Hydrogen Dilution in PECVD Growth of a-SiNx:H Films: Influence on Cr- and Al-gated nc-Si:H TFTs

Abstract This study investigates the influence of hydrogen (H2) dilution during plasma-enhanced chemical vapor deposition (PECVD) growth of hydrogenated amorphous silicon nitride (a-SiNx:H) films on the performance of bottom-gate nanocrystalline silicon (nc-Si:H) thin-film transistors (TFTs). Four sets of a-SiNx:H films were deposited under varying H2 flow rates and characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) in transmittance and attenuated total reflection (ATR) modes, electrical measurements, and stress analysis. Films were grown on Cr- and Al-coated glass substrates to assess the role of gate metal. Results indicate that H2 dilution improves film resistivity, reduces surface roughness, and minimizes interface stress. FTIR analysis revealed significant differences between ATR and transmittance measurements, emphasizing the need for substrate-specific characterization. At the device level, two otherwise identical Al-gated TFTs with a-SiNx:H gate dielectrics deposited with and without H2 dilution were compared; the device incorporating the H2-diluted dielectric showed higher mobility and lower threshold voltage. These findings highlight H2 dilution as a key parameter for optimizing dielectric properties and device reliability.