Mechanism of SiNxHy deposition from N2–SiH4 plasma

The N2 –SiH4 rf glow-discharge plasma has been analyzed by line-of-sight mass spectrometry of species impinging on the deposition electrode (including N atoms), and properties of SiNx Hy films deposited from this plasma have been examined. At high rf power and low SiH4/N2 gas ratio, most of the SiH4 is consumed by reaction of SiHm radicals with N atoms at the film surface and becomes incorporated into the film. No Si–N precursor species are seen in the plasma. This is in contrast to the NH3–SiH4 plasma, where the Si(NH2)3 radical is the key gas-phase precursor. If power is insufficient or SiH4 flow is excessive, disilane is formed in the plasma. Under disilane-free plasma conditions, films slightly N rich with no Si–H bonding and only 11 at. % H (as N–H) can be deposited at high rate (21 nm/min). The film tensile stress characteristic of the NH3 process is absent in the N2 process due to the absence of precursor chemical condensation beneath the growing surface. However, step coverage is much worse in the N2 process due to the much higher sticking coefficients of the reactant radicals. The N2 plasma chemistry is the same using 400 kHz or 13 MHz rf power, but compressive stress and H content are both higher at the lower frequency due to H+ implantation.