DE1273954B - Process for the galvanic coating of p-conducting germanium with antimony, lead or alloys of these metals - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

C23b

German class: 48 a - 5/50

Number: 1273 954

File number: P 12 73 954.7-45 (N 24534)

Filing date: February 29, 1964

Opening day: July 25, 1968

The invention relates to a method for electroplating p-type germanium with antimony, lead or alloys of these metals using an antimony intermediate layer.

There are various methods of electroplating electrically conductive material with Antimony, lead or alloys of these metals are known. In particular, it is known to galvanize germanium to be coated with two layers of antimony, the first layer of antimony being made of one aqueous bath containing sodium citrate, citric acid and potassium antimony tartrate (U.S. Patent 2,817,629).

However, it has been shown that it is with the known Method is not possible, p-type germanium sufficiently evenly with antimony, lead or an alloy of these two metals to cover, as this is for attaching very small low resistance Contacts on germanium transistors is required. The surface of p-type germanium is usually only insufficiently covered with the metal.

Various chemical and electrochemical pretreatments of the p-type germanium, such as chemical Etching using a fluoride bath, anodic pickling in a potassium hydroxide solution, while a short time anodic switching in the lead bath, from which lead is cathodically deposited on it tried unsuccessfully. Electrolysis at elevated temperatures also did not give the desired result.

The invention is based on the object of specifying a method with which a complete covering of p-conducting Gemanium with the metals mentioned is possible. This object is achieved in that the antimony intermediate layer has a thickness from about 0.1 to 1 μ at a cathode potential corresponding to the saturation current without gas evolution is deposited.

A second antimony intermediate layer is preferably applied to the antimony intermediate layer from the same bath made of gray antimony at a cathode potential increased by 200 to 35OmV.

The bath is preferably an aqueous solution of 15 to 19 g / l potassium antimonyl tartrate, 15 to 52 g / l citric acid and 37.5 to 195 g / l sodium citrate with a pH above 6 are used.

In order to galvanically deposit antimony in a compact gray form, it was known that to this Purpose a certain critical value of the current density must not be exceeded, otherwise Black antimony with more or less electroplating processes

of p-type germanium with antimony, lead or alloys of these metals

Applicant:

N. V. Philips' Gloeilampenfabrieken,

Eindhoven (Netherlands)

Representative:

Dipl.-Ing. E. E. Walther, patent attorney,

2000 Hamburg 1, Mönckebergstr. 7th

Named as inventor:
Clara Henderina de Minjer,
Emmasingel, Eindhoven (Netherlands)

Claimed priority:

Netherlands 5 March 1963 (289 818)

porous structure is created. When the invention came about, it was found that just at high current densities, the p-type germanium is completely covered with this black antimony.

It has been found that the current density (z) as a function of the cathode potential (E) has a form as shown in the drawing. This course applies to an antimony bath of the composition

16 g potassium antimonyl tartrate,
82 g sodium citrate and
25 g citric acid

per liter of solution in water and a pH of about 5.8.

The specified EMF is measured against a standard hydrogen electrode. When the potential moves from the less negative to the more negative, light gray antimony begins to deposit at around - 600 mV. If the cathode potential is further reduced to about -850 mV, whereby the saturation current density of about 0.28 A / dm ^{2 is} reached, black antimony begins to form.

809 587/463

Claims (1)

3 4 to part. If the potential is read even further and the current is controlled in such a way, set to below about -950 mV, so begins except that this potential has the desired value. the deposition of black antimony gas The invention is now based on an execution development to occur. The point at which this approximately example explained in more detail. Gas evolution occurs is dependent on the pH of the elec- 5 Germanium strips with dimensions of trolyte dependent. At low pH values, namely 20-2-0.25 mm, the p-type conductivity was due to doping at a pH <C6, gas was evolved by means of indium in an amount of 3.5 · 10 ¹⁵ atoms already over - 950 mV. It is preferable to use a specific resistance per cubic centimeter therefore worked at pH values above 6, otherwise the stand of about 1 ohm-cm, were in the [Hl] - Span in potential between saturation current and io direction sawn from a single crystal, with carbon Occurrence of gas evolution is small. lapped all-round powder and then 15 seconds in It has surprisingly been found that with a mixture of
the so-called black antimony a complete one The surface is covered with p-type Genna- 5 ml HNO ₃ (d = 1.4), nium is possible. Although this precipitate is a 15 10 ml HF 50% and has a somewhat porous structure, it has stained 5 ml of ethanol,
shown that a layer deposited on it made of antimony, lead or an alloy of antimony On one of the sides of the strips, electrical and lead adheres excellently and completely covers them. lytically deposited a thin indium layer and This black antimony is attached to a copper wire as a very thin ao with silver solder. Skin attached with a thickness of about 0.1 to 1 μ. The side of the strip where the copper wire When the layer was attached to a greater thickness, and the copper wire itself were with was brought, it was found that the porous structure covered a nitrocellulose lacquer layer, Nevertheless, there was no problem with what the The strips were in an aqueous electrolyte complete coverage by the subsequently deposited, the per liter
beaten layer concerns. If you put 16 g of potassium antimonyl tartrate on p-type germanium, If you want to deposit an antimony layer, you can add 82 g of sodium citrate and after the thin layer of black antimony 25 g of citric acid
is deposited, by means of any 30 known per se Perform electrolytes. You can also use the contained and adjusted to a pH of 6.5 Attaching the thin layer of black was. Antimony used electrolytes for this purpose. A strip of platinum was used as the anode. That choose and then after the thin layer potential has been through a Haber-Luggin capillary is deposited, the cathode potential by about 35 and a saturated calom electrode by means of a Increase 200 to 350 mV. Set to deposit thicker potentiostats. The electrolysis was at Antimony layers, this bath is carried out less than 20 ° C, suitable. The potential was reduced to - 850 mV (opposite Must be turned on, then on the one with the thin black antimony (a saturated calom electrode) layered p-type germanium lead or 40 quickly brought to -1100 mV, during a an alloy of lead and antimony deposited minute held at this value, then returned, so it is advisable to previously switched from the same to - 850 mV and also 1 minute on the electrolyte another thin layer of gray sem value, held. The strips were from the Antimony, also removed by increasing the cathode bath, rinsed and then a part of the electrical potential around 200 to 350 mV, to be deposited. 45 trolytically with lead and the rest with an alloy When the potential is coated by means of a potentiostatic made of lead and antimony. If an arrangement is made, it must be prevented. The lead bath had the following composition that at the cathode there is a large voltage drop per liter of solution in water: occurs. In this case special attention must be paid to * _{ηη Ώ1} », -m. _Λ u _t be that the connection of germanium with 50 100 g lead as lead fluorate, the power supply wire as low as 80 g fluoroboric acid, Has transition resistance. If this is not the 25 g boric acid and Case, then between the power supply wire .. 0.5 g gelatin,
and the germanium a potential difference of even 1V occur, whereby the required value 55 The alloy bath contained, in addition to the above of the cathode potential for the deposition of black substances mentioned per liter of solution 3 g of antimony as Antimony is not reached. This can be based on antimony fluorate or as Sb ₂ O ₃ and 72 g of tartaric acid, known ways are avoided, e.g. B. by place- The anodes were made of lead. The cathodic The deposition of a thin indium layer on current density was 4 A / dm ² . The bath temperature the scrub-cleaned germanium and 60 were kept at 20 ° C. The alloy low Arrangement of a copper wire with silver solder on impact contained about 3 Vo Sb. this layer. Instead of indium one can get to this all precipitates coated the whole Use a thin layer of another metal, not covered by the nitrocellulose lacquer. z. B. copper, precipitate on the germanium. area of the p-conducting germanium strips. If no potentiostat is used, it is 65. not required, very low-resistance contacts an- l'atentansprucne: bring to. By means of a second contact and a first method for galvanic coating of High-resistance voltmeter can measure the potential of p-conducting germanium with antimony, lead or Alloys of these metals using an antimony intermediate layer, characterized in that that the antimony intermediate layer with a thickness of about 0.1 to 1μ at deposited at a cathode potential corresponding to the saturation current without evolution of gas will. 2. Process for the galvanic coating of p-conducting germanium with lead or a lead-antimony alloy according to claim 1, characterized in that a second antimony intermediate layer from the same bath is applied to the antimony intermediate layer from gray antimony is applied at a cathode potential increased by 200 to 350 mV. 3. The method according to claim 1 and 2, characterized in that an aqueous 15 to 19 g / l Containing potassium antimonyl tartrate, 15 to 52 g / l citric acid and 37.5 to 195 g / l sodium citrate Bath is used and is operated at a pH above 6. Considered publications:
U.S. Patent Nos. 2817629, 2753 299. 1 sheet of drawings 809 587/463 7.68 © Bundesdruckerei Berlin