DE1001077B - Method and arrangement for electrolytic etching of semiconductor bodies or systems - Google Patents

Description

GERMAN

The invention relates to a method for electrolytic Etching of semiconductor bodies or systems, in particular with one or more pn junctions, as they are required, for example, for the construction of junction transistors.

In the past, the body to be etched was connected as an anode or cathode in electrolytic etching and as a counter electrode a metal that is difficult or impossible to attack by the electrolyte, for example a platinum sheet, used.

The disadvantage of this known method is that there are to be applied electrolytes always other than the desired, the etch-causing ions still contain unwanted ions as impurity These interfering ions also migrate närnilich in the electrolysis to the electrodes ¹ and thus sehlagen also on the to be etched semiconductor down as a firmly adhering layer. Although ^one is doing though is only vestigial impurities, but these are sufficient to · in, required for semiconductor purities the surface, the electrical properties of the system in question adversely affecting.

According to the invention, the precipitation of interfering ions is to be etched electrolytically to: semiconductor bodies or systems by ¹ using the known method for the electrolytic cleaning of metal surfaces anodisehe by alternately and cathodic circuit prevented in one and the same bath.

While, however, intended in the known method is, during the first switching state, the surface layer is caused by released hydrogen attacking first and softening as well as incoherent and during the second Switching state to remove the partially dissolved layer, it comes when carrying out the inl The method according to the invention essentially relies on removing the electrolyte from already present in it To free impurities in order to obtain the required degree of cleanliness of the semiconductor surface.

The essence of this process is that the in the case of the circuit of the system as the anode on the surface deposited interfering ions in the the following phase, in which the system is connected as a cathode, leave the surface again and vice versa. Use is made of the fact that it is electrolysis is reversible processes. The intended effect only occurs when the electrolysis is in takes place in two different electrolysis rooms, so that in the course of time all interfering ions from the One room in the other is transported by the method and arrangement

for electrolytic etching

of semiconductor bodies or systems

Applicant:

Telefunken GmbH,
Berlin NW 87, Sickingenstr. 71

Friedrich Wilhelm Dehmelt, Neu-Ulm / Danube,
has been named as the inventor

the one where they can no longer have a harmful effect.

A mere change of the polarity of the electrodes at the usual procedure with only one ¹ Elektrolyseraraum, for example by using AC voltage, would not have the intended result. The interfering ions deposited on the> semiconductor system in the alternating current phase would also be removed again in the following phase. However, since the ions did not leave the original electrolysis space, they would be deposited again on the semiconductor surface ^{if the sign 1 -, change again.} With this method, the interfering ions would only be carried back and forth between the two electrodes.

In the method according to the invention, however, are the interfering ions from the. one electrolysis room transferred to the other, where they are in the course of the Time all of them on the counter electrode located there. The system to be etched thus serves for this process only as an intermediate carrier for the. Interfering ions in their transition from the one, electrolysis room in the other.

A particularly useful arrangement for implementation of the method according to the invention

you, if you put the semiconductor system to be etched between two counter-electrodes at different potentials rotate in an electrolyte and the system receives a potential lying between the potentials of said electrode. DabeL

609 766/360 \

The space lying between the semiconductor body to be etched and the one electrode represents the one electrolysis space, and the space lying between your body to be etched and the other counter electrode represents the other electrolysis space. The counter-electrodes are advantageously made of a material that cannot be attacked by the electrolyte, in order to prevent further interference ions from occurring as a result of chemical reactions on these electrodes. In the case of using an alkali hydroxide, in addition to stainless steel and platinum, indium in particular has proven itself for this purpose. In order, during the etching of framing Hälbleitersystemem that contain one or more pn junctions for the entire system uniform potential to be granted to ^1, it is necessary to bridge the barrier layers by an electrical conductor in the alternative. Care must also be taken that these electrical conductors consist of a material that is chemically indifferent to the electrolyte in order to eliminate the formation of additional interfering ions. Here, too, it is advisable to use an alkali hydroxide as: electrolyte, indium ¹ .

Using an example in which as Electrolyte. Alkalihydiroxyd is used and the semiconductor system between two auxiliary electrodes is set in rotation ", the method according to the invention is explained in more detail below:

In the drawing, 1 denotes an electrolytic trough which is filled, for example, with potassium hydroxide 2 as the electrolyte. The two made of indium or platinum are immersed in these. existing electrodes 3 and 4, which are at different: potentials. For example, in the present! Fall one electrode to negative and the other to positive potential. The semiconductor system to be etched is arranged between these two electrodes, which ¹ in the example consists of an η-conducting germianium base body 5 with an indiium bead 6 alloyed with it and a base carrier 7 soldered on without a barrier layer. The semiconductor system is rotatably mounted by means of the axis 8 and is at one between the potentials! the two electrodes 3 and 4 located potential value, for example at zero potential. The potential distribution described is achieved, for example, by means of a battery 9, the two end terminals of which are connected to the two counter electrodes 3 and 4 via adjustable resistors 10 and 11 and possibly provided switches 12 and 13 and the center tap of which is connected via the axis 8 to the base electrode 7 of the semiconductor system in Connection. Since it is, in the case of Example ^1, the etching of a system containing a barrier layer (Junction * connection), it is necessary to connect the indium layer 6 with the base electrode 7, e.g. B. to be connected conductively by means of an Indiuandrahtes 14 in order to ensure unit S ^{1 potential for the entire system.}

Due to the arrangement of the semiconductor subscribed system between the two electrodes 3 and 4, the entire electrolysis area in a sense wirti ¹ divided into two compartments A and B.

In the position shown for the system, all of the cations contained in space A migrate to the semiconductor system and are deposited as impurities on the surface to be etched. The too. On the other hand, the beginning of the electrolysis anions present on the surface go into solution and migrate together with the anions located in space A to the anode 4. In a corresponding manner , the anions contained in space B move to the semiconductor system and are reflected in the position of the semiconductor system shown Base electrode 7 down, while the cations that may have gone into solution from the base sheet migrate to the cathode 3 and are held there.

Since now the semiconductor system has been changed the axis 8 should rotate, shows after half a revolution the germanium surface to be etched after dter Cathode 3, while the base electrode 7 to the anode 4 shows. The following processes take place in this new position:

The cations deposited on the side of the semiconductor body to be etched from space A go into solution because of the reversibility of the electrolytic processes in space B and move in the direction of the cathode 3, where they are deposited. At the same time, the actual etching process takes place in this new position, in that the OH ions present in space B combine with germanium to form germanium dioxide, which is detached by the electrolyte. On the rear side, the anions deposited on the base electrode 7 from the space B pass into the space A and migrate to the anode 4, where they are also retained. After a further half turn, the original state is restored, but with the difference that the electrolysis room A has now become poorer in interfering cations and anions than at the beginning of the process. The same applies to room B. In this way, it can be achieved that after several revolutions of the system, the etching takes place in the purest electrolyte without the impurities being deposited on the semiconductor surface to be etched.

In a corresponding manner to the method based on the exemplary embodiment for a pn surface rectifier has been described, it can also be used to etch junction transistors.

Claims (5)

PATENT CLAIMS: 1. Application of the process for electrolytic cleaning of metal surfaces by alternating anodic and cathodic connection in one and the same bath to the electrolytic one Etching of semiconductor bodies or systems, in particular with one or more pn junctions. 2. Arrangement for performing the method according to claim 1, characterized in that that the corrosive body in the electrolyte is between two at different potentials Electrodes is arranged, the circuit being made such that the to. corrosive bodies receives a potential lying between the potentials of said electrodes, and that means are provided are to the body to be etched during the electrolysis in rotation or in a periodic To move pivoting movement. 3. Arrangement according to claim 2, characterized in that the one electrode is positive Potential and the other receives negative potential and the one between them to be etched Body is at zero potential. 4. Arrangement according to claim 2 or 3, characterized in that optionally present Barrier layers in the body to be etched by an electrical one that cannot be attacked by the electrolyte Ladder are bridged. 5. Arrangement according to claim 4, characterized in that in the case of the use of Alkali hydroxide as electrolyte the fixed electrodes and the bridging layers metallic conductors made of indium. Documents considered: German Patent No. 741 666. 1 sheet of drawings