Anisotropic Tungsten Etching via Cl2 Plasma and Oxygen Passivation
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Solution Overview
Problem
Current methods for anisotropic etching of tungsten-containing materials on semiconductor substrates, particularly in the presence of dielectric materials like silicon oxide and silicon nitride, are limited, making it difficult to selectively remove tungsten from the bottom of recessed features without affecting the sidewalls.
Innovation Solution
A method involving a plasma etching process using Cl2 as a first process gas to react with tungsten-containing material, followed by oxygen radical passivation, with a high electrical bias applied to the substrate to ensure directional etching, allowing for the selective and anisotropic removal of tungsten-containing material from the bottom of recessed features while preserving the width of the features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used, then tungsten can be removed from the bottom of recessed features, but the etching lacks selectivity and anisotropy, causing horizontal etching that affects sidewall width
Solution Approach 1:
The etching process is segmented into multiple sequential steps with different gas compositions and bias conditions. Each step targets specific aspects of tungsten removal, with alternating high-bias and low-bias phases that create directional etching patterns while preserving sidewalls through selective passivation periods.
Solution Approach 2:
The patent employs periodic alternation between high-bias etching phases and low-bias passivation phases. This periodic action creates cycles of aggressive vertical etching followed by gentle sidewall protection, achieving high anisotropy through rhythmic application of contrasting process conditions.
2Manufacturing precision
If high electrical bias is applied to achieve directional etching, then anisotropy is improved, but the process complexity and control difficulty increase
Solution Approach 1:
The process dynamically adjusts bias voltage and gas composition in real-time during etching cycles. The bias transitions from high to low and gas compositions change between chlorine-rich and oxygen-rich phases, creating a dynamic control system that adapts process conditions to achieve precise anisotropic etching while managing complexity through automated sequencing.
3Manufacturing precision
If selective anisotropic etching is achieved through multiple process steps, then manufacturing precision is improved, but productivity decreases due to longer processing time
Solution Approach 1:
The etching process maintains continuous useful action by eliminating idle transition periods between steps. The alternating high-bias and low-bias phases are seamlessly connected with gas composition changes occurring during active etching, ensuring that every phase contributes to either material removal or sidewall protection without wasted time, thereby maintaining high productivity despite multiple process steps.
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 effectively removes large amounts of tungsten-containing material from the bottom of recessed features with high selectivity and anisotropy, maintaining the width of the features and achieving higher etch rates compared to conventional methods, especially in high aspect ratio features.
Implementation Method 1
introducing a first process gas comprising Cl2 to the plasma etching process chamber and forming a plasma to react the tungsten-containing material with a plasma-activated chlorine
Implementation Method 2
react the tungsten-containing material with a plasma-activated chlorine
Implementation Method 3
forming a plasma comprising oxygen radicals to passivate a surface of the tungsten-containing material
Data Source
AI summary
Methods for anisotropically etching a tungsten-containing material (such as doped or undoped tungsten metal) include cyclic treatment of tungsten surface with Cl2 plasma and with oxygen-containing radicals. Treatment with chlorine plasma is performed while the substrate is electrically biased resulting in predominant etching of horizontal surfaces on the substrate. Treatment with oxygen-containing radicals passivates the surface of the substrate to etching, and protects the vertical surfaces of the substrate, such as sidewalls of recessed features, from etching. Treatment with Cl2 plasma and with oxygen-containing radicals can be repeated in order to remove a desired amount of material. Anisotropic etching can be performed selectively in a presence of dielectric materials such as silicon oxide, silicon nitride, and silicon oxynitride.