LV13910B - Resistive evaporator for depositing of coatigs in vacuum - Google Patents

Abstract

The invention relates to devices for vacuum evaporation of metals and alloys. It may be used, for example, for depositing comparatively thick coatings onto roll substrates and disperse materials in lengthy processes, as well as for producing free metal foils. It is necessary to evaporate considerable amount of the material in order to implement highly productive processes and deposit thick coatings in vacuum. Usually the deposited material feeding into the evaporator during the deposition process is used in order to evaporate so big amount of the material. Evaporation instability and significant variation of the coating thickness are observed under such operation conditions. Process instability increases in evaporating some metals (for example, tin, silver). In accordance with the offered invention the evaporator is provided with the chamber of the evaporation fluctuation damping. It allows expending the range of evaporation rates while using various metals and substrates. If different vapour sources, for example, a thermal copper evaporator and magnetron sputtering device, or thermal evaporators of different evaporation rates are used in one technological process, the offered technical solution allows better co-ordination of deposition rates from the mentioned sources. It also provides the possibility to change the evaporation rate in a wide range and select optimal deposition parameters for each deposited layer and upgrade quality of the final product in this way.

Description

The invention relates to devices for vacuum evaporation of metals and alloys. It can be used, for example, in sustained high-yield processes for the application of relatively thick coatings to roll substrates and dispersed materials, and for the production of free separable condensates in the form of metal foils.

KNOWN TECHNICAL LEVEL

A significant amount of this material needs to be evaporated in order to carry out high-yield processes by applying a thick coating under vacuum. In order to evaporate such a large amount of material per cycle, it is common practice to feed the evaporated material to the evaporator during evaporation. The material can be fed to the evaporator in the form of wire, granules, powder and the like. Sometimes the material to be evaporated is fed to the evaporator in the liquid phase.

Vaporization devices for applying vacuum coatings to roller substrates are known. For example, U.S. Pat. No. 5230923 discloses a device for continuous evaporation of silicon, silicon oxides or small amounts (up to 10%) of these materials with a coating to deposit a coating on a roll of polymeric film. Other metals include tin, indium and aluminum. During the coating process, the material to be evaporated is fed into the evaporator in the form of tablets, small cylinders, wire, powder and the like through its inlet. At the opposite end of the evaporator there is an opening for removing excess evaporative material to ensure uniform evaporation. The device is designed for continuous, continuous evaporation of material. However, the use of moving mechanical devices (in the form of an endless belt or pusher) to feed the evaporated material under vacuum significantly complicates the process and reduces the safety of the device. Since special moving devices are not intended to remove excess material, it is obviously intended that the operation of the feed device may also facilitate the removal of excess material (despite the fact that at least some of this material may also be in a melted state). The long-term reliability of this system raises doubts. Hardening of the smallest material near the outlet means the start of the process blocking. In general, this known device does not have sufficient operational reliability under vacuum and at relatively high temperatures.

A report by I. Ashmanis at the 51st Annual Technical Conference of the Vacuum Coating Society, "Vapor Evaporation from Boats of Hard Melting Material using a Wet Evaporator," proposes a copper vacuum evaporator closest to the proposed invention (I. Ashmanis, V. Klov, E. Yadin, J. Wolf, Wire Fed Evaporation of Copper from Refractory Mint Boats, Proceedings of the 51st Annual Technical Conference, 2007). A known copper evaporator is a unit containing two tubular evaporators mounted in a power supply column. The device also contains an evaporator power wire feed mechanism and a screen system. Each tubular evaporator is a linear structure consisting of a thin-walled tube (screen) and a porous core, the last concentric inside the tube. Tubes and porous core ends are pressed into molybdenum contacts to provide safe electrical and mechanical contact. Copper vapor outlets are provided in the part of the pipe facing the base. Molybdenum contacts have a number of holes to form a power wire melting chamber and channels for the discharge of molten power to the porous core. Due to the comparatively high electrical resistance of the evaporator, the evaporator is heated with a direct current flow. These types of devices work well at relatively high power wire feed rates, but when the wire feed rate is reduced to 5-6 g / min. and below, evaporator malfunctions are observed. At low wire feed speeds the evaporator current fluctuates and the evaporation rate becomes unstable, which significantly reduces the uniformity of the coatings applied. The reason for this phenomenon is that by reducing the feed rate of the evaporated material to 5-6 g / min. and lower during the melting process, the molten metal under the action of surface tension forces the ball to contract. This ball breaks off the evaporator contact and hangs over the melted material at the end of the power wire of the chamber. The wire continues to melt and the size of the ball increases. Once the size is reached, when the force of gravity becomes greater than the surface tension force, the ball breaks away from the wire and falls into the melting chamber, further wetting the porous core, venting along its entire length and evaporating. In the meantime, the wire feed into the melting chamber continues. As soon as the end of the wire comes into contact with the contact, the wire begins to melt, the molten material breaks away from the contact, the ball collapses, and the cycle described above repeats.

It is known that the feeding of easily meltable metals, such as indium, to the evaporator in the form of a wire is quite problematic due to its low melting point. In this case, the metal to be evaporated is fed to the evaporator in a liquid form. Occasionally, small amounts of indium beads at the end of the metal wire and evaporation fluctuations can be observed when the metal feed rate is less than 5-6 g / min. With the help of the evaporator offered by I. Ashmanis A / S SIDRABE 1.5 mm diameter copper wire was evaporated at feed rates of 10, 8, 5 and 3 g / min. If the evaporator supply voltage was correctly selected, no problems were encountered in copper evaporation at wire feed rates of 10 and 8 g / min. Measurements of the control thickness of the coatings applied to the polymer film showed that the resulting thickness of the coatings did not exceed ± 5%. After power stretched feed speed to 5 g / min. current fluctuations were observed with a mean period of about 6 seconds. The beads, which periodically appeared at the end of the wire, were about 5-6 mm in diameter. Measurements of the control of the coating thickness applied to the polymer film showed that there was a large variation in the coating thickness in this mode of operation and that the uniformity of the coating in places reached ± 40%. When other materials (including indium, silver and others) were evaporated, process instability increased.

OBJECT OF THE INVENTION

The object of the present invention is to extend the evaporator's technological capability as a result of process stability and coating quality improvement, including extending the evaporation rate range during the application of various metal coatings.

BRIEF DESCRIPTION OF THE DRAWINGS

The use of the proposed device for metal vaporization by wire feeding is shown in Fig. 1. 2 and 2, where FIG. the structure of the evaporator is shown, including a) - side view, b) top view, c) - cross section of the evaporator in plane A-A, but fig. one of the possible schemes for the evaporator assembly in the vacuum chamber is shown. Fig. 3 the application of the proposed device is shown, where the lighter metal is fed to the evaporator in liquid form.

SPECIFICATION OF MARKS USED IN DRAWINGS:

1- thin-walled tube; 2 - porous cores; 3 - evaporation chamber; 3.3 - vibration damping chambers; 4 - partitions; 5 - steam outlet opening; 6 - power supply contact;

- chamber of melted material; 8 - channel for transferring the molten material to the porous core; 9 thermal bridges; 10 - end contacts; 11 - durable fusible insert; 12 - power supply cooled contacts; 13 - wire feed mechanism of the material to be evaporated; 14 EN 13910 Evaporating wire reel; 15 - wire of the material to be evaporated; 16 - base; 17 vacuum camera; 18 - power supply; 19 - cooling water supply and drainage channels; 2heated tank; 21 - heated metal wire; 22 - Funnel.

DETAILED DESCRIPTION OF THE INVENTION

The evaporator consists of a thin-walled tube 1 with a porous core 2 mounted symmetrically along its axis, thereby creating a partially enclosed space between the tube 1 and the porous core 2. In this space, zone 3 is an evaporation chamber located in the middle portion of the evaporator. Opposite it is a vapor outlet 5 in the tube 1. Through this opening 5 in the tube 1 evaporates and the coatings are applied to the substrate. In accordance with the present invention, additional partitions 4 are provided on both sides of the evaporation chambers 3 and thereby create oscillation chambers 3 'and 3'. These oscillation damping chambers have no openings in the tube 1 for venting steam towards the base. Both ends of the tube and the porous core are pressed into molybdenum contacts 6 to provide safe electrical and mechanical contact. The tube 1 in pins 6 can be rotated about its axis to direct the flow of steam in any desired direction. A number of holes are formed in the molybdenum contacts 6 to form the melted material chamber 7 and the channels 8 for feeding the melted material to the porous core 2. The camera 7 is useful for melting the vaporized metal wire or receiving the evaporated metal in liquid form. The molten metal is further directed to the porous core 2.

The power supply contacts are made of one piece of a hard-melting material such as molybdenum. In order to provide the necessary temperature difference between the melted material chamber 7 and the end contact 10, thermal bridges 9 are provided here to increase the life of the evaporator by inserting a sleeve 11 of material resistant to the evaporated metal at the bottom of the chamber 7. . With the end contacts 10, the evaporator is pressed through the graphite intermediate plates into the cooled copper current leads 12 (see Fig. 2). Fig. 2 a base 16 and a circuit diagram for mounting the evaporator in a vacuum chamber 17 are also shown. In order to heat the evaporator and to ensure its operation and control, a power supply 18 is required with appropriate parameters including a quadrature stabilization mode of the output voltage. The channels 19 feed and drain water for cooling the end contacts 10.

In order to feed the evaporated material into the evaporator, a feed mechanism with a quantity of evaporated material is needed for the entire operating cycle. Example 2 a mechanism 13 for feeding the vaporized material in the form of a wire is also shown. The required amount of vaporizable wire 15 is wound on spool 14. The coating is applied to substrate 16.

Fig. 3 shows the application of the proposed device when lighter metal is used. In this case, the material to be evaporated is fed to the melted material chamber 7 in liquid form. In addition to the evaporator elements mentioned above, this application also comprises a heated tank 20 with a liquid metal and a heated metal conduit 21 for discharging the liquid metal into the chamber 7 through a funnel 22.

The evaporator operates as follows. When the vacuum chamber 17 reaches a pressure lower than 0.1 militers, the evaporator power supply is turned off. An increasing voltage is gradually supplied to the evaporator, which is set at cooling contacts 12. The maximum value of this voltage depends on the size of the evaporator, the material to be evaporated and the required evaporation rate. This is determined experimentally during the installation of the evaporator design. After the evaporator is brought to operating mode, the wire feed mechanism is switched on. The wire 15 from the coil 14 enters the melting chamber 7, is heated, melts and, upon contact with the porous core 2, the molten material flows along the entire length of the porous core 2. It fills the pores and covers the core surface with a thin layer of liquid metal. The evaporation process begins. The material is evaporated from the surface of the core 2. In the middle part of the evaporator, in the evaporator chamber 3, the material vapor, after multiple reflections, flows from the walls of the tube 2 through the opening 5 and sits on the base.

In the damping chambers, the 3 'and 3' material is also evaporated from the core 2, however, since the tube does not have openings for vapor exit outside the evaporator, the vapor condenses again onto the porous core, reflecting multiple times from the inner walls of the tube. Thus, these chambers have a dynamic equilibrium where the number of molecules leaving the melted material layer per core is equal to the number of molecules returning to the core surface from the vapor, i.e., the evaporation rate is equal to the condensation rate.

When the evaporation rate is high enough, for example at 7 to 10 g / min, the above condition in the damping zones is maintained throughout the evaporation process. When the evaporation rate is slow, the formation of a bead of melted material as described above and its fluctuations in feed are observed. Processes in the evaporator can be described as follows. After the bead of molten material is separated from the copper wire, i.e., when the bead falls into the melting chamber and wets the evaporator core, evaporation from the evaporation chamber 3 to the base begins.

In the damping chambers, the 3 'and 3' material is also evaporated from core 2, however, since there are no openings for vapor exit from the evaporator in these zones, the vapor is reflected from the inner walls of the tube many times and condenses again on the porous cores. As the amount of material to be evaporated in the chamber 3 on the core 2 becomes smaller than in the chambers 3 'and 3 ", the temperature of the evaporating chamber 3 increases and the vaporized material is pumped from the chamber 3' and 3" to the chamber 3 to stabilize the evaporation rate. JSC SIDRABE produced some evaporators of this type. One was for the copper-wire evaporation of copper and the other for the liquid-metal evaporation of indium. For both evaporators the tube was 20 mm in diameter and 110 mm in length. The size of the steam outlet was 12 x 43 mm. The opening was made in the center of the pipe 25 mm from the contacts. When the copper is evaporated, it is fed to the melting chamber in the form of a wire 1.5 mm in diameter. During evaporation in India, it is fed to the melting chamber in a melted form from a special tank. Both metals were evaporated to apply coatings on polymer films at feed rates of 10, 7, 5 and 3 g / min. All of the above modes exhibited stable steady evaporation without visible fluctuations of the metals to be evaporated.

Measurements of the thickness control of the coatings applied to the polymer films showed that there were no operating oscillations in the evaporator in any of the tested operating modes. At feed rates of 10, 7 and 5 g / min. the thickness irregularity did not exceed ± 5%. At a feed rate of 3 g / min. the thickness irregularity did not exceed ± 10%.

The present invention provides an extension of the evaporator's technological capabilities and enhancement of the coating quality. This allows the range of evaporation rates to be expanded by using different metals and different substrates. Incidentally, the invention allows coatings to be applied to heat-sensitive substrates without overheating, which is possible by carrying out a process with a lower evaporation rate, a correspondingly lower heat flux and a proportionally lower substrate temperature. When different steam sources are used in the same technological process, such as thermal evaporator and magnetron spray or thermal vaporizers of different speeds, the proposed technical solution allows to better coordinate the application rate of coatings from such different speed sources.

The proposed solution also enables a wide range to change the evaporation rate and to find the optimal parameters for each coating layer, thus improving the quality of the final product. A / S SIDRABE used this method to deposit nichrome and copper on a polyimide film, whereby nichrome was applied by magnetron and copper by thermal evaporator. Another application is the simultaneous evaporation of copper and indium from two separate thermal evaporators to deposit copper and indium on a single substrate. In this case, the offering solution allowed to change the composition of the coating up to 10 times - the ratio of the indium to the copper - and, as a result, find the most suitable regime and produce the material with the required properties.

Claims (3)

A resistive evaporator for applying coatings in a vacuum, comprising: an evaporation chamber; a tubular screen with openings for vaporization of the material to be evaporated; a porous core fixed to the inside of said tubular screen; electrical contacts, at least one molten chamber, a device for supplying the evaporated material to said molten chamber; a channel for feeding said molten material from the molten material chamber to the porous core, characterized in that at least one evaporation oscillation damping chamber is formed between one of the electrical contacts and the evaporation chamber in order to expand the evaporator's technological capabilities and increase the coating quality by evaporation rate stabilization. wherein said oscillation damping chamber is separated from the evaporation chamber by a septum having an opening for a porous core and a flow of liquid material. Device according to claim 1, characterized in that the length of the oscillation damping chamber is not less than one diameter of the evaporation chamber. 3. A device according to claim 1, characterized in that the diameter of the oscillation damping chamber is equal to the diameter of said tubular screen. LV 13S10