Optical Waveguide Filling with Silicon Nitride for Solid-State Imaging
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Solution Overview
Problem
Conventional solid-state imaging devices face challenges in miniaturizing the optical waveguide due to limitations in the concave portion's opening dimension, leading to reduced light collecting performance and sensitivity, primarily due to uneven resist application and the need for resin materials that cannot withstand heat treatment.
Innovation Solution
The solution involves forming a concave portion as an optical waveguide in the first insulating film before creating the pad electrode and interconnection, allowing the use of high refractive index films like silicon nitride to fill the concave portion, which increases the opening dimension and enhances sensitivity without altering the interconnection layout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the concave portion for the optical waveguide is formed after the pad electrode and interconnection are formed, then the aspect ratio of the concave portion can be controlled, but the opening dimension of the concave portion cannot be increased due to uneven resist application
Solution Approach 1:
The patent applies preliminary action by forming the concave portion for the optical waveguide before forming the pad electrode and interconnection. This sequence change allows the lithography process to occur on a flat surface without height differences, enabling even resist application and larger opening dimensions while still achieving the required aspect ratio control in the subsequent filling process
2Ease of manufacture
If resin material is used to fill the concave portion, then the concave portion can be filled effectively, but the material cannot withstand heat treatment
Solution Approach 1:
The patent applies parameter changes by transitioning from organic resin material to inorganic high-refractive-index material (such as silicon nitride) for filling the concave portion. This material substitution maintains the high refractive index parameter needed for optical waveguide functionality while simultaneously achieving heat resistance parameter required for subsequent CVD heat treatment processes
3Use of energy by moving object
If the opening dimension of the concave portion is increased, then light collecting performance improves, but void formation becomes more likely when filling with high refractive index films
Solution Approach 1:
The patent applies preliminary action by performing corner-cut etching on the concave portion before filling it with the high-refractive-index film. This preliminary modification of the concave portion geometry creates a tapered shape that facilitates complete film deposition, eliminating void formation while allowing the opening dimension to be increased for improved light collecting performance
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 enables the optical waveguide to be filled with high refractive index materials, improving light collecting performance and sensitivity by ensuring even resist application and avoiding the formation of voids, thus achieving better optical characteristics.
Implementation Method 1
Since the optical waveguide is structured with a material whose refractive index is high, the incident light can efficiently be propagated to the photodiode without being leaked to the outside of the optical waveguide
Implementation Method 2
Passivation film 36 is made of silicon nitride formed by the chemical vapor deposition (CVD) process
Data Source
AI summary
The present invention achieves an optical characteristic exhibiting excellent sensitivity or the like, by increasing the opening dimension of an optical waveguide without changing the interconnection layout, so that the optical waveguide can surely be filled with a film having high refractive index. Pixel portion A of a solid-state imaging device includes photodiode PD formed on a semiconductor substrate; a first insulating film including a concave portion above photodiode PD; and a second insulating film formed on the first insulating film such that the concave portion is filled with the second insulating film. Peripheral circuit portion B of the solid-state imaging device includes an internal interconnection formed in the first insulating film and a pad electrode formed on the internal interconnection to be electrically connected to the internal interconnection. The pad electrode is formed on the second insulating film.