A method of semiconductor device fabrication includes providing a substrate having a hardmask layer thereover. The hardmask layer is patterned to expose the substrate. The substrate is etched through the patterned hardmask layer to form a first fin element and a second fin element extending from the substrate. An isolation feature between the first and second fin elements is formed, where the isolation feature has a first etch rate in a first solution. A laser anneal process is performed to irradiate the isolation feature with a pulsed laser beam. A pulse duration of the pulsed laser beam is adjusted based on a height of the isolation feature. The isolation feature after performing the laser anneal process has a second etch rate less than the first etch rate in the first solution.