Improved delayering method for soi wafer processing

The benefits of Silicon on Insulator (SOI) technology are to reduce parasitic device capacitance, improving performance as well as smaller build area. Current delayering method to reveal polysilicon using 49% Hydrofluoric (HF) concentration is not suitable for SOI wafer. Furthermore, the method cannot remove small, thin and dense gate poly such as in Static Random Access Memory (SRAM) cells. The implication of the current method will cause Top Silicon to be damaged. A parallel lapping is used to improve surface flatness while exposing the polysilicon layer. Subsequently, Poly-etchant is employed to etch the exposed polysilicon and remaining the oxides. An optimum HF's concentration and etching time are crucial in order to etch the remaining oxides while protect Top Silicon from damage during SOI delayering process. The idea is to halt the oxide etching somewhere in Deep Trench Isolation (DTI) without delaminating Top Silicon on Buried Oxide (BOX). In addition to this process, Interlayer Dielectric (ILD) oxide, Gate Oxide (GOX) and polysilicon layer can be removed completely. Hence, 20% HF and 10 minutes etching time (HFt) followed by supersonic cleaning is a recommended combination for a complete removal of remaining layers on silicon surface, such as metals, polysilicon, nitride, and oxides. A clean exposed silicon substrate is vital to allow wet etchant solution to be carried out successfully to reveal silicon defects. Improved delayering method of Parallel Lapping → Poly-Etchant → Diluted and Time Controlled Hydrofluoric Acid Etching is capable to remove thin and dense polysilicon precisely without damaging the Top Silicon made it suitable for SOI technology.