Chemistry Reference
In-Depth Information
1
0
(3)
10
-1
(2)
(1)
10
-2
10
-3
10
-4
10
-5
0.00
0.05
Oxygen partial pressure [Pa]
0.10
0.15
FIGURE 8.56
Resistivity vs. oxygen partial pressure for different sputtering modes, (1) dc
plasma excitation from metallic target Zn:Al (2) rf plasma excitation from metallic target
Zn:Al (3) rf plasma excitation from a ceramic target ZnO:Al
2
O
3
. (From Ellmer, K., Magnetron
discharges for thin film deposition, in R. Hippler et al., eds.,
Low Temperature Plasma
,Vol.2,
p. 675, Wiley-VCH, Berlin, Germany, 2008.)
their incorporation into the growing film. The feed gas is able to control oxygen
concentration in the film. Therefore, even pure metallic Zn:Al targets can be used for
reactive sputter deposition.
Obviously, the reactive sputtering process requires efficient tools for process con-
trol [389] since only within a narrow parameter window the desired layer properties
can be obtained. In Figure 8.56 the influence of the oxygen partial pressure on the
resistivity of ZnO:Al films is presented. DC and RF sputtering systems as well as
metallic and ceramic targets were investigated [390]. If the oxygen partial pressure
is small, the resistivity as well as the optical transparency is small too. However,
increasing oxygen partial pressure causes the desired transparent ZnO:Al films with
low resistivity. Further increasing oxygen flow improves the transparency of the films
but produces a sharp rise in the resistivity due to the nearly complete oxidation of
Zn to ZnO and Al to Al
2
O
3
. These films contain a mixture of insulating phases. The
same experiments performed with rf-excitation show a similar behavior concerning
the deposition rate and the resistivity, but the discharge voltage does not exhibit step-
like curves. This is due to the fact that in the rf-discharge, the delivery of secondary
electrons is nearly independent of the target material.
8.2.4.2.4 Hard Coatings
8.2.4.2.4.1 Materials and Concepts for Hard Coatings
Hard coatings have been successfully established as wear protection on cutting
tools. Effectiveness and endurance of cutting tools can be improved remarkably by
