Films minces à base de Si nanostructuré pour des cellules ...

maximum power into the plasma.
(a) Reactive sputtering : The principle of introducing a reactive gas (g) such
as H 2 , N 2 , O 2 into the chamber and forming a thin lm through chemical reactions
between the sputtered species and gaseous plasma is known as reactive sputtering.
Oxide and nitride lms are often formed by reactive sputtering and the stochiometry
of the lm can be tuned by controlling the relative ow rates of the inert and reactive
gases. The desired compound is formed at the substrate, depending on the power
and the surface reactivity. In this thesis, the total gas ow was xed at 10 standard
cubic cm/min (sccm) while changing the ratio of the gas ow (in sccm) between
the reactive gas and Ar. The equivalent partial pressure (mTorr) in the chamber
displayed by the pressure indicator for a given gas ow (sccm) was used to calculate
the reactive gas rate (r g %) in percentage by,
tel-00916300, version 1 - 10 Dec 2013
r g (%) = [P g /(P g + P Ar )] ∗ 100 Eqn (2.1)
where P g represents the partial pressure of reactive gas, g (g may be H 2 , N 2 or
O 2 depending on the process) and P Ar represents the partial pressure of Argon.
(b) Eect of magnetron : Magnetron sputtering uses the principle of applying
a magnetic eld to the conventional sputtering target in order to obtain more
ecient ionization of the plasma even at low pressures. The magnets placed behind
and sometimes at the side of the target capture the escaping electron and conne
them to the immediate vicinity of the target. This connement provided by the
magnet is illustrated in the sputter process shown in gure 2.1. Due to the increased
connement as compared to a conventional DC system, the plasma density
often increases at least by an order of magnitude. This results in fast deposition
rates at low pressures. However the major limitation of using magnetron is that the
target erodes inhomogeneously due to the non-uniform magnetic eld.
Experimental set-up and working
The samples for this work were deposited using AJA Orion 5 UHV sputtering unit
from AJA international [AJA 1] which has multiple magnetron sources aimed at a
common focal point (Confocal sputtering). The substrate is placed in the vicinity
of this focal point and is kept under rotation to ensure uniform deposition of the
lm. The sputtering chamber was maintained under vacuum of 10 −7 - 10 −8 mTorr
using a turbo-molecular pump coupled to the primary pump. The substrate and the
target which function as the anode and the cathode repectively, are placed facing
each other in the sputtering chamber and an inert gas (Ar) is introduced. Applying
the RF power and introducing a pressure controlled gas ow leads to the presence
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