JPS6326347A - Production of thin metal boride film - Google Patents

Abstract

PURPOSE:To obtain a thin metal boride film having high adhesiveness to a substrate by ionizing prescribed metal elements at a high rate of ionization, accelerating the combination with evaporating boron at a low temp. and impressing an acceleration voltage thereto. CONSTITUTION:Ti and B are respectively loaded into crucibles 3, 4 provided in a vacuum vessel 1 and after the inside of the vessel is evacuated 2 to 10<-6>Torr, an electron beam generating mechanism 5 is operated and the above- mentioned Ti and B are melted by an electron beam 6. A positive potential of 40V is applied to a bias probe 8 disposed above the respective crucibles to generate an arc discharge and to ionize evaporating components. A shutter 9 is then opened to start ion plating. The bias voltage of the substrate 10 at this time is -500V, the evaporation rate is 10Angstrom /sec and the substrate temp. is 200 deg.C. The results of the investigation made on the films formed by vapor deposition up to 2mum thickness by an X-ray diffraction method reveal that the boride film formed is crystalline TiB2 and that the Mohs' hardness thereof is as high as 9 as shown in the figure. The above-mentioned metals are exemplified by group IVa, VI or VIa metals of the periodic table or the alloys thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for forming metal boride thin films at low temperatures by ion plating.

(Prior art and problems to be solved) TiB2.
Borides of metals in groups ■a, Va, or VIa in the periodic table, such as ZrB2, NbB2, TaB2, CrB, MoB, etc., are heat-resistant and highly conductive ceramics, so they are used as contact materials and diffusion barriers in microelectronics. It is well known that it is used as a highly hard and wear-resistant coating material.

For the production of thin films of this metal boride, for example, Ti
In the case of film formation of B, according to the chemical vapor deposition method (CVD method),
Since TiCQ4 and BCQ3 gases are used, high temperature treatment at 900 to 1100° C. is required to form the film. Therefore, it is possible to form a film with superior adhesion to the base material compared to the physical vapor deposition method (PVD method), but it may form a reaction layer on the surface of the base material, soften the base material, or cause thermal deformation. It had the disadvantage of causing

Under these circumstances, physical vapor deposition is a method developed to form the above-mentioned compound film even under low temperature conditions.

Methods for forming metal boride thin films using this physical vapor deposition method include methods such as vacuum evaporation and sputtering. However, films formed by these methods have poor crystallinity compared to films formed by CVD, resulting in low conductivity, low hardness, and problems with adhesion to substrates.

Incidentally, attempts have been made to form a film using a sputtering vapor deposition method using a TiB target, but the adhesion to the substrate is still poor, and film formation using an ion plating method has not yet been successful.

The present invention was made in order to solve the problems of the prior art described above, and provides a method for producing a metal boride thin film that can be formed at a low temperature by ion plating and that can sufficiently improve adhesion to a substrate. The purpose is to

(Means for Solving the Problems) In order to achieve the object described in item 1, the present invention, in short, ionizes metal elements at a high ionization rate.
The aim is to sufficiently increase the adhesion between the substrate and the thin film by promoting the combination with evaporated boron at a low temperature below 0°C and applying an accelerating voltage.
The composition ratio of the metal or alloy contained in the boride can be strictly controlled, and (1) a crystalline thin film can be obtained at low temperatures because the metal is ionized.

The present invention will be explained in detail below based on examples.

With ordinary vacuum evaporation methods, it is difficult to form a metal compound of boron, and boron tends to bond with oxygen or carbon, which has a strong affinity for boron.

In this regard, in the present invention, the metal is first melted and evaporated in a vacuum chamber using an appropriate means such as an electron beam, and the evaporated metal is excited into an ion state. As a method for ionization, for example, a bias probe is provided near the evaporation source, and 40
Arc discharge is performed by applying a DC voltage of ~80V. At this time, in the case of metals that are difficult to cause discharge, if thermoelectrons or the like are used, it is possible to sustain the discharge state and promote ionization.

Atoms of metals or alloys excited to an ionic state with a high ionization rate in this way easily combine with evaporated boron even at low temperatures of 500°C or less, and since these compounds are good electrical conductors, they do not attach to the substrate. DC bias that is easy to handle
By simply applying 50 to -1500V, the kinetic energy of the ions can be used effectively and the adhesion strength with the substrate can be increased.

In addition, harmful elements such as oxygen, which tend to become impurities in the film, tend to be negatively charged and are repelled by the negatively charged substrate, so that impurities can be effectively prevented from being incorporated into the film.

(Example) A boride thin film was formed on a substrate using an ion plating apparatus equipped with an electron beam melting mechanism shown in FIG.

First, a crucible 3.
4 was charged with titanium and boron, respectively, and the pressure inside the tank was reduced to 10-6 Torr using a vacuum pump through the exhaust port 2. After the pressure reduction was completed, the electron beam generation mechanism 5 was activated, and the electron beam 6 started melting titanium and boron in the crucible 3.4.

After adjusting the electron beam output using the film thickness monitor 7 so that the evaporation rate of each element becomes Ti/B = 1/2, a positive potential of 40 V is applied to the bias probe 8 placed directly above each crucible to discharge an arc. Then, ionization of the evaporated components started.

Next, the shutter 9 was opened and ion plating was started. The bias voltage of the substrate 10 at this time is -500V.
The evaporation rate was 10 persons/see, and the substrate temperature was 200°C.

As a result of examining the film deposited to a thickness of 2 μm using X-ray diffraction, it is clear that the produced boride film is crystalline TjB2, as shown in FIG.

Furthermore, as a result of a scratch hardness test, it showed a high hardness of 9 on the Mohs scale.

Note that when other boride films were deposited in the same manner, crystalline hard thin films could be formed with desired composition ratios. At that time, thermionic filament 11 was used to utilize thermionic electrons when discharge was unlikely to occur.

(Effects of the Invention) As described in detail above, according to the present invention, each metal or alloy of metal borides is dissolved and evaporated, brought into an ionic state with a high ionization rate, combined at a low temperature, and further the compounds are combined at a low temperature. Since the metal boride adheres to the substrate by collision, it is possible to form a metal boride thin film that has excellent adhesion to the substrate and has high hardness. Furthermore, since the composition ratio can be easily controlled, various metal boride thin films can be easily produced, and crystalline thin films can be obtained at low temperatures. Furthermore, since the process can be carried out at low temperatures, softening or thermal deformation of the base material does not occur.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of an ion plating apparatus used in an example of the present invention, and FIG. 2 is a diagram showing an X-ray diffraction result of a boride film obtained in an example of the present invention. 1... Vacuum chamber, 2... Exhaust port, 3.4... Crucible, 5... Electron beam generation mechanism, 6... Electron beam. 7... Film thickness monitor, 8... Bias probe, 9
... Shutter, 10... Substrate, 11... Thermionic filament.

Claims (1)

[Claims] When forming a boride thin film of a group IVa, Va or VIa metal in the periodic table by ion plating, the metal or its alloy and boron are simultaneously melted and evaporated in a vacuum chamber, and the evaporated metal or Ionize and combine the alloys,
A method for producing a metal boride thin film, which further comprises applying an accelerating voltage to the ionized compound so that it collides with and adheres to a substrate placed in the vacuum chamber and heated to a low temperature of 500° C. or less.