Strained Vertical FinFET Channels via Sacrificial Stressor and Anchor Walls
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Solution Overview
Problem
Forming vertical field effect transistors (VFETs) with strained channels is challenging due to relaxation mechanisms in free-standing vertical fins, which lack consistent stress application from a substrate, making it difficult to maintain strain.
Innovation Solution
A method involving the formation of sacrificial stressor layers adjacent to vertical fins to impart strain, followed by the creation of anchor walls that maintain the strain after removal of the sacrificial layers, ensuring the vertical fins remain in a strained state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If vertical fins are formed as free-standing structures, then device scaling is enabled, but strain relaxation occurs making it difficult to maintain channel strain
Solution Approach 1:
The sacrificial stressor layer is formed adjacent to the vertical fins before the fins are fully released, imparting strain to the fins in advance. This preliminary strain application ensures that when the fins become free-standing, they already possess the necessary strain state, overcoming the natural tendency toward strain relaxation in suspended structures.
Solution Approach 2:
The sacrificial stressor layer acts as an intermediary material that transfers stress to the vertical fins. By being in direct contact with the fin sidewalls, it mediates the strain transfer process, allowing external stress to be applied to the fins without requiring continuous substrate support, thus enabling strain maintenance in free-standing structures.
2Reliability
If sacrificial stressor layers are used to impart strain, then carrier mobility is enhanced, but additional fabrication steps are required
Solution Approach 1:
The sacrificial stressor layer serves multiple functions: it acts as a strain-imparting element, provides structural support during subsequent fabrication steps, and serves as a template for anchor wall formation. This multi-functionality reduces the need for separate dedicated structures, offsetting the added fabrication complexity with process integration benefits.
Solution Approach 2:
The sacrificial stressor layer is temporarily retained during fabrication to impart and maintain strain, then selectively removed after serving its purpose. The anchor walls are formed to recover and maintain the strain effect after the sacrificial material is discarded, allowing the process to benefit from temporary strain application without permanent complexity.
3Stability of the object's composition
If anchor walls are formed to maintain strain after sacrificial layer removal, then strain stability is improved, but device structure becomes more complex
Solution Approach 1:
The strain maintenance function is segmented between the sacrificial stressor layer (temporary strain application) and the anchor walls (permanent strain maintenance). This segmentation allows each component to be optimized for its specific function, with the anchor walls providing localized strain maintenance only where needed, rather than requiring a completely different structural approach.
Solution Approach 2:
The sacrificial stressor layer is designed as a temporary, disposable component that serves its strain-imparting function and is then removed. The anchor walls are the permanent structures that maintain strain afterward. This approach allows complex strain maintenance to be achieved through a simple temporary structure followed by simpler permanent structures, rather than requiring a complex single-stage solution.
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 enhances carrier mobility and drive current in VFETs by maintaining the strain in the vertical fin channel, overcoming the limitations of traditional FET structures in scaling down device components.
Implementation Method 1
forming a sacrificial stressor layer adjacent to the vertical fins, wherein the sacrificial stressor layer is in contact with the sidewalls of the adjacent vertical fins, and imparts a strain to the adjacent vertical fins
Data Source
AI summary
A method of forming a vertical fin field effect transistor (vertical finFET) with a strained channel, including forming one or more vertical fins on a substrate, forming a sacrificial stressor layer adjacent to the one or more vertical fins, wherein the sacrificial stressor layer imparts a strain in the adjacent vertical fins, forming a fin trench through one or more vertical fins and the sacrificial stressor layer to form a plurality of fin segments and a plurality of sacrificial stressor layer blocks, forming an anchor wall adjacent to and in contact with one or more fin segment endwalls, and removing at least one of the plurality of the sacrificial stressor layer blocks, wherein the anchor wall maintains the strain of the adjacent fin segments after removal of the sacrificial stressor layer blocks adjacent to the fin segment with the adjacent anchor wall.