Pixel structures of cmos imaging sensors and fabrication method thereof

A pixel structure of a CMOS imaging sensor, comprising:

• a semiconductor substrate doped with first type doping ions;
• a gate structure formed on the semiconductor substrate;
• an epitaxial layer doped with second doping ions with a doping type opposite to a doping type of the first doping ions formed in the semiconductor substrate at one side of the gate structure;
• isolation layers formed between side surfaces of the epitaxial layer and the semiconductor substrate to prevent dark currents from laterally transferring;
• a floating diffusion region formed in the semiconductor substrate at the other side of the gate structure;
• and
• a pinning layer formed on the epitaxial layer,
• wherein the isolation layers is formed by:
• forming a hard mask layer having an opening on the semiconductor substrate;
• forming a trench in the semiconductor substrate using the hard mask layer as an etching mask;
• forming an isolation material layer on side surfaces of the trench and the surface of the hard mask layer;
• and
• performing a mask-less process onto the isolation material layer.