Silicon-on-insulator (SOI) substrate and method for manufacturing the same

A silicon-on-insulator (SOI) substrate comprising:

• a silicon substrate having a field region that surrounds and defines an active region, the field region including
• a first oxygen-ion-injected isolation region disposed under the active region and having a first thickness, the first thickness substantially uniform throughout the first oxygen-ion-injected isolation region, a center of the first oxygen-ion-injected isolation region located at a first depth from a top surface of the silicon substrate;
• and
• a second oxygen-ion-injected isolation region disposed adjacent to the active region and the first oxygen-ion-injected isolation region, the second oxygen-ion-injected isolation region extending to a top surface of the silicon substrate, the second oxygen-ion-injected isolation region having a second thickness that is greater than the first thickness, a center of the second oxygen-ion-injected isolation region located at a second depth from the top surface of the silicon substrate.