Wet Tungsten ALE Using Halogenation for Uniform Low-Roughness Etching
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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, particularly at grain boundaries, which is unsuitable for precise semiconductor manufacturing.
Innovation Solution
A wet etching process using a halogenation agent in a non-aqueous solvent to form a self-limiting tungsten halide passivation layer, followed by a selective dissolution step with an aqueous solution to maintain surface roughness, employing self-limiting reactions in both steps.
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
Solution Approach 1:
The etching process is segmented into two distinct sequential steps: (1) surface modification where tungsten is converted to tungsten oxide, and (2) selective removal where the oxide layer is dissolved. This segmentation allows each step to be optimized independently, achieving uniform material removal while maintaining surface smoothness.
Solution Approach 2:
The surface modification step is performed as a preliminary action before removal. By pre-converting the tungsten surface to tungsten oxide in a controlled manner, the subsequent removal step can proceed uniformly without causing surface roughness, as the modification creates a consistent layer across the polycrystalline surface.
2Productivity
If etching rate is increased for high productivity, then manufacturing efficiency improves, but control over etch precision deteriorates
Solution Approach 1:
By separating the etching process into modification and removal steps, each step can be optimized for its specific function. The modification step ensures uniform coverage, while the removal step provides precise control over the etch rate, allowing high productivity without sacrificing precision.
Solution Approach 2:
The process utilizes parameter changes between steps - the modification step operates under conditions that form a uniform oxide layer, while the removal step uses different conditions (aqueous solution) to dissolve the oxide at a controlled rate. This parameter switching enables both high etch rate and precise control.
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 precise and uniform etching of tungsten with minimal surface roughness, compatible with high-volume manufacturing and improved interface quality.
Implementation Method 1
The surface modification solution comprises a halogenation agent dissolved in a non-aqueous solvent. The halogenation agent reacts with the tungsten surface to form a tungsten halide passivation layer
Implementation Method 2
The dissolution solution reacts with the tungsten halide passivation layer to form soluble species, which are dissolved by the dissolution solution
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 wet etch chemistries to: (a) halogenate a tungsten surface and form a self-limiting, tungsten halide passivation layer in a surface modification step of the wet ALE process, and (b) selectively remove the tungsten halide passivation layer in a dissolution step of the wet ALE process. In the embodiments disclosed herein, a surface modification solution containing a halogenation agent dissolved in non-aqueous solvent is used to form a self-limiting, tungsten halide passivation layer, which is selectively removed in an aqueous dissolution solution via reactive dissolution/hydrolysis.