CN108735595A - Method and apparatus for chemically treating semiconductor substrates - Google Patents

Abstract

The invention relates to a device and a method for asymmetrically treating a wafer (2) in a single step.

Description

Method and apparatus for chemically processing semiconductor substrates

technical field

The invention relates to a method for chemically treating semiconductor substrates. The invention also relates to an apparatus for chemically processing semiconductor substrates. Finally, the invention relates to a method for producing a solar cell.

Background technique

All steps involved in the production of solar cells from wafers include the treatment of the front and back sides of the wafers. It is advantageous here if the front and rear sides of the wafer are processed differently. This usually requires very laborious methods.

Methods for processing semiconductor substrates are known, for example, from patent documents DE 10 2011 056 495 A1 and WO 2016/012 405 A1.

Contents of the invention

A technical problem addressed by the invention consists in improving a method for chemically processing semiconductor substrates.

The above-mentioned technical problem is solved by the method according to the invention, namely a method for chemically treating a semiconductor substrate comprising the following steps:

- preparation of semiconductor substrates with front and back sides,

- preparation of a device for texturing said semiconductor substrate, said device having a groove device for containing an etching medium,

- preparing the etching medium in said tank,

- introducing the semiconductor substrate into the tank, wherein both the front side and the back side of the semiconductor substrate are at least temporarily fully immersed in the etching medium,

- treating the semiconductor substrate by means of the etching medium such that the backside of the semiconductor substrate has a reflectivity which is at least 2% greater than the reflectivity of the front side of the semiconductor substrate.

The core of the invention is that the semiconductor substrate is processed in such a way that it is asymmetrically processed, in particular asymmetrically textured. This means that the texture of the front side of a semiconductor substrate differs from the texture of the back side of the same semiconductor substrate.

In general, the invention relates to any desired method for asymmetrically processing the front and back of a semiconductor substrate. These are, for example, coating methods, deposition methods or structuring methods, in particular etching methods. In particular, the invention is not limited to a certain method.

With the aid of the invention, it is possible to etch back, for example, the emitter on the front side of the semiconductor substrate, for example by producing porous silicon. At the same time, wet-chemical edge insulation can be performed on the rear side of the semiconductor substrate.

The aspects of the invention relating to the texturing of wafers will first be described below.

The texturing of the surface of a semiconductor substrate is usually characterized by its degree of reflectivity. In this context, an average reflectance in the wavelength range between 400 nm and 1100 nm is to be understood at normal incidence. The measurement is usually carried out using a commercially available spectrophotometer in the wavelength range between 300 nm and 1200 nm, wherein the range between 400 nm and 1100 nm is considered for the evaluation. In this case, both diffusely reflected light and directly reflected light are measured using integrating spheres.

In particular, it is provided that the semiconductor substrate is processed by means of an etching medium such that the rear side of the semiconductor substrate has a reflectance _{R R} which is at least 2%, in particular at least 5%, greater than the reflectance RV of the front side of the semiconductor substrate , especially at least 8%.

The reflectivity _RR of the rear side of the semiconductor substrate is in particular greater than 28%, in particular at least 30%, in particular at least 33%.

The reflectance R _V of the front side of the semiconductor substrate is in particular at most 27%, especially at most 23%, especially at most 20%.

The method according to the invention leads in particular to texturing of the front side of the semiconductor substrate and to polishing of the rear side of the semiconductor substrate. A polished side is understood here to be a side with a reflectivity of greater than 28%. It is also sometimes referred to as "reduced texture".

The semiconductor substrate is especially a wafer. In particular, it can be a silicon wafer, especially a wafer made of polysilicon. In particular, the wafer can have a thickness in the range from 50 μm to 1000 μm, in particular in the range from 140 μm to 200 μm. The wafers are sawn from polycrystalline blocks, in particular by means of a diamond wire sawing method.

According to one aspect of the invention, the semiconductor substrate to be treated with the etching medium is introduced into the process bath as follows, so that both the front side and the back side of the semiconductor substrate are completely immersed in the etching medium. According to another aspect, the semiconductor substrate is completely immersed in the etching medium during the entire operation.

The immersion depth of the semiconductor substrate is in particular in the range from 1 mm to 50 mm, in particular in the range to 30 mm, in particular in the range to 20 mm, in particular in the range to 10 mm.

In particular, the rear side of the semiconductor substrate points upwards. In particular, the rear side of the semiconductor substrate faces the free surface of the etching medium in the trench.

It enables a particularly reliable monitoring of the processing of the semiconductor substrate. This makes the semiconductor substrate easier to handle during handling.

According to another aspect of the invention, the semiconductor substrate is immersed in an etching medium untreated. This means that neither the front side nor the back side of the semiconductor substrate for immersion into the etching medium is provided with a protective layer. In other words, the surface of the front side of the semiconductor substrate and the surface of the rear side of the semiconductor substrate are formed by the crystal structure of the semiconductor substrate. However, it is also possible, before the actual texturing step, to remove at least partially, in particular completely, the damage caused by the sawing.

The outlay for carrying out the asymmetric texturing of the semiconductor substrate is thus greatly reduced. According to the invention it is known that a pretreatment of the semiconductor substrate, in particular a coating of the semiconductor substrate with one or more protective layers, can be avoided.

According to another aspect of the invention, the texturing of the front side of the semiconductor substrate and the polishing of the back side of the semiconductor substrate are performed simultaneously. In particular both are carried out in a single process step.

This reduces the outlay for the method. This also leads to saving time.

The method is in particular a double-sided process. It differs from the single-sided process in which the front and back sides of the semiconductor substrate are processed sequentially and/or with different media.

In the method according to the invention, the semiconductor substrate as a whole is located in the trench with the etching medium. It is especially possible that the basic composition of the etching medium in the region of the front side of the semiconductor substrate is approximately the same as the basic composition of the etching medium in the region of the rear side of the semiconductor substrate.

According to an alternative configuration, the composition of the medium, in particular the concentration of components of the medium, is distributed unevenly in the tank. As will be explained in more detail below, provision can be made, in particular, that the processing conditions on the front side of the semiconductor substrate differ from the processing conditions on the rear side of the semiconductor substrate. The medium, in particular components of the medium, in particular reactants and/or reaction products, can have different concentrations and/or temperatures, in particular in the region of the front and back of the semiconductor substrate.

According to another aspect of the invention, an acid is used as the etching medium. In particular, the etching medium can contain metal ions. In particular, it may be an etching medium for metal assisted chemical etching (English: Metal Assisted Chemical Etching, ie MACE).

In particular, the etching medium can comprise hydrofluoric acid (HF) and/or nitric acid (HNO ₃ ) and/or metal nitrates, especially silver nitrate (AgNO ₃ ).

The proportion of hydrofluoric acid in the etching medium is especially in the range from 1% to 25%, especially in the range from 3% to 21%, especially in the range from 15% to 20%, preferably in the range from 15% to the range of 16%.

The proportion of nitric acid in the etching medium is preferably in the range of 5% to 30%, in particular approximately 12% to 20%, especially approximately 15% to at most 20%, preferably in the range of 18% to 20%.

The etching medium has a proportion of silver nitrate in particular in the range of 0.0001% to 0.1%, in particular in the range of at most 0.001% to 0.05%, in particular at most 0.015%.

The above data are mass percentages.

Preferably, the temperature of the etching medium is in the range from 5° C. to 50° C., in particular in the range from 10° C. to 45° C., in particular up to 30° C., during the processing of the semiconductor substrate.

According to a further aspect of the invention, gas bubbles formed during the treatment of the semiconductor substrate by means of an etching medium are at least partially removed from the rear side of the semiconductor substrate.

Surprisingly, this leads to an asymmetric texturing of the semiconductor substrate.

According to a further aspect of the invention, air bubbles on the rear side of the semiconductor substrate are removed mechanically and/or hydrodynamically and/or thermally and/or chemically.

This relates in particular to the selection from one or more suitable methods.

For example, a scraping method is prescribed for removing air bubbles from the back surface of a semiconductor substrate. Air bubbles can especially be removed from the rear side of the semiconductor substrate by means of a wiper roller. The scraping roller can simultaneously serve as a gripper for the semiconductor substrate in the tank. In particular, the scraping roller extends over the entire width of the semiconductor substrate.

Alternatively or additionally, gas bubbles can be removed from the rear side of the semiconductor substrate by means of a flow of the etching medium in the groove, in particular by means of a surface flow of the etching medium in the groove. In particular, a surface flow can be generated by designing the groove as an overflow groove. For this purpose, the groove can have vertically adjustable side walls which act as blocking elements or barriers.

A surface flow of the etching medium can also be produced by means of suitably arranged inflow nozzles for the etching medium. In this alternative, the surface flow can be controlled in a particularly simple manner. In particular, the inflow nozzle can have a control device for controlling the inflow speed and/or direction of the etching medium. In particular, the inflow nozzle can be arranged adjustably relative to the groove.

In order to remove air bubbles from the rear side of the semiconductor substrate, it can also be provided that the rear side of the semiconductor substrate is heated. This can be achieved by means of electromagnetic radiation, in particular infrared radiation. Heating of the backside of the semiconductor substrate can lead to convection between the backside of the semiconductor substrate and the free surface of the etching medium.

The enthalpy of reaction can also cause heating.

In order to remove air bubbles from the backside of the semiconductor substrate, chemical reactions can also be engineered. To this end, chemical additives can be introduced into the etching medium, in particular in the region between the rear side of the semiconductor substrate and the free surface of the etching medium. The chemical additive can be introduced into the etching medium, for example, via nip rolls. Chemical additives can also be introduced into the etch medium as gas streams. Chemical additives can also be introduced into the etching medium through the inflow nozzle.

In order to facilitate the removal of air bubbles from the rear side of the semiconductor substrate, one or more degassing aids can be used in particular.

Ultrasonic methods can also be used to remove air bubbles from the backside of semiconductor substrates. In this case, in particular waves can form in the groove in the region between the rear side of the semiconductor substrate and the free surface of the etching medium.

According to another aspect of the invention, the semiconductor substrate is oriented substantially horizontally in the slot during processing. In this case, the rear side of the semiconductor substrate points in particular upwards, that is to say to the free surface of the etching medium. In particular, the front side of the semiconductor substrate points downwards, that is to say to the bottom of the trench.

In this way, it can be achieved in a simple manner that gas bubbles formed on the downwardly directed front side of the semiconductor substrate are prevented by the semiconductor substrate from rising and escaping from the etching medium. The gas bubbles thus remain at least predominantly on the front side of the semiconductor substrate.

The horizontal orientation of the semiconductor substrate in the groove thus facilitates the realization in a simple manner that the concentration of gas bubbles formed on the front side of the semiconductor substrate during processing of the semiconductor substrate is greater than the concentration of gas bubbles formed on the back side of the semiconductor substrate. concentration.

Bubbles are a specific example with regard to the composition of media used to process semiconductor substrates. As an alternative to gas bubbles, other components of the medium used for processing semiconductor substrates, especially reactants, products, precipitates, catalysts or process conditions, especially the temperature of the processing medium, can be influenced, especially controlled, so that The front side and the back side of the substrate are different from each other.

In this case, the asymmetry of the processing conditions is brought about in particular by the geometric asymmetry, in particular the different volumes of the processing medium below and above the wafer. In particular, it is also possible to irradiate only one side of the semiconductor substrate by means of additional means, such as heating elements and/or a radiation device, in particular for irradiating only one side of the semiconductor substrate with electromagnetic radiation, especially in the infrared range, in the visible range or in the UV range Contributing to the asymmetry of processing conditions.

As mentioned above, asymmetry of the treatment conditions can also be induced by hydrodynamic means.

According to one aspect of the invention, the one or more semiconductor substrates form a separation layer, in particular an at least substantially impermeable separation layer between the lower and upper regions of the one or more semiconductor substrates. Asymmetric processing of the semiconductor substrate can also be facilitated in this way.

For this purpose it is advantageous if the wafer covers the process tank as completely as possible. The sum of the areas of the front or back sides of the semiconductor substrate introduced into the tank is preferably between 40% and 95%, especially between 60% and 80%, especially between 70% and 80% of the cross section of the process tank in the range. In the case where the cross-section of the process tank changes according to its height, the above data are based on the height of the transport plane of the wafer. The value given is also called coverage.

The method for processing semiconductor substrates is in particular a tandem method.

According to a further aspect of the invention, the semiconductor substrate is transported through the slot by means of a transport device during processing. Especially through the groove continuously. This simplifies the process and in particular increases the production capacity.

According to a further aspect of the invention, the semiconductor substrate is held stationary relative to the conveying elements of the conveying device during conveyance through the slot. In particular, the semiconductor substrate can be held stationary relative to the carrier element. In particular, transport through the trough is possible by means of such support elements.

The semiconductor substrate can also be moved relative to one or more carrier elements during transport through the slot. In particular, conveyor rollers of the conveyor device can be used as support elements.

Preferably, the carrier element is designed in such a way that it at the same time forms a flow-influencing device, in particular for influencing the relative flow of the etching medium in the region of the front side of the semiconductor substrate when transporting the semiconductor substrate through the slot. . It is especially possible for the support element to be formed with a deflector. The baffle is preferably designed such that a flow dead zone is formed in the region of the front side of the semiconductor substrate when the semiconductor substrate is transported through the etching medium. This prevents air bubbles formed on the front side of the semiconductor substrate from being removed from the front side of the semiconductor substrate by the transport process.

In particular, the carrier element can bring about a separation of the region on the front side of the semiconductor substrate from the region on the rear side of the semiconductor substrate. In particular, this can form a means for reducing the reaction medium exchange above and below the semiconductor substrate. In particular, this makes it possible to at least partially, in particular to at least 50%, in particular to at least 70%, in particular 90%, in particular completely cover the interspace remaining between two adjacent semiconductor substrates.

The distance between two adjacent semiconductor substrates on the carrier element is preferably at most 20 cm, especially at most 10 cm, especially at most 5 cm, especially at most 3 cm, especially at most 2 cm, especially at most 1 cm, especially at most 5 mm, especially at most 3 mm , especially up to 2mm, especially up to 1mm.

According to another aspect, the invention relates to a method for asymmetrically processing a semiconductor substrate, the method comprising the steps of:

- preparation of semiconductor substrates with front and back sides,

- preparation of a device for asymmetric processing of said semiconductor substrate, wherein said device has a tank for containing a reaction medium,

- preparation of the reaction medium in said tank,

- introducing the semiconductor substrate into the tank, wherein both the front side and the back side of the semiconductor substrate are at least temporarily fully immersed in the reaction medium,

- Influencing the reaction medium in the tank such that regions above the semiconductor substrate are in different process conditions than regions below the semiconductor substrate.

In this case, the semiconductor substrate or the plurality of semiconductor substrates themselves in particular form a separation layer for separating a region above the semiconductor substrate from a region below the semiconductor substrate.

In particular, one or more devices for influencing the temperature of the reaction medium in the region above the wafer and/or in the region below the wafer can be provided.

In particular, one or more means for influencing the concentration of one or more components of a medium for processing the semiconductor substrate in a region above the semiconductor substrate and/or in a region below the semiconductor substrate can be provided. .

For further details and advantages, reference is made to what has been said and to the following description.

The technical problem to be solved by the invention is also that of improving a device for the chemical treatment of semiconductor substrates. This technical problem is solved by a device according to the invention with a device for at least partially removing air bubbles from the surface of a semiconductor substrate arranged in a groove.

Its advantages follow from the above description.

The apparatus is particularly suitable for carrying out the methods already described above.

The apparatus includes a tank for containing an etching medium. Here, in particular, isopipes. The device preferably includes a return device, in particular a circulation pump.

The backflow device is preferably controllable.

The apparatus also includes a conveying device for conveying the semiconductor substrate through the etching medium arranged in the groove. The conveying device is preferably arranged such that a semiconductor substrate conveyed through the tank by means of the conveying device is completely immersed in the etching medium. In particular, the conveying device is arranged at least 1 mm, in particular at least 1 cm, below the lowest upper edge of the groove. This corresponds to the minimum filling height of the tank at which the device is operating

The medium-based inflow forms in particular the tank level above the level of the overflow element. The height difference between the tank level and the upper edge of the overflow element is at least 1 mm, in particular at least 10 mm, in particular at least 15 mm.

The conveyor device can have a plurality of conveyor rollers and/or conveyor belts. The transport device preferably has a carrier element for placing the semiconductor substrate. Refer to the description above for details. The conveying speed is in the range between 0.5 m/min and 2.5 m/min, especially in the range between 2.0 m/min and 2.5 m/min

According to one aspect of the invention, the device for removing gas bubbles at least partially from the surface of a semiconductor substrate arranged in a groove has means for generating a flow of an etching medium in the groove, in particular for causing a flow in the groove Etched media in a device that generates surface flow.

The flow generation device is designed in particular in such a way that the etching medium has a greater horizontal velocity in the region of its free surface than in the region of the conveying plane which is vertically spaced relative to the free surface when the device is in operation. The flow rate at which the semiconductor substrate is transported through the etching medium in the region of the transport plane spaced vertically relative to the free surface.

In particular in this way it can be achieved that the etching medium has a greater flow velocity in the region of the upwardly directed rear side of the semiconductor substrate than in the region of the front side of the semiconductor substrate. This makes it possible to remove air bubbles differently from both sides of the semiconductor substrate.

The differential removal of the gas bubbles from the two sides of the semiconductor substrate is also facilitated by the buoyancy forces acting on the gas bubbles. On the underside of the semiconductor substrate, the rise of the bubbles is blocked by the wafer itself.

The semiconductor substrate is conveyed through the slot along a conveying plane which is oriented substantially horizontally. In particular, the transport plane extends substantially parallel to the free surface of the etching medium in the groove.

In particular, the transport plane can form a separation plane between the upper region of the semiconductor substrate and the lower region of the semiconductor substrate. The separation of the region above the semiconductor substrate from the region below the semiconductor substrate can be effected in particular by the semiconductor substrate itself. The separation can be improved by arranging the semiconductor substrates as gap-free as possible. Optionally, the separation can be brought about by a suitable configuration of the delivery element.

The flow generating device can have at least one vertically adjustable pressure element or overflow element.

The adjustable overflow element of the tank is in particular arranged on a side of the tank extending parallel to the conveying direction of the semiconductor substrate.

The surface flow of the etching medium preferably has a main component which extends substantially perpendicular to the transport direction of the semiconductor substrate. The principal component can also be oriented parallel or obliquely to the conveying direction.

The flow generating device can have one or more inflow nozzles. Refer to the description above for details.

The flow generating device can have means for generating a gas flow in the region of the free surface of the etching medium. The gas flow here preferably extends substantially parallel to the surface of the etching medium. This can facilitate the selective removal of air bubbles from the rear side of the semiconductor substrate.

The means for generating a flow of the etching medium may have means for generating a convection flow on the side of the semiconductor substrate facing the free surface of the etching medium, in particular on the rear side of the semiconductor substrate. This helps to selectively remove air bubbles from that side of the semiconductor substrate.

According to a further aspect of the invention, the device for at least partially removing air bubbles from the surface of the semiconductor substrate arranged in the groove has one or more mechanical elements.

This can be a scraping element (English: Squeegee). The scraping element can at the same time act as a hold-down for holding the semiconductor substrate in a predetermined vertical position in the groove.

In particular, the scraping elements and/or pressure rollers are arranged in the groove pointing substantially perpendicularly to the transport direction of the semiconductor substrates.

In particular, the longitudinal extension of the scraping element and/or the pressure roller is directed substantially parallel to the principal component of the flow of the etching medium in the region of its free surface. This prevents the scraping elements and/or pressure rollers from adversely affecting, in particular hindering, the surface flow.

The scraping elements and/or pressure rollers can also be oriented perpendicular to the principal component of the flow of the etching medium or perpendicular to the transport direction of the semiconductor substrate. The scraping element and/or the pressure roller can be used in particular as means for reducing or in particular for suppressing the exchange of reaction medium between regions adjoining the scraping element and/or the pressure roller. In particular, the separation of the upper region of the semiconductor substrate from the lower region of the semiconductor substrate can thereby be improved.

The mechanical element for removing air bubbles from the surface of the semiconductor substrate may in particular be a roller, in particular a roller with a smooth cylindrical outer surface.

Mechanical elements for removing air bubbles from the surface of the semiconductor substrate, in particular scraping elements and/or pressure rollers, in particular are arranged in a stationary manner in the groove.

According to a further aspect of the invention, the device for at least partially removing air bubbles from the surface of the semiconductor substrate can have means for generating vibrations, in particular a vibration table (also called a shaking table). In particular, a tank for receiving an etching medium can be arranged on such an oscillating table.

According to a further aspect of the invention, the means for at least partially removing air bubbles from the backside of the semiconductor substrate comprises an ultrasonic means. Refer to the description above for details.

According to another aspect of the invention, the means for at least partially removing gas bubbles from the backside of the semiconductor substrate comprises heating the backside of the semiconductor substrate and/or heating the backside of the semiconductor substrate and Heating means for the etching medium in the region between the free surfaces of the etching medium.

In particular, different temperatures of the process medium in the process tank in the region of the front side of the semiconductor substrate and in the region of the rear side of the semiconductor substrate can be set by means of the heating device. The process kinetics when processing semiconductor substrates can be controlled by influencing the temperature. In this way, asymmetric processing can also be achieved or facilitated.

According to another aspect of the invention, the means for at least partially removing gas bubbles from the backside of the semiconductor substrate includes means for controllably adding one or more additives to the etching medium. The chemical additives can in particular be added to the etching medium via the scraping elements and/or pressure rollers. In this way it can be achieved that the chemical additive has a higher concentration in the region of the rear side of the semiconductor substrate than in the region of the front side of the semiconductor substrate.

According to a further aspect of the invention, provision is made for setting and/or influencing the concentration of one or more components of the medium in the region adjoining the rear side of the semiconductor substrate and/or in the region adjoining the front side of the semiconductor substrate device. Asymmetric processing of semiconductor substrates can thus be achieved in a particularly simple manner. In particular, it can be achieved that a specific component of the medium has a different concentration in the region of the front side of the semiconductor substrate than in the region of the rear side of the semiconductor substrate. In particular, the concentrations may differ by at least 5%, especially by at least 10%, especially by at least 20%, especially by at least 30%, especially by at least 50%. In particular, the concentrations may differ by up to 100%, especially up to 200%, especially up to 500%, especially up to 1000%.

In particular, different concentrations of one or more components of the medium can be achieved by suitably adding these components by means of an addition device, for example an addition line or an addition nozzle.

Different concentrations of one or more components of the medium can be produced, for example, by reactions on the top and bottom sides. The reaction consumes reactants and forms products. Through the separation, different concentrations of the components of the medium are provided on the top and bottom sides.

According to a further aspect of the invention, the apparatus comprises a conveying device for conveying the semiconductor substrate through the tank, the conveying device having at least one support element arranged as follows, that is, the semiconductor substrate Immerse completely in the etching medium while conveying through the tank. Refer to the description above for details.

The technical problem to be solved by the invention is also to improve the method for producing solar cells. The technical problem is solved by processing the semiconductor substrate according to the method described above. The contact structures, in particular the doping and shrinkage structures, and the electrically insulating layer are then applied on the front side and the rear side of the semiconductor substrate.

The rear side of the semiconductor substrate can also be passivated by means of an electrically insulating layer.

The method is used in particular for the production of so-called PERC (passivated emitter rear cells) solar cells (English: Passivated Emitter Rear Cell).

The front side of the semiconductor substrate can be provided with an antireflection coating. In this way, the reflectivity of the front can be further reduced. This leads to an increase in the efficiency of the solar cell.

Description of drawings

Details and advantages of the invention emerge from the description of exemplary embodiments with reference to the drawings. In the attached picture:

1 shows a schematic diagram of the construction of an apparatus for processing semiconductor substrates,

Fig. 2 shows the graph that the reflectivity of the front and back side of the semiconductor substrate processed according to the present method is correlated with the wavelength,

FIG. 3 shows a schematic top view of an alternative embodiment of the device according to FIG. 1 ,

FIG. 4 shows a partial schematic view of an alternative embodiment of an apparatus for processing semiconductor substrates.

Detailed ways

An apparatus 1 for chemically processing semiconductor substrates in the form of wafers 2 is firstly described below with reference to FIG. 1 .

Wafer 2 is especially a polysilicon wafer.

The device 1 comprises a process tank 3 for containing an etching medium 4 .

The etching medium 4 is in particular an acidic etching medium, especially an acid. The etching medium 4 is present in the process tank 3 in particular in liquid form.

The etch medium 4 may have 20% nitric acid, 15% hydrofluoric acid and 0.0005% silver nitrate. In particular, the etching medium is kept at a temperature in the range from 10° C. to 45° C. during operation of the device 1 .

The process tank 3 is configured as an overflow tank. It has an overflow channel 5 on at least one side.

The process tank 3 has at least one overflow element 6 which is adjustable in the vertical direction. The overflow element 6 forms a barrier. The device 1 can also have several barriers, in particular barriers on different sides of the process tank 3 .

The device 1 also comprises a conveying device 7 with support elements. In the variant embodiment shown in FIG. 1 , the support elements are designed as conveyor rollers 10 . The transport rollers 10 each have one or more short, in particular up to 1 cm long, contact surfaces relative to the wafer 2 parallel to the axis of rotation of the transport rollers. The support surface of the wafer 2 on the transport roller 10 is preferably substantially punctiform. In particular, the bearing surface has an area of at most 1 cm ² , in particular at most 1 mm ² .

The transport device 7 serves to transport the wafers 2 in the transport plane 9 .

The transport roller 10 is rotatably mounted.

The overflow channel 5 is connected to a storage tank 12 via a return line 11 .

The storage tank 12 is connected to the process tank 3 through a supply device 13 . The supply device 13 includes in particular a pump 14 , in particular a circulation pump.

The supply device 13 in particular forms means for generating a flow of the etching medium 4 in the process bath 3 .

In particular, a surface flow 15 of the etching medium 4 in the process tank 3 can be generated by means of the overflow element 6 . According to the alternative shown in FIG. 1 , the overflow element 6 is arranged perpendicular to the conveying direction 8 . The overflow element 6 is preferably oriented parallel to the conveying direction 8 . In particular, the surface flow 15 can be directed perpendicularly to the conveying direction 8 .

FIG. 3 schematically shows a plan view of a corresponding alternative embodiment of the device 1 .

For introducing wafers 2 into process tank 3 , device 1 can have an introduction device 16 , which is only schematically shown in FIG. 1 .

To remove wafers 2 from process tank 3 , device 1 can have a removal device 17 , which is only schematically shown in FIG. 1 .

The device 1 also includes pinch rollers 18 . The clamping rollers 18 can form part of the conveying device 7 . In particular, the clamping rollers are arranged at a distance from the conveyor roller 10 in the vertical direction. The clamping rollers are preferably oriented horizontally.

The clamping roller 18 can in particular be designed as a pressure roller and have a smooth, cylindrical outer surface. The clamping rollers 18 function as scraping elements for removing air bubbles from the upwardly directed rear side 19 of the wafer 2 when the wafer 2 is transported in the transport direction 8 .

The clamping rollers can also have clamping rings, which lead to a reduced contact surface, in particular essentially point-like contact, with the wafer 2 .

The clamping rollers in particular form part of the device for at least partially removing air bubbles from the surface of the wafer 2 .

The wafer 2 is aligned in the process tank 3 in particular in the horizontal direction. The conveying plane 9 forms a horizontal plane.

Details of the method for chemically processing the wafer 2 are explained below.

Firstly, an etching medium 4 is prepared in the process tank 3 . The wafer 2 is then introduced into the process tank, wherein both the front side 20 and the back side 19 of the wafer 2 are completely immersed in the etching medium 4 .

Wafer 2 is immersed with its front side 20 downwards into etching medium 4 . The immersion depth is, for example, in the range from 2 mm to 10 mm.

Etching the medium 4 leads to an asymmetric texturing of the surface of the wafer 2 . Etching medium 4 leads in particular to texturing of front side 20 of wafer 2 . At the same time, it leads to less texturing of the rear side 19 of the wafer 2 . This is also referred to as "polishing" hereinafter. The texturing of the front side 20 of the wafer 2 and the polishing of the back side 19 of the wafer 2 take place in a single, common process step. Both especially at the same time. The method is in particular a double-sided process.

Bubbles formed on the surface of the wafer 2 during the treatment of the wafer 2 by means of the etching medium 4 are at least partially removed from the rear side 19 of the wafer 2 . Gripping rollers 18 , which are designed in particular as squeeze rollers, serve to remove air bubbles from rear side 19 of wafer 2 . Separate scraping elements can also be provided.

The removal of air bubbles can also be facilitated by generating a surface flow 15 . This flow of the etching medium 4 has a stronger horizontal component, in particular in the region of the free surface of the etching medium, than in the region of the transport plane 9 , in particular in the region of the front side 20 of the wafer 2 .

The method is in particular a so-called in-line method.

Surprisingly, the processing of the wafer 2 with the apparatus 1 resulted in a wafer 2 with asymmetric texturing. The texturing of wafer 2 can be characterized in particular by the reflectivity of front side 20 or rear side 19 of wafer 2 . After carrying out the method described above, the reflectivity of the back side 19 of the wafer 2 is at least 2%, in particular at least 5%, especially at least 8%, greater than the reflectivity of the front side 20 .

The reflectivity _RR of the rear side 19 of the wafer 2 is in particular at least 28%, in particular at least 30%, in particular 33%. Reflectance is to be understood in particular as the mean value of the reflectance in the wavelength range between 400 nm and 1100 nm when the wafer 2 is illuminated perpendicularly, as measured by a spectrophotometer (diffuse reflection and direct reflection light). As an alternative to this, the reflectivity can also be the reflectivity of the individual surfaces of the wafer 2 when irradiated vertically with electromagnetic radiation of a certain wavelength, for example with a wavelength of 400 nm, 450 nm or 500 nm. After carrying out the method described above, the reflectance R _V of the front side 20 of the wafer 2 is in particular approximately at most 27%, in particular at most 23%, especially at most 20%.

After the texturing step, the reflectivity of the front side 20 of the wafer 2 can be further reduced by applying an anti-reflection coating. In this way, the efficiency of solar cells manufactured from the wafer 2 can be further improved. In particular so-called PERC solar cells are produced from the wafer 2 processed according to the invention. For this purpose, an insulating layer and contact structures are also provided on the rear side 19 of the wafer 2 . The principle of the PERC battery is described in detail in "The Passivated Emitter and Rear Cell (PERC): From conception to mass production (Solar Energy Materials & Solar Cells 143 (2015) 190–197)".

An exemplary diagram of the reflective power R _R , R _V of the back side 19 and the front side 20 of the wafer 2 as a function of the wavelength λ is shown in FIG. 2 .

Further details and alternative configurations of the device 1 and the method for processing the wafer 2 are emphasized below. The details described can be combined with one another and with the details of the above-described device 1 or of the above-described method in principle at will.

The method according to the invention can be carried out particularly simply. Different processing of the front side 20 and the back side 19 of the wafer 2 can be dispensed with. In particular, it is not necessary to use different process steps or different etching media for processing the front side 20 and the back side 19 of the wafer 2 .

The conveying speed is in the range between 0.5 m/min and 2.5 m/min, especially between 2.0 m/min and 2.5 m/min. The slot length is 2.00 m to 3.00 m, especially 2.4 m to 2.6 m. The treatment time is less than 2 min, especially less than 1 min.

In particular, wafers 2 with an asymmetric texture can be produced with the aid of the device 1 in a single process tank 3 , in particular in a single process step.

In this case, the wafer can in particular be a wafer on which no etching step has yet been carried out.

It is known from the invention that an asymmetric texturing can be brought about by the at least partial one-sided removal of gas bubbles formed during the processing of the wafer 2 by means of the etching medium 4 . In particular, air bubbles are removed from the upwardly directed rear side 19 of the wafer 2 . This facilitates the reaction of the etching medium 4 with the backside 19 of the wafer 2 . A homogeneous etch stripping over the entire surface and thus polishing of the rear side 19 of the wafer 2 is achieved here.

The removal of air bubbles from the rear side 19 of the wafer 2 can be brought about by different means. In particular, it can be brought about by mechanical and/or hydrodynamic and/or thermal and/or chemical means or methods. The components can each be used individually in the device 1 . The components can also be combined with one another as desired.

In order to transport the wafer 2 through the process tank 3 , the wafer 2 can also be placed on a support element. During transport through the process tank 3 , the wafer 2 remains in a fixed position, in particular relative to the transport elements. In particular, the wafer 2 can be guided through the slot 3 together with the transport elements.

Preferably, the conveying element has flow-guiding means, in particular flow-guiding plates, in particular for producing flow dead zones on the downwardly directed front side 20 of the wafer 2 when the wafer 2 is conveyed through the etching medium 4 .

Other aspects and alternative design solutions of the present invention will be described emphatically below with reference to FIG. 4 .

In general, the invention relates to the asymmetric processing of the two sides 19 , 20 of the wafer 2 . To this end, the wafer 2 is completely immersed in the processing medium in the process tank 3 . Different process conditions, in particular different temperatures _{T 1 , T 2 and} and/or different concentrations C ₁ , C ₂ of one or more components in the medium. The wafer 2 serves here as a separation means for forming a separation layer, in particular a substantially impermeable separation layer between the region above the conveying plane 9 and the region below the conveying plane.

In the edge region of the wafer ₂ , an exchange of reaction medium takes place between the region 41 below the transport plane ₉ and the region 42 above the transport plane. In order to further reduce, in particular prevent, the exchange of reaction medium in the region 42 above the conveying plane, pressure rollers ₁₈ and/or scraping elements or flow guiding elements not shown in the figure can be used as hydrodynamic separation device.

It should be noted that the width of the region must be as small as possible in order to enhance the asymmetrical effect. This can be ensured with a high coverage and/or a high conveying speed (thus reducing the time during which media exchange can take place). The degree of coverage has been determined above, the conveying speed being in the range between 0.5 m/min and 2.5 m/min, in particular between 2.0 m/min and 2.5 m/min.

In particular, the wafer 2 forms a mechanical barrier between the region above the transport plane 9 and the region below the transport plane. Between the two regions, the exchange of the reaction medium, especially the components of the reaction medium, is very limited. In particular, the corresponding exchange can be suppressed to the greatest extent, especially completely. This can be brought about by suitable flow-influencing means.

The different reaction conditions are facilitated by the fact that the volume of the process tank 3 below the conveying level 9 is significantly greater than the volume of the reaction medium in the process tank 3 above the conveying level 9 .

Furthermore, a substantially homogeneous composition of the reaction medium can be achieved in the region below the conveying plane 9 . For this purpose it can be provided that the reaction medium in this region is thoroughly mixed. A circulation device for circulation and/or for exchanging the reaction medium may also be provided. In particular, two separate circuits for circulation and/or for exchanging the reaction medium can be provided in the region above the conveying level 9 and in the region below the conveying level 9 .

Different reaction conditions can also be brought about by influencing, in particular controlling, the temperature of the reaction medium in the region above the conveying plane 9 and/or in the region below the conveying plane 9 . For this purpose, the reaction medium can be heated or cooled directly or indirectly.

The temperature and/or other reaction parameters can be influenced, for example, by irradiation and/or medium supply.

In particular, it can be achieved by means of one or more corresponding control devices that the temperature of the reaction medium on the front side 20 of the wafer 2 differs from the temperature on the back side 19 of the wafer 2 by at least 2° C., in particular at least 5° C., especially at least 10° C. ℃. The temperature difference is in principle less than 20°C. The corresponding temperature difference can also be set without active control based on the reaction enthalpy.

Accordingly, a concentration difference of at least 5%, in particular at least 10%, especially at least 20%, of one or more relevant components of the medium can be achieved.

In the region 4 ₂ above the conveying plane 9 , in particular the concentration c ₂ of the relevant reactants and the temperature T ₂ of the reaction medium are provided. Concentration c ₁ and temperature T ₁ are correspondingly present in region 4 ₁ below conveying plane 9 .

Furthermore, the different concentrations c ₁ ≠ c ₂ are also a result of the ongoing process: reactants are consumed by reactions, especially by etching processes, and products are formed.

Correspondingly, heat is generated in the exothermic reaction.

In this case, the wafer forms the separation layer through which medium exchange cannot take place.

The concentration c ₂ and the temperature T ₂ in the region 4 ₂ above the transport plane 9 , in particular in the region above the wafer 2 , depend on the immersion depth of this wafer. This height can be set variably in order to achieve a desired process result.

Furthermore, the composition of the reaction medium and/or the temperature of the reaction medium in the region 42 above the conveying plane ₉ need not be homogeneous. Concentration and/or temperature deviations can occur in particular in the region between two adjacent wafers 2 and/or in the region directly adjoining the rear side 19 of the wafer 2 . This can be attributed to the exchange of the reaction medium in the intermediate region and/or the ongoing process on the surface of the wafer 2 .

As mentioned above, the extent of the transition region between two adjacent wafers 2 can be achieved by a suitable configuration of the transport rollers 18 and/or alternative flow guiding elements, and/or by the The spacing and/or the transport speed of the wafers is reduced, in particular eliminated.

According to an advantageous alternative embodiment, the arrangement of the conveyor rollers 10 in the groove 3 is variable. The conveying rollers 10 are in particular displaceable in the vertical direction, ie perpendicularly to the conveying plane 9 . In this way, in particular the conveying plane 9 in the tank 3 can be displaced. In particular, it is thereby possible to vary the immersion depth of the wafer 2 into the reaction medium.

The selection of the immersion depth depends inter alia on the viscosity of the reaction medium, the distance between adjacent wafers 2, the dimensions of the wafers, the reaction speed, the concentrations of reactants, catalysts and products and the resulting gas and heat generation or one or more of these parameters.

An asymmetric treatment of wafer 2 can be achieved by means of different temperatures T ₁ , T ₂ in regions 4 ₁ , 4 ₂ below and above transport plane 9 . The temperature difference can be achieved actively or at least assisted. It is also possible to set the temperature difference based on the reaction enthalpy.

Asymmetric processing can be achieved or brought about by different illuminations, in particular of the front side 20 and the rear side 19 of the wafer 2 .

An asymmetric treatment can also be achieved by means of different concentrations c ₁ , c ₂ in the regions 4 ₁ , 4 ₂ below or above the conveying plane 9 . This can be achieved actively by suitable feeding of reactants, catalysts, products, media or one or more of them in the region 41 below the conveying plane ₉ and/or in the region 42 above the conveying plane ₉ .

Different concentrations can also be achieved passively through depletion or enrichment of reactants, catalysts, products, or one or more thereof.

An asymmetric treatment can also be achieved by means of different viscosities of the reaction medium in the regions 4 ₁ , 4 ₂ below or above the conveying plane 9 . This can be done actively by feeding in a medium in liquid, gaseous or solid form. This can also be achieved or facilitated passively by generating reaction products in liquid, dissolved, solid or gaseous form.

Claims (18)

1. method of the one kind for being chemically treated semiconductor substrate (2) comprising following step：

1.1. the semiconductor substrate (2) with positive (20) and the back side (19) is prepared,

1.2. it prepares for carrying out textured equipment (1) to the semiconductor substrate (2), which has for accommodating etching The slot (3) of medium (4),

1.3. the etch media (4) in the slot (3) is prepared,

1.4. the semiconductor substrate (2) is introduced the slot (3),

1.4.1. wherein, the front (20) and the back side (19) of the semiconductor substrate (2) are all temporarily, at least completely immersed in etching Medium (4),

1.5. the semiconductor substrate (2) is handled by the etch media (4) so that the back side of the semiconductor substrate (2) (19) reflectance (R having_R) than the semiconductor substrate (2) front (20) reflectance (R_V) big at least 2%.

2. according to the method for claim 1, which is characterized in that the texturing in the front (20) of the semiconductor substrate (2) Polishing with the back side (19) of the semiconductor substrate (2) is carried out at the same time.

3. according to the method described in one of the claims, which is characterized in that use acid to be used as the etch media (4), In, the etch media (4) especially has metal ion.

4. according to the method described in one of the claims, which is characterized in that described in being handled by the etch media (4) The bubble formed during semiconductor substrate (2) is removed from the back side (19) of the semiconductor substrate (2) at least partly.

5. according to the method for claim 4, which is characterized in that the removal of bubble is by the method for machinery and/or by stream The method of mechanics and/or the method by calorifics and/or the method by chemistry carry out.

6. according to the method described in claim 4 or 5, which is characterized in that in order to remove bubble removing, it is specified that scraping method and/or So that slot (3) in etch media (4) generate surface stream and/or heat the semiconductor substrate (2) the back side (19) and/or to Etch media (4) adds chemical addition agent.

7. according to the method described in one of the claims, which is characterized in that the semiconductor substrate (2) base during processing This is flatly oriented in slot (3).

8. according to the method described in one of the claims, which is characterized in that the semiconductor substrate (2) is borrowed during processing Conveying device (7) conveying is helped to pass through the slot (3).

9. according to the method for claim 8, which is characterized in that the semiconductor substrate (2) passes through the slot (3) in conveying When fixed relative to the delivery element holding position of the conveying device (7).

10. equipment (1) of the one kind for being chemically treated semiconductor substrate (2) comprising：

10.1 slot (3) for accommodating etch media (4),

10.2 for removing bubble from the surface (19) for the semiconductor substrate (2) being arranged in the slot (3) at least partly Device.

11. equipment (1) according to claim 10, which is characterized in that for by bubble from being arranged in the slot (3) The device that the surface (19) of semiconductor substrate (2) removes at least partly has for making the etch media in the slot (3) (4) device of flowing is generated.

12. equipment (1) according to claim 11, which is characterized in that for making etch media (4) generate the device of flowing It is configured to so that the etch media (4) has in the region of its Free Surface than between vertical relative to Free Surface Every the horizontal flow velocity of bigger in the region of the transporting flat (9) of arrangement.

13. according to the equipment (1) described in one of claim 10 to 12, which is characterized in that for bubble is described from being arranged in The device that the surface (19) of semiconductor substrate (2) in slot (3) removes at least partly has one or more mechanical organ.

14. according to the equipment (1) described in one of claim 10 to 13, which is characterized in that the equipment is equipped for half Conductor substrate (2) conveys the conveying device (7) by the slot, and the conveying device (7) has at least one supporting member (10), the supporting member is arranged to so that the semiconductor substrate (2) is described by being completely immersed in when slot (3) in conveying Etch media (4).

15. method of the one kind for asymmetric processing semiconductor substrate (2) comprising following step：

15.1. the semiconductor substrate (2) with positive (20) and the back side (19) is prepared,

15.2. the equipment (1) for carrying out asymmetric processing to the semiconductor substrate (2) is prepared, wherein the equipment (1) With the slot (3) for accommodating reaction medium,

15.3. the reaction medium in the slot (3) is prepared,

15.4. the semiconductor substrate (2) is introduced the slot (3), wherein the front (20) of the semiconductor substrate (2) and The back side (19) is all temporarily, at least completely immersed in reaction medium,

15.5. the reaction medium in slot (3) is influenced so that the region (4 above the semiconductor substrate (2)₂) be in and described half The region (4 of the lower section of conductor substrate (2)₁) in different process conditions.

16. according to the method for claim 15, which is characterized in that be arranged one or more for influence partly led described Region (4 above body substrate (2)₂) in and/or the region (4 in the lower section of the semiconductor substrate (2)₁) in reaction medium Temperature device.

17. according to the method described in claim 15 or 16, which is characterized in that be arranged one or more for influence described Region (4 above semiconductor substrate (2)₂) in and/or the region (4 in the lower section of the semiconductor substrate (2)₁) in, be used for Handle the device of the concentration of one or more component of the medium of the semiconductor substrate (2).

18. a kind of method for manufacturing solar cell comprising following step：

18.1. the semiconductor substrate (2) with positive (20) and the back side (19) is prepared,

18.2. the semiconductor substrate (2) is handled with according to the method described in one of claim 1 to 9 or 15 to 17,

18.3. contact structures are set on the back side (19) of the semiconductor substrate (2).