Dissertation

Synchrotron radiation studies of the chemisorption of chlorine and dichlorosilane on silicon surfaces

Durbin, Mark Thomas David

1994

Overview

Chlorine (Cl$\\sb{2}$) and dichlorosilane (SiCl$\\sb{2}$H$\\sb{2}$) play important roles in the manufacture of semiconductor devices. In this dissertation, the chemisorption of Cl$\\sb2$ and SiCl$\\sb2$H$\\sb2$ with Si is studied using soft x-ray photoelectron spectroscopy (SXPS) and photon stimulated desorption (PSD). SXPS studies show that the geometry of the surface plays an important role in the determining the reaction products formed upon the chemisorption of Cl$\\sb2$ on Si(111)-7 x 7 and Si(100)-2 x 1. On the Si(111)-7 x 7 surface, which has a complex reconstruction, both mono- and polychlorides form on the surface. On Si(100)-2 x 1, which has a dimer reconstruction, predominantly silicon monochlorides form. The breaking of Si-Si substrate bonds by Cl atoms that are liberated when Cl$\\sb2$ dissociates is also demonstrated. The reactivity of these liberated Cl atoms is affected by both the type and concentration of the dopant. This leads to a larger chlorosilyl layer on heavily p-doped than on heavily n-doped Si. It is proposed that the larger concentration of holes in the surface region of p-type material facilitates the breaking of a limited number of substrate Si-Si bonds, leading to these differences. PSD is used to elucidate the mechanism for Cl$\\sp{+}$ desorption from Si. These measurements show that Cl$\\sp{+}$ desorption is the result of a transition from the Cl 3s core-level to unoccupied Cl antibonding levels above the valence band maximum, followed by an intratomic Auger decay to form a repulsive state. At the Si 2p edge, Cl$\\sp{+}$ desorption occurs via an indirect process where secondary electrons induce ESD. This is in contrast to the direct desorption which occurs for F$\\sp{+}$ at the Si 2p edge. The differences between F$\\sp{+}$ and Cl$\\sp{+}$ desorption are discussed. The chemisorption of SiH$\\sb{2}$Cl$\\sb{2}$ on Si is studied to investigate and develop methods for growing Si films by atomic layer epitaxy(ALE). SiCl$\\sb{2}$H$\\sb{2}$ chemisorbs dissociatively on Si(111) and Si(100) surfaces resulting in the formation of an SiCl surface species at all temperatures. The coverage of monochloride displays a maximum at temperatures just above the hydrogen desorption temperature. It is observed that molecular hydrogen is not effective in removing an adsorbed layer of Cl from Si. A method for ALE of Si is proposed, in which SiH$\\sb{2}$Cl$\\sb{2}$ is adsorbed onto Si at 600$\\sp\\circ$C and Cl is removed via reaction with atomic H.

• Publisher: ProQuest Dissertations & Theses
• Subject: Condensation / Condensed matter physics
• ISBN: 9798209434030