DE102011015283B4 - Production of a Semiconductor Device by Laser-Assisted Bonding and Semiconductor Device Manufactured Therewith - Google Patents

Abstract

Method for producing a semiconductor component (10), in particular a diode or a solar cell, comprising the steps of: (a) providing a substrate (1) on which is formed a bonding layer (2, 2.4) containing a metal and having (b) supporting a semiconductor film (3) made of a semiconductor material on the joining layer (2, 2.4), and (c) heating the semiconductor film (3) and the joining layer (2, 2.4) to one Temperature above the eutectic temperature of a composition of the metal and the semiconductor material, wherein a compound of the semiconductor film (3) with the joining layer (2, 2.4) and the bonding layer (2, 2.4) with the substrate (1) is formed, characterized in that - the heating takes place by means of locally acting laser irradiation.

Description

The invention relates to a method for producing a semiconductor device, in particular a diode or a solar cell, for. B. based on Si, wherein a semiconductor film forms at least one eutectic compound with a bonding layer on a substrate. Furthermore, the invention relates to a semiconductor device, in particular a diode or a solar cell, which is produced by the said method.

The cost of photovoltaic modules, z. B. with Si solar cells can be reduced by the solar cells are made with the thinnest possible layers of silicon (Si). These can z. B. be sawn Si wafers or be obtained as semiconductor films by transfer techniques (see, for example, Henley, Henley et al., "Kerf-free 20-150 microns c-Si wafering for thin PV manufacturing" in "Proc 24th EU PVSEC" Hamburg 2009 , 886, and R. Brendel et al., "15.4% -efficient and 25 μm-thin crystalline Si solar cell from layer transfer using porous silicon" in Phys. Stat. Solidi (a) "Vol. 197, 2003, P. 497). The problem arises of further processing the thin Si wafers or films with industrial processes into solar cells. In addition to the breaking strength, in particular the metal contacts are problematic, which must have a certain minimum thickness for the purpose of sufficient conductivity and lead to considerable deflection of the cell in the case of thin wafers.

One way of making solar cells from thin Si films is by V. Gazuz et al. with "Thin (90 μm) multicrystalline Si solar cell with 15% efficiency by Al-bonding to glass Proc." in "23th EU PVSEC" Valencia 2008, pp. 1040-1042 (see also DE 10 2004 033 553 A1 ). The Si foil is bonded to a glass substrate in a combined RTP (RTP: Rapid Thermal Processing) process. After bonding, the substrate can be processed similarly to a Si wafer.

The by V. Gazuz et al. However, the method described has a number of disadvantages. First, in the RTP process, the glass is strongly heated so that it may undesirably change its shape. In addition, the thermal expansion coefficient of the glass is often significantly greater than the thermal expansion coefficient of the silicon. By surface heating can thus create strong tension. In order to avoid these problems, which grow with the surface of the processed substrates, glasses with high temperature stability and low thermal expansion would have to be used. However, such glasses are relatively expensive. Second, in the RTP process, only full surface heating of the substrate is possible. Thus, no localized contacts can be made, as required for solar cells with very high efficiencies. Finally, because of the partly front-side contacts (emitter) and partly back-side contacts of the solar cells, a module connection is complicated.

Methods for metallizing a solar cell are known from the prior art, wherein metallic material is introduced into a surface of the solar cell under the action of laser radiation. For example, according to DE 11 2005 002 592 T5 metallic material, which was deposited in advance on a surface of the solar cell, introduced by the laser radiation into the semiconductor material of the solar cell. Out DE 10 2009 053 776 A1 (published after the priority date of the present invention) and DE 10 2006 044 936 B4 It is known to transfer metal from a separate carrier film to the surface of the solar cell. The backing sheet is placed in contact with the surface or at a distance therefrom and in accordance with the desired pattern of metallization, e.g. B. linear, irradiated. As a result of the irradiation, the metal is separated from the carrier film and deposited on the solar cell. After the transfer of the metal, the carrier foil is removed.

The object of the invention is to provide an improved method for producing a semiconductor component, in particular a diode or a solar cell, with which disadvantages of conventional methods are overcome. The method should in particular make it possible to process thin semiconductor films with layer thicknesses in the sub-mm range in a simplified manner to form semiconductor components. The object of the invention is furthermore to provide an improved semiconductor component, in particular a diode or a solar cell, with which disadvantages of conventional semiconductor components can be overcome. The semiconductor component is to be characterized in particular by a reproducible and precise shape and / or a high degree of flexibility with regard to the provision of contacts and / or dopings.

These objects are achieved by a method or a semiconductor component having the features of the independent claims. Advantageous embodiments and applications of the invention will become apparent from the dependent claims. The features of the preambles of claims 1 and 14 are known from the DE 10 2004 033 553 A1 ,

According to a first aspect of the invention, a method is provided for producing a semiconductor component, in particular a diode or a solar cell, in which a semiconductor film is connected to a substrate by means of laser radiation via a bonding layer (intermediate layer). According to the invention, the Semiconductor film on the joining layer containing a metal, placed. The semiconductor film and the bonding layer are heated by the laser radiation to a temperature above the eutectic temperature of a composition of the metal contained in the bonding layer and the semiconductor material, so that the semiconductor film and the bonding layer merge. The laser radiation is directed in particular to the bonding layer, from which metal, possibly via further intermediate layers, can migrate into the semiconductor film. According to the invention, the laser radiation forms a eutectic connection of the semiconductor film with the bonding layer. The eutectic compound, which may extend over optional further intermediate layers, simultaneously forms a mechanical bond, an electrical contact and a doping region in the semiconductor film. The electrical contact is a contact for connection to a p-type doping region (p-type contact) or a contact for connection to an n-type doped region (n-type contact), depending on the conductivity type of the semiconductor material and the metal. The method thus generally comprises a laser-assisted combined bonding, in particular aluminum bonding, and diffusion for producing the semiconductor component, in particular a Si solar cell or Si diode.

Advantageously, the laser radiation causes locally limited heating in a predetermined region (eutectic region) delimited by the extent of the radiation field of the laser radiation. The laser radiation is locally limited, d. h in an area smaller than the area of the semiconductor film. During irradiation, the eutectic temperature is exceeded in the eutectic region, so that the eutectic compound is formed locally. There is no or negligible warming around the eutectic area. Since the expansion of the eutectic region (diameter preferably less than 1 mm, in particular less than 0.1 mm) is substantially smaller than the substrate sizes of practical interest, the local heating does not change the substrate or the semiconductor film. Undesirable deformations of the substrate and stresses due to different coefficients of expansion are avoided. Furthermore, it is advantageously possible to produce localized contacts distributed over the surface of the semiconductor film. Thus, the inventive method simplifies the production of solar cells with an efficiency above 20%.

According to a second aspect of the invention, there is provided a semiconductor device, in particular a diode or a solar cell, comprising a substrate, a bonding layer containing a metal and formed on the substrate surface, and at least one semiconductor film made of a semiconductor material over at least a eutectic connection is associated with the bonding layer. According to the invention, the at least one eutectic connection is generated by means of local laser irradiation. Furthermore, according to the invention, the semiconductor material is doped at the at least one eutectic compound with the metal such that a charge carrier concentration above 10 ¹⁸ cm ^{-3 is} formed in the semiconductor material. The contacting of the semiconductor component takes place via the bonding layer or its sections (bonding layer sections) which are connected to doping regions in the semiconductor material.

According to the invention, at least one semiconductor film is generally connected to the glass surface of the substrate via a bonding layer. The term "semiconductor film" is any layered semiconductor material referred to, which is preferably provided as a cantilever sheet (sheet, plate) and z. B. comprises a wafer. The layered, preferably self-supporting semiconductor material may be prepared by methods known per se, such as. For example, by sawing, introducing a porous sacrificial layer (see R. Brendel et al., Phys. Stat., Solidi (a), Vol. 197, 2003, pp. 497), proton bombardment, and / or thermal bursting of a bulk material (see F. Henley et al., Proc. 24th EU PVSEC Hamburg 2009, p. The semiconductor material may be doped or undoped. The semiconductor film may carry further layers which in the finished semiconductor component intermediate or outer layers, for. B. for isolation-doping or passivation purposes. On a substrate, a plurality of semiconductor films may be arranged side by side.

Advantages for practical applications of the invention arise when the semiconductor foil is made of silicon. Alternatively, another semiconductor material may be provided, such. Ge or GaAs. According to a further preferred feature of the invention, the semiconductor film has a thickness of less than 200 μm, in particular less than 100 μm.

The term "substrate" denotes any solid having a surface which is suitable as a carrier of the semiconductor material in the semiconductor component. Preferably, at least the surface of the substrate glass or a glass ceramic, ie, the substrate is made entirely of glass or glass ceramic, such as. Example, borosilicate glass, soda-lime glass, glass-ceramic, in particular with main components lithium oxide, aluminum oxide and silicon dioxide, or of another material, in particular ceramic, z. For example, alumina, or polymer, z. B. ethylene vinyl acetate (EVA), which is provided on its surface with a glass or glass ceramic layer. It is for example a plastic substrate provided on the surface of a glass or glass ceramic layer is formed. A glass or glass-ceramic layer provided on the substrate preferably has a thickness of more than 0.5 μm, in particular more than 5 μm.

The term "bonding layer" denotes a metal layer or metal-containing layer which is firmly connected to the surface of the substrate and which can form the eutectic connection with the semiconductor. According to a further preferred feature of the invention, the joining layer has a thickness of less than 30 .mu.m, in particular less than 10 .mu.m, and greater than 0.1 .mu.m, in particular greater than 0.5 .mu.m. Preferably, the joining layer consists of aluminum (Al). A metal-containing layer comprises, for. B. a pure metal layer or alternatively a layer comprising aluminum particles and / or silver particles (each up to a few microns in size) and organic binder. According to further variants of the invention, the joining layer may comprise a plurality of metals, e.g. B. Ag and Ni, which are arranged on the substrate in partial layers next to each other or one above the other. When using several metals, there may be advantages for a targeted doping of the semiconductor.

According to a preferred embodiment of the invention, a heating of the semiconductor film and the bonding layer by means of pulsed laser radiation (pulsed laser radiation) is provided. The use of pulsed laser radiation, z. B. with ns, ps or fs pulses, has advantages in terms of achieving extremely high performance due to the low pulse duration.

According to a further preferred embodiment of the invention, at least one locally limited eutectic compound is formed whose extent is less than the lateral extent of the semiconductor film and the substrate with the joining layer. The localized eutectic compound may be formed by irradiation at a single position or by multiple exposures at adjacent positions. It forms an island-shaped contact section, in which the semiconductor film and the bonding layer are materially connected. In the vicinity of the contact section, the semiconductor film, possibly with further intermediate layers, and the joining layer touch each other loosely. The at least one contact section is advantageously used for producing at least one electrical contact and at the same time for locally limited doping of the semiconductor material. Preferably, the laser irradiation is repeated at different positions, so that at least two contact sections are formed.

According to a further variant of the invention, the locally limited eutectic compounds may have such small distances that a surface-extended connection of the semiconductor foil to the bonding layer is formed.

According to the invention, the joining layer can flatly cover the entire substrate. Alternatively, a structured joining layer is provided, which comprises a multiplicity of joining layer sections which are separated relative to one another. The provision of the bonding layer sections can be advantageous for the formation of delimited contact sections for contacting and / or doping purposes. The joining layer sections can all uniformly contain the same metal or different metals. The joining layer sections can be formed during the deposition of the at least one material of the bonding layer on the substrate, for example by masking. Alternatively, after the substrate has been provided with a surface-applied bonding layer, it can be locally structured and divided into a plurality of bonding layer sections.

According to a further preferred embodiment of the invention, the semiconductor film may have on one or both sides a dielectric passivation layer. The passivation layer can be arranged on the side of the semiconductor film facing away from the substrate and have a passivating and reflection-reducing effect. Particularly preferably, the passivation layer is arranged on the side of the semiconductor film facing the substrate. Advantageously, the laser-assisted joining according to the invention can take place through the passivation layer. Thus, the laser irradiation may preferably be performed at discrete positions distributed over the surface of the substrate to form a plurality of contact portions protruding from the bonding layer or bonding layer portions through the dielectric passivation layer to the semiconductor film, wherein a predominant area portion of the substrate is not irradiated becomes. This makes it possible to provide a plurality of mutually insulated contacts with a lateral extent in the range of 0.5 .mu.m to 100 .mu.m. In contrast to the conventional technique according to V. Gazuz et al. Are the areas of the contacts and thus possibly disturbing effects of the contacts, such. B. interfering recombination effects minimized. Thus, in the manufacture of solar cells, they can be manufactured with increased efficiency.

According to a further preferred embodiment of the invention, the semiconductor film on one or both sides at least one doping layer, the z. As boron or phosphorus contains. By local heating, in particular by means of laser irradiation, a local doping of the semiconductor film by diffusion of atoms of the Doping layer can be obtained in the semiconductor material.

When the doping layer is disposed on the substrate-facing side of the semiconductor film and the bonding layer is divided into a plurality of bonding layer sections, it enables one-side provision of doping regions on the semiconductor film. As a result of the laser irradiation of a first group of the bonding layer sections, first doping regions having a first conductive type can be produced on the side of the semiconductor film facing the substrate. Furthermore, by virtue of the laser irradiation of the doping layer on the side of the semiconductor film facing the substrate, second doping regions having a second conductivity type opposite to the first conductivity type can be produced, which are each connected to joining layer sections of a second group of joining layer sections. The semiconductor component is correspondingly distinguished in this variant of the invention in that, on the side of the semiconductor film facing the substrate, the first doping regions of the first conductivity type are connected to the first group of the bonding layer sections, the second doping regions of the second, opposite conductive type are connected to the second group of bonding layer sections ,

According to an alternative variant, if the doping layer is arranged on the side of the semiconductor film facing the substrate and the bonding layer is divided into a plurality of bonding layer sections, the semiconductor film may additionally have a first doping region with a first conductive type on the side facing away from the substrate. In this case, the laser irradiation of the first group of the bonding layer portions generates contact portions which protrude through the semiconductor film to the first doping region. Furthermore, by the laser irradiation of the doping layer second doping regions are generated with a second, opposite to the first conductivity type conductivity type, which are each connected to Fügeschichtabschnitten a second group of Fügeschichtabschnitten. In this variant of the invention, the semiconductor component is accordingly distinguished by the fact that the first group of the bonding layer sections projects over the contact sections which project through the semiconductor film with the first doping region (FIG. 3.1 ) and the second doping regions on the side of the semiconductor film facing the substrate are connected to the second group of the bonding layer sections.

The joining layer sections of the first and the second group of joining layer sections may each comprise different metals, e.g. As aluminum and silver included. Advantageously, this makes it possible that the contacting of both p- and n-silicon can take place with a similar Al-containing layer. While in conventional techniques p-type silicon is often contacted with Al, contacting by Al of n-type silicon has hitherto been uncommon. A suitable electrical contact can preferably be achieved in particular if a high n-type doping (n ++) (> 10 ¹⁸ cm ^-3 ) is generated locally.

If the semiconductor foil comprises n-type silicon and the bonding layer or the bonding layer portions contain aluminum, the connection of the semiconductor foil with the bonding layer or the bonding layer sections forms an aluminum doping region in the semiconductor material for producing a p-type emitter. Alternatively, when the semiconductor film comprises p-type silicon and the bonding layer or the bonding layer portions contain aluminum, bonding of the semiconductor film with the bonding layer or the bonding layer portions causes an aluminum doping region in the semiconductor material to produce an Back Surface Field (BSF). educated.

According to a further preferred embodiment of the invention, the connection of the semiconductor film to the substrate takes place in an inert or a reducing atmosphere or in a vacuum. In the case of applying a vacuum to the stack of semiconductor film and substrate, it is preferably produced locally selectively at the location of the laser irradiation, so that the semiconductor film and the substrate are pressed together locally.

Further advantages and features of the invention will be described below with reference to the accompanying drawings.

Show it:

1 Embodiments of the inventive production of a semiconductor device with a planar eutectic compound;

2 an embodiment of the inventive production of a semiconductor device with multiple eutectic compounds;

3 : Embodiments of a semiconductor component according to the invention;

4 and 5 : further embodiments of the production according to the invention of a semiconductor component having a plurality of eutectic compounds;

6 : An embodiment of solar cells according to the invention with series electrical connection; and

7 and 8th Further Embodiments of the Production According to the Invention of a Semiconductor Device with Several Eutectic Connections

According to a preferred application of the invention is provided, a thin semiconductor film, for. Example, a Si wafer or a Si foil having a thickness of less than 200 microns, in particular less than 100 microns, to process a highly efficient solar cell (i.e., solar cell with an efficiency potential> 20%), as will be exemplified below. The semiconductor film is laser beamed onto a stable substrate, e.g. As glass or glass-coated polymer, gebonded. During the process, an aluminum-containing joining layer is melted locally. At the same time, a stable mechanical connection, at least one electrical contact and at least one heavily doped region in the Si foil, which is required for the function of the Si solar cell, are produced at the same time. Although the invention is described below by way of example with reference to the production of a Si solar cell, it is emphasized that a diode or another semiconductor component based on Si or another semiconductor can likewise be produced. The choice of other materials and dimensions, in particular the substrate, the bonding layer, the semiconductor film and the eutectic compound, and suitable process parameters, such. As the power of the laser radiation, the skilled person is possible due to his knowledge in the field of semiconductor physics or by simple experiments.

The semiconductor device has a sheet-like sandwich structure with a first side on which the substrate is located and which is referred to below as the rear side of the semiconductor device or in particular of the substrate, and with a second, opposite side the semiconductor film is located and which is referred to below as the front of the semiconductor device or in particular the semiconductor film. The sides of the semiconductor film and the substrate facing each other are also referred to as contact sides of the semiconductor film and the substrate, respectively. If the semiconductor device comprises a solar cell, the front side is typically the illumination side of the solar cell, with transparent layers also being able to be illuminated from the rear side.

Embodiments of the connection of a substrate 1 with a semiconductor foil 3 according to the invention are in 1 shown schematically. In the first step ( 1 .) becomes the substrate 1 made of glass, z. B. borosilicate glass with a thickness of z. B. 1 mm, on one side with an aluminum-containing joining layer 2 Mistake. The marriage story 2 can z. Example by vacuum evaporation of aluminum or screen printing of an Al-containing paste having a thickness of 5 microns on the surface of the substrate 1 be applied. On the marriage story 2 becomes an n-type silicon semiconductor film 3 applied with a thickness of 50 microns, z. B. launched. Optionally, the semiconductor film 3 previously also be coated with aluminum on their contact page. On the front of the semiconductor film 3 is a doping layer 4 provided, which contains phosphorus (P). The doping layer 4 includes z. B. a thin film of a phosphorus-containing solution or paste with a thickness of z. B. 50 nm.

The area of the semiconductor film 3 is less than the area of the substrate 1 with the marriage story 2 , so the marriage story 2 on the edge of the semiconductor film 3 exposed. In the exposed section of the Fügeschicht 2 there is room for a contact electrode (see 2 ., 3 .) created.

At the second step ( 2 .) is irradiated from the back with a laser (L1 or L2). This is the Al-Fügeschicht 2 locally heated above the eutectic temperature of the Al-Si system (577 ° C). To suppress oxidation of the aluminum, it may be expedient to carry out the process in an inert or reducing atmosphere or alternatively in a vacuum. In the latter case, it is advantageous to use only the gap region between the semiconductor film 3 and the substrate 1 to evacuate, so that by the action of an ambient pressure, the flexible semiconductor film 3 is pressed against the joint. Upon cooling, a mechanically stable compound is obtained in the irradiated and heated area 2.1 between the fügeschicht 2 and the semiconductor film 3 , an electrical contact and, moreover, an Al-doped impurity region 3.1 who is in the finished solar cell 10 serves as an emitter contact. A planar processing along the extent of the substrate 1 is achieved by line by line advance of the laser irradiation.

1 illustrates two variants for the second step ( 2 .). According to the first variant (A), irradiation with the laser L1 is provided such that only the eutectic compound 2.1 is formed. The power of the laser L1 and its focusing are adjusted so that the local heating beyond the eutectic temperature on the bonding layer 2 and the adjacent part of the semiconductor film 3 is limited. For this purpose, a laser L1 is preferably used for generating short-pulse radiation (pulse duration: 100 ns). As a result, in the doping region 3.1 Al-doped silicon (p ⁺ -Si) produced. Subsequently, in a third step ( 3 .) on the front side of the semiconductor film 3 a P doped doping region 3.2 (n ⁺ -Si) generated. For this purpose, a further laser irradiation with a laser L3 is provided. The laser L3 is preferably applied from the front to the doping layer 4 and the semiconductor film 3 directed. Under the effect of the laser radiation of the laser L3 local heating takes place, so that P atoms from the doping layer 4 in the semiconductor film 3 diffuse and the doping region 3.2 form.

According to the second variant (B) become the eutectic compound 2.1 between the fügeschicht 2 and the semiconductor film 3 with the formation of the first doping region 3.1 and the formation of the second doping region 3.2 produced together with a single laser irradiation. With the laser L2 is in the joining layer 2 and the adjacent part of the semiconductor film 3 exceeded the eutectic temperature and at the same time in the doping layer 4 Such heating causes locally the P atoms from the doping layer 4 in the semiconductor film 3 diffuse. For this purpose, a laser L2 is preferably used for generating long-pulse radiation (pulse duration: 10 μs).

As a result, the semiconductor device is located 10 before, in the semiconductor (semiconductor film 3 ) with the first and second doping regions 3.1 . 3.2 a pn junction is formed. In addition, the second doping region 3.2 Have advantages for a reduction in front surface recombination. The semiconductor device 10 can be contacted by clicking on the exposed section of the bonding layer 2 , z. B. at 2.2 , and on the second doping region 3.2 , z. B. at 3.3 , one contact electrode each 6.1 . 6.2 , z. B. of silver, is applied.

Subsequently, further process steps are provided, as they are known per se from the production of standard Si solar cells (see the above-mentioned publication by V. Gazuz et al.). Because the composite from the substrate 1 and the semiconductor film 3 has a high mechanical stability, the further processing and in particular the application of the contact electrodes with a thickness above 10 microns is unproblematic. The use of contact electrodes having such a thickness has the advantage that a low series resistance is achieved during the contacting. The contacting is advantageously carried out without heating the semiconductor device 10 , z. B. by vapor deposition, printing by means of an aerosol printer or metal deposition by means of a galvanic process.

While moderate 1 a planar formation of the eutectic compound 2.1 is provided by a repeated laser irradiation, according to a modified variant of the invention, the formation of the eutectic compound in individual contact sections 2.3 be provided as in 2 is illustrated. In this case, in the first step ( 1 .) as in 1 the substrate 1 with a first marriage story 2.4 provided. Deviating from 1 However, the semiconductor film is 3 on the to the substrate 1 facing contact side with a dielectric passivation layer 5 and another fügeschicht 2.5 provided. On the front is the semiconductor foil 3 with a doping layer 4 provided (see 1 ). The passivation layer 5 exists z. B. of silicon nitride, with a thickness of z. B. 50 nm by PECVD (plasma-assisted chemical vapor deposition) on the semiconductor film 3 is applied. The second marriage story 2.4 on the passivation layer 5 exists z. B. aluminum with a thickness of z. B. 1 micron.

The semiconductor foil 3 with the passivation layer 5 , the marriage story 2 and the doping layer 4 gets on the substrate 1 hung up, so that the first and second marriage stories 2.4 . 2.5 touch. At the second step ( 2 .) The arrangement is then irradiated from the back with a laser L1. The locally molten aluminum of the first and second joining stories 2.4 . 2.5 penetrates the passivation layer 5 so that the contact sections 2.3 be formed. In the contact sections 2.3 form the mechanical joining and the electrical contact between the bonding stories 2.4 . 2.5 and the semiconductor film 3 and the local aluminum doping (first doping regions 3.1 ) of the semiconductor film 3 , In the first doping areas 3.1 is formed by the Al doping p-type silicon (p ⁺ -Si).

Finally, in the third step ( 3 .) A local P-doping of the substrate 1 opposite front side of the semiconductor film 3 , As in 1 is shown, a laser irradiation with a laser L2 is provided from the front, under their effect P atoms from the doping layer 4 in the semiconductor film 3 diffuse and the second, n-type doping regions 3.2 form (n ⁺ -Si). In contrast to the planar doping according to 1 be according to 2 however, localized doping regions 3.2 generated.

The result is a semiconductor device 10 provided having a structured pn junction. The contacting of the semiconductor device is carried out by the application of contact electrodes (not shown), as described above with reference to 1 is described.

In 3 are exemplary embodiments of solar cells according to the invention 10 shown, which can be produced by the method according to the invention. According to 3A includes the solar cell 10 the substrate 1 with the marriage story 2 , the semiconductor film 3 with the first doping region 3.1 and the second doping region 3.2 and the contact electrodes 6.1 . 6.2 , In addition, on the front of the solar cell 10 an antireflective layer 7 (AR-layer 7 ), z. B. of silicon nitride with a thickness of z. B. 70 nm, provided. The antireflection layer 7 has a reflection-reducing effect and at the same time serves as a passivation layer of a front surface passivation. It can therefore be like the above-mentioned passivation layer 5 be formed. The semiconductor foil 3 is in this variant of the invention, an n-type Si foil. The first doping region 3.1 includes Al-doped Si, such that a p-type emitter of the solar cell 10 is formed. The second doping region 3.2 is n-doped, so that n ⁺ -Si is formed. The second doping region 3.2 serves to reduce the front surface recombination and improve the electrical properties of the front-side contact electrodes 6.2 , The back contact electrodes 6.1 be z. B. on freestanding sections of the joining layer 2 educated.

3B illustrates a solar cell 10 as semiconductor foil 3 contains a p-doped Si foil. As in 3A includes the solar cell 10 the substrate 1 made of glass with the bonding layer 2 made of aluminum, the semiconductor film 3 with the first doping region 3.1 and the second doping region 3.2 and the contacts 6.1 . 6.2 in connection with the marriage history 2 or the second doping region 3.2 , In this variant of the invention, the rear side provided Al doping (first doping region 3.1 ) the production of a so-called "back-surface-field" (BSF) for reducing a back surface recombination. The front P-doping (second doping region 3.2 , n ⁺ -Si) serves as the n-type emitter of the solar cell 10 ,

3C shows a further embodiment of the solar cell according to the invention 10 , which according to the method in 2 can be made. On the substrate 1 made of glass with the first joining layer 2.4 is the semiconductor foil 3 with the passivation layer 5 and the second marriage story 2.5 bonded on. By a localized laser irradiation are the contact sections 2.3 formed at which by the Al doping p-type emitter (doping regions 3.1 ) in the semiconductor film 3 to be provided. On the free top of the solar cell 10 (Front or lighting side) are as in 3A an antireflective layer 7 and contact electrodes 6.2 intended.

In 4 is another embodiment of the inventive production of a semiconductor device 10 schematically illustrated with a structured eutectic connection between a semiconductor foil and a substrate. In this embodiment, a back contact solar cell having a selective emitter structure is manufactured as a semiconductor device.

In the first step ( 1 .) become the substrate 1 and the semiconductor film 3 provided. The substrate 1 includes z. B. borosilicate glass, on the surface of the joining layer 2 is formed. The marriage story 2 exists z. B. aluminum with a thickness of z. B. 10 microns.

The semiconductor foil 3 consists of n-type silicon z. B. has a phosphorus concentration in the range of 0.5 · 10 ¹⁶ cm ^-3 to 5 · 10 ¹⁶ cm ^-3 . On both sides carries the semiconductor film 3 a dielectric passivation layer 5 or an antireflection layer 7 that both have a passivating effect. The antireflection layer 7 simultaneously reduces reflection. The layers 5 . 7 exist z. As SiN, SiO ₂ , Al ₂ O ₃ , SiC or a combination thereof. The thickness of the layers 5 . 7 is z. B. each 70 nm. Furthermore, is on the substrate 1 pointing contact side of the semiconductor film 3 a doping layer 4 intended. The doping layer 4 forms a dopant source, it consists for. B. of phosphorus-containing glass.

At the second step ( 2 .) become the substrate 1 and the semiconductor film 3 edited while they are not yet connected. The processing in step 2 , serves to form the n-type doping regions 3.2 on the to the substrate 1 facing contact side of the semiconductor film 3 and the structuring of the marriage history 2 in electrically separate joining layer sections 2.6 . 2.7 ,

The doping of the semiconductor film 3 takes place in step 2 ., By the doping layer 4 is locally heated by irradiation with a laser L1. By heating the doping layer 4 Doping atoms diffuse through the passivation layer 5 in the semiconductor film 3 , For example, a heavily doped silicon (n ^{+ +} -Si) having a P concentration of 10 ²⁰ cm ^-3 or higher is formed.

The structuring of the bonding layer 2 for forming the first and second joining layer sections 2.6 . 2.7 is done by ablation by irradiation with a second laser L2. The laser L2 preferably comprises a short-pulse laser with a pulse duration of less than 100 ns. In 4 ( 3 .) Are exemplary schematically three joining layer sections 2.6 and two joining layer sections 2.7 illustrated. In practice, the number, size and arrangement of the first and second joining layer sections will be 2.6 depending on the specific application, in each case a first group of joining layer sections ( 2.6 ) for connection to the semiconductor material of the semiconductor film 3 outside the doping regions 3.2 and a second group of joining layer sections ( 2.7 ) for connection to the doping regions 3.2 in the semiconductor material of the semiconductor film 3 are provided. The Add layer sections 2.6 . 2.7 extend z. B. strip-shaped along the surface of the substrate 1 (please refer 6 ).

Finally, in step 3 , for the production of the back contact solar cell 10 the substrate 1 and the semiconductor film 3 connected with each other. The semiconductor foil 3 becomes with the substrate 1 pointing doping regions 3.2 on the substrate 1 applied and subjected to a local laser irradiation. This will be contact sections 2.3 formed with two different types of contact (p-contact, n-contact). By irradiation with a first laser L4, preferably from the back of the substrate 1 The joining layer is in the first joining layer section 2.6 locally melted and heated so much that the intermediate layers (doping layer 4 , Passivation layer 5 ) are locally destroyed and the eutectic connection (first contact sections 2.3 ) with the semiconductor material of the semiconductor film 3 is formed. At the same time first doping areas 3.1 in the semiconductor film 3 educated. Advantageously, this interferes with the environment of the first contact sections 2.3 existing phosphorus glass the formation of the first doping regions 3.1 not because the P atoms diffuse much more slowly than the Al atoms from the bonding layer 2 , As a result, at the first joining layer sections 2.6 p contacts formed.

Subsequently, by laser irradiation with the laser L3, preferably from the front of the semiconductor film 3 forth, second contact sections 2.3 between the doping regions 3.2 and the joining layer sections 2.7 produced. Contacting the n-type silicon with aluminum is a particular feature of the invention that differs from conventional types of contacting in the prior art. The inventors have found that in particular by the high doping of the doping region 3.2 in step 2 , in connection with the metal, in particular aluminum of the joining layer sections 2.7 ohmic electrical contacts are obtained.

As with the solar cell 10 according to 4 The emitter regions are not formed over the entire surface, but are structured, the lateral distance between the p-type and n-type doping regions 3.1 . 3.2 and correspondingly selected between the associated p and n contacts in the region of the diffusion length of the minority carriers or below. Preferably, the lateral distance is about 30 microns to 300 microns.

5 illustrates a further variant of the production of a semiconductor device with a structured eutectic connection between the substrate 1 and the semiconductor film 3 , In the first step ( 1 .) become the substrate 1 and the semiconductor film 3 provided. The substrate 1 comprises a polymer film, e.g. B. EVA, on its surface an amorphous layer 1.1 (Glass or glass ceramic layer) and a bonding layer 2 are formed. The amorphous layer 1.1 exists z. Example of SiO ₂ , SiN or SiC, with a thickness of z. B. 1 micron. The marriage story 2 is on the amorphous layer 1.1 educated.

The semiconductor foil 3 wears like in 4 on its contact side a doping layer 4 of phosphorus-containing glass and a dielectric passivation layer 5 , Furthermore, different from 4 ( 1 .) The semiconductor film 3 on the from the substrate 1 groundbreaking front a first highly doped doping region 3.1 (p ^{+ +} layer). The first doping region 3.1 is by diffused boron atoms with a doping concentration of z. B. 5 x 10 ¹⁹ cm ^-3 formed. On the front of the first doping region 3.1 the semiconductor film 3 is another dielectric layer as an antireflection layer 7 intended.

At the second step ( 2 .) are like in 4 ( 2 .) By a first laser irradiation with the laser L1, a highly doped second doping region 3.2 (n ^{+ +} -Si) in the semiconductor film 3 and by a second laser irradiation with the laser L2, a structuring of the bonding layer 2 into individual joining layer sections 2.6 . 2.7 provided.

In the third step ( 3 .), the compound of the semiconductor film takes place 3 with the substrate 1 wherein back irradiation with the laser L4 causes such heating of the bonding layer sections 2.6 causes the Al atoms through the semiconductor film 3 to the p-type first doping region 3.1 diffuse and contact sections 3.2 form. At the joining layer sections 2.6 p-contacts are formed. Further, front irradiation with the laser L3 is provided to the bonding layer portion 2.7 with the heavily doped second doping region 3.2 connect to. At the joining layer sections 2.7 n-contacts are formed. Accordingly, in the embodiment according to 5 formed a flat emitter structure, so that the p-contacts larger distances from the n-contacts, z. B. in the range of 0.3 mm to 3 mm, may have, as in the embodiment according to 4 ,

6 illustrates an example of an embodiment of a semiconductor device according to the invention (solar cell 10 ), being on the substrate 1 two separate semiconductor foils 3.4 . 3.5 with the method according to 5 are bonded. On the substrate 1 the Fügeschicht is structured in such a way that three Add layer sections 2.6 . 2.7 and 2.8 be formed. Each of the joining layer sections 2.6 . 2.7 and 2.8 comprises an array of parallel strips electrically connected at one end along the length thereof according to the method of FIG 5 n contacts or p-contacts are formed. The joining layer sections 2.6 . 2.7 and 2.8 are interleaved so that strips alternate with n-contacts and strips with p-contacts. Accordingly, the first joining layer section comprises 2.6 Strip with p-contacts over the first semiconductor foil 3.4 , the third marriage story section 2.8 Strip with n contacts over the second semiconductor foil 3.5 and the second, middle bonding layer section 2.7 Strip with n contacts over the first semiconductor foil 3.4 and p-contact stripes over the second semiconductor foil 3.5 , The result is a solar cell 10 formed with a series connection of the electrical contacts, which is designed for highly effective dissipation of generated charge carriers.

In the embodiments of the invention described above, the bonding layer (s) each contain a predetermined metal selected for the desired doping of the semiconductor film. Differing from these embodiments, according to the invention different metals can be used to form different joining layer sections, as schematically shown in FIG 7 is shown. According to 7A are the substrate 1 and the semiconductor film 3 illustrated schematically before the mutual connection. The substrate 1 includes glass, on its surface joining layer sections 2.6 . 2.7 made of different metals. For example, the middle joining layer section comprises 2.7 Aluminum with a thickness of 10 microns, while the outer joining layer sections 2.6 Include silver with a thickness of 3 microns. The application of the bonding layer sections 2.6 . 2.7 occurs by a local deposition of the metal layers and possibly by an electrical separation of the metal layers through a trench. The semiconductor foil 3 is like in 5 ( 2 .) Is formed of n-type silicon, on the substrate 1 pointing contact side a passivation layer 5 and highly doped n-type doping regions 3.2 are formed. On the opposite side is a highly doped p-type impurity region 3.1 (p ^{+ +} -Si) formed by an antireflective layer 7 is covered.

According to 7B is the mutual connection of the substrate 1 with the semiconductor film 3 analogous to the method in 5 ( 3 .) illustrated. The metal of the joining layer sections 2.6 diffuses under the action of laser irradiation with the laser L7 in the n ^{+ +} -type doping region 3.2 , The metal of the joining layer section 2.7 diffuses under the action of laser irradiation with the laser L8 through the semiconductor film 3 through to the doping region 3.1 , In this case, a p ^{+ +} -type doping region is formed 3.4 educated.

Advantages for the manufacturing process may arise when providing joining layer sections 2.6 . 2.7 from different metals several sub-layers are arranged one above the other, by an insulating intermediate layer 2.9 are separated. This variant of the invention is in 8th schematically illustrated. According to 8A is on the surface of the substrate 1 made of glass a first joining layer section 2.7 made of aluminum, which extends over the substrate surface and of the insulating intermediate layer 2.9 is covered. On the insulating intermediate layer 2.9 are the bonding layer sections 2.6 from another metal, z. As silver formed. The joining layer sections 2.6 are z. B. structured by ablation.

The semiconductor foil 3 is constructed as in 7A is shown. To connect the substrate 1 with the semiconductor film 3 is according to 8B by the laser irradiation with a first laser L8 the contact between the joining layer sections 2.6 and the heavily doped n-type impurity regions 3.2 (n ^{+ +} -Si) of the semiconductor film 3 educated. The laser irradiation with a second laser L9, the contact between the joining layer section 2.7 and the highly doped p-type impurity region 3.1 (p ^{+ +} -Si) formed. Which of the joining layer sections 2.6 or 2.7 can be determined by the choice of the irradiation side, ie by the irradiation of the back or front. When the joining layer sections 2.6 . 2.7 absorb in different wavelength ranges, the irradiation of the bonding layer sections 2.6 also from the side of the substrate 1 Her done (see dotted arrow). In this case, the joining layer section becomes 2.7 irradiated with a wavelength in the joining layer section 2.6 is not or only negligibly weakly absorbed.

In summary, the invention offers the following advantages. According to the invention, thin semiconductor wafers or films may be semiconductor devices such. As solar cells or diodes, are processed. Advantageously, no high processing temperatures are required. The laser irradiation for local heating of the bonding layer and of the semiconductor film can be directed and / or focused by simple optical means into the regions of the desired contact sections. Semiconductor devices according to the invention can be produced with a multiplicity of substrate materials. In particular, glass substrates can be used without special demands being placed on the thermal expansion coefficient or the temperature resistance.

Furthermore, there are advantageously no restrictions with regard to the type and / or doping of the processed semiconductor material. In particular, p- or n-type silicon can be used. The contacting of the doping regions of the semiconductor film can be realized inexpensively. In particular, a one-sided (back) contacting is possible. This simplifies encapsulation of the semiconductor device in such a way that only the semiconductor film, if necessary with an antireflection layer, is exposed. Advantageously, the substrate can be used for encapsulation.

In comparison with conventional methods in which emitters made through the semiconductor material to the back side are formed using through-holes, thin wafers which are further processed on a substrate can be used according to the invention. In particular, the emitter passage according to 7 is filled with highly doped silicon, which is advantageous over the conventional technique using through holes in terms of a low series resistance of the contact.

Solar cells produced according to the invention can be produced with a particularly high degree of efficiency (> 20%) because high-quality silicon can be used, a locally selective and thus highly efficient cell design can be realized by laser processing and the method is suitable for processing n-silicon is that moved to the Czochralski method.

The features of the invention disclosed in the foregoing description, drawings and claims may be significant to the realization of the invention in its various forms both individually and in combination.

Claims (20)

Method for producing a semiconductor device ( 10 ), in particular a diode or a solar cell, with the steps: (a) Provision of a substrate ( 1 ), on which a marriage history ( 2 . 2.4 ) is formed, which contains a metal and with the substrate ( 1 ), (b) support of a semiconductor film ( 3 ) of a semiconductor material on the bonding layer ( 2 . 2.4 ), and (c) heating the semiconductor film ( 3 ) and the marriage history ( 2 . 2.4 ) to a temperature above the eutectic temperature of a composition of the metal and the semiconductor material, wherein a compound of the semiconductor film ( 3 ) with the marriage history ( 2 . 2.4 ) and the marriage history ( 2 . 2.4 ) with the substrate ( 1 ) is formed, characterized in that - the heating takes place by means of locally acting laser irradiation. Process according to claim 1, in which - the compound of the semiconductor film ( 3 ) with the marriage history ( 2 . 2.4 ) is generated by pulsed laser irradiation, - the semiconductor film ( 3 ) consists of silicon, - the semiconductor film ( 3 ) has a thickness less than 200 microns, in particular less than 100 microns, - the substrate ( 1 ) Glass, glass ceramic or a glass or glass-ceramic layer ( 1.1 ) provided polymer, and / or - the joining layer ( 2 . 2.4 ) Contains aluminum. Method according to one of the preceding claims, in which - in step (c) the laser irradiation at different positions of the joining layer ( 2 . 2.4 ) is repeated so that a plurality of contact sections ( 2.3 ) with compounds of the semiconductor film ( 3 ) and the marriage history ( 2 . 2.4 ) are formed. Method according to Claim 3, in which the different positions of the joining layer on which the laser irradiation takes place are so small that a flat connection ( 2.1 ) of the semiconductor film ( 3 ) with the marriage history ( 2 . 2.4 ) is formed. Method according to one of the preceding claims, in which - the joining layer is divided into a plurality of joining layer sections ( 2.6 . 2.7 . 2.8 ) which is on the substrate ( 1 ) are arranged in partial layers next to one another or one above the other and at which in each case in step (c) a connection with the semiconductor film ( 3 ) is formed. Method according to one of the preceding claims, in which - the semiconductor film ( 3 ) on the substrate ( 1 ) side facing a dielectric passivation layer ( 5 ), and - in step (c) the laser irradiation at individual, over the surface of the substrate ( 1 ) distributed positions, so that a plurality of contact sections ( 2.3 ) formed by the marriage history ( 2 . 2.4 ) or the joining layer sections ( 2.6 . 2.7 . 2.8 ) through the dielectric passivation layer ( 5 ) to the semiconductor film ( 3 ), wherein a predominant area proportion of the substrate ( 1 ) is not irradiated. Method according to one of the preceding claims, in which - the semiconductor film ( 3 ) with at least one doping layer ( 4 ), in particular boron or phosphorus-containing, is provided, and before step (b) is provided as a further step: (d) local doping of the semiconductor film ( 3 ) by laser irradiation. Method according to claim 7, in which - the doping layer ( 4 ) on the substrate ( 1 ) facing side of the semiconductor film ( 3 ) and the joining layer is arranged in a plurality of joining layer sections ( 2.6 . 2.7 ), where By the laser irradiation of a first group of the bonding layer sections ( 2.6 ) on the substrate ( 1 ) facing side of the semiconductor film ( 3 ) first doping regions ( 3.1 ) are generated with a first conductivity type, and - by the laser irradiation of the doping layer ( 4 ) on the substrate ( 1 ) facing side of the semiconductor film ( 3 ) second doping regions ( 3.2 ) are produced with a second, opposite conductivity type, each with joining layer sections of a second group of joining layer sections ( 2.7 ) are connected. Method according to claim 7, in which - the doping layer ( 4 ) on the substrate ( 1 ) facing side of the semiconductor film ( 3 ) the joining layer is arranged in a plurality of joining layer sections ( 2.6 . 2.7 ), and the semiconductor film ( 3 ) on the substrate ( 1 ) pioneering side a first doping region ( 3.1 ) having a first conductivity type, wherein - by the laser irradiation of a first group of the bonding layer sections ( 2.6 ) Contact sections ( 2.3 ) generated by the semiconductor film ( 3 ) to the first doping region ( 3.1 ), and - by the laser irradiation of the doping layer ( 4 ) second doping regions ( 3.2 ) are produced with a second, opposite conductivity type, each with joining layer sections of a second group of joining layer sections ( 2.7 ) are connected. Method according to claim 8 or 9, in which - the joining layer sections of the first and the second group of joining layer sections ( 2.6 . 2.7 ) each contain different metals, or - all joining layer sections ( 2.6 . 2.7 ) contain the same metal, in particular aluminum. Method according to one of the preceding claims, the - At least step (c) takes place in an inert or reducing atmosphere or in a vacuum. A method according to claim 11, wherein - The vacuum takes place locally selectively at the location of the laser irradiation. Method according to one of the preceding claims, in which - the semiconductor film ( 3 ) comprises n-type silicon and the bonding layer ( 2 . 2.4 ) or the joining layer sections ( 2.6 . 2.7 . 2.8 ) Aluminum, wherein the compound of the semiconductor film ( 3 ) with the marriage history ( 2 . 2.4 ) or the joining layer sections ( 2.6 . 2.7 . 2.8 ) an aluminum doping region ( 3.1 ) is formed in the semiconductor material to produce a p-type emitter, or - the semiconductor film ( 3 ) comprises p-type silicon and the bonding layer ( 2 . 2.4 ) or the joining layer sections ( 2.6 . 2.7 . 2.8 ) Aluminum, wherein the compound of the semiconductor film ( 3 ) with the marriage history ( 2 . 2.4 ) or the joining layer sections ( 2.6 . 2.7 . 2.8 ) an aluminum doping region ( 3.1 ) is formed in the semiconductor material to produce an electron-reflecting layer (Back Surface Field, BSF). Semiconductor device, in particular a diode or a solar cell, comprising: a substrate ( 1 ), - a marriage history ( 2 . 2.4 ) containing a metal, wherein the joining layer ( 2 . 2.4 ) on the substrate ( 1 ) and with the substrate ( 1 ), and - a semiconductor film ( 3 ) of a semiconductor material which is in at least one eutectic compound with the bonding layer ( 2 . 2.4 ) and the marriage history ( 2 . 2.4 ) with the substrate ( 1 ), characterized in that - the at least one eutectic compound is generated by means of local laser irradiation, and - the semiconductor material is doped at the at least one eutectic compound with the metal such that a charge carrier concentration above 10 ¹⁸ cm ^{-3 is} formed is. Semiconductor device according to claim 14, in which - the semiconductor film ( 3 ) consists of silicon, - the semiconductor film ( 3 ) has a thickness less than 200 microns, in particular less than 100 microns, and / or - the substrate ( 1 ) Glass, glass ceramic or a polymer provided with a glass or glass ceramic layer comprises, the joining layer along the substrate surface into a plurality of joining layer sections ( 2.6 . 2.7 . 2.8 ), at each of which a connection with the semiconductor film ( 3 ) is formed and on the substrate ( 1 ) are arranged in partial layers next to each other or one above the other, and / or - the joining layer ( 2 . 2.4 ) Contains aluminum. A semiconductor device according to claim 14 or 15, wherein - the semiconductor material is doped at the at least one eutectic bond with the metal such that a doped contact section extends over the entire thickness of the semiconductor film ( 3 ). Semiconductor device according to one of Claims 14 to 16, in which - the substrate ( 1 ) comprises a polymer provided with a glass or glass-ceramic layer and the glass or glass-ceramic layer has a thickness of more than 0.5 μm, in particular more than 5 μm. A semiconductor device according to any one of claims 14 to 17, wherein The semiconductor foil ( 3 ) on the substrate ( 1 ) facing side a doping layer ( 4 ) and a dielectric passivation layer ( 5 ), and - the joining layer into a plurality of joining layer sections ( 2.6 . 2.7 ), where - on the substrate ( 1 ) facing side of the semiconductor film ( 3 ) first doping regions ( 3.1 ) of a first type of line connected to a first group of the bonding layer sections ( 2.6 ), and second doping regions ( 3.2 ) of a second, opposite conductivity type are formed with a second group of the joining layer sections ( 2.7 ) are connected. Semiconductor component according to one of Claims 14 to 17, in which - the semiconductor film ( 3 ) on the substrate ( 1 ) facing side a doping layer ( 4 ) and a dielectric passivation layer ( 5 ), - the joining layer into a plurality of joining layer sections ( 2.6 . 2.7 ), and - the semiconductor film ( 3 ) on the substrate ( 1 ) pioneering side a first doping region ( 3.1 ) of a first conductivity type, wherein - a first group of the bonding layer segments ( 2.6 ) via contact sections ( 2.3 ) passing through the semiconductor film ( 3 ), with the first doping region ( 3.1 ), and - on the substrate ( 1 ) facing side of the semiconductor film ( 3 ) second doping regions ( 3.2 ) of a second, opposite conductivity type are formed with a second group of the joining layer sections ( 2.7 ) are connected. Semiconductor device according to one of claims 18 or 19, in which - the joining layer sections of the first and the second group of bonding layer sections ( 2.6 . 2.7 ) each contain different metals, or - all joining layer sections ( 2.6 . 2.7 ) contain the same metal, in particular aluminum.

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