Self-Aligned STI Memory with Rounded Active Corners
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Solution Overview
Problem
Conventional flash memory fabrication processes result in sharp corners due to the shallow trench isolation (STI) process, leading to device degradation, reduced reliability, and scalability issues, as well as challenges in aligning memory cells for denser storage.
Innovation Solution
Performing the STI process before forming the charge-trapping and top-level layers allows for the exposure and rounding of sharp corners, followed by a self-aligned process using a sacrificial top oxide, polish, and etch techniques to create a memory device with rounded corners and improved scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the STI process is performed before forming charge-trapping and top-level layers, then sharp corners can be rounded to improve device reliability, but the fabrication process complexity increases
Solution Approach 1:
The STI process is performed preliminarily before forming charge-trapping and top-level layers, exposing sharp corners that can then be rounded. This preliminary action enables subsequent corner rounding to improve device reliability while maintaining process integration
Solution Approach 2:
A sacrificial oxide layer is introduced as an intermediary element to enable self-aligned processing. The sacrificial oxide facilitates the rounding of sharp corners through selective removal, acting as a mediator between the STI structure and the charge-trapping layers
2Productivity
If memory cells are aligned denser for higher capacity, then manufacturing precision requirements increase, but device performance may deteriorate
Solution Approach 1:
The fabrication process utilizes self-aligned mechanisms where previously formed structures automatically serve as alignment references for subsequent steps. This self-service approach maintains manufacturing precision while enabling denser cell alignment for higher memory capacity
3Ease of manufacture
If sharp corners are left as-is from STI process, then fabrication is simpler, but device performance and reliability degrade
Solution Approach 1:
The sharp corners created by the STI process, which initially appear as harmful defects, are converted into beneficial features through selective rounding. The sacrificial oxide enables this transformation, turning the harmful sharp corners into rounded structures that improve device reliability while maintaining fabrication efficiency
Data Source
AI summary
A method for fabricating a memory device with a self-aligned trap layer and rounded active region corners is disclosed. In the present invention, an STI process is performed before any of the charge-trapping and top-level layers are formed. Immediately after the STI process, the sharp corners of the active regions are exposed. Because these sharp corners are exposed at this time, they are available to be rounded through any number of known rounding techniques. Rounding the corners improves the performance characteristics of the memory device. Subsequent to the rounding process, the charge-trapping structure and other layers can be formed by a self-aligned process.