Recessed Flash Memory Substrate Layout for Current Crowding Relief
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Solution Overview
Problem
The high-voltage operations in flash memory devices lead to deep source/drain implants, causing current crowding at the substrate surface, which affects device performance and efficiency.
Innovation Solution
The formation of flash memory devices on a recessed region of a substrate, with specific patterning and etching processes to create isolated active regions, reducing current crowding and enhancing device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If deep source/drain implants are performed to achieve high-voltage operations in flash memory devices, then the device can operate at higher voltages, but current crowding occurs at the substrate surface which degrades device performance
Solution Approach 1:
The patent introduces a third dimension by recessing the substrate surface to form a depression where the memory device is formed. This vertical dimensionality change allows the source/drain regions to be positioned deeper in the substrate without increasing lateral implant depth, thereby enabling high-voltage operation while preventing current crowding at the substrate surface.
Solution Approach 2:
The substrate is recessed before forming the source/drain regions, creating a pre-prepared depression structure. This preliminary action allows subsequent source/drain formation to occur at a controlled depth, ensuring that high-voltage operation is achieved while maintaining optimal current distribution and preventing surface current crowding.
2Reliability
If the substrate surface is recessed to prevent current crowding, then device performance is improved, but additional fabrication steps are required
Solution Approach 1:
The substrate recessing step is combined with the source/drain formation process. The same etching and filling operations that create the source/drain regions also define the recessed substrate structure, merging multiple functions into a unified process sequence that reduces overall fabrication complexity.
Solution Approach 2:
The recessed substrate structure serves multiple functions simultaneously: it prevents current crowding at the surface, provides mechanical support for the memory device, and defines the depth for source/drain region formation. This multi-functionality reduces the need for separate structural elements and simplifies the overall device architecture.
Data Source
AI summary
A device includes a substrate, a first isolation structure, a transistor, and a source/drain region. The substrate has a first region, a second region, and a transition region between the first region and the second region. A first top surface of the substrate in the first region is lower than a second top surface of the substrate in the second region. The substrate includes a protrusion portion in the transition region. The first isolation structure is embedded in the transition region and covers the protrusion portion. The transistor is over the second region of the substrate. The source/drain region is embedded in the first region of the substrate. A top of the protrusion portion is higher than a bottom of the source/drain region.