SOI Optical Waveguide Insulation via Trench Segmentation
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Solution Overview
Problem
Increasing the thickness of the BOX layer in SOI wafers to reduce propagation loss leads to increased manufacturing costs and potential issues like warpage, slippage, and discharge breakdown during semiconductor device production, affecting yield.
Innovation Solution
A semiconductor device and manufacturing method involving a BOX layer thickness of 1 μm or less, with a trench below the optical waveguide and a buried insulating film, reducing the distance between the optical waveguide and the substrate to 2 μm or more, to minimize propagation loss and manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the thickness of the BOX layer is increased to reduce propagation loss, then propagation loss is reduced, but manufacturing cost increases and manufacturing yield decreases due to warpage, slippage, and discharge breakdown
Solution Approach 1:
The patent divides the insulating structure into two segments: a thin BOX layer (1 μm or less) and a deeper trench filled with buried insulating film. This segmentation allows the optical waveguide to be isolated from the substrate through the combined structure, achieving low propagation loss while keeping the BOX layer thin to avoid manufacturing defects.
Solution Approach 2:
The patent transitions from a single-layer thick BOX structure to a two-dimensional insulating structure comprising a thin BOX layer plus a trench extending deeper into the substrate. This dimensional change enables achieving the required 2 μm or more isolation distance through horizontal trench extension rather than vertical BOX layer thickening.
2Loss of energy
If the thickness of the BOX layer is increased to reduce propagation loss, then propagation loss is reduced, but film-forming time increases leading to increased manufacturing cost
Solution Approach 1:
The patent segments the insulating function between the BOX layer and the buried insulating film in the trench. The thin BOX layer is formed quickly, and the trench is subsequently filled with insulating material to complete the isolation structure, significantly reducing total film-forming time compared to forming a single thick BOX layer.
Solution Approach 2:
Instead of increasing BOX layer thickness in the vertical direction (which increases film-forming time), the patent achieves the required isolation distance by extending the trench horizontally into the substrate and filling it with insulating film, thereby reducing the BOX layer formation time while maintaining low propagation loss.
3Loss of energy
If the thickness of the BOX layer is increased to reduce propagation loss, then propagation loss is reduced, but warpage and slippage occur during heat treatment
Solution Approach 1:
The patent segments the insulating structure into a thin BOX layer and a trench with buried insulating film. This segmentation keeps the BOX layer thin (1 μm or less) to maintain wafer stability during heat treatment, while the trench structure provides the necessary optical isolation to reduce propagation loss.
Solution Approach 2:
The patent achieves optical isolation by extending the trench horizontally into the substrate rather than thickening the BOX layer vertically. This dimensional change maintains wafer stability during heat treatment while providing sufficient isolation distance (2 μm or more) to reduce propagation loss.
4Loss of energy
If the thickness of the BOX layer is increased to reduce propagation loss, then propagation loss is reduced, but discharge breakdown occurs due to charge accumulation
Solution Approach 1:
The patent segments the insulating structure into a thin BOX layer and a trench with buried insulating film. This segmentation reduces charge accumulation in the BOX layer (since it is thin), preventing discharge breakdown, while the trench structure provides sufficient optical isolation to maintain low propagation loss.
Solution Approach 2:
The patent achieves the required 2 μm or more isolation distance by extending the trench horizontally into the substrate rather than thickening the BOX layer vertically. This dimensional change reduces charge accumulation in the BOX layer, preventing discharge breakdown, while maintaining effective optical isolation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces manufacturing costs and improves yield by minimizing warpage, slippage, and discharge breakdown, while reducing propagation loss by 20-30% compared to conventional methods.
Implementation Method 1
a BOX layer formed on the surface insulating film; an optical waveguide formed on the BOX layer... a trench located below the optical waveguide and formed from an interface between the BOX layer and the surface insulating film into the surface insulating film and the first substrate; and a buried insulating film buried in the trench
Implementation Method 2
bonding the first substrate and the second substrate together by bonding the BOX layer to the surface insulating film and the cladding layer on the upper surface side of the first substrate by heat treatment
Data Source
AI summary
A semiconductor device includes: a first substrate; a surface insulating film formed over an upper surface of the first substrate; a BOX layer formed over the surface insulating film; an optical waveguide made of an SOI layer formed on the BOX layer; and a first interlayer insulating film formed over the BOX layer so as to cover the optical waveguide. The semiconductor device further includes: a trench formed in the surface insulating film and the first substrate below the optical waveguide; and a cladding layer made of a buried insulating film buried in the trench. A thickness of the BOX layer is 1 μm or less, and a distance from an interface between the optical waveguide and the BOX layer to a bottom surface of the trench is 2 μm or more.