Metal-Assisted Chemical Etching of Silicon Using Oxygen as an Oxidizing Agent: Influence of HF Concentration on Etching Rate and Pore Morphology

Abstract

Metal-assisted chemical etching of silicon is an electroless method that can produce porous silicon by immersing metal-modified silicon in a HF solution without electrical bias. We have been studying this etching using dissolved oxygen as an oxidizing agent and recently reported that the catalytic activity of noble metal particles including silver, gold, platinum, and rhodium, influences the cathodic reduction of oxygen and controls the etching rate. In this paper, we investigate the influence of the HF concentration on the etching rate and the pore morphology. In the case of high HF concentration, the etching rate is independent of the HF concentration and depends on the oxygen concentration and the catalytic activity of the metal particles. In the low HF concentration case, the etching rate depends on the HF concentration and is independent of the oxygen concentration and the catalytic activity. The pore morphology is also changed by the HF concentration.

General corrosion during metal-assisted etching of n-type silicon using different metal catalysts of silver, gold, and platinum

“…Lianto et al47 performed the etching with patterned Au strips and demonstrated that the pit formation became signicant with increasing the H 2 O 2 concentration. We observed the pore widening with Rh and Pt particles in HF-O 2 systems at low HF concentrations 41. Recently, Akan et al15 demonstrated, for the fabrication of X-ray zone plates, that the surface roughness became signicant and the etching depth under Au catalysts became smaller when the H 2 O 2 concentration is high.…”

“…Formation of mesoporous Si by the metal-assisted etching has been known so far [1][2][3][4][5]7,28,31,32,34,37,40,45,46 as well as pore widening 36,39,41 and pit formation at the location away from the catalysts. 47,48 Such phenomena have been usually observed when using the catalysts with a high catalytic activity for the reduction of oxidizing agents.…”

“…13,15,18,21,27,[31][32][33][34][35][36][37] Metal catalyst is also an important factor to change the porous structure. 25,26,[38][39][40][41] Lee at al. 38 performed the etching of p-Si (100) in HF-H 2 O 2 systems using silver (Ag), gold (Au), and platinum (Pt) particles, and they demonstrated that the etching behavior changes depending on the kind of metal as well as the shape of particles.…”

“…We previously performed the etching of n-Si (100) in HF + O 2 systems using Ag, Au, Pt, and rhodium (Rh) particles deposited with a constant metal coverage and evaluated the etching rate based on the mass loss of substrate. 26,41 When the HF concentration was sufficiently low, the etching rate was determined by the HF concentration but not the kind of metal, indicating that the supply of uoride species was rate-limiting step. When the HF concentration increased, the etching rate was higher in the order of the Rh-, Pt-, Au-, and Ag-deposited substrates.…”

Formation and Dissolution of Mesoporous Layer during Metal-Particle-Assisted Etching of n-Type Silicon

“…Metal catalyst plays an essential role for determining the etching behavior. 18,[28][29][30][31][32][33][34][35][36] Recently, Tamarov et al 36 comprehensively studied the etching behavior using various kinds…”