Specific Process Knowledge/Thin film deposition/Deposition of Gold/Adhesion layers: Difference between revisions

From the cross section profile of the 2nm Au sample (Fig. 2a), it is clear that Au, when deposited directly on SiO2, in order to reduce the interface energy, forms a nanoparticle-like layer in contrast to a continuous �lm. The diameter of the nanoparticles is about 10 nm. The nanoparticle morphology is con�rmed by AFM analysis (Fig. 2b). The RMS surface roughness was measured to be 2.4 nm. For comparison, the RMS roughness of the SiO2 substrate was 0.3 nm. When the thin-�lm nominal thickness is increased to 20 nm (20nm Au sample, Fig. 2c), the Au layer becomes continuous, but a certain degree of surface roughness is still present due to grain coalescence. The AFM image (Fig. 2d) shows an RMS surface roughness of 1.0 nm, which is signi�cantly lower than the 2-Au sample.

From the TEM bright �eld cross section analysis of the 2nm Ti/2nm Au sample, it is observed that 2 nm of Ti forms a continuous layer below the Au layer (Fig. 3a). The Au layer is continuous over the Ti, indicating that Ti is responsible for an interface energy decrease, acting as an adhesive. The AFM analysis of the same sample con�rmed the continuous structure, and an RMS surface roughness of 0.8 nm was measured (Fig. 3b). The 2nm Ti/20nm Au sample also shows a smoother �lm compared to the 20nm Au sample (Fig. 3c), and the AFM analysis shows an RMS surface roughness of 0.5 nm (Fig. 3d), very similar to the one of the Si substrate.

In contrast to the case with the Ti adhesion layer, TEM bright �eld analysis of the 2nm Cr/2nm Au sample shows a single continuous layer (Fig. 4a). The AFM RMS surface roughness is 1.2 nm (Fig. 4b). Increasing the nominal Au thickness to 20 nm for the 2nm Cr/20nm Au sample, the �lm still presented a single-layer morphology (Fig. 4c), while the RMS surface roughness decreased to 0.6 nm (Fig. 4d).

size distribution (Fig. 5b). While the smaller grains have di�erent crystal orientations, the large grains (blue color) all have [111] orientation. Microstructural evolution and growth of metal thin-�lms deposited by physical vapor deposition on amorphous dielectric substrates follows island growth. The �rst thin-�lm growth step is the nucleation of small islands once the activation barrier and the critical nuclei size have been overcome. It is followed by a second step of island growth, during which the impinging atoms contribute to increase island size. The third step, usually happening simultaneously with step 2, is island coalescence, where a strong driving force is present for coarsening through surface atom di�usion and grain boundaries (GB) motion. During this process, the island growth is driven by the minimization of surface and interface energy.