Photodiode Array Via and Trench Etching
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Solution Overview
Problem
Existing methods for manufacturing photodiode arrays with through-wafer vias are inefficient in maximizing surface area and ensuring effective contact formation, as they lack a systematic approach to forming vias and isolation trenches with varying aspect ratios to optimize etching rates and minimize cross-talk between photodiodes.
Innovation Solution
A method involving the simultaneous formation of through-wafer vias and isolation trenches with different aspect ratios in a semiconductor substrate, using reactive ion etching and subsequent doping and dielectric lining to enhance conductivity and reduce surface recombination, allowing for efficient backside contacts and improved photodiode array performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If through-wafer vias are formed to maximize surface area for backside contacts, then the photo receptive surface area is increased, but the manufacturing complexity and difficulty of forming vias with varying aspect ratios increases
Solution Approach 1:
The patent combines the formation of through-wafer vias and isolation trenches into a single simultaneous etching process. By merging these two operations that would traditionally require separate processing steps, the method reduces manufacturing complexity while still achieving the desired different aspect ratios for vias and trenches. The via openings and trench openings are defined by different pattern densities in the photomask, allowing the etch process to self-adjust and create the required aspect ratio differences without additional process steps.
Solution Approach 2:
The patent applies local quality by using different pattern densities in the photomask to create different aspect ratios in specific locations. The via openings have a first pattern density that results in a first aspect ratio, while the isolation trench openings have a second pattern density that results in a second aspect ratio. This local variation in pattern density allows each structure to be optimized for its specific function without requiring different etching processes.
2Reliability
If via depth is increased to achieve through-wafer connectivity, then electrical contact is improved, but etching uniformity and via formation difficulty worsen due to high aspect ratio requirements
Solution Approach 1:
The patent changes the pattern density parameter in the photomask to control the aspect ratio of etched features. By adjusting the pattern density (the ratio of opening width to spacing between openings), the etch process achieves different depths and aspect ratios for vias versus isolation trenches. This parameter change allows the via etching to be optimized for through-wafer penetration while maintaining manufacturing precision through controlled variable aspect ratio etching.
3Object-affected harmful factors
If isolation trenches are formed to minimize cross-talk between photodiodes, then optical isolation is improved, but the manufacturing process complexity increases due to additional trench formation steps
Solution Approach 1:
The patent merges the formation of isolation trenches with the via formation process into a single simultaneous etching operation. Both structures are created in the same etch chamber using a photomask with different pattern densities for via openings versus trench openings. This eliminates the need for separate trench formation steps, reducing process complexity while still achieving effective optical isolation between photodiodes through the formed trenches.
4Manufacturing precision
If different aspect ratios are used for vias and trenches to optimize etching, then etching uniformity is improved, but the photomask design and manufacturing precision requirements increase
Solution Approach 1:
The patent uses parameter changes in the photomask design, specifically varying the pattern density (opening width to spacing ratio) to achieve different aspect ratios for vias and trenches. This approach improves etching uniformity by allowing each feature type to have an optimized aspect ratio for its function, while the photomask design complexity is managed through systematic use of different pattern densities rather than requiring completely different mask designs for each feature type.
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 method enables the effective manufacturing of photodiode arrays with optimized through-wafer vias and isolation trenches, enhancing electrical conductivity and minimizing cross-talk, thereby improving the overall performance and surface area utilization of the photodiode array.
Implementation Method 1
using reactive ion etching
Data Source
AI summary
A method for manufacturing a photodiode array includes providing a semiconductor substrate having first and second main surfaces opposite to each other. The semiconductor substrate has a first layer of a first conductivity proximate the first main surface and a second layer of a second conductivity proximate the second main surface. A via is formed in the substrate which extends to a first depth position relative to the first main surface. The via has a first aspect ratio. Generally simultaneously with forming the via, an isolation trench is formed in the substrate spaced apart from the via which extends to a second depth position relative to the first main surface. The isolation trench has a second aspect ratio different from the first aspect ratio.