Shallow trench filled with two or more dielectrics for isolation and coupling or for stress control

A method for controlling stress in a silicon active area comprising:

• providing a stop layer on a substrate;
• etching a plurality of trenches through said stop layer and into said substrate wherein said trenches surround a silicon active area;
• depositing a first layer over said stop layer and filling said trenches wherein said first layer comprises a dielectric material having a thermal coefficient higher than that of silicon;
• planarizing said first layer to said stop layer leaving said first layer within said trenches;
• thereafter removing said first layer from a subset of said trenches wherein said subset of said trenches surround said silicon active area in a first direction and wherein remaining said trenches surround said silicon active area in a second direction perpendicular to said first direction;
• depositing a second layer over said stop layer and within said subset of trenches wherein said second layer comprises a dielectric material having a thermal coefficient lower than that of silicon;
• and
• planarizing said second layer to said stop layer leaving said second layer within said subset of trenches wherein compressive stress is applied to said silicon active area in said first direction and tensile stress is applied to said silicon active area in said second direction.