Composition for electrochemical deposition of nickel coatings

 

(57) Abstract:

Usage: the invention relates to electrochemistry, in particular the production of Nickel coatings with low contact resistance, for example, ohmic contacts to semiconductor materials. Essence: the existing structures was not possible to obtain ohmic electroplating from aqueous electrolytes semiconductor MnSi, FeSi, CoSi. This is achieved in that the composition contains Nickel sulfate, boric acid, sodium chloride and hydrofluoric acid in the following proportions of ingredients, g/l: Nickel sulfate with NISO47H2O 350 400; boric acid (H3BO325 35; NaCl 4,5 5,5; hydrofluoric acid HF 90 110.

The invention relates to electrochemistry (electroplating), in particular the production of Nickel coatings with low contact resistance, for example, ohmic contacts to semiconductor materials.

There are many compositions for the deposition of Nickel coatings on a wide range of materials, working in a variety of conditions.

One of the urgent tasks of the semiconductor instrumentation is the necessity of creating semiconductor materials ohmic contacts. The floor is of high temperatures, and when normal conditions as sources of EMF to power electrical equipment; sensors radiation in a wide frequency range.

Nickel, used to getting contacts is a material resistant to neutron irradiation; corrosion-resistant and heat-resistant component in the alloys, which is important for the electrochemical formation of the transition (ohmic) contact area of the semiconductor - Nickel; analogous to the structure of the outer electron shells in relation to Cr, Mn, Fe, Co, the 4th period of the periodic table of elements of D. I. Mendeleev) used for the synthesis of MnSi, CoSi, FeSi.

In galvanothermy most common electrolytes on the basis of Nickel sulfate. These electrolytes are mainly used to obtain a protective and decorative coating of machine parts for corrosion protection at elevated temperatures and in special environments (alkalis and some acids).

Known composition to obtain a Nickel coating on the metal, in particular iron [1] . The electrolyte composition contains, g/l: Nickel Sulfate with NISO47H2O 250-300 sodium Chloride NaCl 10-15 Boric acid, H3IN325-40 sodium Fluoride NaF 5-6 Formaldehyde 0,4-0,8 2,6(2,7)-Naphtha - Lin-disulpho - acid 2-4 Self the CoSi, this composition is not acceptable, as it contains a large amount of organic additives, which are captured in the process of electrolysis growing Nickel Deposit. This leads to an increase of electric resistance of the transition region of the Nickel-semiconductor (loss obecnosci).

For the prototype accepted the composition of [2] for the deposition of Nickel coatings containing g/l: Nickel Carbonate NiCO35-15 Hydrofluoric acid HF 1-2 sodium Dihydrophosphate NaH2PO4H2O 15-20 Citric acid3H4(OH)(CO2H)35-7 sodium Hydroxide NaOH 5-10

This composition is intended for the deposition of Nickel coatings on light metal, in particular magnesium.

The disadvantage of this composition is the impossibility of using it to obtain ohmic galvanic coatings on semiconductor materials, in particular on MnSi, FeSi, CoSi, working in conditions of high radiation and high temperatures ( 103OC). The unacceptability of this composition is due to the fact that it is designed for a narrow range of materials light metals, in particular magnesium and contains in its composition of ingredients in this together (NaOH, NaH2PO2H2O, CH4(OH)(CO2H)the data of the electrolyte for magnesium coatings are obtained porous and require subsequent ultrasonic machining in the electrolyte plating.

The aim of the invention is to provide opportunities for ohmic galvanic Nickel coatings on semiconductors MnSi, FeSi, CoSi.

The aim is achieved in that in the known structure for the electrochemical deposition of Nickel coatings including Nickel-containing compound and hydrofluoric acid according to the formula of the invention, as the Nickel compounds used Nickel sulfate, optionally, the electrolyte contains boric acid and sodium chloride is in the following ratio, g/l: Nickel Sulfate with NISO47H2O 350-400 Boric acid (H3BO325-35 NaCl 4,5-5,5 Hydrofluoric acid HF 90-110

The need to use as Nickel compounds with NISO47H2O due to the good solubility of this salt in the proposed structure, which allows to find the optimal concentration of the Nickel component in the electrolyte for a wide range of materials;

the necessity of introducing into the electrolyte H3BO3due to the fact that H3BO3- buffer additive to create a stable concentration of hydrogen ions in the electrolyte - shifts the potential of the deposition of Nickel in electrophoretically s account of Cl-, i.e., provides a stable ion concentration Ni+2due to the continuous dissolution of Nickel anodes, improves the conductivity of the electrolyte at the expense of Na+.

The need to comply with the concentration limits for the ingredients in the electrolyte was determined experimentally. The change of this ratio leads to deterioration of obecnosci the transition region of the Nickel coating is a semiconductor. When going beyond the proposed concentrations necessary for the operation of a semiconductor device level obecnosci (104-106Ohm cm2) disappears.

Thus, each of the features is necessary, and together they are sufficient to achieve the objectives of the invention.

Not known for the claimed combination of features, though separately used ingredients known as constituent parts contained in the electrolyte composition intended for obtaining Nickel coatings. For example, in many electrolytes include Nickel compounds: with NISO47H2O; NiCO3however , being different from the claimed combination of features, they lead to non-achieved a positive effect, namely the fir coatings on semiconductors.

Only through the totality of the stated characteristics, the interaction of all the components drawn in the specified proportions, was able to identify a new property that allows you to manage simultaneously reaching reactions etching (semiconductor and deposited Nickel coating) and the deposition of Nickel on semiconductors changing the current density and polarity, as well as to stimulate the processes of electrolysis semiconductor MnSi, FeSi, CoSi due to its own radiation chemical reactions going on in the volume of the electrolyte and the electrodes, which, in turn, manifested itself in a new positive effect, namely the ability to obtain ohmic galvanic coatings on semiconductors MnSi, FeSi, CoSi. Thus the claimed technical solution meets the criterion of "Significant differences".

For preparation of a composition for electrochemical deposition of Nickel coatings have been used with NISO47H2O; H3BO3; NaCl; HF. Sample was taken in the ratios shown in the table, and was dissolved in water at 80aboutC. as semiconductors, which caused the Nickel coating was used fresh polycrystals MnSi, FeSi, CoSi. As a cell line which was little more than a Nickel, the cathode is a sample of a semiconductor material. The samples were immersed in the cell surface. To prevent deposition of Nickel on the other sides of the sample they previously were isolated from exposure to the electrolyte, a protective coating (e.g., Capon-Lac). The electrolysis is carried out by passing an electric current of 100 A/DM2. When conducting electrolysis within 60 C. was obtained Nickel coating thickness of 10 μm. Contact resistance at the boundary of metal - semiconductor was measured by microprobe analysis.

The results are summarized in table, which shows the concentration of the components in the minimum, average and maximum values.

From the above examples it is seen that in the claimed range of concentrations was able to obtain ohmic galvanic coatings on three types of semiconductors. The measured value of the contact resistance in all examples is in the range of 10-4-10-6Ohm cm2that suggests the possibility of using the obtained Nickel coatings as ohmic contacts. Outside the experimentally found ratios of the components present in this formulation the level of obecnosci below 10-4Ohm cm2that A claimed composition allows to obtain ohmic galvanic coatings on semiconductors MnSi, FeSi, CoSi , which did not provide the composition of the prototype. (56) white, M. A. , Ivanov A. F. Electrodeposition of metallic coatings, M. : 1985, S. 95.

Ivanova N. D. fluoride electroplating. Kiev, 1986 S. 83.

Patent Germany N 3022402, CL H 01 L 21/445, 1980.

COMPOSITION FOR ELECTROCHEMICAL deposition of NICKEL COATINGS including Nickel-containing compound and hydrofluoric acid, characterized in that, in order to obtain ohmic galvanic coatings on semiconductors MnSi, FeSi, CoSi from aqueous electrolytes, as Nickel compounds using Nickel sulfate with NISO47H2O, and the electrolyte further comprises boric acid and sodium chloride is in the following ratio of ingredients, g/l:

With NISO47H2O 350 - 400

H3BO325 - 35

NaCl 4,5 - 5,5

HF 90 - 110

 

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