JP2676091B2 - How to make a thin film - Google Patents

Description

The present invention relates to a method for producing a thin film.

[Summary of the Invention]

INDUSTRIAL APPLICABILITY The present invention applies a microwave electric field and an external magnetic field, introduces a reactive gas into the space or its vicinity using the interaction thereof, and activates, decomposes, or reacts with plasma, so that the whole thin film forming object is formed. In forming a thin film to form a film on the surface, give a limited pulse shape to the microwave electric field, and that pulse shape is stable with other pulse shapes or stationary continuous waves of the same wavelength or stationary continuous waves of other wavelengths. By generating plasma while coexisting with each other, it is possible to form a uniform film against unevenness and realize a large power consumption.

(Prior art)

Conventionally, formation of a thin film has been attempted by many means. For example, it can be said that the diversification of the types such as the CVD method, the sputtering method, and the MBE method brings many possibilities for material development. In particular, it is said that the plasma CVD method, which attempts to form a thin film by activation, decomposition, and reaction using plasma, enables the synthesis of materials that deviate from the stoichiometric viewpoint, and active research and development including mechanism analysis. Have advanced many methods such as high frequency excitation, microwave excitation, and hybrid resonance by magnetic field. A CVD method using resonance by a magnetic field (hereinafter,
With the magnetic field plasma CVD method), it is possible to form a film with high efficiency by using plasma with a much higher density than in the past, so development has been promoted, and it has been expected to be applied in various fields. But,
In the actual film formation work, although it is said that high-quality film formation that has never been possible with the magnetic field plasma CVD method, on the surface of the film-forming substance having an uneven surface,
It is difficult to form a film having a uniform thickness without being affected by unevenness, and therefore practical application as an industrial production means has not progressed at all. It depends on the film formation state as described above, but also because the magnetic field plasma CVD method involves enormous power consumption during its operation.

〔Purpose〕

The present invention is a magnetic field plasma CVD capable of high quality film formation.
The law aims to provide effective operation technology so that it can have higher versatility as a practical production technology.

[Configuration of the invention]

The present invention is characterized by adding a composite wave of a pulse wave and a standing continuous wave in the production of a thin film using a plasma CVD method that is a type of generating plasma using a magnetic field.

Another structure of the present invention uses a composite wave in which a plurality of rectangular pulse waves are combined in the production of a thin film using a plasma CVD method that is a type of generating a plasma using a magnetic field, and the composite wave has two stages. It is characterized by having a peak value and being a discontinuous wave.

There are several possible pulse waveforms given to the microwave. FIG. 3 shows an example of the pulse waveform. (A) is an example in which two types of pulses having different peak values are combined. This is effective in increasing the production of a substance having a certain threshold and suppressing the production of a substance having a lower production energy than that. (B) is an example in which low power microwaves having the same frequency are combined as a stationary continuous wave, and (C) is an example in which electromagnetic waves having low power different frequencies are combined as a stationary continuous wave. This charging method is effective when the stability of the plasma cannot be maintained only by the pulse wave due to the structure of the apparatus or various conditions of film formation. By using such a charging method, it is possible to form a very uniform thin film even on a film-forming object having irregularities due to the characteristic of the pulse plasma that the nucleation is uniform on the substrate surface. As compared with the case where the film is formed by, the film can be formed more efficiently by concentrating high electric power on the pulse peak.

Now, the plasma CVD apparatus in the present invention is 0.3 to 30 to
rr The film is formed at a high pressure of preferably 0.3 to 3 torr by using high density plasma using "hybrid resonance".

These film-forming objects are arranged in a hybrid resonance space or in a space that maintains an active state apart therefrom, and the reaction products are coated on the surface of the object. For this purpose, an object having a surface to be formed is arranged in or near a region where the electric field strength of microwave power is the highest. In addition, high-density plasma is generated at a high pressure of 0.03 to 30 torr,
In order to maintain it, the space with the column is first 1 × 10 ^-4
ECR (Electron Cycloton Resonance) is generated under a low vacuum of ~ 1 × 10 ^-5 torr. A gas is introduced to change the plasma state to a high space pressure of 0.03 to 30 torr, preferably 0.3 to 3 torr while maintaining the plasma state, and the concentration of the product gas in this space per unit space is 10 compared to the conventional ECR CVD method. Increase the concentration by ² to 10 ⁴ times. Then, it becomes possible to form a film of a material that can be decomposed or reacted only at such a high pressure. For example, diamond, i-carbon (diamonda or carbon coating with fine crystal grains),
It is a high melting point metal or insulating ceramic coating.

That is, the present invention applies the force of a magnetic field to the conventionally known plasma CVD method using microwaves and uses the interaction between the electric field and the magnetic field of microwaves. However, 1 × 10 ^-4 ~
ECR (electron cyclotron resonance) conditions effective at 1 × 10 ^-5 torr are not used. The present invention has been carried out to form a film using high-density and high-energy plasma at a high pressure at which "hybrid resonance" of 0.03 to 30 torr is generated. Utilizing the high energy state in the hybrid resonance space, plasma excitation by pulse waves or a combination of pulse waves and stationary continuous waves is performed as described above, a large amount of active species is generated, and a uniform surface on the substrate surface is generated. Cause nucleation,
This enables the formation of thin film materials with excellent reproducibility.

As described above, the power input is pulse (average power 1.5 to 30K
W and pulse peaks are roughly three times higher.
The pulse wavelength of the first pulse wave is 1 to 10 ms, preferably 5 to 8 m
should be s. Further, since the strength of the applied magnetic field can be arbitrarily changed, there is a feature that resonance conditions of not only electrons but also specific ions can be set.

In addition to the configuration of the present invention, a high-energy state is maintained even after the high-density plasma is generated by the interaction between the pulse (or pulse + stationary continuous wave) microwave and the magnetic field, and then until the object surface is reached. In order to maintain it further, when light (for example, ultraviolet light) is irradiated at the same time, and energy is continuously given to the active species, the position (reaction 10 to 50 cm away from the region where the microwave electric field is maximum, that is, the high-density plasma generation region) Even at a position where the active state of the volatile gas can be maintained), carbon atoms excited in a high energy state exist, and it is possible to form a diamond film in a larger space. In the present invention, a cylindrical column is arranged in such a space, a film-forming object is arranged in this column, and a film is formed on the surface thereof.

 Examples are shown below to further describe the present invention.

〔Example〕

FIG. 1 shows a microwave plasma CVD apparatus capable of applying a magnetic field used in the present invention.

In this figure, this device has a plasma generation space (1), an auxiliary space (2) that can be maintained under reduced pressure, electromagnets (5) and (5 ') that generate a magnetic field and its power supply (25), pulse (and pulse +). Microwave oscillator (stationary continuous wave) (4), turbo molecular pump (8) constituting the exhaust system, rotary pump (14), pressure control valve (11), substrate holder (10 ') film forming object (10), Microwave introduction window (15), gas system (6), (7), water cooling system (18), (1
8 ') It is composed of a halogen lamp (20), a reflecting mirror (21), and a heating space (3).

First, the thin film forming object (10) is placed on the substrate holder (10 ') and is placed in the plasma generation space (1) through the gate valve (16). This substrate holder (10 ') is made of quartz so as not to disturb the microwave and magnetic field as much as possible.

As a manufacturing process, first, the whole is evacuated to 1 × 10 ⁻⁶ torr or less by a turbo molecular pump (8) and a rotary pump. Next, a non-product gas (a gas that does not form a solid after the decomposition reaction) such as hydrogen (6) is introduced into the plasma generation region (1) through the 30SCCM gas system (7), and this pressure is set to 1
× 10 ^-4 torr. A microwave with a frequency of 2.45 GHz is applied from the outside with a cycle of 8 ms in the pulse part. A magnetic field of about 2K gauss is applied from the magnets (5) and (5 ') to generate high density plasma in the plasma generation space (1). In the drawing, the gas was made to flow downward from above. However, it may be upward from the lower side, rightward from the left side, or leftward from the right side.

The non-product gas or electrons having higher energy than this high-density plasma region is the object (10) on the substrate holder (10 ').
On the surface of and clean the surface. Next, while introducing this non-product gas, a gas, especially a product gas (a gas that constitutes a solid after decomposition / reaction) is introduced from the gas system (7), and then the pressure of the space is already generated. While maintaining the state, the pressure is changed to 0.03 to 30 torr, preferably 0.1 to 3 torr, for example, 0.5 torr. By increasing the pressure in this space, the concentration of the product gas per unit space can be increased and the film growth rate can be increased.

In this way, once generate plasma at low pressure,
The active concentration of the product gas can be increased while maintaining the plasma state, active species excited by high energy are generated, and the active species are deposited on the object (10) on the substrate holder (10 '). , A thin film material is formed.

In FIG. 1, the magnetic field employs a Helmholtz coil system using two ring-shaped magnets (5) and (5 '). FIG. 2 shows the results of examining the electric and magnetic field strengths in the space (30) divided into four parts.

In FIG. 2 (A), the horizontal axis (X axis) is the horizontal direction (reactive gas release direction) of the space (30), and the vertical axis (R axis).
Indicates the diameter direction of the magnet. The curves in the drawings show the isomagnetic surface of the magnetic field. And the number shown on that line shows the strength of the magnetic field obtained when the magnet (5) is about 2000 gauss. When the strength of the magnet (5) is adjusted, the magnetic field strength is approximately uniform over a large area of the substrate formation surface in a large area in the space (100) (within 875 Gauss ± 185 Gauss) where the electrode and magnetic field interact. The drawing shows isomagnetic surfaces, especially ECR where line (26) is 875 Gauss.
It is an isomagnetic field surface that causes (electron cyclotron resonance) conditions.

As shown in FIG. 2 (B), the space (100) in which this resonance condition is generated is set to a region where the electric field is maximum. The horizontal axis of FIG. 2 (B) indicates the direction in which the reactive gas flows as in FIG. 2 (A), and the vertical axis indicates the strength of the electric field (electric field intensity).

Then, in addition to the electric field region (100), the region (100 ') corresponds to the maximum region. However, the magnetic field (FIG. 2 (A)) corresponding to this has very many uniform magnetic field planes.
That is, in the region (100 '), the variation in film thickness in the diameter direction (vertical axis direction in FIG. 2A) of the surface where the substrate is formed becomes large, and in the ECR condition part satisfying the resonance condition of (26'). Only a good quality film is produced. As a result, a uniform and homogeneous coating cannot be expected.

Needless to say, when a doughnut-shaped film is formed.

On the opposite side of the region (100) with respect to the origin symmetry, there is a region where the electric field is maximum and the magnetic field is constant over a wide region. When it is not necessary to heat the substrate, forming a film in such a space is also effective. However, it is difficult to obtain a means for heating without disturbing the microwave electric field.

As a result, in consideration of the ease of loading / unloading the substrate and heating, in order to obtain a uniform and uniform film, the area (100) in FIG. 2 (A) is the most industrially mass-producible area among the three areas. It was in an excellent position.

As a result, according to the present invention, when the substrate (10) is arranged in the region (100), if the substrate is circular, it is possible to form a uniform and uniform film with a size up to a radius of 100 mm, preferably up to a radius of 50 mm. Became.

To make the area even larger, for example, in order to obtain the same uniform film thickness in the area four times as large as this, if the frequency is set to 1.225 GHz instead of 2.4 GHz, the diameter of this space (R direction in FIG. 2 (A)) ) Can be doubled.

As a concrete example of using the present invention, diamond can be mentioned in the case of the composite pulse as shown in FIG. For diamond and hard carbon films, a structure composed of SP ³ bonds is said to be preferable, and it is important to remove SP ² bonds that are simultaneously formed during film formation. Normal,
Therefore, selective etching with H, 0 plasma is performed. According to the present inventors, the dissociation energy of SP ³ bond and SP ² bond is approximately 6: 5, and the first peak is 5 to 5. 50K
W, stronger than the second peak, for example, 5/6 4.6 to 4
By setting it to 6KW, the increase in SP ³ coupling was realized more reliably. Around the time when the cross section of the thin film was observed with a scanning electron microscope, crystalline diamond was growing in a granular form. In particular, the size of the grains was 5 to 10 times larger than that in the case where a microwave having a steady value (continuous wave) was used. Further, until now, the growth started to have a small diameter, and as the thickness increased, some diamonds became thicker, resulting in poor adhesion to the surface to be formed. However, in the pulse wave method of the present invention, it was also morphologically presumed that the thickness of the diamond on the surface to be formed was large and the adhesion as a crystal was large. An electron diffraction image shows that diamond (single crystal grain) spots are seen and the average output power is 1.5 KW.
Or more, it became a film in which the diamond structure became clearer.

The composite form of pulse and standing continuous wave as shown in FIGS. 3B and 3C can be applied in a wide range of fields. For example, in the case of the same wavelength as shown in FIG. 3 (B), uniform adhesion and power saving could be realized in an appropriate and necessary energy region by combining microwaves and high frequencies. Also in the case of another wavelength region as shown in FIG. 3C, when a microwave pulse was applied to the stationary continuous wave in the high frequency region, very good uniform adhesion was obtained. In such a combination of different wavelengths, various combinations such as a combination of a DC pulse to a microwave continuous continuous wave can be considered according to the purpose. According to the present inventors, as an example which can be formed by them, for example, a silicon carbide polycrystalline film can be formed on a substrate by using a silicon carbide gas (methylsilane). It is also possible to simultaneously flow the boride and the nitride to form a boron nitride coating, for example by reacting diborane with nitrogen. Bi (bismuth) type, YBCO type, Tl
A (thalium) -based or V (vanadium, non-copper) -based oxide superconducting material thin film may be formed. Aluminum nitride, aluminum oxide, zirconia, and boron phosphide can be similarly produced. It is also possible to form a multilayer film of these and diamond. The formation of films of refractory conductors of tungsten, titanium, molybdenum or their silicides on the body can also be made by the decomposition reaction of the halides or hydrides of these metals themselves or by their reaction with silanes.

〔The invention's effect〕

In the plasma film formation by the pulse or the composite wave of the pulse and the continuous wave in the present invention, the growth rate of the formed coating film is increased, and the coating film can be formed even on the side surface of the object having the uneven surface.

By adopting the method experimentally found by the present invention, it becomes possible to manufacture under a wider range of conditions than the conventionally prepared conditions for forming a film having at least a portion of crystallinity. In addition, compared to the conventional method, it became possible to form a uniform thin film on the surface of large unevenness with lower energy consumption than a continuous continuous wave.

[Brief description of the drawings]

FIG. 1 shows an outline of a microwave CVD apparatus using a magnetic field / electric field interaction used in the present invention. FIG. 2 shows magnetic field and electric field characteristics by computer simulation. FIG. 3 shows a schematic diagram of the composite pulse in the present invention. 1 ... Plasma generation space 4 ... Microwave oscillator 5,5 '... External magnetic field generator 8 ... Turbo molecular pump 10 ... Object or substrate for film formation 10' ... Substrate holder 20 ... Halogen lamp 21 ... …Reflector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-123096 (JP, A) JP-A-2-102197 (JP, A)

Claims (6)

(57) [Claims] 1. A method of forming a thin film, which comprises adding a composite wave of a pulse wave and a standing continuous wave in the formation of a thin film using a plasma CVD method in which plasma is generated by using a magnetic field. 2. A method for producing a thin film according to claim 1, wherein the pulse wave and the standing continuous wave have the same wavelength. 3. A method for producing a thin film according to claim 1, wherein the pulse wave and the standing continuous wave have different wavelengths. 4. The method for producing a thin film according to claim 1, wherein the pulse wave and the standing continuous wave are microwaves. 5. The method for producing a thin film according to claim 1, wherein the composite wave has a two-step peak value. 6. A composite wave in which a plurality of rectangular pulse waves are combined is used in the production of a thin film using a plasma CVD method in which a magnetic field is used to generate plasma, and the composite wave has a two-step peak value. A method for producing a thin film, which has a discontinuous wave.