- Email: [email protected]
Structural fluctuation of SiO2 network at the interface with Si
.
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applied
surface science ELSEVIER
Applied Surface Science lOO/lOl
(1996) 268-271
Structural fluctuation of SiO, network at the interface with Si Y. Sugita *, S. Watanabe, N. Awaji, S. Komiya Fujitsu Laboratories
Ltd., 10-I Morinosato-Wakamiva,
Atsugi 243-01, Japan
Received 22 August 1995; accepted 5 November
1995
Abstract We analyzed the density of thermally grown SiO,/Si by X-ray reflectivity measurements and local vibration properties by infrared spectroscopy. The macroscopic density varied with growth conditions. A lower growth temperature caused higher film density. We also found a thin (1 nm) and dense (2.35-2.4 g/cm3) transient layer at the SiO,/Si interface. The film density was constant to the thickness direction without the transient layer. On the other hand, IR properties showed characteristic film thickness dependencies. At a film thickness greater than 10 nm, the frequency of the transverse optic (TO) mode of Si-0 stretching shifted to the red direction, decreasing with the film thickness; while the frequency of the longitudinal optic (LO) mode is unchanged. This red shift of TO mode has no relation to the film density. At a film thickness of less than 6 nm, we found that both the TO and LO mode shift to the red direction simultaneously. The red shifts gradually increased with decreasing film thickness. This indicates that the SiOz network was densified by compressive stress.We assumed that the macroscopic and microscopic fluctuation were related to the oxide growth and formation of a hetero-junction.
1. Introduction It is well known that the density of thermally grown SiOz on Si depends on the oxidation conditions, such as temperature and atmosphere [1,2]. For example, low temperature oxidation ( < 900- 1000°C) leads to film densification [2-41. The reliability of a low-temperature grown oxide is not enough for a MOS device [5]. This is a severe problem for future low-temperature fabrication processes. The precise understanding of the oxide properties related to growth conditions are required in order to improve the oxide reliability.
* Corresponding author. Tel.: + 8 1-462-483 483473: e-mail: [email protected]. 0169.4332/96/$15.00 Copyright PII SO 169.4332(96)00302-9
I 11; fax: + 8 l-462-
Local vibration properties revealed by IR spectroscopy shows that the microscopic structure of the oxide depends on the growth temperature [ 1,6-IO]. IR analysis also shows that the oxide properties depend on the film thickness [6-lo]. It would be very useful to know how to optimize the oxidation conditions, but the relation between the local vibration properties and the macroscopic parameters, such as stress and density are not clear. The measurements of macroscopic parameters are difficult for thin films (< 30 nm) with high accuracy. In this paper, we demonstrate X-ray reflectometry to determine the thin film density and the film structure. These macroscopic parameters were compared with microscopic properties analyzed by IR spectroscopy. The fluctuation of the SiO,/Si structure was observed near the interface. We will discuss
0 1996 Elsevier Science B.V. All rights reserved.
Y. Sugita et al/Applied
Surface Science 100/101
the structural changes both from the macroscopic and microscopic points of view.
2. Experiment We used 4 inch CZ-Si(lO0) n-type 1 Cl cm wafers for X-ray reflectometry and 50 X 15 X 0.5 mm FZ-Si(lO0) prism shaped wafers for IR analysis. The samples were cleaned using wet-chemical solutions with a modified RCA procedure. The samples were oxidized using a device-grade quarz furnace. Oxidation temperatures were 850°C 900°C and 1000°C. The dry oxidation was carried out using pure O? (5 l/min) as the oxidation species. The wet oxidation was done using a hot water (85°C) bobbling system which used pure O? (5 l/min) as a carrier-gas. The oxidation time was varied to prepare samples with different thickness. A part of the samples were etched back using a 0.5% HF solution to reduce the thicknesses. IR spectroscopy was done with a Nicolet 740 FT-IR with a HgCdTe detector which was cooled by liquid N2. The measurement resolution was 4 cm ’ . Transmission measurements were carried out for both s-polarized and p-polarized conditions using a wire grid polarizer which has 10% leakage. Incidence angles of those experiments were between O-70” 1111. The X-ray reflectivity was measured by changing the glancing incidence angle ($1 from 0 to 4.5”by using a 2+-(~ scanning-apparatus-diffractometer. We used a synchrotron radiation beam line which had a Sic1 111 double crystal monochromator at National Laboratory of High Energy Physics (KEK) [ 121. The X-ray wavelength we used was 0.13 nm. We obtained some of the reflectivity-incidence-angle curves, which had the characteristic thin film interference signal. We analyzed the reflectivity data using an optimizing program based on the Marquardt non-linear minimization fitting technique [ 13- 161. The fitting parameters were film thickness, film density, surface roughness, and interface roughness. We also used the complex refractive index of materials from the tables of Henke et al. and the tables of Sasaki [ 17,181. The detail of experimental technique and analysis method were reported elsewhere [ 191.
(1996) 268-271
269
3. Results and discussion Fig. 1 shows the thickness dependence of the transmission IR properties of Si-0 stretching for as-grown SiO,/Si. The frequency peaks of the LO phonon was determined from the p-polarized spectra with the incidence angle of 70”. The frequency peaks of the TO phonon was determined from the spolarized spectra. As seen in Fig. 1, the peak positions of TO varied with film thickness, while the peak positions of LO were almost constant It was reported that both the TO and LO peaks shifted to the red direction simultaneously, in the densified silica glass [20-221. In that case, the bond angle of Si-0-Si decreased by increasing the density [20-231. We concluded that the red shifts of the TO mode seen in Fig. 1 did not result from the film densification. In Fig. 1, small red shifts of the LO phonon was observed at the oxide thickness of less than 10 nm. We measured the IR properties for the oxides which were etched back to near the interface, as shown in Fig. 2. It is clear that the red shift of both the LO and
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80
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120
140
160
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Fig. 1. Thickness dependence of the peak frequency stretching for as-grown SiO, /Si.
of S-0
Y. Sugita et al./Applird
210
Surface Science 100/101
(19961268-271
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Fig. 4. Calculated results for oxide density from X-ray reflectivity measurements. We analyzed the reflectivity curves applying the 2-layer oxides on Si model. i.e. upper SiO, layer/transient SiOz layer/Si substrate. Thickness of the transient layer was about I nm. The film thickness dependency of the density of both the transient layer and upper layer are shown.
wet
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,
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50
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Fig. 2. Thickness dependence of the peak frequency of Si-0 stretching for the oxides etched back by an 0.5% HF solution.
TO mode were observed near the interface, in these films. Fig. 3 shows that the relation of the LO and TO peak frequency extracted from Fig. 2. It is suggested that the SiO, network, which exists within from the interface to 6 nm, is densified by compressive stress.
I
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1085
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Fig. 3. Relation of LO frequency and TO frequency on Si-0 stretching. The solid line at a thickness of less than 6 nm region indicates that the red shift of LO phonon is 2 times larger than the red shift of TO phonon.
We estimated that the thickness of the stressed layer near the interface was about 1 nm. Fig. 4 shows the thickness dependence of the as-grown film densities which were determined by X-ray reflectometry. In Fig. 4, we present the results of 2-layer SiO, on Si model analysis. The 2 layer analysis brought better fit for all cases than the 1 layer SiO, on Si model analysis. The analysis of 3-layer SiO, on Si model did not show any improvement in fitting. As seen in Fig. 4, the oxides density had a growth temperature dependence. These are consistent both with our IR analysis results and previous work. Both results of the l-layer analysis and the 2-layer analysis provided that the macroscopic film densities were almost constant within the same growth temperature samples without the films thinner than 10 nm. The results of 2-layer analysis suggests that the thin (1 nm) and dense (2.35-2.4 g/cm3) transient layer, shown in Fig. 4, exists at the interface. For each film, the macroscopic density of the upper layer ( > 1 nm) was constant throughout the thickness. IR properties also suggested that the SiO, network near the interface (1 nm) were densified. It might be that the compressive stress to the network reduces the filmvolume near the interface and causes the macroscopic densification. as a result. A spectroscopic ellipsometry study revealed that a 1 nm thick transient layer exists at the interface of SiO,/Si [3]. This transient layer is a mixture of Si
Y. Sugita et &./Applied
Surface Science lOO/ 101 (19%) 268-271
and SiO,. It could be viewed as interface roughness. Because the densities of the transient layer we found were larger than the Si density (2.33 g/cm3), it could not be explained by the interface roughness. In our case, it could be a densified SiO, layer. We consider that such structural fluctuations originate in the volume expansion at the oxidation of Si or the lattice distortion of the SiO,/Si hetero-junction.
271
an understanding of thermally grown oxide properties. The joint use of the X-ray reflectometry and the local vibration analysis is an effective way to investigate SiOJSi structures.
References
4. Conclusion
ill W.A. Pliskin, J. Vat. Sci. Technol. 14 (1977) 1064. l21 E.A. Traft, J. Electrochem. Sot. 125 (1978) 968; 127 (1980)
We examined the macroscopic density of SiO, on Si(100) and its local vibration properties. The 2-layers on Si model were successful for all oxides which we measured. The macroscopic density increased as we lowered the growth temperature (< 1000°C). This is consistent with previous studies and it could be explained by viscose flow of SiO, at the growth temperature. A high density (2.35-2.4 g/cm3) and thin (1 nm) layer was found at the SiO,/Si interface. The film density is constant to the thickness direction for each oxides without a transient layer. On the other hand, IR properties have a characteristic thickness dependence. At a film thicker than 6 nm, the frequency of the TO mode of Si-0 stretching shifted to the red-direction with decreasing film thickness, while the frequency of the LO mode is unchanged. We concluded that this red shift of the TO mode does not result from film densification which decrease the angle of Si-0-Si. It is consistent with our X-ray reflectometry results. At a film thinner than 6 nm, both the TO and LO mode shift to the red-direction simultaneously. This red shifts gradually increased with a decrease in the film thickness, indicating that the SiO, network was densified by compressive stress. We estimate the thickness of the stressed layer to be about 1 nm. We supposed that this densification was accompanied by the volume expansion of SiO, at the thermal oxidation or hetero-junction of SiOJSi. The macroscopic fluctuation was consistent with microscopic view. Our results were useful to develop
[31 E.A. Irene, E. Tiemey and J. Angilello, J. Electrochem.
993. Sot. 129 (1982) 2594; Y A. Yakovlev and E.A. Irene, J. Electrochem. Sot. 139 (1992) 1450; Y.A. Yakovlev, Q. Liu and E.A. Irene, J. Vat. Sci. Technol. A 10 (1992) 427. [41 C.R. Helms and B.E. Deal, The Physics and Chemistry of SiOz and the Si-SiO? Interface (Plenum, New York, 1988) p. 139. El A. S&mans, Phys. Rev. Lett. 70 (1993) 1723. lb1 I.W. Boyd and J.I.B. Wilson, J. Appl. Phys. 62 (1987) 3195. [7] G. Lucovsky, M.J. Manitini, J.K. Srivastava and E.A. Irene, J. Vat. Sci. Technol. B 5 (1987) 530. [8] C.H. Bjorkman, T. Yamazaki, S. Miyazaki and M. Hirose, J. Appl. Phys. 77 (1995) 313. [9] K. Ishikawa, H. Ogawa, S. Oshida, K. Suzuki and S. Fujimura, Ext. Abst. Conf. 1995 Solid State Dev. and Mater., Japan. [IO] N. Yasuda and A. Toriumi, Ext. Abst. Conf. 1993 Solid State Dev. and Mater., Japan (1993) 86. [ll] D.W. Berreman, Phys. Rev. 130 (1963) 2193. [12] Y. Horii, H. Tomita and S. Komiya, Rev. Sci. Instr. 66 (1995) 1370. [13] B. Vidal and P. Vincent, Appl. Opt. 23 (1984) 1794. [14] L. Nevot and P. Croce, Rev. Phys. Appl. 15 (1980) 761. [15] L.-G. Paratt, Phys. Rev. 95 (1954) 389. [16] A.A. Bright and G.W. Rubloff, J. Vat. Sci. Technol. A 8 ( 1990) 2046. [17] B.L. Henke, J.C. Davis, E.M. Gullikson and R.C.C. Perera, Lawrence Berkeley Lab. Rep. LBL-26259 (1988). [18] S. Sasaki, KEK Rep. 88-14 (1989). [19] N. Awaji, in preparation for publication in Jpn. J. Appl. Phys.; N. Awaji, Y. Sugita, S. Ohkubo, T. Nakanishi, T. Takasaki and S. Komiya, Jpn. J. Appl. Phys. 34 (1995) L1013. [20] G.E. Walrafen, Y.C. Chu and S. Hokmabadi. J. Chem. Phys. 92 (1990) 6987. [21] R.A.B. Devine, J. Vat. Sci. Technol. A 6 (1988) 3154. [22] P.N. Sen and M.E. Thorpe, Phys. Rev. B 15 (1977) 4030. [23] J.D. Jorgensen, J. Appl. Phys. 49 (1978) 5473.
..i~..:.:ii:::‘~~~~~~~.~~.~~j+::
“‘~.~~.‘.‘.....\............,..................,.. ‘.“‘::‘..::‘:‘:\;:::.:: .... ...... :<,‘:_i:.: ,.,. ,,. 3 “”
., ,, .,
,......( i,ii::
. ...i.. . ~::,::,:.:::~
applied
surface science ELSEVIER
Applied Surface Science lOO/lOl
(1996) 268-271
Structural fluctuation of SiO, network at the interface with Si Y. Sugita *, S. Watanabe, N. Awaji, S. Komiya Fujitsu Laboratories
Ltd., 10-I Morinosato-Wakamiva,
Atsugi 243-01, Japan
Received 22 August 1995; accepted 5 November
1995
Abstract We analyzed the density of thermally grown SiO,/Si by X-ray reflectivity measurements and local vibration properties by infrared spectroscopy. The macroscopic density varied with growth conditions. A lower growth temperature caused higher film density. We also found a thin (1 nm) and dense (2.35-2.4 g/cm3) transient layer at the SiO,/Si interface. The film density was constant to the thickness direction without the transient layer. On the other hand, IR properties showed characteristic film thickness dependencies. At a film thickness greater than 10 nm, the frequency of the transverse optic (TO) mode of Si-0 stretching shifted to the red direction, decreasing with the film thickness; while the frequency of the longitudinal optic (LO) mode is unchanged. This red shift of TO mode has no relation to the film density. At a film thickness of less than 6 nm, we found that both the TO and LO mode shift to the red direction simultaneously. The red shifts gradually increased with decreasing film thickness. This indicates that the SiOz network was densified by compressive stress.We assumed that the macroscopic and microscopic fluctuation were related to the oxide growth and formation of a hetero-junction.
1. Introduction It is well known that the density of thermally grown SiOz on Si depends on the oxidation conditions, such as temperature and atmosphere [1,2]. For example, low temperature oxidation ( < 900- 1000°C) leads to film densification [2-41. The reliability of a low-temperature grown oxide is not enough for a MOS device [5]. This is a severe problem for future low-temperature fabrication processes. The precise understanding of the oxide properties related to growth conditions are required in order to improve the oxide reliability.
* Corresponding author. Tel.: + 8 1-462-483 483473: e-mail: [email protected]. 0169.4332/96/$15.00 Copyright PII SO 169.4332(96)00302-9
I 11; fax: + 8 l-462-
Local vibration properties revealed by IR spectroscopy shows that the microscopic structure of the oxide depends on the growth temperature [ 1,6-IO]. IR analysis also shows that the oxide properties depend on the film thickness [6-lo]. It would be very useful to know how to optimize the oxidation conditions, but the relation between the local vibration properties and the macroscopic parameters, such as stress and density are not clear. The measurements of macroscopic parameters are difficult for thin films (< 30 nm) with high accuracy. In this paper, we demonstrate X-ray reflectometry to determine the thin film density and the film structure. These macroscopic parameters were compared with microscopic properties analyzed by IR spectroscopy. The fluctuation of the SiO,/Si structure was observed near the interface. We will discuss
0 1996 Elsevier Science B.V. All rights reserved.
Y. Sugita et al/Applied
Surface Science 100/101
the structural changes both from the macroscopic and microscopic points of view.
2. Experiment We used 4 inch CZ-Si(lO0) n-type 1 Cl cm wafers for X-ray reflectometry and 50 X 15 X 0.5 mm FZ-Si(lO0) prism shaped wafers for IR analysis. The samples were cleaned using wet-chemical solutions with a modified RCA procedure. The samples were oxidized using a device-grade quarz furnace. Oxidation temperatures were 850°C 900°C and 1000°C. The dry oxidation was carried out using pure O? (5 l/min) as the oxidation species. The wet oxidation was done using a hot water (85°C) bobbling system which used pure O? (5 l/min) as a carrier-gas. The oxidation time was varied to prepare samples with different thickness. A part of the samples were etched back using a 0.5% HF solution to reduce the thicknesses. IR spectroscopy was done with a Nicolet 740 FT-IR with a HgCdTe detector which was cooled by liquid N2. The measurement resolution was 4 cm ’ . Transmission measurements were carried out for both s-polarized and p-polarized conditions using a wire grid polarizer which has 10% leakage. Incidence angles of those experiments were between O-70” 1111. The X-ray reflectivity was measured by changing the glancing incidence angle ($1 from 0 to 4.5”by using a 2+-(~ scanning-apparatus-diffractometer. We used a synchrotron radiation beam line which had a Sic1 111 double crystal monochromator at National Laboratory of High Energy Physics (KEK) [ 121. The X-ray wavelength we used was 0.13 nm. We obtained some of the reflectivity-incidence-angle curves, which had the characteristic thin film interference signal. We analyzed the reflectivity data using an optimizing program based on the Marquardt non-linear minimization fitting technique [ 13- 161. The fitting parameters were film thickness, film density, surface roughness, and interface roughness. We also used the complex refractive index of materials from the tables of Henke et al. and the tables of Sasaki [ 17,181. The detail of experimental technique and analysis method were reported elsewhere [ 191.
(1996) 268-271
269
3. Results and discussion Fig. 1 shows the thickness dependence of the transmission IR properties of Si-0 stretching for as-grown SiO,/Si. The frequency peaks of the LO phonon was determined from the p-polarized spectra with the incidence angle of 70”. The frequency peaks of the TO phonon was determined from the spolarized spectra. As seen in Fig. 1, the peak positions of TO varied with film thickness, while the peak positions of LO were almost constant It was reported that both the TO and LO peaks shifted to the red direction simultaneously, in the densified silica glass [20-221. In that case, the bond angle of Si-0-Si decreased by increasing the density [20-231. We concluded that the red shifts of the TO mode seen in Fig. 1 did not result from the film densification. In Fig. 1, small red shifts of the LO phonon was observed at the oxide thickness of less than 10 nm. We measured the IR properties for the oxides which were etched back to near the interface, as shown in Fig. 2. It is clear that the red shift of both the LO and
1270 c g
1260
g E
1250
8 =
1240
L”““““‘“““““““““‘ I-“-*
I
% 6
1230
s ‘;
E
1080
s s E
1075
8 n Y
1070
I +
1065
e
dry uSOOT.dry -+s-1OOO"Cdry *-a*- 850°C wet ..-m-.900°C wet
&850°C
1060 0
20
40
60
80
Thickness
100
120
140
160
(nm)
Fig. 1. Thickness dependence of the peak frequency stretching for as-grown SiO, /Si.
of S-0
Y. Sugita et al./Applird
210
Surface Science 100/101
(19961268-271
2.50
1270 c;
2.45
f3
m-
'26o
Z '3 o
1250 U9OO"Cdry
'Z x Y 3 $L
1230
s
I,,
';
E
1060
: %
850°C
wet
--.m-
900°C
wet
-..*.-.
I I
dry
---a---
“7
I
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I. I
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.-.1-.900°C wet
-A-IOOOYJdry
---A--1000°C
-I
2.20 7 ”
0
50
100
Thickness
150
200
(nm)
Fig. 4. Calculated results for oxide density from X-ray reflectivity measurements. We analyzed the reflectivity curves applying the 2-layer oxides on Si model. i.e. upper SiO, layer/transient SiOz layer/Si substrate. Thickness of the transient layer was about I nm. The film thickness dependency of the density of both the transient layer and upper layer are shown.
wet
1070
x 2 a
:
2.25
1075
g P
2.35
8
---a-.650°C wet
650"Cdfy
+
s
,
2.49
.Z
-1000°C
1240
E B ~
1065
P
1060 10
20
30
Thickness
40
50
(nm)
Fig. 2. Thickness dependence of the peak frequency of Si-0 stretching for the oxides etched back by an 0.5% HF solution.
TO mode were observed near the interface, in these films. Fig. 3 shows that the relation of the LO and TO peak frequency extracted from Fig. 2. It is suggested that the SiO, network, which exists within from the interface to 6 nm, is densified by compressive stress.
I
1265 6 nm 1260
!
1255
-
Thin b
+
Thick
1
900°C
a
1000°C
1
;r 1235
i 1065
1060
1065
TO-peak
1070
position
1075
1060
1085
(cm-‘)
Fig. 3. Relation of LO frequency and TO frequency on Si-0 stretching. The solid line at a thickness of less than 6 nm region indicates that the red shift of LO phonon is 2 times larger than the red shift of TO phonon.
We estimated that the thickness of the stressed layer near the interface was about 1 nm. Fig. 4 shows the thickness dependence of the as-grown film densities which were determined by X-ray reflectometry. In Fig. 4, we present the results of 2-layer SiO, on Si model analysis. The 2 layer analysis brought better fit for all cases than the 1 layer SiO, on Si model analysis. The analysis of 3-layer SiO, on Si model did not show any improvement in fitting. As seen in Fig. 4, the oxides density had a growth temperature dependence. These are consistent both with our IR analysis results and previous work. Both results of the l-layer analysis and the 2-layer analysis provided that the macroscopic film densities were almost constant within the same growth temperature samples without the films thinner than 10 nm. The results of 2-layer analysis suggests that the thin (1 nm) and dense (2.35-2.4 g/cm3) transient layer, shown in Fig. 4, exists at the interface. For each film, the macroscopic density of the upper layer ( > 1 nm) was constant throughout the thickness. IR properties also suggested that the SiO, network near the interface (1 nm) were densified. It might be that the compressive stress to the network reduces the filmvolume near the interface and causes the macroscopic densification. as a result. A spectroscopic ellipsometry study revealed that a 1 nm thick transient layer exists at the interface of SiO,/Si [3]. This transient layer is a mixture of Si
Y. Sugita et &./Applied
Surface Science lOO/ 101 (19%) 268-271
and SiO,. It could be viewed as interface roughness. Because the densities of the transient layer we found were larger than the Si density (2.33 g/cm3), it could not be explained by the interface roughness. In our case, it could be a densified SiO, layer. We consider that such structural fluctuations originate in the volume expansion at the oxidation of Si or the lattice distortion of the SiO,/Si hetero-junction.
271
an understanding of thermally grown oxide properties. The joint use of the X-ray reflectometry and the local vibration analysis is an effective way to investigate SiOJSi structures.
References
4. Conclusion
ill W.A. Pliskin, J. Vat. Sci. Technol. 14 (1977) 1064. l21 E.A. Traft, J. Electrochem. Sot. 125 (1978) 968; 127 (1980)
We examined the macroscopic density of SiO, on Si(100) and its local vibration properties. The 2-layers on Si model were successful for all oxides which we measured. The macroscopic density increased as we lowered the growth temperature (< 1000°C). This is consistent with previous studies and it could be explained by viscose flow of SiO, at the growth temperature. A high density (2.35-2.4 g/cm3) and thin (1 nm) layer was found at the SiO,/Si interface. The film density is constant to the thickness direction for each oxides without a transient layer. On the other hand, IR properties have a characteristic thickness dependence. At a film thicker than 6 nm, the frequency of the TO mode of Si-0 stretching shifted to the red-direction with decreasing film thickness, while the frequency of the LO mode is unchanged. We concluded that this red shift of the TO mode does not result from film densification which decrease the angle of Si-0-Si. It is consistent with our X-ray reflectometry results. At a film thinner than 6 nm, both the TO and LO mode shift to the red-direction simultaneously. This red shifts gradually increased with a decrease in the film thickness, indicating that the SiO, network was densified by compressive stress. We estimate the thickness of the stressed layer to be about 1 nm. We supposed that this densification was accompanied by the volume expansion of SiO, at the thermal oxidation or hetero-junction of SiOJSi. The macroscopic fluctuation was consistent with microscopic view. Our results were useful to develop
[31 E.A. Irene, E. Tiemey and J. Angilello, J. Electrochem.
993. Sot. 129 (1982) 2594; Y A. Yakovlev and E.A. Irene, J. Electrochem. Sot. 139 (1992) 1450; Y.A. Yakovlev, Q. Liu and E.A. Irene, J. Vat. Sci. Technol. A 10 (1992) 427. [41 C.R. Helms and B.E. Deal, The Physics and Chemistry of SiOz and the Si-SiO? Interface (Plenum, New York, 1988) p. 139. El A. S&mans, Phys. Rev. Lett. 70 (1993) 1723. lb1 I.W. Boyd and J.I.B. Wilson, J. Appl. Phys. 62 (1987) 3195. [7] G. Lucovsky, M.J. Manitini, J.K. Srivastava and E.A. Irene, J. Vat. Sci. Technol. B 5 (1987) 530. [8] C.H. Bjorkman, T. Yamazaki, S. Miyazaki and M. Hirose, J. Appl. Phys. 77 (1995) 313. [9] K. Ishikawa, H. Ogawa, S. Oshida, K. Suzuki and S. Fujimura, Ext. Abst. Conf. 1995 Solid State Dev. and Mater., Japan. [IO] N. Yasuda and A. Toriumi, Ext. Abst. Conf. 1993 Solid State Dev. and Mater., Japan (1993) 86. [ll] D.W. Berreman, Phys. Rev. 130 (1963) 2193. [12] Y. Horii, H. Tomita and S. Komiya, Rev. Sci. Instr. 66 (1995) 1370. [13] B. Vidal and P. Vincent, Appl. Opt. 23 (1984) 1794. [14] L. Nevot and P. Croce, Rev. Phys. Appl. 15 (1980) 761. [15] L.-G. Paratt, Phys. Rev. 95 (1954) 389. [16] A.A. Bright and G.W. Rubloff, J. Vat. Sci. Technol. A 8 ( 1990) 2046. [17] B.L. Henke, J.C. Davis, E.M. Gullikson and R.C.C. Perera, Lawrence Berkeley Lab. Rep. LBL-26259 (1988). [18] S. Sasaki, KEK Rep. 88-14 (1989). [19] N. Awaji, in preparation for publication in Jpn. J. Appl. Phys.; N. Awaji, Y. Sugita, S. Ohkubo, T. Nakanishi, T. Takasaki and S. Komiya, Jpn. J. Appl. Phys. 34 (1995) L1013. [20] G.E. Walrafen, Y.C. Chu and S. Hokmabadi. J. Chem. Phys. 92 (1990) 6987. [21] R.A.B. Devine, J. Vat. Sci. Technol. A 6 (1988) 3154. [22] P.N. Sen and M.E. Thorpe, Phys. Rev. B 15 (1977) 4030. [23] J.D. Jorgensen, J. Appl. Phys. 49 (1978) 5473.