Noble Metal Catalyst Etching for High Aspect Ratio Semiconductor Trenches
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Solution Overview
Problem
Current deep etching techniques for semiconductor substrates, such as isotropic wet etching, anisotropic etching, and dry etching methods like the Bosch process, face limitations in achieving high aspect ratios and are prone to side etching or the formation of scalloped sidewalls, while metal-assisted chemical etching (MacEtch) methods struggle with perpendicularity and generate needle-like residual portions.
Innovation Solution
An etching method using a catalyst layer of noble metal particles on a semiconductor substrate, with an etching solution containing hydrofluoric acid, an oxidizer, and an organic additive, which suppresses the formation of needle-like residual portions and achieves high aspect ratio recesses by promoting uniform etching across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If isotropic wet etching is used, then etching in the depth direction is achieved, but side etching occurs in the widthwise direction making it impossible to achieve high aspect ratio
Solution Approach 1:
The patent uses a catalyst layer with spatially varying properties (different metal compositions or particle densities in different regions) to locally control etching behavior. This allows the etching front to progress vertically while suppressing lateral etching at specific locations, enabling high aspect ratio structures without the uniform side etching problem of conventional isotropic wet etching.
Solution Approach 2:
The patent changes the chemical parameters of the etching system by introducing a catalyst layer that facilitates selective chemical reactions. The catalyst layer modifies the local etching kinetics, enabling anisotropic etching behavior (vertical preference) from an inherently isotropic chemical etching process, thus achieving high aspect ratio without the harmful side etching.
2Manufacturing precision
If anisotropic etching is used to achieve high aspect ratio deep etching, then etching rate difference corresponding to crystal orientation is utilized, but the shape of pattern and crystal orientation must be determined such that etching rate in depth direction is much higher than widthwise direction causing design limitations
Solution Approach 1:
The catalyst layer acts as an intermediary between the isotropic wet etchant and the semiconductor substrate. It mediates the etching process by providing catalytic sites that preferentially promote vertical etching while suppressing lateral etching, without requiring specific crystal orientations or pattern geometries. This intermediary approach decouples the etching anisotropy from the substrate crystal structure, enabling design flexibility.
Solution Approach 2:
The patent changes the controlling parameter for etching direction from crystal orientation (in conventional anisotropic etching) to catalyst layer properties (metal composition, particle density, or thickness distribution). This parameter change allows arbitrary pattern shapes and orientations to be etched with high aspect ratio, removing the design limitations imposed by fixed crystallographic directions.
3Manufacturing precision
If Bosch process is used for deep etching, then plasma etching and sidewall protective film formation are alternately repeated, but fluorocarbon-based deposit remains on sidewalls exerting influence on device performance and sidewalls are formed into scalloped shape
Solution Approach 1:
The patent replaces the mechanical/physical Bosch process (alternating plasma etching and deposit formation) with a chemical approach using catalyst-mediated wet etching. This substitution eliminates the need for cyclic processing and the associated fluorocarbon deposits and scalloped sidewalls, while achieving comparable or superior depth control through the self-limiting nature of catalyst layer consumption.
Solution Approach 2:
The patent extracts and removes the harmful fluorocarbon-based deposit formation step from the etching process by replacing the Bosch process with catalyst-mediated wet etching. The catalyst layer approach inherently avoids fluorocarbon chemistry, thereby eliminating deposit accumulation and scalloped sidewall formation while maintaining precise depth control through catalyst layer thickness management.
4Manufacturing precision
If metal-assisted chemical etching (MacEtch) method is used, then catalyst pattern made of noble metal is formed and semiconductor substrate is dipped in solution mixture, but perpendicularity is not obtained depending on conditions and needle-like residual portions are generated
Solution Approach 1:
The patent applies local quality by creating a catalyst layer with controlled spatial distribution of metal particles or composition. By varying the catalyst density or metal type in different regions, the etching rate and direction are locally controlled to achieve uniform perpendicular sidewalls throughout the structure, preventing the needle-like residual portions that occur with uniform catalyst patterns under varying conditions.
Solution Approach 2:
The patent changes key parameters of the MacEtch process, including using specific metal compositions (Au, Ag, Pt, Pd) at controlled concentrations (0.01-10 wt%), and optimizing oxidizer concentrations (0.1-5 M). These parameter changes stabilize the etching process to consistently produce perpendicular sidewalls and eliminate needle-like residual portions that occur with conventional MacEtch under varying 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
The method effectively achieves high aspect ratio etching with minimal residual portions, enabling the formation of perpendicular trenches or via holes, overcoming the limitations of existing techniques by using an organic additive to enhance etching uniformity and prevent side etching.
Implementation Method 1
a solution mixture of hydrofluoric acid and an oxidizer... the semiconductor substrate is dipped in a solution mixture of hydrofluoric acid and an oxidizer. That portion of the semiconductor substrate, which is in contact with the catalyst, is preferentially etched
Implementation Method 2
a catalyst pattern made of a noble metal is formed on the surface of a semiconductor substrate... That portion of the semiconductor substrate, which is in contact with the catalyst, is preferentially etched
Implementation Method 3
a solution mixture of hydrofluoric acid and an oxidizer... the semiconductor substrate is dipped in a solution mixture
Data Source
AI summary
An etching method according to an embodiment includes forming a catalyst layer made of a noble metal on a structure made of a semiconductor, and dipping the structure in an etching solution containing hydrofluoric acid, an oxidizer, and an organic additive to remove a portion of the structure that is in contact with the catalyst layer.