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SEM images of (A) the stamps of a complex eagle shape consisting of numerous YONSEI letters with circular pillars, rectangular stripes, and closed-curve mixed patterns and (B) the Si substrates mirror-symmetric patterns imprinted with hole arrays, trench arrays, and curved lines.
SEM images of (A) the stamps of a complex eagle shape consisting of numerous YONSEI letters with circular pillars, rectangular stripes, and closed-curve mixed patterns and (B) the Si substrates mirror-symmetric patterns imprinted with hole arrays, trench arrays, and curved lines.
Optical microscope photography of (A) a stamp of a complex eagle shape and (B) a Si substrate imprinted with this shape in a size of 1x1 cm2. Pre-defined patterns in (A) manufactured by direct writing lithography and subsequent processes. Mirror-symmetrical patterns in (B) chemically imprinted to the Si substrates
Optical microscope photography of (A) a stamp of a complex eagle shape and (B) a Si substrate imprinted with this shape in a size of 1x1 cm2. Pre-defined patterns in (A) manufactured by direct writing lithography and subsequent processes. Mirror-symmetrical patterns in (B) chemically imprinted to the Si substrates
Schematic illustration of integrated catalytic stamp for silicon nano/microstructure fabrication via patterning and etching.
Schematic illustration of integrated catalytic stamp for silicon nano/microstructure fabrication via patterning and etching.
Schematic illustration of the chemical imprinting mechanism. The etching occurs as follows: 1) H2O2 is reduced to H2O by the metal catalyst in the etch bath. The holes diffuse through the metal and are injected into the Si. 2) HF dissolves the oxidized Si substrates. The ionized products after the chemical reaction diffuse out through the gap between the stamp and the Si. A fluorocarbon inserted between the stamp material and the metal catalyst served as an effective electric/chemical barrier.
Schematic illustration of the chemical imprinting mechanism. The etching occurs as follows: 1) H2O2 is reduced to H2O by the metal catalyst in the etch bath. The holes diffuse through the metal and are injected into the Si. 2) HF dissolves the oxidized Si substrates. The ionized products after the chemical reaction diffuse out through the gap between the stamp and the Si. A fluorocarbon inserted between the stamp material and the metal catalyst served as an effective electric/chemical barrier.
Metal-assisted Chemical Etching
Metal-assisted Chemical Etching
Metal-assisted chemical etching is an anisotropic etching technique employing a metal catalyst and etchant solution. Since this phenomenon was discovered by Li and Bohn in 2000, it has attracted much attention due to its simple implementation and unique physical properties. Generally accepted mechanisms involve electronic hole transport into the semiconductor by reducing the oxidant using a metal catalyst and a subsequent etch of the oxidized semiconductor with an acid solution.
Metal-assisted chemical etching is an anisotropic etching technique employing a metal catalyst and etchant solution. Since this phenomenon was discovered by Li and Bohn in 2000, it has attracted much attention due to its simple implementation and unique physical properties. Generally accepted mechanisms involve electronic hole transport into the semiconductor by reducing the oxidant using a metal catalyst and a subsequent etch of the oxidized semiconductor with an acid solution.
Metal assisted chemical etching is a simple, low cost, wet-based anisotropic etching with no crystal damages, while dry etch is performed in expensive complicated system and high energy plasma ions induced crystal damages. Metal-assisted chemical etching has 1-dimensional anisotropic property distinguished from the other wet etch techniques which are isotropic or orientation dependent anisotropic property.
Metal assisted chemical etching is a simple, low cost, wet-based anisotropic etching with no crystal damages, while dry etch is performed in expensive complicated system and high energy plasma ions induced crystal damages. Metal-assisted chemical etching has 1-dimensional anisotropic property distinguished from the other wet etch techniques which are isotropic or orientation dependent anisotropic property.
Comparison between conventional etch (wet, dry) and metal-assisted chemical etching
Comparison between conventional etch (wet, dry) and metal-assisted chemical etching
Catalyst thickness dependence
Catalyst thickness dependence
A low temperature with minimal surface damage induced by high energy plasma ions is a crucial requirement for III-V device fabrication because the damaged III-V crystal is not readily repaired by thermal annealing. When ultra-thin catalysts are used, etch properties have strong dependency on metal thickness. From the results, metal-assisted chemical etching of GaAs with different Au catalyst thicknesses can be classified into two regimes: out-of-plane mass transport and in-plane mass transport. These regimes are directly related to the physical properties of the Au catalyst.
A low temperature with minimal surface damage induced by high energy plasma ions is a crucial requirement for III-V device fabrication because the damaged III-V crystal is not readily repaired by thermal annealing. When ultra-thin catalysts are used, etch properties have strong dependency on metal thickness. From the results, metal-assisted chemical etching of GaAs with different Au catalyst thicknesses can be classified into two regimes: out-of-plane mass transport and in-plane mass transport. These regimes are directly related to the physical properties of the Au catalyst.
(left) SEM images of metal-assisted chemical etching of GaAs with a Au catalyst of 3 nm, 5 nm, 7 nm, 10 nm and 15 nm (right) Out-of-plane and in-plane mass transport regimes defined by variations in etch rates as a function of Au catalyst thickness
(left) SEM images of metal-assisted chemical etching of GaAs with a Au catalyst of 3 nm, 5 nm, 7 nm, 10 nm and 15 nm (right) Out-of-plane and in-plane mass transport regimes defined by variations in etch rates as a function of Au catalyst thickness
In-plane & out-of-plane mass transport
In-plane & out-of-plane mass transport
Electrochemically generated nano-pinholes in the metal catalyst not only enhance important catalytic effects in redox reactions, but also act as a diffusion pathway for the reactants (H2SO4) and products (Ga3+ and Asn+ ions) for chemical etching oxidized GaAs. The density of pinholes in the metal catalyst is determined by the metal thickness. This model supports that the etch rate has a strong dependence on Au thickness ranging from 3 to 10nm and is independent of Au thickness ³ 15nm in terms of pinhole density.
Electrochemically generated nano-pinholes in the metal catalyst not only enhance important catalytic effects in redox reactions, but also act as a diffusion pathway for the reactants (H2SO4) and products (Ga3+ and Asn+ ions) for chemical etching oxidized GaAs. The density of pinholes in the metal catalyst is determined by the metal thickness. This model supports that the etch rate has a strong dependence on Au thickness ranging from 3 to 10nm and is independent of Au thickness ³ 15nm in terms of pinhole density.
Schematic illustration of out-of-plane mass transport (left) and in-plane mass transport (right) of reactant and product in metal-assisted chemical etching and SEM image of morphology and surface on Au catalyst after etch.
Schematic illustration of out-of-plane mass transport (left) and in-plane mass transport (right) of reactant and product in metal-assisted chemical etching and SEM image of morphology and surface on Au catalyst after etch.
Various structures fabricated by metal-assisted chemical etching
Various structures fabricated by metal-assisted chemical etching
Controllable fabrication of semiconductor structures is a requirement for their applications. Etching profiles of metal-assisted chemical etching depend on type of metal, metal patterns, thickness, composition of etchant solution, temperature etc. Also there is no limitation on the size of features. By optimizing these parameters, desirable structures can be formed with nano- or micro-scales. Figure shows various structures fabricated metal-assisted chemical etching.
Controllable fabrication of semiconductor structures is a requirement for their applications. Etching profiles of metal-assisted chemical etching depend on type of metal, metal patterns, thickness, composition of etchant solution, temperature etc. Also there is no limitation on the size of features. By optimizing these parameters, desirable structures can be formed with nano- or micro-scales. Figure shows various structures fabricated metal-assisted chemical etching.
Nano- and microstructures fabricated by metal-assisted chemical etching.
Nano- and microstructures fabricated by metal-assisted chemical etching.
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