Backside-Coupled Epitaxial Layers for Low-Drop SRAM Grounding

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Solution Overview

Problem

Legacy SRAM implementations with deep boundary via (DVB) rings consume multiple front side metal layers and result in resistive voltage drops due to lengthy electrical paths from VSS connections to epitaxial structures, limiting SRAM performance and increasing metal resource usage.

Innovation Solution

Direct electrical coupling of epitaxial layers with backside contact metals reduces the need for front side metal layers by providing a shorter path to ground, eliminating the DVB ring and associated resistive voltage drops, thereby enhancing SRAM bit cell read current and reducing bit line and word line capacitance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If deep boundary via (DVB) rings are used to provide VSS to front side epitaxial layers, then electrical connection is established, but multiple front side metal layers are consumed and resistive voltage drops occur

Engineering Contradiction:

Improveelectrical connectionVSAvoidmetal layer usage

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent transitions the electrical connection path from the front side (2D plane) to the back side of the substrate (3D spatial reconfiguration). By providing VSS connections at the back side directly beneath the epitaxial layers, the invention eliminates the need for complex front side metal layer routing while maintaining reliable electrical connection.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

Instead of bringing the VSS connection up to the front side through deep boundary vias, the invention inverts the approach by keeping the connection at the back side and having the epitaxial layers extend downward to contact it. This reversal eliminates the DVB ring structure and reduces metal layer consumption.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If deep boundary via (DVB) rings are used to provide VSS to front side epitaxial layers, then electrical connection is established, but resistive voltage drops occur due to lengthy electrical paths

Engineering Contradiction:

Improveelectrical connectionVSAvoidresistive voltage drop

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

By reconfiguring the electrical connection path from front side routing through multiple metal layers to a direct back side connection, the invention dramatically shortens the current path length. The epitaxial layers extend vertically to contact the back side VSS directly, eliminating the lengthy horizontal and vertical paths through DVB rings and front side metal layers, thus reducing resistive voltage drops.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If multiple front side metal layers are used for VSS connections, then electrical connection is provided, but SRAM performance is limited due to increased capacitance

Engineering Contradiction:

Improveelectrical connectionVSAvoidSRAM read current

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The invention extracts the VSS connection function from the front side metal layer structure and relocates it to the back side substrate. This separation removes the capacitance associated with multiple front side metal layers and their interconnections, thereby improving SRAM read current and overall performance while maintaining necessary electrical connections.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS20230317148A1Epitaxial layers of a transistor electrically coupled with a backside contact metal

Publication Date: 2023.10.05 INTEL CORP

AI summary

Embodiments described herein may be related to apparatuses, processes, systems, and techniques directed to electrical couplings between epitaxial structures and voltage sources within transistors in SRAM bit cells. Embodiments include direct electrical couplings between a backside contact metal (BM0) and a backside of an epitaxial structure, as well as electrical connection structures that electrically couple the BM0 to a front side of an epitaxial structure. Other embodiments may be described and/or claimed.