Frequency effects and properties of plasma deposited fluorinated silicon nitride

Abstract
The properties of low‐hydrogen, fluorinated plasma‐enhanced chemical vapor deposition (PECVD)silicon nitridefilmsgrown using NF3/SiH4/N2 feed mixtures in 200 kHz and 14 MHz discharges were compared. High‐energy ion bombardment at 200 kHz is expected to enhance surface diffusion and chemical reconstruction. Compared to fluorinated silicon nitridedeposited at 14 MHz under otherwise comparable conditions, the 200 kHz films had a lower Si–H bond concentration (≲1×102 1 cm− 3), lower total hydrogen content (5–8×102 1 cm− 3), better resistance to oxidation, lower compressive stress (−0.7 to −1.5 Gdyne/cm), and higher density (3.1 g/cm3). The dielectric constant of better low‐frequency Class I films was constant to 500 MHz, while that of high‐frequency films fell up to 15% between 100 Hz and 10 MHz. The absorption edges of low‐frequency PECVD fluorinated silicon nitridefilms were between 5.0 and 6.1 eV, which compare with 4.4 to 5.6 eV for the high‐excitation frequency fluorinated material and 3 to 4 eV for conventional PECVD nitride. However high‐frequency films may have fewer trap centers and a lower dielectric constant. 14 MHz p‐SiN:F filmsgrown with NH3 as an auxiliary nitrogen source showed absorption edges similar to low‐frequency material grown from NF3/SiH4/N2, but they have substantially more N–H bonding. The dielectric constant and absorption edge of these films were comparable to those of low‐frequency p‐SiN:F from NF3/SiH4/N2.