Technical field

The disclosure relates to a system for a chemical and/or electrolytic surface treatment of a substrate.

Background

When performing chemical and/or electrolytic surface treatments of a substrate, particularly electroplating processes in the microelectronic industry, it is of ever-increasing importance to protect the chemical electrolyte mixtures, which may be complex and expensive and often contain oxidation- sensitive additives, from being consumed by side reactions instead of being available for the deposition process itself. Such side reactions, resulting in a loss of expensive electrolyte and other issues, e.g., increase in chemical waste, are often due to oxidation processes caused by contact of the electrolyte additives with the anode or very rarely considered, contact of the electrolyte with air (which contains oxygen).

The problem is particularly severe for some specific plating processes e.g., gold (Au), SnAg, Cu and/or other metals, where expensive chemical electrolyte mixtures are being applied, which contain oxidation-sensitive additive molecules. These additives, when getting in contact with the anode or even with air (which contains oxygen), may oxidize and become useless.

At the same time, performing surface treatment like electroplating processes in the microelectronic industry to the required standards means achieving extremely high uniformity deposition profiles as fast as possible over the whole surface area of the substrate.

In many cases, complex and expensive equipment must be designed and reliably build, operated, and maintained to warrant the sufficient distribution of the plating electrolyte and the current distribution onto the surface to achieve high treatment speeds, especially with high uniformity at the same time. For example, to achieve this, known systems are generally built to ensure particularly good rotation-symmetrical draining of the electrolyte from the plating chamber.

Hardware features provided in electroplating chambers for improving the desired plating uniformity and plating speed, e.g., an HSP-system (High Speed Plating), symmetric electrolyte draining system, or a two-electrolyte plating system (anolyte and catholyte) may, however, result in electroplating chambers of exceptionally large outer dimensions.

Summary

Hence, there may be a need to provide an improved system for a chemical and/or electrolytic surface treatment of a substrate in terms of deposition uniformity even at high speeds and/or protection of the electrolyte mixtures and/or a system configured so as to allow for a more compact size and/or simplified configuration than the prior art systems.

One or more of these problems are solved by the subject-matter of the independent claim of the present disclosure, wherein further embodiments are incorporated in the dependent claims.

The system for a chemical and/or electrolytic surface treatment of a substrate comprises a catholyte chamber, an anolyte chamber, a distribution body, and a catholyte outlet. The distribution body is arranged in the catholyte chamber and the catholyte chamber is separated from the anolyte chamber by means of a membrane, wherein the membrane is tilted relative to the distribution body. The membrane may be tilted so as to merge and remove bubbles generated at the anode. The removing of bubbles may be supported by the anolyte flow. The distribution body comprises jet openings for distributing a catholyte onto the substrate to be treated and drain openings for draining the catholyte out of a reaction space between the distribution body and the substrate. The catholyte outlet is arranged at the catholyte chamber in an eccentric position.

The advantage of this configuration is that the system allows for ensuring the deposition uniformity even at high speeds and protection of the electrolyte mixtures, i.e., the anolyte and the catholyte, as well as simplification and/or size reduction of the system, due to the synergistic effect of the claimed features. The eccentric configuration allows for simplification of the system. Ideal uniformity may particularly be provided together with the other features. Moreover, using the membrane allows for proper separation of anolyte and catholyte region. Particularly in combination with the other features, it may allow for optimal treatment in terms of uniformity and speed, particularly, when used together with the jet openings and drain openings. As such, a combination of the claimed features may synergistically provide a configuration that is ideal, at the same time in terms of size/complexity of the system and uniform and high-speed treatment. The chemical and/or electrolytic surface treatment of a substrate may comprise an electroplating process, in particular, electroplating of gold (Au), SnAg, Cu, and/or other metals.

The substrate may comprise a conductor plate, a semi-conductor substrate, a film substrate, an essentially plate-shaped, metal or metallized workpiece or the like. The substrate may be held in a substrate holder.

In case of electrolytic surface treatment of a substrate, the substrate and anode are connected via an electrical current supply unit to act mainly as cathode and anode respectively.

The anolyte and the catholyte are liquids providing the function of an electrolyte.

The term “membrane” can be understood as a selective barrier, which allows some parts (small molecules, ions, other small particles, etc.) to pass through, but stops or at least reduces the passage of others.

When the system is arranged for intended use, the membrane may be tilted with respect to a horizontal plane. The distribution body, when the system is arranged for intended use, may be arranged horizontally. This is an optional embodiment. In this disclosure, this means that the jet openings and drain openings are arranged in a horizontally arranged array. This is an optional embodiment. The jet openings and/or drain openings may be arranged to extend vertically when the system is arranged for intended use, particularly when the distribution body is arranged horizontally. The system may be configured to hold a substrate parallel to the distribution body, particularly in a horizontal arrangement, when the system is arranged for intended use.

The eccentric position may refer to a center of the distribution body, particularly a center line extending vertically when the system is arranged for intended use. The eccentric position may refer to a center of the distribution body, particularly a center line extending in a direction perpendicular to a longitudinal direction of the distribution body. When the distribution body has a cylindrical shape, the center to which the eccentricity refers may be the cylinder axis.

The membrane may be a permeable ion-selective anode membrane. It may be configured to allow for ionic communication between anodic and cathodic regions of the system, while preventing certain particles or gas bubbles from the anode region, e.g. particles generated at the anode, from entering the catholyte and from reaching the substrate and/or preventing certain particles from the cathodic region, for examples particles present in the catholyte, from entering the anode region and reaching the anode. The membrane may nonetheless allow for transmission of current and supply of metallic ions to contribute to efficiency of surface treatment. Surface treatment using a membrane is, however, improved synergistically when combined with the other claimed features.

The eccentric arrangement allows for a simpler/less complex and more robust and reliable catholyte exit system from the catholyte chamber, particularly enabling less costly fabrication. In addition, the asymmetric electrolyte exit enables an ultra-compact construction of the electroplating chamber. Another factor that may allow for ultra-compact construction of the electroplating chamber is a special configuration of the distribution body in terms of resistivity, which may be based on geometrical optimization of the electrical passages through the distribution body. The use of such a system may lead to non-uniformity unless combined with the other claimed features.

Jet openings allow for particularly uniform distribution of the catholyte towards the substrate surface through the jet openings, particularly when combine with the drain holes and, optionally, a drain ring.

Moreover, the drain holes, and optionally the drain ring, particularly together with the tilted membrane, allow for using the above-mentioned eccentric catholyte outlet efficiently.

Thus, it can be seen that the claimed features, while each having some advantages of their own, synergistically provide a further improvement.

The catholyte chamber may have a lateral side, which extends essentially perpendicular to a longitudinal direction of the distribution body, and the catholyte outlet may be arranged in the lateral side of the catholyte chamber.

The lateral side may, for example, be a side wall of the catholyte chamber.

The longitudinal direction of the distribution body may be one of the directions along which the jet openings and/or drain openings are arranged. The longitudinal direction may extend horizontally when the distribution body is arranged horizontally.

The catholyte outlet, when the system is arranged for its intended use, may be arranged below the distribution body, particularly in a/the lateral side of the catholyte chamber. In other words, the catholyte outlet may be arranged between the distribution body and the membrane, particularly in a/the lateral side of the catholyte chamber. More specifically, the catholyte outlet, when the system is arranged for its intended use, may open into the catholyte chamber at a position below the distribution body, or, in other words, the catholyte outlet may open into the catholyte chamber at a position between the distribution body and the membrane.

The catholyte chamber, in a cross section, may have a wedge shape.

This means that the height of the catholyte chamber increases from one side of the catholyte chamber to the opposite side of the catholyte chamber. The wedge shape may at least in part be brought about by the tilted arrangement of the membrane.

The catholyte chamber may have a wedge shape and be arranged in such a way that the lower end of the catholyte chamber is tilted out of a horizontal position when arranged for intended use.

The advantage of such a configuration may be that it may be easy to collect catholyte at one end of the wedge, e.g., at the lowest point of the catholyte chamber for draining the catholyte.

Thus, effective draining is possible using only one outlet.

The wedge shaped catholyte chamber may have, in a cross section, a longer and a shorter lateral side and the catholyte outlet may be arranged in the longer lateral side of the catholyte chamber.

In particular, the catholyte outlet may be arranged at the lower end of the longer lateral side when the system is arranged for intended use.

As an example, the upper end of the catholyte chamber may be arranged horizontally when the system is arranged for intended use. The longer lateral side of the catholyte chamber will, accordingly, extend further downwards than the shorter lateral side.

The advantage of such a configuration may be that it may be easy to collect catholyte at one point of the catholyte chamber, e.g., at the lowest point of the catholyte chamber for draining the catholyte.

Thus, effective draining is possible using only one outlet.

The catholyte outlet may be arranged at the catholyte chamber in a non-rotation symmetric position.

The axis to which the position is non-rotation symmetric may be the axis that is orthogonal to the substrate surface and extends through the center of the substrate. This means that the catholyte outlet need not be configured and arranged such that the catholyte can exit from the chamber evenly around the substrate. For example, the catholyte outlet need not be ringshaped. The outlet may rather be configured and arranged such that it is only arranged at one side of the chamber for the catholyte. This simplifies the configuration of the entire system.

In known systems, such an arrangement would not have allowed for the required uniformity. However, the system of the present disclosure still allows for even deposition due to the catholyte inflow by means of the jets and the draining through the drain holes of the distribution body.

The catholyte chamber may comprise a drain ring arranged around the distribution body for draining the catholyte out of the reaction space between the distribution body and the substrate.

This means, that a part-stream of the catholyte will be drained out through the drain ring. As such, the drain ring may, as an example, be used as an open overflow, in order to maintain a constant catholyte level in the reaction space, and an to vent out any bubbles which are generated or transported in the reaction space. This vent method may be supported by a rotating substrate holder.

The drain openings and/or the drain ring may be configured to drain the catholyte essentially perpendicular to a substrate’s surface to be treated.

Perpendicular draining may be particularly efficient for removing catholyte from the reaction space, thereby further improving uniformity.

In particular, such a configuration of the drain openings and/or drain rings may be used with a system configured such that the substrate is arranged horizontally when the system is arranged for intended use. In that case, the openings and/or the drain ring may drain the catholyte in a vertical direction. The draining is thereby optimally aided by gravity.

The jet openings may be configured to distribute the catholyte essentially perpendicular onto the substrate to be treated. This allows for a particularly uniform result of the surface treatment. An even more uniform result may be achieved by employing a rotating substrate holder.

The drain openings may extend from a substrate facing surface of the distribution body to a back surface of the distribution body, which is opposite to the substrate facing surface. This means that the catholyte directly passes through the distribution body to an area where it can easily be collected and/or drained.

The jet openings may extend from the substrate facing surface of the distribution body only partially into the distribution body and lead to at least one catholyte inlet arranged at a lateral side of the distribution body.

This arrangement allows for optimal supply of catholyte to the jet openings and, consequently, high uniformity of the surface treatment.

The catholyte chamber may comprise a protective gas system to provide a protective gas curtain between the catholyte and the surrounding atmosphere.

For example, the protective gas system may comprise a gas inlet, in particular several gas inlets arranged in a common plane so as to face each other. The gas inlet or each gas inlet may be configured to introduce gas into the area where the protective gas curtain is to be formed.

The protective gas system may also comprise an exhaust for the gas.

Nitrogen may be used as a protective gas, for example. However, other types of gas may be used, in particular gas that protects the chamber from entry of oxygen from the surrounding atmosphere.

By use of the protective gas system, the catholyte may be protected from deterioration, particularly from oxidizing or other chemical reactions. In particular, by use of the protective gas system, oxygen sensitive additives in the catholyte may be effectively protected from oxidative composition.

The system may further comprise a catholyte circulation system for circulating the catholyte in the catholyte chamber and an anolyte circulation system for circulating the anolyte in the anolyte chamber, wherein the catholyte circulation system is separate from the anolyte circulation system.

The circulation system may comprise storage tanks for the catholyte and the anolyte and transport devices, for example pumps, that drive circulation of the catholyte and the anolyte through the system. Using separate circulation systems ensure reliable separation of the catholyte and the anolyte throughout the entire system. Furthermore the circulation may ensure a bubble separation in the anolyte / catholyte storage tank, as well as in inline bubble separators upstream the anolyte / catholyte storage tanks. The membrane may be permeable for electric current and metallic ions. This allows for efficient surface treatment.

Switchable separated anodes may be provided, arranged, and configured so as to allow for configuring the electrical field of the anodes to the substrate size. It can be configured for one, two, or more different substrate sizes.

The anolyte chamber may comprise at least one inner anolyte inlet, optionally additional inner or outer anolyte inlets, and at least one anolyte outlet, which are selectable to adjust an anolyte flow to different substrate dimensions. In other words, there may be multiple inlets and/or outlets, e.g., different inlets for different anolyte zones, particularly configured so as to allow independently activating the anolyte zones.

The at least one anolyte outlet can, for example, be located at the highest point in the anolyte chamber. That is, the anolyte outlet may, for example, be arranged so as to ensure that, in operation, potential gas bubbles can be collected at the highest point. The system may, in particular, be configured such that the gas bubbles, e.g. generated mainly from the anode, can be removed through the anolyte outlet, for example supported by anolyte circulation flow. Alternatively or in addition, optionally, an anolyte outlet can also be arranged at the lowest point of the anolyte chamber. That is, an anolyte outlet may be arranged so as to enable removal of potential particles from the anolyte chamber. With the above features, bubbles and/or particles may be easily removed from the anolyte chamber. The highest point and lowest point each refer to an arrangement of the system for intended operation.

For example, an inner anolyte inlet may be arranged closer to the center of the anolyte chamber than the outer anolyte inlet. The anolyte outlet may be arranged at a position opposite the outer anolyte inlet, for example. As such, when the anolyte enters through the inner anolyte inlet, on its way to the anolyte outlet, it will cover less distance compared to anolyte entering through the outer anolyte inlet. This means that, by selecting the inner anolyte inlet or the outer anolyte inlet, the anolyte flow may be adjusted to different substrate dimensions.

The system may have a height in a range from 50 to 350 mm.

In one example, the system may have a height in a range of 50 to 80 mm, preferably 60 to 70 mm. This allows for a particularly compact overall setup while at the same time, due to the configurations as specified in the present disclosure, allowing for reliable protection of the anolyte and the catholyte and fast and uniform surface treatment. The height refers to the system when arranged for intended use.

In one example, e.g. where pellets are used (e.g. Cu, SnAg), the system may have height in a range from 200 mm to 350 mm, particularly 230 mm to 260 mm.

In another embodiment, e.g. where inert anodes are used, the system may have height in a range from 50 to 200mm, more preferable 80 mm to 120 mm.

The height may, for example, refer to a combined height of the anolyte chamber, the catholyte chamber, and the reaction space.

The system may be a modular system and one or more components of the system may be provided with a quick-change configuration that allows for effective adaption of the system, for example, to different substrate sizes or different process requirements. For example, a removable funnel may be provided at the anode. The optional funnel may be used between the segmented anodes for guiding the electrical field inside the anode chamber, when two or more different substrate sizes are configured.

It shall be understood that a preferred embodiment of the disclosure can also be any combination of the dependent claims with the independent claim.

These and other aspects of the present disclosure will become apparent from and be elucidated with reference to the embodiments described hereinafter.

Brief description of the drawings

Exemplary embodiments of the disclosure will be described in the following with reference to the accompanying drawing:

Figure la shows, schematically and exemplarily, a side view of a cross-section of a system for a chemical and/or electrolytic surface treatment of a substrate according to an embodiment;

Figure lb shows schematically and exemplarily, a side view of a cross-section of a system for chemical and/or electrolytic surface treatment of a substrate according to an embodiment; Figure 2 shows, schematically and exemplarily, an enlarged view of part of the system of Figure la or lb;

Figures 3a to 3c show, schematically, catholyte and anolyte flow through the system of Figure la or lb;

Figure 4 shows, schematically and exemplarily, a side view of a cross-section of a system for a chemical and/or electrolytic surface treatment of a substrate according to an embodiment.

Detailed description of embodiments

Figures la and 2 show, schematically and exemplarily, an embodiment of a system 10 for a chemical and/or electrolytic surface treatment of a substrate 11 according to the disclosure. When the system is in use, the substrate 11 may be held in a substrate holder, which is not shown here for the sake of illustration, and is not part of the system of the present disclosure.

The system comprises a catholyte chamber 12 for catholyte 13 and an anolyte chamber 14 for anolyte 15. The catholyte chamber 12 is separated from the anolyte chamber 14 by means of a membrane 18, which is tilted relative to the distribution body 16, which is arranged in the catholyte chamber 12. A membrane that is permeable for electric current and metallic ions may be used as the membrane 18, for example.

It is noted that in the present disclosure the anolyte chamber may have one anolyte zone or may have multiple anolyte zones, e.g., with separated anodes and funnels in between. When the anolyte chamber has multiple anolyte zones, the zones may be configured to be activated independently of each other. For example, there may be an inner zone and an outer zone, and the inner zone may be activated independently from the outer zone, e.g., the inner zone may be activated when the outer zone is deactivated or activated when the outer zone is activated. In other words, the system may be configured for a selective activation of the inner zone and the outer zone, for example such that inner zone and the outer zone may be activated together or independently of each other, based on an automatic and/or user selection. For example, the inner zone may be selectively activated alone or together with the outer zone. There may be multiple inlets and/or outlets, e.g., different inlets for different anolyte zones, particularly configured so as to allow independently activating the anolyte zones. In the example illustrated in Figure la, the anolyte chamber 14 is shown as comprising an inner anolyte inlet 14a, an outer anolyte inlet 14b and an anolyte outlet 14c, which are selectable to adjust an anolyte 15 flow to different substrate dimensions. The different anode zones can be filled with pellets, which may for example be Cu-pellets or SnAg-pellets.

In the present embodiment, the catholyte chamber 12, in a cross section, has a wedge shape, for example. In this embodiment, for example, the wedge shaped catholyte chamber 12 has, in a cross section, a longer lateral side 12a and a shorter lateral side 12b. However, the catholyte chamber 12 may have other cross-sectional shapes.

The system further comprises a catholyte outlet 17. The catholyte outlet 17 is arranged at the catholyte chamber 12 in an eccentric position 20. More specifically, in the present embodiment, the catholyte outlet 17 is arranged in one of the lateral sides of the catholyte chamber 12, as an example in the longer lateral side 12a of the catholyte chamber 12. The catholyte outlet 17 is also arranged at the catholyte chamber 12 in a non-rotation symmetric position 20. However, other arrangements are conceivable.

As can be seen from the Figure, the catholyte outlet 17, when the system is arranged for its intended use, may be arranged at a position below the distribution body 16, particularly in a lateral side of the catholyte chamber. In other words, the catholyte outlet 17 may be arranged between the distribution body 16 and the membrane 18, particularly in a lateral side of the catholyte chamber. More specifically, the catholyte outlet 17, when the system is arranged for its intended use, may open into the catholyte chamber at a position below the distribution body 16, or, in other words, the catholyte outlet 17 may open into the catholyte chamber at a position between the distribution body 16 and the membrane 18.

The catholyte chamber 12 may optionally comprise a protective gas system 12d to provide a protective gas curtain 22 between the catholyte and the surrounding atmosphere 23. Protecting gas maybe also injected into the anolyte and catholyte storage tank.

The protective gas system 12d may be configured to provide the protective gas curtain 22 between the catholyte and the surrounding atmosphere 23. The protective gas system 12d may comprise inlets for the protective gas, for example for nitrogen, and an outlet for the protective gas and/or other gas, e.g., gas created as part of the process.

As mentioned above, the system further comprises the distribution body 16 arranged in the catholyte chamber 12. A reaction space 19 is arranged between the distribution body 16 and the substrate 11.

The distribution body 16 comprises jet openings 16a for distributing the catholyte 13 onto the substrate 11 to be treated. In particular, the jet openings 16a may be configured to distribute the catholyte 13 essentially perpendicular onto the substrate 11 to be treated. However, directions deviating from the perpendicular direction are conceivable.

In Figure la, the jet openings 16a are illustrated as extending from the substrate facing surface 16c of the distribution body 16 only partially into the distribution body 16 and lead to a catholyte inlet 16e arranged at a lateral side 16f of the distribution body 16.

The distribution body further comprises drain openings 16b for draining the catholyte 13 out of the reaction space 19 between the distribution body 16 and the substrate 11 .

In Figure la, the drain openings 16b are shown as extending from a substrate facing surface 16c of the distribution body 16 to a back surface 16d of the distribution body 16, which is opposite to the substrate facing surface 16c. However, other arrangements are conceivable.

The drain openings 16b may be configured to drain the catholyte 13 essentially perpendicular to a substrate’s surface to be treated I la. However, directions deviating from the perpendicular direction are conceivable.

The above-mentioned lateral sides 12a and 12b of the catholyte chamber 12 may extend essentially perpendicular to the substrate facing surface 16c.

A longitudinal direction 21 of the distribution body 16 is indicated in Figure 1 a by a dashed line. In this specific example, the above-mentioned lateral sides 12a and 12b of the catholyte chamber 12 may extend essentially perpendicular to the longitudinal direction 21 of the distribution body 16.

In Figure la, the system 10 is shown, merely as an example, with a catholyte chamber 12 comprising a drain ring 12c arranged around the distribution body 16 for draining the catholyte 13 out of the reaction space 19 between the distribution body 16 and the substrate 11. The drain ring 12c is configured to drain the catholyte 13 essentially perpendicular to a substrate’s surface to be treated I la.

Optionally, the system 10 may comprise a catholyte circulation system 24 for circulating the catholyte 13 in the catholyte chamber 12 and an anolyte circulation system 25 for circulating the anolyte 15 in the anolyte chamber 14. The circulation systems, as illustrated in Figure la may comprise a catholyte tank 24a and an anolyte tank 25a and (not illustrated) pumps or other transport devices. The arrows 24b represent, merely schematically, a flow direction of the catholyte and the arrow 25b represents a flow direction of the anolyte. The catholyte circulation system 24 is separate from the anolyte circulation system 25.

In this context, it is noted that in the Figures an inlet for the anolyte and an inlet for the catholyte, due to the 2D representation of the 3D system, overlap. That is, an inlet for the anolyte (flow direction indicated by arrow 25b) is shown as being arranged in front of an inlet for the catholyte (flow direction indicated by arrow 24b), in the viewing direction.

Figure lb shows a system like the one described above in the context of Figure la. The presence and movements of bubbles 27 are illustrated in said Figure lb. Moreover, it can be seen that the catholyte and anolyte do not fill the tanks completely, so there is a liquid level 28 in the respective tank. As mentioned above, protecting gas maybe also injected into the anolyte and catholyte tank. In this example injection ofN2 is indicated by arrows. Bubbles are let out of the tanks through a respective vent. Exemplary pumps 29 for pumping the catholyte and anolyte and inline gas extractors 30, which serve to remove bubbles, are also shown in Figure lb.

Figure 2 shows, schematically and exemplarily, an enlarged view of part of the system of Figure la or lb. In particular, Figure 2 serves to allow for an enlarged view of the part of the system including the distribution body 16 and the membrane 18. A membrane carrier plate 18a is indicated, as well. It is noted that the membrane may be supported in both directions, wherein the catholyte chamber 12 includes a support plate, which, in intend operation, is an upper support.

Figures 3a to 3c show, schematically, catholyte and anolyte flow through a system according to the present disclosure, in particular, for illustrative purposes, through the system of Figure la or lb. As described above, the anolyte chamber 14 may comprise an inner anolyte inlet 14a, an outer anolyte inlet 14b and an anolyte outlet 14c, which are selectable to adjust an anolyte 15 flow to different substrate dimensions. In the case of Figure 3a, the inner anolyte inlet 14a is selected, whereas in Figure 3 b the inner and outer anolyte inlet are selected together. It is noted that, so as to avoid a cluttered view, the catholyte flow is only shown from the point where it leaves the reaction space in Figures 3a and 3b. Figure 3c shows the flow of the catholyte into the distribution body and through the distribution body.

It is noted that the system of Figures 1 to 3 also includes an anode and a cathode, omitted to avoid cluttering.

It is noted that in general the size of the cathode may, in preferred embodiments, be selected so as to match the anode size and wafer size.

Figure 4 shows, schematically and exemplarily, a side view of a cross-section of a system for a chemical and/or electrolytic surface treatment of a substrate according to an embodiment. The system is configured similarly to the one shown in Figures 1 to 4. However, the height 26 is smaller than in said Figures. This serves to illustrate that a particularly compact build is possible with the claimed system 10.

As an example, the system 10 may have a height 26 in a range of 50 to 80 mm, preferably 60 to 70 mm. However, other dimensions are conceivable.

As an example, the system 10 may have a height 26 in a range of 50 mm to 350 mm. In one embodiment, e.g. where pellets are used (e.g. Cu, SnAg), the height may preferably be in a range of 200 mm to 350 mm, more preferable 230 mm to 260 mm. In another example, where inert anodes are used, the height may preferably be in a range of 50 mm to 200 mm, more preferable 80 mm to 120 mm.

The height may, for example, refer to a combined height of the anolyte chamber, the catholyte chamber, and the reaction space.

While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The disclosure is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed disclosure, from a study of the drawings, the disclosure, and the dependent claims.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.