Solid-State Image Pickup Device Alignment Mark Fabrication
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Solution Overview
Problem
Conventional rear plane irradiation type CMOS solid-state image pickup devices face challenges in accurately exposing multilayer metal wiring and detecting alignment marks due to issues like metal diffusion and insufficient brightness difference between silicon oxide films and substrates, leading to difficulties in process yield and performance.
Innovation Solution
The method involves forming contacts and alignment marks using conducting materials like polycrystal silicon or metal, embedding them in holes within the semiconductor substrate, and surrounding them with insulating films to prevent metal diffusion and enhance visibility, thereby simplifying the manufacturing process and improving alignment accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multilayer metal wiring is formed in conventional rear plane irradiation type CMOS solid-state image pickup devices, then electrical connectivity is achieved, but metal diffusion occurs and alignment mark detection becomes difficult
Solution Approach 1:
A silicon oxide film is introduced as an intermediary layer between the multilayer metal wiring and the semiconductor substrate. This intermediary layer prevents metal diffusion into the substrate while maintaining electrical connectivity through the wiring structure, thereby resolving the contradiction between achieving reliable electrical connection and preventing harmful metal diffusion.
Solution Approach 2:
The patent converts the harmful effect of metal diffusion into a beneficial alignment feature. By controlling the metal wiring formation process, the metal patterns themselves serve as visible alignment marks with sufficient brightness difference, turning the previously harmful metal diffusion issue into a useful alignment reference that eliminates the need for separate alignment mark formation.
Solution Approach 3:
The multilayer metal wiring structure serves multiple functions simultaneously: it provides electrical connectivity for the photodiode and pixel electrode, prevents metal diffusion through the silicon oxide barrier layer, and acts as an alignment mark for subsequent processing steps. This multi-functionality resolves the contradiction by making the wiring structure serve both electrical and alignment purposes.
2Reliability
If silicon oxide films are used for insulation in conventional devices, then electrical insulation is achieved, but brightness difference with substrate is insufficient for alignment mark detection
Solution Approach 1:
The silicon oxide film serves as an intermediary layer that provides both electrical insulation and optical contrast. By positioning the silicon oxide film in specific locations (as insulation layers between metal wiring layers and as a cap layer over the semiconductor substrate), it creates visible brightness differences that enable precise alignment mark detection while maintaining its insulating function.
Solution Approach 2:
The silicon oxide film performs dual functions: electrical insulation between conductive layers and optical contrast for alignment mark visualization. This multi-functionality resolves the contradiction by making the same material serve both electrical and optical purposes, eliminating the need for separate alignment mark structures.
3Measurement precision
If alignment marks are formed separately from contacts in conventional processes, then alignment reference is provided, but the number of processing steps increases
Solution Approach 1:
The patent merges the alignment mark formation with the contact hole filling process. The same metal wiring material that fills the contact holes also forms the alignment marks, eliminating the need for separate alignment mark formation steps. This merging reduces processing complexity while maintaining alignment precision.
Solution Approach 2:
The metal wiring material serves dual purposes: providing electrical connectivity through contact holes and creating visible alignment marks. This multi-functionality resolves the contradiction by making the wiring material serve both electrical and alignment functions, thereby reducing the total number of processing steps required.
4Ease of operation
If the semiconductor substrate is reduced in thickness to expose contacts and alignment marks, then accessibility is improved, but manufacturing precision requirements increase
Solution Approach 1:
The contacts and alignment marks are formed and positioned within the substrate before the substrate thickness reduction step. By completing the critical patterning and material deposition operations while the substrate is still at its original thickness, the patent avoids the need for high-precision thickness control during subsequent handling, thereby reducing manufacturing precision requirements while maintaining accessibility.
Solution Approach 2:
The manufacturing process is segmented into distinct stages: first forming all critical structures (contacts, alignment marks, wiring) within the substrate at full thickness, then reducing substrate thickness as a separate final step. This segmentation allows each stage to be optimized independently, reducing the cumulative precision requirements while ensuring final accessibility.
Data Source
AI summary
A method of manufacturing a solid-state image pickup device according to an embodiment includes forming first and second holes in a semiconductor substrate, forming insulating films on surfaces of the first and second holes, forming a contact and an alignment mark by embedding a conducting material in the first and second holes, forming a photodiode in the semiconductor substrate, forming a wiring layer including a connecting part for connecting to the contact and a wiring for connecting to the connecting part, bonding a supporting substrate on the wiring layer, exposing the contact and the alignment mark on the surface of the semiconductor substrate by reducing the semiconductor substrate in thickness, and forming a filter and a lens on the photodiode based on the alignment mark.