Semiconductor device forming method

The invention relates to a semiconductor device forming method, which comprises the following steps of: providing an interlayer medium layer, a metal layer which is arranged on the surface of the interlayer medium layer, an etching barrier layer which is arranged on the surface of the metal layer, and a first opening which penetrates through the etching barrier layer and the metal layer, wherein the first opening is exposed out of the interlayer medium layer; forming a protection layer which covers the metal layer on the side wall of the first opening; after the protection layer is formed, etching the interlayer medium layer to partial depth to form a second opening; and fully filling the second opening to form an isolating layer, wherein the internal part of the isolating layer is provided with an air gap. The performance of the formed semiconductor device is more stable.