Nanosheet Transistor Bottom Isolation Using Slanted Dielectric Structures
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Solution Overview
Problem
Nanosheet field effect transistors face limitations due to lattice strain-induced defects and challenges in forming adequate bottom isolation with dielectric layers, especially in devices with high aspect ratios where dielectric material pinches off.
Innovation Solution
The method involves forming slanted dielectric structures on a substrate, growing a semiconductor layer that fills gaps between these structures, replacing the lower portion of the semiconductor layer with additional dielectric material to create a complete bottom isolation layer, and using tilted implantation to convert exposed dielectric material, thereby preventing threading dislocations and ensuring full isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dielectric material is used to isolate the bottom of the device, then electrical isolation between fins and substrate is improved, but the dielectric material pinches off in devices with high aspect ratios, preventing adequate filling
Solution Approach 1:
The bottom isolation structure is segmented into multiple components: slanted dielectric structures formed first, then gaps filled with semiconductor material, and finally the lower portion replaced with additional dielectric material. This segmentation allows each component to be optimized independently, solving the pinch-off problem by breaking the single dielectric layer into manageable sections that can be formed sequentially
Solution Approach 2:
The patent introduces slanted dielectric structures with specific倾斜 angles instead of vertical walls, creating a geometric configuration that prevents dielectric material pinch-off. By changing the dimensional geometry from vertical to slanted, the patent enables adequate dielectric material filling in high aspect ratio devices while maintaining electrical isolation
2Shape
If alternating sheets of channel material and sacrificial material are deposited to form nanosheet channels, then nanosheet structure is created, but lattice strain between materials causes defects to form
Solution Approach 1:
The patent extracts and removes the sacrificial material after the nanosheet channel structure is formed, leaving only the channel material. This extraction eliminates the source of lattice strain that would otherwise cause defects, while preserving the desired nanosheet geometry
Solution Approach 2:
The nanosheet channel structure is preliminarily formed using sacrificial material as a template, then the sacrificial material is removed. This preliminary formation approach allows precise control of channel geometry before eliminating the strain-inducing sacrificial material
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 effectively prevents electrical conduction between neighboring fins and the substrate, providing robust bottom isolation and reducing defects, thereby enhancing the performance of nanosheet fin stacks.
Implementation Method 1
A tilted implantation is performed that converts exposed portions of the original dielectric layer to a second dielectric material
Implementation Method 2
A first semiconductor layer is grown from the substrate, using a first semiconductor material, including a lower portion that fills the gaps and an upper portion above the first dielectric material
Data Source
AI summary
Semiconductor devices and methods of forming the same include forming slanted dielectric structures from a first dielectric material on a substrate, with gaps between adjacent slanted dielectric structures. A first semiconductor layer is grown from the substrate, using a first semiconductor material, including a lower portion that fills the gaps and an upper portion above the first dielectric material. The lower portion of the first semiconductor layer is replaced with additional dielectric material.