Semiconductor structure having air gap dielectric and the method of preparing the same

A method of preparing a semiconductor structure, comprising the steps of:

• providing a base layer;
• forming a plurality of conductive lines on the base layer;
• after forming the plurality of conductive lines, forming a plurality of spacers on the base layer and the conductive lines, wherein each of the conductive lines are flanked by the spacers, wherein a top width of each of the spacers is less than a bottom width of each of the spacers;
• forming a plurality of dielectric pillars on the base layer, between the spacers of adjacent two of the plurality of conductive lines, wherein the width of each of the plurality of dielectric pillars gradually increases as they are away from the base layer, and each of the plurality of dielectric pillars has rounding corners, wherein top widths of adjacent two of the plurality of dielectric pillars are different;
• removing the spacers;
• and
• forming a plurality of sealing caps between the conductive lines and the dielectric pillars, wherein the sealing caps are in contact with the conductive lines and the dielectric pillars, and separated from the base layer to form a plurality of air gaps correspondingly positioned between the conductive lines and the dielectric pillars, wherein a top width of each of the air gaps is less than a bottom width of each of the air gaps.