Lateral Silicon Etching With Pulsed Passivation for GAA Indents
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Solution Overview
Problem
Conventional methods for lateral etching in nanosheet/nanowire transistor fabrication face challenges such as poor etch selectivity, pitting, and surface roughness, which hinder the formation of precise indents between nanosheets in gate-all-around (GAA) devices.
Innovation Solution
A plasma processing method involving a passivation phase and an etch phase, where a fluorine agent is pulsed within a nitrogen and hydrogen plasma to dynamically control the etching process, forming passivation layers that protect nanosheets while selectively etching sacrificial layers, thereby improving etch selectivity and surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to laterally etch Si layers, then the etching process can be completed, but poor etch selectivity and surface roughness occur
Solution Approach 1:
The patent applies periodic action by alternating between etching steps and passivation steps in a cyclic manner. During etching steps, fluorine-based plasma selectively removes Si layers, and during passivation steps, the plasma is adjusted to protect SiGe layers by forming a protective oxide layer. This periodic alternation enables precise control over etch selectivity and surface quality that cannot be achieved with continuous etching methods.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting plasma composition, power levels, and gas flow rates between etching and passivation phases. The etching phase uses fluorine-containing gases with specific power settings, while the passivation phase modifies these parameters to promote oxide formation on SiGe surfaces. These parameter transitions enable selective etching while maintaining surface integrity.
2Manufacturing precision
If conventional etching methods are used to form indents between nanosheets, then the indents can be formed, but pitting and poor surface quality occur
Solution Approach 1:
The periodic alternation between etching and passivation prevents pitting by continuously protecting exposed surfaces during the etching process. The passivation steps deposit protective oxide layers on SiGe surfaces before they can be damaged by prolonged plasma exposure, thereby eliminating pitting while maintaining precise indent formation between nanosheets.
Solution Approach 2:
The passivation steps serve as beforehand cushioning by pre-forming protective oxide layers on SiGe surfaces before they are exposed to aggressive etching plasma. This protective layer acts as a cushion that prevents direct plasma-surface interaction that would cause pitting, while still allowing the etching process to proceed on exposed Si surfaces.
3Productivity
If continuous plasma etching is used, then the etching speed is maintained, but selectivity between Si and SiGe layers deteriorates
Solution Approach 1:
The periodic alternation between etching and passivation phases resolves the selectivity-speed contradiction by concentrating etching activity into brief, intense pulses followed by protective passivation periods. During etching pulses, high fluorine concentration enables fast Si removal, while subsequent passivation pulses protect SiGe surfaces. This time-separated approach maintains high average etching speed while ensuring excellent selectivity through repeated protection cycles.
Solution Approach 2:
The patent employs parameter changes by switching plasma composition and power levels between etching and passivation modes. Etching mode uses fluorine-rich plasma with parameters optimized for high Si etch rates, while passivation mode adjusts parameters to promote selective oxide formation on SiGe. These parameter transitions enable the process to achieve both high productivity and high selectivity by optimizing conditions for each specific phase.
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 enables the formation of indents between SiGe layers with enhanced selectivity and reduced surface roughness, addressing the limitations of conventional etching techniques and facilitating the fabrication of GAA devices with improved performance.
Implementation Method 1
applying power to a source electrode and a bias electrode of the plasma processing chamber to generate a plasma in the plasma processing chamber
Implementation Method 2
exposing the substrate to the plasma to laterally etch a portion of the Si layers selectively to the SiGe layers
Implementation Method 3
forming passivation layers on surfaces of the SiGe layers, the surfaces including the exposed sidewalls of the SiGe layers
Data Source
AI summary
A method of processing a substrate that includes: positioning a substrate in a plasma processing chamber, the substrate including a layer stack of alternating layers of silicon (Si) layers and silicon-germanium (SiGe) layers, the substrate including a recess that exposes sidewalls of the Si layers and sidewalls of the SiGe layers; flowing a first process gas into the plasma processing chamber; while flowing the first process gas, pulsing a second process gas into the plasma processing chamber at a pulsing frequency; while flowing the first process gas and pulsing the second process gas, applying power to a source electrode and a bias electrode of the plasma processing chamber to generate a plasma in the plasma processing chamber; and exposing the substrate to the plasma to laterally etch a portion of the Si layers selectively to the SiGe layers and form indents between the SiGe layers.