Method for fabricating a high-density semiconductor memory device

A method for fabricating a high-density semiconductor memory device, comprising:

• forming a trench etching mask on a first side of a semiconductor substrate to define an active region thereon, thereby exposing a region of the first semiconductor substrate, said trench etching mask being made of an insulator material;
• etching said exposed region of the first semiconductor substrate, thereby forming a trench therein;
• filling up said trench with an insulating material, thereby forming an isolation trench;
• planarizing the resulting structure;
• etching a portion of said trench etching mask, thereby forming a contact hole in said trench etching mask;
• depositing a first conductive layer filling said contact hole and patterning said first conductive layer to form a capacitor lower electrode, said capacitor lower electrode being electrically connected to said first semiconductor substrate;
• sequentially forming a dielectric film and a capacitor upper electrode layer overlying said capacitor lower electrode, said capacitor upper electrode layer having a planar top surface;
• bonding said planar top surface of said capacitor upper electrode layer and a second semiconductor substrate with a bonding insulating layer disposed therebetween;
• planarizing a second side of said first semiconductor substrate until said isolation trench is exposed;
• forming a transistor at said planarized surface of said first semiconductor substrate, said transistor having a gate electrode and a junction region;
• forming an interlayer insulating layer overlying said transistor;
• forming a bit line contact hole in said interlayer insulating layer;
• and
• depositing a second conductive layer filling said bit line contact hole and patterning the second conductive layer to form a bit line.