When Integrated circuits are fabricated, a copper layer that forms the contacts
is deposited on a low dielectric (the measure of electrical insulation) material
layer coated on a semiconductor material substrate. In order to reduce RC
time
constant (the time to charge a capacitor) associated with the integrated
circuits
and to improve the frequency or speed of operation of integrated circuits
traditional
methods used result in a high dielectric constant.
Prof. R. O. Dusane and his students of Department of Metallurgical
Engineering and Materials Science have formulated a method of depositing
an amorphous SiC:H barrier layer on a low dielectric material layer. The
method is simple and convenient to carry out, is cost effective and gives
rise
to a composite layer which lowers leakage
of current. The layer is also of
reduced thickness leading to lower
costs of manufacture. The amorphous SiC:H is deposited to form the barrier
layer on deposited material of low dielectric
constant that is coated on the silicon layer. The barrier layer is deposited
by exposing the material layer to hot wire
chemical vapour deposition (HWCVD) using a mixture of silane and acetylene
gases at a temperature of 200 to 300o C
and pressure of 100 to 200 mTorr. HWCVD is done by heating a tungsten wire
at 1700 to 1900o C.
The invention of depositing a barrier layer on the dielectric material
layer by HWCVD eliminates the use of RF generators
and impedance matching circuits thereby rendering the process simple
and convenient to carry and also making it
more cost effective. Further the process has been shown not to damage
the dielectric layer. A barrier layer of 10 nanometers
is adequate to prevent the copper diffusion into the dielectric material
layer. The composite layer of barrier material
and low dielectric constant material has reduced leakage of current.
Thus Integrated circuits fabricated using the composite
layer thus designed will have reduced RC time constant and improved frequency.
Indian patent application no. 4/MUM/2006 Patent grant no. 223221
Inventors: R O Dusane, A A Kumbhar, and S K Singh
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