WF6 Plasma Etch Selectivity for High Aspect Ratio Features
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Solution Overview
Problem
The semiconductor industry faces challenges in etching high aspect ratio features in dielectric material with high selectivity relative to mask materials, often resulting in capping issues and limited feature depth due to tradeoffs between selectivity and capping during the etching process.
Innovation Solution
A method involving the use of a capacitively coupled plasma with a plasma generating gas containing WF6, fluorocarbons, and oxygen, where WF6 dissociates into tungsten-containing and fluorine-containing fragments, preferentially attaching to the feature sidewalls and bottom, respectively, to enhance etch selectivity without increasing capping, allowing for deeper feature formation with thinner mask layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to increase etch selectivity, then mask layer protection is improved, but feature depth is limited due to capping
Solution Approach 1:
The patent changes the chemical parameters of the etching process by introducing WF6 (tungsten hexafluoride) as a plasma generating gas. This chemical parameter change modifies the etching chemistry to achieve superior selectivity without the capping limitation that plagues conventional methods, enabling deeper feature formation while maintaining mask integrity
Solution Approach 2:
The patent uses a composite plasma chemistry approach by combining WF6 with fluorocarbon gases. This composite approach leverages the high selectivity of WF6-based chemistry while the fluorocarbon components provide protective effects, achieving both deep etching and mask protection simultaneously
2Length of moving object
If conventional etching methods are used to increase feature depth, then etch rate is improved, but mask layer integrity deteriorates due to reduced selectivity
Solution Approach 1:
By changing the plasma generating gas to include WF6, the patent achieves a fundamental shift in etching chemistry that provides high selectivity (at least 3.0:1) even at the high etch rates required for deep feature formation. This parameter change decouples the trade-off between etch rate and selectivity that limits conventional methods
3Length of moving object
If mask layer thickness is reduced to allow deeper features, then feature depth potential is improved, but mask protection capability worsens
Solution Approach 1:
The patent changes the etching chemistry parameters to WF6-based plasma, which provides such high selectivity that thinner mask layers can be used without compromising protection capability. The enhanced chemistry compensates for reduced mask thickness, enabling deeper features while maintaining adequate mask integrity
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 improves etch selectivity and allows for the formation of deeper features without capping, using less mask material and maintaining the mask integrity, thus overcoming the limitations of traditional etching methods.
Implementation Method 1
the plasma is generated from a plasma generating gas including WF6, one or more fluorocarbons, and oxygen (O2)... where the plasma is a capacitively coupled plasma generated at an excitation frequency between about 13-169 MHz
Implementation Method 2
WF6 dissociates into tungsten-containing and fluorine-containing fragments, and the tungsten-containing fragments may preferentially attach to upper sidewalls of the feature compared to lower sidewalls of the feature, and the fluorine-containing fragments may travel to the bottom of the feature to further etch the feature
Implementation Method 3
exposing the substrate to a plasma in the reaction chamber to thereby etch the feature in the dielectric material on the substrate... a selectivity of the etch is at least about 3.0, the selectivity being defined as an etch rate of the silicon oxide divided by an etch rate of the mask layer
Data Source
AI summary
Various embodiments herein relate to methods and apparatus for etching a feature in a substrate. Often, the feature is etched in the context of forming a DRAM device. The feature is etched in dielectric material, which often includes silicon oxide. The feature is etched using chemistry that includes WF6. Although WF6 is commonly used as a deposition gas (e.g., to deposit tungsten-containing film), it can also be used during etching. Advantageously, the inclusion of WF6 in the etch chemistry can increase the etch rate of the dielectric material, as well as increase the selectivity of the etch. Unexpectedly, these benefits can be realized without any increase in capping.