Microwave plasma CVD apparatus

Abstract: A microwave CVD apparatus comprises a rectangular applicator with microwave inlets, a bell jar with an inlet and an outlet for reaction gas arranged in the applicator, and a sample-receiving table. Reaction gas is introduced into the bell jar and plasma of the reaction gas is generated therein. At least one of walls of the applicator is movable so as to change distribution of plasma intensity continuously, so that material is uniformly deposited on the whole surface of the sample.

Description: The present invention relates to a microwave plasma CVD apparatus with the features of the introductory portion of claim 1. In such an apparatus microwave is supplied into an applicator, plasma of reaction gas (for example, mixed gas of hydrogen and hydrocarbon, mixed gas of silane and nitrogen, or the like) is generated in a bell jar provided in the applicator, and a sample is exposed in the plasma atmosphere for a long time to deposit material such as diamond on the surface of the sample. Figs. 5 and 6 show structure of an example of a conventional microwave plasma CVD apparatus. Fig. 5 is an explanatory view showing structure of the apparatus shown from a microwave travel direction. Fig. 6 is an explanatory view of the same shown from a direction perpendicular to the microwave travel direction. In the drawings, numeral 101 is an applicator allowing microwaves to enter therein from a plurality of directions, numeral 102 is a bell jar, numeral 103 is a circular sample such as a silicon wafer, and numeral 104 is a rotary sample-receiving table. The rotary sample-receiving table 104 is arranged in the bell jar 102 comprising a silica tube provided in the applicator 101. The applicator 101 is composed of walls fixed by the welding or the like. In using the above apparatus, the inner pressure of the bell jar 102 is set at about 1·3 x 10⁻³ Pa (10⁻⁵ Torr) by exhaust, and a mixed gas of, for example, hydrogen and hydrocarbon or carbon dioxide is charged into the bell jar 102 to a pressure of about 1·3 x 10³ to 5·3 x 10³ Pa (10 to 40 Torr). Then, microwave is supplied into the applicator 101 to generate plasma of the mixed gas in the bell jar 102. Figs. 7 and 8 show distribution of plasma intensity in the plasma CVD apparatus shown in Fig. 6 along the microwave travel direction. In the drawings, numeral 107 is plasma. When the sample 103 is placed on the sample-receiving table 104 and the table 104 is rotated in order to expose the sample 103 in the plasma atmosphere, material such as diamond is deposited on the surface of the sample 103. In the conventional plasma CVD apparatus, however, the applicator is composed of walls (ceiling and side walls) fixed by the welding as stated above to form a rectangular space, so that only plasma having a single intensity distribution is generated. When a film is formed on the sample 103 under this distribution of plasma, since the sample 103 is rotated about the center of the table 104 so that exposure time of a peripheral portion of the sample 103 in the plasma atmosphere is shorter than that of a central portion thereof, film thickness of the peripheral portion becomes thinner than that of the central portion. Accordingly, there has been a problem that the conventional plasma CVD apparatus cannot make samples with uniform film thickness. A microwave CVD apparatus as state of the art is known from EP-A-0 326 998. The applicator of said microwave CVD apparatus is provided with a plunger, moveable perpendicular to the microwave advancing direction in the wave guide for varying the length of the cavity resonator and for reducing the ratio of reflected power to input power. It is an object of the present invention to provide a microwave plasma CVD apparatus capable of uniformly depositing material on a sample by continuously changing the distribution of plasma intensity. In accordance with the aforesaid, in the apparatus of the present invention, distribution of plasma intensity is continuously changed by moving at least one of the walls of the cavity resonator which are provided in parallel to the travel direction of the microwaves in the cavity resonator perpendicular to the travel direction of the microwaves, so that plasma can be uniformly distributed on the whole surface of the sample, resulting in uniform deposition of material on the whole surface of the sample. Fig. 1 is an explanatory view showing structure of an embodiment of the present invention shown from a microwave travel direction; Fig. 2 is an explanatory view showing structure of the embodiment of Fig. 1 shown from a direction perpendicular to the microwave travel direction; Figs. 3 and 4 are explanatory views showing change in distribution of plasma intensity in the apparatus of the present invention observed by moving movable sidewalls; Fig. 5 is an explanatory view showing structure of a conventional plasma CVD apparatus shown from a microwave travel direction; Fig. 6 is an explanatory view showing structure or a conventional plasma CVD apparatus shown from a direction perpendicular to the microwave travel direction; and Figs. 7 and 8 are explanatory views showing distributions of plasma intensity in a conventional plasma CVD apparatus. Figs. 1 and 2 show structure of an embodiment of an apparatus of the present invention. Fig. 1 is an explanatory view showing structure of an embodiment shown from a microwave travel direction, and Fig. 2 is an explanatory view showing structure of an embodiment shown from a direction perpendicular to the microwave travel direction. In the drawings, numeral 1 is an applicator forming a cavity resonator in which microwaves can be supplied thereinto from a plurality of directions and walls (side walls, ceiling and bottom wall) are made movable. In the present specification, the term "wall" includes a side wall, a top wall (i.e. ceiling), and a bottom wall. Numeral 2 is a bell jar, numeral 3 is a sample, numeral 4 is a rotary sample-receiving table, numeral 5 is a movable side wall, and numeral 6 is a movable ceiling. In the above embodiment, microwave can be supplied into the applicator 1 from two directions, and the bell jar 2 is airtightly arranged in the applicator 1 comprising movable side walls 5 and movable ceiling 6. In the bell jar 2, the rotary sample-receiving table 4 on which the sample 3 is to be placed is arranged. The table 4 is rotated by a driving mechanism (not shown) placed outside the applicator 1. After inner pressure of the bell jar 2 is set at about 10⁻⁵ Torr by exhaust, reaction gas is introduced into the bell jar 2 from the upper portion thereof and the inner pressure is controlled in the range of 10 to 40 Torr. While the sample-receiving table 4 is rotated at a speed in the range of 4 to 20 r.p.m., microwaves are supplied into the applicator 1 from two directions to generate plasma of reaction gas in the bell jar 2. After a predetermined time passes from the beginning of generation of plasma, the distribution of plasma intensity is continuously changed by moving the movable side walls 5 or movable ceiling 6, whereby material is deposited on the sample 3. By continuously changing the distribution of plasma intensity, mean intensity of plasma on the surface of the sample 3 for a certain period is kept uniform on every point whereby material is uniformly deposited on the whole surface of the sample 3. Figs. 3 and 4 show examples of change in distribution of plasma intensity due to movement of the movable side walls 5. Plasma shown in Fig. 3 is generated when the distance between side walls and the distance between a ceiling and a bottom wall are so designed as to make electric field mode in a cavity to be TE₂₁. When the distance between side walls is enlarged, distribution of plasma intensity gradually changes from distribution shown in Fig. 3 to that shown in Fig. 4. It is considered that such change in plasma intensity is caused because electric field mode in the cavity changes from TE₂₁ to TE₃₁. In general, electric field mode in the cavity changes from TE 1n to TE 2n , TE 3n ,..., TE kn (wherein n is integar) with enlargement of distance between side walls. Similarly, electric field mode in the cavity changes from TE m1 to TE m2 ,..., TE mℓ (wherein m is integar) with enlargement of distance between the ceiling and bottom wall. Leakage of microwaves from the gaps formed by providing the movable side walls 5 and the movable ceiling 6 can be prevented by providing the movable side walls 5 and the movable ceiling 6 with choke constructions. In addition, when the table 4 is so made as to move up and down, plasma intensity on the surface of the sample 3 is further equalized. Further, more uniform film can be obtained by moving plasma also in the direction of microwave travel direction by a phase converter from the outside. As is mentioned above, according to the present invention, the distribution of plasma intensity can be continuously changed, whereby a uniform film is deposited on a sample and the production efficiency of film deposition on a sample is improved.

Claims: Microwave plasma CVD apparatus, comprising a rectangular applicator (1) having microwave inlet means and forming a cavity resonator, a bell jar (2) arranged in the applicator and having an inlet and an outlet for reaction gas, and a sample-receiving table (4) arranged in the bell jar, wherein microwaves and reaction gas are introduced into the bell jar, to generate plasma of the reaction gas and to deposite material on the surface of a sample (3) arranged on the table (4), characterized in that at least one of the walls (5, 6) of the cavity resonator which are provided in parallel to the travel direction of the microwaves in the cavity resonator are movable perpendicular to the travel direction of the microwaves. Apparatus of claim 1, characterized in that the sample-receiving table (4) is rotatable. Apparatus of claim 1 or 2, characterized in that the sample-receiving table (4) is movable up and down. Apparatus of one of claims 1 to 4, characterized in that the movable walls (5, 6) each are provided with choke constructions. Apparatus of one of claims 1 to 4, characterized in that microwave inlets are provided at a plurality of walls (5) of the applicator (1). Apparatus of one of claims 1 to 5, characterized in that microwave inlets are provided on opposite side walls (5) of the applicator (1).

Inventors: TAKAMURA FUMIO, TAKAMURA, FUMIO
Applicants: JAPAN RADIO CO LTD, NEW JAPAN RADIO CO., LTD.
Application year: 1991
Main classification: C23C16
IPC codes: H01L21, H01J37, C23C16