Stacked Image Sensor Wafer Thinning Without Photodiode Heat Damage
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Solution Overview
Problem
High-temperature processes during the formation of semiconductor wafers for device-over-photodetector (DoP) image sensor devices can damage photodiodes, leading to increased dark current, thermally-induced noise, and reduced quantum efficiency, as well as degrade other semiconductor structures.
Innovation Solution
The formation of a stacked semiconductor die arrangement for image sensor devices is achieved through the use of low-temperature processes such as etching and planarization, facilitated by etch stop layers, to avoid damaging photodiodes and other structures, thereby reducing dark current and enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-temperature annealing operations are performed after bonding semiconductor wafers, then the semiconductor wafer can be thinned and processed, but the photodiodes are damaged resulting in increased dark current and reduced quantum efficiency
Solution Approach 1:
The patent divides the semiconductor wafer into multiple functional layers (sensor circuitry layer, logic layer, photodiode layer) and selectively removes portions of upper layers through etching and planarization to enable thinning without exposing the photodiode layer to high-temperature damage. This segmentation allows independent processing of different layers at appropriate temperatures.
Solution Approach 2:
The patent performs bonding of the semiconductor wafer to the substrate before thinning operations. This preliminary bonding provides mechanical support and enables subsequent low-temperature thinning processes to be performed on the bonded structure, preventing photodiode damage that would occur if thinning were attempted separately at high temperatures.
2Ease of manufacture
If high-temperature processes are used during wafer formation, then semiconductor structures can be formed and bonded, but photodiodes suffer damage leading to thermally-induced noise and reduced quantum efficiency
Solution Approach 1:
The patent introduces a substrate as an intermediary element to which the semiconductor wafer is bonded. This substrate serves as a heat sink and mechanical support, enabling the wafer to be thinned and processed at lower temperatures that do not damage the photodiodes, while still achieving the structural integrity needed for manufacturing.
Solution Approach 2:
The patent replaces high-temperature thermal processing with low-temperature mechanical processes (etching and planarization) for wafer thinning. This substitution eliminates thermal damage to photodiodes while achieving the same structural thinning objective through mechanical material removal.
3Reliability
If low-temperature processes such as etching and planarization are used, then photodiodes are protected from damage and dark current is reduced, but the wafer thinning process becomes more complex
Solution Approach 1:
The patent segments the thinning process into multiple controlled steps: bonding the wafer to a substrate, selective etching of upper layers, and planarization. This segmentation transforms a single complex high-temperature process into multiple simpler low-temperature steps that are easier to control and monitor, reducing overall process complexity despite the increased number of steps.
Data Source
AI summary
An image sensor device may be formed by forming a stacked arrangement of semiconductor dies without the use of a high-temperature operations such as annealing when processing a semiconductor wafer that contains a semiconductor layer in which a sensor circuitry die of the image sensor device is to be formed. Instead, the semiconductor wafer includes one or more etch stop layers that enable a combination of low-temperature processes such as etching and planarization to be performed to thin down semiconductor wafer. The use of low-temperature processes instead of high-temperature processes to thin down the semiconductor wafer reduces the exposure of the photodiode(s) and other layers and/or structures of the sensor wafer to high temperatures that might otherwise damage these photodiode(s) and other layers and/or structures.