Method for fabricating flash memory device having vertical floating gate
A method for fabricating a flash memory device includes forming a control gate having a hollow donut shape over an insulation layer formed over a substrate. The method also includes forming an inter-poly dielectric of a spacer shape on an inner wall of the control gate, filling a conductive layer for a floating gate between the spacer shaped inter-poly dielectrics, and forming an interlayer insulation layer over a resulting product formed with the conductive layer for a floating gate. The method further includes removing a center portion of the conductive layer for a floating gate to form an opening, forming a tunnel insulation layer on an inner face of the opening, and filling with a semiconductor layer the opening formed with the tunnel insulation layer to form an active region.
1. A method for fabricating a flash memory device, the method comprising:
forming a control gate having a hollow donut shape over an insulation layer deposited over a substrate;
forming an inter-poly dielectric having a spacer shape on inner sidewalls of the control gate, wherein the inter-poly dielectric surrounds a hole;
forming a floating gate by depositing a conductive material until the hole surrounded by the inter-poly dielectric on the sidewalls of the control gate is filled;
forming an interlayer insulation layer over a resulting structure including the floating gate;
removing a center portion of the floating gate to form an opening, wherein the opening exposes inner sidewalls of the floating gate;
forming a tunnel insulation layer on an inside of the opening; and,
filling the opening with a semiconductor layer to form an active region.
2. The method of claim 1 , wherein the forming of the inter-poly dielectric comprises:
forming a dielectric layer over the insulation layer formed with the control gate; and
performing an etching process on the dielectric layer to remove portions of the dielectric layer to expose upper surfaces of the insulation layer and the control gate.
3. The method of claim 2 , wherein the dielectric layer comprises a structure of oxide layer/nitride layer/oxide layer.
4. The method of claim 1 , wherein the forming the active region comprises:
forming a semiconductor layer inside the opening; and,
planarizing the semiconductor layer.
5. The method of claim 4 , wherein the forming of the semiconductor layer comprises growing a silicon epitaxial layer or depositing a polysilicon layer.
6. The method of claim 1 further comprising, after forming the interlayer insulation layer over the resulting structure including the floating gate,
repeating forming the control gate, the inter-poly dielectric, the floating gate, and the interlayer insulation layer a predetermined number of times to form a multiple structure, wherein the control gate having the hollow donut shape is formed on the interlayer insulation layer by depositing a polysilicon layer on the interlayer insulation layer and etching the polysilicon layer to expose a portion of a surface of the interlayer insulation layer, the inter-poly dielectric having the spacer shape is formed on the inner side walls of the control gate, and the floating gate is formed by depositing the conductive material on the interlayer insulation layer until the hole surrounded by the inter-poly dielectric is filled.
7. The method of claim 6 , comprising repeating the forming of the control gate, the inter-poly dielectric, the floating gate, the tunnel insulation layer, and the interlayer insulation layer a number of times corresponding to a number of memory cells connected to one cell string.
8. The method of claim 1 , wherein the semiconductor layer acts as a channel.