Deep trench device with single sided connecting structure and fabrication method thereof

A method for fabricating a deep trench device with a single sided connecting structure, comprising:

• forming a buried trench capacitor in a bottom portion of a trench in a substrate, wherein the substrate has a drain region adjacent to the trench;
• forming a collar insulator on top of the buried trench capacitor and disposed on a sidewall of the trench, wherein the collar insulator is formed with a tapered height, and a lowermost height of the collar insulator exposes a portion of the sidewall of the trench and a uppermost height of the collar insulator fully covers a portion of the sidewall of the trench;
• forming a conductive layer on top of the buried trench capacitor and being surrounded by the collar insulator;
• forming a connecting structure on top of the conductive layer to connect the conductive layer to the drain region, wherein the connecting structure comprises a connecting member electrically connected with the conductive layer, and an epitaxial silicon layer is in direct contact with the portion of the sidewall of the trench where the lowermost portion of the collar insulator exposes;
• and
• forming a cap layer in the trench and on top of the connecting structure.