FinFET Fin Height Control via Two-Step Etching
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Solution Overview
Problem
Conventional FinFET fabrication processes often result in fin-shaped structures being lower than surrounding shallow trench isolation due to over-etching, which affects the formation of epitaxial layers.
Innovation Solution
A two-step etching process is employed to remove part of the fin-shaped structures, using HBr for initial etching to expose the top surface, followed by fluorine-based etching to form a polymer layer, and then Cl and NF3 for precise removal, ensuring the top and bottom portions of the fin-shaped structures have distinct slopes, preventing over-etching and enhancing epitaxial layer quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional single-step etching is used to remove fin-shaped structures, then the etching process is simple and fast, but over-etching occurs causing fins to be lower than surrounding STI
Solution Approach 1:
The etching process is divided into multiple sequential steps with different etching solutions. The first step uses a etching solution to remove part of the cap layer and expose the top surface of fins. The second step uses another etching solution to remove part of the fin-shaped structures while forming a polymer layer on the cap layer, creating distinct slopes at top and bottom portions of the fins. This segmentation allows precise control of fin height to prevent over-etching while maintaining etching efficiency.
2Ease of manufacture
If over-etching is performed to completely remove cap layer, then the cap layer is fully removed, but fin-shaped structures become lower than surrounding STI
Solution Approach 1:
A polymer layer is formed on the cap layer during the etching process as a protective barrier. This preliminary formation of the polymer layer prevents complete removal of the cap layer, thereby preventing over-etching that would cause fins to be lower than surrounding STI. The polymer layer acts as a self-limiting mechanism that stops etching at the appropriate depth.
Solution Approach 2:
Different etching solutions with distinct chemical compositions are used in sequential steps. The first etching solution exposes the top surface of fins, while the second etching solution removes part of the fin-shaped structures and forms a polymer layer on the cap layer. By changing etching solution parameters (chemistry, concentration, temperature), the process achieves precise control over cap layer removal and fin height maintenance.
3Manufacturing precision
If multi-step etching with polymer layer formation is used, then fin height control is improved, but the etching process becomes more complex
Solution Approach 1:
The etching process is designed to be self-limiting through automatic polymer layer formation on the cap layer during the etching step itself. The polymer layer forms in-situ during etching and automatically stops the etching process at the desired depth, eliminating the need for additional monitoring steps or complex process control mechanisms. This self-service mechanism simplifies the overall process complexity while maintaining high precision.
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 prevents over-etching and improves the quality of epitaxial layer growth by maintaining the fin-shaped structures' height relative to the trench isolation, thereby improving the overall FinFET fabrication process.
Implementation Method 1
removing part of the cap layer on top of the fin-shaped structure
Implementation Method 2
followed by fluorine-based etching to form a polymer layer
Implementation Method 3
then Cl and NF3 for precise removal, ensuring the top and bottom portions of the fin-shaped structures have distinct slopes
Data Source
AI summary
A method for fabricating semiconductor device is disclosed. The method includes the steps of: providing a substrate; forming a fin-shaped structure on the substrate; forming a cap layer on the fin-shaped structure; removing part of the cap layer on top of the fin-shaped structure; removing part of the fin-shaped structure; removing the remaining cap layer; and removing part of the remaining fin-shaped structure.