Epitaxial Layer Stack Carbon Concentration Control
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Solution Overview
Problem
Current selective epitaxy processes for forming ultra shallow source/drain junctions in semiconductor devices face challenges such as high temperature requirements, uncontrolled etching, and morphological deficiencies like pitting and surface roughness, which increase series resistance and are not versatile for forming silicon-containing compounds with varied elemental concentrations.
Innovation Solution
A method involving the formation of an epitaxial layer stack by depositing alternating carbon-containing silicon layers and non-carbon-containing silicon layers, with the carbon-containing layers encapsulated by non-carbon-containing layers to control carbon concentration and prevent etchant interaction, allowing for lower deposition temperatures and reduced defect formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high reaction temperature (800°C or higher) is used for selective epitaxy, then deposition rate is improved, but thermal budget is exceeded and uncontrolled nitridation reactions occur
Solution Approach 1:
The patent changes the chemical parameters of the deposition process by introducing carbon-containing silicon precursors and controlling their concentration. This allows the epitaxial process to proceed at lower temperatures (below 800°C) while maintaining adequate deposition rates through optimized precursor chemistry rather than relying solely on thermal energy.
Solution Approach 2:
The patent forms composite epitaxial layers containing silicon and carbon (silicon-carbon alloys) by co-depositing carbon-containing silicon precursors with standard silicon precursors. This composite material approach enables lower temperature processing while achieving the desired epitaxial growth, as the carbon incorporation modifies the deposition kinetics and reduces the activation energy barrier.
2Quantity of substance
If carbon-containing silicon layers are deposited to achieve target carbon concentration, then carbon doping is improved, but morphological deficiencies (pitting and surface roughness) increase
Solution Approach 1:
The patent segments the carbon incorporation process into multiple alternating deposition steps: a carbon-containing silicon layer is deposited, then a non-carbon-containing silicon layer is deposited, and this sequence is repeated. This segmentation allows carbon to be introduced in controlled amounts and distributed uniformly throughout the epitaxial layer, preventing local carbon aggregation that causes pitting and surface roughness.
Solution Approach 2:
The patent employs periodic alternation between carbon-containing silicon deposition and non-carbon-containing silicon deposition cycles. This periodic action ensures uniform carbon distribution by allowing the crystal structure to relax and reorganize between carbon incorporation events, thereby maintaining surface morphology while achieving the desired overall carbon concentration.
3Reliability
If non-carbon-containing silicon layers are used to encapsulate carbon-containing layers, then selectivity is maintained and etchant interaction is prevented, but process complexity increases
Solution Approach 1:
The patent merges the encapsulation function with the epitaxial growth process itself by alternating carbon-containing and non-carbon-containing silicon deposition within the same selective epitaxy sequence. The non-carbon-containing silicon layers serve dual purposes: they act as encapsulation barriers to prevent etchant interaction with carbon layers and maintain selectivity, while simultaneously contributing to the overall epitaxial layer formation. This integration reduces process complexity compared to separate encapsulation 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
This approach enables the formation of low-defect silicon-containing epitaxial layers with controlled carbon concentration, maintaining selectivity and reducing series resistance, while operating at lower temperatures and minimizing morphological issues like pitting.
Implementation Method 1
depositing alternating carbon-containing silicon layers and non-carbon-containing silicon layers
Implementation Method 2
The target carbon concentration is achieved based on a total thickness, an initial carbon concentration, and a deposition time for the carbon-containing silicon layers
Data Source
AI summary
In a first aspect, a method is provided for forming an epitaxial layer stack on a substrate. The method includes (1) selecting a target carbon concentration for the epitaxial layer stack; (2) forming a carbon-containing silicon layer on the substrate, the carbon-containing silicon layer having at least one of an initial carbon concentration, a thickness and a deposition time selected based on the selected target carbon concentration; and (3) forming a non-carbon-containing silicon layer on the carbon-containing silicon layer prior to etching. Numerous other aspects are provided.