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SiO2 interface structure
Applied Surface Science 234 (2004) 214–217
Cathodoluminescence study of Si/SiO2 interface structure M.V. Zamoryarskaya*, V.I. Sokolov, V. Plotnikov Ioffe Physyco-Technical Institute, 26, Polytechnicheskaya, St. Petersburg 196024, Russia
Abstract The structure of interface of thermal silicon oxide on p- and n-silicon with different content of activators (boron and phosphorus) was studied by using the method of the local cathodoluminescence (CL). The results of the CL study of the thick silicon oxide layers on silicon show that the content of the defects related with oxygen deficit decreases near the interface. In the same time, new bands in green and red range appear in CL spectra. The CL spectra of the layer with thickness 5–15 nm near interface are analogous to CL spectra of a composite of silicon nanoclusters and silicon oxide. The comparison of CL spectra of silicon oxide grown on p- and n-silicon shows that the film on p-silicon is characterized by higher concentration of silicon-deficit defects and silicon ‘‘islands’’ near the surface. It may be the cause why the electrical hardness of silicon oxide on p-silicon is lower than the one on n-silicon. The integral electro-physical characteristics of silicon oxide also were measured. The bulk charge and the density of interface states of silicon oxide on p-silicon are higher than for oxide on n-silicon. The oxidization of nsilicon with nanostructure surface leads to the appearance of the CL bands related with oxygen deficit and silicon ‘‘islands’’ in silicon oxide. # 2004 Published by Elsevier B.V. Keywords: Silicon oxide film; Local cathodoluminescence; Electrical hardness; Density of interface states; Bulk charge
1. Introduction
2. Methods
Properties of silicon oxide films on silicon play an important role in the creation of all the microelectronic devices. The electro-physical properties of silicon oxide film and its interface define the functional ability and reliability of planar microelectronic devices. In this paper, we try to relate the integral characteristics of the silicon oxide films (density of interface states, the electrical hardness and bulk charge) with the structure of silicon oxide interface. The structure of silicon oxide on silicon was studied by using the local cathodoluminescent method.
Before oxidization of the p- and n-silicon, the surface was mechanically polished and degreased in mixture of sulfuric aside and hydrogen peroxide at 80 8C. After that the surface was flushed out by the mixture of hydrogen peroxide and ammonia hydrate. The silicon oxide films were grown at 1050 8C in dry oxygen on p- and n silicon [1 1 1] substrate simultaneously. p-Silicon was doped with boron and its conductivity was 10 Ocm, n-silicon was doped by phosphorus and its conductivity was 7.5 Ocm. The thickness of oxide films was 100–600 nm. The nanostructure surface of n-silicon was made by using the mixture of fluoric azotic asides. The oxidization of this silicon was made by the same way.
*
Corresponding author. Fax: þ7-812-247-1017.
0169-4332/$ – see front matter # 2004 Published by Elsevier B.V. doi:10.1016/j.apsusc.2004.05.031
M.V. Zamoryarskaya et al. / Applied Surface Science 234 (2004) 214–217
CL measurements were made by two optical spectrometers connected with Microprobe Analyzer ‘‘Camebax’’. These spectrometers record CL spectra in 1.0–1.8 and 1.6–4.4 eV ranges [1]. The spectra were obtained in the regime of the electron beam modulation. CL was exited by electron beam with energy 2.5 keV, current 1–10 nA and diameter 3–5 m. CL spectra were obtained from different depths of silicon oxide films. For this, the silicon oxide films were shaped as a wedge with a small inclination angle by the chemical etching in the dilute hydrofluoric acid. The penetration of electron with energy 2.5 eV in the sample SiO2/Si is about 200 nm. CL spectra were obtained from the wedge of SiO2 with thickness 5, 10, and 15 nm. The contribution of CL emission of the layer near the interface is different. The influence of the interface layers on CL emission is more appreciable for SiO2 wedge with thickness 5 nm. For CL study of thick layer of silicon oxide in IR range (1.0–1.8 eV), the silicon substrates were shaped as a wedge by the chemical etching in the chemical polish mixture (CP-4). In this case, the CL band of silicon substrates at 1.1–1.2 eV could not apparent in CL spectra. The comparison of CL properties of silicon oxides grown on plane silicon surface and nanostructure surface was made. In this case CL was exited by electron beam with energy 5 keV and current 10 nA. The electrical hardness (EB) was studied for silicon oxide on p- and n-silicon with thickness 150 nm. Breakdown voltage was calculated as a ratio of breakdown voltage and the thickness of a silicon oxide: EB ¼
215
temperature and frequency 1 MHz. The density of interface states and the bulk charge in silicon oxide films were determined from the volt-farad characteristics. The stability of the electro-physical characteristic of the silicon oxide films was studied on exposure to gamma irradiation of g-Co60.
3. Results and discussion Cathodoluminescence spectra of silicon oxide in visible range consist of two well-known bands at 2.65 and 1.9 eV assigned to intrinsic defects of oxide matrix. The bands at 2.65 are due to triplet-to-singlet transitions in the twofold-coordinated silicon (oxygen deficit) [2]. The 1.9-eV band is attributed to nonbridging oxygen state (silicon deficit) [3]. In CL spectra of the thin layers of silicon oxide near the interface (5, 15, and 100 nm) in visible and infrared diapasons, the new bands were observed. The position and intensity of these bands depend on the thickness of layer. Fig. 1 shows the CL spectra of silicon oxide on p-silicon. CL spectrum obtained from the layer with thickness 100 nm consists of two strong bands at 2.65 and 1.9 eV and weak bands at 2.2 and 2.35 eV. The CL spectrum from layer at 15 nm has an arm at 2.2 eV, and one from layer at 5 nm has arms at
UB ; d
where UB is breakdown voltage, and d is the thickness of a silicon oxide. The electrical hardness was measured using the electric probe. The measurements were taken in 50 different places of each sample. The electrical hardness of each sample was calculated as arithmetical average of 50 measures. The volt-farad characteristics were measured for silicon oxide films on p- and n-silicon with thickness 600 nm and for the same films cut in half by the chemical etching. MOS structures were made on the surface of the silicon films using thermal evaporation of aluminium. The measures have been made at room
Fig. 1. CL spectra of thin layer of silicon oxide on p-silicon. The thickness of layers are (a) 100 nm, (b) 15 nm, (c) 5 nm.
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M.V. Zamoryarskaya et al. / Applied Surface Science 234 (2004) 214–217
2.1 and 1.85 eV. The intensity of the bands at 1.9 and 2.65 eV changes too. In CL spectrum obtained from the layer at 5 nm, the band at 2.65 eV dominates. Fig. 2 shows the CL spectra of oxide on n-silicon. The thickness of the oxide layers was 5 and 100 nm. The weak bands at 2.2 and 2.4 eV were observed in CL spectrum of oxide with thickness 5 nm. 3.1. CL study of the different composite materials Silicon nanocrystals in buried SiO2 layers, SiOx layers [4] and synthetic opal with silicon nanocrystals in voids [5] show that the emission bands at 2.4– 2.1 eV can be related with the presence of silicon nanoclusters in silicon oxide. The study of the modification of silicon oxide using the electron beam with a high power density shows that the appearance of silicon clusters reduces to the emergence of new CL bands at 2.l–2.3 eV [6]. CL infrared spectra of silicon oxide near the interface are shown on Fig. 3. The structure and intensity of the infrared bands of oxide on p- and n-silicon differ from each other. The broad band at 1.1–1.2 eV is like the emission of silicon. It may be the luminescence of big silicon clusters near the interface. Infrared CL bands at 1.1–1.2 eVon n-silicon are low. That’s why we suppose that the content of the silicon ‘‘islands’’ in silicon oxide
Fig. 2. CL spectra of thin layer of silicon oxide on n-silicon. The thickness of layers are (a) 100 nm, (b) 5 nm.
Fig. 3. CL spectra of thin layer of silicon oxide in IR range on (a) p-silicon (b) n-silicon.
on n-silicon is smaller than in oxide on p-silicon. The band at 1.8–1.9 eV in both spectra relates with the emission attributed to non-bridging oxygen state. This assumption is verified by the study of integral electro-physical characteristics of silicon oxides. The presence of silicon nanoclusters can explain the difference of electrical hardness (EB) of SiO2 films grown on p- and n-silicon. The value of EB is 9.2 MV/cm2 for the oxide on n-silicon and 7.82 MV/cm2 for the oxide on p-silicon. The presence of silicon nanoclusters on interface changes the value of the density of interface states and the bulk charge in oxide films. Fig. 4 shows that the bulk charge of the oxide on n-silicon decreased for the films cut in half. In the same time, the bulk charge of the oxide on p-silicon did not change for the film cut in half. It may be explained, if we suppose that the main values of the defects are concentrated near the interface for silicon oxide grown on p-silicon substrate. The density of interface state for silicon oxide on p-silicon is higher than for the oxide on n-silicon. It increases in the films cut in half. The gamma irradiation leads to increase of the density of interface state for all the films. In the issue, we compared the CL spectra of silicon oxide grown on the plate n-silicon surface and the one grown on the nanostructure surface of n-silicon (Fig. 5). The thickness of silicon oxides was about 100 nm. The band at 2.1 eV is the most intensive in CL
M.V. Zamoryarskaya et al. / Applied Surface Science 234 (2004) 214–217
217
spectrum of the sample with nanostructure surface. The bands at 2.65 and 1.9 eV have the same intensity for two samples. The layer with silicon deficit and silicon ‘‘island’’ must be wider in silicon oxide grown on silicon with nanostructure surface, and its contribution in CL emission is appreciable.
4. Summary
Fig. 4. Dependence of (a) the bulk charge and (b) the density of interface states on exposure to gamma irradiation of g-Co60. (*), Silicon oxide films on p-silicon with thickness 600 nm; (~), the same films on p-silicon cut in half (300 nm); (*), silicon oxide films on n-silicon with thickness 600 nm; and (~), the same films on n-silicon cut in half (300 nm).
The comparison of the CL spectra of SiO2/Si interface and SiO2/Si composite materials shows that interface and layer with thickness 5–15 nm near interface are a composite of silicon nanoclusters and silicon oxide, and the content of silicon nanoclusters in oxide on p-silicon is higher than in oxide on n-silicon. The presence of silicon nanoclusters can explain the difference in electrical hardness (EB) of SiO2 films grown on p- and n-silicon (9.2 and 7.82 MV/cm2 corresponding). The presence of silicon nanoclusters on the interface SiO2/Si of the silicon oxide on p-silicon can explain the high value of the density of interface states and the bulk charge near the interface for the silicon oxide on p-silicon.
Acknowledgements The work presented in this paper was supported partly by grants from Russian Fond of Basic Research #03-02-16621. Presentation of this paper was supported partly by Organizing Committee of 9th International Conference on the Formation of Semiconductor Interfaces, ICFSI-9. References
Fig. 5. CL spectra of the thin layer of silicon oxide on n-silicon: (a) grown on plane surface, and (b) grown on nanostructure surface.
[1] M.V. Zamoryanskaya, L.A. Vainshenker, A.N. Zamoryanskyi, Prib. Tekn. Eksp. 4 (1987) 161. [2] L.N. Skuja, A.R. Silin, Phys. Stat. Solid. A 70 (1982) 43. [3] M. Goldberdge, H.-J. Fittihg, A. Trukhin, J. Non-Cryst. Solids 220 (1997) 69. [4] H. Nishikawa, E. Watanabe, D. Ito, Y. Sakurai, K. Nagasawa, Y. Ohki, J. Appl. Phys. 80 (1996) 3513. [5] C. Diaz-Guerra, J. Piqueras, D.A. Kurdyukov, V.I. Sokolov, M.V. Zamoryanskaya, App. Phys. Lett. (2001) in press. [6] M.V. Zamoryanskaya, V.I. Sokolov, A.A. Sytnikova, Solid State Phenomena 87/88 (2001).
Cathodoluminescence study of Si/SiO2 interface structure M.V. Zamoryarskaya*, V.I. Sokolov, V. Plotnikov Ioffe Physyco-Technical Institute, 26, Polytechnicheskaya, St. Petersburg 196024, Russia
Abstract The structure of interface of thermal silicon oxide on p- and n-silicon with different content of activators (boron and phosphorus) was studied by using the method of the local cathodoluminescence (CL). The results of the CL study of the thick silicon oxide layers on silicon show that the content of the defects related with oxygen deficit decreases near the interface. In the same time, new bands in green and red range appear in CL spectra. The CL spectra of the layer with thickness 5–15 nm near interface are analogous to CL spectra of a composite of silicon nanoclusters and silicon oxide. The comparison of CL spectra of silicon oxide grown on p- and n-silicon shows that the film on p-silicon is characterized by higher concentration of silicon-deficit defects and silicon ‘‘islands’’ near the surface. It may be the cause why the electrical hardness of silicon oxide on p-silicon is lower than the one on n-silicon. The integral electro-physical characteristics of silicon oxide also were measured. The bulk charge and the density of interface states of silicon oxide on p-silicon are higher than for oxide on n-silicon. The oxidization of nsilicon with nanostructure surface leads to the appearance of the CL bands related with oxygen deficit and silicon ‘‘islands’’ in silicon oxide. # 2004 Published by Elsevier B.V. Keywords: Silicon oxide film; Local cathodoluminescence; Electrical hardness; Density of interface states; Bulk charge
1. Introduction
2. Methods
Properties of silicon oxide films on silicon play an important role in the creation of all the microelectronic devices. The electro-physical properties of silicon oxide film and its interface define the functional ability and reliability of planar microelectronic devices. In this paper, we try to relate the integral characteristics of the silicon oxide films (density of interface states, the electrical hardness and bulk charge) with the structure of silicon oxide interface. The structure of silicon oxide on silicon was studied by using the local cathodoluminescent method.
Before oxidization of the p- and n-silicon, the surface was mechanically polished and degreased in mixture of sulfuric aside and hydrogen peroxide at 80 8C. After that the surface was flushed out by the mixture of hydrogen peroxide and ammonia hydrate. The silicon oxide films were grown at 1050 8C in dry oxygen on p- and n silicon [1 1 1] substrate simultaneously. p-Silicon was doped with boron and its conductivity was 10 Ocm, n-silicon was doped by phosphorus and its conductivity was 7.5 Ocm. The thickness of oxide films was 100–600 nm. The nanostructure surface of n-silicon was made by using the mixture of fluoric azotic asides. The oxidization of this silicon was made by the same way.
*
Corresponding author. Fax: þ7-812-247-1017.
0169-4332/$ – see front matter # 2004 Published by Elsevier B.V. doi:10.1016/j.apsusc.2004.05.031
M.V. Zamoryarskaya et al. / Applied Surface Science 234 (2004) 214–217
CL measurements were made by two optical spectrometers connected with Microprobe Analyzer ‘‘Camebax’’. These spectrometers record CL spectra in 1.0–1.8 and 1.6–4.4 eV ranges [1]. The spectra were obtained in the regime of the electron beam modulation. CL was exited by electron beam with energy 2.5 keV, current 1–10 nA and diameter 3–5 m. CL spectra were obtained from different depths of silicon oxide films. For this, the silicon oxide films were shaped as a wedge with a small inclination angle by the chemical etching in the dilute hydrofluoric acid. The penetration of electron with energy 2.5 eV in the sample SiO2/Si is about 200 nm. CL spectra were obtained from the wedge of SiO2 with thickness 5, 10, and 15 nm. The contribution of CL emission of the layer near the interface is different. The influence of the interface layers on CL emission is more appreciable for SiO2 wedge with thickness 5 nm. For CL study of thick layer of silicon oxide in IR range (1.0–1.8 eV), the silicon substrates were shaped as a wedge by the chemical etching in the chemical polish mixture (CP-4). In this case, the CL band of silicon substrates at 1.1–1.2 eV could not apparent in CL spectra. The comparison of CL properties of silicon oxides grown on plane silicon surface and nanostructure surface was made. In this case CL was exited by electron beam with energy 5 keV and current 10 nA. The electrical hardness (EB) was studied for silicon oxide on p- and n-silicon with thickness 150 nm. Breakdown voltage was calculated as a ratio of breakdown voltage and the thickness of a silicon oxide: EB ¼
215
temperature and frequency 1 MHz. The density of interface states and the bulk charge in silicon oxide films were determined from the volt-farad characteristics. The stability of the electro-physical characteristic of the silicon oxide films was studied on exposure to gamma irradiation of g-Co60.
3. Results and discussion Cathodoluminescence spectra of silicon oxide in visible range consist of two well-known bands at 2.65 and 1.9 eV assigned to intrinsic defects of oxide matrix. The bands at 2.65 are due to triplet-to-singlet transitions in the twofold-coordinated silicon (oxygen deficit) [2]. The 1.9-eV band is attributed to nonbridging oxygen state (silicon deficit) [3]. In CL spectra of the thin layers of silicon oxide near the interface (5, 15, and 100 nm) in visible and infrared diapasons, the new bands were observed. The position and intensity of these bands depend on the thickness of layer. Fig. 1 shows the CL spectra of silicon oxide on p-silicon. CL spectrum obtained from the layer with thickness 100 nm consists of two strong bands at 2.65 and 1.9 eV and weak bands at 2.2 and 2.35 eV. The CL spectrum from layer at 15 nm has an arm at 2.2 eV, and one from layer at 5 nm has arms at
UB ; d
where UB is breakdown voltage, and d is the thickness of a silicon oxide. The electrical hardness was measured using the electric probe. The measurements were taken in 50 different places of each sample. The electrical hardness of each sample was calculated as arithmetical average of 50 measures. The volt-farad characteristics were measured for silicon oxide films on p- and n-silicon with thickness 600 nm and for the same films cut in half by the chemical etching. MOS structures were made on the surface of the silicon films using thermal evaporation of aluminium. The measures have been made at room
Fig. 1. CL spectra of thin layer of silicon oxide on p-silicon. The thickness of layers are (a) 100 nm, (b) 15 nm, (c) 5 nm.
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M.V. Zamoryarskaya et al. / Applied Surface Science 234 (2004) 214–217
2.1 and 1.85 eV. The intensity of the bands at 1.9 and 2.65 eV changes too. In CL spectrum obtained from the layer at 5 nm, the band at 2.65 eV dominates. Fig. 2 shows the CL spectra of oxide on n-silicon. The thickness of the oxide layers was 5 and 100 nm. The weak bands at 2.2 and 2.4 eV were observed in CL spectrum of oxide with thickness 5 nm. 3.1. CL study of the different composite materials Silicon nanocrystals in buried SiO2 layers, SiOx layers [4] and synthetic opal with silicon nanocrystals in voids [5] show that the emission bands at 2.4– 2.1 eV can be related with the presence of silicon nanoclusters in silicon oxide. The study of the modification of silicon oxide using the electron beam with a high power density shows that the appearance of silicon clusters reduces to the emergence of new CL bands at 2.l–2.3 eV [6]. CL infrared spectra of silicon oxide near the interface are shown on Fig. 3. The structure and intensity of the infrared bands of oxide on p- and n-silicon differ from each other. The broad band at 1.1–1.2 eV is like the emission of silicon. It may be the luminescence of big silicon clusters near the interface. Infrared CL bands at 1.1–1.2 eVon n-silicon are low. That’s why we suppose that the content of the silicon ‘‘islands’’ in silicon oxide
Fig. 2. CL spectra of thin layer of silicon oxide on n-silicon. The thickness of layers are (a) 100 nm, (b) 5 nm.
Fig. 3. CL spectra of thin layer of silicon oxide in IR range on (a) p-silicon (b) n-silicon.
on n-silicon is smaller than in oxide on p-silicon. The band at 1.8–1.9 eV in both spectra relates with the emission attributed to non-bridging oxygen state. This assumption is verified by the study of integral electro-physical characteristics of silicon oxides. The presence of silicon nanoclusters can explain the difference of electrical hardness (EB) of SiO2 films grown on p- and n-silicon. The value of EB is 9.2 MV/cm2 for the oxide on n-silicon and 7.82 MV/cm2 for the oxide on p-silicon. The presence of silicon nanoclusters on interface changes the value of the density of interface states and the bulk charge in oxide films. Fig. 4 shows that the bulk charge of the oxide on n-silicon decreased for the films cut in half. In the same time, the bulk charge of the oxide on p-silicon did not change for the film cut in half. It may be explained, if we suppose that the main values of the defects are concentrated near the interface for silicon oxide grown on p-silicon substrate. The density of interface state for silicon oxide on p-silicon is higher than for the oxide on n-silicon. It increases in the films cut in half. The gamma irradiation leads to increase of the density of interface state for all the films. In the issue, we compared the CL spectra of silicon oxide grown on the plate n-silicon surface and the one grown on the nanostructure surface of n-silicon (Fig. 5). The thickness of silicon oxides was about 100 nm. The band at 2.1 eV is the most intensive in CL
M.V. Zamoryarskaya et al. / Applied Surface Science 234 (2004) 214–217
217
spectrum of the sample with nanostructure surface. The bands at 2.65 and 1.9 eV have the same intensity for two samples. The layer with silicon deficit and silicon ‘‘island’’ must be wider in silicon oxide grown on silicon with nanostructure surface, and its contribution in CL emission is appreciable.
4. Summary
Fig. 4. Dependence of (a) the bulk charge and (b) the density of interface states on exposure to gamma irradiation of g-Co60. (*), Silicon oxide films on p-silicon with thickness 600 nm; (~), the same films on p-silicon cut in half (300 nm); (*), silicon oxide films on n-silicon with thickness 600 nm; and (~), the same films on n-silicon cut in half (300 nm).
The comparison of the CL spectra of SiO2/Si interface and SiO2/Si composite materials shows that interface and layer with thickness 5–15 nm near interface are a composite of silicon nanoclusters and silicon oxide, and the content of silicon nanoclusters in oxide on p-silicon is higher than in oxide on n-silicon. The presence of silicon nanoclusters can explain the difference in electrical hardness (EB) of SiO2 films grown on p- and n-silicon (9.2 and 7.82 MV/cm2 corresponding). The presence of silicon nanoclusters on the interface SiO2/Si of the silicon oxide on p-silicon can explain the high value of the density of interface states and the bulk charge near the interface for the silicon oxide on p-silicon.
Acknowledgements The work presented in this paper was supported partly by grants from Russian Fond of Basic Research #03-02-16621. Presentation of this paper was supported partly by Organizing Committee of 9th International Conference on the Formation of Semiconductor Interfaces, ICFSI-9. References
Fig. 5. CL spectra of the thin layer of silicon oxide on n-silicon: (a) grown on plane surface, and (b) grown on nanostructure surface.
[1] M.V. Zamoryanskaya, L.A. Vainshenker, A.N. Zamoryanskyi, Prib. Tekn. Eksp. 4 (1987) 161. [2] L.N. Skuja, A.R. Silin, Phys. Stat. Solid. A 70 (1982) 43. [3] M. Goldberdge, H.-J. Fittihg, A. Trukhin, J. Non-Cryst. Solids 220 (1997) 69. [4] H. Nishikawa, E. Watanabe, D. Ito, Y. Sakurai, K. Nagasawa, Y. Ohki, J. Appl. Phys. 80 (1996) 3513. [5] C. Diaz-Guerra, J. Piqueras, D.A. Kurdyukov, V.I. Sokolov, M.V. Zamoryanskaya, App. Phys. Lett. (2001) in press. [6] M.V. Zamoryanskaya, V.I. Sokolov, A.A. Sytnikova, Solid State Phenomena 87/88 (2001).