Backside-Illuminated Imaging Device Pad Insulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Backside-illuminated solid-state imaging devices face issues with leak current due to exposure of the Si layer and Au fine wires, moisture absorption by interlayer dielectric, and electrical instability of the shield film, leading to reliability concerns and increased fabrication steps.
Innovation Solution
An insulating film is extendedly coated from the surface to the internal side-wall of the pad portion opening to insulate the semiconductor layer and wiring layers, preventing current leaks and moisture absorption, while stabilizing the electrical potential of the shield film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pad portion is formed by etching the Si layer to expose Al interconnects for wire-bonding, then electrical connection is achieved, but the Si layer and Au fine wires come into contact causing leak current
Solution Approach 1:
An insulating film is introduced as an intermediary layer between the Si layer and the Au fine wires in the pad portion. This insulating film prevents direct contact between the conductive Si layer and the bonding wires, thereby eliminating the leak current path while maintaining the electrical connection function through the exposed Al interconnects.
2Ease of manufacture
If the interlayer dielectric is exposed from the pad portion opening, then wire-bonding access is achieved, but the interlayer dielectric absorbs moisture leading to deterioration
Solution Approach 1:
The insulating film is extended to coat the internal sidewall of the pad portion opening, forming a protective thin film barrier. This flexible coating approach allows the opening to remain accessible for wire-bonding while preventing moisture from reaching and deteriorating the interlayer dielectric material.
3Object-affected harmful factors
If the shield film is formed over the entire surface including pixel transistors, then electrical shielding is achieved, but the shield film becomes electrically floating causing potential instability
Solution Approach 1:
The shield film is selectively removed from the pad portion region where it would interfere with the insulating film configuration. This extraction allows the shield film to maintain its shielding function over the pixel transistors while preventing it from becoming electrically floating, as the insulating film configuration in the pad portion provides a stable reference potential.
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 solution enhances the reliability of the solid-state imaging device by preventing adverse effects on the semiconductor and wiring layers, improving product reliability and moisture resistance.
Implementation Method 1
an insulating film extendedly coated from the second surface to an internal side-wall of the opening so as to insulate the semiconductor layer
Implementation Method 2
preventing current leaks and moisture absorption
Data Source
AI summary
Disclosed is a solid-state imaging device receiving incident light from a backside thereof. The imaging device includes a semiconductor layer on which a plurality of pixels including photoelectric converters and pixel transistors are formed, a wiring layer formed on a first surface of the semiconductor layer, a pad portion formed on a second surface of the semiconductor layer, an opening formed to reach a conductive layer of the wiring layer, and an insulating film extendedly coated from the second surface to an internal side-wall of the opening so as to insulate the semiconductor layer.