Heating equipment with carbon heating tube used to activate silicon and fabricate solar cells
Toshitaka Kikuchi1, Takashi Sugawara1, Takuma Uehara1, Tomoyoshi Miyazaki1,2, Go Kobayashi3, Masahiko Hasumi1,and Toshiyuki Sameshima1
1

Tokyo University of Agriculture and Technology, Graduate School of Engineering, 2-24-16, Naka-cho, Koganei, Tokyo,184-8588, Japan
2
Techno Research., Ltd., 5-9-10 Shimozato, Higashikurume, Tokyo, 203-0043, Japan3
Orc manufacturing Co., Ltd. 4896 Tamagawa, Chino, 391-0011 Japan
Email: tsameshim@cc.tuat.ac.jp

Introduction
We have proposed a new heating systems with a lamp ofcarbon heating tube (CHT) for rapid thermal heating [1].
The CHT consists of 2-μm-diameter-carbon powders witha 0.1-g weight in quartz tubes with 60-mm long and 4-mm
inter diameter with a packing density of 0.08 [2]. It is
heated to 1279oC by irradiation of 2.45 GHz microwave at
200 W. In This paper, we report development in CHT
heating system for activation of silicon implanted boron
and phosphorus atoms. We also report solar cell fabricationby the CHT heating system.
Experimental
We prepared 4-inch-diameter 17-Ωcm n-type silicon
substrates with a thickness of 500 μm with 100-nm-thickthermally grown SiO2 layers. The ion implantation ofboron atoms was conducted with a dose of 2x1015 cm-2 at
an acceleration energy of 25 keV to the top surface of thesilicon substrates. The peak concentration at the interfaceof the thermally grown SiO2 and silicon. Boron atoms at
1.0 x 1015 cm-2 were effectively implanted in the silicon
substrates. The ion implantation of phosphorus atoms at 75
keV was also conducted for the rear surface of the silicon
substrates with an effective dose of 1.0 x 1015 cm-2. A
silicon substrate was cut to four pieces for activating
implanted regions.
8 numbers of CHTs with 60-mm long and 4-mm interdiameter and a 0.1-g carbon powders and Ar insert gas at
10.5 Torr were prepared. Two quartz rods were jointed at
the edges of the each CHT by thermal welding to hold theCHT in the chamber. The 8 CHTs were placed in parallelwith no gap among the CHTs in the microwave cavity. Asample piece was placed on the 8 CHTs and heated withcontinuous microwave irradiation at 700 W for 150 s. The
CHT temperature was controlled by proportionalintegrated-differential feedback method. The temperature
increased at 32 K/s and heated to 1200oC for 100 s anddecreased at 23 K/s. After heating, the thermally grown
SiO2 layer was removed using hydrofluoric acid.
Microwave transmittance measurement resulted in a sheet
resistivity of 79 /sq and an effective lifetime of 115 s [3].
Comb-type Al electrodes were formed on the top surface
and the rear surface was entirely coated with Al electrodes
by vacuum evaporation. 100-nm-thick AlOx layer wasdeposited on the top surface as anti-reflection layer. Thesample was heated by H2O vaper at 230oC at 0.8 MPa for 3
h to decrease defect states at the doped and the surface ofsilicon substrate [4]. The electrical current density as afunction of voltage (J–V) was measured in dark and underillumination of air mass (AM) 1.5 light at 0.1 W/cm2.
Results and Discussions
Figure 1 shows (a) logarithmic plots of absolute electricalcurrent density as a function of voltage under conditions of
the dark and illumination of AM 1.5 light and (b) solar cellcharacteristic. Typical diode rectified characteristics with alow reverse bias current density of 1.3x10-3 A/cm2 at -1 V
and a high forward bias current density of 0.19 A/cm2 at +1
V were observed in the dark, as shown in Fig. 1(a). Light

illumination clearly showed a photovoltaic characteristic.
Typical solar cell current voltage characteristic wasobtained as shown in Fig. 1(b). The short circuit current
density Jsc, open circuit voltage Voc, fill factor FF, andconversion efficiency were 34 mA/cm2, 0.52 V, 0.63, and11.28%, respectively. These results indicate that implanted
regions were activated well and the build-in potential wasformed well in the depletion region.

Fig.1 (a) logarithmic plots of absolute electrical current density as afunction of voltage under conditions of the dark and illumination ofAM 1.5 light at 0.1 W/cm2 and (b) solar cell characteristic

Acknowledgements
This work was partially supported by Japan Science andTechnology Agency ASTEP (No. AS2911903S). We also
thank NISSIN ION EQUIPMENT CO., LTD for their support.
References
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Hasumi, and T. Sameshima, to be published in proc. ofActive-Matrix Flat Panel Displays and Devices (Kyoto, 2018).
2. S. Kimura, K. Ota, M. Hasumi, A. Suzuki, M. Ushijima,and T. Sameshima, Appl. Phys. A. 122 (2016) 695-1-9.
3. T. Sameshima, T. Motoki, K. Yasuda, T. Nakamura,
M. Hasumi, T. Mizuno, Jpn. J. Appl. Phys. 54,081302-1-6 (2015)
4. J. Takenezawa, M. Hasumi, T. Sameshima, T. Koida, T.
Kaneko, M. Karasawa, and M. Kondo J. of Non-CrystallineSolids 358 (2012) 2285-2288.