JPH0763035B2 - Plasma generation source by microwave excitation - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plasma generation source using electron cyclotron resonance by microwave excitation, which is used in, for example, a plasma CVD apparatus or a plasma etching apparatus.

[Conventional technology]

As a fine and high-definition manufacturing technology for semiconductor LSIs, etching using an activated particle such as plasma and ions, film formation, and ion implantation technology are widely used. Various types of discharge have been studied as a plasma generation source for generating plasma. Among them, plasma discharge using electron cyclotron resonance by microwave excitation (ECR discharge) has a low pressure (1 × 10 ⁻ Discharge is possible at ⁵ Torr or less), the direction of ions is aligned, high-density plasma can be generated, and the life is long because of electrodeless discharge.
It has attracted attention because it has excellent characteristics such as the ability to use active gas.

Fig. 4 shows the basic configuration of a conventional plasma generation source using ECR discharge. 1 is a plasma generation chamber, 2 is a microwave introduction window, 3 is a waveguide, 4 is a magnetic coil, 5 is a gas introduction port,
Reference numeral 6 is a plasma limiter, and 7 is an extracted plasma flow. Gas is introduced into the plasma generation chamber 1 through the gas inlet 5.
A microwave (for example, 2.45 GHz) is introduced from the waveguide 3 (a microwave oscillation source, an isolator, a matching device, and a microwave power meter are omitted in the figure), and a magnetic coil 4
Therefore, when a DC magnetic field (875 Gauss) under the electron cyclotron resonance (ECR) condition is applied in the direction perpendicular to the microwave electric field, the interaction between them causes the plasma generation chamber 1
The gas introduced into the plasma becomes plasma. Normally, the plasma generation source of ECR plasma CVD equipment and ECR ion shower etching equipment has a resonance mode configuration such as TE ₁₁₃ in order to efficiently absorb microwaves into the plasma (for example, Japanese Journal of Applied). * Physics (Japanese Journal of Applied Physics) Vol. 22, No. 4, (1983) L210-212).

[Problems to be solved by the invention]

Generally, the electric field strength of the microwave introduced into the plasma generation chamber 1 in FIG. 4 is small in the vicinity of the microwave introduction window 2 of the plasma generation chamber 1 and becomes 1/4 of the in-tube wavelength as the distance from the microwave introduction window 2 increases. Takes the maximum and minimum in the cycle. This plasma generation source operates by generating a magnetic field (875 Gauss) that satisfies the ECR condition in the vicinity of the microwave introduction window 2. However, since this region is a region where the microwave electric field is weak, it is not always the optimum configuration. I haven't. Moreover, there is a problem in that high-efficiency plasma is not generated even if the ECR condition magnetic field is simply applied to the place where the microwave electric field strength in the plasma generation chamber 1 is high. The reason for this is that when plasma is generated, the permittivity for microwaves inside the plasma generation chamber changes, so that the position where the electric field strength of microwaves is strong changes, and further, in the vicinity of the microwave introduction window 2. Since the state of the generated plasma affects the overall plasma generation, it is presumed that not only the position of the magnetic field that satisfies the ECR condition but also the magnetic field strength and distribution in the vicinity of the microwave introduction window will be a problem.

[Means for solving problems]

The present invention includes a first waveguide for supplying microwaves, the first waveguide having a cross section larger than that of the first waveguide connected to the first waveguide through an opening for introducing microwaves. In the second waveguide, a dielectric region provided on the opening side for propagating the microwave supplied from the first waveguide and a plasma generation region partitioned by the dielectric region are provided. In the dielectric region, at least a region including a boundary with the plasma generation region is filled with a dielectric, and the dielectric region is disposed in a microwave introduction direction from the opening of the second waveguide to the boundary with the plasma generation region. The shortest distance along the distance is an odd multiple of a quarter of the guide wavelength of the microwave propagating through this distance.

[Action]

By appropriately setting the dimensions of the dielectric, the electric field strength of the microwave becomes large at the boundary where the microwave enters the plasma generation region. Moreover, since the electric field distribution in the dielectric body does not change due to the generation of plasma, the position where the electric field is large does not change due to the generation of plasma, and the electric field strength at the boundary portion is always kept large.

〔Example〕

(Embodiment 1) FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 8 is a rectangular waveguide which is the first waveguide, and 9 is a second waveguide.
Plasma generation chamber which is a waveguide of 9A, 9A is a dielectric region, 9B is a plasma generation region, 10 is a magnetic coil, 11 is a gas inlet,
12 is an opening for microwave introduction, 13 is a plasma limiter, 14
Is the plasma flow. The plasma generation chamber 9 has a dielectric region.
9A and plasma generation region 9B. The dielectric filled in the dielectric region 9A propagates microwaves, while the plasma generation region 9B can be evacuated to a vacuum,
Vacuum sealing is performed with an O-ring. As will be described later, the thickness of this dielectric is set so that the electric field strength of the microwave there becomes strong where it contacts the plasma generation region 9B. As the dielectric material, quartz (dielectric constant 4), BN (4), forthulite (6,2), steatite (6), alumina (9) and the like can be used. Incidentally, in the configuration of the dielectric region 9A, non-degassing and heat resistance are required for contact with plasma,
The dielectric is divided into several parts, such as quartz and alumina for the parts that require airtightness and flatness for vacuum sealing, and inexpensive materials for the other parts. It goes without saying that it is okay.

The microwave is a rectangular waveguide 8 and an opening 12 for introducing microwaves.
Through the plasma generation chamber 9. Gas is introduced into the plasma generation region 9B through the gas inlet 11 and microwave (for example, 2.45 GHz) is introduced through the waveguide 8 (a microwave oscillation source, an isolator, a matching box, and a microwave power meter are omitted in the figure). When a DC magnetic field (875 Gauss) under electron cyclotron resonance (ECR) conditions is applied in the direction perpendicular to the microwave electric field by the magnetic coil 10, these Due to the interaction, the gas introduced into the plasma generation region 9B becomes plasma. At this time, in this embodiment, by inserting a dielectric as the dielectric region 9A, the electric field strength of the microwave is increased at the boundary with the plasma generation region 9B regardless of the plasma state. Therefore, high-density plasma can be efficiently generated in the vicinity of the microwave introduction window.

To increase the electric field strength of the microwave at the boundary where the microwave enters the plasma generation region, specifically, n
Is a natural number, the dimension t of the dielectric region 9A in the microwave introduction direction (dielectric thickness) t may be t = λ _g × (2n−1) / 4. Here, λ _g is the guide wavelength of a waveguide filled with a dielectric having a permittivity ε, It is represented by. However, λ _c is a cutoff wavelength and is represented by λ _c = 2πr / 1.84 (TE ₁₁ mode of a cylindrical waveguide; r is a radius), and λ is a wavelength of a microwave in free space.

By doing so, in the dielectric region 9A, for example, the boundary strength distribution is such that the envelope is shown by the broken line in FIG. Here, the electric field strength distribution in the plasma generation region 9B changes depending on the state of the plasma, but the electric field distribution in the dielectric region 9A described above does not change, and the plasma generation region
It always shows the maximum strength at the boundary with 9B. On the other hand, at this boundary, since the electric field distribution of the dielectric region 9A and the electric field distribution of the plasma generation region 9B maintain continuity, the electric field strength of the plasma generation region 9B is forcibly fixed to a large value at the boundary. To be done.

As an example, when a plasma generation chamber with an inner diameter of 20 cm is constructed using 2.45 GHz microwave, the tube wavelength when filled with quartz (dielectric constant 4) is 6.4 cm.
The length (thickness of quartz) should be 1.6 x (2n-1) cm. Generally, as the inner diameter of the plasma generation chamber 9 becomes smaller, the wavelength inside the tube becomes longer, and this method becomes more effective.

Further, when the plasma generation chamber 9 having a cylindrical cavity is filled with a dielectric having a dielectric constant ε, the cutoff frequency f
_c is It is represented by. Therefore, by filling the 2.45 GHz microwave with alumina having a dielectric constant of 9, the inner diameter of the cylinder necessary for propagating the microwave can be 2.4 cm, which makes it possible to construct a very small plasma generation source.

When a small-sized plasma generation chamber having an inner diameter of 7.15 cm or less is constructed with the configuration as shown in FIG. 4, generally, microwaves are blocked and the microwaves cannot be introduced into the plasma generation region not filled with the dielectric. However, in reality, a part of the microwave slightly leaks to the plasma generation region, so that plasma can be generated. Moreover, once plasma is generated, the plasma generation region 9B is equivalent to being filled with a dielectric material (plasma) having a high dielectric constant, and the microwave propagates to the plasma generation region, which is a stationary condition. Plasma is generated. That is, plasma can be generated even when the cavity serving as the plasma generation chamber has a small internal dimension corresponding to a transmission mode in a cutoff region where the introduced microwave is not transmitted in a state where plasma is not generated.

For this reason, the dielectric region of this plasma generation region 9B is
The magnetic field at the boundary with 9A is ECR that makes it easy to start plasma discharge.
It is desirable to set a magnetic field satisfying the conditions and generate plasma immediately, and then adjust the magnetic field distribution to be optimum for high density plasma generation.

Therefore, the plasma generating chamber 9 is configured in this way, and the peripheral waveguide 8 (which can be miniaturized by using a dielectric-filled waveguide), the magnetic coil 10, etc. can be miniaturized together with the plasma generating chamber 9. By doing so, a very small plasma generation source can be constructed. Further, when the size is made small as described above, the power density with respect to the same microwave power becomes high, and high-density plasma can be generated with low power. Furthermore, the smaller the inner diameter of the plasma generation chamber is, the longer the in-tube wavelength of the microwave propagating in the plasma is. Therefore, the region where the microwave is absorbed by the plasma is expanded, and the plasma can be generated more efficiently.

(Embodiment 2) FIG. 2 is a block diagram showing another embodiment of the present invention. Reference numeral 15 denotes a plasma generation chamber, and corresponding to FIG. 3, 15A is a dielectric region, which is composed of an atmospheric space 15A-1 and a dielectric 15A-2, and 15B is a plasma generation region. Dielectric 15A-
2 is vacuum-sealed so that the plasma generation region 15B can be evacuated. Therefore, like the configuration of FIG.
By considering the dielectric constant of the dielectric region 15A and the size and position in the microwave introduction direction, the plasma generation region 15B
The electric field strength of the microwave can be increased at the boundary of. Therefore, it is possible to generate plasma with high efficiency as described in the first embodiment.

A dielectric may be arranged in the atmospheric space 15A-1. In any case, this embodiment has an advantage that it can be easily processed, as compared with the first embodiment, because the dielectric can be a simple disk shape.

(Embodiment 3) FIG. 3 shows a block diagram of a third embodiment of the present invention. This embodiment is basically the same as the embodiment of FIG.
Reference numeral 16 is a gas inlet, and 17 is a plasma generation chamber. 17A is a dielectric region and 17A-1 is an atmospheric space, but it may be a dielectric. 17A-2 is a dielectric, and 17B is a plasma generation region. In this configuration, the vacuum seal is a cup-shaped dielectric
I am going on 17A-2. Also in this case, if the permittivity of the dielectric region 17A, the dimension in the microwave introduction direction, and its position are appropriately determined as described above, the electric field strength of the microwave becomes strong at the boundary of the plasma generation region 17B. Become. Therefore, the plasma generation source can be operated by the same operation as that in the first embodiment, and more efficient plasma can be generated.

In the above, the case where it is mainly used as a plasma / radical generation source has been described. However, if the plasma extraction source of the present invention uses an ion extraction electrode system of a three-electrode configuration of an acceleration-deceleration configuration, high-density / high-current ions can be obtained. Especially effective as a source. Further, if a single-electrode / single-leaf mesh electrode is used, it is also effective as a generation source of low energy ions.

〔The invention's effect〕

According to the present invention, by disposing the dielectric in the vicinity of the microwave introduction window of the plasma generation chamber in the portion where the electric field of the introduced microwave is small, the electric field of the microwave is generated at the place where the microwave enters the plasma generation region. So that
Since microwaves can be absorbed by electrons in plasma within a short distance, it is effective as a plasma generation source / ion source with higher efficiency than before. That is, when used as a plasma generation source for an ECR plasma CVD apparatus or an ECR plasma etching apparatus, there is an advantage that a more efficient apparatus can be constructed.

Also, since it can be used as a source of small plasma, ions, and radicals, it can be used as a compound device in addition to MBE equipment, MOCVD equipment, plasma application equipment, etc. to promote etching, film formation, etc. by promoting surface reaction and doping efficiency. Higher control of technology becomes possible.

Furthermore, by installing an accelerating-decelerating ion extraction electrode, it can be used as a small-sized high-current ion source, which is promising as an ion source for an ion implantation device, and a single-electrode / single-leaf mesh electrode can be used to reduce the It is also effective as a source of energetic ions.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are block diagrams showing other embodiments of the present invention, and FIG. 4 is a block diagram showing a conventional example. 8 ... Waveguide, 9,15,17 ... Plasma generation chamber, 9A, 15A, 17
A: Dielectric area, 9B, 15B, 17B: Plasma generation area, 1
0 …… Magnetic coil, 11,16 …… Gas inlet, 12 …… Microwave inlet.

Claims (1)

[Claims] 1. A first waveguide for supplying microwaves, which has a cross section larger than that of the first waveguide connected to the first waveguide through an opening for introducing microwaves. A micro waveguide provided in the second waveguide, which includes a dielectric region provided on the opening side for propagating the microwave supplied from the first waveguide, and a plasma generation region partitioned by the dielectric region. A plasma generation source by wave excitation, wherein the dielectric region is filled with a dielectric at least in a region including a boundary portion with the plasma generation region, and a boundary between the plasma generation region and the opening of the second waveguide is formed. The shortest distance to the part along the microwave introduction direction is an odd multiple of a quarter of the guide wavelength of the microwave propagating through this distance, and a plasma generation source by microwave excitation. .