Shallow Trench Isolation with Rounded Corners

The patent applies curvature by rounding the corner portions of the STI trench instead of maintaining sharp corners. This is achieved through a multi-step process: etching trenches with rounded corners, depositing a first dielectric material conformally, performing selective oxidation that creates a variable thickness oxide layer (thinner at corners), and filling with insulating material. The rounded corner geometry reduces stress concentration points, thereby reducing dislocation density in the insulating material while maintaining narrow trench dimensions for high device density.

The patent segments the isolation approach by using narrow trenches rather than broad LOCOS regions. The STI structure divides the substrate into isolated regions through precise trench formation, allowing much higher device density compared to LOCOS. The segmented trench approach maintains electrical isolation functionality while consuming minimal active area, enabling densely-packed integrated circuits.

The patent changes the geometric parameters of the trench corner portions from sharp to rounded, and modifies the oxide layer thickness parameter through selective oxidation. This creates a variable thickness profile where the oxide is thinner at rounded corners and thicker on vertical walls. This parameter optimization allows narrow trench widths for high device density while maintaining sufficient insulating capacity by reducing stress-induced defects through the rounded corner geometry.