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For sub 0.25 micron CMOS processes, Shallow Trench Isolation (STI) is required because of its planarity, high packing density and low junction edge capacitance. After trench etch in the STI process, the top corner of the trench must be rounded in order to achieve stable device performance (no kink in the subthreshold slope), reduce inverse narrow width effects and maintain good gate oxide integrity. Several methods of rounding the trench corners have been proposed. A post CMP oxidation step to round the top corner trench has been shown to consume too much of the silicon active area and may not be suitable for sub-0. 1 8m technologies. Furthermore, the post-CMP oxidation can generate a lot of stress even at high (>1075°C) temperatures. It has been shown that a 50 nm radius of curvature provides stable device data [1J and good gate oxide integrity with minimum consumption of the active area (DeltaW). In this paper, we have shown that this radius can be achieved with minimal stress generation using a properly optimized Rapid Thermal Oxidation (RTO) (liner oxide) before oxide fill. Through both 2D oxidation modeling and experimental verification we have shown that an optimum oxidation temperature can be found when coupled with an undercut of the buffer oxide under the silicon nitride mask. Temperature is the primary parameter for rounding of the top corner during oxidation while undercut of the buffer oxide lowers the minimum temperature for a given rounding. A 50 nm radius of curvature can be achieved by the balance of the two parameters. This radius of curvature has been shown to suitable for 0. 15 micron technology and beyond.

An integrated shallow trench isolation process utilizing HDP (High Density Plasma) oxide and a highly manufacturable corner oxidation is described. The choice of trench corner oxidation temperature is shown to be critical in reducing silicon stress, and hence junction leakage, to the levels required by multi-million gate designs. This STI process is shown to be extremely robust and manufacturable. Optimal design of the trench depth and well profiles is shown to provide well-edge isolation adequate for sub-0. 1 8tm technologies.