or plasma dry etching exposing the substrate 1 and the sidewalls of layers 2 a 2 b which are alternately laminated on the substrate 1 in an other embodiment the process conditions of anisotropic etching of stack structure 2 are controlled in order to make the lateral etching rate being significantly less than the longitudinal etching rate obtaining a vertical deep hole or deep trenches 2 tp with high aspect ratio e g aspect ratio ar being greater than or equal to 10 1 the cross sectional shape by cutting parallel to the surface of substrate 1 may be various geometric shapes selected from rectangular square diamond circular semi circular elliptical triangular pentagonal hexagonal octagonal and etc as shown in fig3 the second material layers 2 b in the stack structure 2 are selectively etched e g etched back forming a plurality of recesses 2 r in the side wall of the trenches 2 tp for later defining the floating gates area etching methods include wet etching and dry etching depending on the difference between material of layers 2 a and layers 2 b the selectable wet etching solution comprises hf base etchant for silicon oxide material hot phosphoric acid etchant for silicon nitride material strongly alkaline etchant such as koh or tmah for the polysilicon or amorphous silicon material furthermore oxygen plasma dry etching can be chosen for carbon based materials such as amorphous carbon or dlc making o and c react to.