Study of floating gate nitride etch with high selectivity on flash technology

A new recipe was studied for floating gate etching of flash technology. The scheme for defining floating gate was BARC/SIN/POLY. The main etching step etched through BARC and stopped on SlN, and over etching step etched SIN completely and stopped on poly. Because the selectivity of BARC/SIN was very low with fluorine based recipe, the main step might etch through SIN and make poly loss too much. Four optimum parameters and O₂ was adopted in main etching step to increase the selectivity. Moreover, to reduce poly loss, high polymer gas CH₃F was added in over etching step. The result showed appropriate CH₃F/CF₄ ratio was positive to reduce poly loss. The modified recipe also was tested on the structure wafer and the product. The modified recipe got less poly loss than that of original recipe, and there was no difference on the shape of floating gate for both recipes. The electrical result also showed comparable performance to original CHF₃ based recipe.