Reliable and accurate temperature measurement during microwave processing of ceramic bodies is controversial. Although thermocouples are routinely used in conventional thermal furnaces, their presence in microwave furnaces can locally distort the electromagnetic field, conduct heat away from the sample, induce thermal instabilities and microwave breakdown, and lead to serious measurement errors. These thermocouple effects have been studied and found to be more pronounced in low- and medium-loss ceramic materials. To decrease the thermocouple effects during the processing of advanced ceramic materials, an optical, noncontact temperature sensing system has been developed, calibrated, and incorporated into a computer-controlled microwave furnace.

Temperature Measurements during Microwave Processing: The Significance of Thermocouple Effects

Advances in Induction and Microwave Heating of Mineral and Organic Materials

Ion-implantation is an indispensable technique for planar selective area doping of SiC devices, because thermal diffusion of the desired dopants at temperatures where SiC doesn't decompose is not possible. Incongruent evaporation of Si from the SiC wafer during post-implantation annealing limits the maximum annealing temperature that can be used to repair the lattice damage and steer the implant into the substitutional lattice positions. Other problems include the nonstoichiometric disturbances caused by the ion-implantation, which result in non-uniform Si and C atom concentration and vacancy concentration depth distributions in the implanted region; and the difficulty in restoring the lattice quality back to the virgin level if as-implant lattice damage is of amorphous level. Ion-implantation in SiC needs to be performed at an elevated temperature in the range of 500 - 1000 /spl deg/C. An additional problem is the deep ionization energies of the useful donor (/spl sim/ 80 meV) and acceptor (> 240 meV) impurities in SiC, which limit the maximum carrier concentration . Results of donor, acceptor, and compensation species ion-implantations in 6H- and 4H-SiC are presented.

Maturing ion-implantation technology and its device applications in SiC

Multiple energy N (at 500 °C) and Al (at 800 °C) ion implantations were performed into bulk semi-insulating 4H–SiC at various doses to obtain uniform implant concentrations in the range 1×1018–1×1020 cm−3 to a depth of 1.0 μm. Implant anneals were performed at 1400, 1500, and 1600 °C for 15 min. For both N and Al implants, the carrier concentration measured at room temperature for implant concentrations ⩽1019 cm−3 is limited by carrier ionization energies, whereas for the 1020 cm−3 implant, the carrier concentration is also limited by factors such as the solubility limit of the implanted nitrogen and residual implant damage. Lattice quality of the as-implanted and annealed material was evaluated by Rutherford backscattering spectroscopy measurements. Residual lattice damage was observed in the implanted material even after high temperature annealing. Atomic force microscopy revealed increasing deterioration in surface morphology (due to the evaporation of Si containing species) with increasing annealing t...

Ion-implantation in bulk semi-insulating 4H–SiC

Phosphorus and boron ion implantations were performed at various energies in the 50 keV–4 MeV range. Range statistics of P+ and B+ were established by analyzing the as-implanted secondary ion mass spectrometry depth profiles. Anneals were conducted in the temperature range of 1400–1700 °C using either a conventional resistive heating ceramic processing furnace or a microwave annealing station. The P implant was found to be stable at any annealing temperature investigated, but the B redistributed during the annealing process. The implant damage is effectively annealed as indicated by Rutherford backscattering measurements. For the 250 keV/1.2×1015 cm−2 P implant, annealed at 1600 °C for 15 min, the measured donor activation at room temperature is 34% with a sheet resistance of 4.8×102 Ω/□. The p-type conduction could not be measured for the B implants.

Phosphorus and boron implantation in 6H–SiC

Rapid thermal processing utilizing microwave energy has been used to anneal N, P, and Al ion-implanted 6H-SiC. The microwaves raise the temperature of the sample at a rate of 200°C/min vs 10°C/min for conventional ceramic furnace annealing. Samples were annealed in the temperature range of 1400-1700°C for 2-10 min. The implanted/annealed samples were characterized using van der Pauw Hall, Rutherford backscattering, and secondary ion mass spectrometry. For a given annealing temperature, the characteristics of the microwave-annealed material are similar to those of conventional furnace anneals despite the difference in cycle time.

I. Ahmad

Papers

Rapid thermal annealing of ion implanted 6H-SiC by microwave processing