A NOVEL SHALLOW TRENCH ISOLATION TECHNIQUE

Shallow-trench isolation processes which involve refilling using depos ition of oxide and polysilicon were investigated. Our results show tha t the oxide-filled shallow-trench isolation technology based on chemic al-mechanical polishing (CMP) is difficult to control and results in p oor uniformity. Use of this technology also involves in the dishing ef fect in wide field regions. However, shallow-trench isolation technolo gy using a masking nitride layer, polysilicon refill, the CMP process with high etch selectivity, and local oxidation of polysilicon is easi ly implemented and absolutely field oxide encroachment (bird's beak) f ree. Although the CMP process results in the dishing effect in wide fi eld regions, the local oxidation of polysilicon can reduce the amount of dishing. The polysilicon-filled shallow-trench isolation process ca n also achieve excellent uniformity across 6-inch diameter silicon waf ers due to the high etching selectivity of polysilicon to chemical-vap or-deposited (CVD) oxide and SiN. Moreover, the n(+)/p junction leakag e current of polysilicon-filled shallow trenches is comparable to that of oxide-filled shallow trenches. This simple and easily controllable process is a very promising candidate for shallow trench isolation.