Wet Tungsten Atomic Layer Etching for Uniform Surface Removal
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Solution Overview
Problem
Existing etching processes for polycrystalline materials like tungsten result in non-uniform material removal and increased surface roughness due to differing etch rates at grain boundaries and crystal facets, which is problematic for precise semiconductor manufacturing.
Innovation Solution
A wet etching process using a first etch solution with an oxidizer in a non-aqueous solvent to form a self-limiting transition metal oxide passivation layer, followed by a second etch solution with a ligand to selectively dissolve the passivation layer without affecting the underlying metal, ensuring uniform etching and preserving surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional wet etching is used on polycrystalline tungsten, then material removal occurs, but surface roughness increases and etch uniformity deteriorates due to differing etch rates at grain boundaries and crystal facets
Solution Approach 1:
The etching process is divided into multiple sequential cycles, where each cycle consists of a surface modification step followed by a dissolution step. This segmentation allows precise control over material removal at the atomic layer level, achieving uniform etching while maintaining surface smoothness by removing material in controlled increments rather than a single aggressive etch step.
Solution Approach 2:
Before dissolution, the surface undergoes preliminary modification by forming a controlled oxide layer through exposure to oxygen or ozone. This preliminary action creates a uniform reactive layer that ensures consistent etch rates across different crystal facets and grain boundaries, preventing the roughening that occurs with direct etching of the metal surface.
2Productivity
If aggressive etchants are used to increase etch rate, then productivity improves, but manufacturing precision decreases due to non-uniform material removal
Solution Approach 1:
The etching process uses periodic cycling between surface modification and dissolution steps. Each cycle removes a controlled amount of material through oxidation followed by selective dissolution, allowing accumulation of etch depth over multiple cycles while maintaining uniformity. This periodic approach enables high overall etch rates without sacrificing precision.
Solution Approach 2:
The process changes chemical parameters between steps - using oxidizing conditions (oxygen or ozone exposure) to form the oxide layer, then switching to dissolving conditions (basic solution with ligands) to remove the oxide. This parameter change enables control over etch rate and uniformity independently, allowing optimization of both productivity and precision.
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 process achieves uniform etching of tungsten with minimal surface roughness, maintaining the initial surface quality and enabling precise control of etch amounts suitable for high-volume semiconductor manufacturing.
Implementation Method 1
exposing the surface of the substrate to a surface modification solution comprising an oxidizer dissolved in a non-aqueous solvent. The oxidizer reacts with the tungsten surface to oxidize the tungsten surface and form a tungsten oxide passivation layer
Implementation Method 2
exposing the surface of the substrate to a dissolution solution comprising a ligand to selectively remove the tungsten oxide passivation layer. The dissolution solution reacts with the tungsten oxide passivation layer to form soluble species
Data Source
AI summary
Various embodiments of methods are provided for etching tungsten in a wet ALE process. The methods disclosed herein use a wide variety of techniques and wet etch chemistries to: (a) oxidize a tungsten surface and form a self-limiting, tungsten oxide passivation layer in a surface modification step of the wet ALE process, and (b) selectively remove the tungsten oxide passivation layer in a dissolution step of the wet ALE process. In the embodiments disclosed herein, ligand-assisted dissolution is used to selectively remove the tungsten oxide passivation layer without removing the unmodified tungsten surface underlying the tungsten oxide passivation layer. The ligand added to the dissolution solution prevents the dissolution solution from attacking and removing the unmodified tungsten surface.