Semiconductor devices and methods of forming the same

A semiconductor device comprising:

• a first trench defining a fin, the first trench having a first depth and a first width;
• a first metal gate and a second metal gate on the fin, the first metal gate and the second metal gate traversing the fin and being adjacent to each other;
• a second trench in the fin and between the first metal gate and the second metal gate, the second trench having a second depth that is different from the first depth and a second width that is narrower than the first width;
• and
• a first device isolating layer and a second device isolating layer in the first trench and the second trench, respectively,
• wherein the second trench comprises a lower portion comprising opposing sides that are laterally bulging.

A semiconductor device comprising:

• a first trench defining a fin, the first trench having a first depth and a first width;
• a first metal gate and a second metal gate on the fin, the first metal gate and the second metal gate traversing the fin and being adjacent to each other;
• a first source/drain region on the fin and on a side of the first metal gate;
• a second source/drain region on the fin and on a side of the second metal gate, the first source/drain region and the second source/drain region being adjacent to each other;
• a second trench in the fin and between the first source/drain region and the second source/drain region, the second trench having a second depth that is different from the first depth and a second width that is narrower than the first width;
• a first device isolating layer and a second device isolating layer in the first trench and the second trench, respectively,
• a first interlayer insulating layer on the first metal gate;
• and
• a second interlayer insulating layer on the second device isolating layer,
• wherein the second trench comprises a lower portion comprising opposing sides that are laterally bulging,
• wherein the second depth is greater than each of a distance between an upper surface of the fin to a lowermost end of the first source/drain region and a distance between the upper surface of the fin to a lowermost end of the second source/drain region, and
• wherein a height of a bottom surface of the first interlayer insulating layer and a height of a bottom surface of the second interlayer insulating layer are the same.