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SiO2 with ion beam methods
Nuclear Instruments and Methods in Physics Research B 85 (1994) 936-939 North-Holland
NOMB
Beam Interactions with Materials&Atoms
Production and analysis of buried nitride layers in Si/SiO, with ion beam methods D. Friise *, D. Kollewe Institutfiir Strahlenphysik der UniversitiitStuttgart,Allmandring3, 70569 Stuttgart,Germany
Nitrogen was implanted in (llO)-oriented silicon and in thermally formed silicon dioxide layers. After implantation the systems were annealed to reduce radiation damage. These implanted systems were investigated with ion beam methods as RBS and NRA to determine the depth distribution of the nitrogen and the oxygen with regard to the implantation and annealing parameters.
1. Introduction
2. Experimental
Optical devices like waveguides and electrooptical switches became very important for transmission of information in the last years. By implantation of nitrogen and oxygen in silicon one can produce SiO,N,layers with a gradient in their refractive index [1,2]. These implanted buried layers can then be used as a planar waveguide [3]. However, it is important to now the depth profile of the implanted nitrogen layer. To form well defined buried layers with these characteristics, the tool of ion-implantation was chosen. The implantations were accomplished at sample temperatures up to 500°C; for these temperatures annealing during implantation can be expected. After the implantation the samples were annealed for one to six hours at a temperature of 1300°C. To investigate the composition of the layers, ion beam analysis methods like Rutherford Backscattering (RBS) and Nuclear Reaction Analysis (NRA) were used. In RBS analysis, one problem met is that the kinematic factors for nitrogen and oxygen are closed together. Therefore the signals of the backscattered particles for these materials superpose. To separate the peaks from Si and 0, RBS measurements at 2.4 MeV and 2.9 MeV with a-particles were performed. For the detection of the nitrogen, the “N(p, a)“C reaction was used by performing a measurement with a 1.02 MeV proton beam. The depth distribution is calculated from the measured spectra without fitting any parameter. In this way, the distributions of implanted nitrogen in silicon were measured with regard to annealing durations from 1 to 6 h at 1300°C.
2.1. Implantations in Si The implantations were performed at the Dynamitron-Accelerator in Stuttgart with an energy of 429 keV per r4N-Ion in (llO)-oriented silicon at room temperature. The sample was tilted at 7” from the axis to avoid channeling effects during implantation. The dose was calculated so that in the maximum of the distribution the formation of Si,N, can be expected [4]. At this energy, the Monte-Carlo-Code TRIM 88 [5] yields a projected range R, = 784 nm. A gauss-fit to the TRIM-distribution amounts to a AR, = 72 nm. With these values the dose was determined to No = 1.2 x lOr* N/cm’. After implantation the samples were annealed for one to 6 h under normal atmosphere. 2.2. Implantations in SiO, For these implantations a (llO)-oriented silicon wafer was thermally oxidized for 12 h at 1300°C under normal atmosphere. This process resulted in a SiO,layer, with a thickness determined with RBS to 580 nm. In this layer “N,-molecules were implanted with an energy of 300 keV per atom. The TRIM-calculation yields of the projected range R, = 560 nm, so that the maximum of the N-distribution comes to rest in the SiO,-layer. The implantation temperature was varied from room temperature to 500°C. 2.3. Analysis of the systems
* Corresponding 711 685 3866. 0168-583X/94/$07.00
author,
phone
+49 711 685 3871, fax +49
the 0 1994 - Elsevier
SSDZ0168-583X(93)E0576-3
Science B.V. All rights reserved
The analysis was performed Dynamitron in Stuttgart,
with RBS and NRA at too. For the r4N im-
D. F&e,
937
D. Kollewe / Nucl. Instr. and Meth. in Phys. Res. B 8.5 (1994) 936-939
planted silicon layers the RBS-spectra with 2.95 MeV and 3.3 MeV He+ were measured. These spectra are shown in Fig. 1. At 3.3 MeV the differential cross section of 14N(a, cx)14N is larger than the pure Rutherford cross section and amounts to 100 mb 161,so that the peak of the nitrogen is obvious. For the 15N implanted SiO, layers the NRA method was added to get a separate signal of the nitrogen. The Q-value of the reaction 15N(p, (w)12C is 4.944 MeV, so that the emitted a-particles are clearly separated from the proton spectrum (see Fig. 3). These measurements were performed at an proton energy of 1.02 MeV, the “N(p, c#*C cross section is rather flat and has at this value a maximum with 35 mb [7]. Because the energy loss of the incident protons is very small, the 15N(p, rr)12C-cro ss section does not change significantly in the depth range of the scattering. The detector was not screened of with a mylar foil as usual, so that the proton spectrum was measured, too. The scattering angle for all measurements was 160”, the measurements were performed with a beam current of max. 5 nA to avoid pileup effects. The number of incident particles was ca. 1014 in an area of 1 X 1 mm2 to reduce statistical fluctuations.
3. Results and discussion 31. . “NimSi In Fig. 1 the RBS-spectra of the 14N implanted silicon samples are shown for several annealing durations. For the energies used the peaks of nitrogen and
Fig. 2. Nitrogen distribution for the 14N implanted samples before and after annealing calculated from the spectra shown in Fig. 1.
oxygen can be separated from the background of the silicon yield. The differential cross section of nitrogen and oxygen amounts to ca. 100 mb/s for 3.3 MeV [7,8], so that broad structures due to oxygen can be distinguished from the underlying silicon spectrum.’ The peaks of N, 0 and Si were used to calculate the nitrogen distribution for the different annealing duration as are shown in Fig. 2. It is obvious, that the distributions are very similar, there is no change in distribution with annealing. The well known effect of segregation of nitrogen implanted in (lOO)-silicon [9] was not observed by us in the (llO)-direction for implantations at room temperature.
Ha+2.4
MsV ->
Si
He+23
MeV ->
0
H+f.O2UsV->N de
x 100
fro”,
“N(p.a)‘k ,*
50
Fig. 1.
RBS-spectra for nitrogen implanted (110) silicon before and after annealing. The measurements were performed using He+ particles at a backscattering angle of 160”.
100
150
200
250
Jo!3
350
400
450
SW
550
: 600
650
Fig. 3. Example of measurements for determination of the nitrogen depth profiles in thermally grown SiO, on a (110) silicon substrate. The upper curve shows the backscattering yield of 2.4 MeV He+ ions. From this measurement the Si yield can be obtained. In the middle curve the backscattering yield of 2.9 MeV He + ions is depicted. From this curve the oxygen yield can be extracted and with the Si value from the first measurement the SiO, stoichiometry can be verified. From the proton spectrum the yield of “N can be obtained using the well known “N(p, CU)‘~Cnuclear reaction at 1.02 MeV incident proton energy. XV. SEMICONDU~ORS
D. F&e,
938 3.2. 15N in SiO
D. Kollewe / Nucl. Ins&. and Meth. in Phys. Res. B 85 (1994) 936-939
2
For the determination of the “N-particle distribution three measurements were made for every sample. In a first measurement, the RBS spectrum from He+-
10
5
b
Implanbd
-
Not
25
20
15
Depth
in 10”
Atoms/cm2
at 3OO’C
Anneold
IO
5
20
15
25
ions with 2.4 MeV was recorded. This spectrum was used to obtain mainly the silicon yield close to the surface and in the implanted region. A second spectrum was recorded with 2.9 MeV. At this energy the differential cross section of oxygen increases, the yield due to the oxygen can be separated clearly from the silicon yield. The yield of the implanted nitrogen may superpose in this region, but the cross section has a local minimum [lo], so that the yield of 15N can be neglected. To obtain information about the implanted 15N the i5N(p, u)‘*C-reaction was used as mentioned. Fig.‘3 shows an example of the three measurements for a sample implanted at room temperature. The nitrogen distributions were calculated from the peaks due to the several elements. In Figs. 4a to 4c the direct comparisons of the distributions before and after annealing for three implantation temperatures are shown. The first interesting aspect is the different decrease of the nitrogen concentration with regard to the different implantation temperatures. For the implantation at room temperature only 6.6% of the implanted “N remains in the sample after annealing. In the case of implantation at 3OO”C, the remaining nitrogen amounts to 61.2% after annealing, for the 500°C implantation the value is 66.3%. These values were calculated both from the particle distribution and from the direct number of the detected of or-particles. A second interesting aspect is the segregation of the nitrogen. In the case of the 500°C implantation it is obvious in the spectra, that the distribution becomes narrower, the nitrogen moves in the sample to form a layer with sharper boundaries than before annealing.
4. Conclusions Nitrogen was implanted in Si and SiO,. It was shown, that even for light elements in a heavy matrix the depth distributions of the elements with the methods RBS and NRA can be determined. 14N shows in (llO)-silicon not such a clear effect of segregation as in (lOO)-material, the nitrogen distribution does not change while annealing. 15N implanted in SiO, shows this effect, but the nitrogen disappears partly during the annealing process.
References 5
IO Depth
20
15 I” 10’7
25
Atoms/cm2
Fig. 4. Calculated nitrogen yield for implantations at the temperatures RT, 300°C and 500°C. In every picture the distribution before (thin line) and after (thick line) annealing is shown.
[l] H.R. Phillip, J. Electrochem. Sot. 120 (1973) 295. [2] V.A. Gritsenko, N.D. Dikovskaya and K.P. Mogilnikov, Thin Solid Films 51 (1978) 535. [3] I.K. Naik, Appl. Phys. L&t. 43 (1983) 519. [4] T. Chamas et al., Mater. Sci. Eng. B 2 (l-3) (1989) 175.
D. Friise, D. Kollewe / Nucl. Instr. and Meth. in Phys. Res. B 85 (1994) 936-939
[5] J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids (Pergamon, New York, 1985). [6] E. Kashy, P.D. Miller and J.R Risser, Phys. Rev. 112 (1958) 547.
[7] F.B. Hagedom 1015. [8] J.R. Cameron, [9] J. Belz, Thesis, [lo] H. Smotrich et
939
and J.B. Marion, Phys. Rev. 180 (1975) Phys. Rev. 90 (1953) 839. University of Dortmund (1986). al., Phys. Rev. 122 (1961) 232.
XV. SEMICONDUCTORS
NOMB
Beam Interactions with Materials&Atoms
Production and analysis of buried nitride layers in Si/SiO, with ion beam methods D. Friise *, D. Kollewe Institutfiir Strahlenphysik der UniversitiitStuttgart,Allmandring3, 70569 Stuttgart,Germany
Nitrogen was implanted in (llO)-oriented silicon and in thermally formed silicon dioxide layers. After implantation the systems were annealed to reduce radiation damage. These implanted systems were investigated with ion beam methods as RBS and NRA to determine the depth distribution of the nitrogen and the oxygen with regard to the implantation and annealing parameters.
1. Introduction
2. Experimental
Optical devices like waveguides and electrooptical switches became very important for transmission of information in the last years. By implantation of nitrogen and oxygen in silicon one can produce SiO,N,layers with a gradient in their refractive index [1,2]. These implanted buried layers can then be used as a planar waveguide [3]. However, it is important to now the depth profile of the implanted nitrogen layer. To form well defined buried layers with these characteristics, the tool of ion-implantation was chosen. The implantations were accomplished at sample temperatures up to 500°C; for these temperatures annealing during implantation can be expected. After the implantation the samples were annealed for one to six hours at a temperature of 1300°C. To investigate the composition of the layers, ion beam analysis methods like Rutherford Backscattering (RBS) and Nuclear Reaction Analysis (NRA) were used. In RBS analysis, one problem met is that the kinematic factors for nitrogen and oxygen are closed together. Therefore the signals of the backscattered particles for these materials superpose. To separate the peaks from Si and 0, RBS measurements at 2.4 MeV and 2.9 MeV with a-particles were performed. For the detection of the nitrogen, the “N(p, a)“C reaction was used by performing a measurement with a 1.02 MeV proton beam. The depth distribution is calculated from the measured spectra without fitting any parameter. In this way, the distributions of implanted nitrogen in silicon were measured with regard to annealing durations from 1 to 6 h at 1300°C.
2.1. Implantations in Si The implantations were performed at the Dynamitron-Accelerator in Stuttgart with an energy of 429 keV per r4N-Ion in (llO)-oriented silicon at room temperature. The sample was tilted at 7” from the axis to avoid channeling effects during implantation. The dose was calculated so that in the maximum of the distribution the formation of Si,N, can be expected [4]. At this energy, the Monte-Carlo-Code TRIM 88 [5] yields a projected range R, = 784 nm. A gauss-fit to the TRIM-distribution amounts to a AR, = 72 nm. With these values the dose was determined to No = 1.2 x lOr* N/cm’. After implantation the samples were annealed for one to 6 h under normal atmosphere. 2.2. Implantations in SiO, For these implantations a (llO)-oriented silicon wafer was thermally oxidized for 12 h at 1300°C under normal atmosphere. This process resulted in a SiO,layer, with a thickness determined with RBS to 580 nm. In this layer “N,-molecules were implanted with an energy of 300 keV per atom. The TRIM-calculation yields of the projected range R, = 560 nm, so that the maximum of the N-distribution comes to rest in the SiO,-layer. The implantation temperature was varied from room temperature to 500°C. 2.3. Analysis of the systems
* Corresponding 711 685 3866. 0168-583X/94/$07.00
author,
phone
+49 711 685 3871, fax +49
the 0 1994 - Elsevier
SSDZ0168-583X(93)E0576-3
Science B.V. All rights reserved
The analysis was performed Dynamitron in Stuttgart,
with RBS and NRA at too. For the r4N im-
D. F&e,
937
D. Kollewe / Nucl. Instr. and Meth. in Phys. Res. B 8.5 (1994) 936-939
planted silicon layers the RBS-spectra with 2.95 MeV and 3.3 MeV He+ were measured. These spectra are shown in Fig. 1. At 3.3 MeV the differential cross section of 14N(a, cx)14N is larger than the pure Rutherford cross section and amounts to 100 mb 161,so that the peak of the nitrogen is obvious. For the 15N implanted SiO, layers the NRA method was added to get a separate signal of the nitrogen. The Q-value of the reaction 15N(p, (w)12C is 4.944 MeV, so that the emitted a-particles are clearly separated from the proton spectrum (see Fig. 3). These measurements were performed at an proton energy of 1.02 MeV, the “N(p, c#*C cross section is rather flat and has at this value a maximum with 35 mb [7]. Because the energy loss of the incident protons is very small, the 15N(p, rr)12C-cro ss section does not change significantly in the depth range of the scattering. The detector was not screened of with a mylar foil as usual, so that the proton spectrum was measured, too. The scattering angle for all measurements was 160”, the measurements were performed with a beam current of max. 5 nA to avoid pileup effects. The number of incident particles was ca. 1014 in an area of 1 X 1 mm2 to reduce statistical fluctuations.
3. Results and discussion 31. . “NimSi In Fig. 1 the RBS-spectra of the 14N implanted silicon samples are shown for several annealing durations. For the energies used the peaks of nitrogen and
Fig. 2. Nitrogen distribution for the 14N implanted samples before and after annealing calculated from the spectra shown in Fig. 1.
oxygen can be separated from the background of the silicon yield. The differential cross section of nitrogen and oxygen amounts to ca. 100 mb/s for 3.3 MeV [7,8], so that broad structures due to oxygen can be distinguished from the underlying silicon spectrum.’ The peaks of N, 0 and Si were used to calculate the nitrogen distribution for the different annealing duration as are shown in Fig. 2. It is obvious, that the distributions are very similar, there is no change in distribution with annealing. The well known effect of segregation of nitrogen implanted in (lOO)-silicon [9] was not observed by us in the (llO)-direction for implantations at room temperature.
Ha+2.4
MsV ->
Si
He+23
MeV ->
0
H+f.O2UsV->N de
x 100
fro”,
“N(p.a)‘k ,*
50
Fig. 1.
RBS-spectra for nitrogen implanted (110) silicon before and after annealing. The measurements were performed using He+ particles at a backscattering angle of 160”.
100
150
200
250
Jo!3
350
400
450
SW
550
: 600
650
Fig. 3. Example of measurements for determination of the nitrogen depth profiles in thermally grown SiO, on a (110) silicon substrate. The upper curve shows the backscattering yield of 2.4 MeV He+ ions. From this measurement the Si yield can be obtained. In the middle curve the backscattering yield of 2.9 MeV He + ions is depicted. From this curve the oxygen yield can be extracted and with the Si value from the first measurement the SiO, stoichiometry can be verified. From the proton spectrum the yield of “N can be obtained using the well known “N(p, CU)‘~Cnuclear reaction at 1.02 MeV incident proton energy. XV. SEMICONDU~ORS
D. F&e,
938 3.2. 15N in SiO
D. Kollewe / Nucl. Ins&. and Meth. in Phys. Res. B 85 (1994) 936-939
2
For the determination of the “N-particle distribution three measurements were made for every sample. In a first measurement, the RBS spectrum from He+-
10
5
b
Implanbd
-
Not
25
20
15
Depth
in 10”
Atoms/cm2
at 3OO’C
Anneold
IO
5
20
15
25
ions with 2.4 MeV was recorded. This spectrum was used to obtain mainly the silicon yield close to the surface and in the implanted region. A second spectrum was recorded with 2.9 MeV. At this energy the differential cross section of oxygen increases, the yield due to the oxygen can be separated clearly from the silicon yield. The yield of the implanted nitrogen may superpose in this region, but the cross section has a local minimum [lo], so that the yield of 15N can be neglected. To obtain information about the implanted 15N the i5N(p, u)‘*C-reaction was used as mentioned. Fig.‘3 shows an example of the three measurements for a sample implanted at room temperature. The nitrogen distributions were calculated from the peaks due to the several elements. In Figs. 4a to 4c the direct comparisons of the distributions before and after annealing for three implantation temperatures are shown. The first interesting aspect is the different decrease of the nitrogen concentration with regard to the different implantation temperatures. For the implantation at room temperature only 6.6% of the implanted “N remains in the sample after annealing. In the case of implantation at 3OO”C, the remaining nitrogen amounts to 61.2% after annealing, for the 500°C implantation the value is 66.3%. These values were calculated both from the particle distribution and from the direct number of the detected of or-particles. A second interesting aspect is the segregation of the nitrogen. In the case of the 500°C implantation it is obvious in the spectra, that the distribution becomes narrower, the nitrogen moves in the sample to form a layer with sharper boundaries than before annealing.
4. Conclusions Nitrogen was implanted in Si and SiO,. It was shown, that even for light elements in a heavy matrix the depth distributions of the elements with the methods RBS and NRA can be determined. 14N shows in (llO)-silicon not such a clear effect of segregation as in (lOO)-material, the nitrogen distribution does not change while annealing. 15N implanted in SiO, shows this effect, but the nitrogen disappears partly during the annealing process.
References 5
IO Depth
20
15 I” 10’7
25
Atoms/cm2
Fig. 4. Calculated nitrogen yield for implantations at the temperatures RT, 300°C and 500°C. In every picture the distribution before (thin line) and after (thick line) annealing is shown.
[l] H.R. Phillip, J. Electrochem. Sot. 120 (1973) 295. [2] V.A. Gritsenko, N.D. Dikovskaya and K.P. Mogilnikov, Thin Solid Films 51 (1978) 535. [3] I.K. Naik, Appl. Phys. L&t. 43 (1983) 519. [4] T. Chamas et al., Mater. Sci. Eng. B 2 (l-3) (1989) 175.
D. Friise, D. Kollewe / Nucl. Instr. and Meth. in Phys. Res. B 85 (1994) 936-939
[5] J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids (Pergamon, New York, 1985). [6] E. Kashy, P.D. Miller and J.R Risser, Phys. Rev. 112 (1958) 547.
[7] F.B. Hagedom 1015. [8] J.R. Cameron, [9] J. Belz, Thesis, [lo] H. Smotrich et
939
and J.B. Marion, Phys. Rev. 180 (1975) Phys. Rev. 90 (1953) 839. University of Dortmund (1986). al., Phys. Rev. 122 (1961) 232.
XV. SEMICONDUCTORS