A method of forming a metal line and a contact plug of a flash memory device, wherein if first, second, and third etch processes are performed on an anti-reflection film and regions (a region in which a contact plug through which a gate is exposed is formed/a region in which a contact plug through which a semiconductor substrate is exposed is formed), which have different etch targets and have an irregular thickness, the loss of a semiconductor substrate can be minimized and an increase in the resistance of the contact plugs can be prevented. Furthermore, by reducing variation in the depth of the contact plugs, the reliability of devices can be improved.