Formation Mechanism and Properties of Electrochemically Etched Trenches in n‐Type Silicon

Abstract

Three-dimensional structures in silicon are increasingly coming into use for the fabrication of mechanical and electrical devices. The fabrication of deep trenches is one of the most important problems in VLSI (very large scale integration) technology. In this study the spontaneous trench formation in n-type silicon immersed in hydrofluoric acid under anodic bias is demonstrated and the resulting microstructures are characterized. Trenches with arbitrary cross sections and high aspect ratios for microelectronic (e.g., 42 ~m depth and 0.6 ~m diam) and for power component application (e.g., 60 ~tm depth and 10 ~m diam) have been produced by a standard masking technique. The trench formation is explained by a model which takes into account the conditions of the space charge region the minority carrier current and the crystal orientation. A passivating sidewall layer is not needed in this model. The dimensions and the shape of anodically etched trenches can be varied over a wide range by adjusting the critical parameters.

Controlled nonuniformity in macroporous silicon pore growth

“…© 2005 American Institute of Physics. ͓DOI: 10.1063/1.2137688͔ Porous silicon, 1,2 and in particular, macroporous silicon, 3,4 has attracted a lot of attention as a unique possibility to structure silicon. 5 This material system has been applied to optical shortpass filters 6 as well as to twodimensional ͑2D͒ and three-dimensional ͑3D͒ photonic crystals.…”

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

“…PL spectra corresponding to samples prepared in each solution with the same anodization conditions, current density (56.5 mA cm -2 ), anodization time (10 min) and resistivity [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] cm, are shown in Figure 3. PL spectrum for sample produced from HF-MeCN solution presented a blue shift peak that may depend on the pore depth and diameter.…”

“…7 As a consequence, for the pore formation process, the current efficiencies are due to two electrons per dissolved Si atom, whereas four electrons are necessary for the electropolishing regime. 8,9 In this sense, the global anodic half-reactions during the pore formation may be written as: 7 Si + 6HF H 2 SiF 6 + H 2 + 2H + + 2e and during electropolishing as: 7 Si + 6HF H 2 SiF 6 + 4H + + 4e…”

“…7 As a consequence, for the pore formation process, the current efficiencies are due to two electrons per dissolved Si atom, whereas four electrons are necessary for the electropolishing regime. 8,9 In this sense, the global anodic half-reactions during the pore formation may be written as: 7Si + 6HF H 2 SiF 6 + H 2 + 2H + + 2e and during electropolishing as: 7Si + 6HF H 2 SiF 6 + 4H + + 4eThe final and stable product for Si in HF for both cases is H 2 SiF 6 or some of its ionized forms. This means that during the pore formation only two of the four available Si electrons participate in an interfacial charge transfer, while the remaining two electrons undergo corrosive hydrogen liberation.…”

Photonic crystals in the optical regime — past, present and future

“…Due to the generally`macroscopica (1}50 m) feature size of the electrochemically etched holes, the material thus produced is termed macroporousa silicon, in contrast to its`microporousa relative (Section 4.3.1). Macroporous silicon with feature sizes in the sub-micron range has been demonstrated [27,45], although most PBG-related experimental work is aimed at mid-to far-IR wavelengths [25,26].…”