Metal-Assisted Catalytic Etching (MACE) for Nanofabrication of Semiconductor Powders.

Kurt W Kolasinski

doi:10.3390/mi12070776

Abstract

Electroless etching of semiconductors has been elevated to an advanced micromachining process by the addition of a structured metal catalyst. Patterning of the catalyst by lithographic techniques facilitated the patterning of crystalline and polycrystalline wafer substrates. Galvanic deposition of metals on semiconductors has a natural tendency to produce nanoparticles rather than flat uniform films. This characteristic makes possible the etching of wafers and particles with arbitrary shape and size. While it has been widely recognized that spontaneous deposition of metal nanoparticles can be used in connection with etching to porosify wafers, it is also possible to produced nanostructured powders. Metal-assisted catalytic etching (MACE) can be controlled to produce (1) etch track pores with shapes and sizes closely related to the shape and size of the metal nanoparticle, (2) hierarchically porosified substrates exhibiting combinations of large etch track pores and mesopores, and (3) nanowires with either solid or mesoporous cores. This review discussed the mechanisms of porosification, processing advances, and the properties of the etch product with special emphasis on the etching of silicon powders.

Highlights

It has long been known that metals can spontaneously deposit on semiconductors out of solutions containing dissolved ions [1,2,3]
Demonstrated that thin Au, Pt, or Au/Pd layers could be used to localize the formation of photoluminescent porous silicon in a manner closely related to the galvanic etching [15] process discovered by Kelly et al [16,17]
The conventional high-load Metal-assisted catalytic etching (MACE) regime (HL-MACE) is obtained when metal is deposited at the level of 1 mmol per g of Si

Summary

Introduction

It has long been known that metals can spontaneously deposit on semiconductors out of solutions containing dissolved ions [1,2,3]. Demonstrated that thin Au, Pt, or Au/Pd layers could be used to localize the formation of photoluminescent porous silicon (por-Si) in a manner closely related to the galvanic etching [15] process discovered by Kelly et al [16,17] It was the discovery by KQ Peng et al [13,18] that such anisotropic electron transfer could be used to initiate preferential directional etching of silicon that transformed metal-assisted catalytic etching (MACE, known as metal-assisted etching (MAE), metal-assisted chemical etching, and MacEtching) into a technique for controlled micro- and nano-structuring beyond porosification. Micromachining with MACE is possible because of the formation of etch track pores of roughly the same size as the diameter of the metal nanoparticle. Lithographic and growth methods developed primarily for the electronics industry can be exploited and combined with MACE to generate devices that integrate a range of electronic, optoelectronic, optical, and transport properties This can be useful in sensor, photovoltaic, or energy conversion applications. While the vast majority of MACE studies and reviews have concentrated on wafers [13,37,39,40,68,74,75,76,77], the focus of this review will be on the etching of powders

Mechanistic Aspects of MACE

Materials and Methods

Results of Powder Etching

Patents