Dual STI Liners for Tight Nanosheet Spacing Without Fill Gaps

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Solution Overview

Problem

The challenge in fabricating nanosheet field-effect transistors is the difficulty in achieving aggressive nanosheet spacing due to the narrow shallow trench isolation regions, which can result in gaps or holes in the fill material.

Innovation Solution

The implementation of dual shallow trench isolation (STI) liners, where an upper STI liner is formed on a lower STI liner in the trench, allowing the upper liner to pinch off the small isolation space between transistors, thereby preventing fill gaps in the narrowest portion of the STI trench.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If aggressive nanosheet spacing is implemented, then transistor density is improved, but fill material gaps or holes occur in the narrow STI trench

Engineering Contradiction:

Improvetransistor densityVSAvoidfill material integrity

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The single STI liner is segmented into two separate liners: a first STI liner and a second STI liner. The first liner provides structural support and prevents trench collapse, while the second liner pinches off at the narrowest portion to prevent fill material from entering and creating gaps. This segmentation allows aggressive nanosheet spacing to be achieved while maintaining fill material integrity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The dual liner structure acts as an intermediary mechanism between the narrow STI trench and the fill material. By introducing these intermediate liner layers, particularly the second liner that pinches off, the patent mediates the interaction between fill material and narrow trench geometry, preventing direct contact that would cause gaps while still enabling tight spacing.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If narrow STI trench is used for aggressive spacing, then transistor density is improved, but trench collapse or structural instability occurs

Engineering Contradiction:

Improvetransistor densityVSAvoidSTI trench structural stability

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The STI liner function is segmented into two distinct components: the first liner that extends across the entire trench depth to provide structural support and prevent collapse, and the second liner that provides the pinch-off function. This segmentation allows each liner to be optimized for its specific function, with the first liner ensuring structural stability in narrow trenches.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the STI liner structure are given different qualities and functions. The first liner is designed for structural support with uniform thickness throughout, while the second liner is designed to vary in thickness, pinching off at the narrowest portion. This local differentiation allows the structure to simultaneously provide support where needed and prevent fill gaps where critical.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20250169160A1Dual liners for aggressive nanosheet spacing with backside contacts

Publication Date: 2025.05.22 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

Embodiments of the present disclosure include a semiconductor structure having a transistor adjacent to a shallow trench isolation (STI) region. The STI region includes a first liner, a second liner, and fill material. The second liner is pinched off in a portion of the STI region. A backside contact is coupled to the transistor, the first liner, and the second liner.