Etch stop layer in integrated circuits

An integrated circuit structure comprising:

• a first low-k dielectric layer;
• an etch stop layer comprising:
• a first sub layer comprising a metal carbide;
• a second sub layer over the first sub layer, wherein the second sub layer comprises a metal nitride;
• and
• a third sub layer overlying the second sub layer, wherein the third sub layer comprises a metal compound comprising an element selected from carbon and oxygen;
• a second low-k dielectric layer over the etch stop layer;
• and
• a via comprising a portion in the second low-k dielectric layer, wherein the via penetrates through the etch stop layer.

A method comprising:

• forming an etch stop layer over a first dielectric layer, wherein the forming the etch stop layer comprises:
• forming a metal nitride layer over the first dielectric layer;
• and
• performing a treatment on the metal nitride layer using an oxygen-containing gas or a carbon-containing gas, wherein a top surface layer of the metal nitride layer is converted to a second sub layer of the etch stop layer, and a bottom layer of the metal nitride layer remains untreated to act as a first sub layer of the etch stop layer;
• forming a second dielectric layer over the etch stop layer;
• etching the second dielectric layer, wherein the etching stops on the etch stop layer;
• and
• etching through the etch stop layer.