HK1113565A - Printable medium for the etching of silicon dioxide and silicon nitride layers - Google Patents

Description

Printable medium for etching of silicon dioxide and silicon nitride layers

The present invention relates to novel printable etching media with non-newtonian flow behavior for surface etching in the production of solar cells, and to the use thereof.

The invention furthermore relates to etching and doping media which are suitable both for etching inorganic layers and for doping underlying layers.

In particular, these are corresponding particle-containing compositions by means of which particularly fine structures can be etched highly selectively without damaging or attacking adjacent regions.

The problem of structuring the oxide layer on the support material arises, for example, in the production of solar cells. Crystalline silicon dioxide solar cells are typically composed of a p-conductive substrate into which a layer of an n-conductive substance, such as phosphorus, is diffused to a uniform thickness on the front side. Metal conductive contacts are applied to the front and reverse sides of the chip to conduct the current generated upon incidence of light. With regard to inexpensive production processes suitable for mass production, the contacts are typically produced by screen printing.

In addition to the oxide layer which has to be structured during the production of the solar cell, the silicon nitride layer has to be etched. In order to etch the corresponding nitride layer, the method used must be modified and the etching paste adapted in a suitable manner.

1. Prior art and objects of the invention

The surface of the crystalline silicon solar cell is coated with a thin inorganic layer during the production process, and optionally also after its end. The thickness of these layers is 20-200nm, in most cases 50-150 nm.

During the production process of crystalline silicon dioxide solar cells, it is therefore advantageous in many process steps to etch fine lines into these inorganic layers of the solar cell.

These openings in the surface of the solar cell can be used, for example, to produce so-called selective emitters, also referred to as 2-stage emitters. For this purpose, a high n-doping level is produced in the subsequent diffusion step in the partial opening of the diffusion barrier situated on the silicon, preferably by diffusion into phosphorus.

In the present specification, the inorganic surface means a silicon compound containing an oxide and a nitride, particularly a silicon oxide and a silicon nitride surface. The mode of action of such diffusion barriers is known to the person skilled in the art and is described in the literature [ a.goetzberger; b, vo beta; knobloch, sonnenergie: photovoltaik, Teubner Studienbuecher Stuttgart1997, pp 40; 107]. These diffusion barriers can be produced in various ways:

a very dense silicon dioxide layer, for example, is obtained by thermal treatment of silicon at a temperature in the range of 900 deg.c in an oxygen-containing atmosphere (thermal oxide).

Also known to those skilled in the art is the deposition of silicon dioxide by a CVD process. Depending on the way in which the reaction is carried out, a distinction is made here in particular between the following processes:

APVCD (atmospheric pressure CVD)

PE-CVD (plasma enhanced CVD)

LP-CVD (Low pressure CVD)

A common feature of these processes is the evolution of a gas phase from a volatile precursor, for example Silane (SiH) in the case of silicon dioxide₄) Or TEOS (tetraethyl orthosilicate), the desired inorganic compound being obtained from the deposition and decomposition of the precursor on the target substrate.

The diffusion barrier-forming silicon dioxide layer can also be obtained by wet chemical coating with a liquid or dissolved solid precursor in a solvent or solvent mixture. These liquid systems are usually applied to the substrate to be coated by application. These systems are known to those skilled in the art as spin-on glass (SOG).

In many cases, SiO is applied₂The layer also remains as a passivation layer that reduces reflection. This is for thermally grown SiO₂This is particularly often the case.

Silicon nitride layers are less useful as diffusion barriers in the field of crystalline solar cells, although they are in principle also suitable for this purpose. The silicon nitride layer is mainly used as a passivation and anti-reflection layer.

It is also advantageous in the production of crystalline silicon solar cells to be able to produce openings in the silicon nitride layer in a targeted manner. An example which may be mentioned here is the application of a conductive paste. These metal pastes are typically "fired through" the silicon nitride layer at temperatures in the 600 ℃ region to facilitate electrical contact to the emitter layer. Due to the high temperatures, polymer-based (epoxy or phenolic) metallization pastes cannot be used. Crystal defects and metal contamination in the underlying silicon also result from "burn through process". Due to this system, the passivation layer is additionally completely destroyed by the printed metal paste of the upper side. A narrower opening of the part of the silicon nitride layer for the electrical contact is more advantageous, leaving a passivation layer in the edge region, which is covered by the overlying metallization layer.

In addition to pure diffusion barriers composed of silicon dioxide or silicon nitride, thin glass layers can also be used in the production of crystalline silicon solar cells.

Definition of glass:

glass itself denotes homogeneous materials, such as quartz, window glass, borosilicate glass, and also thin layers of these materials produced by various methods known to the person skilled in the art (in particular CVD, PVD, spin-on, thermal oxidation) on other substrates (e.g. ceramics, metal sheets, silicon wafers).

The following glasses represent materials containing silicon oxide and silicon nitride, which are in a solid amorphous physical state without crystallization of the glass component and with a high degree of structural disorder in the microstructure due to the lack of long range order.

Remove pure SiO₂All glasses (e.g. doped glasses such as borosilicate, phosphosilicate, borophosphosilicate glass, tinted, opalescent and crystalline glasses, optical glasses) comprising, in addition to glass (quartz), the following: SiO 2₂And other components, in particular elements such as calcium, sodium, aluminium, lead, lithium, magnesium, barium, potassium, boron, beryllium, phosphorus, gallium, arsenic, antimony, lanthanum, zinc, thorium, copper, chromium, manganese, iron, cobalt, nickel, molybdenum, vanadium, titanium, gold, platinum, palladium, silver, cerium, caesium, niobium, tantalum, zirconium, yttrium, neodymium, praseodymium, which are present in the glass in the form of oxides, carbonates, nitrates, phosphates, sulphates and/or halides or are used as doping elements in the glass. Doped glasses are, for example, borosilicate, phosphosilicate, borophosphosilicate, colored, opal and crystalline glasses and optical glasses.

The silicon nitride may likewise include other elements such as boron, aluminum, gallium, indium, phosphorus, arsenic, or antimony.

Definition of silicon oxide and silicon nitride based systems:

the silicon oxide-based system is defined below as not belonging to the amorphous SiO given above₂Definition of glass and all crystalline systems based on silica; these may be, in particular, salts and esters of orthosilicic acid and condensation products thereof-generally known by the person skilled in the art as silicates-as well as quartz and glass-ceramics.

Furthermore, other silicon oxide and silicon nitride based systems are included, in particular salts and esters of orthosilicic acid and condensation products thereof. Remove pure SiO₂(Quartz, tridymite, cristobalite) and all SiO materials constructed from₂Class system: SiO 2₂Or "discrete" and/or linked [ SiO ]₄]Tetrahedra, such as mesosilicates, sorosilicates, cyclic silicates, inosilicates, phyllosilicates, tectosilicates, and other components, in particular elements/components, such as calcium, sodium, aluminum, lithium, magnesium, barium, potassium, beryllium, scandium, manganese, iron, titanium, zirconium, zinc, cerium, yttrium, oxygen, hydroxyl, halides.

Silicon nitride based systems are defined below as all crystalline and partially crystalline (often referred to as microcrystalline) systems that do not fall within the definition given above for amorphous silicon nitride glasses/layers. These include the alpha-Si thereof₃N₄And beta-Si₃N₄Form Si₃N₄And all crystalline and partially crystalline SiN_xAnd SiN_xAn H layer. The crystalline silicon nitride may include other elements such as boron, aluminum, gallium, indium, phosphorus, arsenic, and antimony.

Etching of structures

The use of etchants, i.e., chemically aggressive compounds, results in the dissolution of materials exposed to attack by the etchant. In most cases, the goal is to completely remove the layer to be etched. The end of the etch is reached by encountering a layer that is substantially resistant to the etchant. Furthermore, by etching to a generally defined target thickness, there are processes known to the person skilled in the art for partially removing the layer.

Etching of structures on silicon oxide and silicon nitride based glasses and other silicon oxide and silicon nitride based systems:

according to the state of the art, any desired structure can be selectively etched in the silicon oxide and silicon nitride based glass and other silicon oxide and silicon nitride based systems or their variable thickness surfaces and layers directly by laser supported Etching Methods, or after masking, by wet chemical Methods ([1] D.J.Monk, D.S.Soane, R.T.Howe, Thin Solid Films 232(1993), 1; [2] J.Buehler, F.P.Steiner, H.Battes, J.Micromech.Microeng.7(1997), R1) or by dry Etching Methods ([3] M.Koehler "Aetzverfan hrfuer diIkrotechnik" [ Etching Methods of Microtechnology ], Wiley VCH 1983).

In laser-supported etching methods, the laser beam scans the entire etching pattern on the glass point by point or line by line in the case of a vector-oriented system, which, in addition to a high degree of accuracy, also requires considerable adjustment effort and time.

Wet chemical and dry etching methods involve material intensive, time consuming and expensive process steps.

A. Masking areas that are not to be etched, for example, by:

● lithography: creation of positive or negative (resist-dependent) etched structures, coating of substrate surfaces (e.g. by spin-coating with liquid photoresist), drying of the photoresist, exposure of the coated substrate surface, development, washing, optionally drying

B. The structure is etched as follows:

● dipping method (e.g. wet etching in wet chemical benches): immersing the substrate in an etching bath, etching, in H₂Repeatedly cleaning in O cascade tank, and drying

● spin coating or spray method: the etching solution is applied to the rotating substrate and the etching operation can be carried out without/with input of energy (e.g. IR or UV radiation), followed by rinsing and drying

● Dry etching methods, e.g. plasma etching in expensive vacuum units or etching with reactive gases in flow reactors

C. Removing the photoresist:

in the final process step, the photoresist covering the protected area of the substrate must be removed. This can be done by a solvent, such as acetone, or dilute aqueous alkaline solutions. The substrate was finely cleaned and dried.

Full area etching of silicon oxide and silicon nitride based glasses and other silicon oxide and silicon nitride based systems:

for etching silicon oxide and silicon nitride based glasses and other silicon oxide and silicon nitride based systems and their variable thickness layers in the whole area, wet etching methods are mainly used. Silicon oxide and silicon nitride based glasses and other silicon oxide and silicon nitride based systems and layers of variable thickness thereof are immersed in an etching bath, which usually contains additives of toxic and highly caustic hydrofluoric acid and optionally other inorganic acids.

The disadvantages of the etching methods are the time-consuming material-intensive and expensive process steps, which are in some cases complicated in terms of technology and safety and are usually carried out discontinuously.

International application WO01/83391A describes methods for etching inorganic, glassy, amorphous or crystalline surfaces, in particular glass or ceramics, preferably SiO₂Or silicon nitride based systems, in the form of printable, uniform, particle-free etching pastes having non-Newtonian flow behaviour, and the use of these etching media. The use of these particle-free media, especially in surface printing, causes problems due to insufficient resilience of the printed lines, dots or structures (insufficient structure fidelity), meaning that a significant widening of the initial printed lines (bleeding of the etching substances onto the substrate) occurs.

US5688366A uses a particle-containing etching paste for etching a transparent conductive layer (e.g. ITO). The etching paste used was prepared from molten ferric chloride containing water of crystallization, glycerol and polymer particles. These compositions are suitable for etching lines having a width of about 1 mm. Tests have shown that these etching pastes are not suitable for etching very fine lines with a width of less than 1mm clearly and without cracks, irrespective of whether polymer particles with a diameter of 0.01 μm or 30 μm are used for the preparation of the paste.

Purpose(s) to

The object of the present invention is therefore to provide novel, inexpensive etching pastes for etching very uniform, fine lines of widths of less than 100 μm, in particular less than 80 μm, and fine structures on silicon dioxide and/or silicon nitride layers, which layers are located on silicon solar cells. It is a further object of the present invention to provide novel etching media which can be removed from the treated surface after etching in a simple manner under the action of heat without leaving residues.

2. Description of the invention

Recent experiments now show that, in contrast to previous experience, the printability of an etching paste can be advantageously improved if suitably selected polymer particles are added. In this respect, polymer particles which form a network in the prepared paste by physical interaction and/or chemical reaction with the other components of the medium, while causing an increase in the viscosity of the composition, prove particularly suitable. Quite unexpectedly, the added particles also caused an improvement in the printability of the media.

If the addition of the particulate component is chosen appropriately, the addition of the thickener, which is generally homogeneously distributed in the known particle-free pastes, can even be omitted entirely.

The object of the present application is thus achieved by providing a novel printable etching medium having a non-newtonian flow behaviour, in the form of an etching paste for etching inorganic glassy or crystalline surfaces selected from silicon oxide-based glasses and silicon nitride-based glasses, comprising polymer particles consisting of a material selected from the group consisting of: polystyrene, polyacrylic, polyamide, polyimide, polymethacrylate, melamine, urethane, benzoguanine, phenolic resins, silicone resins, fluorinated polymers (in particular PTFE, PVDF) and micronized waxes. The etching medium according to the invention is effective even at temperatures of 15 to 50 ℃ or can optionally be activated by input of energy. Preferred forms of the paste according to the invention and their use are from claims 2 to 18. The invention further relates to a method for etching and optionally simultaneously doping an inorganic glassy crystalline surface according to claims 29 and 33. Claim 28 relates to a specific embodiment of the use of the etching paste according to the invention.

3. Detailed Description

According to the invention, novel etching pastes having thixotropic non-Newtonian behaviour are used for structuring silicon dioxide or silicon nitride layers in a suitable manner during the process for producing photovoltaic, semiconductor technology, high-performance electronics, solar cells or photodiode products. For this purpose, the paste is printed in a single process step onto the surface to be etched and removed again after a predefined reaction time. In this way, the surface is etched and structured in the printed areas, while the unprinted areas remain in the original state.

The surface to be etched may here be the surface or part of the surface of glass of the silicon oxide or silicon nitride type and other silicon oxide and silicon nitride type systems and/or the surface or part of the surface of porous and non-porous layers of glass and other silicon oxide and silicon nitride type systems on a carrier material.

Suitable processes with a high degree of automation and with a high throughput employ printing techniques to transfer the etching paste to the substrate surface to be etched. In particular, screen, pad, printing, inkjet printing processes are printing processes known to the person skilled in the art. Manual application is likewise possible.

Depending on the screen, plate or printed design or cartridge addressing, a printable uniform particle-free etching paste with non-newtonian flow behaviour according to the invention can be applied over the whole area or selectively according to the etching structure pattern in the areas where etching is required. All masking and photolithography steps that are otherwise necessary are therefore superfluous. The etching operation may be carried out with or without energy input, for example in the form of thermal radiation (using IR lamps).

The actual etching process is then completed by washing the surface with water and/or a suitable solvent. More precisely, the printable, polymer particle-containing etching paste with non-newtonian flow behaviour is washed off the etched areas after the etching is completed using a suitable solvent.

The use of the etching pastes according to the invention thus enables the inexpensive etching of long runs (run) in a suitable automated process on an industrial scale.

In a preferred embodiment, the viscosity of the etching paste according to the invention is in the range from 10 to 500Pa.s, preferably in the range from 50 to 200 Pa.s. Viscosity is a material-dependent component of frictional resistance that opposes movement when adjacent liquid layers are displaced. According to newton, the shear resistance in a liquid layer between two sliding surfaces arranged in parallel and moving relative to each other is proportional to the velocity or shear gradient G. The scaling factor is a material constant known as dynamic viscosity and is in mPa · s dimension. In newtonian liquids, the scale factor depends on pressure and temperature. The degree of dependence is here determined by the material composition. Liquids or substances with a non-uniform composition have non-newtonian properties. The viscosity of these materials is additionally dependent on the shear gradient.

For the etching of structures with line widths of <100 μm from printed etching media, it has now been found to be particularly advantageous to use finely divided granular systems instead of particle-free etching pastes for thickening comprising homogeneously distributed polymers (of the type described in WO01/83391A), for completely or partially thickening the etching media. Particularly suitable for this purpose are polymer particles which interact with other components of the composition and form a network at the molecular level by chemical bonds or purely physical interactions. The relative particle size of these systems may be from 10nm to 30 μm. Corresponding polymer particles having a relative particle diameter of from 1 to 10 μm have proven particularly advantageous. Particles particularly suitable for the purposes according to the invention may consist of:

-polystyrene

Polyacrylic acid compound

Polyamides (I)

Polyethylene (E)

-ethylene-vinyl acetate copolymer

-ethylene-acrylic acid-acrylate terpolymer

-ethylene-acrylate-maleic anhydride terpolymer

-polypropylene

-a polyimide,

-polymethacrylates

-melamine, urethane, benzoguanine, phenolic resins

-silicone resins

-fluorinated polymers (PTFE, PVDF), and

-micronizing the wax.

The use of very finely divided polyethylene powders, for example those currently sold by DuPont Polymer powders Switzerland under the trade name COATHYLENE HX ® 1681, the relative particle size d of which has proven particularly suitable in tests₅₀The value was 10 μm.

These particulate thickeners may be added to the etching medium in an amount of from 1 to 50% by weight, advantageously from 10 to 50% by weight, in particular from 25 to 35% by weight.

Also suitable in principle are particulate polymer thickeners based on:

-polystyrene

Polyacrylic acid compound

Polyamides (I)

-a polyimide,

-polymethacrylates

-melamine, urethane, benzoguanine, phenolic resins

-silicone.

The addition of the granular thickener according to the invention enables the following improvements to be achieved compared to the particle-free etching media described in WO 01/83391A:

I. the granular thickening results in improved resilience of the etching medium. The particles form a skeletal structure in the etching medium. With highly disperse silicic acids (e.g. Aerosil)^®) Similar structures are known to those skilled in the art. In particular in the screen printing of etching pastes, can be substantially prevented by the inventionThe widening of the printed structure due to flow is stopped or at least greatly limited. The area printed and thus covered by the paste thus corresponds substantially to the area specified in the wire mesh arrangement. Many inorganic particles, such as silicic acid or modified silicic acid, cannot be used to thicken the etching medium due to their reactivity with the etching components employed. For example, silicic acid and NH₄HF₂A chemical reaction takes place provided that the latter acts as an etching component.

Further by means of granular thickening, lines of larger print height and retained width are printed when using the same screen or mask than when using a corresponding particle-free paste as described in, for example, WO01/83391 a. This simultaneously results in a greater application rate of the etching component per unit area. This is particularly advantageous for a complete etch if a relatively thick silicon dioxide or silicon nitride layer (> 100nm) is to be etched.

The more pronounced non-newtonian or thixotropic behaviour of the etching pastes has a particularly advantageous effect on screen printing and leads to considerably improved results. This is evident, in particular, for the same etching time in a shortened etching time or an increased etching rate and, in particular, in the case of relatively thick layers, in a greater etching depth.

The thickening associated with the addition of the polymer particles according to the invention leads to a considerably lower binding capacity of the etching paste. If the added particles are chosen specifically, an increased etching rate and thus a considerably increased etching depth are surprisingly achieved for the same amount of added etching component.

V. the significantly larger print height achieved under the same printing conditions, i.e. when using the same screen and the same printing parameters, additionally causes a significantly delayed drying of the printed etching species. This enables the etching substance to act on the substrate for a longer time. It is particularly important at high temperatures in the case of accelerated etching. Furthermore, material remaining after the etching process can be significantly removed more easily in the final cleaning process.

The significant improvement in the present composition is obtained in particular by a considerably improved screen printing behaviour, enabling the continuous printing of the surface to be treated without interruptions. The use of the etching pastes according to the invention enables a considerably finer etched structure to be achieved, since the same amount of thickener added in the presence of the polymer particles has a greater viscosity. This enables the paste to be applied with a higher paste layer in the printing and thus etching the layer deeper. The improved cleaning behavior (wafer cleaning) after etching also shortens the time required for subsequent cleaning.

Surprisingly, tests have shown that the addition of corresponding fine polymer particles also has a favourable effect in a selective etching process of inorganic surfaces for producing selective emitter surfaces in solar cells, wherein in addition to etching also for n is required⁺⁺The specific phosphorus doping of the production of the region. Corresponding etching and doping pastes are described, for example, in WO03/034504A 1. In contrast to pure etching pastes, these pastes, after application to the wafer surface to be etched, are heated, depending on the particles present in the paste, over the entire surface or locally to a temperature of 250-350 ℃ for 20-130 seconds and optionally for a further n-⁺⁺Doping, heating to a temperature of > 800 ℃, in particular to a temperature of 800-. The temperature chosen is of course set in such a way that the variation of the particles present in the paste does not cause any disadvantages.

The corresponding etching medium may comprise phosphoric acid in various forms or a suitable phosphate or a compound which decomposes into the corresponding phosphoric acid upon heating, as etching component and as doping component.

It has been found that orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid and salts thereof and in particular ammonium salts ((NH) here₄)₂HPO₄，NH₄H₂PO₄，(NH₄)₃PO₄) And other compounds which form one of these compounds upon thermal decomposition are capable of completely etching away a silicon nitride layer with a thickness of 70mm at a temperature of more than 250 c within a few seconds to a few minutes. The etching time was about 60 seconds at 300 ℃.

To prepare the particle-containing medium according to the invention, the solvent, etching component, thickener, particles and additives are continuously mixed with one another and stirred for a sufficient time until a viscous paste having thixotropic properties is formed. Stirring may be carried out by raising the temperature to an appropriate temperature. The components are generally stirred with one another at room temperature.

The preferred use of the printable etching pastes according to the invention occurs in the described method for structuring the oxide layer applied to the carrier material, to produce solar cells containing a selective emitter layer on the light incidence side and a back side containing a bottom surface field.

To apply the paste to the area to be treated, the paste may be etched by fine-mesh screen printing, the screen containing a printing stencil (or etched wire screen). In a further step, the paste may be fired by a thick layer method in a screen printing process (screen printing of a conductive metal paste) so that the electrical and mechanical properties can be fixed. In the use of the etching pastes according to the invention, the firing (burning through the dielectric layer) can instead also be omitted and the applied etching paste can be washed off with a suitable solvent or solvent mixture after a certain reaction time. The etching action is stopped by washing away.

Particularly suitable printing methods are essentially screen printing with screen spaces or stencil printing without spaces. In screen printing, the spacing a of the screen is typically several hundred μm and the angle of inclination between the edge of the rubber roller and the screen is α, the rubber roller pushing the etching printing paste on the screen. The screen is held by the screen frame while the rubber roll passes over the screen at a rubber roll speed v and a rubber roll pressure P. In the process, the etching paste is pushed over the screen. During this operation, the screen is in contact with the substrate in the form of a wire within the width of the rubber roll. Contact between the screen and the substrate transfers a quantity of screen etching paste located in the free screen openings to the substrate. In the areas covered by the screen holes, the screen printing paste is not transferred to the substrate. This enables the screen printing paste to be transferred in a targeted manner to a certain area of the substrate.

After the end of the movement E, the rubber roller is lifted from the screen. The screen is uniformly tensioned using a screen stretcher using a hydraulic/pneumatic stretching and clamping device. The screen tension was monitored in certain areas by a determined hang of the screen at certain weights using a dial gauge. With a specific pneumatic/hydraulic press, the rubber roller pressure (P), the printing speed (V), the non-contact distance (a) and the rubber roller path (horizontal and vertical, rubber roller angle) can be set with various degrees of automation of the processing steps of the test and production runs.

Printing screens used herein are typically composed of plastic or steel-wire cloth. Depending on the desired layer thickness and wire width, one skilled in the art can select cloths with different wire diameters and mesh widths. These cloths are structured directly or indirectly using a photosensitive material (emulsion layer). For the printing of particularly fine lines and in the case of the necessary high precision of continuous prints, metal stencils can advantageously be used which likewise directly or indirectly provide the apertured or line structure.

For etching, an etching paste as described, for example, in example 1 was prepared. Using an etching paste of this type, it is possible to selectively remove thermal SiO with a thickness of approximately 100nm at 50 ℃ in 60 seconds after screen printing₂. The etching is then terminated by immersing the Si wafer in water and then rinsing with a fine water shower.

To produce a solar cell, for example, a wafer comprising p-doped Pz silicon with a <100> orientation is selected. Wherein a short basic etch can create structures on the surface that improve the light incidence geometry to reduce reflections. A thin dopant coating film comprising a boron-containing compound may be spin coated onto the backside and dried. The wafers prepared in this manner were placed in trays and introduced into an oven preheated to 1000-. An oxygen atmosphere is established in the oven such that an oxide layer forms directly on all wafer surfaces not covered by the boron dopant coating film. At the same time, boron is expelled from the dopant coating film and diffuses into the backside of the wafer. A p + doped region is formed to a depth of about 1-5 μm. This embodiment of the solar cell is known to the person skilled in the art under the term "bottom surface field". The oxide layer formed on the front side can now be structured using the above-described etching pastes.

For example, these oxide layers may be formed as a mask for high n + -phosphorous doping to form a selective emitter layer while targeting significantly less n + -doping in the masked areas.

After the pn junction is opened, the pn junction can cause a short circuit in the solar cell, for example by plasma etching or opening using a laser beam, applying electrical contacts to the front and back sides of the cell. This can be done by two successive screen printing steps using a paste comprising conductive silver particles and/or aluminium in addition to a binder and an oxide additive. After printing, the printed contacts were fired at approximately 700 and 800 ℃.

This description will enable one skilled in the art to make and use the invention. If anything is unclear, it is of course the publications and patent documents cited should be used. Accordingly, these documents are considered to be part of the disclosure of the present specification.

4. Examples of the embodiments

For a better understanding and description of the present invention, the following examples are given, all falling within the scope of the present invention. These examples are also intended to illustrate possible variations. However, the embodiments are not suitable for reducing the scope of the present application to these alone due to the general effectiveness of the inventive principles described.

The temperatures given in the examples are always in degrees Celsius. It goes without saying that the sum of the components in the composition always amounts to 100% of the total in the description and in the examples.

Example 1

Etching paste consisting of homogeneous and granular thickeners

Into a solvent mixture consisting of

15g ethylene glycol monobutyl ether

15g of triethylene glycol monomethyl ether

29g polycarbonate

Continuously adding the mixture under stirring

72g of formic acid (100%) and

46g of ammonium hydrogen difluoride solution 35%.

Then the

46g of polyvinylpyrrolidone (PVP) K-120 were slowly added in portions to the solution with vigorous stirring, and the mixture was further stirred for 30 minutes. The clear paste pre-thickened with a homogeneous thickener (PVP) was then mixed with 60g of Vestosint 2070 and the mixture was stirred for a further 2 hours.

The paste now ready for use can be screen printed using a 280 mesh stainless steel cloth. In principle, polyester or similar screen materials may also be used.

Example 2

Etching paste consisting of a granular thickener

Into a solvent mixture consisting of

From 15g of ethylene glycol monobutyl ether

15g of triethylene glycol monomethyl ether

29g polycarbonate

Continuously adding the mixture under stirring

72g of formic acid (100%) and

46g of ammonium hydrogen difluoride solution 35%.

The clear homogeneous mixture is then mixed with 100g of Vestosint 2070 and the mixture is stirred for a further 2 hours.

The paste now ready for use can be screen printed using a 280 mesh stainless steel cloth. In principle, polyester or similar screen materials may also be used.

The etching pastes prepared proved to be storage-stable over a long period of time and to retain the advantageous etching properties.

Further examples of compositions according to the invention with advantageous properties are given in the following table:

further examples of compositions according to the invention with advantageous properties for etching SiNx are given in the table below:

comparative example: etching paste without particulate additives

For the comparative experiments, the following pressures and etching parameters were used:

silk screen:	steel wire mesh with 280 meshes/inch mesh count, 25 μm filament diameter and 15 μm emulsion thickness
		Arranging:	100 μm line
Screen printing machine:	EKRA E1
		wafer:	monocrystalline silicon wafer having thermal SiO of 100nm2
Etching:	heating at 50 deg.C for 30s

Results: line width after etching and cleaning: average about 180 μm

Comparative example: etching paste with particulate additive

For the comparative experiments, the following pressures and etching parameters were used:

silk screen:	steel wire mesh with 280 meshes/inch mesh count, 25 μm filament diameter and 15 μm emulsion thickness
		Arranging:	100 μm line
Screen printing machine:	EKRA E1
		wafer:	monocrystalline silicon wafer having thermal SiO of 100nm2
Etching:	heating at 50 deg.C for 30s

Results: the width of the etched lines was about 105 μm on average.

Claims (33)

1. Printable etching medium in the form of a paste for etching and optionally doping an inorganic glassy or crystalline layer selected from the group consisting of silica-based glasses and silicon nitride-based glasses, the layer being located on a crystalline or amorphous silicon surface, the medium comprising

a) Etching component

b) Solvent(s)

c) A polymer and/or an inorganic particle,

d) optionally homogeneously dissolved organic thickeners

e) Optionally at least one inorganic and/or organic acid, and optionally

f) Additives, such as antifoams, thixotropic agents, flow control agents, degassing agents, adhesion promoters.

2. Printable etching medium according to claim 1, characterized in that polymer particles with a relative particle size of 10nm to 50 μm, preferably 100nm to 30 μm and very particularly preferably 1 μm to 10 μm are added.

3. The printable etching medium according to claim 1, characterized in that it comprises polymer particles in an amount of 1 to 80 wt.%, based on the total amount.

4. The printable etching medium according to claim 1, characterized in that it comprises polymer particles in an amount of 10 to 50 wt.%, in particular 20 to 40 wt.%, based on the total amount.

5. Printable etching medium according to claim 1, characterized in that the etching component is present in an amount of 12 to 30 wt.%, preferably 2 to 20 wt.% and particularly preferably 5 to 15 wt.%, based on the total amount.

6. The printable etching medium according to claim 1, characterized in that the thickener is present in an amount of 3 to 20 wt.%, based on the total amount.

7. Printable etching medium according to claims 1 to 6, characterized in that it comprises one or different forms of phosphoric acid, phosphates or compounds which decompose upon heating into the corresponding phosphoric acid and act as etching component and as doping component.

8. Printable etching medium according to claims 1 to 7, for glass surfaces, comprising elements selected from the group consisting of: calcium, sodium, aluminum, lead, lithium, magnesium, barium, potassium, boron, beryllium, phosphorus, gallium, arsenic, antimony, lanthanum, scandium, zinc, thorium, copper, chromium, manganese, iron, cobalt, nickel, molybdenum, vanadium, titanium, gold, platinum, palladium, silver, cerium, cesium, niobium, tantalum, zirconium, yttrium, neodymium, and praseodymium.

9. Etching medium according to claims 1 and 5, characterized in that it comprises as etching components:

at least one fluorine compound selected from the group consisting of ammonium, alkali metal and antimony fluorides, ammonium, alkali metal and calcium bifluorides, alkylated ammonium and potassium tetrafluoroborates, and/or optionally

At least one mineral acid selected from hydrochloric acid, phosphoric acid, sulfuric acid and nitric acid, and/or optionally

At least one organic acid selected from alkyl carboxylic acids, hydroxy carboxylic acids and dicarboxylic acids, which may comprise a linear or branched alkyl group containing 1 to 10C atoms.

10. Etching medium according to claim 9, characterized in that it comprises an organic acid selected from the group consisting of formic acid, acetic acid, lactic acid and oxalic acid.

11. Etching medium according to claims 1 to 10, characterized in that the proportion of organic and/or inorganic acids is a concentration of 0 to 80% by weight, based on the total amount of the medium, where the pK of each of the added acids_aThe value is 0 to 5.

12. Etching medium according to claims 1-11, characterized in that it comprises as solvent water, mono-or polyhydric alcohols, such as glycerol, 1, 2-propanediol, 1, 4-butanediol, 1, 3-butanediol, 1, 5-pentanediol, 2-ethyl-1-hexenol, ethylene glycol, diethylene glycol and dipropylene glycol, and their ethers, such as ethylene glycol monobutyl ether, triethylene glycol monomethyl ether, diethylene glycol monobutyl ether and dipropylene glycol monomethyl ether, and esters, such as [2, 2-butoxy (ethoxy) ] ethyl acetate, carbonates, such as propylene carbonate, ketones, such as acetophenone, methyl-2-hexanone, 2-octanone, 4-hydroxy-4-methyl-2-pentanone and 1-methyl-2-pyrrolidone, the solvent is present as such or in a mixture in an amount of from 10 to 90% by weight, preferably in an amount of from 15 to 85% by weight, based on the total amount of medium.

13. Etching medium according to claims 1 to 12, characterized in that it comprises polymer particles as follows: polystyrene, polyacrylic compounds, polyamides, polyimides, polymethacrylates, melamines, urethanes, benzoguanines and phenolics, silicones, micronized cellulose, fluorinated polymers (PTFE, PVDF) and micronized waxes.

14. Etching medium according to claims 1 to 12, characterized in that it comprises inorganic particles as follows: alumina, calcium fluoride, boron oxide and sodium chloride.

15. Etching medium according to claims 1 to 12, characterized in that it comprises one or more of the following homogeneously dissolved thickeners:

cellulose/cellulose derivatives and/or

Starch/starch derivatives and/or

Xanthan gum and/or

Polyvinyl pyrrolidone

Polymers based on acrylates of functionalized vinyl units.

16. Etching medium according to claims 1 to 12, characterized in that it comprises the homogeneously distributed thickener according to claim 15 in an amount of 0.5 to 25% by weight, based on the total amount of etching medium.

17. Etching medium according to claim 1, characterized in that it comprises, on the basis of the total amount, 0 to 5% by weight of additives selected from the group consisting of: antifoams, thixotropic agents, flow control agents, air release agents and adhesion promoters.

18. Etching medium according to claims 1 to 17, characterized in that it is at 20 ℃ for 25s^-1Has a viscosity of 6 to 35 pas, preferably 25s, at a shear rate of^-1Has a viscosity of 10 to 25 pas and very particularly preferably at 25s^-1The viscosity at shear rate of (a) is 15 to 20 pas.

19. Use of an etching medium according to claims 1 to 18 in an etching process, wherein it is applied to the surface to be etched and removed again after a reaction time of 10s to 15min, preferably after 30s to 2 min.

20. Use of the etching media according to claims 1 to 18 in the photovoltaic, semiconductor technology, high-performance electronics, mineralogy or glass industry and for the production of windows for photodiodes, valves or measuring instruments, glass supports for outdoor applications, for the production of etched glass surfaces in the medical, decorative and hygiene sector, etched glass containers for the production of cosmetics, food and beverages, for the production of markings or labels on containers and in the production of flat glass, and for the structuring of glass for flat screen applications.

21. Use of the etching medium according to claims 1 to 18 in non-contact and contact screen, pad, printing, inkjet and manual printing processes.

22. Use of the etching media according to claims 1 to 18 for producing glass supports for solar cells and heat collectors.

23. Use of an etching medium according to claims 1 to 18 for etching SiO-containing₂Or silicon nitride containing glasses are homogeneous single material non-porous and porous solids, or used to etch corresponding non-porous or porous glass layers of varying thickness that have been produced on other substrates.

24. Use of the etching media according to claims 1 to 18 for etching uniform, single-material, non-porous or porous glasses based on silicon dioxide or silicon nitride systems and layers of variable thickness of such systems.

25. Etching medium according to claims 1 to 18 for the removal of silicon dioxide/doped silicon dioxide and silicon nitride layers, for the selective opening of passivation layers comprising silicon dioxide and silicon nitride for the production of dual-stage selective emitters and/or local p⁺Use of a bottom surface field.

26. Use of an etching medium according to claims 1 to 18 for the opening of passivation layers comprising silicon dioxide and silicon nitride in the production process of semiconductor components and their circuits.

27. Use of an etching medium according to claims 1 to 18 for the opening of passivation layers comprising silicon oxide and silicon nitride in the production process of high-performance electronic components.

28. Use of the etching medium according to claims 1 to 18 for mineralogical, geological and microstructural studies.

29. Method for etching inorganic glassy crystalline surfaces, characterized in that an etching medium according to claims 1 to 18 is applied over the entire surface or, in particular, according to an etching structure pattern, only at the points where etching is required, and that after the etching is completed, it is rinsed off with a solvent or a solvent mixture or burnt off by heating.

30. Method according to claim 29, characterized in that the doping is carried out by heating.

31. Method according to claim 29, characterized in that the etching medium is rinsed away with water, preferably after the etching has been completed.

32. Etching method according to claim 29, characterized in that the etching is carried out at an elevated temperature of 30-330 ℃, preferably 40-200 ℃ and very particularly preferably 50-100 ℃.

33. Etching method according to claim 29, characterised in that the SiO etching is carried out at an etching rate of 0.5 to 8nm/s, preferably at an etching rate of 1 to 6nm/s and very particularly preferably at an etching rate of 3 to 4nm/s at an elevated temperature of 50 to 100 ℃₂Or etching of the SiNx layer.