EP2883247A1

EP2883247A1 - Laser-based method and processing table for locally making contact with a semiconductor component

Info

Publication number: EP2883247A1
Application number: EP13745646.3A
Authority: EP
Inventors: Jan Nekarda; Andreas Rodofili; Andreas Brand; Martin Graf; Ralf Preu
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2012-08-10
Filing date: 2013-08-02
Publication date: 2015-06-17
Also published as: DE102012214254A1; CN104737300A; WO2014023668A1

Abstract

The invention relates to a method for locally making contact with a semiconductor component, said semiconductor component being part of a photovoltaic solar cell or of a preliminary stage in the process for producing a photovoltaic solar cell, comprising the following method steps: A applying at least one metal layer to one side of the semiconductor component, B locally heating at least the metal layer, in such a way that at least the metal layer is momentarily melted in a local region. It is essential that a metal foil is used as the metal layer, and that after method step B the non-melted regions of the metal foil are removed in a method step C. The invention furthermore relates to a processing table for carrying out such a method.

Description

Laser-based process and machining table for local

Contacting a Semiconductor Device Description

The invention relates to a method for locally contacting a semiconductor component, which semiconductor component is part of a photovoltaic solar cell or a preliminary stage in the production process of a photovoltaic solar cell, according to the preamble of claim 1 and a processing table for carrying out such a method.

In photovoltaic solar cells charge carriers are typically dissipated by metal structures. In this case, metal structures are known which contact one side of the semiconductor component over the whole area. For use on the side of the solar cell facing the incidence of light during operation and / or for reducing recombination losses at the contact surfaces, metal structures are used which have one or more local electrical contact areas to the semiconductor component.

In its simplest form, the semiconductor device consists of a semiconductor layer with a p-doped region and an n-doped region. The semiconductor layer may comprise additional insulating layers.

The semiconductor component contacted locally by means of the metallic contacting structure is thus part of a photovoltaic solar cell or a preliminary stage of a photovoltaic solar cell in the manufacturing process, wherein the solar cell can have a plurality of semiconductor layers.

For locally contacting photovoltaic solar cells, it is known to produce the metal structure by means of a lift-off process:

For example, Knorz, A., A. Grohe, and R. Preu. Laser ablation of etch resists for structuring and lift-off processes. in Proceedings of the 24 ^th European Photovoltaic Solar Energy Conference. 2009. Hamburg, Germany, a procedure described, in which on a silicon substrate, first an electrically insulating passivation layer and then a lift-off layer is applied. Subsequently, the lift-off layer is opened locally by means of a laser and, in a further step, by means of wet-chemical etching, the insulation layer is opened in the areas in which the lift-off was previously opened. In the wet-chemical etching, the lift-off layer thus serves as a masking layer.

Subsequently, a metal layer is applied over the entire surface, which thus covers the lift-off layer and covers the silicon substrate in the locally opened regions. After wet-chemical removal of the lift-off layer and thus also the metal layer located on the lift-off layer, a metal structure remains in the previously locally opened regions of the insulating layer on the surface of the silicon substrate.

In addition, it is alternatively known to produce the metal structure by means of a screen printing process:

For example, in Hörteis, M. "Fine-Iine Printed Contacts on Crystalline Silicon Solar Cells", Dissertation, University of Konstanz, 2009, a method is described in which a paste is printed through a sieve on a Halbleitererbaueiement and by means of a high-temperature step, an electrical contact is formed to the underlying emitter.

Disadvantages of the prior art methods are that the structures produced lead to significant shadowing, in particular on the front side of a solar cell, and that the use of silver results in high material costs because of the required conductivity.

Furthermore, it is known from DE 10 2006 040 352 B3 to apply a metallic powder to a semiconductor substrate and to locally fuse and / or fuse it by means of a laser beam in order to form a metallic contacting structure. A disadvantage of this method beyond the aforementioned disadvantages is that the effect of heat on the particles of the metallic powder is difficult to dose and, accordingly, the geometric design of the metal structure is imprecisely predetermined. In particular, there is a risk to penetrate a contacted by means of the metallic contacting structure emitter, so that the efficiency of the solar cell is impaired. The present invention has for its object to provide a method for locally contacting a semiconductor device, the use of which improves the contact properties, in particular with respect to the electrical conductivity and adhesion, reduces the shading and which at the same time has a low Prozeßkompexität. Furthermore, the invention is intended to provide a machining table for carrying out such a method.

This object is achieved by a method according to claim 1 and by a processing table for performing such a method according to claim 14. Advantageous embodiments of the method can be found in claims 2 to 1 3. Advantageous embodiments of the processing table for performing the method can be found in the claims 15 and 16. The wording of the claims is hereby incorporated by express reference into the description.

The inventive method is used to produce a metal structure for local electrical contacting, d. H. a metallic contacting structure of a semiconductor device. The semiconductor component is a photovoltaic solar cell or a precursor of a photovoltaic solar cell in the manufacturing process and comprises at least one semiconductor layer. It is within the scope of the invention that the semiconductor layer is formed as a semiconductor substrate, in particular as a silicon wafer.

In particular, the use of the method according to the invention in the production of front side contacts of a solar cell is advantageous in order to produce linear contacts with as little shading as possible, since the electromagnetic radiation is coupled into the semiconductor component via the front side. Typically, solar cells are contacted on the front side by line-like metallic contacting structures that are connected to one another like a comb. However, it is also within the scope of the invention to use the method according to the invention additionally or alternatively in the contacting of a back side of the solar cell and in particular for contacting backside contact cells, ie such solar cells in which both the positive, as well as the negative contact on the back of the solar cell lie. This includes in particular the known MWT and EWT solar cell (EP 985,233 and JM Gee, WK Schubert and PA Basore, "emitter wrap-through solar cell", Proceedings of the 23 ^rd I EEE Photovoltaic Specialists Conference, Louisville, Kentucky, United States , Pp. 265-270 (1993)) and the BJBC cell (Schwartz, RJ, M.D., Lammert, "Silicon solar cells for high concentration applications", Technical Digest often he International Electron Devices Meeting, Washington D.C. , USA, 1975) It is also within the scope of the invention to use the method according to the invention for an n-doped and / or for a p-doped semiarite layer.

The method comprises the following method steps:

In a method step A, at least one metal layer is applied to one side of the semiconductor component.

In a method step B, the metal layer applied in method step A is locally heated. As a result, a melting of at least the metal layer takes place in a local area for a short time.

It is essential that a metal foil is used as the metal layer and that in a method step C, the metal foil is removed in the areas not fused in method step B.

The invention is based on the applicant's knowledge that by using a metal foil as the metal layer after the contacting step, the metal layer in the non-fused regions can be easily removed.

With the method according to the invention, it is possible to produce a local metallic contact structure by local heating and thus selective melting of the metal foil. The resulting flash produces a recoil which pushes the foil against the substrate causing the molten metal to make contact with the semiconductor device. The method according to the invention thus for the first time offers a cost-effective possibility of producing metal structures for local contacting of the semiconductor component. Compared to previously known screen printing method narrower structures with a higher aspect ratio (height to width of the metal structure) can be produced, so that further the use of silver is not absolutely necessary and thereby costs can be saved. Furthermore, commercially available metal foil, for example, in a supermarket, commercially available metal foil can be used in the process according to the invention, which nevertheless has only a small thickness variation. As a result, in particular compared with the previously known method, which uses metallic powder, there is the advantage that the heat action can be metered more accurately and thus, in particular, the size of the melting zone in method step B can be specified more precisely. In comparison to previously known lift-off or masking methods, the application of masks can be dispensed with, so that costs are saved.

It is within the scope of the invention that further intermediate layers are applied before process steps A and / or B.

Preferably, in an additional method step A-a, at least one intermediate layer is applied to one side of the semiconductor component before method step A. This intermediate layer is particularly preferably a dielectric layer. This results in the advantage that the intermediate layer can be formed to increase the efficiency of the solar cell, in particular by forming the intermediate layer as a passivation layer in order to reduce the charge carrier recombination on the surface of the semiconductor layer and / or by forming the intermediate layer as an optical layer in order Reflection properties of the solar cell and thus improve the light absorption. In particular, therefore, an embodiment of the intermediate layer as a dielectric layer, in particular as a silicon dioxide layer or silicon nitride layer is advantageous.

In a further preferred embodiment, in an additional method step Ab between method step Aa and method step A, the intermediate layer applied to one side of the semiconductor component is removed in the local regions. This results in the following Applying the metal foil these in the local contacting areas directly to the surface to be electrically contacted. This results in the advantage that a disturbance of the contact formation in the local melting of the metal foil is avoided by the material of the molten intermediate layer.

The removal of the intermediate layer preferably takes place in such a way that the intermediate layer is ablated in the local regions by means of a laser and / or is removed by a wet-chemical etching process.

Preferably, a multilayer metal foil is used as the metal layer. This has the advantage that multistage metallic contacting structures with different properties in terms of conductivity, adhesion properties, material costs and / or contact resistance can be applied, and thus in particular a high conductivity can be achieved at a reduced cost.

In method step B, the metal layer is preferably locally heated by means of illumination, particularly preferably by means of a laser, in particular preferably by means of a pulsed laser. Preferably, a laser having a wavelength in a range of 190 nm to 1 1 μητι, particularly preferably used with a length of 1 064 nm. Preferably, a laser with a pulse length in the range of 10 ns to 1 0 s is used. It is also within the scope of the invention to use a laser in continuous wave mode (cw) or a cw laser in modulated mode for method step B. Investigations by the inventors have shown that the aforementioned parameters enable a smooth and error-free process flow.

An advantage of the use of a laser for local heating and thus melting of the metal foil is that no determination of a given shape of the metal structure, for example, by a sieve used, as in the method according to the invention, the local melting at any location and with high Accuracy can take place.

Titanium, silver, nickel, aluminum, tin, zinc and / or copper are preferably used as the material for the metal foil. Particularly preferred is for the Coating p-doped semiconductor materials used aluminum, nickel and / or titanium. Particular preference is given to using nickel, more preferably silver, preferably titanium, for the coating of n-doped semiconductor metal materials. The metal foil used to produce the metallic contacting structure of a semiconductor component preferably has a total thickness of more than 10 m, in particular if the entire metallic contacting structure is produced by means of the metal foil.

It is particularly advantageous to use a multilayer metal foil comprising a material suitable for contacting, a low-cost material with high conductivity and a material suitable for interconnecting the semiconductor component in the stated sequence. The individual layers preferably have thicknesses in the range between 100 nm to 10 m.

Particularly preferably, the multilayer metal foils for producing a metallic contacting structure on a p-doped semiconductor component have the following structure:

For locally contacting the p-doped layer, the multilayer metal foil on the side facing the semiconductor component comprises an approximately 100 nm thick nickel layer and / or titanium layer and / or aluminum layer. A middle layer of the multilayer metal foil may be made of a low-cost material that must have good conductivity, preferably copper or tin. The last layer of the multilayer metal foil on the side remote from the semiconductor component is a silver layer and / or tin layer and / or zinc layer and / or copper layer for further interconnection.

In particular, the multilayer metal foils for producing a metallic contacting structure on an n-doped semiconductor component have the following structure:

For local contacting of the n-doped layer, the multilayer metal foil on the side facing the semiconductor component comprises an approximately 100 nm thick nickel layer and / or titanium layer and / or silver layer. A middle layer of the multilayer metal foil may be made of a low-cost material that must have good conductivity, preferably Copper or tin. The last layer of the multilayer metal foil on the side remote from the semiconductor component is a silver layer and / or tin layer and / or zinc layer and / or copper layer for further connection.

In a preferred embodiment, structuring of the metal foil takes place simultaneously during the contacting process. Structuring here means that a separation between the areas in which an electrical contact was generated by means of the metal, and the areas in which the metal foil was not melted, arises. The advantage here is that thereby the metal foil in the areas where no contact has taken place, can be removed easily and without additional separation step from the semiconductor surface. In a further preferred embodiment, predetermined breaking points are introduced into the metal foil in an additional method step B-a before method step C. This has the advantage that, in particular when using thicker and in particular multilayer metal foils, a defined parting line is predetermined. In this way, in particular, the risk that film is torn off when removing the film, even in a molten area, is considerably reduced.

In particular, it is advantageous if the metal foil is at least partially spaced apart from the semi-ferritic component in the non-fused areas before the structuring step so that no contact is made with the semiconductor component at the heated portions. In this way, in particular, it is avoided that the metal foil adheres to the semiconductor device in the non-fused areas during the separation step.

A safe and inexpensive spacing is achieved in a preferred embodiment of the method according to the invention by the metal foil is at least partially spaced from the Haibleiterbauelement by heating the semiconductor device and / or by suction from above, and / or by blowing from below. Preferably, a laser, particularly preferably a pulsed laser, is used in the generation of predetermined breaking parts in the structuring step. The use of a laser for processing solar cells is known per se, so that it is possible to resort to existing devices and in particular deflection units for the laser beam. It is especially made

DE 100 46 170 A1 discloses producing so-called "laser fired contacts" (LFC) by means of local melting of a metaflayer, a dielectric layer and a partial region of the semiconductor layer The devices used for this purpose can in principle also be used for the method according to the invention.

Preferably, a laser with a wavelength range from 1 90 nm to 1 1 μιη used, preferably in the range of 1030 nm to 1064 nm. Preferably, a laser with pulse lengths of one ns to several ps used, more preferably in the range of 1 s to 1 00 με. It is also within the scope of the invention to perform the structuring step with a laser in continuous wave mode (cw) or a cw laser in modulated operation.

In a further preferred embodiment, the metal foil is fastened to the semiconductor component at least during method step B. Examinations by the inventors have shown that the metal foil preferably rests flat against the semiconductor component during melting, since, for example, air entrapment between the foil and the semiconductor component in the region to be fused may result in inaccuracies in the production of the metal structure. This may be due to the fact that the metal foil is completely or partially vaporized due to the lack of thermal contact with the semiconductor device in the local heating and thus forms no or only an insufficient, a high contact resistance having metal structure.

Preferably, the metal foil is therefore stretched during the process step B on the semiconductor device, and / or sucked on this and / or blown on this. In particular, the suction and / or blowing of the metal foil offers a process-technically simple and in particular non-contact possibility of ensuring the contact between metal foil and semiconductor component in method step B. In a further preferred embodiment, in method step B, the heating of the metal foil takes place by illumination of the side of the semiconductor component facing away from the metal foil. This preferred embodiment of the method according to the invention makes it possible to melt the metal foil locally at the boundary layer metal foil semiconductor component.

In this case, a laser is preferably used for the melting of the metal foil which is not or only slightly absorbed by the semiconductor component, in particular by a silicon layer, so that the local heating takes place essentially at the local metal foil semiconductor component at the boundary layer. In particular, in this case the use of a laser having a wavelength in the range of 1200 nm to 1 pm is advantageous, in particular a C0 ₂ laser.

In the case of illumination from the side facing away from the metal foil, use of multilayer metal foils in particular is preferred. In this case, it is advantageous in particular that further possible metal layers are not or only slightly melted on the side of the metal foil facing away from the semiconductor component. This ensures that only the semiconductor component facing layer of the multilayer metal foil is melted to form the electrical contact with the semiconductor device, whereas the other layers of the multilayer metal foil remain unchanged in structure and thus may be formed in particular for a low line resistance. As a result, multilayer metal contacts with different functionalities can be produced in one method step.

This makes it possible, in particular, to use a multilayer film which comprises a copper layer which does not directly adjoin the semiconductor component, ie is a middle layer or the layer facing away from the semiconductor component. Previously, when using a copper layer, the problem was that the copper layer was also melted and therefore copper atoms embedded in the semiconductor device and adversely affected the electrical properties, especially when using a silicon semiconductor device. In a further preferred embodiment, in method step B, a laser is used for melting the metal foil whose beam profile has a higher intensity at the edges than in the middle.

In the context of the present description, "intensity at the edges rather than at the center" means that the intensity of the beam profile perpendicular to the direction of movement of the laser relative to the surface of the semiconductor device has a lower intensity in a middle region than in the two outer regions In particular, it is advantageous to design the straightening profile in such a way that it has a first intensity maximum, an intensity minimum and a second intensity maximum in the order given in that the respective intensity maxima are at the desired distance from one another,

In particular, in this preferred embodiment it is possible to carry out the structuring step simultaneously with the contacting step.

Due to the high laser intensity at the edges of the beam profile, the metal foil is contacted here with the Halbieiterbauelement and simultaneously generates a predetermined breaking point, in the middle region with low laser intensity, the metal foil remains largely preserved and thus ensures sufficient conductivity. The advantage here is that thereby the metal foil in the areas where no contact has taken place, can be removed easily and without additional separation step from the surface of the semiconductor device.

In a further preferred embodiment, the method according to the invention is designed as an at least two-stage metallization process: First, as described above, a metal structure is formed by means of the metal foil. This serves as a seed layer, which is reinforced metallically in a second step of the metallization process. In this case, metal, preferably galvanically, is deposited on the metallic contacts which were produced as a seed layer in the first step, ie the contacts are preferably galvanically reinforced. With regard to the galvanic amplifiers kung can be used on known processes. In particular, it is advantageous to carry out the reinforcement with a different and preferably less expensive metal to the seed layer.

In carrying out the method, a thin metal foil is preferably used to produce the seed layer, so that the contacting step and the structuring step take place simultaneously. This results in a low process complexity. Furthermore, a costly metal, for example silver, is typically used as seed, so that the use of a thin metal foil reduces costs.

Preferably, therefore, the metal foil used in the production of the seed layer has a total thickness of less than 3 pm, preferably less than 2 μιη.

Preferably, a laser with pulse lengths in the range of 10 ns to 100 ns is used for the production of seed layers, in particular when using a metal foil having a total thickness of less than 3 μm, preferably less than 2 m.

For the contacting of n-doped regions, a seed layer of silver, titanium or nickel and, for contacting p-doped regions, a seed layer of aluminum, titanium or nickel is preferably formed by means of the metal foil.

In a further preferred embodiment of the method according to the invention n-doped regions of the semiconductor device are metallized in a first implementation of the method. Preferably, a thin metal foil is used in the first implementation of the method, so that the contacting step and the structuring step occur simultaneously. In a second implementation of the method, p-doped regions of the semiconductor component are metallized. Preferably, in step B-a, a structuring step is carried out to produce predetermined breaking points.

In this preferred embodiment is thus possible in a simple and cost-effective manner to contact p- and n-doped regions. In particular, a cost effective method results if p- and n-doped regions are contacted with the same metal foil. Often, however, to achieve low contact resistances it is advantageous to contact p- and n-doped regions with different metals. In a further preferred embodiment, therefore, different metal foils are used for the contacting of the n-doped regions on the one hand and the p-doped regions on the other hand, so that in particular the metal used in each case can be selected with regard to a low contact resistance. In particular, it is advantageous in this case to heat the last applied metal foil in such a way that heating takes place on the underside. This results in an alloy of the two metal foils, which leads to an electrical and mechanical connection of the two MetaHfolien. It is advantageous in the abovementioned embodiments of the method according to the invention that areas of a semiconductor component which are doped differently by two iterations can be contacted locally and separately. This allows a simple and inexpensive process flow. These preferred embodiments are particularly suitable for

Backside metallization and contacting of a backside contact solar cell.

The above-described object is furthermore achieved by a machining table according to claim 14. The machining table according to the invention serves to carry out the above-described method according to the invention or preferably a preferred embodiment of the method according to the invention.

The processing table according to the invention comprises a support region for a semiconductor component, a fixing region for the semiconductor component, a fixing region for the metal foil and at least one blow-off opening. It is essential that the blow-off opening is arranged between the fixing region for the metal foil and the support region for the semiconductor component. For this purpose, the blow-off opening is preferably connected to a blow-off channel. The support area is preferably arranged centrally. The processing table according to the invention offers considerable advantages when forming a metallic contacting structure for the electrical contacting of a semiconductor component:

The semiconductor device is fixed in the Aufiagebereich when using the work table according to the invention. The fixed semiconductor device is covered with a metal foil. The fixing region for the metal foil is arranged surrounding the central supporting region for the semi-ferritic component and configured in such a way that the metal foil is fixed on the semi-ferritic component without air inclusions. Any air pockets lead in carrying out the method according to the invention that the Metailfoiie is completely or partially evaporated due to the lack of thermal contact with the semiconductor device in the local heating and thus no or only insufficient, a high contact resistance having metal structure is formed.

Because the blow-off opening is arranged between the fixing region for the metal foil and the mounting region for the semiconductor component, a gas, preferably air, can be supplied after the local melting through the blow-off opening, so that the metal foil is blown with the gas and thus into the non-blown fused areas of the Halbieiterbauelement is at least partially spaced. This simplifies the removal of the excess metal foil.

In particular, it is advantageously possible to produce predetermined breaking points after spacing the film by supplying gas through the blow-off opening. This avoids that in the production of predetermined breaking points at the predetermined breaking points Metailfoiie adhered to the Halbieiterbauelement. Furthermore, a thermal contact at the predetermined breaking points between Metailfoiie and Halbieiterbauelement is avoided, so that in a simple manner by means of local heat, preferably by a laser, the metal foil thinned at the Solibruchstellen or can be evaporated.

In a preferred embodiment, the fixing region for the Halbieiterbauelement is designed as at least one suction port, which is connected to a first suction line. Via the first suction line and the suction The semiconductor component can be subjected to a vacuum / negative pressure and thus fixed to the support region.

In a further preferred embodiment, the fixing region for the metal foil is designed as an intake channel enclosing the bearing area for the semiconductor component. The suction channel is connected to a second suction line. Via the second suction line and the suction channel, the IVIetallfolie can be applied with vacuum / negative pressure and thus fixed on the semiconductor device.

In a further preferred embodiment, the support area is formed as a depression, such that when the semiconductor component is inserted in the recess, the semiconductor component and the surface of the processing table adjoining the recess form a planar surface.

This ensures that the sucked metal foil can rest against the semiconductor component without air inclusions.

The inventive method is particularly suitable for the formation of metallic contacting structures on one side contacted solar cells and in particular of back-side contact solar cells. However, it is likewise within the scope of the invention to use the method according to the invention for generating the front-side contacting of solar cells contacted on two sides and / or for contacting any alternately doped semiconductor components.

Further advantageous features and embodiments of the present invention will be explained below with reference to exemplary embodiments and the figures. Showing:

Figure 1 a to Figure 1 e process steps A to D of a first embodiment of the method according to the invention;

Figure 2a to Figure 2d process steps a to d of a second embodiment of the method according to the invention;

3a to 3c process steps of a fourth embodiment of the method according to the invention; 4a to 4h process steps of a third embodiment of the method according to the invention;

FIG. 5 shows a schematic representation of the processing table according to the invention.

FIG. 6 shows a plan view of the schematic illustration of the rear side of a rear-side contact solar cell in the figures, and the same reference symbols designate identical or equivalent elements.

Figures 1 to 4 are schematic views of a semiconductor device which is a photovoltaic solar cell or a precursor of such a solar cell during the manufacturing process. Here, a partial section is shown schematically; the solar cell is continued analogously on both sides. Like reference numerals in the figures indicate the same or equivalent elements.

In the figures 1 a to 1 e, a first embodiment of the method according to the invention is shown schematically.

FIG. 1a shows a semiconductor component 1 comprising a semiconductor layer 2 with a p-doped region 2a and an n-doped region 2b. The n-doped region 2 b is coated with an insulating layer 3. The insulating layer is on the one hand designed to be electrically insulating and moreover has a passivation effect with respect to the surface of the semiconductor layer 2 adjoining the insulating layer 3, so that the charge carrier recombination velocity and thus recombination losses are reduced at this surface. In a method step A of the method, the metal foil 4 is applied to the insulating layer 3. FIG. 1 a thus shows the state after carrying out method step A.

The etallfoläe 4 εst multi-layer of two layers as follows: For local contacting of the n-doped emitter layer 2b comprises the multi-layer metal foil 4 on the side facing the semiconductor device side, an approximately 100 nm thick nickel layer. The second layer of multilayer Metal foil on the side facing away from the Halbieiterbauelement is a silver layer for further interconnection.

FIG. 1 b shows a schematic representation of method step B of the method. Here, the metal foil 4 is locally heated by means of laser beams 5. The laser beams are generated by a laser, not shown, and sequentially directed to the areas 5a, 5b to be heated by means of an optical deflection unit (not shown). The laser used is a pulsed Nd: YAG laser with a wavelength of 1 064 ηττι, and a pulse duration of 100 ns.

The method produces line-like metallic contacting structures. The laser beams are therefore moved approximately along a line which is perpendicular to the plane of the drawing in FIG. 1 (and also in the methods described below for FIGS. 2, 3 and 4).

At the heated areas 5a, 5b, a melt mixture of the metal foil 4, the insulating layer 3 and the Halbieiterschicht 2. After the solidification of the melt mixture is an electrical contact 6 to the underlying semiconductor layer 2. Figure 1 b thus shows the state after performing the process step B.

As shown in FIG. 1 c, the metal foil 4 is lifted off the semiconductor layer 2 at the non-contacted regions before the structuring step. This can be done by, for example, heating the semiconductor device 1. As a result, the metal foil 4 expands and bulges away from the semiconductor layer 2 between the generated contacts 6. Alternatively, the metal foil may also be spaced from the semiconductor device 1 by suction from above or blowing from below. By lifting off the metal foil 4, one or more air gaps 23 are formed between the metal foil 4 and the semiconductor layer 2.

This ensures that there is no mechanical contact between the metal foil 4 and the semiconductor layer 2 in a subsequent structuring step, and it is avoided that the metal foil 4 in the non-fused regions is connected to the semiconductor device during the structuring step. ment 1 is attached.

FIG. 1 d shows the structuring step of the metal foil 4 by means of laser radiation 5. As a result of the local irradiation by means of laser, at the edges of the contacts, 6 solid-state breaking points are engraved in the metal foil 4 which is spaced apart from the semiconductor surface. The predetermined breaking points can be designed as a perforation and / or removal of metal foil for local thickness reduction.

Following the condition shown in FIG. 1d, the metal foil is affixed to the non-fused regions, i. H. outside the contacts 6, removed. This is done by peeling off the film.

FIG. 1 e shows, in a last method step, the remaining previously produced contacts 6 after removal of the metal foil 4.

Figures 2a to 2d show the schematic representation of process steps of a second embodiment of the method according to the invention.

FIG. 2 a shows a semiconductor component 1 equivalent to FIG. 1 a. To avoid repetition, only the differences between the individual exemplary embodiments of the method according to the invention will be discussed below.

In this preferred embodiment, in method step A, a thin metal foil 7, with a thickness of about 2 μm, is applied.

FIG. 2b shows the local heating by means of laser radiation 5 in method step B. A melt mixture of the metal foil 7 and the insulating layer 3 is formed at the heated point. In this case, the metal is melted by the insulating layer 3. When using the thin metal foil 7, the semiconductor layer 2 is not melted with. After the melt mixture has solidified, there is an electrical contact 6 to the underlying semiconductor component 1. In addition, when the thin metal foil 7 is used, the contacted area is simultaneously separated from the foil, because upon solidification, the liquid metal contracts due to the surface tension and releases it. There is a separation between the areas where the metal has been melted and the areas where the metal has not been melted.

At the irradiated points remains an open insulating layer 2 with a semiconductor component 1 covering the contacts 8, shown in Figure 2c.

FIG. 2 d shows the metal-reinforced contacts 9 in an additional method step. For this purpose, metal, for example, is electrodeposited on the metallic contacts 8, which were produced as a seed layer in the first step. For galvanic reinforcement of the seed layer serving as contacts 8 can be made to known methods.

A further exemplary embodiment of the method according to the invention is shown schematically in FIGS. 3a to 3c.

FIG. 3 a shows a semiconductor component 1 equivalent to FIGS. 1 a and 2 a.

The Metallfoüe 4 may optionally be different thickness, made of different materials or multi-layered. In this case, it is possible, for example, to coat the lower side of the film in such a way that the contact formation is improved and the upper side of the film is optimized with regard to a simpler connection. In addition, the central layer of the multilayer metal foil 4 may consist of a low-cost material, which only has to have a good conductivity. In this embodiment, a multilayer metal foil of three layers having the following structure is used. The layer facing the semiconductor device 1 is made of titanium and has a thickness of about 200 nm. This is followed by an aluminum layer with a thickness of approximately 10 μm as the middle layer. The subsequent layer facing away from the semiconductor component 1 is made of aluminum and has a thickness of 200 nm.

FIG. 3b shows the method step B in that the metal foil 4 is locally heated by means of laser radiation 5. In this preferred embodiment, a laser is used with a beam profile having a higher intensity at the edges than at the center. The beam profile has along the dashed line 1 following intensity curve: follows in the order given a minimum of intensity at an intensity minimum and then a second intensity maximum. The intensity of the beam profile therefore has a lower intensity perpendicular to the direction of movement of the laser relative to the surface of the semiconductor component 1 in a middle region than in the two outer regions. This is shown qualitatively (with arbitrary units) in sub-picture 3b.1, where the Y-axis shows the intensity and the X-axis the spatial position along the line 1 1.

A suitable beam profile results, for example, from the superimposition of two laser beams with Gaussian intensity distribution, such that the two intensity maxima have the desired distance from one another.

The local heating produces a melt mixture of ^" melted metal foil 4 and insulating layer 3. Upon solidification, the liquid metal contracts due to the surface tension and creates a separation between the areas where the metal has been melted and the areas where the metal is not was melted.

Subsequently, the unmelted metal foil is mechanically removed.

Figure 3c shows the remaining previously created contacts 6 after peeling off the film.

FIGS. 4a to 4h schematically show the method steps of a further embodiment of the method according to the invention.

Figure 4a shows a semiconductor device 1, which is formed as a precursor of a back-side contact solar cell. The semiconductor device 1 comprises a semiconductor layer 13 with a comb-like doping structure 14 and an insulating layer 3. The comb-like doping structure is common in rear-side contact solar cells and shown as a plan view of the back of the semiconductor device 1 in Figure 6: The base doping of the semiconductor device is back with a comb-like emitter doping as a doping structure 14, so that in the illustration according to FIG. 6 in the direction A there are alternatingly p-doped regions 2a and n-doped regions 2b. FIG. 4b shows the semi-conductor component 1 from FIG. 4h, which is additionally coated with a metal foil 4. In this case, different thicknesses of different materials, preferably titanium, nickel or silver can be used.

FIG. 4c shows the local heating of the metal foil 4 by means of laser radiation 5. At the irradiated parts of the metal foil 4 and the insulating layer 3 are melted. This creates a contact 6 to the underlying semiconductor device. 1 The locations for the local heating are selected such that a p-doped 2a and an n-doped 2b region of the doping structure 14 are alternately contacted.

FIG. 4d shows the remaining metallic contacts 6 which have been produced after the metal foil 4 has been removed. The adjoining p- and n-doped regions of the doping structure 14 are now each separately electrically contacted.

FIG. 4e shows the second iteration of the contacting method. Here is a second thicker metal foil 15 made of a cost-effective material, such. As aluminum, placed on the contact structure 6 previously generated.

FIG. 4f shows the local heating of the second metal foil 15 by means of laser radiation 5. The metafoil 15 melts at the irradiated points and forms an alloy with the contacts 6 present on the underside of the second metal foil 5. This leads to an electrical and mechanical connection of the second metal foil 1 5 with the underlying Kontäktstruktur 6 and thus with the semiconductor device. 1 With the help of suitable focusing optics, an irradiation spot up to Ι Ομιη thin can be realized here.

FIG. 4g shows the structuring step for the second metal foil 15. At the edges of the contacts 5 predetermined breaking points are engraved by means of laser radiation. An air gap 23 between the second metal foil 1 5 and the semiconductor component 1 is located through the first contact structure 6, since the contact structure 6 prevents the metal foil 1 5 from being applied to the semiconductor component 1. The second metal foil 1 5 can thus be severed by means of laser radiation 5, without producing further contacts on the semiconductor device 1. FIG. 4h shows a generated two-layer contact structure for a rear-side contact solar cell after the second metal foil 15 has been removed. The alternating metallic contact 6 corresponds to the doping structure 14 of the rear-side contact solar cell. Here, the direct contact between the semiconductor layer 2 and contact structure 6 is formed with a metallization with low contact resistance and high conductivity. The second part of the contact structure 6 may be formed of a less expensive material.

The embodiment described above relates to the contacting of a rear-side contact solar cell, shown in Figures 4a to 4h. Likewise, it is within the scope of the invention to use the method of the invention for the generation of the front-side and / or for ^"contacting any alternately doped semiconductor elements.

Figure 5a shows a schematic representation of an embodiment of a processing table according to the invention.

The processing table 1 7 comprises a central support region 1 8 for a semiconductor component 1, a fixing region 1 9 for the semiconductor component, a fixing region 20 for the metal foil 4 and a blow-off opening 21. The fixing areas 1 9 and 20 are in the present embodiment suction openings, which are connected to suction lines 24. The blow-off opening 21 is connected to a blow-off channel 22 and arranged between the fixing region for the metal foil 20 and bearing area 1 8.

As shown in FIG. 5 b, the arrangement of the blow-off opening 21 between the fixing region for the metal foil 20 and the support region for the semiconductor component 1 8 after the local melting through the blow-off opening 21 can supply a gas, preferably air, so that the metal foil 4 is blown with the gas and thus at least partially spaced in the non-melted areas of the Haibleiterbauelement 1. As a result, the removal of the excess metal foil 4 is simplified.

Since the metallic contact structures between the metal foil and the semiconductor component do not extend over the entire width of the semiconductor component. They do not form airtight barriers, so that the metal foil is lifted off the surface of the semiconductor device even in the central regions (eg, between two metallic contact structures).

The processing table according to the invention finds in particular an advantageous application when in the method according to the invention after the melting of the metal foil in a further process step predetermined breaking points are generated in the metal foil, such as the associated embodiment of the inventive method, shown in Figures 1 c to 1 d described ,

When using the machining table according to the invention shown in Figure 5 when generating the predetermined breaking points by the local spacing of the metal foil 4 is avoided that the metal foil 4 adheres to the semiconductor device 1 at the points where the predetermined breaking points are generated. Furthermore, a thermal contact at the predetermined breaking points between the metal foil 4 and the semiconductor device 1 is avoided, so that thinned in a simple manner by local heat, preferably by a laser, the metal foil 4 at the predetermined breaking points, d. H. locally, the thickness is reduced, or can be locally evaporated.

The support region 18 is formed as a depression, such that when inserted into the recess semiconductor device 1, the semiconductor device 1 with the laterally adjacent surface of the processing table 17 forms a flat surface.

This ensures that the sucked metal foil 4 rests against the semiconductor component 1 without air entrapments. Any air pockets lead in carrying out the method according to the invention to the fact that the metal foil 4 is completely or partially evaporated due to the lack of thermal contact with the semiconductor device 1 in the local heating and thus no or only insufficient, a high contact resistance having metal structure is formed. Due to the design of the support region for the semiconductor device 1 8 as a recess, such that when inserted into the recess semiconductor device 1, the semiconductor device 1 with the thereto Side-adjacent surface of the processing table 17 forms a flat surface, there is the advantage that the probability of the formation of air bubbles between metal foil 4 and Halbleiterbaueiement 1 is reduced, thereby increasing the quality of the generated metallic Kontaktierungs- structure 6 in terms of adhesion and conductivity ,

Claims

claims

1 . Method for locally contacting a semiconductor component (1), which semiconductor component (1) is part of a photovoltaic solar cell or a preliminary stage in the production process of a photovoltaic solar cell, comprising the following method steps:

A applying at least one metal layer to one side of the semiconductor device (1),

B local heating of at least the metal layer, such that in a local area a melting of at least the metal layer takes place for a short time,

characterized,

that as the metal layer, a metal foil (4) is used and

that after method step B in a method step C, the non-fused regions of the metal foil (4) are removed.

2. The method according to claim 1,

characterized,

that in an additional method step A-a at least one intermediate layer (3) is applied to one side of the semiconductor component (1), preferably a dielectric layer, prior to method step A.

Layer, in particular,

that in a further additional method step A-b between the method step A-A and the method step A, the intermediate layer is removed in the local areas, preferably by means of laser ablation.

3. Method according to one of the preceding claims,

characterized,

that the Metallfoüe (4) is structured simultaneously during the contacting process.

4. Method according to one of the preceding claims,

characterized,

that the local heating during the contacting process generates at least predetermined breaking points (1 1) in the metal foil (4).

5. Method according to one of the preceding claims, characterized in that

that in an additional process step as a structuring step at least predetermined breaking points (1 1) are introduced into the metal foil (4).

6. The method according to claim 5,

characterized,

the metal foil (4) is at least partially spaced apart from the semiconductor component (1) in the non-fused regions before the patterning step.

7. The method according to claim 6,

characterized,

in that the metal foil (4) is at least partially spaced by blowing from below and / or by suction from above and / or heating from the semiconductor component (1).

8. The method according to any one of the preceding claims,

characterized,

the metal foil (4) is tensioned and / or sucked in and / or blown onto the semiconductor component (1) at least during the process step B.

9. The method according to any one of the preceding claims,

characterized,

in that a multilayer metal foil (25) is used as the metal layer.

10. The method according to any one of the preceding claims,

characterized,

in that the method step B takes place by illumination from the side of the semiconductor component (1) remote from the metal foil (4).

1 1. Method according to one of the preceding claims,

characterized, in method step B, a laser (5) is used whose beam profile has a higher intensity at the edges than in the middle.

2. Method according to one of the preceding claims,

characterized,

a metallic seed layer (8) is produced in a first metallization step by means of a method according to one of the preceding claims, which seed layer (8) is reinforced in a second metallization step, preferably galvanically reinforced.

3. Method according to one of the preceding claims,

characterized,

the semiconductor component (1) has both n-doped and p-doped regions on one side and these regions are electrically contacted in method step B by the metal foil (4) being locally applied to the n-doped and p-doped regions is melted, so that after removal of the metal foil (4) according to process step C metallic ontaktierungsstrukturen of both the n-doped, and the p-doped regions are present, preferably,

in a further method step, the metallic contacting structures (1 6) are reinforced metallically, in particular by repeating in the method steps A to C, preferably by using a second metal foil (1 5) which differs from the previously used metal foil (7) Metal has.

4. processing table, in particular for carrying out a method according to one of the preceding claims,

which processing table has a support region (18) for a semiconductor component (1), at least one fixing region (19) for the metal foil (4) and at least one blow-off opening (21), which blow-off opening is connected to a blow-off channel (22) and between fixing region (19 ) and support area (18) is arranged.

5. machining table according to claim 14

characterized, that the fixing region (1 9) relative to the support region (1 8) circumferentially, preferably as an intake chute, which intake chute is connected to a suction channel (24) is formed.

Machining table according to claim 14 or 15,

characterized,

the support region (1 8) is formed as a depression, such that when the semiconductor component (1) is inserted into the depression, the semiconductor component (1) and with the surface of the processing table (7) laterally adjacent thereto form a planar surface.