4 for generating plasma 2, a dielectric window 8 for introducing microwave 14 therein while maintaining a vacuum, and a dielectric window 8 for this dielectric window 8. A taper waveguide 10 is provided which is connected to the portion and which spreads toward the end to introduce the microwave 14 into the plasma generation container 4 through the dielectric window 8. A normal waveguide 12 is connected to the entrance side of the tapered waveguide 10. Further, in this example, a cylindrical magnetic coil 6 is provided on the outer peripheral portion of the plasma generation container 4, and electron cyclotron resonance (ECR) conditions (for example, 875 when the microwave 14 is 2.45 GHz) are provided in the plasma generation container 4. A magnetic field satisfying Gauss is generated, but such a magnetic coil 6 may not be provided.

When the inside of the plasma generation container 4 is evacuated and a gas is introduced into the plasma generation container 4 so as to have a predetermined pressure, and the microwave 14 is introduced, a microwave discharge occurs in the plasma generation container 4 and the gas is discharged and decomposed. The plasma 2 is thereby generated. The plasma 2 can be used for etching, film formation, ion beam extraction, and the like.

Moreover, in order to generate the plasma 2 having a relatively large cross-sectional area and a high density, the microwave plasma source uses the tapered waveguide 10 which is widened to increase its opening area. Thus, the microwave 14 is introduced into the plasma generation container 4 in a large area.

[0005]

[Problems to be solved by the device]

 However, in the above microwave plasma source, when the opening angle α of the tapered waveguide 10 is increased in order to increase the opening area and reduce the size of the tapered waveguide 10 as much as possible, the wave front surface of the microwave 14 is increased. There is a problem that becomes a spherical wave instead of being parallel to the aperture plane. 14s in FIG. 7 schematically shows a spherical wave. When the wave front surface of the microwave 14 becomes a spherical wave, the microwaves 14 having different phases at the central portion and the end portion are incident on the inside of the plasma generation container 4, and the plasma with high density uniformity in the radial direction. It becomes difficult to generate 2.

If the opening angle α of the tapered waveguide 10 is made small and the length L is made long, the above-mentioned drawback can be compensated, but the length L becomes too long, and the microwave plasma source becomes large. I will end up. Note that F in FIG. 7 is the origin of the tapered waveguide 10.

Therefore, the present invention provides a microwave plasma source capable of generating a plasma having a large area and a high uniformity of density, and not requiring an increase in the length of the tapered waveguide. The main purpose is to do.

[0008]

[Means for Solving the Problems]

 In order to achieve the above object, the microwave plasma source of the present invention is characterized in that a radio wave lens for converting a spherical spherical wave of a microwave into a plane wave is provided near the opening of the tapered waveguide as described above. To do.

[0009]

[Action]

 According to the above configuration, the spherical wave in the tapered waveguide is converted into a plane wave by the radio wave lens and is incident into the plasma generation container. As a result, the microwaves propagate in the same phase in the plasma generation container, so that plasma with a large area and high density can be generated in the plasma generation container. Moreover, since the opening angle of the tapered waveguide can be increased, it is not necessary to increase the length of the tapered waveguide.

[0010]

【Example】

 FIG. 1 is a sectional view showing a microwave plasma source according to an embodiment of the present invention. The same or corresponding portions as those of the conventional example in FIG. 7 are denoted by the same reference numerals, and the differences from the conventional example will be mainly described below.

In this embodiment, in the opening portion of the tapered waveguide 10 as described above and in front of the dielectric window 8, as an example of a radio wave lens, a dielectric lens 22 having a convex lens shape is used. A body lens 20 is provided.

The principle of this dielectric lens 20 and radio wave lenses such as a waveguide lens 30 and a pass length lens 40, which will be described later, is described, for example, in “Foundation of Microwave Circuit” (Kizuki Suzuki, Keigaku Shuppan), page 132. Pp. 136, the description will be made by applying it to this embodiment.

That is, referring to FIG. 2, if the relative permittivity of the dielectric 22 is not equal to 1, the velocity v ₂ of the radio wave passing through the dielectric 22 is slower than the velocity v ₁ of the radio wave in the free space. V ₂ <v ₁ . When a radio wave (in this example, the above-described microwave 14; the same applies hereinafter) enters such a dielectric 22, refraction occurs at the boundary surface and the traveling direction of the radio wave changes. Therefore, if the structure of the dielectric 22 is as follows, it can be used as a radio wave lens.

That is, in FIG. 2, the distance between the origin F of the tapered waveguide 10 and an arbitrary point R on the surface of the dielectric 22 is r, the angle from the center axis of the point R is θ, and the origin F is When the distance between the points O on the surface of the dielectric 22 when θ = 0 is d ₁ and the distance between the points P where the perpendicular line from the points O and R intersects the central axis is d ₂ , the radio wave After passing through the dielectric 22, a plane wave with a uniform wave front is obtained by the following relationship: r / v ₁ = (d ₁ / v ₁ ) + (d ₂ / v ₂ ), rcos θ = d ₁ + d ₂ (1) Should be established. When this formula is decomposed and rearranged, v ₁ / v ₂ = (r−d ₁ ) / d ₂ , d ₂ = rcos θ−d ₁ ∴v ₁ / v ₂ = (r−d ₁ ) / (rcos θ−d _{1 ) = n r-d 1 =} nrcosθ-nd 1 r = (d 1 -nd 1) / ( becomes _{1-ncosθ) = d 1 (} 1-n) / (1-ncosθ) ··· (2). n is a refractive index.

If the shape of the front surface 24 of the dielectric 22 is set so as to satisfy the above expression (2), that is, n> 1 (∵v ₂ <v ₁ ), the shape of the front surface 24 is centered on the origin F. A plane wave can be created by using a rotating hyperboloid. Note that E in FIG. 2 indicates the electric field of the radio wave, and H indicates the magnetic field (the same applies to FIGS. 4 and 6).

The dielectric lens 20 satisfies the above relationship, and as shown in FIG. 1, the spherical wave of the microwave 14 supplied from the tapered waveguide 10 is converted into a plane wave to generate a plasma generating container. 4 can be made incident. In FIG. 1, 14s schematically shows a spherical wave and 14p a plane wave (the same applies to FIGS. 3 and 5).

As a result, the microwaves 14 propagate in the plasma generation container 4 in the same phase, so that the plasma 2 having a large area and high density can be generated in the plasma generation container 4. In addition, since the microwave 14 may be a spherical wave in the tapered waveguide 10, the opening angle α of the tapered waveguide 10 can be increased, so that the length L of the tapered waveguide 10 can be increased. You don't have to. As a result, it is possible to prevent the microwave plasma source from increasing in size.

The dielectric lens 20 may also serve as a dielectric window. In this case, the dielectric window 8 described above can be omitted, and thus the structure can be simplified. Can be planned.

Further, if a suitable extraction electrode 16 is provided at the opening of the plasma generation container 4 of such a microwave plasma source, it can be used as an ion source in the plasma 2 in a large area and even in the density uniformity. A high ion beam can be extracted.

In the embodiment of FIG. 3, in a portion in the opening of the tapered waveguide 10 and in front of the dielectric window 8, as another example of the radio wave lens, parallel to the electric field surface E (see FIG. 4). A waveguide lens 30 formed by arranging a number of metal plates 32 is provided.

The principle of this waveguide lens 30 will be described with reference to FIG. When the propagation direction of the radio wave is narrowly partitioned by the metal plate 32, the one space has a shape like a waveguide, and the phase velocity of the radio wave therein is faster than the velocity in the free space. Radio wave phase velocity of the waveguide is v _{p is, v p = C / √ {} 1- (λ / 2a)} can be expressed by (3). Here, C is the speed of light, and λ is the wavelength of the radio wave. That is, the phase velocity v _p increases as the spacing a of the metal plates 32 decreases, and the phase velocity v _p decreases as the spacing a increases.

Therefore, the interval a of the metal plate 32 is narrowed toward the end, or the length of the metal plate 32 is lengthened toward the end, thereby changing the phase velocity of the radio wave to change the spherical wave into a plane wave. Can be converted to. The waveguide lens 30 of this embodiment is an example of the latter.

That is, since the phase velocity V ₂ of the radio wave between the metal plates 32 is the same as the phase velocity v _p in the waveguide, v ₂ = v _p . This v _p is as shown in the equation (3). In order for the velocity of the radio wave in the free space to be v ₁ (= C) and for the wave to pass through the lens 30 and become a plane wave with a uniform wavefront, the following equation must be established. (D ₂ / v _p ) + (r + v ₁ ) = (d ₁ + d ₂ ) / v ₁ = d / v ₁ (4) However, on the origin F of the tapered waveguide 10 and the surface of the lens 30. The distance between arbitrary points R is r, the angle from the center axis of point R is θ, the distance between the origin F and the point O where the perpendicular line from the point R intersects the center axis is d ₁ , and the point O and θ = 0 At this time, the distance between the points P on the surface of the lens 30 is d ₂ , and the distance between the origin F and the point P is d.

Since d ₁ = r cos θ, when substituting this into the above equation (4), (d-d ₁ ) / v _p + r / v ₁ = (d ₁ + d ₂ ) / v ₁ (d-r cos θ) / V _p = (d ₁ + d ₂ −r) / v ₁ = {r (cos θ−1) + (d−r cos θ)} / v ₁ ∴v ₁ / v _p = n = {r (cos θ−1) + (D−rcos θ)} / (d−rcos θ) (5) n is a refractive index.

When this equation (5) is further modified to obtain r, nd−nrcosθ = rcosθ−r + d−rcosθ nd−nrcosθ = d−r∴r = {(1-n) d} / (1-ncosθ ) ... (6)

If the shape of the front surface 34 of the many metal plates 32 is set so as to satisfy the above expression (6), then n <1 immediately, so the shape of the front surface 34 is changed to an ellipsoid of revolution about the origin F. Then you can make a plane wave.

The waveguide lens 30 satisfies the above relationship, and as shown in FIG. 3, the spherical wave of the microwave 14 supplied from the tapered waveguide 10 is converted into a plane wave to generate plasma. It can be made incident into the container 4. Therefore, as in the case of the dielectric lens 20, plasma having a large area and high density uniformity can be generated in the plasma generation container 4, and the length of the tapered waveguide 10 is large. You don't have to.

As described above, a waveguide lens having the same function as that of the waveguide lens 30 can be configured by narrowing the intervals of a large number of metal plates having the same length toward the ends. You can

Referring to FIG. 6 as well, the embodiment of FIG. 5 shows, as another example of the radio wave lens, a radio wave propagating inside the opening of the tapered waveguide 10 and in front of the dielectric window 8. A path length lens (also referred to as a magnetic field surface metal plate lens) 40 is provided, which is tilted by an angle φ with respect to the direction and has a large number of metal plates 42 arranged in parallel to the magnetic field surface H at a constant interval b (<λ / 2). There is.

The principle of the pass length lens 40 will be described below. The difference between the path length lens 40 and the waveguide lens 30 is that in the former, the metal plate 42 is parallel to the magnetic field surface H and perpendicular to the electric field surface E, so the phase velocity in the lens is in the free space. Although it is equal to the phase velocity, the latter is a point that the internal phase velocity becomes faster than that in free space because the metal plate 32 is parallel to the electric field plane E. However, since the metal plate 42 is attached at an angle of φ in the path length lens 40, the traveling speed of the radio wave in the central axis direction is cosφ times in the free space in the lens. This is because the effective path length becomes longer. Since cosφ ≦ 1, the propagation velocity in the lens becomes smaller than the propagation velocity v _{1 in} free space, and this lens 40 acts just like a dielectric lens.

That is, the distance between the origin F of the tapered waveguide 10 and an arbitrary point R on the surface of the lens 40 is r, and the distance between the origin F and the point O on the surface of the lens 40 when θ = 0. Is d ₁ , and the distance between the point P and the point O at which the perpendicular line from the point R and the line in the direction of the angle φ from the point O intersect is s, r / v ₁ = (d ₁ / v ₁ ) + (s / V ₁ ) ... (7) If d ₂ = s cos φ, then d ₂ = r cos θ-d ₁ ; therefore, by transforming the equation (7), r = d ₁ + d ₂ / cos φ = d ₁ + (r cos θ-d ₁ ) / cos φ ... (8) Assuming that the refractive index is n, n = v ₁ / v ₂ = v ₁ / v ₁ cosφ = 1 / cosφ, and therefore the equation (8) is r = d ₁ + n (rcosθ−d ₁ ) ∴r = (N−1) d ₁ / (ncos θ−1) (9)

If the shape of the front surface 44 of a large number of metal plates 42 satisfies the above expression (9), this expression is immediately the same as the above expression (2), so that the shape of the front surface 44 is converted into a hyperboloid of revolution. If so, a plane wave can be created.

The pass-length lens 40 satisfies the above relationship, and as shown in FIG. 5, the spherical wave of the microwave 14 supplied from the tapered waveguide 10 is converted into a plane wave to generate a plasma. It can be injected into the production container 4. Therefore, as in the case of the dielectric lens 20 and the waveguide lens 30, it is possible to generate a plasma having a large area and a high uniformity of density in the plasma generation container 4, and only the tapered waveguide 10 can be generated. You do not have to increase the length.

[0034]

[Effect of device]

 As described above, according to the present invention, since the above-mentioned electromagnetic lens is provided near the opening of the tapered waveguide, the spherical wave in the tapered waveguide is converted into a plane wave by the radio wave lens to generate plasma. Since it is incident on the inside of the container, the microwaves propagate in the plasma generation container in the same phase, so it is possible to generate plasma with a large area and high density in the plasma generation container. You can

Moreover, since the opening angle of the tapered waveguide can be increased, it is not necessary to increase the length of the tapered waveguide. As a result, it is possible to prevent the microwave plasma source from increasing in size.

[Brief description of drawings]

FIG. 1 is a sectional view showing a microwave plasma source according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of the dielectric lens in FIG.

FIG. 3 is a sectional view partially showing a microwave plasma source according to another embodiment of the present invention.

FIG. 4 is a diagram for explaining the principle of the waveguide lens in FIG.

FIG. 5 is a view partially showing a microwave plasma source according to still another embodiment of the present invention.

FIG. 6 is a diagram for explaining the principle of the pass length lens in FIG.

FIG. 7 is a sectional view showing an example of a conventional microwave plasma source.

[Explanation of symbols]

 2 Plasma 4 Plasma Generation Container 8 Dielectric Window 10 Tapered Waveguide 14 Microwave 20 Dielectric Lens 30 Waveguide Lens 40 Path Length Lens

Claims (1)

[Scope of utility model registration request] 1. A plasma generation container for generating plasma, a dielectric window for introducing microwaves therein while maintaining a vacuum therein, and a microwave for introducing microwaves into the plasma generation container through the dielectric window. In a microwave plasma source provided with a divergent tapered waveguide for introduction, a radio wave lens for converting a spherical spherical wave of a microwave into a plane wave is provided in the vicinity of an opening of the tapered waveguide. Microwave plasma source.