Atomic Layer Etching of Refractory Metals for Smooth Etch Fronts
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Solution Overview
Problem
Existing etching processes, such as reactive ion etching, struggle to achieve smooth etch fronts and line edges for refractory metals and high surface binding energy materials, leading to increased resistivity and variability in semiconductor manufacturing.
Innovation Solution
The use of Atomic Layer Etch (ALE) processes, which involve a multi-step self-limiting reaction to achieve precise control over the etching of refractory metals like Mo, Ta, and Ru, resulting in smooth, conformal, and atomically thin etch profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching processes are used on refractory metals, then etching speed may be adequate, but the etch front and line edge smoothness deteriorates
Solution Approach 1:
The etching process is segmented into multiple sequential steps (modification step followed by etch step) rather than a single continuous process. This segmentation allows each step to be optimized independently - the modification step prepares the surface for smooth etching while the etch step removes material, resolving the contradiction between smoothness and speed
Solution Approach 2:
The etching process uses periodic cyclic steps alternating between modification and etching phases. This periodic action enables the surface to be repeatedly prepared and etched in controlled increments, achieving both smooth etch fronts and acceptable overall etching rates through multiple cycles
2Reliability
If conventional etching processes are used, then material removal may be sufficient, but selectivity to surrounding materials deteriorates
Solution Approach 1:
The modification step creates local chemical changes only on the refractory metal surface through targeted exposure to modification gases (O2, Cl2, or CF4). This local quality change enhances selectivity by making the refractory metal chemically distinct from surrounding materials, allowing selective etching while preserving material removal efficiency
Solution Approach 2:
The process changes chemical parameters by introducing specific modification gases that react with refractory metals to form modified surface layers. These parameter changes (chemical composition, surface energy) enable selective removal of refractory metals while maintaining efficiency through optimized etch conditions
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
ALE processes demonstrate the ability to achieve extremely smooth etch surfaces, often exceeding 50% root mean square (RMS) smoothing, while also providing high selectivity to surrounding materials, thereby enhancing the reliability and electrical performance of semiconductor devices.
Implementation Method 1
exposing the refractory metal surface to a modification gas to modify the surface and form a modified refractory metal surface
Implementation Method 2
exposing the modified refractory metal surface to a plasma to remove the modified refractory metal surface
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Etching a refractory metal or other high surface binding energy material on a substrate can maintain or increase the smoothness of the metal/high EO surface, in some cases produce extreme smoothing. A substrate having an exposed refractory metal/high EO surface is provided. The refractory metal/high EO surface is exposed to a modification gas to modify the surface and form a modified refractory metal/high EO surface. The modified refractory metal/high EO surface is exposed to an energetic particle to preferentially remove the modified refractory metal/high EO surface relative to an underlying unmodified refractory metal/high EO surface such that the exposed refractory metal/high EO surface after removing the modified refractory metal/high EO surface is as smooth or smoother than the substrate surface before exposing the substrate surface to the modification gas.