Cheung, N.W.

Gronsky, R.

Im, S.

Washburn, J.

Yu, Kin Man

eScholarship - University of California

Lawrence Berkeley National LaboratoryRecent WorkTitleDefect Control During Solid Phase Epitaxial Growth of SiGe Alloy LayersPermalinkhttps://escholarship.org/uc/item/9vs6m44rAuthorsIm, S.Washburn, J.Gronsky, R.et al.Publication Date1993-02-01eScholarship.org Powered by the California Digital LibraryUniversity of California! .. ··I . ' . LBL-33574 UC-404 Pre print Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA Materials Sciences Division National Center for Electron Microscopy Submitted to Applied Physics Letters Defect Control During Solid Phase Epitaxial Growth of SiGe Alloy Layers S. Im, J. Washburn, R. Gronsky, K.M. Yu, andN.W. Cheung February 1993 Prepared for the U.S. Department of Energy under Contract Number DE-AC03-76SF00098 I I \ -·- --~. --- I H.C1 ol-'-r 'i'iO 0 > ~s:::z: .... c Pl C1 fl)r+O 11) 11) ., ~Dlo< Dl ---II' .... c. IQ . tn s r r II' ..... r ern I 'i 0 w Pl't:l w 'i"< ~j "< . I\) DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of Califomia. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. ..,, Defect Control During Solid Phase Epitaxial Growth of SiGe Alloy Layers S. lm, J. Washburn, R. Gronsky, and K.M. Yu Department of Materials Science & Mineral Engineering University of California , and Materials Science Division Lawrence Berkeley Laboratory Berkeley, CA. 94720 N.W. Cheung Electronics Research Laboratory Department of Electrical Engineering' & Computer Science University of California Berkeley, CA. 94720 ... \ ~ Applied Physics Letters (submitted, 2/93) LBL-33574 This work was supported in ·part by the Director, Office of Energy · Research, Office of Basic Energy Sciences, Materials Science .Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098, and by National Science Foundation, ~ontract No . 442427-21153. .. Defect Control During Solid Phase Epitaxial Growth of SiGe Alloy Layers Seongil lm, Jack Washburn, Ronald Gronsky Department of Materials Science and Mineral Engineering University of California, Berkeley, CA 94720 Nathan W. Cheung . Electronics Research Laboratory. Department of Electrical Engineering & Computer Science University of California, Berkeley, CA 94720 Kin Man Yu Materials Science· Division · Lawrence Berkeley Laboratory, Berkeley, CA 94720 Abstract A systematic study of the processing procedures required for minimizing .. structural defects generated during the solid phase epitaxial (SPE) growth of SiGe alloy layers is described. It includes high dose Ge implantation into Si at liquid nitrogen temperature (LNT), sequential carbon implantation, and an 800°C anneal. The LNT implantation step _considerably reduces the density of end-of-range (EOR) defects relative to that found in SPE grown SiGe layers· implanted at room temperature, while the sequential implantation of carbon ions before annealing effectively suppresses the formation of stacking faults that are found to form at a threshold peak concentration of about 6 at% Ge in the absence of carbon. High dose Ge ion implantation and solid phase epitaxial (SPE) growth of SiGe alloy layers on (1 00) Si substrates have been studied by many investigators as synthesis routes for electronic devices requiring higher current gain than pure Si (e.g. heterojunction bipolar transistors (HBT)) made possible by the lower energy band gap in SiGe alloys1-4. Other investigators have used Ge-preamorphized Si surfaces to retard the diffusion of boron in devices requiring ~table shallow junctions5,6. In every case however, annealing of these SiGe alloy layers induces the formation of dense concentrations of ·end-of-range (EOA) defects. Annealing of buried alloy layers also results in the generation of stacking faults within those regions of the alloy layer having the highest (peak) Ge concentrations. Such defects cause serious degradation of the electrical properties in functioning devices. Although consider~ble effort has been devoted to the suppression of these defects1,2, no sustained attention has been given to the elimination of both classes of defects in one unit process. In the present work, we investigate synthesis and processing methods for the elimination of these defects by lowering the Ge implantation temperature and \ introducing sequential implantation of carbon for strain accommodation. High dose Ge74 ions (Ge+) were implanted into [100]-oriented Si to generate amorphous SiGe alloy layers with three different ~e peak concentrations (12 at%, 7 at% and 5 at%). The corresponding doses were 5x1016 cm-2, 3x1016 cm-2 and 2x1016 cm-2 respectively. AGe ion beam energy of 120keV was chosen and two implantation temperatures of 298K (AT) and 77K (LNT) were used. The 12at% Ge peak concentration alloy layer was then subjected to a second implantation of carbon ions (C+) at room temperature (AT), using a C+ beam energy of 20keV to position the implanted carbon ions at the same depth into the alloy layer as the 12 at% Ge peak. The nominal carbon dose was 2 .• 2x1 o1s cm-2 to yield an anticipated 0.5 at% C peak concentration. The as-implanted Ge profiles were nearly Gaussian with an Rp of 65nm as measured from the Rutherford Back Scattering Spectrometry (RBS) data shown in Fig. 1, and the depth of the amorphous zone w~s 170nm for the LNT implanted alloy .. SPE regrowth was performed at 800°C for 1 hour in a nitrogen ambient, after which there was no significant Ge redistribution according to the RBS data. To characterize the structure and crystallinity of the regrown SiGe alloy layers, cross-sectional transmission electron microscopy (XTEM) was performed using both symmetrical and two-beam (diffraction vector g = 022) conditions in a <110> zone axis orientation .. The XTEM micrographs in Fig. 2 show the results of high dose Ge ion implantation at room temperature. At 5 at% Ge peak concentration the SPE-grown SiGe alloy layer shows no stacking faults, but faults are clearly seen in the 12 at% Ge peak material. Note that both micrographs show a high density of EOR defects. Previous studies3.9 have attributed the formation of stacking faults in the peak concentration regions of the implanted alloy layer to the high strain conditions ·brought about by the localized concentration of the implantation species, and EOR defects have been shown7.a to b~ extrinsic dislocation loops formed by excess recoiled Si interstitials. When implantation is performed at room temperature, the available thermal energy is sufficient to cause dynamic annealing of amorphous SiGe layers as reported previously10. The dynamically-annealed, as-implanted SiGe shows a high density of very small EOR loops which subsequently grow in size during SPE processing . 3 ,,, '.' The micrographs in Fig. 3 exhibit the results of LNT-implantation, after which the density of EOR defects is considerably reduced, as noted by others in earlier studies2.7,8. However, the density of stacking faults is not significantly reduced even though the peak concentration of Ge is down from 12 at% to 7 at% in this sample. Because there were rio stacking faults io the sample with a 5 at% Ge . . peak, it is concluded that the threshold peak concentration of Ge for stacking fault formation is around 6 at%. · The attempt made in this study to restrict the formation of stacking faults in the LNT -implanted materials by sequential implantation of carbon prov~d successful. The small atomic radius of C {0.077 nm) compared to Ge (0.1224 nm), suggests that a controlled dose of C atoms can compensate the lattice strain induced by a high dose of Ge atoms during SPE regrowth of the SiGeC layer as long as both Ge and C atoms occupy substitutional sites in the Si lattice.· In this study, implantation conditions were chosen to deposit a peak concentration of 0.5 at% C at the same depth as the amorphous SiGe alloy layer, 65nm, in the sample with 12-at% peak Ge. The XTEM micrograph in Fig. 4 shows the result of this process followed by SPE regrowth. It is clear that the overall density of all defects, including both stacking faults and EOR loops, is .. dramatically reduced. Fortunately because the diffusivities of C and Ge in the crystalline· Si are so small at the aoooc annealing temperature, the Gaussian concentration profiles of both species remain relatively sharp, (Fig. 1) ir1 agreement with previous findings4.11. In summary, a seque'ntial implantation process (Ge, LNT followed by C, RT) has been found to be an extremely ~ffective method for reducing the defect concentration in SiGe alloy layers produced by Jon Beam Synthesis (IBS). 4 The authors wish to acknowledge the assistance of Kevin Roderick , Prof. Eugene Haller and Dr. lan G. Brown in providing the Ge and C implantation at the Lawrence Berkeley Laboratory. This work was supported by the National Science Foundation under contract No. 442427~21153 and by the Division of Materials Science, Office of Basic Energy Sciences of the U.S. Department of Energy under contract No. DE-AC03-76SF00098. 5 :t·) ~j · References 1. Akira Fukumi, Ken-ichi Shoji, Takahiro Nagano, and Cary Y. Yang, Appl. Phys. Lett., 5(22}, 2345 {1990}. 2. Akita Fukumi, Ken-ichi Shoji, Takahiro Nagano, and Cary Y. Yang, Microelectronic Engineering, 15, 15 (1991). 3. D.C. Paine, D.J. Howard, and N.G. Stoffel, J. Electronic Mateiials, 20 (1 0), 735 (1991). 4. K. M. Yu, I. G. Brown and S.lm, ·Mat. Res. Soc. Symp. Proc., 235,293 (1992). \ 5. A.C. Ajimera, G.A. Rozgonyi, and A.B. Fair, Appl. Phys. Lett., 52 (10), 813 (1988). 6. Mehmet C. Ozturk, Jimme J. Wortman, Carlton M. Osburn, Atul Ajimera, George A. Rozgonyi, Eric Frey, Wei-Kan Chu, and Clin~on Lee, IEEE Trans. Electron Devices, 35 (5), 659 (1988). 7. S. Prussin and K.S. Jones, J. Electrochem. Soc., 137 (6), 1912 (1990). 8. K.S. Jones and D. Venables, J. Appl. Phys. 69 (5}, 2931 (1991). 9. D.C. Paine, D.J. Howard, and J. A. Horton, J. Mater. Res., 5, 1023 (1990). 10. S. lm, J. Washburn, R. Gronsky, N. W. Cheung, and K. M. Yu, MRS Symp. Proc. 1992 (in press). 11. Properties of Silicon, EMIS Datareviews Series No. 4, published by INSPEC, The Institution of Electrical Engineers, New York, (1988) p. 285. 6 f Figure Captions Fig. 1 . Fig. 2 Fig. 3 Fig. 4 As-implanted Ge profile following a high dose of Ge ions, 3x1 016 cm-2 in a 170 nm thick amorphous SiGe layer, measured by RBS. XTEM micrographs of SPE-annealed SiGe alloy layers at 800~C for 1 hr after RTimplantation. The dark line indicates the sample surface. a) Ge dose = 2x1 Q16 cm-2 (5 at% Ge peak} b) Ge dose= 5x1Q16 cm-2 (12 at% Ge peak) XTEM micrographs of LNT-implanted SiGe layers after SPE annealing at 800°C for 1 hr. The dark line indicates the sample · surface. a) Ge dose, 2x1Q16 cm-2 (5 at% Ge peak) b) Ge dose, 3x1Q16 cm-2 (7 at% Ge peak) c) Ge dose, 5x1016 crn-2 (12 at% Ge peak) XTEM micrograph of SiGeC layer regrown after Ge LNT-implant ·and C sequential implant (120 keV Ge, 5x1016 cm-2 + 20 keV C, 2x1 o1s cm-2). 7 c: 0 ·-......, co s-. ......,, c: (]) (.) c: ();) 0 u (.) ·-E 0 ......, <( (_ l., 0 50 Depth·(nm) 100 ,;.'":__ . .-150 200 0 .-1 0 ,..--,.-,..-.....--.,..-..,...---,..---r-o---r---r---r--r--r--,-----r--~--r---,---r---, 0.05 Ge in Ge implanted Si •• 0 ···~ ~ • o Cb0..-i• ~ocP ceooo ~~ ~ 0 0 • • •o • •• • •o .o • .o ,.. 0 .i e Orv-.. eo •~ • e 0 e·o ~ eo i o o0 ~ •o · As-implanted Annealed •o ... •o •eo ~ 0 ,~ • .. o ease 0. 0 0 r 1 1 1· 1 1 1 1 1 1 1 1 1 1 1 · 1 1 , , 1 ... ,'l'!'g(j)$ibi·M 1 1 0 200 400 600 800 1000 Depth (E15 at./cm2) Figure 1 9 ,........___ .c 10 ) ) 11 '""-·- ,_.,.J,J LA~NCEBERKELEYLABORATORY UNIVERSITY OF CALIFORNIA TECHNICAL INFORMATION DEPARTMENT BERKELEY, CALIFORNIA 94720 ~--. ~ 

Defect Control During Solid Phase Epitaxial Growth of SiGe Alloy Layers

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