DE1118361B - Method for applying an ohmic contact to silicon - Google Patents

Description

GERMAN

PATENT OFFICE

N12329Vnic / 21g

REGISTRATION DATE: JUNE 9, 1956

NOTICE THE REGISTRATION AND ISSUE OF THE EDITORIAL: NOVEMBER 30, 1961

The invention relates to a method for applying an ohmic contact to silicon of the η type with a specific resistance higher than 1 Ω cm.

An ohmic contact is understood to be a contact with a high transition resistance Measures is independent of the direction and the value of the current. Semiconducting bodies with such contacts are often used in transistors, crystal diodes, phototransistors and similar semiconducting electrode systems used.

It is already known to make such contacts from any metal, with the exception of the Metals from the III. Group of the periodic table. Apart from the fact that some of these Metals, e.g. Copper, gold and nickel, p-type silicon and e.g. B. Rhodium on n-type silicon There are contacts that have clearly rectifying and / or voltage-dependent effects many metals outside the III. Group that result in poor ohmic contacts, especially if the resistivity of silicon is relatively high.

It is already known to use nickel for the production of such contacts. That was back then Silicon relatively impure, it had a low resistivity and mostly showed a conductivity of the p type. Only later was the production method so perfected that silicon of the η type was available. If in the usual way, e.g. B. by galvanic means or by vapor deposition, Nickel contacts are attached to this silicon with high resistivity, it follows that nickel on silicon, both of the η-type and of the p-type, makes contacts, which have rectifying and voltage-dependent effects. Probably because of this Ohmic contacts on silicon of the η type, in certain cases made of gold.

It is also known to promote the ohmic properties of the contacts on semiconductors such as germanium, silicon or the like by tempering at higher temperatures, which in the case of silicon can be 800 ° C. or more. As examples of the materials for the contacts on these semiconductors, silver, rhodium, copper, aluminum or the like have been mentioned. Obviously, germanium or silicon of the p-type were again thought of, because an acceptor element such as aluminum on these semiconductors of the η-type always results in rectifying contacts. The indication that the ohmic character of the contacts is promoted by tempering is in the process of attaching an ohmic one
Contacts on silicon

Applicant:

NV Philips' Gloeilampenfabrieken,
Eindhoven (Netherlands)

Representative: Dr. rer. nat. P. Roßbach, patent attorney,
Hamburg 1, Mönckebergstr. 7th

Claimed priority:
Netherlands 13 June 1955

Louis Marius Nijland, Eindhoven (Netherlands),
has been named as the inventor

others not generally applicable; especially in the case of contacts that consist of acceptors or donors or that contain such elements, the rectifying properties are not affected by annealing repealed or destroyed.

It has been found that with the help of nickel, if special measures are taken, on Silicon of the η type with a high specific resistance achieves particularly good ohmic contacts can be. Silicon with such a relatively high specific resistance must be particularly be pure. It can e.g. B. be produced in that the material with the help of the so-called Zone melting process is freed of impurities and then processed into a single crystal.

In contrast, the invention relates to the application of an ohmic contact to silicon of the η type with a specific resistance higher than 1 Ω cm.

According to the invention, a nickel layer is applied to the silicon for this purpose, which is at a temperature between 700 ° C and the melting point of the silicon is subjected to a heat treatment, so that diffusion of the nickel into the silicon takes place.

It was found that heating below the mentioned limit of 700 ° C. causes diffusion of the nickel, but does not produce a good ohmic contact. The heat treatment is therefore preferably carried out at a temperature of at least 750 ⁰ C. On the other hand must be taken into account

109 747/453

There was now a voltage of 1 volt between contact 3 and aluminum electrode 2 in the Applied in the forward direction of the diode, the result was a current of about 10 mA.

If, however, the nickel was first attached to the disk 1 and the aluminum electrode was melted on it, so that the nickel had the opportunity to partially ^{diffuse into the silicon at 800 °} C., a forward current of the same resulted

become that the rate of diffusion increases rapidly as the temperature increases. Most of the time
Rectifying electrodes are also present or have to be attached on the semiconducting body in the vicinity of the ohmic contact
and the nickel does not reach its sphere of influence
To penetrate electrodes, it is desirable that the
Temperature not too high to choose for the duration
stop the treatment for a few minutes
can. If the temperature is chosen too high, then the voltage of about 100 mA must be measured, from which the improvement and the treatment time are so short that the process cannot be carried out in practice because of the contact made of nickel. Which emerges.

Treatment is therefore preferably carried out at a temperature. It is not necessary to heat-treat the

temperature of max. 850 ° C. ohmic contact simultaneously with the melting

The heat treatment can, in order to carry out an oxidation of the rectifying contact, to avoid the nickel in a neutral atmosphere. You can melt the latter first, then one Sphere or in a vacuum. Apply nickel layer and this finally the

It follows that the "heat treatment thus obtained is subjected to. In general ohmic contacts of excellent quality, when the most favorable temperatures are, What is surprising, especially since 20 actions are unequal in the same way, initially the one treated Make contacts with germanium of the η type, which has the highest temperature are rectifying. demands.

Finally, it is noted that the application of the

clock material compared to the known, also for the invention is naturally not limited to diodes with the establishment of ohmic contacts under the same 25 molten rectifying electrodes under conditions suitable materials, for example; It can also be used when silver is because nickel adheres better to silicon such electrodes by diffusion or to others, so that mechanically more resistant cones are produced, and are also obtained at other pre-clocking points. Also, the diffusion directions are lower than diodes, which have a semiconducting body speed, so that the setting of the 30 per from silicon of the η type with a relatively treatment duration is less critical. Finally contain high resistivity, e.g. B. in nickel can also easily be de-energized through transistors or phototransistors.
Immersion in baths can be applied to the silicon using the so-called ElektroIess process.

The invention is explained in more detail with reference to the drawing.

The figure shows schematically the section of a crystal diode on an enlarged scale.

This diode was manufactured in the following manner. On the surface of a disc 1 made of silicon of the η type with a specific resistance of

Claims (4)

PATENT CLAIMS: 2 Ω cm, a piece of aluminum was placed, which was cut from a wire with a thickness of 0.3 mm and a length of 0.2 mm. The aluminum piece was then melted by heating the whole thing in a neutral atmosphere of nitrogen or argon to 800 ° C. for 5 minutes. This produced a rectifying electrode 2. The lower side of the disk 1 was then cleaned by grinding and electrolytically nickel-plated in a bath with the following composition: 120 g NiSO4-OH2O, 15 g NH4Cl, 15 g H3BO3, 100OgH2O. This composition is selected from many useful compositions by way of example only. A current of a few milliamperes was passed through the bath for about 1 minute, after which, by appropriate shielding, nickel was deposited on the upper surface of the disk 1. A method for attaching an ohmic contact to silicon of the η-type having a higher resistivity than 1 Ω cm, characterized in that a nickel layer is applied to the silicon, at a temperature between 700 ° C and the melting point of silicon of a Heat treatment is subjected, so that diffusion of the nickel into the silicon takes place. 2. The method according to claim 1, characterized in that the heat treatment at a temperature of at least 750 ° C is carried out. 3. The method according to claim 1 or 2, characterized in that the temperature is at most 850 ° C. 4. Process for the production of an electrode system, which consists of a semiconducting body Contains silicon with a resistivity higher than 1 Ω cm, with an ohmic Contact is applied in the manner of claim 1 or 2 and wherein other heat treatments are also provided be carried out, e.g. B. for melting rectifying electrodes, characterized in that initially the at the Heat treatment taking place at the highest temperature is carried out. Considered publications:
German patent application S 26374 VIIIc / 21g was prevented. In this way a thin 65 was created (announced on 3/5/1953);
Nickel layer 3 with a thickness of about 1 μ. U.S. Patent No. 2,563,504. 1 sheet of drawings © 109 747/453 11.61