Method of making air gaps copper interconnect

A method of forming an inter-level insulator structure comprising the steps of:

• a) providing a first metal layer overlying a substrate;
• b) depositing a first sacrificial layer overlying the first metal layer;
• c) depositing an etch stop overlying the first metal layer;
• d) depositing a second sacrificial layer overlying the etch stop;
• e) forming a double layer hard mask overlying the second sacrificial layer;
• f) patterning the double layer hard mask to produce a via mask and a trench mask;
• g) etching the second sacrificial layer to form a partial via down to the etch stop;
• h) etching an exposed portion of the etch stop;
• i) etching the first sacrificial layer to form a via, whereby the first metal layer is exposed;
• j) etching the second sacrificial layer to form a trench;
• k) depositing a barrier metal and copper;
• l) planarizing the barrier metal and copper to form a second metal layer;
• and
• m) decomposing the first and second sacrificial layer, whereby the first sacrificial layer and the second sacrificial layer are replaced by air gaps.