Semiconductor device having a contact window including a lower with a wider to provide a lower contact resistance

A method of fabricating a semiconductor device comprising:

• forming a lower dielectric layer on a semiconductor substrate;
• forming an upper dielectric layer on the lower dielectric layer;
• anisotropically etching the upper dielectric layer and the lower dielectric layer to form a trench therein, the trench passing through the upper dielectric layer and having a depth less than a combined thickness of the upper dielectric layer and the lower dielectric layer;
• and
• isotropically etching the lower dielectric layer exposed by the trench to form a contact window, wherein a width of a lower region of the contact window is wider than a width of an upper region of the contact window,
• wherein forming the lower dielectric layer comprises:
• forming a first dielectric layer on the semiconductor substrate;
• and
• forming a second dielectric layer on the first dielectric layer, wherein the second dielectric layer has a lower etch rate than the first dielectric layer during the isotropic etching.