Implant Damage and Redistribution of Indium in Indium-Implanted Thin Silicon-On-Insulator

Materials Science and Engineering B 114–115 (2004) 251–254

Implant damage and redistribution of indium in indium-implanted thin silicon-on-insulator

Peng Chena, Zhenghua Anb, Ming Zhua,b, Ricky K.Y. Fua, Paul K. Chua,∗, Neil Montgomeryc, Sukanta Biswasc

a Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong b State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, 200050 Shanghai, China c Cascade Scientiﬁc, Brunel Science Park, Uxbridge, Middlesex UB83PH, UK

Abstract

The indium implant damage and diffusion behavior in thin silicon-on-insulator (SOI) with a 200 nm top silicon layer were studied for different implantation energies and doses. Rutherford backscattering spectrometry in the channeling mode (RBS/C) was used to characterize the implant damage before and after annealing. Secondary ion mass spectrometry (SIMS) was used to study the indium transient enhanced diffusion (TED) behavior in the top Si layer of the SOI structure. An anomalous redistribution of indium after relatively high energy (200 keV) and dose (1 × 1014 cm−2) implantation was observed in both bulk Si and SOI substrates. However, there exist differences in these two substrates that are attributable to the more predominant out-diffusion of indium as well as the inﬂuence of the buried oxide layer in the SOI structure. © 2004 Elsevier B.V. All rights reserved.

Keywords: Indium; Implant damage; Diffusion; SOI; SIMOX

1. Introduction Silicon-on-insulator (SOI) substrates have many advan- tages over bulk silicon in high-speed, low-power devices As a heavy ion, indium has become a promising dopant [10–11] and indium implantation into SOI can further im- to achieve ultra-shallow or steep retrograde channel profiles prove the device performance. Although much research has (SRCP) in advanced metal-oxide-semiconductor field-effect- been devoted to indium implantation and diffusion in bulk transistors (MOSFETs) [1–4]. However, due to its heavy Si, that on indium implantation into SOI is relatively scarce. mass, implantation-induced damage is quite considerable In addition, although some dopants, such as boron and even at relatively low doses typically used in channel dop- phosphorus have been shown to exhibit different diffusion ing. Moreover, the poor electrical activation of indium in Si behavior in SOI compared to bulk Si [12–14], detailed com- due to the high ionization energy [5] and low solid solubility parison between the diffusion of indium in SOI and bulk sil- [6] necessitate the implantation of a higher dose. The large icon has not been carried out. In this work, the implantation amount of ion implantation induced damage will affect both induced damage and indium diffusion characteristics were indium diffusion during subsequent thermal processes and studied. The SOI wafers used were separation by implanta- the electrical characteristics of the final devices. Transient tion of oxygen (SIMOX) wafers that are commonly used for enhanced diffusion (TED) of indium in Si has been observed fully depleted metal-oxide-semiconductor field-effect tran- and the magnitude is comparable to that of boron [6–9], and sistors (MOSFETs) [15]. We investigated systematically the it poses one of the main challenges to form steep and shallow indium ion implantation induced damage under different im- profiles. plant energies and doses. The indium diffusion behavior in the SOI structure, especially in the top Si layer, was also ∗ Corresponding author. Tel.: +852 2788 7724; studied, and the results were compared to those obtained in fax: +852 2788 9549/7830. bulk Si. The difference between the indium diffusion pro- E-mail address: [email protected] (P.K. Chu). files in SIMOX and bulk Si implanted at a relatively high

0921-5107/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2004.07.031 252 P. Chen et al. / Materials Science and Engineering B 114–115 (2004) 251–254 energy (200 keV) and high dose (1 × 1014 cm−2) was evalu- while the broad peak from channel number 200–300 origi- ated. nates from oxygen in the buried SiO2 layer. At around channel number 530 that corresponds to the silicon surface, the sample implanted with 1 × 1014 cm−2 at 200 keV exhibits a sharp 2. Experimental peak in the surface region, clearly indicating that an amorphous surface layer has been produced during the high dose SIMOX SOI wafers were used in our experiments. The and high energy implantation. However, the other three, including the sample implanted at the same energy of 200 keV top silicon layer was 200 nm thick and the buried SiO2 layer × 13 −2 (BOX) was 370 nm thick. <1 0 0> p-type silicon wafers were but at a lower dose of 1 10 cm , do not exhibit this also implanted for comparison. Before implantation, a 10 nm surface peak. It implies that the surface of these three sam- screen oxide was grown using dry oxidation at 950 ◦C. The ples have not been amorphized. This is in agreement with wafers were then implanted at room temperature with two the amorphization threshold dose reported before, which is − × 13 −2 different doses at 150 keV: (1) 5 × 1012 cm 2 and (2) 1 × around 5 10 cm at 200 keV [8]. For a dose less than − × 13 −2 1013 cm 2. Another set of samples was implanted at 200 keV 1 10 cm , the as-implanted samples retain most of the with: (3) 1 × 1013 cm−2 and (4) 1 × 1014 cm−2.A7◦C tilt crystal integrity. angle was employed for all implants to minimize channel- The RBS spectra indicating recrystallization of the amor- × 14 −2 + ing. After implantation, the wafers were annealed either us- phous layer in the SOI implanted with 1 10 cm In at ing rapid thermal annealing (RTA) at 1050 ◦C for 15 s or in 200 keV are shown in Fig. 2. In both spectra acquired after a furnace under nitrogen at 800 ◦C for 2 h. These annealing RTA or furnace annealing, the disappearance of the surface conditoins were chosen to minimize and maximize the ex- peak indicates that during each annealing process, the implant tent of transient enhanced diffusion, respectively [7]. The im- damage has been almost completely repaired and sufficient plantation damage was studied by Rutherford backscattering recrystallization of the amorphous surface layer has taken spectrometry (RBS) in the channeling mode. Secondary ion place. These results indicate that the indium implantation in- mass spectrometry (SIMS) was employed to acquire the ele- duced damage in the top Si layer of the SOI shows no notable mental depth profiles. The analysis was performed on a PHI difference from those created in bulk Si. The intrinsic point Adept-1010 Quadrupole SIMS instrument, using an oxygen defects in the top layer of SIMOX seem to have no significant primary beam with impact energy of 3 keV at an impact an- effects on the indium-related defects. gle of 45◦. The indium detection limit under these conditions Fig. 3 displays the indium SIMS profiles obtained from × 13 −2 was around 1 × 1016 at.cm3. the 1 10 cm samples implanted at 150 keV (Fig. 3a) or at 200 keV (Fig. 3b). In both cases, the shape of the indium profile after annealing at 800 ◦C for 2 h has undergone 3. Results and discussion no significant changes, whereas the tail end or post-peak region has obviously broadened and spread deeper towards the Fig. 1 shows the RBS channeling spectra of the as- top Si–BOX interface. This behavior is similar to the TED implanted samples under four different implantation condi- effect reported in bulk silicon. It should be noted that even tions. The peak at channel 340 shows oxygen in the surface SiO2 layer that has not been removed before RBS analysis

Fig. 2. RBS spectra of SOI implanted with In+ (1 × 1014cm−2 at 200 keV): Fig. 1. RBS channeling spectra acquired from SOI implanted with In+: (a) (1) as-implanted random profile; (2) as-implanted channeled profile; (3) 5 × 1012 cm−2 at 150 keV; (b) 1 × 1013 cm−2 at 150 keV; (c) 1 × 1013 cm−2 channeled profile after RTA; and (4) channeled profile after furnace an- at 200 keV; and (d) 1 × 1014 cm−2 at 200 keV. nealing at 800 ◦C for 2 h. P. Chen et al. / Materials Science and Engineering B 114–115 (2004) 251–254 253

Fig. 4. SIMS profiles of 200 keV 1 × 1014 cm−2 indium implanted samples: 115 + Fig. 3. SIMS profiles of indium in SIMOX implanted with In acquired (a) bulk Si; (b) SOI substrates. from: (a) 1 × 1013 cm−2 at 150 keV; (b) 1 × 1013 cm−2 at 200 keV, before and after furnace annealing at 800 ◦C for 2 h. of the SOI sample. After RTA, significant indium segregation when the implant energy rises to 200 keV, with the implant is observed in both the bulk silicon and SIMOX samples giv- dose still being 1 × 1013 cm−2 as shown in Fig. 3b, the in- ing rise to a peak at 130 nm below the surface. As shown in dium diffusion behavior is still similar to that in bulk Si. The the RBS results above, 1 × 1014 cm−2 indium dose is already higher implant energy only results in more indium dose loss. sufficient to create a completely amorphous layer in SOI. Ac- It seems that the SOI structure has no significant effect on cording to a previous study [9], the interstitials together with indium diffusion in these two cases. As reported in the liter- indium atoms will subsequently be trapped by dislocation ature [7], TED of indium is similar to that of boron, which is loops around the as-implanted amorphous/crystalline inter- also primarily via an interstitial-assisted mechanism. That is, face thereby giving rise to anomalous indium segregation. If with the assistance of a large amount of interstitials produced the as-implanted amorphous layer does not extend towards during implantation, indium atoms are driven deeply into the the surface, there will be two amorphous/crystalline inter- sample. For the relatively low dose SOI samples, at both the faces, one near the surface region and the other around the near surface region and bottom region of the top Si layer, the end-of-range (EOR) region. The leading edge of the indium concentrations of indium and implantation induced defects profile in both the top silicon in the SIMOX sample and bulk are at a low level, and so the surface oxide and BOX layer do silicon exhibits a significant change that appears to be related not affect indium diffusion in the top Si significantly. to indium out-diffusion towards the sample surface. Interest- The indium diffusion behavior in bulk Si and SOI after ingly, in the Si substrate, there is no obvious concentration higher dose implantation is compared. Fig. 4 depicts the in- peak at the near surface region, whereas in SOI, there is a dium profiles obtained from samples implanted with 1 × sharp peak about 40 nm below the surface. This difference 1014 cm−2 indium at 200 keV before and after RTA or fur- is believed to be due to dislocation loops near the surface nace annealing in Si (Fig. 4a) and SOI (Fig. 4b). In the Si region. It has been reported that in bulk Si, the near-surface sample, the as-implanted profile shows a concentration peak dislocation loops dissolve more easily than in a deeper re- 97 nm below the surface. The as-implanted profile in SOI gion at high temperature and thus segregation of indium will substrate is consistent with that in the Si sample, except that move from the near-surface loops to the sample surface [9]. some indium atoms accumulate at the top Si–BOX interface Our data indicate that the near surface dislocation loops in 254 P. Chen et al. / Materials Science and Engineering B 114–115 (2004) 251–254

SIMOX is more stable than those in bulk Si, thus resulting in distribution of indium occurs in both substrates, the indium an additional indium segregation peak compared to bulk Si. diffusion profiles are quite different. The steeper leading edge After furnace annealing, the trend of out diffusion in SOI is in SOI is attributed to the more prominent due to indium out- more prominent than in bulk Si. In bulk Si, besides the highest diffusion and the shallower and lower segregation peak at the segregation peak at the EOR region, the as-implanted con- EOR region in SOI is believed to be due to the top Si–BOX centration peak of indium is still quite high, whereas in the interface as well as the buried oxide layer in SOI. top Si layer of the SOI, there is no concentration peak except the deeper segregation peak. Moreover, the segregation peak in SOI is obviously lower and shallower than that in Si. It is Acknowledgments believed to be due to the effects of the BOX layer including the top Si–BOX interface. Similar to diffusion of indium to This work is financially supported by Hong Kong Re- the sample surface with a surface oxide layer, the low segre- search Grants Council (RGC) Competitive Earmarked Re- gation coefficient at the Si–SiO2 interface and high indium search Grants (CERG) # CityU 1137/03E and City Univer- diffusion coefficient in the oxide lead to deeper indium dif- sity of Hong Kong Strategic Research Grant (SRG) # 7001 fusion towards the BOX layer. The segregation coefficient of 642. indium at the Si–SiO2 interface (CSi/Coxide) is observed to be much <1 at temperature between 800 and 1050 ◦C [16]. The top Si–BOX interface is also found to play an important References role as recombination sites for excess point defects [12]. Un- der high energy and high dose implantation (1 × 1014 cm−2 [1] D.A. Antoniadis, I. Moskowitz, J. Appl. Phys. 53 (12) (1982) 9214. [2] G.G. Shahidi, B. Davari, T.J. Bucelot, P.A. Ronsheim, P.J. Coane, S. at 200 keV), the EOR of indium approaches the buried in- Pollack, C.R. Blair, B. Clark, H.H. Hansen, IEEE Electron Device terface, and thus the interface together with the BOX layer Lett. EDL-14 (1993) 409. can affect the indium profile in the top Si layer. During an- [3] H. Hu, J.R. Jacobs, L.T. Su, D.A. Antoniadis, IEEE Trans. Electron nealing, the interstitials around the EOR region are drawn to Device ED-42 (1995) 669. the top Si–BOX interface, and indium atoms accompanying [4] C. Kizilyalli, T.L. Rich, F.A. Stevie, C.S. Rafferty, J. Appl. Phys. 80 (9) (1996) 4944. the interstitials are also trapped at the interface. In addition [5] H. Boudinov, J.P. de Souza, C.K. Saul, J. Appl. Phys. 86 (1999) to the effects of top Si–BOX interface, it is believed that 5909. the distinct properties of the BOX layer in SIMOX may also [6] S. Solmi, A. Parisini, M. Bersani, D. Giubertoni, V. Soncini, G. facilitate deeper indium diffusion into the oxide layer. For ex- Carnevale, A. Benvenuti, A. Marmiroli, J. Appl. Phys. 92 (2002) ample, the BOX layer in SIMOX has a much higher density 1361. [7] P.B. Griffin, M. Cao, P. Vande Voorde, Y.-L. Chang, W.M. Greene, of oxygen vacancies than in thermal oxide (TOX) [17–19]. Appl. Phys. Lett. 73 (1998) 2986. The abundance of oxygen-related defects in the BOX layer [8] T. Noda, S. Odanaka, H. Umimoto, J. Appl. Phys. 88 (2000) 4980. may thus affect indium diffusion through the BOX layer. [9] T. Noda, J. Appl. Phys. 91 (2) (2002) 639. [10] J.P. Colinge, Silicon-on-Insulator Technology: Materials to VLSI, Kluwer Academic Publishers, Boston, MA, 1991. [11] S. Cristoloveanu, J. Electron. Soc. 138 (1991) 3131. 4. Conclusion [12] S.W. Crowder, C.J. Hsieh, P.B. Griffin, J.D. Plummer, J. Appl. Phys. 76 (5) (1994) 2756. In summary, we have investigated the damage and dif- [13] H. Uchida, Y. Ieki, M. Ichimura, E. Arai, Jpn. J. Appl. Phys. 39 fusion behavior of indium implanted SIMOX SOI. For an (2000) L137. × 13 −2 [14] H. Uchida, M. Ichimura, E. Arai, Jpn. J. Appl. Phys. 41 (2002) implantation dose less than 1 10 cm , the structure re- 4436. 14 −2 tains good crystalline quality. Upon reaching 1 × 10 cm , [15] Y. Nakajima, Y. Takahashi, S. Horiguchi, K. Iwadae, H. Namatsu, an amorphous layer is formed but it can be almost fully re- K. Kurihara, M. Tabe, Appl. Phys. Lett. 65 (1994) 2833. paired via subsequent annealing. Similar to bulk Si, the TED [16] I.C. Kizilyalli, T.L. Rich, F.A. Stevie, C.S. Rafferty, J. Appl. Phys. effect of indium is observed in the top Si layer of the SOI. 80 (9) (1996) 4944. [17] K. Vanheusden, A. Stesmans, Appl. Phys. Lett. 62 (19) (1993) 2405. Comparison of the indium depth profiles in the SIMOX and [18] R.A.B. Devine, J-L. Leray, J. Margail, Appl. Phys. Lett. 59 (18) bulk Si after high dose and high energy implantation (1 × (1991) 2275. − 1014 cm 2 at 200 keV) reveals that although anomalous re- [19] K.S. Seol, A. Leki, Y. Ohki, J. Appl. Phys. 79 (1996) 412.