Photoluminescence spectroscopy of SIMOX

Photoluminescence spectroscopy of SIMOX

Journal of Non-Crystalline Solids 254 (1999) 134±138 www.elsevier.com/locate/jnoncrysol Photoluminescence spectroscopy of SIMOX Ying Xue Li a,*, Xin...

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Journal of Non-Crystalline Solids 254 (1999) 134±138

www.elsevier.com/locate/jnoncrysol

Photoluminescence spectroscopy of SIMOX Ying Xue Li a,*, Xing Zhang a, Yan Luo b,1, Yang Yuan Wang a b

a Institute of Microelectronics, Peking University, Beijing 100871, People's Republic of China Institute of Low Energy Nuclear Physics, Beijing Normal University, Beijing 100875, People's Republic of China

Abstract Photoluminescence spectroscopy (PL) and SIMS technique are employed to determine crystal perfection of the top Si layer and the e€ects of residual oxygen in the top Si layer of oxygen implanted (SIMOX) wafer. From the PL experimental results, we draw the conclusion that the intrinsic peak (a peak, at 0 eV), amplitude of the PL, and the amplitude ratio of b peak (at 0.33 eV) to a peak (b/a) provide an estimation of crystal perfection of the top Si layer of SIMOX wafer. The luminescence peak, b, is assumed to originate from implantation of oxygen ions and high temperature annealing process of SIMOX wafer and it is similar to the phosphorus donor level. The luminescence peak at 0.06 eV in the PL is due to a shallow donor level and the peak at 0.16 eV also acts as a donor level. These donor levels play an important role in making n-type top Si layer from p-type substrate. Ó 1999 Elsevier Science B.V. All rights reserved.

1. Introduction Recently, it has been con®rmed that MOSFET's made on fully depleted ultra thin ®lms (<10 nm) have additional bene®ts of nearly ideal subthreshold slope [1], increased saturation current [2] and reduced short-channel/¯oating body e€ects [3]. In the numerous silicon on insulator (SOI) fabricated techniques, separation by implantation of oxygen (SIMOX) is one of the leading SOI techniques. A SIMOX is formed by implanting oxygen ions in Si, followed by 6 h high temperature (1300°C) annealing. This process often results in the presence of dislocation stacking faults and residual oxygen in the top Si layer of SIMOX. To *

Corresponding author. Tel.: 86-10 6275 2549, fax: 86-10 6275 1789; e-mail: [email protected] 1 Tel.: 86-10 6220 8250 ext. 8001; e-mail: [email protected]

optimize the SIMOX process and determine the resulting structures, a number of investigations have been made which have shown the presence of threading dislocations in the top Si layer of SIMOX [4]. But the e€ects of residual oxygen related to donors and contamination in the top Si layer of SIMOX should be further investigated. Photoluminescence spectroscopy (PL) is a useful technique in the investigation of defects and interactions between vacancies and impurities. In this work, the crystal perfection of the top Si layer of SIMOX, especially the a€ects of residual oxygen in the top Si layer have been investigated by PL spectroscopy and secondary ion mass spectrometry (SIMS) technique. 2. Experiments P type (100) Si wafers were implanted with oxygen ions to a dose of 1.8 ´ 1018 and 1.5 ´ 1018 /cm2

0022-3093/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 9 9 ) 0 0 4 3 8 - X

Y.X. Li et al. / Journal of Non-Crystalline Solids 254 (1999) 134±138

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Table 1 Fabrication procedure of samplesa

a

Symbol of sample

Implantation Energy (keV)

Implantation dose (1018 cmÿ2 )

Temperature of target (°C)

Annealing temperature (°C)

Annealing time (h)

Ambient of annealing

O1 A1 N1 Ibis

180 170 170 200

1.8 1.5 1.5 1.8

680 680 680

1300 1300

6 6

Ar + 0.5%O2 N2

Ibis is the sample of USA provided by Ibis company.

at 180 or 170 keV with the wafer at 680°C during implantation, followed by a 1300°C annealing for 6 h in an ambient of nitrogen or argon plus 0.5% oxygen. For easy comparison, we also used a SIMOX sample prepared by a commercial company (Ibis). PL measurements were carried out by the instrument CaF-PL, with the sample cooled to 15 K. The SIMS measurements by the IMS.4f type instrument were carried out on all samples. Table 1 shows the fabrication procedure for our samples.

3. Results 3.1. PL spectroscopy results Figs. 1 and 2 show the PL spectra of the samples O1 , A1 , N1 , and the Ibis sample. From these ®gures we get the location and amplitude of luminescence peaks in the PL spectroscopy, as shown in Table 2. From Table 2 we can see that there are di€erences in the amplitude of luminescence peaks in the spectra of the di€erent samples. It is obvious that the amplitude of a peak (at 0 eV) of sample Ibis is much larger than that of the other samples. The amplitude of b peak (at 0.33 eV) of sample N1 is larger than that of the other samples. The amplitude of c peak (at 0.35 eV) of sample N1 also larger than that of the other samples. We note that the amplitude ratio of b peak to a peak (b/a) of the sample Ibis is smaller than that of the other samples. We assumed that this parameter (b/a) is probably related to the crystal perfection of the top Si layer of SIMOX.

Fig. 1. Photoluminescence for the samples O1 , A1 , N1 , and Ibis. The measurement temperature was 15 K.

3.2. SIMS measured results The presence of residual oxygen, carbon and nitrogen in the top Si layer of SIMOX wafer were detected by using SIMS. The pro®les of the residual oxygen, carbon, nitrogen for samples O1 , A1 , N1 and Ibis are shown in the Figs. 3±5. From Fig. 3, it is apparent that the amount of residual oxygen in the top Si layer of samples O1 , A1 and N1 are almost the same, but larger than that of the sample Ibis. The pro®les of the carbon in the top Si layer for the samples N1 and A1 are nearly the same, but the amount of carbon of the

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Fig. 3. The amplitude of O by SIMS as a function of depth from the surface of SIMOX wafer for the samples O1 , A1 , N1 and Ibis. (Depth ˆ 0 at surface of samples.)

Fig. 2. Photoluminescence for the samples O1 , A1 , N1 , and Ibis. The measurement temperature was 15 K, at 0.7  0.9 eV.

sample O1 is larger than that of the other samples. This di€erence means that the carbon was introduced into the SIMOX wafer during oxygen implantation. The pro®les of nitrogen (Fig. 5) in the top Si layer of these samples (A1 , N1 and Ibis) are almost the same except for the sample O1 . We note that the nitrogen count in the top Si layer of the sample O1 is larger than that of the other samples. We assume that nitrogen is also introduced into the SIMOX wafer during implantation of oxygen.

Fig. 4. The amplitude of C by SIMS as a function of depth from the surface of SIMOX wafer for the samples O1 , A1 , N1 and Ibis. (Depth ˆ 0 at surface of sample.)

Table 2 The location and amplitude of luminescence peaks in the PL spectroscopy of SIMOX samples

a

The name of peak

a

b

c

Location of peak (eV)a Location of peak (eV)b Sample O1 (amplitude) Sample A1 (amplitude) Sample N1 (amplitude) Sample Ibis (amplitude)

1.09 ‹ 0.01 ~0 1.3 ‹ 0.1 15.7 ‹ 0.1 12.8 ‹ 0.1 52.4 ‹ 0.1

0.77 ‹ 0.01 0.33 15.7 ‹ 0.1 27.0 ‹ 0.1 37.9 ‹ 0.1 13.2 ‹ 0.1

0.75 ‹ 0.01 0.35 11.8 ‹ 0.1 15.9 ‹ 0.1 19.4 ‹ 0.1 10.7 ‹ 0.1

0.94 0.16 4.0 ‹ 0.1 3.9 ‹ 0.1 6.8 ‹ 0.1 4.5 ‹ 0.1

Distance from the top of valence band. Distance from the bottom of conduction band, Eg ÿEpl . c min v ˆ ya =yr , ya is a yield of aligned RBS; yr is a yield of random RBS at the edge of Si peak. b

1.04 0.06 1.0 ‹ 0.1 1.0 ‹ 0.1 1.4 ‹ 0.1 3.8 ‹ 0.1

b/a 12.07 1.72 2.96 0.25

vmin c >3% 6% 3%

Y.X. Li et al. / Journal of Non-Crystalline Solids 254 (1999) 134±138

Fig. 5. The amplitude of N by SIMS as a function of depth from the surface of SIMOX wafer for the samples O1 , A1 , N1 and Ibis. (Depth ˆ 0 at surface of sample.)

After high temperature annealing, nitrogen can be accumulated at the interface between the top Si layer and buried oxide layer of the samples A1 and N1 . This accumulation is related to the annealing ambient [5]. In general, this accumulation at the interface is larger in sample N1 with annealing ambient of nitrogen than that of sample A1 with annealing ambient of argon.

4. Discussion It can be seen from Table 2 that the ratio of b peak to a peak (b/a) may be an estimation of the top Si layer crystal perfection of SIMOX wafer. This proposal is based on the bca ˆ 12.1 in the unannealed sample O1 , being much larger than that of the other samples (and the amplitude of a peak is the smallest), and the b/a of the sample Ibis is the smallest (0.25) (and the amplitude of a peak is the largest). Meanwhile, compared with the results of Rutherford backscattering spectrometry (RBS) (as seen in Table 2), we found that vmin of sample Ibis is 3% close to that of bulk crystalline Si and the vmin of the sample O1 is the largest (not given in Table 2). It demonstrates that the top Si layer of sample Ibis is almost a perfect monocrystal, while the top Si layer crystal perfection of sample O1 is much less. Correspondingly, for

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samples N1 and A1 vmin are 6% and >3%, respectively [6] (as seen in Table 2), while the b/a are 2.96 and 1.72, respectively. We conclude that the larger b/a (and the smaller the amplitude of a peak), the poorer is the crystal perfection of the top Si layer. From Table 2, it is can also be seen that the amplitude of b peak (at 0.33 eV) of sample Ibis is much smaller than that of samples A1 and N1 . Comparing these results with the SIMS results (as seen in Fig. 3) we can see that the residual oxygen in the top Si layer of samples A1 and N1 are larger than that of sample Ibis. It may be that the amplitude of b peak is a€ected by the amount of residual oxygen in the top Si layer of sample. What role does the residual oxygen play? From spread resistance (SPR) measurement results [7], we found that the resistivities of the top Si layer of samples A1 and N1 were much less than that of the sample Ibis. And we also found that the larger the amplitude of b peak, the smaller the resistivity in the top Si layer of samples. In addition, the top Si layer of SIMOX is made n-type from p-type substrate after implantation of oxygen and high temperature annealing. So we assume that the residual oxygen in the top Si layer acts as a donor level, similar to phosphorus [8]. We assume that the luminescence of b originates from an increase in the concentration of residual oxygen (or oxide precipitates) in the top Si layer. This residual oxygen is formed by implantation of oxygen and high temperature annealing process of the SIMOX [8]. The relation between the amplitude of b peak and the resistivity of the top Si layer is unknown. For example, the PL of samples A1 and N1 have an abnormal phenomenon: the amplitude of b peak of sample N1 is larger than that of sample A1 , but the resistivity of the top Si layer of sample N1 is larger than that of sample A1 [7]. We do not have an explanation for this e€ect. The SIMS results show that the peak amplitude of the 0.35 eV c band depends on the content of nitrogen and carbon in the top Si layer of SIMOX (as seen in Fig. 5). The peak at 0.06 eV in the PL spectra is due to shallow donor level, while peak at 0.16 eV is also due to a donor level, which is a stable complex cluster formed by one silicon atom and four oxygen atoms [9,10].

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Our experimental results demonstrate that these donor levels in the top Si layer are important factors in making n-type top Si layer from p-type substrate. 5. Conclusion The PL experiment results show that the intrinsic peak (a peak at 0 eV) amplitude and the ratio of b peak to a peak (b/a) are an estimation of the top Si layer crystal perfection of SIMOX wafer. The luminescence peak b (at 0.33 eV) is assumed to originate from oxygen implantation and high temperature annealing process of SIMOX wafer. It is similar to phosphorus donor level, which is due to the presence of residual oxygen or oxide precipitates in the top Si layer.

References [1] J.-P. Colinge, IEEE Electron Device Lett. EDL-7 (1986) 244±246. [2] J.C. Sturm, K. Tokunga, J.-P. Colinge, IEEE Electron Device Lett. 9 (1988) 460±463. [3] J.-P. Colinge, Electron Lett. 22 (1986) 187±188. [4] S.T. Davey, J.R. Davis, Appl. Phys. Lett. 52 (6) (1988) 465. [5] Y.X. Li, X.M. Xi, Z.J. Wang, X. Zhang, Y.Y. Wang, C.L. Lin, Chinese J. Semiconductor 17 (1) (1996) 11. [6] Y.X. Li, X.M. Xi, Z.J. Wang, X. Zhang, Y.Y. Wang, C.L. Lin, Chinese J. Semiconductor 17 (2) (1996) 93. [7] Y. Luo, Y.X. Li, C.Z. Ji, Y.Y. Wang, X. Zhang, J. Beijing Normal University 34 (1) (1998) 68. [8] H.S. Kang, C.G. Ahn, S.H. Lee, K.I. Kin, B.K. Kang, Electrochem. Soc. Proc. 97±23 (1997) 155. [9] A.G. Milnes, Deep Impurities in Semiconductors, Wiley, 1973, p. 34. [10] G. Davies, Phys. Rep. 176 (1989) 83.