Method for manufacturing a trench capacitor having an isolation trench

A method for manufacturing a trench capacitor having an isolation trench, which comprises:

• forming a trench capacitor in a trench of a semiconductor substrate, the trench capacitor having:
• a lower part formed with an outer electrode, an inner electrode, and a dielectric between the inner and outer electrodes;
• an upper part formed with a collar isolation on sidewalls of the trench;
• wherein a silicon layer covers the trench capacitor on top of the collar isolation and a hard mask covers the silicon layer;
• opening the hard mask to reach a surface of the silicon layer;
• in a first etching step, dry etching with an etching gas comprising chlorine or bromine until the collar isolation is reached;
• and
• in a second etching step, dry etching the semiconductor substrate, the collar isolation and inner electrodes of the trench capacitor with an etching gas including silicon fluoride and oxygen.