Surface chemical processes of CH 2 =CCl 2 on Si(111) 7 7 mediated by low-energy electron and ion irradiation* Z. He, X. Yang and K. T. Leung Department of Chemistry University of Waterloo Waterloo, Ontario N2L 3G1, Canada Work supported by NSERC
Outline Objective Background Si(111) 7 7 Basics Halo Silicon Surface Chemistry Experiment Results Summary Acknowledgement
Objective Adsorption of the dichloroethylene on Si(111) 7 7 surface: Surface states and thermal evolution The surface reaction induced by electron irradiation The surface reaction induced by ion irradiation
Crystal Structure of Silicon
Dimer-Adatom-Stacking fault (DAS) model of Si(111)7 7. (A) Top view. (B) Side view. (C) Structure and bonding.
Clean Si(111)7x7 Si(111)7x7 Introduction DAS model: 12 adatoms, 6 rest atoms, 19 dangling bonds Cleaning: Repeated cycles of Ar sputtering and annealing to 1200 K SiCl x Vibrational feature at 560 600 cm -1 corresponding to Si Cl ing mode C/Si Randomly located, Si C at 780 860 cm -1 C=CH 2 /Si C-H ing: ~ 2910 cm -1 CH 2 scissoring: ~ 1387 cm -1 C=C ing: ~ 1510 cm -1 Si-H ing: ~ 2075 cm -1
Some vibration modes SiCl x related peaks: (1meV=8.065cm -1 ) Si-Cl ing: ~ 560 600 cm -1 Si-C ing: ~780 860 cm -1 CCl x related peaks: ing: ~ 720 cm -1 Hydrocarbon related peaks: C-H ing: ~ 2910 cm -1 CH 2 scissoring: ~ 1387 cm -1 Si-H ing: ~ 2075 cm -1 C=C ing: ~ 1510 cm -1
Research Approach Spectroscopy EELS, TDS, LEED, Auger Reactions Surface Reactions Applications Etching Process, Film growth
Surface analysis techniques involved EELS Electron Energy Loss Spectroscopy Detecting vibrational excitations TDS Temperature Desorption Spectroscopy Determining desorbed species and features LEED Low Energy Electron Diffraction Determining long range order of the surfaces
Surface analysis techniques
H. Yu, PhD thesis, 1998 EELS
TDS http://www.chem.qmw.ac.uk Order of desorption Identify the products of surface reaction The nature and strength of lateral adatom interactions Relative surface coverage of adsorbate Xiang Yang, Chem794
LEED Clean Si(111) 7 7 After 50 L DCE
Adsorption of 1,1-DCE on Si(111) 7 7 530 Si-Cl or C-Cl Si(111) 7x7 1,1-DCE 530 Si-Cl or C-Cl Si(111) 7x7 1,1-DCE Relative Intensity (abitrary units) 1050 C-C C-H 2 scissor 1360 2060 Si-H 3650 O-H 2910 C-H (c) 5 L (b) 2 L Relative Intensity (abitrary units) Si-C 850 C-H 2 scissor 1360 Si-H C-H 2080 2970 (c) 900 K (b) 550 K (a) 1 L 1510 (a) 2 L 1510 C=C C=C 0 1000 2000 3000 4000 5000 Energy Loss (cm -1 ) 0 1000 2000 3000 4000 5000 Energy Loss (cm -1 )
Adsorption of Cl 2 C=CCl 2 Si(111) 7x7 FCE 445 510 Relative Intensity (abitrary units) Si-Cl or C-Cl 530 C-Cl 780 C=C 1510 (e) 850 K (d) 750 K (c) 530 K (b) 410 K Relative Intensity 820 inten0 inten0 1510 (a) 40 L 0 1000 2000 3000 4000 5000 Loss (cm -1 ) 0 1000 2000 Energy Loss (cm -1 )
Adsorption of 1,1-DCE: Saturation x25 Si-Cl or C-Cl Si(111) 7x7 1,1-DCE x25 530 Si-C Si(111) 7x7 1,1-DCE Relative Intensity (abitrary units) 120 530 1050 C-C 1360 C-H 2 scissor 1510 Si-H C=C 2970 C-H 3650 O-H (c) 5 L Electronirradiated 226 microa 300 ev 10 mins (b) 1 kl (a) 5 L Relative Intensity (abitrary units) 135 C-H 2 scissor 1360 Si-H 2060 1050 C-C 1510 C=C C-H 2910 (i) 850 K (h) 790 K (g) 740 K (f) 670 K (e) 620 K (d) 570 K (c) 520 K (b) 410 K (a) 1 kl 0 1000 2000 3000 4000 5000 Loss (cm -1 ) 0 1000 2000 3000 4000 5000 Energy Loss (cm -1 )
Mass spectrum of 1,1-dichloroethylene NIST Chemistry WebBook (http://webbook.nist.gov/chemistry)
TDS results 10 100 L 1,1-DCE on Si(111) 7x7 Relative Intensity 8 6 4 2 0 (f) mass 61 (e) mass 62 (d) mass 96 (c) mass 35 (b) mass 63 (a) mass 98 400 600 800 1000 Temperature (K)
TDS results 10 100 L 1,1-DCE on Si(111) 7x7 8 Relative Intensity 6 4 2 mass 26 0 400 600 800 1000 Temperature (K)
Proposed Adsorption Configuration
Summary H 2 C=CCl 2 chemisorb on Si(111) 7 7 dissociatively at room temperature ~ 5 L exposure of H 2 C=CCl 2 can saturate the surface Successive annealing of the H 2 C=CCl 2 adsorbed surface causes dissociation and desorption of the adsorbates Around 550-650 K, the SiH m surface species are formed due to dehydrogenation of part of CH n surface species During 700 K- 780 K, most of SiH m and CH n desorb from surface During 780 K - 850 K, part of SiCl x come off from surface Beyond 900 K, only SiC species left on the surface The ion-irradiation of Si(111) 7 7 in H 2 C=CCl 2 generates more surface species The effect of low-energy electron irradiation was demonstrated on H 2 C=CCl 2 adsorbed Si(111) 7 7
Acknowledgment Supervisor: Dr. K. T. Leung Colleagues: Xiang Yang Hui Yu Qiang Li Sergey Milton Xiaojing Zhou Committee:
Surface processes Surface adsorption, co-adsorption, surface reaction Electron and ion induced surface processes Ion gun Xiang Yang, Chem 794 H. Yu, PhD thesis, University of Waterloo, 1998 Electron gun
Si(111)7 7 ion-irradiated in 1,1-DCE dependence on exposure, impact energy and temperature Relative Intensity (abitrary units) x25 120 Si-Cl or C-Cl 1360 530 1050 C-C C-H 2 scissor 2060 Si-H 1510 C=C Si(111) 7x7 1,1-DCE (a) 5 L (b) 5 L at 200 ev (c) 100 L at 200 ev (d) 1 kl at 200 ev (e) 1 kl at 500 ev 2910 C-H (e) (d) (c) (b) (a) Relative Intensity (abitrary units) x10 530 165 Si-C 1360 C-H 2 scissor Si-H 2060 C-C 1050 1510 C=C 3650 O-H 2910 C-H Si(111) 7x7 1,1-DCE (j) 950 K (i) 900 K (h) 850 K (g) 800 K (f) 750 K (e) 700 K (d) 620 K (c) 530 K (b) 400 K (a) 1 kl at 500 ev 0 1000 2000 3000 4000 5000 Energy Loss (cm -1 ) 0 1000 2000 3000 4000 5000 Loss (cm -1 )
The effect of electron irradiation dependence on current, impact energy, exposure and temperature Relative Intensity (abitrary units) 135 x25 Si-Cl or C-Cl 530 710 C-C 1050 1360 C-H 2 scissor Si(111) 7x7 1,1-DCE (a) 5 L (b) 10 microa, 50 ev, 5 mins (c) 40 microa, 100 ev, 10 mins (d) 100 microa, 200 ev, 10 mins (e) 226 microa, 300 ev, 10 mins Si-H 2060 1510 C=C C-H 2910 (e) (d) (c) (b) (a) Relative Intensity (abitrary units) x20 530 165 Si-C C-H 2 scissor 1360 Si-H 2060 C-C 1050 1510 C=C 3650 O-H (g) 900 K C-H 2910 Si(111) 7x7 1,1-DCE (f) 850 K (e) 800 K (d) 700 K (c) 600 K (b) 500 K (a) EI after 5 L 0 1000 2000 3000 4000 5000 Energy Loss (cm -1 ) 0 1000 2000 3000 4000 5000 Energy Loss (cm -1 )
Isometric view of ultra vacuum chamber developed at Waterloo