Method of fabricating a floating gate for split gate flash memory

A method of fabricating a floating gate of a flash memory, comprising:

• providing a semiconductor substrate;
• defining an active region of the substrate;
• forming a first insulating layer on the active region;
• forming a first conductive layer on the first insulating layer;
• forming a masking layer on the first conductive layer;
• removing a part of the masking layer to form a first opening;
• forming a second conductive layer to cover the masking layer and a sidewall and a bottom surface of the first opening;
• forming a second insulating layer on the second conductive layer and fills the first opening;
• performing an oxidation process, such that the second conductive layer over the masking layer under the second insulating layer is oxidized into a third insulating layer, while the second conductive layer on the lower sidewall and the bottom surface of the first opening is not fully oxidized, and a poly tip is formed on the remaining second conductive layer at a joint between the sidewall and the bottom surface;
• removing the second and the third insulating layers to form a second opening that exposes the remaining second conductive layer and the poly tip;
• forming a fourth insulating layer on the masking layer and filling the second opening;
• planarizing the fourth insulating layer until the masking layer is exposed, while the fourth insulating layer remains in the second opening as a floating gate insulating layer;
• and
• removing the masking layer uncovered by the floating gate insulating layer and the first conductive layer underlying the uncovered masking layer, with a floating gate formed by the remaining first and second conductive layers.