Elsevier

Surface Science

Volume 600, Issue 2, 15 January 2006, Pages 366-369
Surface Science

Formation of carbon-induced dimer vacancy defects on Si(0 0 1)-2 × 1 by thermal decomposition of organic molecules-lack of dependence on the molecules’ structure

https://doi.org/10.1016/j.susc.2005.11.011Get rights and content

Abstract

Two large and complex adsorbed organic molecules, coronene (C24H12) and C60, have been used to produce Si dimer vacancy defects on Si(0 0 1) by thermal decomposition. Studies by STM show that the aligned structural arrangement of the dimer vacancy defects produced is independent of the chemical structure of the organic molecules. This indicates that the chemistry of the thermally decomposed carbon species produced by decomposition of the organic molecule controls the organization of the Si dimer vacancy defects. It is found that ∼1 C atom is responsible for each dimer vacancy defect for both molecules in accordance with earlier studies of C2H2 decomposition on Si(0 0 1).

Introduction

The thermal decomposition of organic molecules on silicon surfaces to produce SiC is of importance in the fabrication Si- and SiC-based hybrid devices [1]. One might imagine that this process would be dependent on the molecular structure of the organic molecule chosen, and that the carburization process could be controlled both chemically and spatially on the silicon surface by the use of appropriate organic molecules. If this were true, then complex organic molecules with particular structures might be used to produce localized deposits of SiC on Si(0 0 1) which could be useful in lithography.

It is well known that small organic molecules, such as C2H2 and C2H4 will chemisorb on Si(1 0 0) and that thermal decomposition will lead to SiC film formation [2], [3]. The efficiency of production of SiC is high for the strongly bound C2H2 molecule, but low for C2H4, because extensive desorption of C2H4 occurs prior to decomposition of the adsorbed molecule [3].

It has been reported in previous studies that carbon atoms are incorporated into the subsurface region on the clean Si(0 0 1)-2 × 1 surface by thermal annealing at around 600 °C [4]. The incorporated carbon atoms produce carbon-induced dimer vacancy defects (c-DVs). One c-DV is reported to originate from one carbon atom. The c-DVs align in the direction perpendicular to the dimer rows of the Si(0 0 1)-2 × 1 surface. When the coverage of carbon exceeds a critical coverage of 0.05 ML, patches of Si(0 0 1)-c(4 × 4)-C areas start to form. Various carbon sources like graphite [5], [6], [7], C2H2 [2], [4], C2H4 [2], [6], [8], [9], [10], toluene [11], C60 [12], monomethylsilane (CH3SiH3) [13], dimethylsilane ((CH3)2SiH2) [13], dimethylgermane ((CH3)2GeH2) [14], trimethylgallium (Ga(CH3)3) [15] and SiC [16] have been reported to produce the Si(0 0 1)-c(4 × 4)-C structure or the c-DVs on Si(0 0 1). Monomethylsilane adsorbs dissociatively forming –CH3 species, but its analog, C2H6, does not even adsorb on the Si(0 0 1) surface [17], and SiC formation does not occur for C2H6 with useful efficiency.

In the present study, the thermal dissociation of coronene (C24H12) and C60 molecules adsorbed onto the Si(0 0 1)-2 × 1 surface at room temperature was investigated by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). An additional study of coronene adsorption on Si(0 0 1)-2 × 1 will be reported elsewhere [18].

Section snippets

Experiment

The experiments were carried out in a UHV system equipped with a VT-STM (Omicron), a cylindrical mirror analyzer for AES (Physical Electronics) and a quadrupole mass spectrometer. The base pressure of the UHV system is 4 × 10−11 Torr. Sample crystals (0.3 × 1 × 9 mm3) were cut from p-type boron-doped Si(0 0 1) wafers (100 Ω cm). The crystals were ultrasonically cleaned in pure ethanol, acetone and deionized water. Then the crystals were introduced immediately into the UHV chamber. After overnight

Results and discussion

Fig. 1 shows STM images of coronene on the Si(0 0 1) surface (a) before and (b), (c) after thermal annealing. The Si sample was annealed at 550 °C and 650 °C for 10 min in (b) and (c), respectively. Coronene molecules are seen as bright dots on the Si terraces, one of which is indicated by an arrowhead in (a) and (b). The density of the coronene was very low (∼103 molecule/μm2). After thermal annealing at 550 °C, the coronene still remained on the surface at nearly the same density, as indicated in

Acknowledgements

We acknowledge with thanks support for this work by DARPA QuIST through ARO contract number DAAD-19-01-1-0650, from the W.M. Keck Foundation and from NEDO (Japan).

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