Semiconductor Inner Spacer Formation Using Segmented Sacrificial Layers
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Solution Overview
Problem
The formation of inner spacers in semiconductor devices, such as forksheet and CFET devices, is hindered by thicker sacrificial layers, which prevent pinch-off and lead to spacer formation failures.
Innovation Solution
A method involving a device layer stack with a first sub-stack and a second sub-stack, where the second sub-stack has a thicker sacrificial layer made of a different material, allowing selective replacement with a dielectric layer and enabling conformal deposition of inner spacers, thereby facilitating the formation of inner spacers even with thicker sacrificial layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a thicker sacrificial layer is used to increase the height of the insulating wall or separation between devices, then the structural integrity and device separation are improved, but the pinch-off process fails and inner spacer formation is prevented
Solution Approach 1:
The sacrificial layer structure is segmented into multiple layers with different materials (first sacrificial material and second sacrificial material). The second sacrificial layer with different material enables selective removal through the pinch-off process, while the first sacrificial layer provides the necessary thickness for structural support and device separation. This segmentation allows the system to simultaneously achieve both sufficient height and successful spacer formation.
Solution Approach 2:
Different regions of the sacrificial layer structure are assigned different material properties. The second sacrificial layer uses a material that is selectively removable during pinch-off, while the first sacrificial layer uses a material that provides structural integrity. This local differentiation of material quality enables the thicker structure to function both as a structural support and as a removable template for spacer formation.
2Length of moving object
If a thicker sacrificial layer is used to provide greater separation between pFET and nFET devices, then device isolation is improved, but the etching process cannot penetrate through to achieve pinch-off
Solution Approach 1:
The thick sacrificial layer is divided into segments with different etch characteristics. The second sacrificial layer comprises material that is selectively etched during the pinch-off process, enabling the etching front to penetrate through the overall thick structure. This segmentation makes the manufacturing process feasible by creating a pathway through the otherwise impenetrable thick sacrificial layer.
Solution Approach 2:
The material composition parameter of the sacrificial layer is changed in the second layer to be more susceptible to the etching process. By adjusting the material parameters (using a different sacrificial material), the etching rate and selectivity are optimized to allow penetration through the thick structure, while the first sacrificial layer maintains its original parameters for structural support.
3Shape
If inner spacers are formed by conformal deposition on thicker sacrificial layers, then the spacer coverage is improved, but the pinch-off process cannot occur to define the spacer boundaries
Solution Approach 1:
The sacrificial layer is segmented into a first layer for structural support and a second layer for boundary definition. The second sacrificial layer with different material enables the pinch-off etching to occur, creating well-defined boundaries. The conformal deposition then covers the entire structure including the thicker regions, achieving both complete coverage and sharp boundaries.
Solution Approach 2:
The second sacrificial layer acts as an intermediary that facilitates the pinch-off process. It is positioned between the deposition process and the final boundary definition, enabling the etching to penetrate through and create the necessary boundaries while allowing the conformal deposition to occur on the underlying thicker structure.
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 method ensures the successful formation of inner spacers in semiconductor devices, enhancing the structural integrity and electrical performance by maintaining a minimal influence of the dielectric layer on the device's electrical performance.
Implementation Method 1
a dielectric layer is deposited conformally over the channel layer and the sacrificial layers
Implementation Method 2
the second sacrificial layer is removed to form a space in the second sub-stack by selective etching
Data Source
AI summary
The disclosure relates to a method for forming a semiconductor device. The method includes forming a device layer stack on a substrate, the device layer stack having a first sub-stack comprising a first sacrificial layer and on the first sacrificial layer a channel layer defining a topmost layer of the first sub-stack, and a second sub-stack on the first sub-stack and including a first sacrificial layer defining a bottom layer of the second sub-stack, and a second sacrificial layer on the first sacrificial layer, wherein said first sacrificial layers are formed of a first sacrificial semiconductor material, the second sacrificial layer is formed of a second sacrificial semiconductor material, and the channel layer is formed of a semiconductor channel material, and wherein a thickness of the second sub-stack exceeds a thickness of the first sacrificial layer of the first sub-stack. The method comprises replacing the second sacrificial layer of the second sub-stack with a dielectric layer; forming recesses in the device layer stack by laterally etching back end surfaces of the first sacrificial layers of the first and second sub-stacks from opposite sides of the sacrificial gate structure; and forming inner spacers in the recesses.