Electrochemical Etching of SiC

It is possible, however, that under certain conditions etching occurs by direct dissolution without the intermediate oxidation step. 

FIGURE 1 Energy band diagram of the n-type (J-SiC/HF interface under the etching conditions. 

FIGURE 3 Etch rate vs. UV laser intensity for the laser etching of n-type p-SiC in HF [5]. 

The etched surface morphologies reported in [5,9] all exhibited a surface roughness of 3000 A. This has been attributed to defects contained in the material causing local non-uniformities in the etching [5], However, it has been shown that increasing the F concentration while decreasing the pH level can result in much smoother surfaces as will be discussed further below [12], 

FIGURE 4 Etched depth vs. anodisation time for the etching of p-type p-SiC in HF at a constant current 

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O. Jessensky, F. Muller and U. Gosele, Microstructure and photoluminescence of electrochemically etched porous SiC, Thin Solid Films, 297, 224-228 (1997). 

L.M. Sorokin, N.S. Savkina, V.B. Shuman, A.A. Lebedev, G.N. Mosina, J. Hutchinson, Features of the structure of a porous silicon carbide layer obtained by electrochemical etching of a 6H-SiC substrate, Tech. Phys. Lett., 28, 935-938 (2002). 

Figure 1.9 SEM images [34] of (a) original porous SiC surface after PECE, (b) early stage formation of columnar pore in cross-section, (c) porous surface structure 20 pm below the original surface after 90 min of RIE (the inset shows the Fourier transform of a larger area of this picture), and (d) the self-ordered columnar porous structure below the cap layer in cross-section. Reproduced from Y. Ke, R.P. Devaty and W.J. Choyke, Self-ordered nanocolumnar pore formation in the photoelectro-chemical etching of 6H SiC, Electrochem. Solid-State Lett., 10(7), K24-K27 (2007). Copyright 2007, with permission from The Electrochemical Society...

The porous SiC is fabricated from commercial SiC substrate (4H or 6H) by electrochemical etching. An electrolyte is placed in contact with the SiC substrate. A bias is introduced across the electrolyte and the semiconductor materials causing a current to flow between the electrolyte and the semiconductor material. The SiC partially decomposes in this electrolyte and forms high density of pores with nano-scale diameter. This decomposition initiates from the carbon-face of SiC substrate because the carbon-face is less chemically inert compared with the silicon-face. These as-etched pores have a depth of approximately 200 pm but do not reach the silicon-face of SiC. To fabricate porous silicon-face SiC (silicon-face is used as the growth plane for GaN), SiC with thickness of tens of micrometers is polished away from the silicon-face to expose the surface pores. Two surface preparation procedures, hydrogen polishing and chemical mechanical polishing, have been applied to the as-polished silicon-face porous SiC to improve its surface perfection. 

Compound Semiconductors, Electrochemical Decomposition, Fig. 5 Single crystal SiC MEMs structure fabricated by photoanodic etching of n-SiC (Ref [22]. Reprinted with permission from Elsevier 2011)... 

To evaluate the photoelectrochemical reactions in these PECE processes, it is useful to calculate and compare the average number of holes y needed to etch away a single SiC pair. The agreement among different experiments points to a similar electrochemical process, y is calculated using the following expression ... 

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