The structure of plasma-deposited silicon nitride films determined by infrared spectroscopy

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Abstract
Plasma‐deposited silicon nitride, a‐SiN:H, has been deposited at low ammonia‐to‐silane gas ratios. The nitrogen‐to‐silicon ratio in the film is proportional to the NH3/SiH4 flow ratio in the reactor. The Si‐H peak in the infrared spectrum of the a‐SiN:H shifts to lower frequency as the N/Si of the film decreases. We use the random bonding model to calculate the average electronegativity that a Si‐H bond experiences for a particular N/Si ratio in the film. The measured Si‐H frequency correlates with the calculated electronegativities and agrees with a similar correlation of Si‐H obtained for molecules. For N/Si less than 0.27 we observe an additional peak at 650 cm−1 that also appears in the spectrum of plasma‐deposited amorphous Si and is the Si‐H wagging vibration. The random bonding model predicts amorphous Si to be the predominant constituent for N/Si less than 0.27, in agreement with the infrared data.

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