PURPOSE: To manufacture a thin boron nitride film of high hardness contg. cubic boron nitride as the principal component on the surface of a substrate by properly regulating the atomic ratio between boron and nitrogen contained in an evaporating source and an ion seed and the quantity of energy for accelerating ions.

CONSTITUTION: An evaporating source contg. boron is vapor-deposited on a substrate, and an accelerated ion seed is irradiated simultaneously with the vapor deposition to form a thin boron nitride film of high hardness on the substrate. The vapor deposition and the irradiation may be alternately carried out. At this time, the atomic ratio between boron and nitrogen (B/N) contained in the evaporating source and the ion seed is regulated to 0.5W3, and the quantity of energy for accelerating ions in the ion seed is regulated to 5W60KeV per one boron, nitrogen or inert gas atom contained in the ion seed.