Double Trench Isolation
AssigneeSanDisk Technologies LLC
InventorsKatsuo Yamada, Yuji Takahashi, Takuya Futase, Noritaka Fukuo, Tomoyasu Kakegawa
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Abstract
Isolation is provided by forming a first trench, depositing a cover layer on the bottom and sidewalls of the first trench, selectively removing the cover layer from the bottom and forming a second trench extending from the bottom of the first trench. The second trench is then substantially filled by thermal oxide formed by oxidation and the first trench is subsequently filled with a deposited dielectric.
Claims22
A method of forming a Shallow Trench Isolation structure, comprising:
- forming a first trench on a substrate by anisotropic etching;
- depositing a first layer on a bottom and a sidewall of the first trench;
- selectively removing the first layer at the bottom of the first trench by anisotropic etching, while the first layer on the sidewall of the first trench is maintained;
- subsequently, forming a second trench at the bottom of the first trench by anisotropic etching, while using the first layer as a mask, the second trench extending downward from the bottom of the first trench;
- selectively subjecting the second trench to thermal oxidation by using the first layer as a mask, whereby the sidewall of the first trench is not oxidized, and the second trench is substantially filled by a thermal oxide;
- subsequently, removing the first layer by selective isotropic etching with an etching rate of the first layer that is higher than an etching rate of the thermal oxide;
- and
- subsequently, substantially filling the first trench with a deposited dielectric.
The method of claim I wherein the first layer is formed of silicon nitride (SiN) and the selective isotropic etching is performed using a wet etch process.
A method of forming isolating trenches comprising:
- forming a first trench in a silicon substrate;
- subsequently, covering sidewalls of the first trench with a cover layer and leaving a bottom surface of the first trench exposed;
- subsequently, extending a second trench down through the bottom surface of the first trench;
- subsequently, substantially filling the second trench with silicon oxide that is grown on exposed silicon surfaces of the second trench;
- and
- subsequently, substantially filling the first trench with a deposited dielectric.
An isolating structure in a nonvolatile memory comprising:
- a first trench that extends into a silicon substrate between active areas;
- a second trench that extends from the first trench further into the silicon substrate;
- a portion of polysilazane filling the first trench;
- and
- a portion of silicon dioxide filling the second trench.
Dependencies are inferred from the claim text.