JPH07122141B2 - Microwave plasma CVD device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to a microwave plasma CVD method, or ECR
The present invention relates to an apparatus for uniformly forming or etching various functional thin films such as a diamond film on a large area substrate by using (Electron Cyclotron Resonance) type plasma CVD method.

b. Conventional technology As an apparatus for vapor phase synthesis of diamond film on a substrate, CVD (Chemical Vapor
Por deposition (chemical vapor deposition) method is known.

FIG. 7 shows a microwave plasma which has been conventionally used.
It is a conceptual diagram of an example of a CVD apparatus. A case of processing a substrate, for example, synthesizing a diamond film using the same apparatus will be described. The output power of the microwave oscillator 1 frequency 2.45 GHz _z is guided into the reaction chamber 3 through the enlarged waveguide 2 of the enlarged standard waveguide. The reaction chamber 3 is made of a material such as quartz that allows microwaves to pass therethrough with little loss, and a mixed gas of a raw material gas such as a hydrocarbon gas and a hydrogen gas is introduced into the reaction chamber 3 from a gas supply pipe 4. By exhausting at a constant flow rate from the exhaust pipe 5, the inside of the reaction chamber 3 is maintained at a constant pressure. The introduced gas is turned into plasma by the microwave power supplied through the expanding waveguide 2, and forms a diamond film on the substrate 7 placed on the substrate table 6.

c. Problem to be Solved by the Invention According to the above-mentioned conventional technique, a diamond film having good crystallinity can be formed on the large area substrate 7 having a diameter of about 5 inches (127 mm). However, if the synthetic area of the diamond film is further expanded, there are the following problems.

In FIG. 7, microwave power from the microwave oscillator 1 is transmitted through the reaction chamber 3 through the same rectangular or cylindrical expansion waveguide 2 formed by expanding a rectangular waveguide in a tapered shape.
Will be introduced to. Normally, the electric field mode of the microwave propagating in the rectangular waveguide is a TE ₁₀ mode in which the electric field is perpendicular to the microwave traveling direction, as shown in FIG. 6 (b), and the rectangular waveguide is expanded as it is. When it is done or when it is expanded into a cylindrical shape, the electromagnetic field mode becomes TE ₁₀ mode (rectangular waveguide) or TE ₁₁ mode (circular waveguide) of the same form.
The TE ₁₀ or TE ₁₁ mode is the basic mode of the TE mode, and is capable of propagating an electromagnetic wave (microwave) of the same size and the lowest frequency as other modes.

In other words, it has the feature that the cross-sectional size can be minimized at the same frequency. So these TE ₁₀ , T
When trying to generate a body-shaped plasma using the E ₁₁ mode, if the waveguide is expanded too much, other unwanted modes are likely to be excited at the same time, and the electric field becomes non-uniform, resulting in plasma. It becomes separated and becomes unstable. Then, there is a problem that it is difficult to form one large plasma in one unit and a large area substrate cannot be processed.

The present invention has been made in view of the above points, and an object thereof is to solve the above-mentioned problems, to generate a large plasma in a reaction chamber, and to perform uniform thin film formation on a substrate having a large area or uniform etching treatment. Another object is to provide a microwave plasma CVD apparatus.

d. Means for Solving the Problems The constitution of the present invention for achieving the above-mentioned object is to supply a gas to a reaction chamber in which a substrate is placed, and to set an arbitrary gas pressure while exhausting, In a CVD apparatus that excites the gas to generate plasma and form a thin film on the substrate or perform an etching process by introducing a microwave into the reaction chamber through a transmission means, the following (1), It is as in (2).

(1) The transmission means includes a rectangular waveguide, and a resonance hole mode converter having a plurality of slit-shaped coupling holes each having a length of about 1/2 wavelength of a waveguide length of a microwave used, A circular waveguide containing a reaction chamber therein, and the microwave is converted from the rectangular waveguide mode to a predetermined mode of the circular waveguide through the mode converter.

(2) The transmission means includes a rectangular waveguide, and a resonant hole mode converter having a plurality of slit-shaped coupling holes each having a length of about 1/2 wavelength of a waveguide length of a microwave used. And a circular waveguide that houses a reaction chamber therein. The microwave is converted from the rectangular waveguide mode to a predetermined mode of the circular waveguide through the mode conversion unit, and the circular waveguide is used. An electromagnetic coil is arranged around the tube so as to surround the reaction chamber, and a current is applied to the coil to apply a magnetic field to the plasma.

e. Operation Since the present invention is configured as described above, a plurality of slit-shaped slits provided in the resonance hole mode conversion unit and having a length of about 1/2 wavelength of the waveguide length of the microwave used. Microwave propagation is magnetically coupled through the coupling hole of the TE waveguide to the TE ₁₀ mode of the rectangular waveguide to the TE ₀₁ mode of the circular waveguide.
The mode is directly converted to E ₂₁ , TE ₃₁ , and TE ₁₂ modes.

The operation will be described in detail with reference to FIGS. 6 (a) to 6 (e). This is an example of forming a resonant hole mode converter to convert the TE ₁₀ mode of a rectangular waveguide to the TE ₀₁ mode of a circular waveguide.

In the same figure (a), the rectangular waveguide 12a with the terminal short-circuited
The electromagnetic wave propagating inside is divided into two by a partition plate 18 provided in the central axis direction of the rectangular waveguide 12a and travels. On one side near the terminal end, two coupling holes 19 having a length of about 1/2 of the guide wavelength λg and a center interval of about λg / 2 and forming an angle of about 90 ° are provided on the side wall of the waveguide 12a. And on the other hand, the partition plate 1
Two more coupling holes 19 are similarly provided at symmetrical positions with respect to the line 8.

By the partition plate 18 at the entrance of the rectangular waveguide 12a of FIG.
The two separated electromagnetic waves propagate in phase. The end of the circular waveguide 12b is fixed and connected at a right angle to the side wall on one side of the waveguide 12a which is divided into two inside. The rectangular waveguide 12a and the circular waveguide 12b are separated from each other by the common side wall, and the four coupling holes 19 provided in the side wall are symmetrical in the cross section of the circular waveguide 12b. It is arranged.

The electric field component of the TE ₁₀ mode is perpendicular to the traveling direction of the microwave, that is, parallel to the waveguide cross section, and is shown in FIG. 6 (b). The magnetic field component is perpendicular to the electric field component (dotted line in FIG. 6B) and forms a closed curve parallel to the traveling direction of the electromagnetic wave. There are two sets of closed magnetic field components per wavelength,
The winding directions of adjacent closed magnetic field lines are opposite to each other. Partition board
One of the electromagnetic waves separated by 18 is propagated by coupling two adjacent closed magnetic field components to the circular waveguide 12b through the two coupling holes 19. Ie circular waveguide 12b
The entering magnetic field component also forms a closed magnetic field component whose magnetic field lines are parallel to the traveling direction of the electromagnetic wave. The distance between the centers of the two coupling holes 19 is λg / 2, and the two coupling holes 1
The directions of the magnetic lines of force of the two closed magnetic field components entering the circular waveguide 12b side through 9 simultaneously go to the center of the cross section of the circular waveguide 12b or to the outside, as shown in FIG. 6 (e). The other electromagnetic wave separated by the partition plate 18 also propagates to the circular waveguide 12b according to the same principle.

After all, the magnetic field component coupled from the rectangular waveguide 12a to the circular waveguide 12b through the coupling hole 19 has magnetic lines of force in the circular waveguide 12b that are parallel to the traveling direction of the electromagnetic wave, and is approximately 90 °. It forms four closed magnetic field components at an angle of °. Therefore, the electric field component is shown in FIG. 6 (e).
As shown in FIG. 6 (d), a curved line that closes itself is formed so as to penetrate a magnetic field component that is closed as shown in FIG. 6, and is converted into a TE ₀₁ mode having concentric electric field components in the circular waveguide 12b. It was done.

A TE ₀₁ mode circular waveguide can have larger dimensions than other modes at the same frequency,
There is no theoretical limit. Therefore, large plasma can be generated. Further, the mode converter used in the present invention is a direct conversion using a waveguide, and can convert a high power microwave with almost no loss.

Next, the present invention is a so-called ECR in which a magnetic field is further applied to the apparatus of the microwave plasma CVD method by an electromagnetic coil.
The plasma CVD method is superimposed.

f. Embodiment Hereinafter, a preferred embodiment of the present invention will be exemplarily described in detail with reference to the drawings.

Embodiment 1: FIGS. 1 and 2 are views of a microwave plasma CVD apparatus showing an embodiment of the present invention, FIG. 1 is a schematic explanatory view, and FIG. 2 is a line II-II in FIG. It is sectional drawing of the rectangular waveguide by an arrow.

In the figure, the rectangular waveguide 12a connected to a microwave oscillator (not shown) has a cross-section enlarged in the direction of the short side near the end, and is bisected in the central axis direction by a partition plate 18, and The ends are short-circuited. Each of the side walls at the end of the bisected waveguide 12a has a slit shape having a length of about 1/2 of the guide wavelength λg of the microwave used, and the distance between the centers thereof is about λg / 2. About 9
Two coupling holes 19 forming an angle of 0 °, that is, four coupling holes 19 are radially provided. In addition, a circular waveguide 12b is fixed and connected to the side wall portion having the coupling hole 19. Inside the circular waveguide 12b, a quartz reaction chamber 13 is disposed so as to be housed therein, and the reaction chamber 13 is connected to a vacuum pump (not shown) through an exhaust port 15
It is mounted in a vacuum chamber 20 having a. Substrate 17 is reaction chamber 13
It is placed on a substrate table 16 disposed inside. In this state, from the gas supply pipe 14, a mixed gas of methane gas (CH ₄ ) and hydrogen gas (H ₂ ) (volume mixing ratio 1: 100), or other additive gas (for example, O ₂ , CO, CO ₂
More H ₂ O) gas mixture was added traces of such a gas flow rate 300
Introduced at scc / min, the pressure in the reaction chamber 13 from the exhaust port 15 is 40T
The substrate table 16 was evacuated to orr, and electrically heated by an external power source (not shown).

Thus, when a microwave having a frequency of 2.45 GHz and an electric power of 3 kw was introduced into the reaction chamber 13, a plasma that was wider than ever was generated. Therefore, when a circular silicon wafer having a diameter of 5 inches (127 mm) was used as the substrate 17 and a film forming experiment was carried out for 4 hours, a uniform diamond film having a thickness of about 3 μm was obtained. The crystal was also close to natural diamond by analysis of Raman spectrum and the like.

Embodiment 2: FIG. 3 is a microwave plasma CVD of another embodiment of the present invention.
The schematic explanatory drawing of an apparatus is shown. Similar to FIG. 1, FIG. 3 shows that the microwaves mode-converted from the TE ₁₀ mode of the rectangular waveguide 12a to the TE ₀₁ mode of the circular waveguide 12b through the magnetic field coupling hole 19 are Introduced in 12b. Circular waveguide 12b
Themselves form part of the reaction chamber 13 and the vacuum chamber 20. The circular waveguide 12b is kept in airtightness by an airtight window 21 and an O-ring 22 made of a quartz plate arranged in contact with the side wall of the rectangular waveguide 12a provided with the coupling hole 19. The airtight window 21 may be made of an alumina plate or another dielectric material other than the quartz plate as long as it is a material that transmits microwaves without loss.

In this embodiment having such a structure, when plasma is generated under the same synthesis conditions as in the first embodiment and a diamond film forming process is performed, the same result as in the first embodiment is obtained. Further, in this embodiment, the circular waveguide 12b also serves as the reaction chamber 13, and the reaction chamber 13 of the first embodiment is not used, so that the synthetic area of the diamond film can be further expanded.

The positions of the airtight window 21 and the O-ring 22 for maintaining airtightness are not limited to the positions shown in FIG. 3, and the circular waveguide 12b does not come into contact with the side wall portion having the coupling hole 19. It can be installed at any distant position. Further, the substrate table 16 is provided with a position adjusting mechanism 23 for moving the position of the substrate 17 placed on the substrate table 16 up, down, left and right in the figure, and the adjusting mechanism 23. The adjustment knob 23a can be arbitrarily adjusted from the outside.

Embodiment 3: FIG. 4 shows a schematic explanatory view of a microwave plasma CVD apparatus according to still another embodiment of the present invention. This figure shows the first embodiment.
In addition to the same structure as shown in FIG. 1, a solenoid type electromagnetic coil 24 is arranged around the circular waveguide 12b and surrounds the reaction chamber 13. By passing a current through the electromagnetic coil 24, it is possible to apply a magnetic field to the plasma to further accelerate the motion of ionized particles in the plasma and significantly increase the intensity of the plasma. As a result, it became possible to double the growth rate of the diamond film. In this case, the applied magnetic field strength is several hundred Gau.
It is preferably about ss to 3,000 Gauss.

Example 4: In FIG. 4, when the plasma is placed in a magnetic field atmosphere,
In particular, the applied magnetic field strength is called the so-called ECR condition, and it is set to a specific value of 875 Gauss in the microwave frequency 2.45 GHz band, and various functional thin films, insulating films, and high temperature superconducting films are formed and etched. Processing can be performed.

In normal microwave plasma, plasma is not generated when the gas pressure in the reaction chamber is set to 1 Torr or less, but high-density plasma can be generated under the above ECR conditions by applying a magnetic field. The plasma under the ECR condition is characterized by less damage to the thin film due to ion bombardment and efficient and high-quality film forming and etching processes. Also in this embodiment, by adopting this method and appropriately selecting the raw material gas, the SiO ₂ film, the SiN
Various thin films such as films, α-Si films, BN films, and high temperature superconducting films can be formed and etched. Furthermore, in addition to this, according to this embodiment, the diameter is 30 cm.
The uniform plasma described above can be generated, and it has a major feature that it can process a large area several times as large as the conventional ECR plasma CVD method using the TE ₁₁ type resonance mode.

Embodiment 5: FIG. 5 is a schematic explanatory view of a microwave plasma CVD apparatus according to still another embodiment of the present invention. This drawing has the same configuration as that of FIG. 3 shown in the second embodiment, and further includes a solenoid type electromagnetic coil 24 and a circular waveguide 12b which also serves as the reaction chamber 13 as in the third embodiment. It is arranged.
Also in this embodiment, the same effects as those of the third and fourth embodiments can be obtained. It should be noted that the position adjustment mechanism 23 allows the substrate stand 16 to move the circular waveguide 12 even in the vacuum chamber 20.
The position can be arbitrarily moved up and down, left and right, and back and forth along the axial direction of b, and the substrate 17 can be set to an optimum position for plasma.

The movability of the substrate table 7 can be applied to the first, third and fourth embodiments.

According to the apparatus of each of the embodiments described above, the reaction chamber can be enlarged to generate a large-sized, stable and high-density plasma, and a diamond film can be formed on a substrate having a large area, which has never been seen before. Further, the electromagnetic wave mode conversion unit in the present invention is a direct conversion by a waveguide, and has an effect that high-power microwaves can be converted with almost no loss and efficiently supplied to plasma. Then, by applying a magnetic field, the synthesis rate of the diamond film can be improved.

The technique of the present invention is not limited to the technique in the above-described embodiment, and may be implemented by means of another aspect having a similar function, and the technique of the present invention may be variously modified within the scope of the above configuration. Can be added.

g. Effect of the Invention As is apparent from the above description, according to the microwave plasma CVD apparatus of the present invention, the microwave transmission means is composed of a rectangular waveguide, a resonant hole mode converter and a circular waveguide, Direct conversion of microwaves into a predetermined mode of circular waveguide,
That is, high-power microwaves can be converted with almost no loss and efficiently supplied to plasma. Further, since a magnetic field can be applied to this by an electromagnetic coil, a large plasma can be generated in the reaction chamber of the apparatus, and a uniform thin film can be formed on a substrate having a large area, or a uniform etching treatment can be performed. .

Furthermore, when a magnetic field is applied, by performing plasma processing under ECR conditions, various functional thin films can be formed at high speed on a substrate with a large area, or etching processing can be performed, which is extremely valuable industrially. .

[Brief description of drawings]

1 and 2 are views of a microwave plasma CVD apparatus showing an embodiment of the present invention. FIG. 1 is a schematic explanatory view, and FIG. 2 is a rectangle taken along the line II-II of FIG. FIG. 3 is a sectional view of the waveguide, and FIG. 3 is a microwave plasma of another embodiment of the present invention.
4 is a schematic explanatory view of a CVD apparatus, FIG. 4 is a schematic explanatory view of yet another embodiment of the present invention, FIG. 5 is a schematic explanatory view of yet another embodiment of the present invention, and FIG. 6 is a perspective view showing the main structure of the mode converter used in FIG. 6, FIGS. 6 (b) to 6 (e) showing the electromagnetic field distribution in each mode of the converter, and FIG. It is a conceptual diagram of an example of the microwave plasma CVD apparatus which is doing. 12a ... Square waveguide, 12b ... Circular waveguide, 13 ... Reaction chamber, 17 ... Substrate, 18 ... Partition plate, 19 ... Coupling hole, 24 ... Solenoid electromagnetic coil.

Claims (2)

[Claims] 1. A gas is supplied to a reaction chamber in which a substrate is placed, the gas pressure is set to an arbitrary value while exhausted, and a microwave is introduced into the reaction chamber through a transmission means. Exciting the gas to generate plasma,
In the apparatus for forming a thin film on the substrate or for performing an etching process, the transmission means includes a rectangular waveguide and a plurality of slit-shaped coupling holes each having a length of about 1/2 wavelength of a waveguide wavelength of a microwave used. A resonance hole mode converter provided and a circular waveguide that accommodates the reaction chamber therein, the microwave from the rectangular waveguide mode to the circular waveguide through the mode converter. A microwave plasma CVD apparatus characterized by converting to a predetermined mode. 2. A gas is supplied to a reaction chamber in which a substrate is placed, the gas pressure is set to an arbitrary value while exhausting the gas, and a microwave is introduced into the reaction chamber through a transmission means. Exciting the gas to generate plasma,
In the apparatus for forming a thin film on the substrate or for performing an etching process, the transmission means includes a rectangular waveguide and a plurality of slit-shaped coupling holes each having a length of about 1/2 wavelength of a waveguide wavelength of a microwave used. A resonance hole mode converter provided and a circular waveguide that accommodates the reaction chamber therein, the microwave from the rectangular waveguide mode to the circular waveguide through the mode converter. An electromagnetic coil is arranged around the circular waveguide so as to surround the reaction chamber while converting to a predetermined mode, and a current is passed through the coil to apply a magnetic field to the plasma. Microwave plasma CVD equipment.