Integration of germanium photo detector in CMOS processing

A method comprising:

• forming an N-well and a P-well in a silicon-on-insulator (SOI) substrate;
• forming a complementary metal-oxide-semiconductor (CMOS) transistor or resistor on the SOI substrate over the P-well;
• forming a first interlayer dielectric (ILD) over the SOI substrate and the CMOS transistor or resistor;
• depositing a silicon nitride (SiN) layer on the first ILD;
• depositing a polysilicon (poly-Si) or amorphous silicon (a-Si) on the SiN layer;
• removing a portion of the SiN layer, the poly-Si or a-Si layer, the first ILD, and the N-well, forming a trench;
• epitaxially growing germanium (Ge) or germanium-silicon (Ge/Si) in the trench and over the a-Si or poly-Si;
• removing the Ge or Ge/Si, the poly-Si or a-Si layer, and the SiN layer down to an upper surface of the first ILD;
• forming a doped silicon (Si) cap layer on the Ge or Ge/Si, with a portion extending over the first ILD;
• forming a second ILD over the doped Si cap and on the first ILD;
• and
• forming a plurality of contacts through the second ILD.