Active corner engineering in the process integration for shallow trench isolation

The electrical characteristics of metal-oxide-semiconductor field effect tr ansistor devices with shallow trench isolation (STI) have been studied to e valuate the active corner shaping and the trench-fill dielectric densificat ion techniques. The suppression of corner parasitic transistor effects was observed in the two different corner shaping schemes used. in the first app roach, an undercut of pad oxide below the nitride mask defining the active region facilitated corner oxidation during liner oxide growth. in the secon d approach, a high temperature post-chemical mechanical polishing (CMP) oxi dation created a rounded corner, forming a minibird's beak under the nitrid e mask edge. Cross-sectional transmission electron microscopy shows that, w hile the post-CMP oxidation "rounds" the corner, the pad oxide undercut pro duces a concave corner profile. Though both approaches improved the subthre shold characteristics of the transistor, the leakage current of held-edge-i ntensive diodes became very high for post-CMP oxidation. The leakage was al so strongly influenced by the annealing ambient during densification of STI gap-fill dielectric. An oxidizing ambient resulted in high leakage current whereas a nonoxidizing ambient resulted in low levels of leakage current. The excessive leakage is attributed to the silicon defects generated along the sn edge as a result of stress exerted by the gap-fill oxide. Densificat ion in nonoxidizing ambient also helped improve the subthreshold characteri stics of the transistors with STI fabricated using the pad oxide undercut s cheme. (C) 2000 American Vacuum Society. [S0734-211X(00)01802-3].