Silicon-On-Insulator Substrate Step Structure for Flatness
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Solution Overview
Problem
The expansion of the buried oxide layer during annealing in silicon-on-insulator substrate manufacturing can cause surface swelling, leading to substrate steps, which result in focus loss in photolithography and potential cavity formation due to overetching, especially at the edges of the BOX layer.
Innovation Solution
A step is created on the silicon substrate to elevate the region corresponding to the oxide layer, followed by oxygen ion implantation and annealing, with a nitride film formed to protect the substrate and prevent oxygen diffusion, ensuring the surface oxide layer remains within the step and avoids edge thickening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxygen ions are implanted to form a BOX layer in a silicon substrate, then the insulating performance is improved, but the BOX layer expands during annealing causing surface swelling and step formation
Solution Approach 1:
A step structure is formed on the silicon substrate surface before oxygen ion implantation. This preliminary structural preparation provides a buffer zone that accommodates the BOX layer expansion during subsequent annealing, preventing surface swelling and step formation while maintaining the insulating performance of the BOX layer.
Solution Approach 2:
The step structure creates a localized region with different surface height, concentrating the BOX layer formation and expansion within this specific area. The elevated step region provides extra space for the BOX layer to expand without affecting the overall surface flatness, thus resolving the contradiction between insulating performance and surface precision.
2Reliability
If annealing is performed to form the BOX layer, then the oxide layer is formed at the interior, but oxygen diffusion accelerates oxidation at edge areas causing thickening and potential cavity formation
Solution Approach 1:
The step structure creates a localized elevated region where the BOX layer is confined. This local structural differentiation restricts oxygen diffusion and oxidation to occur primarily within the step boundaries, preventing edge thickening and maintaining uniform BOX layer thickness, thus resolving the contradiction between reliable BOX layer formation and thickness uniformity.
3Manufacturing precision
If the surface oxide layer is removed after annealing to achieve a flat surface, then surface flatness is improved, but the BOX layer may be overetched along with the oxide layer forming cavities
Solution Approach 1:
The step structure is formed in advance before oxide layer removal. This preliminary structural preparation creates a protective geometry where the elevated step walls shield the BOX layer edges from overetching during subsequent oxide removal processes, allowing surface flatness to be achieved without compromising substrate integrity.
Solution Approach 2:
The step structure acts as a cushioning protective barrier before the oxide removal process. The elevated step region provides a physical buffer that prevents the etching process from reaching and damaging the BOX layer edges, thus protecting substrate integrity while still enabling surface flatness improvement.
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 process prevents the formation of surface steps and cavities, maintaining device characteristics and preventing particle generation during fabrication by keeping the BOX layer internal and preventing edge oxidation.
Implementation Method 1
implanting oxygen ions in the silicon substrate so as to form the oxide layer (BOX layer)
Implementation Method 2
annealing treatment involving the application of a given amount of heat
Implementation Method 3
oxygen diffuses and oxidation proceeds at the surface of the substrate
Implementation Method 4
oxidation proceeds at the surface of the substrate, forming a surface oxide layer
Data Source
AI summary
A process for manufacturing a silicon-on-insulator substrate comprising a single-crystal silicon substrate in which an oxide layer has been locally buried includes forming a step on the silicon substrate so that a region corresponding to the oxide layer has a greater surface height than other regions; then implanting oxygen ions in the silicon substrate so as to form the oxide layer.