- Email: [email protected]
Damage formation in Si(100) induced by MeV self-ion implantation
Nuclear Instruments and Methods in Physics Research B 82 (1993) 575-578 North-Holland
NOMB
Beam Interactions with Matorials & Atoms
Damage formation in Si( 100) induced by MeV self-ion implantation
*
Qing-tai Zhao and Zhotig-lie Wang Institute of Microelectronics, Peking University, Beijing 100871, China
Tian-bing Xu, Pei-ran Zhu and Jun-si Zhou Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
Xiang-dong Liu, Ji-tian Liu and Ke-ming Wang Department of Physics, Shandong University, Jinan 250100, Shandong, China
Received 11 December 1992 and in revised form 1 April 1993
Damage formation in Si(lO0) induced by MeV self-ion implantation was studied using the Rutherford backscattering and channeling technique. Damage accumulations were found to be produced mainly near the ions’ end of range. Two distinct regions were observed for dose dependence upon damage. One is for low doses, in which the damage increases slowly with dose. The second region is for high-dose implantation, in which the damage increases rapidly as the dose increases. Beam self-annealing was found in MeV Si ion implanted WOO). The effects of the energy depositions on the defect production are also discussed.
1. Introduction MeV ion implantation in silicon has gained increasing attention in recent years because of possible applications in VLSI technology. These include using the damage produced by high energy ions to control the minority-carrier lifetime in Si [l] and to provide buried gettering sites for collection of metallic impurities [2]. High energy ion implantation can be used for the
reduction of secondary defects in predamaged silicon, the so-called ion beam defect engineering technique [3]. Also, retrograde wells and buried conductive layers [4,5] have been formed to enhance the device performance and control latchup in complementary metaloxide-semiconductor (CMOS) ICs. The damage induced by MeV ion implantation plays an important role in these applications. Thus, the understanding of the defect production in semiconductors becomes very important for semiconductor device technology. A lot of reports have been published for the cases of lowand medium-energy-ion implantation in silicon. However, the damage formation induced by MeV ion implantation in silicon has been relatively less studied. Correspondence to: Q. Zhao, Institute of Microelectronics, Peking University, Beijing 100871, China. * Supported by the National Natural Science Foundation of China.
0168-583X/93/$06.00
The total amount and depth distribution of the disorder are influenced by many factors, such as mass and energy of the implant ions, type of crystal, temperature of the implantation process, dose and dose rate. When the implant dose exceeds a critical value an amorphous layer can be formed. This critical value is affected by the implant conditions, such as the target temperature, dose rate, the implant ion species as well as the implant energy. In this paper, the damage formation by MeV selfions at different doses and energies in Si(100) single crystal was studied. We chose the self-ion implantation with Sic ions in order to avoid the possible chemical effects of the implant ion on the damage. Holland et al. [6,7] have studied the characterization of the damage induced by 1.25 MeV Si+ ion implantation. Some similarities between high- and low-energy ion implantation in Si000) have been reported. In this work, we use the Rutherford backscattering and channeling technique to study the damage formation for various doses of ion implantation in silicon. The damage distribution and the depth distribution of the implanted ions calculated by a Monte Carlo simulation (TRIM89) [8] were compared with the experimental damage distribution. From the comparison, beam annealing during the process of ion implantation was found. The effects of the energy deposition on the defect production were also discussed.
0 1993 - Elsevier Science Publishers B.V. All rights reserved
Q. Zhao et al. / Damage formation in Si(100)
516 2. Experimental
methods
Czochralski-grown, p-type Si(100) single crystals with a resistivity of 12 fI cm were used in this study. Ion implantation with 1 MeV, 29Si+ ions to doses ranging from 2 X 1014 to 2 X 10” Si+/cm2, and implantations with 2 and 2.5 MeV 29Si+ ions to a dose of 5 X 10’4/cm2 were performed using a 2 X 1.7 MV tandem accelerator. The use of 29Si+ ions ensures that the 28Si+ beam is free of contaminants, such as molecular ions with the same mass-to-charge ratio (CO, N,). During ion implantation, the wafer was tilted 7” off the incident ion beam in order to avoid possible channeling effects. The dose rate is less than 1 x 101*/cm2s. The temperature rise of the target induced by 1 MeV ion bombardment was less than 7o”C, measured by a thermocouple placed near the implanted region. Rutherford backscattering and channeling (RBS/C) techniques were applied to study the damage in the implanted layer. The analyzing beam was 2.1 MeV He ‘+ ions. The backscattered particles were detected by a silicon surface barrier detector at an angle of 165” to the incoming beam. During the analysis the He2+ beam current was less than 15 nA. All the RBS/C measurements were carried out using the 2 X 1.7 MV tandem accelerator at Shandong University.
3. Results and discussion Fig. 1 shows the RBS/C spectra from Si(100) after implantation with 1 MeV Si ions to doses of (2) 2 X
50
100
150
250 200 CHANNEL
300
3
IO
Fig.1. RBS/C spectra for Si(100) implanted with 1 MeV Si ions to doses of (1) virgin, (2) 2 x 1014,(3) 3 x 1014, (4) 5 x 1014, (5) 8X1014, (6) 1X1015, (7) 1.5X1015, (8) 2~10’~ Sif/cm2, and (9) random spectrum of virgin Si(100).
1
2
DEPTH (P m)
Fig. 2. Damage profiles for Si(100) implanted with 1 MeV Si ions to doses of (1) 3 x 1014, (2) 5 x 1014, (3) 1 x lo”, (4) 1.5 X 1015, and (5) 2~ 10” Si+/cm’.
1014, (3) 3 x 1014, (4) 5 x 1014, (5) 8 x 1014, (6) 1 x 1015, (7) 1.5 x 1015, and (8) 2 X lOi Si+/cm’, respectively. For comparison, the aligned (1) and random (9) spectra of virgin Si(100) are also presented. The deviation of the aligned scattering yield at any point within the implanted sample from that in the virgin crystal indicates the presence of defects. Dechanneling peaks around channel 160 were found. For doses below 1 x 1015/cm2, the scattering yields in the damaged region are far below the level of the random spectrum, while for a dose of 2 X 1015 Si/cm’ the scattering yields nearly reach the level of the random spectrum in the range from channel 140 to 180. The result indicates that a buried amorphous layer was formed after implantation with 1 MeV, 2 X 1015 Si+/cm*. Thus, the critical dose for a transition from crystalline to amorphous can be estimated to be 2 x 10’5/cm2 for 1 MeV 29Si ion implantation in Si(100). Damage profiles were obtained by calculation of the RBS/C spectra in fig. 1. The multiple scattering method as described by Feldman and Rodger [9] was employed in the calculation from RBS/C spectra to damage profiles [lo]. The modification of the stopping power for the aligned Rutherford analyzing beam was considered in the calculation. We suppose that the ratio of the stopping power for the incident He particles in channeling direction and in random direction is 0.7. Fig. 2 gives the results of the calculation for Si(100) implanted with 1 MeV Si ions to doses of (1) 3 x 1014, (2) 5 X 1014, (3) 1 X 1015, (4) 1.5 X 1015, and (5) 2 X 1015 Si/cm2, respectively. The ordinate of fig. 2 is the ratio between the density of the displaced atoms Nd and the atom density of Si single crystal. From fig. 2 we can see
Q. Zhao et al. / Damage formation in Si(100)
‘“I
0' 0
5
10
15
20
25
DOSE(XlE14)
Fig. 3. Dose dependence of the total amount of damage for dlO0) implanted with 1 MeV Si ions.
that the damage density varies along the ion track. Most defects were produced near the end of range (EOR) of the implanted ions. In the region ahead of the ions’ EOR, the damage saturates at a low level, and this saturation increases very slowly with increasing dose. As for the damage peaks, it was found that they appear at almost the same depth for all doses. The width of the heavily damaged region also increases as the implant dose increases. Fig. 3 shows the dose dependence of the total amount of displacements which is calculated by integrating the density of the defects over the total damaged region. It is clear that there are two distinct regions for the damage accumulation. In the first region, at low fluences (3 X 1014-8 X 1014/cm2), the total amount of the damage increases slowly with increasing dose. The second region appears at fluences of 8 X 1014-2 X 1015 Si/cm*. It shows an approximately linear relation of fluence and damage. The damage in this region increases faster than that in the first region. In these two regions, different defect morphologies are dominant [ll]. Simple defects are formed in the first region, while complex defects dominate in the second region. Our results are in agreement with those of Holland et al. [6,7]. Compared with the results for the case of low-energy Si+ implantation in WOO) in ref. [ll], the damage increases faster for low-energy implantation in the second dose region. This is due to the broader distribution of defects, which leads to less formation of complex defects during high-energy ion implantation. For comparison, fig. 4 shows the experimental (1) and theoretical (2) damage profiles for Si(100) implanted with 1 MeV, 5 x 1014 Si/cm2. The theoretical
577
depth distribution of the implanted ions is also presented in arbitrary units in this figure (3). The theoretical results are obtained by Monte Carlo simulation (TRIM89). In the theoretical calculation the threshold displacement energy E, was chosen to be 15 eV. More than 5000 ions were simulated. From fig. 4 it is found that the position of the experimental damage peak is in good agreement with the result of the theoretical calculation. It is located at a depth of about 80% of the projected range of the implanted ions. From the comparison between the theoretical and experimental damage profiles, we can see that the obtained amount of damage is much lower than the theoretical value in the whole damaged region. This is due to the dynamic beam annealing during the process of ion implantation. It can be seen that at least 60% of the defects were removed by beam self-annealing. The dynamic beam self-annealing results from the recombination of point defects, such as interstitials and vacancies. It is responsible for the saturation of defects ahead of the EOR and the slow increase of the damage in the first dose region, in which the form of the defects is simple defects. Fig. 5 shows the relative density of defects, NJN, as a function of nuclear energy deposition E, in the surface region ahead of the EOR where only simple defects were formed. The data of E, are calculated by the TRIM89 code. Curves 1, 2 and 3 represent the results for Si(100) after implantation with 1, 2 and 2.5 MeV Si+ ions to a dose of 5 X 10i4/cm2, respectively. During implantation, the dose rate was kept at the
DEPTH ( p m)
Fig. 4. Comparison of damage profiles between (1) experimental and (2) theoretical (TRIM89) results for 1 MeV, 5 X 1014 Sif/cm2 ion implanted Si(100). Curve 3 is the theoretical depth distribution of the implanted Si ions in arbitrary units.
Q. Zhao et al. / Damage formation in Si(100)
578
high density of electronic excitation may enhance the production of defects during nuclear collisions.
4. Summary
25
48
‘1 I ‘1 I ‘1 I 3’/‘1 / I
20 2 z > z 15
‘/
‘/
IO 5 0. 0
‘/
//
/I
“
,/
,’
/+
/’
‘,2
//
,/ I /
IO
30 20 En (X5E22eVh~31 Fig. 5. The relative density of defects in the surface region as a function of nuclear energy deposition E, for Si(100) implanted at a dose of 5 x 10’4/cm2 at energies of (1) 1 MeV, (2) 2 MeV and (3) 2.5 MeV.
same value of 8.1 x 10” Si+/cm*s for these three cases. From fig. 5 we can see that the density of defects increases with increasing nuclear energy deposition. The increase of the implantation energy induces a slight increase of the defect density at the same value of E,. It is known that the defect production is strongly dependent on the implantation conditions, such as defect production rate and temperature [7,12]. The defect production rate is the same in our experiment because the same value for the dose rate was used during implantations. As for temperature, this was also the same and kept at room temperature (RT) before implantation. The temperature rise of the sample induced by beam irradiation increases with increasing beam power [12]. Therefore, in our cases, the higherenergy implantation caused a larger temperature rise. According to the results of Haynes et al. [12], the damage density decreases as the temperature increases. Thus, the slight increase of the defect density at higher energies is not due to the implantation conditions. At the same value of E,, the electronic energy deposition, which is much larger than the nuclear energy deposition in the surface region for MeV ions, is different at different implantation energies. It increases with increasing implant energy. A possible cause for the slight increase of defect density at higher energy is the high density of the electronic energy deposition. Fabbri et al. [14] have suggested that the energy contribution by ions to the electronic subsystem produces slight displacements of the atoms from the lattice sites. These slight displacements induced by a
The damage formation in Si(100) after implantation with MeV self-ions at different doses and energies was studied by the Rutherford backscattering and channeling technique. The density of defects ahead of the ions’ end of range saturates at a very low level and increases very slowly with increasing implant dose. Two distinct regions for dose dependence were observed. In the first region, for lower-dose implantation, the total amount of defects increases very slowly with increasing dose. The second region corresponds to the high-dose implantation, in which the total amount of defects increases rapidly as the dose increases. Beam self-annealing, which was found by comparison between the experimental profile and the TRIM result, was suggested to be responsible for the saturation of defects ahead of the ions’ end of range and the slow increase of defects in the first region. The effect of electronic excitation upon defect production was also discussed.
References [ll A. Mogro-Camper0 and R.P. Love, J. Electrochem. Sot. 131 (1984) 655. [21 H. Wong, N.W. Cheung, P.K. Chu, J. Liu and J.W. Mayer, Appl. Phys. Lett. 52 (1988) 1023. [31 Z. Wang, B. Zhang, Q. Zhao, Qi Li, R.J. Schreutelkamp, J.R. Liefting and F.W. Saris, J. Appl. Phys. 71 (1992) 3780. [41 K. Tsukamoto, S. Komori, T. Kuroi and Y. Akasaka, Nucl. Instr. and Meth. B 59/60 (1991) 584. 151 Y. Taur, G.J. Hu, R.H. Dennard, L.M. Terman, ChungYu Ting and K.E. Petrillo, IEEE J. Solid State Circuits SC-20 (1985) 123. [61 O.W. Holland, M.K. El-Ghor and C.W. White, Appl. Phys. Lett. 53 (1988) 1282. [71 O.W. Holland and C.W. White, Nucl. Instr. and Meth. B 59/60 (1991) 353. [81 J.P. Biersack, Nucl. Instr. and Meth. 174 (1980) 257. [91 L.C. Feldman and J.W. Rodger, J. Appl. Phys. 41 (1970) 3776. t101 W.K. Chu, J.W. Mayer and M.A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978). t111 O.W. Holland, S.J. Pennycook and G.L. Albert, Appl. Phys. Lett. 55 (1989) 2503. [121 T.E. Haynes and O.W. Holland, Appl. Phys. Lett. 61 (1992) 61. t131 J. Nakata, Phys. Rev. B 43 (1991) 14643. [141 R. Fabbri, M. Servidori, F. Cembali, R. Nipoti and M. Bianconi, Nucl. Instr. and Meth. B 66 (1992) 511.
NOMB
Beam Interactions with Matorials & Atoms
Damage formation in Si( 100) induced by MeV self-ion implantation
*
Qing-tai Zhao and Zhotig-lie Wang Institute of Microelectronics, Peking University, Beijing 100871, China
Tian-bing Xu, Pei-ran Zhu and Jun-si Zhou Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
Xiang-dong Liu, Ji-tian Liu and Ke-ming Wang Department of Physics, Shandong University, Jinan 250100, Shandong, China
Received 11 December 1992 and in revised form 1 April 1993
Damage formation in Si(lO0) induced by MeV self-ion implantation was studied using the Rutherford backscattering and channeling technique. Damage accumulations were found to be produced mainly near the ions’ end of range. Two distinct regions were observed for dose dependence upon damage. One is for low doses, in which the damage increases slowly with dose. The second region is for high-dose implantation, in which the damage increases rapidly as the dose increases. Beam self-annealing was found in MeV Si ion implanted WOO). The effects of the energy depositions on the defect production are also discussed.
1. Introduction MeV ion implantation in silicon has gained increasing attention in recent years because of possible applications in VLSI technology. These include using the damage produced by high energy ions to control the minority-carrier lifetime in Si [l] and to provide buried gettering sites for collection of metallic impurities [2]. High energy ion implantation can be used for the
reduction of secondary defects in predamaged silicon, the so-called ion beam defect engineering technique [3]. Also, retrograde wells and buried conductive layers [4,5] have been formed to enhance the device performance and control latchup in complementary metaloxide-semiconductor (CMOS) ICs. The damage induced by MeV ion implantation plays an important role in these applications. Thus, the understanding of the defect production in semiconductors becomes very important for semiconductor device technology. A lot of reports have been published for the cases of lowand medium-energy-ion implantation in silicon. However, the damage formation induced by MeV ion implantation in silicon has been relatively less studied. Correspondence to: Q. Zhao, Institute of Microelectronics, Peking University, Beijing 100871, China. * Supported by the National Natural Science Foundation of China.
0168-583X/93/$06.00
The total amount and depth distribution of the disorder are influenced by many factors, such as mass and energy of the implant ions, type of crystal, temperature of the implantation process, dose and dose rate. When the implant dose exceeds a critical value an amorphous layer can be formed. This critical value is affected by the implant conditions, such as the target temperature, dose rate, the implant ion species as well as the implant energy. In this paper, the damage formation by MeV selfions at different doses and energies in Si(100) single crystal was studied. We chose the self-ion implantation with Sic ions in order to avoid the possible chemical effects of the implant ion on the damage. Holland et al. [6,7] have studied the characterization of the damage induced by 1.25 MeV Si+ ion implantation. Some similarities between high- and low-energy ion implantation in Si000) have been reported. In this work, we use the Rutherford backscattering and channeling technique to study the damage formation for various doses of ion implantation in silicon. The damage distribution and the depth distribution of the implanted ions calculated by a Monte Carlo simulation (TRIM89) [8] were compared with the experimental damage distribution. From the comparison, beam annealing during the process of ion implantation was found. The effects of the energy deposition on the defect production were also discussed.
0 1993 - Elsevier Science Publishers B.V. All rights reserved
Q. Zhao et al. / Damage formation in Si(100)
516 2. Experimental
methods
Czochralski-grown, p-type Si(100) single crystals with a resistivity of 12 fI cm were used in this study. Ion implantation with 1 MeV, 29Si+ ions to doses ranging from 2 X 1014 to 2 X 10” Si+/cm2, and implantations with 2 and 2.5 MeV 29Si+ ions to a dose of 5 X 10’4/cm2 were performed using a 2 X 1.7 MV tandem accelerator. The use of 29Si+ ions ensures that the 28Si+ beam is free of contaminants, such as molecular ions with the same mass-to-charge ratio (CO, N,). During ion implantation, the wafer was tilted 7” off the incident ion beam in order to avoid possible channeling effects. The dose rate is less than 1 x 101*/cm2s. The temperature rise of the target induced by 1 MeV ion bombardment was less than 7o”C, measured by a thermocouple placed near the implanted region. Rutherford backscattering and channeling (RBS/C) techniques were applied to study the damage in the implanted layer. The analyzing beam was 2.1 MeV He ‘+ ions. The backscattered particles were detected by a silicon surface barrier detector at an angle of 165” to the incoming beam. During the analysis the He2+ beam current was less than 15 nA. All the RBS/C measurements were carried out using the 2 X 1.7 MV tandem accelerator at Shandong University.
3. Results and discussion Fig. 1 shows the RBS/C spectra from Si(100) after implantation with 1 MeV Si ions to doses of (2) 2 X
50
100
150
250 200 CHANNEL
300
3
IO
Fig.1. RBS/C spectra for Si(100) implanted with 1 MeV Si ions to doses of (1) virgin, (2) 2 x 1014,(3) 3 x 1014, (4) 5 x 1014, (5) 8X1014, (6) 1X1015, (7) 1.5X1015, (8) 2~10’~ Sif/cm2, and (9) random spectrum of virgin Si(100).
1
2
DEPTH (P m)
Fig. 2. Damage profiles for Si(100) implanted with 1 MeV Si ions to doses of (1) 3 x 1014, (2) 5 x 1014, (3) 1 x lo”, (4) 1.5 X 1015, and (5) 2~ 10” Si+/cm’.
1014, (3) 3 x 1014, (4) 5 x 1014, (5) 8 x 1014, (6) 1 x 1015, (7) 1.5 x 1015, and (8) 2 X lOi Si+/cm’, respectively. For comparison, the aligned (1) and random (9) spectra of virgin Si(100) are also presented. The deviation of the aligned scattering yield at any point within the implanted sample from that in the virgin crystal indicates the presence of defects. Dechanneling peaks around channel 160 were found. For doses below 1 x 1015/cm2, the scattering yields in the damaged region are far below the level of the random spectrum, while for a dose of 2 X 1015 Si/cm’ the scattering yields nearly reach the level of the random spectrum in the range from channel 140 to 180. The result indicates that a buried amorphous layer was formed after implantation with 1 MeV, 2 X 1015 Si+/cm*. Thus, the critical dose for a transition from crystalline to amorphous can be estimated to be 2 x 10’5/cm2 for 1 MeV 29Si ion implantation in Si(100). Damage profiles were obtained by calculation of the RBS/C spectra in fig. 1. The multiple scattering method as described by Feldman and Rodger [9] was employed in the calculation from RBS/C spectra to damage profiles [lo]. The modification of the stopping power for the aligned Rutherford analyzing beam was considered in the calculation. We suppose that the ratio of the stopping power for the incident He particles in channeling direction and in random direction is 0.7. Fig. 2 gives the results of the calculation for Si(100) implanted with 1 MeV Si ions to doses of (1) 3 x 1014, (2) 5 X 1014, (3) 1 X 1015, (4) 1.5 X 1015, and (5) 2 X 1015 Si/cm2, respectively. The ordinate of fig. 2 is the ratio between the density of the displaced atoms Nd and the atom density of Si single crystal. From fig. 2 we can see
Q. Zhao et al. / Damage formation in Si(100)
‘“I
0' 0
5
10
15
20
25
DOSE(XlE14)
Fig. 3. Dose dependence of the total amount of damage for dlO0) implanted with 1 MeV Si ions.
that the damage density varies along the ion track. Most defects were produced near the end of range (EOR) of the implanted ions. In the region ahead of the ions’ EOR, the damage saturates at a low level, and this saturation increases very slowly with increasing dose. As for the damage peaks, it was found that they appear at almost the same depth for all doses. The width of the heavily damaged region also increases as the implant dose increases. Fig. 3 shows the dose dependence of the total amount of displacements which is calculated by integrating the density of the defects over the total damaged region. It is clear that there are two distinct regions for the damage accumulation. In the first region, at low fluences (3 X 1014-8 X 1014/cm2), the total amount of the damage increases slowly with increasing dose. The second region appears at fluences of 8 X 1014-2 X 1015 Si/cm*. It shows an approximately linear relation of fluence and damage. The damage in this region increases faster than that in the first region. In these two regions, different defect morphologies are dominant [ll]. Simple defects are formed in the first region, while complex defects dominate in the second region. Our results are in agreement with those of Holland et al. [6,7]. Compared with the results for the case of low-energy Si+ implantation in WOO) in ref. [ll], the damage increases faster for low-energy implantation in the second dose region. This is due to the broader distribution of defects, which leads to less formation of complex defects during high-energy ion implantation. For comparison, fig. 4 shows the experimental (1) and theoretical (2) damage profiles for Si(100) implanted with 1 MeV, 5 x 1014 Si/cm2. The theoretical
577
depth distribution of the implanted ions is also presented in arbitrary units in this figure (3). The theoretical results are obtained by Monte Carlo simulation (TRIM89). In the theoretical calculation the threshold displacement energy E, was chosen to be 15 eV. More than 5000 ions were simulated. From fig. 4 it is found that the position of the experimental damage peak is in good agreement with the result of the theoretical calculation. It is located at a depth of about 80% of the projected range of the implanted ions. From the comparison between the theoretical and experimental damage profiles, we can see that the obtained amount of damage is much lower than the theoretical value in the whole damaged region. This is due to the dynamic beam annealing during the process of ion implantation. It can be seen that at least 60% of the defects were removed by beam self-annealing. The dynamic beam self-annealing results from the recombination of point defects, such as interstitials and vacancies. It is responsible for the saturation of defects ahead of the EOR and the slow increase of the damage in the first dose region, in which the form of the defects is simple defects. Fig. 5 shows the relative density of defects, NJN, as a function of nuclear energy deposition E, in the surface region ahead of the EOR where only simple defects were formed. The data of E, are calculated by the TRIM89 code. Curves 1, 2 and 3 represent the results for Si(100) after implantation with 1, 2 and 2.5 MeV Si+ ions to a dose of 5 X 10i4/cm2, respectively. During implantation, the dose rate was kept at the
DEPTH ( p m)
Fig. 4. Comparison of damage profiles between (1) experimental and (2) theoretical (TRIM89) results for 1 MeV, 5 X 1014 Sif/cm2 ion implanted Si(100). Curve 3 is the theoretical depth distribution of the implanted Si ions in arbitrary units.
Q. Zhao et al. / Damage formation in Si(100)
578
high density of electronic excitation may enhance the production of defects during nuclear collisions.
4. Summary
25
48
‘1 I ‘1 I ‘1 I 3’/‘1 / I
20 2 z > z 15
‘/
‘/
IO 5 0. 0
‘/
//
/I
“
,/
,’
/+
/’
‘,2
//
,/ I /
IO
30 20 En (X5E22eVh~31 Fig. 5. The relative density of defects in the surface region as a function of nuclear energy deposition E, for Si(100) implanted at a dose of 5 x 10’4/cm2 at energies of (1) 1 MeV, (2) 2 MeV and (3) 2.5 MeV.
same value of 8.1 x 10” Si+/cm*s for these three cases. From fig. 5 we can see that the density of defects increases with increasing nuclear energy deposition. The increase of the implantation energy induces a slight increase of the defect density at the same value of E,. It is known that the defect production is strongly dependent on the implantation conditions, such as defect production rate and temperature [7,12]. The defect production rate is the same in our experiment because the same value for the dose rate was used during implantations. As for temperature, this was also the same and kept at room temperature (RT) before implantation. The temperature rise of the sample induced by beam irradiation increases with increasing beam power [12]. Therefore, in our cases, the higherenergy implantation caused a larger temperature rise. According to the results of Haynes et al. [12], the damage density decreases as the temperature increases. Thus, the slight increase of the defect density at higher energies is not due to the implantation conditions. At the same value of E,, the electronic energy deposition, which is much larger than the nuclear energy deposition in the surface region for MeV ions, is different at different implantation energies. It increases with increasing implant energy. A possible cause for the slight increase of defect density at higher energy is the high density of the electronic energy deposition. Fabbri et al. [14] have suggested that the energy contribution by ions to the electronic subsystem produces slight displacements of the atoms from the lattice sites. These slight displacements induced by a
The damage formation in Si(100) after implantation with MeV self-ions at different doses and energies was studied by the Rutherford backscattering and channeling technique. The density of defects ahead of the ions’ end of range saturates at a very low level and increases very slowly with increasing implant dose. Two distinct regions for dose dependence were observed. In the first region, for lower-dose implantation, the total amount of defects increases very slowly with increasing dose. The second region corresponds to the high-dose implantation, in which the total amount of defects increases rapidly as the dose increases. Beam self-annealing, which was found by comparison between the experimental profile and the TRIM result, was suggested to be responsible for the saturation of defects ahead of the ions’ end of range and the slow increase of defects in the first region. The effect of electronic excitation upon defect production was also discussed.
References [ll A. Mogro-Camper0 and R.P. Love, J. Electrochem. Sot. 131 (1984) 655. [21 H. Wong, N.W. Cheung, P.K. Chu, J. Liu and J.W. Mayer, Appl. Phys. Lett. 52 (1988) 1023. [31 Z. Wang, B. Zhang, Q. Zhao, Qi Li, R.J. Schreutelkamp, J.R. Liefting and F.W. Saris, J. Appl. Phys. 71 (1992) 3780. [41 K. Tsukamoto, S. Komori, T. Kuroi and Y. Akasaka, Nucl. Instr. and Meth. B 59/60 (1991) 584. 151 Y. Taur, G.J. Hu, R.H. Dennard, L.M. Terman, ChungYu Ting and K.E. Petrillo, IEEE J. Solid State Circuits SC-20 (1985) 123. [61 O.W. Holland, M.K. El-Ghor and C.W. White, Appl. Phys. Lett. 53 (1988) 1282. [71 O.W. Holland and C.W. White, Nucl. Instr. and Meth. B 59/60 (1991) 353. [81 J.P. Biersack, Nucl. Instr. and Meth. 174 (1980) 257. [91 L.C. Feldman and J.W. Rodger, J. Appl. Phys. 41 (1970) 3776. t101 W.K. Chu, J.W. Mayer and M.A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978). t111 O.W. Holland, S.J. Pennycook and G.L. Albert, Appl. Phys. Lett. 55 (1989) 2503. [121 T.E. Haynes and O.W. Holland, Appl. Phys. Lett. 61 (1992) 61. t131 J. Nakata, Phys. Rev. B 43 (1991) 14643. [141 R. Fabbri, M. Servidori, F. Cembali, R. Nipoti and M. Bianconi, Nucl. Instr. and Meth. B 66 (1992) 511.