Method for forming a capacitive isolation trench and substrate comprising such a trench

A device, comprising:

• a semiconductor substrate;
• and
• a capacitive isolation trench including:
• a trench extending into the semiconductor substrate from a first surface, the trench having an upper portion gradually widening from a neck of the trench toward a lower portion of the trench;
• an electrically isolating coating on walls of the trench;
• a first layer of a semiconductor material on the coating;
• an electrically isolating layer on the first layer of the semiconductor material;
• and
• a second layer of the semiconductor material on the electrically isolating layer, the electrically isolating layer disposed between the first and second layers of the semiconductor material.

An image sensor, comprising:

• a semiconductor substrate;
• a capacitive isolation trench including:
• a trench extending into the semiconductor substrate from a first surface, the trench having an upper portion gradually widening from a neck of the trench toward a lower portion of the trench;
• an electrically isolating coating on walls of the trench;
• a first layer of a semiconductor material on the coating;
• an electrically isolating layer on the first layer of the semiconductor material;
• and
• a second layer of the semiconductor material on the electrically isolating layer, the electrically isolating layer disposed between the first and second layers of the semiconductor material;
• and
• a plurality of pixels, wherein at least two pixels of the plurality of pixels are arranged in said substrate and separated by the capacitive isolation trench.