FinFET device and method of forming and monitoring quality of the same

A method of monitoring a quality of a FinFET device, the method comprising:

• providing the FinFET device comprising a fin supported by a substrate;
• and a gate structure having a notch feature in a portion overlapped with sidewalls of the fin;
• measuring a profile of the notch feature by measuring respective outermost widths of the gate structure at respective location of the gate structure, the respective locations being at different heights of the gate structure above substrate;
• and
• obtaining the quality of the FinFET device by comparing the profile of the notch feature with a predetermined criterion.

A method of forming a FinFET device, the method comprising:

• forming a plurality of fins extending from a semiconductor layer, the plurality of fins having a first fin density in a center area of the semiconductor layer and a second fin density different than the first fin density in a periphery area of the semiconductor layer;
• depositing a gate layer on the plurality of fins;
• and
• etching the gate layer with form respective first gates over respective fins in the center area and respective second gates over respective fins in the periphery area, by subjecting the gate layer to an etching gas at a first flow rate in the center area simultaneously with subjecting the gate layer to the etching gas at a second flow rate in the periphery area.