NH3 on Si(111)7x7

Why NH3 on Si(111)7x7 ?

Si3N4 ! ! !Ammonia has been the most frequently used nitrogen source in chemical vapor deposition(CVD) growth.

The structural quality and the chemical stability of the silicon nitride (Si3N4) films are crucial in various industrial applications like as metal-oxide semiconductor devices.The complex Si(111)7x7 reconstruction, which displays a variety of surface sites, provides the opportunity to study the effect of local electronic structure modification.

Purpose of the study

Discover detail information about site-selective NH3 reaction with Si(111)7x7.

Find out the different adsorption and dissociation pathways of NH3 on the surfaces between Si(100) and Si(111).

NH3 -> NH2 + H

NH2 -> NH + H

Si3N4 ?

Si(111)7x7 vs. Si(100)2x1

1x22x1

Adatom : 12

Restatom : 6

Hole :1 Heating up to 1470K

Heating up to 950˚C

M. Björkqvist et al. Phys. Rev. B 57, 2327 (1998)

NH3 on Si(111)7x7: Dissociation and surface reactions

The photoemission experiments using beam line 22 at the National Synchrotron Radiation Facility MAX-LAB(Lund, Sweden)

Jeong Won Kim, Han Woong Yeom Surf. Sci. Lett. 546 (2003) L820-L828

Thermal decomposition of HN3 on the Si(100) surface

The photoemission experiments using X-ray beam line(8A1) connected undulator source at Pohang Accelerator Laboratory(PAL)

Myung-Ho Kang et al. Phys. Rev. B 68, 205307 (2003)

Theory on the site-selective HN3 reaction with Si(111)-(7x7)

Supercomputing Center at POSTECH

Experiments

N 1s core-level spectra

(a) For increasing ammonia exposures at RT

(b) After annealing of the 5L dose surfaceThe case of Si(100) surface

A1 : NH3

A2 : HN2

A3 : NHA4 : NN1 : NN2 : NHN3 : NH2

1L = 1x10-6 Torrxsec

N 1s core-level spectra

NH2 ≤ 650K

200K ≤ NH ≤ 750K N ≤ 700K Coexistence : 650 ~ 700K

NH2 ≤ 600K

500K ≤ NH ≤ 700K500K ≤ NCoexistence : 500 ~ 700K

Si 2p core-level spectra

(a) The clean and ammonia reacted surface at RT

(b) After annealing of the 5L dose surfaceThe case of Si(100) surface

2p1/2 (99.9eV)

2p3/2 (99.3eV)

S1 : restaom

Si 2p3/2

D : Si 2+ (101.1eV)

E : oxidized

silicon

SS : second layer atoms

C : third layer or defect atoms

S : updimer atoms

Valence-band spectra

(a) For increasing ammonia exposures at RT (b) After annealing of the 5L

dose surfaceV1 : N pπ

(4.9eV)

V2 : N-H

(10.6eV)

V3 : Si-H

(5.4eV)

V4 :N2p,Si3p

(7.4eV)

S1 : restatom

DB (0.9eV)

S2 : adatom

DB (0.3eV)

S3 : adatom

backbonds

(1.9eV)

Solid : A Dash : B

DFT (Density functional theory)

Infinite slab geometry

Calculated adsorption energy

Summary

NH3 on Si(100)2x1NH2 -> NH2 + NH -> NH2 + NH + N -> Si3N4 + N

NH3 on Si(111)7x7

NH3 + NH2 + NH -> NH2 + NH + N -> NH + N -> N

-> SiCx + SiNx + SiOx

Adatom : restatom = 2:1

After reaction of NH3 on Si(111)7x7 surface

Adatom : restatom = 1:0

Early saturation of Si restatom feature doesn’t prove easily about the site-selectivity!

What I want to know

Enlarged valence band of the adatom and restatom part using beam energy level hv = 37(40.1)eV

Chemisorption mechanism of NH3 on Si(111)7x7 Under 200K