CN101119609B - Combination of slit and large slit microwave plasma reaction chamber - Google Patents

Abstract

The present invention relates to a narrow gap-big gap combined microwave plasma reaction cavity, belonging to microwave plasma excitation technique field. The reaction comprises a vacuum column shape reaction cavity which is arranged vertically, and the upper part and the lower part of the reaction cavity are both sealed by a demountable flange. An annular wave guide with a rectangular-shaped cross section is winded in the middle part of the reaction cavity. The inner wall of the annular wave guide is coincided with the outer wall of the cavity. The inner wall of the annular wave guide is opened with a narrow gap which is corresponding to the wave node quantity of the standing wave inside the annular wave guide. The narrow gap is positioned at the standing wave node. The outer wall of the annular wave guide is opened with a through hole which is used for connecting with the drop-leaf mode wave guide switch or with the coupled antenna. The present invention is characterized in that the inner wall of the annular wave guide is opened with a big gap which is used for forming a symmetric high field inside the reaction cavity, and the high filed is strongest in the middle and then decreased periphery outward gradually; and the high filed is complemented with the electric field formed by the narrow gap to make the electric field is evenly distributed inside the reaction cavity. The present invention has the advantages of effectively improving the distribution of the electric field, producing more even plasma which can also exist inside the middle of the cavity.

Description

Combination of slit and large slit microwave plasma reaction chamber

technical field

The invention belongs to the technical field of microwave plasma excitation, and in particular relates to the structural design of a reaction chamber for generating large-area microwave plasma. the

Background technique

Plasma has strong practical value in the fields of new materials, microelectronics and other industries and biological research, especially the way of using microwaves to excite plasma. Compared with other plasma excitation methods, the existence of plasma is larger. The density of charged particles is high, so there is a lot of room for application expansion. In particular, large-area (large-volume) microwave plasma has higher application value in related industries. the

Microwave plasma reaction chambers generally use single or mixed microwave modes to generate plasmons inside chambers with different structures. Due to the different structures, the areas of the generated plasma are also different. However, the existing reaction chamber for generating large-area microwave plasma mainly utilizes the diffraction effect of the slit antenna on the microwave, and is called a slit-type reaction chamber. The structure and excitation principle of this type of microwave plasma reaction chamber are shown in Figures 1 and 2. The reaction chamber includes: a circular waveguide surrounded by cylindrical reaction chambers 2 and 22 (currently mature chambers are basically cylindrical) 1, 21, in the combined joints of the ring waveguide and the reaction cavity 3, 28 (the inner wall of the ring waveguide and the outer wall of the reaction cavity), according to the wavelength of the microwave waveguide, the corresponding narrow bands are distributed at the standing wave nodes of the ring waveguide Slots 4, 24 (eight slits are shown in the figure), each slit position corresponds to the node of the standing wave 26, and 27 is the centerline of the ring waveguide; circular holes 5, 25 are opened on the outer wall 29 of the ring waveguide. The microwave energy in the ring waveguide is input into the reaction cavity through the slit to form a surface wave and excite the plasma. Although the plasma area generated by this reaction chamber is large, the electric field generated by the diffraction of the slit antenna is mainly concentrated near the slit, and the electric field in the center of the chamber is generally small, and microwave plasma excitation generally relies on the action of the electric field, so , under relatively high pressure (>10 ⁴ Pa) the plasma formed in the cavity is mostly concentrated near the slit, and it is difficult to form in the center of the cavity, resulting in uneven distribution of plasma in the cavity. This uneven distribution will inevitably limit the use value of microwave plasma. Therefore, it is very necessary to study how to expand the distribution of microwave electric field to make the plasma distribution uniform.

Contents of the invention

The object of the present invention is to overcome the deficiency caused by uneven electric field distribution in the existing slit-type reaction chamber. A microwave plasma reaction chamber combining slit and large slit is proposed, which is improved on the basis of the original slit microwave plasma reaction chamber, and a large slit structure is additionally designed on the ring waveguide, so that it is compatible with the slit With the combination of the structure, the electric field distribution is effectively improved, the generated plasma is more uniform, and it can also exist in the center of the cavity. the

The technical scheme of the present invention is as follows: It includes a vertically placed hollow cylindrical reaction chamber sealed by detachable flanges up and down, in the middle of the chamber, surrounded by a ring waveguide with a rectangular cross section, the inner wall of the ring waveguide coincides with the outer wall of the chamber ; There are slits corresponding to the number of standing wave nodes in the ring waveguide on the inner wall of the ring waveguide, and the position of the slit is just at the standing wave node; the outer wall of the ring waveguide is used to connect with the square-circle mode conversion waveguide (or coupling antenna) A through hole (the microwave is transmitted from the through hole to the ring waveguide through the mode conversion waveguide); it is characterized in that, on the inner wall of the ring waveguide, there is also a large slit, which is used to form the largest in the middle of the reaction chamber and gradually decrease to the periphery. The symmetrical strong electric field is complementary to the electric field formed by the slit, so that the electric field in the reaction chamber is evenly distributed. the

The large slit can be opened at the head end when the microwave just enters the ring waveguide, or at the corresponding end, or at both ends. The center of the large slit is preferably on the line connecting the center of the through hole and the center of the cavity and its extension line

The center of the cavity, the center of the ring waveguide and the center of the slit and the large slit are on the same horizontal plane. the

The above-mentioned entire cavity is made of a metal material that absorbs less microwaves. the

The principle of the present invention is: the process of microwave transmission is: the microwave energy output by the power source is first transmitted through a standard rectangular waveguide, and after passing through standard devices such as a circulator, a pin regulator, a directional coupler, and a short-circuit piston, it is transmitted through a square-circle conversion waveguide. into the ring waveguide, and then enter the reaction chamber through the slit and large slit to form an electric field. It is transmitted into the reaction chamber through the slit on the inner wall of the ring waveguide, so that a certain plane in the middle of the reaction chamber forms a high electric field near the slit. Since the slit is evenly distributed along the outer wall of the reaction chamber, the formed high electric field area tends to be ring-shaped. , and are also distributed in the periphery of the plane in the reaction chamber, and the electric field in the center is very low. Microwaves are also transmitted into the reaction chamber through the large slit, and a symmetrical strong electric field is formed on the plane of the reaction chamber, which is the largest in the middle and gradually decreases toward the periphery, which is complementary to the electric field formed by the slit. This electric field works together with the electric field under the action of the slit, so that the overall electric field value of the plane in the cavity is higher and the distribution becomes uniform, which is conducive to the uniform excitation and distribution of plasma. The electric field formed by the large slit can be optimized by matching the size of the large slit with the size of the reaction chamber, microwave frequency and other parameters. the

The specific dimensions of slits, large slits, and ring waveguides in the cavity vary according to the number of standing waves in the ring waveguide and the frequency of microwave transmission in the design. The circumference of the center line of the ring waveguide is generally an integer multiple of the wavelength of the standing wave in the waveguide. The cross-sectional dimensions of the ring waveguide are similar to the standard rectangular waveguide used to transmit microwaves of this frequency. The height of the slit and the large slit is generally half of the height of the ring waveguide, and the width of the large slit is close to the width of the cross section of the ring waveguide. The specific size can be estimated by electromagnetic theory and optimized with the help of professional software simulation. the

The innovation of the present invention is to propose a structure in which slits and large slits cooperate. This structure will inevitably improve the uniformity of electric field distribution in the reaction chamber and make up for the shortcomings of the reaction chamber with only slit structures. In practical applications, as long as the center of the large slit dug on the inner wall of the ring waveguide is on the line connecting the center of the through hole and the center of the cavity (when the cavity is placed horizontally, the center is the axis of the cavity at the same level as the center of the through hole) and its extension line, or the horizontal or vertical distance between the central position of the large slit and the connection line and its extension line is within half a standing wave wavelength. The shape of the large slit is generally rectangular, and it can also be a symmetrical structure such as a circle or an ellipse. The overall electric field distribution can be significantly improved. the

The size design of the cavity, the selection of the number of slits, and the selection of microwave transmission devices in the present invention belong to mature technologies, and are not the contents to be protected by this patent. the

Beneficial effects of the present invention:

The present invention is based on the existing slit microwave plasma reaction chamber, and additionally sets a large slit structure on the inner wall of the ring waveguide, through the joint action of the slit and the large slit, the electric field distribution in the reaction chamber is uniform , the plasmoid distribution range is expanded, which is helpful for industrial applications. the

Description of drawings

Figure 1 is a schematic diagram of the appearance of a common 8-slit reaction chamber. the

Fig. 2 is a sectional view of the center plane of an ordinary 8-slit reaction chamber. the

Fig. 3 is a sectional view of the central plane of the reaction chamber in the embodiment of the present invention. the

Fig. 4 is a schematic diagram of the action of the electric field in the reaction chamber of this embodiment. the

Fig. 5 is the effect diagram of the electric field in the reaction chamber calculated by the embodiment and the effect diagram of the electric field in the common 8 slit type reaction chamber; wherein (a) is the effect diagram of the electric field in the common 8 slit type reaction chamber, (b) It is the effect diagram of the electric field in the reaction chamber of this embodiment. the

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments. the

The structure of an embodiment of the combined slit and large slit microwave plasma reaction chamber proposed by the present invention is shown in FIG. 3 . In this embodiment, the microwave frequency is input at 2.45 GHz, and the reaction chamber 32 is a hollow cylinder placed vertically, and the top and bottom are sealed by detachable flanges (not shown in the figure). In the middle of the cavity, there is a ring waveguide 31 with a rectangular cross section, the inner wall 38 of the ring waveguide coincides with the outer wall of the reaction chamber; the inner wall of the ring waveguide has eight narrow holes corresponding to the number of nodes of the four standing waves in the ring waveguide. slit 34, the position of the slit is just at the node of the standing wave; the outer wall of the ring waveguide 31 has a through hole 35, which is connected to the square-circle mode conversion waveguide (or coupling antenna), and the microwave passes through the mode conversion waveguide from the through hole to the ring Transmission in the waveguide; there is a large slot 33 at the end of the ring waveguide 31 . The cylindrical reaction cavity 32 and the ring waveguide 31 are made of brass. the

The cross-section of the ring waveguide in this embodiment is rectangular, and its cross-sectional dimension is similar to that of the standard rectangular waveguide (WR430) for microwave transmission. In the ring waveguide, the microwave propagates in TE ₁₀ mode. After calculation, the standing wave wavelength is about 15.5cm, corresponding to the centerline circumference of the ring waveguide is about 62cm, so the average diameter of the ring waveguide is about 20cm. The diameter of the reaction chamber is about 13-14cm, the slit is 100mm high and 15mm wide, and the large slit is 100mm high and 50mm wide.

The working principle of the electric field in the reaction chamber of this embodiment is shown in FIG. 4 , in which the microwave in the ring waveguide 41 will enter the reaction chamber 42 in the TE ₄₁ mode 46 through the slit 44 . However, due to the limitation of the diameter of the reaction chamber, the microwave modes entering the reaction chamber 42 through the large slit 43 are mainly low-order axisymmetric modes 47 such as TE ₁₁ and TM ₀₁ , and most of the high-order modes are cut off and cannot enter the chamber. Therefore, In the cavity, a mixed mode dominated by TE ₁₁ , TM ₀₁ and TE ₄₁ modes will be formed, while the TE ₄₁ mode forms a strong electric field near the slit 44 and decreases toward the center of the cavity, and the TE ₁₁ and TM ₀₁ modes in the cavity A strong electric field is formed at the center and decreases outwards. The superposition of several electric fields just makes the overall electric field more uniform.

Fig. 5 is the effect diagram of the electric field in the reaction chamber calculated by computer, wherein: (a) is the effect diagram of the common eight-slit type reaction chamber, and (b) is the effect diagram of the reaction chamber of the present embodiment. Comparing the ordinary eight-slit reaction chamber with the reaction chamber with two slits combined in this embodiment, it can be clearly seen that the inventive structure improves the electric field in the chamber. In the combination cavity of large slits and slits, after the relevant dimensions are optimized by simulation, the large slits partially overlap with the slits on both sides, which is shown as one large slit and six slits in the figure. It can be seen from the figure that in an ordinary large-area microwave plasma cavity with only eight slits, the high-value region of the electric field (the shade of gray in the figure indicates the level of the electric field value) is concentrated near the slit and in the ring waveguide , which is not conducive to the acquisition of plasma in the center of the cavity, and the cavity structure combined with large slits and slits of the present invention, the high-value region of the electric field obtained is in the entire cavity, and the electric field in the cavity is evenly distributed, and more than 2/3 of the The electric field difference between the area and area is within 30%, which helps to obtain a relatively uniform plasma. At the same time, the electric field in the ring waveguide is low, and the energy conversion efficiency into the cavity is high. the

This embodiment points out that two kinds of seam-fit cavity structures can improve the electric field, and this structure is beneficial to obtain uniform plasma. Utilizing the principle of this combination, cavity structures with combinations of different numbers of slits and large slits can be designed. Since the number of slits and the size of the cavity can be changed, the generated electric field pattern is not necessarily the same as the example, but as long as the comprehensive electric field in the reaction chamber relies on the superposition effect of the electric field generated by the slits and large slits, its uniformity can be improved , should belong to the structure scope covered by the present invention. the

Claims (3)

1. A microwave plasma reaction chamber combined with a slit and a large slit, including a vertically placed hollow cylindrical reaction chamber sealed up and down by detachable flanges, and in the middle of the chamber, there is an annular ring with a rectangular cross section The waveguide, the inner wall of the ring waveguide coincides with the outer wall of the cavity; the inner wall of the ring waveguide has slits corresponding to the number of standing wave nodes in the ring waveguide, and the position of the slit is at the standing wave node; A through hole connected to the mode conversion waveguide or the coupling antenna; it is characterized in that there is a large slit on the inner wall of the ring waveguide, which is used to form a symmetrical strong electric field that is the largest in the middle of the reaction chamber and gradually decreases toward the periphery, and forms with the slit The electric field is complementary, so that the electric field distribution in the reaction chamber is uniform. 2 . The reaction chamber according to claim 1 , wherein the center of the large slit is located on the line connecting the center of the through hole and the center of the cavity and its extension. 3 . 3. The reaction chamber according to claim 1, characterized in that, the shape of the large slit is a rectangular, circular or elliptical symmetrical structure.

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