Stepped Bit Line Layout for Low-Capacitance Memory Cells
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Solution Overview
Problem
Existing semiconductor memory devices face challenges in optimizing the structure of bit lines and contacts to improve electrical characteristics and reduce parasitic capacitance, which affects their performance and efficiency.
Innovation Solution
The semiconductor memory device is designed with a bit line structure that includes a first portion vertically overlapped with the source/drain region and a second portion vertically overlapped with the insulating layer, where the lowermost level of the first portion is lower than the second portion, and a contact structure that maintains a larger width for the first portion to reduce etching and enhance electrical connectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bit line structure is designed with a first portion vertically overlapped with the source/drain region and a second portion vertically overlapped with the insulating layer, then parasitic capacitance between adjacent bit lines is reduced, but the manufacturing complexity increases
Solution Approach 1:
The bit line is divided into two distinct portions: a first portion vertically overlapped with the source/drain region and a second portion vertically overlapped with the insulating layer. This segmentation allows each portion to serve different functional purposes, reducing parasitic capacitance while maintaining electrical connectivity.
Solution Approach 2:
The bit line structure transitions from a conventional planar configuration to a three-dimensional structure with varying vertical levels. The first portion extends lower to overlap with the source/drain region, while the second portion rises to overlap with the insulating layer, creating a stepped configuration that reduces capacitive coupling.
2Reliability
If the lowermost level of the first portion of the bit line is made lower than the second portion, then parasitic capacitance is reduced, but the etching process complexity increases
Solution Approach 1:
The bit line structure exhibits local quality variations where the first portion has a lower vertical level in the region overlapping with the source/drain region, while the second portion has a higher vertical level in the region overlapping with the insulating layer. This localized structural differentiation optimizes electrical characteristics without requiring uniform complex processing throughout the entire device.
3Reliability
If the contact is spaced apart from the line structure, then parasitic capacitance is reduced, but the electrical connectivity and manufacturing precision requirements increase
Solution Approach 1:
The insulating layer serves as an intermediary element between the bit line structure and the contact. By spacing the contact apart from the line structure and allowing the bit line's second portion to overlap with the insulating layer, the design reduces direct capacitive coupling while maintaining electrical connectivity through the insulated conductor path.
Data Source
AI summary
A semiconductor memory device including a substrate including an active pattern that includes a first source/drain region and a second source/drain region; an insulating layer on the substrate; a line structure on the insulating layer and extending in a first direction to cross the active pattern, the line structure penetrating the insulating layer on the first source/drain region and including a bit line electrically connected to the first source/drain region; and a contact spaced apart from the line structure and electrically connected to the second source/drain region, wherein the bit line includes a first portion vertically overlapped with the first source/drain region; and a second portion vertically overlapped with the insulating layer, and wherein a lowermost level of a top surface of the first portion of the bit line is at a level lower than a lowermost level of a top surface of the second portion of the bit line.