Method for fabricating vias in III-V multi-junction solar cells
Through the three-stage laser method steps and the use of organic layers, the time-consuming and labor-intensive problem of the lithography process in the manufacturing of III-V multi-junction solar cell through-holes is solved, and flexible through-hole arrangement and high-quality electrical through-connection are achieved. on different substrate materials.
Patent Information
- Application Number
- CN202410765326.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-06-14
- Filing Date
- 2024-06-14
- Publication Date
- 2024-12-17
AI Technical Summary
In the prior art, when manufacturing through holes of III-V multijunction solar cells, time-consuming and expensive lithography processes are difficult to avoid, and wet chemical etching methods may lead to insufficient etching, affecting the quality of electrical penetration.
Using a three-stage laser method step, a gradually narrowing opening is generated by laser to construct through the through holes, using an organic layer (such as polyimide) as the dielectric layer to avoid the etching process and without changing the III-V layer Electrical connection is achieved when the thickness and material are composed of.
A flexible arrangement of through holes on the upper side of III-V multi-junction solar cells is achieved, avoiding the necessity of lithography, ensuring the quality of electrical penetration and seamlessly for different substrate materials (such as GaAs and Ge) Adapt to avoid the problem of insufficient etching.
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Figure CN119141013A_ABST
Abstract
Description
Background Art
[0001] DE 692 16 502 T2 discloses a laser cutting method for producing through-holes for through-contacts in GaAs or Ge solar cells, wherein the disclosed method is intended to essentially avoid the disadvantages of CVD SiO 2 coatings in the case of through-holes.
[0002] In a first method step, continuous openings with a large diameter are produced by means of laser pulses from a YAG laser. In order to prepare the very rough surface on the side walls of the through-openings produced during the laser irradiation for the subsequent metallization, in a second method step, the side walls are overmolded, mainly with polyimide, or in the case of smaller continuous openings, the openings are completely filled with polyimide. In a subsequent method step, the polyimide is heated for curing.
[0003] The polyimide is referred to as a dielectric layer. In a fourth method step, through-holes with a small diameter are produced in the polyimide by means of a laser, wherein the polyimide has a smooth surface on the newly produced side surfaces after the laser irradiation. In a subsequent method step, the polyimide side surfaces are covered with metal.
[0004] By applying polyimide, the necessity of flattening the side surfaces by aggressive chemical etching is also avoided, and the active region of the solar cell and the GaAs substrate or Ge substrate are protected from etching. In addition, polyimide has good adhesion not only to the substrate, but also to the conductive metallization to be applied. Summary of the invention
[0005] Against this background, the object of the present invention is to specify a method with which the prior art is expanded.
[0006] This object is achieved by a method for producing a through-hole in a III-V multi-junction solar cell having the features of claim 1. Advantageous embodiments of the invention are the subject matter of the dependent claims.
[0007] According to this subject matter, a method for fabricating vias in a III-V multi-junction solar cell is provided.
[0008] The III-V multi-junction solar cell has a top side and a bottom side, wherein the through-hole is formed to pass through from the top side to the bottom side.
[0009] The III-V multi-junction solar cell comprises a substrate arranged on a lower side.
[0010] The substrate has a top side and an epitaxial layer system formed on the top side, which has a plurality of III-V layers.
[0011] The epitaxial layer system comprises at least one first III-V solar cell. An organic layer is arranged on the top side of the first III-V solar cell.
[0012] In a first method step, an opening is produced by means of a laser, which opening has a width X and has a first bottom area formed in the epitaxial layer system.
[0013] In a second method step, an opening is produced by means of a laser, the opening having a width Y and having a second base formed in the substrate, wherein the width Y is smaller than the width X.
[0014] In a third method step, an opening having a width Z is produced by means of a laser for forming a continuous through-hole, wherein the opening has no bottom surface and the width Z is smaller than the width Y.
[0015] The above-described method steps can be carried out in the order indicated or in any order.
[0016] If the above method steps are carried out in the order given, the second method step is carried out after the first method step, and then the third method step is carried out. It should be understood that in the second method step, an opening with a second bottom surface is produced in the first bottom surface, and in the third method step, a continuous opening called a through hole is produced in the second bottom surface.
[0017] If the method steps are not carried out in the order specified, the third method step is carried out first, followed by either the second method step or the first method step.
[0018] Next, the method step that has not yet been performed, ie the first method step or the second method step, is performed. Here, it should be understood that, depending on the sequence, the second bottom surface is formed after the consecutive openings, and the first bottom surface is formed in the last method step.
[0019] In another embodiment, the second method step is first performed and the second bottom surface is formed. Then, either the first method step with the formation of the first bottom surface or the third method step with the formation of the continuous opening is performed. Then, the method step that has not yet been performed, that is, the third method step or the first method step, is performed.
[0020] It should be understood that after performing all three method steps, regardless of the order in which they are implemented, a through-opening with two steps is always constructed. In other words, in a cross-sectional view, through-openings manufactured in different ways correspond to each other or are constructed exactly the same.
[0021] It should be noted that the organic layer comprises a lacquer layer and / or a polyimide layer and / or a plastic layer. It should be understood that the layers are preferably constructed in an unstructured manner in order to avoid masking steps.
[0022] It should also be noted that a through-hole is always an opening extending through a complete layer and formed perpendicularly to the front side. This type of opening can be used for electrical through-connections by forming a metal layer in the through-hole.
[0023] Furthermore, it is to be understood that the substrate is a semiconductor substrate or a semiconductor wafer having a diameter of at least or exactly 100 mm or at least or exactly 150 mm.
[0024] It should also be noted that when using a laser, all method steps are carried out starting from the top.
[0025] It should be noted that in the present context the term "dielectric layer" includes only inorganic layers, in particular oxide and nitride layers.
[0026] It should be understood that the term “epitaxial layer system” refers only to III-V layers produced on a substrate by means of an epitaxial process.
[0027] It should furthermore be noted that the first bottom surface formed in the epitaxial layer system or in the substrate has an opening or a hole, so that the first bottom surface is formed as a peripheral edge surface starting from the opening or the hole.
[0028] It is to be understood that the surface formed in the bottom region, ie the first bottom surface or the surrounding edge surface, is flat or is flat in a first approximation and that it consists exclusively of III-V on the bottom in the epitaxial layer system or exclusively of substrate material in the bottom surface in the substrate.
[0029] It should also be noted that in the laser-based method steps, the side surfaces generated in each case are designed to be exactly vertical or almost vertical. The term "almost vertical" is understood to mean a deviation from the vertical of less than 5°.
[0030] In one embodiment, the opening angle is less than 20° or less than 10°. In this case, the opening angle is understood to be an angle that is inclined relative to the vertical, wherein the inclination is "outward" such that the entire angle is greater than 90°. In other words, the hole in a non-vertical embodiment has a larger diameter on the top side than in the bottom region, and the hole is designed to be conical.
[0031] The advantage is that, with this method, the organic layer, in particular the lacquer layer, can be flexibly provided with continuous through-holes at any location on the top side of the III-V multi-junction solar cell without further structuring by means of complex and expensive photolithography processes. With the help of these through-holes, the top side, i.e. the front side, of the III-V multi-junction solar cell can be electrically contacted from the back side.
[0032] Another advantage is that the at least three-stage laser method is surprisingly insensitive to insignificant changes in the layer structure, in particular the thickness and number of the III-V layers. The method is also insensitive to changes in the substrate material from GaAs to Ge and vice versa. Insignificant changes are in particular changes in the III-V material composition and stoichiometry and changes in the total layer thickness of less than 20 μm.
[0033] A further advantage is that the settings of the laser can also be easily changed in the event of significant changes in the substrate thickness. Significant changes are in particular changes in the substrate thickness of at least 50 μm or at least 100 μm.
[0034] Another advantage of laser-based method steps compared to wet-chemical method steps is that underetching does not occur. Furthermore, the wet-chemical method steps generally require that the protective lacquer be applied in a structured manner to the surface and / or to the side surfaces of the structure to be produced, in particular in the case of multiple steps.
[0035] In one embodiment, the laser method steps are carried out successively by using a laser without intermediate steps, such as wet etching steps or dry etching steps, for example.
[0036] However, it is understood that in another embodiment, instead of three consecutive laser method steps, more than three method steps, for example four or five method steps, can also be carried out using a laser.
[0037] In another embodiment, further method steps not using laser light are carried out between, before or after the at least three-stage opening method.
[0038] In one configuration, at least one further III-V solar cell is formed between the substrate and the first III-V solar cell.
[0039] In one embodiment, the first III-V solar cell as the uppermost III-V solar cell has a larger band gap than the underlying III-V solar cells or a band gap of the same size.
[0040] In order to electrically interconnect III-V solar cells arranged in a stack in series with one another, a plurality of tunnel diode layers are arranged between two III-V solar cells.
[0041] In another embodiment, the two III-V solar cells have the same or different materials. In one embodiment, the uppermost III-V solar cell has an InGaP compound. In one embodiment, the other III-V solar cell is configured as a second III-V solar cell and includes a GaAs compound or an InGaAs compound.
[0042] In one embodiment, the substrate comprises or consists of Ge or GaAs. It will be appreciated that a plurality of III-V layers are arranged on the substrate. Preferably, the layers are epitaxially grown by means of a MOVPE facility.
[0043] In another embodiment, a substrate solar cell is formed in or on the upper side of the substrate. In the case of a GaAs substrate, the substrate solar cell is a III-V solar cell, in the case of a Ge substrate, the substrate solar cell is a VI solar cell.
[0044] It should be noted that when the substrate is constructed as a Ge substrate, the Ge substrate is typically constructed as a p-Ge substrate, and when an n-Ge layer is constructed for constructing a Group VI solar cell, an n layer is produced on or in the surface of the p-Ge substrate by means of internal diffusion of dopants without means of epitaxy.
[0045] In one configuration, the substrate has a thickness in the range between 80 μm and 850 μm. In another configuration, the thickness of the substrate is in the range between 150 μm and 750 μm.
[0046] In one embodiment, a further layer is formed above the first III-V solar cell and below the organic layer.
[0047] In one configuration, the width X is in the range between 5 μm and 5 mm or in the range between 50 μm and 1 mm.
[0048] In one configuration, the width y is in the range between 5 μm and 5 mm or in the range between 50 μm and 1 mm.
[0049] In one embodiment, the ratio of width X to width Y is less than a factor of 10 or less than a factor of 5. In other words, although width X is always greater than width Y, width X is at most 10 times greater than width Y or at most 5 times greater than width Y.
[0050] In another embodiment, the width Z is in the range from 1 μm to 1 mm or the width Z of the through-hole is in the range from 20 μm to 0.5 mm.
[0051] In another embodiment, the organic layer is formed as a continuous layer covering the entire top side of the first III-V solar cell, ie, is formed in an unstructured manner. In this case, the organic layer can be applied not only by spin coating or by another coating method.
[0052] In one configuration, at least one III-V layer and / or at least one dielectric layer is formed between the first III-V solar cell and the organic layer. In another configuration, the dielectric layer includes SiO 2 or consists of SiO 2 .
[0053] In a further configuration, an antireflection layer is formed between the first III-V solar cell and the organic layer.
[0054] In one embodiment, a metal layer is arranged on the top side of the III-V multijunction solar cell in the region of the through-hole between the first III-V solar cell and the organic layer before the first method step, or no metal layer is formed. In other words, the method step can be performed independently of whether a metal layer is formed or not formed at the location of the through-hole to be produced.
[0055] In another embodiment, the through-hole has an oval shape. In one embodiment, the through-hole has a circular opening.
[0056] In one configuration, at least two steps are formed in the through-hole in the direction from the top side to the bottom side of the III-V multi-junction solar cell during the performance of the laser process.
[0057] In a further embodiment, wet-chemical etching is carried out after the three method steps have been carried out by means of laser, in particular for cleaning the surface and the side surfaces.
[0058] In one embodiment, depending on the etching solution used and its duration of use, only one of the two steps is still visible after etching. Preferably, the wet-chemical etching step is carried out directly after the three laser method steps have been carried out.
[0059] In one embodiment, the removal of the organic layer is performed only after the wet-chemical etching step has been carried out. This has the advantage that the surface is protected from etching by the organic layer.
[0060] In one embodiment, a constant diameter or a constant diameter in a first approximation is formed in the through-opening, viewed in a plane formed parallel to the underside. BRIEF DESCRIPTION OF THE DRAWINGS
[0061] In the following, the invention is explained in more detail with reference to the drawings. Identical parts are labeled with the same names. The embodiments shown are highly schematic, i.e. the spacings and the lateral and vertical extensions are not to scale and do not have any derivable geometrical relationships with each other unless otherwise stated. It is shown:
[0062] Figure 1 A cross-sectional view showing an unprocessed multi-junction solar cell structure,
[0063] Figure 2a-2c shows a cross-sectional view of the resulting via structure after different laser method steps,
[0064] Figure 3 A cross-sectional view of a via is shown after a wet etching step. DETAILED DESCRIPTION
[0065] In the cross-sectional views shown below, a fragment of a multijunction solar cell structure MS is respectively shown as part of a complete semiconductor wafer, wherein the multijunction cell structure MS in an embodiment likewise not shown is also constructed as a plurality of multijunction cell structures MS on a semiconductor wafer having a diameter of at least 100 mm.
[0066] Furthermore, the following figures merely show one embodiment in which method steps one to three are performed in the order given, ie, the first method step is performed first, the second method step is performed second, and the third method step is performed third.
[0067] Figure 1 The illustration of shows a cross-sectional view of an unprocessed multijunction solar cell structure MS having an underside US and an upper side OS. A substrate layer SUB composed of germanium or GaAs is formed on the underside US of the multijunction solar cell structure MS.
[0068] An epitaxial layer system ES is formed on the upper side of the substrate layer SUB. The epitaxial layer system ES is arranged on the substrate layer SUB in a material-bonded manner. An organic layer SL formed as a protective lacquer is arranged on the epitaxial layer system ES.
[0069] In the embodiment shown, the organic layer SL is connected to the top of the III-V epitaxial layer system ES in a material-bonded manner.
[0070] In an embodiment (not shown), one or more further layers, in particular a passivation layer, are formed in a materially bonded manner on the epitaxial layer system ES between the epitaxial layer system and the organic layer SL.
[0071] In an embodiment not shown, further organic and / or inorganic layers are formed between the organic layer SL and the epitaxial layer system ES. Preferably, the further layer comprises or consists of a passivation layer, which consists, for example, of silicon oxide and / or silicon nitride.
[0072] It should be understood that the aforementioned layers are arranged in the aforementioned order. It should also be noted that all the aforementioned layers are respectively constructed in the entire surface.
[0073] exist Figures 2a to 2c The diagrams of FIG. 1 show individual cross-sectional views of the resulting through-hole structure, wherein each individual diagram of the diagram shows the resulting through-hole structure after carrying out one of the three laser method steps. In the following, only the through-hole structure related to the laser method step is explained. Figure 1 The difference between the icons.
[0074] exist Figure 2a In a first method step shown in , an opening is produced by means of a laser, which opening has a width X through the organic layer SL and has a first bottom area BO1 formed in the epitaxial layer system. The produced side surfaces are formed almost vertically.
[0075] In a second method step, an opening is produced in the bottom surface by means of a laser, which opening has a width Y and has a second bottom surface BO2 formed in the substrate, wherein the width Y is smaller than the width X. Since the hole is produced only in a part of the first bottom surface BO1 of the epitaxial layer system, a first step STU1 is produced. The side surfaces produced in the second method step are also almost vertical.
[0076] In a third method step, an opening with a width Z is produced by means of a laser for forming a through-hole via VA, wherein the opening has no bottom surface and the width Z is smaller than the width Y. Since the hole is produced only in a part of the second bottom surface BO2 of the epitaxial layer system, a second step STU2 is produced. The side surfaces produced in the third method step are also almost vertical.
[0077] exist Figure 3 A cross-sectional view of a through hole after a wet etching step is shown in FIG. Figure 2c In the following, only the differences from the preceding illustrations are shown.
[0078] On the epitaxial layer system ES, the organic layer SL is removed by means of a stripping process. Preferably, before the organic layer SL is stripped, a wet etching step is performed in order to clean the impurities of the three laser method steps from the sides and other surfaces in the through hole, in particular the surfaces and sides of the two steps STU1 and STU2.
[0079] In the wet etching step, the first step STU1 is overmolded in such a way that the step surface is transferred from the epitaxial layer system ES to the interface between the epitaxial layer system ES and the upper side of the substrate SUB. The depth of the surface of the first step STU1 is also increased. After the etching step, the side surface in the through hole VA is also almost vertical.
[0080] The step face of the second step is also moved slightly deeper in the substrate SUB.
[0081] It is understood that in an embodiment not shown, the method steps performed by means of laser can also be performed in another order. In particular, the second method step can be performed before the first method step.
Claims
1. A method for producing a through-hole (VA) in a III-V multijunction solar cell (MS), the III-V multijunction solar cell having an upper side and an underside, the through-hole (VA) being formed from the upper side (OS) to the underside (US), the III-V multijunction solar cell (MS) comprising a substrate (SUB) arranged on the underside (US), the substrate (SUB) having an upper side and an epitaxial layer system (ES) formed on the upper side, the epitaxial layer system having a plurality of III-V layers, the epitaxial layer system (ES) comprising at least one first III-V solar cell, and an organic layer (SL) being arranged on the upper side of the first III-V solar cell, - in a first method step, an opening is produced by means of a laser, the opening having a width X and having a first bottom area (BO1) formed in the epitaxial layer system (ES), In a second method step, an opening is produced by means of a laser, the opening having a width Y and having a second bottom area (BO2) formed in the substrate, wherein: The width Y is smaller than the width X, in a third method step, an opening having a width Z is produced by means of a laser for forming a continuous through-hole (VA), wherein the opening has no bottom surface and the width Z is smaller than the width Y, - Carry out the above method steps in the order given or in any order.
2. Method for producing a through-hole (VA) in a III-V multi-junction solar cell (MS) according to claim 1, characterized in that At least one further III-V solar cell is formed between the substrate and the first III-V solar cell, and a plurality of tunnel diode layers are arranged between the two III-V solar cells, and the two III-V solar cells include the same or different materials.
3. The method for producing a through hole (VA) in a III-V multi-junction solar cell (MS) according to claim 1 or claim 2, characterized in that The substrate (SUB) comprises or consists of Ge or GaAs.
4. The method for producing a through-hole (VA) in a III-V multi-junction solar cell (MS) according to any one of the preceding claims, characterized in that The substrate (SUB) has a thickness in the range between 80 μm and 850 μm, or the thickness of the substrate (SUB) is in the range between 150 μm and 750 μm.
5. The method for producing a through-hole (VA) in a III-V multi-junction solar cell (MS) according to any one of the preceding claims, characterized in that Further layers are formed above the first III-V solar cell and below the organic layer (SL).
6. Method for producing a through hole (VA) in a III-V multi-junction solar cell (MS) according to any of the preceding claims, characterized in that The organic layer is formed as a continuous layer which covers the entire top side of the first III-V solar cell.
7. Method for producing a through-hole (VA) in a III-V multi-junction solar cell (MS) according to any of the preceding claims, characterized in that At least one III-V layer and / or at least one dielectric layer (SiO 2 ) is formed between the first III-V solar cell and the organic layer.
8. Method for producing a through-hole (VA) in a III-V multi-junction solar cell (MS) according to any of the preceding claims, characterized in that An antireflection layer is arranged between the first III-V solar cell and the organic layer.
9. The method for producing a through-hole (VA) in a III-V multi-junction solar cell (MS) according to any one of the preceding claims, characterized in that On the top side (OS) of the III-V multijunction solar cell (MS) before the first method step, a metal layer is arranged in the region of the through-hole between the first III-V solar cell and the organic layer (SL) or no metal layer is formed.
10. Method for producing a through-hole (VA) in a III-V multi-junction solar cell (MS) according to any of the preceding claims, characterized in that The through-hole has an elliptical shape and at least one first step (STU1) or at least two steps or exactly two steps are formed in the through-hole in the direction from the upper side to the lower side of the III-V multi-junction solar cell (MS).
11. Method for producing a through-hole (VA) in a III-V multi-junction solar cell (MS) according to any of the preceding claims, characterized in that In the through-opening (VA), viewed in a plane formed parallel to the underside, a constant diameter or a constant diameter in a first approximation is formed.