We study the properties of the vertical alignment of liquid crystal on amorphous SiON (a-SiON) thin film exposed by ion beam. a-SiON thin films are deposited on the indium-tin-oxide coated glass substrates by using radio-frequency magnetron sputtering system in the temperature range from 25 to 400 C. The transmittance and surface roughness of a-SiON thin films are enhanced with the increase in deposition temperature. After the substrates were deposited by sputtering system, we exposed them to ion beam and fabricated vertical alignment liquid crystal cells. As a result, the fabricated liquid crystal cells show uniform pretilt angle range from 88 to 89 and high thermal stability over 100 C for 20 hours.