JPH0627340B2 - Hybrid plasma thin film synthesis method and device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hybrid plasma generator that can be used in a thin film synthesizing method, and is applied to various thin film manufacturing technologies, electronic circuit manufacturing technologies, and various sensor manufacturing technologies. It can be widely applied.

(Prior Art) Conventional thin-film synthesis methods using plasma have been performed by generating low-pressure plasma by discharge of high frequency, microwave, pulse, direct current, or the like. Due to the stability of discharge, the cost, and the properties of the resulting thin film, DC discharge is rarely used, and high frequency discharge, microwave discharge, or pulse discharge is used. Methods of applying a high frequency to gas include an inductive coupling type in which a high frequency coil is wound around a container to inject high frequency power, and a capacitive coupling type in which an electrode is inserted inside the container to apply a high frequency voltage. The former is less contaminated from the electrodes, but has the drawback that the film thickness distribution of the thin film formed is larger. The latter is slightly better than the former in that respect. The frequency of the applied high frequency may be 1 MHz or more, and 13.56 MHz is often used. However, a higher quality thin film can be obtained by allowing the reaction gas to flow to the substrate surface. The gases are often mixed outside the container. The composition and properties of the resulting thin film depend on the thin film forming conditions. The formation conditions include total pressure, gas flow rate, gas mixture ratio, injection power, substrate temperature and the like.

In order to sustain the high frequency discharge in this way, it is necessary that the electrons are not captured by the electrodes during one period of the electric field. The lower the frequency, the larger the amplitude of electron motion, so the distance between the electrodes must be large. On the contrary, if the frequency becomes high, the discharge can be maintained even if the distance between the electrodes is small. Therefore, if an electromagnetic wave with a higher frequency is used instead of the high frequency discharge of 13.56 MHz, the distance between the electrodes can be reduced, and therefore the discharge can be performed in a smaller container. 2.45 GHz for frequency
Has been tried with some success. The CVD performed by using such a frequency is microwave discharge CV
Called D.

These plasma CVD devices supply a reaction gas from one of the substrates placed in one of the vacuum chambers, apply a high frequency or a microwave to the substrate, and form an ultrathin thin film on the substrate by the resulting discharge plasma. Is the way.

(Problem to be Solved by the Invention) The conventional method has a problem that it is difficult to control the plasma because one type of high-frequency discharge or microwave discharge is used. Further, a technique has been proposed in which two plasmas are generated by a direct current discharge method using an incandescent filament cathode to control the plasmas, but it is not suitable for reactive plasmas.

(Means for Solving the Problems) The present invention has been conceived to solve the above problems, and in order to carry out the intended thin film synthesis in a reactive plasma, electrons, ions, etc. It is necessary to be able to control energy, electric field, etc. The invention uses two different types of discharges, a high frequency discharge and a microwave discharge, to generate a hybrid plasma from a mixed reaction gas, direct-current biases one of the vacuum vessels, and mixes the two plasmas by a grid between the two discharges. In this way, the above parameters can be controlled.

According to the present invention, the reactive plasma can be easily controlled, and since an incandescent filament cathode is not used, it is optimal for thin film synthesis without being attacked by reactive gas. Therefore, the present invention has developed an apparatus that can be used for plasma CVD or the like in the field of manufacturing electronic devices, semiconductors, functional materials, and the like.

The features of the present invention are as follows.

(1) A second vacuum container in which a waveguide of the same diameter and a cylindrical first vacuum container are insulated and connected to each other, and the other end of the first vacuum container is insulated and connected to the other end of the first vacuum container through a wire mesh grid electrode. And a substrate on the center axis of the waveguide and a high-frequency disc electrode provided on the front surface of the waveguide in the second vacuum container, and a DC bias power source is connected to the first vacuum container to connect the outer periphery of the container. An electromagnet coil is provided to surround and the wire mesh grid is connected, and an ion beam of microwave discharge plasma generated by microwave irradiation in the first vacuum container is injected into the second vacuum container through the grid to generate a second vacuum. Thin film synthesis by hybrid plasma characterized by controlling the growth rate and quality of the thin film formed on the substrate by powering up the energy and density of the beam together with the high frequency plasma discharge by the high frequency electric field in the container Law.

(2) Waveguide for introducing reaction gas and microwave, first cylindrical vacuum container insulated and connected with the same diameter as the waveguide, and connected to the first vacuum container via an insulator Large diameter second vacuum container, an electromagnet coil surrounding the first vacuum container, a wire mesh grid interposed between the first vacuum container and the second vacuum container, and a waveguide A substrate provided in the second vacuum container facing the microwave plasma on the central axis of the tube, a high-frequency disc electrode provided on the front surface of the substrate so as to sandwich the substrate, and connected to the high-frequency disc electrode. And a DC bias power source connected to the first vacuum container, and plasma ions generated by microwave irradiation in the first vacuum container are injected into the high frequency plasma generated in the second vacuum container. The microwave plasma power (1) To control the plasma energy and the plasma density and temperature of the high-frequency plasma applied to the high-frequency electrode by controlling the DC energy applied to the vacuum container and to control the growth rate and the quality of the thin film formed on the substrate. A thin film synthesizing apparatus using hybrid plasma characterized by being configured.

In the present invention microwave power is at least 2.45 GHz
The frequency applied to the high frequency electrode by capacitive coupling with a high frequency power source is preferably at least 13.56 MHz.

According to the method of the present invention, microwave plasma discharge,
By using the high frequency plasma discharge together, the plasma discharge power can be increased to obtain a high quality thin film, the growth rate of the thin film can be remarkably increased, a stable thin film can be formed, and the bias voltage can be adjusted. The feature is that a high-quality thin film can be rapidly obtained by adjusting the density and energy of plasma.

(Structure of Invention) Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an example of the hybrid plasma generator of the present invention, where 1 is a cylindrical stainless steel vacuum container having a diameter of 10 cm and a length of 45 cm and having flanges having an outer diameter of 18.5 cm at both ends, and 2 is connected to this. Outer diameter of 18.5 cm
A cylindrical stainless steel vacuum vessel with a diameter of 30 cm and a length of 30 cm with a flange, 3 is an outer diameter of 18.5 cm, an inner diameter of 10.5 cm and a thickness of 2 cm (made of acrylic), and 4 is a waveguide with a diameter of 10 cm. The stainless steel container 1 is connected to one end via a disk 5 made of fused silica having a diameter of 14 cm and a thickness of 10 mm. 6 is a DC power source, 7 is an electromagnet coil with an inner diameter of 20 cm, an outer diameter of 32 cm and a thickness of 8 cm, and 8 is two stainless wire mesh grid electrodes with an outer diameter of 9 cm. In the present invention, an electromagnet coil 7 is provided outside the cylindrical vacuum container 1, a DC bias voltage is applied to the vacuum container 1, a reaction gas is supplied from the inlet side of the container, and an outlet side of the vacuum container 1 is provided. A wire mesh grid 8 is provided, a substrate 11 is provided in the second vacuum container 2 on the center line of the cylindrical vacuum container 1 through which the reaction gas flows, and a flat plate-shaped high frequency electrode connected to the high frequency power source 10 in front of the substrate 11. 9 to 2
The two are arranged to face each other so that high frequency discharge is performed in the second vacuum container 2. The first vacuum container 1 has a cylindrical shape, and the reaction gas is sent together with the microwave 12 through the waveguide 4 connected to the inlet side of the first vacuum container 1, and the reaction gas becomes microwave discharge plasma in the first vacuum container 1. The plasma is accelerated by the bias voltage applied to the first vacuum container 1,
Through the wire mesh grid 8 into the second vacuum container 2,
The energy of the high frequency discharge is applied while passing between the high frequency electrodes 9, and the microwave discharge plasma is further activated and collides with the substrate 11 to obtain a high quality thin film at a low temperature.

The vacuum container 1 and the vacuum container 2 are connected via an insulator 3.
A waveguide 4 is connected to one end of the vacuum container 1 to enable supply of microwave power (2.45 GHz). A disk 5 made of fused silica is sandwiched between the vacuum container 1 and the waveguide 4 to insulate the vacuum container 1 and the waveguide 4 from each other. Therefore, the DC power supply 6 can apply a voltage between the vacuum containers 1 and 2. The vacuum containers 1 and 2 are evacuated to a high vacuum by a vacuum pump connected to the vacuum container 2. There is an electromagnet coil 7 on the outside of the vacuum container 1, and a magnetic field can be applied up to 1 K gauss. A wire mesh grid 8 made of stainless steel is placed at the connection between the vacuum containers 1 and 2. Electrodes 9 inside the vacuum container 2
Then, a high frequency (13.56 MHz) is applied to this by the high frequency power supply 10 by container coupling. Substrate 1 for growing thin film
1 is placed on the axis of the vacuum container 2.

After evacuating to high vacuum, gas is introduced to bring it to a predetermined pressure. When a 2.45 GHz microwave is introduced into the vacuum chamber 1 from the waveguide 4 after applying a direct current to the electromagnet coil 7 and applying a magnetic field of about 900 gauss, microwave plasma is generated by ECR (electron cyclotron resonance). . Furthermore, when a high frequency is applied to the electrode 9, high frequency plasma can be generated. Therefore, this apparatus can generate a composite plasma (hybrid plasma) composed of two different types of plasma. Since the grid 8 is electrically connected to nothing and is in an insulating state, it has an effect of making the potentials of the two plasmas independent. Vacuum container 2 is grounded, and vacuum container 1
When a positive voltage is applied to the plasma plasma, ions of the microwave plasma can be injected into the high frequency plasma of the vacuum container 2, and the DC power source 6
The voltage can control the energy, and the microwave power can control the density. On the other hand, the density and temperature of the high frequency plasma can be controlled by the high frequency power. Furthermore,
The electric field and electron energy in the hybrid plasma of the vacuum chamber 2 can be controlled by adjusting the strength of the applied magnetic field, the coordination, and the like.

Using the apparatus of FIG. 1, the ion energy distribution states for various DC biases and the behavior of equipotential curves of hybrid plasma and RF plasma when a magnetic field was applied and when no magnetic field was applied were investigated.

(Example) The apparatus used for the experiment is as shown in FIG. 10 cm
And a large diameter second connecting two stainless steel cylindrical vacuum vessels 1 and 2 with different diameters of 30 cm electrically insulated from each other.
The vacuum container 2 and the first vacuum container 1 are provided with two grit 8
And grounded. The other first vacuum container 1 was biased by the bias voltage Vb. A microwave of 2.45 GHz was applied to one end of the first vacuum container 1 to generate a plasma while applying a magnetic field. The measured magnetic field strength in the axial direction is shown in FIG. The lines of magnetic force calculated from the magnetic field strength in the axial direction are shown in a two-dimensional space. The magnetic field lines diverge in the second vacuum container 2. This is because no magnetic field is applied to this area from the outside. Therefore, in the first vacuum container 1, the movement of electrons can be controlled by the magnetic field strength generated by the electromagnet coil. In the second vacuum chamber 2, an additional plasma is generated by applying a high frequency power of 13.56 MHz to a stainless steel plate electrode 9 having a diameter of 8 cm. The other flat plate electrode with the same diameter was placed in parallel with the high-frequency electrode at a distance of 6.5 cm.

In this preliminary experiment for the development of plasma generation and control of thin film formation, it was used to understand the behavior of the inert gas (argon gas) plasma because the reactive gas probe technique is not effective at this stage.

A typical plasma parameter around the high-frequency electrode 9 obtained by the needle probe has an electron density n _e ≈8 × 10 ⁹ cm
^-3 , and the gas temperature P ≈ 5 × 10 ^-4 Torr and the electron temperature Te
≈5 eV. Ion energy distribution function has an outer diameter of 8 mm
It was measured by an electrostatic analyzer consisting of a collector and two grid electrodes, covered by a 4 mm long stainless steel cylinder. The distribution function was obtained from the first derivative function of the collector current with respect to the second grid voltage. Let the analyzer work,
The first grid facing the plasma was at the insulation potential and the ionic current flowing into the negatively biased collector was measured by varying the second grid potential. As shown in FIG. 3, if the distance from the grid electrode is Z, Z = 18 cm
Then, when the bias voltage Vb was increased at both positions of Z = 2 cm, an increase in beam energy was observed. The low-energy ions correspond to the high-frequency plasma ions (bulk ions), and the other high-energy ions correspond to the microwave plasma ions (beam ions). The energy width at half the height of the bulk ions is smaller than that of the beam ions. This means that the ion temperature of the high frequency plasma is lower than the ion temperature of the microwave plasma. On the other hand, it was also found from another measurement example that the density of microwave plasma decreases with increasing distance from the grid. With increasing rf power, the bulk density of ions increases while keeping the beam density approximately constant. At this time, the plasma density increases up to about 30 W, but it becomes constant above 30 W, and the electron temperature becomes 4
It increased a little in the range of ~ 7eV. The beam density can be controlled by changing the microwave power. The potential distribution that gives an electric field to the plasma was measured by an emissive probe in a steady state.

FIG. 4 shows a typical result of the potential distribution r in the two-dimensional space on the Z plane. In the figure, (a) shows the distribution of the hybrid plasma, and (b) and (c) show the distribution of the high frequency plasma only with and without the magnetic field. This distribution changes not only according to the plasma generation position but also due to the magnetic field configuration. This is due to the movement of electrons affected by the magnetic field. This indicates that this electric field can be easily controlled by the strength and shape of the magnetic field used in this device.

(Conclusion) The energy and density of the beam ions can be adjusted by adjusting the bias voltage and the microwave power by biasing the hybrid plasma generated by the microwave and high-frequency discharge by the device of the present invention with a DC power supply. Can control the plasma density of the reaction chamber. The electric field can be controlled by adjusting the strength and shape of the magnetic field. Confirmation of the above results by this realization was made in an inert gas.

(Effects of the Invention) The effects of the device of the present invention are as follows.

(1) Since not only the energy and density of plasma can be controlled but also high-energy ions can be irradiated onto the substrate in the form of a beam, a dense thin film that is hard to peel off can be obtained by using this apparatus for thin film synthesis. In particular, it is effective for synthesizing diamond and tin oxide thin films, but for synthesizing thin films of other new materials, for example, synthesizing thin films of silicon nitride using methane (NH ₃ ) and hydrogen silicide (SiH ₄ ) as reaction gases, or various It can also be used to develop the synthesis of semiconductor thin films.

(2) The growth rate of the thin film and the quality of the thin film can be controlled.

(3) A hybrid plasma is produced to enable ion beam irradiation, and the beam energy, density, electron energy, etc. are controlled.

(3) The apparatus of the present invention enables selectivity of the reactive plasma and the physical process, chemical reaction, etc. of the film. That is, for example, in the diamond thin film synthesis, methane plasma is generated, and the density and energy of the ion beam to be irradiated are adjusted to control the quality of the film such as the selection of graphite, diamond, etc., the hardness of the film, the electric conductivity, etc. It is possible.
On the other hand, the growth rate of the film can be adjusted by controlling the electron energy that acts on the ionization and excitation of molecules / atoms, and the growth rate of the thin film can be significantly increased.

[Brief description of drawings]

1 is an explanatory view of the principle of the hybrid plasma generator for thin film synthesis of the present invention, FIG. 2 (a) is a characteristic diagram showing the magnetic field strength in the axial direction when the device of the present invention is used, and FIG. 2 (b) ) Is a characteristic diagram showing the lines of magnetic force, and FIGS. 3 (a) and 3 (b) are various bias voltages Vb ((a) Z = 2c).
m, (b) Z = 18 cm) characteristic curve diagram showing ion energy distribution, Fig. 4 (a) (b) (c) shows (a) hybrid plasma, high frequency plasma, (b) magnetic field, (c) ) A characteristic diagram showing equipotential lines when there is no magnetic field. 1 ... Cylindrical first vacuum container made of small-diameter stainless steel 2 ... Second vacuum container made of large-diameter stainless steel 3 ... Insulator such as acrylic resin 4 ... Waveguide 5 ... Disk made of fused silica -Shaped insulating plate 6 ... DC power supply, 7 ... Electromagnetic coil 8 ... Wire mesh grid, 9 ... High-frequency electrode 10 ... High-frequency power supply, 11 ... Substrate

Claims (2)

[Claims] 1. A second waveguide in which a waveguide having the same diameter and a cylindrical first vacuum container are insulated and connected, and the other end of the first vacuum container is insulated and connected through a wire mesh grid electrode. A vacuum container is provided,
A substrate and a high-frequency disc electrode provided on the front surface of the substrate are provided on the central axis of the waveguide in the second vacuum container, the first vacuum container is DC biased, and the outer circumference thereof is surrounded by an electromagnet coil, In the second vacuum container, the wire mesh grid is connected, and the ion beam of the microwave discharge plasma generated by microwave irradiation in the first vacuum container is passed through a grid electrically insulated from the first and second vacuum containers. And a high-frequency plasma discharge by a high-frequency electric field in the second vacuum container to increase the beam density and energy and control the growth rate and quality of the thin film formed on the substrate. Thin film synthesis method by plasma. 2. A waveguide for introducing a reaction gas and microwaves, a cylindrical first vacuum container which is insulated and connected to the waveguide with the same diameter, and an insulator for the first vacuum container. A large-diameter second vacuum container connected to each other, an electromagnet coil surrounding the first vacuum container, a wire mesh grid interposed between the first vacuum container and the second vacuum container, A substrate provided in the second vacuum container on the center axis of the waveguide so as to face the microwave plasma, a high-frequency disc electrode provided on the front surface of the substrate so as to sandwich the substrate, and a high-frequency disc electrode. In a high-frequency plasma that is composed of a connected high-frequency power source and a direct-current bias power source connected to the first vacuum container, and generates ions of plasma generated by microwave irradiation in the first vacuum container in the second vacuum container. To the beam plasma by microwave power. The energy of the beam plasma is controlled by the DC bias voltage applied to the first vacuum container, and the density and temperature of the high frequency plasma are controlled by the high frequency power applied to the high frequency electrode, and the growth rate and the thin film of the thin film generated on the substrate are controlled. A thin film synthesizing apparatus using a hybrid plasma, which is configured to control the quality of the thin film.