Method for manufacturing semiconductor flash memory and flash memory cell
View Patent ↗A semiconductor flash memory includes a tunnel oxide film formed over a semiconductor substrate, a first spacer composed of polysilicon formed over the semiconductor substrate including the tunnel oxide film, a second spacer composed of an insulating material formed at sidewalls of the first spacer, a dielectric film formed at the uppermost surface of the first spacer and the second spacer, a control gate formed at the uppermost surface of the dielectric film, and a third spacer composed of an insulating material formed at and contacting sidewalls of the second spacer, the dielectric film and the control gate. A first source/drain region formed may be formed in the semiconductor substrate and self-aligned with the first spacer and a second source/drain region may be formed in the semiconductor substrate and self-aligned with the second spacer.
1. A method comprising:
forming a hard mask pattern by depositing an oxide film over a semiconductor substrate and performing patterning and a first etching process on the oxide film;
forming a tunnel oxide film over the semiconductor substrate including the hard mask;
forming a first spacer serving as a floating gate at sidewalls of the hard mask by depositing a first polysilicon layer over the semiconductor substrate, the hard mask pattern and the tunnel oxide film and then performing a second etching process;
performing a third etching process removing the hard mask pattern and a portion of the tunnel oxide film;
forming a source/drain region self-aligned with the first spacer by conducting a first ion-implantation process on the semiconductor substrate;
forming a second spacer at sidewalls of the first spacer by forming an insulating layer over the entire surface of the semiconductor substrate and then performing a fourth etching process on the insulating layer;
forming a dielectric film over the entire surface of the semiconductor substrate including the first spacer and the second spacer; and then
forming a control gate over the first spacer and the second spacer by depositing a second polysilicon layer over the dielectric film and then patterning and a fifth etching process the second polysilicon layer.
2. The method of claim 1 , wherein the dielectric film comprises an Oxide/Nitride/Oxide (ONO) dielectric film.
3. The method of claim 1 , further comprising, after said forming the control gate:
forming a second source/drain region self-aligned with the second spacer by conducting a second ion-implantation process which ion-implants a conductive dopant having low concentration in the semiconductor substrate; and then
forming a third spacer at and contacting sidewalls of the second spacer, the dielectric film and the control gate by forming a second insulating layer over the entire surface of the semiconductor substrate and then performing a sixth etching process on the insulating layer.