JPS62180057A - Production of thin carbon film - Google Patents

Abstract

PURPOSE:To obtain a thin film of diamondlike or amorphous carbon having satisfactory characteristics by a low temp. process by carrying out sputtering on a substrate with graphite as a target in a gaseous flon-H2 mixture having a specified mixing ratio under a specified pressure. CONSTITUTION:A gaseous flon-H2 mixture contg. 1-100ppm flon is introduced into a vacuum vessel so as to regulate the pressure to 0.7-665Pa. A substrate and a target electrode of graphite are placed in the vessel and a thin carbon film is formed on the substrate by reactive sputtering.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for producing a diamond-like carbon thin film or an amorphous carbon thin film.

B0 Summary of the Invention The present invention involves forming a carbon thin film on a substrate by depositing it on the substrate using a reactive sputtering method using a mixed gas of fluorocarbon gas and hydrogen under a predetermined pressure using graphite as a target. This method is a low-temperature process with excellent film quality and performance, and allows for easy equipment configuration and film formation control.

C. Prior Art Ion beam methods, plasma CVD methods, and the like are well known as methods for producing diamond-like carbon thin films or amorphous carbon thin films.

In the ion beam method, an element (carbon source) is ionized in a vacuum, electrostatically accelerated, and target ions are separated and implanted into a target (substrate) to form a carbon thin film.

In the plasma CVD method, a carbon thin film is formed on a substrate by adding discharge to film formation by a normal CVD method.

D1 Problems to be Solved by the Invention Forming carbon thin films using the conventional ion beam method requires a costly ion accelerator to accelerate carbon ions, and irradiating the substrate with the ion beam causes structural defects at the interface. There were some problems that could easily occur. Furthermore, when attempting to form a carbon thin film on an organic material or a semiconductor, these substrates are attacked by the ion beam, which limits the materials for film formation.

In the conventional plasma CVD method, since hydrocarbon gas is decomposed and used as a carbon source, many types of growth nuclei are likely to occur due to repolymerization, etc., making it difficult to form a thin film with arbitrary film characteristics. In addition, for high quality film formation, the substrate temperature should be adjusted to 200°C.
It is necessary to maintain the temperature above ℃, and a thin film cannot be formed on a substrate made of a material that cannot be maintained at this temperature.

An object of the present invention is to provide a manufacturing method that can form a diamond-like or amorphous carbon thin film of good quality by keeping the substrate at a low temperature and easily controlling the film quality.

Means and operation for solving the E1 problem The present invention has been made in view of the above problems, and uses graphite as a target electrode in a vacuum container, and a fluorocarbon-based gas with a mixing ratio of 1 to 1100 ppm in the vacuum container. Hydrogen mixed gas at 0 pressure
．． 7 Pa to 665 Pa, and a carbon thin film is formed by reactive sputtering on the substrate placed in the vacuum chamber. This method reduces SP3 bonds that worsen insulation resistance, obtains high resistivity, and improves the optical band. The gap and spin density performance is also improved, and transparent thin films ranging from pale yellow to colorless can be obtained.

F. Example FIG. 1 is a cross-sectional view of the main parts of a sputtering apparatus used in the method of the present invention. Vacuum container l is a metal cylinder with flange 2
Both ends are hermetically sealed with a metal upper cover 4 and a lower M5 using an O-ring 3 or the like as a sealing means. This vacuum vessel 1 is provided with an atmosphere gas introduction pipe 6 at the upper side of the cylinder 2, and an exhaust pipe 7 directly connected to a vacuum pump at the center of the lower M5. On the upper M4, an electron extraction counter electrode 8 at a ground potential is provided within the vacuum vessel 1, and a target electrode 9 is provided opposite to this.

A magnetron 11 is provided in an electrode box 10 on the back side of the target electrode 9, and the target electrode 9 is heated by supplying a high frequency current to the magnetron 11 from the outside. Cooling water is passed through the magnetron 11 from a cooling water port 14 to a cooling water outlet 15 by a metal cooling water pipe 12 on the supply side and a metal cooling water pipe 13 on the drain side to cool the magnetron 11 . These water tubes 12, 13 are covered with a shield 16 and are led out of the vacuum vessel l from the side of the cylinder 2 with an airtight shield.

In such a sputtering apparatus, the deposition substrate 17.18 on which a thin film is formed in the method of the present invention is mounted on a substrate holder 19.20 that is insulated and supported on the inner surface of the upper M4 and the inner peripheral surface of the cylinder 2, respectively. , is attached to the counter electrode 8 as a deposition substrate 21.

22 is a board supporting member. Further, the thermocouple 23 is drawn out from the upper M4 with an airtight shield so that the temperature of the deposition substrate 17 can be measured.

Note that the deposition substrates 17 and 18 are placed outside the region where sputtered particles of the plasma excitation source are transported. That is, part A shown by the broken line in the vacuum container l is the electrode 8.
．． If part B is the region where the sputtered particles existing in plasma region A are transported in the plasma state region generated in and around 9, then the deposited substrate 17 and 18 are in region C outside region B. Installed. This area C
Then, the sputtered particles transported from region A are deposited softly on the deposition substrate 17, 18. Note that when placing the deposition substrates 17 and 18 in this region C, since the charged particles, which are the majority of the particles transported to region C, are easily affected by electric fields, etc., it is necessary to maintain a uniform potential. For example, no consideration was given to setting the voltage near the ground potential2.

Further, a mixed gas of hydrogen gas and fluorocarbon gas is introduced from the atmospheric gas introduction pipe 6, and graphite is used for the target electrode 9.

In this way, using a sputtering device, using solid graphite as a carbon source as a target electrode, introducing a mixed gas of hydrogen gas and fluorocarbon gas, and adjusting the pressure inside the vacuum chamber, the deposition substrate 17. A diamond-like or amorphous carbon thin film is formed on 18 or 21.

Examples of the present invention will be described in detail below.

In FIG. 1, solid graphite is used as the target electrode 9, and after setting the deposition substrates 17, 18, and 21, the inside of the vacuum chamber 1 is heated to 1.33X to 5Pa (10-'To
rr), and the mixture ratio of tetrofluoromethane (CF4) and hydrogen (H7) CF4/H2=
5 ppm mixed gas at 67 Pa (0.5 Torr)
to be introduced. After the gas pressure inside the vacuum chamber 1 has stabilized, a high frequency (13.56 MHz) current is applied to the magnetron 11, and this current is 6.8 W/c to the target electrode 9.
The sputtering was performed for 9 hours while controlling the power to be 50 m''.

The properties of the carbon thin films formed on the glass substrates 17, 18 and 21 are shown in the table below.

Table 1 shows the resistivity when 7 is not mixed, and it is clear that the resistivity can be increased by mixing fluorocarbon gas. . Also,
The degree of adhesion of the formed thin film was determined by a peel test in which an adhesive tape was attached to the thin film, and no peeling was observed even on the substrate 17. Furthermore, the substrate temperature during sputtering means that sputtering can be performed at a low temperature outside the transport. In addition, the thin film changed from pale yellow to a colorless transparent thin film.

In addition, by changing the formation conditions variously, the deposition substrate 17.18°21
The measurement results of infrared absorption spectra, resistivity, spin density, etc. for each thin film formed will be explained with reference to FIGS. 2 to 5.

FIG. 2 shows the infrared absorption spectra of the thin film formed on the substrate 17 when the mixed gas pressure was changed from 40 Pa to 267 Pa, and the spectrum was almost the same as when sputtering was performed using only hydrogen gas.

In addition, in these thin films, most of the absorption due to -H stretching vibration is due to SP3 bonds, so SP2 bonds (absorption of 3025 cm-'l) are a factor in lowering electrical resistance.
is small, which corresponds to a high resistivity of lXl0"Ω・cm or more. Also, the optical band gap (Eg
(opt)) is 2.95 eV, spin density is 3 x 1
0"/cm' and 6 X when using only hydrogen gas
It was 10I8/cm3.

Next, Figure 3 shows the mixed gas pressure at 1.33 Pa (0.01 T).
orr).

6.67 Pa (0.05 Torr), 13.3 Pa (
0,ITorr), 40.0Pa(0,3Torr)
, 100T'a (0.75Torr), 133Pa
(1,0 Torr), 200 Pa (1,5 Torr)
The measurement results of the dependence on the resistivity (ρ) of the carbon thin film formed at 267 Pa (2.0 Torr) are not shown.

Similarly, FIG. 4 shows the optical bandgap and spin density for different gas mixture pressures.

From the above, the carbon thin film formed by the manufacturing method according to this embodiment has high resistance with few SP2 bonds that worsen insulation resistance, and has an optical band gap of 2.05 to 3.15.
It is clear that a good quality carbon thin film with a voltage of 'eV can be obtained. Furthermore, the spin density is 2 X 10"~3 X
It is possible to use it as a semiconductor material by doping it with impurities.

Figure 5 shows the resistivity (ρ
) is shown. As is clear from this result, if the CFC content in the mixed gas is less than 1 ppm, the resistivity becomes poor;
If it exceeds 100 pp, it tends to become saturated and the corrosiveness of the fluorocarbons to the container walls increases.

From these facts, it has become clear that the mixed gas ratio is preferably in the range of 1 to 1100 pp.

Also, from the characteristics shown in FIGS. 2 to 5, the mixed gas pressure is 0.
7 Pa to 665 Pa (5 Torr) is desirable. That is, if the gas pressure is lower than 0.7 Pa, the resistivity will be low and the spin density will also increase, resulting in undesirable characteristics.If the gas pressure is higher than 665 Pa, the wavelength of the infrared absorption spectrum shown in Figure 2 is 2960 cm- It is predicted that the absorption coefficient at ' will become even larger and the film quality will change, and the spin density will also tend to increase.

In the embodiment, in order to form a film using a high temperature process, the substrate 17. shown in FIG. 1 is used. A temperature-controlled heater may be added to the tg section, or conversely, to form a film at a low temperature, a cooling pipe may be added to the substrate section to flow a temperature-controlled coolant such as water or liquid nitrogen. In addition, fluorocarbon gases include not only tetrofluoromethane (CF4) but also C-F-, C5Fa, C-C, Fs, and C5F1t.
A similar effect was obtained by replacing the gas with a fluorocarbon gas such as ClIF5.

G1 Effects of the Invention As described above, according to the present invention, diamond-like formation is achieved by using a method that complies with the general sputtering method, and by using graphite as a target and adjusting the mixing ratio of fluorocarbon gas and hydrogen and the pressure inside the container. Alternatively, by depositing an amorphous carbon thin film, the following effects can be obtained.

(1) Since carbon thin films can be formed by low-temperature processes, they can be formed on all kinds of substrates in principle.

(2) A thin film with good properties can be obtained with a relatively simple device configuration and without complicating control.

(3) The substrate arrangement may be outside the plasma transport range, which increases manufacturing efficiency and allows selection of temperature conditions etc. according to the type of substrate.

(4) Compared to conventional methods, the spin density is lower, that is, the number of dangling bonds is smaller, and the optical bandgap is widened, making it possible to obtain a thin film with high resistivity.

(5) The thin film changes from pale yellow to colorless, and has extremely high light transmittance from visible light to infrared light.

(6) Because the film is formed by sputtering, the adhesion between the thin film and the substrate is excellent.

[Brief explanation of drawings]

Figure 1 is a block diagram of the main parts of the sputtering apparatus used in the method of the present invention, Figure 2 is the infrared absorption spectrum of the thin film according to the example, and Figure 3 is the relationship between mixed gas pressure and resistivity for thin film formation in the example. FIG. 4 is a diagram showing the relationship between the mixed gas pressure, optical band gap, and spin density for thin film formation in the example, and FIG. 5 is a diagram showing the relationship between the gas mixture ratio and resistivity for thin film formation in the example. FIG. l...Vacuum container, 6...Gas introduction pipe, 7...Exhaust pipe, 8...Counter electrode, 9...Target electrode, 11
...Magnetron, 17.18.21...Deposition substrate. Figure 3 MSK#/) Ilhff pressure (P+2+CF4HR4
aZ64L PH2+ CF4 (Torr) 1
S L PH20 CF4 (Torr) Figure 5 CF4 Kanga jr: 2 Roari ≦ Crab! ! Pzuε conversion 31&'
< CF4 /H2 (Ppm) January 27, 1988
Day

Claims (2)

[Claims] (1) Graphite is used as a target electrode in a vacuum container, and a mixed gas of fluorocarbon gas and hydrogen at a mixing ratio of 1 to 100 ppm is placed in the vacuum container at a pressure of 0.7 Pa to 665 Pa.
A method for producing a carbon thin film, comprising: forming a carbon thin film on a substrate placed in the vacuum container by a reactive sputtering method. (2) The method for manufacturing a carbon thin film according to claim 1, characterized in that the substrate is provided with a heater or a cooling means.