Split gate trench device
A split gate trench device, including a substrate, an epitaxial layer having a trench, and a split gate structure, is provided. The epitaxial layer is formed on the substrate, and the split gate structure is disposed in the trench. The split gate structure includes a shielding gate, two top gates, a shielding oxide layer, a gate oxide layer, and an inter-gate oxide layer. Each of the two top gates has a shape that is wide at the top and narrow at the bottom.
1 . A split gate trench device, comprising:
a substrate;
an epitaxial layer, formed on the substrate and having a trench, wherein the trench has two vertical sidewalls; and
a split gate structure, disposed in the trench and comprising:
a shielding gate, located inside the trench;
a first top gate and a second top gate, respectively disposed above the shielding gate, wherein each of the first top gate and the second top gate has a shape that is wide at top and narrow at bottom, a surface of the first top gate and a surface of the second top gate close to the two vertical sidewalls of the trench are flat surfaces, and a surface of the first top gate and a surface of the second top gate away from the two vertical sidewalls of the trench comprise symmetrical inclined surfaces, the surface of the first top gate away from one of the two vertical sidewalls of the trench is composed of a first curved surface and a third flat surface, wherein the first curved surface is located above the third flat surface, and the surface of the second top gate away from another one of the two vertical sidewalls of the trench is composed of a second curved surface and a fourth flat surface, wherein the second curved surface is located above the fourth flat surface;
a gate oxide layer, located between the first top gate and the trench and between the second top gate and the trench;
a shielding oxide layer, located between the shielding gate and the trench; and
an inter-gate oxide layer, located between the shielding gate, the first top gate, and the second top gate, wherein the inter-gate oxide layer between the first top gate and the second top gate has a top and a bottom, and in a cross-sectional view, the top is narrower than the bottom,
wherein an included angle between a tangent of a bottom portion of the first curved surface and the third flat surface is greater than 90 degrees, and an included angle between a tangent of a bottom portion of the second curved surface and the fourth flat surface is greater than 90 degrees.
2 . The split gate trench device according to claim 1 , wherein a projection of the shielding gate on the substrate partially overlaps with a projection of the first top gate on the substrate, and the projection of the shielding gate on the substrate partially overlaps with a projection of the second top gate on the substrate.
3 . The split gate trench device according to claim 1 , wherein a bottom surface of the first top gate and a bottom surface of the second top gate are both flat surfaces.
4 . The split gate trench device according to claim 1 , further comprising:
a body region, formed in the epitaxial layer; and
a source region, formed in the body region and close to a top surface of the epitaxial layer.
5 . The split gate trench device according to claim 4 , wherein the gate oxide layer also extends over the source region.
6 . The split gate trench device according to claim 4 , wherein the body region and the source region have different conductivity.
7 . The split gate trench device according to claim 1 , further comprising a drain electrode, disposed on a bottom portion of the substrate.
8 . The split gate trench device according to claim 1 , wherein the gate oxide layer also extends to a top surface of the epitaxial layer.