Tunable Substrate Transition for STI and LOCOS Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing LOCOS process for forming active areas in microelectronic devices does not allow for substrate areas of different heights, which is a limitation in charge trapping and phase change memory technologies where array and peripheral areas need to be at varying heights for proper integration.
Innovation Solution
A two-level substrate is formed using a combination of shallow trench isolation and local oxidation of silicon (LOCOS), where the memory array is at a higher level and the periphery at a lower level, with a tunable transition region to manage the 'bird's beak effect and optimize substrate area usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LOCOS process is used to form active areas, then isolation of active areas is achieved, but substrate areas of different heights cannot be formed
Solution Approach 1:
The patent combines LOCOS oxidation process with shallow trench isolation (STI) process into a single integrated process. The STI trenches are filled with oxide material and then a second LOCOS oxidation is performed, merging the advantages of both isolation techniques to achieve both effective isolation and substrate height variation capability
Solution Approach 2:
The patent introduces vertical dimension variation by creating trenches that extend into the substrate and filling them to create height differences. This allows different regions of the substrate to have different heights, enabling 3D integration of array and periphery circuits while maintaining effective isolation
2Ease of manufacture
If LOCOS oxidation is performed without trench definition, then simple process is maintained, but bird's beak effect occurs causing substrate area consumption
Solution Approach 1:
The patent performs preliminary trench formation and filling with oxide material before conducting the LOCOS oxidation. This preliminary action creates a physical barrier that prevents the bird's beak effect from occurring, as the oxide-filled trenches block the lateral oxidation that would otherwise consume substrate area
Solution Approach 2:
The oxide-filled trenches act as intermediary structures between the LOCOS oxidation process and the substrate. These trenches serve as a barrier that mediates the oxidation process, preventing direct lateral oxidation at the mask edges while still allowing the desired vertical oxidation to proceed
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 enables effective isolation and integration of memory array and periphery circuits by controlling the transition region, reducing dislocation formation and substrate consumption, while avoiding the adverse effects of the bird's beak effect.
Implementation Method 1
an isolation region may be formed by integrating a shallow trench isolation and local oxidation of silicon or LOCOS
Data Source
AI summary
A substrate may have active areas at different levels separated by a mask. Along the mask may be a shallow trench isolation. Along the shallow trench isolation may be a LOCOS isolation. The shape of a substrate transition region between the levels may be tunably controlled. The shallow trench isolation may reduce the bird's beak effect.