JPH04285154A - Formation of carbon thin film - Google Patents

Abstract

PURPOSE:To prevent the generation of a pinhole in a carbon thin film. CONSTITUTION:A carbon thin film having a diamond structure is formed on a base body by simultaneously using both vapor deposition of a carbon atom due to a vaporization source 3 and irradiation of the ion beams of inert gas emitted from an ion source 4. The thin film is former while the base body 2 is irradiated with negatively charged particles such as negative ions and electrons and also irradiated with ultraviolet rays emitted from an ultraviolet- ray irradiating lump 7 by performing high frequency discharge by a high-frequency impressing coil 6. Accumulated positive electric charge is neutralized by irradiating the vapor deposited film with the ion beams of inert gas. Generation of a pinhole is prevented which is caused by charging up the vapor deposited film. Vaporized carbon is regulated to a highly excited state and easily made to a diamond structure. As a result, crystallinity of carbon is enhanced which has the diamond structure in the film formed on the surface of the base body 2. Thus, the deposition of amorphous carbon is inhibited.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention is applicable to diamond structures used in fields where wear resistance and sliding properties are required, or fields where high thermal conductivity is required, or fields where semiconductor properties are required. The present invention relates to a method for producing a carbon thin film having the following properties.

0002

[Prior Art] Diamond has high hardness and high thermal conductivity, as well as high electrical resistance, excellent optical transparency except for some infrared regions, and exhibits semiconducting properties when impurities are added. It is a substance that is expected to have a wide range of applications. On the other hand, the synthesis of diamond required high temperatures and pressures, which required a huge amount of cost, and its uses did not expand.

[0003] If diamond could be made into a thin film at low temperatures without requiring high pressure and synthesized with good adhesion on a substrate, its uses could be dramatically expanded. Until now, methods for synthesizing diamond thin films on substrates include plasma CVD using hydrocarbon and organic compound gases, and photoCVD.
Chemical vapor deposition methods (CVD methods) such as the D method have been used exclusively.

0004

However, in the conventional CVD method as described above, (1) hydrocarbon and organic compound gases tend to cause amorphous carbon to precipitate at the same time as diamond crystal growth. (2) Since it is necessary to heat the substrate and gas atmosphere to a high temperature (for example, 800° C. to 1000° C.) for processing, there are limitations on the materials that can be used as the substrate.

(2) Adhesion of the diamond thin film to the substrate is poor, and the diamond thin film easily peels off from the substrate. ■ Impurities easily enter the diamond thin film, making it difficult to form a high-quality diamond thin film. There were other problems.

[0006] Therefore, the inventors have developed a method for depositing a substance containing a carbon element on a substrate and simultaneously or alternately irradiating the substrate with an ion beam made of an inert gas without heating the substrate. proposed a method to generate diamond-structured carbon in a film. According to this method, irradiated ions bring graphite-structured carbon deposited on a substrate into a highly excited state, and a crystalline structure having a diamond structure is generated in the deposited film. At this time, there is an advantage that there is no need to heat the substrate and the material used for the substrate is not limited.

However, in this method, since carbon having a diamond structure as an insulator is formed in the film,
Ions irradiated during fabrication (positively charged) accumulate positive charges in the film, causing the film to charge up, resulting in local dielectric breakdown and pinholes in the film. It had the disadvantage of causing These pinholes in the film cause deterioration of the film's properties such as insulation, thermal conductivity, weather resistance, and long-term stability.

[0008] Therefore, an object of the present invention is to provide a method for producing a carbon thin film having a diamond structure, which can solve these problems and prevent pinholes from forming in the film.

[0009]

[Means for Solving the Problems] The method for forming a carbon thin film of the present invention involves irradiating a substrate with negatively charged particles such as negative ions and electrons, and forming a thin film while irradiating electromagnetic waves.

0010

[Operation] By generating negatively charged particles such as negative ions or electrons in a vacuum container and irradiating them to the substrate, the positive charges accumulated by ion irradiation of the inert gas to the deposited film are neutralized, This prevents the formation of pinholes caused by charge-up of the deposited film. This improves the properties of the thin film such as insulation or thermal conductivity, and ensures long-term stability such as weather resistance of the thin film.

[0011] Furthermore, by irradiating the deposited film with electromagnetic waves with a particle energy (potential when in an excited state) of 10-2 eV or more and 106 eV or less, the evaporated carbon becomes more highly excited and becomes more likely to form a diamond structure. Become. As a result, the crystallinity of diamond-structured carbon in the film formed on the surface of the substrate is improved, and precipitation of amorphous carbon is suppressed.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing an example of an apparatus for implementing the method according to the present invention. In this apparatus, for example, a substrate 2 on which a carbon thin film is to be formed is attached to a substrate holder 1 in a vacuum container (not shown), and an evaporation source 3 and an ion source 4 are arranged facing the substrate 2. There is.

The evaporation source 3 is an evaporation source using, for example, an electron beam, and is for vaporizing 5' a substance containing carbon element as the evaporation material 5 and depositing it on the substrate 2. However, it is preferable that the evaporation material contains carbon with high purity. At this time, if the evaporation material 5 is sublimable and an evaporation source that uses electron beam heating causes problems such as unstable evaporation rate or slow evaporation rate, use a target made of a substance containing carbon element. An evaporation source that sputters with inert gas ions or the like, or a plasma spray evaporation source that evaporates a carbon element-containing substance by vacuum arc discharge or the like may be used as desired.

The ion source 4 is, for example, a bucket-type ion source that uses a cusp magnetic field for plasma confinement.
This is for ionizing the gas G supplied to the ion source and irradiating the substrate 2 with an ion beam 4'. If this ion source 4 also achieves this purpose,
For example, a Kaufman type method or the like can be used arbitrarily.

In this case, the ion beam 4' contains an ionized inert gas, specifically He, Ne, Ar, Kr, Xe, R, to avoid contamination of impurities in the film.
Any one or two ions consisting of n rare gas elements
An ion beam consisting of a mixture of more than one species is used. Regarding film formation, the inside of the vacuum container is heated to 10-5 to
After evacuation to a high vacuum below rr, one or more inert gases are mixed into the ion source 4 simultaneously or alternately with the evaporation of a substance containing carbon element from the evaporation source 3 onto the substrate 2. The gas G is ionized, and the substrate 2 is irradiated with an ion beam 4' made of the ions. At that time, the number of ions irradiated onto the substrate 2 and the particle ratio of carbon atoms deposited onto the substrate 2 (number of ions/carbon atom transport ratio) should be within the range of 0.1% to 100%. is preferred. If it deviates from this range, the film may be sputtered more than necessary, or excessive carbon may be in an amorphous state and deposited in the film more than necessary.

Reference numeral 10 in FIG. 1 is a film thickness monitor, which uses, for example, a crystal oscillator, and is used to measure the film thickness of the deposited film and to monitor the carbon atoms deposited on the substrate 2. It is used to measure the number of pieces. Also, 1
Reference numeral 1 denotes a current measurement monitor, which is composed of, for example, a Faraday cup, and is used to measure the number of ions irradiated onto the substrate 2. By using the film thickness monitor 10 and the current measurement monitor 11, the aforementioned number of ions/carbon atom transport ratio is calculated.

Further, the acceleration energy of the irradiated ions is preferably set to 10 KeV or less in order to minimize damage (defects) generated in the deposited film due to the irradiation. Note that the lower limit of the ion acceleration energy is realistically 10 eV or more because of the limit to which the ion beam can be extracted. Furthermore, the irradiation angle of the ion beam 4' with respect to the substrate 2 (as shown in FIG.
(the angle between the perpendicular to the surface of the ion beam and the ion beam) θ is 0° ~
Preferably, the angle is within the range of 80°. If it deviates from this range, the sputtering rate of vapor-deposited atoms by the ion beam will increase, and there is a possibility that a predetermined film thickness cannot be obtained.

In the present invention, when forming a carbon element-containing thin film on the substrate 2 by the above method, negatively charged particles such as negative ions or electrons are generated in a vacuum container, and the substrate 2 is irradiated with the negatively charged particles. The first feature is to The method of generating negatively charged particles such as negative ions or electrons is not particularly limited, but they can be obtained, for example, by generating high frequency discharge in a vacuum container. Although there are no particular limitations on the method for generating high-frequency discharge inside the vacuum container, in the present invention, for example, as shown in FIG. Here is an example. The high-frequency oscillator 8 uses, for example, a separately excited crystal oscillation system, and generates a frequency of 13.56 MHz, and the matching circuit 9 matches the incident wave and reflected wave for the high-frequency discharge within the vacuum container. .

The effect of generating negatively charged particles such as negative ions or electrons and irradiating the substrate 2 with them is explained as follows. As carbon having a diamond structure formed by ion irradiation is formed on the substrate 2 by the above method, the deposited film becomes insulating. Therefore, the deposited film begins to charge up due to ion irradiation during its formation, and as a result, excessive charges are accumulated in the film, eventually causing local dielectric breakdown. This causes pinholes to occur in the film, causing deterioration of properties such as insulation and weather resistance of the film.

On the other hand, when high-frequency discharge is generated within a vacuum vessel as in the present invention, plasma is generated within the vacuum vessel due to the discharge, thereby producing a large amount of electrons, which are then converted into ions. It works to neutralize the positive charges in the film that have accumulated excessively due to irradiation. This prevents the film from being charged up and prevents the formation of pinholes in the film caused by the process.

[0021] At this time, it is preferable that the output of the high frequency wave to be applied is 10 W or more. If it is less than 10 W, the effect cannot be sufficiently obtained. Further, the gas pressure in the vacuum container when generating high frequency discharge is preferably 1 x 10-8 torr or more,
If it is less than that, high frequency discharge may not be maintained stably. Furthermore, in this invention, the particle energy is 1
The second feature is that the thin film is created while irradiating the deposited film with electromagnetic waves of 0-2 eV or more and 106 eV or less. As an example of the electromagnetic wave having a particle energy of 10<-2 >eV to 10<6> eV, this embodiment uses the ultraviolet irradiation lamp 7 as shown in Embodiment 1. This ultraviolet irradiation lamp 7 is, for example, a lamp using a mercury arc, and the effect of this ultraviolet irradiation will be explained as follows.

Photons are generated from the ultraviolet irradiation lamp 7,
By the collision of the photon with the deposited carbon atom, or by the deposited carbon atom absorbing the energy of the photon,
Electron transfer occurs between bands, and the deposited carbon atoms become highly excited, creating a pseudo high temperature and high pressure state under non-thermal equilibrium, and as a result, the deposited carbon tends to form a diamond structure.

At this time, the method of ultraviolet irradiation is not particularly limited, and the upper and lower limits of the irradiation amount are appropriately selected depending on the ion irradiation amount, acceleration energy, or ion carbon atom transport ratio. . In addition, in the above, the particle energy is 10-2 eV or more,
This is because if it is smaller than this, the carbon atom will not be in an excited state. Further, the reason why the particle energy is set to be 106 eV or less is because if it is larger than this, there is a risk of irradiation damage. In addition, the particle energy is 10-2 eV or more.
Examples of electromagnetic waves of 0.06 eV or less include various electromagnetic waves in the range of far infrared rays to X-rays (wavelengths of 10-4 to 10-10 m).

(Example 1) Using an apparatus as shown in FIG. 1, after setting a (100) Si substrate on a substrate holder,
Place it in a vacuum container and heat the vacuum container to 2 x 10-8 tor.
It was maintained at a high vacuum below r. Thereafter, an evaporation source using an electron beam is used to evaporate an evaporation substance made of carbon with a purity of 99.9% to form a carbon thin film on the Si substrate, and at the same time, a bucket-type ion source with a purity of 99.99% is evaporated to form a carbon thin film on the Si substrate. % of Ne gas (at this time, the degree of vacuum in the vacuum container was 8×
10 −5 torr), the Ne gas was ionized, and the Si substrate was irradiated with an acceleration energy of 200 eV. In addition, N
The e/C transport ratio is 0.25 and the beam current is 2mA.
Met.

At the same time, a high frequency discharge with a high frequency output of 200 W was generated in the vacuum container, and the vapor deposited film was irradiated with ultraviolet rays using a mercury arc lamp. Note that during the thin film formation, the Si substrate was kept at room temperature by a water cooling mechanism. After forming a deposited film to a thickness of about 1 μm, the crystal structure of the film was evaluated by Raman scattering spectroscopy, and the results are shown in FIG. In the case of Example 1, a peak was observed at a wave number of 1330 cm −1 reflecting the formation of the diamond crystal structure.

Further, when the surface condition of the film was observed using a scanning electron microscope, no pinholes were observed in the film. (Comparative Example 1) As in Example 1, an evaporation substance made of carbon with a purity of 99.9% was evaporated using an evaporation source using an electron beam to form a carbon thin film on a Si substrate, and at the same time Ne gas with a purity of 99.999% was introduced into the type ion source (at this time, the degree of vacuum in the vacuum container was 8 × 10-5
torr), by ionizing the Ne gas and irradiating it onto the Si substrate with acceleration energy of 200 eV, Si
A carbon thin film was created on the substrate. However, at this time, the high frequency discharge and ultraviolet irradiation used in Example 1 were not used. Note that the other conditions were exactly the same as in Example 1.

As in Example 1, the crystal structure of the deposited film was evaluated by Raman scattering spectroscopy, and the results are shown in FIG. In the comparative example, a peak is seen at a wave number of 1330 cm, which indicates the presence of a diamond crystal structure in the film, as in Example 1, but in addition to this, a broad peak in a high wave number region, which indicates the presence of amorphous carbon, is also observed at the same time. It can be seen that more amorphous carbon is contained in the film than in Example 1.

Further, as in Example 1, when the surface condition of the film was observed using a scanning electron microscope, several pinholes were observed in the film.

[0029]

Effects of the Invention According to the present invention, (1) During the production of a thin film, negatively charged particles such as negative ions or electrons are generated in a vacuum container and the substrate is irradiated with the negatively charged particles, thereby reducing the positive charge in the film. is neutralized, and charge-up of the film during thin film formation due to inert gas ion irradiation is prevented. As a result, a high-quality film without pinholes can be created.

(2) By creating a thin film while irradiating the deposited film with electromagnetic waves, it is possible to bring carbon into a sufficiently highly excited state, and it has a diamond structure with less amorphous carbon and good crystallinity. A carbon thin film can be formed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of an apparatus for carrying out the method for producing a carbon thin film of the present invention.

FIG. 2 is a characteristic diagram showing the results of evaluating the crystal structure of the film of Example 1 by Raman scattering spectroscopy.

FIG. 3 is a characteristic diagram showing the results of evaluating the crystal structure of the film of Comparative Example 1 by Raman scattering spectroscopy.

[Explanation of symbols]

1 Base holder 2 Base 3 Evaporation source 4 Ion source 4’ Ion beam 5 Evaporation material 5’ Vaporization 6 High frequency application coil 7 Ultraviolet irradiation lamp 8 High frequency oscillator 9 Matching circuit 10 Film thickness monitor 11 Current measurement monitor

Claims (1)

[Claims] 1. Simultaneously or alternately with the vapor deposition of a substance containing a carbon element onto the substrate, the substrate is irradiated with an ion beam obtained by ionizing an inert gas, whereby the surface of the substrate is irradiated with an ion beam obtained by ionizing an inert gas. A method for producing a carbon thin film that forms a carbon thin film having a diamond structure, which comprises irradiating a substrate with negatively charged particles such as negative ions and electrons, and forming a thin film while irradiating electromagnetic waves. How to make.