Annealing concepts

Capano et al. performed B implantation on 4H-SiC and B and Al implantations on 6H-SiC [6]. The implanted samples were annealed in a resistively heated furnace for various temperatures between 1,500-1,800°C. Most of the samples 

Kawase et al. investigated Si regrowth from the amorphous phase caused by Al implantation recrystallization of the specimens when annealed at temperatures between 800-1,600°C in Ar flow for 30 minutes was achieved [78]. The damage induced by the implantation and the damage reductions by the subsequent annealing were determined by electron spin resonance (ESR) and TEM. 

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In this chapter, we review the current status of doping of SiC by ion implantation. Section 4.2 examines as-implanted depth profiles with respect to the influence of channeling, ion mass, ion energy, implantation temperature, fluence, flux, and SiC-polytype. Experiments and simulations are compared and the validity of different simulation codes is discussed. Section 4.3 deals with postimplant annealing and reviews different annealing concepts. The influence of diffusion (equilibrium and nonequilibrium) on dopant profiles is discussed, as well as a comprehensive review of defect evolution and electrical activation. Section 4.4 offers conclusions and discusses technology barriers and suggestions for future work. 

We noted in Section VII-2B that, given the set of surface tension values for various crystal planes, the Wulff theorem allowed the construction of fhe equilibrium or minimum firee energy shape. This concept may be applied in reverse small crystals will gradually take on their equilibrium shape upon annealing near their melting point and likewise, small air pockets in a crystal will form equilibrium-shaped voids. The latter phenomenon offers the possible advantage that adventitious contamination of the solid-air interface is less likely. 

X-ray diffraction work (11,15) shows that there is an ionomer peak at 4°C which is absent in the acid precursor. This low, broad peak is not affected by annealing or ion type and persists up to 300°C. Since the 4°C peak corresponds to a spacing of about 2.5 nm, it is reasonable to propose a stmctural feature of this dimension in the ionomer. The concept of ionic clusters was initially suggested to explain the large effects on properties of relatively sparse ionic species (1). The exact size of the clusters has been the subject of much debate and has been discussed in a substantial body of Hterature (3,4,18—20). A theoretical treatment has shown that various models can give rise to supramoleculat stmctures containing ionic multiplets which ate about 10 nm in diameter (19). 

A poor surface morphology is a major concern in device fabrication and substantial efforts have been made during the last years to resolve this issue. Different concepts have been developed, such as effective encapsulants (primarily AIN) for protection of the SiC surface [8] and annealing in CVD-reactors using Si overpressure [9]. These concepts appear to be quite successful, at least up to 1,700°C, and are reviewed in Section 4.3.1. 

Regioselective synthesis is examined mainly on the basis of the conception of competitive coordination and the principle of hard and soft acids and bases [14]. A description of polyhedron-programmed synthesis is given, taking into consideration thin structure compounds to be used as ligands (number, nature, and mutual situation of donor centers and the presence and character of organic fragments, annealed to a metal-cycle). 

Whites SR (1984) Concepts of scale in simulated annealing. In Proceedings of the IEEE international conference on computer-aided design, Port Chester, NY, pp 646-651... 

Of course the three effects are interrelated. From theoretical concepts as well as from experimental data it is obvious that crystallisation with extended chains over a length of, say > 10 7 m only takes place if the annealing temperature is in the melting region of extended chain crystals. 

There has been much confusion about the mechanism of formation of extended chains. The most probable conception is that formation direct from the melt is the dominant mechanism unfolding and subsequent lamella-thickening may also take place, especially at lower temperatures and long annealing times. 

In these graphs (Figs. 7 and 8), the quasi vertical part of the curve would correspond to annealing, the rest would be due to chemicrystallization. In this case, all the trajectories would converge towards an embrittlement point not very far from the intersection of both boundaries Uc and M c and the concept of a critical molar mass (scheme A) would apparently be valid. 

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