A research on a technological method for preventing cracking of thick Si3N4 layers during manufacturing process of PICs

Si3N4 waveguides are widely used in the creation of photonic integrated circuits (PIСs). High optical characteristics of PICs are achieved on silicon nitride (Si3N4) films obtained by chemical vapor deposition at reduced pressure (LPCVD). Thick Si3N4 layers (>300 nm) are characterized by a high level of internal mechanical stresses, which, under certain conditions, can lead to the formation of cracks, which reduce the yield of suitable PICs and limit their use. In this work, to prevent cracking of the Si3N4 layer with a silicon oxide (SiO2) sublayer, 120 um wide grooves were formed along the perimeter and inside the working area of the silicon (Si) wafer by plasmochemical etching (PCE). The etching depth was 3.2 um, which significantly exceeded the thickness of the deposited Si3N4 (450 nm). The proposed approach made it possible to produce PICs elements without cracks in the core and cladding with an average optical loss of ∼0.8 dB/cm at a wavelength of 1550 nm.