- Email: [email protected]
Structural and electrical properties of thin SiO2 layers grown by RTP in a mixture of N2O and O2
] O U R N A L OF
ELSEVIER
Journal of Non-Crystalline Solids 187 (1995) 361-364
Section 11. O N O and nitrated oxides
Structural and electrical properties of thin SiO2 layers grown by RTP in a mixture of N 2 0 and 02 A.J. Bauer*, E.P. Burte Fraunhofer-lnstitutfur lntegrierte Schaltungen, Bereich Bauelementechnologie, Schottkystrasse 12, D-91058 Erlangen, Germany
Abstract
Ultrathin ( < 10 nm) dielectric films for application in metal-oxide-semiconductor devices have been fabricated in an 02 : N20 atmosphere using rapid thermal processing. It is shown that with increasing N20 content in the mixtures of N20 and O z, the oxide thickness decreases and the interfacial nitrogen concentration increases. Therefore, the nitrogen concentration at the Si/SiO 2 interface, responsible for improved electrical characteristics, is adjustable by the 02 : NzO ratio. High charge-to-breakdown (QBD)values comparable to oxides processed in pure N20 atmosphere are obtained for electron injection from the Si substrate. For electron injection from the gate, the QBDvalues are considerably higher. For an 02 : NzO ratio of 3 : 1 the highest QBDvalues have been obtained together with a very homogeneous QBDdistribution across the wafer.
1. Introduction
In the near future, the development of highly reliable, very thin SiO 2 films will be of crucial importance for the manufacture of sub-0.25 tam metal-oxide-semiconductor field-effect transistors (MOSFETs). The oxide thickness will decrease from 9 nm for 0.35 ~tm to 6.5 nm for 0.25 ~tm U L S I devices due to device design rules [1]. Using rapid thermal processing (RTP) oxynitride grown in a pure N 2 0 atmosphere on silicon substrates has recently drawn attention to its candidature as a gate dielectric for deep submicron M O S F E T devices. It exhibits high charge-to-breakdown QBo values [2,3] and high hot carrier integrity I-4].
*Corresponding author. Tel: +49-9131 761 308. Telefax: +49-9131 761 390. E-mail: [email protected].
However, thickness and electrical inhomogeneities across the wafer of the dielectric films grown in pure N 2 0 atmosphere are reported [5] and the self-limiting growth of oxynitrides resulting in prolonged processing times increases the thermal budget. In this paper we report on structural and electrical properties of dielectric films processed in mixtures of N 2 0 and 02 by R T P as proposed by [6] and compare them with oxides grown in pure 0 2 and N 2 0 atmospheres. This process has a lower thermal budget due to the enhanced oxidation rate and exhibits a better film thickness homogeneity compared to an oxynitridation process in pure N 2 0 atmosphere. Furthermore, this method provides excellent control of nitrogen peak concentration at the SiO2/Si interface, which is an important parameter determining M O S F E T characteristics [7]. By varying the N 2 0 : O 2 ratio in the gas
0022-3093/95/$09.50 ~, 1995 Elsevier Science B.V. All rights reserved SSDI 0 0 2 2 - 3 0 9 3 ( 9 5 ) 0 0 1 6 4 - 6
362
A.J. Bauer, E.P. B u r t e / J o u r n a l o f N o n - C r y s t a l l i n e Solids 187 (1995) 3 6 1 - 3 6 4
mixture improved QBDdistributions across the wafer and higher QaD values for electron injection from the substrate compared to oxynitride films oxidized in pure N20 atmosphere could be obtained.
3.0
. . . .
I
. . . .
I
. . . .
I
. . . .
I
. . . .
|
. . . .
I
. . . .
2.5
E 2.0 o
& 1.s
2. Experimental procedure The SiO2 and SiOxN r films were grown on 4-6 t2 cm, p-type (1 0 0) Si wafers after a standard wet cleaning procedure by applying the following oxidation and nitridation process steps: (a) oxidation in dry oxygen, (b) oxidation in dry nitrous oxide and (c) oxidation in a mixture of oxygen and nitrous oxide with 0 2 : N 2 0 ratios of 1 : 3, 1 : 1 and 3: 1. The oxidation temperature was 1120°C and the flow rate of the gases during the oxidation was set to 2 slm. After growth of the dielectric, a 500 nm thick polysilicon layer was deposited by low-pressure chemical vapor deposition (LPCVD) at 620°C. The layer was doped with phosphorus at 950°C. The gates of area A = 0.02 nm 2 of MOS capacitors were defined by photolithography and wet etching. The nitrogen depth profiles were determined by secondary ion mass spectroscopy (SIMS) using Cs ÷ bombardment at an energy of 5 keV and CsN ÷ ion detection. The electrical properties of these dielectric films were evaluated by high-frequency (1 MHz) C-V, quasi-static C - V and I - V measurements. The reliability of the dielectric films was evaluated from time-dependent dielectric-breakdown (TDDB) characteristics. The T D D B measurements were performed at negative and positive gate bias on 53 capacitors by applying a constant current density of j = + 200 mA/cm 2. The increase or decrease of the gate voltage observed during the T D D B measurements is related to the buildup of negative or positive charge in the oxide.
3. Results The average oxide thickness obtained was 8.0 _+ 0.5 nm for all the various oxides. The homogeneity of the oxide thickness attained from standard deviation calculations was best with a value of a = 0.1 nm for the O2-oxide and worst (a = 0.6 nm)
"-- 1.0 Z 0.5
0.00.0 ,
, , i .... 0.5
I ....
1.0
i .... 1.5
I .... 2.0
i
2.5
....
i
3,0
.... 3.5
02:N20 Fig. 1. N i t r o g e n p e a k c o n c e n t r a t i o n N of the dielectric films as a function of the 0 2 : N 2 0 ratio. The o x i d a t i o n t e m p e r a t u r e was 1120°C a n d the t o t a l gas flow was 2 slm ( s t a n d a r d liter/minute).
for the N20-oxide. The standard deviation values of the O2:N20-oxides were between the above values in such a way that the value of the O2:NEOoxide with the highest O2:N20 ratio was near the value of the O2-oxide and increased with increasing N20 content in the oxidizing atmosphere. Fig. 1 shows the nitrogen peak concentration N of the various oxynitride films as a function of the O2:N20 ratio during oxidation. The nitrogen concentration increases with increasing N20 content in the oxidizing atmosphere. For all oxides investigated, the density of interfacial traps was as low as D ~ x ~ l . 5 x 101°eV - t cm-2, while the density of fixed interface charges was lower than 0.5 x 10 ~1 cm-2. Fig. 2 shows the dependence of the charge-to-breakdown Qao(63%) values (63% cumulative failure) under constant current stress on the NzO content for both gate polarities. The injection current density was j = + 200 mA/cm 2. If the N20 content in the oxidizing atmosphere is equal to or lower than 50%, then the Qao(63%) values are higher than the values of the O2- and NEO-Oxides for substrate and gate injection. The Qao(63%) values for negative gate polarity are about three times lower than for positive polarity. In Fig. 3 the Weibull plots of the Qaa values of Fig. 2 are presented. A homogeneous Qai~ distribution (for positive and negative gate
363
A.J. Bauer, E.P. Burte / Journal of Non-Crystalline Solids 187 (1995) 361 364 30
I
'
'
'
I
'
•
•
I
=
•
"
I
'
'
'
I
'
'
'
Poly- Oxide p-Si Gate
I
Poly- Oxide p-Si Gate
25 E 20 o Ga
(-) qterface
~10 o
;rface
5 0
I
,
,
=
0
I
,
=
•
20
I
•
•
•
I
4o
,
,
,
I
60
•
,
80
N20 (%)
,
I
'
1 oo
Fig. 2. Dependenceof the QB~63%) values on the N20 content of the oxidizing atmosphere after a constant current injection with a current density of j = + 200mA/cm2 for both gate polarities.
I0
•
=0
•
0
=
0
• O=:N=O/1:3
~
#
• 0=:N20/3:1
~" I v
o
-o N20 = ~
•
~ =
D
Gate+
c::
_.= -2
-3
* ! •
lo*
./'"o
• ~, ,# o = 0 o
•
I
101 Q= (C/cm:')
j=~2OOmA/cm 102
Fig. 3. Weibull plots of charge-to-breakdown in MOS capacitors (area: 0.02 mm2) with different gate dielectrics under both gate polarities.
polarity) across the wafer can be seen only for the Oz-oxides and the 0 2 : N20-oxides which were oxidized in an O2 : N 2 0 atmosphere with an Oa : N 2 0 ratio higher than one. On the other hand, the N z O oxide exhibits above all a broad QBo distribution for electron injection from the gate. The Weibull plots for the O z : N 2 0 ratio of 1:1 are similar to those of the 0 2 : N 2 0 ratio of 3 : 1 and are therefore not shown in Fig. 3.
ric~qlayer
r... ,aye,
Fig. 4. Schematic energy-band diagram with a nitrogen-rich layer at the SiO2/Si interface showing electron injection from poly gate and Si substrate.
4. D i s c u s s i o n
It is well known that an optimized R T P N 2 0 oxidation process can result in high QaD(63%) values [8,9]. This is attributed to nitrogen incorporation into the SiO2/Si interface which strengthens the interface against hot carrier damage. Our results show, too, that nitrogen is incorporated in the bulk of the dielectric film near the SiO2/Si interface (see Fig. 4) after a N / O oxidation at high temperatures (1050°C < T < 1150°C). This nitrogen-rich layer may be responsible for the Qao degradation under negative gate polarity. In this case, the electrons are tunneling from the polysilicon gate into the conduction band of the dielectric film. Here, the electrons are accelerated on account of the applied electric field. F r o m there, they gain sufficient energy to generate traps in the nitrogen-rich layer near the anode by breaking Si-N or O - N bonds, the binding energy of which is lower than the Si-O bond [10]. Hence, if there is a nitrogen-rich layer in the dielectric film near the interface to silicon, more traps than in nitrogen-free oxides are generated resulting in lower QaD(63% ) values. But, if the electrons are injected from the Si substrate, they are tunneling through the nitrogenrich interfacial layer (Fig. 4) and have not yet gained sufficient energy to break N bonds. So, less traps responsible for dielectric breakdown are generated at the anode. Only the beneficial influence of the nitrogen incorporated in the interface becomes
364
A.J. Bauer, E.P. Burte / Journal of Non-Crystalline Solids 187 (1995) 361 364
evident. By that, the b r o a d QBD d i s t r i b u t i o n of the N z O - o x i d e for negative gate p o l a r i t y can be explained. O x i d a t i o n processes in p u r e N z O a t m o sphere show, preferentially in the center of the wafer, a high n i t r o g e n p e a k c o n c e n t r a t i o n at the SiO2/Si interface a n d a low one at the o u t e r a r e a of the wafer. C o n s e q u e n t l y , high QBD values will be seen, where least n i t r o g e n is i n c o r p o r a t e d in the b u l k of the dielectric film. A n o x y n i t r i d a t i o n process, in which the n i t r o g e n i n c o r p o r a t i o n into the dielectric film can be controlled a n d where no n i t r o g e n is i n c o r p o r a t e d in the b u l k oxide, e.g. an o x i d a t i o n in a m i x t u r e of O2 a n d N 2 0 , shows m o r e h o m o g e n e o u s QBD distrib u t i o n s with higher QBD(63%) values t h a n a N E O oxide, therefore.
5. Conclusions In s u m m a r y , excellent c o n t r o l of the n i t r o g e n p e a k c o n c e n t r a t i o n at the SiO2/Si interface by a r a p i d t h e r m a l o x y n i t r i d e process using mixtures of o x y g e n a n d n i t r o u s oxide was established. This process p r o v i d e s lower t h e r m a l budget, better QBD uniformity, a n d higher QBD(63%) values t h a n a process which uses R T P t e m p e r a t u r e a l o n e to
c o n t r o l the n i t r o g e n c o n c e n t r a t i o n . T h e b r o a d QBD d i s t r i b u t i o n a n d the low QBD values of the N 2 0 - o x i d e s for electron injection from the gate can be e x p l a i n e d by a m o d e l which includes a nitrogenrich layer at the SiO2/Si interface.
References [1] E.L. Hall, in: Proc. 1st Int. Rapid Thermal Processing Conf., RTP 93, ed. R.B. Fair and B. Lojek, Scottsdale, Arizona, 8-10 September (1993) p. 22. [2] H. Hwang, W. Ting, D.L. Kwong and J. Lee, |EDM Tech. Dig. (1990) 421. [3] W. Ting, G.Q. Lo, J. Ahn, T.Y. Chu and D.L. Kwong, IEEE Electron. Dev. Lett. 12 (1991) 416. I-4] H. Hwang, W. Ting, D.L. Kwong and J. Lee, |EEE Electron. Dev. Lett. 12 (1991) 495. [5] T.Y. Chu, W.T. Ting, J. Ahn and D.L. Kwong, J. Electrochem. Soc. 138 (1991) L13. [6] Y. Okada, Ph.J. Tobin and R.I. Hegde, Appl. Phys. Lett. 61 (1992) 3163. [7] J. Nulman, in: Reduced Thermal Processing for ULSI, ed. R.A. Levy (Plenum, New York, 1991) p. 1. [8] P. Lange, H. Bernt, E. Hartmannsgruber and F. Naumann, J. Electrochem. Soc. 141 (1994) 259. [9] W. Ting, G.Q. Lo, J. Ahn, T.Y. Chu and D.L. Kwong, IEEE Electron. Dev. Lett. 12 (1991) 416. [10] R.C. Weast, M.J. Astle and W.H. Beyer, eds., CRC Handbook of Chemistry and Physics, 67th Ed. (CRC, Boca Raton, FL, 1985) pp. F174~FI79.
ELSEVIER
Journal of Non-Crystalline Solids 187 (1995) 361-364
Section 11. O N O and nitrated oxides
Structural and electrical properties of thin SiO2 layers grown by RTP in a mixture of N 2 0 and 02 A.J. Bauer*, E.P. Burte Fraunhofer-lnstitutfur lntegrierte Schaltungen, Bereich Bauelementechnologie, Schottkystrasse 12, D-91058 Erlangen, Germany
Abstract
Ultrathin ( < 10 nm) dielectric films for application in metal-oxide-semiconductor devices have been fabricated in an 02 : N20 atmosphere using rapid thermal processing. It is shown that with increasing N20 content in the mixtures of N20 and O z, the oxide thickness decreases and the interfacial nitrogen concentration increases. Therefore, the nitrogen concentration at the Si/SiO 2 interface, responsible for improved electrical characteristics, is adjustable by the 02 : NzO ratio. High charge-to-breakdown (QBD)values comparable to oxides processed in pure N20 atmosphere are obtained for electron injection from the Si substrate. For electron injection from the gate, the QBDvalues are considerably higher. For an 02 : NzO ratio of 3 : 1 the highest QBDvalues have been obtained together with a very homogeneous QBDdistribution across the wafer.
1. Introduction
In the near future, the development of highly reliable, very thin SiO 2 films will be of crucial importance for the manufacture of sub-0.25 tam metal-oxide-semiconductor field-effect transistors (MOSFETs). The oxide thickness will decrease from 9 nm for 0.35 ~tm to 6.5 nm for 0.25 ~tm U L S I devices due to device design rules [1]. Using rapid thermal processing (RTP) oxynitride grown in a pure N 2 0 atmosphere on silicon substrates has recently drawn attention to its candidature as a gate dielectric for deep submicron M O S F E T devices. It exhibits high charge-to-breakdown QBo values [2,3] and high hot carrier integrity I-4].
*Corresponding author. Tel: +49-9131 761 308. Telefax: +49-9131 761 390. E-mail: [email protected].
However, thickness and electrical inhomogeneities across the wafer of the dielectric films grown in pure N 2 0 atmosphere are reported [5] and the self-limiting growth of oxynitrides resulting in prolonged processing times increases the thermal budget. In this paper we report on structural and electrical properties of dielectric films processed in mixtures of N 2 0 and 02 by R T P as proposed by [6] and compare them with oxides grown in pure 0 2 and N 2 0 atmospheres. This process has a lower thermal budget due to the enhanced oxidation rate and exhibits a better film thickness homogeneity compared to an oxynitridation process in pure N 2 0 atmosphere. Furthermore, this method provides excellent control of nitrogen peak concentration at the SiO2/Si interface, which is an important parameter determining M O S F E T characteristics [7]. By varying the N 2 0 : O 2 ratio in the gas
0022-3093/95/$09.50 ~, 1995 Elsevier Science B.V. All rights reserved SSDI 0 0 2 2 - 3 0 9 3 ( 9 5 ) 0 0 1 6 4 - 6
362
A.J. Bauer, E.P. B u r t e / J o u r n a l o f N o n - C r y s t a l l i n e Solids 187 (1995) 3 6 1 - 3 6 4
mixture improved QBDdistributions across the wafer and higher QaD values for electron injection from the substrate compared to oxynitride films oxidized in pure N20 atmosphere could be obtained.
3.0
. . . .
I
. . . .
I
. . . .
I
. . . .
I
. . . .
|
. . . .
I
. . . .
2.5
E 2.0 o
& 1.s
2. Experimental procedure The SiO2 and SiOxN r films were grown on 4-6 t2 cm, p-type (1 0 0) Si wafers after a standard wet cleaning procedure by applying the following oxidation and nitridation process steps: (a) oxidation in dry oxygen, (b) oxidation in dry nitrous oxide and (c) oxidation in a mixture of oxygen and nitrous oxide with 0 2 : N 2 0 ratios of 1 : 3, 1 : 1 and 3: 1. The oxidation temperature was 1120°C and the flow rate of the gases during the oxidation was set to 2 slm. After growth of the dielectric, a 500 nm thick polysilicon layer was deposited by low-pressure chemical vapor deposition (LPCVD) at 620°C. The layer was doped with phosphorus at 950°C. The gates of area A = 0.02 nm 2 of MOS capacitors were defined by photolithography and wet etching. The nitrogen depth profiles were determined by secondary ion mass spectroscopy (SIMS) using Cs ÷ bombardment at an energy of 5 keV and CsN ÷ ion detection. The electrical properties of these dielectric films were evaluated by high-frequency (1 MHz) C-V, quasi-static C - V and I - V measurements. The reliability of the dielectric films was evaluated from time-dependent dielectric-breakdown (TDDB) characteristics. The T D D B measurements were performed at negative and positive gate bias on 53 capacitors by applying a constant current density of j = + 200 mA/cm 2. The increase or decrease of the gate voltage observed during the T D D B measurements is related to the buildup of negative or positive charge in the oxide.
3. Results The average oxide thickness obtained was 8.0 _+ 0.5 nm for all the various oxides. The homogeneity of the oxide thickness attained from standard deviation calculations was best with a value of a = 0.1 nm for the O2-oxide and worst (a = 0.6 nm)
"-- 1.0 Z 0.5
0.00.0 ,
, , i .... 0.5
I ....
1.0
i .... 1.5
I .... 2.0
i
2.5
....
i
3,0
.... 3.5
02:N20 Fig. 1. N i t r o g e n p e a k c o n c e n t r a t i o n N of the dielectric films as a function of the 0 2 : N 2 0 ratio. The o x i d a t i o n t e m p e r a t u r e was 1120°C a n d the t o t a l gas flow was 2 slm ( s t a n d a r d liter/minute).
for the N20-oxide. The standard deviation values of the O2:N20-oxides were between the above values in such a way that the value of the O2:NEOoxide with the highest O2:N20 ratio was near the value of the O2-oxide and increased with increasing N20 content in the oxidizing atmosphere. Fig. 1 shows the nitrogen peak concentration N of the various oxynitride films as a function of the O2:N20 ratio during oxidation. The nitrogen concentration increases with increasing N20 content in the oxidizing atmosphere. For all oxides investigated, the density of interfacial traps was as low as D ~ x ~ l . 5 x 101°eV - t cm-2, while the density of fixed interface charges was lower than 0.5 x 10 ~1 cm-2. Fig. 2 shows the dependence of the charge-to-breakdown Qao(63%) values (63% cumulative failure) under constant current stress on the NzO content for both gate polarities. The injection current density was j = + 200 mA/cm 2. If the N20 content in the oxidizing atmosphere is equal to or lower than 50%, then the Qao(63%) values are higher than the values of the O2- and NEO-Oxides for substrate and gate injection. The Qao(63%) values for negative gate polarity are about three times lower than for positive polarity. In Fig. 3 the Weibull plots of the Qaa values of Fig. 2 are presented. A homogeneous Qai~ distribution (for positive and negative gate
363
A.J. Bauer, E.P. Burte / Journal of Non-Crystalline Solids 187 (1995) 361 364 30
I
'
'
'
I
'
•
•
I
=
•
"
I
'
'
'
I
'
'
'
Poly- Oxide p-Si Gate
I
Poly- Oxide p-Si Gate
25 E 20 o Ga
(-) qterface
~10 o
;rface
5 0
I
,
,
=
0
I
,
=
•
20
I
•
•
•
I
4o
,
,
,
I
60
•
,
80
N20 (%)
,
I
'
1 oo
Fig. 2. Dependenceof the QB~63%) values on the N20 content of the oxidizing atmosphere after a constant current injection with a current density of j = + 200mA/cm2 for both gate polarities.
I0
•
=0
•
0
=
0
• O=:N=O/1:3
~
#
• 0=:N20/3:1
~" I v
o
-o N20 = ~
•
~ =
D
Gate+
c::
_.= -2
-3
* ! •
lo*
./'"o
• ~, ,# o = 0 o
•
I
101 Q= (C/cm:')
j=~2OOmA/cm 102
Fig. 3. Weibull plots of charge-to-breakdown in MOS capacitors (area: 0.02 mm2) with different gate dielectrics under both gate polarities.
polarity) across the wafer can be seen only for the Oz-oxides and the 0 2 : N20-oxides which were oxidized in an O2 : N 2 0 atmosphere with an Oa : N 2 0 ratio higher than one. On the other hand, the N z O oxide exhibits above all a broad QBo distribution for electron injection from the gate. The Weibull plots for the O z : N 2 0 ratio of 1:1 are similar to those of the 0 2 : N 2 0 ratio of 3 : 1 and are therefore not shown in Fig. 3.
ric~qlayer
r... ,aye,
Fig. 4. Schematic energy-band diagram with a nitrogen-rich layer at the SiO2/Si interface showing electron injection from poly gate and Si substrate.
4. D i s c u s s i o n
It is well known that an optimized R T P N 2 0 oxidation process can result in high QaD(63%) values [8,9]. This is attributed to nitrogen incorporation into the SiO2/Si interface which strengthens the interface against hot carrier damage. Our results show, too, that nitrogen is incorporated in the bulk of the dielectric film near the SiO2/Si interface (see Fig. 4) after a N / O oxidation at high temperatures (1050°C < T < 1150°C). This nitrogen-rich layer may be responsible for the Qao degradation under negative gate polarity. In this case, the electrons are tunneling from the polysilicon gate into the conduction band of the dielectric film. Here, the electrons are accelerated on account of the applied electric field. F r o m there, they gain sufficient energy to generate traps in the nitrogen-rich layer near the anode by breaking Si-N or O - N bonds, the binding energy of which is lower than the Si-O bond [10]. Hence, if there is a nitrogen-rich layer in the dielectric film near the interface to silicon, more traps than in nitrogen-free oxides are generated resulting in lower QaD(63% ) values. But, if the electrons are injected from the Si substrate, they are tunneling through the nitrogenrich interfacial layer (Fig. 4) and have not yet gained sufficient energy to break N bonds. So, less traps responsible for dielectric breakdown are generated at the anode. Only the beneficial influence of the nitrogen incorporated in the interface becomes
364
A.J. Bauer, E.P. Burte / Journal of Non-Crystalline Solids 187 (1995) 361 364
evident. By that, the b r o a d QBD d i s t r i b u t i o n of the N z O - o x i d e for negative gate p o l a r i t y can be explained. O x i d a t i o n processes in p u r e N z O a t m o sphere show, preferentially in the center of the wafer, a high n i t r o g e n p e a k c o n c e n t r a t i o n at the SiO2/Si interface a n d a low one at the o u t e r a r e a of the wafer. C o n s e q u e n t l y , high QBD values will be seen, where least n i t r o g e n is i n c o r p o r a t e d in the b u l k of the dielectric film. A n o x y n i t r i d a t i o n process, in which the n i t r o g e n i n c o r p o r a t i o n into the dielectric film can be controlled a n d where no n i t r o g e n is i n c o r p o r a t e d in the b u l k oxide, e.g. an o x i d a t i o n in a m i x t u r e of O2 a n d N 2 0 , shows m o r e h o m o g e n e o u s QBD distrib u t i o n s with higher QBD(63%) values t h a n a N E O oxide, therefore.
5. Conclusions In s u m m a r y , excellent c o n t r o l of the n i t r o g e n p e a k c o n c e n t r a t i o n at the SiO2/Si interface by a r a p i d t h e r m a l o x y n i t r i d e process using mixtures of o x y g e n a n d n i t r o u s oxide was established. This process p r o v i d e s lower t h e r m a l budget, better QBD uniformity, a n d higher QBD(63%) values t h a n a process which uses R T P t e m p e r a t u r e a l o n e to
c o n t r o l the n i t r o g e n c o n c e n t r a t i o n . T h e b r o a d QBD d i s t r i b u t i o n a n d the low QBD values of the N 2 0 - o x i d e s for electron injection from the gate can be e x p l a i n e d by a m o d e l which includes a nitrogenrich layer at the SiO2/Si interface.
References [1] E.L. Hall, in: Proc. 1st Int. Rapid Thermal Processing Conf., RTP 93, ed. R.B. Fair and B. Lojek, Scottsdale, Arizona, 8-10 September (1993) p. 22. [2] H. Hwang, W. Ting, D.L. Kwong and J. Lee, |EDM Tech. Dig. (1990) 421. [3] W. Ting, G.Q. Lo, J. Ahn, T.Y. Chu and D.L. Kwong, IEEE Electron. Dev. Lett. 12 (1991) 416. I-4] H. Hwang, W. Ting, D.L. Kwong and J. Lee, |EEE Electron. Dev. Lett. 12 (1991) 495. [5] T.Y. Chu, W.T. Ting, J. Ahn and D.L. Kwong, J. Electrochem. Soc. 138 (1991) L13. [6] Y. Okada, Ph.J. Tobin and R.I. Hegde, Appl. Phys. Lett. 61 (1992) 3163. [7] J. Nulman, in: Reduced Thermal Processing for ULSI, ed. R.A. Levy (Plenum, New York, 1991) p. 1. [8] P. Lange, H. Bernt, E. Hartmannsgruber and F. Naumann, J. Electrochem. Soc. 141 (1994) 259. [9] W. Ting, G.Q. Lo, J. Ahn, T.Y. Chu and D.L. Kwong, IEEE Electron. Dev. Lett. 12 (1991) 416. [10] R.C. Weast, M.J. Astle and W.H. Beyer, eds., CRC Handbook of Chemistry and Physics, 67th Ed. (CRC, Boca Raton, FL, 1985) pp. F174~FI79.