Silicon photonics coupling structure using an etch stop layer and methods of forming the same

A semiconductor structure comprising a semiconductor die and an optical fiber, wherein:

• the semiconductor die comprises, from bottom to top, a silicon substrate, a buried insulating layer, a silicon grating structure, at least one dielectric material layer, a layer stack of a first dielectric etch stop layer and a second dielectric etch stop layer, and a passivation dielectric layer comprising a dielectric material and including an opening overlying an end portion of the silicon grating structure;
• the optical fiber overlies the opening in the passivation dielectric layer and is optically coupled to the silicon grating structure through the opening in the passivation dielectric layer and is attached to the semiconductor die by an optical molding structure;
• and
• the at least one dielectric material layer comprises at least one dielectric material selected from silicon nitride and silicon oxynitride, wherein:
• each of the first dielectric etch stop layer and the second dielectric etch stop layer comprises a respective dielectric material selected from silicon nitride and silicon oxynitride;
• the second dielectric etch stop layer includes a different dielectric material than the first dielectric etch stop layer;
• each of the first dielectric etch stop layer and a second dielectric etch stop layer is located entirely underneath a bottom surface of the opening;
• and
• one of the first dielectric etch stop layer and the second dielectric etch stop layer is vertically spaced from, and is not exposed to, the opening.

A method of forming an optical structure, comprising:

• forming a silicon grating structure over a buried insulating layer;
• depositing at least one dielectric material layer over the silicon grating structure;
• depositing a layer stack of a first dielectric etch stop layer and a second dielectric etch stop layer over the at least one dielectric material layer, wherein each of the first dielectric etch stop layer and the second dielectric etch stop layer comprises a respective dielectric material selected from silicon nitride and silicon oxynitride, and the second dielectric etch stop layer includes a different dielectric material than the first dielectric etch stop layer;
• forming a passivation dielectric layer comprising a dielectric material over the at least one dielectric etch stop layer;
• forming a patterned etch mask layer over the passivation dielectric layer, wherein the patterned etch mask layer includes an opening in an area that overlies an end portion of the silicon grating structure;
• and
• forming an opening through an unmasked portion of the passivation dielectric layer by performing an anisotropic etch process that etches the dielectric material selective to a silicon nitride or silicon oxynitride using the patterned etch mask layer as a masking structure, wherein:
• the layer stack is spaced from the opening by a portion of the passivation dielectric layer and is not exposed to the opening;
• or
• either the first dielectric etch stop layer or the second dielectric etch stop layer is exposed to the opening and another of the first dielectric etch stop layer and the second dielectric etch stop layer is not exposed to the opening.