Deep Trench Etching Using Composite Hard Mask
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Solution Overview
Problem
Conventional methods for forming deep trenches in semiconductor substrates face challenges in precise profile control, especially as trench dimensions shrink and depths increase, due to insufficient etching selectivity between silicon oxide hard masks and substrates.
Innovation Solution
A method involving multiple sacrificing and insulating layers, with a lining layer and a thick hard mask, is used to form a deep trench, allowing for precise control of sidewall profile and dimension through selective etching and deposition processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional silicon oxide hard mask is used for etching the deep trench, then the etching process can be performed, but the etching selectivity between the hard mask and substrate is not high enough, leading to poor sidewall profile control
Solution Approach 1:
The patent segments the hard mask structure into multiple layers: a first hard mask layer (silicon oxide), a second hard mask layer (silicon nitride), and a third hard mask layer (silicon oxide). This segmentation creates a composite hard mask system where each layer contributes different etching selectivity characteristics, enabling precise sidewall profile control while maintaining reliable etching selectivity between the mask and substrate.
Solution Approach 2:
The patent employs a composite hard mask structure combining silicon oxide and silicon nitride layers. The silicon nitride layer provides high etching selectivity relative to the silicon substrate, while the silicon oxide layers provide appropriate etching rates for profile control. This composite material approach resolves the contradiction by leveraging the complementary properties of different materials within the same mask structure.
2Area of moving object
If the trench dimension is reduced and depth is increased to achieve high integration, then the memory cell size is reduced, but the sidewall profile control becomes more difficult due to insufficient etching selectivity
Solution Approach 1:
The multi-layer hard mask structure segments the etching control function across different materials and depths. The lower silicon nitride layer provides selectivity for deep etching, while the upper silicon oxide layers control the sidewall profile during etching. This segmentation enables precise profile control even as trench dimensions shrink and depth increases for high integration.
Solution Approach 2:
The patent changes the material composition parameters of the hard mask, transitioning from a single silicon oxide layer to a composite structure with silicon nitride and silicon oxide layers. This parameter change in material composition provides the necessary etching selectivity and profile control for miniaturized, deep trenches required in high-integration DRAM devices.
3Ease of manufacture
If a single-layer silicon oxide hard mask is used, then the process is simple, but the etching selectivity is insufficient for precise profile control
Solution Approach 1:
The hard mask is segmented into multiple functional layers with distinct etching properties. The silicon nitride layer handles the bulk etching with high selectivity, while the silicon oxide layers control the sidewall formation. This segmentation achieves precise profile control while maintaining reasonable process complexity through standardized deposition and etching techniques.
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 precise control over the sidewall profile and dimensions of deep trenches, improving the formation of high-aspect-ratio trenches by using a thick hard mask as an etching hard mask, ensuring accurate and controlled etching of the substrate.
Implementation Method 1
A portion of the lining layer is selectively etched away, thereby exposing the first sacrificing layer
Implementation Method 2
Using the thick hard mask as an etching hard mask, the substrate is etched to form a deep trench
Data Source
AI summary
The invention provides a method for forming a deep trench in a substrate. A sacrificial layer and a liner layer are first used to define the deep trench pattern. The sacrificial layer is then replaced with a silicon glass layer. A thick mask layer includes the silicon glass layer, the liner layer and a silicon nitride layer is formed on the substrate. Through an opening of the thick mask layer, a deep trench is etched into the substrate.