Stacked Photodetector Pad Bonding With Rigid Insulating Film
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Solution Overview
Problem
In stacked image sensors, the miniaturization of connection pads leads to reduced metal volume, resulting in decreased heat expansion, which can cause deterioration of contact characteristics due to the use of low dielectric constant insulating materials with lower Young's modulus than silicon oxide, potentially leading to insufficient bonding between pads.
Innovation Solution
The photodetector design incorporates a stacking structure with semiconductor layers and wiring layers, where the insulating film includes a higher rigidity material penetrating the stacking direction and a second metal portion that is more easily plastically deformed, along with a specific configuration of connection pads to enhance bonding between pads during heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low dielectric constant insulating materials are used to reduce parasitic capacitance, then wiring capacitance is reduced, but the Young's modulus decreases leading to insufficient bonding pressure
Solution Approach 1:
The insulating film is constructed as a composite structure with a first insulating film (low dielectric constant material) and a second insulating film (high rigidity material) that penetrates the first insulating film. This composite structure reduces parasitic capacitance while maintaining sufficient bonding pressure through the high rigidity second insulating film.
Solution Approach 2:
The insulating film is divided into multiple segments: a first insulating film for reducing parasitic capacitance and a second insulating film for maintaining bonding pressure. The second insulating film penetrates the first insulating film, creating a segmented structure that fulfills both functional requirements simultaneously.
2Volume of moving object
If connection pad dimensions are reduced for miniaturization, then device size is reduced, but metal volume decreases leading to reduced heat expansion
Solution Approach 1:
The linear expansion coefficient of the insulating film is optimized to be within a specific range (5×10^-6/K to 15×10^-6/K) to compensate for reduced metal expansion. This parameter change ensures reliable bonding contact characteristics even with miniaturized connection pads having reduced metal volume.
3Strength
If the linear expansion coefficient of the insulating film is too high, then bonding pressure is insufficient, but if too low, then dishing occurs on the connection pad surface
Solution Approach 1:
The linear expansion coefficient of the insulating film is precisely controlled within the range of 5×10^-6/K to 15×10^-6/K. This optimized parameter range balances bonding pressure generation with prevention of dishing, achieving both sufficient contact characteristics and surface flatness.
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 configuration effectively prevents the deterioration of contact characteristics between connection pads by ensuring proper expansion and bonding, while also reducing parasitic capacitance and maintaining high-speed operation.
Implementation Method 1
Connection pads are subjected to heat treatment after being superposed on each other. Through this heat treatment, the metal that makes up the connection pads expands.
Implementation Method 2
a second portion provided between the first portion and the insulating film and including a second metal that is more easily plastically deformed than the first metal
Data Source
AI summary
Provided is a photodetector in which the deterioration of contact characteristics between connection pads is prevented. The photodetector includes at least two semiconductor layers, and a wiring layer on one side in a stacking direction and a wiring layer on another side in the stacking direction, the wiring layers being interposed between the semiconductor layers, each including an insulating film and a connection pad provided in the insulating film, and being electrically coupled to each other with surfaces of the connection pads bonded together, in which the at least two semiconductor layers include a semiconductor layer with a photoelectric conversion region on a light incident surface side, the insulating film includes a first insulating film and a second insulating film that includes a material with a higher rigidity than a material of the first insulating film and penetrates the first insulating film in the stacking direction, and the second insulating film is provided between the connection pad and at least one of the semiconductor layers.