Gate Isolation for Multigate Device

A device comprising:

• an isolation feature disposed over a substrate, wherein the isolation feature is disposed between a first fin portion and a second fin portion extending from the substrate;
• a dielectric gate isolation fin disposed over the isolation feature, wherein the dielectric gate isolation fin includes a dielectric feature having an oxide layer disposed over a low-k dielectric layer and a high-k dielectric layer disposed over the dielectric feature;
• a first multigate device having a first channel layer disposed over the first fin portion, a first metal gate that wraps the first channel layer, and first source/drain features, wherein the first metal gate is disposed between the first channel layer and the first fin portion;
• and
• a second multigate device having a second channel layer disposed over the second fin portion, a second metal gate that wraps the second channel layer, and second source/drain features, wherein the second metal gate is disposed between the second channel layer and the second fin portion and the dielectric gate isolation fin separates the first metal gate of the first multigate device from the second metal gate of the second multigate device.

A method comprising:

• forming a first multigate device having a first channel layer, a first metal gate, and first source/drain features, wherein the first channel layer is disposed between the first source/drain features and the first metal gate surrounds the first channel layer;
• forming a second multigate device having a second channel layer, a second metal gate, and second source/drain features, wherein the second channel layer is disposed between the second source/drain features and the second metal gate surrounds the second channel layer;
• and
• forming a dielectric gate isolation fin between and separating the first metal gate and the second metal gate, wherein the dielectric gate isolation fin includes:
• a first dielectric layer having a first dielectric constant, and
• a second dielectric layer having a second dielectric constant disposed over the first dielectric layer, wherein the second dielectric constant is greater than the first dielectric constant;
• and
• wherein the first metal gate is disposed between and physically contacts the first channel layer and the dielectric gate isolation fin, and the second metal gate is disposed between and physically contacts the second channel layer and the dielectric gate isolation fin.