Abstract: A device includes a photonic integrated circuit (PIC) die and an electronic integrated circuit (EIC) die bonded to the PIC die. The PIC die includes a waveguide layer including a waveguide and a grating coupler configured to couple incident light into the waveguide, and a first set of dielectric layers on the waveguide layer. The EIC die includes a semiconductor substrate and a second set of dielectric layers on the semiconductor substrate. The first set of dielectric layers faces the second set of dielectric layers. The PIC die and the EIC die include a trench aligned with the grating coupler, the trench extending through the semiconductor substrate, the second set of dielectric layers, and the first set of dielectric layers to the waveguide layer such that the incident light may pass through the trench to reach the grating coupler. A multi-step dry etching process is used to form the trench.