Atomic Layer Metal Etching for Smooth, Uniform Interconnect Features
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Solution Overview
Problem
Current semiconductor fabrication techniques, particularly the Damascene process for copper interconnects, face challenges in forming small copper features and achieving smooth surfaces due to preferential etching at grain boundaries, leading to increased resistivity and roughness.
Innovation Solution
The method involves atomic layer etching (ALE) of metal-containing layers by modifying a region of the surface with a modification gas and then selectively removing the modified region using an inert bombardment plasma, ensuring precise control over the etching process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If subtractive etching is used to form metal features, then the etching process can be performed, but wider features etch faster than narrower features leading to non-uniform etching
Solution Approach 1:
The etching process is divided into multiple sequential atomic layer etching cycles, where each cycle removes a controlled monolayer thickness. This segmentation of the etching process into discrete steps ensures uniform removal across features of varying widths, eliminating the loading effect where wider features etch faster than narrower ones.
Solution Approach 2:
The ALE process employs periodic alternating exposure to modification gas and inert bombardment plasma. This periodic action allows controlled surface modification followed by selective removal, achieving uniform etching across different feature sizes by resetting the etching conditions with each cycle.
2Manufacturing precision
If traditional etching is used on metal features, then etching can be performed, but sidewalls of metal features become too rough
Solution Approach 1:
The etching is performed in multiple sequential ALE cycles rather than a single continuous etch. Each cycle removes only a monolayer thickness, allowing the surface to remain smooth throughout the process. This segmented approach prevents the sidewall roughening that occurs in traditional high-rate etching methods.
Solution Approach 2:
The ALE process changes the etching parameters by using low-power plasma and controlled gas exposure times. These parameter changes enable slow, controlled removal of modified material, producing smooth sidewalls while maintaining acceptable productivity through process optimization.
3Manufacturing precision
If Damascene processing is used for copper interconnects, then copper features can be formed, but it becomes increasingly difficult to form small copper features as devices shrink
Solution Approach 1:
The patent extracts copper features directly from a blanket copper layer using ALE, eliminating the need for the multi-step Damascene process. This direct subtractive approach simplifies the fabrication process while enabling precise control of small feature dimensions through the self-limiting nature of ALE.
Solution Approach 2:
The complex chemical-mechanical processes of Damascene are replaced with a simplified physical-chemical ALE process. The ALE method uses controlled plasma modification and removal instead of multiple deposition, etching, and planarization steps, reducing process complexity while improving feature size control.
4Manufacturing precision
If subtractive etching is used on metals like molybdenum or ruthenium, then etching can be performed, but grain boundaries are preferentially etched leading to increased resistivity
Solution Approach 1:
The modification gas exposure preliminary alters the surface chemistry of the metal, creating a uniformly modified layer across the entire surface including grain boundaries. This preliminary action ensures that subsequent etching removes material uniformly from all regions, preventing preferential etching at grain boundaries and maintaining low resistivity.
Solution Approach 2:
The ALE process changes the surface chemistry parameters through modification gas exposure, transforming the metal surface into a state that etches uniformly. This parameter change in surface composition eliminates the grain boundary preferential etching that occurs in traditional methods, ensuring uniform surface morphology and consistent electrical properties.
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 approach allows for the formation of smooth surfaces and reduced line width roughness, achieving uniform etching across features of varying aspect ratios, thereby improving the effectiveness of metal interconnects in advanced semiconductor technology.
Implementation Method 1
exposing a surface of the metal containing layer to a modification gas, wherein adjacent to the modified metal containing region remains an unmodified metal containing region
Implementation Method 2
The modified metal containing region is selectively removed with respect to the unmodified metal containing region by exposing the surface of the metal containing layer to an inert bombardment plasma generated from an inert gas
Implementation Method 3
an inert bombardment plasma generated from an inert gas
Data Source
AI summary
A method for atomic layer etching a metal containing layer is provided. At least a region of a surface of the metal containing layer is modified to form a modified metal containing region by exposing a surface of the metal containing layer to a modification gas, wherein adjacent to the modified metal containing region remains an unmodified metal containing region. The modified metal containing region is selectively removed with respect to the unmodified metal containing region by exposing the surface of the metal containing layer to an inert bombardment plasma generated from an inert gas.