High-performance TaN/HfSiON/Si metal-oxide-semiconductor structures prepared byNH 3 post-deposition annealMohammad Shahariar Akbar, S. Gopalan, H.-J. Cho, K. Onishi, R. Choi, R. Nieh, C. S. Kang, Y. H. Kim, J. Han,

S. Krishnan, and Jack C. Lee Citation: Applied Physics Letters 82, 1757 (2003); doi: 10.1063/1.1544062 View online: http://dx.doi.org/10.1063/1.1544062 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/82/11?ver=pdfcov Published by the AIP Publishing

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APPLIED PHYSICS LETTERS VOLUME 82, NUMBER 11 17 MARCH 2003

This article is

High-performance TaN ÕHfSiON ÕSi metal-oxide-semiconductor structuresprepared by NH 3 post-deposition anneal

Mohammad Shahariar Akbar,a) S. Gopalan, H.-J. Cho, K. Onishi, R. Choi, R. Nieh,C. S. Kang, Y. H. Kim, J. Han, S. Krishnan, and Jack C. LeeR9950, Microelectronics Research Center, University of Texas at Austin, 10100 Burnet Road,Austin, Texas 78758

~Received 25 October 2002; accepted 16 December 2002!

Electrical and chemical characteristics of metal-oxide semiconductor field-effect transistors~MOSFETs! prepared by low-thermal-budget~;600 °C! NH3 post-deposition annealing of HfSiONgate dielectric have been investigated. Compared to control Hf-silicate, HfSiON showed excellentthickness scalability, low leakage current density~J!, and superior thermal stability. With properannealing-time optimization, effective oxide thickness as low as 9.2 Å withJ,100 mA/cm2 at gatevoltageVg521.5 V has been achieved.C–V hysteresis of HfSiON MOSFET was found to besmall ~,20 mV!. Unlike NH3 surface nitridation (NH3 pre-treatment prior to Hf-silicatedeposition!, no degradation inGm ~transconductance!, I d–Vg ~drain current–gate voltage!, orI d–Vd ~drain current–drain voltage! characteristics has been observed. ©2003 American Instituteof Physics. @DOI: 10.1063/1.1544062#

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As an alternative gate dielectric, Hf-silicate has draconsiderable attention due to the chemical similarity ofSi/Hf-silicate interface to the Si/SiO2 interface, reasonablestability against crystallization, sufficient immunity to intefacial oxide growth, and low hysteresis.1,2 Recently, nitrogenincorporation using processing techniques, such as NH3 sur-face nitridation (NH3 pre-treatment prior to dielectricdeposition!,3,4 top plasma nitridation of the dielectric,5

plasma nitridation throughout the dielectric6,7 have shownimproved thermal stability, reduced leakage current forsame equivalent oxide thickness~EOT!, improved reliability,and increased crystallization temperature. Among these ndation techniques, NH3 surface nitridation has the trade-obetween improved scalability, lower leakage, higher bredown fields, and degraded metal-oxide-semiconductor fieffect-transistor ~MOSFET! performance ~for example,larger hysteresis and interface related degradation!.4 In thisletter, HfSiON prepared by NH3 post-deposition annea~PDA! has been investigated.

The MOSFET process flow started with cleaning of tactive patterned wafers~p-type! in diluted HF solution. Af-terwards, Hf and Si were deposited via dc magnetronsputtering~40 mTorr, Ar, room temperature!. Film thickness~;40 Å! was measured by ellipsometer. For the control aNH3-annealed samples, the deposited films were annealea rapid thermal anneal~RTA! chamber at 600 °C in N2 andNH3 annealing, respectively. Residual oxygen in the anning chamber orex situatmospheric exposure has been attruted to the proper oxidation of the films in both cases. Toxidation process was reproducible. TaN gate was deposusing dc sputtering (N21Ar, 10 mTorr, room temperature!for a thickness of;2000 Å. After gate patterning, reactivion etching in Cl2 /He mixture was used to pattern the Tagate material. Phosphorous was implanted to dopesource and drain~S/D! regions (energy550 KeV, dose55

a!Electronic mail: shahriar@mail.utexas.edu

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31015 cm22). S/D dopant activation was done by RTA iN2 ambient at 950 °C for 30 s. Sputtered aluminum was ufor both interconnect and back-side metallization. The fisintering was done at 450 °C in forming gas for 20 min.

Electrical characterizations were performed usiHP4194 impedance/gain phase analyzer and HP4156A sconductor parameter analyzer. EOT was extracted fromcumulation capacitance measured at 1 MHz, after accounfor quantum mechanical effects. The film composition achemical bonding states were determined by x-ray phoelectron spectroscopy~XPS!.

Figure 1 shows Hf 4f and N 1s spectra for samples annealed in N2 and NH3 ambient. As shown, Hf peaks for thNH3-annealed sample was shifted to lower binding enewith respect to that of the control sample. The shift increawith longer annealing time. The same was true for the Sipspectra~data not shown!, which was also observed in reactively sputtered HfSiON film.8 For the case of HfOxNy , ni-trogen incorporation results in lower shift of peaks in Hf 4fspectra from HfO2 to HfOxNy film.7,9 Moreover, no N 1speak for the control sample was observed, whereas a cpeak was observed for NH3 annealing, thus confirming thepresence of nitrogen in the film.

Figure 2 shows theC–V and J–V ~leakage currentdensity–voltage! for control and NH3 annealed ~20-s!samples. As shown, for the same EOT@Fig. 2~a!#, leakagewas lower for NH3 PDA sample@Fig. 2~b!#. For example,leakage currents atVg521.5 V were 33 and 7 mA/cm2 forcontrol and NH3-annealed samples, respectively. It has bereported that the tunneling probability is qualitatively relatto the area of the tunneling barrier associated with the oxphysical thickness and the oxide barrier height.10 The lowerleakage current for NH3-annealed Hf-silicate film indicatedthat this nitridation resulted in a slightly larger physicthickness of the bulk HfSiON since the nitrogen blocked tdiffusion of oxygen and reduced the growth of the interfac

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1758 Appl. Phys. Lett., Vol. 82, No. 11, 17 March 2003 Akbar et al.

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layer. Thus, tunneling current was suppressed while mtaining the same gate capacitance.

One of the most promising attributes of NH3 annealingis the possibility of further EOT scaling. A thin EOT of 9.2has been obtained atVg521.5 V with J,100 mA/cm2.This EOT value is among the lowest EOT values of Hsilicate reported in the literature. TheC–V characteristics ofthis sample are shown in the inset of Fig. 2~a!. The low EOThas been attributed to enhanced immunity to oxygen dision into the film.

EOT andJ values were measured at different fabricatisteps@after capacitor, low-temperature oxidation~LTO! andtransistor#. As shown in Fig. 3~a!, both DEOT ~differencewith respect to EOT value immediately after metal-oxidsemiconductor capacitor fabrication! and J were lower forNH3-annealed samples as compared to control samples.confirms higher thermal stability for NH3-annealed samplesAs shown in Fig. 3~b!, the slightly largerC–V hysteresis ofNH3-annealed metal-oxide-semiconductor capacitor~MOS-CAP! as compared to control sample could be suppressignificantly even just after LTO at;520 °C for 45 min. Thisreduction in hysteresis was attributed to the reduction o

FIG. 1. XPS peaks of~a! Hf 4 f spectra and~b! N 1s spectra for controlHf-silicate and HfSiON gate dielectric prepared by 40-s N2 and differentduration of NH3 post-deposition annealing of as-deposited Hf-silicate. Sin Hf 4 f peak to the lower binding energy indicates higher nitrogen incporation with longer time.

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atoms and H-related species, such as Si–H bonds during45-min LTO deposition.11

Figure 4 shows theI d–Vg ~drain current–gate voltage!characteristics of MOSFET. As shown, NH3 post-depositionannealing did not degrade any of the MOSFET charactetics, rather, it demonstrated slight improvement. The sthreshold swings obtained were 84 and 82 mV/dec for ctrol and NH3-annealed samples, respectively. It shouldmentioned that NH3 surface nitridation7 and proposed NH3PDA are nitridation techniques in Hf-silicate films, one at tsurface and other throughout the film, respectively. Bhave the positive attributes of EOT reduction, improved thmal scalability, and leakage current reduction. However,bottlenecks associated with the interface related degradaresulted from NH3 surface nitridation overshadow its benefits.

In summary, by subjecting as deposited Hf-silicate filmto a NH3 PDA, excellent electrical characteristics, suchEOT scalability, leakage current density reduction, supethermal stability, and negligible hysteresis, have beentained. This annealing remedies many of the bottleneckssociated with hafnium silicate dielectric. Unlike NH3 sur-facenitridation, the proposed process does not seem

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FIG. 2. ~a! Gate capacitance and~b! leakage current density versus gavoltages for control and NH3-annealed sample annealed at 600 °C. Inset~a! is theC–V curve for lowest EOT~;9.2 Å! achieved at the same temperature.

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1759Appl. Phys. Lett., Vol. 82, No. 11, 17 March 2003 Akbar et al.

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degrade the interface properties. Therefore, HfSiON by N3

post-deposition anneal might be a promising alternativefuture ultrascaled MOS gate dielectric.

This work was partially supported by the Texas A

FIG. 3. ~a! Thermal stability~leakage current density and change of EOTfabrication steps! and ~b! hysteresis for control and NH3-annealed samplesat different steps of fabrication. MOSCAP annealing temperature600 °C.

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vanced Technology Program, SRC/SEMATECH CenFront End Process~FEP!, Cypress Semiconductor, Intel Coporation and Matsushita Electronics.

1G. D. Wilk, R. M. Wallace, and J. M. Anthony, J. Appl. Phys.87, 484~2000!.

2S. Gopalan, K. Onishi, R. Nieh, C. S. Kang, R. Choi, H.-J. Cho, S. Krinan, and J. C. Lee, Appl. Phys. Lett.80, 4416~2002!.

3R. Choi, C. S. Kang, B. Hun Lee, K. Onishi, R. Nieh, S. Gopalan,Dharmarajan, and J. C. Lee, Symp. VLSI Tech. Dig.2001, 15.

4S. Gopalan, R. Choi, K. Onishi, R. Nieh, C. S. Kang, H.-J. Cho, S. Krinan, and J. C. Lee, DRC Conference Digest2002, 195.

5H.-J. Cho, C. S. Kang, K. Onishi, S. Gopalan, R. Nieh, R. Choi, E. Dhmarajan, and J. C. Lee, Tech. Dig. - Int. Electron Devices Meet.2001, 655~2001!.

6R. Nieh, S. Krishnan, H.-J. Cho, C. S. Kang, S. Gopalan, K. Onishi,Choi, and J. C. Lee, Symp. VLSI Tech. Dig.2002, 186.

7C. S. Kang, H.-J. Cho, K. Onishi, R. Choi, R. Nieh, S. Gopalan, S. Krinan, and J. C. Lee, Symp. VLSI Tech. Dig.2002, 146.

8M. R. Visokay, J. J. Chambers, A. L. P. Rotondaro, A. Shaneware, anColombo, Appl. Phys. Lett.80, 3183~2002!.

9C. S. Kang, H.-J. Cho, K. Onishi, R. Choi, Y. H. Kim, R. Nieh, J. Han,Krishnan, A. Shahriar, and J. C. Lee, Tech. Dig.–Int. Electron DeviMeet.2002, 856.

10Y. Shi, T. P. Ma, S. Prasad, and S. Dhanda, IEEE Trans. Electron Dev45, 2355~1998!.

11C. H. Chen, Y. K. Fang, C. W. Yang, Y. S. Tsair, M. F. Wang, L. G. YaS. C. Chen, C. H. Yu, and M. S. Liang, Solid-State Electron.46, 539~2002!.

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FIG. 4. I d–Vg andGm–Vg for control and NH3-annealed sample. No degradation of drain current and transconductance has been observeNH3-annealed device.

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