JPH03170661A - Method for evaporating sublimable metal - Google Patents

Abstract

PURPOSE:To easily and stably maintain the evaporation velocity of a sublimable metal by selectively evaporating a sublimable metal from an alloy bath consisting of the above sublimable metal and a metal capable of being alloyed with the above sublimable metal, having an eutectic composition, and also having respectively specified melting point and vapor pressure. CONSTITUTION:An alloy bath which consists of a sublimable metal and a metal (1) having a melting point equal to or higher than that of the sublimable metal, (2) capable of being alloyed with the sublimable metal and also having an eutectic composition, and (3) remarkably reduced in the vapor pressure at the same temp. as compared with the sublimable metal is formed. Subsequently, the sublimable metal is selectively evaporated from the above alloy bath. The above requirement (1) is important for the selective evaporation of the sublimable metal from the alloy bath. The requirement (2) is a characteristic essential to the formation of the alloy bath, and, owing to this characteristic, the molten bath can be formed at a lower temp. and the evaporation of the molten metal can be inhibited more effectively. Further, the requirement (3) is important for the selective evaporation of the sublimable metal alone.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of application in industry] The present invention is directed to the use of Cr, Mn. The present invention relates to a method for evaporating sublimable metals such as Go and Mg, and in particular to an improved method that allows easy control of the amount of evaporation of these sublimable metals. Vacuum deposition plating (including ion blating, etc.)
This is useful when carrying out.

[Prior art] When carrying out the vacuum evaporation plating method, the metal raw material to be evaporated is heated and evaporated by an appropriate means such as high frequency or electron beam, and the evaporated metal vapor is deposited on the substrate to perform the evaporation. Forms a film. In this case, since the melting point of ordinary metal raw materials is considerably lower than the temperature at which the vapor pressure is sufficiently increased, the usual procedure is to first melt the raw metal in a raw material tank such as a crucible, and then further raise the temperature. This evaporates metal atoms from the surface of the molten metal bath.

Therefore, the effective evaporation area is equal to the surface area of the molten metal bath, and the amount of evaporation under high vacuum can be controlled primarily by thermal energy. However, sublimable metals such as those mentioned above exhibit high vapor pressure under high vacuum conditions even at temperatures below the melting point of the metal.
When thermal energy is applied to such a metal, evaporation proceeds from the surface of the metal lump, which has not yet begun to melt. Therefore, in this case, the entire surface of the metal lump becomes the effective evaporation area, and the effective evaporation area not only changes significantly depending on the specific surface area of the metal lump, but also as the metal lump becomes smaller as evaporation progresses, the effective evaporation area changes. will increase relatively, so
Even if the applied thermal energy is kept constant, the amount of input energy per unit area, that is, the power density increases, making it impossible to maintain a constant amount of evaporation from the surface of the metal lump.

On the other hand, in order to apply vapor deposition plating with a stable coating amount to the surface of a strip-shaped substrate such as a continuously running steel plate, it is essential to maintain a constant evaporation rate of the metal raw material, and when performing alloy plating, In order to keep the plating composition constant, it is extremely important to keep the evaporation rate of each metal constituting the alloy plating constant according to the target alloy composition. However, when a sublimable metal is used, as mentioned above, the effective evaporation area of the metal lump is uncertain and changes over time, so it is extremely difficult to control the evaporation rate to a constant level. It becomes impossible to maintain a constant amount of deposited plating and alloy composition.

[Problems to be Solved by the Invention] The present invention has been made with attention to the above-mentioned circumstances, and its purpose is to evaporate the sublimable metal to perform vapor deposition plating, etc. The purpose of the present invention is to provide a method that can maintain a stable evaporation rate using simple means.

[Means for solving the problems] The structure of the method of the present invention that can solve the above problems, or
When evaporating a sublimable metal, the sublimable metal must meet the following requirements: - Show a melting point comparable to or higher than the sublimable metal, - Be alloyed with the sublimable metal and have a eutectic composition, - Sublimable metal The gist of this method is to form an alloy bath with a metal that satisfies the following: whose vapor pressure at the same temperature is significantly lower than that of metal, and to selectively evaporate sublimable metals from the alloy bath.

[Function] Hereinafter, the function and effect of the present invention will be explained in detail following the experimental history.

The present inventors used Cr as a representative example of a sublimable metal, and investigated the evaporation behavior of Cr using vacuum evaporation plating equipment schematically shown in FIG. That is, in FIG. 1, 1 is a deposition chamber, 2
is a strip base material (copper strip, etc.), 3 is a support roll, 4 is Cr
A heating electron gun, 5 an electron beam, 6 an exhaust port, 7 a raw material tank, and 8 a Cr ingot (sublimable metal ingot) are placed in the raw material tank 7 in the vapor deposition chamber 1 maintained at a high vacuum. Charged Cr lump 8
was heated and evaporated by an electron beam 5, and Cr vapor was continuously deposited on the surface of the strip-shaped substrate 2 that was continuously traveling above the Cr vapor.

As a result, even when the electron beam output is kept constant, C
It was confirmed that the amount of r deposited varied depending on the specific surface area of the Cr lump 8, and also varied considerably over time.

In contrast, non-sublimable metals (A
When performing vacuum evaporation of materials such as I), the raw metal is first melted in the raw material tank 7 by electron beam heating, and then evaporated successively from the molten bath surface and deposited on the strip-shaped base material, keeping the electron beam output constant. Almost no variation in the amount of vapor deposition was observed when

It is thought that these differences are caused by whether or not the effective evaporation area of the raw metal can be kept constant as described above.

Therefore, we thought that if sublimable metals were once molten and evaporated from the surface of the molten bath, the effective evaporation area would be kept constant at all times, and the evaporation rate could be maintained stably. As a result of further investigation into the means of forming a molten bath of a sublimable metal, we came up with the idea of forming a molten bath by alloying a sublimable metal with a metal that satisfies the following requirements.

■ Shows a melting point comparable to or higher than the sublimable metal; ■ Has an alloy with the sublimable metal and has a eutectic composition; ■ Has a significantly lower vapor pressure at the same temperature than the sublimable metal. Requirements specified in ■ above is an important requirement for selectively evaporating sublimable metals from alloy baths.

That is, in general, the lower the melting point of the metal, the higher the vapor pressure, and the metal of the present invention (hereinafter referred to as
If the melting point of the molten metal (referred to as molten metal) is considerably lower than that of the sublimable metal, a large amount of the molten metal will be mixed into the evaporating sublimable metal vapor, and the vapor-deposited plating will contain the molten metal. It is from.

Furthermore, among the requirements specified in (■) above, the former is an essential characteristic for forming an alloy bath, and in the case of a sublimable metal and a non-alloyed metal, the two simply coexist in a mixed state, and the alloy bath itself no longer formed. Moreover, the latter requirement is extremely important for selectively evaporating only sublimable metals from the alloy bath. In other words, the eutectic composition refers to a specific alloy composition that exhibits a eutectic point lower than the melting point of each of the sublimable metal and the meltable metal alone, as shown in the phase diagram in Figure 2, for example. By using a molten metal, it is possible to form a molten bath at a lower temperature, and as a result, the evaporation of the molten metal is more effectively suppressed.
This is because selective evaporation of sublimable metals is promoted. On the other hand, the phase diagram of the alloy when using a molten metal that does not have a eutectic composition is as shown in Figure 3, for example, and the lowest melting point is reached when the sublimable metal is 100%. As the temperature increases, the melting point becomes higher, and even if an alloy bath is attempted to be formed in such a system, the sublimable metal will evaporate before the alloy bath is formed, so the effect intended by the present invention cannot be expected. .

Furthermore, the above requirement (2) is important for selectively evaporating only sublimable metals. In other words, if the vapor pressure of the molten metal is higher than that of the sublimable metal, the molten metal will evaporate first, and even if the vapor pressure of the molten metal is lower than that of the sublimable metal, both will evaporate. This is because if there is not much difference between the two, a large amount of molten metal vapor will be mixed into the sublimable metal vapor, making it impossible to obtain the target vapor-deposited plating composition.

Cr, Mn. Examples of melting metals that satisfy the above requirements in combination with sublimable metals such as Co and Mg include Ta, Zr, and Nb, and the type of melting metal used depends on the type of sublimable metal used and It may be selected appropriately in consideration of evaporation conditions and the like. Furthermore, it is most preferable to set the blending ratio of the sublimable metal and the meltable metal so that the blending ratio is close to the eutectic composition in order to lower the melting temperature and suppress the evaporation of the meltable metal. In addition, when evaporation is carried out continuously over a long period of time, sublimable metals are selectively evaporated, and as a result, the alloy bath composition gradually shifts to the molten metal-rich side, so If the initial bath composition is maintained by sequentially replenishing the sublimable metal, selective evaporation of the sublimable metal can proceed more efficiently, which is preferable.

As described above, the present invention is characterized in that a sublimable metal is combined with a specific molten metal to form an alloy bath, and the sublimable metal is selectively evaporated from the surface of the molten bath. Various changes and applications can be made by taking advantage of this.

For example, the present invention can be applied to various processes that utilize the evaporation and condensation of sublimable metals, in addition to the vacuum evaporation plating method shown in Figure 1. In addition to substrates, it can also be used for vapor deposition plating of linear, rod-shaped long substrates, spherical substrates, etc. Further, it is preferable to employ an ion plating method instead of a vacuum evaporation method because a plated layer with even better adhesion and bottle hole resistance can be obtained. In addition, although the above explanation mainly focused on the case where a plating layer of only a sublimable metal is formed, a plurality of raw material sources are provided in the vapor deposition chamber to evaporate a plurality of metal vapors, and two or more types of sublimable metals are formed. It is also possible to perform composite plating or multilayer plating that combines a sublimable metal and a non-sublimable metal.

[Example] Using the vacuum evaporation plating equipment shown in FIG. 1, a continuous Cr evaporation plating process was performed on a steel strip under the following conditions.

Plating metal: Cr Steel material to be plated: Ultra-low carbon Ti-added steel (strip shape) Pretreatment of steel material to be plated: Preheating by electron beam (400°C) and surface activation treatment by Ar ion bombardment Vaporization chamber vacuum degree: 8 x 10 -'TorrCr heating source; Electron beam heating (electron gun: 300KW) Cr alloy bath composition: Cr-Zr alloy bath (Cr: about 15%,
Cr was added at intervals according to the amount of Cr evaporated to maintain the Cr concentration> Plating deposition amount: The results of measurement using a fluorescent X-ray film thickness meter are shown in Table 1. Table 1 also shows experimental results in which Cr lumps were used alone as a comparative method and sublimed directly from the lumps.

As is clear from Table 1, the comparative example (Experiment No. 3
), the variation in the amount of Cr adhesion is large, and the amount of Cr deposited is
It is clearly shown that the r evaporation amount is very unstable, but in the example of the present invention (experiment No. 1.2), the Cr source is in a molten state by alloying with Zr. As a result of specifying the effective area for evaporation of Cr as the bath surface area of the raw material tank, the variation in the amount of Cr deposited was reduced to less than % of that of the comparative example. Furthermore, since Zr has a much lower vapor pressure than Cr, almost no Z' is found to be mixed into the plating layer.

[Effects of the Invention] The present invention is structured as described above, and by alloying a sublimable metal with a specific metal and evaporating it from a molten state, the effective evaporation area can be kept stable, and the degree of vacuum and A stable arbitrary amount of evaporation can be maintained by adjusting the heating energy. Therefore, when this evaporation method is used for vacuum deposition of sublimable metals, it is possible to suppress variations in the amount of deposited plating and the composition of alloy plating, and it is possible to obtain a hot-tempered product with stable quality.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram illustrating a vacuum evaporation plating method using a sublimable metal, Figure 2 is a state diagram when an alloy consisting of a sublimable metal and a meltable metal exhibits a eutectic composition, and Figure 3 is a phase diagram of an alloy that does not exhibit a eutectic composition.

Claims (1)

[Claims] In vaporizing a sublimable metal, the sublimable metal must meet the following requirements: (1) It has a melting point comparable to or higher than that of the sublimable metal; (2) It is alloyed with the sublimable metal, and An alloy bath is formed with a metal that has a eutectic composition, (3) has a significantly lower vapor pressure at the same temperature than a sublimable metal, and the sublimable metal is selectively evaporated from the alloy bath. A method for evaporating sublimable metals.