Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/24—Vacuum evaporation
  • C23C14/243—Crucibles for source material
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/24—Vacuum evaporation
  • C23C14/28—Vacuum evaporation by wave energy or particle radiation
  • C23C14/30—Vacuum evaporation by wave energy or particle radiation by electron bombardment

Definitions

• the invention relates to a crucible for an electron beam evaporator, an operating method of the electron beam evaporator and a specific use of the crucible.
• Thin-film solar cells in particular based on chalcogenide semiconductor layers (eg CIGS solar cells), represent an efficient and cost-effective alternative to conventional technologies in photovoltaics.
• Possible production methods for chalcogenide semiconductor layers include cover evaporation, precursor layer chalkogenization, electrodeposition or spray pyrolysis. With regard to the application in thin-film solar cells, the highest energy conversion efficiencies are achieved with cover evaporation techniques - but only with a correspondingly efficient process control.
• Commonly known in the art is the production of polycrystalline chalcogenide semiconductor layers by physical vapor deposition (PVD) .PVD is a standard technique of thin film technology, and when more than one element is deposited simultaneously one of "Coverdampfung".
• a particularly promising variant of the PVD process for the industrial production of thin-film solar modules is that the evaporation of the solids takes place with the aid of an electron beam (so-called EB-PVD process).
• EB-PVD process an electron beam evaporator focuses an electron beam on the solids to be evaporated and thereby makes it possible to achieve very high energy densities and temperatures.
• the large-scale vapor deposition by means of electron beam evaporators requires in the transverse direction, i. perpendicular to the substrate transport direction, homogeneous coating sources; As a rule, large rectangular crucibles are used to hold the metals to be evaporated.
• Crucible geometries with a large width-to-length ratio are also referred to as linear bars, and electron beam evaporators in which such crucibles are used are also known as linear evaporators. It is also known to carry out the crucible in two pieces with outer crucible and inner crucible.
• the inner crucible consists of a material that does not undergo alloys / reactions with the molten material, in particular the liquid metals.
• the outdoor crucible commonly features water cooling.
• the principle of the electron beam evaporator requires that the entire crucible is electrically conductive.
• the electrons "shot" into the crucible during electron beam evaporation must be able to drain off to ground, otherwise the material would become electrically charged always requires an electrically conductive connection between material to be vaporized and ground.
• Copper is often used for the outer crucible.
• the electrical conductivity of the material brings a good thermal conductivity with it.
• the breakpoints of the crucible must therefore be well cooled.
• a conventional electron beam evaporator a large part of the energy which is introduced via the electron beam is dissipated again directly via the cooling water; Usually> 90% of the electron beam evaporator power goes into the cooling water. Only a fraction is used to heat the vapor deposition material at the point of impact of the electron beam. It thus far higher evaporator performance needed than the actual evaporation of the metals would be needed.
• the total energy requirement of a coating system for, for example, large-scale production of PV-active CIGS layers should be as low as possible.
• the production of particularly active CIGS layers by simultaneous evaporation further requires the exact observance of the individual, possibly spatially and / or temporally varying vapor deposition rates of the metals involved in order to comply with the desired stoichiometry.
• the temperature of the melt represents the physical quantity that is directly related to the rate.
• the melt shows a very inhomogeneous temperature distribution due to the cooling of the entire crucible. Temperature measurement in electron beam evaporator systems of conventional design thus can not function precisely because there are large temperature gradients in the crucible between the area being vaporized and the massively water-cooled crucible edge.
• Oscillating quartz measurement does not work or at least not very long with vaporization of the crystals with metal selenides.
• the metal would need to be measured alone (ie, without Se rate); because the Se but not vaporized "quasi-optically", you always measure the sum of a metal vapor and a Se share.
• Atomic absorption spectroscopy suffers from the change in the transmission of the windows by selenium coating - despite heated windows - and the insufficient long-term stability of the intensity measurement.
• Quadrupole measurement systems also do not work reliably in Se atmosphere.
• a problem is z. As the condensation of Se in the quadrupole and / or the cross-beam source.
• the evaporation process must also not generate "spatters" on the substrate; if metals are vaporized, this would cause shorts on the substrate. Often the splashes are triggered by large thermal gradients and strong currents ("boiling, bubbling") in the liquid material, which is why the lowest possible thermal gradient in the melt is desirable.
• a crucible for an electron beam evaporator which comprises an outer crucible made of copper and an inner crucible, wherein between the outer and inner crucible for thermal insulation, an insert made of graphite is introduced.
• the crucible according to the invention comprises an electrically conductive outer crucible and an inner crucible which is designed to accommodate a material to be vaporized and which is likewise electrically conductive, an electrically conductive but thermally insulating insert being arranged between outer crucible and inner crucible.
• the crucible is characterized in that the inner crucible has a thermocouple for detecting a temperature of the inner crucible.
• the invention is based first of the knowledge, by a thermal decoupling of inner crucible and outer crucible, but with the remaining electrical connection of the same a variety of the aforementioned problems can be avoided or at least mitigated.
• there is an electrically conductive insert between the inner crucible and the outer crucible but its thermal conductivity is low in the temperature range relevant to the application.
• the insert ensures that the melt and the inner crucible are thermally decoupled from the remainder of the evaporation source, but that electricity can still flow between the inner crucible and the outer crucible. As a result, the melt and inner crucible heat up evenly.
• the outer crucible with its holding points, ie the mechanical connection to the process chamber, on the other hand remains cooled or only moderately heated.
• the temperature of the melt on the inner crucible wall in the crucible according to the invention is close to the temperature of the material evaporating from the interior of the crucible.
• the temperature of the inner crucible therefore corresponds approximately to the evaporation temperature of the material.
• a control of the vapor deposition rate is now also possible via a control of the inner sealing temperature.
• the inner crucible on a thermocouple for detecting a temperature of the inner crucible An associated method for operating the electron beam evaporator is thus characterized in that the temperature of the inner crucible is used to control an evaporation temperature of the material to be evaporated.
• the insert is preferably made of graphite felt.
• Graphite felt is electrically conductive enough to ensure the necessary grounding of the crucible and thus the outflow of electrons to ground.
• the material has a very low thermal conductivity. In the temperature range of interest during use, the heat losses in the inner crucible are essentially determined by thermal radiation of the inner crucible wall.
• Graphite felt also has a very low vapor pressure which allows use in high vacuum coating equipment.
• the insert has a thickness of 1 to 5 mm.
• the outer crucible has a cooling, in particular water cooling.
• the crucibles according to the invention are preferably used for the production of thin-film solar modules, in particular with CIGS layers.
• FIGURE shows a cross section through a crucible according to the invention for an electron beam evaporator.
• the single figure illustrates in a schematic way a sectional view through a crucible 10 according to the invention for an electron beam evaporator.
• the crucible 10 comprises an electrically conductive outer crucible 12, for example made of copper.
• a water cooling 14 may be integrated.
• the crucible 10 has an inner crucible 16, which is inserted into the outer crucible 12 and consists for example of graphite.
• outer crucible 12 and inner crucible 16 are electrically conductive, but thermally insulating insert 18.
• the insert 18 follows the contour of the inner crucible 16.
• the insert 18 on the outer crucible 12 is applied.
• the insert 18 consists in the present case of graphite felt and has a thickness of 1 to 5 mm.
• a ceramic trough 20 is further provided, which receives the insert 18 and the inner crucible 16.
• the thus acting as a heat shield molybdenum tray 20 in turn rests on ceramic balls 22, so that a cavity 24 between the inner crucible 12 and molybdenum tray 20 and partially the insert 18 remains, which further improves the thermal insulation of the inner crucible 16 relative to the outer crucible 12.
• the crucible 10 further has a thermocouple 26 which detects a temperature of the inner crucible 16.
• the thermocouple 26 serves to control the evaporation temperature of the material to be evaporated, which is located in the inner crucible 16. Due to the thermal insulation of the inner crucible 16 relative to the outer crucible 12, it can be approximately assumed here that the temperature of the inner crucible 16 corresponds to the temperature of the melt of the material to be evaporated located in the inner crucible 16.

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Citations (4)

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• 2009
  • 2009-11-23 DE DE200910046986 patent/DE102009046986A1/de not_active Withdrawn
• 2010
  • 2010-10-13 WO PCT/EP2010/065318 patent/WO2011061013A1/de active Application Filing

Patent Citations (4)

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