Low Temperature Growth of Amorphous and Polycrystalline Silicon Films from a Modified Inductively Coupled Plasma

A conventional inductive rf discharge is modified by inserting a discharge antenna in a plasma vessel with magnetic multipole confinement, which gives a high-density (∼10 11 cm -3 ) silane plasma at very low pressures (∼1 mTorr). This new type of inductively coupled plasma (ICP) enables high-rate deposition (∼1 nm/s) of a-Si:H films at low substrate temperatures of ∼100°C, which have the photoconductivity of 10 -5 –10 -4 S/cm and the dark conductivity of 10 -10 –10 -9 S/cm. Moreover, microcrystalline or polycrystalline silicon films are formed on glass substrates at moderate temperatures of 200–300°C where the dark conductivity becomes comparable to the photoconductivity and the X-ray diffraction pattern shows sharp peaks corresponding to the silicon crystalline surfaces. Mass spectrometric measurements of the highly dissociated silane plasma show unique radical compositions; ∼90% of ions are hydrogen species (H 3 + , H 2 + , H + ) while the density of neutral radicals (SiH 3 , SiH 2 , SiH) is lower than that of ionic radicals (SiH 3 + , SiH 2 + , SiH + , Si + ). Thus, the main precursor of film growth from high-density plasmas may be ionic radicals rather than neutral radicals.