Etching silicon carbide

The successful fabrication of SiC based devices cannot be realized without reliable etching and cleaning processes for this material. The purpose of this Chapter is to review the developments and methods of etching silicon carbide for device applications. The term etching is used to describe the processes by which SiC material can be removed. It also includes chemical machining of a semiconductor as part of the fabrication process, as well as defect delineation. 

Silicon carbide is a very hard snbstance with a Young s modulus of 424 GPa [1]. It is chemically inert and reacts poorly (if at all) with any known material at room temperature. The only known efficient etch at moderate temperatures is molten KOH at 400-600°C. It is practically impossible to diffuse anything into SiC. Dopants need to be implanted or grown into the material. Eurthermore, it lacks a liqnid phase and instead sublimes at temperatures above 1,800°C. The vapor constituents during sublimation are mainly Si, SqC, and SiC in specific ratios, depending on the temperature. 

A progressive etching technique (39,40), combined with x-ray diffraction analysis, revealed the presence of a number of a polytypes within a single crystal of silicon carbide. Work using lattice imaging techniques via transmission electron microscopy has shown that a-silicon carbide formed by transformation from the p-phase (cubic) can consist of a number of the a polytypes in a syntactic array (41). 

J.W. Faust, Jr, The etching of silicon carbide, in Silicon Carbide A High Temperature Semiconductor, J.R. O Connor and J. Smiltens (Eds), Pergamon, Oxford, 1960, pp. 403-419. 

T. L. Rittenhouse, P. W. Bohn, and I. Adesida, Structural and spectroscopic characterization of porous silicon carbide formed by Pt-assisted electroless chemical etching, Solid State Commun. 126, 245-250 (2003). 

C. Hallin, A. S. Baskin, F. Owman, P. Martensson, O. Kordina and E. Jangen, Study of the hydrogen etching of silicon carbide substrates , Silicon Carbide and Related Materials 1995, Kyoto, Japan, Inst. Phys. Conf. Ser. No. 142 (IOP, Bristol, 1996), Ch. 3. 

T. L. Chu and R. B. Campbell, Chemical etching of silicon carbide with hydrogen ,... 

V. Ramachandran, M. F. Brady, A. R. Smith and R. M. Feenstra, Preparation of atomically flat surfaces on silicon carbide using hydrogen etching ,/. Electron. Mater., 27, 308 (1998). 

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). 

The specimen surface is often prepared before measurement to ensure a reproducible and known surface condition. Metallurgical surface preparation techniques are commonly used, these include wet grinding on silicon carbide abrasive papers, polishing with diamond or alumina media, electropolishing, chemical polishing, pickling or etching. 

Diamond, silicon carbide, titanium carbide, and gallium nitride are materials that do not have wet etch processes, but RIE processes do... 

Hollow diamond fibers have been produced by using the CVD process to coat diamond onto a wire, preferably with a relatively low thermal expansion coefficient and having carbide-forming properties [9]. Wires of W, Ti, Ta or copper can be used or fibers of silica and silicon carbide, which are initially abraded with diamond grit to provide nucleation sites. The metals can be etched away in a suitable reagent such as nitric acid for Cu and hydrogen peroxide for W. The diamond deposit has a tensile modulus of about 880 GPa. 

Tables 6-9 present a variety of etchants and corresponding etching conditions for aluminum oxide materials with AI2O3 contents between 94% and 99.8% by weight, as well as Zr02 ceramics, silicon carbide materials, and silicon nitride materials.

Table 8. Chemical etching recipes for silicon carbide materials ...

The conditions for color etching and subsequent grain boundary etching of silicon carbide and grain boundary etching of boron carbide are given below as examples. 

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