Formation of carbon vacancy in 4H silicon carbide during high-temperature processing

Abstract

As-grown and pre-oxidized silicon carbide (SiC) samples of polytype 4H have been annealed at temperatures up to 1950 C for 10 min duration using inductive heating, or at 2000 C for 30 s using microwave heating. The samples consisted of a n-type high-purity epitaxial layer grown on 4 off-axis h0001i n þ-substrate and the evolution of the carbon vacancy (V C) concentration in the epitaxial layer was monitored by deep level transient spectroscopy via the characteristic Z 1/2 peak. Z 1/2 appears at $0.7 eV below the conduction band edge and arises from the doubly negative charge state of V C. The concentration of V C increases strongly after treatment at temperatures ! 1600 C and it reaches almost 10 15 cm À3 after the inductive heating at 1950 C. A formation enthalpy of $5.0 eV is deduced for V C , in close agreement with recent theoretical predictions in the literature, and the entropy factor is found to be $5 k (k denotes Boltzmann's constant). The latter value indicates substantial lattice relaxation around V C , consistent with V C being a negative-U system exhibiting considerable Jahn-Teller distortion. The microwave heated samples show evidence of non-equilibrium conditions due to the short duration used and display a lower content of V C than the inductively heated ones. Finally, concentration-versus-depth profiles of V C favour formation in the "bulk" of the epitaxial layer as the prevailing process and not a Schottky type process at the surface. V

Point Defects in Silicon Carbide

“…8 were obtained from samples heat-treated isochronally (10 min) in an inductively heated furnace under C-rich conditions where the samples were protected by a pyrolyzed resist film (C-cap) and hosted in a graphite box with glassy carbon-coated surfaces under highpurity Ar ambient. Steady-state conditions (thermal equilibrium) were expected to apply above 1600°C as evidenced by (i) the very similar values of [V C ] in the as-grown and as-oxidized samples despite quite different initial conditions, and (ii) rather uniform concentration versus depth profiles of V C (Ayedh et al, 2014). In fact, the depth profiles after the 1950°C treatment exhibited a small decrease ($30%) toward the surface favoring a bulk formation process of V C rather than Schottky formation at the surface with subsequent in-diffusion of V C .…”

“…Very recently, Ayedh et al (2014) exploited this possibility and investigated the V C concentration in high-purity epitaxial layers after heat treatment at different temperatures in the range of 1600-2000°C. Both as-grown and as-oxidized layers were studied, and as illustrated in Fig.…”

Carrier Lifetime Controlling Defects Z1/2 and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC

“…This increase in Z 1/2 concentration is significantly larger than the expected factor 3 increase based on a thermodynamic equilibrium V C density calculation using published experimental and calculated formation energies for V C in n-type doped samples. 22,23 Therefore,…”

Structural and Functional Characterizations of Al+Implanted 4H-SiC Layers and Al+Implanted 4H-SiCp-nJunctions after 1950°C Post Implantation Annealing

“…[5][6][7] 4H-SiC is the SiC poly-type more used for power electronic devices. Aluminum (Al) is the preferred acceptor dopant of 4H-SiC when very high acceptor concentrations are needed.…”

“…[1][2][3][4] While the industry has the understandable need to limit the thermal budget for device fabrication, the academy is exploring extremely high annealing temperatures because this is needed to understand all the phenomena related to the heating of both implanted and unimplanted regions of a SiC crystal. [5][6][7] 4H-SiC is the SiC poly-type more used for power electronic devices. Aluminum (Al) is the preferred acceptor dopant of 4H-SiC when very high acceptor concentrations are needed.…”