Method for FinFET fabrication and structure thereof

A method for FinFET fabrication, comprising:

• providing at least three fins protruding from a substrate;
• depositing a first dielectric layer over top and sidewalls of the three fins, resulting in a seam within the first dielectric layer between first and second of the three fins and a trench between the second and third of the three fins;
• implanting ions into a top portion of the first dielectric layer, wherein the ions are implanted into sidewalls of the trench more deeply than into the first dielectric layer above the seam;
• and
• etching the first dielectric layer to form an isolation feature, such that each of the three fins is above a top surface of the isolation feature.

A method, comprising:

• providing first and second fins protruding from a substrate;
• depositing a first dielectric layer over top and sidewalls of the first and second fins, resulting in a trench between the first and second fins, bottom and two opposing sidewalls of the trench being the first dielectric layer;
• performing a treatment process to a top portion of the first dielectric layer;
• after the performing of the treatment process, depositing a second dielectric layer into the trench, the first and second dielectric layers having different materials;
• and
• recessing the first dielectric layer in an etching process, such that a topmost portion of the first dielectric layer is lower than the second dielectric layer.