Plasmadeposition (CVD - Laboratory)

The ECR-CVD System (ASTex 4100 Microwave-plasma source (2.45 GHz)) is characterized by a remote plasma configuration, where excitation plasma and substrate are spatially separated. The advantages of the ECR-CVD system are a high plasma density at low-pressure conditions in the mTorr-range, (degree of ionistaion 10-³ to 10-²), high deposition rates (up to 35 nm/min for µc-Si and 20 nm/min for epitaxial growth) and independently controllable parameters for ion-current and ion-energy.

One specific feature of such system is the possibility of epitaxial growth of Si at low temperatures (far below 1100°C). Due to the impact of ions on the growing surface the surface energy and therefore also the adatom mobility is increased. Si epitaxy becomes possible already at temperatures below 600°C.
This temperature regime allows the use of cost-effective substrates (e.g. glass) for crystalline Si thin-film solar cells.

The figure shows an about 400 nm thick Si film grown by ECRCVD at 590 °C on a poly-Si seed layer on glass. Due to fact that the structural quality of the grown layers strongly depends on the crystallographic orientation of the seed layer (and of each other Si substrate) differently oriented grains of the substrate lead to different qualities of the thickened grains. At the end, not each grain is epitaxially (i.e. under conservation of its crystallographic information) thickend.

The right region shows and epitaxially thickend grains which is (100) oriented. Whereas the left grain of the seed layer which is not (100) oriented led to a fine-grained growth. Therefore we designed seed layers with a preferential (100) orientation by ALILE. By the use of these layers almost all of the seed layer area (> 80%) could be epitaxially thickened. This is the prerequisite for poly-Si thin-film solar cells on the base of this deposition technology.