(a) 100 µm - Helmholtz-Zentrum Berlin

4.1 Interlayer 69
4.1.2 Molybdenum interface
An attractive alternative to the oxidation of the aluminum layer is the direct depo-
sition of an interlayer. This would allow to deposit the layer stack without breaking
the vacuum which allows much faster sample preparation. On the one hand direct
or reactive deposition of an oxide is an option. However, also very different ap-
proaches can be followed. Here, thin molybdenum layers deposited between the
initial Al and a-Si layers were studied as an alternative to the oxide interlayer. In
Al metallization Mo, W and Ta based Si nitrides and other compounds are used
as diffusion barrier [92, 93]. A Mo target within the DC magnetron sputtering
chamber for Al and a-Si deposition allowed the alternative use of a Mo interlayer
without any vacuum break and resulting oxidation of the Al layer. Since Mo is
used in Al/Si diffusion barriers investigations it was explored wether the diffusion
barrier could be deposited thin enough to allow controlled diffusion between the
two layers.
The controlled deposition of very thin layers is quite challenging especially with
DC magnetron sputtering. To verify the success of the deposition Auger electron
spectroscopy (AES) depth profiles were measured. In Fig. 4.15 the AES results for
specimens with a nominal Mo thickness of dMo = 12 nm, 24 nm and 48 nm between
the initial Al and a-Si layers are shown. It is clearly demonstrated that the amount
of Mo at the interface increased. Thus different thicknesses of the Mo interlayer
were successfully deposited.
In Fig. 4.16 the crystallized fraction RC curves for samples with nominal 12 nm,
24 nm and 48 nm Mo thicknesses are shown. The annealing temperature was
550 °C. With increasing Mo interface thickness the processes is slowed down.
While the layer exchange for the 12 nm Mo sample is finished in 6 − 7 min, the
layer exchange of the sample with 48 nm Mo starts after about 20 min only.
The saturation value of the crystallized fraction decreases gradually with increas-
ing interlayer thickness. While for 12 nm Mo a complete layer exchange can be
observed (RC = 100 %), only about RC = 80 % are reached for 48 nm Mo. In