JPH07316785A - Heating element for evaporating metal - Google Patents

Abstract

PURPOSE:To produce the heating element having a long life. CONSTITUTION:This heating element consists of an electrically conductive ceramic boat of which cavity has gradually increasing cross-sectional area in the directions from the end parts toward the central part of the cavity and also a ratio of the resistance per unit length of each of the end parts to that of the central part of 1.1 to 1.5. The conductive ceramic product is obtained by forming a powdery mixture consisting of powdery hexagonal boron nitride in which the ratio of the weight of the crystallites having >=800Angstrom size (La) to the total crystallite weight is >=50wt.%, powdery titanium diboride and powdery aluminum nitride into a formed body and sintering the formed body in a non-oxidizing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-evaporating heating element comprising a conductive ceramics boat used for evaporating a metal in a vacuum.

[0002]

2. Description of the Related Art Conventionally, as a heating element for metal evaporation of this type, for example, there is a boat made of conductive ceramics having a cavity as shown in Japanese Patent Publication No. 53-20256. The product name is "BN Composite EC" manufactured by Denki Kagaku Kogyo. The method of using this is to connect both ends of the boat with clamps to the electrodes to apply a voltage to generate heat, and melt and evaporate the metal contained in the cavity to obtain a vapor deposition film.

[0003]

[Problems to be Solved by the Invention]
As the number of times of use increases, the boat is melted and damaged by the molten metal, and the resistance gradually increases, so that the vapor deposition film becomes thin and the life of the boat becomes long. When the metal is aluminum, the average life is about 500 times. The purpose of the present invention is to extend this boat life.

[0004]

According to the present invention, the cross-sectional area of the cavity portion is gradually increased from the end portion to the center portion of the cavity, and the cavity end portion has a resistance to the resistance per unit length of the cavity center portion. Of the conductive ceramics boat having a ratio of 1.1 to 1.5, and the conductive ceramics, the crystallite size (La) is 800 A or more. It is obtained by molding a mixed powder containing 50% by weight or more of hexagonal boron nitride powder, titanium diboride powder and aluminum nitride powder, and sintering it in a non-oxidizing atmosphere. A characteristic heating element for metal evaporation.

The present invention will be described in more detail below. The feature of the present invention is that in a boat in which a cavity is provided in a conductive ceramic, the cross-sectional area of the cavity portion changes continuously from the end portion to the central portion of the cavity. By doing so, the heat generation (temperature) distribution of the boat is made uniform throughout and the life of the boat is extended.

The material of the boat used in the present invention is conductive ceramics, such as titanium diboride (TiB ₂ ), aluminum nitride (AlN) and hexagonal boron nitride (BN).
The composite sintered body is generally used, but the conductive material TiB ₂ may be ZrB ₂ .

However, in order to improve the corrosion resistance against molten metal and further extend the boat life, the BN powder has a crystallite size (La) of 800 A or more, particularly 90 or more.
A conductive ceramic produced by using a material in which the proportion of 0 A or more is 50% by weight or more, particularly 80% by weight or more is suitable.

The proportion of each component of the mixed powder is preferably 15 to 50% by weight of BN powder, 30 to 60% by weight of TiB ₂ powder and 10 to 45% by weight of AlN powder. The temperature is preferably 1700 to 2000 ° C. and the time is 30 to 120 minutes in a non-oxidizing atmosphere such as nitrogen or argon.

The heating element (boat) for metal evaporation of the present invention is
A molded body of an appropriate shape is cut out from the above-mentioned conductive ceramics, and a cavity is processed on the surface thereof. At that time, the cross-sectional area of the cavity portion is gradually increased from the end portion of the cavity to the central portion, and the unit length of the central portion of the cavity is increased. The ratio of the resistance per hit to that at the end of the cavity is 1.
It is processed so as to be 1 to 1.5. With such a structure, heat generation (temperature) of the boat
The distribution can be made uniform throughout and the life can be extended.

That is, as in the conventional structure, in the case of the metal-evaporating heating element which is simply a boat provided with a cavity, the temperature distribution due to the heat generation is as shown in FIG. 5, and the cavity central portion has the highest temperature distribution. Both ends of the cavity have the lowest parabolic shape. The temperature in the center of the cavity is 15
When the temperature is 00 ° C., both ends are about 1200 ° C., and the difference is about 300 ° C.

When a metal for vapor deposition is put in a cavity of a boat having such a temperature difference and a voltage is applied, the metal is melted and the wetting spreads throughout the cavity, but vaporization of the metal is caused in the cavity having the highest temperature. Intense in the central area. At the end of the vapor deposition, the molten metal begins to dry from the center of the cavity, but at this stage the molten metal still remains at both ends of the cavity. Therefore, since the resistance of the molten metal is smaller than that of the conductive ceramics, the load is applied to the central portion of the cavity by the amount of the current flowing in the molten metal at both ends of the cavity, and the life is about 500 times.

Therefore, the present inventors have made the above temperature difference as small as possible, for example, 250 ° C. or less, especially 200 ° C.
Various studies were made on the following boat structure, and the above structure was found.

In the present invention, it is necessary to gradually increase the cross-sectional area of the cavity portion from the end portion to the center portion of the cavity, one example of which is shown in FIGS. That is, the cross-sectional area is changed by continuously forming a groove having a slight taper from the cavity adjacent portion slightly beyond the cavity portion to the cavity central portion on the back surface of the boat. The processing of such continuous grooves is not limited to the back surface of the boat, and may be performed on the side surface of the boat or the inner surface of the cavity.

Japanese Patent Publication No. 54-42676 proposes to make the cross-sectional area smaller than that of the cavity by notching the adjacent portion of the cavity in order to prevent the molten metal from creeping up from the cavity. However, since this does not continuously change the cross-sectional area of the cavity itself, it is not possible to achieve a long life as in the present invention (see Comparative Example 3).

Next, in the present invention, it is necessary that the ratio of the resistance per unit length of the central portion of the cavity to that of the end portion of the cavity is 1.1 to 1.5. If this ratio is less than 1.1, the effect of reducing the temperature difference becomes insufficient, and if it exceeds 1.5, the temperature in the vicinity of both ends inside the cavity becomes higher than the temperature in the center of the cavity, and excessive heat generation occurs. May damage the boat.

In order to provide such a resistance ratio, the ratio of the cross-sectional area of the cavity end to the cross-sectional area of the cavity center is 0.7 to 0.
It can be performed by setting 9.

[0017]

【Example】

Example 1 TiB ₂ powder (average particle diameter 12 μm) 45% by weight, BN
Powder (average particle size 0.7 μm, crystallite size (La)
215A) 30% by weight and AlN powder (average particle size 1
0 μm) 25 wt% mixed powder was filled in a graphite die,
200mm diameter by hot pressing at 1750 ℃
× A sintered body having a height of 6 mm was produced.

From this sintered body, width 6 mm × thickness 4 mm ×
A 110 mm long rod-shaped body is cut out, a cavity of 4 mm width x 2 mm depth x 60 mm length is provided in the center of the surface, and a groove is provided on the opposite back side, and a boat as shown in Figs. Was prepared as a heating element for metal evaporation of the present invention.

As shown in FIGS. 2 and 3, the groove has a taper shape with a width of 4 mm having a depth of 0.8 mm at the end of the cavity and 0 mm at the center of the cavity. It is formed from the part adjacent to the cavity that is slightly over. In this boat, the ratio of the cavity end to the resistance per unit length of the cavity center is 1.21, and the ratio of the cavity end cross section to the cavity end is 0.80. When the temperature of the central portion of the cavity heats up to 1500 ° C., the temperature of both ends of the cavity becomes 1320 ° C. (see FIG. 4).

In order to evaluate the life of the boat, the applied voltage was determined and set so that the temperature at the center of the cavity was 1500 ° C. by connecting the end of the boat to the electrode with a clamp. Aluminum amount 80mg per time, energizing time 30 seconds,
A vapor deposition test was performed at a vacuum degree of 2 × 10 ⁻⁴ torr, and this operation was repeated at a set constant applied voltage. The boat life was defined as the number of repetitions when the thickness of the aluminum vapor deposition film at a position 200 mm above the boat became 2000 A or less. The result was 910 times.

Examples 2 to 3 and Comparative Example 2 Example 1 was repeated except that the groove depth was variously changed and the temperature difference, the resistance ratio and the cross sectional area ratio were changed as shown in Table 1. A boat was prepared and evaluated in the same manner as in. The results are shown in Table 1 and FIG.

Comparative Example 1 A boat was prepared and evaluated in the same manner as in Example 1 except that no groove was formed. The results are shown in Table 1 and FIG.

COMPARATIVE EXAMPLE 3 Instead of grooving, 1.5 m was formed in the vicinity of the cavity.
A boat was prepared and evaluated in the same manner as in Example 1 except that a notch of m was provided and the ratio of the cross-sectional area of the cavity to that of the adjacent cavity was 0.94 (Japanese Patent Publication No. 54-42676). Publication equivalent). The results are shown in Table 1.
Shown in.

Example 4 A boat was prepared and evaluated in the same manner as in Example 1 except that BN powder having an average particle size of 3 μm and a crystallite size (La) of 900 A was used. The results are shown in Table 1.

[0025]

[Table 1]

[0026]

According to the present invention, a heating element (boat) for metal evaporation having a long life is provided.

[Brief description of drawings]

FIG. 1 is a perspective view of a heating element for metal evaporation according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

3 is a sectional view taken along line BB of FIG.

FIG. 4 is a diagram showing the relationship between the distance from the center of the cavity and the temperature in the metal-evaporating heating element of Example 1.

FIG. 5 is a relationship diagram between the distance from the center of the cavity and the temperature in the metal evaporation heating element of the conventional example (Comparative Example 1).

FIG. 6 is a diagram showing the relationship between the distance from the center of the cavity and the temperature in the metal-evaporating heating element of Comparative Example 2.

Claims (2)

[Claims] 1. The cross-sectional area of the cavity gradually increases from the end to the center of the cavity, and the ratio of the resistance per unit length at the center of the cavity to that at the end of the cavity is 1.1 to 1. A heating element for metal evaporation, characterized by comprising a conductive ceramics boat of 0.5. 2. The conductive ceramics is a mixed powder containing hexagonal boron nitride powder, titanium diboride powder and aluminum nitride powder in which the ratio of crystallite size (La) of 800 A or more is 50% by weight or more. The heating element for metal evaporation according to claim 1, wherein the heating element is obtained by molding a metal and sintering it in a non-oxidizing atmosphere.