EP1991632A1

EP1991632A1 - Heat reservoir and method for processing a substrate coupled to a heat reservoir

Info

Publication number: EP1991632A1
Application number: EP08701681A
Authority: EP
Inventors: Jörg Müller; Markus Hlusiak
Original assignee: Q Cells SE
Current assignee: Q Cells SE
Priority date: 2007-02-05
Filing date: 2008-02-01
Publication date: 2008-11-19
Also published as: DE102007006455B4; WO2008095873A1; DE102007006455A1

Abstract

The invention relates to a heat reservoir (1) for the thermal coupling to a substrate (S) comprising a heat transport medium, which improves an exchange of thermal energy between a substrate (S) that can be coupled to the heat reservoir (1) and the heat reservoir (1), wherein the heat transport medium is provided in a static manner between the heat reservoir (1) and the substrate (S) that can be coupled to the heat reservoir. According to the invention, the heat transport medium comprises an ionic fluid (2). The existing spectrum of ionic fluids having different physical parameters allows the use thereof to be adapted as a heat transport medium for a wide variety of processing and production methods, which require good heat transport from or to the substrate. The invention further relates to a method for processing a substrate (S) that is thermally coupled to a heat reservoir (1), comprising the provision of a heat reservoir (1) according the characteristics of the invention.

Description

Heat reservoir and method for processing a substrate coupled to a heat reservoir

The present invention relates to a heat reservoir with the features according to the preamble of claim 1 and a method with the method steps according to the preamble of claim 12.

In particular, in the vapor deposition of metal layers on substrates produced on the substrate surface process heat in the form of liberated condensation enthalpy. In order not to exceed a predetermined maximum temperature of the substrate surface in such a situation and at the same time be able to apply the layer to be deposited with a high deposition rate, an efficient dissipation of the process heat from the substrate surface is required. The thinner the substrate is formed, the lower its heat capacity. For example, if flat substrates with a thickness in the range of fractions of a millimeter are used, the heat capacity of the substrate is exhausted within a short time. Therefore, in order to stabilize the temperature on the substrate surface, it is necessary to thermally couple the entire substrate to a heat reservoir by means of a heat transfer medium, the heat reservoir assuming the function of a heat sink in the event of exothermic reactions on the substrate surface. In the case of endothermic reactions, the heat reservoir would be designed as a heat source.

For example, a heat sink according to US Pat. No. 5,350,479 is known from the prior art. This technical solution provides to use a gaseous heat transfer medium in the form of helium on the back of a substrate to be processed. Cool helium is fed through a conduit system to the back of the substrate where it absorbs heat and is then dissipated. In a processing process that is carried out in a vacuum, this variant requires that the substrate rear side is decoupled in a gas-tight manner from the substrate front side. This assumes that the substrate itself has sufficient mechanical stability and no cracks or holes.

In contrast, various other prior art solutions are known that provide a heat transport medium in a static manner for coupling between the heat reservoir and the substrate. The feature "to provide a heat transport medium" in a static manner "is to be understood in the context of the present invention that the position of the heat transfer medium between substrate and a contact surface for exchanging heat energy with a heat reservoir is spatially substantially fixed.

Such solutions are known from EP 0 977 254 A2, from US 2005/036267 A and from US 4,139,051. These documents describe a chuck serving as a heat reservoir, which is thermally coupled to a substrate via a heat transport medium designed as a polymer film. For this purpose, the polymer film can be applied either on the wafer-formed substrate or on the chuck. The thermal contact for heat transfer under vacuum conditions is then realized by means of an electrostatic attraction generated by the chuck.

Such Wärmereservoire have the disadvantage that the generated by the electrostatic attraction thermal contact for the heat transfer between the substrate and the heat reservoir is often insufficient.

The present invention is therefore based on the object to provide a heat reservoir with a statically provided heat transport medium, wherein in a cost effective and simple way an efficient transport of

Heat energy from or to the substrate surface to be made possible. Furthermore, the object of the invention is to provide a method for processing a substrate coupled to a heat reservoir, wherein an efficient transport of heat energy from or to the substrate surface should be made possible in a cost-effective and simple manner.

This object is achieved by a heat reservoir having the features of claim 1 and by a method for processing a substrate coupled to a heat reservoir having the features of claim 12.

According to the invention, it is provided that the heat transport medium comprises an ionic liquid.

Ionic liquids are liquids that consist exclusively of ions. These are liquid salts without the salt being dissolved in a solvent such as water. It is a variety of related compounds known, for example, go in the range of 20 ⁰ C to 200 ⁰ C in the liquid state. Based on the parameters of a machining process in which the heat reservoir is to be used for processing a substrate, it is therefore possible to select an ionic liquid with suitable physical properties. The range of available different ionic liquids brings the advantage of the flexible use of the heat reservoir for a variety of machining processes with it.

For the purposes of the invention falls under the concept of editing in one

Machining process not only any change in the form of an interference with the existing structure of a substrate, for example by etching or polishing, but also the addition of matter to the existing structure of the substrate, for example by depositing a layer on the substrate surface.

Preferably, the heat reservoir on a flat bearing area for a flat formed substrate. In this case, the heat transport medium is arranged with the ionic liquid on the support area. Due to the fact that a plurality of thin substrates is formed flat, it is advantageous to provide a corresponding flat bearing area in order to ensure the largest possible heat transfer between the heat reservoir and the substrate.

The flat bearing area is preferably formed as a flat surface, which advantageously corresponds to a planar substrate. However, it is also conceivable to provide a slightly concave or convex curved surface, if this measure allows for correspondingly curved substrates easier thermal coupling.

Due to the liquid state of aggregation of the ionic liquid used, the combination of a curved substrate with a flat support area or a curved support area with a planar substrate is unproblematic. As long as the heat transport medium holds sufficient ionic liquid to adequately fill the space between the substrate and the bearing surface, a good thermal heat transfer is ensured.

Preferably, the ionic liquid wets the support area at least in sections. To the heat transfer between the substrate and the heat reservoir too - A - optimize, it is advantageous to wet the entire contact surface - which corresponds to the projection of the sheet substrate on the support area - with ionic liquid.

It is preferred to form the heat transport medium as an ionic liquid. That is, the heat transport medium consists solely of a single ionic liquid or a mixture of distinguishable ionic liquids. Nevertheless, it is also conceivable that the heat transport medium has at least one ionic liquid merely as a constituent. For example, a carrier matrix could be provided which receives an ionic liquid or a mixture of ionic liquids similar to a sponge. The heat transport medium is then formed from the combination of the carrier matrix with the ionic liquid (s). Both variants can bring the advantage of uncomplicated handling and cost savings.

For usual processing processes of substrates, it is advantageous to use a heat reservoir with ionic liquids, which are thermally stable above 100 ⁰ C, preferably above 150 ⁰ C, more preferably above 200 ° C. In this way it can be avoided that decay products of the ionic liquid can interact with their environment.

Many processing processes for substrates using the heat reservoir take place under vacuum conditions. For this it is advantageous that the ionic liquid at 25 ° C has a vapor pressure below 0.1 Pa, preferably below 0.01 Pa and more preferably below 0.001 Pa. This ensures that the ionic liquid under vacuum conditions does not significantly affect the processing of the substrate.

Advantageously, the ionic liquid is formed from an anion and a cation, wherein the anion is bis (trifluoromethylsulfonyl) amide, and the cation is selected from the group consisting of optionally substituted alkylimidazolium, tetraalkylammonium, optionally substituted dialkylpiperidinium, and mixtures thereof. Alkyl is an optionally substituted hydrocarbon. The alkyl radicals of the tetraalkylammonium may be the same or different. The alkyl radicals of the dialkylpiperidinium may also be the same or different. For the purposes of the present invention, the term "optionally substituted" includes optionally no substituent or at least one substituent which includes, but is not limited to, a hydrocarbon having 1 to 3 carbon atoms or OH. The cation is preferably selected from the group consisting of 1-ethyl-3-methyl-imidazolium, N-methyl-N-trioctylammonium, 1-methyl-1-propylpiperidinium. More preferably, the ionic liquid is 1-methyl-1-propylpiperidinium bis (trifluoromethylsulfonyl) amide.

According to the above, the anion of the ionic liquid is represented by the following formula (I):

In the case where the cation of the ionic liquid is an optionally substituted alkylimidazolium, the cation is represented by the following formula (II):

wherein R ¹ and R ^{2 are} each an optionally substituted alkyl which are the same or different, preferably different, and wherein alkyl is a hydrocarbon having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms; and wherein R ^{3 is} H or an optionally substituted alkyl that is the same or different, preferably different, from R ¹ and / or R ² , and wherein alkyl is a hydrocarbon having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms. R ³ is most preferably H. For the purposes of the present invention, the term "optionally substituted" does not include a substituent or at least one substituent which includes, but is not limited to, a hydrocarbon of 1 to 3 carbon atoms or OH. In the case where the cation of the ionic liquid is a tetraalkylammonium, the cation is represented by the following formula (III):

wherein R ⁴ , R ⁵ , R ⁶ and R ^{7 are} each an optionally substituted alkyl which may be the same or different and wherein alkyl is a hydrocarbon having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms. For the purposes of the present invention, the term "optionally substituted" does not include a substituent or at least one substituent which includes, but is not limited to, a hydrocarbon having 1 to 3 carbon atoms or OH.

In the case where the cation of the ionic liquid is an optionally substituted dialkylpiperidinium, the cation is represented by the following formula (IV):

wherein R ⁸ and R ^{9 are} each an optionally substituted alkyl, which may be the same or different, and wherein alkyl is a hydrocarbon having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms; and wherein R ^{3 is} H or an optionally substituted alkyl which is the same or different, preferably different, from R ⁸ and / or R ⁹ , and wherein alkyl is a hydrocarbon having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms. R ³ is most preferably H. For the purposes of the present invention, the term "optionally substituted" does not include a substituent or at least one substituent which includes, but is not limited to, a hydrocarbon of 1 to 3 carbon atoms or OH. In a preferred embodiment, the cation of the ionic liquid is 1-ethyl-3-methyl-imidazolium and has the following formula (IIa), ie in the formula (II) R ¹ = C ₂ H ₅ , R ² = CH ₃ and R ³ = H

An ionic liquid formed of an anion of the formula (I) and a cation of the formula (IIa) has a low vapor pressure and a high heat resistance.

In a further preferred embodiment, the cation of the ionic liquid is N-methyl-N-trioctylammonium and has the following formula (IIIa), ie in the formula (III) R ⁴ = CH ₃ and R ⁵ , R ⁶ and R ⁷ each C ₈ H ₁₇ :

An ionic liquid formed of an anion of the formula (I) and a cation of the formula (IIIa) has a low vapor pressure and a high heat resistance, so that decomposition at high temperatures is minimal.

In a further preferred embodiment, the cation of the ionic liquid is 1-methyl-1-propylpiperidinium and has the following formula (IVa), ie in the formula (IV) R ⁸ = CH ₃ , R ⁹ = C ₃ H ₇ and R ³ = H:

That is, the ionic liquid has the following formula (V):

The above-mentioned ionic liquid of the formula (V) has a high heat storage density and a high heat resistance. In particular, the ionic liquid has high heat resistance in vacuum. Furthermore, the ionic liquid of the formula (V) has a low vapor pressure. Decomposition and mass loss of the ionic liquid of formula (V) when used at high temperatures and even in vacuum are therefore minimal.

A further preferred variant of the heat reservoir provides that the support region of the heat reservoir has a multiplicity of openings, designed such that in the case of a substrate placed on the support region

Gas inclusions between substrate and support area can escape via the openings when the pressure surrounding the substrate is reduced. In this way it is prevented that gas inclusions impair the thermal contact between the heat reservoir and the substrate.

An advantageous embodiment of the heat reservoir has means for applying ionic liquid to the support area and / or for applying ionic liquid to a substrate. The means for applying ionic liquid are designed such that they apply the ionic liquid by screen printing, knife coating, dispensing, atomizing or inkjet printing. For the variant that the means for applying ionic liquid are formed on the support area, is also conceivable to provide one or more openings in the support area to supply the support area ionic liquid. By means of said means, the support area and / or the substrate can be prepared in a simple manner for the mutual thermal coupling.

As stated in the introduction to the prior art, it is conceivable to provide the heat reservoir for the absorption of heat energy as well as for the release of heat energy. However, the heat reservoir is preferably designed as a heat sink. This can be achieved by a sufficiently massive structure of the heat reservoir of a material of suitable high heat capacity and

Thermal conductivity and / or be provided by providing an active cooling of the heat reservoir in sections near the support area by means of a liquid or gaseous cooling medium. The structure is to be adapted to the respective requirements of the desired machining process.

The above-mentioned object underlying the invention is also achieved by a method for processing a substrate thermally coupled to a heat reservoir, the method comprising the following steps:

Providing a heat reservoir with the features according to one of the embodiments described above,

Thermal coupling of a substrate with the heat transfer medium of the heat reservoir,

• editing the substrate and

• Removal of the substrate from the heat transport medium.

For the purposes of the invention, the term machining in a machining process not only includes any change in the form of an intervention in the existing structure of a substrate, for example by etching or polishing, but also the addition of matter to the existing structure of the substrate, for example through the Depositing a layer on the substrate surface.

The reference back of the first method step to the previously described embodiments of the heat reservoir comprises all the advantages of the device of the heat reservoir shown in this context. To avoid repetition, reference is made to the preceding statements at this point. Preferably, the method is designed such that the method step of providing the heat reservoir comprises the application of ionic liquid to a support region of the heat reservoir and / or on the substrate. In this way, a thermal contact between substrate and heat reservoir can reliably ensure.

The method step of processing the substrate is preferably designed as a machining process or a combination of machining processes from vacuum technology. The collective term "machining processes from vacuum technology" covers all processes known from the state of the art, such as chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), physical vapor deposition (PVD), in particular sputtering, high-rate electron beam vapor deposition, Etching processes such as plasma etching, reactive ion etching (RIE), ion implantation, etc. At this point, it should be emphasized that the term "machining process from vacuum technology" does not necessarily require that the process according to the invention be carried out at pressures below atmospheric pressure.

With particular advantage, at least one processing process is carried out in vacuo at a pressure below 1 Pa, preferably below 0.01 Pa, more preferably below 0.001 Pa. This is due to the fact that with decreasing pressure ratios, the heat dissipation from a substrate to be processed by convection steadily decreases until finally a heat dissipation can take place practically only by radiation or by thermal contact to a heat transfer medium. By means of the ionic liquid of the heat transport medium, such a thermal contact is provided in the present case in a simple manner.

The machining process or one of the machining processes is preferably carried out at a substrate temperature below 250 ^° C., preferably below 220 ^° C. This has the particular advantage that with thin substrates, a bending is avoided, which can occur during subsequent cooling due to different thermal expansion coefficients.

Particularly preferably, the substrate is formed as a semiconductor wafer, and when processing the semiconductor wafer is an electrically conductive layer, preferably an aluminum layer, on a side to be coated of the semiconductor wafer deposited. Suitable materials are all monocrystalline and multicrystalline semiconductor wafers known from the prior art, in particular the elemental semiconductors silicon or germanium, and the compound semiconductors gallium arsenide, indium antimonide and indium phosphide. Multicrystalline semiconductor wafers can also be used in the form of string-ribbon wafers.

Preferably, the electrically conductive layer is deposited by means of a PVD method. These methods can be used economically, for example as high-rate electron beam or thermal vapor deposition methods, with high deposition rates and thus correspondingly high throughput rates. typical

Layer thicknesses of the electrically conductive layer are in the range of 10 to 30 microns.

Particularly preferably, a semiconductor wafer having a solar cell structure is provided for the processing method. In the context of this invention, the term solar cell structure is understood to mean at least one p-n junction known from the prior art, which is provided in the semiconductor material of the wafer. In addition to this p-n junction, the solar cell structure of the semiconductor wafer may be provided with additional thin layers, for example for improving the reflection properties, and structures, for example a front electrode. The processing method according to the invention thus represents a production method for the production of solar cells. In this way, the stated advantages of the method for the economic production of solar cells based on semiconductor wafers can be used.

Of course, it is also conceivable to replace the substrate in the form of a semiconductor wafer with a solar cell structure by a substrate not formed of semiconductor material with a solar cell structure. Areal substrates of glasses, metals and plastics, on which the solar cell structure has been applied in the form of a thin-film package, have proven useful as alternative carrier materials.

A preferred first variant of the production method for solar cells is designed such that the solar cell structure of the provided semiconductor wafer has an electrode structure on the side of the semiconductor wafer opposite the side to be coated. Preferably, the electrically conductive layer is then deposited on the semiconductor wafer to form a backside electrode. A preferred second variant of the production method for solar cells is designed in such a way that both electrodes of the solar cell structure are formed from the electrically conductive layer deposited on the semiconductor wafer after a subsequent structuring step.

With the deposition and formation of the electrodes for the solar cell based on the semiconductor wafer is practically completed in the solar cell. However, it is conceivable that, in a further preferred variant of the method for producing a solar cell, additional process steps for producing the solar cell from the semiconductor wafer which conclude the production process are provided. These can consist, for example, in the compensation by the deposition of a thin layer or in a thermal after-treatment of the solar cell formed on the semiconductor wafer.

In a further preferred variant, the method for producing a solar cell based on semiconductor wafers is developed in such a way that a plurality of semiconductor wafers formed as solar cells are electrically coupled to one another, fixed on a carrier element and encapsulated against environmental influences by means of foils and frame elements. These method steps occur in such a way that a solar module is formed from the plurality of semiconductor wafers. In this way, the advantages described can also be used for the production of solar modules.

Another aspect of the present invention is the use of a heat transfer medium to exchange heat energy between a heat reservoir and a substrate while subjecting the substrate to a vacuum process machining process. According to the invention, it is provided that the heat transport medium comprises an ionic liquid.

With regard to the advantages of using a heat transfer medium with ionic liquid, reference is made to the advantages described above in connection with the device and the method in order to avoid unnecessary repetitions at this point. Furthermore, the statements made above on the definition of the terms "ionic liquid", "processing" and "processing process from vacuum technology" as well as the explanation of the preferred chemical compositions apply accordingly. Further features and advantages of the invention will be explained in connection with the description of preferred embodiments of apparatus and method in the following figures.

It shows:

FIG. 1 a shows the cross section through a partial region of a heat sink 1 with a heat transport medium designed as ionic liquid 2, which is coupled to a substrate S; Figure 1 b shows an enlarged detail of Figure 1 a, which is shown circled in Figure 1 a labeled Ib; Figure 2 is a schematic perspective view of a heat sink 1 together with means 12 for applying a heat transfer medium in the form of ionic liquid to the heat sink 1; 3a to 3e, the schematic representation of the process flow of a first variant of a method for processing a coupled to a heat reservoir 1 via an ionic liquid 2 as a heat transport medium substrate in the form of a semiconductor wafer S for producing a solar cell; 4a to 4f, the schematic representation of the process flow of a second variant of a method for processing a coupled with a heat reservoir 1 via an ionic liquid 2 as a heat transport medium substrate in the form of a semiconductor wafer S for producing a solar cell and Figure 5 is a schematic representation of process steps for the preparation of a Solar module of a plurality of semiconductor wafers S, from which solar cells were produced in accordance with one of the methods shown in Figures 3a to 3e and in Figures 4a to 4f.

1 a shows the cross section through a partial region of a heat reservoir 1. The heat reservoir 1 is formed in the described embodiments in each case with the functionality of a heat sink. For this reason, only the functionality of a heat sink will be discussed below. The heat sink 1 is formed in the present embodiment as a carrier, which is used in an in-line process. For the concrete training of the carrier 1 a variety of variants are conceivable. On the one hand, it is possible for the carrier 1 to have a sufficient heat capacity and thermal conductivity on account of the selected material (s) of which the carrier 1 is made. For this purpose, various metals, in particular semi-precious metals, such as copper and its alloys are suitable. Furthermore, it is conceivable that the carrier 1 is provided with coolant. These coolants may, for example, have a line system such that the carrier 1 is flowed through by a liquid or gaseous cooling medium. In this case, the cooling medium ensures adequate removal of the heat of the process, so that the carrier 1 acts as a heat sink.

On its surface, the carrier 1 has a support region 10. This support region 10 serves for thermal coupling of the carrier 1 acting as a heat sink to a substrate S. The substrate S is subjected to a processing process in which process heat is generated at least on the side S11 of the substrate S facing away from the carrier 1. In order for this process heat arising on the surface S11 of the substrate S to be processed to be conducted through the substrate S to the carrier l acting as a heat sink, a heat transport medium 2 is provided between the substrate S and the carrier 1. The heat transport medium 2 is formed in the present embodiment as an ionic liquid. This ionic liquid 2 wets the support area 10 of the carrier 1 and the surface S10 of the substrate S facing the support area 10 of the carrier 1 in this way. About the ionic liquid 2, the resulting process heat can be dissipated quickly and reliably in the heat sink.

In the presently described preferred embodiment, the substrate S is formed as a thin semiconductor wafer. The thickness of the wafer S is significantly less than 1 mm. Nowadays, wafer thicknesses in the range of 200 μm are common for the production of solar cells. In order to reduce costs, the aim in the future in solar cell production is to use even thinner wafers as substrates. The semiconductor wafer S can be designed as a multi- or monocrystalline silicon or germanium wafer. Figure 1 b shows the circled in Figure 1 a and provided with the name Ib area in an enlarged view. Identical elements of the heat sink formed as a carrier 1 are provided with the same reference numerals. In this respect, reference is made to the statements made above. Due to the enlarged illustration, it can be seen that the carrier 1 has channels 11 with openings 11 extending to the contact area 10. These openings 11 in the surface of the support area 10 together with the adjoining ducts 110 serve to remove any gas inclusions between the ionic liquid 2, the substrate S and the support area 10, when the carrier 1 is exposed to vacuum conditions with the substrate S thermally coupled thereto becomes. For this purpose, it is necessary to provide a sufficient density of openings 11 in the support area 10 of the carrier 1. A variant provides that per square millimeter an opening 11 is provided with a channel diameter of about 100 microns. It goes without saying that the density and the geometry of the openings 11 together with the adjoining channels 110 can and must be adapted to the respective conditions of use. These channels 110 ensure that any gas pockets in the ionic liquid can escape through the channels 110 when vacuum conditions are set for a machining process. Otherwise there is a risk that the gas inclusions expanding when the vacuum conditions are set lead to detachment of the substrate S from the carrier 1.

In addition, each empty region, which is not filled with ionic liquid 2, between substrate S and carrier 1 represents an undesirable barrier for dissipating the process heat from the substrate surface S 11 to be processed. The higher the negative pressure, the poorer is the heat conduction of the empty regions

Convection, until finally the empty areas allow virtually no more heat dissipation by convection but only by infrared radiation.

Finally, it is emphasized that neither the representation in FIG. 1 a nor the representation of FIG. 1 b must be true to scale. That is the thickness of the

Substrates S and / or the layer thickness of the ionic liquid 2 used as a heat transport medium can vary within wide limits. The process heat produced on the surface to be processed S11 of the substrate S leads to overheating of the substrate S, if it is not derived to a sufficient extent and in sufficient speed on the ionic liquid 2 in the carrier acting as a heat sink 1. For these reasons it will be in most cases it is preferred to form the layer of ionic liquid 2 as thin as possible. Nevertheless, considerations can play a role here, that a slightly thicker layer of ionic liquid 2 will be subject to less heating due to the associated higher heat capacity. The limits and the duration of the thermal stability for the used ionic liquids 2 must therefore be included in the considerations of the selected layer thickness.

Figure 2 shows the schematic perspective view of a heat sink in the form of a carrier 1 together with means 12 for applying a heat transfer medium in the form of ionic liquid on the support surface 10 of the carrier 1. The heat sink is as a carrier 1 for an in-line process with a flat support area 10 trained. The support area 10 has a substantially square basic shape, which in the present case is adapted to the geometry of the substrates to be placed on the support area in the form of square semiconductor wafers. Of course, depending on the geometry of the substrates to be used, an adapted geometry of the support region 10 of the carrier 1 is to be preferred. It is also emphasized that the design of the carrier 1 is completely free in the end section facing away from its support region 10. It can therefore be adapted to the structural and functional conditions for the use of the carrier 1 in the respective in-line process. This is to be illustrated by the curved lines of the illustration in FIG.

The means 12 for applying a heat transport medium on the support region 10 of the carrier 1 are formed in the present case for the use of a heat transfer medium consisting entirely of ionic liquid. These means include means for allowing atomizing, dispensing of ionic liquid on the support area 10, or printing on the support area 10 with ionic liquid by means of an ink jet printing process. For this purpose, the means 12 and / or the carrier 1 are moved relative to each other in order to provide the support area 10 in the desired sections with the necessary amount of ionic liquid. The desired sections can occupy the entire surface of the support area 10. The relative movement of the carrier 1 to the means 12 for applying a heat transfer medium is illustrated by the opposite arrows in Figure 2. Another variant of the means 12 for applying ionic liquid can be seen in Figure 2 in dashed lines. These are means 12, which allows the application of ionic liquid on the support area 10 of the carrier 1 in a screen printing process. For this purpose, a doctor blade 120 is provided which läkelt the ionic liquid by a movement along the double arrow shown in dashed lines in cooperation with a doctor blade on the support area 10.

The heat sink 1 shown in Figure 2 allows the application of ionic liquid as a heat transport medium on the support portion 10 of a heat sink 1, even before the thermal coupling of a substrate via the ionic liquid with the heat sink 1 is made. Of course, it is possible to provide both the heat sink 1 and the substrate S with ionic liquid in order then to thermally couple the two components together. This process is described below with reference to two process variants shown by way of example.

FIGS. 3 a to 3 e show the schematic illustration of the method sequence of a first variant of a method for processing a substrate coupled to a heat reservoir 1 via an ionic liquid 2 as a heat transport medium in the form of a semiconductor wafer S for producing a solar cell.

FIGS. 3 a and 3 b each show in the upper half how the heat sink formed as a carrier 1 is provided with ionic liquid 2 in cooperation with means 12 for applying ionic liquid in the entire support region 10 of the carrier 1. The means 12 bring the ionic liquid 2 to the carrier 1 by spraying, atomizing or dispensing.

In the lower half of FIGS. 3a and 3b, it is correspondingly illustrated how a substrate in the form of a semiconductor wafer with a solar cell structure is provided with ionic liquid 2 on its first surface S10. This first surface S10 has a grid-shaped electrode structure PV1 of a solar cell structure. The

Applying the ionic liquid in this case is done by means 12 comprising a screen printing device with a squeegee 120. When the means 12 are arranged above the semiconductor wafer S, the first surface S 10 of the semiconductor wafers S to be coated is provided with ionic liquid 2 by a movement of the squeegee 120. Thereafter, the semiconductor wafer S is rotated such that the ionic liquid 2 provided with the first surface S10 with the also with ionic Liquid 2 wetted contact area 10 of the carrier 1 is brought into contact. This is shown in FIG. 3c.

The distances of the outer edges of the semiconductor wafer S correspond substantially to the spacings of the outer edges of the carrier 1. As a result, the semiconductor wafer S comes to rest on the support region 10 of the carrier 1 such that the carrier 1 is substantially covered by the semiconductor wafer S and its second , surface to be machined S11 facing away from the carrier 1. The ionic liquid 2 applied both to the support area 10 of the carrier 1 and to the surface S10 of the semiconductor wafer S that is not to be processed produces the desired thermal coupling between the carrier 1 acting as a heat sink and the semiconductor wafer S. The carrier 1 with the semiconductor wafer arranged thereon subsequently passes through a vacuum process in a processing plant BA. In this case, the surface facing away from the carrier 1 surface S11 of the semiconductor wafer S is processed.

For the purposes of the present invention, the term "processing" does not only include process steps that involve a substance intrusion into the existing structure of the surface to be processed, but also the addition of matter, that is, for example, the deposition of layers via CVD or PVD. Procedures on the surface to be processed fall under the "edit" feature.

In the present in-line process for producing a solar cell from a semiconductor wafer S, the surface to be processed S11 of the semiconductor wafer S is provided with an electrically conductive layer SL of aluminum. This process is carried out in the processing plant BA under high-vacuum conditions at pressures below 0.01 Pa. A PVD method, in particular a high-rate electron beam evaporation method or a thermal vapor deposition method, is preferably used to deposit an aluminum layer SL, which is several micrometers thick, on the semiconductor wafer S. As a result of the fact that layer thicknesses beyond the usual "thin layers" are required, a large amount of process heat arises on the substrate surface S11, which must be dissipated sufficiently rapidly to avoid overheating of the semiconductor wafer S. The rapid and reliable heat dissipation of the process heat from the surface to be coated S11 through the semiconductor wafer S through to the heat sink 1 ensures the arranged between the semiconductor wafer S and heat sink 1 ionic liquid 2. Due to the fact that a to the process parameters of adapted ionic liquid 2 having a corresponding heat resistance and a low vapor pressure is used, their use is ensured without interaction with the machining process. A preferred process variant provides for the high-rate deposition of aluminum layers of at least 10 microns thickness, a substrate temperature of about 200 ⁰ C is not exceeded.

In particular, an ionic liquid adapted to the present process is 1-methyl-1-propylpiperidinium bis (trifluoromethylsulfonyl) amide. 1-methyl-1-propylpiperidinium bis (trifluoromethylsulfonyl) amide has a high

Heat resistance and a low vapor pressure in order to meet the requirements imposed by the machining process. Furthermore, 1-ethyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) amide and N-methyl-N-trioctylammonium bis (trifluoromethylsulfonyl) amide are each ionic liquids which are outstandingly suitable for the present processing process.

After completion of the processing process, both the semiconductor wafer S and the carrier 1 are cleaned of the ionic liquid 2. The carrier 1 is again available for the in-line process in order to be thermally coupled to a further semiconductor wafer S. The semiconductor wafer S having the solar cell structure has a back electrode in the form of the deposited electrically conductive layer SL in addition to the grid-shaped front electrode PV1. The semiconductor wafer S thus represents a finished, functional solar cell after passing through the presently described processing process.

A modified variant of a method for producing a solar cell from a semiconductor wafer S is shown schematically in FIGS. 4a to 4f. Compared to the representation from FIGS. 3a to 3e, the same reference numbers are used for identical components. In that regard, reference may be made to the statements made above.

The representation of the application of ionic liquid 2 on the support area 10 of a carrier 1 in the upper half of Figures 4a and 4b corresponds completely to the representation of Figures 3a and 3b. In connection with the semiconductor wafer S in the lower half of FIGS. 4 a and 4 b, unlike in FIGS. 3 a and 3 b, a semiconductor wafer S with a solar cell structure is shown Liquid 2 to surface S10 has no grid-shaped electrode structure. The semiconductor wafer S used here has a solar cell structure with a pn junction, which is not yet provided with electrodes. FIGS. 4c and 4d show, in accordance with the illustration of FIGS. 3c and 3d, that the surface S11 of the semiconductor wafer to be processed is in one

Processing plant BA is provided with an electrically conductive layer SL. Again, this is a multi-micron aluminum layer SL deposited by a PVD process.

FIG. 4e shows, in accordance with the illustration from FIG. 3e, that carriers 1 and

Semiconductor wafer S are cleaned after the processing process in the processing plant BA of ionic liquid 2.

Subordinate to this cleaning step, unlike in the first illustrated process variant for producing a solar cell, an additional

Structuring step provided. In this structuring step, the deposited electrically conductive layer SL is patterned, for example by means of a combined masking and etching process, such that the coated surface S11 of the semiconductor wafer S has a comb-shaped first electrode E1 and a comb-shaped second electrode E2, which engage in one another like a finger.

This semiconductor wafer S also represents a finished, functional solar cell after passing through the machining process described here.

FIG. 5 shows the schematic representation of method steps for producing a solar module from a plurality of semiconductor wafers S, from which solar cells were produced according to one of the methods illustrated in FIGS. 3 a to 3 e and FIGS. 4 a to 4 f.

For this purpose, the solar cells S are connected in series with one another by means of electrical conductors 33 and applied and fixed on a carrier element 3. Subsequently, the front and the back of this flat structure is encapsulated against environmental influences. The planar structure is covered for example by means of films 30, 31. The laminate formed in this way can be bordered along its outer edges with frame elements 32, for example in the form of U-shaped profiles, and fixed by means of an adhesive. In addition, there is still the attachment of a electrical contact means 34 to allow the connection of the encapsulated module to a power grid.

Claims

claims:

1. heat reservoir (1) for thermal coupling with a substrate (S) comprising a heat transport medium, which improves an exchange of heat energy between the heat reservoir (1) thermally coupled substrate (S) and the heat reservoir (1), wherein the heat transport medium between the heat reservoir (1) and the heat reservoir can be coupled to the substrate (S) provided in a static manner, characterized in that the heat transport medium comprises an ionic liquid (2).

2. Warmereservoir (1) according to claim 1, characterized in that the

Warmer reservoir (1) has a flat bearing area (10) for a flat formed substrate (S), wherein the heat transfer medium with the ionic

Liquid (2) on the support area (10) is arranged.

3. Warmer reservoir (1) according to claim 2, characterized in that the ionic liquid (2) wets the support area (10) at least in sections.

4. heat reservoir (1) according to one of claims 1 to 3, characterized in that the heat transport medium is formed as an ionic liquid (2).

5. heat reservoir (1) according to one of claims 2 to 4, characterized in that the support area (10) is formed as a flat surface.

6. heat reservoir (1) according to one of claims 1 to 5, characterized in that the ionic liquid above 100 ⁰ C, preferably above 150 ⁰ C, more preferably above 200 ° C, is thermally stable.

7. A heat reservoir (1) according to any one of claims 1 to 6, characterized in that the ionic liquid at 25 ° C has a vapor pressure below 0.1 Pa, preferably below 0.01 Pa and more preferably below 0.001 Pa.

8. A heat reservoir (1) according to any one of claims 1 to 7, characterized in that the ionic liquid (2) is formed of an anion and a cation, wherein the anion is bis (trifluoromethylsulfonyl) amide and the cation is selected from the group consisting of optionally substituted alkylimidazolium, tetraalkylammonium, optionally substituted dialkylpiperidinium and theirs

Mixtures, wherein alkyl represents an optionally substituted hydrocarbon group, wherein the cation is preferably selected from the group consisting of 1-ethyl-3-methyl-imidazolium, N-methyl-N-trioctylammonium, 1-methyl-1 - propylpiperidinium, and wherein the ionic liquid 1-methyl-1-propylpiperidinium bis (trifluoromethylsulfonyl) amide is more preferred.

9. heat reservoir (1) according to one of claims 2 to 8, characterized in that the support region (10) of the heat reservoir (1) has a plurality of openings (11), designed such that at one on the

Supporting region (10) applied substrate (S) gas inclusions between the substrate and support area via the openings (11) can escape when the pressure surrounding the substrate (S) is reduced.

10. heat reservoir (1) according to one of claims 2 to 8, characterized in that the heat reservoir (1) comprises means (12) for applying ionic liquid to the support area (10) and / or for application to a substrate (S), wherein the ionic liquid applying means (12) is adapted to apply the ionic liquid by screen printing, doctor blade coating, dispensing, atomizing or inkjet printing.

11. Warmer reservoir (1) according to one of the preceding claims, wherein the heat reservoir (1) is designed as a heat sink.

12. A method for processing a with a heat reservoir (1) thermally coupled substrate (S), with the following method steps

Providing a heat reservoir (1) with the features according to one of claims 1 to 11, thermally coupling a substrate (S) with the

Heat transport medium (2) of the heat reservoir (1),

• Edit the substrate (S) and

• Remove the substrate (S) from the heat transport medium (2).

13. The method according to claim 12, characterized in that the method step of providing the heat reservoir (1) comprises the application of ionic liquid (2) on a support region (10) of the heat reservoir and / or on the substrate (S).

14. The method according to claim 12 or 13, characterized in that the method step of processing the substrate (S) is designed as a machining process or a combination of machining processes from the vacuum technology.

15. The method according to claim 14, characterized in that at least one

Processing process is carried out in vacuo at a pressure below 1 Pa, preferably below 0.01 Pa, more preferably below 0.001 Pa.

16. The method according to claim 14, characterized in that the

Machining process or one of the machining processes at a substrate temperature below 250 ⁰ C, preferably below 220 ⁰ C is performed.

17. The method according to any one of claims 12 to 16, characterized in that the

Substrate is formed as a semiconductor wafer (S), and in the processing of the semiconductor wafer (S) an electrically conductive layer (SL), preferably a Aluminum layer is deposited on a side to be coated (S11) of the semiconductor wafer.

18. The method according to claim 17, characterized in that the electrically conductive layer (SL) is deposited by means of a PVD method.

19. The method according to claim 17 or 18, characterized in that the semiconductor wafer (S) is provided with a solar cell structure (PV).

20. The method according to claim 19, characterized in that the

Solar cell structure (PV) of the provided semiconductor wafer (S) has an electrode structure (PV1) on the side to be coated (S11) opposite (S10) side of the semiconductor wafer.

21. The method according to claim 19 or 20, characterized in that the electrically conductive layer (SL) for forming a rear electrode on the

Semiconductor wafer (S) is deposited.

22. The method according to claim 19, characterized in that from the deposited on the semiconductor wafer electrically conductive layer (SL) after a subsequent patterning step, both electrodes (E1, E2) of the solar cell structure are formed.

23. The method according to any one of claims 17 to 22, characterized in that additional final process steps for producing a solar cell from the semiconductor wafer (S) are provided.

24. The method according to claim 23, characterized in that a plurality as

Solar cells formed semiconductor wafer (S) electrically coupled together, on fixed to a carrier element (3) and to environmental influences by means of

Foils (30, 31) and frame elements (32) are encapsulated, such that from the

Plurality of semiconductor wafers (S) a solar module is formed.

25. Use of a heat transport medium (2) for exchanging heat energy between a heat reservoir (1) and a substrate (S) while the substrate (S) is subjected to a processing process from vacuum technology, characterized in that the heat transport medium is an ionic liquid (2 ) having.

26. Use according to claim 25, characterized in that the heat transport medium (2) in a static manner between the substrate (S) and the

Warmer reservoir (1) is provided.

27. Use according to claim 25 or 26, characterized in that the ionic liquid, the substrate (S) and / or a support area (10) of the

Wetting the heat reservoir (1).

28. Use according to any one of claims 25 to 27, characterized in that the heat transport medium is formed as an ionic liquid (2).

29. Use according to any one of claims 25 to 27, characterized in that the ionic liquid (2) above 100 ⁰ C, preferably above 150 ⁰ C, more preferably above 200 ° C, is thermally stable.

30. Use according to one of claims 25 to 28, characterized in that the ionic liquid (2) at 25 ° C has a vapor pressure below 0.1 Pa, preferably below 0.01 Pa and more preferably below

0.001 Pa.

31. Use according to one of claims 25 to 29, characterized in that the ionic liquid (2) is formed from an anion and a cation, wherein the anion is bis (trifluoromethylsulfonyl) amide and the cation is selected from the

A group consisting of optionally substituted alkylimidazolium, tetraalkylammonium, optionally substituted dialkylpiperidinium, and mixtures thereof, wherein alkyl represents an optionally substituted hydrocarbon group, wherein the cation is preferably selected from the group consisting of 1-ethyl-3-methyl-imidazolium, N-methyl N-trioctylammonium, 1-methyl-1-propylpiperidinium, and wherein the ionic liquid 1-methyl-1-propylpiperidinium bis (trifluoromethylsulfonyl) amide is more preferred.