INFLUENCE OF X-RAY IRRADIATED ON JUNCTION …phoenix.eng.psu.ac.th/pec9/icet/paper/ee/P130.pdftechniques the electrical characteristics of the introduced ... The diodes were irradiated

The 5th PSU-UNS International Conference on Engineering and Technology (ICET-2011), Phuket, May 2-3, 2011

Prince of Songkla University, Faculty of Engineering Hat Yai, Songkhla, Thailand 90112

Abstract: In this paper investigate the effect of X-ray irradiated on p-n diode. The change of electrical characteristics of diode can confirm by junction depth. Energy of irradiated are various in the range 40-70 keV at time of exposure 205 second. After irradiated by X-ray the electrical were changed, leakage current were decreased. The change of leakage current can analysis by junction depth, junction depth can be calculated by capacitance-voltage (C-V) characteristics. In junction depth of diode after irradiated the carrier concentration were little change. Key Words: Junction depth/ Capacitance-voltage/ leakage current/ Irradiated 1. INTRODUCTION

Nowadays, semiconductors have to use in many work such as telecommunication [1], electronics [2], and medical [3]. Therefore, it will be to improve performance for support new technology in future. On the other hand, semiconductor device cannot support every work. When use device in radiation work, time to use is less because radiation have high energy. The degradation of device characteristics by irradiation with keV particles has been studied for many decades and is well documented nowadays. Despite this long research effort, the quantitative description of the link between the introduced lattice defects and the observed device degradation is still incomplete and shows considerable deficiencies [4]. In the present paper an attempt is made to bridge part of this gap by a combined effort to characterize with a selection of complementary analysis techniques the electrical characteristics of the introduced lattice damage and to correlate these fundamental defect properties with the observed diode characteristics. Since defects can be generated by ion implantation process or X-ray irradiation, etc, the induced defect will be confirmed by measurement of carrier concentration atjunction depth. New results are presented on the impact of irradiation induced lattice damage on the carrier concentration. For the first time of results are presented to improve performance of diode [5].

2. EXPERIMENT

The process flow of shallow p-n junction diode is compatible with CMOS technology on Thai Microelectronics Center (TMEC).

Fig. 1. Fabrication process of p-n junction diode.

The diode process module consists of (i) deposition of oxide covered substrate, (ii) dry-etching of active area,

INFLUENCE OF X-RAY IRRADIATED ON JUNCTION DEPTH OF P-N DIODE

Itsara Srithanachai and Surasak Niemcharoen Department of Electronics, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang,

Charongkrung Road, Ladkrabang, Bangkok 10520, Thailand Phone: +66-8117-3205-0, Email: [email protected]

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(iii) implantation of phosphorus at energy of 120 kV and dose of 1x1016 cm-2 for ohmic contact on backside wafers, (iv) implantation of boron at same energy and dose on front side wafers (the implantation been followed by a thermal annealing at 1050 oC for 60 min, resulting in a junction depth of about 1 μm) (v) Al metal-deposition, 10 μm thick, on front side and backside [6], the fabrication process shows in Fig. 1. After its fabrication process show in Fig 2, the diode were irradiated by X-ray at room temperature for various energy of exposure. The diodes were irradiated by X-ray for various energy and exposure dose, as shown in Table.1. The current-voltage (I-V) measurement was performed by the use of a HP4156B. The I-V characteristic results were measured on wafer with bias step of 0.025 V from reverse (VR) to forward (VF) voltage, in the range of -10 to +1 V. [7,8]

Fig. 2. Structure of p-n junction diode.

3. RESULTS AND DISCUSSION

Fig. 3 shows the experimental semi-log forward and reverse-bias characteristics of the p-n photodiode. The diode parameters are determined from the I-V characteristics, which is usually described by the thermionic emission theory. I = I0exp(qV/nkT) (1)

Here I is the current, q is the electron charge, V the applied voltage, T the absolute temperature, k the Boltzmann constant, n the ideality factor of p-n photodiode, and I0 is the saturation current. From values of V greater than nkT/q. Fig. 4 shows the leakage current of p-n junction diode were irradiated by X-ray. As discuss in Fig. 4, the value of diode leakage current for before irradiation is dominated by Si bulk defect. Therefore, to evaluate the radiation degradation of the diode accurately, it has to exclude the influence of leakage current before irradiation. The change of IR(ΔIR) by the X-ray irradiation is estimated and shown in Fig. 4.

Fig. 3. Semi-log forward and reverse current of p-n junction diode.

Fig. 4. Leakage current of diode before and after irradiated by X-ray. C-V characteristics of the p-n diode before and after the X-ray irradiation are shown in Fig. 5, revealing an unchanged capacitance, originating from a radiation induced dopant deactivation in the Si layer.

Fig. 5 Reverse voltage versus capacitance of the p-n diode before and after the X-ray irradiation.

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I-V characteristics were decreased at 70 keV of exposure. The effect of X-ray irradiated on I-V characteristics have many caused such as X-ray induced defect in bulk structure, carrier generation lifetime were increased and carrier concentration were changed. In this experiment, we investigated the carrier concentration of diode after irradiated by X-ray. The capacitance of a reverse-biased junction, when considered as a parallel plate capacitor, is C = Ksε0A/W (2)

The biases applied to the front side doping concentration calculate by eq. 3.

ND = 2/[qKsε0d(1/C2)dv] (3) using the identity d(1/C2)/dV = −(2/C3) dC/dV. Note the area dependence in these expressions. Since the area appears as A2, it is very important that the device area be precisely known for accurate doping profiling. From Eq. 4 we find the scr width dependence on capacitance as

W = Ksε0A/C (4) Where ND is the carrier concentration, A is the area of p-n junction, W is the width of depletion region, C is the capacitance, is the permittivity of vacuum, q is the electron charge and Ks is the permittivity of silicon. [8,9]

Fig. 6 Carrier concentration of p-n junction diode before and after irradiated. Fig. 6 shows carrier concentration of diode were changed after irradiated at 55 and 70 keV. This effect can confirm that junction depth were change after irradiated by X-ray. Therefore, we conclude that the I-V characteristics changed were the result of carrier concentration [10,11]. Changes in the carrier concentration were not sufficient to confirm the change of I-V characteristics must be study in the further. 4. CONCLUSIONS

The main conclusions from this work are that the effect by X-ray irradiation on the electrical properties of p-n junction diode. I-V measurements show that there are

increases in the reverse leakage current at 40, 55 keV and 70 keV is decrease. Carrier concentration is one of the causes of the changes the electrical properties. From the results can be concluded that change of leakage current at 70 keV, is made this experiment more attractive. Acknowledgment

The authors would like to thank King Mongkut’s University of Technology North Bangkok (KMTNB) for providing the X-ray exposure equipment for this experiment, Thai Microelectronics Center (TMEC) for fabrication p-n junction diode, National Electronics and Computer Technology Center, Thailand and Thailand Graduate Institute of Science and Technology (TGIST) under scholarship number TG-44-22-53-014D. 5. REFFERENCE

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[2] Yoshinori Matsumoto, Akimichi Nakazono, Taisuke Kitahara, Yasuhiro Koike, High efficiency optical coupler for a small photo acceptance area photodiode used in the high speed plastic optical fiber communication, Sensors and Actuators A: Physical 97-98 (2002) 318-322.

[3] Bogushevich SE, Ugolev II, Inorganic EPR dosimeter for medical radiology, Appl Radiat Isot 52(5) (2000) 1217-9.

[4] E. Simoen, C. Claeys, R. Loo, O. De Gryse, P. Clauws, R. Job, A.G. Ulyashin , W. Fahrner , “Characterisation of oxygen and oxygen-related defects in highly- andlowly-doped silicon”, Materials Science and Engineering B 102, pp. 207-212, (2003).

[5] J. Vanhellemont, E. Simoen and C. Claeys, “On the impact of low fluence irradiation with MeV particles on silicon diode characteristics and related material properties”, IEEE Transactions on Nucleak Science, VOL. 41, NO. 6, PP. 1924-131, 1994.

[6] Poopol Rujanapich, Amporn Poyai, Itsara sithanachai, Putapon Pengpad, Wisut Titiroongruang, "Generation Lifetime Analysis of p-n Junction X-ray Detector”, ITC-CSCC 2010, pp. 157-260, (2010).

[7] Yuwadee Sundarasaradula, Itsara Srithanachai, Poopol Rujanapich, Surada Ueamanapong and Surasak Niemcharoen, “Effect of X-ray Irradiation on The Characteristics of p-n Junction Diodes”, EECON’33, 1, (2010).

[8] D.K. Schoroder, “Semiconductor Matetial and Device Characterization,” John Wiley & Sons,New York, 2006.

[9] K. Takakura, H. Furukawa, S. Kuroki, K. Hayama, T. Kudou, K. Shigaki, H. Ohyama, E. Simoen, G. , C. Claeys, “Radiation defects and degradation of C-doped SiGe diodes irradiated by electrons”, Material Science in Semiconductor Processing, Vol. 9, 2006, pp. 292-295.

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[10] Geert Eneman, Maxime Wiot, Antoine Brugere, Oriol Sicart I Casain, Sushant Sonde, David P. Brunco, Brice De Jaeger, Alessandra Satta, Geert Hellings, “Impact of Donor Concentration, Electric Field, and Temperature Effects on the Leakage Current in Germanium p+/n Junctions”, IEEE Transaction on Electron Devices, Vol. 55, No. 9, September (2008).

[11] R. Glicksman, R. M. Minton, “The effect of p-region carrier concentration on the electrical characteristics of germanium epitaxial tunnel diodes”, Solid-State Electronics, Volume 8, Issue 5, May 1965, Pages 517-519.

ItsaraSrithanachai was born in Chingrai, Thailand. He received the B.S. (’06) degree in applied physics from King Mongkut’s Institute of Technology Ladkrabang (KMITL), and M.Eng. (09’) in electronics engineering from King Mongkut’s Institute of Technology Lad-

krabang (KMITL). His master degree research was in the field of photodetector process. He has 4 years of experience in semiconductor fabrication process. He is now a doctoral student in electrical engineering, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang (KMITL).

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