Dual Spacer Plasma Densification for Semiconductor Etching
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Solution Overview
Problem
In semiconductor processes, the use of a single-layer spacer can lead to damage to the substrate and lightly-doped source/drain regions due to over-etching and material similarity, affecting the electrical performance of MOS transistors.
Innovation Solution
A semiconductor process involving a plasma process without oxygen is performed on a dual spacer to densify the oxide layer, preventing consumption during subsequent etching processes and maintaining the integrity of the oxide layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer spacer is used to form recesses, then the process is simple, but the oxide layer is consumed during etching processes
Solution Approach 1:
The spacer structure is divided into two distinct layers: a first spacer layer (e.g., silicon nitride) and a second spacer layer (oxide layer). This segmentation allows the etching process to selectively remove the first spacer layer while the densified second spacer layer remains intact, preventing oxide layer consumption while maintaining processability.
Solution Approach 2:
The dual spacer structure combines materials with different etching properties - a silicon nitride first spacer layer that is easily removed by phosphoric acid, and an oxide second spacer layer that is densified to resist etching. This composite structure resolves the contradiction between ease of removal and resistance to consumption.
2Ease of operation
If a single-layer spacer is removed after epitaxial layer formation, then the recess is accessible, but the substrate and lightly-doped source/drain regions are damaged due to over-etching
Solution Approach 1:
The first spacer layer acts as an intermediary sacrificial layer that protects the substrate and lightly-doped source/drain regions during the etching process. It can be completely removed after serving its protective function, while the densified second spacer layer remains to prevent over-etching damage.
Solution Approach 2:
The dual spacer structure provides beforehand cushioning by having the densified oxide layer in place before the etching process begins. This layer acts as a protective barrier that prevents over-etching from reaching and damaging the substrate and lightly-doped regions.
3Ease of manufacture
If the oxide layer is not densified, then the plasma process is simple, but the oxide layer is consumed during wet etching processes
Solution Approach 1:
The oxide layer is densified through a plasma process before the wet etching step. This preliminary action enhances the oxide layer's resistance to etching, ensuring it remains intact during subsequent processing steps while adding minimal complexity to the overall manufacturing process.
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 plasma process without oxygen strengthens the oxide layer, preventing its consumption during etching and protecting the first spacer and lightly-doped source/drain regions, thereby enhancing the electrical performance of MOS transistors.
Implementation Method 1
A plasma process without oxygen is performed to densify the oxide layer
Data Source
AI summary
A semiconductor process includes the following steps. A gate structure is formed on a substrate. An oxide layer is formed and covers the gate structure and the substrate. A plasma process without oxygen is performed to densify the oxide layer. A material layer is formed and covers the oxide layer. The material layer and the oxide layer are etched to form a dual spacer.