Self-Aligned Backside Source Contact for Overlay-Tolerant Power Rails
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Solution Overview
Problem
Existing backside contact structures for multi-gate transistors face challenges in forming satisfactory backside power rails without causing short circuits due to overlay variations, particularly between the backside source contact and the gate structure.
Innovation Solution
A self-aligned backside contact structure is implemented, where a bottom self-aligned contact dielectric layer covers the backsides of the source feature and the gate structure, allowing selective access to the source feature and preventing the need for high overlay precision during the formation of backside source contact openings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional backside contact structures are used, then power rail functionality is achieved, but overlay variations cause short circuits between backside source contact and gate structure
Solution Approach 1:
The bottom self-aligned contact dielectric layer is formed in advance to define the future contact opening location. This preliminary structure guides subsequent etching processes to create openings that automatically align with the source feature, eliminating the need for high-precision overlay during backside contact formation and preventing short circuits with the gate structure.
Solution Approach 2:
The bottom self-aligned contact dielectric layer serves as an intermediary structure between the source feature and the backside contact opening. This dielectric layer with its specific pattern provides a template that mediates the alignment process, ensuring that contact openings are formed at correct positions without requiring precise overlay between different lithography steps.
2Manufacturing precision
If high overlay precision is required for backside contact formation, then contact alignment is improved, but process complexity and difficulty increase
Solution Approach 1:
The bottom self-aligned contact dielectric layer is designed to automatically guide the formation of contact openings through self-aligned etching processes. The structure serves itself by providing the alignment reference needed for subsequent processing steps, eliminating the need for external alignment markers or complex overlay control mechanisms, thereby reducing process complexity while maintaining high precision.
3Ease of manufacture
If conventional backside contact formation is used, then manufacturing is simpler, but process window and yield are reduced due to overlay variations
Solution Approach 1:
By pre-forming the bottom self-aligned contact dielectric layer with the correct pattern, the invention establishes a robust framework that tolerates normal overlay variations. This preliminary structure ensures that subsequent contact openings will be properly positioned regardless of minor alignment deviations, thereby maintaining ease of manufacture while significantly improving process window and yield.
Data Source
AI summary
A semiconductor device according to the present disclosure includes a source feature and a drain feature, a plurality of semiconductor nanostructures extending between the source feature and the drain feature, a gate structure wrapping around each of the plurality of semiconductor nanostructures, a bottom dielectric layer over the gate structure and the drain feature, a backside power rail disposed over the bottom dielectric layer, and a backside source contact disposed between the source feature and the backside power rail. The backside source contact extends through the bottom dielectric layer.