© 2015 Elsevier Ltd. All rights reserved. A magnetic-field and pulsed-plasma-enhanced chemical vapor deposition (MPECVD) was developed to fabricate amorphous silicon carbonitride (a-SiCN) diaphragm for environmental-cell transmission electron microscope (E-TEM). The films were prepared by using gaseous hexamethyldisilazane (HMDSN), N2 and Ar with pulse voltages varied between 300 V and 600 V. The deposition rate was increased by enhancement of magnetic-field in comparison with a conventional PECVD. The diaphragms were applied to Si (100) and a Cu grid with 100-μm-diameter holes. Fourier transform infrared spectra and X-ray photoelectron spectra revealed that an elimination of organic compounds and a formation of Si-N and C-N bonds in diaphragms can be promoted with increasing pulse voltage and N2 flow rate and decreasing ambient pressure. The diaphragms were amorphous and transparent at 200 kV electrons and no charge-up was observed by E-TEM. Durability to electron beams and reaction gases in the E-cell was improved when diaphragm was deposited with high pulse voltage.