Back-Side Contacts via Epitaxial Layer Stack

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Solution Overview

Problem

The existing techniques for fabricating back-side contacts on semiconductor layers face challenges such as lateral spread of dopants causing short circuits and substrate deformation, leading to deteriorated source and channel series resistances during the thinning and bonding processes.

Innovation Solution

A semiconductor structure with at least four epitaxial layers, where back-side contacts are formed without front-side implantation, allowing for the integration of back-side semiconductor devices with front-side logic devices, utilizing epitaxial layers with specific conductivity types and doping concentrations to enable efficient contact formation and connection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If front-side implantation is used to form back-side contacts, then the thermal budget limit is circumvented, but lateral spread of dopants causes short circuits between source and drain terminals

Engineering Contradiction:

Improvethermal budgetVSAvoidshort circuit prevention

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

Instead of forming back-side contacts through front-side implantation (conventional approach), the patent inverts the process by forming the contacts directly on the back-side of the semiconductor layer. This reversal eliminates the lateral dopant spread issue while maintaining thermal budget control, as the contacts are formed after thinning when the back-side is accessible.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent performs preliminary thinning of the semiconductor substrate to expose the back-side surface before forming the back-side contacts. This preliminary action enables direct access to the back-side for contact formation, avoiding the need for front-side implantation and its associated dopant spread problems.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If the semiconductor substrate is thinned to fabricate back-side devices, then new system and processing possibilities are opened, but substrate deformation occurs during thinning and bonding processes

Engineering Contradiction:

Improveback-side device fabrication capabilityVSAvoidsubstrate deformation

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The patent segments the semiconductor structure into distinct functional layers: a thinned semiconductor layer containing front-side logic devices, and a separate substrate that provides mechanical support. This segmentation allows the semiconductor layer to be thinned for back-side device fabrication while the substrate maintains structural stability and prevents deformation during processing.

Inventive Principle:

Principle #1Segmentation

3Ease of manufacture

If the semiconductor substrate is thinned to expose the back-side surface, then back-side semiconductor devices can be fabricated, but overlay between back-side contacts and back-side devices deteriorates due to substrate deformation

Engineering Contradiction:

Improveback-side contact fabricationVSAvoidoverlay alignment

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent inverts the conventional sequence by first thinning the substrate to expose the back-side, then forming the back-side contacts and devices in a single alignment step. This reversal ensures that all back-side structures are defined relative to each other without being affected by subsequent substrate deformation, thereby maintaining precise overlay alignment.

Inventive Principle:

Principle #13The other way round (Inversion)

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

This approach allows for the fabrication of back-side contacts that effectively connect back-side semiconductor devices to front-side logic devices without the need for front-side implantation, reducing the risk of short circuits and substrate deformation, thereby improving the reliability and performance of the semiconductor structure.

Implementation Method 1

at least four epitaxial layers, which are arranged on a back-side of the semiconductor layer

Methodology Applied

Scientific EffectEpitaxial growth: Epitaxy

Data Source

PatentUS20230025767A1Semiconductor Structure with an Epitaxial Layer Stack for Fabricating Back-side Contacts

Publication Date: 2023.01.26 INTERUNIVERSITAIR MICRO ELECTRONICS CENT (IMEC VZW)

AI summary

An example includes a semiconductor structure including a semiconductor layer, front-side logic devices arranged in a front-side of the semiconductor layer, four epitaxial layers on a back-side of the semiconductor layer, where the four epitaxial layers include a first epitaxial layer of a first conductivity type, a second epitaxial layer of a second conductivity type, a third epitaxial layer of the second conductivity type, and a fourth epitaxial layer of the first conductivity type, a plurality of back-side contacts exposed at a back-side surface of the fourth epitaxial layer, where the plurality of back-side contacts include a set of first terminal contacts extending into and contacting the fourth epitaxial layer, a set of second terminal contacts extending into and contacting the second epitaxial layer, a set of first gate contacts extending into the third epitaxial layer, and a set of second gate contacts extending into the first epitaxial layer.