SOI Diffusion Break Forming After Source/Drain
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Solution Overview
Problem
The formation of diffusion breaks in field effect transistors (FETs) on semiconductor-on-insulator (SOI) substrates leads to stress degradation and poor epitaxial growth, resulting in performance issues, especially at advanced technology nodes, due to the release of strain in the SOI layer and defects such as agglomerations and reduced growth, which limits active region isolation and increases leakage.
Innovation Solution
A method is developed to form a diffusion break by removing the gate stack of a dummy gate to a buried insulator and filling the opening with a dielectric, creating a self-aligned diffusion break that retains stress in the SOI layer and avoids defects, allowing for better isolation and reduced leakage by forming the diffusion break after source/drain formation and extending it to the upper surface of the buried insulator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diffusion break is formed by removing SOI layer to define recess and filling with dielectric, then active region isolation is achieved, but stress in SOI layer is released causing performance degradation
Solution Approach 1:
The dummy gate structure is formed preliminarily before diffusion break formation. This preliminary structure serves as a template that defines the future diffusion break location and ensures it aligns with the gate, allowing the diffusion break to be formed without disrupting the stress in the channel region of active devices.
Solution Approach 2:
The dummy gate acts as an intermediary structure that enables the formation of the diffusion break without directly compromising the stress in active device channels. By using the dummy gate as a sacrificial template and forming the diffusion break after its removal, the stress in the SOI layer is preserved while still achieving the necessary isolation.
2Reliability
If diffusion break is formed early in the process, then active region isolation is achieved, but poor epitaxial growth and defects occur
Solution Approach 1:
Source/drain regions are formed preliminarily using the dummy gate as an etch mask before the diffusion break is formed. This preliminary formation of raised source/drain regions with proper epitaxial growth occurs without the disruption that would result from early diffusion break formation. The diffusion break is then formed by removing the dummy gate, avoiding defects while maintaining growth quality.
3Productivity
If device size is scaled down to increase density, then FET density increases, but leakage increases due to reduced isolation
Solution Approach 1:
The diffusion break extends vertically to the upper surface of the buried insulator layer, utilizing the vertical dimension to achieve effective isolation. This vertical extension provides robust electrical isolation between adjacent active regions even when lateral dimensions are scaled down, thereby preventing leakage while maintaining high FET density.
Data Source
AI summary
Methods of forming a diffusion break are disclosed. The method includes forming a diffusion break after source/drain formation, by removing a gate stack of the dummy gate to a buried insulator of an SOI substrate, creating a first opening; and filling the first opening with a dielectric to form the diffusion break. An IC structure includes the diffusion break in contact with an upper surface of the buried insulator. In an optional embodiment, the method may also include simultaneously forming an isolation in an active gate to an STI in the SOI substrate.