METHOD FOR STRUCTURING LAYERS OF OXIDIZABLE MATERIALS BY MEANS OF OXIDATION AND SUBSTRATE HAVING A STRUCTURED COATING

Abstract

The present invention relates to a method for structuring layers of oxidisable materials. At least one layer, disposed on a substrate, of an oxidisable material is hereby subjected to local oxidation with at least one oxidation step. In the case of the latter, at least one selected region of the layer of oxidisable material is oxidised so that the layer, after oxidation, is sub-divided into regions, which are electrically insulated from each other, by at least one oxidised region extending over the entire layer thickness.

Claims

1-26. (canceled)

27. A method for structuring layers of oxidisable materials, in which at least one layer, disposed on a substrate, of an oxidisable material is subjected to local oxidation with at least one oxidation step, in which at least one selected region of the layer of oxidisable material is oxidised so that the layer, after the last oxidation step, is subdivided into regions, which are electrically insulated from each other, by at least one oxidising region extending over the entire layer thickness, wherein oxidation of the layer is effected utilizing an oxidising medium and also a metering device for metering the oxidising medium, the oxidising medium being in contact, during oxidation, both with the metering device and with the layer, and an electrical voltage of 1-100 V being applied between the metering device and the layer, by means of which a current flow through the oxidising medium results.

28. The method according to claim 27, wherein the oxidised region, which is produced after the last oxidation step, has an oxidised layer of oxidisable material or consists thereof.

29. The method according to claim 27, wherein the layer is oxidised such that the width of the at least one oxidised region has a width of 100 m.

30. The method according to claim 27, wherein the applied electrical voltage and hence the current which flows through the oxidising medium is pulsed.

31. The method according to claim 27, wherein the oxidising medium is a conductive liquid medium.

32. The method according to claim 27, wherein a stamp is utilized as metering device.

33. The method according to claim 27, wherein a stamp is utilized as metering device and wherein the surface of the stamp has webs a) made of a chemically inert, conductive material, the stamp being immersed firstly in the oxidising medium, so that the webs are made wet with the oxidising medium and subsequently the stamp is contacted with the layer via the oxidising medium wetting the webs; or b) made of a chemically stable, non-conductive, open-cell sponge, the stamp being immersed firstly in the oxidising medium, so that the webs suction up the oxidising medium, and subsequently the stamp is contacted with the layer; or c) as seals which are resistant to the oxidising medium, the oxidising medium being applied firstly on the layer before oxidation and the stamp being contacted subsequently with the layer so that the seals which are resistant to the oxidising medium displace the oxidising medium from regions of the layer which are not to be oxidized; or d) as seals which are resistant to the oxidising medium, the stamp being contacted firstly with the layer before oxidation and the oxidising medium being applied subsequently on regions of the layer to be oxidised through channels disposed inside the stamp.

34. The method according to claim 27, wherein the metering device is a conductive nozzle, through the nozzle head of which the oxidising medium can emerge continuously, the conductive nozzle being guided over the surface of the layer during oxidation.

35. The method according to claim 27, wherein, after the last oxidation step, the at least two regions of the layer, which are electrically insulated from each other, are coated galvanically or chemically with at least one further metal and/or the at least one oxidised region of the layer is detached at least partially.

36. The method according to claim 27, wherein, between two of the oxidation steps, the non-oxidised regions of the layer are coated galvanically or chemically with at least one further metal and the at least one oxidised region of the layer is detached at least partially.

37. The method according to claim 27, wherein the method is selected from the group consisting of instantaneous printing methods, relief printing methods, gravure methods, flatbed methods, porous printing methods and screen printing methods.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The present invention is explained in more detail with reference to the subsequent Figures and also examples without restricting the invention to the specific embodiments shown here.

[0052] FIG. 1 shows a schematic illustration of a meandering aluminium oxide layer which divides the aluminium layer electrically into two regions.

[0053] FIG. 2a shows the variant of the method according to the invention in which a stamp with webs made of a chemically inert, conductive material is used. A cross-section of the stamp and of the substrate is thereby shown before and during the oxidation process. In FIG. 2b, the variant of the method according to the invention is shown, in which a stamp with webs made of a chemically stable, non-conductive sponge or felt is used. A cross-section of the stamp and of the substrate is thereby shown before and during the oxidation process.

[0054] FIG. 3a shows the variant of the method according to the invention during which a stamp with webs as seals which are resistant to the oxidising medium is used and the oxidising medium is firstly applied on the layer of oxidisable material before oxidation. A cross-section of the stamp and of the substrate is thereby shown before and during the oxidation process. In FIG. 3b, the variant of the method according to the invention is shown, in which a stamp with webs as seals which are resistant to the oxidising medium is used and the oxidising medium is applied on regions of the layer of oxidisable material to be oxidised through channels disposed inside the stamp. A cross-section of the stamp and of the substrate is thereby shown before and during the oxidation process. In FIG. 3c, the variant of the method according to the method is shown, in which a conductive nozzle is used, through the nozzle head of which the oxidising medium can emerge continuously. A cross-section of the nozzle and of the substrate is thereby shown during the oxidation process.

[0055] FIG. 4 shows a scanning electron micrograph of the microtome section of an aluminium layer on a silicon wafer, which layer is completely oxidised through by means of electrochemical oxidation. Here, the typical pore structure of the anodically produced aluminium oxide layer is readily visible.

[0056] FIG. 5 shows the substrate after complete oxidation. The oxidised region (viewed on the microtome section) is substantially wider at the surface than at the interface to the substrate. The width of the oxidised region therefore decreases towards the substrate. The decrease in width is up to 20%.

[0057] FIG. 6 likewise shows the substrate after complete oxidation, the oxidised region however having been detached thereafter. It can be seen clearly here that the oxidised aluminium which is situated still on the aluminium layer remains adhering.

[0058] FIG. 7 shows a variant of the method according to the invention in which the method is a screen printing method. The electrochemical processing with electrical contacting of an electrically conductive screen is illustrated. In this embodiment, the metering device (doctor blade) can in addition be contacted electrically.

[0059] FIG. 8 shows a variant of the method according to the invention, in which the method is a screen printing method. The electrochemical processing with electrical contacting of the metering device (doctor blade) is illustrated.

[0060] In this embodiment, also the screen can be contacted electrically in the case of using an electrically conductive screen.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments

[0061] A preferred application of the invention is the structuring of metal layers which are used for contacting solar cells. Aluminium is here the material of most interest because of its advantageous optical and electrical properties, besides titanium. Likewise, electrolytically produced aluminium oxide layers have properties such as transparency and insulation capacity which can be of interest for solar cell processes. Because of the structure thereof, in addition simple possibilities exist for specifically changing these properties.

[0062] In one application example, a 0.5 m thick aluminium layer was deposited by means of PVD on a solar cell with n.sup.++pp.sup.+ doping structure of the silicon wafer on both sides over the entire surface. On the light-collecting n.sup.++ side of the solar cell, sulphuric acid was subsequently applied as oxidising medium. A structured stamp consisting of EPDM material was subsequently pressed at a defined pressure into the regions provided for contact fingers and collector buses. By applying a voltage of 20 V, the regions not provided for metallisation could be oxidised completely within a few seconds. The then optically transparent aluminium oxide could be removed subsequently by applying a flow of compressed air against the edge. In a subsequent zincate process, both n.sup.++ and p.sup.+ side of the solar cell could be prepared for the subsequent galvanisation with nickel, copper and silver.

[0063] In a further application example, a 1 m thick aluminium layer was deposited over the entire surface on the structured diffused n.sup.+ and p.sup.+ regions of a back-contact solar cell by means of PVD. The task exists here in the electrical separation of the p and n doped regions.

[0064] In a first test relating to this application example, the p.sup.+ and n.sup.+ regions (cf. Ill. 1), disposed in a meandering shape, were separated from each other electrically by means of a stainless steel stamp (cf. Ill. 2a) with sulphuric acid within a few seconds (the measured electrical resistance between the aluminium regions was 60 kOhm). Both regions were subsequently prepared with a zincate process for the subsequent galvanic thickening with nickel, copper and tin.

[0065] In a second test relating to this application example, the p.sup.+ and n.sup.+ regions were disposed in the form of interrupted lines over the solar cell. These lines are intended to be connected via a wire electrode, are very thin and correspondingly can be contacted with difficulty under plant engineering aspects. In a first step, comparable to application example 1, a stamp with EPDM material structures which correspond to the appearance of fingers, was pressed onto the aluminium layer after wetting with sulphuric acid. By applying a voltage, the 1 m thick aluminium layer was firstly oxidised only on the upper approx. 300 nm. A subsequent zincate process was then effected, despite complete immersion of the wafer, selectively only on the regions protected by the stamp. A galvanic deposition of nickel, copper and silver was possible over the full surface on all finger structures since a current supply and -distribution was assisted by the still unreacted aluminium layer. Subsequently, the remaining layer could be completely oxidised without using masking. The silver layer of the contacts thereby protected the finger regions from oxidation. Separation of the n.sup.+ and p.sup.+ regions was effected in this second oxidation step.