Silane Oxide Cap Layer for Hydrogen Control in Back-End Metallization
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Solution Overview
Problem
Existing semiconductor fabrication processes struggle to control the generation and migration of hydrogen atoms/ions during back-end processing, leading to device instabilities and reduced performance in CMOS image sensors and non-volatile memory devices, as hydrogen can penetrate gettering/barrier layers and affect floating gate storage capacity.
Innovation Solution
A modified back-end processing method involving the use of TEOS-based oxide inter-level dielectric layers with a high-density, low-moisture-content silane oxide cap layer to minimize hydrogen production, where the cap layer serves as an etch-stop and isolates the hydrogen-rich TEOS-based oxide from the plasma environment during aluminum etch processes, thereby reducing hydrogen migration to front-end structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If TEOS-based oxide is used for ILD layer to achieve better step coverage and gap filling, then manufacturing precision is improved, but hydrogen content increases leading to device instability
Solution Approach 1:
The dielectric structure is segmented into multiple layers: a bottom ILD layer made of TEOS-based oxide for good step coverage, and a top cap layer made of silane oxide with low hydrogen content. This segmentation allows each layer to fulfill its specific function - the TEOS layer provides manufacturing precision while the silane layer provides device stability by blocking hydrogen migration.
Solution Approach 2:
The silane oxide cap layer acts as an intermediary barrier between the TEOS-based oxide ILD layer and the aluminum metallization layer. It mediates the interaction by blocking hydrogen atoms and ions generated during aluminum etching from penetrating into the underlying structures, thus protecting the devices from hydrogen-induced instability while allowing the TEOS layer to maintain its gap-filling advantage.
2Reliability
If gettering/barrier layers are used to prevent hydrogen migration, then device reliability is improved, but fabrication complexity increases
Solution Approach 1:
The invention changes the material parameter of the cap layer by using silane oxide instead of traditional gettering materials like phosphosilicate glass or BPSG. Silane oxide has inherently low hydrogen content and forms a dense structure that effectively blocks hydrogen migration. This parameter change achieves reliable hydrogen blocking with a simpler, more integrated process that combines the cap layer function with the dielectric structure.
3Reliability
If cap layer thickness is increased to improve hydrogen blocking, then device reliability is improved, but etch selectivity becomes more difficult to control
Solution Approach 1:
The dielectric structure uses a composite material system combining TEOS-based oxide and silane oxide in specific thickness ratios. The silane oxide cap layer is maintained at a controlled thickness range (500-5000 Å) to provide effective hydrogen blocking while maintaining etch selectivity. The composite structure leverages the complementary properties of both materials - the etch resistance of TEOS and the hydrogen-blocking capability of silane oxide - achieving both reliability and manufacturability.
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 approach significantly reduces hydrogen generation and migration, improving memory retention and radiation immunity in CMOS image sensors by maintaining beneficial hydrogen levels and preventing harmful hydrogen accumulation, thus enhancing device performance and reducing fabrication costs.
Implementation Method 1
The cap layer serves as an etch-stop and isolates the hydrogen-rich TEOS-based oxide from the plasma environment during aluminum etch processes, thereby reducing hydrogen migration to front-end structures
Implementation Method 2
low-moisture-content oxide cap layer to minimize hydrogen production
Data Source
AI summary
A method for fabricating image sensors and other semiconductor ICs that controls the amount of hydrogen generated during back-end processing. The back-end processing includes forming multiple metallization layers after front-end processing is completed (i.e., after forming the pre-metal dielectric), where each metallization layer includes a patterned aluminum structure, an interlevel dielectric (ILD) layer including TEOS-based oxide formed over the patterned aluminum structure. A cap layer including a low-moisture content oxide such as silane oxide (i.e., SiO2 generated by way of a silane CVD process) is formed over at least one ILD layer. The cap layer serves as an etch-stop for the subsequently-formed metal layer of a next metallization layer by isolating the underlying ILD material from the plasma environment during aluminum over-etch, which significantly reduces the production and migration of hydrogen into front-end structures.