Improvement of crystalline quality in Si1-xGex formed by germanium ion implantation has been found. End‐of‐range defects were drastically reduced in number by lowering the substrate temperature during implantation with doses on the order of 1016 cm−2. This improvement was confirmed by electrical characterization of p‐n junctions formed in the SiGe layer as well as by transmission electron microscopy

Fukami, Akira

Nagano, Takahiro

Shoji, Ken-Ichi

Tokuyama, Takashi

Yang, Cary Y.

English

Scholar Commons - Santa Clara University

Santa Clara UniversityScholar CommonsElectrical Engineering School of Engineering1-27-1992Improved Crystalline Quality of Si1-xGex Formedby Low-temperature Germanium Ion ImplantationKen-Ichi ShojiAkira FukamiTakahiro NaganoTakashi TokuyamaCary Y. YangSanta Clara University, cyang@scu.eduFollow this and additional works at: https://scholarcommons.scu.edu/elecPart of the Electrical and Computer Engineering CommonsCopyright © 1992 American Institute of Physics Publishing. Reprinted with permission.This Article is brought to you for free and open access by the School of Engineering at Scholar Commons. It has been accepted for inclusion inElectrical Engineering by an authorized administrator of Scholar Commons. For more information, please contact rscroggin@scu.edu.Recommended CitationK. Shoji, A. Fukami, T. Nagano, T. Tokuyama, and C.Y. Yang, “Improved Crystalline Quality of Si1-xGex Formed by Low-temperatureGermanium Ion Implantation,” Applied Physics Letters 60, 451-453 (1992). https://doi.org/10.1063/1.106631Improved crystal~ine quality of Si1 -xGex formed by low-temperature germanium ion implantation Ken-ichi Shoji, Akira Fukami, and Takahiro Nagano Hitachi Research Laboratory, Hitachi; Ltd., 4026 Kuji, Hitachi-shi, lbaraki 319-12, Japan Takashi Tokuyama Institute of Applied Physics, University of Tsukuba, Tsukuba-sh1; Jbaraki 305, Japan Cary Y. Yang Microelectronics Laboratory, Santa Clara University, Santa Clara, California 95053 (Received 12 September 1991; accepted for publication 7 November 1991) Improvement of crystalline quality in Si1 - xGex formed by germanium ion implantation has been found. End-of-range defects were drastically reduced in number by lowering the substrate temperature during implantation with doses on the order of 1016 cm - 2• This improvement was confirmed by electrical characterization of p-n junctions formed in the SiGe layer as well as by transmission electron microscopy. Formation of SiGe/Si heterostructures has been inves-tigated by various researchers using techniques such as molecular beam epitaxy and ultrahigh vacuum chemical vapor deposition. l-6 Recently, largely as a result of inter-ests in developing silicon-compatible, high-performance hetero-bipolar technology, SiGe/Si heterostructures have been fabricated by high-dose Ge+ implantation. 7- 11 Low-dose Ge + implantation is a well-established technique to form shallow p-n junctions in preamorphized Si substrates, 12 and is inherently compatible with standard silicon integrated circuit fabrication. However, high-dose Ge + implantation introduces residual defects, which sig-nificantly degrade the crystalline quality. 11 The extent to which these defects affect the device performance is of in-terest to both materials scientists and device technologists. There are two kinds of defects in the recrystallized SiGe layer formed by Ge + implantation and subsequent ther-mal annealing. One consists of misfit dislocations near the surface, while the other consists of dislocations due to re-sidual damage at the interface between the recrystallized SiGe layer and Si substrate. The latter is known as "end-of-range (EOR) defects." Reduction of EOR defect den-sity has been achieved by lowering the substrate tempera-ture during ion implantation. 13- 15 In this letter, we present experimental results on Ge + implantation with doses on the order of 1016 cm - 2 and substrate temperatures as low as - 100 •c. Our results show improvements in the SiGe crystallinity and the p-n junctions characteristics. Cross-sectional transmission electron microscopy (XTEM) was used to estimate the SiGe layer crystallinity. Germanium ions were implanted into p-type Si( 100) through a thermally grown 10-nm oxide at an acceleration energy of 160 keV with a dose of 5 X 1016 cm - 2• The peak germanium concentration was 6X 1021 cm - 3, which cor-responds to a germanium content of 12 at. %. The Si sub-strate temperatures during ion implantation were set at - 100 and 27 •c with liquid nitrogen and water as cool-ants, respectively. The beam current density was kept be-low 0.44 µA/cm 2 during the implantation to eliminate the possibility of crystal regrowth due to beam heating. A tilt angle of 7° was used for implantation. Implanted samples were then annealed in N2 at 700 •c for 8 h. To evaluate the SiGe crystalline quality, a planar p-n structure was fabricated using a standard bipolar process for collector junction formation. This structure is shown schematically in Fig. 1. Antimony was diffused into a p-type Si( 100) substrate to form then + region using a two-step process with predeposition followed by drive-in. An undoped Si epitaxial layer was then grown, followed by phosphorus ion implantation to form the n region. A SiO2 overlayer was deposited, and diffusion windows were opened. Arsenic ions were implanted and a furnace anneal at 950 •c for 30 min was carried out to form the n + + region for metal contact. To form the p region, boron ions were implanted followed by a furnace anneal at 900 •c for 10 min. A SiO2 overlayer was added again, and the Ge + implantation window was opened. Germanium ions were implanted through a thermally grown 10-nm oxide. Con-ditions for Ge+ implantations were the same as those for the samples for XTEM observation. Then, a two-step an-neal ( 700 •c for 8 h and 900 •c for 10 min) was carried out. Figure 2 shows the concentration profile of germanium obtained from secondary ion mass spectroscopy (SIMS) and those of the dopants (antimony, phosphorus, and bo-ron) obtained from process simulation. Comparing the SIMS data, the germanium profile of the - 100 •c im-ANODE CATHODE SiGe p n p- SUBSTRATE FIG. I. Schematic of diode geometry to evaluate SiGe crystalline quality. 451 Appl. Phys. Lett. 60 (4), 27 January 1992 0003-6951 /92/040451-03$03.00 © 1992 American Institute of Physics 451 M 1022 E (..) Ge (SIMS) z 1020 0 i= 1O1a <( a: I-z w 1016 0 z 0 0 1014 0 200 400 600 800 1000 DEPTH (nm) FIG. 2. Concentration profile of Ge obtained from SIMS and those of B, P, and Sb obtained from simulation. The Ge profile is from a sample annealed at 700 'C for 8 h, followed by 900 'C for 10 min. planted sample is found to be identical to the 27 °C im-planted one. The junction depth is 1 SO nm, and the boron and phosphorus concentrations at the junction are about 4 X 1016 cm - 3. The thickness of then layer is 450 nm, with an average doping concentration of around 1016 cm - 3. The germanium content at the p-n junction is approxi-mately 12 at. %, and the germanium distribution extends to the center of the n layer. Figures 3(a) and 3(b) show XTEM photographs for the 700 °C annealed samples with implantations at - 100 and 27 °C, respectively. Two types of defects are observed. One is located near the surface and the other at the EOR. In either case, the surface defect region is about 100 nm deep. However, the surface defects in the - 100 °C im-planted sample do not extend as far as those in the 27 °C implanted sample. The EOR defects in the - 100 and D~D'iS'"'!":r-;,."'\'~~5 ~ --SURFACE (a) (b) 100 nm t----i -DEFECT RECRYSTALLIZED LAYER -EORDEFECT SUBSTRATE -SURFACE DEFECT 100 nm t----i RECRYSTALLIZED LAYER SUBSTRATE FIG. 3. XTEM images of SiGe/ Si heterostructures annealed at 700 'C for 8 h (a ) - lOO 'C Ge + implantation, (b) 27 'C Ge + implantation. 452 Appl. Phys. Lett. , Vol. 60, No. 4, 27 January 1992 10 -3 <( 27 •c implanted SiGe I- 10 ·6 z -1 oo •c implanted w SiGe a: a: ... · .. '-si ~ 10 ·9 0 n~ 1 ff 12 0 0.2 0.4 0.6 0.8 1.0 APPLIED VOLTAGE (V) (a) 10 -11 JUNCTION AREA: 8.5 x 8 (µm 2) ~ 27 •c implanted -12 SiGe I- 10 z w a: a: -13 ~ 0 10 ···· · '-si -14 10 ·2 -1 0 10 10 10 APPLIED VOLTAGE (V) (b) FIG. 4. Comparisons of current-voltage characteristics for diodes formed with - 100 and 27 'C Ge + implantations, and without Ge + implanta-tion (a ) forward bias, ( b) reverse bias. 27 °C implanted samples are centered at about 310 and 280 nm from the surface, respectively, while the density as well as the extent of EOR defects in the low-temperature im-planted sample are substantially less. From the profile shown in Fig. 2, the germanium concentration at the EOR for the - 100 °C implanted sample is S X 1018 cm - 3, whereas that for the 27 °C implanted one is 10 19 cm - 3. Since the residual damage resulting from Ge + bombard-ment increases with local germanium concentration, this difference in concentration at EOR is consistent with the observed difference in defect density. Figure 4 summarizes the results of the room-tempera-ture, current-voltage measurements for three p-n junction diodes. For forward biases between 0.4 and 0. 7 V [Fig. 4(a)], the Si control diode exhibits ideal characteristics as expected. The larger concentrations of recombination cen-ters in the SiGe diodes lead to larger currents and smaller slopes than the Si control diode. This increase in recombi-nation centers is due primarily to the EOR defects within the depletion region of the p-n junction. However, the cur-rent and ideality factor for the - 100 °C implanted diode are smaller than those for the 27 °C implanted one. The ideality factor of the former is 1.3, while that of the latter is 1.5. This confirms that reduction of EOR defects is achieved by lowering the substrate temperature during ger-manium ion implantation. Figure 4(b) compares reverse current-voltage characteristics for the three diodes up to a bias of 1 V. The breakdown voltages of the control, the Shoji et al. 452 27 •c implanted, and the - 100 •c implanted diodes are 6.2, 5.9, and 6.5 V, respectively. Assuming a linearly graded junction model for each diode, these values are consistent with the doping concentrations shown in Fig. 2. The reverse current of the 27 •c implanted diode is about one order of magnitude larger than that of the Si control diode, while the reverse current of the - 100 •c implanted diode is about half of the 27 •c implanted one. This reduc-tion in generation current for the low-temperature im-planted diode must be accompanied by an improvement in crystalline quality in the SiGe layer and near the SiGe Si substrate interface, as demonstrated by the XTEM obser-vations shown in Fig. 3. Compared with the Si control device, the larger reverse current for the - 100 •c im-planted diode may also be partially attributed to a nar-rower band gap in SiGe. In summary, the density of EOR defects in the Si Ge/Si heterostructure formed by Ge + implantation with doses on the order of 1016 cm - 2 followed by thermal annealing is reduced by lowering the substrate temperature during ion implantation to - 100 •c. This is verified by forward and reverse current-voltage characteristics of p-n junctions as well as by XTEM. The authors would like to thank Dr. N. Momma for his encouragement throughout this work. Thanks are also 453 Appl. Phys. Lett., Vol. 60, No. 4, 27 January 1992 due to S. Kawakami, K. Sukegawa, and the technical staff of Hitachi Research Laboratory for their contributions in the device fabrication. 1 J. W. Matthews and A. E. Blakeslee, J. Cryst. Growth 27, 118 ( 1974) 2J . W. Matthews, J. Vac. Sci. Technol. 12, 126 (1975). 3 J. H. van der Merme, J. Appl. Phys. 34, 123 ( 1963). 4 B. S. Meyerson, Appl. Phys. Lett . 48, 797 ( 1986). 5 B. S. Meyerson, F . K . LeGoues, T. N. Nguyen, and D. L. Harame, Appl. Phys. Lett. 50, 113 ( 1987) . 6B. S. Meyerson, K. J. Uram, and F. K. LeGoues, Appl. Phys. Lett. 53, 2555 ( 1988). 7 0 . W . Holland, C. W. White, and D. Fathy, Appl. Phys. Lett. 51, 520 ( 1987). 8 D. Fathy, 0. W. Holland, and C. W. White, Appl. Phys. Lett. 51, 1337 ( 1987). 9 K. Ohta, J. Sakano, and S. Furukawa, Extended Abstracts of 21st Con-ference on Solid State Devices and Materials, Tokyo, August, 1989 (unpublished), p. 555. 10 A . R. Srivasta, S. Sharan, 0. W . Holland, a nd J. Narayan, J . Appl. Phys. 65, 4028 ( 1989). 11 A. Fukami, K. Shoji, T. Nagano, and C. Y. Yang, Appl. Phys. Lett. 57, 2345 ( 1990). 12 K . Kuriyama, S. Aoki , M. Satoh, and M. Nakano, Phys. Res. B 39, 397 ( 1989). 13 K. S. Jones and D. Venables, J . Appl. Phys. 69, 2931 ( 1991 ). 14 S. Prussin and K . S. Jones, J. Electrochem. Soc. 137, 1912 (1990). 15 T. Suzuki, H. Yamaguchi, S. Ohzono, and N. Natsuaki, Extended Ab-stracts of 22nd Conference on Solid State Devices and Materials, Sen-dai, August, 1990 (unpublished), p. 1163. Shoji et al. 453 

Improved Crystalline Quality of Si\u3csub\u3e1-x\u3c/sub\u3eGe\u3csub\u3ex\u3c/sub\u3e Formed by Low-temperature Germanium Ion Implantation

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Improved Crystalline Quality of Si\u3csub\u3e1-x\u3c/sub\u3eGe\u3csub\u3ex\u3c/sub\u3e Formed by Low-temperature Germanium Ion Implantation

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