A two-step switching bias sputtering method which can considerably improve both step coverage and electromigration resistance compared with that attainable by conventional d.c. and d.c, bias sputtering has been developed for the formation of reliable interconnections for LSIs. One-step switching bias sputtering consists of alternating operations of d.c, and d.c, bias sputtering. This method features two-step bias, which consists of deep bias followed by shallow bias sputtering. The first bias enhances step coverage of walls by resputtering Al films at the base of the holes. The second bias removes the contaminated Al layer using Ar. Al films of good quality and electromigration resistance values comparable with those attained by conventional d.c. sputtering can be formed by reducing the cyclic number of alternating operations of two-step switching bias sputtering from 18 to 1. The step coverage of Al films at small contact holes by this method is three times higher than that obtained by conventional d.c. sputtering.