We report a microwave heating system with a carbon heating tube (CHT) which was made by a 4-mm diameter quartz tube filled with carbon particles and Ar gas at 1400 Pa. A 60-mm-long CHT was set in a cavity in which 2.45-GHz microwave was introduced. Via nearly complete absorption of a microwave power of 200 W by carbon in the CHT during multi-reflection of the microwave in the cavity, the CHT was effectively heated to 1279 • C at 33 s after the microwave initiation, which was observed by the radiationtype thermometer. Moreover, the control of the CHT temperature was demonstrated with a home-made proportional-integral-differential feedback circuit which regulated the magnetron power source using a signal of the thermometer. The control of temperature at 1100 • C was successfully realized. Crystallization of a 58-nm-thick amorphous silicon thin film formed on the glass substrate was demonstrated by mechanically moving the silicon sample just below the heated CHT. A high crystalline volume ratio of 0.92 was achieved. Furthermore, heating of 500-µm-thick-n-type silicon substrate implanted with 1.0 × 10 15 cm −2 phosphorus and boron atoms with the CHT resulted in activation of the doped regions. Rectified diode characteristics were achieved. INDEX TERMS Electromagnetic interference, heat treatment, low-microwave power electronics, PID temperature control, silicon.

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We report a microwave heating system with a carbon heating tube (CHT) made by a 4-mm diameter quartz tube filled carbon particles and Ar gas at 1400 Pa. 2.45-GHz microwave at 200 W was introduced to a 300-dimameter metal cavity, in which 60-mm-long CHT was set at the central position. The numerical simulation with a finite element moment method resulted in the standing wave of the electric field caused by three dimensional Fresnel interference effect with low high electric field intensity ranging from from 1 to 6 kV/m because of effective absorption of microwave power by the CHT. The lowest average electrical field intensity of 5 kV/m in the cavity space was given by the electrical conductivity of carbon ranging from 10 to 55 S/m. The CHT with 55 S/m heated to 1200oC by microwave irradiation at 200 W. This heating method was applied to activate 1.0x1015-cm-2 boron and phosphorus implanted regions in n-type crystalline silicon substrate to fabricate pn junction and solar cells. The CHT heating at 1200oC realized decrease in the sheet resistivity to 146 Ω/sq, decrease in the density of defect states to 1.3x1011 and 9.2x1010 cm-2 for boron (p+) and phosphorus (n+) implanted surfaces, and solar cell characteristic with a conversion efficiency of 15% under illumination of air mass 1.5 at 0.1 W/cm2.