Rapid Thermal Processing of III-Nitrides
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nitrides the usual nitrogen sources are NH 3 for Metal Organic Chemical Vapor Deposition (MOCVD)[5] and plasma dissociated N 2 in Molecular Beam Epitaxy (MBE)[6] and Metal Organic Molecular Beam Epitaxy (MOMBE).[7] A disadvantage of NH 3 is the residual hydrogen passivation of p-type dopants that occurs, and must be reversed by annealing at >_ 700'C[8] and this is also an inconvenient ambient for processes such as annealing for implant activation, contact annealing or implant isolation. Similarly, N2 is quite stable (bond energy 226kCal/mol) and thus in simple annealing processes at atmospheric pressure it is not effective in suppressing nitrogen loss from the nitride surface. In this paper we report on a comparison of the relative merits of using GaN, InN or AIN powder as reservoir materials during high temperature RTA of lEl-nitrides. GaN powder appears to provide the most effective surface protection over the widest temperatures range for these materials. However, there is still pitting of surfaces at the temperatures needed for implanted dopant activation in GaN (> 11 00°C), and it will be necessary to employ a more aggressive technique such as AIN encapsulation during annealing.[9] EXPERIMENT Epitaxial films of GaN, AIN, InN and InO. 75A10.25N approximately 0.5ýtm thick were grown on GaAs or Si substrates at temperatures between 550'C(InN) and 900°C(GaN and AIN) as described previously.[10, 11] The layers were predominantly cubic in phase, with threading 401
Mat. Res. Soc. Symp. Proc. Vol. 470 ©01997 Materials Research Society
dislocation densities of -1011 cm 2 measured by plan view transmission electron microscopy. The GaN and AIN were resistive as-grown, while the InN and InAIN were strongly conducting n-type (-1020 cm-)[ 11], due to the presence of native defects. All annealing was performed by placing the samples within a SiC-coated graphite susceptor in which GaN, AIN or InN powder (typical grain size l0jtm)[12] is placed in reservoirs milled into the susceptor, and which are connected to the region in which the wafer is contained. Annealing temperatures were controlled between 600-1175°C (10 secs at peak temperatures) by placing the susceptor in an AG Asoociates 410T furnace. Flowing N2 gas was used as the annealing ambient. We noticed that if either H 2 or 02 was present in this purge gas, the temperature at which surface dissociation was evident was lowered by 100-200'C for each of the nitrides. The root-mean-square (RMS) surface roughness of annealed samples was measured by atomic force microscopy (AFM) in the tapping mode using Si-tips, and the resulting values were normalized to those from unannealed control samples. Scanning electron microscopy (SEM) was also used to examine surface morphology, and both Energy Dispersive
X-ray spectroscopy (EDAX) and Auger Electron Spectroscopy (AES) were employed to determine surface composition changes. RESULTS AND DISCUSSION A comparison of normalized RMS surface roughness measured by AFM on GaN samples annealed at different temperatures with the three diffe
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