3D Ferroelectric RAM Trench Formation to Prevent Fin Collapse
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Solution Overview
Problem
Existing methods for forming three-dimensional ferroelectric random access memory (FeRAM) devices face challenges in achieving high integration density due to the collapse of fin structures during the formation of trenches, leading to defects and reduced production yield.
Innovation Solution
A Litho-Etch-Dep-Litho-Etch-Dep (LEDLED) method is employed, where first and second trenches are formed sequentially, allowing for closer integration of memory cells without collapsing, using lithography and etching techniques to fill the trenches with ferroelectric and dielectric materials, and forming isolation regions to enhance density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If trenches are formed simultaneously to create high integration density, then memory cell density is improved, but fin structures collapse during trench formation causing defects
Solution Approach 1:
The patent divides the trench formation process into multiple sequential steps. First trenches are formed, filled with ferroelectric material, then second trenches are formed in the spaces between. This segmentation prevents fin collapse by avoiding simultaneous deep etching across the entire structure, while still achieving high memory cell density through the interleaved trench arrangement.
Solution Approach 2:
The patent performs preliminary filling of the first trenches with ferroelectric material before forming the second trenches. This preliminary action stabilizes the fin structures by providing structural support in the first trench regions, preventing collapse during the subsequent formation of second trenches and enabling higher integration density.
2Quantity of substance
If fin structures are made narrower to increase integration density, then memory cell density is improved, but aspect ratio increases causing fin collapse
Solution Approach 1:
The patent transitions from a planar trench arrangement to a three-dimensional interleaved structure. By forming first and second trenches in alternating layers with different depth profiles, the design utilizes vertical dimensionality to reduce the horizontal aspect ratio of individual fin structures, enabling narrower effective features without collapse while maintaining high integration density.
3Reliability
If isolation regions are added to prevent fin collapse, then fin structure stability is improved, but device complexity increases
Solution Approach 1:
The patent merges the isolation region formation with the existing trench filling process. The ferroelectric material filling the first trenches serves dual purposes: it provides structural support to prevent fin collapse and simultaneously acts as the isolation medium between adjacent memory cells. This merging eliminates the need for separate isolation region deposition steps, reducing process complexity while maintaining fin structure stability.
Data Source
AI summary
A method of forming a ferroelectric random access memory (FeRAM) device includes: forming a layer stack over a substrate, where the layer stack includes alternating layers of a first dielectric material and a word line (WL) material; forming first trenches extending vertically through the layer stack; filling the first trenches, where filling the first trenches includes forming, in the first trenches, a ferroelectric material, a channel material over the ferroelectric material, and a second dielectric material over the channel material; after filling the first trenches, forming second trenches extending vertically through the layer stack, the second trenches being interleaved with the first trenches; and filling the second trenches, where filling the second trenches includes forming, in the second trenches, the ferroelectric material, the channel material over the ferroelectric material, and the second dielectric material over the channel material.