The Coronin Family of Proteins Subcellular Biochemistry
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1 Introduction The excellent chemical and mechanical properties of SiC make, paradoxically, damage free surface preparation a real challenge. The preparation of SiC wafers can be described in four successive stages corresponding to different objectives: – – – –
Grinding/lapping gives good geometrical parameters to the wafer. Mechanical polishing enables a decrease in roughness and improves the geometrical characteristics of the wafer. The chemical mechanical polishing is the best way to produce surface without any scratches or subsurface damage. The cleaning step is essential to remove the contaminants on the surface.
Alternative preparation methods based on etching have been used to replace the second and third steps. The results are not fully satisfactory in terms of roughness, damage and geometrical wafer characteristics. In this paper, recent results on surface preparation are described with a detailed review of the published work. A description of each step of the preparation is detailed in Sect. 2. We present in Sect. 3 the state of the art results and the influence of surface preparation on epitaxial growth and device performance. A summary will be given in the final section.
2 Preparation Techniques 2.1 Grinding/Lapping and Mechanical Polishing The main objective of this stage is to produce from as-cut wafers, flat and parallel surfaces with a minimum of bow, warp and total thickness variation (TTV). Silicon carbide is one of the hardest materials. Only diamond (C), cubic boron nitrite (BN) and boron carbide (B4 C) are comparable or harder than SiC [1]. Therefore, only these materials can be used as abrasive for mechanical polishing. By using abrasive slurries of decreasing grit size it is possible to obtain a very low roughness but scratches and subsurface damage are still generated. Of course, not only abrasives do influence polishing but
W.J. Choyke et al. (eds.), Silicon Carbide © Springer-Verlag Berlin Heidelberg 2004
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also other parameters like the down pressure, the slurry feed composition and temperature, the rotation speed of the plate or carrier and the polishing pad characteristics [2]–[4]. An interesting attempt combines mechanical lapping/polishing and chemical etching with 600◦ C KOH flux for less than 3 minutes [5]. The surfaces obtained are similar or better to those obtained by commercial suppliers but have to be controlled carefully to avoid revealing bulk defects. Slicing and even more grinding and mechanical polishing generate subsurface damage. The subsurface damage thickness is critical information at each step of the preparation for successful polishing. To assess the subsurface damage thickness, different methods have been used. Depending on the analysed thickness, simple edge Normarski observation [6], transmission electron microscopy [7]–[9], Rutherford backscattering [9], photon backscattering [10]–[12], KOH etching [12] and more recently Raman spectroscopy [13, 14] or positron annihilation [15] have been used. A qualitative measure of su
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