Chlorosilane Production from Chlorine-Exposed Si(111) 7 × 7 and Cu/Si(111) Surfaces

Abstract

The adsorption of chlorine and desorption of chlorosilanes from chlorine-covered Si(111) and Cu/Si surfaces have been studied. The latter include annealed “5 × 5” Cu2Si thin films as well as room-temperature deposited copper films on Si(111). Techniques employed include low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and temperature-programmed desorption (TPD). A Langmuir adsorption mechanism was observed for Cl on the Si(111) 7 × 7 surface, but a mobile precursor mediated process was observed for adsorption on the Cu/Si surfaces. Chlorine-exposed Si(111) 7 × 7 surfaces yield TPD peaks of SiCl2 at ∼650 °C with second-order desorption kinetics. For Cu-containing surfaces, similar TPD peaks were observed at slightly lower temperatures and with different desorption kinetics. The desorption rate includes a dependence on Cl-free sites. The presence of Cu on Si(111) also led to the appearance of two additional low-temperature TPD peaks, at 200 °C and 300 °C, both consisting of SiCl4 and SiCl2 species. We propose that the lower temperature desorption occurs through the formation of an activated SiCl2 precursor on the copper-containing surface.

Chlorine-induced restructuring of the Cu/Si(111) surface

“…2, which is in close agreement with 0.06 ML estimated from the previously determined deposition rate. 3 At Cl exposures in excess of ϳ0.3 ML, no ordering can be discerned in the STM images, and individual adsorbate species are no longer resolvable. There are three distinctive features that can be seen on these images: Cu/Si͑111͒ ''5ϫ5'' areas, apparently ''eroded'' regions, and three-dimensional objects.…”

“…The chlorine and copper coverages of these ''heated and cooled'' surfaces were calculated from the recorded AES spectra. 3 The experimental uncertainty of the coverages was estimated at Ϯ0.05 ML. Figure 1 shows Cu coverages of the surfaces, prepared in the described way, plotted against the associated final Cl coverages.…”

“…The commercial synthesis of methylchlorosilanes from solid silicon/copper mixtures and gaseous CH 3 Cl is the basis of the modern silicone industry. 1,2 Langmuir-Hinshelwood kinetics is assumed, i.e., methylchloride dissociatively chemisorbs on a Cu/Si surface prior to product desorption.…”

“…The interaction of chlorine with different Cu/Si systems and the thermal desorption of chlorosilanes have been the subject of recent investigations. [3][4][5] This paper presents the first structural investigation of the silicon etching and restructuring processes on a Cu/Si surface.…”

“…The ''5ϫ5'' film is stable up to approximately 800°C when Cu evaporates and/or dissolves in the bulk of the substrate. 12 In a recent study 3 we investigated the formation and desorption of chlorosilanes from chlorine-exposed Si͑111͒ 7ϫ7 and Cu/Si͑111͒ surfaces. In particular, we reported that the presence of Cu on a Si͑111͒ surface enables two new pathways for desorption of chlorosilanes ͑two desorption peaks͒ at temperatures as low as 200-300°C.…”