Gapfill structure and manufacturing methods thereof

A method comprising:

• patterning a first trench and a second trench in a semiconductor substrate to define a plurality of semiconductor fins, wherein the first trench is wider than the second trench;
• depositing a first insulating material in the first trench and the second trench, wherein the first insulating material comprises silicon, oxygen, carbon, nitrogen, or a combination thereof;
• etching the first insulating material below tops of the plurality of semiconductor fins;
• and
• depositing a second insulating material over the first insulating material in the first trench and the second trench, wherein the second insulating material comprises a first seam in the first trench and a second seam in the second trench, and wherein the second seam extends closer to the first insulating material than the first seam.

A device comprising:

• a first fin and a second fin extending from a semiconductor substrate;
• a first insulating material between the first fin and the second fin;
• and
• a second insulating material between the first fin and the second fin and over the first insulating material, wherein the second insulating material has a higher k-value than the first insulating material, and wherein a top surface of the first insulating material extends continuously from a sidewall of the first fin to a sidewall of the second fin.