CROSS REFERENCE OF RELATED APPLICATION

This is a U.S. National Stage under 35 U.S.C 371 of the International Application PCT/CN2018/075293, filed Feb. 5, 2018, which claims priority under 35 U.S.C. 119(a-d) to CN 201710244250.3, filed Apr. 14, 2017.

BACKGROUND OF THE PRESENT INVENTION

Field of Invention

The present invention relates to the field of chemical vapor deposition technology. In particular, a microwave resonant cavity and a corresponding reactor relate to the field of plasma chemical vapor deposition technology

Description of Related Arts

Using microwave energy to generate plasma, materials such as diamond and graphene can be fulfilled by microwave plasma chemical vapor deposition (CVD) method. Since the plasma is generated in an electrodeless discharge process, it is relatively pure. When materials are prepared by hot filament CVD method or direct current arc plasma jet CVD method, they are often contaminated by the evaporation of the hot metal filament or the tungsten electrode. Compared with the radiofrequency CVD method, the microwave plasma CVD method has a relatively concentrated discharge region, a higher energy density, and a faster deposition rate. Therefore, this method has received extensive attention and has been widely used in the fields of research and preparation of high-quality diamond materials.

The resonant cavity is the main component of the microwave plasma CVD reactor. However, two tricky problems still remain. On one hand, the cavity structure of the microwave plasma CVD reactor often has a low focusing ability. Therefore, improving the focusing ability to form a strongly focused electric field and generate high-density plasma is preferred to develop new resonant cavity structures. On the other hand, the resonant cavity is less flexible. It should be combined with a specific coupling mechanism and a dielectric window in a microwave plasma CVD reactor. For example, an ellipsoidal resonant cavity needs to be equipped with a coaxial probe antenna as a coupling mechanism and a quartz bell jar as a dielectric window; a cylindrical resonant cavity is generally equipped with a coaxial probe antenna as a coupling mechanism and a quartz plate as a dielectric window; a butterfly resonant cavity needs to be equipped with a coaxial circumferential antenna as a coupling mechanism and a quartz ring as a dielectric window.

In order to overcome the two problems mentioned above, the present invention proposes a novel resonant cavity by utilizing the principle of reflection and interference of electromagnetic waves. The novel resonant cavity has a strong electric field focusing ability and can match different coupling mechanisms and dielectric windows to build microwave plasma CVD reactors.

SUMMARY OF THE PRESENT INVENTION

The present invention provides a plasma chemical vapor deposition reactor with a microwave resonant cavity for the purposes of improving the focusing ability and configuration flexibility.

Based on the above purposes, a rotary body is adopted for the microwave resonant cavity, which is formed by two isosceles triangles intersecting at the vertex angles with a Boolean union operation. Inside the rotary body, there are an upper cavity and a lower cavity. The base angles of the two triangles are 50°˜75°. Between 2nλ˜(2n+0.5) λ, the base lengths of the two triangles are equal or have an nλ difference, where n is an integer, λ is the microwave wavelength. The distance between the centroids of the upper and the lower isosceles triangles is 0˜4/5λ.

Further, an upper cylindrical cavity is provided in the middle part of the rotary body, and a lower cylindrical cavity is provided at the bottom of the lower cavity.

The plasma chemical vapor deposition reactor comprises a microwave coupling mechanism, a dielectric window, a substrate holder, a tuning mechanism, air inlet and outlet holes, and the microwave resonant cavity described above.

Further, in the plasma chemical vapor deposition reactor, the bases of the two isosceles triangles forming the microwave resonant cavity are equal in length. The top of the upper cavity is provided with a coaxial probe coupling antenna. A frequency tuning plate is set at the bottom of the lower cavity, and a microwave shielding elastic piece is placed between the frequency tuning plate and the lower cavity wall. The foot of the quartz bell jar dielectric window is placed on the frequency tuning plate and well-sealed. The top contour of the quartz bell jar dielectric window is higher than the interface of the upper and lower cavities. The substrate holder is set in the middle of the frequency tuning plate. An air inlet and two air outlets on both sides of the substrate holder are given in the frequency tuning plate.

Further, in the plasma chemical vapor deposition reactor, the base of the isosceles triangle forming the upper cavity is longer than that of the isosceles triangle forming the lower cavity. The upper cavity is provided with a coaxial circumferential coupling antenna on the top. The inner side of the top of the upper cavity is provided with a well-sealed quartz ring dielectric window which matches with the coaxial circumferential coupling antenna. In the center of the coaxial circumferential coupling antenna is an air inlet running through the microwave resonant cavity. At the bottom of the lower cavity, a frequency tuning plate is set. Between the frequency tuning plate and the lower cavity wall, a microwave shielding elastic piece is placed. The substrate holder is set in the middle of the frequency tuning plate. Two air outlets on both sides of the substrate holder are given in the frequency tuning plate, and a total air outlet is given at the bottom of the lower cavity.

Further, in the plasma chemical vapor deposition reactor, the base of the isosceles triangle forming the upper cavity is shorter than that of the isosceles triangle forming the lower cavity. The upper cavity is provided with a coaxial probe coupling antenna. A quartz plate dielectric window is horizontally set in the middle of the upper cavity and stuck onto the upper cavity wall. An air inlet is given at the upper cavity wall below the quartz plate dielectric window. A frequency tuning plate is set at the bottom of the lower cavity. Between the frequency tuning plate and the lower cavity wall, a microwave shielding elastic piece is placed. A substrate holder is set in the middle of the frequency tuning plate. On both sides of the substrate holder, two air outlets are given. Besides, a total air outlet at the bottom of the lower cavity is given.

Further, in a structure comprising an upper cylindrical cavity and a lower cylindrical cavity, the plasma chemical vapor deposition reactor is provided, which comprises a microwave coupling mechanism, a dielectric window, a substrate holder, a tuning mechanism, air inlet and outlet holes, and the microwave resonant cavity according to claim2. The top of the upper cavity is provided with a coaxial circumferential coupling antenna. The inner side of the top of the upper cavity is provided with a well-sealed quartz ring dielectric window which matches with the coaxial circumferential coupling antenna. In the center of the antenna is an air inlet running through the microwave resonant cavity. A central first frequency tuning plate is set in the middle of the lower cylindrical cavity, and a substrate holder is set in the middle of the first frequency tuning plate. A second frequency tuning plate perpendicular to the first frequency tuning plate is set around the substrate holder. Two air outlets are given in the second frequency tuning plate on both sides of the substrate holder, and a total air outlet is given at the bottom of the cavity.

When microwaves are coupled into the microwave resonant cavity from the upper part of the reactor, it is hoped that a highly intensive and uniformly distributed focused electric field can be formed at the bottom center of the resonant cavity. Based on the principle of reflection and interference of electromagnetic waves, the strongly focused electric field in this invention is formed by adjusting the base lengths, the base angles and the centroid distance. According to specific applications, different dielectric windows, microwave coupling modes and reaction gas inlet and outlet modes can be selected in the resonant cavity. With simple structures, the resonant cavity is convenient and flexible.

