Atomic Layer Etching of Silicon Oxide Using CF4 and H2 Plasmas
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Solution Overview
Problem
As semiconductor geometries shrink, achieving desired control over ion energy, ion flux, and radical flux in plasma etching becomes challenging, leading to difficulties in etch selectivity, profile, and uniformity, particularly for oxide layers.
Innovation Solution
An atomic layer etching (ALE) process using a fluorinated hydrocarbon plasma, such as CF4, for surface modification followed by a hydrogen plasma for removal, creating a silicon-rich surface layer that can be incrementally etched, allowing for precise control over oxide layer thickness reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching is used to etch oxide layers, then etching can be performed, but control over ion energy, ion flux, and radical flux becomes difficult as geometries shrink, leading to poor etch selectivity, profile, and uniformity
Solution Approach 1:
The etching process is segmented into two distinct sequential steps: (1) a surface modification step using fluorinated hydrocarbon plasma to create a silicon-rich surface layer, and (2) a removal step using hydrogen plasma to etch the modified layer. This segmentation allows independent optimization of each step's parameters, improving control over ion energy, ion flux, and radical flux separately, thereby achieving better etch selectivity and uniformity without increasing overall process complexity.
2Manufacturing precision
If plasma processing parameters are adjusted to improve etch control, then etch performance may improve, but achieving sufficient control over ion energy, ion flux, and radical flux remains unsatisfactory for desired etch results
Solution Approach 1:
The invention changes the fundamental parameters of the etching process by using two different plasma chemistries with distinct roles. The fluorinated hydrocarbon plasma (e.g., CF4) provides surface modification with specific radical and ion characteristics, while the hydrogen plasma provides selective removal with different ion energy and flux characteristics. This parameter change enables sufficient control over ion energy, ion flux, and radical flux that cannot be achieved by merely adjusting parameters within a single plasma chemistry, while maintaining process adaptability through the modular two-step structure.
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
The two-step ALE process provides improved etch selectivity and uniformity, enabling effective reduction of silicon oxide layers in various substrate processes like self-aligned contact etch and oxide spacer trim, while maintaining control over etch rates and profiles.
Implementation Method 1
The ALE modification step includes the use of a fluorinated hydrocarbon such as a carbon tetrafluoride (CF4) based plasma
Implementation Method 2
This modification step preferentially removes oxygen from the surface of the silicon oxide, providing a modified surface layer
Implementation Method 3
The ALE removal step includes the use of a hydrogen (H2) based plasma
Implementation Method 4
This removal step removes the silicon enriched layer formed in the modification step
Data Source
AI summary
In one exemplary embodiment, described herein is an ALE process for etching an oxide. In one embodiment, the oxide is silicon oxide. The ALE modification step includes the use of a carbon tetrafluoride (CF4) based plasma. This modification step preferentially removes oxygen from the surface of the silicon oxide, providing a silicon rich surface. The ALE removal step includes the use of a hydrogen (H2) based plasma. This removal step removes the silicon enriched monolayer formed in the modification step. The silicon oxide etch ALE process utilizing CF4 and H2 steps may be utilized in a wide range of substrate process steps. For example, the ALE process may be utilized for, but is not limited to, self-aligned contact etch steps, silicon fin reveal steps, oxide mandrel pull steps, oxide spacer trim, and oxide liner etch.