Solid-State Imaging Device Lens Refractive Index Gradient
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Solution Overview
Problem
Solid-state imaging devices, particularly MOS image sensors, face challenges in maintaining high light sensitivity and image quality due to light scattering and reflection by metal interconnects, and difficulties in forming smooth, uniform top lenses with conventional heat reflow processes, especially when lens thickness is less than a certain height.
Innovation Solution
A configuration with a multi-layered interconnect layer, first lenses formed on the interconnect layer, and second lenses with a transparent film of lower refractive index than the second lenses, allowing for optimized focal positioning of light above the semiconductor substrate, even when formed using organic materials, thereby improving light collection efficiency and reducing sensitivity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the focal point is situated below the upper face of the substrate to improve sensitivity, then light collection efficiency improves, but light is scattered or reflected by metal interconnects reducing sensitivity
Solution Approach 1:
The patent introduces a resin layer as an intermediary medium between the lens and the semiconductor substrate. This resin layer has a refractive index that is higher than air but lower than the lens material, creating a gradient that guides light smoothly from the lens through the interconnect layer to the photodiode without direct focal point placement that would cause interconnect reflection. The resin layer acts as a mediator that optimizes light transmission while avoiding the harmful reflection from metal interconnects.
2Length of moving object
If the thickness of rectangular patterns is reduced to achieve thinner lenses, then device miniaturization is achieved, but the upper face of the center portion becomes flat making it difficult to obtain smooth curved lens faces
Solution Approach 1:
The patent changes the material parameter by using a resin layer with specific flow characteristics during a reflow process. By controlling the reflow temperature and time parameters, the resin material flows to form a smoothly curved lens surface even when the initial rectangular pattern thickness is small. This parameter change in material behavior enables curved surface formation that would be impossible with conventional materials and processes.
Solution Approach 2:
The patent utilizes the phase transition of the resin material from solid to liquid state during the reflow process. The resin is heated to its melting point, transitions to a liquid state where it can flow and form smooth curved surfaces, then cools and solidifies to maintain the desired lens shape. This phase transition enables the formation of smooth curved lens faces from thin rectangular patterns.
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
The solution enhances light receiving efficiency and maintains high sensitivity characteristics by optimizing the focal position of light and preventing light scattering, while allowing for the formation of thicker, smoothly curved top lenses with improved uniformity.
Implementation Method 1
a transparent film 30 formed on the second lens 28, wherein a refractive index of the transparent film 30 is smaller than a refractive index of the second lens 28
Data Source
AI summary
A solid-state imaging device includes: an imaging area in which light receiving portions are disposed; an interconnect layer disposed on the light receiving portions, the interconnect layer including metal interconnects having openings and first insulating films; inner-layer lenses formed over the interconnect layer in one-to-one relationship with the light receiving portions; a transparent second insulating film formed on the interconnect layer and the inner-layer lenses; top lenses formed on the second insulating film in one-to-one relationship with the light receiving portions, an upper face of each of the top lenses being a convexly curved face; and a transparent film on the top lenses, the transparent film being formed of a material having a refractive index smaller than a refractive index of the top lenses. In this way, a focal point of at least part of incident light can be situated above a semiconductor substrate.