Metal assisted chemical etching of silicon in the gas phase: a nanofabrication platform for X-ray optics

Abstract

Gas-MacEtch of Si with a Pt catalyst allows vertical etching nanostructures with an extreme aspect ratio up to 10 000 : 1.

High‐Aspect‐Ratio Grating Microfabrication by Platinum‐Assisted Chemical Etching and Gold Electroplating

“…Native silicon oxide provides an oxygen-terminated surface [21] that facilitates the metal film dewetting and allows the formation of platinum silicide at the interface. [22] Platinum silicide improves the metal adhesion on the substrate, which prevents the catalyst peeloff when the sample is immersed in heavily concentrated HF solution. [7] Figure 2 shows a series of images by scanning electron microscopy (SEM) of a Pt film (12 nm) deposited on a Si substrate with cleaned native oxide (only oxygen plasma was used to clean the surface before the deposition) and treated at different temperatures.…”

“…[22] Platinum silicide improves the metal adhesion on the substrate, which prevents the catalyst peeloff when the sample is immersed in heavily concentrated HF solution. [7] Figure 2 shows a series of images by scanning electron microscopy (SEM) of a Pt film (12 nm) deposited on a Si substrate with cleaned native oxide (only oxygen plasma was used to clean the surface before the deposition) and treated at different temperatures. The Pt dewetting occurs in agreement with the literature [20] with a progressive increase in film fractures (250-350 ºC), leading to the formation of holes (400-500 ºC) and finally to the coalescence and the growth (550-600 ºC).…”

“…Platinum has a faster reported etching rate for MacEtch [5] due to its superior catalytic activity and has the advantage to form a stable silicide (PtSi and Pt 2 Si) on the Si substrate at a relatively low temperature (180-400 ºC), [32] which ensures a robust adhesion of the metal with the Si substrate during MacEtch in conditions of high HF concentrations. [7] For deep trenches (>20 μm), a high etching rate is desirable as the Si side walls are subjected to secondary undesired etching that degrades the trench profile. We wanted to discriminate which catalyst works better for the fabrication of high-aspect-ratio X-ray gratings.…”

Towards the Fabrication of High-Aspect-Ratio Silicon Gratings by Deep Reactive Ion Etching

“…For the fabrication of HAR gratings, especially G0 and G2 gratings, researchers have several mature technologies to choose from: LIGA (Lithographie, Galvanik und Abformung) [ 8 , 9 ], anisotropic wet-etching [ 10 ], metal assisted chemical etching (MacEtch) [ 11 , 12 , 13 ] and deep reactive ion etching (DRIE) [ 9 , 11 , 14 , 15 ]. The LIGA process relies highly on the availability of a synchrotron source; wet-etching gives very good sidewall smoothness but has poor etching depth uniformity and is very sensitive to precise crystallographic alignment; MacEtch could achieve an extremely high aspect ratio, but still it has limited reliability [ 13 ].…”

Microfabrication of X-ray Optics by Metal Assisted Chemical Etching: A Review

“…Since its discovery in 2000, by Li et al [13], MacEtch of silicon has emerged as a new technique capable of fabricating 3D nano-and micro-structures of several shapes and applications [23]:-nano-porous film, nanowires [24], 3D objects [25], trenches, vias [26], micro-fins [27], nano-scale grooves, surface antireflection texturing [28], optoelectronic devices such as solar cells [29] and photodetectors [30], sensor devices [31], X-ray optics-in a few semiconductors substrates: Si [15], Ge [30], poly-Si [32], GaAs [33], β-Ga 2 O 3 [27], SiC [34], etc.-and different catalysts: Ag, Au, Cu, Pt, and Pd [15]. MacEtch has been developed with a strong controlled vertical directionality with respect to the substrate and successfully applied for producing X-ray zone plates [17,23,[35][36][37][38] and diffraction gratings [19,20,37,[39][40][41]. In MacEtch, a catalyst layer (e.g., Au) is patterned onto the substrate (e.g., Si) to locally increase the dissolution rate of the substrate material in an etchant solution including a fluoride etchant such as hydrofluoric acid (HF) and an oxidizing agent such as hydrogen peroxide (H 2 O 2 ).…”