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n-6H–SiC interface under irradiation by H+-ions
Nuclear Instruments and Methods in Physics Research B 215 (2004) 385–388 www.elsevier.com/locate/nimb
Ion-beam mixing at Ni/n-6H–SiC interface under irradiation by Hþ -ions V.V. Kozlovski a,*, V.N. Lomasov a, D.S. Rumyantsev a, I.V. Grekhov b, P.A. Ivanov b, T.P. Samsonova b, H.I. Helava c, L.O. Ragle c a b
St. Petersburg State Polytechnical University, 29 Polytechnicheskaya, 195251 St.-Petersburg, Russia Ioffe Institute of Russian Academy of Sciences, 26 Polytechnicheskaya, 194021 St.-Petersburg, Russia c The Fox Group, Inc., Livermore, CA 94550, USA Received 13 May 2003; received in revised form 5 August 2003
Abstract It is shown that intermixing at the Ni/n-6H–SiC interface is enhanced when the Ni–SiC sandwich is subjected to irradiation by protons (Hþ ). Possible mechanism of radiation-enhanced intermixing of Ni and SiC is discussed when the bombarding Hþ -particles are braked within the metal film. 2003 Elsevier B.V. All rights reserved. PACS: 68.10.Eq; 68.65.Ln; 68.10.Nq Keywords: Metal–semiconductor interface; Ion-beam mixing; Hydrogen particles; Nickel silicide
1. Introduction The physical and electronic properties of silicon carbide (SiC) make it the foremost semiconductor material for high temperature, radiation resistant and high power/high frequency electronic devices [1]. To realize these advantages in SiC electronic components, some problems have remained to be solved. The problem of vital importance is the development of reliable ohmic contacts to SiC materials. Many researches have reported the
* Corresponding author. Tel.: +7-812-552-7574; fax: +7-812552-3314. E-mail address: [email protected] (V.V. Kozlovski).
electrical, chemical and/or microstructural characteristics of metal–SiC contacts using Ni, Ti, Ta, W as contact metals which can form silicides or carbides [2–5]. From viewpoint of metallurgical reactions, Ni–SiC system is the most studied one. Although Ni deposited at room temperature and annealed to 1000 C to form nickel silicides is the currently favored ohmic contacts to n-type SiC [6–8], much of the physics of contact formation is not still adequately understood, with the reproducibility of metal–SiC contact properties remains poor. Electrical characteristics of metal–semiconductor contacts are mainly determined by the metallo-physical nature of the metal/semiconductor interfaces [9–12]. It is known that ion-beam irradiations of metal–semiconductor structures
0168-583X/$ - see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2003.08.038
386
V.V. Kozlovski et al. / Nucl. Instr. and Meth. in Phys. Res. B 215 (2004) 385–388
can cause large changes in the composition and structure of the interface regions [13–20]. It has been recently shown that high temperature irradiation by Hþ -ions substantially enhance ionbeam mixing (IBM) at the Au–Ge/GaAs interfaces [14,21]. The present investigation was intended to study the effect of simultaneous thermal and Hþ impact on Ni/SiC interface.
2. Experimental Industrial n-6H–SiC Lely-type crystals were used for the experiments. Prior to nickel deposition, SiC samples were cleaned with standard RCA cleaning and then oxidized in a quartz tube furnace at 1150 C during 1 h. The sacrificial oxides were then etched by dipping in 5% HF solution. Finally, the samples were rinsed in deionized water. Ni films were deposited onto (0 0 0 1)Si face by ion-beam sputtering. The thickness of the deposited Ni film, d, was 134 nm. A 10–100 kV NG-200U accelerator was employed for the irradiation by Hþ -particles. The irradiation dose was chosen to be 5.4 · 1016 cm2 , with the ion-beam current density of 5 lA/cm2 . The Ni–SiC wafers can be heated during irradiations up to a maximum temperature of 1000 C. In order to minimize the radiation damage of the semiconductor, an irradiation scheme was chosen as depicted in Fig. 1, with Rp 6 d ð6–7Þrp , where Rp is the projected range of Hþ -ions and rp is the straggling of particle distribution that describes by a PearsonÕs IV function. With 134-nm thick Nifilm, the Hþ -particle energy, providing Rp d=3, was calculated to be about 10 keV using a stan-
semiconductor
metal-film +
H
σp
0
Rp
d
x
Fig. 1. The irradiation scheme: Rp 6 d ð6–7Þrp .
dard TRIM program [22]. Unfortunately, the ratio rp =Rp becomes higher with decreasing particle energy. At E ¼ 10 keV, it is impossible to provide the above condition Rp 6 d ð6–7Þrp . Therefore the Hþ -particle energy was chosen to be 40 keV for the experiments, whereas the projected range Rp and, consequently, straggling rp were properly reduced, to 50 nm and 13 nm [23], respectively, via that the specimen normal was aligned 75 from the Hþ -beam axis. The irradiations were conducted at a temperature 750 C, at which nickel silicide is expected to form [9]. In order to study the interface reactions, Auger profiling with ionic erosion has been performed to determine the chemical depth profiles of Ni, Si and C. The concentrations of silicon, carbon and nickel atoms were determined using 92, 272 and 848 eV AES data, respectively. In addition to AES profiling, optical photographs were made to compare surface morphology of contacts obtained.
3. Results and discussion Fig. 2(a) shows the AES results on the part of the sample which was masked from Hþ -irradiation to reveal the expected ion-beam mixing effect. Fig. 2(b) shows AES depth profiles in the irradiated part of the sample (750 C, 30 min). In non-irradiated part, the following layer sequence is seen starting from the SiC substrate: (1) weak carbon accumulation near the SiC substrate, (2) a Ni–Si gradual intermixing layer and (3) a low carbon content, mainly Ni-silicide layer. By contrast, for irradiated part profiles are very steep near the metal/SiC interface. Two main layers can be seen, starting from the substrate: (1) a carbonrich/low-silicon layer and (2) some Ni-silicide (most probably, some mixture of NiSi and NiSi2 ) – standing over the carbon-rich layer. It is obvious that nickel silicide was formed by consuming silicon in the SiC substrate and, thus, the composition of SiC at the metal/semiconductor interface is shifted toward a silicon-depleted direction. The maximum C/Si ratio in silicon-depleted layer can be taken as a measure of the intermixing degree. It is clear from comparing Figs. 2(a) and 2(b) that radiation impact enhances the interdiffusion at the
V.V. Kozlovski et al. / Nucl. Instr. and Meth. in Phys. Res. B 215 (2004) 385–388
387
80
Atomic percent (%)
(a) 60
Si 40
Ni
20
0
C
0
50
100
150
200
250
300
Depth, nm 80
Atomic percent (%)
(b) 60
Si Ni
40
20
C 0
0
50
100
150
200
250
300
Depth (nm) Fig. 2. AES depth profiles in a Ni–SiC sample: (a) masked part of the sample; (b) part of the sample irradiated at 750 C during 30 min.
Ni/SiC interface: C/Si ¼ 1.2 in non-irradiated part of the sample whereas C/Si ¼ 2.6 in irradiated one, i.e. the relative contribution of IBM is higher than 50%. It is seen from Figs. 2(a) and 2(b) that namely silicon diffusion into the Ni-films is enhanced. Such effect seems to be due to up-hill diffusion mechanism which is described by the equation [24] 1 oC o2 C o2 V ¼ V ðxÞ 2 CðxÞ 2 ; F ot ox ox
ð1Þ
where F ¼ k2 w (here k is the length of diffusion jump, w is the jump probability), C, V are the concentrations of diffusing atoms and vacancies, respectively. The vacancy concentration V can be determined from discontinuity equation:
Fig. 3. Optical photographs of patterned Ni contacts (the outer diameter is 1 mm): (a) masked part of the sample; (b) part of the sample irradiated at 750 C during 30 min.
oV o2 V V ¼ DV 2 þ GðxÞ ; ot ox sV
ð2Þ
where DV and sV are the vacancy diffusion coefficient and lifetime, respectively. At x Rp the distribution of vacancies becomes exponential one: x Rp V ¼ V0 exp ; ð3Þ LV 1=2
is the vacancy diffusion where LV ¼ ðDV sV Þ length. It is seen from Eqs. (1)–(3) that the IBM efficiency is affected by LV value. The maximum concentration of radiation defects (vacancies) is generated within the Ni-film (see Fig. 1). Therefore, in accordance with Eq. (1) the flux of Siatoms toward the high-defect region is higher than the flux of Ni-atoms in opposite direction. Actually, Eq. (1) indicates that up-hill diffusion will be
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V.V. Kozlovski et al. / Nucl. Instr. and Meth. in Phys. Res. B 215 (2004) 385–388
most effective if the distance between the high-defect region and the metal/semiconductor interface, d Rp , does not exceed the ð1–2Þ LV value. With d ¼ 134 nm, Rp ¼ 50 nm, the LV value can be estimated from Eqs. (1)–(3) to be 50 nm that is reasonable one for solids [14]. The LV value also limits the minimum energies of protons that can provide effective IBM effect. In particular, the particle range Rp should be higher than LV . Otherwise, the external surface of the metal film will act as an effective sink of defects generated. The recombination of the defects at the metal surface will substantially reduce the IBM effect. Irradiation of Ni–SiC couple was found to improve contact morphology. Figs. 3(a) and 3(b) present optical appropriate photographs of patterned contacts. As seen, the uniformity of irradiated contacts is much better than that of non-irradiated ones. In case of single thermal treatment the spotty contact image seems to be due to that Ni-metal layer has not fully reacted within the contact area.
4. Conclusion The irradiation of Ni–n-6H–SiC sandwich by hydrogen ions at elevated temperatures of 750 C can enhance silicon diffusion from SiC into the Nifilm due to up-hill diffusion mechanism. In particular, the relative contribution of such ion-beam mixing effect can be as high as 50%.
References [1] M. Bhatnagar, B.J. Baliga, IEEE Trans. Electron. Dev. ED-40 (1993) 645. [2] J. Crofton, P.G. McMullin, J.R. Williams, M.J. Bozak, J. Appl. Phys. 77 (1995) 1317. [3] J.J. Bellina, M.V. Zeller, in: D. Emin, T.L. Aselage, C. Wood (Eds.), Novel Refractory Semiconductors, Material Research Society, Pittsburg, PA, 1987, p. 265.
[4] P.G. McMullin, J.A. Spitznagel, J.R. Szedon, J.A. Costello, in: Proceedings of the ICACSC held in Washington, DC, 1990, p. 294. [5] K.M. Geib, J.E. Mahan, C.W. Wilmsen, in: M.M. Rahman, G.L. Harris, C.Y.-W. Yang (Eds.), SPP Amorphous and Crystalline Silicon Carbide, Vol. 43, Springer-Verlag, Berlin, Heidelberg, 1989, p. 224. [6] K. Robbie, S.T. Jemander, N. Lin, C. Hallin, R. Erlandsson, G.V. Hansson, L.D. Madsen, in: Proceedings of the ICSCRM – 1999, Research Triangle Park, NC, USA, 1999, Materials Science Forum, Vols. 338–342, 2000, p. 981. [7] T. Nakamura, H. Shimada, M. Satoh, Proceedings of the ICSCRM – 1999, Research Triangle Park, NC, USA, 1999, Materials Science Forum, Vols. 338–342, 2000, p. 985. [8] T. Toda, Y. Ueda, M. Sawada, in: Proceedings of the ICSCRM – 1999, Research Triangle Park, NC, USA, 1999, Materials Science Forum, Vols. 338–342, 2000, p. 989. [9] J.M. Poate, K.N. Tu, J.W. Mayer (Eds.), Thin Films – Interdiffusion and Reaction, John Wiley & Sons, NY, 1978. [10] A.K. Sinha, T.E. Smith, H.J. Levinshtein, IEEE Trans. Electron. Dev. ED-22 (1975) 218. [11] B. Schwartz (Ed.), Ohmic Contacts to Semiconductors, Electrochemical Society, NY, 1969. [12] N. Braslau, J.B. Gunn, J. Staples, Solid-State Electron. 10 (1967) 381. [13] J.M. Poate, G. Foti, D.C. Jacobson (Eds.), Surface Modification and Alloying by Laser, Ion, and Electron Beams, Plenum Press, NY, 1983. [14] V.V. Kozlovski, Modification of Semiconductors by Proton Beams, Nauka, St. Petersburg, 2003. [15] R. Kelly, M.F. Da Silva (Eds.), Materials Modification by High-Fluence Ion Beams, Kluwer Academic, Dordrecht, 1987. [16] S.M. Mayers, Nucl. Instr. and Meth. 168 (1980) 265. [17] J.S. Williams, R.G. Elliman, M.C. Ridgway (Eds.), Ion Beam Modification of Materials, North-Holland, 1996. [18] P. Sigmund, A. Gras-Marti, Nucl. Instr. and Meth. 182– 183 (1981) 25. [19] B.Y. Tsaur, Z.L. Liau, J.W. Mayer, Appl. Phys. Lett. 34 (1979) 167. [20] D.K. Sarkar, S. Dhara, K.G.M. Nair, S. Chaudhury, Nucl. Instr. and Meth. B 161 (2002) 992. [21] V.V. Kozlovski, V.A. Kozlov, V.N. Lomasov, Semiconductors 34 (2000) 123. [22] J.P. Biersack, L.G. Haggmark, Nucl. Instr. and Meth. 174 (1980) 257. [23] H.H. Andersen, J.F. Ziegler, Hydrogen Stopping Powers and Ranges in all Elements, Pergamon Press, NY, 1977. [24] Y. Morikawa, K. Yamamoto, K. Nagami, Appl. Phys. Lett. 36 (1980) 997.
Ion-beam mixing at Ni/n-6H–SiC interface under irradiation by Hþ -ions V.V. Kozlovski a,*, V.N. Lomasov a, D.S. Rumyantsev a, I.V. Grekhov b, P.A. Ivanov b, T.P. Samsonova b, H.I. Helava c, L.O. Ragle c a b
St. Petersburg State Polytechnical University, 29 Polytechnicheskaya, 195251 St.-Petersburg, Russia Ioffe Institute of Russian Academy of Sciences, 26 Polytechnicheskaya, 194021 St.-Petersburg, Russia c The Fox Group, Inc., Livermore, CA 94550, USA Received 13 May 2003; received in revised form 5 August 2003
Abstract It is shown that intermixing at the Ni/n-6H–SiC interface is enhanced when the Ni–SiC sandwich is subjected to irradiation by protons (Hþ ). Possible mechanism of radiation-enhanced intermixing of Ni and SiC is discussed when the bombarding Hþ -particles are braked within the metal film. 2003 Elsevier B.V. All rights reserved. PACS: 68.10.Eq; 68.65.Ln; 68.10.Nq Keywords: Metal–semiconductor interface; Ion-beam mixing; Hydrogen particles; Nickel silicide
1. Introduction The physical and electronic properties of silicon carbide (SiC) make it the foremost semiconductor material for high temperature, radiation resistant and high power/high frequency electronic devices [1]. To realize these advantages in SiC electronic components, some problems have remained to be solved. The problem of vital importance is the development of reliable ohmic contacts to SiC materials. Many researches have reported the
* Corresponding author. Tel.: +7-812-552-7574; fax: +7-812552-3314. E-mail address: [email protected] (V.V. Kozlovski).
electrical, chemical and/or microstructural characteristics of metal–SiC contacts using Ni, Ti, Ta, W as contact metals which can form silicides or carbides [2–5]. From viewpoint of metallurgical reactions, Ni–SiC system is the most studied one. Although Ni deposited at room temperature and annealed to 1000 C to form nickel silicides is the currently favored ohmic contacts to n-type SiC [6–8], much of the physics of contact formation is not still adequately understood, with the reproducibility of metal–SiC contact properties remains poor. Electrical characteristics of metal–semiconductor contacts are mainly determined by the metallo-physical nature of the metal/semiconductor interfaces [9–12]. It is known that ion-beam irradiations of metal–semiconductor structures
0168-583X/$ - see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2003.08.038
386
V.V. Kozlovski et al. / Nucl. Instr. and Meth. in Phys. Res. B 215 (2004) 385–388
can cause large changes in the composition and structure of the interface regions [13–20]. It has been recently shown that high temperature irradiation by Hþ -ions substantially enhance ionbeam mixing (IBM) at the Au–Ge/GaAs interfaces [14,21]. The present investigation was intended to study the effect of simultaneous thermal and Hþ impact on Ni/SiC interface.
2. Experimental Industrial n-6H–SiC Lely-type crystals were used for the experiments. Prior to nickel deposition, SiC samples were cleaned with standard RCA cleaning and then oxidized in a quartz tube furnace at 1150 C during 1 h. The sacrificial oxides were then etched by dipping in 5% HF solution. Finally, the samples were rinsed in deionized water. Ni films were deposited onto (0 0 0 1)Si face by ion-beam sputtering. The thickness of the deposited Ni film, d, was 134 nm. A 10–100 kV NG-200U accelerator was employed for the irradiation by Hþ -particles. The irradiation dose was chosen to be 5.4 · 1016 cm2 , with the ion-beam current density of 5 lA/cm2 . The Ni–SiC wafers can be heated during irradiations up to a maximum temperature of 1000 C. In order to minimize the radiation damage of the semiconductor, an irradiation scheme was chosen as depicted in Fig. 1, with Rp 6 d ð6–7Þrp , where Rp is the projected range of Hþ -ions and rp is the straggling of particle distribution that describes by a PearsonÕs IV function. With 134-nm thick Nifilm, the Hþ -particle energy, providing Rp d=3, was calculated to be about 10 keV using a stan-
semiconductor
metal-film +
H
σp
0
Rp
d
x
Fig. 1. The irradiation scheme: Rp 6 d ð6–7Þrp .
dard TRIM program [22]. Unfortunately, the ratio rp =Rp becomes higher with decreasing particle energy. At E ¼ 10 keV, it is impossible to provide the above condition Rp 6 d ð6–7Þrp . Therefore the Hþ -particle energy was chosen to be 40 keV for the experiments, whereas the projected range Rp and, consequently, straggling rp were properly reduced, to 50 nm and 13 nm [23], respectively, via that the specimen normal was aligned 75 from the Hþ -beam axis. The irradiations were conducted at a temperature 750 C, at which nickel silicide is expected to form [9]. In order to study the interface reactions, Auger profiling with ionic erosion has been performed to determine the chemical depth profiles of Ni, Si and C. The concentrations of silicon, carbon and nickel atoms were determined using 92, 272 and 848 eV AES data, respectively. In addition to AES profiling, optical photographs were made to compare surface morphology of contacts obtained.
3. Results and discussion Fig. 2(a) shows the AES results on the part of the sample which was masked from Hþ -irradiation to reveal the expected ion-beam mixing effect. Fig. 2(b) shows AES depth profiles in the irradiated part of the sample (750 C, 30 min). In non-irradiated part, the following layer sequence is seen starting from the SiC substrate: (1) weak carbon accumulation near the SiC substrate, (2) a Ni–Si gradual intermixing layer and (3) a low carbon content, mainly Ni-silicide layer. By contrast, for irradiated part profiles are very steep near the metal/SiC interface. Two main layers can be seen, starting from the substrate: (1) a carbonrich/low-silicon layer and (2) some Ni-silicide (most probably, some mixture of NiSi and NiSi2 ) – standing over the carbon-rich layer. It is obvious that nickel silicide was formed by consuming silicon in the SiC substrate and, thus, the composition of SiC at the metal/semiconductor interface is shifted toward a silicon-depleted direction. The maximum C/Si ratio in silicon-depleted layer can be taken as a measure of the intermixing degree. It is clear from comparing Figs. 2(a) and 2(b) that radiation impact enhances the interdiffusion at the
V.V. Kozlovski et al. / Nucl. Instr. and Meth. in Phys. Res. B 215 (2004) 385–388
387
80
Atomic percent (%)
(a) 60
Si 40
Ni
20
0
C
0
50
100
150
200
250
300
Depth, nm 80
Atomic percent (%)
(b) 60
Si Ni
40
20
C 0
0
50
100
150
200
250
300
Depth (nm) Fig. 2. AES depth profiles in a Ni–SiC sample: (a) masked part of the sample; (b) part of the sample irradiated at 750 C during 30 min.
Ni/SiC interface: C/Si ¼ 1.2 in non-irradiated part of the sample whereas C/Si ¼ 2.6 in irradiated one, i.e. the relative contribution of IBM is higher than 50%. It is seen from Figs. 2(a) and 2(b) that namely silicon diffusion into the Ni-films is enhanced. Such effect seems to be due to up-hill diffusion mechanism which is described by the equation [24] 1 oC o2 C o2 V ¼ V ðxÞ 2 CðxÞ 2 ; F ot ox ox
ð1Þ
where F ¼ k2 w (here k is the length of diffusion jump, w is the jump probability), C, V are the concentrations of diffusing atoms and vacancies, respectively. The vacancy concentration V can be determined from discontinuity equation:
Fig. 3. Optical photographs of patterned Ni contacts (the outer diameter is 1 mm): (a) masked part of the sample; (b) part of the sample irradiated at 750 C during 30 min.
oV o2 V V ¼ DV 2 þ GðxÞ ; ot ox sV
ð2Þ
where DV and sV are the vacancy diffusion coefficient and lifetime, respectively. At x Rp the distribution of vacancies becomes exponential one: x Rp V ¼ V0 exp ; ð3Þ LV 1=2
is the vacancy diffusion where LV ¼ ðDV sV Þ length. It is seen from Eqs. (1)–(3) that the IBM efficiency is affected by LV value. The maximum concentration of radiation defects (vacancies) is generated within the Ni-film (see Fig. 1). Therefore, in accordance with Eq. (1) the flux of Siatoms toward the high-defect region is higher than the flux of Ni-atoms in opposite direction. Actually, Eq. (1) indicates that up-hill diffusion will be
388
V.V. Kozlovski et al. / Nucl. Instr. and Meth. in Phys. Res. B 215 (2004) 385–388
most effective if the distance between the high-defect region and the metal/semiconductor interface, d Rp , does not exceed the ð1–2Þ LV value. With d ¼ 134 nm, Rp ¼ 50 nm, the LV value can be estimated from Eqs. (1)–(3) to be 50 nm that is reasonable one for solids [14]. The LV value also limits the minimum energies of protons that can provide effective IBM effect. In particular, the particle range Rp should be higher than LV . Otherwise, the external surface of the metal film will act as an effective sink of defects generated. The recombination of the defects at the metal surface will substantially reduce the IBM effect. Irradiation of Ni–SiC couple was found to improve contact morphology. Figs. 3(a) and 3(b) present optical appropriate photographs of patterned contacts. As seen, the uniformity of irradiated contacts is much better than that of non-irradiated ones. In case of single thermal treatment the spotty contact image seems to be due to that Ni-metal layer has not fully reacted within the contact area.
4. Conclusion The irradiation of Ni–n-6H–SiC sandwich by hydrogen ions at elevated temperatures of 750 C can enhance silicon diffusion from SiC into the Nifilm due to up-hill diffusion mechanism. In particular, the relative contribution of such ion-beam mixing effect can be as high as 50%.
References [1] M. Bhatnagar, B.J. Baliga, IEEE Trans. Electron. Dev. ED-40 (1993) 645. [2] J. Crofton, P.G. McMullin, J.R. Williams, M.J. Bozak, J. Appl. Phys. 77 (1995) 1317. [3] J.J. Bellina, M.V. Zeller, in: D. Emin, T.L. Aselage, C. Wood (Eds.), Novel Refractory Semiconductors, Material Research Society, Pittsburg, PA, 1987, p. 265.
[4] P.G. McMullin, J.A. Spitznagel, J.R. Szedon, J.A. Costello, in: Proceedings of the ICACSC held in Washington, DC, 1990, p. 294. [5] K.M. Geib, J.E. Mahan, C.W. Wilmsen, in: M.M. Rahman, G.L. Harris, C.Y.-W. Yang (Eds.), SPP Amorphous and Crystalline Silicon Carbide, Vol. 43, Springer-Verlag, Berlin, Heidelberg, 1989, p. 224. [6] K. Robbie, S.T. Jemander, N. Lin, C. Hallin, R. Erlandsson, G.V. Hansson, L.D. Madsen, in: Proceedings of the ICSCRM – 1999, Research Triangle Park, NC, USA, 1999, Materials Science Forum, Vols. 338–342, 2000, p. 981. [7] T. Nakamura, H. Shimada, M. Satoh, Proceedings of the ICSCRM – 1999, Research Triangle Park, NC, USA, 1999, Materials Science Forum, Vols. 338–342, 2000, p. 985. [8] T. Toda, Y. Ueda, M. Sawada, in: Proceedings of the ICSCRM – 1999, Research Triangle Park, NC, USA, 1999, Materials Science Forum, Vols. 338–342, 2000, p. 989. [9] J.M. Poate, K.N. Tu, J.W. Mayer (Eds.), Thin Films – Interdiffusion and Reaction, John Wiley & Sons, NY, 1978. [10] A.K. Sinha, T.E. Smith, H.J. Levinshtein, IEEE Trans. Electron. Dev. ED-22 (1975) 218. [11] B. Schwartz (Ed.), Ohmic Contacts to Semiconductors, Electrochemical Society, NY, 1969. [12] N. Braslau, J.B. Gunn, J. Staples, Solid-State Electron. 10 (1967) 381. [13] J.M. Poate, G. Foti, D.C. Jacobson (Eds.), Surface Modification and Alloying by Laser, Ion, and Electron Beams, Plenum Press, NY, 1983. [14] V.V. Kozlovski, Modification of Semiconductors by Proton Beams, Nauka, St. Petersburg, 2003. [15] R. Kelly, M.F. Da Silva (Eds.), Materials Modification by High-Fluence Ion Beams, Kluwer Academic, Dordrecht, 1987. [16] S.M. Mayers, Nucl. Instr. and Meth. 168 (1980) 265. [17] J.S. Williams, R.G. Elliman, M.C. Ridgway (Eds.), Ion Beam Modification of Materials, North-Holland, 1996. [18] P. Sigmund, A. Gras-Marti, Nucl. Instr. and Meth. 182– 183 (1981) 25. [19] B.Y. Tsaur, Z.L. Liau, J.W. Mayer, Appl. Phys. Lett. 34 (1979) 167. [20] D.K. Sarkar, S. Dhara, K.G.M. Nair, S. Chaudhury, Nucl. Instr. and Meth. B 161 (2002) 992. [21] V.V. Kozlovski, V.A. Kozlov, V.N. Lomasov, Semiconductors 34 (2000) 123. [22] J.P. Biersack, L.G. Haggmark, Nucl. Instr. and Meth. 174 (1980) 257. [23] H.H. Andersen, J.F. Ziegler, Hydrogen Stopping Powers and Ranges in all Elements, Pergamon Press, NY, 1977. [24] Y. Morikawa, K. Yamamoto, K. Nagami, Appl. Phys. Lett. 36 (1980) 997.