Entwicklung von großflächigen PECVD-Prozessen zur kontrollierten, homogenen Abscheidung dünner Siliziumschichten für die Photovoltaik

Hydrogenated microcrystalline silicon (&c-Si:H) is used, among other things, as anabsorber layer in solar cells. To produce &c-Si:H with homogeneous properties ona large-area, industrial scale, using plasma enhanced chemical vapor deposition,reproducible processes need to be established.In the first part of this thesis, the development of a reduced gas flowprocess to producehomogeneous, large-area microcrystalline solar cells is described. There are severalecological and economical advantages when the gas consumption is decreased. Thecosts for purchasing and storage of the feed gas are reduced. Due to the significantlylower feed gas flows, the rotational speed of the vacuum pumps can also be reduced.This results in lower electrical power consumption of the vacuum pumps, an extensionto their maintenance intervals, and an overall increase in their service life. A vacuumsystem with a standard industrial electrode was used during these investigations.The geometry of the gas feed and the exhaust is of great importance when depositing&c-Si:H with a reduced gas flow. A mixture of silane and hydrogen gases is fedinto the process volume through a so called showerhead electrode and is bilaterallyexhausted. As the gas flow is reduced, the residence time of the gas molecules inthe plasma increases. Simultaneously, a higher concentration of silane is used in thefeed gases, resulting in a higher degree of silanemolecule dissociation. A qualitativeplasma-growth model for the large-area deposition of &c-Si:H describes the two maininfluences of reduced gas usage on the local silane concentration in the plasma: ..