a simplified method is disclosed for forming dual damascene patterns using a phase - shifting mask in conjunction with a single photoresist process . first , a method is descried for fabricating a phase - shifting metal mask formed on a quartz substrate having opaque , transparent and semi - light - transmitting regions . the transparent regions comprise hole pattern while the semi - transmitting regions comprise line pattern for a dual damascene pattern . then it is shown how the phase - shifting mask is used to form a dual damascene structure by forming a single photoresist on a silicon substrate having a tri - layer insulating layer , forming the hole and line patterns on the photoresist simultaneously by exposing it through the phase - shifting mask , and then transferring the patterns successively into the top and bottom layers of the insulating layer by etching . having thus formed the vertical hole interconnect and line trench into the insulating layer , metal is deposited into the dual damascene structure . any excess metal on the surface of the insulating layer is then removed by any number of ways including chemical - mechanical polishing , thereby planarizing the surface and readying it for the next semiconductor process .