EP2938760A1

EP2938760A1 - Liquid doping media for the local doping of silicon wafers

Info

Publication number: EP2938760A1
Application number: EP13817655.7A
Authority: EP
Inventors: Ingo Koehler; Oliver Doll; Sebastian Barth
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2012-12-28
Filing date: 2013-12-18
Publication date: 2015-11-04
Also published as: WO2014101990A1; JP2016506631A; KR20150103162A; SG10201705326XA; CN104870699A; US20160218185A1; SG11201504934UA; TW201439372A

Abstract

The invention relates to a novel method for producing printable, low-viscous oxide media and to the use thereof in the production of solar cells.

Description

Liquid doping media for the local doping of

silicon wafers

The present invention relates to a novel process for the preparation of printable, low viscosity oxide media, and their use in solar cell manufacturing, as well as the improved lifetime products produced using these novel media.

The production of simple solar cells or of the solar cells currently represented in the market with the largest market share comprises the essential production steps outlined below:

1. saw damage etching and texture

A silicon wafer (monocrystalline, multicrystalline or quasi-monocrystalline, p- or n-type base doping) is freed of adherent saw damage by means of an etching process and "simultaneously", usually in the same etching bath, texturized in this case, the creation of a preferred Surface (texture) as a result of the etching step or simply to understand the targeted, but not particularly oriented roughening of the wafer surface

Surface of the wafer now as a diffuse reflector and thus reduces the directional, weillängenlängen- and the angle of impact dependent reflection, which ultimately leads to an increase in the absorbed portion of the incident light on the surface and thus the

Conversion efficiency of the solar cell increased.

In the case of monocrystalline wafers, the aforementioned etching solutions for treating the silicon wafers typically consist of dilute potassium hydroxide solution to which isopropyl alcohol has been added as solvent. Instead, other alcohols having a higher vapor pressure or higher boiling point than isopropyl alcohol may be added, provided that the desired etching result can be achieved thereby. Typically, the desired etch result is a morphology that is randomly-etched, or rather etched out of the original surface. Pyramids is characterized by square base. The density, the height and thus the base area of the pyramids can be influenced by a suitable choice of the above-mentioned constituents of the etching solution, the etching temperature and the residence time of the wafers in the etching basin.

Typically, the texturing of the monocrystalline wafer in

Temperature range of 70 - <90 ° C performed, with Ätzabträge of up to 10 pm per wafer side can be achieved.

In the case of multicrystalline silicon wafers, the etching solution may consist of potassium hydroxide solution with an average concentration (10-15%). However, this etching technique is hardly used in industrial practice. More often becomes one

Etching solution consisting of nitric acid, hydrofluoric acid and water used. This etching solution can be modified by various additives such as sulfuric acid, phosphoric acid, acetic acid, N-methylpyrrolidone and also surfactants, which u. a. Wetting properties of the etching solution and their etch rate can be specifically influenced. These acid etch mixtures produce a morphology of interstitially arranged etch pits on the surface. The etching is typically carried out at temperatures in the range between 4 ° C to <10 ° C and the Ätzabtrag here is usually 4 pm to 6 pm.

Immediately following the texturing, the silicon wafers are included

Water is thoroughly cleaned and treated with dilute hydrofluoric acid to prepare the chemical oxide layer formed as a result of the preceding treatment steps and impurities absorbed therein as well as adsorbed thereon in preparation of the following

To remove high temperature treatment.

2. Diffusion and doping

The wafers etched and cleaned in the previous step (in this case p-type base doping) are heated at higher temperatures,

typically between 750 ° C and <1000 ° C, treated with steam consisting of phosphorus oxide. The wafers are placed in a tube furnace in a quartz glass tube of a controlled atmosphere consisting of dried nitrogen, dried oxygen and phosphoryl chloride. The wafers are introduced at temperatures between 600 and 700 ° C in the quartz glass tube. The gas mixture is transported through the quartz glass tube. During transport of the gas mixture through the highly heated tube, the phosphoryl chloride decomposes into a vapor consisting of phosphorus oxide (eg P2O5) and chlorine gas. The vapor of phosphorus oxide is deposited among other things on the wafer surfaces (occupancy). At the same time, the silicon surface is oxidized at these temperatures to form a thin oxide layer. In this layer, the deposited phosphorus oxide is embedded, whereby a mixed oxide of silicon dioxide and phosphorus oxide formed on the wafer surface.

This mixed oxide is called phosphosilicate glass (PSG). This PSG glass has different softening points and, depending on the concentration of the contained phosphorus oxide

different Qiffusionskonstanten with respect to the phosphorus oxide. The mixed oxide serves the silicon wafer as a diffusion source, wherein in the course of the diffusion, the phosphorus oxide diffuses in the direction of the interface between PSG glass and silicon wafer and is reduced there by reaction with the silicon on the wafer surface (silicothermally) to phosphorus. The resulting phosphor has a solubility which is orders of magnitude greater in silicon than in the glass matrix from which it is formed, and thus dissolves preferentially in silicon due to the very high segregation coefficient. After dissolution, the phosphorus in silicon diffuses along the concentration gradient into the volume of silicon. In this diffusion process, concentration gradients of the order of 105 between typical

Surface concentrations of 1021 atoms / cm ² and the base doping in the range of 1016 atoms / cm ² . The typical depth of diffusion is from 250 to 500 nm and depends on the chosen diffusion temperature (eg, 880 ° C) and the total exposure time (heating & loading phase & driving phase & cooling) of the wafers in the highly heated atmosphere. During the coating phase, a PSG layer is formed, which typically has a layer thickness of 40 to 60 nm. in the

Following the wetting of the wafers with the PSG glass, during which diffusion into the volume of the silicon already takes place, the drive-in phase follows. This can be decoupled from the assignment phase, However, conveniently, as a rule, directly in time

Occupancy coupled and therefore usually takes place at the same temperature. The composition of the gas mixture is adjusted so that the further supply of phosphoryl chloride is suppressed. During driving, the surface of the silicon is further oxidized by the oxygen contained in the gas mixture, whereby a phosphorus depleted silicon dioxide layer is also generated between the actual doping source, the phosphorus oxide highly enriched PSG glass and the silicon wafer

Contains phosphorus oxide. The growth of this layer is much faster in relation to the mass flow of the dopant from the source (PSG glass), because the oxide growth is accelerated by the high surface doping of the wafer itself (acceleration by one to two

Orders of magnitude). As a result, in some way a depletion or separation of the doping source is achieved, whose penetration with

is influenced by the flow of phosphorus depending on the temperature and thus the diffusion coefficient. In this way, the doping of the silicon can be controlled within certain limits. A typical duration of diffusion consisting of loading and driving phase is for example 25 minutes. Following this treatment, the tube furnace is automatically cooled and the wafers can be removed from the process tube at temperatures between 600 ° C to 700 ° C.

In the case of a padding of the wafers in the form of an n-type base doping, another method is used, which will not be explained separately here. The doping is in these cases, for example, with

Boron trichloride or boron tribromide. Depending on the choice of

Composition of the gas atmosphere used for doping, the formation of a so-called boron skin can be detected on the wafers. This boron skin is dependent on various influencing factors: decisive for the doping atmosphere, the temperature, the doping time, the

Source concentration and the coupled (or linear combined) aforementioned parameters. In such diffusion processes, it goes without saying that there can be no regions of preferred diffusion and doping in the wafers used (with the exception of those which have arisen due to inhomogeneous gas flows and inhomogeneous gas packets resulting therefrom), unless the substrates are in advance of a corresponding one

Pretreatment were subjected (for example, their structuring with diffusion-inhibiting and / or -unterbindenden layers and

Materials).

For the sake of completeness, it should be pointed out here that there are still other diffusion and doping technologies which have established themselves to varying degrees in the production of crystalline solar cells based on silicon. So be mentioned

- the ion implantation,

the doping mediated via the gas phase deposition of mixed oxides, such as those of PSG and BSG (borosilicate) glass, by means of APCVD, PECVD, MOCVD and LPCVD processes,

- (Co) sputtering of mixed oxides and / or ceramic materials and hard materials (eg boron nitride), the gas phase deposition of both

the latter, the purely thermal gas phase deposition starting from solid dopant sources (eg boron oxide and boron nitride) as well as

- The liquid phase deposition of doping acting liquids

(Inks) and pastes.

The latter are often used in so-called in-line doping in which the corresponding pastes and inks are applied to the side of the wafer to be doped by suitable methods. After or even during the application, the solvents contained in the compositions used for doping are carried through

Temperature and / or vacuum treatment removed. As a result, the actual dopant remains on the wafer surface. As liquid

Doping sources, for example, dilute solutions of phosphoric or boric acid, as well as sol-gel-based systems or solutions of polymeric Borazilverbindungen can be used. Appropriate

Doping pastes are almost exclusively due to the use of

additional thickening polymers characterized, and contain dopants in a suitable form. At the evaporation of Solvents from the aforementioned doping media are usually followed by a high-temperature treatment during which undesirable and interfering additives which cause the formulation are either "burned" and / or pyrolyzed., The removal of solvents and the burn-out may or may not , take place simultaneously.

Subsequently, the coated substrates usually pass through a continuous furnace at temperatures between 800 ° C and 1000 ° C, to shorten the cycle time, the temperatures in comparison to

Gas phase diffusion in the tube furnace can be slightly increased. The prevailing in the continuous furnace gas atmosphere can according to the

Requirements of doping and dry

Nitrogen, dry air, a mixture of dry oxygen and dry nitrogen and / or, depending on the design of the furnace to be passed, zones of one and the other of the above

Gas atmospheres exist. Other gas mixtures are conceivable, but currently have little industrial significance. One

Characteristic of the inline diffusion is that the occupation and the

Driving the dopant can in principle be decoupled from each other.

3. Dopant source removal and optional edge isolation

The wafers present after the doping are coated on both sides with more or less glass on both sides of the surface. More or less in this case refers to modifications that can be applied in the context of the doping process: double-sided diffusion vs. quasi one-sided diffusion mediated by back-to-back arrangement of two wafers in a parking space of the process boats used. The latter

Variant allows a predominantly one-sided doping, but does not completely prevent the diffusion on the back. In both cases, it is currently state of the art to remove the glasses present after doping by etching in dilute hydrofluoric acid from the surfaces. For this purpose, the wafers are on the one hand transhipped in batches in wet process boats and with their help in a solution of dilute hydrofluoric acid, typically 2% to 5%, immersed and left in this until either the surface is completely removed from the glasses, or Process cycle has expired, which represents a sum parameter of the necessary Ätzdauer and the automatic process automation. The complete removal of the glasses can be determined, for example, by the complete dewetting of the silicon wafer surface by the dilute aqueous hydrofluoric acid solution. The complete removal of a PSG glass is achieved under these process conditions, for example with 2% hydrofluoric acid solution within 210 seconds at room temperature. The etching of corresponding BSG glasses is slower and requires longer process times and possibly also higher concentrations of the hydrofluoric acid used. After etching, the wafers are rinsed with water.

On the other hand, the etching of the glasses on the wafer surfaces can also be carried out in a horizontally operating method in which the wafers are introduced in a constant flow into an etching system in which the wafers pass through the corresponding process tanks horizontally (inline system). In this case, the wafers are conveyed on rollers and rollers either through the process tanks and the etching solutions contained therein or the etching media are transported onto the wafer surfaces by means of roller application. The typical residence time of the wafers in the case of etching the PSG glass is about 90 seconds, and the hydrofluoric acid used is somewhat more concentrated than in the batch process

Method to compensate for the shorter residence time due to an increased etch rate. The concentration of hydrofluoric acid is typically 5%. Optionally, in addition, the tank temperature compared to the

Room temperature slightly increased (> 25 ° C <50 ° C).

In the method outlined last, it has become established to carry out the so-called edge isolation sequentially simultaneously, which results in a slightly modified process flow: edge insulation -> glass etching. The edge insulation is a process engineering necessity, which results from the system-inherent characteristics of the double-sided diffusion, even with intentional unilateral back-to-back diffusion. On the (later) back side of the solar cell there is a large-area parasitic pn junction which, although due to process technology, is partly, but not completely, removed in the course of the later processing. As a result, the Front and back of the solar cell via a parasitic and

remaining p-n junction (tunnel junction), which reduces the conversion efficiency of the subsequent solar cell. To remove this transition, the wafers are unilaterally via an etching solution

consisting of nitric acid and hydrofluoric acid. The etching solution may contain as minor constituents, for example, sulfuric acid or phosphoric acid. Alternatively, the etching solution is transported via rollers mediated on the back of the wafer. The etching erosion typically achieved with these methods amounts to approximately 1 μm silicon at temperatures between 4 ° C. to 8 ° C. (including the glass layer present on the surface to be treated). In this method, the glass layer remaining on the opposite side of the wafer serves as a mask before

Caught on this side exerts some protection. These

Glass layer is subsequently using the already described

Glass etching removed.

In addition, the edge isolation can also be done with the help of

Plasma etching processes are performed. This plasma etching is then usually carried out before the glass etching. For this purpose, several wafers are stacked on each other and the outer edges become the plasma

exposed. The plasma is filled with fluorinated gases, for example

Tetrafluoromethane, fed. The plasma decay of these gases

occurring reactive species etch the edges of the wafer. Following the plasma etch, then generally the glass etch

carried out.

4. Coating the front with an antireflection coating

Following the etching of the glass and the optional

Edge insulation finds the coating of the front of the later

Solar cells with an anti-reflection coating instead, which usually consists of amorphous and hydrogen-rich silicon nitride. alternative

Antireflection coatings are conceivable. Possible coatings may include titanium dioxide, magnesium fluoride, tin dioxide and / or

corresponding stacked layers of silicon dioxide and silicon nitride consist. But there are also different compounds

Antireflection coatings technically possible. The coating of the wafer surface with the silicon nitride mentioned above is fulfilled in

essentially two functions: on the one hand, the layer generates an electric field due to the numerous incorporated positive charges that charge carriers in the silicon can keep away from the surface and the recombination of these charge carriers at the

On the other hand, depending on its optical parameters, such as refractive index and layer thickness, this layer generates a reflection-reducing property which contributes to the fact that more light can be coupled into the later solar cell. Both effects can increase the conversion efficiency of the solar cell. typical

Properties of the layers currently used are: a layer thickness of ~ 80 nm using only the above-mentioned silicon nitride, which has a refractive index of about 2.05. The antireflection reduction is most pronounced in the wavelength range of the light of 600 nm. The directional and non-directional reflection shows a value of about 1% to 3% of the originally incident light (perpendicular incidence to the surface normal of the silicon wafer).

The above-mentioned silicon nitride films are currently deposited on the surface generally by direct PECVD method. For this purpose, a gas atmosphere of argon is ignited a plasma, in which silane and ammonia are introduced. The silane and the ammonia are converted in the plasma by ionic and radical reactions to silicon nitride and thereby deposited on the wafer surface. The properties of the layers can z. B. adjusted and controlled by the individual gas flows of the reactants. The deposition of the above-mentioned silicon nitride layers can also be carried out using hydrogen as the carrier gas and / or the reactants alone. Typical deposition temperatures are in the range between 300 ° C to 400 ° C. Alternative deposition methods may be, for example, LPCVD and / or sputtering. 5th generation of front electrode electrode

After depositing the antireflection coating is on with

Silicon nitride coated wafer surface defines the front electrode. In industrial practice, the electrode has been established using the screen printing method using metallic

To produce sinter pastes. This is just one of many

different ways to produce the desired metal contacts.

In screen printing metallization is usually a strong with

Silver particles enriched paste (silver content> = 80%) used. The sum of the residual constituents results from the rheological aids necessary for formulating the paste, such as, for example, solvents, binders and thickeners. Furthermore, the silver paste contains a special Glasfrit mixture, mostly oxides and mixed oxides based on

Silica, borosilicate glass as well as lead oxide and / or bismuth oxide. The glass frit fulfills essentially two functions: on the one hand it serves as a bonding agent between the wafer surface and the mass of the silver particles to be sintered, on the other hand it is responsible for the penetration of the silicon nitride covering layer in order to enable the direct ohmic contact to the underlying silicon. The penetration of the silicon nitride takes place via an etching process with subsequent diffusion of silver present dissolved in the glass frit matrix into the silicon surface, whereby the ohmic contact formation is achieved. In practice, the silver paste is deposited by screen printing on the wafer surface and then dried at temperatures of about 200 ° C to 300 ° C for a few minutes. For the sake of completeness, it should be mentioned that double-printing processes also find industrial application, which make it possible to print on an electrode grid generated during the first printing step, a congruent second. Thus, the strength of the

Silver metallization increases, which can positively influence the conductivity in the electrode grid. During this drying, the solvents contained in the paste are expelled from the paste. Subsequently, the printed wafer passes through a continuous furnace. Such an oven generally has several heating zones, which can be independently controlled and tempered. When passivating the Continuous furnace, the wafers are heated to temperatures up to about 950 ° C. However, the single wafer is typically exposed to this peak temperature for only a few seconds. During the remaining run-up phase, the wafer has temperatures of 600 ° C to 800 ° C. In these

Temperatures are contained in the silver paste contained organic impurities such as binder, and the etching of the

Silicon nitride layer is initiated. During the short time interval of the prevailing peak temperatures, contact formation occurs

Silicon instead. Subsequently, the wafers are allowed to cool.

The process of contact formation outlined so briefly is usually carried out simultaneously with the two remaining contact formations (see Figures 6 and 7), which is why in this case one also speaks of a co-firing process.

The front electrode grid consists of thin fingers

(typical number> = 68), which have a width of typically 80 [im to 140 m, as well as collecting buses with widths in the range of 1, 2 mm to 2.2 mm (depending on their number, typically two to three) , The typical height of the printed silver elements is usually between 10 pm and 25 pm. The aspect ratio is rarely greater than 0.3.

6. Generation of back-bus buses

The rear bus buses are also usually by means of

Screen printing applied and defined. For this purpose, one of the similar silver paste used for front metallization is used. This paste is similarly composed, but contains an alloy of silver and aluminum, wherein the proportion of aluminum is typically 2%. In addition, this paste contains a lower glass frit content. The bus busses, usually two, will be printed with a typical width of 4 mm on the back of the wafer by screen printing and, as already described under point 5, compacted and sintered. 7. Generation of the back electrode

The back electrode is defined following the pressure of the bus buses. The electrode material is made of aluminum, therefore, to define the electrode, an aluminum-containing paste by screen printing on the remaining free area of the wafer back with a

Edge distance <1 mm is printed. The paste is composed of> = 80% aluminum. The remaining components are those already mentioned under point 5 (such as solvents, binders, etc.). The aluminum paste is bonded to the wafer during co-firing by causing the aluminum particles to start to melt during heating and remove silicon from the wafer in the wafer

dissolves molten aluminum. The melt mixture acts as a dopant source and releases aluminum to the silicon (solubility limit:

0.016 atomic percent), whereby the silicon is p ⁺ doped as a result of this input drive. As the wafer cools, a eutectic mixture of aluminum and silicon, which solidifies at 577 ° C. and has a composition with a mole fraction of 0.12 Si, is deposited on the wafer surface, inter alia.

As a result of the driving of the aluminum into the silicon, a highly doped p-type layer is formed on the back side of the wafer, which acts as a kind of mirror on parts of the free charge carriers in the silicon ("electric mirror"). These charge carriers can not do this potential wall

overcome and thus become very efficient from the backward

Keep remote wafer surface, which thus manifests itself in an overall reduced recombination of charge carriers on this surface.

This potential wall is generally referred to as the back surface field or back surface field.

The sequence of process steps described in items 5, 6 and 7 may or may not be the same as outlined herein. The skilled person will see that the sequence of

described process steps can be executed in principle in any imaginable combinatorics. 8. Optional edge isolation

If the edge isolation of the wafer has not already been carried out as described under point 3, this is typically carried out after co-firing with the aid of laser beam methods. For this purpose, a laser beam is directed to the front of the solar cell and the front p-n junction is severed by means of the energy coupled in by this beam. This trench with a depth of up to 5 pm due to

Action of the laser generated. This silicon is over a

Ablation mechanism removed from the treated area or thrown out of the laser ditch. Typically, this laser trench is 30 pm to 60 pm wide and about 200 pm away from the edge of the solar cell.

After production, the solar cells are characterized and

Classified according to their individual performance in individual performance categories.

The person skilled in the art knows solar cell architectures with both n-type and p-type base material. These solar cell types include PERT solar cells

• PERC solar cells

• PERL solar cells

• PERT solar cells

• As a result, MWT-PERT and MWT-PERL solar cells

• Bifacial solar cells

• backside contact cells

• Rear contact cells with interdigitating contacts

The choice of alternative doping technologies, as an alternative to the gas phase doping already described above, can usually be the

Do not resolve the problem of creating locally differently doped regions on the silicon substrate. As alternative technologies here are the landfill doped glasses, or mentioned by amorphous mixed oxides, by means of PECVD and APCVD method. From these glasses, a thermally induced doping of the silicon located under these glasses can be easily achieved. To create locally differently endowed However, areas of these glasses must be etched by means of mask processes in order to get the corresponding structures out of them

prepare. Alternatively, structured diffusion barriers may be deposited on the silicon wafers prior to depositing the glasses to define the regions to be doped. A disadvantage of this method, however, is that in each case only one polarity (n or p) of

Doping can be achieved. Somewhat simpler than the structuring of the doping sources or that of any diffusion barriers is the direct laser-beam driven driving-in of dopants from previously onto the

Wafer surfaces deposited dopant sources. This method makes it possible to save costly structuring steps. Nevertheless, it can not compensate for the disadvantage of a possible simultaneous simultaneous doping of two polarities on the same surface at the same time (co-diffusion), since this method is likewise based on a predeposition of a dopant source, which is activated only subsequently for the emission of the dopant. Disadvantage of this (post-) doping from such sources is the inevitable laser damage to the substrate: the laser beam must by absorbing the radiation into heat

being transformed. Since the conventional dopant sources off

Mixed oxides of the silicon and the dopants to be introduced, ie of boron oxide in the case of boron, are consequently the optical properties of these mixed oxides quite similar to those of the silicon oxide. Therefore, these glasses (mixed oxides) have a very low absorption coefficient for radiation in the relevant wavelength range. For this reason, the silicon located under the optically transparent glasses is used as the absorption source. The silicon is partially heated to the melt, and as a result heats the glass above it. This allows the diffusion of the dopants - and many times faster compared to those at normal

Diffusion temperatures would be expected, resulting in a very short diffusion time for the silicon (less than 1 second). The silicon should cool down relatively quickly after the absorption of the laser radiation due to the strong removal of the heat in the remaining, unirradiated volume of silicon and thereby epitaxially on the not

solidify molten material. The overall process, however, is in reality accompanied by the formation of laser-induced defects, possibly due to incomplete epitaxial solidification and thus the formation of crystal defects. This can

for example, due to dislocations and the formation of voids and defects as a result of the shocking process. Another disadvantage of laser-assisted diffusion is the relative

Inefficiency, when large areas are to be doped quickly, because the laser system scans the surface in a dot-matrix method. For narrow areas to be doped, this disadvantage naturally has a lower weight. However, laser doping requires sequential deposition of the aftertreatable glasses.

Problem of the present invention

By the technologies used in the industrial production of solar cells usual way for doping, namely by the

gas-phase-mediated diffusion with reactive precursors, such as

Phosphoryl chloride and / or boron tribromide, it is not possible to selectively generate local dopants and / or locally different dopants on silicon wafers. The creation of such structures is only possible by the use of known doping technologies by costly and expensive structuring of the substrates. When structuring different

Mask processes are coordinated, which makes the industrial mass production of such substrates very complex. For this reason, concepts for the production of solar cells, which require such a structuring, have not been able to prevail. It is therefore an object of the present invention to provide a simple and inexpensive process feasible, as well as employable in this method medium, whereby these problems can be eliminated.

Subject of the invention

It has been found that the problems described above can be solved by a process for the preparation of printable and low-viscosity oxide media (viscosity <500 mPas) when used in an anhydrous sol-gel-based synthesis by condensation of alkoxysilanes with symmetrical and asymmetric carboxylic anhydrides by controlled gelation low-viscosity, low-viscosity media (inks) are produced.

Particularly good process results are achieved when an anhydrous sol-gel-based synthesis by condensation of

Alkoxysilanes or alkoxyalkylsilanes with

a) symmetric and asymmetric carboxylic acid anhydrides

i. in the presence of boron-containing compounds

and or

ii. in the presence of phosphorus-containing compounds

is carried out and controlled by low-viscosity gelation

Dotiermedien (doping inks) are produced.

Alkoxysilanes or alkoxyalkylsilanes which may contain individual or various saturated, unsaturated, branched, unbranched aliphatic, alicyclic and aromatic radicals, which in turn may be attached at any position of the alkoxide radical by heteroatoms selected from the group O, N, may be used to carry out the process according to the invention. S, Cl, Br can be functionalized.

The alkoxysilanes of the invention are

Silicon compounds having hydrolyzable radicals and optionally one or two non-hydrolyzable radical (s). This means that the alkoxysilanes used according to the invention can have saturated, unsaturated, branched, unbranched aliphatic, alicyclic and aromatic radicals individually or different of these radicals, which in turn can be attached to any position of the alkoxide radical by heteroatoms selected from the group O, N, S, Cl , Br can be functionalized.

Examples of hydrolyzable radicals are halogen (F, Cl, Br or I, preferably Cl and Br), alkoxy (especially C ₁ alkoxy, such as

Methoxy, ethoxy, n-propoxy, i-propoxy and butoxy), aryloxy (especially C _6- io aryloxy, eg, phenoxy). Particularly preferred hydrolysable radicals are alkoxy groups, in particular methoxy and ethoxy.

Examples of non-hydrolyzable radicals R ¹ in the context of the invention are alkyl, in particular C _1-4 -alkyl (such as, for example, methyl, ethyl, propyl and butyl), alkenyl (in particular C ₂ -alkenyl, for example vinyl, -propenyl, 2-propenyl and butenyl), alkynyl (especially C _2- 4-AIkinyl such as acetylenyl and propargyl), and aryl, in particular C ₆ -aryl, for example phenyl and naphthyl), wherein the groups just mentioned, optionally one or more Substituents, such as halogen and alkoxy, may have.

Essential for the use according to the invention is that the alkoxysilanes used in the sol-gel reaction can form a three-dimensional network, which can form a thin layer during drying and compression, which is convertible by thermal treatment in a dense glass layer. Alkoxysilanes are therefore preferably used in the invention, the low-boiling radicals

cleaved. Therefore, the radicals are preferably methoxy, ethoxy, n-propoxy, i-propoxy and butoxy, most preferably methoxy and ethoxy. Particular preference is therefore given to the alkoxysilanes

Tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS) worked. However, it is also possible to work with alkoxyalkylsilanes in which one or two of the radicals have the meaning of alkyl, in particular C 1-4 -alkyl, such as e.g. Methyl, ethyl, propyl or butyl. In this case, preference is given to silanes which have one or two methyl or ethyl radicals in addition to the alkoxy groups.

Although the sol-gel reaction is carried out anhydrous, the

Reaction mixture, a solvent or a solvent mixture are added in an appropriate amount, so that the reaction can be carried out in sufficient speed. Suitable solvents for this purpose are those which are also formed by the condensation reaction itself, for example methanol, ethanol, propanol, butanol or other alcohols. Since protic solvents also lead to the termination of the condensation reaction, they can only be added in limited amounts. Aprotic, polar solvents, such as tetrahydrofuran, are therefore preferable. Suitable inert solvents other than tetrahydrofuran are other sufficiently polar and non-protic solubilizers, for example 1,4-dioxane and dibenzyl ether, into consideration, it being possible to use further solvents having corresponding properties for this purpose. By a suitable choice of the synthesis conditions, it is possible to adjust the viscosity of the doping ink between a few mPas, for example 3 mPas, and 100 mPas.

This can u. a. also by a targeted demolition of

Condensation reaction (sol-gel reaction) can be achieved by adding a sufficient amount of a protic solvent upon reaching a desired viscosity. Such protic solvents may include, for example, branched and unbranched, aliphatic, cyclic, saturated and unsaturated and aromatic mono-, di-, tri- and polyols, d. H. Alcohols, as well as glycols, their monoethers, monoacetates and

The like, propylene glycols, their monoethers and monoacetates, as well as binary, tertiary, quaternary and higher mixtures of such solvents in any volume and / or mass mixture ratios, said protic solvents may be combined with any desired polar and non-polar aprotic solvents. The term

Solvent is not explicitly limited to substances that are added to

Room temperature in liquid state, such. B.

Tetramethylolpropane, 2, 2-dimethyl-1, 3-pentanediol, tetradecanol or the like.

For the preparation of boron-containing doping inks are used as boron-containing

Compounds used are those selected from the group boron oxide, boric acid and boric acid esters.

Are in the process according to the invention phosphorus

Compounds used, can be obtained oxide media with good properties, when the phosphorus-containing compounds are selected from the group of phosphorus (V) oxide, phosphoric acid, polyphosphoric acid, phosphoric acid esters and phosphonic acid esters with alpha and beta-functional siloxane-functionalized groups. According to the described method, the printable oxide media in the form of doping media based on hybrid sols and or gels, using alcoholates / esters, hydroxides or oxides of aluminum, gallium, germanium, zinc, tin, titanium, zirconium, or Lead, as well as their mixtures, so that a "hybrid" sol or gel is obtained using these components.These hybrid sols can be made sterically by addition of suitable masking agents, complexing agents and chelating agents in a sub stoichiometric ratio stabilize and on the other hand in terms of their

Condensation and gelling rate, but also in terms of rheological properties targeted influence and control. suitable

Masking and complexing agents, as well as chelating agents are those skilled in the patent applications WO 2012/19686 A,

WO2012119685 A1 and WO20121 9684 A are known. The content of these publications is therefore included in the disclosure of the present application.

According to the invention, the oxide medium is up to a highly viscous, (nearly) glassy mass and the resulting product is brought back into solution, either by addition of a suitable solvent or solvent mixture. For this protic and / or polar solvents are suitable, such as propanol, isopropanol, butanol, butyl acetate, or ethyl acetate u. a. Ethyl acetate, ethylene glycol monobutyl ether,

Diethyl glycol, diethylene glycol, diethylene glycol monobutyl ether,

Dipropylene glycol monomethyl ether, and other glycols and their ethers and others, and mixtures of such solvents in which

Condensation both have sufficient solubility, but also have a suitable vapor pressure for this purpose.

In this way, a stable mixture is prepared by the process according to the invention, which is storage stable for a period of at least three months.

The doping media produced by the process according to the invention are storage-stable, can be prepared reproducibly and are characterized by a constant, ie independent of the storage life, Doping power off. Furthermore, such media can be modified by the targeted addition of monofunctional or monoreactive (capping agent) siloxanes, so that the storage stability of the

Doping is specifically improved. Suitable monofunctional siloxanes for this purpose include: acetoxytrialkylsilanes, alkoxytrialkylsilanes, such as ethoxytrimethylsilane, halo-trialkylsilanes and their derivatives, and comparable compounds. That is, when "capping agents" are added to the oxide media during manufacture, this results in a further improvement in the stability of the resulting oxide media, making them particularly well suited for use as doped inks

photovoltaic, microelectronic, micromechanical and micro-optical applications are used.

The oxide media produced according to the invention may vary depending on the consistency, i. H. depending on their theological properties, such as, for example, their viscosity, by spin coating or dip coating, drop casting, curtain or slot dye coating, screen printing or flexoprinting, gravure, ink jet or aerosol jet printing, offset printing, Micro Contact Printing, Electrohydrodynamic

Dispensing, Roller or Spray Coating, Ultrasonic Spray Coating, Pipe Jetting, Laser Transfer Printing, Päd Printing, Flatbed Screen Printing

Rotary screen printing be printed.

Correspondingly prepared oxide media are particularly well suited for the production of PERC, PERL, PERT, IBC solar cells BJBC or BCBJ) and others, wherein the solar cells further architectural features such as MWT, EWT, Selective Emitter, Selective Front Surface Field, Selective Back Surface field and bifaciality. Furthermore, the

Oxide media according to the invention for the production of thinner, denser

Glass layers are used, which act as a sodium and potassium diffusion barrier in the LCD technique as a result of thermal treatment, but in particular for the production of thin, dense glass layers on the cover glass of a display consisting of doped SiO ₂ , the diffusion of ions from the Prevent coverslip into the liquid crystalline phase. The present invention accordingly relates to the new, according to the invention Oxidmedien which have been prepared according to the method described above and which binary or ternary systems from the group S1O2-P2O5, S1O2-B2O3, SiO ₂ -P ₂ O ₅ - B2O3 and S1O2-Al2O3-B2O3 and / or mixtures of higher degree, which result from the use of alcoholates / esters, hydroxides or oxides of aluminum, gallium, germanium, zinc, tin, titanium, zirconium or lead during manufacture. As already mentioned above, these hybrid sols can be obtained by addition of suitable

Masking agents, complex and chelating in a sub stoichiometric to a stoichiometric ratio on the one hand sterically stabilize and on the other hand in terms of their condensation and gelation rate but also in terms of the theological properties specifically influence and control. Suitable masking and complexing agents, as well

Chelating agents are known to those skilled in the patent applications WO 2012/119686 A, WO2012119685 A1 and WO2012119684 A.

By means of the oxide media thus obtained, it is possible to produce a grip and abrasion resistant layer on silicon wafers. This can be in one

Process are carried out, wherein the surface-printed oxide medium, which is prepared by a method in the context of the invention, in a temperature range between 50 ° C and 750 ° C, preferably between 50 ° C and 500 ° C, more preferably between 50 ° C. and 400 ° C, using one or more, to be carried out sequentially Temperschritten (tempering by means of a step function) and / or an annealing ramp, dried and compacted to the glazing, whereby a grip and abrasion resistant layer is formed with a thickness of up to 500 nm.

Subsequently, the heat treatment of the glazed on the surfaces layers at a temperature in the range between 750 ° C and 1100 ° C, preferably between 850 ° C and 1100 ° C, more preferably between 850 ° C and 000 ° C. As a result, silicon-doping atoms, such as boron and / or phosphorus, by silicothermal reduction of the respective oxides on the substrate surface to the substrate itself deliver, whereby the conductivity of the silicon substrate is favorably favored favorable. It is particularly advantageous that due to the heat treatment of the printed substrate, the dopants depending on the

Treatment time and time transported in depths of up to 1 pm and electrical sheet resistances of less than 10 Ω / sqr generated.

The surface concentrations of the dopant can usually assume values of greater than or equal to 1 ^× 10 ¹⁹ to 1 ^× 10 ²¹ atoms / cm ³ . This depends on the nature of the dopant used in the printable oxide medium.

It has proved to be particularly advantageous that

then the surface concentration of the parasitic doping of not previously intentionally protected (masked) and with the printable

Oxide media not covered surface areas of the silicon substrate against those areas intentionally with the printable

Oxide media were covered by at least two powers of ten

Doping intentionally differentiates doped regions.

This result is achieved, regardless of whether the oxide medium is printed as a doping medium on hydrophilic and / or hydrophobic silicon wafer surfaces. In this context, "hydrophilic" means

wet-chemically applied and / or native oxide provided surface. The term "hydrophobic" in this context means: surfaces provided with silane termination, which does not exclude thin silicon layers on the surface

Silicon substrate to use, and such silicon wafers with the

To print the doping inks according to the invention and to excite the dopant for diffusion into the substrate. The effective dose of doping in the silicon substrate is thus affected by the temperature during the treatment and its duration, as well as indirectly by the diffusivity of the dopant in the thin oxide layer, but also by the temperature dependent segregation coefficients of the dopant between the silicon of the substrate and the

Silicon dioxide layer. In general, the process according to the invention for the production of grip- and abrasion-resistant layers on silicon and silicon wafers can be characterized in that

a. Silicon wafers are printed with the oxide media as n-type dopant (for example, by ink jet printing), the printed Dotiermedien dried, compacted and then exposed to a subsequent gas phase diffusion with phosphoryl chloride, whereby high dopants are obtained in the printed areas and lower doping in the Be achieved areas that are exposed exclusively to the gas phase diffusion, or

b. Silicon wafers are printed with the oxide media as a p-type oxide medium, in this case with boron-containing precursors, the printed on doping dried, compacted and then exposed to a subsequent gas phase diffusion with boron trichloride or boron tribromide, whereby high doping is obtained in the printed areas and a lower doping is achieved in the areas which are exposed exclusively to the gas phase diffusion or

c. Silicon wafer with the oxide media printed as n- or p-type dopant printed structured, the printed on Dotiermedien dried, compacted and then a subsequent gas phase diffusion with, for example, phosphoryl chloride in the case of a used n-type doping medium or with, for example, boron trichloride or boron tribromide in the case of a p-type used Doping medium can be exposed, whereby high doping in the non-printed areas and lower dopants can be obtained in the printed areas, insofar as the source concentration of the oxidic doping media used controlled by the synthesis kept low and the glasses obtained from the doping a diffusion barrier against those from the gas phase to the Wafer surface transported and deposited depict gas phase diffuser

or

d. Silicon wafers with the oxide media as p-type doping media, in this case boron-containing precursors, printed on the printed

Doping dried, compacted and then one be exposed to subsequent gas phase diffusion with boron trichloride or boron tribromide, thereby obtaining high doping in the printed areas and lower dopants in the areas that are exposed exclusively to the gas phase diffusion, and obtained in this case at the wafer surface Borhaut subsequently using, for example, sequential wet chemical treatment is removed from the wafer surface with nitric and hydrofluoric acid or

e. on the silicon wafer over the entire surface deposited oxide medium as

Doping medium is dried and / or compressed and from the compacted doped oxide medium by means of

Laser irradiation, the local doping of the underlying

Substrate material is initiated,

or

f. on the silicon wafer over the entire surface deposited oxide medium as

Doping medium is dried and compacted and from the

compressed doping oxide medium is initiated by means of a suitable heat treatment, the doping of the underlying substrate, and subsequent to this doping process with subsequent local laser irradiation, the local doping of the underlying substrate material amplified and the dopant is driven deeper into the volume of the substrate

or

G. the silicon wafer is printed either over the whole area or locally with oxide media as doping media, which may be n- and p-doping media, optionally through

alternating structures which are dried and densified on printed structures and coated with suitable diffusion barrier materials, such as sol-gel based silica layers, sputtered or APCVD or PECVD based silicon dioxide, silicon nitride or silicon dioxide

Siliconoxynitridschichten encapsulated and the doping acting oxide media are brought by suitable heat treatment for doping of the substrate,

or H. the silicon wafer is printed either over the whole area or locally with oxide media as doping media, which may be n- and p-doping media. This may optionally have an alternating sequence of structures, such as printed n-doping oxide medium with any

Structure width, for example, line width, adjacent to non-printed silicon surface, which also any

Has structure width. The printed structures are dried and compacted, and subsequently the wafer surface can be provided with a doping medium of oppositely inducing majority charge carrier polarity over the entire surface or selectively printed on the already printed surface. In this case, the last-mentioned doping media can be printable sol-gel-based oxidic doping materials, other printable doping inks and / or pastes, APCVD and / or PECVD glasses doped with dopants and dopants from conventional gas phase diffusion and doping. The overlapping arranged and doping

acting doping are brought by suitable heat treatment for doping of the substrate. In this context, due to suitable segregation coefficients and insufficient diffusion lengths, the respectively underside printed, doping oxide medium acts as a diffusion barrier to the one above it, and behaves as the majority majority carrier polarity-inducing dopant medium; Moreover, the opposite side of the

Wafer surface may be covered with a different and otherwise deposited (printed, CVD, PVD) diffusion barrier, such as a silicon dioxide, silicon nitride or

silicon oxynitride;

or

i. the silicon wafer is printed either over the whole area or locally with oxide media as doping media, which may be n- and p-doping media, optionally in alternating sequence, such as printed n-doping

acting oxide medium of any structure width, for example, any line width, adjacent to non-printed Silicon surface, which also has any structural width. The printed structures are dried and compacted, after which the wafer surface can be provided over the entire area with a doping medium with opposite inducing majority charge carrier polarity on the already printed wafer surface, and wherein the latter doping media can be printable sol-gel based oxidic dopants or other printable dopant inks and / or or pastes, doped APCVD and / or PECVD glasses, but also dopants from conventional gas phase diffusion and doping. The overlapping arranged and doping acting doping media are brought by suitable heat treatment for doping of the substrate. In this case, the respectively underside, printed, doping oxide medium is due to appropriate

Segregation coefficients and insufficient diffusion lengths as a diffusion barrier to the one above it

Oxid medium behave, and the latter contrary

Majority carrier polarity induced; At the same time, the opposite wafer surface can be covered by means of a different and otherwise deposited dopant source (printable sol-gel-based oxidic dopants, other printable

Doping inks and / or pastes, doped APCVD and / or PECVD glasses as well as dopants from conventional gas phase diffusion), which can induce the same or opposite doping, as that of the bottom

located layer of the opposite wafer surface.

Simultaneous co-diffusion from the layers formed by printed oxide media to form n- and p-type layers or those layers of only a majority carrier polarity, which may have differing doses of dopant, occurs in the thus characterized layer sequence.

For the formation of hydrophobic silicon wafer surfaces are in this process after the printing of the invention

Oxide media, their drying, and compaction and / or doping By thermal treatment resulting glass layers with a

Acid mixture containing hydrofluoric acid and optionally phosphoric acid, etched. The etchant used in this case contains as etchant hydrofluoric acid in a concentration of 0.001 to 10 wt .-% or 0.001 to 10 wt .-% hydrofluoric acid and 0.001 to 10 wt .-% phosphoric acid in the mixture.

The dried and compacted doping glasses can furthermore be removed from the wafer surface with other etching mixtures:

buffered hydrofluoric acid mixtures (BHF), buffered oxide etch mixtures, etching mixtures consisting of hydrofluoric and nitric acid, such as the so-called p-type etching, R-etching, S-etching, or etching mixtures, consisting of hydrofluoric acid and sulfuric acid, the aforementioned list not the Claim to completeness.

An already mentioned alternative doping technology is the so-called in-line diffusion. This is based on the landfill of

Dotierstoffquelle on the silicon wafers, after which they pass through a belt furnace of appropriate length and temperature and release as a result of this treatment, the desired dopant to the silicon wafer. Inline diffusion is in principle the most efficient variant of doping silicon wafers, taking into account the industrial mass production of components that are manufactured under considerable cost pressure from two directions in billions of units. The cost pressure results both from a very pronounced political and market competitive situation. Inline diffusion can achieve industrial throughput rates that are typically between 15 to 25% higher than the usual

Throughput rates of conventional horizontal tube furnace systems are - wherein the application finding inline-diffusion-capable furnace systems are usually cheaper than the typical horizontal tube furnace systems. The inline diffusion should therefore in principle have a significant intrinsic

Generate cost advantage over the conventionally used for doping technology. Nevertheless, this advantage has hardly been put into practice efficiently. There are multiple reasons for that. One important reason is, for example, the dumping of the dopant source. Usually, in inline diffusion, the dopant sources are applied to the wafers wet by means of suitable coating methods (spraying, rolling, screen printing, etc.), thermally dried, compacted and brought into the furnace system for diffusion. Typical and commonly used sources of dopants are dilute ones

alcoholic (in ethanol or isopropanol) or aqueous solutions of phosphoric or boric acid. Optimally, these solutions should lead to a homogeneous film on the silicon surfaces, so that a uniform delivery of the dopant to the silicon is possible. As a rule, for various reasons, in particular on very rough surfaces, such as those of the textured silicon wafer surfaces, no homogeneous coating is achieved. Phosphoric and boric acids have an increasing oxidic character upon drying of the solution and thermal transformation to polymeric species. The oxides in question are volatile and therefore can very easily contribute to auto-doping of regions of the substrate that were not initially homogeneously covered with the dopant source. However, the volatility also impedes the spatial control of the dopant species whose mobility contributes not only to the doping on the treated surface itself (beneficial), but also to the doping of wafers and their surfaces that are not directly provided with the source (analogous to conventional

Gas phase doping). Due to the use of said

Flüssigphasendotiermedien there are also process-related problems, such as corrosion of the deposition systems and the furnace system. The corrosion manifests itself, for example, both in the spray nozzles typically used and in the wafer delivery systems. As a result, metal ions can enter the dopant source, which are then driven into the silicon during the subsequent high-temperature process (see below).

Coming back to the already mentioned new solar cell architectures, they all have in common that they are fundamentally based on structured substrates. However, the structuring also relates to the creation of differently doped regions in a basically arbitrary, but often alternating, sequence in which either high and low-doped regions of a polarity (n- or p-type) or doped regions of alternating polarities (n - on p-type and vice versa) alternate. To create such structures is both the structuring of the substrate as well as the deposition of thin functional layers conceivable.

The bridging between the mentioned structuring requirements and, for example, the in-line diffusion arises insofar as suitable doping media can combine these two concepts, as long as they satisfy at least the following requirements:

• Dopant sources must be printable to allow decoupling of the

Predeposition and diffusion is enabled so that

Dopant sources of different polarities in two

successive printing steps in small structures on the

Wafer surface can be deposited

• The printable dopant sources offer the potential to allow sufficient surface concentrations of dopants for the subsequent ohmic contacting of the doped regions

The printable dopant sources must be able to be driven into the treated silicon wafer in a co-diffusion step and thus simultaneously

• have a low gas phase enrichment (vaporization of the source) in order to achieve exclusively sharply delimiting and therefore local doping

• The printable sources of dopant must be in their necessary

Have sufficient chemical purity formulation, which is mandatory for the treatment of semiconductor devices.

Although the choice of liquid phase dopant sources allows this

structured application of doping sources, the doping effect of these media remains, as described above, but generally not limited to these structured areas. There is a considerable carry-over (auto- and proximity-doping) of dopants from the doping source, which negates the advantage of structured landfill. With the hitherto known solutions, the doping can therefore not be limited specifically to the deposited areas. Known doping media also have a number of other significant disadvantages, which entail considerable application restrictions. A typical side effect in the use of such

Dotiefmedien is the occurrence of a significant collapse of the

Minority carrier lifetime of treated silicon wafers. The

Minority carrier lifetime is an essential basic parameter that decides on the conversion efficiency of a solar cell: low lifetime equal low efficiency and vice versa. Therefore, for the expert speaks against the use of the previously known printable doping media. The adverse effect on carrier lifetime is evident by the raw materials used to make the dopant media

caused. In particular, the auxiliaries necessary for the paste formulation, and in particular the polymeric binders, are a source of contamination which is difficult to control and which has a negative effect on the performance of the silicon. These adjuvants may contain unwanted, harmful metals and metal ions whose concentration is typically in the per mil range. However, silicon reacts very sensitively to metallic contaminations already in the range of ppb to a few ppm - especially when the

Silicon treatment follows a high-temperature phase, which allows for the most effective distribution of these harmful contaminants in the bulk (via diffusion and "doping") of silicon. Such diffusions in wafers typically occur as a result of

High temperature processes, which in turn occur for purposes for which the doping media has been deposited on the wafer surfaces. Typical and particularly harmful contaminants are, for example, iron, copper, titanium, nickel and other transition metals from this group of

Periodic Table of the Elements. These metals belong to the same time. the medium fast to very fast diffusing in silicon dopants, so that during the exposure period of the doping much deeper into the

Volume can penetrate than the desired dopants themselves, and thus can affect not only the surface of the silicon, but also its entire volume. So in case of iron, with the

Distance most widespread and usually with the highest concentration of contaminants, with a typical

theoretical diffusion depth, which under typical Diffusion conditions, such as with a plateau time of 30 minutes at 900 ° C, the usual silicon wafer thickness of 180 pm or less can easily exceed many times. The result is a significant reduction of the minority carrier lifetime already mentioned and, because the solar cell is a "volume component", the efficiency of the solar cell as a whole.

The binders added in the formulation of pastes are generally very difficult to even chemically clean up or free of their cargo of metallic trace elements. The effort to clean them is high and is due to the high cost in any

Relationship to the claim of creating a cost-effective and thus competitive, for example, screen printable source of dopants. Thus, these auxiliaries are a constant source of contamination, are favored by the unwanted contamination in the form of metallic species greatly.

Another, not insignificant, source of contaminants is the application device for applying and printing liquid dopants on silicon wafer surfaces. Conventional liquid phase dopants, which are used, for example, in inline diffusion, as mentioned above, corrosive to the printing equipment used, where is usually a spraying device. In this, often creeping corrosion metal ions are dissolved out of the material and transferred to the Dotiertintenstrom and dragged through it. In this way, the metal ions become with the

Liquid phase dopant deposited on the silicon wafer surface. In the subsequent drying of the liquid dopant, the metal ions contained in the ink are enriched in the remaining residue. The enrichment factor is of the concentration in the liquid

Doping medium and remaining on the wafer dried on doping layer, and thus the real or virtual solid content in the doping ink dependent. The enrichment factor can be between 10 and 100. That is, with a metal ion load of 10 ppbw of any element, 100 ppbw to 1 ppmw in the dried

Dotierschicht remain or accumulated accordingly in this can be. The layer containing the dopant thus represents a comparatively highly concentrated source of possible metal ions for the silicon substrate underneath. The release of the metal ions from this layer is strongly dependent on the temperature and the

Material properties, such as the segregation coefficient of the dopant layer over the silicon wafer dependent. In general, it can be stated that the thermal activation of the dopant layer, in order to allow the dopant to diffuse in silicon, can also considerably mobilize the metal ions. It is also general that the diffusivity of most metal ions is many orders of magnitude higher than that of all dopants. Metal ions (3d subgroup elements) diffused into the silicon, although they can form silicides and partially precipitate as such, behave and / or precipitate on oxides and oxygen clusters and grain boundaries and dislocations, in some cases also very strongly. by electronically inducing deep impurities in the silicon. These depths

Impurities have a pronounced recombination activity for the minority carriers. On the other hand, the

Minority carrier lifetime or diffusion length is one of the basic quality parameters of the silicon used for solar cell fabrication, it significantly determines the maximum conversion efficiency to be achieved. A very high one

Minority carrier lifetime of the silicon accordingly excludes the co-presence of highly recombinant

Impurities in the silicon categorically.

Surprisingly, these problems can be solved by the present invention described, by printable, low viscosity oxide media of the present invention which can be prepared by a sol-gel process. In the context of the present invention, these oxide media can be produced by suitable additives as printable doping media. By a correspondingly adapted method and by optimized synthesis approaches, the production of printable doping media is made possible,

• have excellent storage stability, • the excellent printing performance to the exclusion of

Show sticking, closing and gelation in spray and pressure nozzles,

• have a very low intrinsic contamination load on metallic species and thus the lifetime of the

do not adversely affect treated silicon wafers

• have enough doping ability to self-assemble

easy to produce low-resistance emitters on textured silicon wafers,

• which can be adjusted in their content of dopants in such a way that doping profiles and the associated electrical film resistances can be set and controlled very well over a wide range,

• the very homogeneous doping of the treated silicon wafers

enable,

• whose residues can be easily removed from the surface of treated wafers after thermal treatment, and

• which, due to the optimized synthesis, have an extremely slight behavior of the so-called auto-doping.

The novel doping media can be synthesized on the basis of the sol-gel process and, if this is necessary, can be further formulated.

The synthesis of the doping ink can be achieved by adding

Condensation initiators, e.g. be controlled by a carboxylic anhydride in the absence of water. In this way, the degree of crosslinking in the ink is above the stoichiometry of the addition,

for example, the acid anhydride, controllable. At a low

Degree of crosslinking, the resulting ink is low viscosity and low viscosity. As a result, it is perfectly processable with suitable printing methods.

Suitable printing methods can be the following: Spin or Dip Coating, Drop Casting, Curtain or Slot Dye Coating, Screen or Flexo Printing, Gravure or Ink Jet or Aerosol Jet Printing, Offset Printing, Microcontact Printing, Electrohydrodynamic Dispensing, Roller or Spray Coating, Ultrasonic Spray Coating, Pipe Jetting, Laser Transfer Printing, Päd Printing, Flatbed Screen Printing and Rotary Screen Printing. This list is not exhaustive, and other printing methods may be suitable.

Furthermore, by adding further additives, the properties of the doping media according to the invention can be adjusted in a targeted manner, so that they are optimally suitable for special printing processes and for application to specific surfaces, with which they can interact intensively. In this way you can target properties, such as

For example, set surface tension, viscosity, wetting behavior, drying behavior and adhesion. Depending on

Demands on the doping media produced, it is also possible to add further additives. These can be:

Surfactants, tensio-active compounds for influencing the wetting and drying behavior,

Defoamer and deaerator for influencing the drying behavior,

• other high and low boiling polar protic and aprotic

Solvent for influencing the particle size distribution, the degree of pre-condensation, condensation, wetting and drying as well as printing behavior,

• other high and low boiling nonpolar solvents

Influencing the particle size distribution, the degree of pre-condensation, condensation, wetting and drying as well as printing behavior,

• particulate additives to influence the theological

Properties,

• particulate additives (eg aluminum hydroxides and

Aluminum oxides, silicon dioxide) for influencing the dry film thicknesses resulting after drying and their morphology, • particulate additives (eg aluminum hydroxides and

Aluminas, silica) to influence the scratch resistance of the dried films,

• Oxides, hydroxides, basic oxides, alkoxides, precondensed alkoxides of boron, gallium, silicon, germanium, zinc, tin, phosphorus, titanium, zirconium, yttrium, nickel, cobalt, iron, cerium, niobium, arsenic, lead and others for the formulation of hybrid brines,

In particular, simple and polymeric oxides, hydroxides, alkoxides, acetates of boron and phosphorus for the formulation of semiconducting, in particular silicon, doping formulations.

In this context, it goes without saying that each printing and coating method has its own requirements for the ink to be printed. Typically, parameters to be set individually for the respective printing method are those such as the surface tension, the

Viscosity and the total vapor pressure of the ink.

The printable media, in addition to their use as a doping source as scratch protection and corrosion protection layers, eg. Example, in the manufacture of components in the metal industry, preferably in the electronics industry, and in particular in the production of microelectronic, photovoltaic and microelectromechanical (MEMS) components, application. In this context, photovoltaic components are in particular solar cells and modules. Furthermore, applications in the electronics industry are characterized by the use of said inks and pastes in the following, by way of example, but not exhaustive fields: fabrication of thin film solar cells from thin film solar modules, organic solar cell manufacturing, printed circuit and organic electronics manufacturing, manufacturing from

Display elements based on the technologies of thin-film transistors (TFT), liquid crystals (LCD), organic light-emitting diodes (OLED) and touch-sensitive capacitive and resistive sensors.

The present description enables one skilled in the art to fully embrace the invention. Also without further explanations becomes therefore It is assumed that a person skilled in the art can make the most of the above description.

Any ambiguity goes without saying, the quoted

Publications and patent literature. Accordingly, these documents are considered part of the disclosure of the present application

Description.

For a better understanding and clarification of the invention, examples are given below which are within the scope of the present invention. These examples are also used for

Illustration of possible variants. Due to the general validity of the described principle of the invention, however, the examples are not suitable for reducing the scope of protection of the present application only to these.

Furthermore, it is self-evident to the person skilled in the art that both in the given examples and in the remainder of the description, the amounts of components contained in the compositions amount in the sum to only 100% by weight, molar or vol

Aggregate composition and can not exceed it, even if higher values could result from the indicated percentage ranges. Unless otherwise stated, therefore,% data are in terms of weight, mol or vol.%.

The temperatures given in the examples and the description as well as in the claims are always in ° C. Examples of Low-viscosity Doping Media Example 1

In a 250 ml round bottomed flask, 5.8 g are placed in a desiccator.

dried ortho-phosphoric acid in 10 g of acetic anhydride by brief heating. This solution slowly becomes 19.4 g with stirring Tetraethylorthosilicate added dropwise. With stirring and constant heating to 100 ° C, the resulting ethyl acetate is distilled off. To adjust the viscosity, another 1-10 g of acetic anhydride can be added. To terminate the reaction, 25-50 g of a protic solvent are then added. This solvent can be arbitrarily selected from the group mentioned in the description for this purpose.

It can be shown by a ³¹ P-NMR examination of the resulting ink that the phosphorus species are incorporated into the Si0 ₂ network.

The dopants prepared according to this method are

storage-stable,

Fig. 1 shows a ³¹ P-NMR measurement of an ink resulting in Example 1. The chemical shift of free phosphoric acid is 0 ppm and is not detectable in this example. The phosphoric acid must therefore be firmly bound in the Si0 ₂ matrix.

Example 2:

Several doping media batches, following Example 1 outlined above, are prepared and each polished, p-type is polished

Silicon wafer after HF cleaning by spin coating (2000 rpm for 30 s) printed with the doping inks. After afterwards

Baking for 2 minutes on a hotplate (100 ° C), diffusion at 900 ° C for 8 minutes results in a sheet resistance of 50 Ω / sq. In Fig. 2, a resulting ECV profile of the diffused emitter is shown.

FIG. 2 shows the doping profiles of the doping tests as repeatable

prepared doping media. The doping media have a reproducibly doping effect. Example 3:

A polished p-type silicon wafer is after HF cleaning with a phosphorus doped Si0 ₂ matrix according to Example 1 means

Spin coating (2000 rpm for 30 s) printed. To

subsequent baking for 2 minutes on a hotplate (100 ° C), diffusion at 900 ° C for 8 minutes results in a sheet resistance of 50 Ω / sq. In Fig. 3, a resulting ECV profile of the diffused emitter is additionally shown the behavior of the auto and / or proximity doping. The proximity is according to an arrangement of silicon wafers

examined according to FIG. 3. Based on the two doping profiles (source vs. sink), it should be noted that the doping effect on the source and the sink differ by a factor> 1000 with respect to the respectively determined surface concentrations.

FIG. 3 shows the ECV profiles of the above-described doping experiments. Example 4:

A textured p-type silicon wafer is after HF cleaning with a phosphorus doped Si0 ₂ matrix according to Example 1 with isopropanol or a comparable solvent, defined by vapor pressure and / or Hansen-solubility parameter, ethyl acetate or a comparable

Solvent, defined by vapor pressure and / or Hansen solubility parameter, and butanol or a comparable solvent, defined by vapor pressure and / or Hansen solubility parameter as

Solvent, (mass ratio 1: 1: 0.25) printed by spray coating. After subsequent baking for 2 minutes on a hotplate (100 ° C), diffusion at 900 ° C for 15 minutes leads to a

Sheet resistance of 40 - 50 Ω / sqr. To assess the homogeneity of the applied layer, a scanning electron micrograph of the applied layer after diffusion is shown in FIG. Figure 4 shows a scanning electron micrograph (50,000X magnification) of the deposited diffusion layer on a pyramid of an alkaline textured (100) wafer. It is easy to see the homogeneous coverage of the surface by the sprayed-on PSG layer. The measured layer thickness is 44 nm.

Another doping test with an ink according to Example 1 below

Using the coating conditions described above, but using a longer diffusion period, 20 minutes, gives an average sheet resistance of 28 Ω / sqr with a surface concentration of 8 * 10 ²⁰ atoms / cm ² .

FIG. 5 shows the sheet resistance distribution (top right) on a full-area ink deposited with doping medium according to example 1. The ECV profile (bottom left) gives a typical measurement point on the sample.

Example 5:

A textured p-type silicon wafer is after HF cleaning with a phosphorus doped SiO ₂ matrix according to Example 1, with

Dipropylene glycol monomethyl ether as solvent, locally printed by inkjet. After subsequent baking for 2 minutes on a hotplate (100 ° C), diffusion at 900 ° C for 15 minutes leads to a

Sheet resistance of 40 - 50 Ω / sqr. In order to assess the phosphorus outgassing from the printed PSG, a resultant ECV profile of the diffused emitter and a measurement 1 mm apart from the printed location are shown in FIG. The surface concentrations of the two areas differed by a factor> 00.

Fig. 6 shows the ECV profile of the diffused emitter and a reference measurement 1 mm next to the printed area. Example 6:

Spin coating (2000 rpm for 30 s) printed on both sides. After baking for 2 minutes on a hotplate (100 ° C), diffusion at 900 ° C for 8 minutes results in a sheet resistance of 30 Ω / sq.

In Fig. 7, the life of a market-accompanying doping ink after doping under similar conditions (p-type wafer, polished on one side, conductivity 1 - 10 Ω ^{"1 *} cm ^{" 1} ) to achieve a comparable

Sheet resistance of 50 Ω / sqr, determined via QSSPC measurement (quasi-stationary photoconductivity measurement) and read out at one

Injection density of 1 ^* 10 ¹⁵ minority charge carriers / cm ³ , demonstrated. The life span is 130 ps. The lifetime of a comparable but untreated, ie undoped, reference wafer is 320 ps. The wafers are wet-chemically passivated by methanol-quinhydrone process.

FIG. 7 shows a comparative lifetime measurement of a p-type wafer doped with a commercially available doping ink against one

comparable reference wafer.

FIG. 8 compares the service life of a p-type wafer according to the procedure outlined above using a doping ink according to Example 1 of the lifetime of a commercially available doping ink. The lifetime of the wafer coated with an ink of the invention is 520 ps, which is four times larger than that of the competitive approach. The increase in lifetime is due to the optimized synthesis method using very pure chemicals and the adequate pre-purification of the solvents used.

Fig. 8 shows the comparative lifetime measurement of one using one prepared according to the optimized synthesis method and using adequately pretreated solvent treated wafers compared to a wafer after its doping with a commercially available doping ink. The additional increase in the lifetime of the wafer, treated with the doping ink according to the invention, compared to that of

Reference wafer is due to the additional getter effect (sink for

Contaminants) due to the diffusion with phosphorus. In contrast, the commercially available doping ink acts as a source for

Contaminants.

Example 7 (comparative example):

In a comparative experiment, a doping ink is prepared according to the following conditions: in a 250 ml flask, weigh 67.3 g of ethanol, 54.2 ethyl acetate, 13.3 g of acetic acid, 32.5 g of tetraethylorthosilicate, mix thoroughly and add 6.7 g of water. In this mixture, 1, 7 g of phosphorus pentoxide (P4O10) are dissolved and the mixture is heated to reflux for 24 h. After the synthesis of the doping ink is stored in a refrigerator at +8 ° C and used at certain time intervals for doping of silicon wafers. For this purpose, the ink is in each case by means of the spin coating process on a one-side polished, p-type wafer with a conductivity of 1-10 Q ^* cm

spin-coated (2000 rpm, for 30 s). Subsequently, the wafer is dried at 00 ° C on a hot plate for 2 minutes and then fed to the doping in a conventional muffle furnace at 900 ° C for 20 minutes. After diffusion, the resulting PSG glass is removed from the wafer surface by dilute hydrofluoric acid (~ 2%) and the sheet resistance is determined by four-peak measurement. The doping effect of the doping ink prepared according to this method demonstrates a pronounced time dependence of the doping effect to be observed. There is a proportional relationship: as the storage time of the doping medium increases, its doping capacity decreases. The doping medium shows no long-term storage stability.

In FIG. 9, the doping potential of a manufactured according to Example 6

Doping medium applied as a function of the storage time: too Achieving layer resistance as a function of storage time of the doping medium during cooling.

The above-described observation is independent of the order of addition of the phosphorus pentoxide: initial and subsequent addition of the solvent or presentation of the solvent and then use of

Phosphorus pentoxide and subsequent addition of the organosilicon compound, acetic acid and water, etc. always gives the same behavior. The observation is furthermore independent of which type of phosphorus compound and in which order it is added: aqueous or crystalline phosphoric acid, polyphosphoric acid,

Phosphoric acid esters, such as mono-, di- and tributyl phosphate or phosphorus pentoxide itself.

Furthermore, the previously described observations are independent of the choice of solvents used. Experiments with propanol,

Isopropanol, butanol, ethylene glycol monobutyl ether, diethyl glycol,

Diethylene glycol, diethylene glycol monobutyl ether, other glycyls and their ethers, mixed with simple alcohols or ethyl acetate or butyl acetate or other suitable solvents always provide a comparable result, as shown in Fig. 9.

The use of inorganic and organic phosphonic acids leads to the same observations, with the exception that such

Doping media, balancing the differing relative

Mass fractions of the phosphor contained in the precursor substances, still have a low doping effect as such, which are prepared with pentavalent phosphorus sources. Such phosphonic acids may be, for example, phosphonic acid, dibutylphosphonate,

Diethyl triethoxysilylethylphosphonate and etidronic acid.

The "postdoping" of pre-condensed polysiloxanes, prepared according to the method described above, except for the addition of phosphorus pentoxide, with aqueous and / or crystalline phosphoric acid, as well as with phosphorus pentoxide regularly leads to rapid gelation (within a few hours) of the thus prepared doping solution. Such solutions do not prove to be sufficiently stable to storage in accordance with the industrial demands placed on such media.

Example 8:

In a 250 ml round bottom flask, add 3.6 g in a desiccator

predried boric acid in 12.5 g of tetrahydrofuran ran with stirring at 70 ° C dissolved. With stirring, 12.3 g of acetic anhydride are added and then added dropwise 19.4 g of tetraethyl orthosilicate slowly. The solution is heated to 100 ° C after complete addition of the tetraethyl orthosilicate and freed from volatile solvents. Subsequently, 55 g of a protic solvent are added (suitable

Solvents are given in the description). Alternatively, a solvent mixture according to Example 4 can be added in an appropriate amount. The resulting mixture is kept under

Refluxed until a completely clear solution is formed.

Alternatively, the doping ink may be synthesized using a mixture of tetraethyl orthosilicate and aluminum isobutylate. The partial substitution of tetraethyl orthosilicate by aluminum isobutylate may require the substoichiometric addition of complexing ligands, such as those of acetylacetone, salicylic acid, 2,3-dihydroxy- and 3,4-dihydroxybenzoic acid, or mixtures thereof.

Example 9:

A polished n-type silicon wafer after RF cleaning with a boron-doped Si0 ₂ matrix according to Example 8 by means of spin coating (2000 rev / min for 30 s) printed on one side. After baking for 2 minutes on a hotplate (100 ° C), diffusion at 1000 ° C for 30 minutes in a muffle furnace results in a sheet resistance of 30 Ω / sq. An alternative diffusion in a tube furnace at 950 ° C for 30 minutes in nitrogen flow gives a sheet resistance of 105 Ω / sqr. 10 shows the curve of the doping potential (ECV profile) of a doping medium prepared according to Example 8 (red = boron concentration, blue = basic doping (P)). The doping was carried out at 1000 ° C in a muffle furnace for 30 minutes.

11 shows the curve of the doping potential (ECV profile) of a dopant produced according to Example 8 (red = boron concentration, blue = basic doping (P)). The doping was carried out at 950 ° C in a tube furnace for 30 minutes in a nitrogen atmosphere.

Example 10:

In a stirrer apparatus, 83 g are placed in a desiccator

pre-dried crystalline phosphoric acid weighed out and with 150 g

Tetrahydrofuran added. The resulting mixture is brought to reflux using an oil bath (80 ° C). In the boiling mixture 100 g of acetic anhydride are rapidly added dropwise from an attached dropping funnel. In this mixture from another dropping funnel 190 g

Tetraethylorthosilicate (TEOS) slowly added dropwise to the mixture introduced in the apparatus with vigorous stirring. After the addition of the tetraethyl orthosilicate, the temperature of the oil bath is raised to 20 ° C and the mixture is left under vigorous stirring for one hour at this temperature. The reaction is then followed by a

Solvent mixture consisting of 150 g of ethyl acetate, 600 g of isopropanol and 150 g of ethoxypropanol, quenched and refluxed for a further 60 minutes. The doping ink enables a homogeneous spray coating of

Silicon wafers.

The content of acetic anhydride in the reaction mixture according to this Example 10 can be varied. It has proven to be advantageous to use masses between 90 g and 380 g of the reactant. The crosslinking of the oxide network can be determined by the amount of added acetic anhydride, the amount of tetrahydrofuran contained in the reaction mixture, the duration of the heating of the

Reaction mixture at 120 ° C, as well as the temperature of the heating are controlled. The duration of heating can after complete Add all reactants between 30 minutes and 240 minutes. As inert solvents other tetra hydrofu ran other sufficiently polar and non-protic solubilizers, such as

For example, 4-dioxane and dibenzyl, into consideration, for which purpose more solvents can be used with appropriate properties. By suitably selecting the above-mentioned synthesis conditions, it is possible to adjust the viscosity of the doping ink between a few mPas, for example 3 mPas, and 100 mPas. The stabilization of

Dotiertinte can following the synthesis by means of already

described capping agent can be achieved. This is the ink

advantageously directly during quenching with one or more of said solvents with a suitable capping agent, such as preferably provided ethoxytrimethylsilane. It has proved to be advantageous, 10 ml to 50 ml of the capping material, in this case

Ethoxytrimethylsilane to use. For the production of very inkjet-capable doping media, it has proved to be advantageous to others

Use solvent to quench the reaction mixture.

Suitable solvents are mentioned in connection with Example 5. It goes without saying that all of the described syntheses of the doping inks can also be carried out with boron-containing precursors, substituting the phosphorus precursor.

List of pictures

Fig. 1: P-NMR profile of an ink according to Example 1. The chemical shift of free phosphoric acid is 0 ppm and is not detectable in this example.

FIG. 2: Doping profiles of doping tests according to Example 2 with

reproducible doping media and constant doping effect.

3: ECV profiles of doping tests according to Example 3

Fig. 4: Scanning electron micrograph (50,000 times

Magnification) of an applied diffusion layer on a pyramid of an alkaline textured (100) wafer. It's good the homogeneous

Covering the surface to be detected by sprayed PSG layer. The measured layer thickness is 44 nm.

FIG. 5: Sheet resistance distribution (top right) on a whole-area wafer treated with doping medium according to Example 1. The ECV profile (bottom left) corresponds to a typical measurement point on the sample

Fig. 6: ECV profile of a diffused emitter and a

Reference measurement 1 mm next to the printed area

FIG. 7: Comparative lifetime measurement of a p-type wafer doped with a commercially available doping ink versus a comparable one. FIG

reference wafer

FIG. 8: Comparative lifetime measurement of a wafer treated with a solvent produced according to the optimized synthesis method and using adequately pretreated solvent in comparison to a wafer after its doping with a commercially available doping ink

FIG. 9: Doping potential of a doping medium prepared according to Example 6; FIG. Layer resistance as a function of under cooling

Storage duration of the doping medium FIG. 10: Doping potential (ECV profile) of a dopant prepared according to Example 8 (red = boron concentration, blue = basic doping (P)); FIG.

Doping at 000 ° C in a muffle oven for 30 minutes

FIG. 11: Doping potential (ECV profile) of a doping medium prepared according to Example 8 (red = boron concentration, blue = base doping (P)); FIG.

Doping at 950 ° C in a tube furnace for 30 minutes in a nitrogen atmosphere

Claims

P A T E N T A N S P R E C H E

Process according to the claim for the production of printable,

low-viscosity oxide media in the form of doping media, characterized in that an anhydrous sol-gel-based synthesis by condensation of alkoxysilanes and / or alkoxyalkylsilanes with symmetrical and asymmetric carboxylic acid anhydrides

i. in the presence of boron-containing compounds

and or

iL in the presence of phosphorus-containing compounds

is carried out and low-viscosity dopants (doping inks) are prepared by controlled gelation.

A process according to claim 1, wherein the alkoxysilanes and / or alkoxyalkylsilanes used have saturated, unsaturated, branched, unbranched aliphatic, alicyclic and aromatic radicals individually or different therefrom, which in turn are at any position of the alkoxide and / or alkyl radical by heteroatoms selected from the group O, N, S, Cl, Br can be functionalized.

Method according to one or more of claims 1 or 2, wherein the boron-containing compounds are selected from the group boron oxide, boric acid and boric acid esters.

Method according to one or more of claims 1 to 3, wherein the phosphorus-containing compounds are selected from the group phosphorus (V) oxide, phosphoric acid, polyphosphoric acid,

Phosphoric acid esters and phosphonic acid esters with alpha- and beta-functional siloxane-functionalized groups.

A process as claimed in one or more of claims 1 to 4, wherein the carboxylic acid anhydrides used are anhydrides from the group of acetic anhydride (acetic anhydride), ethyl formate (anhydride of formic and acetic acid), propionic anhydride, Succinic anhydride, maleic anhydride, sorbic anhydride, phthalic anhydride and benzoic anhydride.

6. The method according to one or more of claims 1 to 5, characterized in that the printable oxide media in the form of

Doping media based on hybrid sols and or gels (such as SiO2-P2O5-B2O3 and SiO3-AI2O3-B2O3), below

Use of alcoholates / esters, hydroxides or oxides of aluminum, gallium, germanium, zinc, tin, titanium, zirconium, or lead, and mixtures thereof.

7. The method according to claims 5 or 6, characterized in that a solvent selected from the group propanol,

Isopropanol, butanol, butyl acetate, ethyl acetate,

Ethylene glycol monobutyl ether, diethyl glycol, diethylene glycol,

Diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, used alone or in a mixture as a solvent.

8. Use of an oxide medium, which is prepared according to a

Method according to one or more of claims 1-7 for producing a grip and abrasion resistant layer on silicon wafers, characterized in that the surface printed on the oxide medium, in a temperature range between 50 ° C and 750 ° C, preferably between 50 ° C and 500 ° C, more preferably between 50 ° C and 400 ° C, using one or more, to be carried out sequentially Temperschritten (heat treatment by means of a step function) and / or an annealing ramp, dried and compacted to the glazing, thereby reaching a handle and abrasion resistant layers with a thickness of up to 500 nm can form.

9. The method according to one or more of claims 1-8, characterized in that are added to improve the stability of the oxide media "capping agent" selected from the group acetoxytrialkylsilanes, alkoxytrialkylsilanes, Halogentrialkylsilane and derivatives thereof.

10. Use of an oxide medium, produced by a process according to one or more of claims 1 - 9 as a doping medium in the processing of silicon wafers for photovoltaic,

microelectronic, micromechanical and micro-optical applications.

11. Use according to claim 10, characterized in that from the glazed on the surfaces of layers by heat treatment at a temperature in the range between 750 ° C and 1100 ° C, preferably between 850 ° C and 1100 ° C, more preferably between 850 ° C. and 000 ° C, silicon doping atoms, such as boron and / or phosphorus, are deposited on the substrate, whereby the

Conductivity of the substrate is affected.

12. Use according to claim 11, characterized in that by temperature treatment of the layers formed from the printed oxide media, a co-diffusion to form

of n- and p-type layers takes place.

13. Use of an oxide medium prepared by a process

according to one or more of claims 1-12 for the production of PERC, PERL, PERT, IBC solar cells and others, wherein the

Solar cells have further architectural features such as MWT, EWT, Selective Emitter, Selective Front Surface Field, Selective Back Surface Field and Bifaciality.

14. Use of a low-viscosity oxide medium prepared according to

a method according to one or more of claims 1-12 for producing thin, dense glass layers, which act as a sodium and potassium diffusion barrier in the LCD technique as a result of a thermal treatment, or of corresponding glass layers on the

_Cover glass of a display, consisting of doped SiO _2l, which _prevent the diffusion of ions from the cover glass into the liquid-crystalline phase.