Oxygen Vacancy Passivation in Vertical Transport FETs
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Solution Overview
Problem
The continued scaling of vertical transport field effect transistors (VFETs) is restricted due to the increase in p-type FET threshold voltage caused by the thermal budget required for downstream processing steps, which affects device performance.
Innovation Solution
A bilayer bottom spacer is used in VFET fabrication, where the high-k film in pFET regions extends to the outside of the work function metal gate, and the oxygen-donating SiO2 layer provides oxygen to passivate oxygen vacancies in the high-k film, while in nFET regions, the high-k film only contacts the non-oxygen donating dielectric material, thereby controlling the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal budget is increased for downstream processing steps, then device performance is improved, but pFET threshold voltage increases
Solution Approach 1:
The patent applies different dielectric materials with distinct oxygen-donating properties to different device regions. Oxygen-donating dielectric material is used in pFET regions to passivate oxygen vacancies and reduce threshold voltage, while non-oxygen-donating dielectric material is used in nFET regions to maintain higher threshold voltage. This local differentiation resolves the contradiction by allowing thermal processing to benefit device performance without causing unwanted threshold voltage shifts in specific device types.
Solution Approach 2:
The oxygen-donating dielectric material acts as an intermediary that mediates the interaction between thermal processing and the high-k dielectric film. During downstream thermal processing steps, this intermediary material donates oxygen to passivate oxygen vacancies in the high-k dielectric, thereby preventing the harmful increase in pFET threshold voltage while still allowing the thermal budget to improve overall device performance.
2Reliability
If high-k dielectric film is used to improve device performance, then device performance is enhanced, but oxygen vacancies are generated affecting threshold voltage
Solution Approach 1:
The oxygen-donating dielectric material is positioned adjacent to the high-k dielectric film before downstream processing steps occur. This preliminary arrangement ensures that when thermal processing is applied, oxygen is already available from the adjacent dielectric material to passivate any oxygen vacancies that form in the high-k dielectric film, thereby maintaining precise threshold voltage control while still achieving performance enhancement.
Solution Approach 2:
The patent converts the potentially harmful effect of oxygen vacancy formation in high-k dielectric films into a beneficial outcome. By positioning oxygen-donating dielectric material adjacent to the high-k dielectric, the oxygen vacancies that form during thermal processing are immediately passivated by oxygen donation from the adjacent material. This transforms the harmful oxygen vacancy formation into a controlled process that ultimately improves device performance without compromising threshold voltage control.
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 reduces pFET threshold voltages and maintains higher nFET threshold voltages, mitigating the increase in pFET threshold voltage resulting from downstream process flows, thus enhancing device performance.
Implementation Method 1
the oxygen-donating SiO2 layer provides oxygen to passivate oxygen vacancies in the high-k film
Data Source
AI summary
Embodiments of the present invention are directed to fabrication method and resulting structures for vertical tunneling field effect transistors (VFETs) having an oxygen vacancy passivating bottom spacer. In a non-limiting embodiment of the invention, a first semiconductor fin is formed in a first region of a substrate and a second semiconductor fin is formed in a second region of the substrate. A bilayer bottom spacer is formed in direct contact with sidewalls of the semiconductor fins. The bilayer bottom spacer includes a first layer and an oxygen-donating second layer positioned on the first layer. A first dielectric film is formed on the sidewalls of the first semiconductor fin. The first dielectric film terminates on the first layer. A second dielectric film is formed on the sidewalls of the second semiconductor fin. The second dielectric film extends onto a surface of the oxygen-donating second layer.