Device for etching semiconductors with a large surface area

p0001The invention relates to a device for etching large-area semiconductor wafers. For a variety of novel products or processing steps in the field of semiconductor technology, it is advantageous or unavoidable to employ not only chemical but also electrochemical etching methods. This applies in particular to the production of a large variety of pores in, for example, silicon, GaAs, InP or GaP, which can be produced only by electrochemical methods.

p0002As a rule, an anodic current is passed through the semiconductor (ie positive pole of the current source on the semiconductor) for such etching, which induces a chemical reaction at the transition semiconductor electrolyte which leads to the dissolution of the semiconductor material. The structure to be produced, for example so-called macropores with diameters in the range of 1 μm and depths of a few 100 μm, should be homogeneous on the entire semiconductor surface; Moreover, a simple, safe and fast process is highly desirable.

p0003Electrochemical (pore) etching in silicon is typically applied in technology fields such as:<ul><li>Microelectronics and microsystem technology,</li><li>Biotechnology; Eg biochips or biosensors,</li><li>Sensor technology in general,</li><li>Production of so-called SOI (Silicon On Insulator) wafers,</li><li>Production of photonic crystals, special filters and elements of quantum optics or non-linear optics,</li><li>Solarics (eg for the production of antireflection coatings),</li><li>Fuel cells (as a porous electrode),</li><li>Nanotechnology; Eg in the production of nanocutrades.</li></ul>

p0004These applications involve requirements which are very difficult to fulfill for large-area semiconductor wafers, eg silicon wafers with diameters of 300 mm; Even for smaller samples with areas in the range of a few cm² A homogeneous etching is not easily achieved. The difficulties result from the combination of several peculiarities, which with surfaces larger than a few cm² In sum very quickly lead to the limits of conventional etching cells. In particular, the following factors are critical and must be considered:<ul><li>Homogeneous transport of the electrolyte back to the reactive interface. In simple electrolyte-purged cells, the flow pattern of the electrolyte will always cause inhomogeneities of the etching.</li><li>Homogeneous electrical contact to the back of the semiconductor. This contact must be able to carry large currents. At etching current densities in the range of up to 100 mA / cm² Are typical Si wafers with areas in the range of 100 cm² Total currents of 10 A or more, which can lead to electrical and thermal problems.</li><li>Possibility of homogeneously lighting the back with high intensity light. This is required for several applications.</li><li>Control of the temperature within narrow limits (without influencing the optimized flow behavior).</li><li>Absolute tightness of both the disc holder and the entire apparatus.</li><li>No disc breakage, even in samples which have become highly porous due to the etching and are therefore mechanically very susceptible.</li><li>Resistance of all materials that are wetted with the electrolyte against very aggressive chemicals (eg mixtures of HF and organic, highly polar solvents). </li><li>Effortless removal of large amounts of gases which can be generated during the etching (generally H₂ And O₂, But also the extremely poisonous gases PH₃, AsH₃).</li><li>Usability for semiconductors of all types, eg n- and p-doped silicon, GaAs, InP, etc.</li></ul>

p0005The Japanese patent publications are state of the art <nplcit id="ncit0001" npl-type="j"><text>PATENT AB-STRACTS OF JAPAN, No. 11, No. 108 (E-495</text></nplcit>) &amp; <patcit id="pcit0001" dnum="JP61255028A"><text>JP 61 255 028 A</text></patcit> In which there is described an apparatus for etching the semiconductor substrate which moves a reaction vessel with two rods, and further the apparatus for etching the semiconductor substrate <patcit id="pcit0002" dnum="US6235147B1"><text>US-B1 6,235,147</text></patcit>, Which describes a device for etching semiconductors with a high-pressure spray device.

p0006Finally, in the writings <patcit id="pcit0003" dnum="EP0853332A"><text>E P-A 0 853 332</text></patcit> and <patcit id="pcit0004" dnum="US5374325A"><text>U.S. Patent No. 5,374,325</text></patcit> Apparatus for etching semiconductor substrates in which a complex circulation process is intended to ensure uniform fluid exchange on the etching surface.

p0007The invention allows etching with the above-mentioned boundary conditions with a device having the features of the main claim, which fulfills all the aforementioned requirements. The subclaims represent advantageous embodiments.

p0008In the following, only the application for macroporen etching in the semiconductor silicon, for p-doped silicon in which the above-mentioned requirements are most difficult to satisfy, will now be discussed, for example, for all applications. The transmission to other porosity (eg micro- and mesopores) and semiconductors, in particular from the group of III-V compounds, is then basically possible, with only trivial changes which are state of the art (eg use of other electrolytes or other geometry of the samples) ) Are required. In addition, the application to non-semiconductors is also possible.

p0009With the device according to the invention, a galvanic deposition (coating) can also be performed. The specific advantages of the invention, besides the fulfillment of the points already mentioned, are, in particular, the following specific points:<ol><li>1. Resistance to electrolytes which, in addition to the hydrofluoric acid (HF) always required for the Si etching, also contain aggressive organic solvents, for example acetonitrile, dimethylformamide, formamide, dimethyl sulfoxide, hexamethylphosphoric triamide or dimethylacetamide. These chemicals attack not only most common plastics, but also auxiliary materials such as so-called plasticizers in plastics, adhesives, hoses or O-rings.</li><li>2. Homogeneous etching or flow patterns for many different types of electrolytes with, for example, different viscosities.</li><li>3. Easy adjustment of sample holder to samples of various sizes and geometry without loss of homogeneity.</li><li>4. variability in back-contacting; Back lighting as an option.</li><li>5. In-situ control of all etching parameters.</li></ol>

p0010The novel device realizes this in particular by the realization of the following points:<ol><li>I. Complete separation of etching trough and "sample head"</li><li>Ii. Possibility to operate with the side to be etched down (normal case).</li><li>Iii. Production of homogeneous etching conditions by homogeneous electrolyte flow (on average); Realized by easily controllable tilting movements of the sample head and etching trough.</li><li>Iv. Production of sample head and etching trough from one piece of suitable material (eg PTFE, trade name mostly Teflon^®). Absolute run-out safety is therefore guaranteed</li><li>V. Contacting the backside by means of edge contacts, full-surface metal contacts (especially usable in metallized backside samples), by a glass plate coated with "ITO" (= indium tin oxide, transparent conductor) or a plexiglass plate wrapped with fine platinum wires Back lighting.</li><li>Vi. Control of the electrolyte quality (with the parameters temperature, dissolved gases, concentrations of the components) and the etching parameters (voltage, current, illumination intensity, but also eg impedance); Processing by appropriate software and corresponding "real-time" control.</li></ol>

p0011The device for etching large-area semiconductor wafers consists of a trough-shaped receptacle with a liquid electrolyte, at least one probe head provided within the movably supported etching trough, with a device for holding at least one semiconductor wafer (a wafer).

p0012The sample head is attached to the etching trough, while the etching trough can be pivoted about at least one axis for carrying out tilting movements. A tilting movement can be dispensed with when the head is moved horizontally back and forth in the basin, so that a similar electrolyte flow is formed as by the tilting movement. To improve the turbulent flow of the electrolyte, it is proposed to provide channels at the bottom of the etching path and / or at the bottom side of the sample head.

p0013However, it is preferred that the sample head is mounted on the tiltable etching trolley with it movably via interchangeable spacers for setting different electrolyte layer thicknesses on the semiconductor wafer which is held down on the underside of the probe head above the underlying bottom of the etching trough with the side to be etched.

p0014In order to support the partially extremely fragile semiconductor wafer when enabling backlighting, it is proposed to arrange on the probe head an exchangeable mounting block above the semiconductor wafer, which is provided with edge joints which can be evacuated via a vacuum line and which are sealed off from the electrolyte by annular seals at the edge region of the semiconductor wafer . In order to enable an illumination of the semiconductor wafer, the mounting block should preferably be optically transparent, and a diode array should be arranged as illumination on its upper side above a transparent plate which seals the mounting block surrounding the mounting block.

p0015In order to avoid leakage-prone passages, it is proposed to make contact with a large-area printed circuit electrode at the bottom of the etching process, which is contacted with platinum wires which rise on the inside of the etching process over its edge. The semiconductor wafer is contacted at its (upper) rear side via edge contacts, full-surface metal contacts, through a glass plate coated with ITO (indium tin oxide) or a Plexiglas plate coated with fine platinum wires.

p0016At least one temperature control for heating and / or cooling the electrolyte with cooling / heating channels can be provided on the underside of the etching trough. For forming a protective gas atmosphere above the electrolyte of the etching troughs, or the etching head can also be provided with a cover and with inlets and outlets for protective gas.

p0017In producing a turbulent flow for the respectively differently viscous electrolytes, it is proposed to effect a movement of the etching path adapted to the semiconductor slices to be etched and to adjust the distance between the semiconductor wafer and the etching bottom via the previously inserted suitable spacings between the latter.

p0018In order to balance the consuming acids in the electrolyte, highly concentrated electrolyte is advantageously added during the progressive etching in order to maintain the electrolyte concentration.

p0019Further advantages and features of the invention are explained in the following with reference to the attached drawing. FIG.<ul><li><figref idrefs="f0001"><b>FIG</b></figref> Schematically the structure of the device,</li><li><figref idrefs="f0002"><b>FIG</b></figref> The etching trough,</li><li><figref idrefs="f0003"><b>FIG</b></figref> The sample head with sample chamber, and</li><li><figref idrefs="f0004"><b>FIG</b></figref> A detailed illustration of the illumination of the sample back.</li></ul>

p0020<figref idrefs="f0001">FIG</figref> Shows the basic components, the etching trough <b>10</b> And the sample head <b>12.</b> Between these the electrolyte becomes <b>14</b> brought in. The entire assembly is mounted on a bracket rotatable about a horizontal axis; In operation, a rocking motion with a total angle of (5 ° -25 °) and a tilting frequency of about 0.25 Hz (more generally between 0 and 2 Hz) is carried out, whereby the electrolyte is very effectively circulated and homogeneous etching even of large surfaces is very simple Is to be achieved.

p0021For operation, therefore, no pump is required which would have to circulate the electrolyte with correspondingly high pumping power. This also prevents the need for connecting pieces, valves, hoses, etc., which are subjected to considerable mechanical loads and the aggressive electrolytes. Furthermore, almost all pumps produce pressure surges, which can lead to a time-incoherent etching. Problems with respect to possibly necessary pressure reducers and dampers also do not occur. When using a pump, the electrolyte must be fanned from the pump connection to the wafer by means of a suitable guide. This is also superfluous by the above design. In particular, however, the operational reliability of the device is greatly increased since the electrolyte "sees" only Teflon. Leaks due to leaks, breaks etc.,

p0022The temperature of the electrolyte <b>14</b> Is kept constant and can be adjusted to 0.1 ° C and can be modified during the etching. The geometries of the etching process<b>10</b> And the sample head <b>12</b> Are described in the following:

p0023In <figref idrefs="f0002">FIG</figref> Is the etching trough made of a block Teflon <b>10</b> Respectively. It ensures leakage resistance and resistance even in the most aggressive electrolytes. A large-area counterelectrode<b>16</b> Of preferably platinum is at the bottom of the etching trough <b>10</b> built-in. The bottom of the trough is further covered with channels<b>18</b> Which after closure is provided with, for example, an aluminum plate <b>20</b> Allow the temperature of the electrolyte to be controlled by a circulating heating fluid. connections<b>22</b> Of platinum wire for the platinum counterelectrode <b>16</b> Are guided over the edge so that bores and seals are avoided. With reference<b>24</b> An inlet and outlet for the electrolyte liquid is shown.

p0024The <figref idrefs="f0003">FIG</figref> Illustrated sample head <b>12</b> Is now introduced as the center of the device with the surface to be etched downwards into the etching trough. The distance between the etching head bottom and the sample head can be determined in the simplest manner by means of spacers<b>26</b> Are varied. This arrangement together with the rocking movement of the entire device ensures the observance of the decisive (in particular flow) parameters during etching.

p0025The sample head <b>12</b> Is also made of a Teflon block to ensure tightness and durability even in the most aggressive electrolytes.

p0026The seal of the wafer is made by two sealing rings <b>28,</b> Which bear against the rear side, the sample head <b>12</b> For accommodating the sealing rings <b>28</b> Next to a sample chamber <b>30</b> Is provided with a peripheral notch. The one for holding the wafer<b>32</b> Required contact pressure can be obtained by evacuating the sample chamber <b>30</b> With a vacuum system (not shown) at the port <b>38</b> be generated.

p0027Since electrolytic electrolyte can be sucked into the vacuum system, for example in the case of breakage, an electrolyte-resistant collecting container is installed as a precaution in the vacuum system.

p0028Temperature sensors and reference electrodes (not shown) are mounted as close as possible to the wafer in order to obtain reliable values ​​for the control.

p0029The electrical contacting of the wafer takes place over the large area over the rear side. Various options are possible:<ul><li>I) contacting the sample (usually - but not necessarily - a round wafer) through a suitable metal plate or foil, for example aluminum, by means of a mounting block made of PVC, for example, using the vacuum in the sample chamber. The external connection is made by one or more wires which are led out from the edge of the metal plate.</li></ul>

p0030This contacting is suitable for all specimens which have a highly conductive backside and do not require backlighting. <ul><li>Ii) contacting the sample <b>32</b> So as to make back lighting possible. For this purpose, instead of the metal plate and a mounting block, either a glass plate coated with ITO (indium tin oxide) or a contact plate made of transparent plastic (eg Plexiglas®, PMMA) or glass and covered with fine platinum wires is used. The wrapping is to be carried out in such a way that the transparency is not significantly hindered. A light emitting diode array<b>40</b> Above the (now transparent) end plate 42 allows intensive and homogeneous illumination.</li></ul>

p0031Alternatively, contacting of only the edge of the sample by contact needles is also possible. However, this is usually disadvantageous, since the homogeneity of the current flow is then more difficult to achieve.

p0032The device is completed by:<ul><li>A powerful potentiostat and / or galvanostat which can provide the required relatively high voltages and currents and which can be controlled from the central measuring computer.</li><li>A pump unit with a sufficient throughput (approx. 30 l / min) for vacuum suction.</li><li>A "Wulf bottle" (made of electrolyte-resistant material) integrated into the vacuum system so that the aggressive electrolytes can not get into the vacuum pump or into the environment even when the wafer is broken.</li><li>A temperature unit which allows the electrolyte temperature to be kept constant to at least +/- 0.2 ° C by means of a heat exchanger principle; At a temperature setting which is in the range of approximately -10 ° C to + 40 ° C. The unit must also be controllable from the central computer.</li><li>A unit for carrying out the rocking movement; Either a conventional rocker table or a simple hydraulic / mechanical / pneumatic device.</li><li>A computer that controls the device. </li><li>Corresponding software.</li><li>An optional light source (controllable via the measuring computer) for backlighting the sample. This light source is preferably, but not necessarily, represented by a light-emitting diode matrix.</li><li>The transparent contact plates made of indium tin oxide (ITO) coated glass or fine PT wires wrapped transparent material.</li><li>A system of bores integrated into the cell head, through which protective gases can be introduced into the electrolyte (eg "nitrogen bubbling" to expel dissolved oxygen).</li></ul>

p0033The uniformity of the current supply and the electrolyte flow are decisive for a homogeneous etching over large areas. The homogeneity of the current supply is ensured by the described contacting methods, more difficult to achieve is the homogeneity of the electrolyte flow on the average time.

p0034In contrast to known etching methods, in which electrolyte flow homogeneity can only be ensured for a fixed parameter set (in particular fixed sample size) and only after lengthy iterative optimization, the device according to the teaching of the invention is easily adaptable to various conditions. In order to optimize the flow conditions at a given parameter set (eg temperature - dependent viscosity of the electrolyte, size of the disk to be etched (typically between 50 mm and 300 mm diameter, conductivity of the electrolyte), the tilt angle, the tilting frequency and the distance between the sample head etching bottom Wherein the homogeneity of the flow can be directly controlled by observation.

p0035This is done by fitting a transparent disk (using a transparent mounting block) instead of the actual sample, and adding a small amount of floating particles (eg conductive silver) to the electrolyte. The flow conditions are then clearly visible and can be optimized very quickly for the respective application. For the etching of p-type silicon wafers with a specific resistance in the range 0.001-50 Ωcm as well as with a 100 mm diameter, tilting angles of 6 ° -25 °, tipping frequencies 0.05-2 Hz and an electrolyte volume of 1-3 liters prove to be suitable.

p0036The optimum temperature for etching is important; It has to be adjusted according to the material and the type of pore. A temperature constant of +/- 0.1 ° C is required for some etching and can be achieved according to the teachings of the invention. For particularly demanding etching, eg macropores in p-type silicon with depths> 100μm, it may be necessary to change the temperature during the etching in a targeted manner. For p-type silicon with a specific resistance of 10 Ωcm into which macropores with depths of 200 μm are to be etched, for example, a continuous temperature change from 20 ° C. to 12 ° C. is advantageous.

p0037For most applications it is recommended to etch with constant current. The potentiostat / galvanostat must then be able to provide the required voltage, which can easily reach the order of 100V.

p0038The desired parameters and, if necessary, their temporal changes are programmed in the measuring computer; Then the etching process can start.

p0039The semiconductor wafer to be etched should preferably displace via a low-resistance back contact, which is produced by conventional implantation of a p⁺Layer in p-type semiconductors or n⁺Layer in n-type semiconductors, followed by the usual annealing and metallization steps, but a (non-transparent) metallization is only required in the case of samples which do not require backlighting; But at least the areas to be etched must be spared.

p0040It is recommended to clean the front of the sample; Cleaning methods for this are numerous described in the literature.

p0041The disc rear side is contacted as described above. As a rule, thin metal foils have been proven to be best suited for pressing onto the sample via the assembly block made of relatively soft plastic. Thick metal plates must be polished very well in order to obtain a homogeneous contact.

p0042The thickness of the mounting block is of decisive importance. It must be set precisely so that, on the one hand, a certain deflection of the specimen is still possible in order to produce a sufficient contact pressure for the tightness, but on the other hand the deflection is limited so as to prevent breakage of the specimen even in the porous state. The figures required for this are dependent on the sample type and the sample size, but are easily determinable.

p0043When n-type semiconductors with a large diffusion length (usually Si and Ge) are used, a modification of the contacting is used as described above. For example, an ITO-coated glass plate is firmly pressed onto the back of the semiconductor sample; The ITO layer is contacted at the edge. Over the array, a light emitting diode array is placed, with a spectral radiation distribution adapted to the semiconductor, ie at a frequency maximum slightly below the absorption edge of the semiconductor. Thus, the rear side of the semiconductor wafer can be illuminated at least locally.

p0044To adjust a constant current density, the light output of the light-emitting diode array is now preferably adapted.

p0045The semiconductor wafers can also be structured on the front, ie have a masking layer which is resistant to the electrolyte used. The etching attack is then restricted to the open areas; The total current must be adapted so that the current density in the unprotected regions reaches the desired value.

p0046After basic adjustment and programming of the device and assembly of the sample, the etching is started. The entire process is now running automatically; Typical etching times are between 10 minutes and 24 hours.

In summary, the process can thus be summarized as follows:

p0047For the etching of large-area semiconductor wafers, in a trough-shaped receptacle with a liquid electrolyte, with at least one sample head <b>12</b> Within a movably supported etching path <b>10,</b> Comprising means for holding at least one semiconductor wafer <b>32</b> Is set in motion by a rocking device of the electrolytes, the probe head <b>12</b> With the surface to be etched (front) being arranged downwards in the etching trough, and for the adjustment of different electrolyte layer thicknesses, interchangeable spacings for the spacing etching bottom probe head are provided, and electrical contacts for electrochemical etching are arranged on the rear side.

p0048Advantageously, the sample head is firmly fixed to the trough, while the etching trough can be pivoted about at least one axis for carrying out tilting movements, and / or there are further channels for turbulent circulation of the electrolyte at the bottom of the etching trough <b>10</b> And / or on the underside of the sample head <b>12</b> Are provided.

p0049On the sample head <b>12</b> Can be a replaceable mounting block <b>30</b> Above the semiconductor wafer <b>32</b> Which is provided with edge joints which are connected via a vacuum line <b>38</b> Are evacuatable and which are arranged opposite the electrolyte by annular seals <b>28</b> Are sealed at the edge region of the semiconductor wafer.

p0050A preferably related platinum counterelectrode <b>16</b> At the bottom of the etching process with platinum wires <b>22,</b> Which are guided on the inside of the etching process in ascending manner over the edge thereof, and the semiconductor wafer is provided on its (upper) rear side via metal contact contacts contacting edge contacts, through a glass plate coated with ITO (indium tin oxide) or one with fine platinum wires Wrapped Plexiglas plate, are further suggested.

p0051Preferably at least one temperature control should be provided for heating and / or cooling the electrolyte with cooling / heating channels on the underside of the etching process. On the etching trough<b>10</b> A cover, which is provided with inlets and outlets for protective gas, should also be provided for the formation of an overpressure atmosphere above the electrolyte.

p0052In the etching trough, a place wetted by the electrolyte can also be provided for the arrangement of drying means, which can remove water traces from the electrolyte. If the assembly block<b>30</b> A diode array can be optically transparent on its upper side <b>40</b> As illumination above a transparent plate sealing against the vacuum surrounding the mounting block <b>42</b> to be ordered.

p0053As a result, a turbulent inflow of differently viscous electrolytes can occur on the semiconductor disks to be etched <b>32</b> By adapted movement of the etching process and adjustment of the distance between the semiconductor wafer and the etching trough base by means of the prior insertion of suitable spacings <b>26</b> Between them.

p0054During the etching, preference is then given to the progressive addition of highly concentrated electrolyte for maintaining the electrolyte concentration, wherein the electrolyte may be admixed with added drying agent.

p0055Finally, the rear side can alternatively be illuminated with a laser beam scanning over the illumination surface.

p0056The attached table gives, for example, parameter sets for a few of the possible pore etchings. <tables id="tabl0001" num="0001"><table frame="all"><title>ANNEX: TABLE 1</title><tgroup cols="9"><colspec colnum="1" colname="col1" colwidth="22mm" /><colspec colnum="2" colname="col2" colwidth="14mm" /><colspec colnum="3" colname="col3" colwidth="17mm" /><colspec colnum="4" colname="col4" colwidth="15mm" /><colspec colnum="5" colname="col5" colwidth="21mm" /><colspec colnum="6" colname="col6" colwidth="22mm" /><colspec colnum="7" colname="col7" colwidth="17mm" /><colspec colnum="8" colname="col8" colwidth="14mm" /><colspec colnum="9" colname="col9" colwidth="14mm" /><thead><row><entry namest="col1" nameend="col9" align="left" valign="top"><b><i>Some typical parameter sets</i></b></entry></row><row><entry align="center" valign="top"><b>material</b></entry><entry namest="col2" nameend="col4" align="center" valign="top"><b>P-silicon</b></entry><entry align="center" valign="top"><b>N-Si</b></entry><entry align="center" valign="top"><b>N⁺-Si</b></entry><entry align="center" valign="top"><b>N-GaAs</b></entry><entry namest="col8" nameend="col9" align="center" valign="top"><b>N-InP</b></entry></row></thead><tbody><row><entry><b>Pore ​​type</b></entry><entry>macro</entry><entry>micro</entry><entry>Trench</entry><entry>macro</entry><entry>macro</entry><entry>Crysto</entry><entry>Crysto</entry><entry>Curro</entry></row><row><entry><b>electrolyte</b></entry><entry>Org</entry><entry>Aqu / Fa</entry><entry>Org</entry><entry>Aqu M-Org</entry><entry>Aqu / HMPA</entry><entry>Aqu</entry><entry>Aqu</entry><entry>Aqu</entry></row><row><entry><b>Temp.</b></entry><entry>20 ° C</entry><entry>20 ° C</entry><entry>20 ° C</entry><entry>14 ° C</entry><entry>20 ° C</entry><entry>20 ° C</entry><entry>20 ° C</entry><entry>20 ° C</entry></row><row><entry><i>J</i><b>[A / cm²]</b></entry><entry>0.002</entry><entry>0.025</entry><entry>0.0005</entry><entry>0.002-0.03</entry><entry>0.002-0.008</entry><entry>&lt;0.9</entry><entry>&lt;0.1</entry><entry>0.1-1</entry></row><row><entry><i>U</i>[V]</entry><entry>2-16</entry><entry>20-40</entry><entry>1-2</entry><entry>1.4</entry><entry>1-2</entry><entry>20-90</entry><entry>20-60</entry><entry>30-90</entry></row><row><entry><b>Lighting</b></entry><entry>No</entry><entry>No</entry><entry>No</entry><entry>Yes</entry><entry>No</entry><entry>No</entry><entry>No</entry><entry>No</entry></row><row><entry><b>Kippfreq.</b></entry><entry>0.3Hz</entry><entry>0.2Hz</entry><entry>0.3Hz</entry><entry>0.2Hz</entry><entry>0.8Hz</entry><entry>0.3Hz</entry><entry>0.8Hz</entry></row><row><entry><b>Tilting angle</b></entry><entry>8th</entry><entry>8th</entry><entry>8th</entry><entry>8th</entry><entry>5 °</entry><entry>4 °</entry><entry>8th</entry><entry>3 °</entry></row><row><entry><b>Gap width</b></entry><entry>10mm</entry><entry>8-11mm</entry><entry>8mm</entry><entry>10mm</entry><entry>8-10mm</entry><entry>6mm</entry><entry>8mm</entry><entry>5 mm</entry></row></tbody></tgroup></table></tables><b>Table 1</b> The abbreviations mean: Macro, meso, micro = macro, meso, micropores according to IUTPC, Crysto, Curro = "crystallogaphically" or "current-line oriented" pores, <i>J</i> = Current density, <i>U</i> = Voltage. In the case of electrolytes, Org = organic electrolyte, Aqu = aqueous electrolyte.