Catalytic activity of noble metals for metal-assisted chemical etching of silicon

Abstract

Metal-assisted chemical etching of silicon is an electroless method that can produce porous silicon by immersing metal-modified silicon in a hydrofluoric acid solution without electrical bias. We have been studying the metal-assisted hydrofluoric acid etching of silicon using dissolved oxygen as an oxidizing agent. Three major factors control the etching reaction and the porous silicon structure: photoillumination during etching, oxidizing agents, and metal particles. In this study, the influence of noble metal particles, silver, gold, platinum, and rhodium, on this etching is investigated under dark conditions: the absence of photogenerated charges in the silicon. The silicon dissolution is localized under the particles, and nanopores are formed whose diameters resemble the size of the metal nanoparticles. The etching rate of the silicon and the catalytic activity of the metals for the cathodic reduction of oxygen in the hydrofluoric acid solution increase in the order of silver, gold, platinum, and rhodium.

Porous Silicon Formation by Metal Nanoparticle-Assisted Etching

“…The etching can be done in various HF solutions containing an oxidizing agent, typically H 2 O 2 (Li and Bohn 2000;Tsujino and Matsumura 2005a, b, 2006a, 2007Peng et al 2008;Huang et al 2007;Chartier et al 2008;Lee et al 2008;Megouda et al 2009a). Other oxidizing agents such as Fe(NO 3 ) 3 (Peng et al 2005b(Peng et al , 2006b), Mg(NO 3 ) 2 (Peng et al 2006b), Na 2 S 2 O 8 (Hadjersi et al 2004(Hadjersi et al , 2005aDouani et al 2008;Hadjersi 2007), KMnO 4 (Hadjersi et al 2004(Hadjersi et al , 2005aDouani et al 2008), K 2 Cr 2 O 7 (Douani et al 2008;Hadjersi et al 2005b;Waheed et al 2010), KBrO 3 or KIO 3 (Waheed et al 2010), Co(NO 3 ) 2 (Megouda et al 2009b), molecular O 2 dissolved in H 2 O (Yae et al 2003(Yae et al , 2005(Yae et al , 2006(Yae et al , 2008a(Yae et al , b, 2010a(Yae et al , 2012Masayuki et al 2011), and electrical holes, h + by anodization (Zhao et al 2007;Chouroua et al 2010;Huang et al 2010a), are also used. The deposited metals under the form of nanoparticles or colloidal particles or patterned thin film are most generally noble metals such as Ag (Hadjersi et al 2004(Hadjersi et al , 2005bTsujino and Matsumura 2005a, 2007Peng et al 2005...…”

Fabrication of ultrahigh aspect ratio silicon nanostructures using self-assembled gold metal-assisted chemical etching

“…While MacEtch has been shown to work with a variety of metals, 3,14 our work focuses on gold for several reasons: silver has been studied most extensively, but its percolation threshold is relatively thick and the resulting self-assembled structures subsequently form features much larger than 10 nm. Silver also has the undesirable characteristic of etching slowly in H 2 O 2 ; 7 this can lead to imperfect pattern reproduction as the silver pattern dissolves in the etching solution.…”

“…[6][7][8][9][10] MacEtch has been demonstrated on lithographically patterned 6,11,12 and self-assembled metal patterns. 4,5,7,8,[13][14][15] With self-assembly, it is possible to reach geometrical features far smaller than what can be realized by lithographic patterning. The most common self-assembly approach uses a metal salt bath, such as AgNO 3 , 8,9,14,[16][17][18] where the etch geometry is defined by silver dendrite formation from the solution.…”

“…4,5,7,8,[13][14][15] With self-assembly, it is possible to reach geometrical features far smaller than what can be realized by lithographic patterning. The most common self-assembly approach uses a metal salt bath, such as AgNO 3 , 8,9,14,[16][17][18] where the etch geometry is defined by silver dendrite formation from the solution. While modest control of the dendrite geometry has been demonstrated, 18 the resulting etched features are larger than 50 nm.…”

Morphology-controlled synthesis of silver nanoparticles on the silicon substrate by a facile silver mirror reaction

“…nanoporous and nanowires. [1][2][3][4][5][6][7][31][32][33][34] These different nanostructures can be used in antireflection layer of solar cell devices. In etching process, the nanostructure can be controlled by changing the morphology of Ag-Nps.…”