Integrated circuit devices include trenches in a material layer that divide the material layer into fins. With such devices, an insulator partially fills the trenches and contacts the material layer. The top surface of the insulator (e.g., the surface opposite where the insulator contacts the material layer) has a convex dome shape between at least two of the fins. The dome shape has a first thickness from (from the bottom of the trench) where the insulator contacts the fins, and a second thickness that is greater than the first thickness where the insulator is between the fins. Further, there is a maximum thickness difference between the first and second thicknesses at the midpoint between the fins (e.g., the highest point of the dome shape is at the midpoint between the fins). Also, the top surface of the first insulator has concave divots where the first insulator contacts the fins.