Molybdenum Atomic Layer Etching for Uniform High-Aspect Features
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Solution Overview
Problem
Existing etching techniques for molybdenum in semiconductor fabrication lack precision and control, particularly in isotropic and directional etching, leading to non-uniformity and aspect ratio-dependent etching issues in high aspect ratio features.
Innovation Solution
A method involving sequential exposure of a molybdenum layer to an oxygen-containing reactant for oxidation, followed by boron trichloride to convert molybdenum oxide to volatile molybdenum oxychloride, and then removal with a fluorine-containing reactant, allowing for controlled etching of atomic layers with each cycle, suitable for isotropic or directional etching as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching techniques (RIE, wet etching) are used for molybdenum, then etching can be performed, but manufacturing precision and uniformity deteriorate due to lack of atomic-level control and aspect ratio-dependent etching
Solution Approach 1:
The etching process is segmented into three distinct sequential steps: (1) oxidation of molybdenum to molybdenum oxide, (2) conversion of molybdenum oxide to volatile molybdenum oxychloride, and (3) removal of boron oxide byproduct. Each step is independently controlled with specific reactants and parameters, enabling atomic-level precision while managing process complexity through modular design
Solution Approach 2:
The etching process employs periodic cyclic action where the three-step sequence is repeated multiple times to achieve the desired total etch depth. Each cycle removes a controlled amount of material (e.g., 1-3 nm per cycle), allowing cumulative precision control for deep high aspect ratio features while maintaining uniformity throughout the etch process
2Manufacturing precision
If conventional etching is used for high aspect ratio features, then etching can proceed, but uniformity deteriorates due to aspect ratio-dependent etching
Solution Approach 1:
The oxidation step is performed as a preliminary action before conversion, forming a uniform molybdenum oxide layer across the entire substrate surface including deep high aspect ratio features. This preliminary oxidation ensures that subsequent conversion and removal steps act uniformly on all surfaces, eliminating aspect ratio-dependent etching while maintaining high productivity through efficient volatile byproduct formation
Solution Approach 2:
The process utilizes parameter changes by transitioning between different chemical states and reaction conditions: oxidation conditions (oxygen plasma/gas at specific temperature and pressure), conversion conditions (boron trichloride exposure), and cleaning conditions (fluorine-containing reactant). These parameter changes enable uniform etching across high aspect ratio features while optimizing the overall etching rate
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
Enables precise and uniform etching of molybdenum with atomic-level control, suitable for high aspect ratio features, reducing non-uniformity and aspect ratio-dependent etching, particularly beneficial for 3D NAND structure fabrication.
Implementation Method 1
exposing the semiconductor substrate to an oxygen-containing reactant to oxidize at least a portion of the molybdenum layer to molybdenum oxide
Implementation Method 2
exposing the semiconductor substrate to boron trichloride to convert the molybdenum oxide to a volatile molybdenum oxychloride
Implementation Method 3
exposing the semiconductor substrate to a fluorine-containing reactant to remove the boron oxide from the semiconductor substrate
Data Source
AI summary
Molybdenum is etched in a highly controllable manner by performing one or more etch cycles, where each cycle involves exposing the substrate having a molybdenum layer to an oxygen-containing reactant to form molybdenum oxide followed by treatment with boron trichloride to convert molybdenum oxide to a volatile molybdenum oxychloride with subsequent treatment of the substrate with a fluorine-containing reactant to remove boron oxide that has formed in a previous reaction, from the surface of the substrate. In some embodiments the method is performed in an absence of plasma and results in a substantially isotropic etching. The method can be used in a variety of applications in semiconductor processing, such as in wordline isolation in 3D NAND fabrication.