Low-temperature Raman scattering measurements were carried out to characterize Si-on-SiO2 structures formed by oxygen implantation and subsequent furnace or lamp annealing. The experiments were conducted with 413.1 nm laser light to probe only the thin Si layers at the top of the structures. The Raman spectra of the furnace-annealed samples are red shifted and broadened when compared with a virgin Si surface. The shifts and broadenings decrease with increasing annealing temperatures but they are still present in samples annealed above 1250°C for 3 h. No shifts or broadenings affect the Raman peaks of the layers, which were lamp annealed at 1405°C for half an hour. The red shifts indicate that the recrystallized Si layers are under tensile strains, whose origin is attributed to oxide precipitates. Quantitative estimates of the strains and associated stresses are obtained from the measured Raman shifts

Baumgart, H.

Celler, G.K.

Olego, D.J.

English

Old Dominion University

Old Dominion University ODU Digital Commons Electrical & Computer Engineering Faculty Publications Electrical & Computer Engineering 1988 Strains in Si-onSiO2 Structures Formed By Oxygen Implantation: Raman Scattering Characterization D.J. Olego H. Baumgart Old Dominion University, hbaumgar@odu.edu G.K. Celler Follow this and additional works at: https://digitalcommons.odu.edu/ece_fac_pubs  Part of the Electrical and Computer Engineering Commons, and the Materials Science and Engineering Commons Original Publication Citation Olego, D. J., Baumgart, H., & Celler, G. K. (1988). Strains in Si-on-SiO² structures formed by oxygen implantation: Raman scattering characterization. Applied Physics Letters, 52(6), 483-485. doi:10.1063/1.99451 This Article is brought to you for free and open access by the Electrical & Computer Engineering at ODU Digital Commons. It has been accepted for inclusion in Electrical & Computer Engineering Faculty Publications by an authorized administrator of ODU Digital Commons. For more information, please contact digitalcommons@odu.edu. Appl. Phys. Lett. 52, 483 (1988); https://doi.org/10.1063/1.99451 52, 483© 1988 American Institute of Physics.Strains in Si-on-SiO2 structures formed byoxygen implantation: Raman scatteringcharacterizationCite as: Appl. Phys. Lett. 52, 483 (1988); https://doi.org/10.1063/1.99451Submitted: 22 October 1987 . Accepted: 02 December 1987 . Published Online: 04 August 1998D. J. Olego, H. Baumgart, and G. K. CellerARTICLES YOU MAY BE INTERESTED INStress measurements in silicon devices through Raman spectroscopy: Bridging the gapbetween theory and experimentJournal of Applied Physics 79, 7148 (1996); https://doi.org/10.1063/1.361485SiGe-free strained Si on insulator by wafer bonding and layer transferApplied Physics Letters 82, 4256 (2003); https://doi.org/10.1063/1.1581371The relative Raman cross sections of vitreous SiO2, GeO2, B2O3, and P2O5Applied Physics Letters 32, 34 (1978); https://doi.org/10.1063/1.89823Strains In Simon .. Si02 structures formed by oxygen implantation: Raman scattering characterization D. J. Olego and H. Baumgarta ) Philips Laboratories, North American Philips Corporation, BriarcliflManor, New York 10510 G. K. Ceiler .4T& T Bell Laboratorie~~ Murray Hill, New Jersey 07974 (Received 22 October 1987; accepted for publication 2 December 1987) Low-temperature Raman scattering measurements were carried out to characterize Si-on-Si02 structures formed by oxygen implantation and subsequent furnace or lamp annealing. The experiments were conducted with 413.1 nm laser light to probe only the thin Si layers at the top of the structures. The Raman spectra of the furnace-annealed samples are red shifted and broadened when compared with a virgin Si surface. The shifts and broadenings decrease with increasing annealing temperatures but they are still present in samples annealed above 1250 °C for 3 h. No shifts or broadenings affect the Raman peaks of the layers, which were lamp annealed at 1405 "C for half an hour. The red shifts indicate that the recrystallized Si layers are under tensile strains, whose origin is attributed to oxide precipitates. Quantitative estimates of the strains and associated stresses are obtained from the measured Raman shifts. Great efforts are being devoted to the development of silicon-on-insulator (SOl) technologies for high-speed and radiation-hardened devices. Among the potential technolo-gies, the process of creating a buried insulator by ion implan-tation into the Si wafer is attractlng considerable attention because of the promising device results obtained so far. Typi-cal structures consist of a 5i substrate, a 200-400-nm-thick buried insulator under a l00-300-nm-thick Si layer at the top. The direct synthesis of a buried SiOz layer by the im-plantation process is known by the acronym SIMOX (for separation by implanted oxygen).1 Implantation of N to form Si3 N4 has also been studied.2 In these methods a dose of ions, usually in excess of i X lOlg em - 2 and with energies in the range of 100-200 keY, is implanted deep into the Si wafer, which is kept during the implantation at a tempera-ture above 450°C to minimize damage in the bombarded Si layer. After implantation a thermal treatment above 1100 cC is required to improve the stoichiometry of the buried insula-tor, to sharpen the interfaces between the insulator and the Si below and above it, and to funy restore the crystallinity of the top 5i layer. Conventional furnace annealing and a novel approach utilizing high-intensity lamps for radiant heating have been investigated. 3 Characterization of the properties and quality of the top Si layer above the buried insulator becomes important, be-cause the active devices are fabricated in it. Many diagnostic techniques, such as transmission electron microscopy (TEM), Rutherford backscattering (RES), secondary ion mass spectrometry (SIMS)' and x-ray photoelectron spec-troscopy (XPS), have yielded important information about structural and chemical characteristics of the top Si films, and elucidated the relationship between the film properties and the thermal history of the sample. 3•4 Optical characteri-zation techniques have been applied only recently to the a) Present address: Philips Research Laboratories, P.O. Box 80000, 5600 lA, Eindhoven, The Netherlands. study ofSIMOX,s,6 in spite ofthe fact that they are nondes-tructive and provide fast analysis. In this letter we present a Raman scattering characterization of the top 8i layers of SIMOX samples. By a careful selection ofthe incoming laser wavelength, one can achieve the spatial resolution required to probe only the top layers of the structures. Under these conditions the Raman data can be related to the quality and intrinsic properties of the recrystallized layers. We have de-tected the presence of strains in the top Si films of SIMOX structures and followed them as Ii function of the annealing procedures. We present results for samples that have been annealed by the conventional furnace method and with the novel lamp furnace system. The SIMOX samples were obtained by implanting 160 keY 0 ~ ions ata dose of 1.8 X 1018 em - 2 into (100) surfaces of Si wafers, which were maintained at 560 °C during the implantation. Before annealing, the implanted surfaces were coated for protection purposes with a 550-nm-thick cap of Si02 deposited by low-pressure chemical vapor deposition. Conventional furnace heat treatments were then performed in a N2 atmosphere for 3 h at temperatures covering the span between 1100 and 1300 °C in increments of 50°C. Structures were also annealed at 1405 °C for 30 min by using the special lamp arrangement described in Ref. 3. In this case the wafers were suspended between a bank of high-intensity lamps and a water cooled base with the back side of each sample heid at the melting temperature of Si ( 1412 °C) by means of a natu-ral feedback based on the optical properties of Si. The im-planted side of the wafers was then about 7 °C cooler because of the temperature gradient imposed by one-sided radiant heating. After the annealing procedures, selected samples were checked by TEM in order to gain insight into the evolu-tion of the thickness d Si of the top Si layer and dSi02 of the buried oxide. It was found that d s)s 184 nm for the as-im-planted sample, 170 nm for the samples annealed at 1150 and 1200 °C, and 142.5!lm for the lamp-annealed surfaces. Conversely, dSiO increases from 248 nm for the as-implant-ed sample to 306 urn for the sample annealed at 1150 'C, to 483 Appl. Phys. Lett. 52 (6), 8 February 1988 0003-6951/88/060483-03$01.00 (C) 1988 American Institute of PhYSics 463 330 nm for the 1200 °C case, and finally to 365 urn for the lamp-annealed sample. The trends in thickness variations with annealing temperatures are in agreement with similar observations reported by others, 3,4 The structural properties of the Si layers also follow patterns established previously, The as-implanted Si surface is highly defective with 11 consid-erable amount of disorder, particularly in regions dose to the interface with the buried oxide, The annealed layers are crystalHne, and the dominant defects are oxide precipitates and threading dislocations. The number of precipitates de-creases with increasing annealing temperature, and they are almost nonexistent in the lamp-annealed sample. The dislo-cation density is on the order of 3 X 109 cm" 2 for the 1150 °C annealed sample, This value decreases with annealing tem-perature, but reaches a saturation value of about 3 X 108 em -2 for samples annealed at or above 1250 °C.3 The Raman scattering measurements were performed in backscattering configuration with near ultraviolet incom-ing laser photons generated by a Kr -i -ion laser operating at 413,1 nm, These photons are absorbed within a skin depth of z 150 nm/ which is comparable to dSi ' The Raman light originates only in the top Si layer, and therefore one can probe this part of the sample without interference from the underlying Si substrate or the buried SiOz layer. The Raman scattered light was analyzed in frequency with a double-monochromator and detected with photon-counting elec-tronics, The position of the Raman peaks was measured with an accuracy of ± 0,1 cm - 1 and the linewidths with a spec-tral resolution better than 0,6 cm- I, To improve on the abi-lity to establish frequency shifts and line broadenings, we performed the Raman experiments at a low temperature with the samples mounted in a cold finger of a closed cycle cryostat and kept at :::::: 12 K, Figure 1 shows typical first-order Stokes-Raman spec-tra for several of the investigated SIMOX samples, including also for comparison data taken from a virgin (not implanted, STOKES SHIFTS (cm-') FIG, L First-order Raman spectra of the top Si layers ofSIMOX structures for different annealing treatments, The temperature in the lamp-annealing case was 1045"c' For comparison, data are included for an as-implanted (not annealed) and virgin Si surface (not implanted, not annealed), 484 AppL Phys. Lett., Vol. 52, No, 6, 8 February 1988 not annealed) Si (100) surface. The spectra arise from scat-tering by long-wavelength transverse optical phonons,8 For clarity, the Raman peaks have been displaced vertically with the horizontal solid lines representing the background levels in each case, The following experimental conclusions are apparent from the result in Fig. I: The position and linewidth of the Raman peak corresponding to the lamp-annealed sample are within the experimental uncertainties the same as those of the virgin Si surface, On the other ex-treme, the implanted and not-annealed sample shows a Ra-man band with a pronounced shift to lower frequencies (red shift) and a clear asymmetrical broadening compared to the reference Si surface, The low-frequency wing rises above the background level faster than the high-frequency one, The spectra of the furnace-annealed samples are also red shifted and broadened with respect to the virgin case, However, the red shifts and broadenings decrease with increasing anneal-ing temperature TA , Important to point out is the fact that these broadenings are symmetrical, as opposed to the as-implanted case, The measured peak positions (U and linewidths r (corrected for instrumental widths), as wen as the shifts I::.{t) and broadenings tor with respect to the control Si sample, are summarized in Table I for an the investigated samples, The values of (t) and r for the virgin Si surface are in excellent agreement with those reported in the literature. 9 We also scanned the spectral region at around 480 cm- I to look for the typical Raman signal of amorphous SL No scat-tering intensity readily identifiable as due to amorphous Si was observed at these frequencies in the Raman spectra of the SIMOX samples, In what follows we discuss the results of Fig. 1, particu-larly the fact that the Raman lines of the annealed samples are symmetrical, but nevertheless red shifted, The symmetri-cal Raman line shapes confirm the crystalline nature of the top 8i layer, If a high degree of disorder were present in the network because of microcrystalline grains, then wave vec-tor non conservation will dominate the scattering process. 8 The Raman spectra would then be asymmetrically broad-ened, which is indeed the case for the as-implanted layer. Ruling out the effects of structural disorder in the Raman data of the annealed layers is important, because it excludes phonon confinement as the origin of the phonon shifts,s,w We attribute .6.w to the presence of strain in the crystalline layers, and we win show that the strains are of tensile nature, TABLE 1. Measured parameters of the Raman lines at 12 K of SIMOX samples: peak positions C1J, linewidths r, and shifts Aa) and broadcnings Ar with respect to the virgin sample, Ali these parameters are in units of cm I. Also included are the determined values of the strain € and stress X. The latter are in kbars. Sample (U Am I' AI' € X Virgin 524,2 0 L3 0 0 0 As-implanted 518,9 - 5,3 6.2 4,9 l100"C fum, ann, 521.9 - 2.3 4.1 2,8 0,007 11.5 1150 'C fum, ann. 522.3 ~ 1.9 3,7 204 0,005 8.3 120() 'C furn, ann, 523,5 --0.7 2.4 Ll 0.002 3,3 1250"C fum. ann. 523,8 -- 0.4 1.4 0,1 0,001 1.7 1300 'c fum, ann, 523,9 -0.3 1.3 (J 0,0009 L5 1405 'C lamp ann. 524.2 0 1.3 0 0 0 Olego, Baumgart, and Celler 484 Softening of the lattice modes has been observed in other semiconductor systems implanted at very high doses and attributed to large volume expansions in the bombarded re-gions along directions perpendicular to the surfaces of the layers. IO•11 We can obtain quantitative estimates of the maximum strains expected in the top Si layers from the measured f).b), and theoretical expressions and parameters of Ref. 12. Ifwe assume that the layers are allowed to relax only in the z direction,IO,11 then the relationships aU} = - 32310 = - 0.195X hold between 6.w (in em - I), the strain ezz = E, and the associated stress X = {7zz = ell 10 (in kbar). c! 1 is the corresponding elastic stiffness constant of Si. The convention adopted is that E is positive for tension, z is per-pendicular to the implanted surface, and x and y lie in the plane ofthe layer. Replacing il(j) by the measured quantities in the expressions above yield the values of E and X given in Table L The strains are of tensile nature, and their magni-tude decreases with increasing annealing temperature TA • However, even the highest furnace-annealing temperatures are not effective in removing all traces of strain. Within the accuracy of the Raman determination, strain-free material is obtained only in the lamp-annealed specimens, We have not attempted to estimate the strain in the as-implanted layer, because the contribution of phonon confinement has to be elucidated first. 1O The task implies a detailed fitting of the line shape which is beyond the scope of the present work. However, we point out that f).(J) for this sample is larger than the shifts measured in polycrystaHine Si with comparable ill, and therefore some strain is also bunt in the as-implant-ed layer,13 We ascribe the origin ofthe strain in the annealed layers to the presence of the oxide precipitates. Their inclusion in the 5i matrix occurs at the expense of creating a volume expansion of the layers along the z direction. The decrease of E with TA certainly tracks the reduction of the density of precipitates until they are almost eliminated in the lamp-annealed sample for which {; = O. The magnitude and sign of the strains in Table I are comparable to those reported in other SOl structures, such as recrystallized Si directly on quartz (Si02 ).14 In these systems the strains are attributed to the mismatch in thermal expansion between Si and SiOl , In the SIMOX case this effect cannot be invoked, because dSiO, and the thermal mismatch increase, and dSi decreases with increasing TA , and therefore larger values of E should be expected for the samples annealed at the highest tempera-tures. This is in contradiction with the experimental find-ings, The broadening ~r of the Raman peaks can be under-485 Appl. Phys. Lett, Vol. 52, No.6, 8 February 1988 .......... -.. .;.;.;.; .................... :.:.:.;.:' ..... ·.·.'.·.·.·.:·:·:·;.;·,..·.·.·.·.·.:·:·~·:·z·:·.·.'.·.·.· ....... ;.;.:.: ..•.....• ,. ..•.. --; .•.....• -.... , .... . stood in terms of inhomogeneities in E, In the interpretation of the results, we have not involved the threading disloca-tions. We estimate that they do not affect the positions or widths of the Raman peaks, because their separation is much larger than any expected correlation lengths for the phon-ons,s In summary, we have shown how Raman spectroscopy can be applied to the characterization ofSIMOX structures. We established that the recrystallized Si layers are under tensile strains, which are attributed to the oxide precipitates in the Si matrix. Strain measurements by Raman scattering can be used to gauge rapidly and nondestructiveIy the quali~ ty and uniformity of SIMOX wafers. Such determinations by means of the conventionally used structural characteriza-tion techniques are cumbersome and destructive. The real-ization that strains can be present is relevant for the analysis of the transport properties of devices built in the recrystal-lized layers or for the subsequent growth of epitaxial Si on Si. Since the implantation parameters and annealing tempera-ture and time settings selected in this study are quite stan-dard, we expect that our findings can be extended to SIMOX structures fabricated in other laboratories. We would like to acknowledge J. Petruzzello for the transmission electron microscopy measurements and S. Lu-kasik for the help with the furnace annealings. 'K, Izumi. M, Doken, and H. Ariyoshi, Electron. Lett. 14, 593 (1978). 2K. 1. Reeson, P. L. F. Hemment, C. D. Meekisoll, G. R. Booker, 1. A. Kilner, R. 1. Chater, R J. Davis, and G. K. Celler, Appl. Phys. Lett. 51l. 1882 (1987), 'G. K. Ccller, SoEd State Tedmoi. 30, 93, (1987). 4B. y, Mao, p, H. Chang, H. W. Lam, B. W, Shell, and J. A, Keenan, in Mater. Res. Soc. Symp. 53: Semicondllctor-on~Jnsulator and Thin Film Transistor Technology, edited by A. Chiang, M. Geis, and L Pfeiffer (Ma-terials Research Society, Pittsburgh, 1986), p. 251; P. H. Chang and B. Y. Mao. App!. Phys. Lett. 5C, 152 (1987). 5S. N. Bunker, p, Sioshansi, M. M. Sanfacon, and S. P. Tobin, App!. Phys. Lett. 50,1900 (1987). 6J. Narayan, S. Y. Kim, K. Vedam, and R. Manukonda, App!. Phys. Lett. 51,343 (1987). 7D. Aspnes and A. A. Studna, Phys. Rev. B 27, 985 (1983). 8M. Cardona, in Ligh; Scattering in Solids II, edited by M. Cardona and G. Giintherodt (Springer, Heidelberg, 1982), p. 19. 9M. Balkanski, R. F. Wallis, and E. Ham, Physo Rev. B 28, 1928 (1983). lOG, Bums, F. R Dacol, C. R. Wie, E. Burstein, and M. Cardona, Solid State Comrnun. 62. 449 (1987). "0. R. Myers, I'. L. Gourley, and P. S. Peerey, J. App\. Phys, 54, 5032 U983j. '2E. Annastassakis, A. Pinczuk, E. Burstein, E H. Pollak, and M. Cardona, Solid State Commull. 11,133 (1970). Dr. H. Campbell and P. M. Fauchet, Solid State Commun. 58, 739 (1986). "s, A. Lyon, R. J. Nemanich, No M. Johnson, and D. K. Biegeisen, App!. Phys, Lett. 40, 316 (1983). Olego, Baumgart, and Celler 485 

Strains in Si-onSiO\u3csub\u3e2\u3c/sub\u3e Structures Formed By Oxygen Implantation: Raman Scattering Characterization

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Strains in Si-onSiO\u3csub\u3e2\u3c/sub\u3e Structures Formed By Oxygen Implantation: Raman Scattering Characterization

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