Gate Metal Patterning for Nanosheet Devices via Selective Wet Etching
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Solution Overview
Problem
In the production of nanosheet semiconductor devices, especially in CMOS technology, there is a challenge in protecting the gate metal on one conductivity type while removing it from another, leading to uncontrolled excessive etching and damage to the underlying gate dielectric and channel semiconductor material.
Innovation Solution
A dual metal layer scheme is implemented, comprising an etch stop layer and a work function adjusting layer, where the etch stop layer is composed of a first metal nitride and the work function adjusting layer is composed of a second metal nitride, allowing for selective removal of the work function adjusting layer using wet etch chemistry that is selective to the etch stop layer, thereby protecting the gate dielectric and channel region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single metal layer is used for gate conductor, then the process is simple, but selective removal of gate metal for different conductivity types cannot be achieved
Solution Approach 1:
The gate metal layer is segmented into two distinct layers: a work function adjusting layer (first metal layer) and an etch stop layer (second metal layer). This segmentation allows the work function adjusting layer to be selectively removed for different conductivity types while the etch stop layer remains to protect the gate dielectric, thereby achieving selective removal capability without compromising structural integrity.
Solution Approach 2:
The etch stop layer acts as an intermediary between the work function adjusting layer and the gate dielectric. It provides a protective barrier that prevents direct contact between the etch chemistry and the gate dielectric during selective removal processes, enabling selective removal of the work function adjusting layer while protecting underlying structures.
2Ease of manufacture
If wet etch chemistry is used to remove gate metal, then the etching process is simple, but uncontrolled excessive etching damages the gate dielectric and channel material
Solution Approach 1:
The etch stop layer is deposited beforehand to establish a protective barrier before the selective removal process. This preliminary action ensures that when wet etch chemistry is applied, the etching is automatically halted at the etch stop layer interface, preventing uncontrolled excessive etching of the gate dielectric and channel material while maintaining process simplicity.
Solution Approach 2:
The etch stop layer serves as an intermediary that mediates between the etch chemistry and the gate dielectric. It allows the use of simple wet etch chemistry while preventing the harmful effects of uncontrolled etching by providing a defined stopping point that protects the underlying sensitive structures.
3Productivity
If the work function adjusting layer is completely removed for one conductivity type, then the gate metal can be fully replaced, but the gate dielectric edges become exposed and vulnerable to damage
Solution Approach 1:
The etch stop layer acts as a protective intermediary that remains after the work function adjusting layer is completely removed. It covers and protects the edges and upper sheet surface of the channel region, preventing exposure and damage to the gate dielectric while allowing complete removal of the work function adjusting layer for the desired conductivity type.
Solution Approach 2:
The work function adjusting layer is extracted (completely removed) for regions requiring one conductivity type, while the etch stop layer remains in place to provide protection. This selective extraction achieves complete gate metal replacement where needed while maintaining protective coverage through the etch stop layer.
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 prevents over-etching and damage to the gate dielectric and channel material, enabling precise processing of both n-type and p-type nanosheet devices on the same substrate without compromising the integrity of the gate structure.
Implementation Method 1
the etch stop layer has a composition that provides that the work function adjusting layer is removable by a wet etch chemistry that is selective to the etch stop layer
Data Source
AI summary
A method of forming gate structures to a nanosheet device that includes forming at least two stacks of nanosheets, wherein each nanosheet includes a channel region portion having a gate dielectric layer present thereon. The method may further include forming a dual metal layer scheme on the gate dielectric layer of each nanosheet. The dual metal layer scheme including an etch stop layer of a first composition and a work function adjusting layer of a second composition, wherein the etch stop layer has a composition that provides that the work function adjusting layer is removable by a wet etch chemistry that is selective to the etch stop layer.