Fast macropore growth in n‐type silicon

Abstract

Deep macropores can be grown in classical aqueous HF electrolytes only at slow etching speeds, fast macropores can only be grown to modest depths (150 μm). The addition of acid acetic to the electrolyte can roughly double the etching speed of the macropores, enabling quick and easy etching of pore depths as deep as 520 μm, and potentially more, if wafers thicker than 550 μm would be used. The addition of carboxymethylcellulose sodium salt (CMC) to the electrolyte decreases the roughness of the pore walls significantly. It is successfully shown that electrolytes consisting of HF + acetic acid + CMC can be utilized to produce fast, deep, and smooth macropores simultaneously in n‐type silicon, required for a multitude of potential applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Macroporous silicon as an absorber for thin heterojunction solar cells

“…The electrolyte is a < 5 wt.% aqueous hydrofluoric acid at 20°C. Additionally a wetting agent such as acetic acid can be added to improve lateral etching homogeneity and pore smoothness [21]. The non illuminated edge of the wafer is about 1 em wide in our setup.…”

In‐situ FFT impedance spectroscopy in new modes applied to pore growth in semiconductors

“…First, increasing the viscosity reduces diffusion in the electrolyte; more important, however, is the reduction Contributed Article of the leakage currents for the electrolyte chosen (cf. [2,4,7,8] for details). The net result are larger pore depths and far better pore qualities as expressed, e.g.…”

Controlled Microfabrication of High‐Aspect‐Ratio Structures in Silicon at the Highest Etching Rates: The Role of H2O2 in the Anodic Dissolution of Silicon in Acidic Electrolytes

“…AR values over 100 are obtained for ordered pores and systems with micrometric features, though the etching rate (about 2 µm min −1 at low AR) reduces to 0.5 µm min −1 at the highest ARs (blue circles in Figure 1). [21] However, only pore fabrication (no microstructures) has been demonstrated with such an increased HF concentration. [21] However, only pore fabrication (no microstructures) has been demonstrated with such an increased HF concentration.…”

“…This sets a novel record among either commercial or state-ofthe-art silicon etching technologies. [24] By increasing the etching time to 60 min, macropores with mean depth of 177.93 µm (sd = 0.37 µm) were etched using the electrolyte with [H 2 O 2 ] = 25%, whereas macropores Comparison between this work and commercial/state-of-the-art silicon microfabrication technologies, namely deep reactive ion etching (DRIE), [10] metal-assisted chemical etching (MaCE), [12,13] electric biasattenuated MaCE (EMaCE), [15] electrochemical etching (ECE) at [HF] of 5% and 10%, [21] in terms of etching rate (ratio between etch depth and etch time [µm min −1 ]) versus aspect ratio (ratio between the depth of in-silicon vertical feature and its width). The presence of H 2 O 2 acts both in dropping the valence of the silicon dissolution process to 1, thus rendering the electrochemical etching more effective, and in catalyzing the etching rate by opening a more efficient path for silicon dissolution with respect to the well-known Gerischer mechanism, [22,23] thus increasing the etching speed at both shorter and higher depths.…”

“…Increasing the HF concentration from 5 to 10 vol% allowed maintaining the etching rate constant at 2.2 µm min −1 regardless of the AR value, in the range from 17 to 88 (orange hexagrams in Figure 1). [21] However, only pore fabrication (no microstructures) has been demonstrated with such an increased HF concentration.…”