Epitaxial Silicon Carbon Layer Formation via Periodic Etching
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Solution Overview
Problem
Current selective epitaxy processes for forming silicon-containing epitaxial layers in semiconductor devices face challenges such as the need for precise temperature control, potential for uncontrolled nitridation, and slow growth rates at lower temperatures, which affect the incorporation of substitutional carbon and the selectivity of the process.
Innovation Solution
A method involving alternating gas supply cycles of deposition and etching, using a silicon source, a carbon source, and a dopant source, with chlorine as an etchant to reduce the overall process temperature and enhance the deposition rate, while maintaining high substitutional carbon levels and selectivity, is employed. This method includes forming undoped and doped layers sequentially and purging the chamber to achieve the desired epitaxial layer thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lower temperatures are used for epitaxial deposition, then substitutional carbon incorporation is improved, but growth rate decreases
Solution Approach 1:
The patent employs periodic alternation between deposition and etching cycles. During deposition, carbon-containing silicon material is deposited at lower temperatures to ensure high substitutional carbon incorporation. During etching, the deposited material is partially removed. This periodic cycling allows the process to accumulate material with high substitutional carbon content while maintaining reasonable overall growth rates, as the etching step removes only the polycrystalline material deposited on dielectric surfaces.
Solution Approach 2:
The patent changes process parameters dynamically by alternating between deposition conditions (lower temperature for high substitutional carbon) and etching conditions. The etching step uses conditions that selectively remove polycrystalline silicon while preserving the quality of the epitaxial layer. This parameter change strategy allows optimization of substitutional carbon incorporation during deposition while compensating for the reduced growth rate through the cumulative effect of multiple cycles.
2Manufacturing precision
If selective epitaxy is performed to grow epilayers on silicon surfaces, then selectivity is improved, but polycrystalline deposition occurs on dielectric areas
Solution Approach 1:
The patent extracts and removes the harmful polycrystalline deposition from the dielectric surfaces by incorporating an etching step that selectively removes material deposited on dielectric areas. The etching process targets the polycrystalline silicon formed on dielectric surfaces during the deposition phase, effectively taking out this unwanted material while preserving the desired epitaxial growth on silicon surfaces.
Solution Approach 2:
The patent uses the etching step to rapidly remove polycrystalline deposits on dielectric surfaces, skipping over the unwanted material. The alternating deposition-etching cycles allow the process to rush through the removal of polycrystalline contaminants efficiently, preventing their accumulation on dielectric areas while maintaining selectivity for epitaxial growth on silicon.
3Productivity
If high temperatures are used for epitaxial deposition, then growth rate is improved, but uncontrolled nitridation occurs
Solution Approach 1:
The patent uses periodic alternation between deposition and etching cycles to avoid continuous high-temperature exposure. During deposition, material is deposited at controlled temperatures. The subsequent etching step occurs at different conditions, allowing removal of excess material and preventing nitridation. This periodic action enables the process to achieve reasonable growth rates without the harmful effects of sustained high-temperature nitridation.
Solution Approach 2:
The etching step acts as an intermediary between deposition cycles. It provides a transition phase that removes deposited material and resets the surface conditions, preventing the accumulation of nitrided layers that would occur during continuous high-temperature deposition. This intermediary step mediates between the need for growth and the need to prevent nitridation.
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 allows for the efficient formation of silicon-containing epitaxial layers with high substitutional carbon concentration at lower temperatures, improving the crystallinity and selectivity of the epitaxial growth, thereby enhancing the performance of semiconductor devices like MOSFETs by achieving faster growth rates and maintaining high substitutional carbon levels.
Implementation Method 1
A method involving alternating gas supply cycles of deposition and etching, using a silicon source, a carbon source, and a dopant source, with chlorine as an etchant to reduce the overall process temperature and enhance the deposition rate
Implementation Method 2
A typical selective epitaxy process involves a deposition reaction and an etch reaction. During the deposition process, the epitaxial layer is formed on a monocrystalline surface
Implementation Method 3
A method involving alternating gas supply cycles of deposition and etching, using a silicon source, a carbon source, and a dopant source
Data Source
AI summary
Methods for formation of epitaxial layers containing silicon are disclosed. Specific embodiments pertain to the formation and treatment of epitaxial layers in semiconductor devices, for example, Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices. In specific embodiments, the formation of the epitaxial layer involves exposing a substrate in a process chamber to deposition gases including two or more silicon source such as silane and a higher order silane. Embodiments include flowing dopant source such as a phosphorus dopant, during formation of the epitaxial layer, and continuing the deposition with the silicon source gas without the phosphorus dopant.