Method of forming floating gate of flash memory

A method of forming the floating gate of a flash memory unit, comprising the steps of:

• forming a tunnel oxide layer and a first floating gate layer over a substrate;
• patterning the first floating gate layer, the tunnel oxide layer and the substrate to form an opening;
• forming a first dielectric layer covering an interior surface of the opening and the first floating gate layer but without completely filling the opening;
• forming a second dielectric layer over the first floating gate layer and the first dielectric layer so that the opening is completely filled;
• planarizing the second dielectric layer to expose the first dielectric layer that was formed over the first floating gate layer;
• removing a portion of the first dielectric layer to expose the first floating gate layer and to make the second dielectric layer raise above a top surface of a remaining first dielectric layer;
• forming a second floating gate layer that covers the first dielectric layer, the second dielectric layer and the first floating gate layer;
• and
• planarizing the second floating gate layer to expose the second dielectric layer, so that a remaining second floating gate layer covers the first floating gate layer as well as extending over the remained first dielectric layer.