Wet Copper ALE Using Ligand Complexation for Monolayer Selectivity
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Solution Overview
Problem
Conventional etching techniques for copper in semiconductor manufacturing lack atomic layer control and selectivity, particularly for sub-32 nm back end of the line (BEOL) Cu lines and sub-100 nm Cu bond pads, due to aggressive oxidants used in self-limiting oxidation steps, which result in poor copper recess control and uniformity.
Innovation Solution
A wet atomic layer etching (ALE) process using a cyclical method with a complexation step involving a carboxylate-based ligand and a dissolution step with an aqueous base, such as ammonium hydroxide, to selectively remove copper oxalate layers without etching the underlying copper metal, allowing for precise control and high selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching techniques are used for copper, then etching speed is maintained, but manufacturing precision and surface finish deteriorate due to lack of atomic layer control
Solution Approach 1:
The etching process is segmented into multiple sequential steps: oxidation step to form copper oxide, complexation step to form ligand-metal complex, and dissolution step to remove the complex. Each step is self-limiting and contributes to precise atomic layer control, transforming a single aggressive etch into controlled sequential operations
Solution Approach 2:
The patent employs periodic cyclic etching operations where the substrate undergoes repeated cycles of oxidation, complexation, and dissolution. Each cycle removes a controlled monolayer of copper, enabling precise depth control through the number of cycles performed, thereby achieving atomic layer precision
2Manufacturing precision
If aggressive oxidants are used to etch copper, then etching rate is maintained, but surface roughness increases and uniformity deteriorates
Solution Approach 1:
The patent changes chemical parameters by using mild oxidants (oxygen plasma or hydrogen peroxide) instead of aggressive oxidants, controlling oxidation to form only a thin surface layer of copper oxide. This parameter change enables uniform surface treatment without the roughening effects of aggressive chemistry
Solution Approach 2:
The etching process applies different chemical treatments to different depths: mild oxidation only at the surface to form a thin oxide layer, followed by selective complexation and dissolution. This local quality approach ensures uniform surface treatment while preventing subsurface damage and maintaining overall surface uniformity
3Manufacturing precision
If conventional wet etching is used, then process simplicity is maintained, but selectivity and atomic layer control are lost
Solution Approach 1:
The patent introduces a ligand-metal complex as an intermediary species between the copper oxide and the final dissolved copper. The complexing agent forms a stable complex with copper ions that can be selectively dissolved, enabling precise control of material removal while maintaining process selectivity
Solution Approach 2:
Each step in the etching process is self-limiting: oxidation stops when the copper oxide layer is formed, complexation stops when the ligand-metal complex is complete, and dissolution stops when the complex is removed. This self-service nature of each step enables precise atomic layer control without requiring complex external control mechanisms
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 sub-nanometer control of copper pad recesses with high selectivity to dielectric materials, providing atomic level etch control and uniformity, suitable for small feature sizes, and eliminates issues like seams and keyholes in three-dimensional interconnects.
Implementation Method 1
a complexation step, which involves exposing the surface of the substrate to a complexation solution comprising a complexing agent to bind the complexing agent to the oxidized copper surface layer and form a complex-bound oxidized copper surface layer
Implementation Method 2
a dissolution step, which involves selectively removing the complex-bound oxidized copper surface layer from the copper metal layer
Implementation Method 3
the dissolution solution may react with the copper metal layer to re-oxidize the copper metal layer and form a new oxidized copper surface layer
Data Source
AI summary
The present disclosure provides a new wet atomic layer etch (ALE) process for etching copper. More specifically, the present disclosure provides various embodiments of methods that utilize new etch chemistries for etching copper in a wet ALE process. By utilizing the new etch chemistries disclosed herein within a wet ALE process, the present disclosure provides a highly selective etch of copper with monolayer precision.