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Spontaneous N incorporationinto the Si(100) surface

J. W. Kim, Y. D. Chung, C. N. Hwang, H. W. Yeom* (Yonsei University)K. J. Kong, D. Y. Ahn, B. D. Yu (University of Seoul)

Y. H. Ha, D. W. Moon (Korea Research Institute of Standards & Science)

◎ Introduction - Si oxynitride as gate dielectrics - Review of previous results◎ Experiments - MEIS & PLS U7 experimental chamber◎ Results and Discussion - N 1s core-level spectra - MEIS result of NO/Si(100) - Stable geometry for N-incorporation by calculation◎ Conclusion

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Importance of N incorporation in silicon (oxy)nitride

• Application to gate dielectrics• Initial formation of Silicon nitride and N-rich layer at SiOxNy/Si interface

Gusev, IBM J. Res. Devel. (1999)

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* Complete dissociative adsorption of NO at RT and formation of Nitride at elevated temperatures

Previous Results of NO, NH3/Si(100)

Si

N N O

Si

Si Si

NHH

H

H

O

NH H

Si

H NH H

NH

N

anneal

Questions about the dissociated N species : Chemical configuration, depth population, energetically favorable geometries

* Sucessive dissociation of N-H as temperature goes up

RT

RT

500~700 K

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•Unique soft X-ray undulator beam line in PLS•Total resolution : 350 meV for N 1s

Sample manipulator(5-axis motion)

SES200 analyzer

Photon

Experiments - HRPES (PLS U7) & MEIS (KRISS)

Anal. chamber

Prep. chamber

5-axisSample manipulator

H+ beam Load lock

•H+ energy : ~ 100 keV•Toroidal electrostatic energy analyzer with 2-axis motion

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PES Results : NO, NH3 /Si(100) – N 1s core levels

hυ = 500 eV hυ = 450 eV

NSi3

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MEIS Results : NO/Si(100)

91 92 93 94 95 96 97 980

50

100

150

200

250

surface N

surface O

surface Si

Co

un

ts 5

4

3

2

1

0

0.0 0.5 1.0 1.5 2.0

Relative Population

Si l

ayer

O N

Energy (keV)

91 92 93 94 95 96 97 980

50

100

150

200

250

NO 100L at RT 950 K 2min annealing

Co

un

ts(a

rb.u

nit

)

Energy(keV)

Location of each element in N-Si3 species

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Calculations of initial adsorption geometry and its energy

Site Ead

D 0.0 BR 0.23 BD 0.30 TD 0.35 C 0.53 H 0.62

Density-functional theory (DFT) in the local density approximation (LDA) Norm-conserving pseudopotential of Troullier and Martins Plane wave basis set with Ecut = 50 Ry Iterative scheme for minimization of total energy p(2 x 2) surface unit cell with 9 Si layers + 5 vacuum layers Fully relaxed geometry by Hellman-Feynman forces

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Stable N-incorporation geometry: three-fold

Hexagonal Center (-0.25 eV)

Substitution of down Si dimer (-0.59 eV)

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BR down (-0.57 eV)

D-down (-0.05 eV)

1.78

1.92 1.91

1.78

Stable N-incorporation geometry: four-fold

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Conclusion

• N atoms incorporate into the subsurface Si layers spontaneously after N-O dissociation or N-H bond breaking from initial adsorption of NO and NH3.

• Chemical configuration (N-Si3) and depth population (3rd or 4th layer) of the stable N atom are proved by PES & MEIS experimentally.

• Subsurface incorporation is stabilized by a few possible geometries which are suggested by ab initio LDA calculation.

: Hexagonal center or Substitution of down Si dimer

• This unusual behavior of N-incorporation successfully explains initial nitridation & the N-rich layer formation on the oxynitride/Si interface.

http://ipap.yonsei.ac.kr/~assl/