JP2619428B2 - Hard conductive carbon film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hard conductive carbon film suitable for a heater for a thermal head, an electrode layer of a laminated semiconductor functional material such as a MIM, and the like.

(Prior art)

In general, a mixed gas of CH ₄ and H ₂ is decomposed by RF glow discharge or the like, and a thin film deposited on a glass substrate or the like contains a small amount of H (14% or less), and is hard (Hv-9500 kg · m
m ⁻² ), high specific resistance (ρ〜10 ⁹ Ω · cm) and exhibit properties similar to diamond. a-C: electronic states of C network H film C ₁₅ plasmon loss ESCA (X-ray photoelectron spectroscopy by irradiation), the structure is evaluated by X-ray diffraction, diamond manner
An amorphous structure in which sp ³ bonds and graphite-like sp ² bonds are locally mixed, that is, an aC: H film (i-carbon film) is formed.

Unbonded C atoms present in the aC: H film prepared under the following conditions were measured by ESR (electron spin resonance).
At g = 2.0036, an ESR signal with a half width of 7 G was observed, and the spin density determined from the integrated intensity was about 6 × 10 ¹⁹ / cm ³ .

RF output: 20 to 100 W Pressure: 10 ^{-3 to 1} Torr Gas: CH ₄ / H ₂ = 100 to 20% Substrate temperature: room temperature As described above, the aC: H film formed near room temperature has unbonded bonds. The film structure is unstable because it contains many. In addition, due to the localized level created by these uncoupled hands in the forbidden band,
Electrical conduction is dominated by hopping, a-C: H
This makes it difficult to improve the conductivity of the film. In addition, for example, when an aC: H film (i-carbon film) is used for a functional device such as a MIM, it is difficult to bond C with various metal materials such as Al and Ni, so that adhesion to a metal is difficult. There is a problem that the property is not good.

〔Purpose〕

The present invention solves the above-mentioned problems and precipitates graphite microcrystals in the aC: H film (in a microcrystalline state), reduces the dangling bonds of C,
It is an object of the present invention to provide a hard conductive carbon film capable of controlling conductivity to a desired value while maintaining diamond grade hardness.

〔Constitution〕

The hard conductive carbon film of the present invention contains carbon and hydrogen as main components, and a-C: H in which sp ³ bonds and sp ² bonds of carbon are mixed.
The aC: H film contains 1 graphite microcrystal.
It is characterized by being contained in 0 to 75%.

Incidentally, the present inventors, by plasma CVD method on the substrate, when producing an aC: H film containing carbon and hydrogen as main components and sp ³ bonds and sp ² bonds of carbon mixed at room temperature. After forming the film, annealing at 150 to 450 ° C. or forming the film at a substrate temperature of 150 to 450 ° C.
-C: 10-70% of microcrystalline graphite precipitates in the H film,
Can be reduced from the order of 10 ^{20 to the} order of 10 ¹⁹ to complete the present invention.

FIG. 1 shows the results of measuring the unbonded hand density by ESR measurement in each case by changing the annealing temperature of an aC: H film formed on a substrate at room temperature by a plasma CVD method. FIG. 1 shows that the number of dangling bonds of C decreases as the heat treatment temperature increases. It is considered that the membrane structure is stabilized by the reduction of the dangling bonds, and the electrical conduction becomes dominant from hopping conduction to activated conduction.

FIG. 2 shows the mixing ratio between the amorphous portion and the graphite microcrystal portion when the substrate temperature is changed when the aC: H film is formed by the plasma CVD method.
The mixture ratio shown in FIG.
^-1 peak: is calculated from the ratio of (a-C H) and 1570 cm ^-1 peak (graphite peak). FIG. 2 shows that when the substrate temperature is changed from room temperature to 450 ° C., the mixing ratio of the graphite microcrystals increases to 75%. Since the specific resistance of graphite crystals is small to 0.2 Ω · cm, the specific resistance of the aC: H film in which graphite microcrystals are mixed is greatly reduced, and the mixing ratio of 75% is of the order of 10 ³ Ω · cm. Becomes

The decrease in dangling bonds associated with an increase in the annealing temperature after film formation at room temperature is related to the mixing ratio of the graphite microcrystals precipitated in the film. Hands are reduced.

In the present invention, the main point is that the mixing ratio of the graphite microcrystals mixed in the aC: H film is 10 to 75%. If this mixing ratio is less than 10%, the effect of improving the conductivity by the precipitation of graphite microcrystals is not sufficient, the number of unbonded atoms does not decrease so much, and the film stability is inferior. The film quality is degraded with the increase in hardness, and the hardness becomes insufficient.
The preferred mixing ratio of graphite is 20 to 50%. According to the theory of percolation, fine crystal grains are connected to each other at a crystallization ratio of 20% or more to form a conduction path, so that it can be expected that the conductivity is particularly improved.

To achieve such a graphite mixing ratio, a-C: H
It can be obtained by setting the substrate temperature at 150 to 450 ° C. when forming the film, or by annealing at 150 to 450 ° C. after forming the film at room temperature.

In the aC: H film mixed with 10 to 75% of graphite microcrystals in this way, the number of unbonded atoms of C atoms is reduced, the film stability is excellent, and the activated conduction becomes dominant. It can be controlled to have a desired electrical conductivity according to the graphite crystal mixing ratio. In addition,
The aC: H film according to the present invention is easy to form intercalation using alkali metal ions as donors or oxygen or halogen ions as acceptors in microcrystalline graphite mixed therein, so that the electrical properties of the hard carbon film can be improved. In order to further improve the conductivity, a material doped with an element serving as a donor or an acceptor as described above can be used.

〔effect〕

According to the present invention as described above, desired electrical conductivity can be controlled by controlling the mixing ratio of microcrystalline graphite to be deposited while maintaining the characteristics of the hard carbon film. Therefore, a thin film heater such as a thermal head can be used, and the i-carbon film
When used for a functional device such as M, there is an effect that it can be suitably used as a stable electrode material having good adhesion to an i-carbon film.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the annealing temperature of an aC: H film formed by a plasma CVD method at room temperature and the density of dangling bonds of C in the film. FIG. 2 is a diagram showing the relationship between the substrate temperature and the mixing ratio of microcrystalline graphite during the formation of the aC: H film.

Claims (1)

(57) [Claims] 1. A mainly composed of carbon and hydrogen, sp ³ carbons
In a hard carbon film composed of aC: H in which a bond and an sp ² bond are mixed, 10 to 75% of graphite microcrystals are contained in a / C: H.
A hard conductive carbon film characterized by being included.