Multi-purpose composite mask for dual damascene patterning

A method of forming a multi-purpose composite mask for dual damascene patterning comprising the steps of:

• providing a substrate having a first metal layer formed thereon;
• forming a first dielectric layer over said first metal layer;
• forming a second dielectric layer over said first dielectric layer wherein said second dielectric layer comprises a low-k material including black diamond;
• forming a third dielectric layer over said second dielectric layer;
• forming a fourth dielectric layer over said third dielectric layer;
• forming a fifth dielectric layer over said fourth dielectric layer;
• forming a via opening starting from said fifth dielectric layer until reaching to and stopping on said first dielectric layer on said substrate;
• forming a polymeric dielectric layer over said substrate, including over said via opening;
• forming a silicon based dielectric layer over said polymeric dielectric layer;
• patterning said silicon based dielectric layer to define a hard mask for trench opening;
• using said silicon based dielectric layer as a hard mask, etching to transfer said trench opening into said polymeric dielectric layer, while at the same time leaving a portion of said polymeric dielectric in said via opening;
• using said silicon based and polymeric dielectric layers as a mask, further trench etching the underlying said fifth and fourth dielectric layers until stopping on said third dielectric layer;
• and
• removing said portion of said polymeric dielectric from the bottom of said via opening until said first dielectric via is reached, and said dual damascene structure is formed.