Method of patterning dielectric

A method of patterning a dielectric layer, wherein a substrate having a metal wiring layer formed thereon is provided, comprising:

• forming a first dielectric layer on the metal wiring layer;
• forming a first masking layer on the first dielectric layer, and a first cap insulation layer on the first masking layer;
• forming a first opening aligned with the metal wiring layer by etching the first cap insulation layer, so that the underlying first masking layer is exposed;
• etching the exposed first masking layer to expose the first dielectric layer;
• forming a second dielectric layer, a second masking layer and a second cap insulation over the substrate in sequence;
• forming a second opening by etching the second cap insulation, so that the second masking layer is open within the second opening;
• etching the exposed second masking layer and the underlying second dielectric layer, and etching the first dielectric layer by using the second cap insulation layer as a mask until the metal wiring layer is exposed;
• and
• forming a conductive layer over the substrate.