Isotropic Wet Etching of Copper Using Complexing Agents
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Solution Overview
Problem
Conventional wet copper etching techniques in semiconductor fabrication are anisotropic, leading to preferential etching in specific directions, surface roughening, and non-uniform removal, which is undesirable for semiconductor manufacturing where smooth and isotropic copper removal is required.
Innovation Solution
A method and apparatus for isotropic wet chemical etching using a substrate holder and nozzles to apply a peroxide-containing etching solution and a quenching solution, along with a pH-adjusted etching solution comprising complexing agents and oxidizers, to achieve uniform copper removal without surface roughening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional wet copper etching techniques are used, then copper removal efficiency is achieved, but surface roughening and non-uniform removal occur due to anisotropic etching
Solution Approach 1:
The patent modifies the chemical parameters of the etching solution by incorporating specific complexing agents (EDTA, DTPA, NTA) alongside oxidizing agents and buffers. This chemical parameter change transforms the etching mechanism from anisotropic to isotropic, enabling uniform copper removal in all directions while maintaining high etching rates, thus resolving the contradiction between removal efficiency and surface uniformity
Solution Approach 2:
The etching solution employs a composite chemical formulation combining multiple functional components: complexing agents (to control copper ion solubility and prevent precipitation), oxidizing agents (to drive the etching reaction), and buffers (to maintain pH stability). This composite approach synergistically achieves both high productivity and manufacturing precision that cannot be attained with single-component etchants
2Speed
If anisotropic etching is used for copper removal, then etching rate is improved in specific directions, but preferential etching of grain orientations leads to surface roughening
Solution Approach 1:
The patent changes the chemical environment parameters by introducing complexing agents that form stable soluble complexes with copper ions. This parameter change eliminates the grain boundary preference effect characteristic of anisotropic etching, as the complexing agents uniformly interact with copper surfaces regardless of grain orientation, thereby achieving both high etching speed and surface smoothness through isotropic removal
3Ease of manufacture
If conventional etching chemistries are used, then copper etching is achieved, but integration into semiconductor fabrication processes is limited due to non-uniform etching
Solution Approach 1:
The patent optimizes solution parameters including pH control (using buffers to maintain stable pH), temperature ranges, and component concentrations to achieve reproducible isotropic etching behavior. These controlled parameter changes enable consistent etching uniformity across different semiconductor fabrication processes, thereby improving ease of manufacture and process integration while maintaining manufacturing precision
Solution Approach 2:
The etching solution formulation is designed to be universally applicable to various copper structures and fabrication processes. The combination of complexing agents, oxidizing agents, and buffers creates a multi-functional solution that provides uniform etching across different copper grain structures, patterns, and device geometries, enhancing both process integration capability and etching 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 method enables efficient, isotropic removal of copper with high etch rates (up to 1000 Å/min) and maintains surface smoothness and reflectivity, reducing surface roughness and aspect ratios of features, thus improving semiconductor processing.
Implementation Method 1
The etching solution comprises a bidentate, tridentate or quadridentate complexing agent
Implementation Method 2
The etching solution comprises an oxidizer
Data Source
AI summary
Exposed copper regions on a semiconductor substrate can be etched by a wet etching solution comprising (i) one or more complexing agents selected from the group consisting of bidentate, tridentate, and quadridentate complexing agents; and (ii) an oxidizer, at a pH of between about 5 and 12. In many embodiments, the etching is substantially isotropic and occurs without visible formation of insoluble species on the surface of copper. The etching is useful in a number of processes in semiconductor fabrication, including for partial or complete removal of copper overburden, for planarization of copper surfaces, and for forming recesses in copper-filled damascene features. Examples of suitable etching solutions include solutions comprising a diamine (e.g., ethylenediamine) and/or a triamine (e.g., diethylenetriamine) as bidentate and tridentate complexing agents respectively and hydrogen peroxide as an oxidizer. In some embodiments, the etching solutions further include pH adjustors, such as sulfuric acid, aminoacids, and carboxylic acids.