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Properties of SOI structures formed by high dose oxygen implantation into silicon
Vacuum/volume 39/numbers Printed in Great Britain
2_4/pages
0042-207X/89$3.00+.00 Pergamon Press pk.
219 to 221 11989
Properties of SOI structures formed oxygen implantation into silicon
by high dose
Lu Diantong, Lu Wuxing University, Beijing, PRC
Physics, Beijing Normal
and Wang
Zhonglie,
Institute
of Physics, Beijing
University,
of 1 ow Energy Nuclear
and Du Yongchang.
Department
Beijing,
PRC
and Zheng
Huaide,
Institute
of Semiconductors,
Academia
Sinica, PRC
and MO Dang
and
Liang
Zhongning.
Department
of Physics, Zhongshan
University,
PRC
Sol (silicon on insulator) structures have been formed by high dose (2.0~ 1018 cm-‘) 0’ implantation into n-type (100) silicon. The structures have been evaluated by RBS (Rutherford backscattering). SR (spreading resistance), EPS (elliptical polarization spectroscopy) and IR (infrared) absorption spectroscopy. After high temperature annealing the thickness of the surface crystal silicon layers in SOI structures is between 2400 and 3500 A” and that of buried Si02 layers between 2800 and 4600 A”. There are three major characteristic peaks in the IR spectra of SOI structures. These three absorption peaks: P, (1070-7085 cm-‘), P2 (SOO-SOS cm-‘) and P, (455-460 cm-‘) are characteristic of silicon dioxide (Naoyuki Nagasima, Japan J Appl Phys, 9.879 (1970) ; Naoyuki Nagasima, J appl Phys, 43.3378 (1972)). The three absorption coefficients have been calculated and a new non-destructive method to determine the thickness of buried Si02 layers in SOI samples is suggested.
1. Introduction
3. Results and discussion
Buried oxide formation using oxygen implantation into Si is an attractive isolation technique that may some day replace silicon on sapphire (SOS). Such substrates provide good materials for fabricating high speed CMOS circuits and radiation hardened devices3. Properties of SO1 structures formed by different procedures have been reported in many studies mostly by RBS, TEM and In this study, both RBS and SR, EPS and SIMS techniques”‘. IR have been used to investigate the properties of SO1 structures.
Figure 1 shows random RBS spectra from samples implanted with 2 x lOI* cm- * at 200 keV. The upper is non-annealed and lower is annealed at 1200°C for 2 h in Nz atmosphere. The oxygen signal lies between channels 400 and 550 and is superimposed upon the yield due to the silicon substrate. From the convex area, the actual implanted dose was calculated to be 1.6 x 10” O+ cm-’ The lower atomic density of Si in the implanted layer leads to a reduced yield; a dip shape, between channels 760 and 880,
2. Experimental procedure Four to eight ohm-cm n-type silicon wafers with a (100) orientation were implanted with an oxygen dose of 2.0 x 10 ’ * cm- * at 200 keV and 350 keV at room temperature. The total beam current was about 40-70 PA. It took 69 h to finish each wafer of diameter 35 mm. After implantation, the wafers were annealed in a N, atmosphere. The implanted samples were examined by RBS, SR, EPS and IR methods. Fourier-transform infrared was used for the IR spectra in the energy range 400-l 600 cm- ‘. After IR measurements the surface of the buried Si02 layer was exposed by plasmaetching the overlying silicon layer. The thickness of the buried oxide layer was measured by an elliptical meter. We have calculated the absorption coefficients from the IR spectra and the thickness of the buried SiO, layer. Using our experimental data, the thickness of the buried SiO, layer will be determined by IR spectra without destroying the SO1 sample.
0
I 200
I
I
400
600
Channel
number
Figure 1. Random RBS spectra from wafers implanted with 2.0 x IO” Of cm-’ at 200 keV: no 45-2, as-implanted; no 45-4, annealed at 1200-C for 2 h in flowing Nz, 219
Lu Diantong
whcrc
eta/:
Propertles of SOI structures
the thickness
thickness
ol’ the buried
of the surface
channels
bctwccn
silicon
‘. causing
RBS spectra. ditfuscd
dioxide
Figures no
and
IO’“c111
the 2 at
with 2.0 x 10’” cm The thickness d,,
of the profile
sides of
layer during
is shown Before
annealed
the unanncalcd
wafcl
implanted
wafer no 5-
stoi-
with
1 implanted
Si layer (Is, and the buried
lays
in Table 2.
HTA
(high
After
the surface
temperature
in the depth
the same rcsistivity
laycr
annealing)
of (r/,,+r/,,)
the wafer
with
became a single crystal
as that in the substrate.
into the surfazc
The lower
layer with resistivity
’ implan-
layer.
3 shows the thickness
SiO, layer from
had an
high rcsistivitq.
in the surface layer of wafer no 45-I?. is the result of As Table
:I
annealing.
’ at 350 kcV
of the surface
layer
tation
Y--l
that oxygen
to form
45-12,
200 keV and annealed
amorphous HTA
from no
no
I .38 x 10’”
the high temperature
wafer
1.
..-•\ I ‘\.
shapes in the
indicated
the intcrfacc
2 and i show SR profiles
45-2
2.0 x
both
I
the
in Table
dose
dip and convex
The
from
shown
arc
than the critical
the saturated
The flattening
towards
chiometric
Iaycr was obtwincd. wah cstimatcd
880 and 940. All results
In our USC the dose is larger O+ cm
SiO, layer
of the surface Si layer and huricd
EPS measurements.
I :
-.-
45-2
;
-.-
45-12
The results arc in good agrccmcnt
with
those of RBS and SK
nicasurcmcnts. ICipurc 4 shows
I R spectra from the as-implanted and anne:~led I. rcspectivcly) implanted with ?. x t 0’”
warcrs (no 45-Z and no 4% 0’
’ iIt 200 koV.
cm Thcrc
cm
'.
are three
major
peaks
111 the energy
The first peak P, (107@ IOX
0 stretching Si stretching
vibration vibration
mode; mode
cm
range
400~ 1600
‘) is the w&known
the second Pz (X03 X05 cm and the third
Si ‘). SI
P; (455 460 cm
Table 2. SR result\
15-2 45-I?
200 200
100 5. I
150
7 x lo’* 7x IO“0 5x lO“AS 2 x IO”
Now
TOLlI 1100 C. 1 Il. N? ix0 t I00 C‘. IO s. N 7 1200 C, ? h. N _ 3600
ho00
2x00 4500
‘).
Lu DkWong
et a/: Properties
of SOI structures
Table 3. EPS results Wafer
Energy
ll0
(kev)
Dose (cm _ ‘)
Annealing
ds, (A)
d, (A)
45-2 45-12
200 200 100 200
2x 2x 5x 2x
None 12OO”C, 2 h 1 lOO”C, 10 s 12OO”C, 2 h
3400
3600
3050 3550
3450 3700
45-13
10’8 lotx 10” As+ 10IX
45-2
where A is the absorbance or optical density at the minimum, I, and Z, the incident and transmitted intensities, respectively, CIthe absorption coefficient, and t, the sample thickness. This property will be utilized as a non-destructive method of determining the thickness of buried SiOZ layer in SOI structures by IR absorption spectroscopy, if the absorption coefficient of the buried SiOz is obtained. After plasma-etching the surface silicon layer with CF, gas, the d, was measured by an ellipsometer. The thickness of the buried layer d, and absorption coefficients from our work and others I2 are shown in Table 4. The coefficient of the buried SiO, layer in the SOI structures from the sample after HTA is in good agreement with that of the thermal SiO, film. 4. Summary Silicon wafers were implanted with 2.0 x IO” cm-’ (the actual dose was 1.6 x 10” cm- *, as checked by RBS and IR measurement) at 200 and 350 keV. After HTA, SO1 structures were formed with Cr,, (240&3600 A) and d, (280@4500 A). The top silicon layer was recrystallized. The structure of the buried SiOz layer is nearly the same as that of thermal SiO, film. The three major peaks and their absorption coefficients are almost the same as that of thermal dioxide. Using the coefficients we have given above, the thickness of the buried SiO, layer in SO1 can be non-destructively determined by IR absorption spectra.
45-l
Acknowledgements The authors thank Chan Ruyi for carrying out the implantation and Luo Ye for SR measurements. This work was supported by the Science Foundation from China State Education Commission. References
%-
400
Wovenumbers
( cm-’ )
Figure 4. IR spectra from wafers implanted 200 keV : no 45-2. as-implanted in N2 atmosphere.
with 2.0 x IO” O+ cm-* at at 12OO’C for 2 h
; no 45-1, annealed
Si-0-Si bending vibration mode’,‘. After HTA, the three peaks moved to the higher wave numbers and sharpened in the halfband widths. This indicated that the thermal energy caused oxygen rearrangement, structural changes in the silica network and reduced the lattice strain introduced by Of implantation. The positions and shapes of the peaks are nearly the same as those of the thermal SiO, film”,’ ‘. The infrared transmission minima in Si02 films obey the Lambert-Bouguer law’* :
A = log (Z,/Z) = 0.434at
(I)
’ Naoyuki Nagasima, Japan .I Appl Phys, 9,879 (1970). ’ Naoyuki Nagasima, J appl Phys, 43, 3378 (1972). ’ K Hashimoto, T I Kamins, K M Cham and S Y Chiang, IEDM 85,672 (1985). “Yukio Irita, Yasuo Kunii, Mitsutoshi Takahashi and Kenji Kajiyama, Japan J Appl Phys, 20, L909 (1981). ‘P L F Hemment, E Maydell-ondrusz and K G Stephens, Nucl Instrum Meth,
209/210, 157 (1983). “F Namavar, J I Budnick, F H Sanchez and H C Hauden,
Marer Rrs (1986). ‘P L F Hemment, R F Peart, M F Yao, K G Stephens, R P Arrowsmith, R J Chater and J A Kilner, Nucl Instrum Merh, B6, 292 (I 985). ‘G K Celler, P L F Hemment, K W West and J M Gibson, Appl PhJJs Left, 48(S), 532 (1986). ’ K J Reeson, Nucl Instrum Meth, B19/20, 269 (1987). “I J E Dial, R E Gong and J N Fordemwalt, J Elecrrochem Sot, 115, 326 (1968). ’ ’ W A Pliskin and H S Lehman, J Electrochem Sot, 112, 1013 (1965). “Joe Wong, J Electron Muter, 5, 113 (1976). Sot Symp Proc, 45,317
Table 4. Absorption coefficient from IR and referencesI Wafer no 45-2 45-I Thermal Si0212 CVD” SiO *
Annealing
d, (A)
None 1200°C. 2 h
3193 3256
P, (Sip0) (cm- ‘)
P2 (SipSi)
P, (SiX&Si)
(cm- ‘)
(cm- ‘)
2.39 3.10 3.20 2.56
0.285 x IO4 0.344 x lo4 0.345 x IO4 0.25 x lo4
1.27 1.30 1.08 0.76
x x x x
lo4 lo4 lo4 IO4
x x x x
lo4 lo4 IO4 lo4
221
2_4/pages
0042-207X/89$3.00+.00 Pergamon Press pk.
219 to 221 11989
Properties of SOI structures formed oxygen implantation into silicon
by high dose
Lu Diantong, Lu Wuxing University, Beijing, PRC
Physics, Beijing Normal
and Wang
Zhonglie,
Institute
of Physics, Beijing
University,
of 1 ow Energy Nuclear
and Du Yongchang.
Department
Beijing,
PRC
and Zheng
Huaide,
Institute
of Semiconductors,
Academia
Sinica, PRC
and MO Dang
and
Liang
Zhongning.
Department
of Physics, Zhongshan
University,
PRC
Sol (silicon on insulator) structures have been formed by high dose (2.0~ 1018 cm-‘) 0’ implantation into n-type (100) silicon. The structures have been evaluated by RBS (Rutherford backscattering). SR (spreading resistance), EPS (elliptical polarization spectroscopy) and IR (infrared) absorption spectroscopy. After high temperature annealing the thickness of the surface crystal silicon layers in SOI structures is between 2400 and 3500 A” and that of buried Si02 layers between 2800 and 4600 A”. There are three major characteristic peaks in the IR spectra of SOI structures. These three absorption peaks: P, (1070-7085 cm-‘), P2 (SOO-SOS cm-‘) and P, (455-460 cm-‘) are characteristic of silicon dioxide (Naoyuki Nagasima, Japan J Appl Phys, 9.879 (1970) ; Naoyuki Nagasima, J appl Phys, 43.3378 (1972)). The three absorption coefficients have been calculated and a new non-destructive method to determine the thickness of buried Si02 layers in SOI samples is suggested.
1. Introduction
3. Results and discussion
Buried oxide formation using oxygen implantation into Si is an attractive isolation technique that may some day replace silicon on sapphire (SOS). Such substrates provide good materials for fabricating high speed CMOS circuits and radiation hardened devices3. Properties of SO1 structures formed by different procedures have been reported in many studies mostly by RBS, TEM and In this study, both RBS and SR, EPS and SIMS techniques”‘. IR have been used to investigate the properties of SO1 structures.
Figure 1 shows random RBS spectra from samples implanted with 2 x lOI* cm- * at 200 keV. The upper is non-annealed and lower is annealed at 1200°C for 2 h in Nz atmosphere. The oxygen signal lies between channels 400 and 550 and is superimposed upon the yield due to the silicon substrate. From the convex area, the actual implanted dose was calculated to be 1.6 x 10” O+ cm-’ The lower atomic density of Si in the implanted layer leads to a reduced yield; a dip shape, between channels 760 and 880,
2. Experimental procedure Four to eight ohm-cm n-type silicon wafers with a (100) orientation were implanted with an oxygen dose of 2.0 x 10 ’ * cm- * at 200 keV and 350 keV at room temperature. The total beam current was about 40-70 PA. It took 69 h to finish each wafer of diameter 35 mm. After implantation, the wafers were annealed in a N, atmosphere. The implanted samples were examined by RBS, SR, EPS and IR methods. Fourier-transform infrared was used for the IR spectra in the energy range 400-l 600 cm- ‘. After IR measurements the surface of the buried Si02 layer was exposed by plasmaetching the overlying silicon layer. The thickness of the buried oxide layer was measured by an elliptical meter. We have calculated the absorption coefficients from the IR spectra and the thickness of the buried SiO, layer. Using our experimental data, the thickness of the buried SiO, layer will be determined by IR spectra without destroying the SO1 sample.
0
I 200
I
I
400
600
Channel
number
Figure 1. Random RBS spectra from wafers implanted with 2.0 x IO” Of cm-’ at 200 keV: no 45-2, as-implanted; no 45-4, annealed at 1200-C for 2 h in flowing Nz, 219
Lu Diantong
whcrc
eta/:
Propertles of SOI structures
the thickness
thickness
ol’ the buried
of the surface
channels
bctwccn
silicon
‘. causing
RBS spectra. ditfuscd
dioxide
Figures no
and
IO’“c111
the 2 at
with 2.0 x 10’” cm The thickness d,,
of the profile
sides of
layer during
is shown Before
annealed
the unanncalcd
wafcl
implanted
wafer no 5-
stoi-
with
1 implanted
Si layer (Is, and the buried
lays
in Table 2.
HTA
(high
After
the surface
temperature
in the depth
the same rcsistivity
laycr
annealing)
of (r/,,+r/,,)
the wafer
with
became a single crystal
as that in the substrate.
into the surfazc
The lower
layer with resistivity
’ implan-
layer.
3 shows the thickness
SiO, layer from
had an
high rcsistivitq.
in the surface layer of wafer no 45-I?. is the result of As Table
:I
annealing.
’ at 350 kcV
of the surface
layer
tation
Y--l
that oxygen
to form
45-12,
200 keV and annealed
amorphous HTA
from no
no
I .38 x 10’”
the high temperature
wafer
1.
..-•\ I ‘\.
shapes in the
indicated
the intcrfacc
2 and i show SR profiles
45-2
2.0 x
both
I
the
in Table
dose
dip and convex
The
from
shown
arc
than the critical
the saturated
The flattening
towards
chiometric
Iaycr was obtwincd. wah cstimatcd
880 and 940. All results
In our USC the dose is larger O+ cm
SiO, layer
of the surface Si layer and huricd
EPS measurements.
I :
-.-
45-2
;
-.-
45-12
The results arc in good agrccmcnt
with
those of RBS and SK
nicasurcmcnts. ICipurc 4 shows
I R spectra from the as-implanted and anne:~led I. rcspectivcly) implanted with ?. x t 0’”
warcrs (no 45-Z and no 4% 0’
’ iIt 200 koV.
cm Thcrc
cm
'.
are three
major
peaks
111 the energy
The first peak P, (107@ IOX
0 stretching Si stretching
vibration vibration
mode; mode
cm
range
400~ 1600
‘) is the w&known
the second Pz (X03 X05 cm and the third
Si ‘). SI
P; (455 460 cm
Table 2. SR result\
15-2 45-I?
200 200
100 5. I
150
7 x lo’* 7x IO“0 5x lO“AS 2 x IO”
Now
TOLlI 1100 C. 1 Il. N? ix0 t I00 C‘. IO s. N 7 1200 C, ? h. N _ 3600
ho00
2x00 4500
‘).
Lu DkWong
et a/: Properties
of SOI structures
Table 3. EPS results Wafer
Energy
ll0
(kev)
Dose (cm _ ‘)
Annealing
ds, (A)
d, (A)
45-2 45-12
200 200 100 200
2x 2x 5x 2x
None 12OO”C, 2 h 1 lOO”C, 10 s 12OO”C, 2 h
3400
3600
3050 3550
3450 3700
45-13
10’8 lotx 10” As+ 10IX
45-2
where A is the absorbance or optical density at the minimum, I, and Z, the incident and transmitted intensities, respectively, CIthe absorption coefficient, and t, the sample thickness. This property will be utilized as a non-destructive method of determining the thickness of buried SiOZ layer in SOI structures by IR absorption spectroscopy, if the absorption coefficient of the buried SiOz is obtained. After plasma-etching the surface silicon layer with CF, gas, the d, was measured by an ellipsometer. The thickness of the buried layer d, and absorption coefficients from our work and others I2 are shown in Table 4. The coefficient of the buried SiO, layer in the SOI structures from the sample after HTA is in good agreement with that of the thermal SiO, film. 4. Summary Silicon wafers were implanted with 2.0 x IO” cm-’ (the actual dose was 1.6 x 10” cm- *, as checked by RBS and IR measurement) at 200 and 350 keV. After HTA, SO1 structures were formed with Cr,, (240&3600 A) and d, (280@4500 A). The top silicon layer was recrystallized. The structure of the buried SiOz layer is nearly the same as that of thermal SiO, film. The three major peaks and their absorption coefficients are almost the same as that of thermal dioxide. Using the coefficients we have given above, the thickness of the buried SiO, layer in SO1 can be non-destructively determined by IR absorption spectra.
45-l
Acknowledgements The authors thank Chan Ruyi for carrying out the implantation and Luo Ye for SR measurements. This work was supported by the Science Foundation from China State Education Commission. References
%-
400
Wovenumbers
( cm-’ )
Figure 4. IR spectra from wafers implanted 200 keV : no 45-2. as-implanted in N2 atmosphere.
with 2.0 x IO” O+ cm-* at at 12OO’C for 2 h
; no 45-1, annealed
Si-0-Si bending vibration mode’,‘. After HTA, the three peaks moved to the higher wave numbers and sharpened in the halfband widths. This indicated that the thermal energy caused oxygen rearrangement, structural changes in the silica network and reduced the lattice strain introduced by Of implantation. The positions and shapes of the peaks are nearly the same as those of the thermal SiO, film”,’ ‘. The infrared transmission minima in Si02 films obey the Lambert-Bouguer law’* :
A = log (Z,/Z) = 0.434at
(I)
’ Naoyuki Nagasima, Japan .I Appl Phys, 9,879 (1970). ’ Naoyuki Nagasima, J appl Phys, 43, 3378 (1972). ’ K Hashimoto, T I Kamins, K M Cham and S Y Chiang, IEDM 85,672 (1985). “Yukio Irita, Yasuo Kunii, Mitsutoshi Takahashi and Kenji Kajiyama, Japan J Appl Phys, 20, L909 (1981). ‘P L F Hemment, E Maydell-ondrusz and K G Stephens, Nucl Instrum Meth,
209/210, 157 (1983). “F Namavar, J I Budnick, F H Sanchez and H C Hauden,
Marer Rrs (1986). ‘P L F Hemment, R F Peart, M F Yao, K G Stephens, R P Arrowsmith, R J Chater and J A Kilner, Nucl Instrum Merh, B6, 292 (I 985). ‘G K Celler, P L F Hemment, K W West and J M Gibson, Appl PhJJs Left, 48(S), 532 (1986). ’ K J Reeson, Nucl Instrum Meth, B19/20, 269 (1987). “I J E Dial, R E Gong and J N Fordemwalt, J Elecrrochem Sot, 115, 326 (1968). ’ ’ W A Pliskin and H S Lehman, J Electrochem Sot, 112, 1013 (1965). “Joe Wong, J Electron Muter, 5, 113 (1976). Sot Symp Proc, 45,317
Table 4. Absorption coefficient from IR and referencesI Wafer no 45-2 45-I Thermal Si0212 CVD” SiO *
Annealing
d, (A)
None 1200°C. 2 h
3193 3256
P, (Sip0) (cm- ‘)
P2 (SipSi)
P, (SiX&Si)
(cm- ‘)
(cm- ‘)
2.39 3.10 3.20 2.56
0.285 x IO4 0.344 x lo4 0.345 x IO4 0.25 x lo4
1.27 1.30 1.08 0.76
x x x x
lo4 lo4 lo4 IO4
x x x x
lo4 lo4 IO4 lo4
221