Specific Process Knowledge/Thin film deposition/Deposition of Gold/Adhesion layers: Difference between revisions
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of the Au grain coalescence, observed in Section 6.2, using the geometrical | of the Au grain coalescence, observed in Section 6.2, using the geometrical | ||
concept of the Euler angles. | concept of the Euler angles. | ||
== Evolution of the Au nanostructure with temperature == | |||
Figure 6.1 shows the TKD maps of �lm nanostructure evolution for a di�erent | |||
set of temperatures of a 20 nm pure Au �lm (left column), 2 nm Ti/20 | |||
nm Au (center column) and 2 nm Cr/20 nm Au (right column) bilayer | |||
systems. | |||
The nanostructure of pure Au at room temperature consisted of small | |||
grains having [100] and [110] crystal orientations with respect to the sample | |||
surface orientation and larger grains having [111] orientation, as already | |||
described in the previous chapters. The �lm started to dewet between 100°C | |||
and 200°C. In general, the evolution of the nanostructure was in agreement | |||
with the results reported in Chapters 3 and 4. When Ti was used as adhesion | |||
layer, the nanostructure of Au at room temperature had a smaller grain size | |||
and complete [111] orientation, as described in Subsection 5.2.1. When the | |||
sample was treated with the same annealing conditions as pure Au, the e�ect | |||
of the temperature on the nanostructure was very di�erent: the annealing | |||
did not a�ect the continuity of the �lm up to 500°C and up to 200°C there | |||
was little grain growth. From 400°C the grain size started to increase, but | |||
not at the levels of pure Au. For the Cr/Au bilayer system, the Au �lm | |||
had a slightly smaller average grain size than in the Ti/Au case. Due to | |||
the low average grain size, a lot of grains were not properly indexed and are | |||
displayed as black areas. The Au layer maintained a continuous morphology | |||
up to 500°C also in this case, but the increase of the grain size was more | |||
limited than in the Ti/Au sample. | |||
A more quantitative analysis of the grain size increase for all three samples | |||
was performed between the map at room temperature and the one | |||
after the annealing at 200°C, since at such temperature the nanostructure | |||
of Au was still continuous and the dewetting was not a�ecting the analysis | |||
signi�cantly. The results are reported in Fig. 6.2. | |||
The average grain size of the pure Au sample increased from 97 nm to | |||
105 nm in the evaluated temperature range (Fig. 6.2a), the one of the Ti/Au | |||
sample from 45 nm to 56 nm (Fig. 6.2b) and the one of the Cr/Au sample | |||
almost did not change, increasing from 34 nm to 36 nm (Fig. 6.2c). | |||
At higher temperatures, the Au grain size increase was very di�erent | |||
between the two adhesion layers. Figure 6.3a shows the variation for Ti/Au | |||
between room temperature and 500°C: the plotted average grain size value | |||
increased from 45 nm to 113 nm after the annealing. Figure 6.3b shows the | |||
variation for Cr/Au: in this case the grain size increase is lower, varying from | |||
34 nm to 44 nm, highlighting the higher nanostructure stability guaranteed | |||
by Cr respect to Ti. | |||
In the pure Au and Ti/Au samples, was clearly visible with a visual | |||
inspection of the maps that the grain growth proceeded through grain coalescence | |||
(marked by white circles in the maps of Fig. 6.4). However, the | |||
mechanism of growth looks slightly di�erent between the two samples. In | |||
pure Au, the growth proceeds trough the coalescence between the smaller | |||
[100] and [110] grains and the larger and more energetically stable [111] | |||
grains, as already described in Subsection 4.4.2. In the Ti/Au sample instead, | |||
the coalescence takes place between [111] grains, since they are the | |||
only ones present in the nanostructure. The grain size increase in the Cr/Au | |||
sample is due to a mechanism most likely similar to the one of Ti/Au, as also | |||
this sample only [111] Au grains are present; however the grain coalescence | |||
was not immediately visible due to the higher stability of the Au nanostructure. | |||
The next section presents the introduction of the geometrical concept | |||
of the Euler angles in relation to a preliminary and non-conclusive study | |||
of the coalescence process observed here, having the �nal aim of a better | |||
comprehension of its mechanism. | |||