Method of making a slot via filled dual damascene structure with a middle stop layer

A method of forming an interconnect structure comprising:

• forming a slot via in a first dielectric layer of inorganic dielectric material, the slot via having a width and a length extending in a first direction in the first dielectric layer;
• depositing inorganic dielectric material in the slot via and on the first dielectric layer to form a second dielectric layer on the first dielectric layer;
• simultaneously etching in the second dielectric layer and the slot via in the first dielectric layer to form a trench having a width and a length extending in a second direction in the second dielectric layer, and a via in the first dielectric layer, wherein the first and second directions are substantially normal to one another, the width of the trench is less than the length of the slot via, and the via has a width substantially equal to the width of the trench and is substantially entirely under the trench;
• and
• filling the via and the trench with conductive material;
• wherein the inorganic dielectric material in the first dielectric layer and the inorganic dielectric material in the second dielectric layer are the same inorganic low k dielectric material.