FIELD OF INVENTION
This invention relates to a method of fabricating electrical contacts and the
electrical contacts produced thereby.
This invention further relates to a method of fabricating electrical contacts with the
compound semi-conductor formed from at least one metal selected from class III to
V of the periodic table.
BACKGROUND OF INVENTION
The difficulties in making good ohmic contacts to the class III-V compounds of
semi-conductor such as InP, GaAs and InGaAs are well known. These materials on
the other hand are very important for the fabrication of various electronic devices
in general and thermo photovoltaic cells in particular. As a consequence, utilisation
of such material for various applications depends upon the ability to make low
resistance ohmic contact on them.
Ni and its compound are well known contacting material to the above semi-
conductors. However, methods for deposition of these materials are difficult.
Normal method is to deposit these materials by vacuum technique or radio
frequency technique. However, each of the above methods has their own
limitations.
OBJECTS OF THE INVENTION
It is therefore an object of this invention to propose a method of fabricating
electrical contacts using a simple technique.
It is a further object of this invention to propose propose a method of fabricating
electrical contacts using a simple technique which is cost-effective.
At the outset of the description which follows, it is to be understood that the
ensuing description only illustrates a particular form of this invention. However,

At the outset of the description which follows, it is to be understood that the ensuing
description only illustrates a particular form of this invention. However, such a
particular form is only an exemplary embodiment and the teachings of the invention
is not intended to be taken restrictively.
BRIEF DESCRIPTION OF INVENTION
Thus according to this invention is provided a method of fabricating electrical
contacts comprising
preparing a solution of atleast a salt of nickel,
warming the solution to a temperature in the range of 90 to 95°C and preparing an
electrolytic bath therewith,
subjecting a substrate surface to a pre-treatment with a sensitiser and activator,
placing the substrate in the bath and subjecting the same to electrolytic deposition
of NixPy layer thereon, where x= 1 to 0.88, y= 0 to 0.12.
This invention further relates to electrical contacts produced by the process.
In accordance with this invention, an electroless technique is employed for the
deposition of NixPy on semi-conducting substrates like InP, GaAs and InGaAs
solution is prepared for the surface treatment of semi-conducting substrates like
InP, GaAs, InGaAs, etc. In this electroless technique, a special type of solution bath
is prepared. The solution consists of salts of Ni like NiCl2 or MSO4, reducing agent
like Na2HPO2, a complexing agent and a stabiliser. The above chemicals are mixed
in particular proportion to have the exact solution. The above solution is then
warmed to a temperature in the range of 90 to 95°C. The semi-conductor of the
above categories is then treated in two other solutions. These are sensitizer and
activator. The sensitizer solution is a mixture of salt like SnCl2 and an acid like HCl.
Activator is a chemical solution containing a mixture of PdCl2, HCl and H2O.
Before deposition of NixPy layer, the substrate surface requires cleaning in cleaning
solution to remove contaminations like grease. The substrate is then

treated with a sensitizer solution to sensitize the substrate surface. After
sensitization, the substrate is activated in activator solution. After activation, the
substrate is dipped in plating bath to deposit NixPy coating. Deposition is allowed
for 7-10 mins. to have good coating.
According to an embodiment of this invention is provided a method of fabricating
electrical contacts comprising preparing a solution of atleast a salt of nickel,
wanning the solution to a temperature in the range of 65 to 70° C, and
preparing an electrolytic bath therewith,
subjecting the substrate surface to electroplating for the deposition of NixPy layer
thereon.
In accordance with the embodiment of the invention, an electroplating technique is
employed. The electroplating bath is prepared by mixing the following chemical in
particular proportion. The chemicals are NiCl2, NiSO4, NiCO3, H3PO3 and H3PO4.
The solution is then warmed to a temperature range of 65-70° C. The substrate is
first cleaned to remove contamination like grease. The substrate is then held in a
vacuum device and electrical contact is taken out and the substrate is connected to
the negative terminal of a d c source. A Ni counter electrode is kept in the plating
bath. The counter electrode is connected to the positive terminal of the d c source.
A suitable amount of d c electricity is allowed to pass through the substrate and the
counter electrode. As a result, a NixPy layer is deposited over the substrate. The
strength of the current is fixed according to the % of P to be incorporated into the
deposit According to the present invention for deposition of 10% of P, a current
density of 1000-1200 A/m2 is required. The substrate is then annealed in air at a
temperature in the range of 200-250° C. The annealing enhances the contacting
performance.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The invention will now be explained in greater detail with the help of the
accompanying drawings wherein
Fig.1 is a cross sectional view of a schematic drawing of the preferred embodiment
of the semi-con ducting devices normally used;
Fig.2 is the schematic diagram for the arrangement for electroplating;
Fig.3a is the current voltage characteristics using electroless technique;
Fig.3b is the current voltage characteristics using electroplating technique.
Fig.1 stands for the device structure those that are generally used. The layer 10
stands for the back metallic layer, the layer 11 stands for semi-conductor like InP
or GaAs, the layer 12 stands for InGaAs and layer 13 stands for top metallic
contact.

WE CLAIM;
1. A method of fabricating electrical contacts comprising
preparing a solution of atleast a salt of nickel,
warming the solution to a temperature in the range of 90 to 95°C and
preparing an electrolytic bath therewith,
subjecting a substrate surface to a pre-treatment with a sensitiser and
activator,
placing the substrate in the bath and subjecting the same to electrolytic
deposition of NixPy layer thereon, where x= 1 to 0.88, y= 0 to 0.12.
2. The method as claimed in claim 1 wherein said substrate is a semi-
conducting substrate such as Indium phosphide, Gallium arsenide, Indium
gallium arsenide and the like.
3. The method as claimed in claim 1, wherein said solution of nickel comprises
salts of nickel such as nickel chloride, nickel sulphate, a reducing agent such
as nickel hydrogen phosphate a complexing agent and a stabiliser.
4. The method as claimed in claim 1, wherein said sensitizer solution is an
aqueous solution of a salt such as tin chloride and an inorganic acid.
5. The method as claimed in claim 1, wherein said activator solution is an
aqueous solution of PdCl2 and an inorganic acid.

6. The method as claimed in claim 1, wherein said electroplating bath
comprises compounds of nickel such as nickel chloride, nickel sulphate,
nickel carbonate and phosphorous and phosphoric acids.
7. The method as claimed in claim 1, wherein said substrate surface is
cleaned before electrode position.
8. The method as claimed in claim 1, wherein deposition is conducted for 7
to 10 mlns.
9. The method as claimed in claim 1, wherein for deposition of 1-% of
Phosphide, a current density of 1000 to 1200 A/m2 is used.
10. The method as claimed in claim 1, wherein after deposition the substrate
is annealed at a temperature in the range of 200 to 250oC.

ABSTRACT

TITLE: A METHOD OF FABRICATING ELECTRICAL CONTACTS
This invention relates to a method of fabricating electrical contacts comprising preparing
a solution of atleast a salt of nickel, warming the solution to a temperature in the range of
90 to 95°C and preparing an electrolytic bath therewith, subjecting a substrate surface to a
pre-treatment with a sensitiser and activator, placing the substrate in the bath and
subjecting the same to electrolytic deposition of NixPy layer thereon, where x= 1 to 0.88,
y= 0 to 0.12.