Image Sensor Fabrication with Dual Stop Films for Etch Protection
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Solution Overview
Problem
CMOS image sensors face challenges in preventing interlayer insulating layers from being lost or damaged during etching and planarizing processes, which affects their sensitivity.
Innovation Solution
A method for fabricating an image sensor that involves forming a photodiode in a substrate, followed by specific layers such as a first and second stop film, insulating films, and a zero wiring layer, with etch selectivity between these layers to prevent damage and improve sensitivity, including the use of silicon nitride and HfO2 films for stop layers and conductive materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching and planarizing processes are used to form wiring layers, then manufacturing efficiency is maintained, but interlayer insulating layers may be lost or damaged, reducing image sensor sensitivity
Solution Approach 1:
A second stop film is formed on the insulating film before the etching process to protect the interlayer insulating layer from being lost or damaged during subsequent etching and planarizing operations. This preliminary protective layer prevents harmful effects before they can occur to the sensitive interlayer insulating layer.
Solution Approach 2:
The second stop film acts as an intermediary protective layer between the etching/planarizing processes and the interlayer insulating layer. It absorbs the mechanical and chemical stress from these processes, preventing direct damage to the interlayer insulating layer while allowing the necessary fabrication steps to proceed.
2Reliability
If multiple protective layers and stop films are added to prevent damage, then layer protection is improved, but fabrication process complexity increases
Solution Approach 1:
The patent specifies particular material compositions and thickness ranges for the stop films and insulating layers (e.g., silicon nitride film, HfO2 film with specific thicknesses) to optimize protection while controlling process complexity. By carefully controlling these parameters, reliable protection is achieved without unnecessarily increasing the number of fabrication steps.
Solution Approach 2:
The patent employs composite layer structures combining different materials (silicon nitride, HfO2, conductive materials) with specific properties. Each material is selected for its particular characteristics - etch resistance, mechanical strength, or electrical properties - creating a composite structure that provides comprehensive protection while maintaining process efficiency.
3Manufacturing precision
If etch selectivity between layers is increased to protect underlying layers, then manufacturing precision improves, but process difficulty increases
Solution Approach 1:
The patent achieves high etch selectivity by carefully controlling material composition and thickness parameters. The first stop film (silicon nitride) and second stop film (HfO2) are selected and dimensioned to provide distinct etch resistance characteristics, enabling precise selective etching. This parameter control allows the etching process to distinguish between different layers without requiring excessively difficult process conditions.
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 effectively prevents interlayer insulating layer loss and wiring damage, enhancing the sensitivity of the image sensor by ensuring precise layer formation and etching processes.
Implementation Method 1
the insulating film and the first stop film may have etch selectivity of approximately 8 ̃10:1 therebetween and/or the conductive material and the second stop film may have selectivity over approximately 100:1 therebetween
Data Source
AI summary
A method for fabricating an image sensor having a pixel region and a logic region, which includes one of: (1) forming a photodiode in a substrate at the pixel region, (2) forming a first interlayer insulating layer on the substrate, (3) forming a first stop film on the first interlayer insulating layer, (4) forming an insulating film on the first stop film, (5) forming a second stop film on the insulating film, (6) forming at least one trench by selective etching of the second stop film and the insulating film positioned at the pixel region for exposing the first stop film, (7) forming conductive material on the second stop film to fill the at least one trench, and (8) forming a zero wiring layer in the at least one trench by planarizing the conductive material until the second stop film is exposed.