JP2752225B2 - Method for synthesizing hard carbon film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for synthesizing a hard carbon thin film.

2. Description of the Related Art Conventionally, many hard thin films including carbides and nitrides such as SiC and TiN have been used for wear-resistant surface protection of tools and the like. However, recently, diamond-like carbon (DLC)
C film) is drawing attention.

Although the DLC film is amorphous, its physical properties are close to those of diamond, so it is expected to be applied to various fields using electrical and optical characteristics. It is one of the most suitable materials for a protective film because the hardness of the DLC film can reach 5000 kg / mm ² or more in Knoop hardness depending on the conditions, and it has chemical stability against chemicals and corrosion resistance. .

FIG. 3 shows an outline of a typical conventional apparatus for synthesizing a DLC film. In the film formation, raw material gas molecules are ionized by thermoelectrons from the internal hot filament 2, and the motion of electrons is accelerated by using a magnetic field in the outer peripheral coil 4 to generate high-density plasma. Is applied to extract ions in the plasma to perform synthesis.

Problems to be Solved by the Invention The method for synthesizing a DLC film mainly composed of ions as described above has the following problems. That is, since the DLC film is insulative, ionic charges are accumulated and the film surface is charged up as the film is deposited.

Assuming that the charge per unit time per unit area accumulated in the synthesized DLC film is Q, the dielectric constant ε of the film and the film thickness d, the surface potential V of the film is expressed by the following equation.

V = Qd / ε The DLC film deposited on the substrate acts as a capacitor, and the accumulated charge increases with time, and the surface potential also increases. FIG. 4 is a diagram showing an example of a change in surface potential of a film with respect to a film forming time when a DLC film is synthesized by the apparatus configuration of FIG.

Due to the increase in the surface potential of the DLC film, the acceleration voltage substantially acting on the ions decreases. This becomes more remarkable as the film formation time becomes longer. If the film formation is continued in this state, a film having a non-uniform film quality is formed in the film thickness direction, and the reproducibility is poor, and it is difficult to precisely control the film quality. Met.

Means for Solving the Problems The present invention converts a gas containing at least carbon as a constituent element into a plasma under a reduced pressure of 10 ^-2 to 10 ^-4 Torr, extracts ions from the plasma, and separates the substrate from the plasma. In the method for synthesizing a hard carbon film in which ions are accelerated and deposited thereon, a detection unit for monitoring the surface potential of the film is provided on the surface of the film, and with the increase in the surface potential of the film being synthesized,
A method for synthesizing a hard film, comprising adjusting the voltage applied to the substrate to increase and synthesizing the film while constantly controlling the potential difference between the surface potential of the film and the plasma potential to be constant.

In the present invention, the increase in the surface potential during the synthesis of the DLC film is constantly monitored in real time, whereby the voltage applied to the substrate is also increased, and the potential difference between the plasma potential and the surface potential of the film is kept constant. Therefore, the acceleration voltage of the ions in the plasma becomes constant, and a DLC film having a uniform film quality in the film thickness direction can be synthesized. This allows
Precise control of film quality becomes possible.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view schematically showing a DLC film synthesizing apparatus used in one embodiment of the present invention.

Benzene is introduced as a raw material gas through the gas inlet 1,
The internal pressure was kept at 0.005 Torr. The hot filament 2 installed in the plasma chamber 3 was heated by energization to emit thermoelectrons, and the magnetic field of the external coil 4 was applied to accelerate the electrons to generate plasma.

This is confined in the plasma chamber by the mesh-shaped electrode 10 to which a positive voltage is applied, and a negative voltage of 100 to 10,000 V is applied to the substrate holder 6 which is set apart from the plasma to extract ions in the plasma. To
DLC film was synthesized. Therefore, as for the plasma potential, the current of the hot filament 2, the voltage of the mesh electrode 10, the applied voltage of the coil 4, and the like are kept constant.

On the other hand, since the surface potential fluctuates, a terminal 7 for measuring the surface potential is placed close to the film surface on the substrate 5 and the substrate voltage is applied while monitoring with an externally connected voltmeter 9. It was directly connected to the power supply 8 for use, and was adjusted so that the potential difference between the plasma potential and the surface potential of the film was always constant.

As a first example, the DLC film was synthesized by adjusting the voltage applied to the substrate 5 so that the ion acceleration voltage was constant. FIG. 2 shows the relationship between the Nuev hardness and internal stress of the DLC film and the acceleration voltage.

The hardness and internal stress of the DLC film largely depend on the ion acceleration voltage. By changing the acceleration voltage, the hardness and internal stress of the film were controlled, and uniform film quality was obtained in the film thickness direction.

As a first comparative example, the initial substrate potential was set to 3000 V, and a DLC film was synthesized for 30 minutes under two conditions of (a) synthesis while adjusting the substrate voltage, and (b) synthesis without adjusting the substrate voltage. Then, the film hardness and internal stress were examined. Table 1 shows the results.

As is clear from the table, when the substrate voltage is not adjusted, the internal stress increases because the substantial ion acceleration voltage decreases.

As a second comparative example, in order to further synthesize a hard DLC film, the initial setting value of the substrate voltage was set to 700 V, and as in the first embodiment, the DLC film was synthesized for 30 minutes with or without the adjustment of the substrate voltage. went. Table 2 shows the results. As is clear from the table, when the substrate voltage is not adjusted, the internal stress increases, the hardness of the film decreases, and the film quality clearly decreases.

As a third comparative example, a DLC film was synthesized under the same conditions as in the second comparative example with a deposition time of 90 minutes. Table 3 shows the results. As is apparent from the table, when the substrate voltage was not adjusted, the internal stress of the film was increased by performing the synthesis for a long time, and peeling occurred.

As is clear from the above comparative examples, when the substrate voltage is not adjusted during the synthesis of the DLC film, the initial conditions of the synthesis fluctuate, so that precise film control cannot be performed and a desired film quality is hardly obtained. . By adjusting and applying the substrate voltage so that the potential difference between the surface potential of the film and the plasma potential is always constant, precise control of the film quality becomes possible.

Preferably, the acceleration voltage is in the range of 100V to 10,000V. When the accelerating voltage is 100 V or less, the ion has too small an accelerating energy, so that a soft organic film is formed. On the other hand, if it exceeds 10,000 V, the acceleration energy is too large, so that the synthesized film is sputtered and damaged at the same time, and a graphite-like film having a sufficient film quality cannot be obtained.

Advantageous Effects of the Invention As is apparent from the above description, the present invention corrects a charge-up amount of a film being synthesized in a method of synthesizing a hard carbon film mainly composed of ions so that acceleration energy of ions is always constant. Therefore, precise control of the film quality of the hard carbon film can be realized, and the industrial value is high in terms of synthesizing a wear-resistant protective film on various substrates.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a synthesizing apparatus used for a method of synthesizing a hard carbon film according to one embodiment of the present invention, and FIG. 2 is a relation between film hardness, internal stress and ion accelerating voltage in the embodiment. FIG. 3 is a schematic sectional view showing a conventional synthesizing apparatus, and FIG. 4 is a graph showing an example of a change in a surface potential of a conventional film with respect to a film forming time. DESCRIPTION OF SYMBOLS 1 ... Gas inlet, 2 ... Hot filament, 3 ... Plasma chamber, 4 ... Coil, 5 ... Substrate, 6 ... Substrate holder, 7 ... Surface potential measuring terminal, 8 ... Application of substrate voltage Power supply, 9: Electrometer, 10: Mesh electrode.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-25570 (JP, A) JP-A-63-190162 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 16/00-16/56 C23C 14/54 H01L 21 / 205,21 / 31 C30B 29/04

Claims (1)

(57) [Claims] A gas containing at least carbon as a constituent element is converted into a plasma under a reduced pressure of 10 ^-2 to 10 ^-4 Torr, ions are extracted from the plasma, and the ions are accelerated onto a substrate separated from the plasma. In the method for synthesizing a hard carbon film to be deposited by depositing, a detection unit for monitoring a surface potential of the film is provided on a surface of the film, and a voltage applied to the substrate is increased with an increase in a surface potential of the film being synthesized. Wherein the potential difference between the surface potential of the film and the plasma potential is controlled so as to be constantly constant.