Wet Molybdenum ALE Using Ligand-Limited Oxide Passivation
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Solution Overview
Problem
Existing wet etch chemistries for molybdenum result in rough post-etch surfaces due to differential etch rates at grain boundaries, leading to poor surface morphology and device performance issues.
Innovation Solution
A wet etch process using a first etch solution with an oxidizer and polydentate ligand in an aqueous solvent forms a self-limiting molybdenum oxide passivation layer, followed by a second etch solution to selectively dissolve this layer without affecting the underlying molybdenum, ensuring uniform etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional wet etch chemistries are used for molybdenum, then etching can proceed, but surface roughness increases due to differential etch rates at grain boundaries
Solution Approach 1:
The etching process is divided into multiple sequential cycles, each consisting of a surface modification step followed by a removal step. This segmentation allows precise control over the etching mechanism, enabling uniform material removal while maintaining surface smoothness by addressing the entire surface uniformly in each cycle rather than allowing differential etching at grain boundaries
Solution Approach 2:
Before the actual etching/removal occurs, a surface modification step is performed that uniformly alters the entire molybdenum surface. This preliminary modification ensures that subsequent removal affects the entire surface uniformly, preventing the differential etching that causes roughness while maintaining controlled etch rates
2Loss of substance
If conventional wet etching is used, then material removal occurs, but etch uniformity across the wafer deteriorates
Solution Approach 1:
The etching process employs periodic cyclic operations where the substrate is repeatedly exposed to surface modification and removal steps. This periodic action ensures uniform etching across the entire wafer surface by systematically treating all areas through multiple cycles, achieving both complete material removal and homogeneous etch distribution
Solution Approach 2:
The self-limiting nature of the surface modification step provides inherent feedback control, where the modification reaction naturally terminates when a monolayer is formed, preventing over-etching and ensuring uniform material removal across the wafer while maintaining precise control over etch depth and uniformity
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 a smooth post-etch surface with controlled etch rates, improving device performance by reducing surface roughness and enhancing wafer-scale uniformity.
Implementation Method 1
The oxidizer reacts with the molybdenum surface to oxidize the molybdenum surface and form a molybdenum oxide passivation layer
Implementation Method 2
The polydentate ligand binds to the molybdenum oxide passivation layer to form a surface species that is insoluble in the aqueous solvent
Implementation Method 3
The dissolution solution reacts with the molybdenum oxide passivation layer to form soluble species that are dissolved by the dissolution solution
Data Source
AI summary
Methods are provided for etching molybdenum in a wet ALE process. The methods disclosed herein use a wide variety of techniques and wet etch chemistries to oxidize a molybdenum surface and form a self-limiting, molybdenum oxide passivation layer in a surface modification step of the wet ALE process. In the wet ALE processes and methods disclosed herein, self-limiting behavior is provided in the oxidation step by adding a polydentate ligand to an aqueous oxidizing solution. The polydentate ligand reacts with and binds to the oxidized molybdenum surface to form a stable, ligand-molybdenum oxide complex, which is insoluble within the aqueous oxidizing solution. The insolubility of the ligand-molybdenum complex in the aqueous oxidizing solution provides self-limiting behavior in the oxidation step. After forming the molybdenum oxide passivation layer, the passivation layer is selectively removed in a dissolution step of the wet ALE process to etch the molybdenum surface.