SiGe-Si Epitaxial Interfaces Using Surfactants to Limit Ge Segregation
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Solution Overview
Problem
In the formation of gate-all-around devices, the transition between silicon germanium (SiGe) and silicon (Si) layers is often disrupted due to the energetic favorability of germanium, leading to the segregation of germanium and the formation of undesirably large interfacial layers, which affects device performance and variability.
Innovation Solution
The use of surfactant precursors such as gallium, tellurium, antimony, indium, aluminum, and tin, along with germanium precursors like germane and germanium halides, during the epitaxial growth of SiGe and Si layers in a reaction chamber, helps mitigate germanium migration and form a thin, abrupt interface by controlling the flow rates and periods of these precursors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If germanium is allowed to segregate during epitaxial growth, then the interface between SiGe and Si layers becomes gradual and thick, but device performance and variability are degraded
Solution Approach 1:
A surfactant layer is introduced as an intermediary between the SiGe and Si layers during epitaxial growth. This surfactant layer prevents germanium segregation at the interface, enabling the formation of an abrupt interface with minimal intermixing. The surfactant acts as a mediator that blocks the energetically favorable segregation of germanium while allowing controlled growth of both layers.
Solution Approach 2:
The surfactant is applied in advance before the silicon layer growth begins, during or after the SiGe layer formation. This preliminary action prepares the interface to prevent germanium segregation before the silicon atoms are deposited, thereby preventing the formation of a thick graded interface layer from the outset.
2Manufacturing precision
If the surfactant is applied continuously throughout the entire growth process, then germanium segregation is prevented, but growth time and process complexity increase
Solution Approach 1:
The surfactant application is implemented periodically rather than continuously. The surfactant is introduced at specific stages (during or after SiGe growth, and/or at the beginning of Si growth), then removed or reduced before subsequent growth stages. This periodic application maintains interface quality while minimizing unnecessary process time and complexity.
Solution Approach 2:
The epitaxial growth process is segmented into distinct stages with surfactant applied only during critical transition periods. Rather than continuous surfactant presence, the process is divided into phases where surfactant is introduced, allowed to act during critical interface formation, then removed or reduced for subsequent growth stages.
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 enables the formation of structures with improved performance and reduced performance variability by creating a consistent and abrupt transition between SiGe and Si layers, enhancing the fabrication of high-density, high-performance electronic devices.
Implementation Method 1
a surfactant precursor is provided to the reaction chamber during at least a portion of the step of forming the first layer. The surfactant is thought to contribute a species to the first layer that can mitigate migration of other species (e.g., germanium) within the first layer
Implementation Method 2
forming a first layer comprising silicon and germanium overlying a surface of the substrate
Implementation Method 3
a germanium precursor comprising a halogen is provided to the reaction chamber during the step of forming the first layer
Data Source
AI summary
Methods and systems for forming structures including one or more layers comprising silicon germanium and one or more layers comprising silicon are disclosed. Exemplary methods can include using a surfactant, using particular precursors, and/or using a transition step to improve an interface between adjacent layers comprising silicon germanium and comprising silicon.