Inner Spacer Formation With Dual-Step Etch-Back in Nanosheet Devices
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Solution Overview
Problem
The formation of inner spacers in nanosheet devices is complicated by material diffusion from sacrificial layers into channel layers, leading to imperfect etching and curved spacer profiles, which can result in damage to source/drain structures due to incomplete protection.
Innovation Solution
A dual-step etch-back process is employed to form robust inner spacers, where sacrificial layers are recessed using a first etch to create curved recesses, dielectric plugs are formed to protect the sacrificial material, and a second etch trims the sacrificial material tails, preventing etchant access to source/drain structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single etch-back process is used to remove sacrificial material, then the process is simple and fast, but the inner spacer profile becomes curved and non-uniform due to material diffusion
Solution Approach 1:
The single etch-back process is divided into two sequential etching steps: a first etch that removes the bulk of the sacrificial material, and a second etch that completes the removal. This segmentation allows each step to be optimized independently, preventing the curved profile issue while maintaining overall efficiency.
Solution Approach 2:
Before the final etch-back, dielectric plugs are deposited into the recesses to protect the channel material interfaces. This preliminary protective action prevents etchant from attacking the channel material during the second etch step, ensuring a flat, uniform inner spacer profile.
2Loss of substance
If the sacrificial material is etched back completely, then no sacrificial material remains, but etchant reaches and damages the source/drain structures causing voids
Solution Approach 1:
Inner spacers are formed as intermediary structures between the sacrificial material and the source/drain regions. These spacers act as protective barriers that prevent etchant from reaching and damaging the source/drain structures during the sacrificial material removal process.
Solution Approach 2:
The inner spacers are formed before the complete removal of sacrificial material. This preliminary formation ensures that protective structures are in place before the etchant could potentially damage the source/drain regions.
3Manufacturing precision
If the inner spacer is formed with uniform thickness, then protection is consistent, but the etching process becomes complex due to material diffusion
Solution Approach 1:
The etching process is segmented into two steps with different objectives: the first step removes the majority of sacrificial material, and the second step is a controlled, protected etch that achieves uniform thickness. This segmentation simplifies the complexity management by breaking down the challenging single step into two more manageable steps.
Solution Approach 2:
Dielectric plugs serve as intermediaries that protect the channel material interfaces during the second etch step. This protection allows for a more controlled and uniform etching process, achieving consistent inner spacer thickness without excessive process complexity.
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 formation of inner spacers without substantial thinning at the top and bottom, providing superior protection for source and drain regions during sacrificial layer removal, preventing voids and ensuring structural integrity.
Implementation Method 1
recessing sacrificial layers in a stack of alternating sacrificial layers and channel layers using a first etch to form curved recesses
Implementation Method 2
The tails of sacrificial material are etched back using a second etch to expand the recesses
Implementation Method 3
The sacrificial layers are etched away after forming the inner spacers, using a third etch that does not form voids in the source/drain structures
Data Source
AI summary
Semiconductor devices and methods of forming the same include recessing sacrificial layers in a stack of alternating sacrificial layers and channel layers using a first etch to form curved recesses at sidewalls of each sacrificial layer in the stack, with tails of sacrificial material being present at a top and bottom of each curved recess. Dielectric plugs are formed that each partially fill a respective curved recess, leaving exposed at least a portion of each tail of sacrificial material. The tails of sacrificial material are etched back using a second etch to expand the recesses. Inner spacers are formed in the expanded recesses.