Germanium Nanowire Release Etch Passivation
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Solution Overview
Problem
Conventional methods for releasing nanowires from germanium-based semiconductor structures often result in loss of Ge-containing channel material due to poor selectivity and lack of effective passivation, leading to rounded corners and incomplete exposure of channel regions, which hinders the formation of rectangular-shaped nanowires essential for advanced device architectures.
Innovation Solution
Employing a hydrosulfide-based chemistry that acts as both a sacrificial layer etchant and a passivating agent, using ammonium sulfide (NH4)2S and ammonium hydrosulfide (NH4SH) to selectively etch sacrificial layers while preserving germanium-based nanowires, thereby achieving high selectivity and preventing Ge oxidation during the etch process, allowing for the formation of rectangular-shaped nanowires with squared corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional release etch methods are used to remove sacrificial layers, then the sacrificial layer can be removed, but Ge-containing channel material is lost due to poor selectivity and lack of passivation
Solution Approach 1:
A sulfur-based passivation layer is introduced as an intermediary substance during the release etch process. This passivation layer selectively forms on Ge-containing structures, acting as a protective mediator that prevents the etchant from attacking the channel material while allowing removal of the sacrificial layer.
Solution Approach 2:
The etch process parameters are changed by introducing a sulfur-containing compound that alters the chemical environment. This parameter change enables selective passivation of Ge surfaces through sulfur adsorption, transforming the etch selectivity to favor sacrificial layer removal while protecting Ge channel material.
2Shape
If conventional etchants are used without passivation, then the sacrificial layer can be etched, but Ge surfaces become oxidized and rounded corners form
Solution Approach 1:
Sulfur-based passivation is applied preliminarily during the release etch process to counteract the harmful oxidation effect before it can occur. The sulfur atoms adsorb onto Ge surfaces in advance, creating a protective barrier that prevents oxygen from attacking and rounding the nanowire corners.
Solution Approach 2:
The sulfur-containing etchant, which could potentially be harmful through over-etching, is converted into a beneficial agent by its ability to selectively passivate Ge surfaces. The same chemical environment that enables sacrificial layer removal also provides protective passivation, turning a potential harm into a benefit.
3Reliability
If multi-gate or gate-all-around devices are manufactured with non-Si channel materials, then device performance can be improved, but process integration complexity increases
Solution Approach 1:
The sulfur-based release etch process serves multiple functions simultaneously: it removes sacrificial layers, passivates Ge surfaces, prevents oxidation, and maintains nanowire structural integrity. This multi-functionality simplifies the overall fabrication process for non-Si channel materials while maintaining high device performance.
Solution Approach 2:
The release etch and passivation steps are merged into a single combined process using sulfur-containing compounds. This consolidation eliminates the need for separate passivation steps, reducing process integration complexity while enabling high-performance multi-gate devices with non-Si channel materials.
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
The method effectively conserves Ge-containing nanowire material, enabling the fabrication of rectangular-shaped nanowires with squared corners, which is crucial for high-performance semiconductor devices, by simultaneously etching sacrificial layers and passivating the germanium surface, thus improving the integration of germanium-based nanowire architectures in semiconductor devices.
Implementation Method 1
a selective and passivating wet etch is used to remove a silicon-rich material
Implementation Method 2
passivating exposed portions of the germanium-rich layers... preventing Ge oxidation during the etch process
Data Source
Figure 1A~1B
Figure 2~3B
Figure 4A~4C
AI summary
Non-planar semiconductor devices having germanium-based active regions with release etch-passivation surfaces are described. For example, a semiconductor device includes a vertical arrangement of a plurality of germanium-rich nanowires disposed above a substrate. Each nanowire includes a channel region having a sulfur-passivated outer surface. A gate stack is disposed on and completely surrounds the channel region of each of the germanium-rich nanowires. The gate stack includes a gate dielectric layer disposed on and surrounding the sulfur-passivated outer surface and a gate electrode disposed on the gate dielectric layer. Source and drain regions are disposed on either side of the channel regions of the germanium-rich nanowires.