MOS Transistor Epitaxial Structure Formation Sequence
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Solution Overview
Problem
In MOS transistor fabrication, the diffusion of ingredients from epitaxial structures due to high temperature or ion implantation processes degrades performance, and surface damage during source/drain formation affects the quality of epitaxial structures, leading to reduced carrier mobility and increased circuit leakages.
Innovation Solution
A MOS transistor process that forms recesses and performs a cleaning process after source/drains are formed, followed by the formation of epitaxial structures, thereby preventing ingredient diffusion and removing substrate damage, which enhances the quality and performance of the epitaxial structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If source/drain ion implantation and annealing processes are performed to form source/drains, then source/drain structures are formed, but ingredients in the epitaxial structure diffuse outwards and stresses forcing gate channels decrease, leading to circuit leakages
Solution Approach 1:
The epitaxial structure is formed before the source/drain ion implantation and annealing processes. This preliminary formation allows the epitaxial structure to be established with proper ingredient concentration and stress characteristics before subsequent processing that would otherwise cause diffusion and degradation of these properties.
2Manufacturing precision
If source/drain formation processes are performed, then source/drains are formed, but substrate damage and impurities are introduced, affecting the quality of epitaxial structures
Solution Approach 1:
The substrate surface is prepared and the epitaxial structure is formed before source/drain formation processes that cause damage and impurities. This preliminary preparation ensures that the epitaxial structure is established on a clean, undamaged substrate surface, maintaining manufacturing precision.
Solution Approach 2:
The harmful effects of source/drain formation processes (ion implantation damage, high temperature annealing) are separated from the epitaxial structure formation process. By performing source/drain formation after epitaxial structure formation, the damaging effects are extracted and isolated from the sensitive epitaxial structure.
3Reliability
If epitaxial structures are formed before source/drains, then ingredient diffusion and stress degradation occur, but if epitaxial structures are formed after source/drains, then substrate damage affects epitaxial quality
Solution Approach 1:
The epitaxial structure is formed in a preliminary step before source/drain formation. This allows the epitaxial structure to be created under optimal conditions without subsequent damage from ion implantation or high temperature annealing, while the preliminary nature ensures no prior substrate damage exists.
Solution Approach 2:
The process sequence uses the completion of source/drain formation as an intermediary milestone. The epitaxial structure formation is positioned as a separate process stage that occurs after source/drain formation, using the source/drain structures as a reference point or mediator for subsequent alignment and formation 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 improves the performance of epitaxial structures by preventing ingredient diffusion and reducing substrate damage, leading to increased carrier mobility and reduced circuit leakages, thus enhancing the overall performance of MOS transistors.
Implementation Method 1
An epitaxial structure is formed in the recess
Data Source
AI summary
A MOS transistor process includes the following steps. A gate structure is formed on a substrate. A source/drain is formed in the substrate beside the gate structure. After the source/drain is formed, (1) at least a recess is formed in the substrate beside the gate structure. An epitaxial structure is formed in the recess. (2) A cleaning process may be performed to clean the surface of the substrate beside the gate structure. An epitaxial structure is formed in the substrate beside the gate structure.