Graded SiGe Superlattice Structure for GAA Gate Control
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Solution Overview
Problem
The scaling down of silicon metal oxide semiconductor (MOS) devices has led to challenges such as short channel effects and insufficient carrier mobility, necessitating improvements in multi-gate devices like gate-all-around (GAA) transistors.
Innovation Solution
The implementation of superlattice structures with graded germanium concentrations and epitaxial deposition processes to form SiGe/Si layers, providing improved hole mobility and reduced dislocations, which are used in GAA transistor devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transistor dimensions are scaled down to smaller technology nodes, then production efficiency is improved and costs are lowered, but short channel effects increase and gate control deteriorates
Solution Approach 1:
The patent transitions from planar 2D gate control to three-dimensional gate-all-around structures that completely surround the channel region. This dimensional change enables the gate to control the channel from all directions (top, bottom, and sidewalls), providing superior electrostatic control and fuller depletion at scaled dimensions where conventional planar gates fail.
Solution Approach 2:
The patent employs composite material structures including semiconductor-sacrificial layer stacks with alternating high and low germanium concentration layers. These composite structures enable selective etching to form suspended nanowire channels surrounded by gate material, achieving complete gate coverage and improved gate control necessary for scaled devices.
2Length of moving object
If transistor dimensions are scaled down, then device size is reduced, but carrier mobility becomes insufficient
Solution Approach 1:
The patent implements local quality variations through graded germanium concentration profiles in the semiconductor layers. By varying the germanium content locally (higher at interfaces, lower in channel regions), the structure provides lattice matching to reduce dislocations at interfaces while maintaining high carrier mobility in the channel regions where germanium concentration is optimized.
Solution Approach 2:
The patent changes material composition parameters by incorporating germanium-silicon alloy layers with varying germanium concentrations (e.g., 10-30% Ge). This parameter variation enables optimization of both lattice matching (reducing dislocations) and carrier mobility (through appropriate Ge content in channel regions), allowing scaled devices to maintain sufficient speed performance.
3Reliability
If multi-gate devices are introduced to improve gate control, then short channel effects are reduced, but device complexity increases
Solution Approach 1:
The patent segments the semiconductor structure into multiple functional layers including sacrificial layers, semiconductor layers, and gate layers. The semiconductor structure is divided into suspended nanowire segments surrounded by gate material, with each segment independently controllable. This segmentation enables complete gate coverage for superior SCE control while using standardized fabrication processes.
Solution Approach 2:
The patent uses sacrificial layers as intermediary structures during fabrication. These temporary layers are deposited, patterned, and etched to define the final nanowire channel geometry, then completely removed to leave suspended channels. This intermediary approach simplifies the overall process by enabling complex 3D structures to be formed through sequential 2D processing steps.
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
Enhances device performance by minimizing dislocations, improving hole mobility, and reducing short channel effects, thus enabling faster and more efficient electronic devices.
Implementation Method 1
epitaxial deposition processes to form SiGe/Si layers
Implementation Method 2
graded germanium concentrations... The first germanium concentration and the third germanium concentration are greater than the second germanium concentration
Data Source
AI summary
Silicon germanium (SiGe)/silicon containing superlattice structures and methods for forming the same are provided. Various embodiments utilize SiGe layers in a SiGe/Si superlattice structure, which include varying concentrations of germanium throughout the layer. For example, in some embodiments, for each SiGe layer there is a core SiGe film with a low Ge content and two thinner SiGe layers or cladding layers positioned on opposing sides of the core SiGe film with each of the SiGe cladding layers having a higher Ge content then the core SiGe film. Various embodiments provide for SiGe layers having a germanium depth profile enabling strained SiGe superlattice deposition on Si{110} substrates.