JPH01208451A - Method for evaporating sublimable substance and crucible - Google Patents

Abstract

PURPOSE:To stabilize evaporation and to reduce fluctuations in evaporation rate by placing sublimable substances in plural small crucibles and simultaneously heating these crucibles to evaporate the sublimable substances. CONSTITUTION:Plural heaters for small crucibles are formed in the middle of a tungsten wire and respective heater parts are coated with alumina and baked, by which small crucibles 1, 2, 3, 4, 5, 6, 7, 8, 9 are formed. The above small crucibles 1-9 have sectional forms broadening from the bottoms toward the upper parts, respectively, and sublimable substances are placed in these crucibles. When the small crucibles 1-9 are simultaneously heated by the above constitution and the sublimable substances are evaporated, the amount of evaporation can be averaged as a whole and phenomena, such as bumping, can be prevented and, as a result, stable evaporation can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the evaporation of sublimable substances, particularly sublimable substances suitable for producing vapor-deposited thin films and ultrafine particles.

Concerning evaporation methods and crucibles for evaporating sublimable substances.

[Prior Art] Sublimation and evaporation of substances include not only liquids but also sublimation from solids. In the case of liquids, the part that becomes hot usually increases in volume,
It rises and evaporates at the upper surface. In vacuum evaporation, the amount of evaporation is controlled by controlling the current flowing through the heating filament. A similar evaporation method is used for sublimable substances.

Figure 6 shows an example of a crucible used for resistance heating vacuum evaporation, a filament 21 of a high melting point metal such as tungsten.
Defining the skeleton of the crucible, a chemically inert, heat-resistant material such as alumina coats the filament to form the container. Alumina is fired at high temperatures. Crucibles are made in various sizes depending on how much vaporized material is to be loaded. Such a crucible is placed in a vacuum container, loaded with a target substance, and heated by passing an electric current through the filament from a low-voltage, high-current circuit.

Evaporate.

[Problems to be Solved by the Invention] When a sublimable substance is evaporated in a normal crucible, phenomena such as bumping are likely to occur, and changes over time are large.

It is conceivable to monitor the amount of evaporation and feed it back to the heating power source, but this would complicate the device and would not provide good controllability.

Analysis performed to solve problem E] In the case of vapor deposition of a sublimable substance, the substance remains solid in the crucible. If it is a liquid, the heated portion of the crucible wall will rise and cause convection, so the temperature distribution within the crucible will be averaged and the evaporation rate will be constant. However, in the case of sublimable substances, they do not mix due to convection.

In the case of a crucible in which a filament for resistance heating is embedded, if you compare the part in contact with the wall of the crucible with the inside of the crucible,
The part that is in contact with the wall gets hotter. therefore,
Evaporation and sublimation of sublimable substances occur only on the crucible wall. Since the crucible is loaded with a sublimable substance, the vapor molecules that evaporate on the bottom wall cannot just fly out to the outside, and will feel trapped, since the amount of sublimable substance on the top is small. , if it is mechanically fragile, it may break and the evaporated molecules may fly out.

Furthermore, when the portion in contact with the wall surface evaporates, a gap is created between the wall surface and the sublimable substance. The part separated from the wall through the gap will be heated only by radiation.When the shape of the remaining sublimable material becomes unstable, the sublimable material collapses and the sublimable material returns to the crucible wall. These phenomena may be accidental and difficult to control; bumping is considered to be a phenomenon peculiar to sublimable substances.

[Means for Solving the Problems] In order to improve the above problems, according to the present invention, sublimable substances are simultaneously evaporated from a plurality of small crucibles.

A common lid member having openings may be provided over the plurality of small crucibles.

[Function] In the planar area where the small crucible and the upper surface of the sublimable substance are in contact, the sublimable substance will be able to freely evaporate.Using a plurality of small crucibles increases this freely evaporated area.

By reducing the size of one crucible, even if phenomena such as bumping cannot be prevented, their scale can be reduced.

Furthermore, since the variation in the amount of evaporation in each crucible will occur as an independent event, the variation in the amount of evaporation from all the small crucibles will be averaged and will be close to a constant value.

When a lid member with openings is used, the only evaporation source seen from the outside is the opening; 1. The evaporated molecules are temporarily stored, and the vapor of the sublimable substance with reduced fluctuation in evaporation amount is generated from the openings.

[Example] FIG. 1 shows a multi-layer crucible according to an example of the present invention.
A plurality of small crucible heaters are formed in the middle of one tungsten wire 11. Each heater part is coated with alumina and fired, and the small crucibles 1, 2, 3, 4, 5, 6,
7, 8.9 are formed. Each crucible has a cross-sectional shape that widens from the bottom toward the top. A plurality of small crucibles are arranged closely to form one planar evaporation source. Although a shape in which a plurality of small crucibles are arranged in a folded manner is shown, the arrangement may be such that the small crucibles are lined up on one circumference. In that case, each car crucible will be under the same conditions, making it easier to maintain uniformity among the small crucibles. Of course, other placement shapes are also possible; as shown in Figure 1, the small crucibles are placed inside and the small crucibles are placed outside. When there is a small crucible to be
By adjusting the pitch of the heater, it is possible to improve the uniformity of heating of each crucible.

The series-connected multi-unit crucible shown in Figure 1 has a power supply current of 1
As in the case of multiple small crucibles, the electric voltage is multiplied by the number of small crucibles. Therefore, for example, a relatively simple low-current, high-voltage type power supply such as a Slydac can be used.

FIG. 2 shows a multi-rate crucible according to another embodiment of the present invention. Winter crucibles 1, 2, 3, 4.5, 6° 7.8.9 are similar to those in FIG. As described, a plurality of small crucibles are placed in close proximity to each other. Electrically, multiple crucibles are connected in parallel, and power lines 12.13
connected between. In the case of the serial type multi-rate crucible shown in Figure 1,
If there is non-uniformity among the small crucibles, only some of the small crucibles tend to reach high temperatures, but the parallel-connected multi-rate crucible of this embodiment can improve this point. In other words, if some small crucibles become hotter than others, the metal in the heater has a higher resistance as the temperature rises, so the resistance of that small crucible's heater increases, limiting the current. , which works to lower the temperature, thus automatically adjusting the winter crucible to operate evenly.

In the case of the multiple crucible shown in FIG. 2, the current is multiplied by the number of small crucibles, so a low voltage, large current power source as shown in FIG. 3 is suitable for driving. In FIG. 3, the slider 15 is connected to the commercial AC power supply 14, and the slider 15 is connected to the commercial AC power supply 14.
A low voltage transformer 16 is connected to the output side of. A group of small crucibles is connected to the output of the low voltage transformer. Furthermore, a control circuit may be provided.

Another embodiment of the crucible group 18, shown in FIG. 4, is as shown in FIG. 1 or 2. This small melting pot group 1
A lid member 20 having an aperture 19 is disposed above the cover 8 . The lid member 20 is shown in FIG. A heater 17 is arranged on the inner surface of the lid member 20 with the opening 19 removed. Referring to FIG. 4, the vapor of the sublimable substance evaporated from the small crucible group 18 is stored between the small crucible group 18 and the lid member 20. The vapor of the stored sublimable substance is ejected from the aperture 19. The opening 19 of the lid member 20 allows the combination of the small crucible group and the lid member to perform a similar function as a Knudsen cell.
The steam that has hit other parts is heated by the heater 17 and is not solidified and deposited on the lid member 20, but is trapped between the small crucible group 18 and the lid member 20. Temporal fluctuations are thought to be smoothed out by creating an intermediate state where steam is temporarily stored. Figure 0 shows a semi-open configuration, but it is also possible to embed the small crucibles in an alumina plate and make them contact with the lid member. For example, the sealing effect may be further enhanced.

[Effects of the invention: Since multiple small crucibles are used simultaneously to evaporate sublimable substances, the number of stable evaporation sources increases, and rapid increases in evaporation, such as large-scale bumping, are restricted, and the evaporation rate is reduced. Variability is reduced.

Further, by using a lid member having an opening, fluctuations can be further reduced.

[Brief explanation of the drawing]

FIG. 1 is a top diagram showing a multi-component crucible according to one embodiment of the present invention, FIG. 2 is a top diagram showing a multi-component crucible according to another embodiment, and FIG. 3 is a power supply circuit. 4 is a line diagram of the front side showing a crucible structure according to another embodiment, FIG. 5 is a line diagram of the lower surface of the lid member 20 of FIG. 4, and FIG. 6 is a diagram showing an example of a crucible according to the prior art. FIG. Explanation of symbols 1.2, 3, 4, 5° 6.7, 8.9 Small crucible 11 Filament 12.13
Power line 15 Slider 16 Low voltage transformer 17 Heater 18 Small crucible group 19 Opening 20 Lid member

Claims (4)

[Claims] (1) A method for evaporating a sublimable substance, which comprises storing a sublimable substance in a plurality of small crucibles, and heating the plurality of small crucibles simultaneously to evaporate the sublimable substance. (2) The method for evaporating a sublimable substance according to claim 1, further comprising covering the plurality of small crucibles with a lid member having openings, and the vapor evaporated from the plurality of small crucibles is evaporated from the openings. A method of evaporating a sublimable substance, which is characterized by evaporating through pores. (3) having a plurality of electrically connected resistive heating filaments, each filament defining a space for a crucible, and covering each filament with a chemically inert and heat resistant material; 1. A crucible for evaporating a sublimable substance, characterized by forming several small crucibles. (4) The crucible for evaporating a sublimable substance according to claim 3, further comprising a common lid member having an opening and covering the plurality of crucibles. Crucible used.