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The GAAFET Fabrication Process

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • GAAFET is more promising than FinFET; the latter faces issues with mobility and variability when the fin width nears 5nm.

  • GAAFETS are based on either nanosheets or nanowires.

  • GAAFETs are used in high-performance computing, memory modules, mobile phones, and Internet-of-Things applications.

GAAFET is the improved version of FinFET

GAAFET is the improved version of FinFET

Multi-gate devices were introduced as a solution to increasing fabrication costs and variabilities that hindered CMOS semiconductor technology scaling. Some popular multi-gate devices include FinFETs and GAAFETs.

Multi-gate devices have specific geometry that provide improved control over the transistor channel. GAAFETs are more promising than FinFETs; the latter faces issues with mobility and variability when the fin width nears 5nm. Below 5 nm, GAAFETs can replace FinFETs, as they offer high performance with gates all around.

The GAAFET fabrication process is more complex than FinFET fabrication. Let’s explore why that is. 

The GAAFET Fabrication Process

The GAAFET fabrication process is all about layering silicon and silicon-Germanium (SiGe) alternately into pillar-like patterns. The process differs slightly depending on whether you are using a nanosheet GAAFET or a nanowire GAAFET.

Nanosheet GAAFET Fabrication Process

Process

Explanation

Create SiGe heterostructure

The process is similar to any heterostructure creation in other semiconductor devices.

Pillar patterning

The pillars in GAAFET are analogous to fins in FinFET, which is why the patterning is similar to the fin.

Make an indentation in the SiGe layer

The indentation in SiGe provides space between the source and drain – generally called an inner spacer. The space will later be occupied by the gate. The source and drain are deposited near the gate and pillar. 

Remove SiGe

Remove SiGe through etching (since the inner spacers are fixed).

Deposit the gate dielectric

Deposit the gate dielectric using the atomic layer deposition method. 

Metallize areas between silicon nanosheets

Metallize spaces between nanosheets using atomic layer deposition. 

Nanowire GAAFET Fabrication Process

Process

Explanation

Form landing pads

Form two landing pads on a substrate. 

Form and suspend nanowires

Horizontally suspend nanowires on landing pads once they are formed.

Pattern gates

Pattern multiple vertically aligned gates on the suspended nanowires. 

Cut silicon nanowires

Cut silicon nanowires outside the gates after spacers are formed. 

Grow in-situ doped silicon epitaxial

Grow in-situ doped silicon epitaxially on the edges of the silicon nanowire, which is exposed due to the spacer.  

Form contacts and interconnections

Establish silicide and nickel-based contacts and copper-based interconnections. 

GAAFET Fabrication Process Challenges 

The finFET manufacturing process reaches a roadblock when the fin width approaches 5 nm or less. In most FinFETs, there is only one fin, and the average of the fins can be not greater than two. FinFET functionality is limited; GAAFET offers more functionality, better performance, curred leakage, greater speed, and less power consumption because of the stacked nanosheets or nanowires.

However, the introduction of nanosheets and nanowires adds complexity to the GAAFET fabrication process. It is challenging to epitaxially grow stacked nanowires; the process involves growing Si-GE sacrificial layers between the silicon channel layers. Another challenge is etching the fin structure before selectively removing the Si-Ge layers.

Even though the GAAFET fabrication process is more complex than FinFET fabrication, there is no limit to its usage in high-performance computing, memory modules, mobile phones, Internet-of-things applications, etc.

Cadence software can help you design GAAFET-based integrated circuits. Leading electronics providers rely on Cadence products to optimize power, space, and energy needs for a wide variety of market applications. If you’re looking to learn more about our innovative solutions, talk to our team of experts or subscribe to our YouTube channel.