Device and method of dielectric layer

A method comprising:

• etching a semiconductor substrate to form a trench extending from a top surface of the semiconductor substrate into the semiconductor substrate;
• depositing a first liner layer over sidewalls and a bottom of the trench using a first Si-containing precursor;
• depositing a second liner layer conformally over the first liner layer using a second Si-containing precursor different from the first Si-containing precursor;
• depositing a third liner layer conformally over the second liner layer using the first Si-containing precursor;
• filling a dielectric material into the trench and over the third liner layer;
• and
• removing excess portions of the dielectric material over the top surface of the semiconductor substrate.

A device comprising:

• a first dielectric layer;
• a first conductor in the first dielectric layer;
• an etch stop layer over the first dielectric layer, wherein the etch stop layer has a first surface facing the first dielectric layer and a second surface facing away from the first dielectric layer, and a concentration of carbon in the etch stop layer periodically varies from the first surface to the second surface;
• a second dielectric layer over the etch stop layer;
• and
• a second conductor in the second dielectric layer and etch stop layer and electrically connected to the first conductor.