Diploma Thesis - Erich Schmid Institute

Basic Physical Properties
6. Basic Physical Properties of layer and substrate materials
6.1. Polycrystalline aluminium on monocrystalline silicon
6.1.1. Properties of aluminium layer
Aluminium ore, most commonly bauxite, occurs mainly in tropical and sub-tropical
areas. The raw material bauxite is converted into alumina in the Bayer process, which
is reduced to aluminium metal in electrolytic cells known as pots by adding cryolite [9].
Pure aluminium shows no phase transformation in the solid state and will crystallise at
an equilibrium temperature of about 660°C in a closed packed face centred lattice [10]
with a mono-atomar basis (figure 6.1).
As basis for the stress evaluation the anisotropic elastic behaviour of a cubic material
is represented in equation 6.1, where the low number of independent elastic constants
corresponds to the high symmetry of the cubic system [3, 4].
⎛s11
⎜
⎜s12
⎜s12
s = ⎜
⎜ 0
⎜ 0
⎜
⎝ 0
s
s
s
12
11
12
0
0
0
s
s
s
12
12
11
0
0
0
s
0
0
0
44
0
0
Figure 6.1: Cubic face centred unit cell
s
0
0
0
0
44
0
0 ⎞
⎟
0 ⎟
0 ⎟
⎟
0 ⎟
0 ⎟
⎟
s ⎟
44 ⎠
⎛ c
⎜
⎜c
⎜c
c = ⎜
⎜ 0
⎜ 0
⎜
⎝ 0
11
12
12
c
c
c
12
11
12
0
0
0
c
c
c
12
12
11
0
0
0
c
0
0
0
44
0
0
c
0
0
0
0
44
0
0 ⎞
⎟
0 ⎟
0 ⎟
⎟
0 ⎟
0 ⎟
⎟
c ⎟
44 ⎠
(equ 6.1)
15