DEPOSITION OF DOPED POLYSILICON FILMS BY PLASMA-ENHANCED CHEMICAL VAPOR-DEPOSITION FROM ASH3/SIH4 OR B2H6/SIH4 MIXTURES

Polycrystalline silicon thin films prepared by the pyrolysis of silane with the assistance of a plasma have been investigated. The films were deposited in an experimental CVD reactor at a deposition pressure of 6 mtorr, and over the temperature range of 500’ to 800°C. The foremost characteristic of the plasma was the enhancement of the growth rate of the film. A thirtyfold increase in growth rate was observed in films deposited at 600°C by plasma enhancement over similar films deposited thermally. The films deposited below 600°C were amorphous. The glow-discharge was also seen to favor the nucleation of <220> islands in the polysilicon film, but had no effect on the electrical properties of the film. In situ doped n-type polysilicon films were deposited by plasma enhancement from AsH3/SiH4 mixtures. The growth rate of the latter films was found to be weakly sensitive to the arsine dilution in silane. For p-type depositions from B2H6/SiH4 mixtures, the plasma promoted the decomposition of the reactant gas, resulting in a growth rate enhancement. The texture of the doped polysilicon films deposited with plasma enhancement was insensitive to dopant dilution in the reactant gas. Moreover, the conductivities of the n- and p-type doped films were successfully modulated by over six orders of magnitude when the dopant dilution in the reactant gas was increased from 0 to 500 ppm. Finally, a segregation of the dopant atoms from the gas phase to the solid phase was observed for both p- and n-type dopants. copyright. © 1990, The Electrochemical Society, Inc. All rights reserved.