WO2007045215A1

WO2007045215A1 - Method and apparatus for evaporating material for coatings

Info

Publication number: WO2007045215A1
Application number: PCT/DE2006/001785
Authority: WO
Inventors: Carsten Deus; Bernd Teichert; Henrik Obst
Original assignee: Von Ardenne Anlagentechnik Gmbh
Priority date: 2005-10-17
Filing date: 2006-10-10
Publication date: 2007-04-26
Also published as: DE102005049906B4; DE102005049906A1

Abstract

The invention relates to an apparatus and a method for evaporating evaporation material that is in a crucible (1) by heating the evaporation material (3, 4, 5) by means of supplying energy from a controllable power generator (12) to a temperature at which part of the evaporation material (5) is in the gas phase. The invention is based on the object of providing a method and an apparatus for evaporating evaporation material (3, 4, 5) that allow the vapour stream at the vapour outlet (10) to be stabilized by means of simple, reliable and low-cost monitoring and regulating capabilities. This object is achieved by an evaporating method in which energy is supplied to and/or extracted from the evaporation material in such a way that, during the stable phase of the process, it is simultaneously in the gaseous phase (5), solid phase (3) and liquid phase (4) and the temperature at the surface of the liquid evaporation material corresponds approximately to the temperature of its triple point. An apparatus for carrying out the method has a measuring device (14, 15) for determining the degree of solidification and/or a partly heatable (12) and/or coolable (13) wall (1).

Description

METHOD AND DEVICE FOR EVAPORATING MATERIAL FOR COATINGS

The invention relates to a method for evaporating evaporation material which is present in a vessel (crucible) by adjusting by means of suitable energy supply such a temperature of the evaporation material, in which a part of the evaporation material is in the gas phase.

Furthermore, the invention relates to a device for carrying out the method, wherein the crucible has a steam outlet and the device is connected to a controllable power generator for heating the evaporation material.

The evaporation of evaporation material z. For example, for the thermal vapor deposition of a wide variety of substrates usually takes place from the liquid phase of the evaporation material by being heated in a vessel, a crucible, until complete melt. For example, EP 0 735 157 discloses a process for evaporating magnesium. According to the method, a magnesium source is provided in a vessel with a narrow opening and with a reflector plate arranged outside the opening. The vessel is heated to a temperature of 670 ⁰ C to 770 ⁰ C, wherein the magnesium source is melted and the magnesium is evaporated. The magnesium vapor is passed through a heated to at least 500 ⁰ C channel from the outlet of the vessel to a positioned at the channel exit substrate.

In such an evaporator arrangement, the amount of steam delivered depends very much on the temperature of the evaporation material. Therefore usual feeding a constant Gere ^¬ apply heating power for evaporating material or its temperature control. A response to setpoint changes, such as the layer thickness, or to disturbances is subject to severe There are limitations due to the available heat output as well as the thermal inertia of the evaporator arrangement. Frequently the temperature is not measured directly in the evaporation material, but in the outer parts of the evaporator to avoid direct contact with the often aggressive evaporation material.

Faster changes in the vapor flow can be achieved by changing the conductivity of the channel between the evaporator and the substrate to be coated z. B. be generated by means of adjustable valves. The disadvantage here is that any change in the steam flow leads to a change in the power balance on the evaporation material. The adjustment of these fluctuations in the power balance is opposed by the inertia of the power or temperature controller. In addition, the inertia of other temporal factors depends, z. B. a drift due to the decreasing amount of the evaporation material during the evaporation process or a discontinuous loading with new evaporation material. Likewise, in the course of the evaporation, the coupling between the power generator for heating the evaporation material, for. As a radiation or an induction heater, and change the evaporation material.

There are also methods of measuring the vapor pressure of the vaporization material (e.g., atomic absorption spectrometry) or layer thickness (e.g., X-ray fluorescence spectroscopy) which could be used for control. The disadvantage, however, is their financial and material expense, their time constants and sensitivity to disturbances. Even if these disadvantages are accepted, the problem with evaporation processes remains that rapid and precise monitoring and / or readjustment of the evaporation rate is very difficult.

Thus, the invention has for its object to provide a method and an apparatus for evaporating evaporation material, which stabilize the steam Enable electricity at the steam outlet by means of simple, safe and cost-effective control and regulation options.

In terms of the method, the object is achieved by supplying and / or discharging energy to the evaporation material in such a way that it is simultaneously in gaseous, solid and liquid phases during the stable process phase and the temperature at the surface of the liquid evaporation material approaches approximately Temperature of its triple point corresponds.

At the triple point, where the solid, liquid and gaseous phases of the evaporation material are in equilibrium with each other, the variables of the system of vapor pressure and temperature are determined. It is only the relative ratio of the different phases to each other variable. As long as all three phases are approximately in equilibrium, the temperature and thus the saturation vapor pressure of the evaporation material is determined only by its material constant. Changes in the current account, e.g. due to disturbance variables or changes in steam flow rates as a result of valve positioning operations, the change in temperature does not lead to such a change

Evaporation material, such as liquid and solid phases are present simultaneously. There is a heat exchange between solid and liquid phase, so that the temperature of the liquid phase is maintained at approximately triple point temperature and only further evaporating material melts or solidifies. Thus, the transitions between solid and liquid phases with the required or released heat act as a buffer.

This stabilizing effect can also be exploited in the event of a deviation from the saturation vapor pressure above the evaporation material, which sets in when steam is taken off for the coating task. By setting the triple point the temperature is stabilized directly on the surface of the evaporation material and a constant steam pressure, so that the control of the evaporation rate takes place indirectly through the control of the phase transitions, which considerably simplifies them.

The possible difference according to the invention between the set surface temperature of the evaporation material and its triple point depends on the preferred buffer effect of the phase system and the various factors which influence the bufferability. In particular, a large amount of material and a small temperature gradient within the melt have a stabilizing effect. Also, the size of the area of the phase boundary as well as the relative movement between solid and liquid phases has an effect, and such material which does not form a discrete phase boundary and forms individual solid components dispersed in the liquid phase has a good buffering ability.

The supply of energy to heat the vaporization material and supply the required heat of fusion can be accomplished by any known method, e.g. via energy radiation by CFC heater, jacket tube heater, heating wire, ceramic radiant heater or similar. Likewise, the supply via electromagnetic energy, for example by means of induction heating or resistance heating in the evaporation material itself or by bombardment with an electron beam is possible.

An energy dissipation is required to compensate for excess heat or heat of solidification if the heat output can not be sufficiently reduced, for example, with reduced evaporation rate due to a reduction in the amount of steam flow or interruption of the coating task. It can be done by active or by passive cooling. While in an active cooling of the selected portions of the wall of the crucible are contacted with a coolant in contact for passive cooling for example, a thermal insulation which surrounds the wall of the crucible, from ^¬ sectionally reduced or removed. The type of cooling depends on the one hand on the amount of energy to be derived, which will be greater, for example, in the continuous supply of molten vaporization material. On the other hand, the design of the entire evaporator arrangement has influence, for example, the arrangement of the evaporator in a vacuum chamber or the execution of a movable crucible.

A significant influence on the energy balance of the system and thus on the regulation of the energy supply and, where appropriate, the energy dissipation has the fitting of the crucible with new evaporation material. The replacement of the spent, evaporated material with new is done in various ways. Thus, the assembly of solid material, in particular charged, as well as the continuous supply of already molten evaporation material. While a continuous input of energy is associated with the continuous supply of molten material, the phase equilibrium must always be re-established in the case of charged loading with solid material due to temporarily increased energy input.

To keep the vaporizer constantly in the process in which the buffering effect is positive both in the case of a positive power balance in which the sum of the supplied heating power, the power losses to the environment due to heat radiation and heat conduction, and the vaporization power converted is given, as well as in the case of a negative power balance, the supply of the heating power required for evaporation or the derivative of the excess heating power depending on the degree of melting of the evaporation material is controlled. Consequently, according to a particularly advantageous embodiment of the invention, the energy supply and / or energy dissipation is regulated as a function of the degree of solidification of the evaporation material, which is to be defined as the ratio of the solid content of the evaporation material to the total amount. The control is not critical because of the described material-dependent temperature stabilization at the triple point and must be Let prevent complete melting or complete solidification of the evaporation material.

Since the equilibrium of all three phases must be maintained to stabilize the temperature and the vapor pressure, a coarse determination of the degree of solidification is generally sufficient. For example, an arithmetic dimensioning of the energy balance and the calculation of a preferred degree of solidification for the stability of the process can be done. If this shifts to the liquid phase or to the solid phase, a different power balance can be deduced and these can be compensated by supplying energy or dissipating energy.

For this purpose, a device which serves to solve the problem, a measuring device which determines the degree of solidification of the evaporation material. Depending on the evaporation material and also on the temperature regime, the solid may be separated from the liquid phase both by an interface, the solidification front, and by a region in which both phases are mixed. Accordingly, the MesSeinrichtung is to be selected, the degree of solidification can also be determined indirectly. The various embodiments of the device according to the invention are suitable for providing the required information about the state of melting.

The method according to the invention also includes the variant that, taking into account the energy continuously evacuated by the heat of evaporation and heat conduction, the maintenance of the equilibrium of all three phases according to the invention is also achieved, for example, by means of the regulation of the energy dissipation by active cooling otherwise constant energy supply is possible.

Based on this, an advantageous embodiment of the method according to the invention provides that for maintaining the phase equilibrium in the undisturbed evaporation process required energy input and / or energy dissipation are calculated and thus carried out substantially continuously and that a cooling of the evaporation material over a portion of the wall of the crucible takes place, which includes the solid phase and almost to the equilibrium phase boundary borders and / or that a heating of the evaporation material over a portion of the wall of the crucible takes place, which surrounds the liquid phase and is almost adjacent to the equilibrium phase boundary.

With a positive power balance, more vaporization material would be continuously melted than vaporized, thus decreasing the degree of solidification, and hence the boundary between the solid and liquid phases, which occurs during the calculated energy supply and cooling of the undisturbed system. If this falls below a limit which, for example, is defined by the correspondingly dimensioned and locally limited cooling with respect to this limit, the excess energy is dissipated by increased cooling. As a result of the locally defined cooling of the melt in the vicinity of the phase boundary, the thermal coupling between the liquid evaporation material and the cooled wall increases disproportionately when the degree of solidification is reduced. In the opposite case, an increasing solidification of the material reduces the energy losses due to reduced cooling.

A comparable, alternatively or additionally usable self-adjustment of the evaporation process is also possible by a corresponding heating of the wall, which borders on the liquid phase. If this section of the wall is heated, increases in the degree of solidification and the concomitant increase in the phase boundary occurs an increase in the coupling to the heated wall and the decrease in the phase boundary, a reduction in the coupling. With these various options, a quick balancing of the current account is always possible directly and in both directions. borrowed. The energy dissipation takes place, as well as the energy supply directly, so that can be responded to a variety of disturbances in the short term.

Since, as shown above, the control of the evaporation rate can be reduced to ensure the simultaneous presence of solid, liquid and gaseous phases, a self-stabilizing evaporation process can be carried out by dimensioning the energy source and dimensioning and arranging the cooling or heating of the crucible wall. This method is applicable either within predetermined limits of the total amount of evaporating material present or when continuously charged with new liquid evaporating material.

If according to a particular embodiment of the inventive method, the energy supply is tracked in the system of discharged steam, the efficiency and the stability of the process can be improved and the control can be facilitated because the solidification front moves less.

Another device, which serves to carry out the described self-stabilizing evaporation process, is designed such that at undisturbed evaporation process with coexisting gaseous, liquid and solid phase, only that part of the wall adjacent to the solid phase, at least in the boundary between solid and liquid phase approximately adjacent region is coolable and / or only that part of the wall to which the liquid phase adjoins, at least in the area adjacent to the boundary between solid and liquid phase approximately heatable area is heated. The cooling or the heating is designed so that from a predetermined deviation of the degree of solidification, the thermal coupling between the evaporating and cooled or heated wall increases or decreases. The normal value of the degree of solidification is defined by the computationally determined, continuous energy input into the system, which in particular in Dependence on the evaporation material, the required for the coating task evaporation rate and the energy losses of the system is determined.

In this case, it depends in particular on the process parameters and the process design, the type of assembly with new evaporation material, the design of the crucible and the energy supply in the system for liquefaction of the evaporation material, whether the heating of the wall of the crucible for self-stabilization is realized by this energy source or a separate energy source is provided. The same applies to the cooling, which serves to dissipate energy from the system, and the locally limited cooling of the wall for self-stabilization. Thus, for example, a separation of the cooling at the bottom and on the lateral wall according to the two functions or even a cooling for self-stabilization is possible, which can equally be used for cooling the device, for example, to interrupt the evaporation process.

Irrespective of whether the process according to the invention is carried out in a self-stabilizing manner or not, it proves to be of

Advantage, when inhomogeneities in the melt of the evaporation material are compensated by stirring. In particular, an elevated temperature gradient or melt dispersed solid components are such inhomogeneities that may occur depending on the type of evaporation material. By stirring, the heat transfer between solid and liquid phase is improved and the surface temperature approaches the triple point. Suitable are various means, according to an embodiment of the device in particular those which electromagnetically or mechanically excite a movement of the melt.

The determination of the degree of solidification of the evaporation material is possible in various ways. Thus, the determination is carried out for example by means of electromagnetic sensors. For the Metallic evaporation material is particularly suitable for the eddy-current method in which eddy currents are induced in the evaporation material. Among other things, this method provides information on the conductivity of the material, so that the evaluation of the degree of solidification is possible due to the temperature dependence of the conductivity and the frequent increase in the conductivity of metals in the phase transition solid / liquid. This measurement can be done separately or in combination with vortex flow heating and electromagnetic stirring.

Ultrasonic methods are suitable for measuring temperature-dependent acoustic material constants and in particular for melts which have a diffuse phase transition solid / liquid with a proportion of solid constituents in the liquid phase. They are also suitable for determining temperature-dependent velocities of the electromagnetically or mechanically moved melt by means of Doppler methods as well as for detecting the position of interfaces between the phases.

A temperature measurement on the wall of the crucible, according to a further embodiment by means of a temperature sensor field, can directly detect the position of the phase front or the position and extent of a phase mixture, so that a shift can be detected directly.

Also useful is a visual assessment of the degree of solidification, which can be viewed in the crucible with a camera through a heated window (e.g., quartz) and evaluated by automated image processing. The evaluation of the movement of the melt, which is stirred by one of the methods described, by means of optical or mechanical evaluation is suitable to determine the degree of solidification.

In addition to the evaluation and use of the degree of solidification for the regulation of energy supply and energy dissipation, the control of the degree of solidification in the self-stabilizing drive advantageous because this method is stable within certain limits and the achievement of this range is observable at startup of the process or may require an intervention when approaching such a limit. For this purpose, various embodiments of the device provide above-described means for determining the degree of solidification.

Continuous coating of moving substrates requires the provision of a continuous stream of vapor for which several evaporators are connected in parallel to a coating line and connected one or more in a row to the coating line while the remainder are serviced or charged with new material from the line are separated.

A parallel arrangement of a plurality of evaporators is also required for the mixed evaporation in which one of the components to be mixed evaporates in each evaporator and regulates its vapor flow, for example for mixing in the coating apparatus by means of a variable conductivity actuator, which is preferably arranged in the steam outlet becomes.

When connecting or disconnecting individual evaporators by means of valves, which are preferably arranged at the steam outlet of each individual evaporator, large fluctuations occur regularly in the steam flow and thus in the evaporation rate. These can be largely compensated with the device according to the invention, wherein it proves to be advantageous if the components of the steam outlet and the regulation of the steam flow are heated to a temperature at which a condensation of steam on these components is avoided. In this way, deposits of solidified evaporation material on these components and thus impairments of their function as well as a negative influence on the equilibrium system and the energy balance are avoided. The invention will be explained in more detail with reference to an embodiment. In the accompanying drawing, the drawing figure shows the vertical section of an evaporation device according to the invention.

A trough-shaped crucible 1 is closed by a cover plate 2. The interior of the crucible 1 is completely filled with evaporation material, for example magnesium, which is in the solid 3, above in the liquid 4 and above in the gaseous state 5, in the illustrated example, the liquid 4 and gaseous vaporization material together, approximately equal to each other Share more than two-thirds of the total volume. The phase boundary between the solid and liquid phases of the evaporation material is formed by a discrete solidification front 6.

A stirrer 8 protrudes into the crucible 1 in a sealing and height-adjustable manner through a first opening 7 in the cover plate 2 so that it can homogenize the liquid evaporation material 4. By a second opening 9 in the cover plate 2, also a sealing, a steam outlet 10 is arranged, in which the derived Dampfström by means of a valve 11 is controllable. Steam outlet 10 and valve 11 are temperature controlled by means not shown heating systems. In the area of the upper third of the wall of the crucible 1, a radiant heater 12 in the form of an electrical resistance heater is circumferentially arranged. Another radiant heater 12 has the cover plate 2. The wall of the crucible 1 is surrounded in the region of the lower third and the bottom of cooling tubes 13, through which a coolant is passed.

In the wall of the crucible 1 temperature sensors 14 are integrated in the lower two thirds. In the area of the illustrated phase boundary between the solid 3 and liquid 4 evaporation material, an electromagnetic sensor 15 for detecting the solidification front 6 is furthermore arranged.

In the described embodiment, the crucible 1 is initially equipped with solid evaporation material 3, which By means of the radiant heaters 12 on the cover plate 2 and the wall is heated so far that a part of the material is melted. In the process, the already melted part of the evaporation material 4 is continuously stirred with the aid of the stirrer 8. By means of the electromagnetic sensor 15, the conductivity of the sensor 15 within the crucible 1 opposite material is continuously measured and thus determined when the solidification front 6 is lowered to the height of the sensor 15 via the eddy current method. Parallel or alternatively, a temperature field is measured by means of the temperature sensors 14 and the change in the course of the melting process is monitored by means of the latter.

If the solidification front 6 has fallen approximately to the level of the electromagnetic sensor 15, a continuous energy supply is set only by the radiant heater on the cover plate 2, which corresponds to the calculated energy supply for maintaining the set degree of solidification in an undisturbed evaporation process. At the same time, a constant cooling of the wall of the crucible 1 is set in accordance with the calculated values by keeping the flow of a suitable cooling medium approximately constant. According to the dissipated for coating time variable amount of steam in the embodiment, the heating power of the radiant heater 12 on the cover plate 2 also tracked the time-variable energy demand for vaporizing this amount of steam.

Decreases the solidification front 6 in the course of the evaporation process, for example, by reducing the amount of steam flow, the thermal coupling between the liquid evaporation material and the cooling increases, which leads to increased energy dissipation until a new balance between energy supply by itself with a changed position of the solidification front and energy dissipation

The evaporation device shown in the figure also supports the execution of an evaporation method, which is based on the regulation of the cooling and heating elements. tion, alternatively one of these two possibilities. The control is carried out as a function of the determined by means of temperature field measurement and electromagnetic sensor 15 solidification of the evaporation material. By controlling the cooling and / or heating power, the solidification front is stabilized in the region above the cooling, wherein this control can be carried out according to the evaluation of the measurements of the electromagnetic sensor 15 and / or the temperature field evaluation or according to mathematically determined specifications.

The vapor pressure of the gaseous evaporation material 5 which is established above the liquid evaporation material 4 is stabilized as long as the evaporation material is present simultaneously in all three phases and is controllably supplied via the steam outlet 10 to a coating installation. The device also evaporates other materials such as aluminum, copper, zinc, indium, gallium, cadmium telluride (CdTe) and cadmium sulfide (CdS).

LIST OF REFERENCE NUMBERS

1 crucible

2 cover plate

3 solid evaporation material

4 liquid evaporation material, melt

5 gaseous evaporation material

6 solidification front

7 first opening

8 stirrer

9 second opening

10 steam outlet

11 valve, nozzle, nozzle system

12 radiant heating

13 cooling tubes

14 temperature sensor

15 electromagnetic sensor

Claims

claims

A process for evaporating evaporation material which is present in a vessel (crucible) by adjusting, by means of a suitable supply of energy, a temperature of the evaporation material at which a part of the evaporation material is in the gas phase, characterized in that the evaporation material in that way Energy is supplied and / or derived that it is present during the stable process phase simultaneously in the gaseous, solid and liquid phase and the temperature at the surface of the liquid evaporation material approximately corresponds to the temperature of its triple point.

2. A method for evaporating evaporation material according to claim 1, characterized in that the regulation of the energy supply and / or energy dissipation depending on the degree of solidification of the evaporation material, wherein the degree of solidification should be defined as the ratio of the amount of the solid evaporation material (3) to the total amount ,

3. A method for evaporating evaporation material according to claim 1, characterized in that for maintaining the phase balance in the undisturbed evaporation process required energy supply and / or energy dissipation are determined by calculation and accordingly takes place substantially continuously and that a cooling of the evaporation material over a portion of the wall of the Crucible (1), which encloses the solid phase and almost reaches the equilibrium adjacent the sensitive phase boundary and / or that a heating of the evaporation material over a portion of the wall of the crucible (1) takes place, which encloses the liquid phase and almost borders on the equilibrium phase boundary.

4. A method for evaporating evaporation material according to claim 3, characterized in that the energy supply of the discharged steam quantity is tracked.

5. A method for evaporating evaporation material according to any one of claims 1 to 4, characterized in that inhomogeneities in the melt (4) of the evaporation material are compensated by stirring.

6. A method for evaporating evaporation material according to any one of claims 1 to 5, characterized marked, that the solidification of the evaporation material by means of electromagnetic sensors (15) is determined.

7. A method for evaporating evaporation material according to one of claims 1 to 5, characterized in that the solidification degree of the evaporation material is determined by the solidification front (6) by means of temperature sensors (14) is determined.

8. A method for evaporating evaporation material according to claim 7, characterized in that the degree of solidification of the evaporation material is determined by determining a temperature field of the wall surface of the crucible (1) and from its change to a displacement of the solidification front (6) becomes.

9. A method for evaporating evaporation material according to any one of claims 1 to 5, marked thereby, that the solidification degree of the evaporation material is determined by means of ultrasonic measurement.

10. A method for evaporating evaporation material according to any one of claims 1 to 5, characterized net, that the degree of solidification of the evaporation material by mechanical or electromagnetic excitation of the melt (4) and optical, mechanical or Ultraschallaus- evaluation of the movement of the melt (4) is determined.

11. A device for evaporating evaporation material, consisting of a vessel (crucible) with a steam outlet and connected to a controllable power generator for heating the evaporation material, characterized in that the device comprises a measuring device for determining the degree of solidification of the evaporation material.

12. A device for evaporating evaporation material, consisting of a vessel (crucible) with a steam outlet and connected to a controllable power generator for heating the evaporation material, characterized in that "in undisturbed evaporation process with coexisting gaseous, liquid and solid phase of that part of the wall to which the solid phase borders, at least in the region approximately adjacent to the boundary between the solid and liquid phases, and / or that part of the wall to which the liquid phase adjoins, at least in the region approximately adjacent to the boundary between solid and liquid phases is heatable.

13. A device for evaporating evaporation material according to claim 12, characterized in that the device comprises a measuring device for determining the degree of solidification of the evaporation material.

14. A device for evaporating evaporation material according to any one of claims 11 to 13, characterized in that means for electromagnetic or mechanical movement excitation of the melt (4) are arranged.

15. Device for evaporating evaporation material according to claim 11 or 14, characterized in that the measuring device comprises an electromagnetic sensor (15). for detecting the solidification front (6).

16. A device for evaporating evaporation material according to any one of claims 11, 13 or 14, characterized in that the measuring device comprises a temperature sensor (14) for detecting the solidification front (6).

17, apparatus for evaporating evaporation material according to claim 16, characterized in that a plurality of temperature sensors (14) on the wall of the crucible (1) are arranged such that a limited temperature field of the surface temperature of the wall is to be determined.

18. A device for evaporating evaporation material according to any one of claims 11, 13 or 14, characterized in that the measuring device comprises means for optical and / or mechanical or ultrasonic evaluation of the movement of the melt (4).

19. A device for evaporating evaporation material according to one of claims 11 to 18, characterized in that the steam outlet (10) derived Dampfström is adjustable.

20. A device for evaporating evaporation material according to claim 19, characterized in that an actuator with variable conductance at the steam outlet (10) is arranged to regulate the steam flow.

21. Apparatus for evaporating evaporating material according to claim 19, wherein said evaporator material evaporates according to claim 19

Setting the distribution of the steam flow, a nozzle or a nozzle system (11) on the steam outlet (10) is arranged.

22. A device for evaporating evaporation material according to one of claims 19 to 21, characterized in that the components of the steam outlet (10) and / or the components for regulating the steam flow to a temperature equal to or higher than the melting temperature of the evaporation material is tempered, in which a con- condensation of steam on these components is avoided.