12.4
`
`Low-Leakage and Highly-Reliable 1.5 nm SiON Gate-Dielectric
`Using Radical Oxynitridation for Sub-0.1 um CMOS
`M. Togo, K. Watanabe, T. Yamamoto, N. Ikarashi, K. Shiba, T. Tatsumi, H. Ono, and T. Mogami
`Silicon Systems Research Labs., NEC Corporation
`1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198, Japan
`
`ABSTRACT
`
`We have developed a low-leakage and highly-reliable
`1.5 nm SiON gate-dielectric, by using radical oxynitridation.
`In this development, we
`introduce a new method for
`determining ultra-thin SiON gate-dielectric thickness based
`on the threshold voltage dependence on the substrate bias in
`MOSFETs.
`It was found that radical oxidation followed by
`radical nitridation provides 1.5 nm thick SiON in which
`leakage current is two orders of magnitude Tess than that of
`1.5 nm thick SiO, without degrading device performance.
`The 1.5 nm thick SiON was also found to be ten times more
`reliable than 1.5 nm thick SiO,,.
`INTRODUCTION
`
`A low-leakage and highly-reliable gate-dielectric is
`essential for high-performance sub-0.1 um CMOSFETs[1].
`Oxynitridation is one of the key techniques to achieve low-
`leakage gate-dielectrics [2]. The radial process can be also
`useful to improve SiO, quality [3]. We have investigated 1.5
`nm SiON gate-dielectrics by using radical oxynitridation.
`In
`this investigation, we will
`introduce a new method of gate-
`dielectric thickness measurement, because it is important to
`measureelectrical oxide equivalent thickness (Tox<q).
`THICKNESS DETERMINATION
`
`Large gate leakage currentofthe ultra-thin SiO, disturbs
`thickness measurement by using C-V characteristics (Fig. 1).
`A newly proposed thickness measurement method is based on
`the general relationship between the threshold voltage (V1)
`and the substrate bias voltage (Vg).
`In this method, the gate
`leakage current does not affect Vp, of a transistor (Fig. 2).
`Fig. 3 shows Vy; dependence on Vz, which is expressed as
`the following general equation:
`(1)
`Vai = ((2€€09Nen)“/Cox)( Vt 2bp)? + Vent20,
`where Ng, is the channel concentration and Cox is the gate-
`dielectric capacitance where the oxide electrical
`thickness
`(Tox.ee)
`1S a Component part.
`In Fig. 3,
`the line slope
`consists of N,, and Tox... and the y-intercept indicates Vr,.
`To determine Tox, of the ultra-thin SiO,, we fabricated a 6
`nm thick SiO, gate-dielectric NMOSFET using the same
`fabrication process as that used to make ultra-thin SiO, gate-
`dielectric NMOSFETs.
`First, we obtained Cox by measuring
`the C-V curve of the 6 nm thick SiO,, and obtained accurate
`N., by using (1) and the Coy. Next, we calculated the ultra-
`thin SiO,
`thickness (Tox...) by using (1) and Ny. Tox
`consists of an oxide thickness
`(Tox.,) and a parasitic
`thickness
`(Tox,para)s which is composed of poly-Si gate
`depletion and inversion Jayer quantization.
`Tox.para Was
`extracted by using the C-V curve for 6 nm-thick (“Toxph,
`physica} thickness, = Tox.,) gate SiO, shown in Fig.
`1.
`Finally, we obtained the electrical oxide equivalent thickness
`(Tox-eq) of the ultra-thin SiO, by using Tox... and Tox nara (Tox.
`eq = Tox-ex - Tox-para) Fig. 4 shows that obtained Tox
`almost the same as measured Toxphy in SiO,. Thus thisSfim
`for
`thickness determination method is a suitable means
`obtaining Tox, of not only ultra-thin SiO,, but also SiON
`with heavy nitrogen concentration and other types of gate-
`dielectric films having high ¢ and a stacked structure.
`RADICAL OXYNITRIDATION
`
`We used radical oxygen and nitrogen from an electron-
`cyclotron resonance (ECR) plasmato form an ultra-thin SiON
`
`116
`
`0-7803-6305-4/00/$10.00 © 2000 IEEE
`
`film in an ultra-high vacuum (UHV) system where the base
`pressure was less than 1*10° Torr to produce a clean Si
`surface [4]. Four types of radical processes were tested as
`ways
`to form the films:
`radical oxidation (O*),
`radical
`nitridation after radical oxidation (O*4N*), radical oxidation
`and nitridation simultaneously (O*+N*) and radical oxidation
`after radical nitridation (N*-O*).
`Fig. 5 shows SIMS
`profiles of nitrogen in a gate oxide fabricated by the radical
`process [5]. Radical oxidation and nitridation enables us to
`control the nitrogen profile in an ultra-thin gate-ox ynitride.
`NITROGEN PROFILE ENGINEERING
`
`Fig. 6 shows Ip, Ig-Vg characteristics of 1.5 nm thick
`gate-dielectric NMOSFETs using O* and O* 4N*. The use
`of 7% nitrogen decreased gate leakage current by two orders
`of magnitude without decreasing the drain current.
`Fig. 7
`shows the gate leakage current of SION and SiO, formed by
`the radical processes and the conventional thermal process at
`the same bias. The leakage current of SiON is much lower
`than that of SiO,. The SiON film formed by the O*-N*
`process with 7% nitrogen have lowest Icakage current.
`Fig.
`8 shows cross-sectional TEM photographs of the SION whose
`gate leakage current is shown in Fig. 7. Table 1 compares
`the dielectric properties obtained with different
`radical
`processes. Nitrogen concentration in the SION film formed
`by O*-—4N* is lower than that in the SiON film formed by
`N*-—50*. However, the dielectric constant of the SiON film
`formed by O*—N* is larger than that of one formed by
`N*—0*.
`Fig. 9 and 10 show that
`the drivability of the
`NMOSFETformed by the O*-N* process with 7% nitrogen
`is comparable to that formed by O* at the supply voltage
`regime.
`Fig.
`11
`shows Typ distribution under constant
`voltage stress.
`In Fig. 11(a), the 1.5 nm thick SiON formed
`by the O* 5N* process was not broken within 10°s, which is
`ten times morereliable than 1.5 nm thick SiO, formed by the
`O* process.
`Furthermore, as the figure (b) indicates, a 1.5
`nm-thick (=Tox.eq) SION formed by the O*_4N* process with
`7% nitrogen is more reliable than a 2.3 nm-thick (=Toxpny)
`SiO, formed by thermal oxidation.
`Fig. 12 shows that the
`chemical shift of N 1s orbital for SION films depends on the
`radical process. These results indicate that the nitrogen state
`depends on the nitrogen profile in SiON and mayaffect the
`dielectric property and electrical reliability.
`CONCLUSIONS
`
`By using radical oxynitridation, we have successfully
`achieved a low-leakage and highly-reliable 1.5 nm SiON with
`no degradation of device performance.
`This 1.5 nm thick
`SiON has two orders of magnitude less leakage current than
`1.5 nm thick SiO, and shows ten times morereliable than 1.5
`nm thick SiO, We have developed a new thickness
`determination method that is useful for measuring ultra-thin
`SIONthickness.
`
`ACKNOWLEDGMENTS
`
`The authors thank M. Fukuma, T. Kunio, T. Tashiro, and
`Y. Miura for their encouragement and helpful discussions.
`REFERENCES
`(1] H.S. Momoseet al., IEDM Tech. Dig., p. 819, 1999.
`(2) H. Yanget al., IEDM Tech. Dig., p. 245, 1999.
`[3] M. Nagamineet al., IEDM Tech. Dig., p. 593, 1998.
`[4] K. Watanabe et a]., MRS 1999 Spring Meeting Abstract, p. 268, 1999.
`[5] K. Watanabe et al., MRS 1999 Fall Meeting Abstract, 1999.
`
`2000 Symposium on VLSI Technology Digest of Technical Papers
`TSMC 1316
`
`TSMC 1316
`
`
`
`Low-Leakage and Highly-Reliable 1.5 nm SiON Gate-Dielectric
`Using Radical Oxynitridation for Sub-0.1 um CMOS
`M. Togo, K. Watanabe, T. Yamamoto, N. Ikarashi, K. Shiba, T. Tatsumi, H. Ono, and T. Mogami
`Silicon Systems Research Labs., NEC Corporation
`1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198, Japan
`
`ABSTRACT
`
`We have developed a low-leakage and highly-reliable
`1.5 nm SiON gate-dielectric, by using radical oxynitridation.
`In this development, we
`introduce a new method for
`determining ultra-thin SiON gate-dielectric thickness based
`on the threshold voltage dependence on the substrate bias in
`MOSFETs.
`It was found that radical oxidation followed by
`radical nitridation provides 1.5 nm thick SiON in which
`leakage current is two orders of magnitude Tess than that of
`1.5 nm thick SiO, without degrading device performance.
`The 1.5 nm thick SiON was also found to be ten times more
`reliable than 1.5 nm thick SiO,,.
`INTRODUCTION
`
`A low-leakage and highly-reliable gate-dielectric is
`essential for high-performance sub-0.1 um CMOSFETs[1].
`Oxynitridation is one of the key techniques to achieve low-
`leakage gate-dielectrics [2]. The radial process can be also
`useful to improve SiO, quality [3]. We have investigated 1.5
`nm SiON gate-dielectrics by using radical oxynitridation.
`In
`this investigation, we will
`introduce a new method of gate-
`dielectric thickness measurement, because it is important to
`measureelectrical oxide equivalent thickness (Tox<q).
`THICKNESS DETERMINATION
`
`Large gate leakage currentofthe ultra-thin SiO, disturbs
`thickness measurement by using C-V characteristics (Fig. 1).
`A newly proposed thickness measurement method is based on
`the general relationship between the threshold voltage (V1)
`and the substrate bias voltage (Vg).
`In this method, the gate
`leakage current does not affect Vp, of a transistor (Fig. 2).
`Fig. 3 shows Vy; dependence on Vz, which is expressed as
`the following general equation:
`(1)
`Vai = ((2€€09Nen)“/Cox)( Vt 2bp)? + Vent20,
`where Ng, is the channel concentration and Cox is the gate-
`dielectric capacitance where the oxide electrical
`thickness
`(Tox.ee)
`1S a Component part.
`In Fig. 3,
`the line slope
`consists of N,, and Tox... and the y-intercept indicates Vr,.
`To determine Tox, of the ultra-thin SiO,, we fabricated a 6
`nm thick SiO, gate-dielectric NMOSFET using the same
`fabrication process as that used to make ultra-thin SiO, gate-
`dielectric NMOSFETs.
`First, we obtained Cox by measuring
`the C-V curve of the 6 nm thick SiO,, and obtained accurate
`N., by using (1) and the Coy. Next, we calculated the ultra-
`thin SiO,
`thickness (Tox...) by using (1) and Ny. Tox
`consists of an oxide thickness
`(Tox.,) and a parasitic
`thickness
`(Tox,para)s which is composed of poly-Si gate
`depletion and inversion Jayer quantization.
`Tox.para Was
`extracted by using the C-V curve for 6 nm-thick (“Toxph,
`physica} thickness, = Tox.,) gate SiO, shown in Fig.
`1.
`Finally, we obtained the electrical oxide equivalent thickness
`(Tox-eq) of the ultra-thin SiO, by using Tox... and Tox nara (Tox.
`eq = Tox-ex - Tox-para) Fig. 4 shows that obtained Tox
`almost the same as measured Toxphy in SiO,. Thus thisSfim
`for
`thickness determination method is a suitable means
`obtaining Tox, of not only ultra-thin SiO,, but also SiON
`with heavy nitrogen concentration and other types of gate-
`dielectric films having high ¢ and a stacked structure.
`RADICAL OXYNITRIDATION
`
`We used radical oxygen and nitrogen from an electron-
`cyclotron resonance (ECR) plasmato form an ultra-thin SiON
`
`116
`
`0-7803-6305-4/00/$10.00 © 2000 IEEE
`
`film in an ultra-high vacuum (UHV) system where the base
`pressure was less than 1*10° Torr to produce a clean Si
`surface [4]. Four types of radical processes were tested as
`ways
`to form the films:
`radical oxidation (O*),
`radical
`nitridation after radical oxidation (O*4N*), radical oxidation
`and nitridation simultaneously (O*+N*) and radical oxidation
`after radical nitridation (N*-O*).
`Fig. 5 shows SIMS
`profiles of nitrogen in a gate oxide fabricated by the radical
`process [5]. Radical oxidation and nitridation enables us to
`control the nitrogen profile in an ultra-thin gate-ox ynitride.
`NITROGEN PROFILE ENGINEERING
`
`Fig. 6 shows Ip, Ig-Vg characteristics of 1.5 nm thick
`gate-dielectric NMOSFETs using O* and O* 4N*. The use
`of 7% nitrogen decreased gate leakage current by two orders
`of magnitude without decreasing the drain current.
`Fig. 7
`shows the gate leakage current of SION and SiO, formed by
`the radical processes and the conventional thermal process at
`the same bias. The leakage current of SiON is much lower
`than that of SiO,. The SiON film formed by the O*-N*
`process with 7% nitrogen have lowest Icakage current.
`Fig.
`8 shows cross-sectional TEM photographs of the SION whose
`gate leakage current is shown in Fig. 7. Table 1 compares
`the dielectric properties obtained with different
`radical
`processes. Nitrogen concentration in the SION film formed
`by O*-—4N* is lower than that in the SiON film formed by
`N*-—50*. However, the dielectric constant of the SiON film
`formed by O*—N* is larger than that of one formed by
`N*—0*.
`Fig. 9 and 10 show that
`the drivability of the
`NMOSFETformed by the O*-N* process with 7% nitrogen
`is comparable to that formed by O* at the supply voltage
`regime.
`Fig.
`11
`shows Typ distribution under constant
`voltage stress.
`In Fig. 11(a), the 1.5 nm thick SiON formed
`by the O* 5N* process was not broken within 10°s, which is
`ten times morereliable than 1.5 nm thick SiO, formed by the
`O* process.
`Furthermore, as the figure (b) indicates, a 1.5
`nm-thick (=Tox.eq) SION formed by the O*_4N* process with
`7% nitrogen is more reliable than a 2.3 nm-thick (=Toxpny)
`SiO, formed by thermal oxidation.
`Fig. 12 shows that the
`chemical shift of N 1s orbital for SION films depends on the
`radical process. These results indicate that the nitrogen state
`depends on the nitrogen profile in SiON and mayaffect the
`dielectric property and electrical reliability.
`CONCLUSIONS
`
`By using radical oxynitridation, we have successfully
`achieved a low-leakage and highly-reliable 1.5 nm SiON with
`no degradation of device performance.
`This 1.5 nm thick
`SiON has two orders of magnitude less leakage current than
`1.5 nm thick SiO, and shows ten times morereliable than 1.5
`nm thick SiO, We have developed a new thickness
`determination method that is useful for measuring ultra-thin
`SIONthickness.
`
`ACKNOWLEDGMENTS
`
`The authors thank M. Fukuma, T. Kunio, T. Tashiro, and
`Y. Miura for their encouragement and helpful discussions.
`REFERENCES
`(1] H.S. Momoseet al., IEDM Tech. Dig., p. 819, 1999.
`(2) H. Yanget al., IEDM Tech. Dig., p. 245, 1999.
`[3] M. Nagamineet al., IEDM Tech. Dig., p. 593, 1998.
`[4] K. Watanabe et a]., MRS 1999 Spring Meeting Abstract, p. 268, 1999.
`[5] K. Watanabe et al., MRS 1999 Fall Meeting Abstract, 1999.
`
`2000 Symposium on VLSI Technology Digest of Technical Papers
`TSMC 1316
`
`TSMC 1316
`
`
`
`
`
`ObtainedTox-0q(nm)
`
`“ “STEM & Ellipsometry 0
`
`6
`4
`2
`Measured Tox.phy(mm)
`
`s
`
`Fig. 4 Tp,.,, obtained by Viy
`dependence on substrate bias
`and Toxsy measured
`by
`TEM andellipsometry. Toy.<,
`= Tox-ete ~ Tox-para
`
`‘Universal Mobilit
`_ O'Nt
`5. 7% (XPS)
`
`O*+N*
`
`wa
`Tox-eqn1-9 nm
`
`
`
`
`
`NitrogenConcentration(atomic%)
`
`Qo
`
`=7%
`
`Toxequ1-5 nm
`
`_ONitr
`
`N*
`en Conc.
`PS)
`
`5
`Depth (nm)
`
`0
`
`0.5
`Ve-Vin (V)
`
`1
`
`1.5
`
`
`
`=0.9/0.1V
`NO-Dry-0
`
`1.5
`Tox-eq (nm)
`
`
`
`
`
`
`
`Capacitance(pF/um’)
`
`
`
`1
`
`Vo (Vv)
`
`NMOS L,=0.8 wm
`
`Vp=1V Vp-0~-3V
`
`0.5
`
`1
`Va (V)
`
`18
`
`1.2
`
`NMOS
`L,=0.8 wm
`
`Tox-pny=8.0 nny
`
`Vy=1V¥
`
`2
`(Vo+2¢,)"(v"”)
`
`1 C-V curves of thin and
`Fig.
`thick gate oxide dielectrics.
`
`Fig. 2 I,, [g-V, characteristics
`as a parameter of substrate
`bias for NMOSFEPwith thin
`
`oxide gate dielectric.
`
`Fig. 3 Vj, as a function of
`substrate bias for NMOSFETs
`with thin and thick oxide gate
`dielectrics.
`
`Een (MV/cm)
`Fig. § SIMS profiles
`Fig. 9 Comparison of Lees for
`Fig. 7 Gate leakage current vs.
`Fig. 6 1, 1,-V, characteristics of
`SION and SiO, using radical
`
`
`
`of nitrogen in SiON using__radicalNMOSFETs Toxeq Of SION and SiO, using
`processes.
`using radical processes
`processes
`(O*
`and O*—N*),
`radical
`processes
`and
`using
`
`
`(O*5N*, OF +N*, and XPSspectra intensity determines|conventional thermal processes
`
`N*¥->0*),.
`nitrogen concentration.
`(Dry-O, Wet-O and NO—Dry-O).
`
`Table 1 Comparison of dielectric properties.
`
`Radical
`
`|Nitrogen|Physical/Electrical|Dielectric
`
` SEUa
`
`8
`Cross-sectional
`TEM
`ay
`Fig.
`oo[7%[2sisames_|
`», photographs.
`hi (a) Radical nitridation after radical
`INO"[12%_[asionm[sa__|
`| oxidation. N=7%, Toy.,=1.5 nm.
`%§ (b) Radical oxidation after radical
`* nitridation, N=12%, Tox..4= 1.9 nm.
`“=== (c) Radical oxidation. To,..=1.5 nm.
`
`
`jor[ow[rsisnm[30
`
`
`
` 2
`
`Vo-Virn=1V, Vp=1.2V
`NMOS Tox.og=1.5 nm
`
`O*SN" 7%
`Tap» 10°s
`
`=
`=
`f ,
`Fr
`x
`~_
`E
`a
`—
`a
`wy
`
`Tox-eq=1-9 nm
`
`0
`
`0.6
`
`0.4
`0.2
`Le (4m)
`Fig. 10 Comparison ofI, for SION
`and SiO, using radical processes.
`
`_0
`ira
`=
`Cc
`z
`£2
`
`4
`
`107
`
`eee®
`On+Nt
`od
`
`NO—Dry-0
`
`107
`
`10?
`
`ton
`T who
`a
`4
`23am=1.5nm
`10°
`10°
`10°
`Tap (sec)
`Teo (sec)
`Fig. 11 Tap distributions for SiON and SiO, using radical processes
`and conventional thermal oxidation.
`SION using
`(a) Same Tpy..4.
`O*—>N* with 7% nitrogen was not broken within 10°s at -2.4V+Ve,.
`(b) Same Tox.pny:
`
`_
`5
`2
`&
`2
`2
`s
`
`=
`
`395
`400
`405
`Binding Energy (eV)
`Fig. 12 XPS spectra of N
`1s orbital for SION using
`radical processes (N*¥-O*
`and O*>N*).
`
`2000 Symposium on VLSI Technology Digest of Technical Papers
`
`117
`
`
Accessing this document will incur an additional charge of $.
After purchase, you can access this document again without charge.
Accept $ Charge
Still Working On It
This document is taking longer than usual to download. This can happen if we need to contact the court directly to obtain the document and their servers are running slowly.
Give it another minute or two to complete, and then try the refresh button.
A few More Minutes ... Still Working
It can take up to 5 minutes for us to download a document if the court servers are running slowly.
Thank you for your continued patience.
This document could not be displayed.
We could not find this document within its docket. Please go back to the docket page and check the link. If that does not work, go back to the docket and refresh it to pull the newest information.
Your account does not support viewing this document.
You need a Paid Account to view this document. Click here to change your account type.
Your account does not support viewing this document.
Set your membership
status to view this document.
With a Docket Alarm membership, you'll
get a whole lot more, including:
- Up-to-date information for this case.
- Email alerts whenever there is an update.
- Full text search for other cases.
- Get email alerts whenever a new case matches your search.
One Moment Please
The filing “” is large (MB) and is being downloaded.
Please refresh this page in a few minutes to see if the filing has been downloaded. The filing will also be emailed to you when the download completes.
Your document is on its way!
If you do not receive the document in five minutes, contact support at support@docketalarm.com.
Sealed Document
We are unable to display this document, it may be under a court ordered seal.
If you have proper credentials to access the file, you may proceed directly to the court's system using your government issued username and password.
Access Government Site
