DE1226855B - Process for electroless gold plating of electrodes made of aluminum or an aluminum alloy in a semiconductor arrangement - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

Number: File number: Filing date:
Display day:

C 23 c

German class: 48 b -3/00

J 20088 VI b / 48 b
June 15, 1961
October 13, 1966

The invention relates to a method for electroless gold plating, in particular for targeted Deposition of gold on alloy contacts of silicon semiconductor assemblies by electroless Gild.

The invention is described below for the specific application in silicon diodes which Have aluminum alloys as contacts. As an aluminum alloy, both essentially pure aluminum as well as aluminum alloys are understood, which during the Alloying of rectifying pn junctions or can be used as an alloy material.

In view of the fact that aluminum and alloys with high aluminum content on their If the surface has an oxide layer, the attachment of lead wires hits the alloy contacts made of aluminum with silicon diodes on difficulties, since both welds and soldering can also be made more difficult by the presence of the oxide layer. The present invention intends to provide a method by which aluminum electrodes are selectively gold plated, the To facilitate making electrical contacts with these electrodes.

The invention therefore relates to a method for electroless gold plating made of aluminum or a Aluminum alloy electrodes of a semiconductor arrangement, in particular a silicon semiconductor arrangement, for the production of electrical contacts, according to the invention distinguishes that the semiconductor device in a hot alkali hydroxide solution of such a concentration is immersed so that only the electrode material is attacked, then the solution immersed semiconductor device is continuously diluted with hot water while draining, until it consists of clear water, then below the water with the arrangement immersed in it Maintaining a temperature of about 80 ° C a solution of a gold-amino complex for gilding added and the pH of the gold plating bath using an ammonium hydroxide solution a value between 7 and 8 is set and held.

The further development and advantages of the invention will become apparent in the following description Hand of the drawing showing the sequence of the individual process steps.

The first process step according to the invention process for electroless gold plating from
Aluminum or an aluminum alloy
existing electrodes of a semiconductor device

Applicant:

German ITT Industries
Company with limited liability,
Freiburg (Breisgau), Hans-Bunte-Str. 19th

Named as inventor:

Tmothy Mocanu, Quincy, Mass. (V. St. A.)

Claimed priority:

V. St. v. America June 24, 1960 (38 631)

is that the completed diode array or other equivalent object in a bath is immersed, which essentially consists of a 2 normal solution of sodium or potassium hydroxide consists. The temperature of the solution is expediently kept at about 80.degree. The diving is carried out for about 3 to 4 minutes or any other suitable time during which the oxide layer is removed from the surface of the aluminum electrode of the diode without affecting the rectifying Transition or the surface properties of the silicon wafer are adversely affected.

At the end of the immersion time, the alkali hydroxide bath is continuously filled with hot, preferably diluted in boiling water without removing the diode from the bath. The dilution is continued until the bath is largely free of hydroxide and essentially consists of water. The temperature of the bath is preferably kept at about 80 ° C.

By the water bath that by the ongoing dilution has been obtained, the diode is purged without exposing it to air.

A suitable solution of a gold-amino complex is added to the water bath. Furthermore, a sufficient amount of ammonium hydroxide is added periodically, as much as necessary is to adjust and maintain the pH of the solution between 7 and 8, as the ammonium hydroxide evaporates. As in the previous

609 670/333

In process steps, the temperature of the solution is about 80 ° C within a limit of "" ± 5 ° C held. The amount of added gold-amino solution for gilding is of course dependent of the volume of the cleaning bath and the concentration required for gilding.

Example,.

The diodes are first immersed in 50 ecm of a 2 normal sodium hydroxide solution (4 g of sodium hydroxide on 50 cm ^{3 of} H ₂ O) at a temperature of about 80 ° C. After 4 minutes, without exposure to the atmosphere, the diodes are rinsed by continuously diluting the bath with boiling water, after which the 50 cm. ³ volume of the bath consists essentially of pure water.

^{5 cm 3 of} a gold-amino complex are added to this amount of water. If it is necessary, heat is applied in order to keep the solution at 80 + 5 ^° C. After about one minute, 2 cm ^{3 of} a 28% ammonium hydroxide solution is added to the solution in order to keep it alkaline at a pH between 7 and 8. Because ammonia _{vapor (NH 3} ^{) escapes, a further 3 cm 3 of} a 28% ammonium hydroxide solution are added after 3 minutes in order to maintain the desired pH. -The gold plating is continued for a further 3 minutes, after which the diodes are removed, cleaned and dried. -

As a result of this treatment, the diodes have a smooth, shiny, continuous gold plating on the aluminum electrodes * without any detectable gold plating of the silicon surface. It could no gilding or impairment of the rectifying transitions nor any other disadvantageous Appearances on the semiconductor wafers can be detected. - ■ ''

It should be noted that it is important ^{to avoid extreme deviations of more than + 10 0} G from the intended temperature of -80 ° C. In principle, a slightly lower temperature for the hydroxide bath would be permissible. However, in order to accelerate or facilitate the setting of the more or less critical temperature of 80 + 5 ^° C., which is more or less critical for the plating bath, it is advisable to dilute the hydroxide bath with boiling or almost boiling water so that the cleaning bath obtained is a Has a temperature of almost 100 ° C. This makes it possible to add the gold plating solution and the ammonium hydroxide at room temperature without the temperature of the bath dropping significantly below 80 ° C. The supply of heat via an external heat source can then be reduced or avoided entirely.

The various times set are not critical, although that set for gilding Time may lead to undesired gold plating of the rectifying junction, if it is excessively elongated.

Essentially, the invention consists in that the oxide layer is removed from the surface of the aluminum or the aluminum alloy and that the surface is kept oxide-free until the gold layer is applied without adversely affecting the diode. ■ ■ ^: ■ ''

Claims (1)

Claim: '"" Method for electroless gold-plating of aluminum or an aluminum alloy consisting of: electrodes of a semiconductor arrangement, in particular a silicon-semiconductor & ränöfdnurig ", for the production of -electrical ¹ -contacts, characterized in that the semiconductor arrangement is in a hot alkali hydroxide solution of such Concentration is immersed so that only the electrode material is attacked, then ^ the solution with immersed semiconductor arrangement -continuously -is diluted with hot water while draining; until it consists of -clear water, then the water with the arrangement immersed in it "while keeping it open" A solution of a gold-amino complex is added to the gold-plating process at a temperature of approx. 80 ° C and the pH value of the gold-plating bath is adjusted to a value between 7 and 8 using an 'ammonium hydroxide solution'. Considered publications:
German Patent Nos. 813 472, 932 858;
German interpretative document No. 1000 533;
Ff annhauser, »Galvanotechnik«, 1950, vol. I, p. 912. ■ "■■■" ■ "■: ■■■■■ 609 670/333 10.66 © Bundesdruckerei Berlin