PURPOSE: To suppress external diffusion of aluminum by forming a thin film of aluminum compound in advance on the main surface of a semiconductor substrate, implanting aluminum ions via the thin film, and heat treating it.

CONSTITUTION: A thin film 2 of aluminum nitride(AlN) of 500 thick is formed in advance on the main surface of a silicon substrate 1 by using a magnetron sputtering unit. Then, aluminum ions are implanted via the A&N thin film 2 by using an ion implanting unit. The implanting conditions of the aluminum ions 3 in this case include 60keV of accelerating voltage, 27Al+ of ion seed, and 5×1015afoms/cm3 of does. The ions 3 are implanted to form an ion implanted region 4 in the substrate 1. A heat treatment of 1250°C for 16 hours is conducted in this state to form an aluminum diffused layer 5 in the substrate 1.