Cap Layer for Spacer-Constrained Epitaxial Growth on FinFET Fins
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Solution Overview
Problem
In FinFET devices, the epitaxial material growth can lead to merging across densely-spaced fins, causing increased resistance and potential short circuits between separate devices, especially in CMOS technology, where merged epitaxial structures result in different device characteristics and contact size discrepancies.
Innovation Solution
The method involves forming fin spacers on semiconductor fins, recessing the fins to constrain epitaxial growth, and applying a cap layer to protect the epitaxial material during spacer removal, preventing lateral extension and merging of epitaxial material across adjacent fins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If epitaxial material is grown on densely-spaced fins without spacers, then the growth process is simple, but the epitaxial material merges across adjacent fins causing short circuits and increased resistance
Solution Approach 1:
The spacer structure is formed on the fins before the epitaxial growth process begins. This preliminary action constrains the epitaxial material during growth, preventing it from merging across adjacent fins. The spacer acts as a physical barrier that maintains separation between epitaxial layers on neighboring fins, thereby preventing short circuits while allowing the growth process to proceed
2Reliability
If spacers are used to constrain epitaxial growth, then merging is prevented, but the epitaxial material is damaged during spacer removal
Solution Approach 1:
A cap layer is deposited over the epitaxial material before spacer removal. This cap layer serves as a protective intermediary that shields the epitaxial material from damage during the spacer removal process. The cap layer absorbs mechanical stresses and prevents direct contact between removal tools and the fragile epitaxial structures, allowing spacer removal to proceed without compromising material integrity
Solution Approach 2:
The cap layer is applied in advance of the spacer removal operation, providing cushioning protection to the epitaxial material before any damaging forces are applied. This beforehand cushioning ensures that when spacers are removed, the epitaxial material is already protected and can withstand the mechanical stresses of the removal process without breaking or deforming
3Manufacturing precision
If fins are not recessed before epitaxial growth, then the process is simpler, but epitaxial material extends laterally and merges across fins
Solution Approach 1:
The fins are recessed below the spacer structure before the epitaxial growth process begins. This preliminary recessing action creates a depth difference that, combined with the spacer, forms a containment structure. The epitaxial material grows vertically on the recessed fin surfaces but is physically blocked from extending laterally by the spacer, ensuring precise growth control and preventing merging with adjacent fins
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 short circuits and ensures consistent fin height across regions of varying fin density, maintaining device functionality and reducing resistance by controlling epitaxial growth and protecting the epitaxial material during spacer removal.
Implementation Method 1
epitaxial material is formed on the recessed fin. The lateral extension of the epitaxial material is constrained by the fin spacer
Implementation Method 2
A cap layer is formed on the epitaxial material. The fin spacer is removed. The cap layer protects the epitaxial material during the removal of the fin spacer
Data Source
AI summary
A method includes forming at least one fin in a semiconductor substrate. A fin spacer is formed on at least a first portion of the at least one fin. The fin spacer has an upper surface. The at least one fin is recessed to thereby define a recessed fin with a recessed upper surface that it is at a level below the upper surface of the fin spacer. A first epitaxial material is formed on the recessed fin. A lateral extension of the first epitaxial material is constrained by the fin spacer. A cap layer is formed on the first epitaxial material. The fin spacer is removed. The cap layer protects the first epitaxial material during the removal of the fin spacer.