THE ETCHING EFFECT OF NH4OH LAST CLEANING ON THE SILICON SURFACES

As semiconductor device density increases, proper silicon surface prep aration becomes essential for the well growing of gate oxide, and resu ltantly for higher reliability of devices. Especially, the surface pre paration of the pre-gate oxide is most important. The traditional NH4O H-based cleaning (SC-1) shows excellent particle removal capability. H owever, SC-1 cleaning reveals some limitations. such as metallic impur ity contamination, native oxide growth, micro-roughness, etc. The aim of this study is, therefore, to characterize the effect of SC-I pre-ga te oxide cleaning with solutions of various mixing ratios on the devic e properties. The silicon wafers were dipped in NR4OH:H2O2:H2O solutio ns with the ratio of 1:1:5, and 0,25:1:5, and the surfaces were invest igated by Atomic Force Microscope (AFM). Also, the effects of addition al HF (50:1, 250 sec) cleaning were investigated, and compared with th e conventional SC-1 cleaning. After each cleaning, the separate wafers were oxidized and the gate oxide integrity (GOI) was investigated. Al so, the threshold variation due to silicon etching was confirmed by co mputer simulation.