Method and structure for gap filling improvement

A method for forming a semiconductor structure, comprising:

• providing a substrate having isolation features formed therein, wherein a first fin structure and a second fin structure are disposed on the substrate, the first and second fin structures extending in a first direction and being separated by a first distance;
• providing first and second gate structures disposed over the substrate and over the first and second fin structures, the first and second gate structures extending in a second direction perpendicular to the first direction and being separated by a second distance, wherein a gap is formed by the first distance between sidewalls of the first and second fin structures and by the second distance between sidewalls of the first and second gate structures;
• preparing a first solution having a first viscosity;
• coating the first solution on the substrate to form a first anti-reflective coating (ARC) layer on the substrate having the isolation features formed therein that partially fills the gap, such that the first ARC layer directly contacts the respective sidewalls of the first and second fin structures and the respective sidewalls of the first and second gate structures;
• preparing a second solution having a second viscosity, the second viscosity being greater than the first viscosity;
• coating the second solution on the first ARC layer to form a second anti-reflective coating (ARC) layer that fills a remaining portion of the gap, such that the second ARC layer directly contacts the respective sidewalls of the first and second fin structures and the respective sidewalls of the first and second gate structures;
• and
• planarizing the second ARC layer, such that a height of the first ARC layer and the second ARC layer combined is greater than a height of the first and second fin structures and about equal to a height of the first and second gate structures, thereby exposing a top surface of the gate structures.

A method for filling gaps defined between fins and gate structures overlying the fins disposed over a substrate, the method comprising:

• partially filling the gaps defined between the fins and the gate structures by forming a contact etch stop layer over the substrate, wherein the contact etch stop layer is disposed along sidewalls of the gate structures;
• partially filling the gaps defined between the fins and the gate structures by spin coating a first dielectric coating solution having a first viscosity on the contact etch stop layer to form a first interlayer dielectric layer having a first thickness on the contact etch stop layer, wherein a height of the fins and a height of the gate structures is greater than the first thickness after the spin coating of the first dielectric coating solution;
• and
• filling a remaining portion of the gaps defined between the fins and the gate structures by spin coating a second dielectric coating solution having a second viscosity on the first interlayer dielectric layer to form a second interlayer dielectric layer having a second thickness on the first interlayer dielectric layer, wherein the second viscosity is greater than the first viscosity, and further wherein the second interlayer dielectric layer is polished, such that a sum of the first thickness and the second thickness is greater than the height of the fins and about equal to the height of the gate structures, thereby exposing a top surface of the gate structures, and further wherein the first interlayer dielectric layer and the second interlayer dielectric layer each directly contact a portion of the contact etch stop layer disposed along the sidewalls of the gate structure.