Large area VUV source for thin film processing

A large area disc shaped vacuum ultraviolet (VUV) light source, from 2 cm to 20 cm in diameter, has been developed. It employs a soft vacuum electron beam emitted from a cathode of ring shape to excite the disc shaped plasma. The Lyman alpha emission 2p ²P⁰-1s ²S at the wavelength of 121.6 nm, dominates the emission spectra when running a hydrogen discharge while the N I line 3s ⁴P-2p ⁴S⁰ at 120.0 nm, dominates in a disc shaped nitrogen discharge. The 121.5 nm 4d ²D-2p ²P⁰ line of He II is observed to dominate in the helium discharge when measurements are made through a 10-15 cm long column of neutral helium. The intensity of VUV emission has a measured uniformity of ±6% over the central 15 cm of the 20 cm diameter disc using atomic helium, molecular N₂ and H₂. The windowless disc plasma is also a source of radical and excited atomic gas species. VUV photons, excited species, and radicals can all assist dissociation of CVD feedstock reactants via volume photo-absorption and sensitized atom-molecule collisions, respectively. In addition, the excited radical flux and VUV impingement on the film may also assist heterogeneous surface reactions and increase surface mobility of absorbed species. Thin films of aluminum nitride, Si₃N₄, and hydrogenated amorphous silicon have been deposited at temperatures between 100-400°C. The deposited films show significant improvement over other photo-assisted CVD processes in the film quality achieved, the substrate temperature required and the maximum deposition rates achieved.