Method for through-contact

Abstract

The invention relates to a method for through-contact by means of through-openings in a semiconductor disk, comprising at least the following steps: providing a semiconductor disk having an upper side and an lower side, said semiconductor disk having a plurality of solar cell stacks and comprising a substrate on the lower side, each solar cell stack has at least two III-V sub-cells arranged on the substrate and at least one through-opening extending from the upper side to the lower side of the semiconductor disk, the through-opening having a continuous side wall, the through opening has a first edge region on the upper side and a second edge region on the lower side; applying an insulating layer to a portion of the first edge region, the side wall and the second edge region by means of a first printing method; an electrically conductive layer is applied by means of a second printing method to the insulating layer on the upper side and to a portion of the first edge region, to the insulating layer on the side walls and to a portion of the insulating layer on the lower side.

Description

[0001] This case is a divisional application of a patent application with an application date of March 2, 2022, application number 202210197895.7, and invention name “Method for through contact”. Technical Field

[0002] The invention relates to a method for through-contacting. Background Art

[0003] In order to reduce the shading of the front side of the solar cell, it is possible to arrange both the positive external contact surface and the negative external contact surface on the back side. In the case of so-called metal wrap through (MWT) solar cells, the front side of the solar cell is provided with a through-contact opening, for example. Access from the back side.

[0004] Different methods are known for producing holes or through-hole openings through solar cells. The metallization is insulated from the layers of the solar cell stack by means of an insulation layer.

[0005] For example, US Pat. No. 9,680,035 B1 discloses a solar cell stack consisting of a plurality of III-V subcells on a GaAs substrate having a front side with back-side contact, wherein holes extending from the upper side of the solar cell through the subcells into the substrate layer that has not yet been thinned are produced by means of a wet-chemical etching process. The etching process is based on the fact that the etching rates do not differ significantly, at least for the different III-V materials used for the solar cell stack. Passivation and metallization of the front side and the holes are performed before thinning the substrate layer. Summary of the invention

[0006] Against this background, the object of the present invention is to specify a device which expands the prior art.

[0007] This object is achieved by a method having the features according to the invention. Advantageous configurations of the invention are preferred embodiments.

[0008] According to the subject matter of the invention, a method for through-contacting a semiconductor disk is provided, wherein the method comprises a plurality of steps.

[0009] In a first process step, a semiconductor disk having a top side and an underside is provided, wherein the semiconductor disk has a plurality of solar cell stacks and comprises a substrate on the underside.

[0010] Each solar cell stack has at least two III-V group subcells arranged on a substrate and at least one through-opening extending from the upper side to the lower side of the semiconductor disk and having continuous side walls. The through-opening has a first edge region at the upper side and a second edge region at the lower side.

[0011] In a second process step, an insulating layer is applied to a portion of the first edge region, to a portion of the side flanks and to the second edge region by means of a first printing method.

[0012] In a third process step, a conductive layer is applied to the insulation layer on the top side and to a part of the first edge region, to the insulation layer at the side walls, and to a part of the insulation layer at the bottom side by means of a second printing method.

[0013] It will be appreciated that the process steps are performed in the order mentioned.

[0014] It should be noted that the term “insulating layer” is also understood to mean, in particular, a dielectric layer system comprising an insulating layer. Furthermore, the term “edge region” refers to a region on the top side and on the bottom side which is arranged directly adjacent to the through-opening.

[0015] It should be noted that light shines onto the upper side. In order to shade the upper side as little as possible, the upper side is electrically connected by means of metal finger structures.

[0016] Preferably, the band gap decreases from subcell to subcell in the direction of the substrate starting from the top. Typically, the subcells of the respective solar cell stack have an n-on-p arrangement. It is understood that a tunnel diode is respectively formed between two subcells in order to electrically connect the individual subcells in series. In particular, the uppermost subcell comprises a compound composed of InGaP and has a band gap of greater than 1.7 eV.

[0017] It is understood that a top metallization which is usually implemented in finger-like manner is arranged on the top side in order to electrically connect the positive side. In the following, the top metallization is also referred to as metal structure.

[0018] It should be noted that the through opening is preferably elliptically configured. In the present case, the term "elliptically" also includes circular, in particular circular, egg-shaped and elliptical shapes. In another embodiment, the through opening is configured as a quadrilateral with rounded corners. It is understood that in each solar cell stack, the front side is electrically connected from the back side by means of one or more through openings.

[0019] Preferably, before forming the through-opening, the semiconductor disk, which typically has a diameter of 100 mm or 150 mm, is thinned to the desired final thickness. To this end, substrate material is removed on the back side.

[0020] Furthermore, it should be noted that the semiconductor disk has a plurality of unseparated solar cell stacks, wherein the substrate forms the underside of the semiconductor disk. It is understood that the solar cell stack also has 3 or 4 or 5 or a maximum of 6 subcells.

[0021] One advantage of this method is that by means of the multiple structured application by means of a printing method, i.e. both the insulating layer and the metal layer, photolithographic process steps are avoided. In particular, the associated process uncertainties when applying lacquer layers under large topography are avoided. The formation of through-openings (i.e. the formation of the front side electrically connected from the back side) is required to simplify the electrical connection of the solar cell stack and to form a reliable protection of the insulating layer in the region of the through-openings.

[0022] In particular, the time and technical expenditure as well as the material consumption are low compared to the prior art. Another advantage is that the reliability and productivity are increased.

[0023] In other words, the through opening and the regions adjoining the through opening on the upper side and on the lower side are covered only by means of a printing method. With this process, efficient and reliable multijunction solar cells can be produced in a simple and cost-effective manner, the front side of which is electrically connected to the back side.

[0024] In one embodiment, a first heating step is performed after the first printing method and before the second printing method is performed. In another embodiment, a second heating step is performed after the second printing method. The insulating layer and the conductive layer are conditioned separately by means of the heating step. Preferably, the heating step is performed in a temperature range between 100° C. and 450° C.

[0025] In one embodiment, a paste is used to form the insulating layer. Preferably, the paste contains an organic component.

[0026] In a further configuration, a paste containing metal particles is used to form the electrically conductive layer.

[0027] In one embodiment, the first printing method and / or the second printing method is performed only from the front side or only from the back side. Alternatively, the first printing method and / or the second printing method is performed both from the front side and from the back side.

[0028] In another embodiment, after the insulating layer has been formed, the through-opening still has a through hole. Alternatively, the through-opening is opened in the central region by means of a laser.

[0029] In one embodiment, after the electrically conductive layer is formed, the through-opening is partially or completely closed. Alternatively, after the electrically conductive layer is formed, the through-opening still has a through hole.

[0030] Preferably, the electrically conductive layer on the first edge region and in the through-opening and on the second edge region consists of the same material. In an alternative embodiment, different compositions are used to form the electrically conductive layer on the top side and on the bottom side.

[0031] If the through-opening is completely closed by means of the conductive layer, then in one embodiment the conductive layer protrudes above the upper side and / or at the lower side. Alternatively, the conductive layer at the lower side is formed approximately on the insulating layer. ) flat surface, wherein the conductive layer is located in the center of the through opening.

[0032] In one embodiment, the first edge region on the upper side has a different, in particular smaller, diameter than the second edge region on the lower side.

[0033] In another embodiment, the first edge region and the second edge region are each designed as an edge region completely surrounding the through-opening. Preferably, the respective edge region has a diameter of at least 10 μm and at most 3.0 mm parallel to the semiconductor disk. Alternatively, the respective edge region has a diameter of at least 100 μm and at most 1.0 mm parallel to the semiconductor disk.

[0034] In one embodiment, the printing method is carried out by means of an inkjet method or a screen printing method or by means of a dispensing method. Alternatively, the printing method is carried out by means of a stencil printing method. In another embodiment, at least two of the different printing methods are combined.

[0035] In a further configuration, the through-opening of the semiconductor disk has an overall height of at most 500 μm and at least 30 μm or at most 200 μm and at least 50 μm.

[0036] In one embodiment, the through-opening has an elliptical outer circumference in cross section, in particular a circular outer circumference. Preferably, before applying the first printing method, the through-opening has a diameter between 25 μm and 1 mm. Alternatively, the diameter is in the range between 50 μm and 300 μm.

[0037] In one embodiment, before the first printing method is applied, the diameter of the through-opening in the substrate is approximately equal or exactly equal starting from the top to the bottom. Alternatively, the diameter of the through-opening decreases starting from the top in the direction of the bottom, wherein this tapering is preferably designed as a step. In one embodiment, the through-opening has an hourglass-shaped view in cross section. In this case, the cross section tapers to approximately half the total thickness.

[0038] In a further embodiment, the tapering comprises exactly one step running in the through-opening or exactly two completely circumferential steps.

[0039] In another embodiment, the substrate is designed to be electrically conductive. Preferably, the substrate comprises germanium or GaAs or silicon or consists of one of the aforementioned materials. Alternatively, the substrate comprises a metal foil or comprises an electrically conductive plastic.

[0040] Preferably, the semiconductor disc or substrate has a size of 100 mm or 150 mm or more.

[0041] If the substrate comprises germanium or consists of germanium, the germanium substrate forms the underside of the semiconductor disk. Preferably, a first subcell is formed as a Ge subcell in the Ge substrate on the side facing away from the underside, wherein the Ge subcell has the smallest band gap of the subcells of the solar cell stack.

[0042] When Ge is used as substrate, the first step is formed at the interface between the Ge subcell and the supporting III-V subcell. The second step is preferably formed between the Ge subcell and the Ge substrate.

[0043] Preferably, the through-opening also tapers in the Ge substrate. A stepped or conical embodiment of the through-opening has the advantage that, in particular in the case of a preferably uniform deposition of the insulating layer and / or other layers to be applied, the layer thickness can be adequately constructed on the side surfaces within the scope of the metallization.

[0044] In one configuration, a further step is formed on the upper side of the semiconductor disk at the interface between the metal structure and the upper side of the uppermost III-V subcell.

[0045] In one embodiment, the solar cell stack has a germanium subcell. As a result, the solar cell stack comprises at least 3 subcells.

[0046] In another embodiment, a portion of the insulation layer on the top is formed on the metal surface. This ensures that the metal structure on the top, ie the front side of the solar cell stack, is connected.

[0047] In other words, since the conductive layer overlaps the insulating layer on the upper side and forms a material-locked connection with a portion of the metal structure, but only covers the portion of the second edge area directly adjacent to the through-opening on the lower side, a contact area for electrically connecting the metal structure MV is formed on the lower side. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The invention is explained in more detail below with reference to the drawings. Components of the same type are marked with the same reference numerals. The embodiments shown are highly schematic, i.e. the spacings and the lateral and vertical extensions are not to scale and, unless otherwise indicated, do not have any derivable geometrical relationships with one another.

[0049] Figure 1 : A cross-sectional view of a metallized through-opening in one embodiment;

[0050] Figure 2 : A cross-sectional view of a metallized through-opening in another embodiment;

[0051] Figure 3 : A cross-sectional view of a metallized through-opening in another embodiment;

[0052] Figure 4a : Corresponding to the combination Figure 3 A top view of the upper side of the metallized through-opening of the embodiment shown in the figure;

[0053] Figure 4b : Corresponding to the combination Figure 3 A top view of the underside of the metallized through-opening of the embodiment shown in the figure;

[0054] Figure 5 : Top view of a semiconductor disk with two solar cell stacks. DETAILED DESCRIPTION

[0055] Figure 1 The illustration of exemplifies a cross-sectional view of a metallized through-opening 22 of a semiconductor disk 10 .

[0056] A semiconductor disk 10 is provided, which has an upper side 10 . 1 , an underside 10 . 2 and a through-opening 22 extending from the upper side 10 . 1 to the underside 10 . 2 and having a continuous side wall 22 . 1 .

[0057] The semiconductor disk 10 comprises a plurality of not yet separated solar cell stacks 12 , of which only one solar cell stack 12 is shown in the present case, each having a layer sequence consisting of a substrate 14 forming the bottom side 10 . 2 , a first III-V subcell 18 and a second III-V subcell 20 forming the top side 10 . 1 .

[0058] A metal structure MV is formed on the upper side 10 . 1 . The metal structure MV is formed almost exclusively as a finger-like structure and, in particular in the first edge region 11 of the through-opening 22 , has a continuous metal surface formed approximately completely around the through-opening 22 .

[0059] On the bottom side 10.2, a full-area back metallization MR is formed in order to connect the conductive substrate 14. It is understood that the respective solar cell stack 12 is electrically connected to both metallizations MV and MR.

[0060] The through-opening 22 has a first edge region 11.1 on the upper side 10.1 and a second edge region 11.2 on the lower side 10.2. The first edge region 11.1 is formed directly on the metal structure MV and the second edge region 11.2 is formed directly on the back metallization MR.

[0061] The portion of the first edge region 11.1 directly surrounding the through-opening 22 and the entire second edge region 11.2 as well as the side walls 22.1 of the through-opening 22 are coated with an insulating layer 24, wherein the insulating layer 24 is formed by a first printing method. It is understood that the side walls 22.1 in the through-opening 22 are completely covered by the insulating layer 24.

[0062] By means of a second printing method, the conductive layer 32 is applied over the entire area of ​​the first edge region 11.1 and completely over the entire surface of the side wall 22.1 and to the part of the second edge region 11.2 that directly adjoins the through-opening 22. In the present case, even after the conductive layer 32 is formed, the through-opening 22 remains open.

[0063] Since the conductive layer 32 overlaps the insulating layer 24 on the upper side 10.1 and forms a material-bonded connection with a portion of the metal structure MV, but only covers the portion of the second edge region 11.2 directly adjacent to the through-opening 22 on the lower side 10.2, a contact region for connecting the metal structure MV is formed on the lower side 10.2.

[0064] exist Figure 2 Another embodiment is shown in the figure of FIG. Figure 1 The difference between the diagrams.

[0065] In the embodiment shown, the electrically conductive layer 32 meets in the center of the substrate 14 and forms a contour in the form of an hourglass.

[0066] exist Figure 3 Another embodiment is shown in the figure of FIG. Figure 1 The difference between the diagrams.

[0067] In the embodiment shown, the through-opening 22 is completely filled with the electrically conductive layer 32 and forms a projection protruding from the top side 10 . 1 and a projection protruding from the bottom side 10 . 2 .

[0068] exist Figure 4a The diagram shows the corresponding combination Figure 3 The figure shows a top view of the upper side of the metallized through-opening 22 of the embodiment shown.

[0069] The first edge region 11.1 - as part of the metal structure MV - completely surrounds the through-opening 22. The part of the first edge region 11.1 covered by the insulating layer 24 is drawn in dashed lines. The figure shows that the electrically conductive layer 22 completely covers the insulating layer 24 on the top side 10.1.

[0070] exist Figure 4b The diagram shows the corresponding combination Figure 3 The figure shows a top view of the underside of the metallized through-opening 22 of the embodiment shown.

[0071] The second edge region 11.2 - as part of the back metallization MR - completely surrounds the through-opening 22. The part of the second edge region 11.2 covered by the insulating layer 24 is now larger than the part covered by the conductive layer 22. In other words, the conductive layer 22 only partially covers the insulating layer 24 on the bottom side 10.2.

[0072] exist Figure 5 The diagram of FIG. 1 shows a top view of a semiconductor disk 10 with two solar cell stacks. In the present case, the semiconductor disk 10 has exactly two solar cell stacks 12. It is understood that in embodiments not shown, more than two solar cell stacks 12 may also be formed on the semiconductor disk 10.

Claims

1. A method for making a through-contact by means of a through-opening (22) in a semiconductor disk (10), the method comprising at least the following steps: A semiconductor disk (10) is provided, the semiconductor disk (10) having an upper side (10.1) and a lower side (10.2), wherein the semiconductor disk (10) comprises a substrate (14) and two III-V subcells (18, 20) on the lower side, the two III-V subcells (18, 20) being arranged in a stack on the substrate (14), The semiconductor disk (10) has at least one through-opening (22), which extends from an upper side (10.1) of the semiconductor disk (10) to an underside (10.2) of the semiconductor disk (10) and has a continuous side wall (22.1), wherein the through-opening has a first edge region (11.1) at the upper side (10.1) and a second edge region (11.2) at the underside (10.2); characterised in that the diameter of the through-opening decreases starting from the top in the direction of the bottom, wherein this tapering is designed in a step-like manner, In a first method step, an insulating layer (24) is applied to a part of the first edge region (11.1), to a part of the side wall (22.1) and to the second edge region (11.2) by means of a first printing method while leaving the through-opening (22) unobstructed, so that after forming the insulating layer, the through-opening still has a continuous hole, In the next method step, a first heating step is performed. And then, in a further method step, a conductive layer (32) is applied to the insulating layer (24) on the upper side (10.1) and to a part of the first edge region (11.1), to the insulating layer (24) at the side wall (22.1) and to a part of the insulating layer (24) at the lower side (10.2) by means of a second printing method.

2. The method according to claim 1, characterized in that: A paste is used to construct the insulating layer (24), and the paste includes an organic component.

3. The method according to claim 1 or 2, characterized in that: The conductive layer (32) is structured using a paste containing metal particles.

4. The method according to any one of the preceding claims, characterized in that The first printing method and / or the second printing method is performed only from the front side or only from the back side.

5. The method according to any one of the preceding claims, characterized in that After the insulating layer (24) has been formed, the through-opening (22) still has a through hole.

6. The method according to any one of the preceding claims, characterized in that After the electrically conductive layer (32) has been formed, the through-opening is partially or completely closed or it still has a through hole.

7. The method according to any one of the preceding claims, characterized in that Compared to the second edge region (11.2), the first edge region (11.1) has a different, in particular smaller, diameter.

8. The method according to any one of the preceding claims, characterized in that The first edge region (11.1) and the second edge region (11.2) are each configured as an edge region completely surrounding the through-opening (22), and the respective edge region (11.1, 11.2) has a diameter of at least 10 μm and at most 3.0 mm parallel to the semiconductor disk (10), or the respective edge region has a diameter of at least 100 μm and at most 1.0 mm parallel to the semiconductor disk (10).

9. The method according to any one of the preceding claims, characterized in that The printing method is carried out by means of an inkjet method or by means of a screen printing method or by means of a dispensing method or by means of a stencil printing method.

10. The method according to any one of the preceding claims, characterized in that The through-opening (22) of the semiconductor disk (10) has an overall height (H1) of not more than 500 μm and at least 30 μm or an overall height (H1) of not more than 200 μm and at least 50 μm.

11. The method according to any one of the preceding claims, characterized in that The through-opening (22) of the semiconductor disk (10) has an outer circumference with an elliptical cross section, in particular a circular outer circumference.

12. The method according to any one of the preceding claims, characterized in that Before applying the first printing method, the through-opening (22) has a diameter between 25 μm and 1 mm or typically between 50 μm and 300 μm.

13. The method according to any one of the preceding claims, characterized in that The diameter of the through-opening (22) in the substrate (14) is approximately equal or exactly equal in the direction from the upper side (10.1) to the lower side (10.2).

14. The method according to any one of the preceding claims, characterized in that The first edge region at the upper side has a different diameter than the second edge region at the lower side.

15. The method according to any one of the preceding claims, characterized in that The solar cell stack has a Ge subcell (16).

16. The method according to any one of the preceding claims, characterized in that A portion of the insulating layer on the top side (10.1) is formed on a metallic surface.

17. The method according to claim 1, characterized in that After performing the second printing method, a second heating step is performed.

18. The method according to claim 17, characterized in that Two heating steps were performed in the temperature range between 100°C and 450°C.

Images