Hydrogen-dominated plasma, due to silane depletion, for microcrystalline silicon deposition
Schematic of a plasma deposition reactor (Ref. 5). Silane and hydrogen flow into the reactor where they are dissociated by electron impact. Silane radicals diffuse to the walls resulting in Si:H deposition with release of . H atoms diffuse to the walls and recombine on the H-saturated surface, also releasing . Hydrogen and undissociated silane are pumped out of the reactor, possibly accompanied by polysilanes and dust particles.
Number density fractions of silane, silane radicals, hydrogen molecules, and atoms calculated from Eq. (7) as a function of (a) silane depletion for , (b) silane depletion for , and (c) electron density. Pure silane inlet flow of 1000 SCCM at 100 Pa pressure and 500 K temperature; reactor dimensions . The silane radical fraction limit is indicated as .
Relation between electron density and silane fractional depletion from Eq. (10) using the same parameters as Fig. 2 for which , , and . The right-hand axis, , is the gas phase Damköhler ratio of the volume reaction rate to the inverse gas residence time as commonly used in chemical reactor engineering.
Ratio of the pumping speeds with and without plasma, using Eq. (11), as a function of (a) silane fractional depletion and (b) electron density. Each graph shows the limits for dissociation into molecular hydrogen (molecular limit) and for dissociation into atomic hydrogen (radical limit). The parameters are the same as for Figs. 2 and 3.
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