Ccr Description Science

PART II
EXPERIMENTAL DESCRIPTION

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PART II – EXPERIMENTAL DESCRIPTION
In this part there is a detailed description of the deposition sets used for the preparation of
DLC structures. It is of capital importance not only choosing the most adequate deposition
method, but also designing properly the reactor and providing it a complete data
acquisition system for an accurateprocess control.
The DLC samples were deposited by using low-pressure plasma techniques in two
different vacuum chambers, as described in chapter 3. Amorphous hydrogenated carbon
(a-C:H or DLC) films were prepared by pulsed-DC PECVD using only methane as
precursor. All the processes were carried out at room temperature, because, as explained in
introductory chapter 2, film growth on cold substratesfavours the amorphous state. DLC
films with uniform metal content (Me-DLC) were deposited in another reactor by
pulsed-DC reactive magnetron sputtering of metallic targets in an atmosphere with argon
and methane. By modifying the vessel configuration it was possible to deposit multilayer
structures of carbon/metal/…/metal (Me/a-C). A list containing the deposited samples in
this study can befound in appendix A.
In-situ characterization of the glow discharge responsible of DLC growth by PECVD was
performed through a computer controlled fast Langmuir probe, which recorded I(V)
characteristics with a high time resolution. For this purpose, a time-delay circuit was
constructed in order to diminish the frequency of the power supply trigger and therefore
register synchronously theplasma parameters. Gas pressure was red by manometers, and
set by both gas flow variation and quenching of the vacuum line through a manual valve.
The time evolution of cathode voltage was monitored by an oscilloscope.
The technology employed for the ulterior characterization of the samples is listed in
chapter 4. The morphological and structural study was carried out mainly by TEM, XRD
andAFM. Composition was studied by XPS and EPMA. Mechanical and tribological
properties were obtained by nanoindentation, scratch and Calo-wear tests, and new
accessories based in AFM for nano-tribology measurements and based in SPM for surface
conductivity scanning were also developed.

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Chapter 3
Experimental set for deposition

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3 – Experimental set for deposition

Thin filmstructures of diamond-like carbon prepared by pulsed plasma techniques

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Chapter 3 – Experimental set for deposition

3.1. Experimental set for deposition of amorphous carbon by pulsed-DC
plasma enhanced CVD (PECVD)
The deposition system consisted in a plasma reactor with a load-lock chamber and a
computer controlled gas supply and pumping system. Figure 3.1 shows a schematic of thisreactor. The deposition chamber was a cylindrical stainless-steel vacuum vessel of 30 cm
diameter, with two faced planar electrodes of 70 and 400 cm2 in area, which are placed
vertically 4 cm away. They worked as cathode and as grounded electrode, respectively.
This configuration should be reproduced if preparation of additional samples with
comparable properties is required, because therelationship between bias voltage and
supplied power for a given system depends on the electrode geometry [Liebermann M.A.,
2005].
The substrates were placed onto the PECVD cathode, which was maintained at room
temperature during all the processes by using a cool-water circuit. Figure 3.6 in section 3.2
shows a cross-section of a sputtering header, whose architecture was similar to that of
PECVDcathode. Because of the vertical surface of substrate electrode, the substrates were
fixed by using Loctite glue.

ANODE

SUBSTRATE

GAS INLET

GATE
VALVE

CATHODE

PUMPING

Figure 3.1: Schematic diagram of the pulsed-DC PECVD system.

PULSED DC

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3 – Experimental set for deposition

The CH4 gas was introduced into the reactor at flow rate of 30 sccm as measured by a...