DRAM Isolation Trench Profile for Leakage and Crosstalk Control
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Solution Overview
Problem
In advanced DRAM technologies, the close arrangement of memory cells leads to significant leakage and signal crosstalk issues due to inadequate electrical isolation, necessitating improved methods for ensuring isolation between memory cells.
Innovation Solution
A two-stage etching process is employed to form isolation trenches with distinct sidewall slopes, allowing for better filling with a dielectric layer to enhance electrical isolation between memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If memory cells are arranged closer together to increase array density, then productivity is improved, but electrical isolation between memory cells deteriorates, causing leakage and signal crosstalk
Solution Approach 1:
The isolation structure is divided into two distinct portions: a first portion extending from the substrate surface to a first depth, and a second portion extending from the first depth to a second depth. This segmentation allows each portion to be optimized independently for different functions, improving overall electrical isolation effectiveness while maintaining high array density.
Solution Approach 2:
Different regions of the isolation structure are assigned different properties: the first portion has a first cross-sectional area and the second portion has a second cross-sectional area, creating local quality variations. This allows the isolation structure to provide enhanced isolation where needed while minimizing impact on adjacent memory cells, thus resolving the contradiction between density and isolation.
2Ease of manufacture
If conventional single-stage etching is used to form isolation trenches, then manufacturing process is simpler, but the trenches cannot be properly filled with dielectric layer, resulting in poor electrical isolation
Solution Approach 1:
The etching process is segmented into two stages: a first etching process forming the first isolation trench to a first depth, and a second etching process forming the second isolation trench to a second depth. This segmentation enables proper dielectric layer filling in each stage, ensuring complete trench filling and effective electrical isolation, while keeping each individual etching step relatively simple.
Solution Approach 2:
The first etching process is performed as a preliminary action before the second etching process. This preliminary action creates the first isolation trench that can be properly filled with dielectric material, establishing a foundation for the subsequent second etching process to form the deeper second isolation trench, ensuring complete filling and effective isolation.
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
The two-stage etching process effectively improves electrical isolation by ensuring complete filling of isolation trenches, reducing leakage and signal crosstalk, and maintaining critical dimensions for improved semiconductor device performance.
Implementation Method 1
a second etching process is performed to etch the substrate to form a plurality of second trenches respectively directly under the first trenches
Data Source
AI summary
A semiconductor device includes a substrate, a plurality of active regions disposed in the substrate and respectively extending along a first direction and arranged into an array, and a plurality of isolation structures disposed in the substrate between the active regions. The isolation structures respectively comprise an upper portion and a lower portion, wherein a sidewall of the upper portion comprises a first slope, a sidewall of the lower portion comprises a second slop, and the first slope and the second slope are different. The semiconductor device further includes a plurality of semiconductor layers disposed between the upper portions of the isolation structures and the active regions.